{"gene":"CCR2","run_date":"2026-06-09T22:57:17","timeline":{"discoveries":[{"year":2022,"finding":"Cryo-EM structure of the CCL2-CCR2-G-protein complex reveals that CCL2 inserts deeply into the extracellular half of the transmembrane domain, with the N-terminal glutamine of CCL2 forming key interactions. Interactions around intracellular loop 2 (ICL2) of CCR2 are conserved and play a more critical role in G-protein activation than those around ICL3. Extensive hydrophobic and polar interactions between CCR2 and Gα-protein contribute to constitutive receptor activity.","method":"Cryo-electron microscopy structure determination of CCL2-CCR2-Gprotein complex, complemented by functional mutagenesis experiments","journal":"Cell discovery","confidence":"High","confidence_rationale":"Tier 1 / Strong — cryo-EM structure with functional validation by mutagenesis, rigorous mechanistic detail in a single study","pmids":["35570218"],"is_preprint":false},{"year":2023,"finding":"CCR2 functions as a dual-function receptor: it promotes monocyte infiltration via G-protein-coupled signaling in response to CCL2, and it also scavenges CCL2 from the extracellular environment by constitutively internalizing and recycling to the cell surface. The scavenging function occurs independently of G proteins, GRKs, β-arrestins, and clathrin, distinguishing it from canonical GPCR internalization and from other professional chemokine scavenger receptors.","method":"CRISPR knockout cell lines for G proteins, GRKs, β-arrestins, and clathrin; CCL2 scavenging and internalization assays; recycling assays","journal":"Science signaling","confidence":"High","confidence_rationale":"Tier 1 / Moderate — multiple CRISPR KO lines with orthogonal functional assays in a single rigorous study","pmids":["36719944"],"is_preprint":false},{"year":2019,"finding":"Molecular dynamics simulations and Markov-state modeling show that orthosteric and allosteric antagonists shift CCR2 into distinct stable inactive conformations and disrupt an internal water and sodium ion pathway, preventing transitions to an active-like state. A cryptic drug-binding pocket near the allosteric site was identified in metastable conformations.","method":"Long-timescale molecular dynamics simulations coupled with Markov-state model theory; computational structural analysis","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Low","confidence_rationale":"Tier 4 / Moderate — computational prediction only, no in vitro or mutagenesis validation reported in abstract","pmids":["30975755"],"is_preprint":false},{"year":2008,"finding":"CCR2 directly interacts with transportin1 (TRN1), an interaction that increases upon agonist treatment and promotes CCR2 nuclear translocation in a TRN1-dependent manner. Following translocation, the receptor localizes at the outer edge of the nuclear envelope where it is released from TRN1.","method":"Modified CCR2 used as bait to identify interacting proteins; co-immunoprecipitation; nuclear fractionation; fluorescence imaging","journal":"Proteomics","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — pulldown/co-IP with localization data, single lab, multiple methods but no functional consequence of nuclear localization established","pmids":["18846510"],"is_preprint":false},{"year":2016,"finding":"Filamin A (FLNa) is required for proper endosomal trafficking and recycling of activated CCR2B. In FLNa-knockdown cells, activated CCR2B accumulates in enlarged EEA-1-positive early endosomes. CCR2B and β2AR signaling induces phosphorylation of FLNa at residue S2152, and this phosphorylation event contributes to sustaining CCR2B recycling back to the plasma membrane.","method":"FLNa siRNA knockdown; super-resolution microscopy; endosomal localization assays; phosphorylation site mutagenesis; FRAP","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KD with defined trafficking phenotype plus phosphorylation site identification, single lab with multiple orthogonal methods","pmids":["27909248"],"is_preprint":false},{"year":2016,"finding":"CYTL1 (cytokine-like 1) is a functional ligand for CCR2B. CYTL1 induces chemotaxis of human monocytes via CCR2B and the CCR2B-ERK signaling pathway. This was demonstrated by chemotaxis, receptor internalization, and radioactive binding assays in HEK293 cells expressing CCR2B, and confirmed in macrophages from wild-type but not Ccr2-/- mice. CYTL1 activity is sensitive to pertussis toxin, indicating Gi-protein coupling.","method":"Chemotaxis assays, receptor internalization assays, radioactive ligand binding assays in HEK293-CCR2B cells; Ccr2-/- macrophage chemotaxis; pertussis toxin inhibition","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstituted receptor binding and functional assays with multiple orthogonal methods and genetic knockout confirmation","pmids":["27084102"],"is_preprint":false},{"year":1997,"finding":"CCR2 mRNA stability is regulated by LPS through a two-step process: first deadenylation, then degradation of the mRNA body. LPS does not affect the rate of nuclear transcription of CCR2 but reduces mRNA half-life. IL-2 augments CCR2 mRNA levels in monocytes and NK cells. The predominant CCR2 transcript in activated NK cells and mononuclear phagocytes is a long (3.4 kb) form consisting of CCR2B followed by a novel sequence (X) and a CCR2A-specific portion.","method":"Northern blotting, RNase protection assays, nuclear run-on transcription assay, mRNA half-life measurements, Poly(A) RNA analysis","journal":"Journal of leukocyte biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — nuclear run-on + mRNA decay experiments with multiple orthogonal methods in a single mechanistic study","pmids":["9225989","9365120"],"is_preprint":false},{"year":1997,"finding":"LPS induces rapid deadenylation followed by degradation of CCR2 mRNA body, demonstrating that post-transcriptional mRNA stability regulation is a mechanism controlling CCR2 expression levels. This is distinct from chemokine mRNAs that contain ARE motifs and are stabilized by LPS.","method":"mRNA half-life analysis; Poly(A) CCR2 mRNA decay measurements; comparison with CCR2 nuclear transcription rates by run-on assay","journal":"Journal of leukocyte biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct mRNA stability and decay mechanistic experiments with multiple methods in a single study","pmids":["9365120"],"is_preprint":false},{"year":2001,"finding":"The anti-CCR2 monoclonal antibody MC-21 blocks ligand binding to murine CCR2 with an IC50 of 0.09 μg/ml, reduces murine MCP-1 (CCL2) activity by 95%, and almost completely prevents monocyte influx in thioglycollate-induced peritonitis. CCR2 is homogeneously expressed on murine monocytes and 2–15% of T cells.","method":"mAb generation; ligand-induced CCR2 internalization assay; in vivo peritonitis model with antibody blockade; flow cytometry","journal":"Journal of immunology (Baltimore, Md. : 1950)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional antibody blockade with in vitro ligand competition and in vivo validation, single lab","pmids":["11254730"],"is_preprint":false},{"year":2019,"finding":"Tissue-resident CCR2+ cardiac macrophages promote monocyte recruitment through an MYD88-dependent mechanism that results in release of monocyte chemoattractant proteins (MCPs) and monocyte mobilization. In contrast, tissue-resident CCR2- cardiac macrophages inhibit monocyte recruitment. Selective depletion of either population before myocardial infarction has divergent effects on cardiac function and remodeling.","method":"Syngeneic cardiac transplantation; intravital 2-photon microscopy; CCR2-DTR and CD169-DTR selective depletion; single-cell RNA sequencing; MYD88-dependent pathway analysis","journal":"Circulation research","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple genetic depletion models, intravital imaging, and scRNA-seq identifying MYD88-dependent mechanism, replicated across multiple injury models","pmids":["30582448"],"is_preprint":false},{"year":2022,"finding":"CCR2 on circulating monocytes is required for their transition into immature macrophages within the inflamed vasculature. This transition begins intravascularly and relies on CCR2 in circulating cells and TNFR2 in parenchymal cells. Mechanistically, TNF-TNFR2-activated endothelial cells generate CCR2 ligands that drive monocyte differentiation, establishing a CCR2-based autocrine feed-forward loop amplifying renal inflammation.","method":"Single-cell RNA sequencing; in vitro monocyte-endothelial cell co-culture; CCR2 knockout mice; flow cytometry; glomerulonephritis mouse model","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo genetic models plus mechanistic in vitro reconstitution with scRNA-seq, identifying specific molecular pathway","pmids":["35404389"],"is_preprint":false},{"year":2023,"finding":"Complete autosomal recessive loss-of-function CCR2 deficiency in humans abolishes CCL2-stimulated Ca2+ signaling in and migration of monocytic cells, demonstrating that CCR2 is required for monocyte CCL2-dependent chemotaxis and for monocyte migration to the lungs. CCR2-deficient patients have high blood CCL2 (elevated due to impaired CCL2 consumption/scavenging) and approximately half the normal alveolar macrophage counts, causing pulmonary alveolar proteinosis and polycystic lung disease.","method":"Human genetic study with functional validation: Ca2+ signaling assays, monocyte migration assays, alveolar macrophage enumeration, gene expression profiling in loss-of-function CCR2 patients","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — human loss-of-function genetics with direct functional validation of receptor signaling and migration, multiple kindreds and orthogonal methods","pmids":["38157855"],"is_preprint":false},{"year":2019,"finding":"SphK1 (sphingosine kinase 1) in hepatic stellate cells (HSCs) upregulates CCR2 expression by downregulating miR-19b-3p. miR-19b-3p directly suppresses CCR2 expression in HSCs. This SphK1/miR-19b-3p/CCR2 axis in HSCs contributes to their activation and migration during liver fibrosis.","method":"SphK1 knockout mice; bone marrow transplantation; miR-19b-3p overexpression/knockdown; CCR2 expression measurement in HSCs; CCl4 and BDL liver fibrosis models","journal":"Hepatology (Baltimore, Md.)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic knockout plus miRNA functional manipulation with in vivo validation, single lab","pmids":["29572892"],"is_preprint":false},{"year":2019,"finding":"PSMP (PC3-secreted microprotein/MSMP) is a CCR2 ligand that promotes liver fibrosis through CCR2. PSMP induced by HMGB-1 and IL-33 from hepatocytes drives CCR2+ monocyte infiltration into liver, macrophage M1 polarization, and hepatic stellate cell activation via CCR2. Overexpression of PSMP in Psmp-/- mouse livers reversed fibrosis attenuation in a CCR2-dependent manner.","method":"Psmp-/- mice; CCl4 and BDL fibrosis models; adeno-associated virus-8 PSMP overexpression; PSMP-neutralizing antibody; in vitro macrophage and LX-2 cell assays; CCR2-dependence confirmed genetically","journal":"Journal of hepatology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple genetic models, AAV rescue experiment establishing CCR2 dependence, antibody blockade, and in vitro cell assays in one study","pmids":["31813573"],"is_preprint":false},{"year":2017,"finding":"PSMP chemoattracts Ly6Chi monocytes in a CCR2-dependent manner, confirmed by in situ chemotaxis and adoptive transfer assays. LPS and muramyl dipeptide induced PSMP expression in colonic epithelial cells, and PSMP promoted M1 macrophages to produce CCL2.","method":"In situ chemotaxis assay; adoptive transfer of monocytes; anti-PSMP neutralizing antibody; DSS colitis model; in vitro macrophage stimulation","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo and in vitro functional assays demonstrating CCR2-dependent chemotaxis, single lab","pmids":["28698550"],"is_preprint":false},{"year":2015,"finding":"A CCR2-positive macrophage subpopulation constitutes the majority of fibrin-internalizing cells in the dermis. Fibrin endocytosis is dependent on plasminogen and plasminogen activator but is independent of fibrinogen receptors αMβ2, ICAM-1, the myeloid cell integrin-binding site on fibrin, or the mannose receptor. Elimination of CCR2-expressing cells diminishes cellular fibrin uptake.","method":"Intravital microscopy; CCR2+ cell depletion; fibrin internalization assay; knockout mice for fibrinogen receptors; lysosomal targeting assay","journal":"Blood","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — intravital microscopy with genetic depletion and multiple receptor knockouts, single lab","pmids":["26647393"],"is_preprint":false},{"year":2004,"finding":"CCR2 is expressed on murine type II alveolar epithelial cells (AECs) and mediates MCP-1-dependent chemotaxis and wound closure in these non-immune cells. AECs from CCR2-/- mice failed to migrate in response to MCP-1 and showed delayed closure of mechanical wounds compared to wild-type AECs.","method":"CCR2 mRNA expression in primary AECs; chemotaxis/haptotaxis assays; mechanical wound closure assay in CCR2-/- vs. wild-type AECs; anti-MCP-1 antibody blockade","journal":"American journal of physiology. Lung cellular and molecular physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — CCR2 KO with defined migration phenotype in primary cells, multiple assays, single lab","pmids":["14656700"],"is_preprint":false},{"year":2000,"finding":"CCR2 mediates MCP-1-dependent haptotactic migration of pleural mesothelial cells (PMCs). IL-2 upregulates CCR2 expression and increases haptotactic migration; LPS initially downregulates CCR2 and decreases migration. Blocking CCR2 with neutralizing antibodies decreases haptotactic response of PMCs to MCP-1.","method":"Haptotaxis assay; CCR2 neutralizing antibody blockade; flow cytometry; RT-PCR; PMC cultures with IL-2 and LPS treatment","journal":"American journal of physiology. Lung cellular and molecular physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — CCR2 antibody blockade with functional migration assay and receptor expression correlation, single lab","pmids":["10710532"],"is_preprint":false},{"year":2006,"finding":"CCR2 is expressed in human mesangial cells (HMCs) and mediates direct pro-inflammatory effects. MCP-1 binding to CCR2 on HMCs induces a two-fold increase in ICAM-1 expression at 24 h, enhancing monocyte adhesion. CCR2 blockade with RS102895 prevents MCP-1-induced ICAM-1 upregulation. Mechanical stretch reduces CCR2 mRNA and protein expression in HMCs via an MCP-1-independent mechanism and does not induce ICAM-1 via CCR2.","method":"CCR2 antagonist (RS102895) blockade; immunofluorescence; cytofluorimetry; monocyte-HMC adhesion assay; RT-PCR; immunoblotting; flow cytometry","journal":"Kidney international","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological CCR2 blockade with multiple readouts establishing direct signaling, single lab","pmids":["16518346"],"is_preprint":false},{"year":2017,"finding":"PCSK9 reduces LDL-R expression on monocytes, which in turn decreases LDL-C/LDL-R-mediated CCR2 expression on monocytes, impairing MCP-1-directed monocyte migration. LDL-C increases monocyte CCR2 expression. VSMC-derived PCSK9 (induced via TLR-4/SAPK/JNK signaling) inhibits LDL-C-dependent monocyte chemotaxis toward MCP-1.","method":"Conditioned media from LPS-stimulated VSMCs applied to monocytes; recombinant PCSK9; LDL-R blocking antibody; CCR2 expression measurement; monocyte migration assay; kinase inhibitor pharmacology","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple functional assays linking PCSK9→LDL-R→CCR2 regulatory axis, single lab","pmids":["28232185"],"is_preprint":false},{"year":2017,"finding":"NOX4 in hepatic stellate cells (HSCs) stabilizes CCR2 and CCL2 mRNA by promoting Ser221 phosphorylation and cytoplasmic shuttling of the RNA-binding protein HuR. HSC-specific NOX4 knockout mice showed significantly reduced CCR2 and CCL2 expression in alcohol-induced liver injury.","method":"HSC-specific NOX4 KO mice; mRNA half-life measurement; HuR phosphorylation and localization assay; alcohol diet model","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — tissue-specific KO plus mechanistic mRNA stability and HuR phosphorylation data, single lab","pmids":["28383062"],"is_preprint":false},{"year":2013,"finding":"Rab GTPases required for cell surface expression and signal transduction (FAK activation) of CCR2 differ from those required for the CXCR4/CCR2 heterodimer, demonstrating that heterodimer formation alters the anterograde trafficking pathway of CCR2.","method":"Dominant negative and wild-type Rab GTPase transfection; biotin-streptavidin cell surface expression assay; FAK activation (signal transduction) assay; PC3 prostate cancer cells","journal":"Cellular physiology and biochemistry","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, single method per readout, limited mechanistic detail in abstract","pmids":["23839224"],"is_preprint":false},{"year":2016,"finding":"CCR2 expressed on cancer cells (in addition to monocytes) suppresses anti-tumor adaptive immunity. Deletion of Ccr2 specifically in breast cancer cells increased CTL infiltration and activation, increased CD103+ cross-presenting DCs, upregulated MHC class I, and downregulated PD-L1. CCR2 signaling in cancer cells prevents DC maturation toward the CD103+ subtype and reduces cancer cell sensitivity to CTLs.","method":"Orthotopic isograft breast cancer mouse model; Ccr2 deletion in cancer cells (genetic); pharmacological CCR2 inhibition; Batf3-/- mice lacking CD103+ DCs; flow cytometry; tumor growth and survival analysis","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — cancer cell-specific genetic deletion plus pharmacological inhibition with epistasis using Batf3-/- mice, multiple immune phenotypes measured","pmids":["32667673"],"is_preprint":false},{"year":2021,"finding":"CCR2 signaling in mice promotes infiltration of classical monocytes into the lung and expansion of monocyte-derived cells that play a protective role against SARS-CoV-2. CCR2-deficient mice showed higher viral loads, increased viral dissemination, and elevated inflammatory cytokine responses, demonstrating CCR2-dependent monocyte recruitment is mechanistically required for viral control.","method":"Mouse-adapted SARS-CoV-2 infection of CCR2-/- mice; intravital antibody labeling; scRNA-seq of lung homogenates; flow cytometry; viral burden measurement","journal":"mBio","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — CCR2 KO with defined viral and inflammatory phenotypes plus scRNA-seq mechanistic profiling, single lab","pmids":["34749524"],"is_preprint":false},{"year":2016,"finding":"CCL2 and CCR2 are required for formation of osteoclasts and foreign body giant cells (FBGC). Bone marrow from CCL2-/- and CCR2-/- mice produced significantly fewer and smaller osteoclasts and FBGC. Addition of exogenous CCL2 to CCL2-/- bone marrow cultures rescued osteoclast and FBGC formation, demonstrating CCL2/CCR2 signaling is required for monocyte/macrophage fusion.","method":"CCL2-/- and CCR2-/- mouse bone marrow cultures; rescue with exogenous CCL2; quantification of osteoclast/FBGC number, nuclei, and size","journal":"Journal of cellular biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — dual knockout models with rescue experiment, single lab","pmids":["26205994"],"is_preprint":false},{"year":2004,"finding":"CCR2 signaling is required for complete skeletal muscle regeneration after freeze injury. CCR2-/- mice showed impaired muscle regeneration, prolonged inflammation, fibrosis, fat infiltration, and impaired strength recovery by day 14–28 post-injury. CCR2 co-localizes with activated macrophages (Mac-3+) and activated muscle precursor cells (myogenin+) in injured muscle, while NCAM expression was more elevated in CCR2-/- injured muscle.","method":"CCR2-/- mouse freeze-injury model; histology; immunohistochemistry for CCR2, Mac-3, myogenin, MyoD, NCAM; strength testing","journal":"FASEB journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — CCR2 KO with defined regeneration phenotype and co-localization data, single lab","pmids":["15601671"],"is_preprint":false},{"year":2018,"finding":"CCR2 inhibition by a novel scFv (58C) that binds the N-terminal domain of CCR2 (KD = 59.8 nM) inhibits monocyte and cancer cell migration and induces M1 macrophage polarization. Multivalent display of 58C-scFv on liposomes further reduces migration by 25–40% and enhances M1 polarization by 200% over monomeric scFv, demonstrating that multivalent CCR2 engagement amplifies downstream signaling effects on macrophage fate.","method":"Phage library affinity selection; KD measurement; migration assay; macrophage polarization assay (iNOS/Arg-1, IL-6/Mgl2 ratios); liposomal multivalent display","journal":"Molecular pharmaceutics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro receptor binding and functional assays with multivalency comparison, single lab, multiple readouts","pmids":["29791797"],"is_preprint":false},{"year":2017,"finding":"Gas6 promotes the specific recruitment of inflammatory CCR2hiCX3CR1lo monocytes during venous thrombosis via Gas6-dependent regulation of CCR2 expression on monocytes and CCL2 expression on endothelial cells. Gas6-dependent CCL2 expression and monocyte migration were mediated via JNK (c-Jun N-terminal kinase) signaling.","method":"Gas6-/- mice; anti-CCR2 and anti-CCL2 antibody depletion; flow cytometry; in vitro monocyte migration assay; JNK inhibitor; FeCl3 and flow-reduction deep venous thrombosis models","journal":"Arteriosclerosis, thrombosis, and vascular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic KO plus antibody depletion with pathway inhibitor, single lab","pmids":["28450294"],"is_preprint":false},{"year":2017,"finding":"CCR2+ macrophages are the predominant source of IGF2 in the neonatal pancreas and support β cell proliferation via IGF1R-mediated signaling. CCR2-specific depletion in neonatal mice leads to a striking reduction in β cell proliferation, dysfunctional islet phenotypes, and glucose intolerance. Adoptive transfer of CCR2+ myeloid cells rescues these defects.","method":"CCR2-specific depletion models; adoptive transfer; gene profiling of pancreatic CCR2+ myeloid cells; β cell proliferation assay; glucose tolerance test","journal":"JCI insight","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — CCR2+ cell depletion with adoptive transfer rescue and IGF2 mechanism identified, single lab","pmids":["28768911"],"is_preprint":false},{"year":2014,"finding":"siRNA silencing of CCR2 (siCCR2) delivered via nanoparticles reduces Ly6Chigh monocyte numbers in hearts of mice with autoimmune myocarditis by 69% and is active in both monocytes and bone marrow hematopoietic progenitor cells. siCCR2 reduces migration of bone marrow granulocyte-macrophage progenitors into blood and improves ejection fraction.","method":"Nanoparticle-encapsulated siRNA delivery; flow cytometry; histology; cellular MRI with macrophage-avid nanoparticles; cardiac MRI volumetry","journal":"European heart journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — RNAi knockdown with multiple functional and imaging readouts, single lab","pmids":["24950695"],"is_preprint":false},{"year":2022,"finding":"CCR2+ macrophages in the inflamed kidney promote monocyte-to-macrophage transition intravascularly. CCR2-dependent monocyte differentiation generates CCR2 ligands that form an autocrine feed-forward loop. Single-cell RNA sequencing of in vitro cocultures defines a CCR2-dependent monocyte differentiation path associated with acquisition of immune effector functions.","method":"scRNA-seq of monocyte-endothelial cocultures; CCR2 KO mice; glomerulonephritis mouse model; flow cytometry","journal":"The Journal of experimental medicine","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO plus scRNA-seq mechanistic pathway definition plus in vitro reconstitution, multiple orthogonal methods","pmids":["35404389"],"is_preprint":false},{"year":1999,"finding":"The CCR2-64I polymorphism (V64I substitution) does not alter CCR5 mRNA levels, CCR5 cell surface expression, or CCR5 coreceptor function in CD4+ T cells. CCR2-64I is linked to CCR5 promoter polymorphisms (208G, 303A, 627C, 676A) but these do not affect CCR5 transcriptional activity in transfected reporter constructs.","method":"Flow cytometry for CCR5 surface expression; RT-PCR for CCR5/CCR2 mRNA; CCR5 coreceptor function assay; transfected CCR5 promoter reporter constructs","journal":"Journal of virology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal assays establishing a negative mechanistic result, single lab","pmids":["9971830"],"is_preprint":false},{"year":2007,"finding":"Alveolar macrophages do not express CCR2 (confirmed by microarray, RT-PCR, and flow cytometry) and do not migrate toward CCL2, in contrast to peripheral blood monocytes. This establishes that CCR2 loss accompanies monocyte-to-alveolar macrophage differentiation in vivo.","method":"Microarray analysis; RT-PCR; flow cytometry; migration assay; comparison of peripheral blood monocytes and alveolar macrophages from same donors","journal":"Journal of inflammation (London, England)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods on human primary cells, single lab, informative negative result","pmids":["17888174"],"is_preprint":false},{"year":2024,"finding":"The obesity-induced functional shift of CCR2-expressing macrophages in the heart is mechanistically mediated by the CCR2/ATF3 (activating transcription factor 3)/lysozyme 1/NF-κB signaling axis. Lysozyme 1 acts as a transcriptional activator by binding to the RelA promoter and driving NF-κB signaling, promoting cardiac inflammation in obesity. Inducible ablation of CCR2+CX3CR1+ macrophages or selective deletion of macrophage CCR2 prevents obesity-induced cardiac dysfunction.","method":"scRNA-seq; CUTANA ChIP; luciferase assay; macrophage-specific lentivirus transfection; dual recombinase CCR2+ macrophage ablation; macrophage-specific CCR2 deletion; chromatin immunoprecipitation-PCR","journal":"Circulation research","confidence":"High","confidence_rationale":"Tier 1 / Moderate — multiple orthogonal methods (ChIP, luciferase, scRNA-seq, genetic deletion) in single study defining molecular mechanism","pmids":["39056179"],"is_preprint":false}],"current_model":"CCR2 is a Gi-coupled seven-transmembrane chemokine receptor that binds CCL2 (and related ligands including CCL7, CCL8, CYTL1, and PSMP) at the extracellular transmembrane domain—as revealed by cryo-EM structure—triggering ERK- and G-protein-dependent monocyte chemotaxis; it also functions as a dual-function scavenger receptor by constitutively internalizing CCL2 independently of G proteins, GRKs, β-arrestins, and clathrin; receptor recycling is regulated by filamin A phosphorylation at S2152 and by transportin1-mediated nuclear translocation; CCR2 mRNA stability is post-transcriptionally controlled by deadenylation/degradation downstream of LPS and by NOX4/HuR signaling and miR-19b-3p; on immune cells, CCR2 is the principal driver of classical monocyte egress from bone marrow and recruitment to inflamed tissues (including heart, kidney, lung, liver, brain, and tumors), where CCR2+ macrophages promote or restrict inflammation depending on context; CCR2 on cancer cells additionally suppresses adaptive immunity by limiting CD103+ DC maturation and promoting PD-L1 expression; and human complete CCR2 deficiency causes impaired CCL2-dependent monocyte lung recruitment, pulmonary alveolar proteinosis, and polycystic lung disease."},"narrative":{"mechanistic_narrative":"CCR2 is a Gi-coupled seven-transmembrane chemokine receptor that drives chemotactic recruitment of classical monocytes and macrophages to inflamed tissues, and its complete loss-of-function in humans abolishes CCL2-dependent monocyte Ca2+ signaling and lung migration, causing pulmonary alveolar proteinosis and polycystic lung disease [PMID:38157855]. Cryo-EM of the CCL2–CCR2–G-protein complex shows the chemokine inserting deeply into the extracellular half of the transmembrane domain, with intracellular loop 2 contacts being more critical for G-protein activation than ICL3 [PMID:35570218]. Beyond CCL2, CCR2 is activated by additional ligands including CYTL1 [PMID:27084102] and the secreted microprotein PSMP, both driving CCR2-dependent monocyte chemotaxis via Gi/ERK signaling [PMID:31813573, PMID:28698550]. CCR2 is also a dual-function receptor that constitutively scavenges extracellular CCL2 by internalizing and recycling independently of G proteins, GRKs, β-arrestins, and clathrin [PMID:36719944], with recycling supported by filamin A trafficking and its phosphorylation at S2152 [PMID:27909248]. CCR2 expression is post-transcriptionally controlled through regulated mRNA stability: LPS triggers deadenylation and decay [PMID:9225989, PMID:9365120], while NOX4/HuR signaling stabilizes the transcript [PMID:28383062] and miR-19b-3p suppresses it [PMID:29572892]. Functionally, CCR2 governs monocyte egress and tissue infiltration in heart, kidney, lung, liver, and other organs, where CCR2+ macrophages can either amplify inflammation through feed-forward ligand loops [PMID:35404389, PMID:30582448] or support tissue repair and homeostasis [PMID:34749524, PMID:28768911], and CCR2 on cancer cells suppresses anti-tumor immunity by limiting CD103+ DC maturation and upregulating PD-L1 [PMID:32667673].","teleology":[{"year":1997,"claim":"Established that CCR2 abundance is set not only by transcription but by regulated mRNA turnover, defining a post-transcriptional control point for receptor expression on activated leukocytes.","evidence":"Nuclear run-on, RNase protection, and mRNA half-life/poly(A) decay measurements in LPS- and IL-2-treated monocytes/NK cells","pmids":["9225989","9365120"],"confidence":"High","gaps":["Identity of the deadenylase/decay machinery acting on CCR2 mRNA not defined","Cis-elements distinguishing CCR2 from ARE-containing chemokine transcripts not mapped"]},{"year":2008,"claim":"Addressed whether CCR2 has trafficking destinations beyond the plasma membrane by identifying transportin1 as an agonist-enhanced interactor driving receptor nuclear translocation.","evidence":"Bait pulldown, co-immunoprecipitation, nuclear fractionation, and fluorescence imaging","pmids":["18846510"],"confidence":"Medium","gaps":["Functional consequence of nuclear CCR2 localization not established","Interaction shown in a single lab without reciprocal validation"]},{"year":2016,"claim":"Resolved how activated CCR2 returns to the surface by showing filamin A and its S2152 phosphorylation are required for endosomal recycling.","evidence":"FLNa siRNA knockdown, super-resolution microscopy, phosphosite mutagenesis, and FRAP in CCR2B-expressing cells","pmids":["27909248"],"confidence":"Medium","gaps":["Kinase responsible for S2152 phosphorylation not identified","Single-lab study"]},{"year":2016,"claim":"Expanded the CCR2 ligand repertoire beyond CCL2 by demonstrating CYTL1 acts as a functional Gi-coupled agonist driving monocyte chemotaxis.","evidence":"Chemotaxis, internalization, and radioligand binding in HEK293-CCR2B cells plus Ccr2-/- macrophage confirmation and pertussis toxin sensitivity","pmids":["27084102"],"confidence":"High","gaps":["Structural basis of CYTL1–CCR2 engagement not determined","Relative physiological contribution versus CCL2 unclear"]},{"year":2019,"claim":"Provided atomic-level mechanism of agonist activation, showing CCL2 inserts into the transmembrane core and that ICL2 contacts dominate G-protein activation.","evidence":"Cryo-EM of CCL2–CCR2–G-protein complex with functional mutagenesis","pmids":["35570218"],"confidence":"High","gaps":["Conformational basis of ligand bias or scavenging not captured","Structures with alternative ligands (CYTL1, PSMP) not solved"]},{"year":2019,"claim":"Identified PSMP as an additional CCR2 ligand driving CCR2-dependent monocyte infiltration and fibrosis, with genetic rescue establishing CCR2 dependence.","evidence":"Psmp-/- mice, AAV8-PSMP overexpression rescue, neutralizing antibody, and in vitro macrophage/LX-2 assays in liver fibrosis models","pmids":["31813573","28698550"],"confidence":"High","gaps":["Direct PSMP–CCR2 binding affinity not quantified","Whether PSMP and CCL2 compete at the same site unknown"]},{"year":2022,"claim":"Defined a non-canonical scavenging function: CCR2 constitutively internalizes and recycles CCL2 independently of G proteins, GRKs, β-arrestins, and clathrin, distinguishing it from a signaling-only receptor.","evidence":"CRISPR knockout panels for G proteins, GRKs, β-arrestins, and clathrin with scavenging, internalization, and recycling assays","pmids":["36719944"],"confidence":"High","gaps":["Molecular machinery mediating clathrin-independent internalization unidentified","Physiological balance between signaling and scavenging not quantified"]},{"year":2022,"claim":"Showed CCR2 on circulating monocytes is required for intravascular monocyte-to-macrophage transition, establishing an autocrine CCR2-ligand feed-forward loop amplifying tissue inflammation.","evidence":"scRNA-seq, CCR2 knockout mice, and monocyte–endothelial cocultures in a glomerulonephritis model","pmids":["35404389"],"confidence":"High","gaps":["Identity of the autocrine CCR2 ligands generated during differentiation not fully resolved","Generalizability beyond renal inflammation untested"]},{"year":2023,"claim":"Established CCR2 as essential and non-redundant in humans by showing complete loss-of-function abolishes CCL2-dependent monocyte signaling and lung recruitment, causing pulmonary alveolar proteinosis.","evidence":"Human loss-of-function genetics with Ca2+ signaling, migration, and alveolar macrophage enumeration across multiple kindreds","pmids":["38157855"],"confidence":"High","gaps":["Why CCR2 loss specifically manifests as polycystic lung disease mechanistically unclear","Therapeutic correction not 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Increases NMDA-mediated synaptic transmission in both dopamine D1 and D2 receptor-containing neurons, which may be caused by MAPK/ERK-dependent phosphorylation of GRIN2B/NMDAR2B (By similarity). 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Interactions around intracellular loop 2 (ICL2) of CCR2 are conserved and play a more critical role in G-protein activation than those around ICL3. Extensive hydrophobic and polar interactions between CCR2 and Gα-protein contribute to constitutive receptor activity.\",\n      \"method\": \"Cryo-electron microscopy structure determination of CCL2-CCR2-Gprotein complex, complemented by functional mutagenesis experiments\",\n      \"journal\": \"Cell discovery\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — cryo-EM structure with functional validation by mutagenesis, rigorous mechanistic detail in a single study\",\n      \"pmids\": [\"35570218\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"CCR2 functions as a dual-function receptor: it promotes monocyte infiltration via G-protein-coupled signaling in response to CCL2, and it also scavenges CCL2 from the extracellular environment by constitutively internalizing and recycling to the cell surface. The scavenging function occurs independently of G proteins, GRKs, β-arrestins, and clathrin, distinguishing it from canonical GPCR internalization and from other professional chemokine scavenger receptors.\",\n      \"method\": \"CRISPR knockout cell lines for G proteins, GRKs, β-arrestins, and clathrin; CCL2 scavenging and internalization assays; recycling assays\",\n      \"journal\": \"Science signaling\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — multiple CRISPR KO lines with orthogonal functional assays in a single rigorous study\",\n      \"pmids\": [\"36719944\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Molecular dynamics simulations and Markov-state modeling show that orthosteric and allosteric antagonists shift CCR2 into distinct stable inactive conformations and disrupt an internal water and sodium ion pathway, preventing transitions to an active-like state. A cryptic drug-binding pocket near the allosteric site was identified in metastable conformations.\",\n      \"method\": \"Long-timescale molecular dynamics simulations coupled with Markov-state model theory; computational structural analysis\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 4 / Moderate — computational prediction only, no in vitro or mutagenesis validation reported in abstract\",\n      \"pmids\": [\"30975755\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"CCR2 directly interacts with transportin1 (TRN1), an interaction that increases upon agonist treatment and promotes CCR2 nuclear translocation in a TRN1-dependent manner. Following translocation, the receptor localizes at the outer edge of the nuclear envelope where it is released from TRN1.\",\n      \"method\": \"Modified CCR2 used as bait to identify interacting proteins; co-immunoprecipitation; nuclear fractionation; fluorescence imaging\",\n      \"journal\": \"Proteomics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — pulldown/co-IP with localization data, single lab, multiple methods but no functional consequence of nuclear localization established\",\n      \"pmids\": [\"18846510\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Filamin A (FLNa) is required for proper endosomal trafficking and recycling of activated CCR2B. In FLNa-knockdown cells, activated CCR2B accumulates in enlarged EEA-1-positive early endosomes. CCR2B and β2AR signaling induces phosphorylation of FLNa at residue S2152, and this phosphorylation event contributes to sustaining CCR2B recycling back to the plasma membrane.\",\n      \"method\": \"FLNa siRNA knockdown; super-resolution microscopy; endosomal localization assays; phosphorylation site mutagenesis; FRAP\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KD with defined trafficking phenotype plus phosphorylation site identification, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"27909248\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"CYTL1 (cytokine-like 1) is a functional ligand for CCR2B. CYTL1 induces chemotaxis of human monocytes via CCR2B and the CCR2B-ERK signaling pathway. This was demonstrated by chemotaxis, receptor internalization, and radioactive binding assays in HEK293 cells expressing CCR2B, and confirmed in macrophages from wild-type but not Ccr2-/- mice. CYTL1 activity is sensitive to pertussis toxin, indicating Gi-protein coupling.\",\n      \"method\": \"Chemotaxis assays, receptor internalization assays, radioactive ligand binding assays in HEK293-CCR2B cells; Ccr2-/- macrophage chemotaxis; pertussis toxin inhibition\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstituted receptor binding and functional assays with multiple orthogonal methods and genetic knockout confirmation\",\n      \"pmids\": [\"27084102\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"CCR2 mRNA stability is regulated by LPS through a two-step process: first deadenylation, then degradation of the mRNA body. LPS does not affect the rate of nuclear transcription of CCR2 but reduces mRNA half-life. IL-2 augments CCR2 mRNA levels in monocytes and NK cells. The predominant CCR2 transcript in activated NK cells and mononuclear phagocytes is a long (3.4 kb) form consisting of CCR2B followed by a novel sequence (X) and a CCR2A-specific portion.\",\n      \"method\": \"Northern blotting, RNase protection assays, nuclear run-on transcription assay, mRNA half-life measurements, Poly(A) RNA analysis\",\n      \"journal\": \"Journal of leukocyte biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — nuclear run-on + mRNA decay experiments with multiple orthogonal methods in a single mechanistic study\",\n      \"pmids\": [\"9225989\", \"9365120\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"LPS induces rapid deadenylation followed by degradation of CCR2 mRNA body, demonstrating that post-transcriptional mRNA stability regulation is a mechanism controlling CCR2 expression levels. This is distinct from chemokine mRNAs that contain ARE motifs and are stabilized by LPS.\",\n      \"method\": \"mRNA half-life analysis; Poly(A) CCR2 mRNA decay measurements; comparison with CCR2 nuclear transcription rates by run-on assay\",\n      \"journal\": \"Journal of leukocyte biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct mRNA stability and decay mechanistic experiments with multiple methods in a single study\",\n      \"pmids\": [\"9365120\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"The anti-CCR2 monoclonal antibody MC-21 blocks ligand binding to murine CCR2 with an IC50 of 0.09 μg/ml, reduces murine MCP-1 (CCL2) activity by 95%, and almost completely prevents monocyte influx in thioglycollate-induced peritonitis. CCR2 is homogeneously expressed on murine monocytes and 2–15% of T cells.\",\n      \"method\": \"mAb generation; ligand-induced CCR2 internalization assay; in vivo peritonitis model with antibody blockade; flow cytometry\",\n      \"journal\": \"Journal of immunology (Baltimore, Md. : 1950)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional antibody blockade with in vitro ligand competition and in vivo validation, single lab\",\n      \"pmids\": [\"11254730\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Tissue-resident CCR2+ cardiac macrophages promote monocyte recruitment through an MYD88-dependent mechanism that results in release of monocyte chemoattractant proteins (MCPs) and monocyte mobilization. In contrast, tissue-resident CCR2- cardiac macrophages inhibit monocyte recruitment. Selective depletion of either population before myocardial infarction has divergent effects on cardiac function and remodeling.\",\n      \"method\": \"Syngeneic cardiac transplantation; intravital 2-photon microscopy; CCR2-DTR and CD169-DTR selective depletion; single-cell RNA sequencing; MYD88-dependent pathway analysis\",\n      \"journal\": \"Circulation research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple genetic depletion models, intravital imaging, and scRNA-seq identifying MYD88-dependent mechanism, replicated across multiple injury models\",\n      \"pmids\": [\"30582448\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"CCR2 on circulating monocytes is required for their transition into immature macrophages within the inflamed vasculature. This transition begins intravascularly and relies on CCR2 in circulating cells and TNFR2 in parenchymal cells. Mechanistically, TNF-TNFR2-activated endothelial cells generate CCR2 ligands that drive monocyte differentiation, establishing a CCR2-based autocrine feed-forward loop amplifying renal inflammation.\",\n      \"method\": \"Single-cell RNA sequencing; in vitro monocyte-endothelial cell co-culture; CCR2 knockout mice; flow cytometry; glomerulonephritis mouse model\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo genetic models plus mechanistic in vitro reconstitution with scRNA-seq, identifying specific molecular pathway\",\n      \"pmids\": [\"35404389\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Complete autosomal recessive loss-of-function CCR2 deficiency in humans abolishes CCL2-stimulated Ca2+ signaling in and migration of monocytic cells, demonstrating that CCR2 is required for monocyte CCL2-dependent chemotaxis and for monocyte migration to the lungs. CCR2-deficient patients have high blood CCL2 (elevated due to impaired CCL2 consumption/scavenging) and approximately half the normal alveolar macrophage counts, causing pulmonary alveolar proteinosis and polycystic lung disease.\",\n      \"method\": \"Human genetic study with functional validation: Ca2+ signaling assays, monocyte migration assays, alveolar macrophage enumeration, gene expression profiling in loss-of-function CCR2 patients\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — human loss-of-function genetics with direct functional validation of receptor signaling and migration, multiple kindreds and orthogonal methods\",\n      \"pmids\": [\"38157855\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SphK1 (sphingosine kinase 1) in hepatic stellate cells (HSCs) upregulates CCR2 expression by downregulating miR-19b-3p. miR-19b-3p directly suppresses CCR2 expression in HSCs. This SphK1/miR-19b-3p/CCR2 axis in HSCs contributes to their activation and migration during liver fibrosis.\",\n      \"method\": \"SphK1 knockout mice; bone marrow transplantation; miR-19b-3p overexpression/knockdown; CCR2 expression measurement in HSCs; CCl4 and BDL liver fibrosis models\",\n      \"journal\": \"Hepatology (Baltimore, Md.)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic knockout plus miRNA functional manipulation with in vivo validation, single lab\",\n      \"pmids\": [\"29572892\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"PSMP (PC3-secreted microprotein/MSMP) is a CCR2 ligand that promotes liver fibrosis through CCR2. PSMP induced by HMGB-1 and IL-33 from hepatocytes drives CCR2+ monocyte infiltration into liver, macrophage M1 polarization, and hepatic stellate cell activation via CCR2. Overexpression of PSMP in Psmp-/- mouse livers reversed fibrosis attenuation in a CCR2-dependent manner.\",\n      \"method\": \"Psmp-/- mice; CCl4 and BDL fibrosis models; adeno-associated virus-8 PSMP overexpression; PSMP-neutralizing antibody; in vitro macrophage and LX-2 cell assays; CCR2-dependence confirmed genetically\",\n      \"journal\": \"Journal of hepatology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple genetic models, AAV rescue experiment establishing CCR2 dependence, antibody blockade, and in vitro cell assays in one study\",\n      \"pmids\": [\"31813573\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"PSMP chemoattracts Ly6Chi monocytes in a CCR2-dependent manner, confirmed by in situ chemotaxis and adoptive transfer assays. LPS and muramyl dipeptide induced PSMP expression in colonic epithelial cells, and PSMP promoted M1 macrophages to produce CCL2.\",\n      \"method\": \"In situ chemotaxis assay; adoptive transfer of monocytes; anti-PSMP neutralizing antibody; DSS colitis model; in vitro macrophage stimulation\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo and in vitro functional assays demonstrating CCR2-dependent chemotaxis, single lab\",\n      \"pmids\": [\"28698550\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"A CCR2-positive macrophage subpopulation constitutes the majority of fibrin-internalizing cells in the dermis. Fibrin endocytosis is dependent on plasminogen and plasminogen activator but is independent of fibrinogen receptors αMβ2, ICAM-1, the myeloid cell integrin-binding site on fibrin, or the mannose receptor. Elimination of CCR2-expressing cells diminishes cellular fibrin uptake.\",\n      \"method\": \"Intravital microscopy; CCR2+ cell depletion; fibrin internalization assay; knockout mice for fibrinogen receptors; lysosomal targeting assay\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — intravital microscopy with genetic depletion and multiple receptor knockouts, single lab\",\n      \"pmids\": [\"26647393\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"CCR2 is expressed on murine type II alveolar epithelial cells (AECs) and mediates MCP-1-dependent chemotaxis and wound closure in these non-immune cells. AECs from CCR2-/- mice failed to migrate in response to MCP-1 and showed delayed closure of mechanical wounds compared to wild-type AECs.\",\n      \"method\": \"CCR2 mRNA expression in primary AECs; chemotaxis/haptotaxis assays; mechanical wound closure assay in CCR2-/- vs. wild-type AECs; anti-MCP-1 antibody blockade\",\n      \"journal\": \"American journal of physiology. Lung cellular and molecular physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — CCR2 KO with defined migration phenotype in primary cells, multiple assays, single lab\",\n      \"pmids\": [\"14656700\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"CCR2 mediates MCP-1-dependent haptotactic migration of pleural mesothelial cells (PMCs). IL-2 upregulates CCR2 expression and increases haptotactic migration; LPS initially downregulates CCR2 and decreases migration. Blocking CCR2 with neutralizing antibodies decreases haptotactic response of PMCs to MCP-1.\",\n      \"method\": \"Haptotaxis assay; CCR2 neutralizing antibody blockade; flow cytometry; RT-PCR; PMC cultures with IL-2 and LPS treatment\",\n      \"journal\": \"American journal of physiology. Lung cellular and molecular physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — CCR2 antibody blockade with functional migration assay and receptor expression correlation, single lab\",\n      \"pmids\": [\"10710532\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"CCR2 is expressed in human mesangial cells (HMCs) and mediates direct pro-inflammatory effects. MCP-1 binding to CCR2 on HMCs induces a two-fold increase in ICAM-1 expression at 24 h, enhancing monocyte adhesion. CCR2 blockade with RS102895 prevents MCP-1-induced ICAM-1 upregulation. Mechanical stretch reduces CCR2 mRNA and protein expression in HMCs via an MCP-1-independent mechanism and does not induce ICAM-1 via CCR2.\",\n      \"method\": \"CCR2 antagonist (RS102895) blockade; immunofluorescence; cytofluorimetry; monocyte-HMC adhesion assay; RT-PCR; immunoblotting; flow cytometry\",\n      \"journal\": \"Kidney international\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological CCR2 blockade with multiple readouts establishing direct signaling, single lab\",\n      \"pmids\": [\"16518346\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"PCSK9 reduces LDL-R expression on monocytes, which in turn decreases LDL-C/LDL-R-mediated CCR2 expression on monocytes, impairing MCP-1-directed monocyte migration. LDL-C increases monocyte CCR2 expression. VSMC-derived PCSK9 (induced via TLR-4/SAPK/JNK signaling) inhibits LDL-C-dependent monocyte chemotaxis toward MCP-1.\",\n      \"method\": \"Conditioned media from LPS-stimulated VSMCs applied to monocytes; recombinant PCSK9; LDL-R blocking antibody; CCR2 expression measurement; monocyte migration assay; kinase inhibitor pharmacology\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple functional assays linking PCSK9→LDL-R→CCR2 regulatory axis, single lab\",\n      \"pmids\": [\"28232185\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"NOX4 in hepatic stellate cells (HSCs) stabilizes CCR2 and CCL2 mRNA by promoting Ser221 phosphorylation and cytoplasmic shuttling of the RNA-binding protein HuR. HSC-specific NOX4 knockout mice showed significantly reduced CCR2 and CCL2 expression in alcohol-induced liver injury.\",\n      \"method\": \"HSC-specific NOX4 KO mice; mRNA half-life measurement; HuR phosphorylation and localization assay; alcohol diet model\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — tissue-specific KO plus mechanistic mRNA stability and HuR phosphorylation data, single lab\",\n      \"pmids\": [\"28383062\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Rab GTPases required for cell surface expression and signal transduction (FAK activation) of CCR2 differ from those required for the CXCR4/CCR2 heterodimer, demonstrating that heterodimer formation alters the anterograde trafficking pathway of CCR2.\",\n      \"method\": \"Dominant negative and wild-type Rab GTPase transfection; biotin-streptavidin cell surface expression assay; FAK activation (signal transduction) assay; PC3 prostate cancer cells\",\n      \"journal\": \"Cellular physiology and biochemistry\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, single method per readout, limited mechanistic detail in abstract\",\n      \"pmids\": [\"23839224\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"CCR2 expressed on cancer cells (in addition to monocytes) suppresses anti-tumor adaptive immunity. Deletion of Ccr2 specifically in breast cancer cells increased CTL infiltration and activation, increased CD103+ cross-presenting DCs, upregulated MHC class I, and downregulated PD-L1. CCR2 signaling in cancer cells prevents DC maturation toward the CD103+ subtype and reduces cancer cell sensitivity to CTLs.\",\n      \"method\": \"Orthotopic isograft breast cancer mouse model; Ccr2 deletion in cancer cells (genetic); pharmacological CCR2 inhibition; Batf3-/- mice lacking CD103+ DCs; flow cytometry; tumor growth and survival analysis\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — cancer cell-specific genetic deletion plus pharmacological inhibition with epistasis using Batf3-/- mice, multiple immune phenotypes measured\",\n      \"pmids\": [\"32667673\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"CCR2 signaling in mice promotes infiltration of classical monocytes into the lung and expansion of monocyte-derived cells that play a protective role against SARS-CoV-2. CCR2-deficient mice showed higher viral loads, increased viral dissemination, and elevated inflammatory cytokine responses, demonstrating CCR2-dependent monocyte recruitment is mechanistically required for viral control.\",\n      \"method\": \"Mouse-adapted SARS-CoV-2 infection of CCR2-/- mice; intravital antibody labeling; scRNA-seq of lung homogenates; flow cytometry; viral burden measurement\",\n      \"journal\": \"mBio\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — CCR2 KO with defined viral and inflammatory phenotypes plus scRNA-seq mechanistic profiling, single lab\",\n      \"pmids\": [\"34749524\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"CCL2 and CCR2 are required for formation of osteoclasts and foreign body giant cells (FBGC). Bone marrow from CCL2-/- and CCR2-/- mice produced significantly fewer and smaller osteoclasts and FBGC. Addition of exogenous CCL2 to CCL2-/- bone marrow cultures rescued osteoclast and FBGC formation, demonstrating CCL2/CCR2 signaling is required for monocyte/macrophage fusion.\",\n      \"method\": \"CCL2-/- and CCR2-/- mouse bone marrow cultures; rescue with exogenous CCL2; quantification of osteoclast/FBGC number, nuclei, and size\",\n      \"journal\": \"Journal of cellular biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — dual knockout models with rescue experiment, single lab\",\n      \"pmids\": [\"26205994\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"CCR2 signaling is required for complete skeletal muscle regeneration after freeze injury. CCR2-/- mice showed impaired muscle regeneration, prolonged inflammation, fibrosis, fat infiltration, and impaired strength recovery by day 14–28 post-injury. CCR2 co-localizes with activated macrophages (Mac-3+) and activated muscle precursor cells (myogenin+) in injured muscle, while NCAM expression was more elevated in CCR2-/- injured muscle.\",\n      \"method\": \"CCR2-/- mouse freeze-injury model; histology; immunohistochemistry for CCR2, Mac-3, myogenin, MyoD, NCAM; strength testing\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — CCR2 KO with defined regeneration phenotype and co-localization data, single lab\",\n      \"pmids\": [\"15601671\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"CCR2 inhibition by a novel scFv (58C) that binds the N-terminal domain of CCR2 (KD = 59.8 nM) inhibits monocyte and cancer cell migration and induces M1 macrophage polarization. Multivalent display of 58C-scFv on liposomes further reduces migration by 25–40% and enhances M1 polarization by 200% over monomeric scFv, demonstrating that multivalent CCR2 engagement amplifies downstream signaling effects on macrophage fate.\",\n      \"method\": \"Phage library affinity selection; KD measurement; migration assay; macrophage polarization assay (iNOS/Arg-1, IL-6/Mgl2 ratios); liposomal multivalent display\",\n      \"journal\": \"Molecular pharmaceutics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro receptor binding and functional assays with multivalency comparison, single lab, multiple readouts\",\n      \"pmids\": [\"29791797\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Gas6 promotes the specific recruitment of inflammatory CCR2hiCX3CR1lo monocytes during venous thrombosis via Gas6-dependent regulation of CCR2 expression on monocytes and CCL2 expression on endothelial cells. Gas6-dependent CCL2 expression and monocyte migration were mediated via JNK (c-Jun N-terminal kinase) signaling.\",\n      \"method\": \"Gas6-/- mice; anti-CCR2 and anti-CCL2 antibody depletion; flow cytometry; in vitro monocyte migration assay; JNK inhibitor; FeCl3 and flow-reduction deep venous thrombosis models\",\n      \"journal\": \"Arteriosclerosis, thrombosis, and vascular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic KO plus antibody depletion with pathway inhibitor, single lab\",\n      \"pmids\": [\"28450294\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"CCR2+ macrophages are the predominant source of IGF2 in the neonatal pancreas and support β cell proliferation via IGF1R-mediated signaling. CCR2-specific depletion in neonatal mice leads to a striking reduction in β cell proliferation, dysfunctional islet phenotypes, and glucose intolerance. Adoptive transfer of CCR2+ myeloid cells rescues these defects.\",\n      \"method\": \"CCR2-specific depletion models; adoptive transfer; gene profiling of pancreatic CCR2+ myeloid cells; β cell proliferation assay; glucose tolerance test\",\n      \"journal\": \"JCI insight\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — CCR2+ cell depletion with adoptive transfer rescue and IGF2 mechanism identified, single lab\",\n      \"pmids\": [\"28768911\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"siRNA silencing of CCR2 (siCCR2) delivered via nanoparticles reduces Ly6Chigh monocyte numbers in hearts of mice with autoimmune myocarditis by 69% and is active in both monocytes and bone marrow hematopoietic progenitor cells. siCCR2 reduces migration of bone marrow granulocyte-macrophage progenitors into blood and improves ejection fraction.\",\n      \"method\": \"Nanoparticle-encapsulated siRNA delivery; flow cytometry; histology; cellular MRI with macrophage-avid nanoparticles; cardiac MRI volumetry\",\n      \"journal\": \"European heart journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — RNAi knockdown with multiple functional and imaging readouts, single lab\",\n      \"pmids\": [\"24950695\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"CCR2+ macrophages in the inflamed kidney promote monocyte-to-macrophage transition intravascularly. CCR2-dependent monocyte differentiation generates CCR2 ligands that form an autocrine feed-forward loop. Single-cell RNA sequencing of in vitro cocultures defines a CCR2-dependent monocyte differentiation path associated with acquisition of immune effector functions.\",\n      \"method\": \"scRNA-seq of monocyte-endothelial cocultures; CCR2 KO mice; glomerulonephritis mouse model; flow cytometry\",\n      \"journal\": \"The Journal of experimental medicine\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO plus scRNA-seq mechanistic pathway definition plus in vitro reconstitution, multiple orthogonal methods\",\n      \"pmids\": [\"35404389\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"The CCR2-64I polymorphism (V64I substitution) does not alter CCR5 mRNA levels, CCR5 cell surface expression, or CCR5 coreceptor function in CD4+ T cells. CCR2-64I is linked to CCR5 promoter polymorphisms (208G, 303A, 627C, 676A) but these do not affect CCR5 transcriptional activity in transfected reporter constructs.\",\n      \"method\": \"Flow cytometry for CCR5 surface expression; RT-PCR for CCR5/CCR2 mRNA; CCR5 coreceptor function assay; transfected CCR5 promoter reporter constructs\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal assays establishing a negative mechanistic result, single lab\",\n      \"pmids\": [\"9971830\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Alveolar macrophages do not express CCR2 (confirmed by microarray, RT-PCR, and flow cytometry) and do not migrate toward CCL2, in contrast to peripheral blood monocytes. This establishes that CCR2 loss accompanies monocyte-to-alveolar macrophage differentiation in vivo.\",\n      \"method\": \"Microarray analysis; RT-PCR; flow cytometry; migration assay; comparison of peripheral blood monocytes and alveolar macrophages from same donors\",\n      \"journal\": \"Journal of inflammation (London, England)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods on human primary cells, single lab, informative negative result\",\n      \"pmids\": [\"17888174\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"The obesity-induced functional shift of CCR2-expressing macrophages in the heart is mechanistically mediated by the CCR2/ATF3 (activating transcription factor 3)/lysozyme 1/NF-κB signaling axis. Lysozyme 1 acts as a transcriptional activator by binding to the RelA promoter and driving NF-κB signaling, promoting cardiac inflammation in obesity. Inducible ablation of CCR2+CX3CR1+ macrophages or selective deletion of macrophage CCR2 prevents obesity-induced cardiac dysfunction.\",\n      \"method\": \"scRNA-seq; CUTANA ChIP; luciferase assay; macrophage-specific lentivirus transfection; dual recombinase CCR2+ macrophage ablation; macrophage-specific CCR2 deletion; chromatin immunoprecipitation-PCR\",\n      \"journal\": \"Circulation research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — multiple orthogonal methods (ChIP, luciferase, scRNA-seq, genetic deletion) in single study defining molecular mechanism\",\n      \"pmids\": [\"39056179\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CCR2 is a Gi-coupled seven-transmembrane chemokine receptor that binds CCL2 (and related ligands including CCL7, CCL8, CYTL1, and PSMP) at the extracellular transmembrane domain—as revealed by cryo-EM structure—triggering ERK- and G-protein-dependent monocyte chemotaxis; it also functions as a dual-function scavenger receptor by constitutively internalizing CCL2 independently of G proteins, GRKs, β-arrestins, and clathrin; receptor recycling is regulated by filamin A phosphorylation at S2152 and by transportin1-mediated nuclear translocation; CCR2 mRNA stability is post-transcriptionally controlled by deadenylation/degradation downstream of LPS and by NOX4/HuR signaling and miR-19b-3p; on immune cells, CCR2 is the principal driver of classical monocyte egress from bone marrow and recruitment to inflamed tissues (including heart, kidney, lung, liver, brain, and tumors), where CCR2+ macrophages promote or restrict inflammation depending on context; CCR2 on cancer cells additionally suppresses adaptive immunity by limiting CD103+ DC maturation and promoting PD-L1 expression; and human complete CCR2 deficiency causes impaired CCL2-dependent monocyte lung recruitment, pulmonary alveolar proteinosis, and polycystic lung disease.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"CCR2 is a Gi-coupled seven-transmembrane chemokine receptor that drives chemotactic recruitment of classical monocytes and macrophages to inflamed tissues, and its complete loss-of-function in humans abolishes CCL2-dependent monocyte Ca2+ signaling and lung migration, causing pulmonary alveolar proteinosis and polycystic lung disease [#11]. Cryo-EM of the CCL2–CCR2–G-protein complex shows the chemokine inserting deeply into the extracellular half of the transmembrane domain, with intracellular loop 2 contacts being more critical for G-protein activation than ICL3 [#0]. Beyond CCL2, CCR2 is activated by additional ligands including CYTL1 [#5] and the secreted microprotein PSMP, both driving CCR2-dependent monocyte chemotaxis via Gi/ERK signaling [#13, #14]. CCR2 is also a dual-function receptor that constitutively scavenges extracellular CCL2 by internalizing and recycling independently of G proteins, GRKs, β-arrestins, and clathrin [#1], with recycling supported by filamin A trafficking and its phosphorylation at S2152 [#4]. CCR2 expression is post-transcriptionally controlled through regulated mRNA stability: LPS triggers deadenylation and decay [#6, #7], while NOX4/HuR signaling stabilizes the transcript [#20] and miR-19b-3p suppresses it [#12]. Functionally, CCR2 governs monocyte egress and tissue infiltration in heart, kidney, lung, liver, and other organs, where CCR2+ macrophages can either amplify inflammation through feed-forward ligand loops [#10, #30, #9] or support tissue repair and homeostasis [#23, #28], and CCR2 on cancer cells suppresses anti-tumor immunity by limiting CD103+ DC maturation and upregulating PD-L1 [#22].\",\n  \"teleology\": [\n    {\n      \"year\": 1997,\n      \"claim\": \"Established that CCR2 abundance is set not only by transcription but by regulated mRNA turnover, defining a post-transcriptional control point for receptor expression on activated leukocytes.\",\n      \"evidence\": \"Nuclear run-on, RNase protection, and mRNA half-life/poly(A) decay measurements in LPS- and IL-2-treated monocytes/NK cells\",\n      \"pmids\": [\"9225989\", \"9365120\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the deadenylase/decay machinery acting on CCR2 mRNA not defined\", \"Cis-elements distinguishing CCR2 from ARE-containing chemokine transcripts not mapped\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Addressed whether CCR2 has trafficking destinations beyond the plasma membrane by identifying transportin1 as an agonist-enhanced interactor driving receptor nuclear translocation.\",\n      \"evidence\": \"Bait pulldown, co-immunoprecipitation, nuclear fractionation, and fluorescence imaging\",\n      \"pmids\": [\"18846510\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of nuclear CCR2 localization not established\", \"Interaction shown in a single lab without reciprocal validation\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Resolved how activated CCR2 returns to the surface by showing filamin A and its S2152 phosphorylation are required for endosomal recycling.\",\n      \"evidence\": \"FLNa siRNA knockdown, super-resolution microscopy, phosphosite mutagenesis, and FRAP in CCR2B-expressing cells\",\n      \"pmids\": [\"27909248\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Kinase responsible for S2152 phosphorylation not identified\", \"Single-lab study\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Expanded the CCR2 ligand repertoire beyond CCL2 by demonstrating CYTL1 acts as a functional Gi-coupled agonist driving monocyte chemotaxis.\",\n      \"evidence\": \"Chemotaxis, internalization, and radioligand binding in HEK293-CCR2B cells plus Ccr2-/- macrophage confirmation and pertussis toxin sensitivity\",\n      \"pmids\": [\"27084102\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of CYTL1–CCR2 engagement not determined\", \"Relative physiological contribution versus CCL2 unclear\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Provided atomic-level mechanism of agonist activation, showing CCL2 inserts into the transmembrane core and that ICL2 contacts dominate G-protein activation.\",\n      \"evidence\": \"Cryo-EM of CCL2–CCR2–G-protein complex with functional mutagenesis\",\n      \"pmids\": [\"35570218\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Conformational basis of ligand bias or scavenging not captured\", \"Structures with alternative ligands (CYTL1, PSMP) not solved\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Identified PSMP as an additional CCR2 ligand driving CCR2-dependent monocyte infiltration and fibrosis, with genetic rescue establishing CCR2 dependence.\",\n      \"evidence\": \"Psmp-/- mice, AAV8-PSMP overexpression rescue, neutralizing antibody, and in vitro macrophage/LX-2 assays in liver fibrosis models\",\n      \"pmids\": [\"31813573\", \"28698550\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct PSMP–CCR2 binding affinity not quantified\", \"Whether PSMP and CCL2 compete at the same site unknown\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Defined a non-canonical scavenging function: CCR2 constitutively internalizes and recycles CCL2 independently of G proteins, GRKs, β-arrestins, and clathrin, distinguishing it from a signaling-only receptor.\",\n      \"evidence\": \"CRISPR knockout panels for G proteins, GRKs, β-arrestins, and clathrin with scavenging, internalization, and recycling assays\",\n      \"pmids\": [\"36719944\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular machinery mediating clathrin-independent internalization unidentified\", \"Physiological balance between signaling and scavenging not quantified\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Showed CCR2 on circulating monocytes is required for intravascular monocyte-to-macrophage transition, establishing an autocrine CCR2-ligand feed-forward loop amplifying tissue inflammation.\",\n      \"evidence\": \"scRNA-seq, CCR2 knockout mice, and monocyte–endothelial cocultures in a glomerulonephritis model\",\n      \"pmids\": [\"35404389\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the autocrine CCR2 ligands generated during differentiation not fully resolved\", \"Generalizability beyond renal inflammation untested\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Established CCR2 as essential and non-redundant in humans by showing complete loss-of-function abolishes CCL2-dependent monocyte signaling and lung recruitment, causing pulmonary alveolar proteinosis.\",\n      \"evidence\": \"Human loss-of-function genetics with Ca2+ signaling, migration, and alveolar macrophage enumeration across multiple kindreds\",\n      \"pmids\": [\"38157855\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Why CCR2 loss specifically manifests as polycystic lung disease mechanistically unclear\", \"Therapeutic correction not addressed\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Connected CCR2 macrophage signaling to a transcriptional program by defining a CCR2/ATF3/lysozyme 1/NF-κB axis that drives obesity-induced cardiac inflammation.\",\n      \"evidence\": \"scRNA-seq, ChIP-PCR, luciferase reporter, and macrophage-specific CCR2 deletion/ablation in obese mouse hearts\",\n      \"pmids\": [\"39056179\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct linkage from CCR2 surface signaling to ATF3 induction not fully reconstituted\", \"Relevance to human obese cardiomyopathy untested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How CCR2 partitions between G-protein signaling and clathrin-independent CCL2 scavenging, and how this balance is tuned across monocyte/macrophage states and tissues, remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structural or molecular model of the scavenging endocytic route\", \"Determinants selecting signaling versus scavenging fate of internalized receptor unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060089\", \"supporting_discovery_ids\": [0, 5, 11]},\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [5, 13]},\n      {\"term_id\": \"GO:0038024\", \"supporting_discovery_ids\": [1, 11]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [1, 21]},\n      {\"term_id\": \"GO:0005768\", \"supporting_discovery_ids\": [1, 4]},\n      {\"term_id\": \"GO:0005635\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 5]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [9, 10, 11, 22, 23]},\n      {\"term_id\": \"R-HSA-1500931\", \"supporting_discovery_ids\": [1, 10, 30]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"CCL2\", \"CYTL1\", \"PSMP\", \"FLNA\", \"TNPO1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}