{"gene":"HILPDA","run_date":"2026-04-28T18:06:53","timeline":{"discoveries":[{"year":2005,"finding":"HIG2 (HILPDA) protein is secreted extracellularly and binds to frizzled homologue 10 (FZD10) to activate oncogenic Wnt signaling, functioning as an autocrine growth factor; siRNA knockdown suppressed RCC cell growth and antibody addition induced apoptosis.","method":"Co-expression in COS7 cells, siRNA knockdown, exogenous antibody addition to culture medium, ELISA","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2 — multiple functional assays in cells; binding to FZD10 inferred but not directly demonstrated by pulldown or co-IP","pmids":["15930302"],"is_preprint":false},{"year":2014,"finding":"HILPDA is a direct PPARα target gene via a conserved PPAR response element located ~1200 bp upstream of the transcription start site; hepatic overexpression increases liver triglyceride storage ~4-fold and impairs hepatic triglyceride secretion without affecting lipolysis or lipogenesis gene expression.","method":"Transactivation assay, chromatin immunoprecipitation (ChIP), adeno-associated virus-mediated hepatic overexpression in mice, intracellular lipase activity assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — direct ChIP confirming PPRE binding, in vivo gain-of-function with lipid secretion assay; multiple orthogonal methods","pmids":["24876382"],"is_preprint":false},{"year":2017,"finding":"In macrophages, HILPDA is a HIF-1 target gene and localizes to the endoplasmic reticulum–lipid droplet interface; its conditional knockout abolished hypoxic lipid accumulation and storage of oxidized LDL, cholesteryl esters, and triglycerides, independent of glycolytic switch or fatty acid uptake. HILPDA-deficient macrophages also showed dysregulated LPS-stimulated prostaglandin-E2 production, indicating a substrate buffer/reservoir role of lipid droplets for eicosanoid production.","method":"Conditional Tie2-Cre knockout in mice, subcellular fractionation/localization, lipid accumulation assays, prostaglandin-E2 ELISA, ROS measurement","journal":"FASEB journal","confidence":"High","confidence_rationale":"Tier 2 — clean myeloid-specific KO with multiple orthogonal readouts replicated mechanistic loss-of-function in macrophages","pmids":["28760743"],"is_preprint":false},{"year":2019,"finding":"HILPDA promotes lipid droplet accumulation by inhibiting ATGL-mediated lipolysis; genetic ablation elevates lipolysis correctable by ATGL inhibition. The N-terminal hydrophobic domain of HILPDA is sufficient for targeting to lipid droplets and restoration of triglyceride storage. Nutrient deprivation upregulates HILPDA protein post-transcriptionally requiring autophagic flux.","method":"HILPDA knockout mouse embryonic fibroblasts and tumor cells, ATGL inhibitor rescue, domain-deletion mutants, lipidomic analysis, xenograft tumor growth assay","journal":"Molecular cancer research","confidence":"High","confidence_rationale":"Tier 1-2 — genetic KO with inhibitor rescue, domain mapping, lipidomics; multiple orthogonal methods in one study","pmids":["31308147"],"is_preprint":false},{"year":2020,"finding":"HILPDA is a physiological inhibitor of ATGL-mediated lipolysis in macrophages; HILPDA-deficient macrophages show decreased lipid storage rescued by ATGL inhibition and display increased oxidative metabolism. Lipid droplet accumulation in adipose tissue macrophages driven by HILPDA does not causally drive obesity-induced inflammation.","method":"Myeloid-specific HILPDA knockout mice (diet-induced obesity model), ATGL inhibitor rescue, fatty acid uptake assay, metabolic profiling","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 — clean myeloid-specific KO with ATGL inhibitor rescue; functional epistasis established","pmids":["32049012"],"is_preprint":false},{"year":2020,"finding":"HILPDA increases lipid droplet accumulation by inhibiting ATGL-mediated triglyceride hydrolysis and stimulating triglyceride synthesis via DGAT1; HILPDA localizes to the endoplasmic reticulum and around lipid droplets.","method":"Review synthesizing gain- and loss-of-function experiments; subcellular localization by fractionation/imaging","journal":"Biochimica et biophysica acta. Molecular and cell biology of lipids","confidence":"Medium","confidence_rationale":"Tier 3 — review summarizing prior experimental data; DGAT1 stimulation not independently verified by primary experiment in this paper","pmids":["32417386"],"is_preprint":false},{"year":2022,"finding":"HIG2/HILPDA lacks a G0S2-like hairpin structure and is dependent on ATGL for its full lipid droplet targeting; a homologous hydrophobic domain mediates ATGL binding. ATGL-independent ER localization is absent for HIG2, unlike G0S2.","method":"Structural prediction, cell-based localization studies with deletion mutants, ATGL co-expression rescue","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 — structure-guided mutagenesis with cell-based localization; single study","pmids":["36420951"],"is_preprint":false},{"year":2023,"finding":"HILPDA deficiency in HCC cells shifts polyunsaturated fatty acids to membrane phospholipids and saturated fatty acids to ceramide synthesis, exacerbating lipid peroxidation and apoptosis under hypoxia; pharmacological inhibition of ceramide synthesis reverses HILPDA-deficiency-induced apoptosis. Hepatocyte-specific Hilpda knockout in mice reduces NASH-driven hepatic steatosis and tumorigenesis.","method":"HILPDA KO HCC cells, lipidomics (shotgun and targeted), ceramide synthesis inhibitor rescue, 3D spheroid growth assay, hepatocyte-specific knockout mouse (HilpdaΔHep) on Western diet + CCl4, single-cell RNA-seq","journal":"Journal of hepatology","confidence":"High","confidence_rationale":"Tier 1-2 — lipidomics with pharmacological rescue, in vivo hepatocyte-specific KO, multiple orthogonal methods","pmids":["37061197"],"is_preprint":false},{"year":2023,"finding":"HILPDA mediates a fatty acid-induced autocrine negative feedback loop in adipocytes: elevated intra- or extracellular fatty acids upregulate HILPDA via ER stress and fatty acid receptor 4 (FFAR4) activation, which in turn downregulates ATGL protein levels to suppress lipolysis and maintain lipid homeostasis; HILPDA deficiency under fatty acid overload elevates lipotoxic stress.","method":"Wild-type, HILPDA-deficient and HILPDA-overexpressing adipocytes and mice; ER stress markers; NEFA/glycerol lipolysis assays in vitro and in vivo; FFAR4 pharmacological activation","journal":"Molecular metabolism","confidence":"High","confidence_rationale":"Tier 2 — three genetic models (WT, KO, OE) with in vivo and in vitro lipolysis assays and receptor pharmacology; mechanistic loop established","pmids":["37422000"],"is_preprint":false},{"year":2023,"finding":"HILPDA inhibits PINK1-mediated CLS1 ubiquitination and degradation, leading to elevated cardiolipin (CL) levels in mitochondria, which promotes mitophagy in response to irradiation and contributes to radioresistance in nasopharyngeal carcinoma.","method":"HILPDA overexpression/knockdown in NPC cells, lipidomics, co-immunoprecipitation, ubiquitination assays, mitophagy assays, mitophagy inhibitor + irradiation combination experiments","journal":"Cellular and molecular life sciences","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP and functional rescue with pathway inhibitor; single lab study","pmids":["37552373"],"is_preprint":false},{"year":2024,"finding":"HIF-1α transcriptionally induces HILPDA expression in glioblastoma; HIG-2 binding to FZD10 activates Wnt/β-catenin signaling and increases IGFBP2 levels in microparticles derived from glioma stem cells, decreasing radiosensitivity and immunogenicity of recipient cells.","method":"HIF1α ChIP on HIG2 promoter, FZD10 binding assay, microparticle isolation, Wnt/β-catenin reporter, irradiation assays","journal":"Apoptosis","confidence":"Medium","confidence_rationale":"Tier 2 — ChIP and binding assay with functional readout; single lab study","pmids":["39633113"],"is_preprint":false},{"year":2024,"finding":"FOXS1 directly interacts with HILPDA (by Co-IP) and together they activate the FAK/PI3K/AKT pathway to facilitate epithelial-mesenchymal transition (EMT) in prostate cancer cells.","method":"Co-immunoprecipitation, siRNA knockdown/overexpression, CCK-8, wound healing, Transwell assay, western blot for FAK/PI3K/AKT pathway components","journal":"FASEB journal","confidence":"Low","confidence_rationale":"Tier 3 — single Co-IP with pathway western blots; no in vitro reconstitution or rescue","pmids":["38780613"],"is_preprint":false},{"year":2024,"finding":"HILPDA overexpression in renal tubular cells downregulates ATGL to promote triglyceride overload and defective fatty acid β-oxidation, causing mitochondrial dysfunction, G2/M phase arrest, and profibrogenic factor upregulation; HILPDA deficiency rescues these phenotypes in vitro (HK-2 cells) and in vivo (UUO/UIRI mouse models).","method":"Hilpda overexpression and knockdown in HK-2 cells, UUO and UIRI mouse models, ATGL western blot, fatty acid oxidation assay, cell cycle analysis, fibrosis markers","journal":"Biochimica et biophysica acta. Molecular basis of disease","confidence":"Medium","confidence_rationale":"Tier 2 — multiple in vitro and in vivo loss/gain-of-function with mechanistic readouts; single lab","pmids":["36990128"],"is_preprint":false},{"year":2024,"finding":"AGT directly binds HIF-1α to prevent its degradation and Ang II stabilizes HIF-1α via the MAPK pathway; HIF-1α then transcriptionally regulates HILPDA expression. HILPDA accumulation promotes lipid droplet formation that suppresses ferroptosis, contributing to radioresistance in nasopharyngeal carcinoma.","method":"Co-immunoprecipitation (AGT–HIF-1α interaction), dual-luciferase assay, qRT-PCR, western blot, ferroptosis markers (MDA, lipid peroxidation), colony formation assay, xenograft model","journal":"Radiotherapy and oncology","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP plus luciferase for pathway placement, functional ferroptosis readouts; single lab","pmids":["39709027"],"is_preprint":false},{"year":2025,"finding":"HIF-2α (but not HIF-1α) transcriptionally induces HILPDA in trophoblasts; HILPDA sensitizes trophoblasts to ferroptosis (increased lipid peroxidation, MDA; decreased GSH and GPX4); HILPDA knockdown/knockout significantly attenuates HIF-2α agonist-induced ferroptotic death.","method":"siRNA knockdown and CRISPR-Cas9 knockout of HILPDA in HTR-8/SVneo trophoblasts, HIF-2α pharmacological activation, C11-BODIPY lipid peroxidation assay, MDA/GSH quantification, CCK-8 viability, western blot","journal":"Placenta","confidence":"Medium","confidence_rationale":"Tier 2 — two genetic perturbation approaches (siRNA + CRISPR) with pharmacological pathway activation and multiple ferroptosis readouts; single lab","pmids":["41422655"],"is_preprint":false},{"year":2024,"finding":"HILPDA promotes lipid droplet accumulation in macrophages during Candida albicans challenge by consuming intracellular ER membrane and altering RAC1 translocation and GTPase activity, which restricts phagosome formation; Hilpda-deficient macrophages are more susceptible to systemic C. albicans infection.","method":"Hilpda-deficient macrophages, RAC1 localization/GTPase activity assay, phagosome quantification, in vivo fungal infection model, ATGL inhibitor (Atglistatin) treatment","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 — genetic KO with RAC1 mechanistic readout and in vivo rescue; preprint, not yet peer-reviewed","pmids":["bio_10.1101_2024.06.11.598578"],"is_preprint":true}],"current_model":"HILPDA is a small lipid droplet- and ER-associated protein transcriptionally induced by HIF-1/2 and PPARα that functions primarily as a physiological inhibitor of ATGL-mediated intracellular lipolysis, thereby promoting triglyceride storage in hepatocytes, macrophages, adipocytes, and cancer cells; it additionally modulates lipid droplet composition to regulate ferroptosis sensitivity, mitophagy (via CLS1 stabilization), and phagosome formation (via RAC1), and can bind FZD10 to activate Wnt/β-catenin signaling in certain cancer contexts."},"narrative":{"teleology":[{"year":2005,"claim":"The first functional assignment for HILPDA established it as a secreted ligand for FZD10 that activates Wnt signaling and promotes renal cell carcinoma cell survival, answering how a hypoxia-inducible gene product could act as an autocrine growth factor.","evidence":"Co-expression in COS7, siRNA knockdown, and anti-HIG2 antibody-induced apoptosis in RCC cells","pmids":["15930302"],"confidence":"Medium","gaps":["Direct biophysical demonstration of HILPDA–FZD10 binding not provided","Secretion mechanism uncharacterized","Wnt activation not confirmed in non-RCC contexts at that time"]},{"year":2014,"claim":"Identification of HILPDA as a direct PPARα target gene with a functional PPRE, and demonstration that hepatic overexpression drives triglyceride accumulation without altering lipogenesis genes, established HILPDA as a lipid storage effector rather than a lipogenic transcription factor target.","evidence":"ChIP for PPARα binding, transactivation assay, AAV-mediated hepatic overexpression in mice with triglyceride secretion assays","pmids":["24876382"],"confidence":"High","gaps":["Molecular target of HILPDA-mediated triglyceride retention unknown at this point","Mechanism of impaired TG secretion not delineated"]},{"year":2017,"claim":"Myeloid-specific knockout revealed HILPDA as essential for hypoxia-driven lipid droplet accumulation in macrophages and demonstrated that these lipid droplets serve as reservoirs for prostaglandin-E2 synthesis, linking lipid storage to inflammatory eicosanoid production.","evidence":"Tie2-Cre conditional KO mice, subcellular fractionation showing ER–lipid droplet localization, PGE2 ELISA after LPS stimulation","pmids":["28760743"],"confidence":"High","gaps":["Direct lipolytic target not yet identified in macrophages","Whether HILPDA loss affects other eicosanoid species unknown"]},{"year":2019,"claim":"Genetic ablation and inhibitor rescue experiments identified ATGL as the direct functional target of HILPDA, establishing HILPDA as a bona fide ATGL inhibitor; domain mapping showed the N-terminal hydrophobic region suffices for lipid droplet targeting and triglyceride restoration.","evidence":"HILPDA KO MEFs and tumor cells, Atglistatin rescue of lipolysis, deletion-mutant mapping, lipidomics","pmids":["31308147"],"confidence":"High","gaps":["Direct binding affinity and stoichiometry of HILPDA–ATGL not measured","Relationship to G0S2 inhibition not resolved"]},{"year":2020,"claim":"Confirmation that HILPDA inhibits ATGL in macrophages in vivo, and the unexpected finding that macrophage lipid droplet loss does not ameliorate obesity-driven inflammation, separating lipid storage from inflammatory signaling in adipose tissue macrophages.","evidence":"Myeloid-specific HILPDA KO in diet-induced obesity mouse model with ATGL inhibitor rescue and metabolic profiling","pmids":["32049012"],"confidence":"High","gaps":["Whether HILPDA affects macrophage ATGL post-translationally or via protein–protein occlusion not resolved","Impact on tissue-resident macrophage subtypes beyond adipose not tested"]},{"year":2022,"claim":"Structural comparison with G0S2 showed HILPDA lacks a G0S2-like hairpin and that its lipid droplet localization depends on ATGL co-expression, defining HILPDA as an ATGL-dependent LD resident rather than an autonomous LD-targeting protein.","evidence":"Structure prediction, deletion-mutant localization studies, ATGL co-expression rescue in cells","pmids":["36420951"],"confidence":"Medium","gaps":["No crystal or cryo-EM structure of HILPDA or HILPDA–ATGL complex","Whether ATGL-dependence applies in all cell types untested"]},{"year":2023,"claim":"Three studies collectively expanded HILPDA's role beyond lipolysis: (1) in hepatocellular carcinoma, HILPDA deficiency redirects PUFAs to membrane phospholipids and saturated FAs to ceramides, exacerbating lipid peroxidation and apoptosis under hypoxia; (2) in adipocytes, HILPDA participates in a fatty acid–FFAR4–ER stress negative feedback loop that downregulates ATGL; (3) in nasopharyngeal carcinoma, HILPDA stabilizes CLS1 against PINK1-mediated ubiquitination, increasing cardiolipin and promoting mitophagy-dependent radioresistance.","evidence":"Hepatocyte-specific KO mice on Western diet + CCl4, shotgun lipidomics with ceramide inhibitor rescue (PMID:37061197); WT/KO/OE adipocytes with FFAR4 pharmacology and in vivo lipolysis (PMID:37422000); Co-IP of HILPDA–CLS1, ubiquitination assays, mitophagy inhibitor + irradiation in NPC cells (PMID:37552373)","pmids":["37061197","37422000","37552373"],"confidence":"High","gaps":["Direct mechanism by which HILPDA inhibits PINK1-mediated CLS1 ubiquitination unclear","Whether ceramide-mediated apoptosis is a general feature of HILPDA loss beyond HCC not established","FFAR4-to-HILPDA transcriptional intermediaries not fully mapped"]},{"year":2024,"claim":"Multiple 2024 studies extended HILPDA biology to renal fibrosis, ferroptosis suppression via lipid droplets, Wnt signaling in glioblastoma, and phagosome regulation: HILPDA-driven triglyceride overload causes mitochondrial dysfunction and G2/M arrest in tubular cells; lipid droplet formation downstream of HIF-1α–HILPDA suppresses ferroptosis in NPC; HILPDA–FZD10 activates Wnt/β-catenin in glioma stem cell microparticles; and HILPDA-dependent LD growth restricts RAC1-mediated phagosome formation in macrophages.","evidence":"HILPDA OE/KD in HK-2 cells and UUO/UIRI mouse models (PMID:36990128); AGT–HIF-1α Co-IP, luciferase, ferroptosis markers in NPC xenografts (PMID:39709027); HIF-1α ChIP, FZD10 binding, microparticle Wnt reporter in glioma (PMID:39633113); HILPDA-KO macrophages with RAC1 GTPase assay and in vivo Candida model (preprint: bio_10.1101_2024.06.11.598578)","pmids":["36990128","39709027","39633113"],"confidence":"Medium","gaps":["FOXS1–HILPDA interaction (PMID:38780613) lacks reciprocal validation","Phagosome/RAC1 mechanism from preprint awaits peer review","Whether ferroptosis modulation by HILPDA is cell-type-general or context-specific is unresolved"]},{"year":2025,"claim":"HIF-2α (distinct from HIF-1α) was identified as the transcriptional inducer of HILPDA in trophoblasts, where HILPDA sensitizes cells to ferroptosis rather than suppressing it, revealing cell-type-dependent directionality of HILPDA's effect on ferroptosis.","evidence":"siRNA and CRISPR KO of HILPDA in trophoblasts with HIF-2α agonist, C11-BODIPY lipid peroxidation, MDA/GSH quantification","pmids":["41422655"],"confidence":"Medium","gaps":["Mechanism by which HILPDA promotes ferroptosis in trophoblasts while suppressing it in NPC cells is unexplained","Direct HIF-2α ChIP on HILPDA promoter in trophoblasts not shown"]},{"year":null,"claim":"Key unresolved questions include: the atomic-resolution structure of HILPDA and the HILPDA–ATGL complex; the basis for opposing ferroptosis outcomes across cell types; whether the secreted/Wnt-activating and intracellular lipolysis-inhibiting functions are mediated by distinct pools or post-translational isoforms; and in vivo validation of the RAC1/phagosome axis.","evidence":"","pmids":[],"confidence":"Low","gaps":["No structural model of HILPDA or HILPDA–ATGL complex exists","Dual ferroptosis phenotype (pro- vs. anti-) mechanistically unexplained","Secretory pathway for HILPDA and FZD10 binding interface uncharacterized"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[3,4,8,12]},{"term_id":"GO:0048018","term_label":"receptor ligand activity","supporting_discovery_ids":[0,10]}],"localization":[{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[2,5,6]},{"term_id":"GO:0005811","term_label":"lipid droplet","supporting_discovery_ids":[2,3,5,6]},{"term_id":"GO:0005576","term_label":"extracellular region","supporting_discovery_ids":[0,10]}],"pathway":[{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[1,3,4,7,8,12]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[0,10]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[7,13,14]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[9]}],"complexes":[],"partners":["PNPLA2","FZD10","CLS1","FOXS1","RAC1"],"other_free_text":[]},"mechanistic_narrative":"HILPDA is a hypoxia- and lipid-inducible lipid droplet-associated protein that functions as a physiological inhibitor of ATGL-mediated intracellular lipolysis, thereby promoting triglyceride storage in hepatocytes, macrophages, adipocytes, and tumor cells [PMID:31308147, PMID:32049012, PMID:37422000]. Transcriptionally regulated by HIF-1α, HIF-2α, and PPARα via direct promoter binding, HILPDA localizes to the ER–lipid droplet interface through an N-terminal hydrophobic domain that also mediates ATGL interaction, and its lipid droplet targeting is partly ATGL-dependent [PMID:24876382, PMID:28760743, PMID:36420951]. By controlling lipid droplet abundance and fatty acid partitioning, HILPDA modulates ferroptosis sensitivity through redistribution of polyunsaturated fatty acids into membrane phospholipids, promotes mitophagy via stabilization of CLS1 and cardiolipin accumulation, and buffers eicosanoid precursors for prostaglandin synthesis [PMID:37061197, PMID:37552373, PMID:28760743, PMID:41422655]. In certain cancer contexts, secreted HILPDA binds FZD10 to activate Wnt/β-catenin signaling, functioning as an autocrine growth and immune-evasion factor [PMID:15930302, PMID:39633113]."},"prefetch_data":{"uniprot":{"accession":"Q9Y5L2","full_name":"Hypoxia-inducible lipid droplet-associated protein","aliases":["Hypoxia-inducible gene 2 protein"],"length_aa":63,"mass_kda":7.0,"function":"Increases intracellular lipid accumulation. Stimulates expression of cytokines including IL6, MIF and VEGFA. Enhances cell growth and proliferation","subcellular_location":"Lipid droplet; Secreted; Membrane","url":"https://www.uniprot.org/uniprotkb/Q9Y5L2/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/HILPDA","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/HILPDA","total_profiled":1310},"omim":[{"mim_id":"617905","title":"HYPOXIA-INDUCIBLE LIPID DROPLET-ASSOCIATED PROTEIN; HILPDA","url":"https://www.omim.org/entry/617905"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Lipid droplets","reliability":"Supported"},{"location":"Nucleoplasm","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"esophagus","ntpm":158.6}],"url":"https://www.proteinatlas.org/search/HILPDA"},"hgnc":{"alias_symbol":["FLJ21076","HIG-2","HIG2"],"prev_symbol":["C7orf68"]},"alphafold":{"accession":"Q9Y5L2","domains":[{"cath_id":"1.20.5","chopping":"1-25","consensus_level":"medium","plddt":94.6424,"start":1,"end":25}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9Y5L2","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9Y5L2-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9Y5L2-F1-predicted_aligned_error_v6.png","plddt_mean":72.44},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=HILPDA","jax_strain_url":"https://www.jax.org/strain/search?query=HILPDA"},"sequence":{"accession":"Q9Y5L2","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9Y5L2.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9Y5L2/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9Y5L2"}},"corpus_meta":[{"pmid":"15930302","id":"PMC_15930302","title":"Hypoxia-inducible protein 2 (HIG2), a novel diagnostic marker for renal cell carcinoma and potential target for molecular therapy.","date":"2005","source":"Cancer research","url":"https://pubmed.ncbi.nlm.nih.gov/15930302","citation_count":86,"is_preprint":false},{"pmid":"24876382","id":"PMC_24876382","title":"Hypoxia-inducible lipid droplet-associated (HILPDA) is a novel peroxisome proliferator-activated receptor (PPAR) target involved in hepatic triglyceride secretion.","date":"2014","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/24876382","citation_count":60,"is_preprint":false},{"pmid":"31308147","id":"PMC_31308147","title":"HILPDA Regulates Lipid Metabolism, Lipid Droplet Abundance, and Response to Microenvironmental Stress in Solid Tumors.","date":"2019","source":"Molecular cancer research : MCR","url":"https://pubmed.ncbi.nlm.nih.gov/31308147","citation_count":57,"is_preprint":false},{"pmid":"28760743","id":"PMC_28760743","title":"Hypoxia-inducible protein 2 Hig2/Hilpda mediates neutral lipid accumulation in macrophages and contributes to atherosclerosis in apolipoprotein E-deficient mice.","date":"2017","source":"FASEB journal : official publication of the Federation of American Societies for Experimental Biology","url":"https://pubmed.ncbi.nlm.nih.gov/28760743","citation_count":55,"is_preprint":false},{"pmid":"30205391","id":"PMC_30205391","title":"Long Non-Coding RNA PVT1/miR-150/ HIG2 Axis Regulates the Proliferation, Invasion and the Balance of Iron Metabolism of Hepatocellular Carcinoma.","date":"2018","source":"Cellular physiology and biochemistry : international journal of experimental cellular physiology, biochemistry, and pharmacology","url":"https://pubmed.ncbi.nlm.nih.gov/30205391","citation_count":54,"is_preprint":false},{"pmid":"32049012","id":"PMC_32049012","title":"HILPDA Uncouples Lipid Droplet Accumulation in Adipose Tissue Macrophages from Inflammation and Metabolic Dysregulation.","date":"2020","source":"Cell reports","url":"https://pubmed.ncbi.nlm.nih.gov/32049012","citation_count":50,"is_preprint":false},{"pmid":"32417386","id":"PMC_32417386","title":"Regulation of lipid droplet homeostasis by hypoxia inducible lipid droplet associated HILPDA.","date":"2020","source":"Biochimica et biophysica acta. Molecular and cell biology of lipids","url":"https://pubmed.ncbi.nlm.nih.gov/32417386","citation_count":48,"is_preprint":false},{"pmid":"37061197","id":"PMC_37061197","title":"HILPDA promotes NASH-driven HCC development by restraining intracellular fatty acid flux in hypoxia.","date":"2023","source":"Journal of hepatology","url":"https://pubmed.ncbi.nlm.nih.gov/37061197","citation_count":38,"is_preprint":false},{"pmid":"32818550","id":"PMC_32818550","title":"Hypoxia, hypoxia-inducible gene 2 (HIG2)/HILPDA, and intracellular lipolysis in cancer.","date":"2020","source":"Cancer letters","url":"https://pubmed.ncbi.nlm.nih.gov/32818550","citation_count":32,"is_preprint":false},{"pmid":"27329597","id":"PMC_27329597","title":"Hypoxia upregulates HIG2 expression and contributes to bevacizumab resistance in glioblastoma.","date":"2016","source":"Oncotarget","url":"https://pubmed.ncbi.nlm.nih.gov/27329597","citation_count":26,"is_preprint":false},{"pmid":"23916472","id":"PMC_23916472","title":"HIG2 promotes colorectal cancer progression via hypoxia-dependent and independent pathways.","date":"2013","source":"Cancer letters","url":"https://pubmed.ncbi.nlm.nih.gov/23916472","citation_count":23,"is_preprint":false},{"pmid":"37552373","id":"PMC_37552373","title":"HILPDA-mediated lipidomic remodelling promotes radiotherapy resistance in nasopharyngeal carcinoma by accelerating mitophagy.","date":"2023","source":"Cellular and molecular life sciences : CMLS","url":"https://pubmed.ncbi.nlm.nih.gov/37552373","citation_count":23,"is_preprint":false},{"pmid":"38335255","id":"PMC_38335255","title":"Targeting MYC induces lipid droplet accumulation by upregulation of HILPDA in clear cell renal cell carcinoma.","date":"2024","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/38335255","citation_count":22,"is_preprint":false},{"pmid":"26757780","id":"PMC_26757780","title":"SOX11 and HIG-2 are cross-regulated and affect growth in mantle cell lymphoma.","date":"2016","source":"Leukemia & lymphoma","url":"https://pubmed.ncbi.nlm.nih.gov/26757780","citation_count":14,"is_preprint":false},{"pmid":"27757561","id":"PMC_27757561","title":"Effective induction of cytotoxic T cells recognizing an epitope peptide derived from hypoxia-inducible protein 2 (HIG2) in patients with metastatic renal cell carcinoma.","date":"2016","source":"Cancer immunology, immunotherapy : CII","url":"https://pubmed.ncbi.nlm.nih.gov/27757561","citation_count":14,"is_preprint":false},{"pmid":"24416375","id":"PMC_24416375","title":"Identification of an HLA-A2-restricted epitope peptide derived from hypoxia-inducible protein 2 (HIG2).","date":"2014","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/24416375","citation_count":11,"is_preprint":false},{"pmid":"28739822","id":"PMC_28739822","title":"Stress-responsive HILPDA is necessary for thermoregulation during fasting.","date":"2017","source":"The Journal of endocrinology","url":"https://pubmed.ncbi.nlm.nih.gov/28739822","citation_count":8,"is_preprint":false},{"pmid":"37422000","id":"PMC_37422000","title":"HILPDA is a lipotoxic marker in adipocytes that mediates the autocrine negative feedback regulation of triglyceride hydrolysis by fatty acids and alleviates cellular lipotoxic stress.","date":"2023","source":"Molecular metabolism","url":"https://pubmed.ncbi.nlm.nih.gov/37422000","citation_count":8,"is_preprint":false},{"pmid":"38757390","id":"PMC_38757390","title":"Astrocytic HILPDA promotes lipid droplets generation to drive cognitive dysfunction in mice with sepsis-associated encephalopathy.","date":"2024","source":"CNS neuroscience & therapeutics","url":"https://pubmed.ncbi.nlm.nih.gov/38757390","citation_count":8,"is_preprint":false},{"pmid":"36990128","id":"PMC_36990128","title":"Downregulation of fatty acid oxidation led by Hilpda increases G2/M arrest/delay-induced kidney fibrosis.","date":"2023","source":"Biochimica et biophysica acta. Molecular basis of disease","url":"https://pubmed.ncbi.nlm.nih.gov/36990128","citation_count":6,"is_preprint":false},{"pmid":"39709027","id":"PMC_39709027","title":"Modulation of the local angiotensin II: Suppression of ferroptosis and radiosensitivity in nasopharyngeal carcinoma via the HIF-1α-HILPDA axis.","date":"2024","source":"Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology","url":"https://pubmed.ncbi.nlm.nih.gov/39709027","citation_count":6,"is_preprint":false},{"pmid":"38780613","id":"PMC_38780613","title":"FOXS1 acts as an oncogene and induces EMT through FAK/PI3K/AKT pathway by upregulating HILPDA in prostate cancer.","date":"2024","source":"FASEB journal : official publication of the Federation of American Societies for Experimental Biology","url":"https://pubmed.ncbi.nlm.nih.gov/38780613","citation_count":6,"is_preprint":false},{"pmid":"21614900","id":"PMC_21614900","title":"Expression of hypoxia-inducible 2 (HIG2) protein in uterine cancer.","date":"2011","source":"European journal of gynaecological oncology","url":"https://pubmed.ncbi.nlm.nih.gov/21614900","citation_count":6,"is_preprint":false},{"pmid":"33535136","id":"PMC_33535136","title":"Hypoxia-inducible lipid droplet-associated (HILPDA) facilitates the malignant phenotype of lung adenocarcinoma cells in vitro through modulating cell cycle pathways.","date":"2021","source":"Tissue & cell","url":"https://pubmed.ncbi.nlm.nih.gov/33535136","citation_count":5,"is_preprint":false},{"pmid":"36420951","id":"PMC_36420951","title":"Identification of motifs and mechanisms for lipid droplet targeting of the lipolytic inhibitors G0S2 and HIG2.","date":"2022","source":"Journal of cell science","url":"https://pubmed.ncbi.nlm.nih.gov/36420951","citation_count":4,"is_preprint":false},{"pmid":"39173873","id":"PMC_39173873","title":"Hypoxia-inducible lipid droplet-associated protein (HILPDA) and cystathionine β-synthase (CBS) co-contribute to protecting intestinal epithelial cells from Staphylococcus aureus via regulating lipid droplets formation.","date":"2024","source":"Biochimica et biophysica acta. Molecular and cell biology of lipids","url":"https://pubmed.ncbi.nlm.nih.gov/39173873","citation_count":1,"is_preprint":false},{"pmid":"39633113","id":"PMC_39633113","title":"HIG-2 promotes glioma stemness and radioresistance mediated by IGFBP2-rich microparticles in hypoxia.","date":"2024","source":"Apoptosis : an international journal on programmed cell death","url":"https://pubmed.ncbi.nlm.nih.gov/39633113","citation_count":0,"is_preprint":false},{"pmid":"41246996","id":"PMC_41246996","title":"FOXA1 Upregulates HILPDA to Enhance Lipid Droplet Accumulation and Anoikis Resistance in Lung Adenocarcinoma.","date":"2025","source":"FASEB journal : official publication of the Federation of American Societies for Experimental Biology","url":"https://pubmed.ncbi.nlm.nih.gov/41246996","citation_count":0,"is_preprint":false},{"pmid":"38957783","id":"PMC_38957783","title":"LncRNA HILPDA promotes contrast-induced acute kidney injury by recruiting eIF4B to upregulate XPO1 expression.","date":"2024","source":"Toxicology research","url":"https://pubmed.ncbi.nlm.nih.gov/38957783","citation_count":0,"is_preprint":false},{"pmid":"40861438","id":"PMC_40861438","title":"Identification and validation of expression and functions of ferroptosis-related gene HILPDA in early-onset preeclampsia placentas.","date":"2025","source":"Frontiers in immunology","url":"https://pubmed.ncbi.nlm.nih.gov/40861438","citation_count":0,"is_preprint":false},{"pmid":"41422655","id":"PMC_41422655","title":"HIF-2α / HILPDA promotes ferroptosis sensitivity in placenta trophoblast cells of early-onset preeclampsia.","date":"2025","source":"Placenta","url":"https://pubmed.ncbi.nlm.nih.gov/41422655","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2024.06.11.598578","title":"Lipid droplets restrict phagosome formation during<i>Candida</i>challenge","date":"2024-06-12","source":"bioRxiv","url":"https://doi.org/10.1101/2024.06.11.598578","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2025.10.14.25337882","title":"Germline genetic risk converges through intercellular crosstalk in tumor microenvironment","date":"2025-10-17","source":"bioRxiv","url":"https://doi.org/10.1101/2025.10.14.25337882","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":18261,"output_tokens":4047,"usd":0.057744},"stage2":{"model":"claude-opus-4-6","input_tokens":7548,"output_tokens":3235,"usd":0.177923},"total_usd":0.235667,"stage1_batch_id":"msgbatch_01DzrsgVgYngY1hvM3DU1yF2","stage2_batch_id":"msgbatch_01KA9b7iRzKFdhoBUT7vCvSe","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2005,\n      \"finding\": \"HIG2 (HILPDA) protein is secreted extracellularly and binds to frizzled homologue 10 (FZD10) to activate oncogenic Wnt signaling, functioning as an autocrine growth factor; siRNA knockdown suppressed RCC cell growth and antibody addition induced apoptosis.\",\n      \"method\": \"Co-expression in COS7 cells, siRNA knockdown, exogenous antibody addition to culture medium, ELISA\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple functional assays in cells; binding to FZD10 inferred but not directly demonstrated by pulldown or co-IP\",\n      \"pmids\": [\"15930302\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"HILPDA is a direct PPARα target gene via a conserved PPAR response element located ~1200 bp upstream of the transcription start site; hepatic overexpression increases liver triglyceride storage ~4-fold and impairs hepatic triglyceride secretion without affecting lipolysis or lipogenesis gene expression.\",\n      \"method\": \"Transactivation assay, chromatin immunoprecipitation (ChIP), adeno-associated virus-mediated hepatic overexpression in mice, intracellular lipase activity assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — direct ChIP confirming PPRE binding, in vivo gain-of-function with lipid secretion assay; multiple orthogonal methods\",\n      \"pmids\": [\"24876382\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"In macrophages, HILPDA is a HIF-1 target gene and localizes to the endoplasmic reticulum–lipid droplet interface; its conditional knockout abolished hypoxic lipid accumulation and storage of oxidized LDL, cholesteryl esters, and triglycerides, independent of glycolytic switch or fatty acid uptake. HILPDA-deficient macrophages also showed dysregulated LPS-stimulated prostaglandin-E2 production, indicating a substrate buffer/reservoir role of lipid droplets for eicosanoid production.\",\n      \"method\": \"Conditional Tie2-Cre knockout in mice, subcellular fractionation/localization, lipid accumulation assays, prostaglandin-E2 ELISA, ROS measurement\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean myeloid-specific KO with multiple orthogonal readouts replicated mechanistic loss-of-function in macrophages\",\n      \"pmids\": [\"28760743\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"HILPDA promotes lipid droplet accumulation by inhibiting ATGL-mediated lipolysis; genetic ablation elevates lipolysis correctable by ATGL inhibition. The N-terminal hydrophobic domain of HILPDA is sufficient for targeting to lipid droplets and restoration of triglyceride storage. Nutrient deprivation upregulates HILPDA protein post-transcriptionally requiring autophagic flux.\",\n      \"method\": \"HILPDA knockout mouse embryonic fibroblasts and tumor cells, ATGL inhibitor rescue, domain-deletion mutants, lipidomic analysis, xenograft tumor growth assay\",\n      \"journal\": \"Molecular cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — genetic KO with inhibitor rescue, domain mapping, lipidomics; multiple orthogonal methods in one study\",\n      \"pmids\": [\"31308147\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"HILPDA is a physiological inhibitor of ATGL-mediated lipolysis in macrophages; HILPDA-deficient macrophages show decreased lipid storage rescued by ATGL inhibition and display increased oxidative metabolism. Lipid droplet accumulation in adipose tissue macrophages driven by HILPDA does not causally drive obesity-induced inflammation.\",\n      \"method\": \"Myeloid-specific HILPDA knockout mice (diet-induced obesity model), ATGL inhibitor rescue, fatty acid uptake assay, metabolic profiling\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean myeloid-specific KO with ATGL inhibitor rescue; functional epistasis established\",\n      \"pmids\": [\"32049012\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"HILPDA increases lipid droplet accumulation by inhibiting ATGL-mediated triglyceride hydrolysis and stimulating triglyceride synthesis via DGAT1; HILPDA localizes to the endoplasmic reticulum and around lipid droplets.\",\n      \"method\": \"Review synthesizing gain- and loss-of-function experiments; subcellular localization by fractionation/imaging\",\n      \"journal\": \"Biochimica et biophysica acta. Molecular and cell biology of lipids\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — review summarizing prior experimental data; DGAT1 stimulation not independently verified by primary experiment in this paper\",\n      \"pmids\": [\"32417386\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"HIG2/HILPDA lacks a G0S2-like hairpin structure and is dependent on ATGL for its full lipid droplet targeting; a homologous hydrophobic domain mediates ATGL binding. ATGL-independent ER localization is absent for HIG2, unlike G0S2.\",\n      \"method\": \"Structural prediction, cell-based localization studies with deletion mutants, ATGL co-expression rescue\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — structure-guided mutagenesis with cell-based localization; single study\",\n      \"pmids\": [\"36420951\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"HILPDA deficiency in HCC cells shifts polyunsaturated fatty acids to membrane phospholipids and saturated fatty acids to ceramide synthesis, exacerbating lipid peroxidation and apoptosis under hypoxia; pharmacological inhibition of ceramide synthesis reverses HILPDA-deficiency-induced apoptosis. Hepatocyte-specific Hilpda knockout in mice reduces NASH-driven hepatic steatosis and tumorigenesis.\",\n      \"method\": \"HILPDA KO HCC cells, lipidomics (shotgun and targeted), ceramide synthesis inhibitor rescue, 3D spheroid growth assay, hepatocyte-specific knockout mouse (HilpdaΔHep) on Western diet + CCl4, single-cell RNA-seq\",\n      \"journal\": \"Journal of hepatology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — lipidomics with pharmacological rescue, in vivo hepatocyte-specific KO, multiple orthogonal methods\",\n      \"pmids\": [\"37061197\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"HILPDA mediates a fatty acid-induced autocrine negative feedback loop in adipocytes: elevated intra- or extracellular fatty acids upregulate HILPDA via ER stress and fatty acid receptor 4 (FFAR4) activation, which in turn downregulates ATGL protein levels to suppress lipolysis and maintain lipid homeostasis; HILPDA deficiency under fatty acid overload elevates lipotoxic stress.\",\n      \"method\": \"Wild-type, HILPDA-deficient and HILPDA-overexpressing adipocytes and mice; ER stress markers; NEFA/glycerol lipolysis assays in vitro and in vivo; FFAR4 pharmacological activation\",\n      \"journal\": \"Molecular metabolism\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — three genetic models (WT, KO, OE) with in vivo and in vitro lipolysis assays and receptor pharmacology; mechanistic loop established\",\n      \"pmids\": [\"37422000\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"HILPDA inhibits PINK1-mediated CLS1 ubiquitination and degradation, leading to elevated cardiolipin (CL) levels in mitochondria, which promotes mitophagy in response to irradiation and contributes to radioresistance in nasopharyngeal carcinoma.\",\n      \"method\": \"HILPDA overexpression/knockdown in NPC cells, lipidomics, co-immunoprecipitation, ubiquitination assays, mitophagy assays, mitophagy inhibitor + irradiation combination experiments\",\n      \"journal\": \"Cellular and molecular life sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP and functional rescue with pathway inhibitor; single lab study\",\n      \"pmids\": [\"37552373\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"HIF-1α transcriptionally induces HILPDA expression in glioblastoma; HIG-2 binding to FZD10 activates Wnt/β-catenin signaling and increases IGFBP2 levels in microparticles derived from glioma stem cells, decreasing radiosensitivity and immunogenicity of recipient cells.\",\n      \"method\": \"HIF1α ChIP on HIG2 promoter, FZD10 binding assay, microparticle isolation, Wnt/β-catenin reporter, irradiation assays\",\n      \"journal\": \"Apoptosis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — ChIP and binding assay with functional readout; single lab study\",\n      \"pmids\": [\"39633113\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"FOXS1 directly interacts with HILPDA (by Co-IP) and together they activate the FAK/PI3K/AKT pathway to facilitate epithelial-mesenchymal transition (EMT) in prostate cancer cells.\",\n      \"method\": \"Co-immunoprecipitation, siRNA knockdown/overexpression, CCK-8, wound healing, Transwell assay, western blot for FAK/PI3K/AKT pathway components\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single Co-IP with pathway western blots; no in vitro reconstitution or rescue\",\n      \"pmids\": [\"38780613\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"HILPDA overexpression in renal tubular cells downregulates ATGL to promote triglyceride overload and defective fatty acid β-oxidation, causing mitochondrial dysfunction, G2/M phase arrest, and profibrogenic factor upregulation; HILPDA deficiency rescues these phenotypes in vitro (HK-2 cells) and in vivo (UUO/UIRI mouse models).\",\n      \"method\": \"Hilpda overexpression and knockdown in HK-2 cells, UUO and UIRI mouse models, ATGL western blot, fatty acid oxidation assay, cell cycle analysis, fibrosis markers\",\n      \"journal\": \"Biochimica et biophysica acta. Molecular basis of disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple in vitro and in vivo loss/gain-of-function with mechanistic readouts; single lab\",\n      \"pmids\": [\"36990128\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"AGT directly binds HIF-1α to prevent its degradation and Ang II stabilizes HIF-1α via the MAPK pathway; HIF-1α then transcriptionally regulates HILPDA expression. HILPDA accumulation promotes lipid droplet formation that suppresses ferroptosis, contributing to radioresistance in nasopharyngeal carcinoma.\",\n      \"method\": \"Co-immunoprecipitation (AGT–HIF-1α interaction), dual-luciferase assay, qRT-PCR, western blot, ferroptosis markers (MDA, lipid peroxidation), colony formation assay, xenograft model\",\n      \"journal\": \"Radiotherapy and oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP plus luciferase for pathway placement, functional ferroptosis readouts; single lab\",\n      \"pmids\": [\"39709027\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"HIF-2α (but not HIF-1α) transcriptionally induces HILPDA in trophoblasts; HILPDA sensitizes trophoblasts to ferroptosis (increased lipid peroxidation, MDA; decreased GSH and GPX4); HILPDA knockdown/knockout significantly attenuates HIF-2α agonist-induced ferroptotic death.\",\n      \"method\": \"siRNA knockdown and CRISPR-Cas9 knockout of HILPDA in HTR-8/SVneo trophoblasts, HIF-2α pharmacological activation, C11-BODIPY lipid peroxidation assay, MDA/GSH quantification, CCK-8 viability, western blot\",\n      \"journal\": \"Placenta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — two genetic perturbation approaches (siRNA + CRISPR) with pharmacological pathway activation and multiple ferroptosis readouts; single lab\",\n      \"pmids\": [\"41422655\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"HILPDA promotes lipid droplet accumulation in macrophages during Candida albicans challenge by consuming intracellular ER membrane and altering RAC1 translocation and GTPase activity, which restricts phagosome formation; Hilpda-deficient macrophages are more susceptible to systemic C. albicans infection.\",\n      \"method\": \"Hilpda-deficient macrophages, RAC1 localization/GTPase activity assay, phagosome quantification, in vivo fungal infection model, ATGL inhibitor (Atglistatin) treatment\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with RAC1 mechanistic readout and in vivo rescue; preprint, not yet peer-reviewed\",\n      \"pmids\": [\"bio_10.1101_2024.06.11.598578\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"HILPDA is a small lipid droplet- and ER-associated protein transcriptionally induced by HIF-1/2 and PPARα that functions primarily as a physiological inhibitor of ATGL-mediated intracellular lipolysis, thereby promoting triglyceride storage in hepatocytes, macrophages, adipocytes, and cancer cells; it additionally modulates lipid droplet composition to regulate ferroptosis sensitivity, mitophagy (via CLS1 stabilization), and phagosome formation (via RAC1), and can bind FZD10 to activate Wnt/β-catenin signaling in certain cancer contexts.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"HILPDA is a hypoxia- and lipid-inducible lipid droplet-associated protein that functions as a physiological inhibitor of ATGL-mediated intracellular lipolysis, thereby promoting triglyceride storage in hepatocytes, macrophages, adipocytes, and tumor cells [PMID:31308147, PMID:32049012, PMID:37422000]. Transcriptionally regulated by HIF-1α, HIF-2α, and PPARα via direct promoter binding, HILPDA localizes to the ER–lipid droplet interface through an N-terminal hydrophobic domain that also mediates ATGL interaction, and its lipid droplet targeting is partly ATGL-dependent [PMID:24876382, PMID:28760743, PMID:36420951]. By controlling lipid droplet abundance and fatty acid partitioning, HILPDA modulates ferroptosis sensitivity through redistribution of polyunsaturated fatty acids into membrane phospholipids, promotes mitophagy via stabilization of CLS1 and cardiolipin accumulation, and buffers eicosanoid precursors for prostaglandin synthesis [PMID:37061197, PMID:37552373, PMID:28760743, PMID:41422655]. In certain cancer contexts, secreted HILPDA binds FZD10 to activate Wnt/β-catenin signaling, functioning as an autocrine growth and immune-evasion factor [PMID:15930302, PMID:39633113].\",\n  \"teleology\": [\n    {\n      \"year\": 2005,\n      \"claim\": \"The first functional assignment for HILPDA established it as a secreted ligand for FZD10 that activates Wnt signaling and promotes renal cell carcinoma cell survival, answering how a hypoxia-inducible gene product could act as an autocrine growth factor.\",\n      \"evidence\": \"Co-expression in COS7, siRNA knockdown, and anti-HIG2 antibody-induced apoptosis in RCC cells\",\n      \"pmids\": [\"15930302\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct biophysical demonstration of HILPDA–FZD10 binding not provided\", \"Secretion mechanism uncharacterized\", \"Wnt activation not confirmed in non-RCC contexts at that time\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Identification of HILPDA as a direct PPARα target gene with a functional PPRE, and demonstration that hepatic overexpression drives triglyceride accumulation without altering lipogenesis genes, established HILPDA as a lipid storage effector rather than a lipogenic transcription factor target.\",\n      \"evidence\": \"ChIP for PPARα binding, transactivation assay, AAV-mediated hepatic overexpression in mice with triglyceride secretion assays\",\n      \"pmids\": [\"24876382\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular target of HILPDA-mediated triglyceride retention unknown at this point\", \"Mechanism of impaired TG secretion not delineated\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Myeloid-specific knockout revealed HILPDA as essential for hypoxia-driven lipid droplet accumulation in macrophages and demonstrated that these lipid droplets serve as reservoirs for prostaglandin-E2 synthesis, linking lipid storage to inflammatory eicosanoid production.\",\n      \"evidence\": \"Tie2-Cre conditional KO mice, subcellular fractionation showing ER–lipid droplet localization, PGE2 ELISA after LPS stimulation\",\n      \"pmids\": [\"28760743\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct lipolytic target not yet identified in macrophages\", \"Whether HILPDA loss affects other eicosanoid species unknown\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Genetic ablation and inhibitor rescue experiments identified ATGL as the direct functional target of HILPDA, establishing HILPDA as a bona fide ATGL inhibitor; domain mapping showed the N-terminal hydrophobic region suffices for lipid droplet targeting and triglyceride restoration.\",\n      \"evidence\": \"HILPDA KO MEFs and tumor cells, Atglistatin rescue of lipolysis, deletion-mutant mapping, lipidomics\",\n      \"pmids\": [\"31308147\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct binding affinity and stoichiometry of HILPDA–ATGL not measured\", \"Relationship to G0S2 inhibition not resolved\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Confirmation that HILPDA inhibits ATGL in macrophages in vivo, and the unexpected finding that macrophage lipid droplet loss does not ameliorate obesity-driven inflammation, separating lipid storage from inflammatory signaling in adipose tissue macrophages.\",\n      \"evidence\": \"Myeloid-specific HILPDA KO in diet-induced obesity mouse model with ATGL inhibitor rescue and metabolic profiling\",\n      \"pmids\": [\"32049012\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether HILPDA affects macrophage ATGL post-translationally or via protein–protein occlusion not resolved\", \"Impact on tissue-resident macrophage subtypes beyond adipose not tested\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Structural comparison with G0S2 showed HILPDA lacks a G0S2-like hairpin and that its lipid droplet localization depends on ATGL co-expression, defining HILPDA as an ATGL-dependent LD resident rather than an autonomous LD-targeting protein.\",\n      \"evidence\": \"Structure prediction, deletion-mutant localization studies, ATGL co-expression rescue in cells\",\n      \"pmids\": [\"36420951\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No crystal or cryo-EM structure of HILPDA or HILPDA–ATGL complex\", \"Whether ATGL-dependence applies in all cell types untested\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Three studies collectively expanded HILPDA's role beyond lipolysis: (1) in hepatocellular carcinoma, HILPDA deficiency redirects PUFAs to membrane phospholipids and saturated FAs to ceramides, exacerbating lipid peroxidation and apoptosis under hypoxia; (2) in adipocytes, HILPDA participates in a fatty acid–FFAR4–ER stress negative feedback loop that downregulates ATGL; (3) in nasopharyngeal carcinoma, HILPDA stabilizes CLS1 against PINK1-mediated ubiquitination, increasing cardiolipin and promoting mitophagy-dependent radioresistance.\",\n      \"evidence\": \"Hepatocyte-specific KO mice on Western diet + CCl4, shotgun lipidomics with ceramide inhibitor rescue (PMID:37061197); WT/KO/OE adipocytes with FFAR4 pharmacology and in vivo lipolysis (PMID:37422000); Co-IP of HILPDA–CLS1, ubiquitination assays, mitophagy inhibitor + irradiation in NPC cells (PMID:37552373)\",\n      \"pmids\": [\"37061197\", \"37422000\", \"37552373\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct mechanism by which HILPDA inhibits PINK1-mediated CLS1 ubiquitination unclear\", \"Whether ceramide-mediated apoptosis is a general feature of HILPDA loss beyond HCC not established\", \"FFAR4-to-HILPDA transcriptional intermediaries not fully mapped\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Multiple 2024 studies extended HILPDA biology to renal fibrosis, ferroptosis suppression via lipid droplets, Wnt signaling in glioblastoma, and phagosome regulation: HILPDA-driven triglyceride overload causes mitochondrial dysfunction and G2/M arrest in tubular cells; lipid droplet formation downstream of HIF-1α–HILPDA suppresses ferroptosis in NPC; HILPDA–FZD10 activates Wnt/β-catenin in glioma stem cell microparticles; and HILPDA-dependent LD growth restricts RAC1-mediated phagosome formation in macrophages.\",\n      \"evidence\": \"HILPDA OE/KD in HK-2 cells and UUO/UIRI mouse models (PMID:36990128); AGT–HIF-1α Co-IP, luciferase, ferroptosis markers in NPC xenografts (PMID:39709027); HIF-1α ChIP, FZD10 binding, microparticle Wnt reporter in glioma (PMID:39633113); HILPDA-KO macrophages with RAC1 GTPase assay and in vivo Candida model (preprint: bio_10.1101_2024.06.11.598578)\",\n      \"pmids\": [\"36990128\", \"39709027\", \"39633113\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"FOXS1–HILPDA interaction (PMID:38780613) lacks reciprocal validation\", \"Phagosome/RAC1 mechanism from preprint awaits peer review\", \"Whether ferroptosis modulation by HILPDA is cell-type-general or context-specific is unresolved\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"HIF-2α (distinct from HIF-1α) was identified as the transcriptional inducer of HILPDA in trophoblasts, where HILPDA sensitizes cells to ferroptosis rather than suppressing it, revealing cell-type-dependent directionality of HILPDA's effect on ferroptosis.\",\n      \"evidence\": \"siRNA and CRISPR KO of HILPDA in trophoblasts with HIF-2α agonist, C11-BODIPY lipid peroxidation, MDA/GSH quantification\",\n      \"pmids\": [\"41422655\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which HILPDA promotes ferroptosis in trophoblasts while suppressing it in NPC cells is unexplained\", \"Direct HIF-2α ChIP on HILPDA promoter in trophoblasts not shown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include: the atomic-resolution structure of HILPDA and the HILPDA–ATGL complex; the basis for opposing ferroptosis outcomes across cell types; whether the secreted/Wnt-activating and intracellular lipolysis-inhibiting functions are mediated by distinct pools or post-translational isoforms; and in vivo validation of the RAC1/phagosome axis.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No structural model of HILPDA or HILPDA–ATGL complex exists\", \"Dual ferroptosis phenotype (pro- vs. anti-) mechanistically unexplained\", \"Secretory pathway for HILPDA and FZD10 binding interface uncharacterized\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [3, 4, 8, 12]},\n      {\"term_id\": \"GO:0048018\", \"supporting_discovery_ids\": [0, 10]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [2, 5, 6]},\n      {\"term_id\": \"GO:0005811\", \"supporting_discovery_ids\": [2, 3, 5, 6]},\n      {\"term_id\": \"GO:0005576\", \"supporting_discovery_ids\": [0, 10]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [1, 3, 4, 7, 8, 12]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [0, 10]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [7, 13, 14]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [9]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"PNPLA2\",\n      \"FZD10\",\n      \"CLS1\",\n      \"FOXS1\",\n      \"RAC1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}