Affinage

APOA4

Apolipoprotein A-IV · UniProt P06727

Length
396 aa
Mass
45.4 kDa
Annotated
2026-04-28
37 papers in source corpus 12 papers cited in narrative 12 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

APOA4 is a secreted apolipoprotein that functions in lipid transport, immune modulation, glucose homeostasis, and vascular barrier maintenance. It circulates on HDL and chylomicrons, forms dimers and trimers, and serves as a chaperone for sphingosine 1-phosphate (S1P), directly binding S1P and activating S1P receptors to promote endothelial barrier function (PMID:31462513, PMID:25997739). In adipose tissue, APOA4 signals through the LRP1 receptor to stimulate glucose uptake via PI3K-AKT, and in liver it suppresses pro-inflammatory macrophage and granulocyte activation during high-fat feeding, while also inducing SERPINA3 transcription through nuclear receptors NR4A1 and NR1D1 (PMID:34168225, PMID:36426356, PMID:28412351). Autosomal dominant missense mutations in the N-terminal amyloidogenic region of APOA4 (p.L66V, p.D33N) cause hereditary medullary amyloidosis with kidney disease (PMID:38096951).

Mechanistic history

Synthesis pass · year-by-year structured walk · 9 steps
  1. 1986 High

    Structural analysis of the APOA4 gene established that it shares a common ancestor with APOA1 and APOC3 but lost one ancestral intron, placing it within a linked apolipoprotein gene family and framing subsequent functional studies.

    Evidence Gene isolation, restriction mapping, and intron-exon comparison in human genomic DNA

    PMID:3095836

    Open questions at the time
    • Gene structure alone did not reveal any non-lipid-transport functions
    • No functional assays performed
  2. 2011 Medium

    Identification of LUMAN/CREB3 as a direct transcriptional regulator of APOA4 in dendritic cells revealed that APOA4 expression extends beyond enterocytes and hepatocytes, suggesting immune-relevant roles.

    Evidence Microarray with constitutively active LUMAN overexpression, promoter analysis, and silencing in bone marrow-derived DCs

    PMID:22209087

    Open questions at the time
    • Physiological relevance of DC-derived APOA4 not tested in vivo
    • LUMAN binding site on APOA4 promoter not mapped at nucleotide resolution
  3. 2015 Medium

    Biochemical characterization showed that lipid-free APOA4 forms dimers and exhibits distinct functional properties from ApoA-I — including lower LCAT activation and inhibition of acetylated LDL uptake only in lipid-free state — clarifying its mode of action on HDL.

    Evidence Native gel electrophoresis, BS3 crosslinking, reconstituted HDL formation, LCAT activation, and acetylated LDL uptake assays

    PMID:25997739

    Open questions at the time
    • No high-resolution structure of ApoA4 dimers or trimers
    • In vivo relevance of lipid-free vs. lipid-bound conformations not established
  4. 2016 High

    Discovery that the lncRNA APOA4-AS stabilizes APOA4 mRNA through direct interaction with HuR established a post-transcriptional regulatory axis controlling APOA4 abundance in hepatocytes and in vivo.

    Evidence RNA pulldown, RIP assay, siRNA knockdown in vitro and in ob/ob mice, qPCR

    PMID:27131369

    Open questions at the time
    • Whether APOA4-AS/HuR regulation operates in non-hepatic tissues is unknown
    • Precise HuR binding site on APOA4 mRNA not mapped
  5. 2017 High

    ApoA4 was shown to regulate hepatocyte gene expression by inducing SERPINA3 transcription through nuclear receptors NR4A1 and NR1D1, revealing an intracellular signaling role beyond lipid transport.

    Evidence ChIP, luciferase reporter, and siRNA knockdown of NR4A1/NR1D1 in mouse hepatocytes

    PMID:28412351

    Open questions at the time
    • How extracellular ApoA4 activates intracellular nuclear receptors is mechanistically unclear
    • Downstream physiological consequence of SERPINA3 induction by ApoA4 not defined
  6. 2019 High

    Identification of ApoA4 as an S1P chaperone that binds S1P and activates S1P receptors to strengthen endothelial barriers expanded its function beyond lipoprotein metabolism to vascular signaling.

    Evidence Recombinant ApoA4 binding assays, S1P receptor activation, endothelial barrier assays, and ApoM/albumin double-KO mice

    PMID:31462513

    Open questions at the time
    • Quantitative contribution of ApoA4-S1P relative to ApoM-S1P and albumin-S1P in vivo not determined
    • Structural basis of ApoA4-S1P interaction unknown
  7. 2021 High

    Three concurrent advances defined APOA4's receptor-mediated signaling, anti-inflammatory role, and upstream transcriptional regulation: LRP1 was identified as the adipocyte receptor mediating APOA4-dependent glucose uptake via PI3K-AKT; ApoA4 deficiency was shown to unleash hepatic inflammatory macrophage and granulocyte subsets in NAFL; and HGF/c-Met was established as a transcriptional inducer of APOA4 in hepatocytes.

    Evidence Co-IP/MS and siRNA in 3T3-L1 adipocytes (LRP1); scRNA-seq of WT vs. ApoA4-KO mouse liver (inflammation); rh-HGF treatment of primary human hepatocytes with c-Met inhibitor (HGF/c-Met)

    PMID:33925510 PMID:34168225 PMID:36426356

    Open questions at the time
    • LRP1-APOA4 interaction domain not mapped
    • Whether anti-inflammatory effects are direct or secondary to lipid changes is unresolved
    • In vivo validation of HGF/c-Met–APOA4 axis in human liver not performed
  8. 2023 High

    Missense mutations (p.L66V, p.D33N) in APOA4 were shown to cause autosomal dominant hereditary medullary amyloidosis, linking the N-terminal region to amyloidogenic propensity and establishing APOA4 as a disease gene.

    Evidence WGS of affected families, kidney biopsy with mass spectrometry identifying mutant ApoA4 as amyloid constituent

    PMID:38096951

    Open questions at the time
    • In vitro amyloid fibril formation assays for these variants not reported
    • Whether wild-type ApoA4 contributes to sporadic amyloidosis is unknown
  9. 2025 Medium

    A reciprocal regulatory relationship between PCSK9 and APOA4 in hepatocytes was demonstrated, linking APOA4 to cholesterol metabolism and cholelithiasis pathways.

    Evidence siRNA knockdown and overexpression in AML12 hepatocytes with in vivo murine cholelithiasis model

    PMID:40206272

    Open questions at the time
    • Mechanism of reciprocal regulation (direct vs. indirect) not defined
    • Relevance to human gallstone disease not established

Open questions

Synthesis pass · forward-looking unresolved questions
  • Key unresolved questions include the structural basis of ApoA4's multifunctional activity (lipid transport, S1P chaperoning, receptor engagement), the mechanism by which extracellular ApoA4 activates intracellular nuclear receptors, and whether the anti-inflammatory and glucose-sensitizing functions are interdependent or independent pathways.
  • No high-resolution structure of full-length ApoA4 in lipid-bound or lipid-free state
  • Integrated in vivo model testing S1P, LRP1, and anti-inflammatory functions simultaneously is lacking
  • Relative contribution of intestinal vs. hepatic APOA4 to systemic functions not dissected

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0008289 lipid binding 2 GO:0048018 receptor ligand activity 2 GO:0140104 molecular carrier activity 1
Localization
GO:0005576 extracellular region 4
Pathway
R-HSA-1430728 Metabolism 2 R-HSA-162582 Signal Transduction 2 R-HSA-1643685 Disease 1 R-HSA-168256 Immune System 1
Partners
CD300LGHURLRP1NR1D1NR4A1PCSK9

Evidence

Reading pass · 12 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1986 The human APOA4 gene contains only two introns (unlike APOA1 and APOC3 which have three), with introns separating sequences encoding the signal peptide and amphipathic domains, indicating APOA4, APOA1, and APOC3 share a common evolutionary ancestor and APOA4 lost one ancestral intron during evolution. Gene isolation, restriction mapping, and structural characterization Proceedings of the National Academy of Sciences of the United States of America High 3095836
2016 The lncRNA APOA4-AS directly interacts with the mRNA-stabilizing protein HuR to stabilize APOA4 mRNA; knockdown of APOA4-AS reduces APOA4 expression both in vitro and in vivo, and deletion of HuR dramatically reduces both APOA4-AS and APOA4 transcripts. RNA pulldown, RIP assay, siRNA knockdown in vitro and in vivo (ob/ob mice), quantitative PCR Nucleic acids research High 27131369
2019 ApoA4 functions as a sphingosine 1-phosphate (S1P) chaperone: recombinant ApoA4 directly binds S1P, activates multiple S1P receptors, and promotes vascular endothelial barrier function, identified in ApoM- and albumin-double-knockout mice that retain ~25% plasma S1P. Recombinant protein binding assay, S1P receptor activation assay, endothelial barrier function assay, ApoM/albumin double-KO mouse model Journal of lipid research High 31462513
2021 LRP1 (low-density lipoprotein receptor-related protein 1) is identified as a receptor for APOA4 in adipose tissue; LRP1 co-localizes and co-immunoprecipitates with APOA4 in adipocytes, their interaction is enhanced during lipid feeding, and LRP1 knockdown abrogates APOA4-induced glucose uptake and PI3K-AKT activation in 3T3-L1 adipocytes. Co-immunoprecipitation coupled with mass spectrometry, co-localization (immunofluorescence), siRNA knockdown, glucose uptake assay, PI3K-AKT signaling assay Scientific reports High 34168225
2017 ApoA4 stimulates SERPINA3 (serine proteinase inhibitor) gene expression in mouse hepatocytes by binding nuclear receptors NR4A1 and NR1D1, which then act on the SERPINA3 promoter; confirmed by ChIP, luciferase reporter assay, and siRNA-mediated knockdown of NR4A1 or NR1D1. ChIP assay, luciferase reporter assay, RNA interference-mediated knockdown, in vivo and in vitro expression assays Biochemical and biophysical research communications High 28412351
2011 The transcription factor LUMAN (CREB3/LZIP) directly regulates ApoA4 gene expression in dendritic cells; expression of a constitutively active LUMAN in DC cell line D2SC/1 identified ApoA4 as a target gene, confirmed by promoter analysis and silencing studies in bone marrow-derived DCs. Microarray analysis, constitutively active LUMAN overexpression, bioinformatics-based promoter analysis, gene silencing Molecular immunology Medium 22209087
2015 In lipid-free state, ApoA4 exists predominantly as a dimer (up to dimer by crosslinking) with two distinct bands on native gel, while in reconstituted HDL (rHDL) state it forms dimers and trimers; ApoA4 shows lower phospholipid binding ability, lower LCAT activation, and inhibits acetylated LDL uptake only in lipid-free state compared to ApoA-I. Native gel electrophoresis, BS3 chemical crosslinking, reconstituted HDL formation, LCAT activation assay, acetylated LDL uptake assay Molecules and cells Medium 25997739
2021 ApoA4 deficiency in mice fed a high-fat diet leads to increased abundance of specific inflammatory macrophage subsets (Cxcl9+ and Cxcl2+ macrophages) and activated granulocytes (Wfdc17+) in liver, with elevated NE and IL-1β expression in these cells, establishing ApoA4 as a suppressor of hepatic immune cell activation in NAFL. Single-cell RNA sequencing of liver immune cells from WT vs. ApoA4-deficient mice, immunostaining, qRT-PCR Frontiers in immunology Medium 36426356
2023 Autosomal dominant missense mutations in APOA4 (p.L66V and p.D33N) cause medullary amyloidosis with kidney disease; mutated ApoA4 protein is identified as the predominant amyloid constituent in kidney biopsies by mass spectrometry, and mutations are predicted to expand the amyloidogenic hotspot in the ApoA4 structure. Whole genome sequencing, kidney biopsy pathology, mass spectrometry of amyloid constituents, clinical genotype-phenotype analysis Kidney international High 38096951
2021 Recombinant human HGF (rh-HGF) induces APOA4 expression in liver via the c-Met receptor; APOA4 induction at mRNA and protein levels was observed in primary cultured human hepatocytes and was inhibited by a c-Met inhibitor, demonstrating c-Met-dependent transcriptional regulation of APOA4. In vivo mouse liver gene expression analysis, primary human hepatocyte culture, c-Met inhibitor treatment, mRNA and protein quantification International journal of molecular sciences Medium 33925510
2025 CD300LG acts as a receptor for triglyceride-rich lipoproteins (TRLs) through a direct interaction with ApoA4 to facilitate TRL clearance at the microvascular endothelium; CD300LG deficiency causes postprandial hypertriglyceridemia in mice. Direct binding assay (CD300LG–ApoA4 interaction), CD300LG-deficient mouse model, postprandial triglyceride clearance assay, human genetic analysis bioRxivpreprint Medium bio_10.1101_2025.08.08.669356
2025 PCSK9 knockdown increases APOA4 expression and APOA4 overexpression reduces PCSK9 expression in AML12 hepatocytes, establishing a reciprocal feedback regulatory relationship between PCSK9 and APOA4 in cholesterol metabolism; TMAO upregulates hepatic PCSK9 and reduces APOA4, promoting lithogenesis. siRNA knockdown, overexpression plasmids, in vitro hepatocyte model (AML12), in vivo murine cholelithiasis model, RNA sequencing Journal of clinical and translational hepatology Medium 40206272

Source papers

Stage 0 corpus · 37 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
1986 Structure, evolution, and polymorphisms of the human apolipoprotein A4 gene (APOA4). Proceedings of the National Academy of Sciences of the United States of America 81 3095836
1988 DNA polymorphism haplotypes of the human apolipoprotein APOA1-APOC3-APOA4 gene cluster. Human genetics 70 2903847
2016 A long non-coding RNA, APOA4-AS, regulates APOA4 expression depending on HuR in mice. Nucleic acids research 65 27131369
2015 Decreased expression of the APOA1-APOC3-APOA4 gene cluster is associated with risk of Alzheimer's disease. Drug design, development and therapy 45 26491253
2003 The study of APOA1, APOC3 and APOA4 variability in healthy ageing people reveals another paradox in the oldest old subjects. Annals of human genetics 42 12556235
2019 Identification of ApoA4 as a sphingosine 1-phosphate chaperone in ApoM- and albumin-deficient mice. Journal of lipid research 39 31462513
2021 Low-density lipoprotein receptor-related protein 1 (LRP1) is a novel receptor for apolipoprotein A4 (APOA4) in adipose tissue. Scientific reports 38 34168225
2011 Effect of walnut-enriched meat on the relationship between VCAM, ICAM, and LTB4 levels and PON-1 activity in ApoA4 360 and PON-1 allele carriers at increased cardiovascular risk. European journal of clinical nutrition 37 21407247
2016 Interactions of Environmental Factors and APOA1-APOC3-APOA4-APOA5 Gene Cluster Gene Polymorphisms with Metabolic Syndrome. PloS one 34 26824674
2017 Effect of ApoA4 on SERPINA3 mediated by nuclear receptors NR4A1 and NR1D1 in hepatocytes. Biochemical and biophysical research communications 28 28412351
1996 Population distributions of APOE, APOH, and APOA4 polymorphisms and their relationships with quantitative plasma lipid levels among the Evenki herders of Siberia. Human biology 25 8838914
2010 APOA1 and APOA4 gene polymorphisms influence the effects of dietary fat on LDL particle size and oxidation in healthy young adults. The Journal of nutrition 24 20164363
2018 Serum ApoA4 levels predicted the progression of renal impairment in T2DM. European journal of clinical investigation 21 29675916
2011 Analysis of genes regulated by the transcription factor LUMAN identifies ApoA4 as a target gene in dendritic cells. Molecular immunology 21 22209087
2015 Effects of Polymorphisms in APOA4-APOA5-ZNF259-BUD13 Gene Cluster on Plasma Levels of Triglycerides and Risk of Coronary Heart Disease in a Chinese Han Population. PloS one 20 26397108
2011 APOA4 polymorphism as a risk factor for unfavorable lipid serum profile and depression: a cross-sectional study. Journal of investigative medicine : the official publication of the American Federation for Clinical Research 19 21712729
2022 Single-cell RNA sequencing reveals a novel inhibitory effect of ApoA4 on NAFL mediated by liver-specific subsets of myeloid cells. Frontiers in immunology 14 36426356
2023 Autosomal dominant ApoA4 mutations present as tubulointerstitial kidney disease with medullary amyloidosis. Kidney international 11 38096951
2015 Different Functional and Structural Characteristics between ApoA-I and ApoA-4 in Lipid-Free and Reconstituted HDL State: ApoA-4 Showed Less Anti-Atherogenic Activity. Molecules and cells 11 25997739
2023 HDL anti-inflammatory function is impaired and associated with high SAA1 and low APOA4 levels in aneurysmal subarachnoid hemorrhage. Journal of cerebral blood flow and metabolism : official journal of the International Society of Cerebral Blood Flow and Metabolism 10 37357772
2019 The significance of calprotectin, CD147, APOA4 and DJ-1 in non-invasive detection of urinary bladder carcinoma. Neoplasma 10 31607136
2019 Interaction of polymorphisms in APOA4-APOA5-ZPR1-BUD13 gene cluster and sleep duration on 5-year lipid changes in middle aged and older Chinese. Sleep 8 31181149
2012 Minor allele of the APOA4 gene T347S polymorphism predisposes to obesity in postmenopausal Turkish women. Molecular biology reports 8 23096082
2025 PCSK9 and APOA4: The Dynamic Duo in TMAO-induced Cholesterol Metabolism and Cholelithiasis. Journal of clinical and translational hepatology 6 40206272
2021 The Variants at APOA1 and APOA4 Contribute to the Susceptibility of Schizophrenia With Inhibiting mRNA Expression in Peripheral Blood Leukocytes. Frontiers in molecular biosciences 6 34938775
2015 Transcriptome Reveals 1400-Fold Upregulation of APOA4-APOC3 and 1100-Fold Downregulation of GIF in the Patients with Polycythemia-Induced Gastric Injury. PloS one 6 26485402
2021 Depression Augments Plasma APOA4 without Changes of Plasma Lipids and Glucose in Female Adolescents Carrying G Allele of APOA4 rs5104. Journal of molecular neuroscience : MN 5 33403595
1992 Linkage heterogeneity between the C3 and LDLR and the APOA4 and APOA1 loci in baboons. Genomics 5 1427832
2024 Miniaturized 3D-printed ratiometric electrochemical immunosensing platform for ultrasensitive detection of depression biomarker Apo-A4. Talanta 3 39566154
2021 Serum APOA4 Pharmacodynamically Represents Administered Recombinant Human Hepatocyte Growth Factor (E3112). International journal of molecular sciences 3 33925510
2016 LEP, LDLR and APOA4 gene polymorphisms and their relationship with the risk of overweight, obesity and chronic diseases in adults of the State of Sucre, Venezuela. Biomedica : revista del Instituto Nacional de Salud 3 27622441
1988 NcoI dimorphic site located 8kb 3' to the human apolipoprotein AIV (APOA4) gene. Nucleic acids research 3 2894008
2025 Therapeutic potential of simvastatin in ALS: Enhanced axonal integrity and motor neuron survival through Apoa4 and Alb modulation. Biomolecules & biomedicine 1 39569650
2025 Establishment and characterization of liver-specific Apoa4-Cre and Cyp2c11-Cre rat models in juvenile and adult stages. Animal models and experimental medicine 1 39916324
2025 Genome-wide study links cardiometabolic factors to cognition via APOA4-APOA5-ZPR1-BUD13 and other loci in rural Indians. Alzheimer's & dementia : the journal of the Alzheimer's Association 1 40665476
2026 Predictive value of serum apolipoprotein panel (ApoA1 / ApoA2 / ApoA4) as a biomarker for individual radiosensitivity. Lipids in health and disease 0 41582167
2026 Wharton's jelly mesenchymal stem cell-secretome enhances skin rejuvenation via ApoA4 and SERPINH1. Regenerative therapy 0 41684813