Affinage

COL8A2

Collagen alpha-2(VIII) chain · UniProt P25067

Length
703 aa
Mass
67.2 kDa
Annotated
2026-06-09
33 papers in source corpus 10 papers cited in narrative 10 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 5/5 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

COL8A2 encodes the alpha2 chain of type VIII collagen, a structural extracellular matrix protein that is a major component of Descemet's membrane, where type VIII collagen (requiring both Col8a1 and Col8a2 subunits) is required for normal anterior segment development and corneal endothelial cell proliferation (PMID:16051690). Heterozygous missense mutations clustered in the triple helical domain (Q455K, L450W, Q455V) cause early-onset Fuchs endothelial corneal dystrophy and posterior polymorphous corneal dystrophy, establishing COL8A2 as the first molecularly defined gene for corneal endothelial dystrophies (PMID:11689488, PMID:15914606, PMID:18464802). These mutations act through a misfolding/secretory-pathway mechanism: mutant COL8A2 is retained in the rough endoplasmic reticulum, triggering the unfolded protein response and upregulation of autophagy markers such as DRAM1, with downstream accumulation and aberrant assembly of collagen VIII, collagen IV, fibronectin, and laminin in a thickened Descemet's membrane alongside abnormal mitochondria and progressive endothelial cell loss (PMID:16303941, PMID:17471329, PMID:23422828). Beyond its structural role, COL8A2 is required for corneal endothelial cell identity and function, where its expression governs proliferation, WNT/β-catenin and TGF-β signaling, and a YAP/HIPPO–mitochondrial axis controlling endothelial barrier and pump function (PMID:32931574, PMID:39395654). Pathway-level dysregulation of ECM remodeling, ER stress, and immune signaling precedes visible morphological disease in knock-in models (PMID:41575439).

Mechanistic history

Synthesis pass · year-by-year structured walk · 7 steps
  1. 2001 High

    Established the genetic basis of corneal endothelial dystrophy by linking COL8A2 to disease, answering whether an inherited endothelial dystrophy had a defined molecular cause.

    Evidence Genome-wide linkage and direct sequencing identifying a segregating Q455K substitution in the triple helical domain in FECD/PPCD families

    PMID:11689488

    Open questions at the time
    • Did not establish the cellular mechanism by which the mutation causes disease
    • Did not define the role of normal COL8A2 in the endothelium
  2. 2005 High

    Defined L450W as a distinct early-onset subtype and showed that mutations cause massive ECM accumulation in Descemet's membrane, shifting the question from genetics toward a structural assembly defect.

    Evidence Linkage and sequencing with confocal specular microscopy plus immunohistochemistry, TEM, and immunogold on carrier corneas

    PMID:15914606 PMID:16303941

    Open questions at the time
    • Immunogold ER localization implied retention but did not directly demonstrate the UPR
    • Mechanism connecting ECM accumulation to endothelial cell loss unresolved
  3. 2005 High

    Demonstrated the normal developmental requirement for type VIII collagen, separating loss-of-function consequences from the dominant mutant phenotype.

    Evidence Col8a1/Col8a2 double-knockout mice with histology, endothelial cell counts, and growth factor-stimulated proliferation assays

    PMID:16051690

    Open questions at the time
    • Did not model the dominant missense disease mechanism
    • Did not resolve which subunit contributes which function
  4. 2013 High

    Linked COL8A2 mutations mechanistically to ER stress and autophagy, answering how misfolded collagen drives endothelial pathology.

    Evidence L450W and Q455K knock-in mice with TEM, qPCR and Western blot for UPR genes and the autophagy marker DRAM1, validated in human FECD tissue

    PMID:23422828

    Open questions at the time
    • Did not establish whether UPR/autophagy activation is causal or compensatory for cell loss
    • Allele-specific severity differences not mechanistically explained
  5. 2020 Medium

    Showed COL8A2 is required for corneal endothelial cell identity and proliferation beyond its structural ECM role, via knockdown rather than mutation.

    Evidence siRNA knockdown in human and rat CECs with viability, S-phase, cyclin D1, WNT/β-catenin, SMAD2, SNAI1 readouts and an in vivo rat transfection model

    PMID:32931574

    Open questions at the time
    • Single lab
    • Mechanism connecting an ECM protein to intracellular signaling pathways not defined
  6. 2024 Medium

    Identified a COL8A2 → YAP/HIPPO → mitochondrial axis governing endothelial barrier and pump function, providing a signaling framework for COL8A2's functional role.

    Evidence CRISPR/dCas9 activation of COL8A2 in hCECs with TEER, ATP, mitochondrial membrane potential assays, proteomics, and a rat wound-healing model

    PMID:39395654

    Open questions at the time
    • Single lab
    • Causal chain from extracellular COL8A2 to intracellular YAP phosphorylation not mechanistically traced
  7. 2026 Medium

    Defined the early molecular events preceding morphological disease, addressing which pathways initiate pathogenesis versus which are late consequences.

    Evidence Q455K knock-in mice with transcriptomic profiling of pre-pathology endothelium validated by qPCR and immunofluorescence

    PMID:41575439

    Open questions at the time
    • Single lab
    • Causal ordering among ECM remodeling, ER stress, and immune pathways not established
    • Immune pathway involvement functionally untested

Open questions

Synthesis pass · forward-looking unresolved questions
  • How extracellular/ER-retained COL8A2 transduces signals to intracellular YAP/HIPPO and mitochondrial programs, and whether targeting UPR or autophagy alters disease progression, remains unresolved.
  • No defined receptor or transducer linking COL8A2 to YAP/HIPPO
  • Therapeutic modulation of UPR/autophagy untested for disease modification

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0005198 structural molecule activity 3
Localization
GO:0005783 endoplasmic reticulum 3 GO:0005576 extracellular region 2 GO:0031012 extracellular matrix 2
Pathway
R-HSA-1474244 Extracellular matrix organization 3 R-HSA-1643685 Disease 3 R-HSA-8953897 Cellular responses to stimuli 2
Partners
COL8A1
Complex memberships
Descemet's membranetype VIII collagen

Evidence

Reading pass · 10 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2001 Missense mutations in COL8A2 (encoding the alpha2 chain of type VIII collagen) cause early-onset Fuchs endothelial corneal dystrophy (FECD) and posterior polymorphous corneal dystrophy (PPCD). A Gln455Lys substitution in the triple helical domain was identified by linkage mapping and coding sequence analysis in a three-generation FECD family, with additional missense mutations found in familial/sporadic FECD and PPCD cases, establishing COL8A2 as the first molecularly characterized gene for corneal endothelial dystrophies. Genome-wide linkage analysis, PCR amplification and direct sequencing of COL8A2 coding sequence in affected families and controls Human molecular genetics High 11689488
2005 A novel L450W (Leu450Trp) missense mutation in COL8A2 defines a distinct early-onset subtype of Fuchs corneal dystrophy with disease onset in infancy, small rounded endothelial guttae centered on the cell, and a 25-year progression from early to late stages, contrasting with the larger peaked guttae and ~50-year onset of common late-onset FCD. Genome-wide linkage scan, PCR sequencing of COL8A2 exons, confocal specular microscopy of guttae morphology, clinical severity grading Investigative ophthalmology & visual science High 15914606
2005 The L450W COL8A2 mutation causes massive accumulation and abnormal assembly of collagen VIII within Descemet's membrane (DM), with DM several-fold thicker than normal, refractile strands/blebs intensely staining for COL8A2, elevated COL8A1/COL8A2 along the anterior DM edge, and an unusual internal layer with ~120 nm periodicity. Collagen IV, fibronectin, and laminin depositions are also greatly increased in posterior DM. Ultrastructurally, endothelial cells show COL8A2 immunogold signal associated with rough ER ribosomes and abnormal mitochondria, indicating abnormal basement membrane assembly rather than a primary metabolic defect. Immunohistochemistry with antibodies to COL8A1, COL8A2, collagen IV, fibronectin, laminin on corneal explants; transmission electron microscopy; immunogold labeling Investigative ophthalmology & visual science High 16303941
2005 Targeted disruption of both Col8a1 and Col8a2 in mice results in anterior segment dysgenesis: keratoglobus-like anterior chamber protrusion, thinned Descemet's membrane, enlarged and reduced-number corneal endothelial cells, and markedly thinned corneal stroma. Corneal endothelial cells from double-knockout mice show decreased proliferative capacity in response to growth factors in vitro, establishing that type VIII collagen (requiring both subunits) is required for normal anterior eye development and endothelial cell proliferation. Targeted gene inactivation (knockout) of Col8a1 and Col8a2 in mice; histological and ultrastructural analysis of anterior segment; in vitro growth factor-stimulated proliferation assays FASEB journal High 16051690
2006 In corneas from patients with L450W COL8A2 mutation at different disease stages, progressive accumulation of extracellular matrix in DM is accompanied by increased and aberrant deposition of COL8A1, COL8A2, collagen IV, laminin, and fibronectin. Ultrastructurally, endothelial cells show abnormal rough ER and accumulating swollen mitochondria, with COL8A2 immunogold signal associated with the rough ER, indicating that the mutant protein is retained/misprocessed in the secretory pathway. Immunohistochemistry with confocal and bright-field microscopy, electron microscopy, immunogold electron microscopy on staged surgical corneal explants Transactions of the American Ophthalmological Society Medium 17471329
2013 Col8a2 L450W/L450W and Q455K/Q455K knock-in mice both exhibit FECD hallmarks including corneal endothelial cell loss and morphological changes, with Q455K homozygotes showing a more severe phenotype. Both models show dilated rough endoplasmic reticulum and upregulation of unfolded protein response (UPR)-associated genes and proteins. DRAM1, an autophagy marker, is upregulated 2.1-fold in L450W and 5.2-fold in Q455K mouse CECs, and 10.4-fold in human FECD endothelium, linking COL8A2 mutation-induced UPR to altered autophagy in FECD pathogenesis. Col8a2 knock-in mouse models; confocal microscopy for in vivo CEC morphology; transmission electron microscopy; real-time PCR and Western blotting for UPR and autophagy markers; comparison with human FECD tissues Investigative ophthalmology & visual science High 23422828
2020 Knockdown of COL8A2 (siRNA) in cultured human corneal endothelial cells (hCECs) reduces cell viability, proliferation, cyclin D1 expression, and S-phase cell fraction; induces fibroblast-like cell morphology; alters WNT signaling (β-catenin), TGF-β signaling (pSMAD2), SNAI1, and mitochondrial oxidative stress. In vivo siCOL8A2 transfection in rat CECs increases corneal opacity and alters endothelial cell morphology, establishing COL8A2 as required for normal CEC function and identity. siRNA knockdown of COL8A2 in human and rat CECs; cell viability assay; BrdU/S-phase analysis; Western blotting and RT-PCR for cyclin D1, WNT/β-catenin, SMAD2, SNAI1; mitochondrial oxidative stress measurement; in vivo rat transfection model Investigative ophthalmology & visual science Medium 32931574
2024 CRISPR/dCas9-mediated activation of COL8A2 (aCOL8A2) in human corneal endothelial cells increases COL8A2 expression, phospho-YAP (HIPPO signaling), transendothelial electrical resistance (barrier function), and ATP production; attenuates actin cytoskeleton; polarizes mitochondrial membrane potential; and redistributes mitochondria widely. In rats, aCOL8A2 accelerates corneal endothelial wound healing. Proteomic analysis links COL8A2 activation to ECM-receptor interaction, cytoskeletal regulation, and NADP activity pathways, establishing a COL8A2 → YAP/HIPPO → mitochondrial function axis regulating CEC pump and barrier function. CRISPR/dCas9 activation system; Western blotting; proteomic analysis; TEER measurement; ATP production assay; mitochondrial membrane potential assay; rat corneal wound healing model; Gene Ontology analysis Matrix biology Medium 39395654
2008 A novel heterozygous Q455V missense mutation in COL8A2 exon 2 was identified in Korean FECD families and absent from unaffected controls, expanding the allelic series of disease-causing COL8A2 mutations in the triple helical domain region (residues 450–455). PCR-SSCP and direct sequencing of COL8A2 in FECD patients and controls; segregation analysis; computational pathogenicity prediction (SIFT, PolyPhen) Eye (London, England) Medium 18464802
2026 Col8a2 Q455K/Q455K knock-in mice show no observable corneal abnormality before 2 months, with morphological endothelial changes appearing at 4 months. Transcriptomic analysis of early-stage mutant corneal endothelium (before visible pathology) reveals 221 upregulated and 55 downregulated genes, predominantly enriched in ECM remodeling (Lgals3, Timp1, Mmp3), ER stress (Hspa5, Dnajb9, Atf3), and immune-related pathways (Icam1, Bpifb1, C1q), validated by qPCR and immunofluorescence, establishing that these pathways are activated prior to morphological disease onset. Col8a2 Q455K/Q455K knock-in mouse model; slit-lamp microscopy; OCT; confocal microscopy; transcriptomic analysis of corneal endothelial cells; qPCR; immunofluorescence staining Investigative ophthalmology & visual science Medium 41575439

Source papers

Stage 0 corpus · 33 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2001 Missense mutations in COL8A2, the gene encoding the alpha2 chain of type VIII collagen, cause two forms of corneal endothelial dystrophy. Human molecular genetics 311 11689488
2005 Inheritance of a novel COL8A2 mutation defines a distinct early-onset subtype of fuchs corneal dystrophy. Investigative ophthalmology & visual science 180 15914606
2005 Fuchs corneal dystrophy: aberrant collagen distribution in an L450W mutant of the COL8A2 gene. Investigative ophthalmology & visual science 118 16303941
2005 Targeted disruption of Col8a1 and Col8a2 genes in mice leads to anterior segment abnormalities in the eye. FASEB journal : official publication of the Federation of American Societies for Experimental Biology 101 16051690
2013 L450W and Q455K Col8a2 knock-in mouse models of Fuchs endothelial corneal dystrophy show distinct phenotypes and evidence for altered autophagy. Investigative ophthalmology & visual science 67 23422828
2008 Q455V mutation in COL8A2 is associated with Fuchs' corneal dystrophy in Korean patients. Eye (London, England) 60 18464802
2006 Immunohistochemistry and electron microscopy of early-onset fuchs corneal dystrophy in three cases with the same L450W COL8A2 mutation. Transactions of the American Ophthalmological Society 52 17471329
2004 Analysis of COL8A2 gene mutation in Japanese patients with Fuchs' endothelial dystrophy and posterior polymorphous dystrophy. Japanese journal of ophthalmology 46 15175909
2012 Population-based meta-analysis in Caucasians confirms association with COL5A1 and ZNF469 but not COL8A2 with central corneal thickness. Human genetics 45 22814818
2011 Oligomerization of SLC4A11 protein and the severity of FECD and CHED2 corneal dystrophies caused by SLC4A11 mutations. Human mutation 45 22072594
2020 Nano-scale zero valent iron modulates Fe/Cd transporters and immobilizes soil Cd for production of Cd free rice. Chemosphere 41 32679374
2006 No pathogenic mutations identified in the COL8A1 and COL8A2 genes in familial Fuchs corneal dystrophy. Investigative ophthalmology & visual science 34 16936088
2014 Biosynthetic and functional defects in newly identified SLC4A11 mutants and absence of COL8A2 mutations in Fuchs endothelial corneal dystrophy. Journal of human genetics 32 25007886
2011 Real-world experience with adjuvant fec-d chemotherapy in four Ontario regional cancer centres. Current oncology (Toronto, Ont.) 32 21655158
2010 Distribution of COL8A2 and COL8A1 gene variants in Caucasian primary open angle glaucoma patients with thin central corneal thickness. Molecular vision 32 21139683
2020 COL8A2 Regulates the Fate of Corneal Endothelial Cells. Investigative ophthalmology & visual science 29 32931574
2019 Impact of Cumulative Chemotherapy Dose on Survival With Adjuvant FEC-D Chemotherapy for Breast Cancer. Journal of the National Comprehensive Cancer Network : JNCCN 27 31390594
2007 Keratoconus is not associated with mutations in COL8A1 and COL8A2. Cornea 24 17721297
2005 No pathogenic mutations identified in the COL8A2 gene or four positional candidate genes in patients with posterior polymorphous corneal dystrophy. Investigative ophthalmology & visual science 22 15851557
2016 Analysis of SLC4A11, ZEB1, LOXHD1, COL8A2 and TCF4 gene sequences in a multi-generational family with late-onset Fuchs corneal dystrophy. International journal of molecular medicine 16 27121161
2019 Observation of nine previously reported and 10 non-reported SLC4A11 mutations among 20 Iranian CHED probands and identification of an MPDZ mutation as possible cause of CHED and FECD in one family. The British journal of ophthalmology 15 31420327
2021 Collagen type VIII alpha 2 chain (COL8A2), an important component of the basement membrane of the corneal endothelium, facilitates the malignant development of glioblastoma cells via inducing EMT. Journal of bioenergetics and biomembranes 12 33405048
2021 Characterization of a dual media system for culturing primary normal and Fuchs endothelial corneal dystrophy (FECD) endothelial cells. PloS one 10 34587219
2019 TCF4 and COL8A2 Gene Polymorphism Screening in a Greek Population of Late-onset Fuchs Endothelial Corneal Dystrophy. In vivo (Athens, Greece) 9 31028223
2024 COL8A2 activation enhances function of corneal endothelial cells through HIPPO signaling/mitochondria pathway. Matrix biology : journal of the International Society for Matrix Biology 3 39395654
2016 Distinct Clinical Phenotype of Corneal Dystrophy Predicts the p.(Leu450Trp) Substitution in COL8A2. Cornea 2 26989952
2025 Generation of FECD Phenotypes in the Mouse Cornea by UVA Exposure and Surgical Removal of its Corneal Endothelial Layer. Bio-protocol 1 40395849
2013 [Effects of Fe-Cd interaction on the lipid peroxidation and antioxidative enzyme activities of rice]. Ying yong sheng tai xue bao = The journal of applied ecology 1 24380336
2026 Identification of COL8A2, MICAL2, and TNFSF10 as potential biomarkers associated with both exercise response and osteoarthritis: a multi-omics integration study. 3 Biotech 0 41550487
2026 Early Transcriptomic and Pathologic Changes of Col8a2 Mutant Fuchs Endothelial Corneal Dystrophy. Investigative ophthalmology & visual science 0 41575439
2026 Identification of potential therapeutic target SPP1 and related RNA regulatory pathway in FECD through bioinformatics. iScience 0 42028016
2025 Biomarker driven drug repurposing for Fuchs' endothelial corneal dystrophy (FECD): a computational study. In silico pharmacology 0 41384081
2022 Descemet membrane endothelial keratoplasty in eyes with COL8A2-associated corneal dystrophy. American journal of ophthalmology case reports 0 35540705

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