Identification of COL4A2 as a Biomarker of Extracellular Matrix Remodeling and Vascular Scaffold in Choroid for Myopia

Purpose: To investigate the extracellular matrix (ECM) change in choroid and explore the key regulator of choroidal vascular scaffold in axial myopia.

Methods: Myopia was induced in pigmented rabbits and guinea pigs using the form-deprivation approach. Quantitative label-free proteomics were performed using the samples of rabbits to investigate the differentially expressed proteins (DEPs) in myopic choroid. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment was conducted to explore the potential biomarkers and signal pathways that form the scaffold and regulate the choroid morphology in myopia. Immunoblotting and immunofluorescence were applied to determine the expression and distribution of DEPs in choroid. Adeno-associated virus was used to knock down the expression of COL4A2 to verify its biological function in refraction development and choroid morphology.

Results: Long-term form deprivation significantly induced myopia shifts and decreased the choroidal thickness in pigmented rabbits. Proteomic analysis revealed that COL4A2 negatively regulates vasculature development. Masson’s trichome staining and immunofluorescence showed decreased choroidal thickness and lumen scaffold deformation with decreased collagen IV in form-deprivation myopia (FDM) choroid. Immunoblotting revealed that COL4A2 rather than COL4A1 contributes to the downregulation of collagen IV in FDM choroid. Dysfunction of COL4A2 hindered choroidal vascular scaffold formation, decreased guinea pig choroidal thickness, and promoted myopia shifts with refraction change and axial elongation.

Conclusions: Type IV collagen is a key ECM in construction of the choroidal vascular lumen. COL4A2 is downregulated in FDM choroid, and suppression of COL4A2 impairs the choroid vascular scaffold and promotes myopia shift with decreased choroidal thickness.