Role of CCN5 in the fibrotic deformation of retinal pigmented epithelium

Abstract

Retinal pigment epithelium (RPE) plays an essential role in maintaining retinal function, and its defect is thought to be critically implicated in various ocular disorders. I examined the role of the matricellular protein CCN5 in the fibrosis-related processes in ARPE-19 cells and human iPSC-derived RPE cells. This study demonstrated that CCN5 was down-regulated in ARPE-19 cells treated with the pro-fibrotic agent transforming growth factor (TGF)-β. A recombinant adenovirus expressing CCN5 (AdCCN5) prevented TGF-β-induced fibrotic changes, including disruption of tight junctions, collagen gel contraction, up-regulation of mesenchymal marker proteins, and down-regulation of epithelial marker proteins. In addition, AdCCN5 prevented TGF-β-induced functional defects, including increased migratory activity and reduced phagocytic activity. Notably, AdCCN5 reversed morphological and functional defects pre-established by TGF-β prior to viral infection. Moreover, modified mRNA of CCN5 and purified CCN5 protein can also effectively reverse pre-formed characteristics of fibroblast-like RPE cells induced by TGF-β. In addition, ethylene glycol tetraacetic acid (EGTA), epidermal growth factor (EGF), fibroblast growth factor-2 (FGF-2) combination-induced fibrotic deformation of RPE cells was inhibited by AdCCN5. Furthermore, CCN5 suppressed the adverse side-effect of anti-VEGF drugs that induce fibrotic changes in RPE cells. Finally, The CCN5 level was down-regulated in RPE of 18-month-old Ccl2-/- mice, which exhibited retinal defects. Restoration of the CCN5 level via intravitreal injection of adeno-associated virus harboring CCN5 (AAV-CCN5) normalized the altered expression of mesenchymal, epithelial, and functional marker proteins, as assessed by western blotting and immunohistochemistry. Taken together, these data suggest that down-regulation of CCN5 is associated with fibrotic deformation of RPE under diverse pathological conditions and that restoration of the CCN5 level effectively promotes recovery of deformed RPE.