circSIRT2/miR-542-3p/VASH1 axis regulates endothelial-to-mesenchymal transition (EndMT) in subretinal fibrosis in age-related macular degeneration models

Neovascular age-related macular degeneration (nAMD), characterized by choroidal neovascularization (CNV), is one of the leading causes of severe visual impairment and irreversible vision loss around the world. Subretinal fibrosis (SRF) contributes to the incomplete response to anti-vascular endothelial growth factor (VEGF) treatment and is one of the main reasons for long-term poor visual outcomes in nAMD. Reducing SRF is urgently needed in the anti-VEGF era. The role of non-coding RNAs has been implicated in CNV; however, their roles in SRF have not been elucidated yet. Herein, we comprehensively investigated circular RNA (circRNA) profiles in the laser-induced mouse SRF model and the transforming growth factor-β (TGF-β) induced human umbilical vein endothelial cell (HUVEC) fibrosis model. A novel circRNA, circSIRT2, was identified, and its function in SRF and endothelial-to-mesenchymal transition (EndMT) regulation was investigated. circSIRT2 was consistently upregulated in fibrotic models in vivo and in vitro. circSIRT2 overexpression downregulated the fibrotic markers and inhibited the proliferation and migration of endothelial cells in vitro. circSIRT2 overexpression in vivo also reduced SRF area in mice. Mechanistically, circSIRT2 functioned by sponging miR-542-3p, which further upregulated the expression of vasohibin-1 (VASH1) and reduced SRF lesion development. Vitreous delivery of miR-542-3p and VASH1 in the mouse SRF model also confirmed the pro-fibrotic function of miR-542-3p and anti-fibrotic function of VASH1, respectively. In conclusion, circSIRT2 inhibited SRF by binding miR-542-3p, which stimulated the VASH1 expression and subsequently suppressed EndMT. The circSIRT2/miR-542-3p/VASH1 axis may serve as a promising therapeutic target for SRF in nAMD.