Exosome-transmitted circ-CARD6 facilitates posterior capsule opacification development by miR-31/FGF7 axis

Posterior capsular opacification (PCO) is the major vision-disrupting complication arising after cataract surgery. Circular RNAs (circRNAs) are biological active RNAs which were involved in various physiological functions. So far, the role of circRNA caspase recruitment domain family member 6 (circ-CARD6) in PCO is still unclear. Quantitative real-time polymerase chain reaction (qRT-PCR) was applied to detect the expression of circ-CARD6, microRNA 31 (miR-31) and fibroblast growth factor 7 (FGF7) message RNA (mRNA). Western blot was used to analyze the protein expression. Transmission electron microscopy (TEM) was employed to capture the exosome image. The proliferation and metastasis were analyzed by cell counting kit-8 (CCK8), transwell and wound healing assays. The potential binding sequences between miR-31 and circ-CARD6 or FGF7 were respectively predicted by Circinteractome and Targetscan online tool, and verified by dual-luciferase reporter and RNA binding protein immunoprecipitation (RIP) assays. Exosome-transmitted circ-CARD6 was highly expressed in PCO tissues and TGF-β2-treated SRA01/04 cells. Circ-CARD6 deletion repressed the proliferation, metastasis, EMT process and MAPK pathway, which was reversed by anti-miR-31 in TGF-β2-treated SRA01/04 cells. Meanwhile, circ-CARD6 sponged miR-31 which directly targeted FGF7 in TGF-β2-treated SRA01/04 cells. FGF7 overexpression allayed miR-31 overexpression-induced suppression in proliferation, metastasis, EMT process and MAPK pathway. Besides, circ-CARD6 regulated FGF7 expression by sponging miR-31. Circ-CARD6 promoted PCO development via miR-31/FGF7 axis. This finding might contribute to the development of the targeted therapy for PCO.