circCOL3A1-859267 regulates type I collagen expression by sponging miR-29c in human dermal fibroblasts

The genes COL1A1 and COL1A2 encode the pro-alpha 1 and pro-alpha 2 chains of type I collagen, respectively, which is one of the main components of skin dermis. We have previously demonstrated that a circular RNA (a class of recently identified non-coding RNAs that exhibit regulatory potency by sequestering miRNAs like a sponge), which we termed circCOL3A1-859267, is downregulated and regulates type I collagen expression in UVA-exposed human dermal fibroblasts (HDFs). However, the precise mechanisms of circCOL3A1-859267-mediated collagen expression in UVA-irradiated HDFs remain unclear. To elucidate the mechanism of circCOL3A1-859267-mediated regulation of type I collagen expression. We initially predicted miRNA binding sites on circCOL3A1-859267 based on a bioinformatic method, and a dual luciferase reporter assay was used to determine miRNA binding to circCOL3A1-859267 in HEK 293 cells. The effect of UVA irradiation on the expression of miRNAs as well as circCOL3A1-859267-mediated type I collagen expression was further investigated in HDFs. miR-29a, miR-29b, miR-29c, miR-767, and miR-133a were predicted to bind both circCOL3A1-859267 and COL1A1/COL1A2, however, only miR-29c was shown to bind to circCOL3A1-859267 based on the dual luciferase reporter assay. In UVA-exposed HDFs, only miR-29c was upregulated. Finally, transfection of a small interfering RNA targeting circCOL3A1-859267 or miR-29c mimic suppressed the expression of type I collagen in HDFs; the miR-29c mimic-induced down-regulation was restored via overexpression of circCOL3A1-859267 using a lentiviral-based expression system. Our results indicate that circCOL3A1-859267 regulates type I collagen expression by sponging and sequestering miR-29c in HDFs.