MiR-375 and miR-5691 exert anti-fibroproliferative effects on hypertrophic scar fibroblasts by suppressing thrombospondin 1 expression

Background: Hypertrophic scar (HS) is characterized by the hyperproliferation of fibroblasts and the excessive deposition of extracellular matrix (ECM). Thrombospondin 1 (THBS1) is a component of the ECM, which has been implicated in HS formation. Objectives: This study aimed to explore whether miR-375/miR-5691 could modulate HS formation by targeting THBS1. Methods: The expression levels of miR-375/miR-5691/THBS1 in HS and normal skin tissues were measured by quantitative reverse transcription-polymerase chain reaction. 3-(4,5)-dimethylthiahiazo (-z-y1)-2,5-di-phenytetrazoliumromide and Western blot assays were performed on fibroblasts isolated from HS tissues (HSFBs) to determine cell proliferation and the expression levels of proliferating cell nuclear antigen (PCNA), apoptosis-related proteins (caspase3/9, cleaved caspase3/9, Bax, and Bcl-2), and ECM-related proteins. The binding sites between THBS1 and miR-375/miR-5691 were predicted by the TargetScan. Dual-luciferase reporter and anti-Ago2 immunoprecipitation assays were applied to confirm the interactions between THBS1 and miR-375/miR-5691. Results: The expression levels of both miR-375 and miR-5691 were downregulated in HS tissues and HSFBs, which were negatively correlated with THBS1 expression levels. The overexpression of miR-375/miR-5691 inhibited cell proliferation and ECM production, and promoted apoptosis of HSFBs, while silencing of miR-375/miR-5691 led to an opposite result. In the mechanism analysis, THBS1 was confirmed as the direct target gene of miR-375/miR-5691. Furthermore, rescue experiments showed that the suppressed growth of HSFBs and ECM production induced by silencing of THBS1 was reversed by miR-375/miR-5691 inhibitors. Conclusion: MiR-375/miR-5691 was downregulated in HS tissues, and it could suppress the hyperproliferation and ECM production of HSFBs by targeting THBS1.