MicroRNA-21 Mediates a Positive Feedback on Angiotensin II-Induced Myofibroblast Transformation

Objective: Post myocardial infarction (MI) fibrosis has been identified as an important factor in the progression of heart failure. Previous studies have revealed that microRNA-21 (miR-21) plays an important role in the pathogenesis of fibrosis. The purpose of this study was to explore the role of miR-21 in post-MI cardiac fibrosis. Material and Methods: MI was established in wild-type (WT) and miR-21 knockout (KO) mice. Primary mice cardiac fibroblasts (CFs) were isolated from WT and miR-21 KO mice and were treated with angiotensin II (Ang II) or Sprouty1 (Spry1) siRNA. Histological analysis and echocardiography were used to determine the extent of fibrosis and cardiac function. Results: Compared with WT mice, miR-21 KO mice displayed smaller fibrotic areas and decreased expression of fibrotic markers and inflammatory cytokines. In parallel, Ang II-induced myofibroblasts transformation was partially inhibited upon miR-21 KO in primary CFs. Mechanistically, we found that the expression of Spry1, a previously reported target of miR-21, was markedly increased in miR-21 KO mice post ME further inhibiting ERK1/2 activation. In vitro studies showed that Ang II activated ERK1/2/TGF-beta/Smad2/3 pathway. Phosphorylated Smad2/3 further enhanced the expression of alpha-SMA and FAP and may promote the maturation of miR-21, thereby downregulating Spry1. Additionally, these effects of miR-21 KO on fibrosis were reversed by siRNA-mediated knockdown of Spry1. Conclusion: Our findings suggest that miR-21 promotes post-MI fibrosis by targeting Spry1. Furthermore, it mediates a positive feedback on Ang II, thereby inducing the ERK/TGF-beta/Smad pathway. Therefore, targeting the miR-21-Spry1 axis may be a promising therapeutic option for ameliorating post-MI cardiac fibrosis.