No abstract

MiRNAs regulate the cardiomyocyte (CM) cell cycle at the post-transcriptional level, affect cell proliferation, and intervene in harmed CM repair post-injury. The present study was undertaken to characterize the role of let-7i-5p in the processes of CM cell cycle and proliferation and to reveal the mechanisms thereof. In the present study, we used real-time qPCR (RT-qPCR) to determine the up-regulated let-7i-5p in CMs during the postnatal switch from proliferation to terminal differentiation and further validated the role of let-7i-5p by loss- and gain-of-function of let-7i-5p in CMs in vitro and in vivo. We found that the overexpression of let-7i-5p inhibited CM proliferation, whereas the suppression of let-7i-5p significantly facilitated CM proliferation. E2F2 and CCND2 were identified as the targets of let-7i-5p, mediating its effect in regulating the cell cycle of CMs. Supperession of let-7i-5p promoted the recovery of heart function post-myocardial infarction by enhancing E2F2 and CCND2. Collectively, our results revealed that let-7i-5p is involved in the regulation of the CM cell cycle and further impacts proliferation, which may offer a new potential therapeutic strategy for cardiac repair after ischemic injury.

The long non-coding RNA (lncRNA) PTENP1 is a pseudogene of phosphatase and tensin homologue deleted on chromosome ten (PTEN), has been implicated in smooth muscle cell (SMC) proliferation and apoptosis. PTENP1 is the pseudogene of PTEN. However, it is unclear whether and how PTENP1 functions in the proliferation and apoptosis of human aortic SMCs (HASMCs). Here, we hypothesised that PTENP1 inhibits HASMC proliferation and enhances apoptosis by promoting PTEN expression. PCR analysis and Western blot assays respectively showed that both PTENP1 and PTEN were up-regulated in human aortic dissection (AD) samples. PTENP1 overexpression significantly increased the protein expression of PTEN, promoted apoptosis and inhibited the proliferation of HASMCs. PTENP1 silencing exhibited the opposite effects and mitigated H2O2-induced apoptosis of HASMCs. In an angiotensin II (Ang II)-induced mouse aortic aneurysm (AA) model, PTENP1 overexpression potentiated aortic SMC apoptosis, exacerbated aneurysm formation. Mechanistically, RNA pull-down assay and a series of luciferase reporter assays using miR-21 mimics or inhibitors identified PTENP1 as a molecular sponge for miR-21 to endogenously compete for the binding between miR-21 and the PTEN transcript, releasing PTEN expression. This finding was further supported by in vitro immunofluorescent evidence showing decreased cell apoptosis upon miR-21 mimic administration under baseline PTENP1 overexpression. Ex vivo rescue of PTEN significantly mitigated the SMC apoptosis induced by PTENP1 overexpression. Finally, Western blot assays showed substantially reduced Akt phosphorylation and cyclin D1 and cyclin E levels with up-regulated PTENP1 in HASMCs. Our study identified PTENP1 as a mediator of HASMC homeostasis and suggests that PTENP1 is a potential target in AD or AA intervention.