Stem cells are considered as the next generation drug treatment in patients with cardiovascular disease who are resistant to conventional treatment. Among several stem cells used in the clinical setting, cardiac stem cells (CSCs) which reside in the myocardium and epicardium of the heart have been shown to be an effective option for the source of stem cells. In normal circumstances, CSCs primarily function as a cell store to replace the physiologically depleted cardiovascular cells, while under the diseased condition they have been shown to experimentally regenerate the diseased myocardium. In spite of their major functional role, molecular mechanisms regulating the CSCs proliferation and differentiation are still unknown. MicroRNAs (miRs) are small, noncoding RNA molecules that regulate gene expression at the posttranscriptional level. Recent studies have demonstrated the important role of miRs in regulating stem cell proliferation and differentiation, as well as other physiological and pathological processes related to stem cell function. This review summarises the current understanding of the role of miRs in CSCs. A deeper understanding of the mechanisms by which miRs regulate CSCs may lead to advances in the mode of stem cell therapies for the treatment of cardiovascular diseases.

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Aims/hypothesis Diabetes mellitus causes a progressive loss of functional efficacy in stem cells, including cardiac progenitor cells (CPCs). The underlying molecular mechanism is still not known. MicroRNAs (miRNAs) are small, non-coding RNA molecules that regulate genes at the post-transcriptional level. We aimed to determine if diabetes mellitus induces dysregulation of miRNAs in CPCs and to test if in vitro therapeutic modulation of miRNAs would improve the functions of diabetic CPCs. Methods CPCs were isolated from a mouse model of type 2 diabetes (db/db), non-diabetic mice and human right atrial appendage heart tissue. Total RNA isolated from mouse CPCs was miRNA profiled using Nanostring analysis. Bioinformatic analysis was employed to predict the functional effects of altered miRNAs. MS analysis was applied to determine the targets, which were confirmed by western blot analysis. Finally, to assess the beneficial effects of therapeutic modulation of miRNAs in vitro and in vivo, prosurvival miR-30c-5p was overexpressed in mouse and human diabetic CPCs, and the functional consequences were determined by measuring the level of apoptotic cell death, cardiac function and mitochondrial membrane potential (MMP). Results Among 599 miRNAs analysed in mouse CPCs via Nanostring analysis, 16 miRNAs showed significant dysregulation in the diabetic CPCs. Using bioinformatics tools and quantitative real-time PCR (qPCR) validation, four altered miRNAs (miR-30c-5p, miR-329-3p, miR-376c-3p and miR-495-3p) were identified to play an important role in cell proliferation and survival. Diabetes mellitus significantly downregulated miR-30c-5p, while it upregulated miR-329-3p, miR-376c-3p and miR-495-3p. MS analysis revealed proapoptotic voltage-dependent anion-selective channel 1 (VDAC1) as a direct target for miR-30c-5p, and cell cycle regulator, cyclin-dependent protein kinase 6 (CDK6), as the direct target for miR-329-3p, miR-376c-3p and miR-495-3p. Western blot analyses showed a marked increase in VDAC1 expression, while CDK6 expression was downregulated in diabetic CPCs. Finally, in vitro and in vivo overexpression of miR-30c-5p markedly reduced the apoptotic cell death and preserved MMP in diabetic CPCs via inhibition of VDAC1. Conclusions/interpretation Our results demonstrate that diabetes mellitus induces a marked dysregulation of miRNAs associated with stem cell survival, proliferation and differentiation, and that therapeutic overexpression of prosurvival miR-30c-5p reduced diabetes-induced cell death and loss of MMP in CPCs via the newly identified target for miR-30c-5p, VDAC1.Keywords Cardiac progenitor cells . Diabetes mellitus . microRNA . miR-30c-5p . Mitochondrial membrane potential . Stem cell therapyAndrew Bahn and Rajesh Katare contributed equally to the study.