miR-132 controls pancreatic beta cell proliferation and survival through the Pten/Akt/Foxo3 signaling

Abstract Objective microRNAs (miRNAs) play an integral role in maintaining beta cell function and identity. Deciphering their targets and precise role, however, remains a challenge. In this study we aimed to identify miRNAs and their downstream targets involved in regeneration of islet beta cells following partial pancreatectomy in mice. Methods RNA from laser capture microdissected (LCM) islets of partially pancreatectomized and sham-operated mice were profiled with microarrays to identify putative miRNAs implicated in beta cell regeneration. Altered expression of selected miRNAs, including miR-132, was verified by RT-PCR. Potential targets of miR-132 were selected through bioinformatic data mining. Predicted miR-132 targets were validated for their changed RNA and protein expression levels and signaling upon miR-132 knockdown and/or overexpression in mouse MIN6 and human EndoC-βH1 insulinoma cells. The ability of miR-132 to foster beta cell proliferation in vivo was further assessed in pancreatectomized miR-132-/- and control mice. Results Partial pancreatectomy significantly increased the number of BrdU+/insulin+ islet cells. Microarray profiling revealed 14 miRNAs, including miR-132 and -141, to be significantly upregulated in LCM islets of partially pancreatectomized compared to LCM islets of control mice. In the same comparison miR-760 was the only miRNA found to be downregulated. Changed expression of these miRNAs in islets of partially pancreatectomized mice was confirmed by RT-PCR only in the case of miR-132 and -141. Based on previous knowledge of its function, we focused our attention on miR-132. Downregulation of miR-132 reduced the proliferation of MIN6 cells while enhancing the levels of pro-apoptotic cleaved caspase-9. Opposite observations were made in miR-132 overexpressing MIN6 cells. Microarray profiling, RT-PCR and immunoblotting of the latter cells revealed their downregulated expression of Pten, with concomitant increased levels of pro-proliferative factors phospho-Akt and phospho-Creb as well as inactivation of pro-apoptotic Foxo3a via its phosphorylation. Downregulation of Pten was further confirmed in LCM islets of pancreatectomized mice in comparison to sham operated mice. Moreover, overexpression of miR-132 correlated with increased proliferation of EndoC-βH1 cells. Finally, regeneration of beta cells following partial pancreatectomy was reduced in miR-132/212-/- mice compared to control littermates. Conclusions/Interpretations: Our study provides compelling evidence about the critical role of miR-132 for regeneration of mouse islet beta cells through downregulation of its target Pten. Hence, the miR-132/Pten/Akt/Foxo3 signaling pathway may represent a suitable target to enhance beta cell mass.