Aim and Hypothesis: microRNAs (miRNAs) play an integral role in maintaining beta cell function and identity. We aimed to identify miRNAs and their downstream targets involved in regeneration of islet beta cells following partial pancreatectomy (pP) in mice.
Methods: RNA from laser capture microdissected islets of pP and sham-operated mice were profiled with microarrays to identify miRNAs implicated in control of 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 overexpression in mouse MIN6 cells and human EndoC-βH1 insulinoma cells. The ability of miR-132 to foster beta cell proliferation in vivo was further assessed in pP miR-132-/-and control mice.
Results: pP significantly increased the number of BrdU+/insulin+ positive islet cells. Microarray profiling revealed 14 miRNAs, including miR-132, to be significantly upregulated in LCM islets of partially pancreatectomized mice and confirmed by RT-PCR. Downregulation of miR-132 in MIN6 cells reduced proliferation while enhancing the levels of pro-apoptotic cleaved caspase-9. Microarray profiling, RT-PCR and immunoblotting revealed downregulated expression of Pten, with concomitant increased levels of pro-proliferative factors as well as inactivation of pro-apoptotic Foxo3. Overexpression of miR-132 in human insulinoma cells EndoC-βH1 validated the findings. In vivo regeneration of beta cells was reduced in pP miR-132-/- mice compared to control mice.
Conclusions: Our study provides compelling evidence for miR-132 being critical for regeneration of mouse islet beta cells in vivo through downregulation of its target Pten. Hence, the miR-132/Pten/Akt/Foxo3 signaling pathway may represent a suitable target to enhance beta cell regeneration.
S. Kersting: None. H. Mziaut: None.
German Center for Diabetes Research (to S.K.)