Role of miR-30d in insulin gene expression in pancreatic beta cells

My long-term goal is to study the role of microRNAs (miRNAs) in regulating beta-cell function and to elucidate the role of mIRNAs in the development of type-Il diabetes. MiRNAs are small noncoding ribonucleotides that bind mRNAs and function mainly as translational repressors in mammals. miRNAs have been implicated to play a role in many diseases, including diabetes. Several reports indicate an important function for miRNAs in insulin secretion and pancreatic beta cell development. We have recently carried out a screen in the pancreatic beta cell line MIN6 to identify miRNAs with altered abundance in response to changes in glucose concentrations. This screen resulted in identification of more than 50 glucose-regulated miRNAs from a total of 108 miRNAs detectable in MIN6 cells. Many of the identified miRNAs, including miR-124a, miR-107 and miR-30d were upregulated in the presence of high glucose. Interestingly, we found that overexpression of miR-30d increased insulin gene transcription. Moreover, the induction of insulin by overexpression of miR-30d is associated with increased expression of the beta-cell specific transcription factor MafA. This suggests that the putative target genes of miR-30d may be negative regulators of MafA/insulin gene expression. To determine the function of miR-30d in insulin gene transcription, I will: 1) Identify miR-30d target genes involved in regulation of insulin gene transcription. 2) Characterize the biological function of miR-30d in pancreatic beta cell lines and primary mouse islets. The verified targets will be analyzed for their role in insulin gene expression by siRNA knock-down techniques. Moreover, the effect of miR-30d on the target downstream signaling will be characterized. Finally, the function of miR-30d in primary mouse islets will be confirmed using a recombinant adenovirus expressing miR-30d. The finding from this proposal will contribute to our understanding of miRNA function in insulin gene transcription.