MicroRNA Expression in Alpha and Beta Cells of Human Pancreatic Islets

microRNAs (miRNAs) play an important role in pancreatic development and adult beta-cell physiology. Our hypothesis is based on the assumption that each islet cell type has a specific pattern of miRNA expression. We sought to determine the profile of miRNA expression in alpha- and beta-cells, the main components of pancreatic islets, because this analysis may lead to a better understanding of islet gene regulatory pathways. Highly enriched (>98%) subsets of human alpha- and beta-cells were obtained by flow cytometric sorting after intracellular staining with c-peptide and glucagon antibody. The method of sorting based on intracellular staining is possible because miRNAs are stable after fixation. MiRNA expression levels were determined by quantitative high throughput PCR-based miRNA array platform screening. Most of the miRNAs were preferentially expressed in beta-cells. From the total of 667 miRNAs screened, the Significant Analysis of Microarray identified 141 miRNAs, of which only 7 were expressed more in alpha-cells (alpha-miRNAs) and 134 were expressed more in beta-cells (beta-miRNAs). Bioinformatic analysis identified potential targets of beta-miRNAs analyzing the Beta Cell Gene Atlas, described in the T1Dbase, the web platform, supporting the type 1 diabetes (T1D) community. cMaf, a transcription factor regulating glucagon expression expressed selectively in alpha-cells (TF alpha) is targeted by beta-miRNAs; miR-200c, miR-125b and miR-182. Min6 cells treated with inhibitors of these miRNAs show an increased expression of cMaf RNA. Conversely, over expression of miR-200c, miR-125b or miR-182 in the mouse alpha cell line alpha TC6 decreases the level of cMAF mRNA and protein. MiR-200c also inhibits the expression of Zfpm2, a TF alpha that inhibits the PI3K signaling pathway, at both RNA and protein levels. In conclusion, we identified miRNAs differentially expressed in pancreatic alpha- and beta-cells and their potential transcription factor targets that could add new insights into different aspects of islet biology and pathophysiology.