MicroRNAs miR-23a-3p, miR-23b-3p, and miR-149-5p Regulate the Expression of Proapoptotic BH3-Only Proteins DP5 and PUMA in Human Pancreatic β-Cells

Type 1 diabetes (T1D) is an autoimmune disease leading to β-cell destruction. MicroRNAs (miRNAs) are small noncoding RNAs that control gene expression and organ formation. They participate in the pathogenesis of several autoimmune diseases, but the nature of miRNAs contributing to β-cell death in T1D and their target genes remain to be clarified. We performed an miRNA expression profile on human islet preparations exposed to the cytokines IL-1β plus IFN-γ. Confirmation of miRNA and target gene modification in human β-cells was performed by real-time quantitative PCR. Single-stranded miRNAs inhibitors were used to block selected endogenous miRNAs. Cell death was measured by Hoechst/propidium iodide staining and activation of caspase-3. Fifty-seven miRNAs were detected as modulated by cytokines. Three of them, namely miR-23a-3p, miR-23b-3p, and miR-149-5p, were downregulated by cytokines and selected for further studies. These miRNAs were found to regulate the expression of the proapoptotic Bcl-2 proteins DP5 and PUMA and consequent human β-cell apoptosis. These results identify a novel cross talk between a key family of miRNAs and proapoptotic Bcl-2 proteins in human pancreatic β-cells, broadening our understanding of cytokine-induced β-cell apoptosis in early T1D.

Emerging roles of non-coding RNAs in pancreatic β-cell function and dysfunction

Pancreatic β-cells play a central role in glucose homeostasis by tightly regulating insulin release according to the organism's demand. Impairment of β-cell function due to hostile environment, such as hyperglycaemia and hyperlipidaemia, or due to autoimmune destruction of β-cells, results in diabetes onset. Both environmental factors and genetic predisposition are known to be involved in the development of the disease, but the exact mechanisms leading to β-cell dysfunction and death remain to be characterized. Non-coding RNA molecules, such as microRNAs (miRNAs), have been suggested to be necessary for proper β-cell development and function. The present review aims at summarizing the most recent findings about the role of non-coding RNAs in the control of β-cell functions and their involvement in diabetes. We will also provide a perspective view of the future research directions in the field of non-coding RNAs. In particular, we will discuss the implications for diabetes research of the discovery of a new communication mechanism based on cell-to-cell miRNA transfer. Moreover, we will highlight the emerging interconnections between miRNAs and epigenetics and the possible role of long non-coding RNAs in the control of β-cell activities.