MiR-25 and miR-92b regulate insulin biosynthesis and pancreatic β-cell apoptosis

Abstract

Pancreatic β-cell failure is a central hallmark of the pathogenesis of diabetes mellitus; however, the molecular basis underlying chronic inflammation-caused β-cell failure remains unclear. This study reported here specifically assessed the association between miR-25/miR-92b family and β-cell failure in diabetes. IL-1β and two additional ER stress activators, palmitate and tunicamycin were applied to evaluate the expression level miR-25 by Taqman® RT-PCR. Glucose- and potassium-stimulated insulin secretion assays were performed to assess β-cell function. Dual-luciferase activity, and western blotting assays were utilized for miR-25 target gene verification. CCK-8 and TUNEL staining were used to evaluate β-cell viability and apoptosis. miRNA ChIP identified the increased level of miR-25 in INS-1 cells by IL-1β treatment. Expression levels of miR-25 were significantly upregulated with the treatment of IL-1β, palmitate or tunicamycin in both INS-1 cells and human islets. Ectopic elevation of miR-25 recapitulated most featured β-cell defects caused by IL-1β, including inhibition of insulin biosynthesis and increased β-cell apoptosis. These detrimental effects of miR-25 relied on its seed sequence recognition and repressed expression of its target genes Neurod1 and Mcl1. The miR-25/NEUROD1 axis reduced insulin biosynthesis via transcriptional regulation of β-cell specific genes. The miR-25/MCL1 axis caused β-cell apoptosis in a CASPASE-3/PARP1-dependent manner. Comparable impairments were generated by miR-92b and miR-25, emphasizing the redundant biological roles of miRNA family members with the same seed sequence. MiR-25/miR-92b family plays a major role in β-cell failure occurring under inflammation and diabetes states.