miR-146a-5p contributes to inflammation-mediated β cell mitochondrial dysfunction and apoptosis

MicroRNAs (miRNAs) are small non-coding RNAs that function as modulators of gene expression. We previously showed that miR-146a-5p is upregulated in pancreatic islets treated with pro-inflammatory cytokines and in pancreatic sections from organ donors with type 1 diabetes (T1D). Other studies have associated overexpression of miR-146a-5p with β cell apoptosis and impaired insulin secretion; however, the molecular mechanisms mediating these effects remain elusive. To investigate the role of miR-146a-5p in β cell function, we developed stable MIN6 cell lines transduced with lentiviral vectors to either overexpress or inhibit the expression of miR-146a-5p. Monoclonal cell populations were treated with pro-inflammatory cytokines (IL1β, IFNg, and TNFα) to model T1D in vitro. We found that overexpression of miR-146a-5p increased the cell death of MIN6 cells under inflammatory stress, whereas inhibition of miR-146a-5p reversed these effects. Additionally, inhibition of miR-146a-5p increased mitochondrial DNA copy number, respiration rate, and ATP production, suggesting that miR-146a-5p inhibition improves mitochondrial function. In support of this finding, we also observed that miR-146a-5p is enriched in the mitochondria of MIN6 cells treated with cytokines. Consistently, bioinformatic analysis of RNA sequencing data using MIN6 stable cells showed enrichment of pathways related to insulin secretion, apoptosis, and mitochondrial function when the expression levels of miR-146a-5p were altered. Overall, the findings from our study show for the first time that miR-146a-5p upregulation during inflammatory stress may promote β cell dysfunction and death by suppressing mitochondrial function.