Dysfunctional mitochondrial bioenergetics and oxidative stress in Akita+/Ins2-derived β-cells

Insulin release from pancreatic beta-cells plays a critical role in blood glucose homeostasis, and beta-cell dysfunction leads to the development of diabetes mellitus. In cases of monogenic type 1 diabetes mellitus (T1DM) that involve mutations in the insulin gene, we hypothesized that misfolding of insulin could result in endoplasmic reticulum (ER) stress, oxidant production, and mitochondrial damage. To address this, we used the Akita(+/Ins2) T1DM model in which misfolding of the insulin 2 gene leads to ER stress-mediated beta-cell death and thapsigargin to induce ER stress in two different beta-cell lines and in intact mouse islets. Using transformed pancreatic beta-cell lines generated from wild-type Ins2(-/-) (WT) and Akita(+/Ins2) mice, we evaluated cellular bioenergetics, oxidative stress, mitochondrial protein levels, and autophagic flux to determine whether changes in these processes contribute to beta-cell dysfunction. In addition, we induced ER stress pharmacologically using thapsigargin in WT beta-cells, INS-1 cells, and intact mouse islets to examine the effects of ER stress on mitochondrial function. Our data reveal that Akita(+/Ins2)-derived beta-cells have increased mitochondrial dysfunction, oxidant production, mtDNA damage, and alterations in mitochondrial protein levels that are not corrected by autophagy. Together, these findings suggest that deterioration in mitochondrial function due to an oxidative environment and ER stress contributes to beta-cell dysfunction and could contribute to T1DM in which mutations in insulin occur.