Mitophagy protects β cells from inflammatory damage in diabetes

Abstract

Inflammatory damage contributes to β-cell failure in type 1 and 2 diabetes (T1D and T2D). Mitochondria are damaged by inflammatory signaling in β-cells, resulting in impaired bioenergetics and initiation of pro-apoptotic machinery. Hence, the identification of protective responses to inflammation could lead to new therapeutic targets. Here we report that mitophagy serves as a protective response to inflammatory stress in both human and rodent β-cells. Utilizing in vivo mitophagy reporters, we observed that diabetogenic pro-inflammatory cytokines induced mitophagy in response to nitrosative/oxidative mitochondrial damage. Mitophagy-deficient β-cells were sensitized to inflammatory stress, leading to the accumulation of fragmented dysfunctional mitochondria, increased β-cell death, and hyperglycemia. Overexpression of CLEC16A, a T1D gene and mitophagy regulator whose expression in islets is protective against T1D, ameliorated cytokine-induced human β-cell apoptosis. Thus, mitophagy promotes β-cell survival and prevents diabetes by countering inflammatory injury. Targeting this pathway has the potential to prevent βcell failure in diabetes and may be beneficial in other inflammatory conditions.

Mitofusin 1 and 2 regulation of mitochondrial DNA content is a critical determinant of glucose homeostasis

“…While β-cells from all groups had the expected appearance of electron dense insulin granules, β-cells from β-Mfn1/2 DKO mice had reductions in mitochondrial aspect ratio, form factor, and perimeter, and increased mitochondrial circularity ( Figures 2B-C), indicating smaller, fragmented mitochondria. Secondly, we examined mitochondrial morphology and networks utilizing high-resolution deconvolution imaging of the mitochondrial marker succinate dehydrogenase A (SDHA) to generate three-dimensional (3D) reconstructions of β-cell mitochondria (13,14). Consistent with our findings using TEM, the 3D mitochondrial appearance was similar between Ctrl and single β-Mfn1 KO or β-Mfn2 KO β-cells ( Figure 2D).…”

“…Mitochondrial morphology and subcellular localization analyses were performed on immunostained paraffin-embedded mouse pancreas tissue sections and dissociated islet cells as previously described (13). Z-stack images of immunostained pancreatic sections were captured with an IX81 microscope (Olympus) using an ORCA Flash4 CMOS digital camera (Hamamatsu) and subjected to deconvolution (CellSens; Olympus).…”

“…Fluozin-3 (Thermo Fisher Scientific), and resuspended in phenol red-free islet culture medium as previously described (13). Samples were analyzed on an LSR Fortessa flow cytometer (BD Biosciences).…”

“…Samples were analyzed on an LSR Fortessa flow cytometer (BD Biosciences). Single cells were gated using forward scatter and side scatter (FSC and SSC, respectively) plots, DAPI staining was used to exclude dead cells, and Fluozin-3 was used to identify β-cells as previously described (13,61). Mtphagy measurements in β-cells were made using 488 nm excitation laser with a 710 nm emission filter and analyzed using FlowJo (Tree Star Inc.).…”

“…All assays were performed as previously described (13,53,54). β-cell mass was quantified as previously described (54).…”