Real-time in vivo analysis of murine β cells reveals autophagic flux defects before onset of autoimmune diabetes.

Autophagy, a vital catabolic process, plays a crucial role in maintaining pancreatic β cell function and is disrupted in established type 1 diabetes. However, it is unclear when and how this critical cell process becomes defective during type 1 diabetes pathogenesis. To study the nature of autophagy dysfunction in the context of autoimmune diabetes, we used real-time intravital microscopy to study autophagic flux in vivo. We generated an AAV8-packaged mCherry-eGFP-LC3B biosensor driven by the insulin promoter for β cell-selective expression. For real-time autophagic flux evaluation, fluorescent signals from eGFP and mCherry fluorophores were correlated in space and time to follow the process of autophagosome-lysosome fusion. We observed autophagic flux defects in the β cells of the nonobese diabetic (NOD) mouse model of type 1 diabetes before hyperglycemia onset at both baseline and in response to interferon-α. These defects were still present, although less apparent, in immunodeficient NOD/scid/il2rg (NSG) mice. We also observed heterogeneous autophagic flux in human donor islets transplanted under the kidney capsules of NSG mice. In sum, the ability to visualize autophagic flux in β cells over time in vivo revealed impairments in those β cells that preceded the onset of autoimmune diabetes.