Real Time In vivo Analysis of Pancreatic Beta-cell Autophagic Flux Reveals Impairment Before Onset of Autoimmune Diabetes

The catabolic pathway of autophagy is critical for pancreatic beta-cell function and is defective in established type 1 diabetes (T1D). However, it is unclear when and how this critical cell process becomes defective during diabetes pathogenesis. To study the nature of autophagy dysfunction in the context of autoimmune diabetes, we utilized intravital microscopy to study autophagic flux in vivo in real time. We generated a custom AAV8- packaged mCherry-eGFP-LC3B biosensor driven by the insulin promoter for beta-cell-selective expression. For real time autophagic flux evaluation, fluorescent signal from eGFP and mCherry fluorophores was correlated in space and time to follow the process of autophagosome-lysosome fusion. We observed autophagic flux defects in the beta-cells of non-obese diabetic (NOD) mouse model of T1D prior to hyperglycemia onset that were less apparent in mice without a functional immune system. We also evaluated autophagic flux in human donor islets that were transplanted under the kidney capsule of immune incompetent mice. Collectively, we provide the first evaluation of autophagic flux in vivo in 4D and demonstrate that autophagy defects precede hyperglycemia in NOD mice suggesting a potential causative role for these defects in beta-cell demise during T1D pathogenesis.