Pancreatic beta cell autophagy is impaired in type 1 diabetes

Abstract

Aims/hypothesis Pancreatic beta cells are subjected to exogenous damaging factors such as proinflammatory cytokines or excess glucose that can cause accumulation of damage-inducing reactive oxygen species during the pathogenesis of diabetes. We and others have shown that beta cell autophagy can reduce reactive oxygen species to protect against apoptosis. While impaired islet autophagy has been demonstrated in human type 2 diabetes, it is unknown if islet autophagy is perturbed in the pathogenesis of type 1 diabetes. We hypothesised that beta cell autophagy is dysfunctional in type 1 diabetes, and that there is a progressive loss during early diabetes development. Methods Pancreases were collected from chloroquine-injected and non-injected non-obese diabetes-resistant (NOR) and non-obese diabetic (NOD) mice. Age- and BMI-matched pancreas tissue sections from human organ donors (N = 34) were obtained from the Network for Pancreatic Organ Donors with Diabetes (nPOD). Tissue sections were stained with antibodies against proinsulin or insulin (beta cell markers), microtubule-associated protein 1 light chain 3 A/B (LC3A/B; autophagosome marker), lysosomal-associated membrane protein 1 (LAMP1; lysosome marker) and p62 (autophagy adaptor). Images collected on a scanning laser confocal microscope were analysed with CellProfiler and ImageJ. Secondary lysosomes and telolysosomes were assessed in electron micrographs of human pancreatic tissue sections (n = 12), and energy dispersive x-ray analysis was performed to assess distribution of elements (n = 5). Results We observed increased autophagosome numbers in islets of diabetic NOD mice (p = 0.008) and increased p62 in islets of both non-diabetic and diabetic NOD mice (p < 0.001) vs NOR mice. There was also a reduction in LC3–LAMP1 colocalisation in islets of diabetic NOD mice compared with both non-diabetic NOD (p < 0.001) and NOR mice (p < 0.001). Chloroquine elicited accumulation of autophagosomes in the islets of NOR (p = 0.003) and non-diabetic NOD mice (p < 0.001), but not in islets of diabetic NOD mice; and stimulated accumulation of p62 in NOR (p < 0.001), but not in NOD mice. We observed reduced LC3–LAMP1 colocalisation (p < 0.001) in residual beta cells of human donors with type 1 diabetes vs non-diabetic participants. We also observed reduced colocalisation of proinsulin with LAMP1 in donors with type 1 diabetes (p < 0.001). Electron microscopy also revealed accumulation of telolysosomes with nitrogen-dense rings in beta cells of autoantibody-positive donors (p = 0.002). Conclusions/interpretation We provide evidence of islet macroautophagy/crinophagy impairment in human type 1 diabetes. We also document accumulation of telolysosomes with peripheral nitrogen in beta cells of autoantibody-positive donors, demonstrating altered lysosome content that may be associated with lysosome dysfunction before clinical hyperglycaemia. Similar macroautophagy impairments are present in the NOD mouse model of type 1 diabetes. Graphical abstract

Glucose Variability: How Does It Work?

“…This cellular recycling is vital for highly differentiated cells, including neurons, podocytes, cardiomyocytes, retinal cells and beta cells [111,112]. The impaired autophagy plays a role in the development of both T1D and T2D [113][114][115][116], and diabetic kidney disease [117][118][119].…”

Making Insulin and Staying Out of Autoimmune Trouble: The Beta-Cell Conundrum

“…While the role of these different types of autophagy has been extensively studied in type 2 diabetes, investigations in T1D are scanty. One recent study (13) reported defective macro-autophagy and diminished crinophagy in the beta cells of non-obese diabetic (NOD) mice compared to non-diabetic NOD littermates and non-obese resistant (NOR) mice. These conclusions were confirmed in T1D pancreas specimens and were based on the lack of colocalization of the lysosomal marker Lamp1 with either the granule marker proinsulin or the autophagosome marker LC3, thus suggesting a defect in the late stage of autophagy, when granules/autophagosomes fuse with lysosomes.…”

Loss of Secretory Pathway Ca2+ ATPase (SPCA1) Impairs Insulin Secretion and Reduces Autophagy in the Pancreatic Islet

“…For Golgi volumetric analysis, z-stack images were analyzed using ImageJ. For LC3 puncta and colocalization analysis, CellProfiler 4.1.3 (cellprofiler.org) [27] was used as previously described [28]. Further information can be found in the Supporting Information.…”

“…The copyright holder for this preprint this version posted August 31, 2021. ; https://doi.org/10.1101/2021.08.30.458203 doi: bioRxiv preprint 8 [27] was used as previously described [28]. Further information can be found in the Supporting Information.…”