Autophagy in enterovirus- infected pancreatic cells: Unraveling the mechanistic link between Type 1 diabetes and virus infection

Background: Human Enteroviruses (HEV) have been long suspected as triggering factor of Type 1 diabetes (T1D). However, how HEV directly impacts the pancreatic islets and trigger chronic beta-cell distress remains unknown. This study aimed to investigate effect of HEV on islet and beta cell autophagy, a major regulator of pancreatic beta cell homeostasis. Methods: Autophagy activity in clonal beta cells (INS-1 832/13) and human islets following infection with a beta cell tropic strain of Echovirus 16 (E16) was quantified by counting the number of autophagosomes, lysosomes, and autophagolysosomes by using confocal microscopy and Cellomics Arrayscan platform. Cyto ID green autophagy dye and electron microscopy were also used to monitor autophagy flux. Insulin secretion in response to glucose stimulation and expression of key autophagy-related genes were determined. Results: In vitro infection of INS 1 beta cell line and human islets with E16, resulted in impairment of autophagy leading to accumulation of autophagosomes and inhibition of autophagic turnover. This was accompanied by an increased extracellular virus production and reduction in glucose-stimulated insulin secretion, but not in cellular viability. Analysis of islet cell autophagy in an autoantibody positive high-risk individual revealed disruption of the autophagic process in a similar fashion as E16-infected islets. Conclusions: These data demonstrate for the first time that HEVs infection subvert autophagy pathways in pancreatic beta cells to promote their own replication and nonlytic viral spread resulting in impaired beta cell function. We suggest that accumulation of virus-induced autophagosomes through inactivation of lysosomes would provide a mechanism by which HEVs prolong their survival in infected pancreatic cells and trigger beta-cell dysfunction and T1D.