1239-P: Evidence of Altered Alpha- and Beta-Cell Lysosomes prior to Onset of Type 1 Diabetes

Abstract

Autophagic degradation is a dynamic recycling process that contributes to cellular homeostasis and mitigation of cellular stress. While there are multiple forms of -phagic degradation processes, a common endpoint is the final degradation step in the lumen of the acidic lysosomes. Post-mitotic cells, including beta cells, can accumulate tertiary lysosomes called telolysosomes which contain oxidized proteins and lipids that are not completely digested. We recently found that autophagy is impaired in the beta cells of individuals with T1D and also in islets of diabetic NOD mice. We also observed a significant increase in the number of autophagosomes, and telolysosomes in the beta cells of autoantibody positive organ donors when compared to nondiabetic organ donors. We now also find a 1.5-fold increase in the number of telolysosomes in the alpha cells of autoantibody positive donors when compared to nondiabetic organ donors (p=0.03). This was mirrored by our previous observation of globally increased lysosome numbers across the islets of pre-diabetic NOD mice, suggesting that these lysosomes may be dysfunctional. To test this, we performed a lysosomal enzyme activity assay to analyze the lysosomal cysteine protease Cathepsin H (a T1D susceptibility locus). Interestingly, we found that the activity of Cathepsin H was increased by ~2-fold in islets of pre-diabetic NOD mice when compared to NOR controls (p=0.02). Taken together, these data suggest a compensatory hyperactivation of the lysosomal enzyme Cathepsin H in the islets of pre-diabetic NOD mice, potentially as a mechanism to rid the cell of degradation-resistant oxidized proteins and lipids whose accumulation in lysosomes might lead to the presence of telolysosomes. Disclosure C. Muralidharan: None. J. Crowder: None. A. K. Linnemann: None. Funding Network for Pancreatic Organ Donors with Diabetes (nPOD; RRID:SCR_014641); JDRF (nPOD: 5-SRA-2018-557-Q-R); The Leona M. and Harry B. Helmsley Charitable Trust (2018PG-T1D053)