Rohit Ray
Pronouns: he/him
Research Mentor(s): Rachel Reinert
Co-Presenter:
Research Mentor School/College/Department: Internal Medicine/MEND / Medicine
Presentation Date: April 20
Presentation Type: Poster
Session: Session 1 – 10am – 10:50am
Room: League Ballroom
Authors: Rohit Ray, Anna Chiara Russo, Rachel Reinert
Presenter: 110
Abstract
Endoplasmic reticulum (ER) homeostasis is essential for efficient prohormone synthesis and folding in endocrine cells. Endoplasmic reticulum-associated degradation (ERAD) and autophagy are integral protein quality control mechanisms that maintain ER homeostasis and insulin production in pancreatic islet beta cells, thus protecting from diabetes. The role of these quality control pathways in neighboring islet alpha cells, which support beta cell function through release of proglucagon-derived peptides, has been unexplored. ERAD targets misfolded proteins for proteasomal degradation through two conserved ER membrane proteins: the ubiquitin ligase Hrd1 and its critical adaptor protein, Sel1L. Autophagy is a conserved mechanism for recycling ER and cytosolic products through lysosomal degradation and uses the key autophagosome protein Atg7. To explore the synergistic role of ERAD and autophagy in islet alpha cells, Sel1L and Atg7 were targeted for deletion with the Cre-lox system, using mice that express Cre recombinase under the endogenous proglucagon promoter. Previously, we found that these double knockout (DKO) mice had a dramatic loss of alpha cells after weaning, leading to a 77% reduction in pancreatic glucagon content and impaired glucagon secretion in response to fasting or hypoglycemia. To further investigate whether depletion of islet alpha cells affected islet function under nutritional stress, we used a high-fat diet (HFD) to promote diet-induced obesity. DKO mice and littermate controls were transitioned to a diet with 60% of calories from fat at 8 weeks of age, and metabolic parameters were assessed over the next two months. HFD-fed mice of both sexes showed variable weight gain, independent of genotype. By immunohistochemistry, islets from all genotypes showed expansion of the beta cell population, without an obvious increase in the organization or proportion of alpha cells within the islets. Supporting this, pancreatic glucagon content was not significantly increased in HFD-fed DKO mice compared to chow-fed controls, and remained much lower than that in littermate controls. Blood glucose levels were measured in response to oral glucose and Ensure (mixed meal) boluses, revealing no significant differences in glucose homeostasis between genotypes. Preliminary data shows that circulating glucagon levels in vivo were suppressed in response to HFD in all genotypes. Samples have been collected to also assess pancreatic insulin content and insulin secretion in vivo. These data suggest that alpha cell depletion does not dramatically affect systemic glucose metabolism or islet function in response to high-fat feeding. Future studies will explore how other forms of nutritional stress (e.g., time-restricted feeding or protein excess) affect alpha-to-beta cell signaling. Ultimately, this work will help us better understand how alpha cells influence islet function in normal physiology and in the pathogenesis of diabetes.
Biomedical Sciences, Interdisciplinary
