FRI027 Regulation Of A Novel Sortilin Splice Variant Expression In Human Diabetic Adipocytes By GLP-1 To Maintain Glucose Homeostasis

Abstract Disclosure: N.A. Patel: None. R.S. Patel: None. A. Liu: None. Type 2 diabetes mellitus (T2DM) is a chronic and progressive metabolic disease with no cure. 37.3 million Americans have T2DM as of 2021 and 96 million (1 in 3) are prediabetic. Globally 462 million people are estimated to be living with T2DM. T2DM is a complex, polygenic metabolic disease characterized by hyperglycemia and insulin resistance. Adipocytes play a crucial role in glucose homeostasis. In response to insulin, translocation of major glucose transporter-4 (Glut4) from cytoplasm to the plasma membrane facilitates uptake of glucose into the adipocytes. Sortilin, an important constituent of Glut4 storage vesicles, binds to Glut4 with its luminal domain while its C-terminal tail guides intracellular trafficking. In insulin resistant adipocytes, glucose uptake is impaired. In this study, we used human adipose stem cells (hASC) from diabetic (DM) and nondiabetic (NDM) donors and differentiated them in vitro to mature adipocytes. We report that in addition to constitutively spliced full-length sortilin (Sort_FL), we identified an alternatively spliced sortilin variant in human adipocytes. Results show that alternative exon inclusion resulted in inclusion of STOP codon which produced a truncated C-terminal (Sort_T) protein whose expression was significantly increased in DM adipocytes. We elucidated the role and function of Sort_T and our results show that hyperglycemic conditions promoted an increase in Sort_T levels in NDM adipocytes. Overexpression of Sort_T in NDM adipocytes resulted in reduced insulin-stimulated Glut4 translocation and decreased glucose uptake. However, overexpression of Sort_FL does not rescue glucose uptake in DM adipocytes. Computational modeling and molecular dynamics results suggested that Glut4 bound tightly to both Sort_T and Sort_FL. This was validated using co-immunoprecipitation assays which demonstrated robust binding of Sort_T to Glut4. Immunocytochemistry was performed to determine localization of sortilin variants in DM and NDM adipocytes. Results demonstrated that Glut4 co-localized with both Sort_T and Sort_FL and Pearson’s coefficient demonstrated increased Sort_T co-localization with Glut4 in DM adipocytes. Incretin hormone glucagon-like peptide-1 (GLP1) and its analog liraglutide is used to manage T2DM. We evaluated the effect of GLP1 and liraglutide treatment in DM adipocytes on sortilin variant expression and our results demonstrate decreased Sort_T levels at physiological doses (8nM). Using a sortilin splicing minigene, our results demonstrate that GLP1 regulates splicing of Sort_T pre-mRNA and splice factor SRSF10 is involved in GLP1-mediated sortilin alternative splicing in adipocytes. Our study concludes that Sort_T expression in diabetic adipocytes hinders glucose metabolism and Sort_T is a target of GLP1 for maintaining glucose homeostasis. Presentation: Friday, June 16, 2023