Abstract MP33: Coordination Of Metabolic Functions By SR-BI And PCPE2 In Adipocytes

Abstract

Obesity continues to be an epidemic in the United States, placing individuals at a higher risk of developing other comorbidities such as type 2 diabetes and cardiovascular disease. Adipocytes accumulate excess triglycerides and undergo hypertrophic expansion as a protective mechanism to avoid lipotoxicity. Adipocytes are also highly dynamic cells that perform many key metabolic processes including lipid and glucose metabolism. Recent collaborative studies demonstrated that SR-BI function may require the extracellular matrix protein procollagen C-endopeptidase enhancer 2 (PCPE2) in to regulate cholesterol transport in hepatocytes and adipocytes. However, the roles of SR-BI and PCPE2 in other adipocyte metabolic processes remain unclear. This knowledge gap prompted our novel hypothesis that PCPE2 facilitates SR-BI’s ability to regulate metabolic processes in adipocytes. To test our hypothesis, we have optimized an adipocyte model system where mesenchymal stem cells isolated from the outer ears of wild-type (WT), SR-BI knockout (SR-BI -/- ), and PCPE2 -/- mice were differentiated into adipocyte-like cells. We validated our adipocyte model system by demonstrating increased Oil Red O staining, mRNA expression of adipogenesis markers, and adiponectin secretion over a 9-day post-differentiation period for all three genotypes. This model system was then used to test the roles of SR-BI and PCPE2 on various metabolic functions. Preliminary data suggests that absence of SR-BI or PCPE2 slightly impairs fatty acid uptake into adipocytes despite elevated gene expression of fatty acid transporters (FABP4, CD36) compared to WT. These data further suggest that SR-BI may rely on PCPE2 to aid in transport of fatty acids. Adipocytes lacking SR-BI or PCPE2 also displayed higher levels of mitochondrial reactive oxygen species, indicating that SR-BI and PCPE2 may be important for maintaining healthy mitochondria in adipocytes. These changes in function do not appear to depend on SR-BI oligomerization, as BS 3 crosslinking studies demonstrated the presence of SR-BI oligomers in adipocytes despite the loss of PCPE2. Altogether, these data suggest that SR-BI and PCPE2 may be reliant on each other and are important for mediating metabolic processes in adipocytes.