Presentations

Abstract

Introduction: Hallmarks of type 2 Diabetes (T2D) include insulin resistance, progressive pancreatic β cell failure and subsequent decline in insulin secretion. Adipsin is an adipocyte-derived protease that catalyze the formation of C3 convertase, acting upstream in the alternative complement pathway, producing complement component C3a and C3b. Lo et al. 2014 has shown that adipsin plays a role in the secretion of insulin, in which adipsin-knockout mouse lines exhibited reduced glucose tolerance, insulin secretion, and pancreatic β cell size. C3a binds to C3aR1, a G-coupled protein receptor, expressed in many tissues. We are interested in uncovering the impact of C3aR1 receptor on pancreatic β cell secretion of insulin, under the scope of understanding pathophysiology of type 2 diabetes.

Methods: I bred mice colonies with whole body C3aR1 KO, C3aR1-Ins1Cre genotype, as well as colonies of Ins1-Cre genotype only, as a control population. Injecting 2.5g/kg of glucose, I measured each population's glucose tolerance over 180min, collected plasma at 0, 5, 20min for insulin Elisa to measure insulin secretion at each time point. Then, harvested pancreatic islets for ex vivo glucose stimulated insulin secretion, and qPCR on whole islets to measure intracellular gene expression genes associated to insulin production and secretion. Glucose tolerance test with a larger sample size, harvest pancreatic β cell mass measurements as well as expression levels of apoptosis and dedifferentiation markers are currently pending.

Results: At 15 weeks on chow (regular diet), both female and male cohorts exhibited no difference in glucose tolerance and insulin secretion between Ins1-cre control genotype and KO genotypes. Regular diet females exhibited no difference between fasting glucose and weight levels prior to glucose challenge and exhibited no differences in glucose tolerance and insulin secretion throughout the glucose challenge. In vitro glucose stimulated insulin secretion study on harvest whole islets had similar results between control and KO genotypes. These findings were replicated in the male cohorts. In male cohorts after 22 weeks on a high caloric diet, harvested islets from the KO cohort showed a significant decrease in C3aR1 expression, but a significant increase in gcg expression. The KO genotype also showed a trend toward reduced expression of Dusp26 and Aldh1a3. Other markers, Mafa, Nkx6.1, Emr1 had no significant differences between genotypes. Further glucose tolerance tests, insulin ELISA, apoptosis and dedifferentiation expression, and β cell mass studies with larger sample sizes are currently under progress.

Conclusion: Without a metabolic challenge of a high caloric diet, C3aR1 KO may not incur a significant influence on insulin secretion. Furthermore, increases in apoptosis markers can indicate a decrease in β cell composition within pancreatic islets of C3aR1 KO mice populations. Although statistically insignificant, the trend toward reduced expression of tumor suppressors Dusp26, and Aldh1a3 may be a sign of dedifferentiation or degradation of function of β cells. Experiments to validate our findings with a larger sample size, as well as β cell mass measurements, and qPCRs to measure gene expression markers within whole islets are currently underway. I believe they will provide a deeper insight on our findings and contribute to our understanding of the behaviors of pancreatic β cells throughout consistent intake of high fat foods.