OBJECTIVE AND METHODS: Pancreatic β cell dysfunction is critical to the development of type 2 diabetes (T2D). Our previous studies suggested that C3aR1 on β cells promotes insulin secretion and cell survival. However, as C3aR1 is expressed on many other cell types including within the islets, whole-body C3aR1 knockout models confound the analyses of direct impacts on β cells. To clarify the role of C3aR1 in β cells under T2D conditions, we generated β cell-specific C3aR1 knockout mice. We assessed glucose homeostasis, focusing on β cell function and mass under metabolic stress conditions, to interrogate the effects of C3aR1 on β cells in a mouse model of T2D. We performed proteomic analyses on islets from control and β cell-specific C3aR1 knockout mice. To determine potential translational relevance, C3AR1 was assessed alongside glucose-stimulated insulin secretion in human islets.

RESULTS: We show that the complement receptor C3aR1 on β cells plays an essential role in maintaining β cell homeostasis, especially under the metabolic duress of obesity and T2D. Male mice with β cell specific deletion of C3ar1 (β-C3aR1 KO) exhibit worse glucose tolerance and lower insulin levels when fed regular or high fat diet. Under high fat diet, β-C3aR1 KO also have diminished β cell mass. Islets from β-C3aR1 KO mice demonstrate impaired insulin secretion. β cells lacking C3aR1 display increased susceptibility to lipotoxicity-mediated cell death. Markers of β cell identity are decreased in β-C3aR1 KO mice while stress markers are elevated. Disruption of C3ar1 on β cells ablates the insulin secretory response to C3a, establishing a signaling axis between C3a and β cell-derived C3aR1. Islet proteomic analyses highlight the MAPK pathway and mitochondrial dysfunction with C3aR1 loss in β cells. Finally, we show that C3AR1 is positively correlated with insulin secretion in human islets.

CONCLUSIONS: These findings indicate that C3aR1 expression on β cells is necessary to maintain optimal β cell function and preserve β cell mass in T2D.