Novel Function for Endothelial Protease-Activated Receptors in Modulating Insulin Receptor Activity With Implications for Diabetes.

BACKGROUND: Thrombin, a serine protease with increased activity in people with diabetes, signals through PAR (protease-activated receptor) 1 and 4 on endothelial cells (ECs). On these cells, PAR1 is a high-expressing, high-affinity, low-potency thrombin receptor, whereas PAR4 is a low-expressing, low-affinity, high-potency receptor. This study aims to determine how endothelial PARs influence diabetic pathology, thereby providing deeper insights into the roles and relationships between these receptors. METHODS: We generated mice with inducible deletion of Par1/Par4 in ECs (Par1/4(iECko)) and induced diabetes with streptozotocin treatment. Blood glucose and insulin levels were assessed after streptozotocin administration. In addition, we measured insulin and glucose tolerance in Par1/4(iECko) mice. Lastly, we measured how the loss of endothelial PARs in cultured primary ECs affected IR (insulin receptor) activity/phosphorylation, and insulin transcytosis. RESULTS: While studying the roles of endothelial PAR1/4 in diabetic pathology, we found that Par1/4(iECko) mice displayed increased insulin sensitivity and were protected against streptozotocin-induced diabetes. Concordantly, we found that cultured primary ECs with PAR1/4 deficiency exhibited increased basal activity and phosphorylation of IR in a Gα(q)/protein kinase C-dependent manner, as well as enhanced insulin transcytosis. This elevated IR activity correlated with reduced activity of PTP1B (protein tyrosine phosphatase 1B), a negative regulator of IR. Lastly, Par1/4(iECko) mice with additional deletion of 1 allele of the endothelial IR gene demonstrated restoration of diabetic phenotypes after streptozotocin treatment, indicating that insulin sensitivity in Par1/4(iECko) mice was driven by heightened IR activity in ECs. CONCLUSIONS: These findings establish a novel link between endothelial PAR signaling and insulin sensitivity, underscoring the critical role of ECs in metabolic homeostasis and identifying a potential therapeutic target for diabetes.