Dicker, A. | Search bioRxiv

bioRxiv2023

Diet-induced obesity results in endothelial cell desensitization to VEGF-A and permanent islet vascular dysfunction

BackgroundPancreatic islet microvasculature is essential for optimal islet function and glucose homeostasis. However, islet vessel pathogenesis and its role in the manifestation of metabolic disorders remain understudied. Here we depict a time-resolved decline of intra-islet endothelial cell sensitivity to vascular endothelial cell growth factor A (VEGF-A) in a mouse model of diet-induced obesity. MethodsMice were transplanted with reporter islets in their eyes and put on different diet schemes for 48 weeks. Islet vascular morphology, VEGF-A signaling activity in islet endothelial cells and vessel function were longitudinally monitored by in vivo imaging, while the metabolic implication of islet vessel alterations was measured by glucose tolerance tests and insulin secretion assays. ResultsIn parallel with substantial islet vasculature remodeling, diminished VEGF-A response in islet endothelial cells emerged after 12 weeks of western diet feeding. This led to vessel barrier dysfunction and hemodynamic dysregulation, which delayed transportation of secreted insulin into the blood. Islet vessels also exhibited a remarkable metabolic memory long after the removal of western diet. Neither islet endothelial cell VEGF-A sensitivity nor the vascular damage elicited by 24 weeks of western diet feeding was restored by switching to control diet for another 24 weeks. As a result, these refed mice still exhibited mild but significant impairment in glucose clearance, despite a complete normalization of body weight and insulin sensitivity. While plasma levels of soluble VEGF receptor 1 - the natural VEGF-A trap - were similar in all diet groups, increased activity of atypical protein kinase C (aPKC) was observed under both western diet and recovery conditions, which inhibited VEGF receptor 2 (VEGFR2) internalization and dampened VEGF-A triggered signal transduction in vivo and in human endothelial cells cultured under diet-mimicking conditions. ConclusionsLong-term western diet feeding causes irreversible VEGF-A desensitization in islet endothelial cells and islet vessel dysfunction which undermines glucose homeostasis.

physiology↗

bioRxiv2019

Islet vascularization is regulated by primary endothelial cilia via VEGF-A dependent signaling

RationaleAccumulating evidence point to a role for primary cilia in endothelial cell function. Islet vascularization is an important determinant of islet function and glucose homeostasis. We have previously shown that {beta}-cell cilia directly regulate insulin secretion. However, it is unclear whether primary cilia are also implicated in islet vascularization and thus contribute to glucose homeostasis.\n\nObjectiveTo characterize the role of primary cilia in islet vascularization.\n\nMethods and ResultsAt four weeks, Bbs4-/- islets show markedly lower intra-islet capillary density with enlarged diameters. We transplanted islets into the anterior chamber (ACE) of mouse eyes for longitudinal and non-invasive in vivo monitoring of vascular morphology. Bbs4-/- islets exhibited significantly delayed re-vascularization and enlarged vessels during engraftment. Similar vascular phenotypes were observed in two other ciliopathy models. By shifting the relative contributions of host versus donor endothelial cells in islet revascularization, we found that primary cilia on endothelial cells is essential for this process. Electron microscopy analysis further revealed a lack of fenestration in engrafted Bbs4-/- islets, partially impairing vascular permeability and glucose delivery to {beta}-cells. Finally, we identified that Vascular endothelial cell growth factor A (VEGF-A)/VEGF receptor 2 (VEGFR2) signalling is involved in islet vascularization, islet function and vascular fenestration. In vitro silencing of two different ciliary genes in endothelial cells disrupts VEGF-A/ VEGFR2 internalization and phospho-activation of downstream signalling components. Consequently, key features of angiogenesis including proliferation, migration and tube formation are attenuated in BBS4 silenced endothelial cells.\n\nConclusionsEndothelial cell primary cilia regulate islet vascularization and vascular barrier function via VEGF-A/ VEGFR2 signaling pathway. Islet vascularization is impaired in four weeks old Bbs4-/- mice. Long-time monitoring of re-vascularization of WT and Bbs4-/- islets recapitulates the phenotype and demonstrates a role for cilia in islet vascularization and vascular barrier function. VEGF-A/ VEGFR2-dependent signalling is regulated by endothelial primary cilia.

physiology↗