Abstract P181: Endothelial Ciliary Muscarinic Receptors and the Pathogenesis of Hypertension in Polycystic Kidney Disease

Abstract

Primary endothelial cilia are mechanosensory organelles that are projected into the lumen of blood vessels. Defects in cilia assembly or function can lead to multiple human pathologies, collectively known as ciliopathies, including hypertension. Acetylcholine, a neurotransmitter, is implicated in essential hypertension in humans and animal models. It has been demonstrated that vascular endothelia require primary cilia to sense and transmit external mechanical stimuli into internal biochemical reactions. One of these reactions includes the biosynthesis and release of nitric oxide, which is one of the most potent endogenous vasodilators. This idea has only been investigated in cultured endothelial cells in vitro . Based on this finding, however, a very bold hypothesis is formed to test that abnormal cilia function results in vascular hypertension. Though both primary cilia and muscarinic acetylcholine receptors play important roles in vascular hypertension, their relationship has never been explored. To determine the roles of the cholinergic system and mechanosensory cilia, we studied the effects of acetylcholine on ciliary length and function in wild-type (WT) and mechano-insensitive cilia mutant endothelial cells ( Pkd1 –/– and Tg737 orpk/orpk ). We show for the first time that mouse vascular endothelia exhibit muscarinic receptor-type 1, 3 and 5 (AChM1, 3, and 5R), which co-localizes to primary endothelial cilia. AChM3R activation significantly increases cilia length in cells treated with AChM3R agonist compared to non-treated cells (1.63±0.01 vs.1.92±0.01). Furthermore, the chemosensory function of cilia can alter the mechanosensory function through changes in sensitivity to fluid-shear stress. We propose that activated ciliary AChM3R has a functional mechanosensory role in endothelial cells. A series of conditional mouse models are used, coupled with high-resolution microscopy techniques. We used vascular-specific mouse models of Pkd1, Tg737 and AChM3R to study systolic/diastolic blood pressure. Our data corroborate our hypothesis, that cilia function knockout in the vascular system is associated with elevated blood pressure compared to wildtype controls (123±6 vs. 135±6 systolic and 79±6 vs. 89±5 diastolic).