ROLE OF TRPV4 CHANNEL SIGNALING IN SHEAR STRESS RESPONSES

Abstract

Shear stress along the vascular intima promotes blood flow and preserves vascular wall structure, providing vital protection against progressive cardiovascular disease. Indeed, obstructive cardiovascular disease states such as atherosclerosis are associated with early shear stress disruption that leads to endothelial dysfunction and vascular remodeling. A key feature of shear stress action is a rapid and sustained increase in dynamic (spatially and temporally) Ca2+ signals within the endothelium, which promotes vasodilation and opposes inflammation. Although specific mechanisms remain unclear, recent studies have implicated mechanosensitive TRPV4 cation channels in shear stress mediated Ca2+ entry. We hypothesize that shear stress‐induced endothelial Ca2+ signals arise from graded recruitment of TRPV4 Ca2+ transients. We performed Ca2+ imaging studies on arteries isolated from wild type and genetically altered TRPV4 knockout mice. Carotid arteries were isolated, opened, and mounted in specialized flow chambers. The chambers were connected to a peristaltic pump and placed on the stage of a microscope adapted for high‐speed confocal imaging (488 nm ex, 510 nm emission; 8 frames/s). Endothelial Ca2+ dynamics were recorded at increasing flow rates (shear stress 0, 12, 52, 75, and 102 dynes/cm2). Image analysis was performed using ImageJ and custom software (LC_Pro) designed to discern distinct profiles of signal frequency, amplitude, duration and spatial spread. Artery segments were also subjected to immunostaining to assess relative expression and distribution of TRPV4 channels. We found that the wild type and TRPV4 knockouts both responded to shear stress. The TRPV4 knockout exhibited a reduced Ca2+ event frequency and shorter event durations compared to wild type controls in response to physiologic elevations in shear stress. Future experiments will focus on expounding upon the flow response, particularly the importance of TRPV4 channels in the time‐course of Ca2+ signal patterning changes under chronic low flow conditions.Support or Funding InformationSponsored by Mark Taylor and David Weber, Ph.D., Department of Physiology/Cell Biology, University of South Alabama College of Medicine, Mobile, AL. Summer Medical Student Research Program