Function and molecular organization of vascular Trp channels

Trp cation channels have recently emerged as a novel family of signal transduction proteins involved in agonist- induced Ca2+ entry. Our current knowledge on the Trp family suggests these proteins as essential elements of receptor/phospholipase C-regulated cation channels involved in Ca2+ homeostasis of non-excitable and excitable cells. Trp proteins are expressed in vascular smooth muscle, and are likely to contribute to phospholipase C- mediated activation either in terms of formation of a Ca2+ entry pathway or by mediating cation entry that causes membrane depolarization and activation of voltage-gated Ca2+ channels. So far, the physiological role and the function of Trp proteins as well as the molecular organization of Trp channels in vascular smooth muscle is elusive. The aims of the projected work are i) to delineate the expression pattern and the subcellular localization of Trp isoforms in vascular smooth muscle, ii) to identify Trp-related membrane conductances, and iii) to investigate the crosstalk of specific vascular Trp channels with regulatory proteins as well as the targeting of Trp species into cellular microdomains to form specialized signaling complexes. The anticipated gain in knowledge on the function and physiological role of this novel family of ion channels will lead to a better understanding of neurohumoral control of blood vessel function and may serve as basis for the development of entirely new concepts in pharmacotherapy of cardiovascular diseases.

TRP (transient receptor potential) proteins are considered as highly versatile signal transduction molecules that govern a variety of cellular functions. Several members of the classical (TRPC) subfamily including TRPC1, TRPC3, TRPC4 and TRPC6 have been suggested as important players in cardiovascular physiology and pathophysiology. The aim of this project was to elucidate the molecular nature, regulatory properties and the exact physiological relevance of these channels in blood vessels, with the long term objective to exploit TRPC proteins as novel therapeutic targets. The particular focus of this work was on the function of the TRPC3 isoform, which is significantly expressed in vascular smooth muscle and endothelial cells. We identified TRPC3 channels as potential sensors for cellular stress situations, specifically for redox stress, and obtained evidence for a strict dependence of TRPC3 channels on cellular cholesterol homeostasis. Control of cellular Ca2+ signals by TRPC3 channels was found to involve a unique signaling partnership with another ion transport system, the cardiac type Na+ /Ca 2+ exchanger. To further test the biological relevance of TRPC3 channels we developed a novel strategy for knock-down of TRPC channel function in native tissues, which is based on the expression of an antibody-sensitive channel mutant. The results of our investigations support the concept of vascular TRPC3 channels as a potential target for drug therapy and suggest modulation of TRPC3 channels as an attractive novel strategy to prevent vascular dysfunctions ranging from disturbances of angiogenesis to atherosclerosis and diabetic vascular dysfunction.