Inducible cardiac specific TRPC channel inhibition

The family of TRPC (classical Transient Receptor Potential) cation channels consists of seven members (TRPC1- 7) that function as channel subunits and assemble to form tetramers in the plasma membrane permitting a non selective (Na+ /Ca 2+) cation entry. Recently, TRPC channels have been identified as crucial components of Ca2+ signalling pathways that promote maladaptive growth of the myocardium, a critical pathophysiological situation known to precede heart failure and sudden cardiac death. TRPC proteins were shown upregulated in hypertrophic hearts, and transgenic mice with cardiac specific TRPC overexpression exhibited an increased propensity towards hypertrophic progression when pressure overload was applied. Functional interaction between TRPC channels and the hypertrophic calcineurin/NFAT signaling pathway has been suggested from a series of recent studies. TRPC activation in response PLC stimulation was found to activate the Ca2+ dependent phosphatase calcineurin and its effector, the transcription factor NFAT, which regulates expression of a number of hypertrophic genes. Nonetheless, clear evidence for a pathophysiological role of TRPCs is still missing but could be advanced by selective inhibition of TRPC channels in the heart. In this proposal, we plan to employ an in vivo approach to inhibit cardiac TRPC channels by the use of transgenic mice expressing dominant negative (dn) TRPC mutants: a dn-TRPC3 mutant to disrupt TRPC3/6/7 heteromers and a TRPC5 dn-mutant to disrupt the integrity of TRPC1/4/5 heteromeric channels. Expression of both transgenes will be controlled by the tetracycline induction system. Cardiac functional parameters (echocardiography) and histological alterations of dnTRPC3/and dnTRPC5 mice will be analyzed at baseline (without hypertrophic induction), as well as after hypertrophic stimulation. Effects of TRPC channel inhibition on calcineurin/NFAT signalling, as well as on the cardiac gene expression profile will be examined. Measurements of intracellular Ca2+ signals will complement these investigations and will provide information on the importance of TRPC channel inhibtion for Ca2+ homeostasis of cardiac myocytes. The proposed work is expected to contribute to a better understanding of the role of TRPC channels in cardiac Ca2+ signalling and in the generation of maladaptive hypertrophy and associated cardiac dysfunctions.