title: TRPC4α and TRPC4β Similarly Affect Neonatal Cardiomyocyte Survival during Chronic GPCR Stimulation.
abstract: The Transient Receptor Potential Channel Subunit 4 (TRPC4) has been considered as a crucial Ca2+ component in cardiomyocytes promoting structural and functional remodeling in the course of pathological cardiac hypertrophy. TRPC4 assembles as homo or hetero-tetramer in the plasma membrane, allowing a non-selective Na+ and Ca2+ influx. Gαq protein-coupled receptor (GPCR) stimulation is known to increase TRPC4 channel activity and a TRPC4-mediated Ca2+ influx which has been regarded as ideal Ca2+ source for calcineurin and subsequent nuclear factor of activated T-cells (NFAT) activation. Functional properties of TRPC4 are also based on the expression of the TRPC4 splice variants TRPC4α and TRPC4β. Aim of the present study was to analyze cytosolic Ca2+ signals, signaling, hypertrophy and vitality of cardiomyocytes in dependence on the expression level of either TRPC4α or TRPC4β. The analysis of Ca2+ transients in neonatal rat cardiomyocytes (NRCs) showed that TRPC4α and TRPC4β affected Ca2+ cycling in beating cardiomyocytes with both splice variants inducing an elevation of the Ca2+ transient amplitude at baseline and TRPC4β increasing the Ca2+ peak during angiotensin II (Ang II) stimulation. NRCs infected with TRPC4β (Ad-C4β) also responded with a sustained Ca2+ influx when treated with Ang II under non-pacing conditions. Consistent with the Ca2+ data, NRCs infected with TRPC4α (Ad-C4α) showed an elevated calcineurin/NFAT activity and a baseline hypertrophic phenotype but did not further develop hypertrophy during chronic Ang II/phenylephrine stimulation. Down-regulation of endogenous TRPC4α reversed these effects, resulting in less hypertrophy of NRCs at baseline but a markedly increased hypertrophic enlargement after chronic agonist stimulation. Ad-C4β NRCs did not exhibit baseline calcineurin/NFAT activity or hypertrophy but responded with an increased calcineurin/NFAT activity after GPCR stimulation. However, this effect was not translated into an increased propensity towards hypertrophy but rather less hypertrophy during GPCR stimulation. Further analyses revealed that, although hypertrophy was preserved in Ad-C4α NRCs and even attenuated in Ad-C4β NRCs, cardiomyocytes had an increased apoptosis rate and thus were less viable after chronic GPCR stimulation. These findings suggest that TRPC4α and TRPC4β differentially affect Ca2+ signals, calcineurin/NFAT signaling and hypertrophy but similarly impair cardiomyocyte viability during GPCR stimulation.
authors.affiliation: Department of Internal Medicine I, University Hospital Würzburg, Würzburg, Germany.|Comprehensive Heart Failure Center Würzburg, University Hospital Würzburg, Würzburg, Germany.
authors.forename: Nadine
authors.initials: N
authors.lastname: Kirschmer
authors.affiliation: Department of Internal Medicine I, University Hospital Würzburg, Würzburg, Germany.|Comprehensive Heart Failure Center Würzburg, University Hospital Würzburg, Würzburg, Germany.
authors.forename: Sandra
authors.initials: S
authors.lastname: Bandleon
authors.affiliation: Department of Internal Medicine I, University Hospital Würzburg, Würzburg, Germany.|Comprehensive Heart Failure Center Würzburg, University Hospital Würzburg, Würzburg, Germany.
authors.forename: Viktor
authors.initials: V
authors.lastname: von Ehrlich-Treuenstätt
authors.affiliation: Center for Pharmacometrics and Systems Pharmacology, Department of Pharmaceutics, College of Pharmacy, University of Florida, Orlando, United States of America.
authors.forename: Sonja
authors.initials: S
authors.lastname: Hartmann
authors.affiliation: Department of Internal Medicine I, University Hospital Würzburg, Würzburg, Germany.|Comprehensive Heart Failure Center Würzburg, University Hospital Würzburg, Würzburg, Germany.
authors.forename: Alice
authors.initials: A
authors.lastname: Schaaf
authors.affiliation: Department of Internal Medicine I, University Hospital Würzburg, Würzburg, Germany.|Comprehensive Heart Failure Center Würzburg, University Hospital Würzburg, Würzburg, Germany.
authors.forename: Anna-Karina
authors.initials: AK
authors.lastname: Lamprecht
authors.affiliation: Institute of Physiology, University of Würzburg, Würzburg, Germany.
authors.forename: Erick
authors.initials: E
authors.lastname: Miranda-Laferte
authors.affiliation: Department of Therapeutic Radiology and Oncology, Medical University of Graz, Graz, Austria.
authors.forename: Tanja
authors.initials: T
authors.lastname: Langsenlehner
authors.affiliation: Department of Cardiology and Pulmology, Brandenburg Medical School, University Hospital Brandenburg, Brandenburg, Germany.
authors.forename: Oliver
authors.initials: O
authors.lastname: Ritter
authors.affiliation: Department of Internal Medicine I, University Hospital Würzburg, Würzburg, Germany.|Comprehensive Heart Failure Center Würzburg, University Hospital Würzburg, Würzburg, Germany.
authors.forename: Petra
authors.initials: P
authors.lastname: Eder
mesh_terms: D017398:Alternative Splicing; D000818:Animals; D000831:Animals, Newborn; D019703:Calcineurin / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D006332:Cardiomegaly / Q000235:genetics / Q000378:metabolism*; D002470:Cell Survival; D002478:Cells, Cultured; D004195:Disease Models, Animal; D051379:Mice; D032383:Myocytes, Cardiac / Q000166:cytology* / Q000378:metabolism; D050778:NFATC Transcription Factors / Q000378:metabolism; D051381:Rats; D015398:Signal Transduction; D050052:TRPC Cation Channels / Q000235:genetics* / Q000378:metabolism*
chemical_list: D050778:NFATC Transcription Factors; D050052:TRPC Cation Channels; C489571:TRPC4 ion channel; D019703:Calcineurin; D002118:Calcium