Stretch-Induced Activation of NFAT Signaling in Hl-1 Cardiomyocytes

Abstract

Mechanical forces are efficiently converted into cellular signals to initiate structural and functional remodeling of cardiac myocytes. Molecular mechanisms underlying cardiac mechanotransduction are still barely understood. Nuclear Factor of Activated T-cells (NFAT) is an important calcium-responsive transcription factor and a key player in cardiac remodeling processes. In this study, we investigated the involvement of Ca2+ signaling molecules as a link between mechanical stretch and NFAT translocation in HL-1 atrial myocytes. We specifically focused on the potential role of receptor-operated and/or store-operated Ca2+ permeable channels of the TRPCs (classical transient receptor potential) and the Orai family. Populations of HL-1 cells overexpressing GFP-NFAT were exposed to a single-stretch by 20% for 20 minutes on commercially available silicon membranes and NFAT localization was then analyzed by fluorescence microscopy. Results revealed that stretched HL-1 cells significantly increased NFAT nuclear translocation when compared to unstretched cells. Similar NFAT activation was obtained when HL-1 cells were stimulated by either endothelin-1 (100 nM) or thapsigargin (1μM) in the absence of a stretch stimulus. These results demonstrate that similar levels of NFAT activation are induced in HL-1 cells by either mechanical stress, cell activation via Gq-coupled receptors or depletion of internal Ca2+ stores. HL-1 cells were found to express several TRPC isoforms that might contribute to mechanotransduction. Our data suggest a linkage between mechanical stretch and cardiac remodeling involving Ca2+ entry and NFAT activation.This work is funded by FWF (Austrian research fund) projects P21925-B19, P22565-B18 and the DK Metabolic and Cardiovascular Disease grant W1226-B18.