TRPC3-Dependent Fibroblast Regulation in Atrial Fibrillation
Background—Fibroblast proliferation and differentiation are central in atrial fibrillation (AF)-promoting remodeling. Here, we investigated fibroblast regulation by Ca2+-permeable transient receptor potential canonical-3 (TRPC3) channels.
Methods and Results—Freshly-isolated rat cardiac-fibroblasts abundantly expressed TRPC3 and had appreciable non-selective cation currents (INSC) sensitive to a selective TPRC3-channel blocker, pyrazole-3 (3-μmol/L). Pyrazole-3 suppressed angiotensin-II-induced Ca2+-influx, proliferation and α-smooth-muscle actin (αSMA) protein-expression in fibroblasts. Ca2+-removal and TRPC3-blockade suppressed extracellular-signal regulated kinase (ERK)-phosphorylation, and ERK-phosphorylation inhibition reduced fibroblast-proliferation. TRPC3-expression was upregulated in atria from AF-patients, goats with electrically-maintained AF and tachypacing-induced heart-failure dogs. TRPC3-knockdown (shRNA-based) decreased canine atrial-fibroblast proliferation. In left-atrial (LA) fibroblasts freshly isolated from dogs kept in AF for 1 week by atrial-tachypacing, TRPC3 protein-expression, currents, ERK-phosphorylation and extracellular-matrix gene-expression were all significantly increased. In cultured LA-fibroblasts from AF-dogs, proliferation-rates, αSMA-expression and ERK-phosphorylation were increased, and suppressed by pyrazole-3. MicroRNA-26 was downregulated in canine AF-atria; experimental micro-RNA-26 knockdown reproduced AF-induced TRPC3-upregulation and fibroblast-activation. MicroRNA-26 has Nuclear Factor of Activated T-cells (NFAT) binding-sites in the 5'-promoter-region. NFAT-activation increased in AF-fibroblasts and NFAT negatively regulated microRNA-26 transcription. In vivo pyrazole-3 administration suppressed AF while decreasing fibroblast proliferation and extracellular-matrix gene-expression.
Conclusions—TRPC3-channels regulate cardiac fibroblast proliferation and differentiation, likely by controlling Ca2+-influx that activates ERK-signaling. AF increases TRPC3-channel expression by causing NFAT-mediated downregulation of microRNA-26 and causes TRPC3-dependent enhancement of fibroblast proliferation and differentiation. In vivo TRPC3-block prevents AF-substrate development in a dog model of electrically-maintained AF. TRPC3 likely plays an important role in AF-promoting fibroblast pathophysiology and is a novel potential therapeutic target.
- Received May 31, 2012.
- Accepted August 10, 2012.
- Copyright © 2012, American Heart Association, Inc. All rights reserved. Unauthorized use prohibited