title: Transient receptor potential canonical-3 channel-dependent fibroblast regulation in atrial fibrillation.
abstract: BACKGROUND
  Fibroblast proliferation and differentiation are central in atrial fibrillation (AF)-promoting remodeling. Here, we investigated fibroblast regulation by Ca(2+)-permeable transient receptor potential canonical-3 (TRPC3) channels.
  
  
  RESULTS
  Freshly isolated rat cardiac fibroblasts abundantly expressed TRPC3 and had appreciable nonselective cation currents (I(NSC)) sensitive to a selective TPRC3 channel blocker, pyrazole-3 (3 μmol/L). Pyrazole-3 suppressed angiotensin II-induced Ca(2+) influx, proliferation, and α-smooth muscle actin protein expression in fibroblasts. Ca(2+) removal and TRPC3 blockade suppressed extracellular signal-regulated kinase phosphorylation, and extracellular signal-regulated kinase phosphorylation inhibition reduced fibroblast proliferation. TRPC3 expression was upregulated in atria from AF patients, goats with electrically maintained AF, and dogs with tachypacing-induced heart failure. TRPC3 knockdown (based on short hairpin RNA [shRNA]) decreased canine atrial fibroblast proliferation. In left atrial fibroblasts freshly isolated from dogs kept in AF for 1 week by atrial tachypacing, TRPC3 protein expression, currents, extracellular signal-regulated kinase phosphorylation, and extracellular matrix gene expression were all significantly increased. In cultured left atrial fibroblasts from AF dogs, proliferation rates, α-smooth muscle actin expression, and extracellular signal-regulated kinase phosphorylation were increased and were suppressed by pyrazole-3. MicroRNA-26 was downregulated in canine AF atria; experimental microRNA-26 knockdown reproduced AF-induced TRPC3 upregulation and fibroblast activation. MicroRNA-26 has NFAT (nuclear factor of activated T cells) 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 the Ca(2+) influx that activates extracellular signal-regulated kinase 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 blockade prevents AF substrate development in a dog model of electrically maintained AF. TRPC3 likely plays an important role in AF by promoting fibroblast pathophysiology and is a novel potential therapeutic target.
authors.affiliation: Department of Medicine and Research Center, Montreal Heart Institute and Universite´ de Montre´al, Montreal, Quebec, Canada.
authors.forename: Masahide
authors.initials: M
authors.lastname: Harada
authors.forename: Xiaobin
authors.initials: X
authors.lastname: Luo
authors.forename: Xiao Yan
authors.initials: XY
authors.lastname: Qi
authors.forename: Artavazd
authors.initials: A
authors.lastname: Tadevosyan
authors.forename: Ange
authors.initials: A
authors.lastname: Maguy
authors.forename: Balazs
authors.initials: B
authors.lastname: Ordog
authors.forename: Jonathan
authors.initials: J
authors.lastname: Ledoux
authors.forename: Takeshi
authors.initials: T
authors.lastname: Kato
authors.forename: Patrice
authors.initials: P
authors.lastname: Naud
authors.forename: Niels
authors.initials: N
authors.lastname: Voigt
authors.forename: Yanfen
authors.initials: Y
authors.lastname: Shi
authors.forename: Kaichiro
authors.initials: K
authors.lastname: Kamiya
authors.forename: Toyoaki
authors.initials: T
authors.lastname: Murohara
authors.forename: Itsuo
authors.initials: I
authors.lastname: Kodama
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Tardif
authors.forename: Ulrich
authors.initials: U
authors.lastname: Schotten
authors.forename: David R
authors.initials: DR
authors.lastname: Van Wagoner
authors.forename: Dobromir
authors.initials: D
authors.lastname: Dobrev
authors.forename: Stanley
authors.initials: S
authors.lastname: Nattel
mesh_terms: D000818:Animals; D001281:Atrial Fibrillation / Q000235:genetics / Q000378:metabolism* / Q000473:pathology*; D016280:Atrial Function, Right / Q000235:genetics; D049109:Cell Proliferation; D002478:Cells, Cultured; D004285:Dogs; D015536:Down-Regulation / Q000235:genetics; D005347:Fibroblasts / Q000378:metabolism* / Q000473:pathology; D055785:Gene Knockdown Techniques / Q000379:methods; D006041:Goats; D057809:HEK293 Cells; D006801:Humans; D051381:Rats; D050052:TRPC Cation Channels / Q000235:genetics / Q000502:physiology*
chemical_list: D050052:TRPC Cation Channels; C104603:TRPC3 cation channel