title: FAK mediates the activation of cardiac fibroblasts induced by mechanical stress through regulation of the mTOR complex.
abstract: OBJECTIVE
  Cardiac fibroblasts are activated by mechanical stress, but the underlying mechanisms involved remain poorly understood. In this study, we investigated whether focal adhesion kinase (FAK) plays a role in the activation of cardiac fibroblasts in response to cyclic stretch.
  
  
  RESULTS
  Neonatal (NF-P3/80--third passage, 80% confluence) and adult (AF-P1/80--first passage, 80% confluence) rat cardiac fibroblasts were exposed to cyclic stretch (biaxial, 1 Hz), which enhanced FAK phosphorylation at Tyr397. Proliferation (anti-5-bromo-2'-deoxyuridine and anti-Ki67 nuclear labelling), differentiation into myofibroblasts (expression of alpha-smooth muscle actin--alpha-SMA), and the activity of matrix metalloproteinase-2 were equally enhanced in stretched NF-P3/80 and AF-P1/80. Treatment with the integrin inhibitor RGD peptide impaired FAK phosphorylation and increased apoptosis (TUNEL) in non-stretched and stretched NF-P3/80, whereas FAK silencing induced by small interfering RNA modestly enhanced apoptosis only in stretched cells. RGD peptide or FAK silencing suppressed the activation of NF-P3/80 invoked by cyclic stretch. In addition, NF-P3/80 depleted of FAK were defective in AKT Ser473, TSC-2 Thr1462, and S6 kinase Thr389 phosphorylation induced by cyclic stretch. The activation of NF-P3/80 invoked by cyclic stretch was prevented by pre-treatment with the mammalian target of rapamycin (mTOR) inhibitor rapamycin, whereas supplementation with the amino acid, leucine, activated S6K and rescued the stretch-induced activation of NF-P3/80 depleted of FAK.
  
  
  CONCLUSIONS
  These findings demonstrate a critical role for the mTOR complex, downstream from FAK, in mediating the activation of cardiac fibroblasts in response to mechanical stress.
authors.affiliation: Department of Internal Medicine, School of Medicine and Department of Cell Biology, State University of Campinas, Campinas, SP, Brazil.
authors.forename: Ana Paula
authors.initials: AP
authors.lastname: Dalla Costa
authors.forename: Carolina F M Z
authors.initials: CF
authors.lastname: Clemente
authors.forename: Hernandes F
authors.initials: HF
authors.lastname: Carvalho
authors.forename: José B
authors.initials: JB
authors.lastname: Carvalheira
authors.forename: Wilson
authors.initials: W
authors.lastname: Nadruz
authors.forename: Kleber G
authors.initials: KG
authors.lastname: Franchini
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D000831:Animals, Newborn; D017209:Apoptosis; D002454:Cell Differentiation; D049109:Cell Proliferation; D002478:Cells, Cultured; D024042:Collagen Type I / Q000378:metabolism; D004789:Enzyme Activation; D005347:Fibroblasts / Q000187:drug effects / Q000201:enzymology*; D051417:Focal Adhesion Kinase 1 / Q000235:genetics / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D007930:Leucine / Q000378:metabolism; D020778:Matrix Metalloproteinase 2 / Q000378:metabolism; D040542:Mechanotransduction, Cellular / Q000187:drug effects; D009206:Myocardium / Q000166:cytology / Q000201:enzymology*; D009842:Oligopeptides / Q000494:pharmacology; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D034622:RNA Interference; D051381:Rats; D017208:Rats, Wistar; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism; D012694:Serine; D020123:Sirolimus / Q000494:pharmacology; D013314:Stress, Mechanical; D058570:TOR Serine-Threonine Kinases; D013912:Threonine; D013997:Time Factors; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins / Q000378:metabolism; D014443:Tyrosine
chemical_list: D000199:Actins; D024042:Collagen Type I; D051417:Focal Adhesion Kinase 1; D047908:Intracellular Signaling Peptides and Proteins; D007930:Leucine; D020778:Matrix Metalloproteinase 2; D009842:Oligopeptides; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D019893:Ribosomal Protein S6 Kinases; D012694:Serine; D020123:Sirolimus; D058570:TOR Serine-Threonine Kinases; D013912:Threonine; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins; D014443:Tyrosine; C498862:Acta2 protein, rat; C047981:arginyl-glycyl-aspartic acid; C546843:mTOR protein, mouse; C546845:mTOR protein, rat; C496052:Ptk2 protein, rat; C522362:Mmp2 protein, mouse