Equibiaxial strain and strain rate stimulate early activation of G proteins in cardiac fibroblasts.

Cardiac fibroblasts are responsible for the production of the extracellular matrix of the heart, with alterations of fibroblast function implicated in myocardial infarction and cardiac hypertrophy. Here the role of heterotrimeric GTP-binding proteins (G proteins) in the mechanotransduction of strain in rat cardiac fibroblasts was investigated. Cells in an equibiaxial stretch device were incubated with the photoreactive GTP analog azidoanalido [α-32P]GTP (AAGTP) and were subjected to various regimens of strain. Autoradiographic analysis showed a 42-kDa protein labeled for cells exposed to 12 cycles of 3% strain or 6 cycles of 6% strain over 60 s (strain rate of 1.2%/s), whereas 6 cycles of 3% strain (0.6%/s) elicited no measurable response. To further investigate the role of strain rate, a single 6% cycle over 10 or 60 s (1.2% and 0.2%/s, respectively) was applied, with the more rapid cycle stimulating AAGTP binding, whereas the lower strain rate showed no response. In cells subjected to a single 6% cycle/10 s, immunoprecipitation identified the AAGTP-labeled 42-kDa band as the G protein subunits Gαq and Gαi1. These results demonstrate that G protein activation represents one of the early mechanotransduction events in cardiac fibroblasts subjected to mechanical strain, with the rate at which the strain is applied modulating this response.

[1]  J. Frangos,et al.  CHAPTER 5 – Effects of Flow on Anchorage-Dependent Mammalian Cells—Secreted Products , 1993 .

[2]  D. Ingber,et al.  Integrins as mechanochemical transducers. , 1991, Current opinion in cell biology.

[3]  G. Dorn,et al.  Transgenic Gαq overexpression induces cardiac contractile failure in mice , 1997 .

[4]  H. Vandenburgh,et al.  Mechanical stimulation of skeletal muscle increases prostaglandin F2α production, cyclooxygenase activity, and cell growth by a pertussis toxin sensitive mechanism , 1995, Journal of cellular physiology.

[5]  T Delhaas,et al.  An equibiaxial strain system for cultured cells. , 1996, The American journal of physiology.

[6]  G. Booz,et al.  Molecular signalling mechanisms controlling growth and function of cardiac fibroblasts. , 1995, Cardiovascular research.

[7]  Y. Yazaki,et al.  Mechanical loading stimulates cell hypertrophy and specific gene expression in cultured rat cardiac myocytes. Possible role of protein kinase C activation. , 1991, The Journal of biological chemistry.

[8]  C. Turner,et al.  Focal adhesions: transmembrane junctions between the extracellular matrix and the cytoskeleton. , 1988, Annual review of cell biology.

[9]  J. Sadoshima,et al.  Molecular characterization of the stretch-induced adaptation of cultured cardiac cells. An in vitro model of load-induced cardiac hypertrophy. , 1992, The Journal of biological chemistry.

[10]  B. Sumpio,et al.  Chronic cyclic strain reduces adenylate cyclase activity and stimulatory G protein subunit levels in coronary smooth muscle cells. , 1994, Experimental cell research.

[11]  J. Frangos,et al.  Flow‐induced prostacyclin production is mediated by a pertussis toxin‐sensitive G protein , 1992, FEBS letters.

[12]  J A Frangos,et al.  Steady shear and step changes in shear stimulate endothelium via independent mechanisms--superposition of transient and sustained nitric oxide production. , 1996, Biochemical and biophysical research communications.

[13]  A D McCulloch,et al.  Transmural distribution of three-dimensional strain in the isolated arrested canine left ventricle. , 1991, The American journal of physiology.

[14]  T. Borg,et al.  Collagen expression in mechanically stimulated cardiac fibroblasts. , 1991, Circulation research.

[15]  J. Exton Cell signalling through guanine-nucleotide-binding regulatory proteins (G proteins) and phospholipases. , 1997, European journal of biochemistry.

[16]  P. Davies,et al.  Quantitative studies of endothelial cell adhesion. Directional remodeling of focal adhesion sites in response to flow forces. , 1994, The Journal of clinical investigation.

[17]  K. Baker,et al.  Cardiac Hypertrophy: Mechanical, Neural, and Endocrine Dependence , 1991 .

[18]  M. Eghbali Cardiac fibroblasts: function, regulation of gene expression, and phenotypic modulation. , 1992, Basic research in cardiology.

[19]  D. Carey,et al.  Localization of a heterotrimeric G protein gamma subunit to focal adhesions and associated stress fibers , 1994, The Journal of cell biology.

[20]  K. Shirato,et al.  Pertussis toxin-sensitive G protein mediates coronary microvascular control during autoregulation and ischemia in canine heart. , 1994, Circulation research.

[21]  Y. Fung,et al.  Biomechanics: Mechanical Properties of Living Tissues , 1981 .

[22]  G. Laurent,et al.  Mechanical Load and Polypeptide Growth Factors Stimulate Cardiac Fibroblast Activity , 1995, Annals of the New York Academy of Sciences.

[23]  T. K. Harden,et al.  G-protein-mediated regulation of phospholipase C Involvement of βγ subunits. , 1994, Trends in cardiovascular medicine.

[24]  T. Borg,et al.  The cell biology of the cardiac interstitium. , 1996, Trends in cardiovascular medicine.

[25]  H. Vandenburgh Mechanical forces and their second messengers in stimulating cell growth in vitro. , 1992, The American journal of physiology.

[26]  A. McCulloch,et al.  Angiotensin II stimulates the autocrine production of transforming growth factor-β1 in adult rat cardiac fibroblasts , 1995 .

[27]  P. Davies,et al.  Flow-mediated endothelial mechanotransduction. , 1995, Physiological reviews.

[28]  Noel N Kim,et al.  Identification of Functional Angiotensin II Receptors on Rat Cardiac Fibroblasts , 1993, Circulation.

[29]  Melvin I. Simon,et al.  Diversity of G proteins in signal transduction , 1991, Science.

[30]  J. Frangos,et al.  Fluid flow rapidly activates G proteins in human endothelial cells. Involvement of G proteins in mechanochemical signal transduction. , 1996, Circulation research.

[31]  L. Waldman,et al.  Technique for Measuring Regional Two‐Dimensional Finite Strains in Canine Left Ventricle , 1988, Circulation research.