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Alpha 7 integrin is essential for normal heart shape and function
ABSTRACTS / Journal of Molecular and Cellular Cardiology 40 (2006) 920 – 1015
227. Alpha 7 integrin is essential for normal heart shape and function R. Nadif-Savey a, M. Emerson b, E.J. Cartwright a, U. Mayer c, L. Neyses a. a Division of Cardiology, University of Manchester, Manchester M13 9PT, UK. b Wellcome Trust Centre for Cell-Matrix Research, University of Manchester, Manchester M13 9PT, UK. c Faculty of Life Sciences Imperial College London, UK Cellular signal exchanges between the extracellular matrix (ECM) and the cell are essential for normal heart physiology. a7h1 integrin is the major integrin-type receptor for laminin in cardiac and skeletal muscle, we therefore studied the structural and functional role of integrin a7 in the heart in alpha7 nullmutant (a7/) mice. a7/ mice have a shorter life span and gross morphological examination of the heart showed an abnormally elongated structure compared with age-matched controls. M-mode echocardiography revealed significant time-dependent changes in heart structure characterised by thickened diastolic interventricular septum, reduced left ventricular end-diastolic diameter and decreased left ventricular diameter to length ratio. The structural changes seen in the left ventricle were accompanied by significantly impaired stroke volume. a7/ mice displayed cardiac hypertrophy by 6 months of age indicated by a marked increase in cell size and in heart weight to body weight ratio. After 9 months of age, a7/ mice exhibited a significant decrease in heart weight suggesting cellular loss. Further examinations showed no evidence of apoptosis; however, penetration of inflammatory cells, a marker of necrosis, was strikingly increased in a7/ hearts. In conclusion, absence of the a7 gene in mice leads to a small and abnormally shaped heart with low stroke volume; opposite to expectations, cardiac myocytes were hypertrophied thus implying cell loss, likely due to necrosis. a7 integrin is therefore required for the maintenance of correct heart structure. doi:10.1016/j.yjmcc.2006.03.242
228. The sarcolemmal calcium pump, alpha-1 syntrophin and neuronal nitric oxide synthase are part of a macromolecular protein complex Tamer M.A. Mohamed, Judith C. Williams, Angel L. Armesilla, Cassandra L. Hagarty, Delvac Oceandy, Elizabeth J. Cartwright, Ludwig Neyses. Division of Cardiovascular and Endocrine Sciences, University of Manchester, UK Plasma membrane calcium ATPase (PMCA), a calcium extruding enzyme, is assumed to be involved in excitation – contraction coupling, although its precise role in the myocardium is not entirely clear. Recently we, and others, have suggested a new function for PMCA as a modulator of signal transduction pathways. This work shows the physical interaction between PMCA (isoforms 1 and 4) and a1-syntrophin, and proposes a ternary complex of interaction between endogenous PMCA, a1-syntrophin and NOS-1 in cardiac cells. We have
1003
identified that the region corresponding to amino acids 399– 447 of a1-syntrophin, is crucial for interaction with PMCA1 and 4. The functionality of the interaction was demonstrated by investigating the inhibition of neuronal nitric oxide synthase (NOS-1); PMCA is a negative regulator of NOS-1-dependent NO production, and over-expression of a1-syntrophin and PMCA4 resulted in strongly increased inhibition of NO production. Analysis of the expression levels of a1-syntrophin protein in the heart, skeletal muscle, brain or kidney of PMCA4/ mice, did not reveal any differences when compared to those found in the same tissues of wild type mice. These results suggest that PMCA4 is tethered to the syntrophin complex as a regulator of NOS-I but its absence does not cause collapse of the complex, contrary to what has been reported for other proteins within the complex such as dystrophin. In conclusion, the present data demonstrate for the first time the localisation of PMCA1b and 4b to the syntrophin/ dystrophin complex in the heart, and provide a specific molecular mechanism of interaction as well as functionality. doi:10.1016/j.yjmcc.2006.03.243
229. The sarcolemmal calcium pump modulates B-adrenergic hypertrophic signalling Min Zi, Sukhpal Prehar, Elizabeth J. Cartwright, Michael Emerson, Ludwig Neyses. Division of Cardiovascular and Endocrine Sciences, University of Manchester, United Kingdom The role of plasma membrane calcium ATPase (PMCA), an enzyme extruding calcium from the cytosol, in the heart is not completely understood. Previously we have demonstrated that PMCA4 interacts and downregulates neuronal nitric oxide synthase (nNOS) activity in non-cardiac cells. Others reported that mice lacking nNOS develop left ventricular hypertrophy and suppressed beta-adrenergic inotropic responses. We therefore investigated the role of PMCA4 in isoproterenol-induced hypertrophy. Cardiac hypertrophy was induced in 3-month-old PMCA4/ mice and wild type littermates by treatment with isoproterenol (10 mg/kg body weight/day) for 7 days. One group of mice was pre-treated with the specific nNOS inhibitor, N Npropyl-l-arginine (l-NPA; 10 mg/kg body weight), prior to each isoproterenol injection. Cardiac function was assessed using echocardiography and invasive haemodynamic assessment. The heart weight to tibia length ratio (H/T) was increased by 24% to 30% in both wild type and knockout after isoproterenol treatment compared to saline controls (P < 0.002, n 9 in each group). No significant difference however was observed between wild type and knockout groups. In wild type mice, pre-treatment with l-NPA further increased H/T by 16% compared to treatment with isoproterenol alone (P < 0.05, n 13 in each group). However, in PMCA4/ mice, pre-treatment with l-NPA did not increase the isoproterenol-induced hypertrophy (n 9). No difference in terms of fractional shortening, dP/dtmax, and dP/dtmin was observed between isoproterenol,
227. Alpha 7 integrin is essential for normal heart shape and function R. Nadif-Savey a, M. Emerson b, E.J. Cartwright a, U. Mayer c, L. Neyses a. a Division of Cardiology, University of Manchester, Manchester M13 9PT, UK. b Wellcome Trust Centre for Cell-Matrix Research, University of Manchester, Manchester M13 9PT, UK. c Faculty of Life Sciences Imperial College London, UK Cellular signal exchanges between the extracellular matrix (ECM) and the cell are essential for normal heart physiology. a7h1 integrin is the major integrin-type receptor for laminin in cardiac and skeletal muscle, we therefore studied the structural and functional role of integrin a7 in the heart in alpha7 nullmutant (a7/) mice. a7/ mice have a shorter life span and gross morphological examination of the heart showed an abnormally elongated structure compared with age-matched controls. M-mode echocardiography revealed significant time-dependent changes in heart structure characterised by thickened diastolic interventricular septum, reduced left ventricular end-diastolic diameter and decreased left ventricular diameter to length ratio. The structural changes seen in the left ventricle were accompanied by significantly impaired stroke volume. a7/ mice displayed cardiac hypertrophy by 6 months of age indicated by a marked increase in cell size and in heart weight to body weight ratio. After 9 months of age, a7/ mice exhibited a significant decrease in heart weight suggesting cellular loss. Further examinations showed no evidence of apoptosis; however, penetration of inflammatory cells, a marker of necrosis, was strikingly increased in a7/ hearts. In conclusion, absence of the a7 gene in mice leads to a small and abnormally shaped heart with low stroke volume; opposite to expectations, cardiac myocytes were hypertrophied thus implying cell loss, likely due to necrosis. a7 integrin is therefore required for the maintenance of correct heart structure. doi:10.1016/j.yjmcc.2006.03.242
228. The sarcolemmal calcium pump, alpha-1 syntrophin and neuronal nitric oxide synthase are part of a macromolecular protein complex Tamer M.A. Mohamed, Judith C. Williams, Angel L. Armesilla, Cassandra L. Hagarty, Delvac Oceandy, Elizabeth J. Cartwright, Ludwig Neyses. Division of Cardiovascular and Endocrine Sciences, University of Manchester, UK Plasma membrane calcium ATPase (PMCA), a calcium extruding enzyme, is assumed to be involved in excitation – contraction coupling, although its precise role in the myocardium is not entirely clear. Recently we, and others, have suggested a new function for PMCA as a modulator of signal transduction pathways. This work shows the physical interaction between PMCA (isoforms 1 and 4) and a1-syntrophin, and proposes a ternary complex of interaction between endogenous PMCA, a1-syntrophin and NOS-1 in cardiac cells. We have
1003
identified that the region corresponding to amino acids 399– 447 of a1-syntrophin, is crucial for interaction with PMCA1 and 4. The functionality of the interaction was demonstrated by investigating the inhibition of neuronal nitric oxide synthase (NOS-1); PMCA is a negative regulator of NOS-1-dependent NO production, and over-expression of a1-syntrophin and PMCA4 resulted in strongly increased inhibition of NO production. Analysis of the expression levels of a1-syntrophin protein in the heart, skeletal muscle, brain or kidney of PMCA4/ mice, did not reveal any differences when compared to those found in the same tissues of wild type mice. These results suggest that PMCA4 is tethered to the syntrophin complex as a regulator of NOS-I but its absence does not cause collapse of the complex, contrary to what has been reported for other proteins within the complex such as dystrophin. In conclusion, the present data demonstrate for the first time the localisation of PMCA1b and 4b to the syntrophin/ dystrophin complex in the heart, and provide a specific molecular mechanism of interaction as well as functionality. doi:10.1016/j.yjmcc.2006.03.243
229. The sarcolemmal calcium pump modulates B-adrenergic hypertrophic signalling Min Zi, Sukhpal Prehar, Elizabeth J. Cartwright, Michael Emerson, Ludwig Neyses. Division of Cardiovascular and Endocrine Sciences, University of Manchester, United Kingdom The role of plasma membrane calcium ATPase (PMCA), an enzyme extruding calcium from the cytosol, in the heart is not completely understood. Previously we have demonstrated that PMCA4 interacts and downregulates neuronal nitric oxide synthase (nNOS) activity in non-cardiac cells. Others reported that mice lacking nNOS develop left ventricular hypertrophy and suppressed beta-adrenergic inotropic responses. We therefore investigated the role of PMCA4 in isoproterenol-induced hypertrophy. Cardiac hypertrophy was induced in 3-month-old PMCA4/ mice and wild type littermates by treatment with isoproterenol (10 mg/kg body weight/day) for 7 days. One group of mice was pre-treated with the specific nNOS inhibitor, N Npropyl-l-arginine (l-NPA; 10 mg/kg body weight), prior to each isoproterenol injection. Cardiac function was assessed using echocardiography and invasive haemodynamic assessment. The heart weight to tibia length ratio (H/T) was increased by 24% to 30% in both wild type and knockout after isoproterenol treatment compared to saline controls (P < 0.002, n 9 in each group). No significant difference however was observed between wild type and knockout groups. In wild type mice, pre-treatment with l-NPA further increased H/T by 16% compared to treatment with isoproterenol alone (P < 0.05, n 13 in each group). However, in PMCA4/ mice, pre-treatment with l-NPA did not increase the isoproterenol-induced hypertrophy (n 9). No difference in terms of fractional shortening, dP/dtmax, and dP/dtmin was observed between isoproterenol,