Connective tissue growth factor (CTGF) inhibits myocardial growth, but preserves myocardial function

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ABSTRACTS / Journal of Molecular and Cellular Cardiology 42 (2007) S102–S124

The C-zone in vertebrate striated muscle is the region in each half A-band where myosin binding protein C (MyBPC) forms 7 bands of 43 nm spacing. Mutations in MyBPC are a major cause of familial hypertrophic cardiomyopathy; hence there is great interest in understanding its role in the sarcomere. We have found that the organisation of the C-zone is very similar in cardiac and skeletal muscle. Here we report on the 3D organisation of the C-zone by electron tomography of an exceptionally well-preserved frog skeletal muscle. Our reconstruction shows similar structure within each 43 nm band which comprises 3 layers of myosin head “crowns” of separation ∼ 14.3 nm. Layer 1 is the very dense MyBPC layer. Layers 2 and 3 are simple myosin head crowns. What is intriguing about Layer 1 is that it comprises strong density sharply defined along a narrow axial zone. It is highly reminiscent of the model proposed by Moolman-Smook et al. (Circ Res, 2002, 91:704–711) in which 3 MyBPC molecules attach via domains C10 to C5 around the thick filament in a collar-like manner with domains C4 to C0 free to interact with myosin S2 and/or the thin filament. We show the results of modelling myosin S1 and MyBPC models into the 3D reconstruction. Keywords: Contractile proteins; Hypertrophic cardiomyopathy; Structure–function doi:10.1016/j.yjmcc.2007.03.282

Connective tissue growth factor (CTGF) inhibits myocardial growth, but preserves myocardial function M. Ahmed, T. Lueder, J. Gravning, T. Edvardsen, E. Øie, O. Smiseth, H. Attramadal. Institute for Surgical Research, Rikshospitalet, University of Oslo Myocardial expression of CTGF is repressed in postnatal life, but is dramatically induced in heart failure (HF).To elucidate the putative physiologic actions of myocardial CTGF in heart failure, transgenic mice (Tg-CTGF) with cardiac-restricted overexpression of CTGF were generated. Cardiac mass and echocardiographic indices of cardiac dimensions were slightly decreased in Tg-CTGF mice vs. non-transgenic littermate control mice (NLC). LV pressure-volume (PV) analysis did not disclose significant alterations of contractility and cardiac output. Increased myocardial collagen was confirmed in Tg-CTGF mice by quantitation of myocardial hydroxyproline contents by HPLC (1.10 ± 0.03 vs. 0.82 ± 0.05 pmol/mg; p < 0.05). Increased myocardial expression of antihypertrophic TGF-β2 and GDF-15 mRNA in Tg-CTGF vs. NLC mice was detected. Four weeks after abdominal aortic banding (AB), significant elevations of cardiac mass were observed in NLC-AB mice. However, cardiac hypertrophy was substantially diminished in TgCTGF-AB mice. Simultaneous PV-analysis provided evidence of overt cardiac dysfunction in NLC-AB whereas systolic and diastolic function is remarkably rescued in Tg-CTGF-AB mice . Consistently, elevations of myocardial BNP and skeletal α-actin mRNA levels were significantly attenuated in Tg-CTGFAB compared to NLC-AB mice. In conclusion, CTGF inhibits car-

diac growth, causes slight elevations of cardiac collagen, but no evidence of restrictive cardiac dysfunction, and preserves left ventricular function in pressure overload. Keywords: Heart failure; Hypertrophy; Growth factor doi:10.1016/j.yjmcc.2007.03.283

Neonatal and adult ventricular myofibroblasts display a synthetic as well as a contractile phenotype Aran L. Dangerfield, J.-J. Santiago, K.L. Bathe, Sunil G. Rattan, Elissavet Kardami, Ian M.C. Dixon. University of Manitoba, Winnipeg, Canada In cardiac wound healing, ventricular fibroblasts switch from a quiescent noncontractile phenotype to a highly synthetic and contractile phenotype. Recent evidence indicates that primary ventricular myofibroblasts are key players in matrix remodeling and thus contribute as disease modifiers in heart failure. Further, a number of studies have used neonatal ventricular cells as models of fibroblast function, but their precise phenotype remains unresolved. In the present study we compared expression of major contractile, structural, cytoskeletal and receptor proteins to assess the status of phenotype in neonatal rat fibroblasts and myofibroblasts to adult cells (P0 to P3). Western blot analysis revealed that both neonatal and adult fibroblasts undergo rapid phenotypic transition to myofibroblastic cells as inferred by elevated αSMA and SMemb expression in P1 to P3 passages vs. P0 cells. Furthermore the ED-A variant of fibronectin as well as paxillin, tensin and Smad7 proteins were significantly upregulated in both cell types from P1 through P3 cells when compared to P0 cells. These changes were accompanied by significantly increased basal synthesis of procollagen type I monomeric protein in both types of cells passaged beyond P0. We confirmed a correlation between the development of a highly synthetic phenotype in association with elevated contractile protein synthesis in ventricular cells. We suggest that neonatal and adult ventricular myofibroblasts share similar expression of contractile proteins. Acknowledgment Supported by the Canadian Institutes for Health Research. Keywords: Contractile proteins; Cellular phenotype switching; Cardiac myofibroblasts doi:10.1016/j.yjmcc.2007.03.284

Essential roles of constitutive autophagy in quality control of proteins in the hearts Hiroshi Akazawa, Chien-hui Liao, Yoko Kudo, Sumiyo Kudoh, Issei Komuro. Department of Cardiovasc Sci & Med, Chiba University, Japan