Shiojima I, Aikawa M, Suzuki J, Yazaki Y, Nagai R
Department of Cardiovascular Medicine, University of Tokyo Graduate School of Medicine, Japan.
Jpn Heart J. 1999 Nov;40(6):803-18. doi: 10.1536/jhj.40.803.
Left ventricular hypertrophy (LVH) is a secondary adaptation to increased external load. Various qualitative and quantitative changes in myocytes and extracellular components occur during the development of LVH. It has recently been demonstrated that alpha-smooth muscle actin (alpha-SMA)-expressing myofibroblasts appear in the interstitium of the heart subjected to increased workload suggesting that cardiac fibroblasts as well as myocytes alter their phenotype in response to pressure overload. In the present study, to explore the load-induced response and phenotypic modulation of cardiac fibroblasts, the localization of embryonic smooth muscle myosin heavy chain (SMemb) and alpha-SMA in thoracic aorta-constricted rat hearts was investigated by immunohistochemistry, and the morphology of the SMemb-expressing cells was examined by electron microscopy. In addition, to clarify the mechanisms by which SMemb is induced in pressure-overloaded hearts, mRNA expression of SMemb in aorta-constricted rat hearts and in transforming growth factor-beta1 (TGF-beta1)-treated or mechanically-stretched cultured cardiac fibroblasts was investigated. Enhanced staining of SMemb and alpha-SMA was detected in the interstitial spindle-shaped cells in the fibrotic lesions of the pressure-overloaded left ventricles by immunohistochemistry. These cells were demonstrated by electron microscopy to have features specific for activated fibroblasts such as serrated nuclei or prominent rough endoplasmic reticulum. These cells also had characteristic features of myofibroblasts, i.e. irregularly arranged actin filaments and scattered dense bodies. Northern blot analysis revealed increased mRNA levels of SMemb both in aorta-constricted rat hearts and in cultured cardiac fibroblasts stimulated by TGF-beta1 or by mechanical stretch. These results suggest that SMemb may be a molecular marker both for the detection of activated cardiac fibroblasts that may play important roles in the remodeling of pressure-overloaded cardiac interstitium, and for the identification of the regu latory mechanisms that control the phenotypic modulation of cardiac fibroblasts in response to pressure overload.
左心室肥厚（LVH）是对增加的外部负荷的一种继发性适应。在LVH发展过程中，心肌细胞和细胞外成分会发生各种定性和定量变化。最近有研究表明，在承受增加工作量的心脏间质中出现了表达α-平滑肌肌动蛋白（α-SMA）的肌成纤维细胞，这表明心脏成纤维细胞以及心肌细胞会因压力过载而改变其表型。在本研究中，为了探究负荷诱导的心脏成纤维细胞反应和表型调节，通过免疫组织化学研究了胸主动脉缩窄大鼠心脏中胚胎平滑肌肌球蛋白重链（SMemb）和α-SMA的定位，并通过电子显微镜检查了表达SMemb的细胞的形态。此外，为了阐明在压力过载心脏中诱导SMemb的机制，研究了胸主动脉缩窄大鼠心脏以及经转化生长因子-β1（TGF-β1）处理或机械拉伸的培养心脏成纤维细胞中SMemb的mRNA表达。通过免疫组织化学在压力过载左心室纤维化病变的间质梭形细胞中检测到SMemb和α-SMA染色增强。电子显微镜显示这些细胞具有活化成纤维细胞的特异性特征，如锯齿状核或突出的粗面内质网。这些细胞还具有肌成纤维细胞的特征，即肌动蛋白丝排列不规则和散在的致密体。Northern印迹分析显示，在胸主动脉缩窄大鼠心脏以及经TGF-β1或机械拉伸刺激的培养心脏成纤维细胞中，SMemb的mRNA水平均升高。这些结果表明，SMemb可能是一种分子标志物，既用于检测可能在压力过载心脏间质重塑中起重要作用的活化心脏成纤维细胞，也用于识别控制心脏成纤维细胞对压力过载反应的表型调节的调控机制。
