Ramsdell A F, Moreno-Rodriguez R A, Wienecke M M, Sugi Y, Turner D K, Mjaatvedt C H, Markwald R R
Cardiovascular Developmental Biology Center and Department of Cell Biology and Anatomy, Medical University of South Carolina, Charleston, S.C., USA.
Acta Anat (Basel). 1998;162(1):1-15. doi: 10.1159/000046463.
Endocardial cushion tissue is formed by an epithelial-mesenchymal transformation of endocardial cells, a process which results from an inductive interaction between the myocardium and endocardium within the atrioventricular (AV) and outflow tract (OT) regions of the heart. We report here that a protein previously found to be required for myocardially induced transformation of endocardial cells in vitro, ES/130, is highly expressed within the AV and OT regions not only by myocardial cells, but also by the endocardium and its mesenchymal progeny. Given these findings and others, we have tested the hypothesis that endocardial cushion tissue secretes factors which autoregulate its transformation to mesenchyme. Endocardial cushion tissue was cultured and its conditioned growth medium was harvested and applied to nontransformed endocardial cells maintained in the absence of the inductive myocardium. This treatment resulted in endocardial cell invasion into three-dimensional collagen gels plus increased expression of proteins associated with endocardial cell transformation in vivo. Whereas endocardial cushion tissue was found to express ES/130 protein in vivo and in vitro, minimal detection of ES/130 in its conditioned growth medium was observed in immunoblots. Attempts to inhibit the mesenchyme-promoting activity of the conditioned medium with ES/130 antisense were unsuccessful. However, strong intracellular ES/130 expression was detected in endocardial cells, and this expression correlated with the ability of endocardial cells to transform. For example, the minority of endocardial cultures that failed to transform in response to conditioned medium treatment also failed to undergo increased expression of ES/130. These observations are interpreted to suggest that (i) endocardial cushion tissue secretes factors that promote its transformation to mesenchyme, and (ii) while endocardial cushion tissue appears to signal through secretion of factors other than or in addition to ES/130, intracellular ES/130 expression nevertheless may be a target endocardial cell response required for endocardial cell transformation.
心内膜垫组织由心内膜细胞的上皮-间充质转化形成，这一过程源于心脏房室（AV）和流出道（OT）区域中心肌与心内膜之间的诱导性相互作用。我们在此报告，一种先前发现的体外心肌诱导心内膜细胞转化所必需的蛋白质ES/130，不仅在AV和OT区域的心肌细胞中高表达，而且在心内膜及其间充质后代中也高表达。基于这些发现及其他研究结果，我们检验了以下假设：心内膜垫组织分泌可自动调节其向间充质转化的因子。培养心内膜垫组织，收集其条件生长培养基，并将其应用于在无诱导性心肌的情况下培养的未转化心内膜细胞。这种处理导致心内膜细胞侵入三维胶原凝胶，并增加了体内与心内膜细胞转化相关的蛋白质表达。虽然发现心内膜垫组织在体内和体外均表达ES/130蛋白，但在其条件生长培养基的免疫印迹中仅检测到极少量的ES/130。用ES/130反义核酸抑制条件培养基的间充质促进活性的尝试未成功。然而，在心内膜细胞中检测到强烈的细胞内ES/130表达，且这种表达与心内膜细胞的转化能力相关。例如，少数未对条件培养基处理产生转化反应的心内膜培养物也未出现ES/130表达增加。这些观察结果表明：（i）心内膜垫组织分泌促进其向间充质转化的因子；（ii）虽然心内膜垫组织似乎通过分泌ES/130以外或除ES/130之外的因子发出信号，但细胞内ES/130表达可能仍是心内膜细胞转化所需的心内膜细胞反应靶点。
