Taimor G, Schlüter K D, Frischkopf K, Flesch M, Rosenkranz S, Piper H M
Physiologisches Institut, Justus-Liebig-Universität Giessen, Germany.
J Mol Cell Cardiol. 1999 Dec;31(12):2127-36. doi: 10.1006/jmcc.1999.1055.
As shown before, TGF beta acts in an autocrine manner on the induction of hypertrophic responsiveness to beta-adrenoceptor stimulation in cultured ventricular cardiomyocytes of adult rat. We now investigated how TGF beta expression and activation is regulated in these cultures and how beta-adrenoceptor stimulation influences TGF beta -mRNA expression. It was found that freshly isolated cardiomyocytes secrete latent TGF beta in the culture medium. Supplementation of the cultures with 20% FCS resulted in activation of the secreted TGF beta to 4.1+/-0.2 ng/ml active TGF beta after 6 days. Presence of the protease inhibitor aprotinin (50 microg/ml) reduced TGF beta activity by 44+/-5% (n=5, P<0.05). In cultures supplemented with 5% FCS, TGF beta was not activated. Active TGF beta downregulated its mRNA-expression: after 6 days TGF beta(1)-mRNA was reduced to 55.1+/-11.0%, TGF beta(2)-mRNA to 30.1+/-16.5%, and TGF beta(3)-mRNA to 0.3+/-0.4% in 20% FCS-cultures as compared to their expression in freshly isolated cells (n=4, P<0.05). TGF beta-mRNA expression did not change in cultures without active TGF beta. Isoprenaline (1 microm) increased TGF beta(1)-mRNA only in cultures which had been pre-exposed to active TGF beta. This effect was also seen when hearts from normal mice were compared with hearts from transgenic mice overexpressing TGF beta(1): only in hearts from transgenic animals perfusion with isoprenaline increased TGF beta(1)-mRNA. In conclusion, isolated cardiomyocytes release latent TGF beta, which is activated by external proteases. Active TGF beta downregulates its own mRNA expression. Preexposure to TGF beta is necessary for a beta-adrenoceptor-mediated increase in TGF beta(1)-mRNA in cardiomyocytes.
如前所示，转化生长因子β（TGFβ）以自分泌方式作用于成年大鼠培养心室心肌细胞中对β -肾上腺素能受体刺激的肥厚反应性诱导。我们现在研究了在这些培养物中TGFβ的表达和激活是如何调节的，以及β -肾上腺素能受体刺激如何影响TGFβ -mRNA表达。结果发现，新鲜分离的心肌细胞在培养基中分泌潜伏性TGFβ。在培养物中添加20%胎牛血清（FCS），6天后分泌的TGFβ被激活至4.1±0.2 ng/ml活性TGFβ。蛋白酶抑制剂抑肽酶（50μg/ml）的存在使TGFβ活性降低44±5%（n = 5，P < 0.05）。在添加5% FCS的培养物中，TGFβ未被激活。活性TGFβ下调其mRNA表达：与新鲜分离细胞中的表达相比，在20% FCS培养物中，6天后TGFβ(1)-mRNA降至55.1±11.0%，TGFβ(2)-mRNA降至30.1±16.5%，TGFβ(3)-mRNA降至0.3±0.4%（n = 4，P < 0.05）。在没有活性TGFβ的培养物中，TGFβ -mRNA表达没有变化。异丙肾上腺素（1μM）仅在预先暴露于活性TGFβ的培养物中增加TGFβ(1)-mRNA。当将正常小鼠的心脏与过表达TGFβ(1)的转基因小鼠的心脏进行比较时也观察到了这种效应：只有在转基因动物的心脏中，用异丙肾上腺素灌注会增加TGFβ(1)-mRNA。总之，分离的心肌细胞释放潜伏性TGFβ，其被外源性蛋白酶激活。活性TGFβ下调其自身的mRNA表达。预先暴露于TGFβ是心肌细胞中β -肾上腺素能受体介导的TGFβ(1)-mRNA增加所必需的。
