Venkatraman Gayathri, Gomes Aldrin V, Kerrick W Glenn L, Potter James D
Department of Molecular and Cellular Pharmacology and Physiology and Biophysics, University of Miami School of Medicine, Miami, Florida 33101, USA.
J Biol Chem. 2005 May 6;280(18):17584-92. doi: 10.1074/jbc.M409337200. Epub 2004 Dec 28.
The major goal of this study was to elucidate how troponin T (TnT) dilated cardiomyopathy (DCM) mutations in fetal TnT and fetal troponin affect the functional properties of the fetal heart that lead to infantile cardiomyopathy. The DCM mutations R141W and DeltaK210 were created in the TnT1 isoform, the primary isoform of cardiac TnT in the embryonic heart. In addition to a different TnT isoform, a different troponin I (TnI) isoform, slow skeletal TnI (ssTnI), is the dominant isoform in the embryonic heart. In skinned fiber studies, TnT1-wild-type (WT)-treated fibers reconstituted with cardiac TnI.troponin C (TnC) or ssTnI.TnC significantly increased Ca(2+) sensitivity of force development when compared with TnT3-WT-treated fibers at both pH 7.0 and pH 6.5. Porcine cardiac fibers treated with TnT1 that contained the DCM mutations (R141W and DeltaK210), when reconstituted with either cardiac TnI.TnC or ssTnI.TnC, significantly decreased Ca(2+) sensitivity of force development compared with TnT1-WT at both pH values. The R141W mutation, which showed no significant change in the Ca(2+) sensitivity of force development in the TnT3 isoform, caused a significant decrease in the TnT1 isoform. The DeltaK210 mutation caused a greater decrease in Ca(2+) sensitivity and maximal isometric force development compared with the R141W mutation in both the fetal and adult TnT isoforms. When complexed with cardiac TnI.TnC or ssTnI.TnC, both TnT1 DCM mutations strongly decreased maximal actomyosin ATPase activity as compared with TnT1-WT. Our results suggest that a decrease in maximal actomyosin ATPase activity in conjunction with decreased Ca(2+) sensitivity of force development may cause a severe DCM phenotype in infants with the mutations.
本研究的主要目的是阐明胎儿肌钙蛋白T（TnT）和胎儿肌钙蛋白中的扩张型心肌病（DCM）突变如何影响胎儿心脏的功能特性，进而导致婴儿期心肌病。DCM突变R141W和DeltaK210是在TnT1同工型中产生的，TnT1是胚胎心脏中心脏TnT的主要同工型。除了不同的TnT同工型外，另一种不同的肌钙蛋白I（TnI）同工型，即慢骨骼肌TnI（ssTnI），是胚胎心脏中的主要同工型。在皮肤纤维研究中，与在pH 7.0和pH 6.5条件下用TnT3野生型（WT）处理的纤维相比，用心脏TnI.肌钙蛋白C（TnC）或ssTnI.TnC重构的TnT1野生型处理的纤维显著提高了力产生的Ca(2+)敏感性。用含有DCM突变（R141W和DeltaK210）的TnT1处理的猪心脏纤维，在用心脏TnI.TnC或ssTnI.TnC重构后，在两个pH值下与TnT1-WT相比，力产生的Ca(2+)敏感性均显著降低。R141W突变在TnT3同工型中力产生的Ca(2+)敏感性没有显著变化，但在TnT1同工型中导致了显著降低。与R141W突变相比，DeltaK210突变在胎儿和成人TnT同工型中导致Ca(2+)敏感性和最大等长力产生的降低更大。当与心脏TnI.TnC或ssTnI.TnC复合时，与TnT1-WT相比，两种TnT1 DCM突变均强烈降低了最大肌动球蛋白ATP酶活性。我们的结果表明，最大肌动球蛋白ATP酶活性的降低以及力产生的Ca(2+)敏感性的降低可能会在具有这些突变的婴儿中导致严重的DCM表型。
