Ca2+-Independent Alterations in Diastolic Sarcomere Length and Relaxation Kinetics in a Mouse Model of Lipotoxic Diabetic Cardiomyopathy
Ca2+-Independent Alterations in Diastolic Sarcomere Length and Relaxation Kinetics in a Mouse Model of Lipotoxic Diabetic Cardiomyopathy
复制标题
DOI：
10.1161/circresaha.108.186809
复制
发表时间：
2009-01-02
影响因子：
20.1
通讯作者：
Nerbonne, Jeanne M.
中科院分区：
文献类型：
--
作者：
Flagg, Thomas P.;Cazorla, Olivier;Nerbonne, Jeanne M.
先前的研究表明，MHC-FATP 转基因小鼠在 α-肌球蛋白重链 (α-MHC) 启动子的控制下，在心脏中过度表达脂肪酸转运蛋白 (FATP) 1，从而增加了脂肪酸的摄取和代谢。多普勒组织成像和血流动力学测量显示舒张功能障碍，但收缩功能没有变化。这里的实验直接检验了这样的假设：MHC-FATP 小鼠的舒张功能障碍反映了心室肌细胞收缩功能受损。分离的成年 MHC-FATP 心室肌细胞的体外成像显示，平均舒张肌节长度显着 (P < 0.01) 短于野生型 (WT) 细胞（1.79 +/- 0.01 与 1.84 +/- 0.01 μm）。此外，MHC-FATP 中的松弛率 (dL/dt) 显着 (P < 0.05) 慢于 WT 肌细胞（1.58 +/- 0.09 与 1.92 +/- 0.13 μm/s），而缩短分数和收缩率没有不同。应用 40 mmol/L 2,3-丁二酮肟（一种可放松肌动蛋白-肌球蛋白相互作用的非特异性 ATP 酶抑制剂）可将 WT 和 MHC-FATP 肌细胞的舒张肌节长度增加至相同长度，表明 MHC-FATP 肌细胞在休息时部分激活。细胞内 Ca2+ 的直接测量表明，MHC-FATP 肌细胞中的舒张 [Ca2+](i) 没有变化，并且 MHC-FATP 肌细胞中的钙去除速率出乎意料地比 WT 肌细胞更快。此外，MHC-FATP和WT心肌细胞的舒张肌节长度不受细胞外Ca2+去除或Ca2+螯合剂BAPTA（100μmol/L）缓冲细胞内Ca2+的影响，表明细胞内Ca2+升高并不是MHC-FATP心室肌细胞舒张功能受损的基础。然而，对带皮肌细胞的功能评估表明，与 WT 心室细胞相比，MHC-FATP 中的肌丝 Ca2+ 敏感性显着增加。此外，生化实验表明，与 WT 心室相比，MHC-FATP 中 β-MHC 同种型的表达增加，这可能导致 MHC-FATP 肌细胞中观察到的舒张速率减慢。总的来说，这些数据表明，MHC-FATP 心室中脂质代谢的紊乱（与糖尿病心脏中观察到的相似）会导致舒张功能受损，这主要反映了肌丝功能的变化，而不是 Ca2+ 循环的改变。 （Circ Res. 2009；104：95-103。）
Previous studies demonstrated increased fatty acid uptake and metabolism in MHC-FATP transgenic mice that overexpress fatty acid transport protein (FATP) 1 in the heart under the control of the alpha-myosin heavy chain (alpha-MHC) promoter. Doppler tissue imaging and hemodynamic measurements revealed diastolic dysfunction, in the absence of changes in systolic function. The experiments here directly test the hypothesis that the diastolic dysfunction in MHC-FATP mice reflects impaired ventricular myocyte contractile function. In vitro imaging of isolated adult MHC-FATP ventricular myocytes revealed that mean diastolic sarcomere length is significantly (P < 0.01) shorter than in wild-type (WT) cells (1.79 +/- 0.01 versus 1.84 +/- 0.01 mu m). In addition, the relaxation rate (dL/dt) is significantly (P < 0.05) slower in MHC-FATP than WT myocytes (1.58 +/- 0.09 versus 1.92 +/- 0.13 mu m/s), whereas both fractional shortening and contraction rates are not different. Application of 40 mmol/L 2,3-butadionemonoxime ( a nonspecific ATPase inhibitor that relaxes actin-myosin interactions) increased diastolic sarcomere length in both WT and MHC-FATP myocytes to the same length, suggesting that MHC-FATP myocytes are partially activated at rest. Direct measurements of intracellular Ca2+ revealed that diastolic [Ca2+](i) is unchanged in MHC-FATP myocytes and the rate of calcium removal is unexpectedly faster in MHC-FATP than WT myocytes. Moreover, diastolic sarcomere length in MHC-FATP and WT myocytes was unaffected by removal of extracellular Ca2+ or by buffering of intracellular Ca2+ with the Ca2+ chelator BAPTA (100 mu mol/L), indicating that elevated intracellular Ca2+ does not underlie impaired diastolic function in MHC-FATP ventricular myocytes. Functional assessment of skinned myocytes, however, revealed that myofilament Ca2+ sensitivity is markedly increased in MHC-FATP, compared with WT, ventricular cells. In addition, biochemical experiments demonstrated increased expression of the beta-MHC isoform in MHC-FATP, compared with WT ventricles, which likely contributes to the slower relaxation rate observed in MHC-FATP myocytes. Collectively, these data demonstrate that derangements in lipid metabolism in MHC-FATP ventricles, which are similar to those observed in the diabetic heart, result in impaired diastolic function that primarily reflects changes in myofilament function, rather than altered Ca2+ cycling. (Circ Res. 2009; 104: 95-103.)