Role of Rho-kinase signaling in heart and its involvement of cardiac diseases

RhoA/ rho激酶/肌球蛋白磷酸酶（MP）信号在心脏中的作用及其在心脏疾病中的作用已被研究。肌球蛋白磷酸酶靶亚基2 （MYPT2）可与1型磷酸酶δ异构体催化亚基（PP1cδ）和HS-M_<21>相互作用形成心肌肌球蛋白磷酸酶全酶。MYPT2被鉴定为RhoA活性形式的靶标。rho激酶磷酸化MYPT2，其硫代磷酸化可诱导MP活性抑制。培养的过表达MYPT2-PP1cδ的大鼠新生心肌细胞显示出较低的肌球蛋白轻链2 （MLC2）磷酸化水平，并对血管血管素II诱导的肌瘤组织具有抗性，表明MYPT2-PP1cδ可以作为MP参与肌瘤组织。心肌特异性MYPT2-PP1cδ转基因小鼠（Tg）的心脏表现出扩张的心肌病样表型，包括左室尺寸增大，左室壁变薄，左室分数分数降低。与野生型相比，Tg心肌乳头肌Ca^<2+>收缩敏感性降低，MLC2磷酸化水平显著降低。上述结果提示MP可调节MLC2磷酸化，且MLC2磷酸化水平对维持体内正常心功能具有重要意义。为了分析rho激酶在心脏中的功能，我们制备了rho激酶显性阴性片段或组成活性片段过表达的条件转基因小鼠。然而，每种Tg的双转基因小鼠和心脏特异性Cre小鼠未能诱导出足够数量的每个片段，也未观察到表型。因此，我们构建了过表达白血病相关Rho鸟嘌呤核苷酸交换因子（large - tg）活性片段的条件转基因小鼠，以研究心脏中Rho/Rho激酶信号传导。我们将继续制作LARG-Tg和Cre双转基因小鼠，研究其表型，以了解Rho/Rho激酶信号在心脏中的作用。少

The roles of RhoA/Rho-kinase/myosin phosphatase (MP) signaling in heart and its involvement in cardiac diseases had been investigated.Myosin phosphatase target subunit 2 (MYPT2) could interact with a catalytic subunit of type 1 phosphatase δ isoform (PP1cδ) and HS-M_<21> to form a cardiac myosin phosphatase holoenzyne. MYPT2 was identified to be a target of the active form of RhoA. Rho-kinase phosphorylated MYPT2 and its thiophosphorylation could induce the inhibition of MP activity. The cultured rat neonatal cardiomyocytes overexpressing MYPT2-PP1cδ showed the lower levels of myosin light chain 2 (MLC2) phosphorylation and were resistant to the sarcomere organization induced by angitensin II, indicating that MYPT2-PP1cδ could act as MP and was involved in sarcomere organization.The heart of the cardiac-specific MYPT2-PP1cδ transgenic mice (Tg) showed the dilated cardiomyopathy-like phenotypes, including the enlargement of LV dimension, thinning of LV wall and the reduced fractional sh … More ortening. The papillary muscle of Tg heart showed the reduced Ca^<2+> sensitivity of contraction and the phosphorylation levels of MLC2 were signfficantly lower as compared with wild type. These results suggested that MP play a role to regulate MLC2 phosphorylation and MLC2 phosphorylation level is important to maintain normal cardiac functions in vivo.To analyze the functions of Rho-kinase in heart, the conditional transgenic mice overexpressing the dominant negative or the constitutively active fragment of Rho-kinase were generated. However, the double transgenic mice of each Tg and heart-specific Cre mice failed to induce an enough amount of each fragment and no phenotypes were observed. Therefore, the conditional transgenic mice overexpressing the active fragment of leukemia-associated Rho guanine nucleotide exchange factors (LARG-Tg) were generated to investigate the Rho/Rho-kinase signaling in heart. We will continue to make the double transgenic mice of LARG-Tg and Cre mice to investigate its phenotypes to understand the role of Rho/Rho-kinase signaling in heart. Less