Relationship of IGF 1 Pathway with Mitochondrial Electrochemical Gradient and Cytosolic HSP60

• Main Authors: Hui-Chin Lai, 賴慧卿
• Other Authors: Ping H. Wang
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/55254520674809469296

博士 === 國立陽明大學 === 臨床醫學研究所 === 95 === Insulin-like growth factor-1 (IGF 1) suppresses myocardial apoptosis and improves myocardial function in experimental models of cardiomyopathy. Apoptosis is triggered by mitochondria dysfunction and subsequent activation of caspases. We had previously shown that IGF 1 inhibited cardiomyocyte apoptosis via suppression of caspase, however, how IGF 1 and its signaling pathway modulates mitochondria function in cardiac muscle is not yet known. In this study we investigated how IGF 1 signaling modulates mitochondria membrane depolarization in the cardiomyocytes treated with doxorubicin. doxorubicin rapidly induced loss of mitochondria electrochemical gradient and triggered mitochondria depolarization in primary cardiomyocytes, whereas addition of IGF 1 restored mitochondria electrochemical gradient. The effects of IGF 1 was blocked by a chemical inhibitor of PI 3 kinase and a dominant negative Akt, suggesting that IGF 1 signaling to mitochondria involves the PI 3 kinase-Akt pathway. Transducing cardiomyocytes with constitutive active PI 3 kinase partially restored the mitochondria electrochemical gradient in doxorubicintreated cells. These findings provide direct evidence that IGF 1 modulation of mitochondria function is mediated through activation of PI 3 kinase and Akt. Additional experiments using agonist and antagonist of mitochondria K-ATP channel suggest that IGF 1 signaling to mitochondria membrane does not directly involve K-ATP channel. These findings suggest that cytosolic signaling to mitochondria may play a fundamental role in the cardiotoxic actions of doxorubicin and cardioprotective actions of IGF 1. Insulin deficiency down-regulates HSP60 and IGF 1 receptor signaling and disrupts intracellular signaling homeostasis in diabetic cardiac muscle. Our previous studies had shown that IGF 1 receptor signaling can be modulated by the abundance of HSP60. Since HSP60 localized in the cytoplasmic compartment and mitochondria, this study was carried out to determine the distribution of cytosolic and mitochondria HSP60 in diabetic myocardium and to explore whether cytosolic HSP60 can modulate IGF 1 receptor signaling in cardiac muscle cells. In streptozotocin-induced diabetic rats, the cytosolic and mitochondrial fractions of HSP60 were both decreased in the myocardium. Incubating primary cardiomyocytes with insulin lead to increased abundance of HSP60 in the cytosolic and mitochondria compartments. To determine whether cytosolic HSP60 can modulate IGF 1 receptor signaling, we used Rhodamine 6G to deplete functional mitochondria in cardiomyocytes. In the mitochondria-depleted cells, overexpression of HSP60 with adenoviral vector increased the abundance of IGF 1 receptor, enhanced IGF 1 activated receptor phosphorylation, and augmented IGF 1 activation of Akt and Erk. Thus, overexpressing HSP60 in the cytosolic compartment enhanced IGF 1 receptor signaling through up-regulation of IGF 1 receptor protein. However, IGF 1 receptor signaling was significantly reduced in the mitochondria-depleted cells, which suggested that maintaining normal IGF 1 receptor signaling in cardiomyocytes required functioning mitochondria. The effect of cytosolic HSP60 involved suppression of ubiquitin conjugation to IGF 1 receptor in cardiomyocytes. These data suggest two different mechanisms that can regulate IGF 1 signaling, via cytosolic HSP60 suppression of IGF 1 receptor ubiquitination and via mitochondria modulation. These findings provide new insight into the regulation of IGF 1 signaling in diabetic cardiomyopathy.