MECHANISMS OF CYTOKINE INJURY TO MYOCARDIUM IN SURGERY

抑制心肌收缩功能往往是一个关键的决定因素 心脏手术和体外循环术后患者的结局， 移植排斥败血症和炎性心肌炎虽然 这些不同状态下心肌功能障碍的病因是 无疑是多因素的，越来越多的证据表明， 一个重要的共同因素是当地生产的高浓度的 细胞因子通过活化的淋巴细胞和巨噬细胞。细胞因子发挥其 对靶细胞（通常被认为是免疫细胞）的影响， 触发特定的细胞内信号通路， 激活有效的调节酶。蛋白激酶C（PKC）是一种 这种调节酶已被证明是信号的中心 许多细胞因子如肿瘤坏死因子的转导途径， 白细胞介素-1 β、白细胞介素-2和白细胞介素-8。PKC能够 对细胞代谢的许多方面产生深远的影响， 包括钙调节、底物代谢和线粒体 功能，基因转录和翻译。蛋白激酶C在 心肌功能知之甚少，但 有证据表明，PKC活性增加可损害收缩性， 和氧化代谢，以及有助于发展 心肌肥厚 目前，这些影响的机制是 不确定 我们最近的研究表明，PKC转位和激活发生在 心脏对促炎细胞因子的反应，这是 伴随着严重的收缩功能障碍，早期氧气消耗， 加速葡萄糖转化为乳酸，最后通过抑制 氧化代谢这些作用被PKC抑制剂所阻止 活化和PKC酶活性抑制剂。在分离的肌细胞中， 细胞因子如IL-2、IL-8或TNF刺激细胞的易位， 以剂量依赖性方式抑制PKC的ε-亚型，并产生活性 在其他组织中发现的裂解产物具有更高的 酶活性和降低的靶特异性。 因此，我们假设PKC参与了一个重要的，但很差的 炎症性心肌损伤的发生机制。 具体来说，该项目将使用分离的工作兔心脏， 新鲜分离培养的兔心肌细胞，以检验以下假设： 细胞因子刺激产生PKC的信号转导机制 激活，以及PKC介导的关键磷酸化 细胞内靶点导致收缩蛋白和线粒体 功能障碍我们的总体目标是要发展一个更完整的理解 探讨PKC在心肌损伤中的作用， 有效的治疗策略。

Depressed myocardial contractile function is often a critical determinant of outcome in patients after cardiac surgery and cardiopulmonary bypass, transplant rejection, sepsis, and inflammatory myocarditis. Although the etiologies of myocardial dysfunction in these various states is undoubtedly multifactorial, there is increasing evidence that one important common factor is the local production of high concentrations of cytokines by activated lymphocytes and macrophages. Cytokines exert their effects upon target cells (usually considered to be immune cells) by triggering specific intracellular signaling pathways that result in the activation of potent regulatory enzymes. Protein kinase C (PKC) is one such regulatory enzyme that has been shown to be central to the signal transduction pathway of many cytokines such as tumor necrosis factor, interleukin-1beta, interleukin-2, and interleukin-8. PKC is capable of exerting profound effects upon numerous aspects of cellular metabolism, including calcium regulation, substrate metabolism and mitochondrial function, and gene transcription and translation. The role of PKC in myocardial function is poorly understood, but there is substantial evidence to suggest that increased PKC activity can impair contractility and oxidative metabolism, as well as contribute to the development of myocardial hypertrophy. At present, the mechanisms for these effects are uncertain. We have recently shown that PKC translocation and activation occurs in the heart in response to pro-inflammatory cytokines, and that this is accompanied by profound contractile dysfunction, early oxygen wastage, accelerated conversion of glucose to lactate, and finally by inhibition of oxidative metabolism. These effects were prevented by inhibitors of PKC activation and by inhibitors of PKC enzyme activity. In isolated myocytes, cytokines such as lL-2, IL-8, or TNF stimulate translocation of the epsilon-isoform of PKC in a dose-dependent fashion and generate an active cleavage product that has been found in other tissues to have higher enzyme activity and reduced target specificity. We therefore hypothesize that PKC contributes in an important but poorly defined way to the genesis of inflammatory myocardial injury. Specifically, this project will use isolated working rabbit hearts and freshly isolated cultured rabbit myocytes to test the hypothesis that cytokines stimulate signal transduction mechanisms producing PKC activation, and that PKC-mediated phosphorylation of critical intracellular targets results in contractile protein and mitochondrial dysfunction. Our overall goal is to develop a more complete understanding of the role PKC plays in myocardial injury, and thereby develop rational and effective treatment strategies.