Characterization of Burn-Induced Hepatic Apoptosis

描述(申请人提供)：肝脏在烧伤后反应中的作用基本上是未知的，许多烧伤和创伤外科医生认为肝脏不重要，对烧伤后结果几乎没有影响。其他人强烈建议，完整的肝功能和完整性对于烧伤患者的康复至关重要，因为肝脏调节代谢途径、炎症过程、免疫功能和急性期反应。我们的初步数据表明，严重的烫伤通过诱导肝细胞内质网应激(ER应激)和肝细胞凋亡而导致肝脏损伤和功能障碍。我们假设肝脏内质网应激和随后的细胞凋亡与烧伤后的不良结局有关，减轻肝脏内质网应激和细胞凋亡将增强肝功能，这与改善烧伤后的发病率和死亡率有关。烧伤导致肝脏内质网应激、细胞凋亡和功能障碍的确切机制尚不清楚，限制了治疗干预。在初步研究中，我们发现这些病理生理过程与肝脏炎症、磷脂酰肌醇3-激酶(PI3K)/蛋白激酶B(Akt)信号的改变、肝脏钙储备的耗竭、未折叠蛋白反应(UPR)和线粒体功能障碍有关。我们现在建议描述烧伤后导致肝细胞凋亡和功能障碍的分子和生理变化。假说二认为烧伤通过改变PI3K/Akt和三磷酸肌醇受体(IP3R)信号通路，导致钙储备耗竭、细胞色素c释放、内质网应激/UPR，从而导致肝细胞凋亡，从而导致肝损伤。在目标1中，我们将确定烧伤后肝细胞内质网应激和细胞凋亡是否与发病率和死亡率有关。目的2探讨烧伤后肝细胞内钙离子、内质网应激、UPR和肝细胞凋亡变化的细胞和亚细胞机制。AIM 3旨在确定和描述一种将改善烧伤后肝脏完整性和功能的干预措施，并易于在临床环境中使用。根据我们的初步数据，我们将使用胰岛素，它可以减轻烧伤后的肝脏损伤，改善肝功能。这些作用的机制尚不清楚；我们假设烧伤后应用胰岛素可通过使细胞内钙离子和IP3R信号通路正常化，减少细胞色素c的释放，减少内质网应激/UPR，从而显著减少肝细胞凋亡，从而改善肝细胞的活力和肝功能。我们进一步假设，胰岛素通过激活胰岛素特有的信号转导途径发挥作用。我们将通过比较胰岛素对肝细胞内质网应激/UPR和细胞凋亡的影响与降糖药物以及化学内质网伴侣对内质网应激/UPR、细胞凋亡和烧伤后结局的影响来检验这一假说。识别和了解胰岛素或葡萄糖调节将改善预后的细胞和分子机制可能会导致为严重烧伤患者建立新的治疗方案。 公共卫生相关性：这项研究的一个关键和新颖的方面是我们的假设，即肝脏细胞凋亡和ER应激在烧伤后发病率和死亡率中扮演着重要角色，而胰岛素治疗通过减少肝脏细胞凋亡和ER应激来改善这些不利结果。这项研究很重要，因为表征和识别与烧伤诱导的肝脏细胞凋亡和内质网应激相关的分子机制将有助于改善严重烧伤患者的临床护理。

DESCRIPTION (provided by applicant): The role of the liver during the post-burn response is essentially unknown, and many burn and trauma surgeons consider the liver as unimportant, with little or no effect on post-burn outcomes. Others strongly suggest that intact liver function and integrity are essential for burn patients' recovery, because the liver modulates metabolic pathways, inflammatory processes, immune functions, and acute-phase responses. Our preliminary data indicate that a severe thermal injury causes hepatic damage and dysfunction by inducing hepatocyte endoplasmic reticulum stress (ER stress) and hepatocyte apoptosis. We hypothesize that hepatic ER stress and subsequent apoptosis contribute to adverse post-burn outcomes, and that attenuating hepatic ER stress and apoptosis will enhance hepatic function, which is associated with improved post-burn morbidity and mortality. The exact mechanisms by which a burn induces hepatic ER stress, apoptosis, and dysfunction are not known, limiting therapeutic intervention. In preliminary studies we found that these pathophysiological processes are related to hepatic inflammation, altered phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt) signaling, depletion of the hepatic calcium stores, the unfolded protein response (UPR), and mitochondrial dysfunction. We now propose to characterize the post-burn molecular and physiological changes that lead to hepatic apoptosis and dysfunction. Hypothesis 2 is that burn induces hepatic damage by altering the PI3K/Akt and inositol 1, 4, 5,-triphosphate receptor (IP3R) signaling pathways, leading to calcium store depletion, cytochrome c release, ER stress/UPR, and consequently to hepatocyte apoptosis. In Aim 1 we will determine whether post-burn hepatocyte ER stress and apoptosis contribute to morbidity and mortality. Aim 2 is to determine in vivo the cellular and sub-cellular mechanisms which cause post-burn alterations in hepatic intracellular calcium, ER stress and UPR, and hepatocyte apoptosis. Aim 3 is designed to identify and characterize an intervention that will improve hepatic integrity and function post-burn and is readily available in the clinical setting. Based on our preliminary data we will use insulin, which attenuates hepatic damage and improves liver function post-burn. The mechanisms underlying these effects are not understood; we hypothesize that post-burn insulin administration improves hepatocyte viability and liver function via normalization of intracellular calcium and IP3R signaling pathways, attenuation of cytochrome c release, and reduction of ER stress/UPR, leading to markedly decreased hepatocyte apoptosis. We further hypothesize that insulin exerts its effects via insulin-specific signal transduction pathway activation. We will test this hypothesis by comparing the effects of insulin on hepatocyte ER stress/UPR and apoptosis to the effects of a glucose- lowering drug, as well as chemical ER chaperones on ER stress/UPR, apoptosis, and post-burn outcomes. Identifying and understanding the cellular and molecular mechanisms by which insulin or glucose modulation will improve outcomes could lead to the establishment of novel treatment options for severely burned patients. PUBLIC HEALTH RELEVANCE: A key and novel aspect of this study is our hypothesis that hepatic apoptosis and ER stress play an important role in post-burn morbidity and mortality, and that insulin administration improves these adverse outcomes by decreasing hepatic apoptosis and ER stress. This study is important because characterizing and identifying the molecular mechanisms associated with burn-induced hepatic apoptosis and ER stress will lead to improvements in the clinical care of severely burned patients.