Mechanisms of diaphragm muscle dysfunction in critical-illness myopathy

描述（由申请人提供）： 本申请的长期目标是更好地了解重症肌病对膈肌（DIA）肌肉功能的影响;重点是功能障碍的分子机制。重症监护室中的获得性肌无力，称为“危重病肌病”，通常发生在接受长期机械通气联合神经肌肉接头阻滞剂（NMBA）和皮质类固醇（甲基强的松龙，MP）的患者中。这些患者很难脱离机械通气。DIA功能障碍的机制尚不清楚，但可能是多因素的;包括增强的蛋白水解作为一个关键因素。泛素-蛋白酶体是骨骼肌中重要的蛋白水解系统。然而，目前尚不清楚上游途径的作用，即，在控制性机械通气（CMV）联合NMBA和MP下，DIA肌肉中的IGF-1/PI 3 K/Akt/Foxo。我们最近的初步研究-比较2天的CMV，高剂量MP，或组合CMV-MP -显示DIA力和IGF-1 mRNA降低到相同的程度，这表明这些病理扰动激活了一个共同的信号通路。然而，尚不清楚CMV-NMBA与高剂量或低剂量MP的组合是否产生相似水平的DIA功能障碍，或由相似的机制引起。此外，没有关于体内施用rhIGF-1是否会减轻DIA功能障碍的信息。本申请描述了两个具体目的以检验以下假设：I）CMV-NMBA加MP对DIA功能的影响是剂量依赖性的，低剂量MP由于通过Akt/mTOR增加的蛋白质合成和通过Akt/Foxo途径减少的蛋白质水解而保护DIA功能。我们将确定3天的CMV-NMBA没有或与高剂量或低剂量MP对DIA收缩，结构和分子特性的相互作用。如果组合的CMV-NMBA加低剂量MP保持与对照相当的DIA力产生，则我们的假设将得到支持。II）rhIGF-1减轻DIA力损失。在CMV-NMBA加MP期间，我们将比较单独的rhIGF-1、组合的rhIGF-1加PI 3 K抑制剂（渥曼青霉素）或组合的rhIGF-1加mTOR抑制剂（雷帕霉素）3天对DIA收缩、结构和分子特性的影响。如果rhIGF-1治疗防止DIA力损失，而rhIGF-1加PI 3 K抑制剂或mTOR抑制剂治疗消除其有益作用，则我们的假设将得到支持。将对无病原体新西兰白色家兔进行研究。在特定目标I中，将动物随机分为4组，分别接受3天CMV-NMBA（顺铂）、CMV-NMBA-MP3（3 mg/kg/d）、CMV-NMBA-MP30（30 mg/kg/d）或0 cm H2O持续气道正压通气（CPAP [对照]）。在特定目的II中，根据特定目的I处理的动物组将进一步分为单独接受rhIGF-1、rhIGF-1加渥曼青霉素或雷帕霉素的亚组。将对DIA进行功能、形态、生化、细胞/分子测量。 公共卫生相关性： 与退伍军人健康的相关性三分之一的重症监护室（ICU）患者需要机械通气。开始机械通气的主要适应症是急性呼吸衰竭。当排除术后原因时，肺炎、慢性阻塞性肺疾病（COPD）和充血性心力衰竭是开始机械通气的前三大原因。所有这三种诊断都在退伍军人群体中普遍存在，其中COPD占患者的很大比例。这些患者中的许多人在疾病恶化后的不同持续时间内需要皮质类固醇和机械辅助支持。此外，当疾病（例如，肺炎）演变为或表现为急性呼吸窘迫综合征（ARDS），可以使用麻痹药物来促进机械通气。尽管短期、高剂量或低剂量皮质类固醇治疗COPD急性加重有效，或短期给予麻痹药物以改善患者-呼吸机相互作用或减少炎性细胞因子产生，但这些都是获得性肌无力的风险因素。获得性肌无力与脱机时间延长、机械通气持续时间延长、ICU和住院时间延长以及治疗成本增加相关，不仅包括住院治疗，还包括门诊康复。这项研究将阐明危重病肌病早期发展的机制，以及低剂量皮质类固醇的可能预防或现有药物的潜在治疗。这项研究有可能刺激药物的开发，以改善或预防获得性肌无力。

DESCRIPTION (provided by applicant): The long-term objectives of this application are to develop a better understanding of the effects of critical- illness myopathy on diaphragm (DIA) muscle function; focusing on the molecular mechanisms of the dysfunction. Acquired muscle weakness in the Intensive Care Unit, referred to "critical-illness myopathy," occurs commonly in patients receiving prolonged mechanical ventilation combined with both neuromuscular junction blocking agents (NMBA) and corticosteroid (methylprednisolone, MP). These patients have difficulty weaning from mechanical ventilation. The mechanisms of DIA dysfunction are unknown, but are likely multifactorial; including enhanced proteolysis as a key factor. The ubiquitin-proteasome is an important proteolytic system in skeletal muscle. However, currently unknown is the role of upstream pathways -- i.e., the IGF-1/PI3K/Akt/Foxo within the DIA muscle under controlled mechanical ventilation (CMV) combined with NMBA, and MP. Our recent preliminary studies -- comparing 2 days of CMV, high-dose MP, or combined CMV-MP -- showed that DIA force and IGF-1 mRNA were reduced to the same extent, suggesting that these pathological perturbations activate a common signaling pathway. However, unknown is whether the combination of CMV-NMBA with high- or low-dose MP produces similar levels of DIA dysfunction, or results from similar mechanisms. Additionally, no information is available about whether in vivo administration of rhIGF-1 will mitigate DIA dysfunction. This application describes two specific aims to test the hypothesis that I) the effects of CMV-NMBA plus MP on DIA function is dose-dependent, with low-dose MP being protective of DIA function due both to increased protein synthesis via Akt/mTOR and decreased proteolysis via Akt/Foxo pathway. We will determine the interactive effects of 3 days of CMV-NMBA without or with high- or low-dose MP on DIA contractile, structural and molecular properties. Our hypothesis will be supported if the combined CMV-NMBA plus low-dose MP preserves DIA force production comparable to that in controls. II) rhIGF-1 mitigates DIA force-loss. During CMV-NMBA plus MP, we will compare the effects of 3 days of rhIGF-1 alone; combined rhIGF-1 plus PI3K-inhibitor (wortmannin), or combined rhIGF-1 plus mTOR- inhibitor (rapamycin) on DIA contractile, structural, and molecular properties. Our hypothesis will be supported if rhIGF-1 treatment prevents DIA force-loss, while treatments with rhIGF-1 plus either PI3K inhibitor, or mTOR inhibitor abolishes its beneficial effects. Pathogen-free New Zealand White rabbits will be studied. In Specific Aim I, the animals will be randomly assigned into four groups receiving either 3 days of CMV-NMBA (cisatracurium); CMV-NMBA-MP3 (3 mg/kg/d), CMV-NMBA-MP30 (30 mg/kg/d) or 0 cm H2O of continuous positive airway pressure (CPAP [control]). In Specific Aim II, groups of animals treated per Specific Aim I will be further divided into subgroups to receive rhIGF-1 alone, rhIGF-1 plus either wortmannin, or rapamycin. Functional, morphological, biochemical; cellular/molecular measurements of the DIA will be performed. PUBLIC HEALTH RELEVANCE: Relevance to Veterans Health One-third of patients admitted to the Intensive Care Unit (ICU) require mechanical ventilation. The major indication for the initiation of mechanical ventilation is acute respiratory failure. When post-operative causes are excluded, pneumonia, chronic obstructive pulmonary disease (COPD), and congestive heart failure comprise the top three reasons for initiating mechanical ventilation. All three diagnoses are prevalent in the veteran populations, with COPD comprising a large proportion of patients. Many of these patients require corticosteroid and mechanical ventilatory support for various durations following exacerbation of their disease. In addition, when the disease (e.g., pneumonia) evolves into or manifests as acute respiratory distress syndrome (ARDS), a paralyzing drug may be administered to facilitate mechanical ventilation. Despite the efficacy of short-term, high- or low-dose corticosteroid in COPD exacerbation, or of short-term paralyzing drug administration to improve patient-ventilator interaction, or to reduce inflammatory cytokine production, these are risk factors for acquired muscle weakness. Acquired muscle weakness is associated with prolonged weaning time and longer duration of mechanical ventilation, longer ICU and hospital stay, and increased treatment costs, not only for inpatient care, but also for outpatient rehabilitation. The proposed study will shed light on the mechanisms of early development of critical-illness myopathy, and its possible prevention with low- dose corticosteroid or potential treatment with existing drugs. The study has the potential to stimulate developments of drugs to ameliorate or prevent acquired muscle weakness.