Novel gastrocnemius muscle characteristics in peripheral artery disease patients associated with impaired functional performance

下肢外周动脉疾病（PAD）显著影响老年人群， 损伤虽然寻找有效的PAD干预措施的临床重要性是公认的，但很少有研究表明， 目前已有药物治疗。PAD是使用踝臂指数（ABI）诊断的，ABI是一种测量 血液流向下肢ABI较低与功能较差相关;然而， 不能完全解释PAD的功能障碍。小型研究报告了氧化应激，线粒体 PAD患者腓肠肌活检中的功能障碍和/或纤维损伤，提示骨骼肌 肌肉扰动可能导致功能下降。我们报告了高度可变的纤维类型组成 和纤维类型分组，并观察到缺乏肌原纤维间线粒体 （IMFM-）在氧化，肌球蛋白重链（MyHC）I型纤维。我们有了新的初步数据 提示对持续去神经支配的反应以及纤维类型和线粒体适应的变化， 垫.本研究的目的是确定与受损的PAD相关的肌肉的具体特征， 通过对400块基线腓肠肌进行详细的免疫组织化学分析获得的行走性能 活检标本储存在西北生物储存库，收集自9个不同的临床试验。这个生物储藏库 PAD患者的肌肉是独一无二的，与详细的临床和功能特征相关 的捐助者。我们推测，纤维大小、纤维类型和线粒体适应性的变化， 缺血再灌注损伤和去神经支配对预测PAD患者的行走有价值 损伤在目标1中，我们将量化I型肌纤维中IMFM区域与正常I型肌细胞的比例。 丰度或IIX型MyHC和/或LC 3的积累，自噬的标志物，并确定相关性 与纤维类型组成和纤维大小，以及肌肉特征与步行性能的关系， 垫.我们假设LC 3将与IIX MyHC共定位于IMFM区域，这表明两者都是不完全的。 IIX型肌纤维向I型肌纤维转变过程中IIX型MyHC的自噬清除和线粒体生物发生 因为去神经支配和神经再生。在目标2中，我们将量化失神经支配的NCAM+纤维和纤维 氧化损伤标志物升高我们假设PAD中的去神经支配将 优先影响表达IIX MyHC的纤维，并且只有积累IIX MyHC的IMFM区域才会受到影响。 NCAM+。在目标3中，我们将使用以下方法对PAD疾病严重程度和功能损害进行预测建模： 目标1和2中量化的肌肉形态学特征作为生物标志物， 监督分类方法。在目标4中，我们将检验以下假设： 将预测6个月随访时的纵向功能结局。该模型将提供一个强大的工具， 帮助确定有针对性的干预措施的生物过程，并评估作用机制， 在正在进行的PAD临床试验中，当前药物和运动干预的有效性。

Lower extremity peripheral artery disease (PAD) significantly affects aging populations and results in functional impairment. Although the clinical importance of finding efficacious interventions for PAD is well-recognized, few medical therapies are currently available. PAD is diagnosed using the ankle brachial index (ABI), a measure of blood flow to the lower extremities. Lower ABI is associated with worse function; however, low ABI alone cannot fully explain functional impairments in PAD. Small studies have reported oxidative stress, mitochondrial dysfunction and/or fiber damage in gastrocnemius muscle biopsies from PAD patients, suggesting skeletal muscle perturbations may contribute to functional decline. We reported highly variable fiber type composition and fiber type grouping in a small cohort of PAD patients, and observed lack of intermyofibrillar mitochondria (IMFM-) in oxidative, myosin heavy chain (MyHC) type I fibers. We have provocative new preliminary data suggesting variability in response to ongoing denervation, and in fiber type and mitochondrial adaptations, with PAD. The purpose of this study is to define specific characteristics of muscle in PAD associated with impaired walking performance through detailed immunohistochemical analyses of 400 baseline gastrocnemius muscle biopsies stored in the Northwestern biorepository, collected from 9 different clinical trials. This biorepository of muscle from PAD patients is one-of-a-kind and is associated with detailed clinical and functional characteristics of the donors. We hypothesize that variability in fiber size, fiber type and mitochondrial adaptations in response to ischemia-reperfusion damage and denervation in individuals with PAD will have value in predicting walking impairment. In Aim 1, we will quantify the proportion of IMFM- areas in type I fibers with normal type I MyHC abundance, or accumulation of type IIX MyHC and/or LC3, a marker of autophagy, and determine associations with fiber type composition and fiber size, as well as relationships of muscle features to walking performance in PAD. We hypothesize that LC3 will co-localize with IIX MyHC in IMFM- areas, suggesting both incomplete autophagic clearance of IIX MyHC and mitochondrial biogenesis during fiber transition from type IIX to type I as a result of denervation and reinnervation. In Aim 2 we will quantify denervated, NCAM+ fibers and fibers with elevated oxidative damage markers by fiber type. We hypothesize that denervation in PAD will preferentially affect fibers expressing IIX MyHC and that only IMFM- areas that accumulate IIX MyHC will be NCAM+. In Aim 3 we will perform predictive modeling of PAD disease severity and functional impairment using morphological characteristics of muscle quantified in Aims 1 and 2 as biomarkers in conjunction with supervised classification approaches. In Aim 4 we will test the hypothesis that baseline muscle characteristics will predict longitudinal functional outcomes at 6-month follow up. This model will provide a powerful tool to aide in identifying biologic processes for targeted interventions and to assess the mechanism of action and effectiveness of current pharmacological and exercise interventions in ongoing PAD clinical trials.