Dysregulation of sarcomere stabilizing proteins cause muscle atrophy and weakness during cancer cachexia

 描述（由申请人提供）：恶病质的特征是进行性骨骼肌和体重减轻，影响高达80%的癌症患者。这种肌肉质量的损失导致显著的肌肉无力和身体功能下降，并与对化疗的耐受性降低和手术/放疗并发症增加有关。因此，恶病质降低了癌症患者的生活质量和生存时间，恶病质本身导致了高达30%的癌症相关死亡。 有趣的是，来自癌症恶病质的临床前模型以及恶病质人类癌症患者的肌肉显示出肌节和肌纤维膜完整性的破坏，尽管缺乏损伤刺激，并且推测这些破坏可能引发导致肌肉萎缩和虚弱的分解代谢过程。我们实验室未发表的初步数据已经确定，脊柱后凸肽酶（Ky）（对肌节Z盘的结构完整性至关重要）和肌球蛋白（Myoc）（对肌膜肌营养不良蛋白相关蛋白复合物（DAPC）至关重要）在肿瘤进展期间的肌肉萎缩和无力之前和平行的时间点在mRNA和蛋白质水平高度下调。此外，初步数据显示，Ky在荷瘤小鼠肌肉中的过表达抑制肌纤维萎缩。这些观察结果支持我们的第一个假设，即Ky和Myoc的下调是导致肌肉结构丧失的原因，导致癌症恶病质进展期间的肌肉消耗和虚弱。 对C26荷瘤小鼠骨骼肌中显着下调的基因的-1kb至+1kb近端启动子进行的未发表的生物信息学分析显示，肌细胞增强因子-2（MEF 2）的保守共识结合基序是最常见的基序之一。此外，Ky和Myoc基因启动子都含有保守的MEF 2结合基序。这一观察结果，再加上MEF 2蛋白c（MEF 2c）在荷瘤小鼠的mRNA和蛋白质水平上降低的发现，支持我们的第二个假设，即在荷瘤宿主的骨骼肌中MEF 2c转录活性的丧失是Ky和Myoc下调的原因，并启动了肌纤维完整性和肌肉萎缩的破坏。因此，我们的两个具体目标是：具体目标1：检验脊柱后凸肽酶（Ky）和Myocilin（Myoc）的下调在癌症诱导的肌纤维完整性丧失和肌肉萎缩开始中起致病作用的假设。 具体目标二：为了检验MEF 2c转录活性的丧失是癌症诱导的Ky和Myoc下调的原因并启动肌肉萎缩的假设。这些研究的结果将为涉及蛋白质下调的转录机制提供新的见解，这些转录机制引发癌症诱导的肌肉萎缩和虚弱，为治疗干预开辟了新的途径。

 DESCRIPTION (provided by applicant): Cachexia is characterized by progressive skeletal muscle and body weight loss and affects up to 80% of cancer patients. This loss of muscle mass contributes to significant muscle weakness and diminished physical function and is associated with reduced tolerance to chemotherapy and increased complications from surgical/radiotherapeutic treatments. Consequently, cachexia decreases both quality of life and survival time in cancer patients and cachexia itself is responsible for up to 30% of all cancer-related deaths. Interestingly muscles from preclinical models of cancer cachexia as well as cachectic human cancer patients show disruptions in sarcomere and myofiber membrane integrity despite the lack of an injury stimulus, and there is speculation that these disruptions may initiate catabolic processes which lead to the muscle atrophy and weakness. Unpublished and preliminary data from our lab has identified that Kyphoscoliosis peptidase (Ky), which is essential to the structural integrity of the sarcomeric Z-disk, and Myocilin (Myoc), which is important to the sarcolemmal dystrophin associated protein complex (DAPC), are highly downregulated at the mRNA and protein level at time points which precede and parallel muscle atrophy and weakness during tumor progression. Moreover, preliminary data show that overexpression of Ky in the muscles of tumor bearing mice inhibits muscle fiber atrophy. These observations support our first hypothesis that the downregulation of Ky and Myoc are causative to the loss of muscle structure leading to muscle wasting and weakness during the progression of cancer cachexia. Unpublished bioinformatics analyses of the -1kb to +1kb proximal promoters of genes significantly downregulated in skeletal muscle of C26 tumor-bearing mice revealed a conserved consensus binding motif for myocyte enhancing factor-2 (MEF2) among the top most commonly shared motifs. Moreover, both the Ky and Myoc gene promoters contain conserved MEF2 binding motifs. This observation, coupled with the findings that MEF2 protein c (MEF2c) is decreased at the mRNA and protein level in tumor bearing mice, supports our second hypothesis that loss of MEF2c transcriptional activity in skeletal muscle of tumor-bearing hosts is causative in the downregulation of Ky and Myoc, and initiates disruptions in muscle fiber integrity and muscle wasting. Thus, our two specific aims are: Specific Aim 1: To test the hypothesis that the downregulation of Kyphoscoliosis peptidase (Ky) and Myocilin (Myoc) play causative roles in the cancer-induced loss of muscle fiber integrity and the initiation of muscle wasting. Specific Aim 2: To test the hypothesis that loss of MEF2c transcriptional activity is causative in the cancer- induced downregulation of Ky and Myoc and initiates muscle wasting. The results of these studies will provide new insight into transcriptional mechanisms involving protein downregulation which initiate cancer-induced muscle wasting and weakness, opening up new avenues for therapeutic interventions.