肿瘤细胞外泌体中PTHrP对恶病质肌肉萎缩的机制研究

Cachexia is a marker of unfavorable prognosis, and affects the majority of patients with advanced cancer. About 50% -80% of cancer patients will enter a state of cachexia, which leads to the direct cause of approximately 30% of cancer deaths. The most critical feature of cachexia is unstoppable skeletal muscle atrophy or muscle wasting. The findings from animal models of cancer cachexia suggest that the blockade of the signaling pathway of muscle atrophy significantly extends lifespan and improves the quality of life for cachexic mice, but failure in clinical translation due to the lack of deep investigation of mechanisms. Exosomes are extracellular nanovesicles released by most cells. They are specifically equipped to mediate intercellular communication，acting as a cell-cell messenger. Tumor-derived exosomes cross-talk and/or influence major tumor-related pathways, but fewer studies relate to cachexia muscle atrophy. Parathyroid hormone-related protein(PTHrP) is a principal factor in causing cancer cachexia. A study reported that PTHrP mediated energy wasting in fat tissues and contributes to broader aspects of cancer cachexia. Our preliminary data initially indicated that tumor-derived exosomes carrying PTHrP can decrease the size of muscle fibers in vitro, suggesting tumor produced PTHrP can be transported to muscle cells through exosomes and thus cause muscle atrophy. The research goal of this subject is to combine my years of research in muscle atrophy signaling pathways, investigate the molecular mechanisms of tumor-derived exosomes and their cargo molecular PTHrP mediating cancer cachexia muscle atrophy and muscle growth inhibition in depth, and lay a solid theoretical basis for discovering precise tumor cachexia treatment targets and improve cancer treatment.

绝大部分癌症患者会进入恶病质状态，恶病质最关键特征是进行性肌肉萎缩。单纯肌肉萎缩的阻断就可显著提高癌症恶病质老鼠的生存期和生活质量，但由于对肌肉萎缩机制缺乏深入研究无法进行临床转化。外泌体是一种新型的细胞间信使，癌细胞产生的外泌体参与了肿瘤发生的各个方面，但其对恶病质肌肉萎缩的研究报道甚少 。甲状旁腺激素相关蛋白(PTHrP)是一个与肿瘤相关的主要因子，已发现PTHrP会导致白色脂肪组织棕色化。我们初步实验结果首次显示肿瘤细胞外泌体含有PTHrP并使肌管细胞显著变细，提示肿瘤细胞分泌的PTHrP可能通过外泌体形式参与了肌肉萎缩。基于我们多年的癌症恶病质肌肉萎缩研究工作积累和有趣的初步结果，结合当前相关领域的最新进展，本课题拟深入研究外泌体中PTHrP及其他分子对肌肉萎缩的重要信号通路的调控机制，为阐明癌症恶病质及恶病质肌肉萎缩的病因，为提高癌症病人的生存期和生存质量提供更精准的诊治靶点。

绝大部分癌症患者会进入恶病质状态，癌症恶病质不仅是癌症发展的结果，也是导致30%癌症相关死亡的直接原因。恶病质状态的关键特征是进行性肌肉萎缩和脂肪消耗，严重影响患者的生活质量。通过对体外建立的癌症恶病质老鼠模型研究发现，单纯肌肉萎缩的阻断就可显著提高生存期和生活质量，抑制白色脂肪组织的棕色化可以缓解脂肪萎缩及肿瘤所致恶病质脂肪消耗，但要进行临床转化还需要对恶病质引起的肌肉萎缩及脂肪消耗机制进行更加深入的研究。肿瘤细胞分泌的细胞因子、激素、炎症因子等可诱导癌症患者发生恶病质。.外泌体(EVs)是一种新型的细胞间信使，肿瘤细胞分泌的外泌体可参与炎症免疫反应、细胞间信号通讯等过程，癌细胞产生的外泌体所携带的分子可能在脂肪萎缩和肌肉蛋白分解代谢的信号传导中发挥重要作用，有关癌细胞产生的外泌体在恶病质中的作用的研究报道较少。本课题中研究的甲状旁腺激素相关蛋白(PTHrP)，其为一个与肿瘤相关的重要因子之一，可导致白色脂肪组织棕色化。在体外细胞水平的研究发现肺癌细胞LLC来源的外泌体携带 PTHrP，可被 3T3-L1 脂肪细胞摄取进而激活PKA 信号通路促进脂肪分解；使用抗 PTHrP 的中和抗体以及shRNA 干扰 PTHR 表达均可抑制LLC-exos 和 PTHrP 诱导的3T3-L1脂肪细胞中的脂肪动员和能量消耗。在恶病质小鼠模型中，干扰肺癌细胞LLC中外泌体生成基因 Rab27A 表达后，对白色脂肪组织棕色化和脂肪动员过程均显著抑制。以及肿瘤细胞来源的外泌体中所携带的重要的细胞因子IL-6，可被脂肪细胞和骨骼肌细胞摄取，通过激活转录信号转导活化蛋白质 3（Signal transducing activator of transcription, STAT3），从而促进肌管萎缩和脂肪消耗，使用IL-6的中和性抗体或者STAT3的特异性抑制剂 S3I-201 均可缓解LLC细胞分泌的外泌体诱导的肌管萎缩和脂肪消耗。本课题的研究结果为阐明癌症恶病质及恶病质肌肉萎缩和脂肪消耗的分子机制，为提高癌症病人的生存期和生存质量提供更精准的诊治靶点。