代谢小分子乙酰乙酸以信号分子方式调控骨骼肌再生与骨骼肌疾病的功能与分子机制

The significance of intrinsic small metabolites as signaling molecules in regulating various cellular activities has received renewed attention in recent years. Close correlation between cell proliferation and metabolic alterations has been shown in various tumor types. However, the signaling role of metabolites in regulating cellular function of non-cancer cells is just beginning to emerge. Acetoacetate (AA) and 3-?-hydroxybutyrate (3HB) are the main ketone bodies. Produced by the liver, they are used peripherally as an energy source by various organs, particularly the skeletal muscle and the brain. Recently, we discovered a novel and previously unanticipated function of AA that is distinct from its function as an energy source. AA promoted skeletal muscle cell proliferation and differentiation in vitro and significantly accelerated muscle regeneration in normal mice by stimulating the muscle stem cell activation, proliferation and differentiation. More significantly, we found that AA promoted C2C12 cell proliferation through activation of the Mek1-Erk1/2 pathway as a signaling molecule. In light of our novel findings, we aim to achieve the following two objectives with multiple experimental approaches in this proposal: 1) Provide molecular mechanism to account for the action of AA in regulating skeletal muscle development and regeneration. We will test our hypothesis that AA acts as a signaling molecule independent of its canonical energetic role in regulating muscle cell functions through the Mek-Erk1/2-cyclin D1 signaling pathway; 2) Investigate therapeutic potential of AA for treatment of dystrophic DMD muscles using the mdx mouse model. The anticipating results will ensure that AA could be a promising candidate for development as an ameliorative treatment for human Duchenne Muscular Dystrophy. In summary, our findings from the proposed work will not only provide additional proof of the concept that small metabolites act in coupling cell metabolism and muscle stem cell function, but also provide a rationale for utilizing this metabolite in the pharmacological therapy of diseases associated with muscle wasting in humans.

小分子代谢产物以信号分子方式参与调节细胞功能已逐渐成为一个新的热点研究领域。最近对肿瘤细胞信号转导的研究表明，内源性代谢产物以信号分子方式参与基因的表达调控，而代谢产物在非肿瘤细胞中的信号转导功能研究还未见报道。本实验室前期研究发现，内源性代谢产物乙酰乙酸可以促进小鼠成肌细胞增殖和分化，并加速骨骼肌损伤后再生，更重要的是我们发现乙酰乙酸是以信号分子方式激活Erk信号通路来促进C2C12细胞增殖的。我们的结果提示，在细胞内乙酰乙酸除可以产生能量外，还可能具有信号转导的新功能。因此，基于我们的前期研究结果，本项目的科学问题是进一步解析乙酰乙酸以信号分子方式发挥功能的分子机制，探索乙酰乙酸在骨骼肌疾病治疗中的作用。这一新功能的发现将为证明代谢小分子作为细胞代谢与生长之间的信号桥梁分子具有普遍的生物学意义。同时，在临床方面也将为利用这些内源性代谢小分子治疗和缓解骨骼肌疾病提供新的思路和方向。

乙酰乙酸作为一种酮体为不同组织和细胞活动提供能量。我们发现了乙酰乙酸的新功能，以非能量依赖的方式促进骨骼肌细胞的增殖。进一步在小鼠体内证明了乙酰乙酸调节肌细胞的功能。乙酰乙酸可以在正常小鼠骨骼肌损伤过程中促进骨骼肌损伤修复进程。同时，在肌营养不良的小鼠疾病模型中，本研究发现乙酰乙酸可以改善mdx小鼠肌营养不良的状态。在机制方面，我们从多个角度证明了乙酰乙酸是以非能量依赖的形式来发挥其调控肌细胞的功能的。另外，我们发现乙酰乙酸可以激活MEK1-ERK1/2-cyclin D1这条信号通路。总之，本项目发现了代谢小分子乙酰乙酸可以作为信号调控分子调节肌细胞的功能。该研究结果揭示了在哺乳动物细胞中，内源性代谢小分子不仅可以作为合成原料或代谢底物提供能量，而且可以作为信号分子调控细胞功能。