蛋白磷酸酶PPM1A促进白色脂肪棕色化的效应与机制研究

Obesity, a widespread metabolic disease, causes heavy burden on healthcare and economy worldwide. Dysfunction of adipose tissue acts as one of the major inducedment of obese disorder. As reported in resent years, the process and mechanism of myf5 negative mature white adipocytes exhibiting typical myf5 positive brown adipocytes characters (active energy uncoupling and thermogenesis) were defined as fat browning. It was demonstrated that promoting fat browning could obviously improve metabolic disorders in vivo. Our previous study showed that PPM1A could enhance phosphorylated AKT, browning co-activator PGC-1, UCP1 and mitochondrial related genes in mature white adipocytes differentiated from preadipocytes cell line 3T3-L1. Based on pathway analysis and our present results, we hypothesized that PPM1A could ameliorate obese disorder by inducing fat browning via PI3K/AKT-PGC-1 axis. Then, we constructed a cellular effect as well as metabolism exploring system in vitro and in vivo to verify our hypothesis. Firstly, the cell effects of PPM1A were studied in detail in primary preadipocytes. Nextly, signaling transduction pathway downstream of PPM1A was explored by kinase specific inhibitor management and gene knock-down in cell-based assays. Lastly, metabolic improving function of PPM1A specifically overexpressed in white adipose tissues was testified in animal obese models. Our project aims in revealing new signal protein and medical target in fat browning and providing new candidate for therapeutic strategy discovery of obesity and its related metabolic dysfunction.

肥胖是一类带来沉重健康与经济负担的代谢性疾病。脂肪组织功能异常是导致肥胖的重要原因。近期研究显示一类白色脂肪细胞可以展现棕色脂肪细胞解偶联与产热活跃的特征，这种脂肪棕色化效应能显著改善机体能量代谢。在前期研究中我们发现丝/苏氨酸蛋白磷酸酶PPM1A可以上调白色脂肪细胞AKT磷酸化、棕色化共激活因子PGC-1alpha、解偶联蛋白与线粒体蛋白的水平。结合通路分析，我们推测PPM1A通过PI3K/AKT-PGC-1alpha通路促进脂肪棕色化，改善肥胖能量代谢。项目通过三部分在体内外验证假设：首先在原代细胞中详细研究PPM1A促进白色脂肪细胞棕色化的细胞效应；其次，通过特异抑制剂与基因敲减在细胞水平挖掘PPM1A促进棕色化的信号传导通路；最后在肥胖模型中确证脂肪组织特异过表达PPM1A对代谢紊乱的改善作用。项目通过探索脂肪棕色化的新靶点与通路为肥胖代谢紊乱治疗策略的研发提供新理论依据。

脂肪组织不仅是胰岛素三大靶器官之一，也是机体保持能量稳态的重要代谢器官和内分泌器官。脂肪组织主要分为进行能量贮存的白色脂肪细胞和进行能量消耗的棕色脂肪细胞两大类。脂肪细胞功能失调是导致肥胖及各类糖脂代谢异常的重要原因。研究显示白色脂肪细胞可以在特定诱导条件下展现棕色脂肪细胞解偶联与产热活跃的特征，这种脂肪棕色化效应能显著提高机体基础能量代谢水平从而改善肥胖等代谢异常症状。在前期研究中我们发现丝/苏氨酸蛋白磷酸酶可以上调白色脂肪细胞AKT磷酸化、解偶联蛋白与线粒体蛋白的水平。结合丝/苏氨酸蛋白磷酸酶的蛋白特性与相关通路分析，我们推测丝/苏氨酸蛋白磷酸酶是通过PI3K/AKT-PGC-1alpha通路促进脂肪棕色化及棕色脂肪细胞功能活化，促进能量消耗改善代谢失衡。项目围绕假设按照细胞水平效应探索、分子水平信号传导机制挖掘与动物模型验证的层次，并通过传统细胞功能和信号通路研究与模型动物多组学生物信息联合分析的技术手段对丝/苏氨酸蛋白磷酸酶的新功能进行多维度揭示。项目表明，丝/苏氨酸蛋白磷酸酶及其激动剂均能通过激活IR/PI3K/PDK-1/AKT磷酸化级联通路，激活棕色化转录因子PGC-1alpha，改善炎症因子谱，并增强线粒体蛋白和解偶联蛋白的表达，促进脂肪棕色化及棕色脂肪细胞功能活化。动物模型中的转录与翻译水平多组学联合分析进一步表明了丝/苏氨酸蛋白磷酸酶响应棕色化刺激及其信号通路网络。本项目不仅揭示了丝/苏氨酸蛋白磷酸酶在脂肪棕色化中的新功能，同时也为肥胖等代谢紊乱治疗新策略的研发提供新理论依据。