关于Stk40在脂肪分化中的功能和机制的研究

Previous study in our laboratory indicated that Stk40, a putative serine/threonine kinase, could promote mouse embryonic stem cell differentiation into extraembryonic endoderm lineage through activation of the Erk/MAPK signaling pathway. However, the functions of Stk40 in the cell fate determination of other lineages have not been explored. Using the model of Stk40 knock out (KO) mice, generated by homologous recombination, we found that Stk40 deficiency enhanced adipocyte differentiation from mouse embryonic fibroblasts (MEFs) after hormone induction. Overexpression of Stk40 could rescue this phenotype. Expression of known late adipogenic genes such as C/EBPa, Ppar g and aP2 in KO MEFs was significantly higher than in wild type MEFs. In addition, overexpression of Stk40 in mesenchymal stem cells inhibited adipocyte differentiation. Therefore, Stk40 might be an important new regulator for adipogenesis. Nevertheless, the mechanisms underlying the function of Stk40 remain unknown. In this project, we plan to conduct the following studies: 1. Systemically study and confirm the function of Stk40 in adipocyte differentiation; 2. Elucidate the potential mechanisms by which Stk40 regulate adipogenesis. These studies will help us to understand the physiological functions and the molecular regulation of adipocyte differentiation in general. Moreover, these studies could also pave ways to find new strategies for treating obesity and related diseases.

Stk40是一个含有丝苏氨酸激酶结构域的蛋白。本课题组过去的研究表明该蛋白通过激活Erk/MAPK通路诱导小鼠胚胎干细胞向胚外内胚层分化。我们发现Stk40缺失的小鼠胚胎成纤维细胞（MEF）会发生脂肪分化。在激素诱导条件下，KO MEF的脂肪细胞分化比野生MEF明显增强。在此过程中，脂肪分化的标志性因子C/EBPa，Pparg和aP2等，在KO 细胞中的表达水平明显升高。此外，在间充质干细胞系中过表达Stk40能有效地抑制脂肪分化。因此，Stk40可能是参与脂肪分化调控的重要新基因。尽管如此，我们对Stk40调节脂肪分化的分子机制尚不清楚。因此，在本项目中我们拟开展以下研究内容：系统研究和明确Stk40在脂肪细胞分化中的作用；阐明Stk40作用的潜在分子机制。这些研究对阐明Stk40本身的生理功能以及脂肪分化的分子机制有重要意义。同时也为发现治疗肥胖等相关疾病的策略提供依据。

Stk40（Serine/threonine kinase 40）是一个含有丝氨酸苏氨酸激酶结构域并在进化上保守的蛋白,目前对其结构和功能的研究甚少。过去本课题组研究表明在小鼠胚胎干细胞 (Mouse embryonic stem cells，mESCs)中Stk40 是胚胎干细胞发育全能性相关转录因子Oct4 的下游靶基因，可以通过激活Erk/MAPK 信号通路诱导mESCs 向胚外内胚层分化。对本课题组建立的Stk40 基因敲除（Stk40-/-, knock out, KO）小鼠的研究表明Stk40-/-小鼠出生后24 小时内死亡，肺部发育存在异常。为了全面了解Stk40 基因的生理功能，本课题研究了Stk40 在小鼠脂肪和骨骼肌细胞分化过程中的功能和机制。本研究发现Stk40 基因敲除或者表达下调（Knock down，KD）增强原代小鼠胚胎成纤维细胞（Mouse embryonic fibroblasts，MEFs）和间充质干细胞(Mesenchymal stem cells，MSCs)的成脂分化。机制方面，Stk40 通过抑制脂肪细胞分化的重要转录因子C/EBP（CCAAT/enhancer binding protein）β 和 C/EBPδ的蛋白合成来实现对成脂分化的调控。具体来说，Stk40 使4E-BP1（eIF4E-binding protein1）磷酸化的水平降低，引起翻译起始因子eIF4E（Eukaryotic initiation factors 4E）功能的减弱，从而减弱了依赖于eIF4E 的C/EBPs 的蛋白翻译过程，进而抑制了MEFs 和MSCs 的成脂分化。本研究揭示Stk40 通过调控细胞成脂的重要调控因子的蛋白质水平实现对脂肪细胞分化的抑制功能。这些研究结果为阐明Stk40 基因的生理功能、探索肥胖和肥胖相关疾病的机制开辟了新的视角。