DEPTOR调控骨髓间充质干细胞分化及体内脂肪形成与骨形成之间平衡的作用及其机制研究

Obesity and osteoporosis are closely related. Treatment of the two diseases depends on the balance lipogenesis and bone formation. Moreover, maintenance of bone mass and homeostasis also relies on coordinated adipogenesis and osteogenesis. Bone marrow mesenchymal stem cells (BMSCs) has the potential to differentiate into adipocytes and osteoblasts, and the differentiation directions of BMSCs has emerged as a new target for osteoporosis treatment. As an endogenous inhibitory factor of mTOR, DEPTOR has been reported to regulate stem cell differentiation, while its role in BMSCs differentiation is unclear. DEPTOR also has been reported to participate in the regulation of body fat formation, its role in the balance between adipogenesis and bone formation in the body, however, awaits further investigation. Our previous data showed that DEPTOR exerted essential roles in determining the differentiation of BMSCs into osteoblasts or adipocytes, and may be involved in regulating the balance between adipogenesis and bone formation in the body, while the responsible mechanisms remain to be further studied. In the present study, we intend to construct mouse models with DEPTOR knockout in the whole body and specifically in BMSCs and with disease of obesity and osteoporosis, so as to investigate the role of DEPTOR in differentiation of BMSCs and in the balance between lipogenesis and bone formation in the body and provide theoretical support for the prevention and treatment of obesity and osteoporosis.

肥胖和骨质疏松二者密切相关，调控体内脂肪形成与骨形成之间的平衡可能有助于这两种疾病的治疗。脂肪形成与骨形成之间的平衡对骨量和骨内环境稳态的维持也至关重要。骨髓间充质干细胞（BMSCs）具有向脂肪和成骨细胞分化的潜能，调控其分化方向是治疗骨质疏松的新靶标。DEPTOR是mTOR的内源性抑制因子。DEPTOR可调控干细胞分化及体内脂肪形成，而其是否调控BMSCs分化及体内脂肪形成与骨形成之间的平衡却尚不清楚。课题组前期研究发现DEPTOR可调控BMSCs向成骨细胞或脂肪细胞分化的定向，还可能参与调控体内脂肪形成与骨形成之间的平衡，但相关机制有待进一步研究。本项目拟构建全身敲除和BMSCs特异性敲除DEPTOR的小鼠、细胞以及肥胖和骨质疏松的小鼠模型，多层次研究DEPTOR在调控BMSCs分化及体内脂肪形成与骨形成平衡中的作用及相关机制，以期为肥胖与骨质疏松的的防治提供理论支撑。

骨髓间充质干细胞(BMSCs)向成骨细胞分化减少，向脂肪细胞分化增加是导致骨质疏松与骨髓脂肪堆积的重要原因。既往研究发现Deptor可调控干细胞分化及体内脂肪形成，但它对BMSC分化的调节和骨质疏松发生的作用和机制目前还不清楚。本项目利用Deptor基因敲除的小鼠和细胞模型，以及去卵巢（OVX）小鼠骨质疏松模型，研究Deptor在调控BMSCs成骨/成脂分化方向的作用和机制。我们发现：（1）OVX小鼠骨量减少、骨髓脂肪含量增加，这与BMSC内Deptor表达上调有关；（2）前成骨细胞（Preosteoblast，pOB）也具有成骨/成脂双向分化潜能。pOB内特异敲除Deptor不影响骨骼发育，但可缓解OVX小鼠的骨量丢失、减少其骨髓脂肪含量；（3）Deptor抑制BMSCs的成骨分化，促进其成脂分化；（4）Deptor同时调控Runx2和PPARγ的转录活性：抑制Runx2、激活PPARγ；（5）Deptor通过TAZ调控Runx2和PPARγ，Deptor通过其PDZ结构域(PDZ Domain)与TAZ C端的PDZ结合模体（PDZ binding motif）直接结合并抑制其TAZ的转录活性; (6) Deptor通过TAZ-Runx2/PPARγ调控BMSC的成骨/成脂分化。因此，本研究揭示了Deptor在调控BMSC成骨/成脂分化方向中的关键作用和机制，BMSC内Deptor表达上调是骨质疏松和骨髓脂肪堆积的重要致病因素，靶向抑制Deptor可能是防治骨质疏松有效策略。