哺乳动物雷帕霉素靶蛋白复合体1 (mTORC1)在肾脏水转运调节中的作用和机制

肾脏对水的重吸收主要通过由近端小管水通道1(AQP1)介导的组成性重吸收和由集合管AQP2-4介导的可调节性重吸收而实现。哺乳动物雷帕霉素靶蛋白（mTOR）是一种丝／苏氨酸蛋白激酶，调节细胞生长和代谢。雷帕霉素通过抑制mTOR复合体1（mTORC1）活性用于肿瘤及移植排斥治疗，但常导致水代谢紊乱。我们前期研究表明禁水抑制肾脏mTORC1活性，雷帕霉素处理显著减少小鼠尿量，集合管特异性TSC1（mTORC1抑制分子）敲除小鼠尿量明显增加，提示mTORC1可能在肾脏水转运调节中发挥重要作用。本课题将：1）在近端小管和集合管特异性TSC1敲除小鼠研究mTORC1在肾脏水代谢调节中的作用；2）在细胞水平阐明mTORC1调控肾脏水转运的机制；3）在锂诱导尿崩症模型明确雷帕霉素的治疗作用。本课题的开展不仅为阐明肾脏水稳态调控的机制提供实验依据，也可能为雷帕霉素所致水肿及锂诱导多尿症的治疗提供新思路。

The kidney is the central organ in maintaining water homeostasis through regulating urine concentration. Renal water reabsorption includes a constitutive water transport via the aquaporin 1 (AQP1) in the proximal tubules and the descending limbs of Henle’s loop and an regulatory water transport via AQP2-4 in the collecting ducts. Antidiuretic hormone (ADH) regulates water reabsorption by controlling the expression of AQP2 localized in the apical membrane of the epithelial cells of the renal collecting ducts. Dysfunction of ADH and its signal pathway results in severe diseases with disrupted water homeostasis including central and nephrotic diabetes insipidus and edema. The mammalian target of rapamycin (mTOR), a highly conserved Serine/threonine protein kinase, is a master regulator of cell growth, metabolism and survival. The mTOR complex 1 (mTORC1) is sensitive to rapamycin, which is widely used in the clinic because of its anti-tumor and immunosuppressive property. However, the use of rapamycin is frequently associated with attenuated urine concentration capacity and peripheral edema. Our previous study showed that water deprivation can inhibit mTORC1 activation in mouse kidney. Rapamycin treatment markedly decreased, while collecting duct-specific activation of mTORC1 significantly increased, urine output. These findings suggest that mTORC1 may play an important role in the regulation of renal water reabsorption. To test this hypothesis, we will generate mouse lines with proximal tubule (PT)- and collecting duct (CD)-specific mTORC1 activation via deleting the TSC1 expression using the Cre-loxp system. These mice will be used to define the role of mTORC1 in the water reabsorption in the proximal tubules and collecting ducts. Then, we will culture mouse PT and CD cells from wild-type, PT-TSC1 deficient mice and CD-TSC1 deficient mice to characterize the underlying mechanisms by which mTORC1 modulates the expression and function of AQP1-4. Finally, we will use an lithium-induced mouse model of nephrotic diabetes insipidus (NDI) to determine therapeutic effect of rapamycin on polyuria. The completion of this project will not only advance our understanding of renal water homeostasis regulation, but also help identify novel therapeutic target for the treatment of the disorders with disrupted water homeostasis.