肾近曲小管是铀化学毒性的主要靶点，无法促进蓄积于细胞内铀的排出是治疗铀肾毒性面临的重要难题。过量的铀晶体沉积于溶酶体导致其膜破裂是铀致细胞死亡的根本原因，提示促进溶酶体胞吐可能是一种有效的治疗措施。据文献报道，溶酶体膜上的Ca2+通道蛋白TRPML1和胞质膜上的Syntaxin 3及由AP-1 μ1B基因调控的Syntaxin 4蛋白的极性分布是决定溶酶体胞吐及其方向的关键调节子。我们前期研究发现，TRPML1激动剂能有效促进人HK-2细胞内铀的释放。据此我们提出科学假设：TRPML1激活协同Syntaxin 3/4在肾PTECs顶端膜的定位能促进溶酶体靶向顶端膜胞吐而阻止其向基侧膜胞吐，促进细胞内铀排出。本项目拟通过上调/下调或回复上述基因在极性人肾PTECs中的表达及应用TRPML1激动剂、基因敲除小鼠等实验手段，从细胞水平和动物水平验证这一假设，为铀促排剂的研发提供新靶点和新启示。

Kidney proximal tubule is a major target of uranium chemical toxicity, and the removal of the intracellular deposits of uranium is the most challenging problem in the treatment of human uranium nephrotoxicity. The excessive accumulation of uranium crystals precipitated within lysosomal bodies is the fundamental cause of uranium-induced lysosomal dysfunction and subsequent cell death. Therefore, induction of lysosomal exocytosis is an attractive therapeutic approach for reducing uranium accumulation in renal proximal tubule epithelial cells (PTECs). TRPML1 is a Ca2+ release channel in the lysosome membrane. It has been demonstrated that TRPML1 and polarized distribution of Syntaxin 3 and AP-1 μ1B-regulated Syntaxin 4 in plasma membranes are the key regulators of the lysosomal exocytosis and exocytosis direction. In our preliminary studies, we have found that a TRPML1 agonist can effectively promote the release of intracellular uranium in human HK-2 cells. We therefore hypothesize that TRPML1 activation and the apical localization of Syntaxin 3/4 in renal PTECs can synergistically promote the apical lysosomal exocytosis and inhibit the basolateral exocytosis to induce decorporation of intracellular deposited uranium. The objective of this project will be accomplished through various experimental approaches and models including overexpression, knockdown or re-expression of TRPML1, Syntaxin 3 and AP-1 μ1B genes in polarized human renal PTECs, activation of TRPMLL1 with TRPML1 agonists in polarized human renal PTECs, TRPML1-null mice, Syntaxin 3-null mice and AP-1 μ1B-null mice. Successful completion of this research project will provide a novel molecular target and strategy for decorporation of uranium accumulated in kidneys.