Toxicity of the kidney proximal tubule by cadmium-metallothionein: Role of lipocalin-2 receptor-mediated endocytosis, vesicle trafficking and lysosomal DMT1

慢性暴露于环境污染物镉（Cd）损害肾近端小管（PT）。在体内，镉与金属硫蛋白（MT）结合，从血液中过滤出来并被PT重新吸收，从而引起肾脏损伤。在之前的研究中，我们已经用培养的PT细胞证明CdMT的摄取和毒性涉及受体介导的内吞作用（RME），其中部分由巨噬细胞苷和立方蛋白介导。小GTPase ARF6调节CdMT的早期内体运输和受体再循环到细胞表面。二价金属转运体DMT1在PT溶酶体中表达并参与CdMT毒性。利用体外培养的PT细胞和megalinor dmt1敲除动物模型，将在PT细胞中研究另一种受体lipocalin-2受体对CdMT RME的作用。此外，将研究调节蛋白ARF1在CdMT从核内体转运到溶酶体中的重要性，并表征CdMT复合物的降解机制。最后，将确定dmt1介导的Cd从溶酶体流向Cd毒性靶细胞器（特别是线粒体）的膜过程。阐明这些机制可能为cd毒性的预防和治疗提供理论依据和策略。

Chronic exposure to the environmental contaminant cadmium (Cd) damages the kidney proximal tubule (PT). In the body Cd is bound to the protein metallothionein (MT), which is filtrated from the blood and reabsorbed by the PT to induce renal damage. In previous studies, we have shown using cultured PT cells that CdMT uptake and toxicity involves receptor-mediated endocytosis (RME), which is partly mediated by megalin and cubilin. The small GTPase ARF6 regulates early endosomal trafficking of CdMT and receptor recycling to the cell surface. The divalent metal transporter DMT1 is expressed in lysosomes of PT and participates in CdMT toxicity. Using cultured PT cells and megalinor DMT1-knockout animal models in vivo, the role of an additional receptor, the lipocalin-2 receptor, will be investigated in PT cells for RME of CdMT. Furthermore, the significance of the regulatory protein ARF1 for trafficking of CdMT from endosomes to lysosomes will be studied and degradation mechanisms of the CdMT complex will be characterized. Finally, membrane processes will be determined that are responsible for DMT1-mediated Cd fluxes from lysosomes to target organelles of Cd-toxicity (particularly mitochondria). Elucidation of these mechanisms may lead to rationales and strategies for prevention and therapy of Cd-toxicity.