Dong Medicine Key laboratory of Hunan Province, Department of laboratory medicine, Hunan University of Medicine, Huaihua, 418000, Hunan, China; Department of Nephrology, Department of Pathology, Changzhi Peace Hospital, Changzhi Medical College, Changzhi, 046000, Shanxi, China.
Dong Medicine Key laboratory of Hunan Province, Department of laboratory medicine, Hunan University of Medicine, Huaihua, 418000, Hunan, China.
Toxicol Lett. 2018 Dec 15;299:226-235. doi: 10.1016/j.toxlet.2018.09.005. Epub 2018 Sep 18.
Semaphorin 3A (sema 3A) is one of a class of secretory proteins belonging to a family of axon-directed factors found in podocytes, distal tubules, and collecting tubes of the kidney. It is considered to be a potential target molecule involved in the mammalian target of the rapamycin (mTOR) pathway in renal injury or renal diseases, but it has an unknown role in the course of hexavalent chromium-Cr(VI) induced nephrotoxicity. In the present study, an acute kidney injury (AKI) model in rats or cultured tubular epithelial HK-2 cells was employed for Cr(VI) exposure alone or in combination with rapamycin (Rap) or N-acetyl-l-cysteine (NAC) or recombinant sema 3A. The methods of histopathology, biochemics, and western blotting were applied to evaluate tubular injury and the role of sema 3A. The results showed that a significant increase of urinary sema 3A indicates an early occurrence of AKI exposed to Cr(VI), accompanied with a significant increase of tubular injury score and phosphorylated mTOR proteins. Further, Cr(VI) treatment, in combination with pretreatment of the mTOR pathway inhibitor, Rap, showed a considerably stronger protective effect of Rap in protecting against Cr(VI)-induced nephrotoxicity than that seen with the free radical scavenger NAC, highlighting the dominant renal protective role of the mTOR pathway in inhibiting toxicity by downregulating the expressed levels of sema 3A in renal tissue. This study has demonstrated that an increased expression of sema 3A occurs in Cr(VI)-induced AKI resulting from activation of the mTOR pathway, and that inhibition of this pathway has been shown to decrease the severity of the toxicity. In conclusion, this study has shown that increased urinary sema 3A is indicative of an activated mTOR pathway and is a valuable biomarker of the early AKI induced by Cr(VI) exposure.
信号蛋白 3A（sema3A）是一类分泌蛋白中的一种，属于轴突导向因子家族，存在于肾脏的足细胞、远曲小管和集合管中。它被认为是哺乳动物雷帕霉素靶蛋白（mTOR）通路中涉及肾损伤或肾脏疾病的潜在靶分子，但在六价铬-Cr（VI）诱导的肾毒性过程中其作用尚不清楚。在本研究中，采用大鼠急性肾损伤（AKI）模型或培养的肾小管上皮细胞 HK-2 细胞，单独或联合使用雷帕霉素（Rap）、N-乙酰-L-半胱氨酸（NAC）或重组 sema3A 进行 Cr（VI）暴露。采用组织病理学、生物化学和 Western blot 方法评估肾小管损伤和 sema3A 的作用。结果表明，Cr（VI）暴露后，尿 sema3A 显著增加，表明 AKI 早期发生，同时肾小管损伤评分和磷酸化 mTOR 蛋白显著增加。此外，Cr（VI）处理联合 mTOR 通路抑制剂 Rap 预处理，与自由基清除剂 NAC 相比，Rap 对 Cr（VI）诱导的肾毒性具有更强的保护作用，这突出了 mTOR 通路在抑制毒性方面的主要肾保护作用，下调肾组织中 sema3A 的表达水平。本研究表明，Cr（VI）诱导的 AKI 中 mTOR 通路激活导致 sema3A 表达增加，抑制该通路可降低毒性的严重程度。总之，本研究表明，尿 sema3A 增加表明 mTOR 通路激活，是 Cr（VI）暴露诱导早期 AKI 的有价值的生物标志物。
