Department of Medical Laboratory Sciences, Kitasato University School of Allied Health Sciences , Kanagawa , Japan.
Department of Pathological Biochemistry, Kitasato University School of Allied Health Sciences , Kanagawa , Japan.
Am J Physiol Renal Physiol. 2018 Mar 1;314(3):F462-F470. doi: 10.1152/ajprenal.00108.2017. Epub 2017 Nov 29.
Megalin, an endocytic receptor expressed in proximal tubule cells, plays a critical role in renal tubular protein reabsorption and is associated with the albuminuria observed in diabetic nephropathy. We have previously reported increased oxidant production in the renal cortex during the normoalbuminuric stage of diabetes mellitus (DM); however, the relationship between oxidative stress and renal megalin expression during the normoalbuminuric stage of DM remains unclear. In the present study, we evaluated whether oxidative stress affects megalin expression in the normoalbuminuric stage of DM in a streptozotocin-induced diabetic rat model and in immortalized human proximal tubular cells (HK-2). We demonstrated that increased expression of renal megalin accompanies oxidative stress during the early stage of DM, before albuminuria development. Telmisartan treatment prevented the diabetes-induced elevation in megalin level, possibly through an oxidative stress-dependent mechanism. In HK-2 cells, hydrogen peroxide significantly increased megalin levels in a dose- and time-dependent manner; however, the elevation in megalin expression was decreased following prolonged exposure to severe oxidative stress induced by 0.4 mmol/l hydrogen peroxide. High-glucose treatment also significantly increased megalin expression in HK-2 cells. Concurrent administration of the antioxidant N-acetyl-cysteine blocked the effects of high glucose on megalin expression. Furthermore, the hydrogen peroxide-induced increase in megalin expression was blocked by treatment with phosphatidylinositol 3-kinase and Akt inhibitors. Increase of phosphorylated Akt expression was also seen in the renal cortex of diabetic rats. Taken together, our results indicate that mild oxidative stress increases renal megalin expression through the phosphatidylinositol 3-kinase-Akt pathway in the normoalbuminuric stage of DM.
巨球蛋白，一种在近端肾小管细胞中表达的内吞受体，在肾小管蛋白重吸收中发挥关键作用，与糖尿病肾病中观察到的白蛋白尿有关。我们之前报道过，在糖尿病（DM）的正常白蛋白尿期，肾脏皮质中氧化产物的产生增加；然而，在 DM 的正常白蛋白尿期，氧化应激与肾脏巨球蛋白表达之间的关系仍不清楚。在本研究中，我们评估了氧化应激是否会影响链脲佐菌素诱导的糖尿病大鼠模型和永生化人近端肾小管细胞（HK-2）中 DM 的正常白蛋白尿期的巨球蛋白表达。我们证明，在白蛋白尿发生之前，在 DM 的早期阶段，肾脏巨球蛋白的表达增加伴随着氧化应激。替米沙坦治疗可预防糖尿病引起的巨球蛋白水平升高，这可能是通过氧化应激依赖的机制。在 HK-2 细胞中，过氧化氢以剂量和时间依赖的方式显著增加巨球蛋白水平；然而，在暴露于 0.4 mmol/l 过氧化氢诱导的严重氧化应激后，巨球蛋白表达的升高会降低。高葡萄糖处理也显著增加了 HK-2 细胞中巨球蛋白的表达。抗氧化剂 N-乙酰半胱氨酸的同时给药阻断了高葡萄糖对巨球蛋白表达的影响。此外，用磷脂酰肌醇 3-激酶和 Akt 抑制剂处理可阻断过氧化氢诱导的巨球蛋白表达增加。糖尿病大鼠肾脏皮质中也观察到磷酸化 Akt 表达增加。综上所述，我们的结果表明，在 DM 的正常白蛋白尿期，轻度氧化应激通过磷脂酰肌醇 3-激酶-Akt 通路增加肾脏巨球蛋白表达。
