Division of Urology, Department of Surgery, Far Eastern Memorial Hospital, New Taipei, Taiwan.
Divisions of Urology, Department of Surgery, Cardinal Tien Hospital, New Taipei, Taiwan.
Am J Physiol Renal Physiol. 2021 May 1;320(5):F799-F813. doi: 10.1152/ajprenal.00461.2020. Epub 2021 Mar 22.
Glutamate -methyl-d-aspartate receptor (NMDAR) hyperfunction is known to contribute to acute renal failure due to ischemia-reperfusion and endotoxemia. d-Serine is a coagonist for NMDAR activation, but whether NMDARs play a role in d-serine-mediated nephrotoxicity remains unclear. Here, we demonstrate that NMDAR blockade ameliorated d-serine-induced renal injury. In NMDAR-expressing LLC-PK cells, which were used as a proximal tubule model, d-serine but not l-serine induced cytotoxicity in a dose-dependent manner, which was abrogated by the selective NMDAR blockers MK-801 and AP-5. Time-dependent oxidative stress, evidenced by gradually increased superoxide and HO production, was associated with d-serine-mediated cytotoxicity; these reactive oxygen species could be alleviated not only after NMDAR inhibition but also by NADPH oxidase (NOX) inhibition. Activation of protein kinase C (PKC)-δ and PKC-ζ is a downstream signal for NMDAR-mediated NOX activation because PKC inhibition diminishes the NOX activity that is induced by d-serine. Renal injury was further confirmed in male Wistar rats that intraperitoneally received d-serine but not l-serine. Peak changes in glucosuria, proteinuria, and urinary excretion of lactate dehydrogenase and malondialdehyde were found after 24 h of treatment. Persistent tubular damage was observed after 7 days of treatment. Cotreatment with the NMDAR blocker MK-801 for 24 h abolished d-serine-induced functional insufficiency and tubular damage. MK-801 attenuated renal superoxide formation by lowering NOX activity and protein upregulation of NOX4 but not NOX2. These results reveal that NMDAR hyperfunction underlies d-serine-induced renal injury via the effects of NOX4 on triggering oxidative stress. Ionotropic -methyl-d-aspartate receptors (NMDARs) are not only present in the nervous system but also expressed in the kidney. Overstimulation of renal NMDARs leads to oxidative stress via the signal pathway of calcium/protein kinase C/NADPH oxidase in d-serine-mediated tubular cell damage. Intervention of NMDAR blockade may prevent acute renal injury caused by d-serine.
谷氨酸 -N- 甲基-D- 天冬氨酸受体（NMDAR）过度活跃已知会导致缺血再灌注和内毒素血症引起的急性肾衰竭。D-丝氨酸是 NMDAR 激活的共激动剂，但 NMDAR 是否在 D-丝氨酸介导的肾毒性中发挥作用尚不清楚。在这里，我们证明了 NMDAR 阻断可改善 D-丝氨酸诱导的肾损伤。在作为近端肾小管模型的 NMDAR 表达的 LLC-PK 细胞中，D-丝氨酸而非 L-丝氨酸以剂量依赖性方式诱导细胞毒性，而选择性 NMDAR 阻断剂 MK-801 和 AP-5 则可阻断该毒性。与 D-丝氨酸介导的细胞毒性相关的时间依赖性氧化应激，表现为超氧化物和 HO 产生逐渐增加，不仅在 NMDAR 抑制后，而且在 NADPH 氧化酶（NOX）抑制后，这些活性氧物质均可减轻。蛋白激酶 C（PKC）-δ和 PKC-ζ的激活是 NMDAR 介导的 NOX 激活的下游信号，因为 PKC 抑制可减弱 D-丝氨酸诱导的 NOX 活性。在腹腔内接受 D-丝氨酸而非 L-丝氨酸的雄性 Wistar 大鼠中进一步证实了肾损伤。治疗 24 小时后，观察到尿葡萄糖、蛋白尿和乳酸脱氢酶和丙二醛排泄的峰值变化。治疗 7 天后观察到持续的肾小管损伤。24 小时共处理 NMDAR 阻断剂 MK-801 可消除 D-丝氨酸诱导的功能不全和肾小管损伤。MK-801 通过降低 NOX 活性和 NOX4 的蛋白上调而非 NOX2 来减轻肾超氧化物的形成。这些结果表明，NMDAR 功能过度活跃是 D-丝氨酸诱导肾损伤的基础，其通过 NOX4 触发氧化应激的作用。离子型 -N- 甲基-D- 天冬氨酸受体（NMDAR）不仅存在于神经系统中，也存在于肾脏中。在 D-丝氨酸介导的肾小管细胞损伤中，过度刺激肾 NMDAR 会通过钙/蛋白激酶 C/NADPH 氧化酶信号通路导致氧化应激。NMDAR 阻断的干预可能会防止由 D-丝氨酸引起的急性肾损伤。
