Department of Nephrology, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, Henan, 450052, China.
Division of Kidney disease and Hypertension, Brown Medical School, Providence, RI, 02903, USA.
Cell Death Dis. 2020 Jun 2;11(6):413. doi: 10.1038/s41419-020-2630-x.
Diabetic kidney disease (DKD) is one of the most common complications of diabetes, and the most common cause of end-stage renal disease, for which no effective therapies are yet available. RNA-binding proteins (RBPs) play a pivotal role in epigenetic regulation; tristetraprolin (TTP) and human antigen R (HuR) competitively bind cytokine mRNAs, exert contrasting effects on RNA stability, and drive inflammation. However, RBPs' roles in diabetes-related glomerulopathy are poorly understood. Herein, we investigated whether TTP and HuR are involved in post-transcriptional regulation of podocytopathic molecules and inflammatory cytokines in DKD. In DKD patients and db/db mice, TTP expression was significantly decreased and HuR expression was increased in glomerular podocytes, concurrent with podocyte injury, histological signs of DKD, and augmented glomerular expression of interleukin (IL)-17 and claudin-1, which are targets of TTP and HuR, as evidenced by RNA immunoprecipitation. In cultured podocytes, exposure to high ambient glucose amplified HuR expression and repressed TTP expression, upregulated IL-17 and claudin-1, and promoted podocyte injury. Thus, TTP hypoactivity or HuR hyperactivity is sufficient and essential to diabetic podocytopathy. Moreover, in silico analysis revealed that several kinases govern phosphorylation and activation of TTP and HuR, and glycogen synthase kinase (GSK)-3β activated both TTP and HuR, which harbor putative GSK-3β consensus phosphorylation motifs. Treatment of db/db mice with a small molecule inhibitor of GSK-3β abrogated the changes in TTP and HuR in glomeruli and mitigated the overexpression of their target genes (IL-17, claudin-1, B7-1, and MCP-1) thus also mitigating proteinuria and DKD pathology. Our study indicates that TTP and HuR are dysregulated in DKD via a GSK-3β-mediated mechanism and play crucial roles in podocyte injury through post-transcriptional regulation of diverse genes. It also provides novel insights into DKD's pathophysiology and identifies potential therapeutic targets.
糖尿病肾病（DKD）是糖尿病最常见的并发症之一，也是终末期肾病最常见的原因，目前尚无有效的治疗方法。RNA 结合蛋白（RBPs）在表观遗传调控中发挥关键作用；三肽重复蛋白（TTP）和人抗原 R（HuR）竞争性结合细胞因子 mRNA，对 RNA 稳定性产生相反的影响，并驱动炎症。然而，RBPs 在糖尿病相关肾小球病中的作用尚不清楚。在此，我们研究了 TTP 和 HuR 是否参与 DKD 中足细胞病变分子和炎症细胞因子的转录后调节。在 DKD 患者和 db/db 小鼠中，肾小球足细胞中 TTP 的表达显著降低，HuR 的表达增加，同时伴有足细胞损伤、DKD 的组织学特征以及肾小球中白细胞介素 (IL)-17 和闭合蛋白-1 的表达增加，这是 TTP 和 HuR 的靶点，这一点通过 RNA 免疫沉淀得到了证明。在培养的足细胞中，高环境葡萄糖暴露会增强 HuR 的表达并抑制 TTP 的表达，上调 IL-17 和闭合蛋白-1，并促进足细胞损伤。因此，TTP 活性降低或 HuR 活性增加足以且必须导致糖尿病性足细胞病。此外，计算机分析表明，几种激酶控制 TTP 和 HuR 的磷酸化和激活，糖原合酶激酶 (GSK)-3β 激活 TTP 和 HuR，它们都含有 GSK-3β 潜在的磷酸化共识基序。用 GSK-3β 的小分子抑制剂治疗 db/db 小鼠可消除肾小球中 TTP 和 HuR 的变化，并减轻其靶基因（IL-17、闭合蛋白-1、B7-1 和 MCP-1）的过度表达，从而也减轻蛋白尿和 DKD 病理。我们的研究表明，TTP 和 HuR 通过 GSK-3β 介导的机制在 DKD 中失调，并通过对多种基因的转录后调节在足细胞损伤中发挥关键作用。它还为 DKD 的病理生理学提供了新的见解，并确定了潜在的治疗靶点。
