RNA-binding proteins tristetraprolin and human antigen R are novel modulators of podocyte injury in diabetic kidney disease

Jia Guo,Rujun Gong,Fei Cheng,Yong Liu,Zhangsuo Liu,Yali Zhou,Mengwen Zhou,Min Lei,Wen Zheng

doi:10.1038/s41419-020-2630-x

Abstract

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.

Highlights

Diabetic kidney disease (DKD) is a common complication of diabetes and the most common cause of end-stage renal disease
Fluorescence staining showed that expression of the podocyte-specific molecules podocin, synaptopodin, and WT-1 was significantly lower in the glomeruli of DKD patients, indicating podocyte injury (Fig. 1c–e)
Immunohistological and immunoblot analyses showed decreased expression of the podocyte-specific molecules podocin, synaptopodin, and WT-1, and increased expression of claudin-1 and interleukin 17 (IL-17) in isolated glomeruli (Fig. 2c, d, h), which was accompanied with altered expression of TTP and human antigen R (HuR) (Fig. 2e–g, i)

Summary

Introduction

Diabetic kidney disease (DKD) is a common complication of diabetes and the most common cause of end-stage renal disease. DKD is detected as proteinuria[1]; Official journal of the Cell Death Differentiation Association. Guo et al Cell Death and Disease (2020)11:413 elements (AREs) in 3′-untranslated regions (3′-UTRs) are features of mRNAs encoding multiple mediators of inflammation, such as cyclooxygenase 2, tumor necrosis factor-alpha (TNF-α), IL-10, and monocyte chemoattractant protein-110. Tristetraprolin (TTP, NCBI reference NP_035886.1) is an ARE-binding protein belonging to the zinc finger protein 36 family[11]. Members of this family are structurally similar, they have cell typespecific expression patterns and exert distinct functions by regulating different target mRNAs12. Tristetraprolin binds to the AREs of mRNAs encoding multiple inflammatory cytokines and promotes their degradation[13]. We previously reported that urinary and serum levels of TTP are lower in patients with diabetes and clinical proteinuria than in healthy individuals[16], indicating that TTP might negatively modulate DKD progression

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