Oxymatrine Inhibits Renal Tubular EMT Induced by High Glucose via Upregulation of SnoN and Inhibition of TGF-β1/Smad Signaling Pathway.

Lirong Liu,Shuang Li,Mingjun Shi,Rui Yan,Bing Guo,Ying Xiao,Yuanyuan Wang,Wing-Kin Syn

doi:10.1371/journal.pone.0151986

Lirong Liu, Shuang Li + Show 6 more

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https://doi.org/10.1371/journal.pone.0151986

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Abstract

Transforming growth factor-β1 (TGF-β1) signaling has been shown to play a critical role in the development of diabetic nephropathy (DN). The nuclear transcription co-repressor Ski-related novel protein N (SnoN) is an important negative regulator of TGF-β1/Smad signal transduction, and subsequent biological responses including tubule epithelial-mesenchymal transition (EMT), extracellular matrix accumulation and tubulointerstitial fibrosis. Oxymatrine (OM) is an alkaloid extracted from the Chinese herb Sophora japonica and has been demonstrated to prevent fibrosis. However, the anti-fibrosis effect of OM in DN is still unclear. In this study, we cultured normal rat renal tubular epithelial cells (NRK52Es) in high glucose and high glucose plus OM, and detected the expression of E-cadherin, α-SMA, FN, TGF-β1, SnoN, Arkadia, p-Smad2 and p-Smad3 and poly-ubiquitination of SnoN. The results showed that E-cadherin and SnoN expression in NRK52Es decreased significantly, but poly-ubiquitination of SnoN, TGF-β1, α-SMA, FN, Arkadia, p-Smad2 and p-Smad3 expression significantly increased due to high glucose stimulation, which could be almost completely reversed by OM, suggesting that OM may alleviate EMT induced by high glucose via upregulating SnoN expression and inhibiting TGF-β1/Smad signaling pathway activation. Hence, OM could be a novel therapeutic for DN.

Highlights

Diabetic nephropathy (DN) is one of the most common and serious microvascular complications of diabetes mellitus (DM) [1]
This study aimed to investigate whether OM inhibited epithelial-mesenchymal transition (EMT) induced by high glucose in normal rat renal tubular epithelial cells (NRK52Es) in vitro and identify the potential molecular mechanisms in order to provide important experimental evidence to support the use of OM in the prevention and treatment of DN
NRK52Es, which implied that high glucose-induced downregulation of Ski-related novel protein N (SnoN) expression was not caused primarily by an alteration at gene transcriptional level but probably resulted from an enhanced protein ubiquitin-dependent degradation. These results demonstrated that OM could reverse the EMT induced by high glucose via downregulating Transforming growth factor-β1 (TGF-β1) expression and upregulating SnoN expression

Summary

Introduction

Diabetic nephropathy (DN) is one of the most common and serious microvascular complications of diabetes mellitus (DM) [1]. Transforming growth factor-β1 (TGF-β1) is known as a key mediator of fibrogenesis, which induces and regulates the EMT, ECM accumulation and TIF progression by the TGF-β1/Smad signaling pathway in DN [7,8,9,10]. SnoN associates with Smads to block the transduction of TGF-β1 signaling and inhibit the transcriptional activation of TGF-β1 responsive genes [11, 12]. In order to counteract inhibition of transcription by SnoN, TGF-β1/Smad signaling induces the degradation of SnoN by the ubiquitin-proteasome pathway (UUP) [13, 14]. Upon activation of TGF-β1 signaling, Arkadia binds to phosphorylated Smad2/3 (p-Smad2/ 3) and induces degradation of Smad and SnoN/Ski, enabling transcription of TGF-β1 target genes [15,16,17,18,19]

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