SUMOylation of PPARγ by Rosiglitazone Prevents LPS-Induced NCoR Degradation Mediating Down Regulation of Chemokines Expression in Renal Proximal Tubular Cells

Ying Lu,Jian Liu,Nan Chen,Qiao Zhou,Xu Hao,Yongbing Shi,Weiming Wang,Cong Li,Fang Zhong,Paul Proost

doi:10.1371/journal.pone.0079815

Abstract

Rosiglitazone (RGL), a synthetic agonist for peroxisome proliferator activated receptor γ (PPARγ), exhibits a potent anti-inflammatory activity by attenuating local infiltration of neutrophils and monocytes in the renal interstitium. To evaluate the mechanisms that account for inhibiting inflammatory cells infiltration, we investigated the effect of RGL on chemokines secretion and nuclear factor-kappa B (NF-κB) activation in human renal proximal tubular cells (PTCs). We demonstrated that RGL significantly inhibited lipopolysaccharide (LPS)-induced interleukin-8 (IL-8) and monocyte chemoattractant protein-1 (MCP-1) production in a dose-dependent manner, without appreciable cytotoxicity. Chromatin immunoprecipitation (ChIP) assays clearly revealed that, RGL inhibited p65 binding to IL-8/MCP-1 gene promoters in LPS-stimulated PTCs. Interestingly, further experiments showed RGL reversed LPS-induced nuclear receptor corepressor (NCoR) degradation. In addition, knockdown of protein inhibitor of activated STAT1 (PIAS1), an indispensable small ubiquitin-like modiﬁer (SUMO) ligase, abrogated the effects of RGL on antagonizing LPS-induced IL-8/MCP-1 overexpression and NCoR degradation. These findings suggest that, RGL activates PPARγ SUMOylation, inhibiting NCoR degradation and NF-κB activation in LPS-stimulated PTCs, which in turn decrease chemokines expression. The results unveil a new mechanism triggered by RGL for prevention of tubular inflammatory injury.

Highlights

Inflammatory cell infiltration in the renal interstitium is a prominent feature of a variety of progressive renal diseases
Assessment of cell toxicity of rosiglitazone To exclude the possibility that reductions of the levels of inflammatory cytokine from the cells was due to direct toxicity of RGL to the cells, we evaluated cell toxicity of RGL at different concentrations (0-20 μM) for 24 hours using Methyl thiazolyl tetrazolium (MTT) assay
To evaluate the influence of RGL on LPS-induced IL-8 and monocyte chemoattractant protein-1 (MCP-1) production, HK-2 cells were treated with RGL, in the absence or presence of GW9662, an irreversible peroxisome proliferator activated receptor γ (PPARγ) antagonist

Summary

Introduction

Inflammatory cell infiltration in the renal interstitium is a prominent feature of a variety of progressive renal diseases. Recruiting leukocytes into the kidney involves local expression of chemotactic cytokines, that is, chemokines. Both vitro and vivo studies have demonstrated that proximal tubular epithelial cells are an important source of different cytokines/chemokines and thereby play a central role in regulation of the local inflammatory response[1,2]. Overproduced IL-8 ( known as CXCL8) and MCP-1 ( known as CCL2) mainly by proximal tubular epithelial cells initiate local infiltration of leukocytes, which are closely related to tubulointerstitial inflammation and fibrosis[2,3]. Unveiling the mechanisms modulating tubular epithelial cells secreting IL-8/MCP-1 may provide insights into development of therapeutic targets for renal disease

Methods

Results

Conclusion