Bardoxolone ameliorates TGF-β1-associated renal fibrosis through Nrf2/Smad7 elevation.

Abstract

Transforming growth factor-β (TGF-β) is a potent pathogenic factor of renal injury through the upregulation of extracellular matrix (ECM) expression and facilitation of renal fibrosis. Nuclear factor erythroid 2-like 2 (Nfe2l2; Nrf2), a master regulator of antioxidant and detoxifying systems, is mainly controlled by the binding with cytosolic protein Kelch-like ECH-associated protein 1 (Keap1) and subsequent proteasomal degradation. The protective effect of Nrf2 on renal injury has been attributed to its antioxidant role, where it aids in coping with oxidative stress-associated progression of renal disease. In this study, we investigated the effect of Nrf2 activation on ECM production and TGF-β/Smad signaling using Keap1-silenced MES-13 cells (a genetic glomerular mesangial cell model with Nrf2 overexpression). The TGF-β1-inducible expression of fibronectin and α-smooth muscle actin (α-Sma) was suppressed and Smad2/3 phosphorylation was blocked in Nrf2-high mesangial cells as compared with that in control cells. Notably, in these Nrf2-high mesangial cells, levels of TGF-β1 receptor 1 (TβR1) were substantially diminished, and the protein levels of Smad7, an inhibitor TGF-β1/Smad signaling, were increased. Nrf2-mediated Smad7 elevation and its anti-fibrotic role in Keap1-silenced cells were confirmed by studies with Nrf2-or Smad7-silencing. As a molecular link for Smad7 elevation in Nrf2-high cells, the reduction of Smad-ubiquitination-regulatory factor 1 (Smurf1), an E3 ubiquitin ligase for Smad7, was notable. Silencing of Smurf1 increased Smad7 in the control mesangial cells; however, forced expression of Smurf1 repressed Smad7 levels in Keap1-silenced cells. Additionally, we demonstrate that bardoxolone (BARD; CDDO-methyl), a pharmacological activator of Nrf2, increased Smad7 levels and attenuated TGF-β/Smad/ECM expression in MES-13. Moreover, in an aristolochic acid (AA)-mediated nephropathy mouse model, the renal expression of Nrf2 and Smad7 was elevated by BARD treatment, and AA-induced tubular necrosis and interstitial fibrosis were substantially ameliorated by BARD. Collectively, these results indicate that the Nrf2-Smad7 axis plays a key role in the protection of TGF-β-induced renal fibrosis, and further suggest a novel molecular mechanism of beneficial effect of BARD on renal disease.

• Authors: Min-Kyun Song, Jin-Hee Lee, In-Geun Ryoo, Sang-Hwan Lee, Sae-Kwang Ku, Mi-Kyoung Kwak
• Journal: Free radical biology & medicine (Free Radic Biol Med) Vol. 138 Pg. 33-42 (07 2019) ISSN: 1873-4596 [Electronic] United States
• PMID: 31059771 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
• Copyright: Copyright © 2019 Elsevier Inc. All rights reserved.

Chemical References

• Aristolochic Acids
• Keap1 protein, mouse
• Kelch-Like ECH-Associated Protein 1
• NF-E2-Related Factor 2
• Nfe2l2 protein, mouse
• RNA, Small Interfering
• Smad7 Protein
• Smad7 protein, mouse
• Tgfb1 protein, mouse
• Transforming Growth Factor beta1
• Oleanolic Acid
• aristolochic acid I
• bardoxolone methyl
• Smurf1 protein, mouse
• Ubiquitin-Protein Ligases

Topics

• Animals
• Aristolochic Acids (administration & dosage)
• Cell Line
• Extracellular Matrix (metabolism, pathology)
• Fibrosis
• Gene Expression Regulation
• Gene Knockdown Techniques
• HEK293 Cells
• Humans
• Kelch-Like ECH-Associated Protein 1 (deficiency, genetics)
• Kidney Diseases (chemically induced, drug therapy, genetics, pathology)
• Male
• Mesangial Cells (drug effects, metabolism, pathology)
• Mice
• Mice, Inbred C57BL
• NF-E2-Related Factor 2 (genetics, metabolism)
• Oleanolic Acid (analogs & derivatives, pharmacology)
• RNA, Small Interfering (genetics, metabolism)
• Signal Transduction
• Smad7 Protein (genetics, metabolism)
• Transforming Growth Factor beta1 (genetics, metabolism)
• Ubiquitin-Protein Ligases (antagonists & inhibitors, genetics, metabolism)