Nrf2 protects stellate cells from Smad-dependent cell activation

Abstract

Hepatic stellate cells (HSC) orchestrate the deposition of extracellular matrix (ECM) and are the primary effector of liver fibrosis. Several factors, including TGF-β1, PDGF and oxidative stress, have been shown to trigger HSC activation. However, the involvement of cellular defence mechanisms, such as the activation of antioxidant response by Nrf2/Keap1 in the modulation of HSC activation is not known. The aim of this work was to elucidate the role of Nrf2 pathway in HSC trans-differentiation involved in the development of fibrosis. To this end, we repressed Nrf2 and Keap1 expression in HSC with specific siRNAs. We then assessed activation markers, as well as proliferation and migration, in both primary and immortalised human HSCs exposed to Smad inhibitors (SB-431542 hydrate and SB-525334), TGF-β1 and/or PDGF. Our results indicate that knocking down Nrf2 induces HSC activation, as shown by an increase in αSMA-positive cells and by gene expression induction of ECM components (collagens and fibronectin). HSC with reduced Nrf2-levels also showed an increase in migration and a decrease in proliferation. We could also demonstrate that the activation of Nrf2-deficient HSC involves the TGF-β1/Smad pathway, as the activation was successfully inhibited with the two tested Smad inhibitors. Moreover, TGF-β1 elicited a stronger induction of HSC activation markers in Nrf2 deficient cells than in wild type cells. Thus, our data suggest that Nrf2 limits HSCs activation, through the inhibition of the TGF-β1/Smad pathway in HSCs.

Metabolic Hallmarks of Hepatic Stellate Cells in Liver Fibrosis

“…The nuclear factor E2-related factor 2 (Nrf2) is a transcription factor that orchestrates the cellular antioxidant response by binding to the antioxidant response element (ARE) present in the promoter regions of a large set of ROS-scavenging genes. In HSCs, Nrf2 knock-down by RNA interference leads to activation and a more pronounced response to TGFβ1 pointing to the possible role of this defense pathway in the development of fibrosis [143]. This study was supported by various data showing an aggravation of liver injury in the absence of Nrf2 [144,145]; however, contradictory data have also been reported [146,147].…”

TGF-β in Hepatic Stellate Cell Activation and Liver Fibrogenesis—Updated 2019

“…Sulforaphane, an Nrf2 activator, inhibited TGF-β signaling and reduced hepatic fibrosis in the BDL model [156]. Nrf2 -deficient HSC were much stronger activated by TGF-β treatment as compared to wild type cells [157]. Another Nrf2 activator, tBHQ, was also shown to attenuate intestinal fibrosis by inhibiting the ROS-dependent TGF-β/SMAD pathway [158].…”

Inhibitory Effects of Oxymatrine on Transdifferentiation of Neonatal Rat Cardiac Fibroblasts to Myofibroblasts Induced by Aldosterone via Keap1/Nrf2 Signaling Pathways In Vitro

“…Our data indicate that Nrf2 participates in the antioxidant effects of OMT, and the anti-fibrotic effect of OMT might occur by decreasing oxidative stress levels and promoting anti-oxidative GSH and SOD activity. Nrf2 is the key regulator of the antioxidant response and anti-fibrotic effects [44]. Our results suggest that ALD promotes the protein expression of Nrf2 and Keap1 in cytoplasm, and decreases Nrf2 in the nucleus and HO-1 in CFBs, and these effects were reversed by OMT, spironolactone, and curcumin.…”