Evaluation of the Therapeutic Potential of NRF2 Activation to Prevent TGF-β1 Induced Liver Fibrosis

Liver fibrosis is caused by chronic liver injury and is characterised by the excessive accumulation of extracellular matrix (ECM) proteins in the liver which disrupt the architecture and function, thereby leading to liver failure. If left untreated, liver fibrosis can lead to liver cirrhosis and hepatocellular carcinoma (HCC). Oxidative stress (OS) and inflammation play a key role in developing liver fibrosis. Nuclear factor erythroid 2-related factor 2 (NRF2) is a transcription factor which upregulates a plethora of cytoprotective genes, including anti-inflammatory and antioxidant genes. NRF2 activation has been shown to inhibit the progression of liver fibrosis. Transforming growth factor, beta 1 (TGF-β1) is a pro-fibrotic cytokine which upregulates the expression of ECM proteins. It also plays a role in the activation of hepatic stellate cells (HSC), epithelial to mesenchymal transition (EMT) of hepatocytes and the polarisation of macrophages. Therefore, in this project, we investigated whether RTA-405, a potent electrophilic NRF2 activator, prevents the pro-fibrotic response of macrophages and hepatocytes to TGF-β1. Hepa1c1c7 and RAW 264.7 cells were pre-treated with RTA-405 for either 3 or 24 hours, before being co-treated with TGF-β1 for either 1 or 24 hours. RT-qPCR and western blotting were performed on whole cell lysates to determine the mRNA and protein levels of NRF2 and its transcriptional targets, as well as markers of TGF-β1 signalling. We found a reciprocal relation between TGF-β1 and NRF2, whereby TGF-β1 suppresses NRF2 activation by RTA-405 in hepatocytes and macrophages. RTA-405 suppresses TGF-β1-induced collagen and fibronectin expression without affecting SMAD2/3 activation in hepatocytes; and macrophages express low collagen and fibronectin levels. Non-canonical TGF-β1 signalling appears to operate in macrophages, but not hepatocytes. Taken together with previous findings, these results suggest that the pharmacological NRF2 activator RTA-405 has promise for the prevention of liver fibrosis.