The Redox-Responsive Transcription Factor Nrf2 Is Required For Optimal p38MAPK Signalling In Dendritic Cells

LM Abbas Al-Huseini, S Sethu, J Hamdam, N Alhumeed, HX Aw Yeang, CE Goldring, BK Park, JG Sathish. University of Liverpool, Liverpool, UK

Drugs and/or their metabolites can induce oxidative stress in a variety of cell types including immune cells. Immune cells underlie many of the mechanisms that drive adverse drug reactions. The transcription factor Nrf2 governs the cellular adaptive response to oxidative stress induced by drugs and/or their metabolites. Nrf2 activation leads to the upregulation of phase II detoxification enzymes and antioxidant proteins. Redox homeostasis is critical for the optimal functioning of immune cells such as the dendritic cell (DC). DCs are antigen-presenting cells with the principal function to acquire antigens from the environment and present them to naïve T cells to initiate an immune response. Nrf2 maintains redox homeostasis in DCs and loss of Nrf2 is found to cause altered DC phenotype and function. In particular, using DCs derived from Nrf2 deficient mice, we have previously shown that Nrf2 deficient immature DCs have elevated levels of reactive oxygen species (ROS), express high levels of co-stimulatory molecules, and induce significant T cell activation. It is unclear if this altered phenotype and function is due to changes in reactive oxygen species (ROS) levels and/or perturbation in intracellular signalling pathways such as the p38MAPK pathway. The p38MAPK pathway contributes to costimulatory receptor expression in DCs and can be affected by elevated intracellular ROS. In the present study, using bone-marrow derived DCs, we demonstrate that elevated ROS levels in Nrf2 deficient DCs can be reversed by the ROS scavengers, Vitamins C and E. However, restoring ROS in Nrf2 deficient DCs to wild type levels did not reduce the enhanced co-stimulatory molecule expression and T-cell activation. Examination of the p38MAPK pathway revealed that phosphorylation of p38MAPK was marginally greater in Nrf2 deficient DCs compared to wild type DCs. A significantly greater degree of phosphorylation of the p38MAPK downstream effectors, CREB and ATF was observed. CREB and ATF mediate the gene transcription of the cytokine IL-10 and we demonstrate increased secretion of IL-10 by Nrf2 deficient DCs compared to wild type. Using an inhibitor of p38 MAPK, SB203580, we demonstrate that phosphorylation of CREB and ATF can be reduced. Significantly, treatment of Nrf2 deficient DCs with SB203580 reduced the enhanced costimulatory receptor expression, IL-10 secretion and T cell activation. Our findings suggest that Nrf2 is involved in maintaining the integrity of the p38MAPK signalling pathways in DCs.