Bruton's Tyrosine Kinase and Nrf2 mediate TLR-induced activation of Heme oxygenase-1 gene expression in macrophages (116.16)

Abstract

Abstract The inducible isoform of heme oxygenase (HO)-1, is involved in heme degradation producing CO and biliverdin, mediating cytoprotection against oxidative stress. Recently, HO-1 has been shown to evoke potent anti-inflammatory and immunomodulatory effects in macrophages. Here we demonstrate that Bruton's tyrosine kinase (Btk), the gene of which is mutated in human immunodeficiency X-linked agammaglobulinemia, is involved in toll-like receptor (TLR)-induced gene expression of HO-1 in macrophages. The Btk inhibitor LFM-A13 blocked the induction of HO-1 by LPS (TLR4 ligand) in RAW264.7 macrophages and primary mouse alveolar macrophages. Furthermore, LPS-stimulated up-regulation of HO-1 gene expression was abrogated in alveolar macrophages from Btk-/- mice. In addition, inhibition of Btk with LFM-A13 attenuated the LPS-induced luciferase activity of the HO-1 promoter in transfection studies in RAW264.7 cells. This effect was mediated by the transcription factor Nrf2, which is a master regulator of the cellular antioxidant defense. Immunofluorescence studies revealed that the nuclear translocation of Nrf2 in LPS-treated macrophages was reduced by Btk inhibition. Moreover, the generation of reactive oxygen species (ROS), but not that of NO, was involved in this regulatory pathway. Btk-dependent induction of HO-1 gene expression via Nrf2 was also observed upon stimulation by TLR7 and TLR9 ligands, suggesting Btk to be generally involved in TLR-mediated HO-1 gene activation.