The CNC-bZIP transcription factor Nrf2 controls expression of matrix metalloproteases in murine macrophages

Liver fibrosis is a chronic condition that often leads to organ failure. Currently, no effective treatment exists for advanced liver fibrosis. De-repression of the transcription factor Nrf2, by inhibition of the ubiquitin ligase substrate adaptor Keap1, is a promising strategy to treat liver fibrosis because Nrf2 augments cytoprotection and blunts the profibrotic TGF-β pathway. Herein, Nrf2 is reported to control matrix metalloproteinase (MMP) expression during chronic liver injury, and more specifically in macrophages, which play a key role in the resolution of fibrosis. We found impaired expression of Mmp8, Mmp9, Mmp12, and Mmp14 in the livers of Nrf2-knockout (Nrf2-ko) mice compared to wild-type (WT) mice, both basally and following CCl4 damage. Investigation of bone-marrow-derived macrophages (BMDMs) revealed profoundly impaired expression of Mmp8 and Mmp12 in Nrf2-ko BMDMs and a concomitant hyper-expression in Keap1-knockdown (Keap1-kd) BMDMs, which were corroborated by siRNA knockdown of Nrf2 and macrophage-specific conditional knockout of Nrf2. This trend was observed under basal conditions and post-efferocytosis. Total MMP activity was also found to be highest in the conditioned medium of Keap1-kd post-efferocytosis BMDMs. ChIP-seq revealed Nrf2-binding sites upstream of Mmp12, which also showed the strongest expression response to Nrf2. Lastly, through pharmacological de-repression of Nrf2, using TBE-31 to inhibit Keap1, upregulation of MMP expression was observed in BMDMs and livers of mice following acute liver injury. In conclusion, Nrf2 has been shown to be a regulator of MMP expression and activity in stimulated macrophages, which reveals a new mechanism by which Nrf2 regulates macrophage function.