NRF2-Dependent Anti-Inflammatory Activity of Indole via Cell Surface Receptor Signaling in Murine Macrophages

In this study, we report indoles anti-inflammatory effects to be AhR-independent in RAW 264.7 macrophages. To explore the possibility of indoles surface-receptor mediated signaling, we developed an indole-bovine serum albumin conjugate (I3B), which primarily engage cell surface receptors and has limited intracellular engagement. Treatment with 10 M of I3B led to a comparable reduction of TNF- production in LPS-stimulated RAW 264.7 macrophages to that observed with 500 M of free indole. Transcriptome profiling of I3B-treated LPS-stimulated RAW 264.7 macrophages revealed, I3B blunts pro-inflammatory response and induces gene signatures consistent with NRF2 activation. LPS-stimulated NRF2-/- Bone Marrow-derived Macrophages (BMM) treated with I3B, showed higher levels of pro-inflammatory cytokine production relative to non-treated BMM. To define the upstream pathways responsible for this NRF2-depedent response, we examined GPCR-mediated signaling and found that I3B engages a Gq-coupled receptor to induce PKC{delta} phosphorylation, and subsequent NRF2 phosphorylation. Our results suggest I3B signals through a surface-receptor in a NRF2-dependent manner to reduce inflammation in murine macrophages. TeaserA cell-impermeant indole conjugate inhibits inflammatory signaling in macrophages through an NRF2-dependent mechanism.