Counter Regulation of Spic by NF-κB and STAT Signaling Controls Inflammation and Iron Metabolism in Macrophages.

Activated macrophages must carefully calibrate their inflammatory responses to balance efficient pathogen control with inflammation-mediated tissue damage, but the molecular underpinnings of this "balancing act" remain unclear. Using genetically engineered mouse models and primary macrophage cultures, we show that Toll-like receptor (TLR) signaling induces the expression of the transcription factor Spic selectively in patrolling monocytes and tissue macrophages by a nuclear factor κB (NF-κB)-dependent mechanism. Functionally, Spic downregulates pro-inflammatory cytokines and promotes iron efflux by regulating ferroportin expression in activated macrophages. Notably, interferon-gamma blocks Spic expression in a STAT1-dependent manner. High levels of interferon-gamma are indicative of ongoing infection, and in its absence, activated macrophages appear to engage a "default" Spic -dependent anti-inflammatory pathway. We also provide evidence for the engagement of this pathway in sterile inflammation. Taken together, our findings uncover a pathway wherein counter-regulation of Spic by NF-κB and STATs attune inflammatory responses and iron metabolism in macrophages. • The transcription factor Spic restrains inflammatory responses in macrophages • Spic promotes the expression of the iron exporter ferroportin in activated macrophages • NF-κB activity is required for the expression of Spic in activated macrophages • Interferon-gamma suppresses Spic expression in activated macrophages Activated macrophages must fine-tune their inflammatory responses to promote host defense while limiting tissue damage. Alam et al. find that the transcription factor Spic restrains inflammatory responses and promotes iron efflux from activated macrophages, thereby calibrating macrophage responses during the resolution of inflammation. [ABSTRACT FROM AUTHOR]