Inflammatory macrophages resist ferroptosis via distinct GCH1-BH4-iNOS axis adaptations, a targetable survival mechanism.

Macrophages in inflammatory tissue niches face intense oxidative stress from their own production of reactive oxygen and nitrogen species, a crucial part of antimicrobial defense. This self-inflicted stress can lead to ferroptotic cell death, a form of regulated iron-dependent cell death. Understanding how these immune cells survive prolonged inflammation is critical, as their persistence contributes to chronic inflammatory diseases. Current anti-inflammatory strategies often lack specificity or have systemic side effects, highlighting a need for novel targets that modulate macrophage viability without broad immunosuppression.

Researchers investigated the redox-protective mechanisms employed by inflammatory macrophages to survive oxidative stress, specifically focusing on LPS-activated macrophages (M(LPS)) and LPS+IFN-γ-activated macrophages (M(LPS-IFN-γ)). They examined the roles of the GTP cyclohydrolase 1 (GCH1)-tetrahydrobiopterin (BH4) pathway and inducible nitric oxide synthase (iNOS) in conferring ferroptosis resistance. The study design involved activating primary macrophages with specific inflammatory stimuli and then assessing their susceptibility to ferroptosis under various conditions, including inhibition or removal of key metabolic pathways. They also evaluated the reversibility of these protective phenotypes upon withdrawal of inflammatory stimuli.

Inflammatory macrophages deploy distinct, context-dependent redox-protective mechanisms to survive self-inflicted oxidative stress and avoid ferroptosis. Specifically, M(LPS) macrophages primarily rely on the GCH1-BH4 pathway for ferroptosis resistance. In contrast, M(LPS-IFN-γ) macrophages depend predominantly on nitric oxide produced by iNOS, with the BH4 pathway acting as a compensatory mechanism, suppressing cell death when nitric oxide production is absent or inhibited. This differential reliance highlights a novel regulatory network. > These distinct adaptations uncover a novel GCH1-BH4-iNOS axis that governs macrophage ferroptosis susceptibility, revealing how these cells preserve viability during prolonged inflammatory activation.The redox-protective phenotype in both LPS and LPS+IFN-γ activated settings was found to be reversible; removal of the inflammatory stimuli completely abolished the protection, indicating that this metabolic programming requires continuous stimulation and is not a permanently fixed state.