Hydrogen peroxide (H2O2) is a key extracellular redox signaling molecule that regulates diverse physiological processes, including immune cell activation and proliferation. However, its role in maintaining extracellular redox balance and mediating intercellular signaling remains underexplored. In this study, we investigated how extracellular depletion of H2O2 by catalase modulates intracellular signaling pathways in macrophages. Catalase treatment effectively depleted extracellular H2O2 in a concentration- and time-dependent manner, leading to activation of mitogen-activated protein kinase (MAPK) pathways, including extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38, as well as nuclear translocation of the nuclear factor κB (NF-κB) p65 subunit. Perturbation of extracellular redox status resulted in robust upregulation of inflammatory and oxidative stress–related genes, including cyclooxygenase-2 (COX-2), C-C motif chemokine ligand 5 (CCL5), inducible nitric oxide synthase (iNOS), and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. This transcriptional response was accompanied by increased nitric oxide (NO) production and enhanced nuclear translocation and DNA-binding activity of nuclear factor erythroid 2–related factor 2 (Nrf2). Mechanistically, our data suggest that NO-mediated S-nitrosylation contributes to activation of the cellular antioxidant response. In addition, catalase-mediated depletion of extracellular H2O2 significantly (p < 0.05) suppressed 5-bromo-2′-deoxyuridine (BrdU) incorporation, indicating inhibition of macrophage proliferation. Together, these findings demonstrate that extracellular H2O2 functions as a physiological redox signal that maintains cellular homeostasis, and that its removal triggers a coordinated intracellular response involving both inflammatory activation and antioxidant defense. This study highlights the critical role of extracellular redox balance in shaping macrophage function and provides mechanistic insight into how changes in the oxidative environment regulate downstream immune signaling pathways.
Mu et al. (Fri,) studied this question.