Mitochondrial Reactive Oxygen Species in Neutrophil Biology: Mechanisms, Netosis, and Therapeutic Perspectives

Abstract

Neutrophils have traditionally been viewed as highly glycolytic, short-lived effector cells in which mitochondria primarily govern apoptosis. This interpretation is now incomplete. Although mitochondrial oxidative phosphorylation contributes little to the acute energetic requirements of mature neutrophils, mitochondria function as spatially organized signaling platforms that regulate calcium handling, migration, degranulation, survival, hypoxic adaptation, antimicrobial activity, and neutrophil extracellular trap (NET) formation. Mitochondrial reactive oxygen species (mROS), generated mainly through electron leakage at respiratory-chain complexes I and III, operate at low-to-moderate levels as second messengers but become injurious when production exceeds antioxidant control. In neutrophils, mROS interact with NADPH oxidase 2 (NOX2), mitogen-activated protein kinases, phosphoinositide 3-kinase, protein kinase C, mitochondrial calcium uptake, and peptidylarginine deiminase 4 (PAD4). These interactions create stimulus-specific routes to NET formation. Protein kinase C activation by phorbol esters generally favors NOX2-dependent, lytic NETosis, whereas calcium ionophores, sterile injury, and selected inflammatory signals can induce NOX-independent NET formation that depends strongly on mitochondrial calcium loading and mROS. Oxidized mitochondrial DNA released within NETs is not merely structural material; it acts as a damage-associated molecular pattern capable of activating Toll-like receptor 9 and cyclic GMP-AMP synthase-stimulator of interferon genes signaling, thereby linking mitochondrial redox stress to type I interferon responses, thrombosis, endothelial injury, autoimmunity, and cancer progression. Therapeutic approaches include mitochondria-targeted antioxidants, mitochondrial calcium and dynamics modulators, PAD4 inhibition, DNase-based NET dismantling, blockade of oxidized mitochondrial DNA sensing, and disease-specific upstream anti-inflammatory strategies. However, broad suppression of mROS or NETosis may compromise antimicrobial defense. Future translation therefore requires stimulus-resolved biomarkers, rigorous NET detection, cell-selective delivery, and treatments that normalize pathological mitochondrial signaling without eliminating protective neutrophil functions.