Alkaline pH Promotes NADPH Oxidase-Independent Neutrophil Extracellular Trap Formation: A Matter of Mitochondrial Reactive Oxygen Species Generation and Citrullination and Cleavage of Histone

This study investigates the influence of pH on NADPH oxidase (NOX)-independent neutrophil extracellular trap (NET) formation. The researchers hypothesized that alkaline pH promotes NOX-independent NET formation by increasing calcium influx, mitochondrial reactive oxygen species (mROS) generation, histone citrullination, and histone cleavage. Experiments using human neutrophils and calcium ionophores (A23187 and ionomycin) at varying pH levels demonstrated that alkaline pH significantly increased NET formation. This increase was linked to elevated intracellular calcium, mROS production, and enhanced PAD4 activity (evidenced by increased histone 3 citrullination) and histone 4 cleavage. The use of an mROS scavenger, MitoTempo, confirmed the importance of mROS in this pH-dependent NETosis. The findings highlight a novel mechanism by which pH regulates NOX-independent NET formation, with implications for understanding sterile inflammation and potential therapeutic interventions.

Cristiane Naffah de Souza, Leandro C. D. Breda, Meraj A. Khan, Sandro Rogério de Almeida, Niels Olsen Saraiva Câmara, Neil Sweezey, Nades Palaniyar