PROK2 defines a pathogenic neutrophil subset and serves as a clinical indicator of neutrophilic inflammation in COPD

Chronic obstructive pulmonary disease (COPD) is a chronic inflammatory lung disease with progressive airflow limitation. However, the key pathogenic immune cell subset remains unknown. A cigarette smoke-induced COPD mouse model was established. The composition, phenotypic state, and intercellular communication of immune cells in the lungs were characterized using scRNA-seq and flow cytometry. PROK2 and inflammatory mediators were validated by multiplex immunofluorescence and by ELISA in mice and patients with COPD. Chronic cigarette smoke (CS) exposure caused COPD and neutrophil-dominant immune remodeling. Notably, a neutrophil subset, PROK2+ neutrophils (Neu-PROK2), became the dominant neutrophil population, and exhibited elevated expression of matrix metalloproteinases (MMPs), NADPH oxidase components, and neutrophil extracellular traps-related genes, contributing to tissue injury under CS. Multiplex immunofluorescence also revealed PROK2 was primarily localized in alveolar LY6G⁺ neutrophils in CS lungs. Furthermore, Neu-PROK2 comprised an intermediate Ltf lo reservoir and a terminal hyperinflammatory Ltf hi state, forming a CS-driven continuum that progresses from Neu-PROK2 Ltf lo toward Ltf hi, with FOSL1 acting as an upstream driver. Importantly, Serum PROK2 was elevated in stable COPD, correlated positively with neutrophil-associated inflammatory/NET markers, and was inversely associated with eosinophil strata and lung function. Our study nominates PROK2⁺ neutrophils as a key pathogenic neutrophil subset in COPD and posits FOSL1 as a putative upstream driver. These findings suggest that PROK2 may serve as a candidate circulating biomarker associated with neutrophil-related inflammatory activity in COPD.