Peripheral Neutrophil Activation and Extracellular Trap Formation in Amyotrophic Lateral Sclerosis

OBJECTIVES: Peripheral neutrophil levels in amyotrophic lateral sclerosis (ALS) inversely correlate with survival, suggesting a role for neutrophils in disease progression. Here, we characterize markers of several neutrophil activation pathways and evaluate their associations with survival to identify potential mechanisms of disease. METHODS: Blood samples were obtained from participants at the University of Michigan ALS Clinic or from healthy controls. Ex vivo neutrophil extracellular trap (NET) formation was quantified via image analysis of primary neutrophils. Neutrophil function markers of general activation (calprotectin), migration (matrix-metalloproteinase 9 [MMP9]), and degranulation (neutrophil gelatinase-associated lipocalin [NGAL]) were then quantified in plasma via ELISA; NET formation (double-stranded DNA [dsDNA]) was assessed via fluorescence assay. These markers were then associated with ALS survival using Cox proportional hazard regression models, and analyses were stratified by sex. RESULTS: Spontaneous ex vivo NET formation (N = 20 controls, 66 ALS) was increased in ALS (1.0% vs. 9.7%; p = 0.017). In plasma (N = 233 controls, 178 ALS), calprotectin (294 vs. 372 ng/mL; p < 0.001), MMP9 (106 vs. 152 ng/mL; p < 0.001), and NGAL (61 vs. 66 ng/mL; p = 0.01) were elevated in ALS. Calprotectin, MMP9, and NGAL levels were not associated with ALS survival; however, dsDNA was associated with poorer ALS survival but only in females (HR = 1.77 [95% CI, 1.20-2.61]; p = 0.004). INTERPRETATION: Neutrophil function is altered in ALS, and NET formation is a potential mechanism by which neutrophils contribute to ALS, particularly in females.