N-Formyl Methionine Peptide-Mediated Neutrophil Activation in Systemic Sclerosis

Runa Kuley,Ting Wang,Christian Lood,Roger Hesselstrand,Ryan D Stultz,Bhargavi Duvvuri,J Lee Nelson,Marvin J Fritzler

doi:10.3389/fimmu.2021.785275

Abstract

Exaggerated neutrophil activation and formation of neutrophil extracellular traps (NETs) are reported in systemic sclerosis (SSc) but its involvement in SSc pathogenesis is not clear. In the present study we assessed markers of neutrophil activation and NET formation in SSc patients in relation to markers of inflammation and disease phenotype. Factors promoting neutrophil activation in SSc remain largely unknown. Among the neutrophil activating factors, mitochondrial-derived N-formyl methionine (fMet) has been reported in several autoinflammatory conditions. The aim of the current study is to assess whether SSc patients have elevated levels of fMet and the role of fMet in neutrophil-mediated inflammation on SSc pathogenesis. Markers of neutrophil activation (calprotectin, NETs) and levels of fMet were analyzed in plasma from two SSc cohorts (n=80 and n=20, respectively) using ELISA. Neutrophil activation assays were performed in presence or absence of formyl peptide receptor 1 (FPR1) inhibitor cyclosporin H. Elevated levels of calprotectin and NETs were observed in SSc patients as compared to healthy controls (p<0.0001) associating with SSc clinical disease characteristics. Further, SSc patients had elevated levels of circulating fMet as compared to healthy controls (p<0.0001). Consistent with a role for fMet-mediated neutrophil activation, fMet levels correlated with levels of calprotectin and NETs (r=0.34, p=0.002; r=0.29, p<0.01 respectively). Additionally, plasma samples from SSc patients with high levels of fMet induced de novo neutrophil activation through FPR1-dependent mechanisms. Our data for the first time implicates an important role for the mitochondrial component fMet in promoting neutrophil-mediated inflammation in SSc.

Highlights

Systemic sclerosis (SSc) is a rare chronic autoimmune disease characterized by vasculopathy, inflammation, and fibrosis of the skin and internal organs
To investigate if neutrophil activation occurs in SSc, we analyzed levels of calprotectin (S100A8/A9) as well as neutrophil extracellular traps (NETs) (MPO-DNA complexes) in plasma samples from a large cohort of patients with SSc (n=80, Cohort I, Table 1) as well as in a smaller validation cohort (n=20, Cohort II, Table 1) and compared them with levels found in healthy controls (n=40, Cohort I and n= 24, Cohort II)
The plasma levels of calprotectin but not NETs positively correlated with their corresponding brain natriuretic peptide levels in the SSc patients in Cohort II (r= 0.59, p=0.01, Figure 2D)

Summary

Introduction

Systemic sclerosis (SSc) is a rare chronic autoimmune disease characterized by vasculopathy, inflammation, and fibrosis of the skin and internal organs. Among the innate immune cells, neutrophils are prominent contributors of inflammation in several autoimmune diseases including rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE), and have been implicated in SSc pathogenesis [6,7,8,9]. Neutrophil involvement in induction of endothelial cell apoptosis, an early event leading to fibrosis, has been reported in SSc [14]. These studies indicate a critical pathogenic or modulatory role of neutrophils in SSc

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