NETs activate Notch- γ secretase signaling in hidradenitis suppurativa.

BACKGROUND Hidradenitis suppurativa (HS) is an inflammatory chronic skin disorder of unknown etiology characterized by inflamed abscess-like nodules and boils resulting in sinus tract formation, tissue scarring and massive infiltration of neutrophils. Multiple lines of evidence have highlighted the potential association between alterations in the Notch pathway and HS pathogenesis, but the mechanisms remain incompletely characterized. OBJECTIVE Herein, we aim to elucidate the role of neutrophil extracellular traps in Notch-γ-secretase, signaling. METHODS Twenty-six HS lesional tissues, primary HS macrophages and skin fibroblasts were interrogated by quantitative PCR, western blot, and Elisa analyses. γ-Secretase, and TACE activities were measured in HS skin lesions, macrophages and skin fibroblasts. Immunofluorescence and RNAscope analyzes were performed in HS and control skin. RESULTS A prominent presence of Notch ligands, DLL4 and JAG2 were detected at the protein and mRNA levels in HS skin lesion when compared to control. Levels of DLL4, JAG1, cit-H3-DNA and γ-secretase activity correlated with HS disease severity. Additionally, significantly elevated levels of Notch ligands and γ-secretase activity were found in dissected sinus tracts when compared to the rest of HS tissue. Immunofluorescence microscopy in HS skin lesions showed activation of Notch 1 signaling in macrophages and skin fibroblasts. Neutrophil extracellular traps (NETs) purified from HS patients displayed elevated levels of DLL4. HS-NETs activated the Notch pathway in macrophages and dermal fibroblasts isolated from HS patients. HS skin fibroblasts displayed elevated levels of CD90 and DPP4 in association with increased migratory capacity and Notch activation. Inhibition of Notch decreased migratory capacity and pro-fibrotic markers in HS fibroblasts. CONCLUSION These data support a pathogenic connection between NETs, Notch- γ-secretase activation and the release of pro-fibrotic molecules that promote dysregulation of macrophages and skin fibroblasts in HS. Unveiling the relevance of these molecular events not only expands our understanding of HS but also opens new venues for the development of targeted therapies to address the fibrotic complications of advanced stages of HS.