Inflammatory loop involving Staphylococcus aureus, IL-36γ, and cathepsin S drives immunity disorders in familial acne...

Acne inversa (AI) is an inflammatory skin disease associated with nicastrin (NCSTN) mutations. Despite the dysregulated bacterial-host immune interactions being an essential event in AI, the interaction between bacteria and keratinocytes in AI pathophysiology remains unclear. In this study, the NCSTN gene was suppressed using short hairpin RNA in HaCaT cells. Using RNA sequencing, real-time polymerase chain reaction, and western blotting, the expression of IL-36 cytokines was analyzed. The impact of Staphylococcus aureus on AI keratinocyte inflammation and underlying regulatory molecules was investigated by exposing the HaCaT cells to S. aureus. By stimulating NCSTN knockdown HaCaT cells with IFN-γ, the expression and regulatory mechanism of Cathepsin S (Cat S), an IL-36γ cleavage and activating protease, were investigated. After NCSTN knockdown, the IL-36α expression increased, and the IL-36Ra expression was downregulated. NCSTN/MEK/ERK impairment-induced Krüppel-like factor 4 (KLF4) up-regulation in concert with S. aureus-induced nuclear factor kappa B elevation acts synergistically to promote IL-36γ production with the subsequent IL-8 activation in HaCaT cells. NCSTN/MEK/ERK impairment was also observed in familial AI lesions. IFN-γ-induced Cat S in keratinocytes was enhanced after NCSTN knockdown. The expression of IFN-II pathway molecules was significantly upregulated in both NCSTN knockdown HaCaT cells and familial AI lesions. The Cat S expression was significantly elevated in the patient's AI lesions. Our findings suggested a synergistic relationship between S. aureus and NCSTN/MAPK/KLF4 axis in IL-36γ-induced familial AI keratinocytes.