Abstract: Objective: To explore the possible molecular mechanisms by which cigarette smoking influences the pathogenesis of hidradenitis suppurativa (HS). Methods: To simulate cigarette smoke exposure, HaCaT cells were treated with benzo(a)pyrene (BaP). The underlying regulatory mechanisms were investigated using aryl hydrocarbon receptor (AhR)-siRNA and the Notch pathway inhibitor DAPT. The expression of genes related to the Notch pathway and lipid metabolism (specifically FASN and SREBP1) was quantified via qRT-PCR and Western Blot. Nile Red staining and CCK-8 assays were employed to evaluate lipid synthesis capacity and cell viability, respectively. Furthermore, single-cell RNA sequencing was utilized to analyze expression differences in the Notch pathway within epidermal keratinocytes between smoking and non-smoking patients with HS. Results: BaP treatment significantly inhibited NOTCH1 expression and reduced lipid synthesis in HaCaT cells, an effect mirrored by the Notch inhibitor DAPT. Mechanistic studies confirmed that BaP regulates NOTCH1 expression through the AhR. Notably, siRNA-mediated knockdown of AhR partially rescued the BaP-induced suppression of NOTCH1. Consistent with these in vitro findings, single-cell RNA sequencing analysis demonstrated a down-regulation of Notch pathway in the lesional keratinocytes of smoking HS patients compared to non-smoking counterparts. Conclusion: BaP in cigarette smoke inhibits the Notch pathway and cellular lipogenesis via an AhR-dependent manner, which could be one of the underlying molecular mechanisms by which smoking exacerbates HS.

Key words: benzo(a)pyrene, hidradenitis suppurativa, aryl hydrocarbon receptor, Notch, keratinocytes