Hair follicle stem cell replication stress drives IFI16/STING-dependent inflammation in hidradenitis suppurativa.

Hidradenitis suppurativa (HS) is a chronic, relapsing, inflammatory skin disease. HS appears to be a primary abnormality in the pilosebaceous-apocrine unit. In this work, we characterized hair follicle stem cells (HFSCs) isolated from HS patients and more precisely the outer root sheath cells (ORSCs). We showed that hair follicle cells from HS patients had an increased number of proliferating progenitor cells and lost quiescent stem cells. Remarkably, we also showed that the progression of replication forks was altered in ORSCs from hair follicles of HS patients, leading to activation of the ATR/CHK1 pathway. These alterations were associated with an increased number of micronuclei and with the presence of cytoplasmic ssDNA, leading to the activation of the IFI16/STING pathway and the production of type I IFNs. This mechanistic analysis of the etiology of HS in the HFSC compartment establishes a formal link between genetic predisposition and skin inflammation observed in HS.