JAK-STAT1 as therapeutic target for EGFR deficiency-associated inflammation and scarring alopecia (scRNA-seq)

The hair follicle stem cell niche is an immune-privileged microenvironment, characterized by reduced antigen presentation, thus shielding against permanent immune-mediated tissue damage. In this study, we demonstrated the protective role of hair follicle-specific epidermal growth factor receptor (EGFR) against scarring hair follicle destruction. Mechanistically, disruption of EGFR signalling generated a cell-intrinsic hypersensitivity within the JAK-STAT1 pathway, which, synergistically with interferon gamma expressing CD8 T-cell and NK-cell-mediated inflammation, compromised the stem cell niche. Hair follicle-specific genetic depletion of either JAK1/2 or STAT1 or therapeutic inhibition of JAK1/2 ameliorated the inflammation, restored skin barrier function and activated the residual stem cells to resume hair growth in mouse models of epidermal and hair follicle-specific EGFR deletion. Skin biopsies from EGFR inhibitor-treated and cicatricial alopecia patients indicated active STAT1 signalling and interferon target expression. Notably, a case study of folliculitis decalvans, characterized by progressive hair loss, scaling and perifollicular erythema, demonstrated successful treatment with JAK1/2 inhibition. Our findings offer molecular insights and present a mechanism-based therapeutic strategy for addressing chronic folliculitis associated with EGFR-inhibitor anti-cancer therapy and cicatricial alopecia. In order to expand the depth of the immunological analysis, we performed single-cell RNA sequencing of the hair follicle and immune cell compartment of 4 EGFRdeltaEgr2 mice at 3 months of age.