Dermal papillary fibroblasts promote persistent granulation tissue formation in junctional epidermolysis bullosa.

The skin is composed of multiple fibroblast subpopulations with different functions in homeostasis and repair, but their role in skin diseases is largely unknown. Junctional epidermolysis bullosa (JEB) is a hereditary skin disorder characterised by severe skin fragility and aberrant granulation tissue formation, caused by loss-of-function variants in basement membrane proteins, including laminin-332. We developed JEB-like organotypic (OT) cultures with distinct fibroblast subpopulations and explored their role in an inducible JEB in vivo disease model, mimicking key features of the human disease. Mechanistically, papillary fibroblasts are highly increased in the granulation tissue of blistered JEB skin, promoting pathological αvβ6 integrin and TGFβ signalling in JEB keratinocytes. Treatment with the TGFβ receptor inhibitor RepSox not only normalised aberrant cell proliferation, differentiation, and cytokine signalling in JEB OTs but also reduced aberrant granulation tissue formation and skin blistering in laminin-332-depleted mice. Collectively, our study reveals that papillary fibroblasts promote JEB pathogenesis through increasing αvβ6 integrin and TGFβ signalling and disruption of these pathological signalling interactions significantly improved skin health and regeneration in JEB.