Functional role of β1 integrin-mediated signalling in the human hair follicle

Integrins are transmembrane adhesion proteins that convey critical topobiological information and exert crucial signalling functions. In skin and hair follicle biology, β1 integrins and their ligands are of particular interest. It is not yet known whether β1 integrins play any role in the regulation of human hair growth and the expression pattern of β1 integrin in the human pilosebaceous unit remains ill-defined. Here, we show that pilosebaceous immunoreactivity for β1 integrin is most prominent in the outermost layer of the outer root sheath and the surrounding connective tissue sheath of human scalp hair follicles in situ and in vitro. Sites of β1 integrin immunoreactivity co-express fibronectin and tenascin-C. Contrary to previous reports, β1 integrin immunoreactivity in situ was not significantly upregulated in the human bulge region. Functionally, two β1 integrin-activating antibodies (12G10, TS2/16) and ligand-mimicking RGD peptides promoted the growth of microdissected, organ-cultured human scalp hair follicles in vitro and inhibited spontaneous hair follicle regression. This supports the concept that β1 integrin-mediated signalling is also important in human hair growth control. The physiologically relevant organ culture assay employed here is a potential research tool for exploring whether targeted stimulation of β1 integrin-mediated signalling is a suitable candidate for human hair loss management.