In vitro degradation of the inner root sheath in human hair follicles lacking sebaceous glands

BACKGROUND: Cultured hair follicles lacking sebaceous glands do not appear to degrade the inner root sheath (IRS), suggesting that the gland may be involved in this process. OBJECTIVES: To examine this supposition in cultured hair follicles. METHODS: Pilosebaceous units were isolated from hair follicles cultured in vitro, and IRS degradation was studied by histology. RESULTS: When grown in culture, the fibres of follicles lacking sebaceous glands were encased in a layer of translucent tissue. During hair growth in vitro this tissue remained intact at the distal end of the follicle but disappeared further down towards the bulb and then reappeared towards the proximal end. Transection within the region lacking this tissue resulted in the release of a naked hair fibre and the production of hair with no attached tissue upon subsequent hair growth. The translucent tissue represented the IRS, thereby demonstrating that this tissue is indeed degraded in vitro. Histological comparison with freshly isolated pilosebaceous units indicated that IRS degradation in vitro strongly resembled the process that occurs in vivo. CONCLUSIONS: These data suggest that the sebaceous gland does not itself participate in IRS degradation. Indeed, this phenomenon appears to be a function of the follicle itself and is probably intimately linked with the processes of cellular proliferation, differentiation and death that occur during hair biogenesis.