Tight Junction Barriers in Human Hair Follicles – Role of Claudin-1

The study investigated the tight junction (TJ) barrier function in human hair follicles (HFs) and found that a continuous TJ barrier exists from the infundibulum to the lower central part of anagen HFs, as well as surrounding the club in catagen and telogen HFs. This barrier is less tight in HF keratinocytes compared to interfollicular keratinocytes in cell culture experiments. The knock-down of claudin-1, a TJ protein less expressed in HFs of atopic dermatitis patients, led to impaired barrier function, reduced proliferation, and increased apoptosis in hair keratinocytes. These findings suggest that claudin-1 plays a crucial role in HF barrier function and hair growth, as evidenced by the hair growth phenotype in claudin-1 deficient patients and mice.