Identification of Clustered Cells in Human Hair Follicle Responsible for MMP-9 Gelatinolytic Activity: Consequences for the Regulation of Hair Growth

The study investigated the role of matrix metalloproteinases (MMPs), specifically MMP-2 and MMP-9, in human hair follicles and their regulation by cytokines and epidermal growth factor (EGF). Using zymography and immunohistochemistry, researchers found that human hair follicles in vitro predominantly produce MMP-2 and MMP-9. Stimulation with EGF, tumor necrosis factor-α (TNF-α), or interleukin-1α (IL-1α) significantly increased MMP-9 production. MMP-9 was localized in the lower part of the inner root sheath of anagen hair follicles. The study concluded that the upregulation of MMP-9 by cytokines and EGF in the lower epithelial compartment of the hair bulb is a key mechanism contributing to hair follicle involution, which is observed in conditions like alopecia.