Effects of All-Trans Retinoic Acid on the Laminin 1 Expression in Rat Hair Follicles

ABSTRACT

Laminins, a subset of glycoproteins, are main components of the basement membrane along with fibronectin, type IV collagen, and heparan sulfate proteoglycan and influence the biologic features, such as growth and polarization, of all tissues attached on the basement membrane. Although evidence has been suggested that laminins are involved in the process of hair follicle formation in mammalian skin tissues, the significance of laminin on the physiology of hair follicles remains to be fully understood. In this study, we assessed whether the distribution of laminin is associated with the growth of hair follicles and whether all-trans retinoic acid (RA), a stimulus of hair follicle growth, affects the expression profile of laminins. To observe the distribution of laminin varied depending on the developmental stages, fetuses(at day 20 of gestation) and pups(at day 1 and 3 after birth) of Sprague- Dawley rats were used. To examine the effect of RA, 5 days-old pups were administered with RA and their skin tissues were removed post mortem 2, 4, or 7 days later. Skin specimens were sectioned and observed using the immunohistochemical staining, immunogold staining for electron microscopy, and in situ RT-PCR assays. In fetuses at day 20 of gestation and 1 and 3-days-old pups, the distribution of laminin within hair follicles was restricted in the cytoplasm of fibroblasts located in hair papilla and dermal root sheath, basement membrane, and glassy membrane. Following RA treatment for 2 and 4 days, laminin expression was increased in the basement membrane, glassy membrane, outer root sheath, and dermal root sheath in hair follicles. Following RA treatment for 2 and 4 days, the level of laminin was increased in fibroblasts and matrix cells present in hair follicles, as shown in immunogold staining. The expression of laminin at day 7 post administration with RA was decreased at the level comparable with that of untreated controls. In in situ RT-PCR assays, matrix cells in hair follicles exhibited an increase in the levels of laminin alpha1 and beta1 transcripts following RA administration. Thus, these results suggest that matrix cells play a role in the growth of hair by enhancing laminin gene expression and all-trans retinoic acid promotes this induction.