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

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.

Effects of Retinoic Acid on the Mesenchyme in the Palatine Process of the Fetal Rat

In this experiment, pregnant Sprague-Dawley rats were treated with 100mg/kg of alltrans retinoic acid at 10th day of gestation. Pregnant rats were sacrificed at gestation day 14, 15, 16 and 18. Fetuses were delivered, and palatal processes were dissected. The specimens were prepared with fibronectin immunohistochemical stain, and mesenchymal changes were observed with electron microscope. The results were as follows. 1. In the findings fo fibronectin immunohistochemial stain, a part of the mesenchyme of the palatine process of the control group showed weak positive reaction at 14th gestation day, and the reactivity increased progressively by each day. In retinoic acid treated group, the positive reaction was trace at 14th day of gestation, and the reactivity increased progressively, but it was weaker than that of the control group. 2. Examination under transmission electron microscopy revealed well-developed rough endoplasmic reticulum, Goigi apparatus, mitochondrias which were found at the palatine process of the control group. In the retinoic acid treated group, at 16th and 18th day of gestation, the mesenchymal cells of the elevated palatine process had fragmented, sacculated rough endoplasmic reticulums, their mitochondrias were swollen and dissolved, In all cases with retinoic acid treated group, mitotic cells at various stages were more frequently found than in control group. In conclusion, the retinoic acid induces alterations of the intracytoplasmic organells. This finding suggests that retinoic acid is ditectly cytotoxic to mesenchymal cells. Positive fibronectin reaction was demonstrated before palatal elevation at th 15th day of gestation. Therefore, it could be postulated that mesenchymal cells synthesize and release the fibronectin. In the retinoic acid treated group, fibronectin showed positive reaction before and after palatal elevation, and it suggests that fibronectin would be involved in palatal elevation.