Molecular mechanisms of retinoid actions in skin.

For more than 40 years, it has been appreciated that vitamin A is a critical regulator of growth and differentiation of developing and adult mammalian and avian skin. Vitamin A deficiency and hypervitaminosis A cause disruption of normal cellular homeostatic mechanisms, resulting in impairment of skin barrier function. More recent studies demonstrating all-trans retinoic acid as the major biologically active form of vitamin A, and nuclear retinoid receptors as the major mediators of all-trans retinoic acid actions, have provided exciting new insights into the molecular basis of vitamin A actions. These recent insights have been the driving force for important advances in the many areas of retinoid research made during the past 6 years. Nowhere has this new knowledge been more extensively applied than toward understanding the molecular basis of retinoid physiology and pharmacology in skin. This article will review these recent findings and attempt to synthesize their meaning to provide a view into the mechanisms whereby retinoids participate in regulation of skin function.