Effect of ultraviolet light on the release of neuropeptides and neuroendocrine hormones in the skin: Mediators of photodermatitis and cutaneous inflammation

Ultraviolet (UV) irradiation of the skin causes both inflammation and alter ations in the skin immune system. There is increasing experimental evidence that UV-induced skin inflammation is influenced by the sensory nervous sys tem and the neuroendocrine system in the skin. The resulting complex networ k of cytokines, chemokines, neuropeptides, neuropeptide-degrading enzymes, neurohormones, and other inflammatory mediators mediate photodermatitis and cutaneous inflammation. Neuropeptides such as substance P (SP) and calcito nin gene-related peptide (CGRP) are released from sensory nerves innervatin g the skin upon UV exposure. In addition, a variety of cells in the skin pr oduce increased neuroendocrine hormones such as proopiomelanocortin (POMC) peptides and their receptors as well as neurotrophins after UV exposure. Ne uropeptides and neurohormones are capable of directly or indirectly mediati ng UV-induced cutaneous neurogenic inflammation by the induction of vasodil atation, plasma extravasation, and augmentation of W-induced cytokine, chem okine, or cellular adhesion molecule expression required for activation and trafficking of inflammatory cells into the inflamed tissue. Neuropeptides and neurotrophins may also play a role in the repair of cutaneous UV injury . In addition to proinflammatory effects, UV-induced neuropeptides and neur ohormones such as CGRP and alpha-melanocyte-stimulating hormone may have im munosuppressive effects in the skin. This review will focus on the role tha t SP, CGRP, POMC peptides, and their receptors may play in modulating UV-in duced inflammation in the skin.