Role of the Neuropeptide Galanin in Human Skin

Neuropeptides (NPs) are expressed by neuronal and non-neuronal tissues in various organs including the skin. In this organ, which constitutes the first barrier against external stress, NPs like corticotrophin releasing hormone (CRH) and pro-opiomelanocortin (POMC)-derived NPs are considered to be involved in preservation of the cutaneous and, in consequence, body homeostasis. These NPs exert potent growth- and immunomodulatory effects and thereby link the neuronal-immune-endocrine axis to the skin. Recently, we have gained preliminary evidence that the NP Galanin (GAL) is a NP, outside of the CRH/POMC system, expressed in non-neuronal cells of the human skin including keratinocytes (KC). To further study the regulation of expression and possible biological effects of GAL we propose to investigate GAL gene expression and the expression of galanin receptors in the skin. To this end human skin will be analysed by immunohistochemistry (IH) in pathological conditions like psoriasis and atopic dermatitis, which have been shown to be regulated by neurological influences. Furthermore, a broad spectrum of skin diseases will be screened by IH for altered expression of GAL. The influence of GAL in immune responses like the contact hypersensitivity will be studied in a galanin-knock-out- mouse model compared to wild-type background mice. Possible effects of GAL relevant in wound healing will be further defined by a series of experiments with controlled thermal injury of normal human skin followed by analysis by IH and receptor-binding assays. Since we have gained preliminary evidence that the expression in cultured KC is upregulated by thermal injury, we will try to characterise the putative heat response element of the human preprogalanin gene by chloramphenicol acetyl transferase analysis in human KC and a squamous cell carcinoma cell-line. Recent data in rodents indicate that GAL might represent a parallel system of opioids for suppression of pain. We will follow this line of evidence by probing a possible statistical correlation of pain perception, bum wounds and GAL expression. These studies will show if GAL has distinct effects on the cutaneous system including allergic reactions and wound healing.

The skin is the outer barrier of the human body shielding inner organs against potential external noxae. The regulation of this barrier is mainly being carried out by the cutaneous nervous system. In addition to direct nerval communication with the central nervous system, neuropeptides of the skin have a vital local regulatory function. In this project we have described for the first time expression and function of the galanin peptide family in skin. Neuropeptide galanin (GAL) is expressed abundantly in keratinocytes, smooth muscle cells, ductal cells of sweat glands and nerve endings. Since we were able to detect neither expression of GAL receptors nor any physiological effect of GAL on keratinocytes, we investigated a possible antimicrobial activity of GAL. In fact, we were able to show that the galanin-message associated peptide (GMAP), which is part of the GAL precursor molecule, exhibits antifungal activity and therefore establishes GMAP as a component of innate immune system. Receptor-mediated functions of GAL in the skin are located in the dermis, where we found receptor expression near sweat glands and vessels. This implicates a possible thermal regulatory function, a fact that is also being suggested by the heat sensibility of GAL knock-out mice. Our data on the regulation of the microvasculature in vivo in the murine model are also supporting this hypothesis. In this model we found that GAL inhibits plasma extravasation postsynaptically, most likely via activation of the galanin receptor GalR2. Another member of the galanin peptide family, galanin-like peptide (GALP) has been localized in the dermal parts of human skin. Similar to GAL it inhibits substance P and calcitonin-gene related peptide induced plasma extravasation. To our best knowledge this is the first demonstration of a peripheral effect of GALP. Investigations of GALP peptide expression led us to the identification of a novel splice variant of GALP, which we termed Alarin. Preliminary work shows that this peptide is expressed in specific neuronal structures and around certain blood vessels. For alarin we were also able to demonstrate regulation of vascular activity. In summary, we have identified members of the GAL peptide family, including GAL, GALP and Alarin as novel regulators of homeostatic function in the skin. These results direct further work to determine role and possible therapeutic implications in pathological conditions like skin infections, burns, urticaria and immunological processes.