Andrzej Slominski

PRODUCTION AND RELEASE OF PROOPIOMELANOCORTIN (POMC) DERIVED PEPTIDES BY HUMAN MELANOCYTES AND KERATINOCYTES IN CULTURE : REGULATION BY ULTRAVIOLET B

It is demonstrated that ultraviolet B (UVB) radiation stimulates increased expression of the proopiomelanocortin (POMC) gene which is accompanied by production and release of alpha-melanocyte stimulating hormone (alpha-MSH) and adrenocorticotropin (ACTH) by both normal and malignant human melanocytes and keratinocytes. The production and release of both peptides are also stimulated by dibutyryl cyclic adenosine monophosphate (dbcAMP) and interleukin 1 alpha (IL-1 alpha) but not by endothelin-1 (ET-1) or tumor necrosis factor-alpha (TNF-alpha). N-acetyl-cysteine (NAC), a precursor of glutathione (GSH), an intracellular free radical scavenger, abolishes the UVB-stimulated POMC peptide production and secretion. Conclusions are as follows: (1) Cultured human cells of cutaneous origin, namely keratinocytes and melanocytes, can produce and express POMC; (2) POMC expression is enhanced by exposure to UVB, possibly through a cyclic AMP-dependent pathway; and (3) The action of UVB on POMC production may involve a cellular response to oxidative stress.

Melatonin membrane receptors in peripheral tissues: distribution and functions.

Many of melatonins actions are mediated through interaction with the G-protein coupled membrane bound melatonin receptors type 1 and type 2 (MT1 and MT2, respectively) or, indirectly with nuclear orphan receptors from the RORα/RZR family. Melatonin also binds to the quinone reductase II enzyme, previously defined the MT3 receptor. Melatonin receptors are widely distributed in the body; herein we summarize their expression and actions in non-neural tissues. Several controversies still exist regarding, for example, whether melatonin binds the RORα/RZR family. Studies of the peripheral distribution of melatonin receptors are important since they are attractive targets for immunomodulation, regulation of endocrine, reproductive and cardiovascular functions, modulation of skin pigmentation, hair growth, cancerogenesis, and aging. Melatonin receptor agonists and antagonists have an exciting future since they could define multiple mechanisms by which melatonin modulates the complexity of such a wide variety of physiological and pathological processes.

The cutaneous serotoninergic/melatoninergic system: securing a place under the sun

It was recently discovered that mammalian skin can produce serotonin and transform it into melatonin. Pathways for the biosynthesis and biodegradation of serotonin and melatonin have been characterized in human and rodent skin and in their major cellular populations. Moreover, receptors for serotonin and melatonin receptors are expressed in keratinocytes, melanocytes, and fibroblasts and these mediate phenotypic actions on cellular proliferation and differentiation. Melatonin exerts receptor‐independent effects, including activation of pathways protective of oxidative stress and the modification of cellular metabolism. While serotonin is known to have several roles in skin—e.g., pro‐edema, vasodilatory, proinflammatory, and pruritogenic—melatonin has been experimentally implicated in hair growth cycling, pigmentation physiology, and melanoma control. Thus, the widespread expression of a cutaneous seorotoninergic/melatoninergic system(s) indicates considerable selectivity of action to facilitate intra‐, auto‐, or paracrine mechanisms that define and influence skin function in a highly compartmentalized manner. Notably, the cutaneous melatoninergic system is organized to respond to continuous stimulation in contrast to the pineal gland, which (being insulated from the external environment) responds to discontinuous activation by the circadian clock. Overall, the cutaneous serotoninergic/melatoninergic system could counteract or buffer external (environmental) or internal stresses to preserve the biological integrity of the organ and to maintain its homeostasis.—Slominski, A. J., Wortsman, J., Tobin, D. J. The cutaneous serotoninergic/melatoninergic system: securing a place under the sun. FASEB J. 19, 176–194 (2005)

Sensing the environment: regulation of local and global homeostasis by the skin's neuroendocrine system.

Skin, the bodys largest organ, is strategically located at the interface with the external environment where it detects, integrates, and responds to a diverse range of stressors including solar radiation. It has already been established that the skin is an important peripheral neuro-endocrine-immune organ that is tightly networked to central regulatory systems. These capabilities contribute to the maintenance of peripheral homeostasis. Specifically, epidermal and dermal cells produce and respond to classical stress neurotransmitters, neuropeptides, and hormones. Such production is stimulated by ultraviolet radiation (UVR), biological factors (infectious and noninfectious), and other physical and chemical agents. Examples of local biologically active products are cytokines, biogenic amines (catecholamines, histamine, serotonin, and N-acetyl-serotonin), melatonin, acetylocholine, neuropeptides including pituitary (proopiomelanocortin-derived ACTH, beta-endorphin or MSH peptides, thyroid-stimulating hormone) and hypothalamic (corticotropin-releasing factor and related urocortins, thyroid-releasing hormone) hormones as well as enkephalins and dynorphins, thyroid hormones, steroids (glucocorticoids, mineralocorticoids, sex hormones, 7-delta steroids), secosteroids, opioids, and endocannabinoids. The production of these molecules is hierarchical, organized along the algorithms of classical neuroendocrine axes such as hypothalamic-pituitary-adrenal axis (HPA), hypothalamic-thyroid axis (HPT), serotoninergic, melatoninergic, catecholaminergic, cholinergic, steroid/secosteroidogenic, opioid, and endocannbinoid systems. Dysregulation of these axes or of communication between them may lead to skin and/ or systemic diseases. These local neuroendocrine networks are also addressed at restricting maximally the effect of noxious environmental agents to preserve local and consequently global homeostasis. Moreover, the skin-derived factors/systems can also activate cutaneous nerve endings to alert the brain on changes in the epidermal or dermal environments, or alternatively to activate other coordinating centers by direct (spinal cord) neurotransmission without brain involvement. Furthermore, rapid and reciprocal communications between epidermal and dermal and adnexal compartments are also mediated by neurotransmission including antidromic modes of conduction. In conclusion, skin cells and skin as an organ coordinate and/or regulate not only peripheral but also global homeostasis.

Cutaneous expression of corticotropin-releasing hormone (CRH), urocortin, and CRH receptors

Studies in mammalian skin have shown expression of the genes for corticotropin‐releasing hormone (CRH) and the related urocortin peptide, with subsequent production of the respective peptides. Recent molecular and biochemical analyses have further revealed the presence of CRH receptors (CRH‐Rs). These CRH‐Rs are functional, responding to CRH and urocortin peptides (exogenous or produced locally) through activation of receptor(s)‐mediated pathways to modify skin cell phenotype. Thus, when taken together with the previous findings of cutaneous expression of POMC and its receptors, these observations extend the range of regulatory elements of the hypo‐thalamic‐pituitary‐adrenal axis expressed in mammalian skin. Overall, the cutaneous CRH/POMC expression is highly reactive to common stressors such as immune cytokines, ultraviolet radiation, cutaneous pathology, or even the physiological changes associated with the hair cycle phase. Therefore, similar to its central analog, the local expression and action of CRH/POMC elements appear to be highly organized and entrained, representing general mechanism of cutaneous response to stressful stimuli. In such a CRH/ POMC system, the CRH‐Rs may be a central element.—Slominski, A., Wortsman, J., Pisarchik, A., Zbytek, B., Linton, E. A., Mazurkiewicz, J., Wei, E. T. Cutaneous expression of corticotropin‐releasing hormone (CRH), urocortin, and CRH receptors. FASEB J. 15, 1678–1693 (2001)

Melanogenesis is coupled to murine anagen: Toward new concepts for the role of melanocytes and the regulation of melanogenesis in hair growth

Hair is actively pigmented only when it grows: the melanogenic activity of follicular melanocytes (MC) is strictly coupled to the anagen stage of the hair cycle. In catagen, melanin formation is switched off and is absent throughout telogen. The appearance of pigmentation is preceded, and further accompanied by, a time-frame - restricted, differential pattern of tyrosinase transcription, translation, and enzyme activities during the development of anagen follicles. In this speculative review, we argue that signals required for melanin synthesis and pigment transfer to bulb keratinocytes (KC) are intrinsic to the skin, rather than coming from the serum. First, the proopiomelanocortin (POMC) gene is expressed and translated during anagen, but is below the level of detectability in telogen; POMC is a precursor protein for adrenocorticotropin and melanotropins, which are potent regulators of MC proliferation and differentiation. Second, fibroblasts and KC produce factors that affect MC proliferation and differentiation. We suggest that signals regulating follicular MC activity partially derive from cutaneous cells expressing POMC. Vice versa, MC transfer to surrounding KC pigment granules with potent bioregulatory properties. MC also produce and secrete various signal molecules that can regulate mesenchymal and epithelial cell functions. Anagen-associated melanogenesis and the cyclic production of a pigmented hair shaft result from programmed and tightly coordinated epithelial-mesenchymal-neuroectodermal interactions, in which MC may act not only as pigmentary, but also as hair growth-regulatory cells.

Serotoninergic and melatoninergic systems are fully expressed in human skin

We investigated the cutaneous expression of genes and enzymes responsible for the multistep conversion of tryptophan to serotonin and further to melatonin. Samples tested were human skin, normal and pathologic (basal cell carcinoma and melanoma), cultured normal epidermal and follicular melanocytes, melanoma cell lines, normal neonatal and adult epidermal and follicular keratinocytes, squamous cell carcinoma cells, and fibroblasts from dermis and follicular papilla. The majority of the samples showed simultaneous expression of the genes for tryptophan hydroxylase, arylalkylamine N‐acetyltransferase (AANAT), and hydroxyindole‐Omethyltransferase (HIOMT). The products of AANAT activity were identified by RP‐HPLC with fluorimetric detection in human skin and in cultured normal and malignant melanocytes and immortalized keratinocytes; HIOMT activity was detected in human skin, keratinocytes, and melanoma cells. N‐acetylserotonin (NAS) was detected by RP‐HPLC in human skin extracts. NAS identity was confirmed further by LC/MS in keratinocytes. In conclusion, we provide evidence that the human skin expresses intrinsic serotonin and melatonin biosynthetic pathways.

Differential expression of HPA axis homolog in the skin

Human skin expresses elements of the hypothalamo-pituitary-adrenal (HPA) axis including pro-opiomelanocortin (POMC), corticotropin releasing hormone (CRH), the CRH receptor-1 (CRH-R1), key enzymes of corticosteroid synthesis and synthesizes glucocorticoids. Expression of these elements is organized in functional, cell type-specific regulatory loops, which imitate the signaling hierarchy of the HPA axis. In melanocytes and fibroblasts CRH-induced CRH-R1 stimulation upregulates POMC expression and production of ACTH through activation of cAMP dependent pathway(s). Melanocytes respond with enhanced production of cortisol and corticosterone, which is dependent on POMC activity. Fibroblasts respond to CRH and ACTH with enhanced production of corticosterone, but not cortisol, which is produced constitutively. Organ-cultured human scalp hair follicles also show a fully functional HPA axis equivalent, including cortisol synthesis and secretion and negative feedback regulation by cortisol on CRH expression. Thus, differential, CRH-driven responses of defined cutaneous cell populations reproduce key features of the central HPA axis at the tissue/single cell levels.

On the role of melatonin in skin physiology and pathology

Melatonin has been experimentally implicated in skin functions such as hair growth cycling, fur pigmentation, and melanoma control, and melatonin receptors are expressed in several skin cells including normal and malignant keratinocytes, melanocytes, and fibroblasts. Melatonin is also able to suppress ultraviolet (U)-induced damage to skin cells and shows strong antioxidant activity in Uexposed cells. Moreover, we recently uncovered expression in the skin of the biochemical machinery involved in the sequential transformation of l-tryptophan to serotonin and melatonin. Existence of the biosynthetic pathway was confirmed by detection of the corresponding genes and proteins with actual demonstration of enzymatic activities for tryptophan hydroxylase, serotonin N-acetyl-transferase, and hydroxyindole-O-methyltransferase in extracts from skin and skin cells. Initial evidence for in vivo synthesis of melatonin and its metabolism was obtained in hamster skin organ culture and in one melanoma line. Therefore, we propose that melatonin (synthesized locally or delivered topically)could counteract or buffer external (environmental)or internal stresses to preserve the biological integrity of the organ and to maintain its homeostasis. Furthermore, melatonin could have a role in protection against solar radiation or even in the management of skin diseases.

Alternative splicing of CRH-R1 receptors in human and mouse skin: identification of new variants and their differential expression

We identified four new isoforms of human CRH‐R1 (e‐h) and three of mouse (mCRH‐R1c, e, and f). In all new forms exon 6 was missing. Human CRH‐R1e was characterized by the deletion of exons 3 and 4; exon 12 from CRH‐R1f; exon 11, 27 base pairs (bp) of exon 10 and 28 bp of exon 12 from CRH‐R1g and CRH‐R1h by the addition of a cryptic exon. In mouse CRH‐R1c exon 3 was spliced out; in mCRH‐R1e exons 3 and 4 and in mCRH‐R1f exon 11 were spliced from mRNA. CRH‐R1 was expressed in all skin specimens in patterns dependent on the cell type, physiological status, and presence of pathology. CRH‐R1α, the most prevalent form, was detected in almost all samples. Ultraviolet radiation (UV) changed the splicing pattern and induced or increased expression of CRH‐R1α in cultured skin cells. Continuing UV treatment of succeeding generations of cells resulted in a progressive increase in the number of CRH‐R1 isoforms, which suggests that receptor heterogeneity might favor cell survival. TPA (phorbol 12‐myristate 13‐acetate), forskolin, dbcAMP (N6, 2′‐O‐dibutyryladenosine 3′:5′‐cyclic monophospate sodium), and IBMX (3‐isobutyl‐1‐methylxanthine) also changed the splicing pattern. We suggest that a polymorphism of CRH‐R1 expression is related to anatomic location, skin physiological or pathologic status, specific cell type, and external stress (UV), and that cAMP‐dependent pathways and TPA may regulate CRH‐R1.