Characterization of the serotoninergic system in the C57BL/6 mouse skin

Abstract

We showed expression of the tryptophan hydroxylase gene and of tryptophan hydroxylase protein immunoreactivity in mouse skin and skin cells. Extracts from skin and melanocyte samples acetylated serotonin to N-acetylserotonin and tryptamine to N-acetyltryptamine. A different enzyme from arylalkylamine N-acetyltransferase mediated this reaction, as this gene was defective in the C57BL6 mouse, coding predominantly for a protein without enzymatic activity. Serotonin (but not tryptamine) acetylation varied according to hair cycle phase and anatomic location. Serotonin was also metabolized to 5-hydroxytryptophol and 5-hydroxyindole acetic acid, probably through stepwise transformation catalyzed by monoamine oxidase, aldehyde dehydrogenase and aldehyde reductase. Activity of the melatonin-forming enzyme hydroxyindole-O-methyltransferase was notably below detectable levels in all samples of mouse corporal skin, although it was detectable at low levels in the ears and in Cloudman melanoma (derived from the DBA/2 J mouse strain). In conclusion, mouse skin has the molecular and biochemical apparatus necessary to produce and metabolize serotonin and N-acetylserotonin, and its activity is determined by topography, physiological status of the skin, cell type and mouse strain.Keywords: mouse skin; serotonin acetylation; arylalkylamine N-acetyltransferase; tryptophan hydroxylase; hair cycle.The skin is the largest body organ and functions as a metabolically active biological barrier regulating internal homeostasis and separating the internal milieu from noxious environmental factors [1]. These functions are mediated by the skin immune, pigmentary, neuroendocrine, adnexal and vascular systems [1][2][3][4][5][6][7]. Most recently we have uncovered local serotoninergic and melatoninergic systems as novel elements of the cutaneous neuroendocrine components of human and hamster skin [8][9][10][11][12]. Serotonin is the product of a multistep metabolic pathway that starts with the hydroxylation of the aromatic aminoacid L-tryptophan by tryptophan hydroxylase (TPH) [13,14]. Serotonin can be acetylated by arylalkylamine N-acetyltransferase (AANAT) to N-acetylserotonin (NAS), which is further transformed to melatonin by hydroxyindole-O-methyltransferase (HIOMT) [13,15].Serotonin can act as a neurohormone, regulator of vascular tone, immunomodulator and growth factor, while melatonin can act as a hormone, neurotransmitter, cytokine or biological modifier [2,[15][16][17]. Some of these functions may be pertinent to skin physiology, which exhibits basic differences among the mammalian species. In rodents (mostly nocturnal animals) the skin is shielded from the damaging effect of solar radiation by fur [18], and the morphology of the entire mouse skin changes in close coordination with the cyclic activity of the hair follicle [19]. Mouse hair follicle cycling is characterized by a precisely regulated, time frame-restricted and differential pattern in the expression and activity of melanogenesis related proteins, PH, pterins and thioredoxin ...

A novel pathway for sequential transformation of 7‐dehydrocholesterol and expression of the P450scc system in mammalian skin

“…Adrenals were obtained from Wistar rats killed under anesthesia. Male rats aged 3 months were obtained from the vivarium of the Department of Biotestings of Bioorganic Chemistry Institute (Minsk, Belarus) (detailed protocols were described previously) [21]. The Institutional Animal Care and Use Committee at AMC approved the original protocol, and a similar protocol for mice was approved at UTHSC; for LC/MS assays the experiments were approved by the Belarus University Animal Care and Use Committee.…”

“…The methodology followed standard protocols described in our laboratories [21,31]. Briefly, mitochondrial fractions prepared as described above for detection of P450scc or adrenodoxin reductase or proteins extracted with 1% (v/v) Triton X-100 (to test StAR expression) from placenta, skin or cultured cells were dissolved in Laemmli buffer and separated on an SDS/12% polyacrylamide gel, transferred to an Immobilon P [poly(vinylidene difluoride)] membrane (Millipore Corp, Bedford, MA, USA); nonspecific binding sites were blocked by incubation in 5% (w/v) nonfat powdered milk in buffer containing 50 mM Tris/HCl, pH 7.5, 150 mM NaCl, and 0.01% (v/v) Tween-20, for 3 h at room temperature.…”

On the Role of Melatonin in Skin Physiology and Pathology

“…1) ( 5 ). This included detection of the genes and proteins for tryptophan hydroxylase (TPH), serotonin N-acetyl-transferase (NAS), and hydroxyindole-O-methyltransferase (HIOMT) in the whole skin and skin cells, and actual demonstration of the corresponding enzymatic activities ( [23][24][25][26][27][28] ).…”

“…NAS can in fact be produced in the C57BL/6 mouse strain ( 25 ), which represents natural AANAT "knockdown" ( 33 ), through an alternate pathway ( 5,25 ). NAS produced in the skin may be released into the circulation ( 5 ), and could be transformed into melatonin after delivery to organs expressing HIOMT ( 34 ).…”

Vertebrate melanophores as potential model for drug discovery and development: A review

“…It was was reported that human melanoma cells can synthesize and metabolize serotonin [119]. Later, a characterization of the serotonergic system in the C57BL/6 mouse skin was presented emphasizing that mouse skin has the molecular and biochemical apparatus necessary to produce and metabolize serotonin and N-acetylserotonin [137]. Furthermore, the immunofluorescence of skin biopsies tended to localize TPH protein and serotonin immunoreactivity to normal and malignant melanocytes in vivo, and the cutaneous pathway for local serotonin synthesis in melanocytes was also reported [138,142], implicating the skin as a target of bioregulation by serotonin.…”