Physiology of endocrine skin interrelations

The Expression of the Endogenous mTORC1 Inhibitor Sestrin 2 Is Induced by UVB and Balanced with the Expression Level of Sestrin 1

Sestrin 2 (SESN2) is an evolutionarily conserved regulator of mechanistic target of rapamycin complex 1 (mTORC1) which controls central cellular processes such as protein translation and autophagy. Previous studies have suggested that SESN2 itself is subjected to regulation at multiple levels. Here, we investigated the expression of SESN2 in the skin and in isolated skin cells. SESN2 was detected by immunofluorescence analysis in fibroblasts and keratinocytes of human skin. Differentiation of epidermal keratinocytes was not associated with altered SESN2 expression and siRNA-mediated knockdown of SESN2 did not impair stratum corneum formation in vitro. However, SESN2 was increased in both cell types when the expression of its paralog SESN1 was blocked by siRNA-mediated knock down, indicating a compensatory mechanism for the control of expression. Irradiation with UVB but not with UVA significantly increased SESN2 expression in both keratinocytes and fibroblasts. Upregulation of SESN2 expression could be completely blocked by suppression of p53. These results suggest that SESN2 is dispensable for normal epidermal keratinization but involved in the UVB stress response of skin cells.

Epithelialization in Wound Healing: A Comprehensive Review

Significance: Keratinocytes, a major cellular component of the epidermis, are responsible for restoring the epidermis after injury through a process termed epithelialization. This review will focus on the pivotal role of keratinocytes in epithelialization, including cellular processes and mechanisms of their regulation during re-epithelialization, and their cross talk with other cell types participating in wound healing. Recent Advances: Discoveries in epidermal stem cells, keratinocyte immune function, and the role of the epidermis as an independent neuroendocrine organ will be reviewed. Novel mechanisms of gene expression regulation important for re-epithelialization, including microRNAs and histone modifications, will also be discussed. Critical Issues: Epithelialization is an essential component of wound healing used as a defining parameter of a successful wound closure. A wound cannot be considered healed in the absence of re-epithelialization. The epithelialization process is impaired in all types of chronic wounds. Future Directions: A comprehensive understanding of the epithelialization process will ultimately lead to the development of novel therapeutic approaches to promote wound closure.

Nicotinic acetylcholine receptor stimulation impairs epidermal permeability barrier function and recovery and modulates cornified envelope proteins

AIM

To characterize how nicotinic acetylcholine receptors (nAChRs) influence epidermal barrier function and recovery following prolonged stress or direct nAChR activation or antagonism.

MAIN METHODS

Mice were subjected to psychological stress or treated topically with nAChR agonist or antagonist for 3 days. We assessed barrier permeability and recovery by measuring transepidermal water loss (TEWL) before and after barrier disruption. In parallel, we analyzed the production and localization of several epidermal cornified envelope proteins in mouse skin and in human EpiDerm™ organotypic constructs stimulated with a nAChR agonist (nicotine) and/or a nAChR selective antagonist (α-bungarotoxin).

KEY FINDINGS

We determined that psychological stress in mice impairs barrier permeability function and recovery, an effect that is reversed by application of the α7 selective nAChR antagonist, α-bungarotoxin (Bung). In the absence of stress, both topical nicotine or Bung treatment alone impaired barrier permeability. We further observed that stress, topical nicotine, or topical Bung treatment in mice influenced the abundance and/or localization of filaggrin, loricrin, and involucrin. Similar alterations in these three major cornified envelope proteins were observed in human EpiDerm™ cultures.

SIGNIFICANCE

Perceived psychological stress and nicotine usage can both initiate or exacerbate several dermatoses by altering the cutaneous permeability barrier. Modulation of nAChRs by topical agonists or antagonists may be used to improve epidermal barrier function in skin diseases associated with defects in epidermal barrier permeability.

Cholinergic regulation of keratinocyte innate immunity and permeability barrier integrity: new perspectives in epidermal immunity and disease

Several cutaneous inflammatory diseases and their clinical phenotypes are recapitulated in animal models of skin disease. However, the identification of shared pathways for disease progression is limited by the ability to delineate the complex biochemical processes fundamental for development of the disease. Identifying common signaling pathways that contribute to cutaneous inflammation and immune function will facilitate better scientific and therapeutic strategies to span a variety of inflammatory skin diseases. Aberrant antimicrobial peptide (AMP) expression and activity is one mechanism behind the development and severity of several inflammatory skin diseases and directly influences the susceptibility of skin to microbial infections. Our studies have recently exposed a newly identified pathway for negative regulation of AMPs in the skin by the cholinergic anti-inflammatory pathway via acetylcholine (ACh). The role of ACh in AMP regulation of immune and permeability barrier function in keratinocytes is reviewed, and the importance for a better comprehension of cutaneous disease progression by cholinergic signaling is discussed.

Estimulação tátil-cinestésica: uma integração entre pele e sistema endócrino?

Apresenta-se uma revisão da literatura sobre os aspectos neuroendócrinos da pele e as conseqüências da estimulação tátil-cinestésica sobre o córtex adrenal. Os artigos foram identificados a partir das bases de dados MEDLINE e LILACS, usando as palavras-chave "córtex supra-renal", "pele", "massagem", "lactentes", "glicocorticóide" e "ritmo circadiano". O período pesquisado foi de 1990 a 2003. Foram também consultados artigos de destaque publicados antes desse período. Estudos reconhecem o hipotálamo, a hipófise e a glândula adrenal como órgãos dinâmicos durante o desenvolvimento fetal e neonatal, e que respostas de estresse estão presentes ao nascer. A maioria dos estudos revisados, utilizando a estimulação tátil-cinestésica, seja em humanos ou animais, evidencia a capacidade da pele em metabolizar, coordenar e organizar estímulos externos, procurando manter a homeostase interna e externa, demonstrando a interação entre sistema neuroendócrino e a pele. A estimulação tátil-cinestésica parece ter um efeito sobre a reatividade hormonal, porém essa questão merece uma investigação mais aprofundada.

Dermatologic manifestations of hypopituitarism

Hypopituitarism is characterized by diminished or absent secretion of one or more pituitary hormones. The clinical features of hypopituitarism vary depending on age, rapidity of onset, hormones involved, and degree of deficiency. Dermatologic signs of hypopituitarism may involve alterations in pigmentation, the epidermal and dermal skin structures, and the pilosebaceous unit. We describe the causes and presentation of hypopituitarism with an emphasis on its dermatologic manifestations.

Retrospective evaluation of sex hormones and steroid hormone intermediates in dogs with alopecia

The purpose of this study was to determine if there are specific steroid hormone aberrations associated with suspect endocrine alopecias in dogs in whom hypothyroidism and hyperadrenocorticism have been excluded. Steroid hormone panels submitted to the UTCVM endocrinology laboratory over a 7.5-year period (783 samples) from dogs with alopecia were reviewed. During this period, 276 dogs met the criteria for inclusion and were comprised of 54 different breeds. Approximately 73% of dogs had at least one baseline or post-ACTH stimulation steroid hormone intermediate greater than the normal range. The most frequent hormone elevation noted was for progesterone (57.6% of samples). When compared with normal dogs, oestradiol was significantly greater in Keeshond dogs and progesterone was significantly greater in Pomeranian and Siberian Husky dogs. Not all individual dogs had hormone abnormalities. Chow Chow, Samoyed and Malamute dogs had the greatest percentage of normal steroid hormone intermediates of the dogs in this study. Baseline cortisol concentrations were significantly correlated with progesterone, 17-hydroxyprogesterone (17-OHP) and androstenedione. Results of this study suggest that the pathomechanism of the alopecia, at least for some breeds, may not relate to steroid hormone intermediates and emphasizes the need for breed specific normals.

Morfologia e histoquímica da pele de ratas hipotireóideas castradas e não castradas

Foram estudadas as alterações cutâneas de ratas Wistar adultas castradas e não castradas, mantidas em estado hipotireóideo por 120 dias. Dois grupos eutireóideos, um castrado e outro não castrado, serviram de controle. Secções da pele abdominal ventral e torácica dorsal foram coradas pelas técnicas de HE, PAS, azul de alcian (alcian blue), picro-sirius red-luz polarizada e Verhoeff. Adelgaçamento da epiderme, atrofia de glândulas sebáceas, redução parcial ou total de fibras elásticas e do colágeno do tipo III da derme caracterizaram tanto o hipotireoidismo quanto a castração. Retardo no crescimento dos folículos pilosos e hiperceratose foram vistos apenas na deficiência dos hormônios tireoidianos, independente do estado funcional das gônadas. A associação hipotireoidismo e castração caracterizou-se por adelgaçamento da epiderme da região abdominal ventral e espessamento e aumento da celularidade na região torácica dorsal, com derme adelgaçada e desprovida de fibras elásticas e de colágeno do tipo III. Conclui-se que a deficiência dos hormônios sexuais ou tireoidianos altera todos os componentes da pele e que as lesões são agravadas na associação hipotireoidismo-castração.

Melasma: histopathological characteristics in 56 Korean patients

BACKGROUND

Melasma is a common acquired symmetrical hypermelanosis characterized by irregular light to dark brown macules and patches on sun-exposed areas of the skin. Its histopathological characteristics are not fully understood.

OBJECTIVES

To characterize the histopathological features of facial melasma skin in comparison with adjacent normal skin.

METHODS

Biopsies were taken from both melasma lesional skin and adjacent perilesional normal skin in 56 Korean women with melasma. The sections were stained using haematoxylin and eosin, Fontana-Masson, diastase-resistant periodic acid-Schiff, Masson trichrome and Verhoeff-van Gieson stains, and immunostaining for melanocytes. Data on the changes in number of melanocytes and melanin contents of the epidermis were analysed by a computer-assisted image analysis program. The ultrastructure of the skin was also examined.

RESULTS

The amount of melanin was significantly increased in all epidermal layers in melasma skin. The staining intensity and number of epidermal melanocytes increased in melasma lesions. Lesional skin showed more prominent solar elastosis compared with normal skin. Melanosomes increased in number and were more widely dispersed in the keratinocytes of the lesional skin. Lesional melanocytes had many more mitochondria, Golgi apparatus, rough endoplasmic reticulum and ribosomes in their cytoplasm. A dihydroxyphenylalanine reaction was apparent in the cisternae and vesicles of the trans-Golgi network in melanocytes from lesional skin.

CONCLUSIONS

Melasma is characterized by epidermal hyperpigmentation, possibly caused both by an increased number of melanocytes and by an increased activity of melanogenic enzymes overlying dermal changes caused by solar radiation.

Xerosis in hypothyroidism: a potential role for the use of topical thyroid hormone in euthyroid patients

Xerosis is an extraordinarily common problem in dermatology. Despite the knowledge of well recognized aggravating factors, its etiology is an enigma, and the management of the condition is often suboptimal. Dry skin may be a manifestation of hypothyroidism. The nature of this association is reviewed, culminating in the speculation that topical thyroid hormone may represent a useful modality in euthyroid patients with xerosis or other disorders of keratinization.

The activity of fatty acid synthase of epidermal keratinocytes is regulated in the lower stratum spinousum and the stratum basale by local inflammation rather than by circulating hormones

The epidermal keratinocytes produce and secrete lipids to maintain the water barrier of the epidermis. To clarify the regulation of epidermal lipid synthesis, we investigated the hormonal effect on the activity of fatty acid synthase (FAS) of the keratinocytes, and the expression of FAS in the human skin. In cultured keratinocytes, the FAS activity, assayed by measuring the oxidation of NADPH, was slightly increased by hydrocortisone or testosterone, but not influenced by thyroid hormone, estrogen, progesterone or insulin. In immunohistochemical study of normal human epidermis, FAS was expressed strongly in the stratum granulosum and moderately in the uppermost layer of the stratum spinousum (SS), suggesting that fatty acid synthesis may increase during normal epidermal differentiation. In inflammatory disorders, such as psoriasis, lichen planus, and atopic dermatitis, FAS was also expressed in the lower SS and the stratum basale (SB), resulting in strong staining in the whole layers of the epidermis. Remarkable increase of FAS expression was only observed in the lower SS and the SB. Therefore, the activity of FAS in the epidermis may be regulated in the lower SS and the SB by local inflammation rather than by circulating hormones. In other components of the skin, FAS was strongly expressed not only in adipose tissue and sebaceous glands, which are known as active sites of lipid synthesis, but also in sweat glands, suggesting that the sweat glands can synthesize abundant fatty acids de novo.

Neuroendocrinology of the skin

The classical observations of the skin as a target for melanotropins have been complemented by the discovery of their actual production at the local level. In fact, all of the elements controlling the activity of the hypothalamus-pituitary-adrenal axis are expressed in the skin including CRH, urocortin, and POMC, with its products ACTH, alpha-MSH, and beta-endorphin. Demonstration of the corresponding receptors in the same cells suggests para- or autocrine mechanisms of action. These findings, together with the demonstration of cutaneous production of numerous other hormones including vitamin D3, PTH-related protein (PTHrP), catecholamines, and acetylcholine that share regulation by environmental stressors such as UV light, underlie a role for these agents in the skin response to stress. The endocrine mediators with their receptors are organized into dermal and epidermal units that allow precise control of their activity in a field-restricted manner. The skin neuroendocrine system communicates with itself and with the systemic level through humoral and neural pathways to induce vascular, immune, or pigmentary changes, to directly buffer noxious agents or neutralize the elicited local reactions. Therefore, we suggest that the skin neuroendocrine system acts by preserving and maintaining the skin structural and functional integrity and, by inference, systemic homeostasis.

Luteinizing hormone/human chorionic gonadotrophin receptors in various epidermal structures

Two different monoclonal antibodies recognizing different epitopes were used to study the localization of luteinizing hormone/human chorionic gonadotrophin (LH/hCG) receptors in human skin. Immunolabelling was observed only in the epidermis and derived structures but not in the dermis. The basal, spinal and granular layers were stained, whereas no receptors were detected in the non-nucleated horny cells. In the growing (anagen) hair, immunostaining was found in the inner root sheath below the level of the sebaceous glands and in the outer root sheath above this level. In the resting (telogen) hair, only the latter staining was observed. In the sebaceous glands, only the thin cells close to the walls of the ducts were immunolabelled. In the eccrine sweat glands, the external clear cells were stained in the secretory portion of the gland, whereas only the cells close to the lumen were labelled in the ducts. The distribution of LH/hCG receptors was compared with that of steroidogenic enzymes (side chain cleavage cytochrome P450, adrenodoxin, 3-beta-hydroxy-5-ene steroid dehydrogenase Delta5-Delta4 isomerase, 17-hydroxylase cytochrome P450 and cytochrome P450 aromatase). Only partial overlaps were observed. The presence of LH receptor mRNA in the skin was confirmed by reverse transcription-polymerase chain reaction. Monoclonal antibodies raised against the human follicle-stimulating hormone receptor failed to detect the latter in the epidermal structures and in the dermis. The role of LH and hCG in skin modifications occurring during pregnancy and after the menopause is unknown. These hormones may possibly act by regulating steroidogenic enzymes or by modulating cell growth and differentiation.

Risk factors for reduced skin thickness and bone density: possible clues regarding pathophysiology, prevention, and treatment

The decline in skin thickness that occurs with aging interests many different groups. Among these are pharmaceutical, cosmeceutical, and cosmetic companies promoting antiaging or antiwrinkling products, geriatricians and rheumatologists treating elderly and steroid-dependent patients who are "outliving" their skin, cosmetic surgeons, and dermatologists. Dermatologists are frequently asked how to prevent or slow aging of the skin. The answer regarding "photoaging" of sun-exposed skin is obvious; the answer regarding aging of photoprotected skin is not. Although the bulk of epidemiologic literature about aging and thinning of photoprotected skin is from the 1970s, literature regarding risk factors for and treatment of aging and thinning of the bony skeleton is more recent. Because both skin and bone are composed of more than 70% type I collagen, it may be hypothesized that the pathophysiologic processes involved in chronological atrophy of both tissues may overlap, thereby providing a foundation for further investigation of the skin. A better understanding of skin and bone loss may motivate the "appearance-conscious" public to modify risk factors (e.g., begin exercising) or select hormonal therapies (e.g., postmenopausal hormone replacement) to reduce aging of the skin. These measures may provide additional benefits, such as decreasing the risk of osteoporosis.

Activation of keratinocyte nicotinic cholinergic receptors stimulates calcium influx and enhances cell differentiation

Human epidermal keratinocytes synthesize, secrete, and degrade acetylcholine and use their cell-surface nicotinic and muscarinic cholinergic receptors to mediate the autocrine and paracrine effects of acetyl-choline. Because acetylcholine modulates transmembrane Ca2+ transport and intracellular metabolism in several types of cells, we hypothesized that cholinergic agents might have similar effects on keratinocytes. Nicotine increased in a concentration-dependent manner the amount of 45Ca2+ taken up by keratinocytes isolated from human neonatal fore-skins. This effect was abolished in the presence of the specific nicotinic antagonist mecamylamine, indicating that it was mediated by keratinocyte nicotinic acetylcholine receptor(s). The sequences encoding the alpha 5 and alpha 7 nicotinic receptor subunits were amplified from cDNA isolated from cultured keratinocytes. These subunits, as well as the alpha 3, beta 2, and beta 4 subunits previously found in keratinocytes, can be components of Ca(2+)-permeable nicotinic receptor channels. To learn how activation of keratinocyte nicotinic receptors affected the rate of cell differentiation, we measured the nicotinic cholinergic effects on the expression of differentiation markers by cultured keratinocytes. Long-term incubations with micromolar concentrations of nicotine markedly increased the number of cells forming cornified envelopes and the number of cells staining with antibodies to suprabasal keratin 10, transglutaminase type I, involucrin, and filaggrin. The increased production of these differentiation-associated proteins was verified by Western blotting. Because nicotinic cholinergic stimulation causes transmembrane Ca2+ transport into keratinocytes, and because changes in concentrations of intracellular Ca2+ are known to alter various keratinocyte functions, including differentiation, the subcellular mechanisms mediating the autocrine and paracrine actions of epidermal acetylcholine on keratinocytes may involve Ca2+ as a second messenger.