Corticotropin-releasing hormone induces keratinocyte differentiation in the adult human epidermis

Exploring the interplay between stress mediators and skin microbiota in shaping age-related hallmarks: A review

Psychological stress is a major contributing factor to several health problems (e.g., depression, cardiovascular disease). Around 35 % of the world's population suffers from it, including younger generations. Physiologically, stress manifests through neuroendocrine pathways (Hypothalamic-Pituitary-Adrenal (HPA) axis and Sympathetic-Adrenal-Medullary (SAM) system) which culminate in the production of stress mediators like cortisol, epinephrine and norepinephrine. Stress and its mediators have been associated to body aging, through molecular mechanisms such as telomere attrition, mitochondrial dysfunction, cellular senescence, chronic inflammation, and dysbiosis, among others. Regarding its impact in the skin, stress impacts its structural integrity and physiological function. Despite this review focusing on several hallmarks of aging, emphasis was placed on skin microbiota dysbiosis. In this line, several studies, comprising different age groups, demographic contexts and body sites, have reported skin microbiota alterations associated with aging, and some effects of stress mediators on skin microbiota have also been reviewed in this paper. From a different perspective, since it is not a "traditional" stress mediator, oxytocin, a cortisol antagonist, has been related to glucorticoids inhibition and to display positive effects on cellular aging. This hormone dysregulation has been associated to psychological issues such as depression, whereas its upregulation has been linked to positive social interaction.

Integrated transcriptomic and metabolomic investigation of the genes and metabolites involved in swine follicular cyst formation

Follicular cysts are a common reproductive disorder in mammals that is usually caused by stress. However, the pathogenesis of follicular cysts in sows remains unclear. To provide new insights into the mechanisms of follicular cyst formation in pigs, we conducted a combined transcriptomic and metabolomic analysis on theca interna and mural granulosa cells of follicular cysts and mature follicles. We identified 2,533 up-regulated and 1,355 down-regulated genes in follicular cysts, compared with mature follicles. These differentially expressed genes were mainly found in signaling pathways related to tumor formation and cortisol synthesis and secretion as shown by Ingenuity Pathway Analysis, which predicted 4,362 upstream regulatory factors. The combined gene expression and pathway analysis identified the following genes as potential biomarkers for porcine follicular cysts: cytochrome P450 family 2 subfamily C polypeptide 18, L-lactate dehydrogenase, carbamoyl-phosphate synthase, fibroblast growth factor 7, integrin binding sialoprotein, interleukin 23 receptor, prolactin receptor, epiregulin, interleukin 1 receptor type II, arginine vasopressin receptor 1A, fibroblast growth factor 10, claudin 7, G Protein Subunit Gamma 3, cholecystokinin B receptor and cytosolic phospholipase A2. Metabolomics analysis found significant differences in 87 metabolites, which were enriched in unsaturated fatty acid biosynthesis, and sphingolipid signaling pathways. These results provide valuable information on the molecular mechanisms of follicular cyst formation, which may facilitate the development of new therapeutics to prevent and treat follicular cysts.

Polymorphisms in corticotrophin-releasing hormone-proopiomalanocortin (CRH-POMC) system genes: Neuroimmune contributions to psoriasis disease

BACKGROUND

Skin is a target organ and source of the corticotropin-releasing hormone-proopiomelanocortin (CRH-POMC) system, operating as a coordinator and executor of responses to stress. Environmental stress exacerbates and triggers inflammatory skin diseases through modifying the cellular components of the immune system supporting the importance of CRH-POMC system in the pathogenesis of psoriasis. The aim of this study was to analyse the association of CRH-POMC polymorphisms with psoriasis and evaluate transcript expression of lesional psoriatic and normal skin in RNA-seq data.

METHODS

Samples of 104 patients with psoriasis and 174 healthy controls were genotyped for 42 single nucleotide polymorphisms (SNPs) of CRH-POMC using Applied Biosystems SNPlex™ method. The transcript quantification was performed using Salmon software v1.3.0.

RESULTS

This study demonstrated the associations between melanocortin 1 receptor (MC1R) polymorphisms rs2228479, rs3212369, dopachrome tautomerase (DCT) polymorphisms rs7987802, rs2031526, rs9524501 and psoriasis in the Tatar population. Very strong association was evident for the SNP rs7987802 in the DCT gene (pc  = 5.95е-006) in psoriasis patients. Additionally, the haplotype analysis provided AT DCT (rs7992630 and rs7987802) and AGA MC1R (rs3212358, 2228479 and 885479) haplotypes significantly associated (pc  ˂ 0.05) with psoriasis in the Tatar population, supporting the involvement of DCT and MC1R to the psoriasis susceptibility. Moreover, MC1R-203 and DCT-201 expression levels were decreased in psoriasis lesional skin compared with healthy control skin.

CONCLUSIONS

This study is the first to identify genetic variants of the MC1R and DCT genes significantly associated with psoriasis in Tatar population. Our results support potential roles of CRH-POMC system genes and DCT in the pathogenesis of psoriasis.

Neuroendocrine signaling in the skin with a special focus on the epidermal neuropeptides

The skin, which is comprised of the epidermis, dermis, and subcutaneous tissue, is the largest organ in the human body and it plays a crucial role in the regulation of the body's homeostasis. These functions are regulated by local neuroendocrine and immune systems with a plethora of signaling molecules produced by resident and immune cells. In addition, neurotransmitters, endocrine factors, neuropeptides, and cytokines released from nerve endings play a central role in the skin's responses to stress. These molecules act on the corresponding receptors in an intra-, juxta-, para-, or autocrine fashion. The epidermis as the outer most component of skin forms a barrier directly protecting against environmental stressors. This protection is assured by an intrinsic keratinocyte differentiation program, pigmentary system, and local nervous, immune, endocrine, and microbiome elements. These constituents communicate cross-functionally among themselves and with corresponding systems in the dermis and hypodermis to secure the basic epidermal functions to maintain local (skin) and global (systemic) homeostasis. The neurohormonal mediators and cytokines used in these communications regulate physiological skin functions separately or in concert. Disturbances in the functions in these systems lead to cutaneous pathology that includes inflammatory (i.e., psoriasis, allergic, or atopic dermatitis, etc.) and keratinocytic hyperproliferative disorders (i.e., seborrheic and solar keratoses), dysfunction of adnexal structure (i.e., hair follicles, eccrine, and sebaceous glands), hypersensitivity reactions, pigmentary disorders (vitiligo, melasma, and hypo- or hyperpigmentary responses), premature aging, and malignancies (melanoma and nonmelanoma skin cancers). These cellular, molecular, and neural components preserve skin integrity and protect against skin pathologies and can act as "messengers of the skin" to the central organs, all to preserve organismal survival.

Type 1 Corticotropin-Releasing Factor Receptor Differentially Modulates Neurotransmitter Levels in the Nucleus Accumbens of Juvenile versus Adult Rats

Adversity is particularly pernicious in early life, increasing the likelihood of developing psychiatric disorders in adulthood. Juvenile and adult rats exposed to social isolation show differences in anxiety-like behaviors and significant changes in dopamine (DA) neurotransmission in the nucleus accumbens (NAc). Brain response to stress is partly mediated by the corticotropin-releasing factor (CRF) system, composed of CRF and its two main receptors, CRF-R1 and CRF-R2. In the NAc shell of adult rats, CRF induces anxiety-like behavior and changes local DA balance. However, the role of CRF receptors in the control of neurotransmission in the NAc is not fully understood, nor is it known whether there are differences between life stages. Our previous data showed that infusion of a CRF-R1 antagonist into the NAc of juvenile rats increased DA levels in response to a depolarizing stimulus and decreased basal glutamate levels. To extend this analysis, we now evaluated the effect of a CRF-R1 antagonist infusion in the NAc of adult rats. Here, we describe that the opposite occurred in the NAc of adult compared to juvenile rats. Infusion of a CRF-R1 antagonist decreased DA and increased glutamate levels in response to a depolarizing stimulus. Furthermore, basal levels of DA, glutamate, and γ-Aminobutyric acid (GABA) were similar in juvenile animals compared to adults. CRF-R1 protein levels and localization were not different in juvenile compared to adult rats. Interestingly, we observed differences in the signaling pathways of CRF-R1 in the NAc of juveniles compared to adult rats. We propose that the function of CRF-R1 receptors is differentially modulated in the NAc according to life stage.

The Brain-Skin Axis in Psoriasis-Psychological, Psychiatric, Hormonal, and Dermatological Aspects

Psoriasis is a chronic inflammatory skin disease with systemic manifestation, in which psychological factors play an important role. The etiology of psoriasis is complex and multifactorial, including genetic background and environmental factors such as emotional or physical stress. Psychological stress may also play a role in exacerbation of psoriasis, by dysregulation of the hypothalamic–pituitary–adrenal (HPA) axis, sympathetic–adrenal–medullary axis, peripheral nervous system, and immune system. Skin cells also express various neuropeptides and hormones in response to stress, including the fully functional analog of the HPA axis. The deterioration of psoriatic lesions is accompanied by increased production of inflammatory mediators, which could contribute to the imbalance of neurotransmitters and the development of symptoms of depression and anxiety. Therefore, deregulation of the crosstalk between endocrine, paracrine, and autocrine stress signaling pathways contributes to clinical manifestations of psoriasis, which requires multidisciplinary approaches.

Modulation of dermal equivalent of hypothalamus-pituitary-adrenal axis in mastocytosis

Introduction

Mastocytosis is a rare disease characterized by abnormal growth and accumulation of tissue mast cells (MC) in one or more organ systems and is classified as being either cutaneous mastocytosis (CM) or systemic mastocytosis (SM). In the pioneer studies of Slominski's group, a fully functional hypothalamic-pituitary-adrenal axis equivalent has been discovered in various tissues, including skin.

Aim

In the present study we investigated potential involvement of hypothalamus-pituitary-adrenal (HPA) cutaneous equivalent in ongoing mastocytosis.

Material and methods

The expression of HPA elements: CRH, UCN1, UCN2, UCN3, CRHR1, POMC, MC1R, MC2R and NR3C1 was assessed for their mRNA level in skin biopsies of adult patients with mastocytosis and healthy donors (n = 16 and 19, respectively), while CRH, UCN1, CRHR1, ACTH and MC1R were selected for immunostaining assay (n = 13 and 7, respectively). The expression of CRH receptor 1 (CRHR1) isomers was investigated by RT-PCR. The ELISA was used for detection of cortisol, CRH, UCN and ACTH in the serum.

Results

The decrease in the expression of HPA element of skin equivalent was observed on both mRNA and protein levels, however quantification of immunohistochemical data was impeded due to melanin in epidermis. Furthermore, we observed infiltration of dermis with HPA elements overexpressing mononuclear cells, which is in the agreement with an in vitro study showing a high expression of HPA elements by mast cells.

Conclusions

Taken together, it was confirmed that the expression elements of HPA was modulated in mastocytosis, thus the potential involvement of general and local stress responses in its pathogenesis should be postulated and further investigated.

The significance of CYP11A1 expression in skin physiology and pathology

CYP11A1, a member of the cytochrome P450 family, plays several key roles in the human body. It catalyzes the first and rate-limiting step in steroidogenesis, converting cholesterol to pregnenolone. Aside from the classical steroidogenic tissues such as the adrenals, gonads and placenta, CYP11A1 has also been found in the brain, gastrointestinal tract, immune systems, and finally the skin. CYP11A1 activity in the skin is regulated predominately by StAR protein and hence cholesterol levels in the mitochondria. However, UVB, UVC, CRH, ACTH, cAMP, and cytokines IL-1, IL-6 and TNFα can also regulate its expression and activity. Indeed, CYP11A1 plays several critical roles in the skin through its initiation of local steroidogenesis and specific metabolism of vitamin D, lumisterol, and 7-dehydrocholesterol. Products of these pathways regulate the protective barrier and skin immune functions in a context-dependent fashion through interactions with a number of receptors. Disturbances in CYP11A1 activity can lead to skin pathology.

Insights into interplay of immunopathophysiological events and molecular mechanistic cascades in psoriasis and its associated comorbidities

Psoriasis is an inflammatory skin disease with complex pathogenesis and multiple etiological factors. Besides the essential role of autoreactive T cells and constellation of cytokines, the discovery of IL-23/Th17 axis as a central signaling pathway has unraveled the mechanism of accelerated inflammation in psoriasis. This has provided insights into psoriasis pathogenesis and revolutionized the development of effective biological therapies. Moreover, genome-wide association studies have identified several candidate genes and susceptibility loci associated with this disease. Although involvement of cellular innate and adaptive immune responses and dysregulation of immune cells have been implicated in psoriasis initiation and maintenance, there is still a lack of unifying mechanism for understanding the pathogenesis of this disease. Emerging evidence suggests that psoriasis is a high-mortality disease with additional burden of comorbidities, which adversely affects the treatment response and overall quality of life of patients. Furthermore, changing trends of psoriasis-associated comorbidities and shared patterns of genetic susceptibility, risk factors and pathophysiological mechanisms manifest psoriasis as a multifactorial systemic disease. This review highlights the recent progress in understanding the crucial role of different immune cells, proinflammatory cytokines and microRNAs in psoriasis pathogenesis. In addition, we comprehensively discuss the involvement of various complex signaling pathways and their interplay with immune cell markers to comprehend the underlying pathophysiological mechanism, which may lead to exploration of new therapeutic targets and development of novel treatment strategies to reduce the disastrous nature of psoriasis and associated comorbidities.

New effects of caffeine on corticotropin-releasing hormone (CRH)-induced stress along the intrafollicular classical hypothalamic-pituitary-adrenal (HPA) axis (CRH-R1/2, IP3 -R, ACTH, MC-R2) and the neurogenic non-HPA axis (substance P, p75NTR and TrkA) in ex vivo human male androgenetic scalp hair follicles

BACKGROUND

Human hair is highly responsive to stress, and human scalp hair follicles (HFs) contain a peripheral neuroendocrine equivalent of the systemic hypothalamic-pituitary-adrenal (HPA) stress axis. Androgenetic alopecia (AGA) is supposed to be aggravated by stress. We used corticotropin-releasing hormone (CRH), which triggers the HPA axis, to induce a stress response in human ex vivo male AGA HFs. Caffeine is known to reverse testosterone-mediated hair growth inhibition in the same hair organ culture model.

OBJECTIVES

To investigate whether caffeine would antagonize CRH-mediated stress in these HFs.

METHODS

HFs from balding vertex area scalp biopsies of men affected by AGA were incubated with CRH (10-7 mol L-1 ) with or without caffeine (0·001% or 0·005%).

RESULTS

Compared to controls, CRH significantly enhanced the expression of catagen-inducing transforming growth factor-β2 (TGF-β2) (P < 0·001), CRH receptors 1 and 2 (CRH-R1/2) (P < 0·01), adrenocorticotropic hormone (ACTH) (P < 0·001) and melanocortin receptor 2 (MC-R2) (P < 0·001), and additional stress-associated parameters, substance P and p75 neurotrophin receptor (p75NTR ). CRH inhibited matrix keratinocyte proliferation and expression of anagen-promoting insulin-like growth factor-1 (IGF-1) and the pro-proliferative nerve growth factor receptor NGF-tyrosine kinase receptor A (TrkA). Caffeine significantly counteracted all described stress effects and additionally enhanced inositol trisphosphate receptor (IP3 -R), for the first time detected in human HFs.

CONCLUSIONS

These findings provide the first evidence in ex vivo human AGA HFs that the stress mediator CRH induces not only a complex intrafollicular HPA response, but also a non-HPA-related stress response. Moreover, we show that these effects can be effectively antagonized by caffeine. Thus, these data strongly support the hypothesis that stress can impair human hair physiology and induce hair loss, and that caffeine may effectively counteract stress-induced hair damage and possibly prevent stress-induced hair loss.

The local hypothalamic-pituitary-adrenal axis in cultured human dermal papilla cells

BACKGROUND

Stress is an important cause of skin disease, including hair loss. The hormonal response to stress is due to the HPA axis, which comprises hormones such as corticotropin releasing factor (CRF), adrenocorticotropic hormone (ACTH), and cortisol. Many reports have shown that CRF, a crucial stress hormone, inhibits hair growth and induces hair loss. However, the underlying mechanisms are still unclear. The aim of this study was to examine the effect of CRF on human dermal papilla cells (DPCs) as well as hair follicles and to investigate whether the HPA axis was established in cultured human DPCs.

RESULTS

CRF inhibited hair shaft elongation and induced early catagen transition in human hair follicles. Hair follicle cells, both human DPCs and human ORSCs, expressed CRF and its receptors and responded to CRF. CRF inhibited the proliferation of human DPCs through cell cycle arrest at G2/M phase and induced the accumulation of reactive oxygen species (ROS). Anagen-related cytokine levels were downregulated in CRF-treated human DPCs. Interestingly, increases in proopiomelanocortin (POMC), ACTH, and cortisol were induced by CRF in human DPCs, and antagonists for the CRF receptor blocked the effects of this hormone.

CONCLUSION

The results of this study showed that stress can cause hair loss by acting through stress hormones. Additionally, these results suggested that a fully functional HPA axis exists in human DPCs and that CRF directly affects human DPCs as well as human hair follicles under stress conditions.

Neuroendocrinology and neurobiology of sebaceous glands

The nervous system communicates with peripheral tissues through nerve fibres and the systemic release of hypothalamic and pituitary neurohormones. Communication between the nervous system and the largest human organ, skin, has traditionally received little attention. In particular, the neuro-regulation of sebaceous glands (SGs), a major skin appendage, is rarely considered. Yet, it is clear that the SG is under stringent pituitary control, and forms a fascinating, clinically relevant peripheral target organ in which to study the neuroendocrine and neural regulation of epithelia. Sebum, the major secretory product of the SG, is composed of a complex mixture of lipids resulting from the holocrine secretion of specialised epithelial cells (sebocytes). It is indicative of a role of the neuroendocrine system in SG function that excess circulating levels of growth hormone, thyroxine or prolactin result in increased sebum production (seborrhoea). Conversely, growth hormone deficiency, hypothyroidism, and adrenal insufficiency result in reduced sebum production and dry skin. Furthermore, the androgen sensitivity of SGs appears to be under neuroendocrine control, as hypophysectomy (removal of the pituitary) renders SGs largely insensitive to stimulation by testosterone, which is crucial for maintaining SG homeostasis. However, several neurohormones, such as adrenocorticotropic hormone and α-melanocyte-stimulating hormone, can stimulate sebum production independently of either the testes or the adrenal glands, further underscoring the importance of neuroendocrine control in SG biology. Moreover, sebocytes synthesise several neurohormones and express their receptors, suggestive of the presence of neuro-autocrine mechanisms of sebocyte modulation. Aside from the neuroendocrine system, it is conceivable that secretion of neuropeptides and neurotransmitters from cutaneous nerve endings may also act on sebocytes or their progenitors, given that the skin is richly innervated. However, to date, the neural controls of SG development and function remain poorly investigated and incompletely understood. Botulinum toxin-mediated or facial paresis-associated reduction of human sebum secretion suggests that cutaneous nerve-derived substances modulate lipid and inflammatory cytokine synthesis by sebocytes, possibly implicating the nervous system in acne pathogenesis. Additionally, evidence suggests that cutaneous denervation in mice alters the expression of key regulators of SG homeostasis. In this review, we examine the current evidence regarding neuroendocrine and neurobiological regulation of human SG function in physiology and pathology. We further call attention to this line of research as an instructive model for probing and therapeutically manipulating the mechanistic links between the nervous system and mammalian skin.

Is prolactin a negative neuroendocrine regulator of human skin re-epithelisation after wounding?

Chronic wounds remain a major unmet healthcare challenge, associated with substantial morbidity and economic costs. Therefore, novel treatment strategies and therapeutic approaches need to be urgently developed. Yet, despite the increasingly recognized importance of neurohormonal signaling in skin physiology, the neuroendocrine regulation of cutaneous wound healing has received surprisingly little attention. Human skin, and its appendages, locally express the pleiotropic neurohormone prolactin (PRL), which not only regulates lactation but also hair follicle cycling, angiogenesis, keratinocyte proliferation, and epithelial stem cell functions. Therefore, we examined the effects of PRL in experimentally wounded female human skin organ culture. Overall, this revealed that PRL slightly, but significantly, inhibited epidermal regeneration (reepithelialisation), cytokeratin 6 protein expression and intraepidermal mitochondrial activity (MTCO1 expression), while it promoted keratinocyte terminal differentiation (i.e. involucrin expression) ex vivo. If the current pilot data are confirmed by further studies, PRL may serve as one of the-rarely studied-negative regulators of cutaneous wound healing that control excessive reepithelialisation. This raises the intriguing and clinically relevant question of whether PRL receptor antagonists could actually promote epidermal repair after human skin wounding.

Association between Stress and the HPA Axis in the Atopic Dermatitis

The hypothalamic–pituitary–adrenal (HPA) axis is one of the body’s neuroendocrine networks that responds to psychological stress (PS). In the skin, there exists a peripheral HPA axis similar to the central axis. Glucocorticoids (GCs) are key effector molecules of the HPA axis and are essential for cutaneous homeostasis. Atopic dermatitis (AD) is a condition typically characterized by a chronic relapsing course that often results in PS. HPA dysfunction is present in AD patients by the decreased response of GCs elevation to stress as compared to those unaffected by AD. Nevertheless, in skin, acute PS activates several metabolic responses that are of immediate benefit to the host. During the acute phase of PS, increased endogenous GCs have been shown to provide benefit rather than by aggravating cutaneous inflammatory dermatoses. However, a chronic T helper cell type 2 (Th2) predominant cytokine profile acts as a negative feedback loop to blunt the HPA axis response in AD. In this article, we reviewed the role of CRF, pro-opiomelanocortin (POMC)-derived peptides, GCs of the HPA, and 11β-hydroxysteroid dehydrogenase 1 (11β-HSD1) in AD, with a discussion of the pathogenetic mechanisms of inflammation and skin barrier functions, including antimicrobial defense, and their association with PS.

Differentiation of Keratinocytes Modulates Skin HPA Analog

It is well established, that epidermal keratinocytes express functional equivalent of hypothalamus-pituitary-adrenal axis (HPA) in order to respond to changing environment and maintain internal homeostasis. We are presenting data indicating that differentiation of primary neonatal human keratinocytes (HPEKp), induced by prolonged incubation or calcium is accompanied by significant changes in the expression of the elements of skin analog of HPA (sHPA). Expression of CRF, UCN1-3, POMC, ACTH, CRFR1, CRFR2, MC1R, MC2R, and GR (coded by NR3C1 gene) were observed on gene/protein levels along differentiation of keratinocytes in culture with similar pattern seen by immunohistochemistry on full thickness skin biopsies. Expression of CRF was more pronounced in less differentiated keratinocytes, which corresponded to the detection of CRF immunoreactivity preferentially in the stratum basale. POMC expression was enhanced in more differentiated keratinocytes, which corresponded to detection of ACTH immunoreactivity, predominantly in the stratum spinosum and stratum granulosum. Expression of urocortins was also affected by induction of HPEKp differentiation. Immunohistochemical studies showed high prevalence of CRFR1 in well differentiated keratinocytes, while smaller keratinocytes showed predominantly CRFR2 immunoreactivity. MC2R mRNA levels were elevated from days 4 to 8 of in vitro incubation, while MC2R immunoreactivity was the highest in the upper layers of epidermis. Similar changes in mRNA/protein levels of sHPA elements were observed in HPEKp keratinocytes treated with calcium. Summarizing, preferential expression of CRF and POMC (ACTH) by populations of keratinocytes on different stage of differentiation resembles organization of central HPA axis suggesting their distinct role in physiology and pathology of the epidermis. J. Cell. Physiol. 232: 154-166, 2017. © 2016 Wiley Periodicals, Inc.

Inhibiting interleukin-18 production through the mitogen-activated protein kinase pathway, a potential role of corticotropin-releasing hormone in chronic plaque psoriasis

Corticotropin-releasing hormone (CRH) and CRH receptors (CRH-Rs) are expressed in the skin; CRH-R1 is the predominant receptor. Whether the CRH/CRH-R1 system plays a role in psoriasis has not yet been assessed. Immunohistochemistry, real-time RT-PCR, ELISA assay, and Western blot analysis were used to investigate the expression of CRH/CRH-R1 in patients with chronic plaque psoriasis and that of IL-18 in CRH-treated HaCaT cells. CRH and CRH-R1 were downregulated in patients with chronic plaque psoriasis. In vitro, CRH attenuated the expression of IL-18 by a mitogen-activated protein kinase signaling pathway through CRH-R1 in HaCaT cells. Thus, an aberrant cutaneous CRH/CRH-R1 system exists in lesions from chronic plaque psoriasis which might play a role in psoriasis and offers further evidence for the study of CRH in the skin.

On the role of skin in the regulation of local and systemic steroidogenic activities

The mammalian skin is a heterogeneous organ/tissue covering our body, showing regional variations and endowed with neuroendocrine activities. The latter is represented by its ability to produce and respond to neurotransmitters, neuropeptides, hormones and neurohormones, of which expression and phenotypic activities can be modified by ultraviolet radiation, chemical and physical factors, as well as by cytokines. The neuroendocrine contribution to the responses of skin to stress is served, in part, by local synthesis of all elements of the hypothalamo-pituitary-adrenal axis. Skin with subcutis can also be classified as a steroidogenic tissue because it expresses the enzyme, CYP11A1, which initiates steroid synthesis by converting cholesterol to pregnenolone, as in other steroidogenic tissues. Pregnenolone, or steroidal precursors from the circulation, are further transformed in the skin to corticosteroids or sex hormones. Furthermore, in the skin CYP11A1 acts on 7-dehydrocholesterol with production of 7-dehydropregnolone, which can be further metabolized to other Δ7steroids, which after exposure to UVB undergo photochemical transformation to vitamin D like compounds with a short side chain. Vitamin D and lumisterol, produced in the skin after exposure to UVB, are also metabolized by CYP11A1 to several hydroxyderivatives. Vitamin D hydroxyderivatives generated by action of CYP11A1 are biologically active and are subject to further hydroxylations by CYP27B1, CYP27A1 and CP24A. Establishment of which intermediates are produced in the epidermis in vivo and whether they circulate on the systemic level represent a future research challenge. In summary, skin is a neuroendocrine organ endowed with steroid/secosteroidogenic activities.

CP-154,526 Modifies CREB Phosphorylation and Thioredoxin-1 Expression in the Dentate Gyrus following Morphine-Induced Conditioned Place Preference

Corticotropin-releasing factor (CRF) acts as neuro-regulator of the behavioral and emotional integration of environmental and endogenous stimuli associated with drug dependence. Thioredoxin-1 (Trx-1) is a functional protein controlling the redox status of several proteins, which is involved in addictive processes. In the present study, we have evaluated the role of CRF1 receptor (CRF1R) in the rewarding properties of morphine by using the conditioned place preference (CPP) paradigm. We also investigate the effects of the CRF1R antagonist, CP-154,526, on the morphine CPP-induced activation of CRF neurons, CREB phosphorylation and Trx expression in paraventricular nucleus (PVN) and dentate gyrus (DG) of the mice brain. CP-154,526 abolished the acquisition of morphine CPP and the increase of CRF/pCREB positive neurons in PVN. Moreover, this CRF1R antagonist prevented morphine-induced CRF-immunoreactive fibers in DG, as well as the increase in pCREB expression in both the PVN and DG. In addition, morphine exposure induced an increase in Trx-1 expression in DG without any alterations in PVN. We also observed that the majority of pCREB positive neurons in DG co-expressed Trx-1, suggesting that Trx-1 could activate CREB in the DG, a brain region involved in memory consolidation. Altogether, these results support the idea that CRF1R antagonist blocked Trx-1 expression and pCREB/Trx-1 co-localization, indicating a critical role of CRF, through CRF1R, in molecular changes involved in morphine associated behaviors.

Brain-skin connection: stress, inflammation and skin aging

The intricate relationship between stress and skin conditions has been documented since ancient times. Recent clinical observations also link psychological stress to the onset or aggravation of multiple skin diseases. However, the exact underlying mechanisms have only been studied and partially revealed in the past 20 years or so. In this review, the authors will discuss the recent discoveries in the field of “Brain-Skin Connection”, summarizing findings from the overlapping fields of psychology, endocrinology, skin neurobiology, skin inflammation, immunology, and pharmacology.

Key role of CRF in the skin stress response system

The discovery of corticotropin-releasing factor (CRF) or CRH defining the upper regulatory arm of the hypothalamic-pituitary-adrenal (HPA) axis, along with the identification of the corresponding receptors (CRFRs 1 and 2), represents a milestone in our understanding of central mechanisms regulating body and local homeostasis. We focused on the CRF-led signaling systems in the skin and offer a model for regulation of peripheral homeostasis based on the interaction of CRF and the structurally related urocortins with corresponding receptors and the resulting direct or indirect phenotypic effects that include regulation of epidermal barrier function, skin immune, pigmentary, adnexal, and dermal functions necessary to maintain local and systemic homeostasis. The regulatory modes of action include the classical CRF-led cutaneous equivalent of the central HPA axis, the expression and function of CRF and related peptides, and the stimulation of pro-opiomelanocortin peptides or cytokines. The key regulatory role is assigned to the CRFR-1α receptor, with other isoforms having modulatory effects. CRF can be released from sensory nerves and immune cells in response to emotional and environmental stressors. The expression sequence of peptides includes urocortin/CRF→pro-opiomelanocortin→ACTH, MSH, and β-endorphin. Expression of these peptides and of CRFR-1α is environmentally regulated, and their dysfunction can lead to skin and systemic diseases. Environmentally stressed skin can activate both the central and local HPA axis through either sensory nerves or humoral factors to turn on homeostatic responses counteracting cutaneous and systemic environmental damage. CRF and CRFR-1 may constitute novel targets through the use of specific agonists or antagonists, especially for therapy of skin diseases that worsen with stress, such as atopic dermatitis and psoriasis.

Role of neuropeptides, neurotrophins, and neurohormones in skin wound healing

Due to the close interactions between the skin and peripheral nervous system, there is increasing evidence that the cutaneous innervation is an important modulator of the normal wound healing process. The communication between sensory neurons and skin cells involves a variety of molecules (neuropeptides, neurohormones, and neurotrophins) and their specific receptors expressed by both neuronal and nonneuronal skin cells. It is well established that neurotransmitters and nerve growth factors released in skin have immunoregulatory roles and can exert mitogenic actions; they could also influence the functions of the different skin cell types during the wound healing process.

Corticotropin-releasing hormone exerts direct effects on neuronal progenitor cells: implications for neuroprotection

Neurogenesis during embryonic and adult life is tightly regulated by a network of transcriptional, growth and hormonal factors. Emerging evidence indicates that activation of the stress response, via the associated glucocorticoid increase, reduces neurogenesis and contributes to the development of adult diseases.As corticotrophin-releasing hormone (CRH) or factor is the major mediator of adaptive response to stressors, we sought to investigate its involvement in this process. Accordingly, we found that CRH could reverse the damaging effects of glucocorticoid on neural stem/progenitor cells (NS/PCs), while its genetic deficiency results in compromised proliferation and enhanced apoptosis during neurogenesis. Analyses in fetal and adult mouse brain revealed significant expression of CRH receptors in proliferating neuronal progenitors. Furthermore, by using primary cultures of NS/PCs, we characterized the molecular mechanisms and identified CRH receptor-1 as the receptor mediating the neuroprotective effects of CRH. Finally, we demonstrate the expression of CRH receptors in human fetal brain from early gestational age, in areas of active neuronal proliferation. These observations raise the intriguing possibility for CRH-mediated pharmacological applications in diseases characterized by altered neuronal homeostasis, including depression, dementia, neurodegenerative diseases, brain traumas and obesity.

Cutaneous hypothalamic-pituitary-adrenal axis homolog: regulation by ultraviolet radiation

The hypothalamic-pituitary-adrenal (HPA) axis maintains basal and stress-related homeostasis in vertebrates. Skin expresses all elements of the HPA axis including corticotropin-releasing hormone (CRH), proopiomelanocortin (POMC), ACTH, β-endorphin (β-END) with corresponding receptors, the glucocorticoidogenic pathway, and the glucocorticoid receptor (GR). To test the hypothesis that cutaneous responses to environmental stressors follow the organizational structure of the central response to stress, the activity of the "cutaneous HPA" axis homolog was investigated after exposure to ultraviolet radiation (UVR) wavelengths of UVA (320-400 nm), UVB (280-320 nm), and UVC (100-280 nm) in human skin organ culture and in co-cultured keratinocytes/melanocytes. The level of stimulation of CRH, POMC, MC1R, MC2R, CYP11A1, and CYP11B1 genes was dependent on UV wavelengths and doses, with the highest effects observed for highly energetic UVC and UVB. ELISA and Western assays showed significant production of CRH, POMC, ACTH, and CYP11A1 proteins and of cortisol, with a decrease in GR expression only after UVB and UVC. However, β-END expression was also stimulated by UVA. Immunocytochemistry localized the deposition of the aforesaid antigens predominantly to the epidermis with additional accumulation of CRH, β-END, and ACTH in the dermis. UVR-stimulated CYP11A1 expression was seen in the basal layer of the epidermis and cells of adjacent dermis. Thus, the capacity to activate or change the spatial distribution of the cutaneous HPA axis elements is dependent on highly energetic wavelengths (UVC and UVB), implying a dependence of a local stress response on their noxious activity with overlapping or alternative mechanisms activated by UVA.

Neuroendocrinology of the skin: An overview and selective analysis

The concept on the skin neuro-endocrine has been formulated ten years ago, and recent advances in the field further strengthened this role. Thus, skin forms a bidirectional platform for a signal exchange with other peripheral organs, endocrine and immune systems or brain to enable rapid and selective responses to the environment in order to maintain local and systemic homeostasis. In this context, it is not surprising that the function of the skin is tightly regulated by systemic neuro-endocrine system. Skin cells and skin appendages not only respond to neuropeptides, steroids and other regulatory signals, but also actively synthesis variety of hormones. The stress responses within the skin are tightly regulated by locally synthesized factors and their receptor expression. There is growing evidence for alternative splicing playing an important role in stress signaling. Deregulation of the skin neuro-endocrine signaling can lead or/and be a marker of variety of skin diseases. The major problem in this area relates to their detailed mechanisms of crosstalk between skin and brain and between the local and global endocrine as well as immune systems.

Corticotropin-releasing hormone attenuates vascular endothelial growth factor release from human HaCaT keratinocytes

OBJECTIVES

Corticotropin-releasing hormone (CRH) is a central component of the local hypothalamic-pituitary-adrenal (HPA) axis, which has a functional equivalent in the skin. To determine whether CRH and its receptor, CRH-R1, modulate the expression of vascular endothelial growth factor (VEGF), which is overexpressed in psoriatic epidermis and plays a causal role in the pathogenesis of psoriasis, we investigated the effect of CRH on the expression of VEGF in a human keratinocyte cell line (HaCaT) and whether this effect is via the mitogen-activated protein kinase (MAPK) signal transduction pathways.

METHODS

Real-time RT-PCR, ELISA assay and western blot were used in the present study to investigate the expression of VEGF in CRH-treated HaCaT cells.

RESULTS

The mRNA and protein levels of VEGF in CRH-treated HaCaT cells were significantly attenuated. However, this downregulation was abrogated by pretreatment with antalarmin, SB203580 and SP600125; pretreatment with PD98059 did not attenuate the effects of CRH on the expression of VEGF. In addition, CRH treatment induced rapid phosphorylation of p38 MAPK and JNK1/2, and antalarmin, SB203580 and SP600125 inhibited CRH-induced phosphorylation of p38 MAPK and JNK1/2.

CONCLUSIONS

CRH might downregulate the expression of VEGF through the CRH-R1 and MAPK (p38 MAPK and JNK1/2) signaling pathways in human HaCaT cells.

Role of corticotropin-releasing hormone and receptor in the pathogenesis of psoriasis

Psoriasis is a chronic inflammatory disease characterized by epidermal keratinocytic hyperproliferation and abnormal differentiation. It is one of the most illustrative examples of the close relation between exacerbation of disease and the psychopathologic burden of the patients. However, the mechanism remains poorly understood. In recent years, evidence has suggested that endocrine stress responses not only are under control of the central nervous system but also occur in peripheral tissue, outside of the classical HPA axis. Corticotrophin-releasing hormone (CRH) is a central component of the hypothalamic-pituitary-adrenal (HPA) axis and is an important coordinator of the systemic stress response. In peripheral sites, cutaneous CRH and CRH-receptor1 (CRH-R1) is believed to regulate various functions of the skin that are important for local homeostasis. These findings have shed new light on the role of peripheral CRH and CRH-R1 in cutaneous diseases, especially psoriasis. Many researchers focus on the pro-inflammatory role of CRH, such as CRH-induced activation of mast cells in the phenomenon of stress related exacerbation of cutaneous inflammatory diseases, and some researches demonstrated that CRH protein expression was increased in the affected skin of psoriasis. Meanwhile, it is reported that CRH could downregulate pro-inflammatory factors, such as IL-18. Tagen found CRH-R1 mRNA expression in psoriasis skin lower than that in normal controls. Previous studies revealed that the functional role of the CRH/CRH-R1 system in pathological human skin conditions remains to be identified. Interestingly, we found that both CRH and CRH-R1 were presented in psoriatic lesion, perilesional skin and normal control skin by immunohistochemistry, and lesions from patients with psoriasis showed significantly lower CRH/CRH-R1 expression compared with psoriatic perilesional skin and normal control skin. Presumably a localized circuit regulates the peripheral functions of cutaneous CRH/CRH-R1, and the aberrant expression of CRH/CRH-R1 in the skin disturbs the local homeostasis and leads to abnormal differentiation and proliferation in keratinocytes. However, dysfunction of keratinocytes may decrease CRH/CRH-R1 expression because of disharmony in differentiation and proliferation of keratinocytes. Thus, we hypothesize that a cutaneous CRH/CRH-R1 system might be aberrant in lesions of psoriasis. The detuning of CRH/CRH-R1 regulation might contribute to the formation of plaque in psoriasis. What is more important, we hypothesize that the role of CRH/CRH-R1 system might play a protective role in the pathogenesis of psoriasis. This would provide a new treatment for psoriasis. Thus, further study in vitro and in vivo has to be done to test our hypothesis.

Involvement of the corticotropin-releasing hormone system in the pathogenesis of acne vulgaris

BACKGROUND

The sebaceous gland exhibits an independent peripheral endocrine function and expresses receptors for neuropeptides. Previous reports have confirmed the presence of a complete corticotropin-releasing hormone (CRH) system in human sebocytes in vitro. The capability of hypothalamic CRH to induce lipid synthesis, induce steroidogenesis and interact with testosterone and growth hormone implicates a possibility of its involvement in the clinical development of acne.

OBJECTIVES

The purpose of the study was to detect expression changes of CRH/CRH binding protein (CRHBP)/CRH receptors (CRHRs) in acne-involved skin, especially in the sebaceous glands.

METHODS

Expression of CRH/CRHBP/CRHRs was analysed by immunohistochemistry in biopsies from facial skin of 33 patients with acne, noninvolved thigh skin of the same patients and normal skin of eight age-matched healthy volunteers.

RESULTS

Very strong positive reaction for CRH was observed in acne-involved skin in all types of sebaceous gland cells, irrespective of their differentiation stage, whereas in noninvolved and normal skin sebaceous glands exhibited a weaker CRH staining depending upon the differentiation stage of sebocytes. The strongest reaction for CRHBP in acne-involved sebaceous glands was in differentiating sebocytes. CRHR-1 and CRHR-2 exhibited the strongest expression in sweat glands and sebaceous glands, respectively.

CONCLUSIONS

Expression of the complete CRH system is abundant in acne-involved skin, especially in the sebaceous glands, possibly activating pathways which affect immune and inflammatory processes leading to the development and stress-induced exacerbation of acne.

Corticotropin-releasing factor decreases IL-18 in the monocyte-derived dendritic cell

Recent evidence suggests that crosstalk between mast cells, nerves and keratinocytes might be involved in the exacerbation of inflammatory conditions by stress, but the mechanism by which this occurs remains unclear. Corticotropin-releasing factor (CRF), which activates the hypothalamo-pituitary-adrenal (HPA) axis under stress, also has pro-inflammatory peripheral effects. However, there have been no reports about CRF receptor expression and the functional role of CRF in the dendritic cell (DC), which is considered to be the link between allergen uptake and the clinical manifestations of allergic diseases, such as atopic dermatitis. The purpose of this study was to investigate the expression of CRF receptors and the functional role of CRF in the monocyte-derived DC (MoDC) of atopic dermatitis patients and non-atopic healthy controls. In this study, mRNAs for CRF-R1alpha and 1beta, as well as the CRF-R1 protein, were detected in MoDCs. CRF-R2alpha (but not R2beta or R2gamma) mRNA and the CRF-R2 protein were present in MoDCs. Exposure of DCs to CRF resulted in a decrease of IL-18 in both atopic dermatitis patients and non-atopic healthy controls. However, CRF did not alter the expression of IL-6, CCL17, CCL18, and CCL22. Therefore, our results demonstrate that CRF could modulate immune responses by acting directly upon DCs.

Skin as an endocrine organ: implications for its function

Described as the body's largest organ, the skin is strategically located at the interface with the external environment where it has evolved to detect, integrate and respond to a diverse range of stressors. A flurry of recent findings has established the skin as an important peripheral (neuro)endocrine organ that is tightly networked to central stress axes. This capability is contributing to the maintenance of body homeostasis, and in this way could be harnessed for therapeutic strategies.

20-Hydroxyvitamin D3, a product of vitamin D3 hydroxylation by cytochrome P450scc, stimulates keratinocyte differentiation

It has been shown that mammalian cytochrome P450scc can metabolize vitamin D3 to 20-hydroxyvitamin D3 (20(OH)D3) and 20,22(OH)2D3. To define the biological significance of this pathway, we tested the effects of 20(OH)D3 on the differentiation program of keratinocytes and on the expression of enzymes engaged in vitamin D3 metabolism. Immortalized HaCaT and adult human epidermal keratinocytes were used as a model and the effects of 20(OH)D3 were compared with those of 25(OH)D3 and 1,25(OH)2D3. 20(OH)D3 inhibited proliferation and caused G2/M arrest. 20(OH)D3 stimulated involucrin and inhibited cytokeratin 14 expression. The potency of 20(OH)D3 was comparable to that of 1,25(OH)2D3. 20(OH)D3 decreased the expression of cytochrome P450 enzyme (CYP)27A1 and CYP27B1, however, having only slight effect on CYP24. The effect of 20(OH)D3 was dependent on the vitamin D receptor (VDR). As shown by electrophoretic mobility shift assay, 20(OH)D3 stimulated the binding of nuclear proteins to the VDRE. Transfection of cells with VDR-specific siRNA decreased 20(OH)D3-stimulated transcriptional activity of the VDRE promoter and the expression of involucrin and CYP24 mRNA. Therefore, the above studies identify 20(OH)D3 as a biologically active secosteroid that induces keratinocyte differentiation. These data imply that the previously unreported pathway of vitamin D3 metabolism by P450scc may have wider biological implications depending, for example, on the extent of adrenal gland or cutaneous metabolism.

Urocortin2 inhibits tumor growth via effects on vascularization and cell proliferation

The corticotropin-releasing factor (CRF) receptor CRFR2 is expressed widely in peripheral tissues and in the vasculature, although its functional roles in those tissues have only recently begun to be elucidated. Previously we found that genetic deletion of CRFR2 resulted in profound postnatal hypervascularization in mice, characterized by both an increase in total vessel number and a dramatic increase in vessel diameter. These data strongly suggested that ligands for CRFR2 act to limit tissue vascularity, perhaps as a counterbalance to factors that promote neovascularization. Urocortin 2 (Ucn2) is a specific ligand for the CRFR2. We hypothesized that activation of CRFR2 by Ucn2 might thus suppress tumor vascularization and consequently limit tumor growth. Here, we show that viral-mediated expression of Ucn2 strikingly inhibits the growth and vascularization of Lewis Lung Carcinoma Cell (LLCC) tumors in vivo. Further, we found that this effect on tumor growth inhibition was independent of whether exposure to Ucn2 occurred before or after establishment of measurable tumors. In vitro, Ucn2 directly inhibited the proliferation of LLCC, suggesting that the tumor-suppressing effects of CRFR2 activation involve a dual mechanism of both a direct inhibition of tumor cell cycling and the suppression of tumor vascularization. These results establish that Ucn2 inhibits tumor growth, suggesting a potential therapeutic role for CRFR2 ligands in clinical malignancies.

Expression of molecular equivalent of hypothalamic-pituitary-adrenal axis in adult retinal pigment epithelium

We have investigated expression of molecular elements of the hypothalamic-pituitary-adrenal (HPA) axis in the human retinal pigment epithelium (RPE) cells. The presence of corticotropin-releasing factor (CRF); urocortins I, II and III; CRF receptor type 1 (CRFR1); POMC and prohormone convertases 1 and 2 (PC1 and PC2) mRNAs were shown by RT-PCR; the protein products were detected by ELISA, western blot or immunocytochemical methods in an ARPE-19 cell line derived from an adult human donor. CRFR2 was below the level of detectability. The CRFR1 was functional as evidenced by CRF stimulation of cAMP and inositol triphosphate production as well as by ligand induction of transcriptional activity of inducible cis-elements cAMP responsive element (CRE), activator protein 1 responsive element (AP-1) and POMC promoter) in ARPE-19 using luciferase reporter assay. Immunoreactivities representative of CRF, pre-urocortin, CRFR1 receptor and ACTH were also detected in mouse retina by in situ immunocytochemistry. Finally, using RT-PCR, we detected expression of genes encoding four key enzymes participating in steroids synthesis (CYP11A1, CYP11B1, CYP17 and CYP21A2) and showed transformation of progesterone into cortisol-immunoreactivity in cultured ARPE-19 cells. Therefore, we suggest that ocular tissue expresses CRF-driven signalling system that follows organisational structure of the HPA axis.

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.

CRH inhibits NF-kappa B signaling in human melanocytes

Corticotropin releasing hormone (CRH), a messenger of stress at the central level, is expressed in the epidermis where it operates within local equivalent of hypothalamo-pituitary axis. CRH inhibits NF-kappaB activity in human immortalized epidermal (PIG1) melanocytes. In melanocytes CRH stimulates pro-opiomelanocortin (POMC) mRNA and adrenocorticotropin (ACTH) peptide production. Knockdown of POMC levels by transfecting cells with antisense oligonucleotides blocks the effect of CRH on NF-kappaB signaling indicating that the above inhibition is indirect, e.g. through activation of POMC. We suggest that induction of POMC by CRH serves as a feedback mechanism to self-restrict inflammatory response in the skin.

Molecular cloning and initial characterization of African green monkey (Cercopithecus aethiops) corticotropin releasing factor receptor type 1 (CRF1) from COS-7 cells

We report the expression of endogenous CRF1 in COS-7 cells (African green monkey origin). Cloning of the coding region of CRF1 gene identified three alternatively spliced isoforms with nucleotide and predicted amino acid sequences corresponding to the membrane bound alpha and c and soluble e isoforms. DNA sequencing of the main isoform CRF1alpha showed homologies of 99%, 97% and 91% with the rhesus monkey, human and rodent genes, respectively; the deduced protein sequence differed in only one amino acid with rhesus monkey and human. Western blot analysis with antibodies against human CRF1 demonstrated immunoreactive proteins with MW of 37, 52, 70 and 80-85 in crude membrane or cytoplasm preparation; two additional species of 40 and 60 kDa were detected only in the cytoplasmic fraction. On immunocytochemistry CRF1 was localized to both the cell surface and intracellularly. The receptor was functional, e.g., addition of CRF to COS-7 cells inhibited cell proliferation and stimulated release of arachidonic acid; nevertheless, it was poorly coupled to cAMP production (its stimulation was minimal in native cells). In conclusion, COS cells that are routinely used for the study of transfected CRF receptors do express endogenous CRF1 mRNA with splicing behavior similar to that reported in human and rodent cells, and translated into functional CRF1 receptors.

Corticotropin releasing hormone and the skin

Cotricotropin-releasing hormone (CRH) and related peptides are produced in skin that is dependent on species and anatomical location. Local peptide production is regulated by ultraviolet radiation (UVR), glucocorticoids and phase of the hair cycle. The skin also expresses the corresponding receptors (CRH-R1 and CRH-R2), with CRH-R1 being the major receptor in humans. CRH-R1 is expressed in epidermal and dermal compartments, and CRH-R2 predominantly in dermal structures. The gene coding for CRH-R1 generates multiple isoforms through a process modulated by UVR, cyclic adenosine monophosphate (cAMP) and phorbol 12-myristate 13-acetate. The phenotypic effects of CRH in human skin cells are largely mediated by CRH-R1alpha through increases in concentrations of cAMP, inositol triphosphate (IP3), or Ca2+ with subsequent activation of protein kinases A (PKA) and C (PKC) dependent pathways. CRH also modulates the activity of nuclear factor of kappa light polypeptide gene enhancer in B-cells (NF-kappaB), activator protein 1 (AP-1) and cAMP responsive element binding protein (CREB). The cellular functions affected by CRH depend on cell type and nutritional status and include modulation of differentiation program(s), proliferation, viability and immune activity. The accumulated evidence indicates that cutaneous CRH is also a component of a local structure organized similarly to the hypothalamo-pituitary-adrenal axis.

Corticotropin releasing factor (CRF) receptor signaling in the central nervous system: new molecular targets

Corticotropin-releasing factor (CRF) and the related urocortin peptides mediate behavioral, cognitive, autonomic, neuroendocrine and immunologic responses to aversive stimuli by activating CRF(1) or CRF(2) receptors in the central nervous system and anterior pituitary. Markers of hyperactive central CRF systems, including CRF hypersecretion and abnormal hypothalamic-pituitary-adrenal axis functioning, have been identified in subpopulations of patients with anxiety, stress and depressive disorders. Because CRF receptors are rapidly desensitized in the presence of high agonist concentrations, CRF hypersecretion alone may be insufficient to account for the enhanced CRF neurotransmission observed in these patients. Concomitant dysregulation of mechanisms stringently controlling magnitude and duration of CRF receptor signaling also may contribute to this phenomenon. While it is well established that the CRF(1) receptor mediates many anxiety- and depression-like behaviors as well as HPA axis stress responses, CRF(2) receptor functions are not well understood at present. One hypothesis holds that CRF(1) receptor activation initiates fear and anxiety-like responses, while CRF(2) receptor activation re-establishes homeostasis by counteracting the aversive effects of CRF(1) receptor signaling. An alternative hypothesis posits that CRF(1) and CRF(2) receptors contribute to opposite defensive modes, with CRF(1) receptors mediating active defensive responses triggered by escapable stressors, and CRF(2) receptors mediating anxiety- and depression-like responses induced by inescapable, uncontrollable stressors. CRF(1) receptor antagonists are being developed as novel treatments for affective and stress disorders. If it is confirmed that the CRF(2) receptor contributes importantly to anxiety and depression, the development of small molecule CRF(2) receptor antagonists would be therapeutically useful.

The role of corticotropin-releasing hormone in immune-mediated cutaneous inflammatory disease

Corticotropin-releasing hormone (CRH) coordinates the systemic stress response via hypothalamic-pituitary-adrenal (HPA) axis activation with subsequent modulation of the inflammatory response. Stress is known to affect expression of immune-mediated inflammatory diseases, many of which are associated with HPA axis abnormalities. HPA axis components including CRH and its receptors (CRH-R) exist in the skin and exhibit differential expression according to cell type, physiological fluctuations and disease states. This confirms a local functioning cutaneous HPA-like system. Peripheral CRH may exhibit proinflammatory effects. Animal studies confirm that peripheral CRH is required for induction of the inflammatory response in vivo. CRH and CRH-R are upregulated in inflammatory arthritis synovium and psoriatic skin. CRH may influence mast cell activation, direct modulation of immune cells, angiogenesis and induction of the novel orphan nuclear receptor NURR1. This transcription factor is part of the steroid/thyroid superfamily of related nuclear receptors that includes receptors for steroids, retinoids and vitamin D; ligands of these receptors are effective in treating psoriasis. The roles of CRH and NURR1 in psoriasis and inflammatory skin diseases, especially those associated with stress, remain to be elucidated. This stress may be psychological or physical. CRH, produced locally or delivered by peripheral nerves, may mediate interactions between a cutaneous HPA axis-like system and the central HPA axis--the "brain-skin axis".

Modulation of the human hair follicle pigmentary unit by corticotropin-releasing hormone and urocortin peptides

Human skin is a local source of corticotropin-releasing hormone (CRH) and expresses CRH and CRH receptors (CRH-R) at mRNA and protein levels. Epidermal melanocytes respond to CRH by induction of cAMP with up-regulation of pro-opiomelanocortin gene expression and subsequent production of adrenocorticotropin hormone. However, the role of CRH/CRH-R in melanocyte biology is complicated by the significant heterogeneity of cutaneous melanocyte subpopulations, from continuously active and UV-responsive melanocytes in epidermis to UV nonresponsive, hair growth cycle-coupled melanogenesis in hair follicles. In the present study we report that normal human scalp hair follicle melanocytes express CRH at the mRNA level. Furthermore, CRH, urocortin and CRH-R 1 and 2 were differentially expressed in follicular melanocytes, fibroblasts, and keratinocytes depending on anatomic location and differentiation status in situ and in vitro. Stimulation of follicular melanocytes with CRH and CRH peptides, modified for selectivity for CRH-R1 and/or CRH-R2, variably induced cell melanogenesis, dendricity, and proliferation. CRH-peptides also stimulated the expression and activity of Tyrosinase, and expression of Tyrosinase-related protein-1 and-2. However, a modified urocortin peptide highly selective for CRH-R2 down-regulated melanocyte differentiation phenotype. This study indicates that CRH peptides can differentially influence hair follicle melanocyte behavior not only via CRH-R1 signaling but also by complex cross-talk between CRH-R1 and CRH-R2.

Teneurin C-terminal associated peptides: an enigmatic family of neuropeptides with structural similarity to the corticotropin-releasing factor and calcitonin families of peptides

The proliferation of genomic sequence data in recent years has led to the identification of numerous orthologous and paralogous genes in a variety of divergent taxa. Phylogenetic comparisons of this sequence information have led not only to the construction of improved evolutionary relationships among genes and species, but also led to greater understanding of how genes and their proteins evolve differently throughout the Metazoa. Our recent characterization of a biologically active corticotropin-releasing factor (CRF)-like sequence at the C-terminal region of the teneurin transmembrane proteins has led to a number of questions of how peptide genes evolve and develop new functions in the Metazoa. The teneurin C-terminal associated peptides show structural similarity to the calcitonin family of peptides as well as the CRF family, and like both peptide families, plays a role in the regulation of stress and anxiety.

CRH functions as a growth factor/cytokine in the skin

We tested the effect of CRH and related peptides in a large panel of human skin cells for growth factor/cytokine activities. In skin cells CRH action is mediated by CRH-R1, a subject to posttranslational modification with expression of alternatively spliced isoforms. Activation of CRH-R1 induced generation of both cAMP and IP3 in the majority of epidermal and dermal cells (except for normal keratinocytes and one melanoma line), indicating cell type-dependent coupling to signal transduction pathways. Phenotypic effects on cell proliferation were however dependent on both cell type and nutrition conditions. Specifically, CRH stimulated dermal fibroblasts proliferation, by increasing transition from G1/0 to the S phase, while in keratinocytes CRH inhibited cell proliferation. In normal and immortalized melanocytes CRH effect showed dichotomy and thus, it inhibited melanocyte proliferation in serum-containing medium CRH through G2 arrest, while serum free media led instead to CRH enhanced DNA synthesis (through increased transition from G1/G0 to S phase and decreased subG1 signal, indicating DNA degradation). CRH also induced inhibition of early and late apoptosis in the same cells, demonstrated by analysis with the annexin V stains. Thus, CRH acts on epidermal melanocytes as a survival factor under the stress of starvation (anti-apoptotic) as well as inhibitor of growth factors induced cell proliferation. In conclusion, CRH and related peptides can couple CRH-R1 to any of diverse signal transduction pathways; they also regulate cell viability and proliferation in cell type and growth condition-dependent manners.

Enzymatic metabolism of ergosterol by cytochrome p450scc to biologically active 17alpha,24-dihydroxyergosterol

We demonstrate the metabolism of ergosterol by cytochrome P450scc in either a reconstituted system or isolated adrenal mitochondria. The major reaction product was identified as 17alpha,24-dihydroxyergosterol. Purified P450scc also generated hydroxyergosterol as a minor product, which is probably an intermediate in the synthesis of 17alpha,24-dihydroxyergosterol. In contrast to cholesterol and 7-dehydrocholesterol, cleavage of the ergosterol side chain was not observed. NMR analysis clearly located one hydroxyl group to C24, with evidence that the second hydroxyl group is at C17. 17alpha,24-Dihydroxyergosterol inhibited cell proliferation of HaCaT keratinocytes and melanoma cells. Thus, in comparison with cholesterol and 7-dehydrocholesterol, the 24-methyl group and the C22-C23 double bond of ergosterol prevent side chain cleavage by P450scc and change the enzyme's hydroxylase activity from C22 and C20, to C24 and C17, generating bioactive product.

Neuroendocrine system of the skin

Evidence is accumulating that the skin can serve as a peripheral neuroendocrine organ. The skin neuroendocrine activities are predominantly independent of regulation from the central level (which controls classical hormone secretion) but are rather regulated by local cutaneous factors. These endocrine factors would represent an exquisite regulatory layer addressed at restricting maximally the effect of noxious agents in the skin to preserve local and consequently global homeostasis.

Corticotropin-Releasing Factor and the Urocortins Induce the Expression of TLR4 in Macrophages via Activation of the Transcription Factors PU.1 and AP-1

Corticotropin-releasing factor (CRF) augments LPS-induced proinflammatory cytokine production from macrophages. The aim of the present study was to determine the mechanism by which CRF and its related peptides urocortins (UCN) 1 and 2 affect LPS-induced cytokine production. We examined their role on TLR4 expression, the signal-transducing receptor of LPS. For this purpose, the murine macrophage cell line RAW 264.7 and primary murine peritoneal macrophages were used. Exposure of peritoneal macrophages and RAW 264.7 cells to CRF, UCN1, or UCN2 up-regulated TLR4 mRNA and protein levels. To study whether that effect occurred at the transcriptional level, RAW 264.7 cells were transfected with a construct containing the proximal region of the TLR4 promoter linked to the luciferase gene. CRF peptides induced activation of the TLR4 promoter, an effect abolished upon mutation of a proximal PU.1-binding consensus or upon mutation of an AP-1-binding element. Indeed, all three peptides promoted PU.1 binding to the proximal PU.1 site and increased DNA-binding activity to the AP-1 site. The effects of CRF peptides were inhibited by the CRF2 antagonist anti-sauvagine-30, but not by the CRF1 antagonist antalarmin, suggesting that CRF peptides mediated the up-regulation of TLR4 via the CRF2 receptor. Finally, CRF peptides blocked the inhibitory effect of LPS on TLR4 expression. In conclusion, our data suggest that CRF peptides play an important role on macrophage function. They augment the effect of LPS by inducing Tlr4 gene expression, through CRF2, via activation of the transcription factors PU.1 and AP-1.