Corticotropin releasing hormone and the skin

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.

Effects on peripheral and central nervous system of key inflammatory intercellular signalling peptides and proteins in psoriasis

Psoriasis is a chronic systemic inflammatory cutaneous disease. Where the immune system plays an important role in its pathogenesis, with key inflammatory intercellular signalling peptides and proteins including IL-17 and IL-23. The psychoneurological system also figures prominently in development of psoriasis. There is a high prevalence of comorbidity between psoriasis and mental health disorders such as depression, anxiety and mania. Patients with psoriasis often suffer from pathological pain in the lesions, and their neurological accidents could improve the lesions in innervated areas. The immune system and the psychoneurological system interact closely in the pathogenesis of psoriasis. Patients with psoriasis exhibit abnormal levels of neuropeptides both in circulating and localized lesion, acting as immunomodulators involved in the inflammatory response. Moreover, receptors for inflammatory factors are expressed in both peripheral and central nervous systems (CNSs), suggesting that nervous system can receive and be influenced by signals from immune system. Key inflammatory intercellular signalling peptides and proteins in psoriasis, such as IL-17 and IL-23, can be involved in sensory signalling and may affect synaptic plasticity and the blood-brain barrier of CNS through the circulation. This review provides an overview of the multiple effects on the peripheral and CNS under conditions of systemic inflammation in psoriasis, providing a framework and inspiration for in-depth studies of neuroimmunomodulation in psoriasis.

Psychological stress induces hair regenerative disorders through corticotropin-releasing hormone-mediated autophagy inhibition

Psychosocial stress is increasing, causing a growing number of people to suffer from hair loss. Stress-related corticotropin-releasing hormone (CRH) is associated with hair loss, but the mechanism by which hair follicles respond to stress and CRH remain poorly understood. The aim of the study is to elucidate the association between CRH and stress-related hair regenerative disorders, and reveal the potential pathological mechanisms. A chronic unpredictable stress mouse model and a chronic social defeat stress mouse model were used to examine the role of CRH and stress-related hair regrowth. Chronic unpredictable stress and chronic social defeat stress increased the expression of CRH and CRH receptors (CRHRs), and contributed to the onset of hair-cycle abnormalities. Psychoemotional stress and stress-related CRH blocked hair follicle regrowth, which could be restored by astressin, a CRHR antagonist. Long-term exposure to either chronic unpredictable stress or CRH induced a decrease in autophagy, which could be partially rescued by astressin. Activating CRHR, by stress or CRH administration, decreased autophagy via the mTOR-ULK1 signaling pathway to mediate hair regenerative disorders, which could be partially reversed through enhancing autophagy by administration of brefeldin A. These findings indicate that CRH-mediated autophagy inhibition play an important role in stress-induced hair regenerative disorders. CRH regulates the local hypothalamic-pituitary-adrenal axis of hair follicles, but also plays an independent pathogenic role in stress-related hair regenerative disorders through CRH-mediated autophagy inhibition. This work contributes to the present understanding of hair loss and suggests that enhancing autophagy may have a therapeutic effect on stress-induced hair loss.

Secondary glaucoma: Toward interventions based on molecular underpinnings

Glaucoma is a heterogeneous group of progressive diseases that leads to irreversible blindness. Secondary glaucoma refers to glaucoma caused by a known underlying condition. Pseudoexfoliation and pigment dispersion syndromes are common causes of secondary glaucoma. Their respective deposits may obstruct the trabecular meshwork, leading to aqueous humor outflow resistance, ocular hypertension, and optic neuropathy. There are no disease-specific interventions available for either. Pseudoexfoliation syndrome is characterized by fibrillar deposits (pseudoexfoliative material) on anterior segment structures. Over a decade of multiomics analyses taken together with the current knowledge on pseudoexfoliative glaucoma warrant a re-think of mechanistic possibilities. We propose that the presence of nucleation centers (e.g., vitamin D binding protein), crosslinking enzymes (e.g., transglutaminase 2), aberrant extracellular matrix, flawed endocytosis, and abnormal aqueous-blood barrier contribute to the formation of proteolytically resistant pseudoexfoliative material. Pigment dispersion syndrome is characterized by abnormal iridolenticular contact that disrupts iris pigment epithelium and liberates melanin granules. Iris melanogenesis is aberrant in this condition. Cytotoxic melanogenesis intermediates leak out of melanosomes and cause iris melanocyte and pigment epithelium cell death. Targeting melanogenesis can likely decrease the risk of pigmentary glaucoma. Skin and melanoma research provides insights into potential therapeutics. We propose that specific prostanoid agonists and fenofibrates may reduce melanogenesis by inhibiting cholesterol internalization and de novo synthesis. Additionally, melatonin is a potent melanogenesis suppressor, antioxidant, and hypotensive agent, rendering it a valuable agent for pigmentary glaucoma. In pseudoexfoliative glaucoma, where environmental insults drive pseudoexfoliative material formation, melatonin's antioxidant and hypotensive properties may offer adjunct therapeutic benefits. This article is categorized under: Neurological Diseases > Molecular and Cellular Physiology.

Natural tyrosinase enzyme inhibitors: A path from melanin to melanoma and its reported pharmacological activities

The skin containing melanin pigment acts as a protective barrier and counteracts the UVR and other environmental stressors to maintain or restore disrupted cutaneous homeostasis. The production of melanin pigment is dependent on tyrosine levels. L-tyrosine and L-dihydroxyphenylalanine (L-DOPA) can serve both as a substrates and intermediates of melanin synthetic pathway and as inducers and positive regulators of melanogenesis. The biosynthesis of melanin is stimulated upon exposure to UVR, which can also stimulate local production of hormonal factors, which can stimulate melanoma development by altering the chemical properties of eu- and pheomelanin. The process of melanogenesis can be altered by several pathways. One involves activation of POMC, with the production of POMC peptides including MSH and ACTH, which increase intracellular cAMP levels, which activates the MITF, and helps to stimulate tyrosinase (TYR) expression and activity. Defects in OCA1 to 4 affects melanogenic activity via posttranslational modifications resulting in proteasomal degradation and reducing pigmentation. Further, altering, the MITF factor, helps to regulate the expression of MRGE in melanoma, and helps to increase the TYR glycosylation in ER. CRH stimulates POMC peptides that regulate melanogenesis and also by itself can stimulate melanogenesis. The POMC, P53, ACTH, MSH, MC1R, MITF, and 6-BH4 are found to be important regulators for pigmentation. Melanogenesis can affect melanoma behaviour and inhibit immune responses. Therefore, we reviewed natural products that would alter melanin production. Our special focus was on targeting melanin synthesis and TYR enzyme activity to inhibit melanogenesis as an adjuvant therapy of melanotic melanoma. Furthermore, this review also outlines the current updated pharmacological studies targeting the TYR enzyme from natural sources and its consequential effects on melanin production.

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.

Corticotropin-Releasing Hormone: Biology and Therapeutic Opportunities

In 1981, Wylie Vale, Joachim Spiess, Catherine Rivier, and Jean Rivier reported on the characterization of a 41-amino-acid peptide from ovine hypothalamic extracts with high potency and intrinsic activity stimulating the secretion of adrenocorticotropic hormone and β-endorphin by cultured anterior pituitary cells. With its sequence known, this neuropeptide was determined to be a hormone and consequently named corticotropin-releasing hormone (CRH), although the term corticotropin-releasing factor (CRF) is still used and preferred in some circumstances. Several decades have passed since this seminal contribution that opened a new research era, expanding the understanding of the coding of stress-related processes. The characterization of CRH receptors, the availability of CRH agonists and antagonists, and advanced immunocytochemical staining techniques have provided evidence that CRH plays a role in the regulation of several biological systems. The purpose of this review is to summarize the present knowledge of this 41-amino-acid peptide.

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.

Vitamin D Signaling in Psoriasis: Pathogenesis and Therapy

Psoriasis is a systemic, chronic, immune-mediated disease that affects approximately 2–3% of the world’s population. The etiology and pathophysiology of psoriasis are still unknown, but the activation of the adaptive immune system with the main role of T-cells is key in psoriasis pathogenesis. The modulation of the local neuroendocrine system with the downregulation of pro-inflammatory and the upregulation of anti-inflammatory messengers represent a promising adjuvant treatment in psoriasis therapies. Vitamin D receptors and vitamin D-mediated signaling pathways function in the skin and are essential in maintaining the skin homeostasis. The active forms of vitamin D act as powerful immunomodulators of clinical response in psoriatic patients and represent the effective and safe adjuvant treatments for psoriasis, even when high doses of vitamin D are administered. The phototherapy of psoriasis, especially UVB-based, changes the serum level of 25(OH)D, but the correlation of 25(OH)D changes and psoriasis improvement need more clinical trials, since contradictory data have been published. Vitamin D derivatives can improve the efficacy of psoriasis phototherapy without inducing adverse side effects. The anti-psoriatic treatment could include non-calcemic CYP11A1-derived vitamin D hydroxyderivatives that would act on the VDR or as inverse agonists on RORs or activate alternative nuclear receptors including AhR and LXRs. In conclusion, vitamin D signaling can play an important role in the natural history of psoriasis. Selective targeting of proper nuclear receptors could represent potential treatment options in psoriasis.

Corticotropin-Releasing Factor Aggravates Ischemic Stroke Injury by the Inflammatory Activation of Microglia

Ischemic stroke is the second leading cause of death worldwide. Therefore, exploring effective and emerging molecular targets for ischemic stroke is a primary task of basic and clinical research. The aim of the present study was to investigate the function of corticotropin-releasing factor (CRF) in ischemic stroke and its related mechanisms, to provide a reference for the treatment of ischemic stroke. CRF, antalarmin, or astressin-2B were used to activate or block the CRF1 (CRF receptor 1) or CRF2 (CRF receptor 2) in BV2 cells and adult male mice, thus constructing a distal middle cerebral artery occlusion (dMCAO) model. CRF not only accelerated microglial activity by promoting transcription and production of inflammatory factors, but also promoted the transformation of activated BV2 cells from a neuroprotective phenotype (M2) to cytotoxic phenotype (M1), and these effects were mediated by the TLR4/NF-κB signaling pathway. These effects can be blocked by antalarmin but not by astressin-2B. CRF significantly aggravated the neurological deficit, increased infarction volume, and exacerbated neuronal injuries. Additionally, CRF significantly improved the levels of TNF-α and phospho-NF-κB in the ischemia penumbra. Finally, CRF significantly increased the number of CD16/Iba-1-positive cells and decreased the number of CD206/Iba-1-positive cells in the ischemia penumbra. These results provide evidence of the proinflammatory role of CRF in an ischemic stroke model and a possible underlying mechanism, which may facilitate the elucidation of potential treatment approaches for ischemic stroke.

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.

Cutaneous innervation in impaired diabetic wound healing

Type 2 diabetes is associated with several potential comorbidities, among them impaired wound healing, chronic ulcerations, and the requirement for lower extremity amputation. Disease-associated abnormal cellular responses, infection, immunological and microvascular dysfunction, and peripheral neuropathy are implicated in the pathogenesis of the wound healing impairment and the diabetic foot ulcer. The skin houses a dense network of sensory nerve afferents and nerve-derived modulators, which communicate with epidermal keratinocytes and dermal fibroblasts bidirectionally to effect normal wound healing after trauma. However, the mechanisms through which cutaneous innervation modulates wound healing are poorly understood, especially in humans. Better understanding of these mechanisms may provide the basis for targeted treatments for chronic diabetic wounds. This review provides an overview of wound healing pathophysiology with a focus on neural involvement in normal and diabetic wound healing, as well as future therapeutic perspectives to address the unmet needs of diabetic patients with chronic wounds.

Neurocosmetics in Skincare—The Fascinating World of Skin–Brain Connection: A Review to Explore Ingredients, Commercial Products for Skin Aging, and Cosmetic Regulation

The “modern” cosmetology industry is focusing on research devoted to discovering novel neurocosmetic functional ingredients that could improve the interactions between the skin and the nervous system. Many cosmetic companies have started to formulate neurocosmetic products that exhibit their activity on the cutaneous nervous system by affecting the skin’s neuromediators through different mechanisms of action. This review aims to clarify the definition of neurocosmetics, and to describe the features of some functional ingredients and products available on the market, with a look at the regulatory aspect. The attention is devoted to neurocosmetic ingredients for combating skin stress, explaining the stress pathways, which are also correlated with skin aging. “Neuro-relaxing” anti-aging ingredients derived from plant extracts and neurocosmetic strategies to combat inflammatory responses related to skin stress are presented. Afterwards, the molecular basis of sensitive skin and the suitable neurocosmetic ingredients to improve this problem are discussed. With the aim of presenting the major application of Botox-like ingredients as the first neurocosmetics on the market, skin aging is also introduced, and its theory is presented. To confirm the efficacy of the cosmetic products on the market, the concept of cosmetic claims is discussed.

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.

Participation of keratinocyte- and fibroblast-derived factors in melanocyte homeostasis, the response to UV, and pigmentary disorders

Human epidermal melanocytes play a central role in sensing the environment and protecting the skin from the drastic effects of solar ultraviolet radiation and other environmental toxins or inflammatory agents. Melanocytes survive in the epidermis for decades, which subjects them to chronic environmental insults. Melanocytes have a poor self-renewal capacity; therefore, it is critical to ensure their survival with genomic stability. The function and survival of melanocytes is regulated by an elaborate network of paracrine factors synthesized mainly by epidermal keratinocytes and dermal fibroblasts. A symbiotic relationship exists between epidermal melanocytes and keratinocytes on the one hand, and between melanocytes and dermal fibroblasts on the other hand. Melanocytes protect epidermal keratinocytes and dermal fibroblasts from the damaging effects of solar radiation, and the latter cells synthesize biochemical mediators that maintain the homeostasis, and regulate the stress response of melanocytes. Disruption of the paracrine network results in pigmentary disorders, due to abnormal regulation of melanin synthesis, and compromise of melanocyte survival or genomic stability. This review provides an update of the current knowledge of keratinocyte- and fibroblast-derived paracrine factors and their contribution to melanocyte physiology, and how their abnormal production is involved in the pathogenesis of common pigmentary disorders.

Hormonal regulation in male androgenetic alopecia-Sex hormones and beyond: Evidence from recent genetic studies

Male-pattern hair loss, also termed androgenetic alopecia (AGA), is a highly prevalent age-related condition that is characterized by a distinct pattern of hair loss from the frontotemporal and vertex regions of the scalp. The phenotype is highly heritable and hormone dependent, with androgens being the recognized critical hormonal factor. Numerous molecular genetic studies have focused on genetic variation in and around the gene that encodes the androgen receptor. More recently, however, the availability of high-throughput molecular genetic methods, novel methods of data analysis and sufficiently large sample sizes have rendered possible the systematic investigation of the contribution of other components of the androgen receptor pathway or hormonal pathways beyond the androgen receptor signalling pathways. Over the past decade, genome-wide association studies of increasingly large cohorts have enabled the genome-wide identification of genetic risk factors for AGA, and yielded unprecedented insights into the underlying pathobiology. The present review discusses some of the most intriguing genetic findings on the relevance of (sex)hormonal signalling in AGA.

Psychological Stress and Chronic Urticaria: A Neuro-immuno-cutaneous Crosstalk. A Systematic Review of the Existing Evidence

PURPOSE

It has been observed that certain patients with chronic spontaneous or idiopathic urticaria (CSU/CIU) have a personal history of a significant stressor before urticaria onset, while the prevalence of any psychopathology among these patients is significantly higher than in healthy individuals. Research has confirmed that skin is both an immediate stress perceiver and a target of stress responses. These complex interactions between stress, skin, and the nervous system may contribute to the onset of chronic urticaria. This systematic review investigated the association between CSU/CIU and neuroimmune inflammation with or without evidence of co-existing psychological stress from in vivo and ex vivo studies in human beings.

METHODS

PubMed and Scopus were searched to September 2019 for reports in human beings describing neuroimmune inflammation, stress, and CSU/CIU. A comprehensive search strategy was used that included all the relevant synonyms for the central concept.

FINDINGS

A total of 674 potentially relevant articles were identified. Only 13 satisfied the predefined inclusion criteria and were included in the systematic review. Five of these 13 studies evaluated the correlation between CSU/CIU, stress, and neuro-immune-cutaneous factors, while the remaining 8 focused on the association between CSU/CIU and these factors without examining any evidence of stress.

IMPLICATIONS

The complex neuro-immune-cutaneous model that involves numerous neuropeptides and neurokinins, inflammatory mediators and cells, hypothalamic-pituitary-adrenal axis hormones, and the skin may better explain the underlying pathophysiological mechanisms involved in the onset of urticaria. In addition, the elevated psychological stress level that has been closely related to CSU/CIU could be attributed to the imbalance or irregularity of this neuro-immune-cutaneous circuit. It is still unclear and must be further investigated whether any psychological stress results in or triggers CSU/CIU onset on top of a preexisting neuroimmune dysregulation. Nevertheless, new psycho-phenotypic or neuro-endotypic CSU/CIU subsets should be considered as the era of personalized treatment strategies emerges. A better understanding of CSU/CIU pathophysiology and consideration of the patient as a whole is vital for identifying targets for new potential treatment options.

Pathogenesis of psoriasis in the "omic" era. Part I. Epidemiology, clinical manifestation, immunological and neuroendocrine disturbances

Psoriasis is a common, chronic, inflammatory, immune-mediated skin disease affecting about 2% of the world's population. According to current knowledge, psoriasis is a complex disease that involves various genes and environmental factors, such as stress, injuries, infections and certain medications. The chronic inflammation of psoriasis lesions develops upon epidermal infiltration, activation, and expansion of type 1 and type 17 Th cells. Despite the enormous progress in understanding the mechanisms that cause psoriasis, the target cells and antigens that drive pathogenic T cell responses in psoriatic lesions are still unproven and the autoimmune basis of psoriasis still remains hypothetical. However, since the identification of the Th17 cell subset, the IL-23/Th17 immune axis has been considered a key driver of psoriatic inflammation, which has led to the development of biologic agents that target crucial elements of this pathway. Here we present the current understanding of various aspects in psoriasis pathogenesis.

Extra-adrenal glucocorticoid biosynthesis: implications for autoimmune and inflammatory disorders

Glucocorticoid synthesis is a complex, multistep process that starts with cholesterol being delivered to the inner membrane of mitochondria by StAR and StAR-related proteins. Here its side chain is cleaved by CYP11A1 producing pregnenolone. Pregnenolone is converted to cortisol by the enzymes 3-βHSD, CYP17A1, CYP21A2 and CYP11B1. Glucocorticoids play a critical role in the regulation of the immune system and exert their action through the glucocorticoid receptor (GR). Although corticosteroids are primarily produced in the adrenal gland, they can also be produced in a number of extra-adrenal tissue including the immune system, skin, brain, and intestine. Glucocorticoid production is regulated by ACTH, CRH, and cytokines such as IL-1, IL-6 and TNFα. The bioavailability of cortisol is also dependent on its interconversion to cortisone which is inactive, by 11βHSD1/2. Local and systemic glucocorticoid biosynthesis can be stimulated by ultraviolet B, explaining its immunosuppressive activity. In this review, we want to emphasize that dysregulation of extra-adrenal glucocorticoid production can play a key role in a variety of autoimmune diseases including multiple sclerosis (MS), lupus erythematosus (LE), rheumatoid arthritis (RA), and skin inflammatory disorders such as psoriasis and atopic dermatitis (AD). Further research on local glucocorticoid production and its bioavailability may open doors into new therapies for autoimmune diseases.

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.

POMC: The Physiological Power of Hormone Processing

Pro-opiomelanocortin (POMC) is the archetypal polypeptide precursor of hormones and neuropeptides. In this review, we examine the variability in the individual peptides produced in different tissues and the impact of the simultaneous presence of their precursors or fragments. We also discuss the problems inherent in accurately measuring which of the precursors and their derived peptides are present in biological samples. We address how not being able to measure all the combinations of precursors and fragments quantitatively has affected our understanding of the pathophysiology associated with POMC processing. To understand how different ratios of peptides arise, we describe the role of the pro-hormone convertases (PCs) and their tissue specificities and consider the cellular processing pathways which enable regulated secretion of different peptides that play crucial roles in integrating a range of vital physiological functions. In the pituitary, correct processing of POMC peptides is essential to maintain the hypothalamic-pituitary-adrenal axis, and this processing can be disrupted in POMC-expressing tumors. In hypothalamic neurons expressing POMC, abnormalities in processing critically impact on the regulation of appetite, energy homeostasis, and body composition. More work is needed to understand whether expression of the POMC gene in a tissue equates to release of bioactive peptides. We suggest that this comprehensive view of POMC processing, with a focus on gaining a better understanding of the combination of peptides produced and their relative bioactivity, is a necessity for all involved in studying this fascinating physiological regulatory phenomenon.

The Corticotropin-Releasing Factor Family: Physiology of the Stress Response

The physiological stress response is responsible for the maintenance of homeostasis in the presence of real or perceived challenges. In this function, the brain activates adaptive responses that involve numerous neural circuits and effector molecules to adapt to the current and future demands. A maladaptive stress response has been linked to the etiology of a variety of disorders, such as anxiety and mood disorders, eating disorders, and the metabolic syndrome. The neuropeptide corticotropin-releasing factor (CRF) and its relatives, the urocortins 1–3, in concert with their receptors (CRFR1, CRFR2), have emerged as central components of the physiological stress response. This central peptidergic system impinges on a broad spectrum of physiological processes that are the basis for successful adaptation and concomitantly integrate autonomic, neuroendocrine, and behavioral stress responses. This review focuses on the physiology of CRF-related peptides and their cognate receptors with the aim of providing a comprehensive up-to-date overview of the field. We describe the major molecular features covering aspects of gene expression and regulation, structural properties, and molecular interactions, as well as mechanisms of signal transduction and their surveillance. In addition, we discuss the large body of published experimental studies focusing on state-of-the-art genetic approaches with high temporal and spatial precision, which collectively aimed to dissect the contribution of CRF-related ligands and receptors to different levels of the stress response. We discuss the controversies in the field and unravel knowledge gaps that might pave the way for future research directions and open up novel opportunities for therapeutic intervention.

Intrinsic and extrinsic regulation of human skin melanogenesis and pigmentation

In human skin, melanogenesis is a tightly regulated process. Indeed, several extracellular signals are transduced via dedicated signalling pathways and mostly converge to MITF, a transcription factor integrating upstream signalling and regulating downstream genes involved in the various inherent mechanisms modulating melanogenesis. The synthesis of melanin pigments occurs in melanocytes inside melanosomes where melanogenic enzymes (tyrosinase and related proteins) are addressed with the help of specific protein complexes. The melanosomes loaded with melanin are then transferred to keratinocytes. A more elaborate level of melanogenesis regulation comes into play via the action of non-coding RNAs (microRNAs, lncRNAs). Besides this canonical regulation, melanogenesis can also be modulated by other non-specific intrinsic pathways (hormonal environment, inflammation) and by extrinsic factors (solar irradiation such as ultraviolet irradiation, environmental pollution). We developed a bioinformatic interaction network gathering the multiple aspects of melanogenesis and skin pigmentation as a resource to better understand and study skin pigmentation biology.

How UV Light Touches the Brain and Endocrine System Through Skin, and Why

The skin, a self-regulating protective barrier organ, is empowered with sensory and computing capabilities to counteract the environmental stressors to maintain and restore disrupted cutaneous homeostasis. These complex functions are coordinated by a cutaneous neuro-endocrine system that also communicates in a bidirectional fashion with the central nervous, endocrine, and immune systems, all acting in concert to control body homeostasis. Although UV energy has played an important role in the origin and evolution of life, UV absorption by the skin not only triggers mechanisms that defend skin integrity and regulate global homeostasis but also induces skin pathology (e.g., cancer, aging, autoimmune responses). These effects are secondary to the transduction of UV electromagnetic energy into chemical, hormonal, and neural signals, defined by the nature of the chromophores and tissue compartments receiving specific UV wavelength. UV radiation can upregulate local neuroendocrine axes, with UVB being markedly more efficient than UVA. The locally induced cytokines, corticotropin-releasing hormone, urocortins, proopiomelanocortin-peptides, enkephalins, or others can be released into circulation to exert systemic effects, including activation of the central hypothalamic-pituitary-adrenal axis, opioidogenic effects, and immunosuppression, independent of vitamin D synthesis. Similar effects are seen after exposure of the eyes and skin to UV, through which UVB activates hypothalamic paraventricular and arcuate nuclei and exerts very rapid stimulatory effects on the brain. Thus, UV touches the brain and central neuroendocrine system to reset body homeostasis. This invites multiple therapeutic applications of UV radiation, for example, in the management of autoimmune and mood disorders, addiction, and obesity.

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.

cAMP-dependent cell differentiation triggered by activated CRHR1 in hippocampal neuronal cells

Corticotropin-releasing hormone receptor 1 (CRHR1) activates the atypical soluble adenylyl cyclase (sAC) in addition to transmembrane adenylyl cyclases (tmACs). Both cAMP sources were shown to be required for the phosphorylation of ERK1/2 triggered by activated G protein coupled receptor (GPCR) CRHR1 in neuronal and neuroendocrine contexts. Here, we show that activated CRHR1 promotes growth arrest and neurite elongation in neuronal hippocampal cells (HT22-CRHR1 cells). By characterising CRHR1 signalling mechanisms involved in the neuritogenic effect, we demonstrate that neurite outgrowth in HT22-CRHR1 cells takes place by a sAC-dependent, ERK1/2-independent signalling cascade. Both tmACs and sAC are involved in corticotropin-releasing hormone (CRH)-mediated CREB phosphorylation and c-fos induction, but only sAC-generated cAMP pools are critical for the neuritogenic effect of CRH, further highlighting the engagement of two sources of cAMP downstream of the activation of a GPCR, and reinforcing the notion that restricted cAMP microdomains may regulate independent cellular processes.

Neuroendocrinology of mast cells: Challenges and controversies

Mast cells (MC) are hemotopoietically derived tissue immune cells that are ubiquitous in the body, including neuroendocrine organs such as the hypothalamus, pineal, pituitary, ovaries, pancreas and uterus where their action is not well understood. Mast cells have historically been associated with allergies because of their rich content of histamine and tryptase, but more recently with regulation of immunity and inflammation due to their synthesis and release of numerous cytokines and chemokines. Mast cells are located perivascularly and express numerous receptors for diverse ligands such as allergens, pathogens, neurotransmitters, neuropeptides and hormones including acetylcholine, calcitonin gene-related peptide (CGRP), corticosteroids, corticotropin-releasing hormone (CRH), β-endorphin, epinephrine, 17β-oestradiol, gonadotrophins, hemokinin-A (HKA), leptin, melatonin, neurotensin (NT), parathyroid hormone (PTH), substance P (SP) and vasoactive intestinal peptide (VIP). Moreover, MC can synthesize and release most of their neurohormonal triggers, including adrenocorticotropin hormone (ACTH), CRH, endorphins, HKA, leptin, melatonin, NT, SP and VIP. Animal experiments have shown that diencephalic MC increase in number during courting in doves, while stimulation of brain and nasal MC leads to activation of the hypothalamic-pituitary-adrenal (HPA) axis. Recent evidence indicates that MC reactivity exhibits diurnal variations, and it is interesting that melatonin appears to regulate MC secretion. However, the way MC change their phenotype or secrete specific molecules selectively at different pathophysiological settings still remains unknown. Mast cells developed over 500 million years ago and may have served as the original prototype neuroimmunoendocrine cell and then evolved into a master regulator of such interactions, especially as most of the known diseases involve neuroinflammation that worsens with stress.

Bioactive forms of vitamin D selectively stimulate the skin analog of the hypothalamus-pituitary-adrenal axis in human epidermal keratinocytes

Ultraviolet radiation B stimulates both the production of vitamin D3 in the skin and the activation of the skin analog of the hypothalamic-pituitary-adrenal axis (HPA) as well as the central HPA. Since the role of vitamin D3 in the regulation of the HPA is largely unknown, we investigated the impact of 1,25(OH)2D3 and its noncalcemic analogs, 20(OH)D3 and 21(OH)pD, on the expression of the local HPA in human epidermal keratinocytes. The noncalcemic analogs showed similar efficacy to 1,25(OH)2D3 in stimulating the expression of neuropeptides, CRF, urocortins and POMC, and their receptors, CRFR1, CRFR2, MC1R, MC2R, MC3R and MC4R. Interestingly, unlike other secosteroids, the activity of 21(OH)pD did not correlate with induction of differentiation, suggesting a separate but overlapping mechanism of action. Thus, biologically active forms of vitamin D can regulate different elements of the local equivalent of the HPA with implications for the systemic HPA.

Neuroendocrinology of the skin

The skin is considered the mirror of the soul and is affected by neurohormonal triggers, especially stress. Hair follicles, keratinocytes, mast cells, melanocytes, and sebocytes all express sex and stress hormones implicating them in a local "hypothalamic-pituitary-adrenal axis." In particular, the peptides corticotropin-releasing hormone (CRH) and neurotensin (NT) have synergistic action stimulating mast cells and are uniquely elevated in the serum of patients with skin diseases exacerbated by stress. Addressing the neurohormonal regulation of skin function could lead to new targets for effective treatment of inflammatory skin diseases.

Stress-related skin disorders

Emerging research has suggested that the skin is not only a target of organismal distress but also an active participant of the stress response through production of local "HPA axis" components, peripheral nerve endings, and resident skin cells, including keratinocytes, mast cells, and immune/immune accessory cells. There are also bidirectional communication pathways between the brain and the skin, which play significant roles in integrating these interactions. In this review, we summarize the intricate relations between stress and several skin conditions. We have tried to identify the underlying mechanisms that link stress to the common dermatoses according to the latest scientific findings.

Phenotypic correlates of melanization in two Sceloporus occidentalis (Phrynosomatidae) populations: Behavior, androgens, stress reactivity, and ectoparasites

Mechanisms underlying production of animal coloration can affect key traits besides coloration. Melanin, and molecules regulating melanin, can directly and indirectly affect other phenotypic traits including aggression, stress-reactivity, and immune function. We studied correlation of melanization with these other traits, comparing within- and between-population differences of adult male western fence lizards, Sceloporus occidentalis. We compared one high- and one low-elevation population in California where individuals are increasingly darker at higher elevations, working during comparable periods of the breeding season at each site (first egg clutch). We measured agonistic behaviors of free-ranging males in response to staged territorial intrusions (STIs). In other sets of males we measured baseline testosterone and corticosterone levels, and hormonal-reactivity to a stress handling paradigm. We counted ectoparasite loads for all males. There were no significant associations between individual variation in melanization and individual variation in any of the variables measured. However, analysis of behavior from the STIs revealed that males in the darker high-elevation population responded with more aggressive behavior compared to males in the lighter low-elevation population. Males in the low-elevation population had significantly higher mean baseline testosterone, but the two populations did not differ in adrenal function (baseline corticosterone or corticosterone after 1-h confinement stress). Males in the darker high-elevation population had higher mean mite loads compared to males in the lighter population. This array of phenotypic differences between the two populations, and the absence of trait associations when assessing individual variation, do not parallel the patterns in other vertebrates. We describe potential differences in selective regimes that could produce these different patterns across vertebrates. These data suggest that hormonal pleiotropy does not constrain phenotypic variation.

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.

Somato stimulation and acupuncture therapy

Acupuncture is an oldest somato stimulus medical technique. As the most representative peripheral nerve stimulation therapy, it has a complete system of theory and application and is applicable to a large population. This paper expounds the bionic origins of acupuncture and analyzes the physiological mechanism by which acupuncture works. For living creatures, functionally sound viscera and effective endurance of pain are essential for survival. This paper discusses the way in which acupuncture increases the pain threshold of living creatures and the underlying mechanism from the perspective of bionics. Acupuncture can also help to adjust visceral functions and works most effectively in facilitating the process of digestion and restraining visceral pain. This paper makes an in-depth overview of peripheral nerve stimulation therapy represented by acupuncture. We look forward to the revival of acupuncture, a long-standing somato stimulus medicine, in the modern medical systems.

BuShenYiQi granule inhibits atopic dermatitis via improving central and skin Hypothalamic-Pituitary-Adrenal axis function

BACKGROUND

Dysfunction of central and skin Hypothalamic-Pituitary-Adrenal (HPA) axis play important roles in pathogenesis of atopic dermatitis (AD). Our previous studies showed that several Chinese herbs could improve HPA axis function. In this study, we evaluated the anti-inflammatory effects of BuShenYiQi granule (BSYQ), a Chinese herbs formula, in AD mice and explored the effective mechanism from regulation of HPA axis.

METHODS

The ovalbumin (OVA) induced AD mice model were established and treated with BSYQ. We evaluated dermatitis score and histology analysis of dorsal skin lesions, meanwhile, serum corticosterone (CORT), adrenocorticotropic hormone (ACTH), corticotropin-releasing hormone (CRH) and inflammatory cytokines were determined by ELISA. The changes of CRH/proopiomelanocortin(POMC) axis elements, corresponding functional receptors and crucial genes of glucocorticosteroidogenesis in the skin were measured by quantitative real-time PCR and western blot, respectively.

RESULTS

The symptoms and pathological changes in skin of AD mice were significantly improved and several markers of inflammation and allergy descended obviously after BSYQ treatment. We found that AD mice had insufficient central HPA tone, but these conditions were markedly improved after BSYQ treatment. The AD mice also showed a disturbed expression of skin HPA. In lesion skin of AD mice, the mRNA and protein expressions of CRH decreased significantly, on the contrary, POMC and cytochrome P450 side-chain cleavage enzyme (CYP11A1) increased markedly, meanwhile, NR3C1 (mouse GR), CRHR2 and 11-hydroxylase type 1(CYP11B1) were reduced locally. Most of these tested indexes were improved after BSYQ treatment.

CONCLUSIONS

AD mice displayed the differential expression pattern of central and skin HPA axis and BSYQ treatment significantly alleviated the symptoms of AD mice and presented anti-inflammatory and anti-allergic effects via regulating the expression of central and skin HPA axis.

UVB Activates Hypothalamic-Pituitary-Adrenal Axis in C57BL/6 Mice

To test the hypothesis that ultraviolet B (UVB) can activate the hypothalamic-pituitary-adrenal (HPA) axis, the shaved back skin of C57BL/6 mice was exposed to 400 mJ/cm² of UVB or was shame irradiated. After 12 and 24 h of exposure, plasma, skin, brain, and adrenals were collected and processed to measure corticotropin-releasing hormone (CRH), urocortin (Ucn), β-endorphin (β-END), ACTH and corticosterone (CORT) or brain was fixed for immunohistochemical detection of CRH. UVB stimulated plasma levels of CRH, Ucn, β-END, ACTH and CORT, and increased skin expression of Ucn, β-END and CORT at the gene and protein/peptide levels. UVB stimulated CRH gene and protein expression in the brain that was localized to the paraventricular nucleus of the hypothalamus. In adrenal glands it increased mRNAs of melanocortin receptor type 2, StAR and CYP11B1. Hypophysectomy abolished UVB stimulation of plasma but not of skin CORT levels, and had no effect on UVB stimulation of CRH and Ucn levels in the plasma, demonstrating the requirement of an intact pituitary for the systemic effect. In conclusion, we identify mechanism of the regulation of body homeostasis by UVB through activation of the HPA axis that originates in the skin and requires pituitary for the systemic effect.

Cytochromes p450 and skin cancer: role of local endocrine pathways

Skin is the largest body organ forming a metabolically active barrier between external and internal environments. The metabolic barrier is composed of cytochromes P450 (CYPs) that regulate its homeostasis through activation or inactivation of biologically relevant molecules. In this review we focus our attention on local steroidogenic and secosteroidogenic systems in relation to skin cancer, e.g., prevention, attenuation of tumor progression and therapy. The local steroidogenic system is composed of locally expressed CYPs involved in local production of androgens, estrogens, gluco- and mineralo-corticosteroids from cholesterol (initiated by CYP11A1) or from steroid precursors delivered to the skin, and of their metabolism and/or inactivation. Cutaneous 7-hydroxylases (CYP7A1, CYP7B1 and CYP39) potentially can produce 7-hydroxy/oxy-steroids/sterols with modifying effects on local tumorigenesis. CYP11A1 also transforms 7-dehydrocholesterol (7DHC)→22(OH)7DHC→20,22(OH)2-7DHC→7-dehydropregnenolone, which can be further metabolized to other 5,7- steroidal dienes. These 5,7-dienal intermediates are converted by ultraviolet radiation B (UVB) into secosteroids which show pro-differentiation and anti-cancer properties. Finally, the skin is the site of activation of vitamin D3 through two alternative pathways. The classical one involves sequential hydroxylation at positions 25 and 1 to produce active 1,25(OH)2D3, which is further inactivated through hydroxylation at C24. The novel pathway is initiated by CYP11A1 with predominant production of 20(OH)D3 which is further metabolized to biologically active but non-calcemic D3-hydroxyderivatives. Classical and non-classical (novel) vitamin D analogs show pro-differentiation, anti-proliferative and anticancer properties. In addition, melatonin is metabolized by local CYPs. In conclusion cutaneously expressed CYPs have significant effects on skin physiology and pathology trough regulation of its chemical milieu.

Corticotropin-releasing hormone, microglia and mental disorders

Microglia derive from mononuclear myeloid progenitors and are a major glial complement of the central nervous system. When microglia are activated they secrete inflammatory cytokines and toxic mediators which amplify the inflammatory response. In addition, the microglia inflammatory products are implicated in the neuronal destruction usually observed in various neurodegenerative diseases. Microglia cells express corticotropin releasing hormone (CRH) receptors, and activation of microglia by CRH releases bioactive molecules which have a biological effect in the brain and regulate several neurological diseases. CRH plays a pivotal role in stress responses and is a key mediator of the hypothalamic-pituitary-adrenocortical system. CRH is expressed in human mast cells, leading to autocrine effects and participates in inflammatory response together with neuropeptides, and stimulates mast cells. IL-33-activated mast cells release vascular endothelial growth factor in response to CRH and act synergistically to increase vascular permeability. CRH also up-regulates IL-18 expression by increasing intracellular reactive oxygen in microglia cells. Here we report the relationship between CRH, microglia and mental disorders.

Putative role of HIF transcriptional activity in melanocytes and melanoma biology

Hypoxia-inducible factor-1α (HIF-1α) is a highly oxygen sensitive bHLH protein that is part of the heterodimeric HIF-1 transcription factor. Under hypoxic stress, HIF-1 activity is induced to control expression of multiple downstream target genes, including vascular endothelial growth factor (VEGF). The normal epidermis exists in a constant mild hypoxic microenvironment and constitutively expresses HIF-1α and HIF-2α. Expression of HIF-1α and/or HIF-2α has been suggested to correlate with the increased malignant potential of melanocytes, therefore, failures of melanoma therapies may be partially linked to high HIF activity. Notably, melanomas that have the V600E BRAF mutation exhibit increased HIF-1α expression. We have utilized a bioinformatics approach to identify putative hypoxia response elements (HREs) in a set of genes known to participate in the process of melanogenesis (includingTRPM1, SLC45A2, HRAS, C-KIT, PMEL and CRH). While some of the mechanistic links between these genes and the HIF pathway have been previously explored, others await further investigation. Although agents targeting HIF activity have been proposed as novel treatment modalities for melanoma, there are currently no clinical trials in progress to test their efficacy in melanoma.

Study of progesterone and cortisol concentrations in the Italian Friesian claw

The present research was conducted to study progesterone and cortisol concentrations in the claw of cattle and to verify whether the cattle claw could be considered an efficient matrix to provide retrospective information regarding progesterone and cortisol concentrations related to pregnancy and peripartum periods. These 2 steroids are involved in hoof growth. The study was performed on 32 calves and 24 pregnant milking cows of the Holstein breed, which were clinically healthy and lacking any claw disorders. Samples of at least 0.5cm in thickness were taken from the sole. Progesterone and cortisol concentrations were determined by RIA. The cortisol concentration in the horny shoe of calves from 0 to 30 d of age was significantly higher than the concentration at 31 to 60 and 61 to 120 d of age. Conversely, the progesterone concentration showed no statistically significant difference in relation to age. The horn progesterone concentrations recorded in the milking dairy cows at 7 mo of pregnancy showed high variability in the horizontal sections of the sole (the individual coefficient of variation ranged between 0.09 and 1.11). In 6 cows, genuine extreme values (genuine outliers) of the progesterone level were found. Moreover, significant differences existed among the progesterone concentrations of the sole's transverse sections. We detected a significant positive correlation between the weight of the horn samples after freeze-drying and their weight after hydration. The cortisol and progesterone levels in soaked horn samples were found to be significantly lower than in the same dry samples. These results show that cortisol and progesterone can be measured in the cattle claw horn. The claws of mature dairy cows could not be used as a matrix to provide a retrospective measure of cumulative hormone secretion, whereas the analysis of the calves' claw horns showed retrospective hormonal information similar to hair samples.

Chronic stress suppresses the expression of cutaneous hypothalamic-pituitary-adrenocortical axis elements and melanogenesis

Chronic stress can affect skin function, and some skin diseases might be triggered or aggravated by stress. Stress can activate the central hypothalamic–pituitary–adrenocortical (HPA) axis, which causes glucocorticoid levels to increase. The skin has HPA axis elements that react to environmental stressors to regulate skin functions, such as melanogenesis. This study explores the mechanism whereby chronic stress affects skin pigmentation, focusing on the HPA axis, and investigates the role of glucocorticoids in this pathway. We exposed C57BL/6 male mice to two types of chronic stress, chronic restraint stress (CRS) and chronic unpredictable mild stress (CUMS). Mice subjected to either stress condition showed reduced melanogenesis. Interestingly, CRS and CUMS triggered reductions in the mRNA expression levels of key factors involved in the HPA axis in the skin. In mice administered corticosterone, decreased melanin synthesis and reduced expression of HPA axis elements were observed. The reduced expression of HPA axis elements and melanogenesis in the skin of stressed mice were reversed by RU486 (a glucocorticoid receptor antagonist) treatment. Glucocorticoids had no significant inhibitory effect on melanogenesis in vitro. These results suggest that, high levels of serum corticosterone induced by chronic stress can reduce the expression of elements of the skin HPA axis by glucocorticoid-dependent negative feedback. These activities can eventually result in decreased skin pigmentation. Our findings raise the possibility that chronic stress could be a risk factor for depigmentation by disrupting the cutaneous HPA axis and should prompt dermatologists to exercise more caution when using glucocorticoids for treatment.

Immunomodulatory effects of sex hormones: requirements for pregnancy and relevance in melanoma

Similarities between the pathologic progression of cancer and the physiologic process of placentation (eg, proliferation, invasion, and local/systemic tolerance) have been recognized for many years. Sex hormones such as human chorionic gonadotropin, estrogens, progesterone, and others contribute to induction of immunologic tolerance at the beginning of gestation. Sex hormones have been shown to play contributory roles in the growth of cancers such as breast cancer, prostrate cancer, endometrial cancer, and ovarian cancer, but their involvement as putative mediators of the immunologic escape of cancer is still being elucidated. Herein, we compare the emerging mechanism by which sex hormones modulate systemic immunity in pregnancy and their potentially similar role in cancer. To do this, we conducted a PubMed search using combinations of the following keywords: "immune regulation," "sex hormones," "pregnancy," "melanoma," and "cancer." We did not limit our search to specific publication dates. Mimicking the maternal immune response to pregnancy, especially in late gestation, might aid in design of better therapies to reconstitute endogenous antitumor immunity and improve survival.

Corticotropin-releasing factor peptide antagonists: design, characterization and potential clinical relevance

Elusive for more than half a century, corticotropin-releasing factor (CRF) was finally isolated and characterized in 1981 from ovine hypothalami and shortly thereafter, from rat brains. Thirty years later, much has been learned about the function and localization of CRF and related family members (Urocortins 1, 2 and 3) and their 2 receptors, CRF receptor type 1 (CRFR1) and CRF receptor type 2 (CRFR2). Here, we report the stepwise development of peptide CRF agonists and antagonists, which led to the CRFR1 agonist Stressin1; the long-acting antagonists Astressin2-B which is specific for CRFR2; and Astressin B, which binds to both CRFR1 and CRFR2.This analog has potential for the treatment of CRF-dependent diseases in the periphery, such as irritable bowel syndrome.

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.

Genetic variation of the cutaneous HPA axis: an analysis of UVB-induced differential responses

Mammalian skin incorporates a local equivalent of the hypothalamic-pituitary-adrenal (HPA) axis that is critical in coordinating homeostatic responses against external noxious stimuli. Ultraviolet radiation B (UVB) is a skin-specific stressor that can activate this cutaneous HPA axis. Since C57BL/6 (B6) and DBA/2J (D2) strains of mice have different predispositions to sensorineural pathway activation, we quantified expression of HPA axis components at the gene and protein levels in skin incubated ex vivo after UVB or sham irradiation. Urocortin mRNA was up-regulated after all doses of UVB with a maximum level at 50 mJ/cm(2) after 12h for D2 and at 200 mJ/cm(2) after 24h for B6. Proopiomelanocortin mRNA was enhanced after 6h with the peak after 12h and at 200 mJ/cm(2) for both genotypes of mice. ACTH levels in tissue and media increased after 24h in B6 but not in D2. UVB stimulated β-endorphin expression was higher in D2 than in B6. Melanocortin receptor 2 mRNA was stimulated by UVB in a dose-dependent manner, with a peak at 200 mJ/cm(2) after 12h for both strains. The expression of Cyp11a1 mRNA - a key mitochondrial P450 enzyme in steroidogenesis, was stimulated at all doses of UVB irradiation, with the most pronounced effect after 12-24h. UVB radiation caused, independently of genotype, a dose-dependent increase in corticosterone production in the skin, mainly after 24h of histoculture. Thus, basal and UVB stimulated expression of the cutaneous HPA axis differs as a function of genotype: D2 responds to UVB earlier and with higher amplitude than B6, while B6 shows prolonged (up to 48 h) stress response to a noxious stimulus such as UVB.

Steroidogenesis in the skin: implications for local immune functions

The skin has developed a hierarchy of systems that encompasses the skin immune and local steroidogenic activities in order to protect the body against the external environment and biological factors and to maintain local homeostasis. Most recently it has been established that skin cells contain the entire biochemical apparatus necessary for production of glucocorticoids, androgens and estrogens either from precursors of systemic origin or, alternatively, through the conversion of cholesterol to pregnenolone and its subsequent transformation to biologically active steroids. Examples of these products are corticosterone, cortisol, testosterone, dihydrotesterone and estradiol. Their local production can be regulated by locally produced corticotropin releasing hormone (CRH), adrenocorticotropic hormone (ACTH) or cytokines. Furthermore the production of glucocorticoids is affected by ultraviolet B radiation. The level of production and nature of the final steroid products are dependent on the cell type or cutaneous compartment, e.g., epidermis, dermis, adnexal structures or adipose tissue. Locally produced glucocorticoids, androgens and estrogens affect functions of the epidermis and adnexal structures as well as local immune activity. Malfunction of these steroidogenic activities can lead to inflammatory disorders or autoimmune diseases. The cutaneous steroidogenic system can also have systemic effects, which are emphasized by significant skin contribution to circulating androgens and/or estrogens. Furthermore, local activity of CYP11A1 can produce novel 7Δ-steroids and secosteroids that are biologically active. Therefore, modulation of local steroidogenic activity may serve as a new therapeutic approach for treatment of inflammatory disorders, autoimmune processes or other skin disorders. In conclusion, the skin can be defined as an independent steroidogenic organ, whose activity can affect its functions and the development of local or systemic inflammatory or autoimmune diseases. This article is part of a Special Issue entitled 'CSR 2013'.

Local blockade of glucocorticoid activation reverses stress- and glucocorticoid-induced delays in cutaneous wound healing

Stress slows cutaneous wound healing (WH) in an endogenous glucocorticoid (GC)-dependent fashion. We investigated whether stress/GC-induced delays in WH require further intracutaneous activation of endogenous GC; and whether blockade or down-regulation of peripheral activation normalizes WH in the face of stress. Delayed WH in our motion-restricted murine model of stress could be attributed to elevated systemic GC, because blockade of GC production (using corticotropin-releasing factor inhibitor, antalarmin), or of peripheral binding to the GC receptor [GCr], with an antagonist, Ru-486, normalized WH. We next investigated whether local blockade or down-regulation of the peripheral GC-activating enzyme, 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1), accelerates cutaneous WH. Topical applications of nonspecific (carbenoxolone) as well as an isoform-specific 11β-HSD1 inhibitor overcame stress and exogenous GC-induced delays in WH. Moreover, two liver X receptor ligands, TO901317 and GW3695, down-regulated expression of 11β-HSD1, attenuating stress-induced delays in WH. Combined inhibitor and liver X receptor ligand applications accelerated WH in the face of stress/systemic GC. Thus: (1) intracutaneous conversion of inactive-to-active GC accounts for stress (GC)-induced delays in WH; and (2) blockade or down-regulation of 11β-HSD1 and/or GCr normalize cutaneous WH in the face of stress/GC. Local blockade or down-regulation of cutaneous GC activation could help enhance WH in various clinical settings.