Hormonal regulation of POMC gene expression

Zebrafish Bioassay for Screening Therapeutic Candidates Based on Melanotrophic Activity

In this study, we used the zebrafish animal model to establish a bioassay by which physiological efficacy differential of alpha-melanocyte-stimulating hormone (α-MSH) analogues could be measured by melanosome dispersion in zebrafish larvae. Brain-skin connection research has purported the interconnectedness between the nervous system and skin physiology. Accordingly, the neuropeptide α-MSH is a key regulator in several physiological processes, such as skin pigmentation in fish. In mammals, α-MSH has been found to regulate motivated behavior, appetite, and emotion, including stimulation of satiety and anxiety. Several clinical and animal model studies of autism spectrum disorder (ASD) have already demonstrated the effectiveness of α-MSH in restoring the social deficits of autism. Therefore, we sought to analyze the effect of synthetic and naturally-occurring α-MSH variants amongst different species. Our results showed that unique α-MSH derivatives from several fish species produced differential effects on the degree of melanophore dispersion. Using α-MSH human form as a standard, we could identify derivatives that induced greater physiological effects; particularly, the synthetic analogue melanotan-II (MT-II) exhibited a higher capacity for melanophore dispersion than human α-MSH. This was consistent with previous findings in an ASD mouse model demonstrating the effectiveness of MT-II in improving ASD behavioral symptoms. Thus, the melanophore assay may serve as a useful screening tool for therapeutic candidates for novel drug discovery.

Left-right side-specific endocrine signaling complements neural pathways to mediate acute asymmetric effects of brain injury

Brain injuries can interrupt descending neural pathways that convey motor commands from the cortex to spinal motoneurons. Here, we demonstrate that a unilateral injury of the hindlimb sensorimotor cortex of rats with completely transected thoracic spinal cord produces hindlimb postural asymmetry with contralateral flexion and asymmetric hindlimb withdrawal reflexes within 3 hr, as well as asymmetry in gene expression patterns in the lumbar spinal cord. The injury-induced postural effects were abolished by hypophysectomy and were mimicked by transfusion of serum from animals with brain injury. Administration of the pituitary neurohormones β-endorphin or Arg-vasopressin-induced side-specific hindlimb responses in naive animals, while antagonists of the opioid and vasopressin receptors blocked hindlimb postural asymmetry in rats with brain injury. Thus, in addition to the well-established involvement of motor pathways descending from the brain to spinal circuits, the side-specific humoral signaling may also add to postural and reflex asymmetries seen after brain injury.

The vasotocinergic system and its role in the regulation of stress in birds

The regulation of stress in birds includes a complex interaction of neural systems affecting the hypothalamic-pituitary-adrenal (HPA) axis. In addition to the hypothalamic paraventricular nucleus, a structure called the nucleus of the hippocampal commissure likewise affects the output of pituitary stress hormones and appears to be unique to avian species. Within the anterior pituitary, the avian V1a and V1b receptors were found in corticotropes. Based on our studies with central administration of hormones in the chicken, corticotropic releasing hormone (CRH) is a more potent ACTH secretagogue than arginine vasotocin (AVT). In contrast, when applied peripherally, AVT is more efficacious. Co-administration of AVT and CRH peripherally, resulted in a synergistic stimulation of corticosterone release. Data suggest receptor oligomerization as one possible mechanism. In birds, vasotocin receptors associated with stress responses include the V1a and V1b receptors. Three-dimensional, homology-based structural models of the avian V1aR were built to test agonists and antagonists for each receptor that were screened by molecular docking to map their binding sites on each receptor. Additionally, binding affinity values for each available peptide antagonist to the V1aR and V1bR were determined. An anterior pituitary primary culture system was developed to determine how effective each antagonist blocked the function of each receptor in culture when stimulated by a combination of AVT/CRH administration. Use of an antagonist in subsequent in vivo studies identified the V1aR in regulating food intake in birds. The V1aR was likewise found in circumventricular organs of the brain, suggesting a possible function in stress.

Identification of avian vasotocin receptor subtype-specific antagonists involved in the stress response of the chicken, Gallus gallus

Vasotocin 1a and 1b receptors (V1aR and V1bR) have been shown to play important roles in the neuroendocrine regulation of stress responses via the anterior pituitary (AP) of birds. To identify effective subtype-specific antagonists for the chicken V1aR (cV1aR) and cV1bR, potential antagonists to the mammalian V1R were screened against the cV1aR and cV1bR 3D structural models by molecular docking analysis with determination of binding pocket/amino acid residues involved in the interaction. The antagonistic effects of the selected ligands were examined by measuring pro-opiomelanocortin (POMC) heteronuclear RNA (hnPOMC) levels following the in vitro stress administration to primary chicken AP cells. Results of in silico analysis showed that the Manning compound and several other antagonists were bound to cV1bR with higher affinity than the natural agonist, arginine vasotocin (AVT). Similarities and differences in the antagonist-receptor binding interface with receptors were characterized for each ligand. Non-peptide mammalian V1bR antagonists, SSR-149415 and L-368899, were shown to be effective and had an additive effect in blocking POMC hnRNA expression in pituitary cell culture studies. SR-49059 antagonized the effect(s) of AVT/CRH on the downregulation of the cV1aR and the upregulation of the cCRH-R2 expression but not the cV1bR and cCRH-R1. The Manning compound antagonized the downregulation of cV1aR, cV1bR and cCRH-R1 and the upregulation of cCRH-R2 expression. The specificity of antagonists apparently resulted from unique differences in the interacting residues and their binding affinities. Collectively, these results provide valuable leads for future development of novel compounds capable of blocking or attenuating the AP stress response of avian species and perhaps other non-mammalian vertebrates as well.

Do Neuroendocrine Peptides and Their Receptors Qualify as Novel Therapeutic Targets in Osteoarthritis?

Joint tissues like synovium, articular cartilage, meniscus and subchondral bone, are targets for neuropeptides. Resident cells of these tissues express receptors for various neuroendocrine-derived peptides including proopiomelanocortin (POMC)-derived peptides, i.e., α-melanocyte-stimulating hormone (α-MSH), adrenocorticotropin (ACTH) and β-endorphin (β-ED), and sympathetic neuropeptides like vasoactive intestinal peptide (VIP) and neuropeptide y (NPY). Melanocortins attained particular attention due to their immunomodulatory and anti-inflammatory effects in several tissues and organs. In particular, α-MSH, ACTH and specific melanocortin-receptor (MCR) agonists appear to have promising anti-inflammatory actions demonstrated in animal models of experimentally induced arthritis and osteoarthritis (OA). Sympathetic neuropeptides have obtained increasing attention as they have crucial trophic effects that are critical for joint tissue and bone homeostasis. VIP and NPY are implicated in direct and indirect activation of several anabolic signaling pathways in bone and synovial cells. Additionally, pituitary adenylate cyclase-activating polypeptide (PACAP) proved to be chondroprotective and, thus, might be a novel target in OA. Taken together, it appears more and more likely that the anabolic effects of these neuroendocrine peptides or their respective receptor agonists/antagonists may be exploited for the treatment of patients with inflammatory and degenerative joint diseases in the future.

Neonatal overfeeding disrupts pituitary ghrelin signalling in female rats long-term; Implications for the stress response

The hypothalamic-pituitary-adrenal (HPA) axis responses to psychological stress are exacerbated in adult female but not male rats made obese due to overfeeding in early life. Ghrelin, traditionally known for its role in energy homeostasis, has been recently recognised for its role in coordinating the HPA responses to stress, particularly by acting directly at the anterior pituitary where the growth hormone secretagogue receptor (GHSR), the receptor for acyl ghrelin, is abundantly expressed. We therefore hypothesised that neonatal overfeeding in female rats would compromise pituitary responsiveness to ghrelin, contributing to a hyperactive central stress responsiveness. Unlike in males where hypothalamic ghrelin signalling is compromised by neonatal overfeeding, there was no effect of early life diet on circulating ghrelin or hypothalamic ghrelin signalling in females, indicating hypothalamic feeding and metabolic ghrelin circuitry remains intact. However, neonatal overfeeding did lead to long-term alterations in the pituitary ghrelin system. The neonatally overfed females had increased neonatal and reduced adult expression of GHSR and ghrelin-O-acyl transferase (GOAT) in the pituitary as well as reduced pituitary responsiveness to exogenous acyl ghrelin-induced adrenocorticotropic hormone (ACTH) release in vitro. These data suggest that neonatal overfeeding dysregulates pituitary ghrelin signalling long-term in females, potentially accounting for the hyper-responsive HPA axis in these animals. These findings have implications for how females may respond to stress throughout life, suggesting the way ghrelin modifies the stress response at the level of the pituitary may be less efficient in the neonatally overfed.

The Pulsatility of ACTH Secretion in the Rat Anterior Pituitary Cell Perifusion System

Aims: This study aimed to examine the physiological mechanism whereby the corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP) exert their influence on adrenocorticotropic hormone (ACTH) secretion in pituitary cells. Methods: Anterior pituitary cells were harvested from male rats and placed in the perifusion system. Cells were perifused with serum-free medium for 6 hours before fraction collection. After 30-minute of baseline collection, perifusion media was changed to expose the cells to CRH with or without AVP. ACTH concentration in each fraction was measured using enzyme immunoassay chemiluminescent kit. Results: The lowest physiological concentration of CRH (10 pM) or AVP (10 pM) was not able to induce a marked increase in ACTH secretion. Higher concentration of CRH (30 pM) or AVP (100 pM) in the physiological range caused sustained elevation of ACTH secretion (P < 0.001), while the secretion remained at similar levels for up to 1 hour with continuous stimulation. Perifusion with 10 pM AVP and 10 pM or 30 pM CRH caused a 2.38-fold and 2.99-fold increase in pulsatile ACTH secretion in pituitary cells, respectively. The duration of pulsatility caused by perifusion with 10 pM AVP and 30 pM CRH was close to that observed under physiological condition. Conclusions: By using the rat anterior pituitary cell perifusion system, we found that CRH and AVP potentiate the effect of each other on ACTH secretion, but AVP was a less potent agonist than CRH. The data suggest that CRH and AVP are essential for the pulsatility of ACTH, and AVP acts like a switch of the pulsatility.

Glucocorticoid Fast Feedback Inhibition of Stress-Induced ACTH Secretion in the Male Rat: Rate Independence and Stress-State Resistance

Normal glucocorticoid secretion is critical for physiological and mental health. Glucocorticoid secretion is dynamically regulated by glucocorticoid-negative feedback; however, the mechanisms of that feedback process are poorly understood. We assessed the temporal characteristics of glucocorticoid-negative feedback in vivo using a procedure for drug infusions and serial blood collection in unanesthetized rats that produced a minimal disruption of basal ACTH plasma levels. We compared the negative feedback effectiveness present when stress onset coincides with corticosterone's (CORT) rapidly rising phase (30 sec pretreatment), high plateau phase (15 min pretreatment), or restored basal phase (60 min pretreatment) as well as effectiveness when CORT infusion occurs after the onset of stress (5 min poststress onset). CORT treatment prior to stress onset acted remarkably fast (within 30 sec) to suppress stress-induced ACTH secretion. Furthermore, fast feedback induction did not require rapid increases in CORT at the time of stress onset (hormone rate independent), and those feedback actions were relatively long lasting (≥15 min). In contrast, CORT elevation after stress onset produced limited and delayed ACTH suppression (stress state resistance). There was a parallel stress-state resistance for CORT inhibition of stress-induced Crh heteronuclear RNA in the paraventricular nucleus but not Pomc heteronuclear RNA in the anterior pituitary. CORT treatment did not suppress stress-induced prolactin secretion, suggesting that CORT feedback is restricted to the control of hypothalamic-pituitary-adrenal axis elements of a stress response. These temporal, stress-state, and system-level features of in vivo CORT feedback provide an important physiological context for ex vivo studies of molecular and cellular mechanisms of CORT-negative feedback.

Regulation of the hypothalamic-pituitary-adrenal axis by neuropeptides

The major endocrine response to stress occurs via activation of the hypothalamic-pituitary-adrenal (HPA) axis, leading ultimately to increases in circulating glucocorticoids, which are essential for the metabolic adaptation to stress. The major players in the HPA axis are the hypothalamic neuropeptide, corticotropin releasing hormone (CRH), the pituitary hormone adrenocorticotropic hormone, and the negative feedback effects of adrenal glucocorticoids. In addition, a number of other neuropeptides, including vasopressin (VP), angiotensin II, oxytocin, pituitary adenylate cyclase activating peptide, orexin and cholecystokinin, and nesfatin can affect HPA axis activity by influencing the expression and secretion of CRH, and also by modulating pituitary corticotroph function or adrenal steroidogenesis. Of these peptides, VP co-secreted with CRH from axonal terminals in the external zone of the median eminence plays a prominent role by potentiating the stimulatory effect of CRH and by increasing the number of pituitary corticotrophs during chronic challenge. Although the precise role and significance of many of these neuropeptides in regulating HPA axis activity requires further investigation, it is likely that they are part of a multifactorial system mediating the fine tuning of HPA axis activity during adaptation to a variety of physiological and stressful conditions.

Regulation of gene expression of vasotocin and corticotropin-releasing hormone receptors in the avian anterior pituitary by corticosterone

The effect of chronic stress (CS) on gene expression of the chicken arginine vasotocin (AVT) and corticotropin-releasing hormone (CRH) receptors [VT2R, VT4R, CRH-R1, and CRH-R2] was examined by measuring receptor mRNA levels in the anterior pituitary gland of the chicken after chronic immobilization stress compared to acute stress (AS). Radioimmunoassay results showed that blood circulating corticosterone (CORT) levels in the CS group were significantly decreased compared to that of birds in the AS group (P<0.05). The VT2R and CRH-R2 mRNA in CS birds were significantly decreased to that of controls. The VT4R mRNA was significantly decreased compared to controls in AC birds and was further decreased in the CS group compared to controls (P<0.05). The CRH-R1 mRNA was significantly decreased in the AS birds compared to controls. However, there was no significant difference of CRH-R1 mRNA between acute stress and chronic stress birds. Using primary anterior pituitary cell cultures, the effect of exogenous CORT on VT/CRH receptor gene expression was examined. Receptor mRNA levels were measured after treatment of CORT followed by AVT/CRH administration. The CORT pretreatment resulted in a dose-dependent decrease of proopiomelanocortin heteronuclear RNA, a molecular marker of a stress-induced anterior pituitary. Without CORT pretreatment of anterior pituitary cell cultures, the VT2R, VT4R and CRH-R1mRNA levels were significantly increased within 15 min and then decreased at 1 h and 6 h by AVT/CRH administration (P<0.05). Pretreatment of CORT in anterior pituitary cells induced a dose-dependent increase of VT2R, VT4R and CRH-R2 mRNA levels, and a significant decrease of CRH-R1 mRNA levels at only the high dose (10 ng/ml) of CORT (P<0.05).Taken together, results suggest a modulatory role of CORT on the regulation of VT/CRH receptor gene expression in the avian anterior pituitary gland dependent upon CORT levels.

The size of a melanin-based plumage ornament correlates with glucocorticoid receptor concentrations in the skin of that ornament

Glucocorticoid hormones such as corticosterone (CORT) play crucial roles in many physiological processes. CORT's actions are primarily mediated via binding to two receptors (glucocorticoid receptors (GRs) and mineralocorticoid receptors (MRs)) in different target tissues. CORT receptors can be independently regulated from circulating hormone titres, from tissue to tissue and even within different regions of the same tissue type. Increasing evidence has shown relationships between circulating CORT and melanin-based pigmentation in skin and feathers, yet to our knowledge, there have been no studies of CORT receptors in the skin of melanized ornaments. Male house sparrows (Passer domesticus) have a black, melanized bib, and evidence suggests that bib size is an important intraspecific signal. We examined the relationship between bib area and tissue sensitivity to CORT by quantifying GR and MR in bib skin and in adjacent paler-feathered belly skin (as a control tissue) at different life-history stages using radioligand binding assays. Males with larger bibs relative to their life-history stage had less GR in bib skin, but not belly skin, than males with smaller bibs. These results suggest a connection between the size of a melanin-based ornament and the underlying tissue's responsiveness to CORT.

Stress responsiveness of the hypothalamic-pituitary-adrenal axis: age-related features of the vasopressinergic regulation

The hypothalamic-pituitary-adrenal (HPA) axis plays a key role in adaptation to environmental stresses. Parvicellular neurons of the hypothalamic paraventricular nucleus secrete corticotrophin releasing hormone (CRH) and arginine vasopressin (AVP) into pituitary portal system; CRH and AVP stimulate adrenocorticotropic hormone (ACTH) release through specific G-protein-coupled membrane receptors on pituitary corticotrophs, CRHR1 for CRH and V1b for AVP; the adrenal gland cortex secretes glucocorticoids in response to ACTH. The glucocorticoids activate specific receptors in brain and peripheral tissues thereby triggering the necessary metabolic, immune, neuromodulatory, and behavioral changes to resist stress. While importance of CRH, as a key hypothalamic factor of HPA axis regulation in basal and stress conditions in most species, is generally recognized, role of AVP remains to be clarified. This review focuses on the role of AVP in the regulation of stress responsiveness of the HPA axis with emphasis on the effects of aging on vasopressinergic regulation of HPA axis stress responsiveness. Under most of the known stressors, AVP is necessary for acute ACTH secretion but in a context-specific manner. The current data on the AVP role in regulation of HPA responsiveness to chronic stress in adulthood are rather contradictory. The importance of the vasopressinergic regulation of the HPA stress responsiveness is greatest during fetal development, in neonatal period, and in the lactating adult. Aging associated with increased variability in several parameters of HPA function including basal state, responsiveness to stressors, and special testing. Reports on the possible role of the AVP/V1b receptor system in the increase of HPA axis hyperactivity with aging are contradictory and requires further research. Many contradictory results may be due to age and species differences in the HPA function of rodents and primates.

Role of proopiomelanocortin-derived peptides and their receptors in the osteoarticular system: from basic to translational research

Proopiomelanocortin (POMC)-derived peptides such as melanocortins and β-endorphin (β-ED) exert their pleiotropic effects via binding to melanocortin receptors (MCR) and opioid receptors (OR). There is now compelling evidence for the existence of a functional POMC system within the osteoarticular system. Accordingly, distinct cell types of the synovial tissue and bone have been identified to generate POMC-derived peptides like β-ED, ACTH, or α-MSH. MCR subtypes, especially MC1R, MC2R (the ACTH receptor), MC3R, and MC4R, but also the μ-OR and δ-OR, have been detected in various cells of the synovium, cartilage, and bone. The respective ligands of these POMC-derived peptide receptors mediate an increasing number of newly recognized biological effects in the osteoarticular system. These include bone mineralization and longitudinal growth, cell proliferation and differentiation, extracellular matrix synthesis, osteoprotection, and immunomodulation. Importantly, bone formation is also regulated by the central melanocortin system via a complex hormonal interplay with other organs and tissues involved in energy metabolism. Among the POMC-derived peptides examined in cell culture systems from osteoarticular tissue and in animal models of experimentally induced arthritis, α-MSH, ACTH, and MC3R-specific agonists appear to have the most promising antiinflammatory actions. The effects of these melanocortin peptides may be exploited in future for the treatment of patients with inflammatory and degenerative joint diseases.

Inhibitory effects of corticosterone in the hypothalamic paraventricular nucleus (PVN) on stress-induced adrenocorticotrophic hormone secretion and gene expression in the PVN and anterior pituitary

Endogenous glucocorticoid negative-feedback influence on the hypothalamic-pituitary-adrenal (HPA) axis depends on glucocorticoid actions exerted on multiple glucocorticoid-sensitive tissues and differential glucocorticoid effects that are expressed within several distinct temporal domains. The relative contribution and underlying molecular mechanisms of action for the effects of location and timing of glucocorticoid exposure on HPA axis activity remain to be determined. In the present study, we examined the effects of acute exposure to corticosterone (CORT) at the level of the paraventricular nucleus (PVN) on the HPA axis response to a subsequent stressor in a short-term (1 h) timeframe. Intra-PVN CORT microinjection 1 h before restraint suppressed the adrenocorticotrophic hormone (ACTH) response and blunted restraint-induced corticotrophin-releasing hormone (CRH) heterogeneous nuclear (hn)RNA expression in the PVN and pro-opiomelanocortin hnRNA expression in the anterior pituitary (AP); however, it had no effect on restraint-induced plasma prolactin levels and c-fos mRNA expression (PVN and AP). This pattern of results suggests that CORT acts locally at the level of the PVN within a short-term timeframe to suppress stress-induced excitation-exocytosis coupling within CRH neurones and CRH gene induction without altering the stress-associated trans-synaptic input and intracellular signal transduction that converges on PVN c-fos gene induction. The present study is the first to demonstrate that an acute infusion of CORT into the PVN is sufficient to suppress the ACTH response to stress initiated 1 h after CORT infusion.

Cardiovascular effects of melanocortins

Melanocortins (MSH's) are three structurally related peptides derived from proopiomelanocortin. They regulate several physiologic functions including energy metabolism, appetite, and inflammation. Recent work in rodents has also identified important effects of MSH's, particularly γ-MSH, on sodium metabolism and blood pressure regulation. Normal rats and mice respond to a high sodium diet with an increase in the plasma concentration of γ-MSH, and remain normotensive, while those with genetic or pharmacologic γ-MSH deficiency become hypertensive on a high sodium diet. This hypertension is corrected by exogenous administration of the peptide. Mice lacking the γ-MSH receptor (the melanocortin 3 receptor, Mc3r) also become hypertensive on a high sodium diet but remain so when administered γ-MSH, and infusions of physiologic levels of the peptide stimulate urinary sodium excretion in normal rats and mice, but not in mice with deletion of Mc3r. The salt-sensitive hypertension in rodents with impaired γ-MSH signaling appears due to stimulation of noradrenergic activity, since plasma noradrenaline is increased and the hypertension is rapidly corrected with infusion of the α-adrenoceptor antagonist phentolamine. In contrast to the antihypertensive property of physiologic levels of γ-MSH, intravenous or intracerebroventricular injections of high levels of the peptide raise blood pressure. This occurs in mice lacking Mc3r, indicating an interaction with some other central receptor. Finally, the salt-sensitive hypertension in rodents with disruption of γ-MSH signaling is accompanied by insulin resistance, an observation which offers a new window into the study of the association of salt-sensitive hypertension with insulin resistance and type II diabetes.

HPA axis responsiveness to stress: implications for healthy aging

The major neuroendocrine response mediating stress adaptation is activation of the hypothalamic pituitary adrenal axis, with stimulation of corticotropin releasing hormone (CRH) and vasopressin (VP) from parvocellular neurons of the hypothalamic paraventricular nucleus, leading to stimulation of pituitary ACTH secretion and increases in glucocorticoid secretion from the adrenal cortex. Basal production and transient increases during stress of glucocorticoids and its hypothalamic regulators are essential for neuronal plasticity and normal brain function. While activation of the HPA axis is essential for survival during stress, chronic exposure to stress hormones can predispose to psychological, metabolic and immune alterations. Thus, prompt termination of the stress response is essential to prevent negative effects of inappropriate levels of CRH and glucocorticoids. This review addresses the regulation of HPA axis activity with emphasis on the mechanisms of termination of CRH transcription, which is a critical step in this process. In addition, the actions by which glucocorticoids, CRH and VP can affect the aging process will be discussed.

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.

Possible roles of epidermal opioid systems in pruritus of atopic dermatitis

The micro-opioid (beta-endorphin/micro-opioid receptor) and kappa-opioid (dynorphin A (DynA)/kappa-opioid receptor) systems play pivotal roles in the modulation of pruritus in the central nervous system. The micro-opioid system has also been identified in human epidermis, raising the possibility that the system controls the peripheral itch. However, the precise distribution of the kappa-opioid system has not yet been clarified in human epidermis. To address this issue, reverse transcription-PCR and immunohistochemical analyses were performed on cultured keratinocytes and normal skins from humans. The analyses revealed that epidermal keratinocytes express kappa-opioid receptor and its ligands, DynA (1-17) and DynA (1-8). Moreover, expression for micro- and kappa-opioid systems was examined immunohistochemically in skin biopsies from healthy volunteers and patients with atopic dermatitis (AD) before and after psoralen-ultraviolet A (PUVA) therapy. Our expression analyses showed that only the kappa-opioid system, not the micro-opioid system, was downregulated in the epidermis of AD patients. The downregulation of the micro-opioid system and the restoration of the kappa-opioid system by PUVA therapy were observed in the AD patients, concomitant with a decrease of VAS (visual analogue scale) scores. These results suggest epidermal opioid systems are associated with the modulation of pruritus in AD. This new finding may help us to understand the control mechanism of peripheral itch.

Cardiovascular and renal actions of melanocyte-stimulating hormone peptides

PURPOSE OF REVIEW

Melanocyte stimulating hormones (MSHs, melanocortins) have important roles in feeding and energy metabolism and in inflammation. Recent observations have uncovered major functions for these peptides, particularly gamma-MSH, in cardiovascular regulation and sodium metabolism.

RECENT FINDINGS

Both alpha- and gamma-MSH acutely elevate blood pressure and heart rate through central stimulation of sympathetic nervous outflow. This action of alpha-MSH is mediated by the melanocortin 4 receptor (MC4R), whereas sympathetic nervous stimulation by gamma-MSH does not involve its receptor MC3R but rather is likely due to activation of a sodium channel in the central nervous system. In contrast, gamma-MSH deficiency in rodents, or disruption of MC3R, leads to marked salt-sensitive hypertension, again through a central mechanism: a small dose of exogenous peptide delivered into the cerebroventricular system of mice with gamma-MSH deficiency restores blood pressure to normal. This salt-sensitive hypertension is accompanied by the development of insulin resistance; the mechanism linking these two consequences of a high-salt diet is not yet known but may involve activation of the sympathetic nervous system.

SUMMARY

The study of MSH peptides in blood pressure regulation offers a new opportunity to gain insight into the mechanisms underlying salt sensitivity and its link to insulin resistance, and to new therapies.

Regulation of proopiomelanocortin gene transcription during single and repeated immobilization stress

We have previously reported that repeated immobilization produces persistent activation of the hypothalamic-pituitary-adrenocortical axis in rats. In an attempt to assess whether any adaptational responses occur at the pituitary level, we examined the detailed time courses of proopiomelanocortin (POMC) gene transcription in the anterior pituitary (AP) in comparison with those of corticotropin-releasing hormone (CRH) gene transcription in the hypothalamic paraventricular nucleus (PVN) during single and repeated immobilization using both intronic and exonic probes. During single immobilization, there was a robust and rapid increase in both CRH heteronuclear RNA (hnRNA) in the PVN and POMC hnRNA in the AP, together with a slower increase in CRH mRNA, but no significant increase in POMC mRNA. Single immobilization also caused significant increases in the plasma concentrations of both ACTH and corticosterone. Daily immobilization for 6 days increased the basal levels of CRH hnRNA and CRH mRNA in the PVN and POMC mRNA in the AP. Both CRH hnRNA and POMC hnRNA responded rapidly to a final episode of acute immobilization on day 7, whereas the peak values of CRH hnRNA and POMC hnRNA after 15 min of the final stress were smaller than those during single immobilization. In contrast to single stress, CRH mRNA did not change significantly, whereas POMC mRNA robustly increased after the final immobilization on day 7. Plasma ACTH increased to a similar degree to single stress, but its initial increase at 5 min was significantly higher than that during single immobilization. The increase in the plasma corticosterone concentration was higher during final immobilization than during single stress. These results suggest that, in response to the hypothalamic drive during repeated immobilization stress, pituitary corticotrophs are capable of upregulating the basal and stress-induced POMC mRNA levels via increased efficiency of the posttranscriptional processing of the hnRNA and/or increased mRNA stability.

Involvement of corticotropin-releasing hormone- and interleukin (IL)-6-dependent proopiomelanocortin induction in the anterior pituitary during hypothalamic-pituitary-adrenal axis activation by IL-1alpha

IL-1alpha/beta and IL-6 are endogenous modulator of hypothalamo-pituitary-adrenal axis (HPAA) and are thought to play key roles in immune-neuroendocrine interactions during inflammation. Here, we show IL-1alpha induced a normal HPAA activation in IL-1alpha/beta knockout (KO) and IL-6 KO mice at 1 h; however, at 6 h HPAA activation was reduced relative to wild-type mice, indicating a role for endogenous IL-1alpha/beta and IL-6 in prolonged HPAA activation. We found that the induction of proopiomelanocortin (POMC) transcript in the anterior pituitary (AP) at 6 h in response to IL-1alpha was reduced in IL-1alpha/beta KO and IL-6 KO mice, as well as in CRH KO mice, suggesting IL-1alpha/beta, IL-6, and CRH are all required for POMC induction. The induction of CRH transcript in the paraventricular nucleus at 6 h and plasma IL-6 levels, in response to IL-1alpha, were reduced in IL-1alpha/beta KO mice. Because IL-1alpha-induced activation of signal transducer and activator of transcription 3 in the AP was also suppressed in IL-6 KO mice, we suggest that plasma IL-6 is first induced by IL-1alpha, and IL-6 activates signal transducer and activator of transcription 3 in the AP, leading to the induction of POMC in concert with CRH. Our results suggest a role for IL-1alpha/beta in the induction of POMC in the AP through the induction of two independent pathways, CRH and IL-6.

Selective activation of adrenergic β1receptors induces heme oxygenase 1 production in RAW264.7 cells

We hypothesized that catecholamines through beta-adrenoceptor might modulate macrophage function. We showed that isoproterenol concentration-dependently induced HO-1 production through beta(1)-but not beta(2)-adrenoceptor. Production was increased by forskolin and inhibited by pretreatment with the PKA inhibitor, H-89. Furthermore, induction of HO-1 by isoproterenol effectively protected RAW264.7 cells from effects of glucose oxidase treatment, which was abrogated either by HO-1 inhibitor, ZnPP IX and beta-adenoceptor antagonist, propranolol. Thus, stimulation of HO-1 production through beta(1)-adenoceptors, and via the PKA pathways by isoproterenol, can enable RAW264.7 cells to resist oxidant stress, suggesting that catecholamine hormones may be necessary, at least, to maximize defending role of macrophages.

Genomic structure of the proopiomelanocortin gene and expression during acute low-water stress in channel catfish

Proopiomelanocortin (POMC) is an important gene involved in the stress response of the hypothalamic-pituitary-adrenal axis. It is a precursor of several peptide hormones including adrenocorticotropic hormone, melanocyte stimulating hormones, and beta-endorphin. Our study aims to determine genomic structure and expression of POMC gene during temporal stress in channel catfish (Ictalurus punctatus). The catfish POMC gene consisting of three exons and two introns has a similar structural organization to that of other species. The catfish and mammalian POMC promoters do not exhibit regions of conservation except that of one TATA box. Genomic Southern blot analysis indicated POMC is present as a single copy gene in the catfish genome. Real-time PCR allowed us to monitor temporal expression of the POMC mRNA in catfish pituitary during low-water stress. Plasma cortisol concentrations were also measured as an indicator of stress. Within 15 min after the onset of low-water stress, POMC mRNA expression was elevated 1.87-fold above the control value. The POMC mRNA level had declined after 30 min (1.29-fold) and 1h (1.1-fold) at which time stress was removed. After 1h recovery, a significant increase in the POMC mRNA expression was detected (2.44-fold, P<0.05) followed by a decline 2h later (1.52-fold) when the experiment was terminated. Plasma cortisol levels in stressed fish were significantly above the cortisol levels in control fish during stress application (t=15 min, t=30 min, and t=1h, P<0.05), which then returned to normal during recovery. We conclude that POMC and cortisol are both involved in the low-water stress response during which cortisol may serve as a negative regulator of POMC expression in catfish.

Strain-dependent influences on the hypothalamo-pituitary-adrenal axis profoundly affect the 7B2 and PC2 null phenotypes

Two null mouse models have previously been created to study the role of the prohormone convertase (PC2) and its helper protein 7B2; unexpectedly, the phenotypes of these two nulls differ profoundly, with the 7B2 but not the PC2 null dying at 5 wk. The genetic backgrounds of these two models differ, with the 7B2 null in a 129/SvEv (129) background and the PC2 null in a mixed C57BL/N6:129/SvEv (B6:129) background. Because background can contribute greatly to phenotype, we have here examined strain influence on the hypothalamo-pituitary-adrenal (HPA) axis and glucose levels in wild-type, 7B2 null, and PC2 null mice. Wild-type B6 and 129 mice differed in basal corticosterone and glucose levels. When 7B2 nulls were transferred onto the B6 background, they survived and showed greatly decreased circulating corticosterone and increased blood glucose levels, most likely due to the comparatively higher adrenal resistance of the B6 strain to ACTH stimulation. Circulating ACTH levels were increased over wild-type in the B6 7B2 null but did not reach levels as high as the 129 7B2 null. Conversely, when the mixed-strain PC2 nulls were bred into the 129 background at the N6 generation, they began to exhibit the Cushing's-like phenotype characteristic of 129 7B2 null mice and died before 6 wk of age. Taken together, these results indicate that background effects are critical because they increase the phenotypic differences between the 7B2 and PC2 nulls and play a life-or-death role in the ACTH hypersecretion syndrome present in both 129 nulls.

Preservation of eumelanin hair pigmentation in proopiomelanocortin-deficient mice on a nonagouti (a/a) genetic background

The original strain of proopiomelanocortin (POMC)-deficient mice (Pomc-/-) was generated by homologous recombination in 129X1/SvJ (A(w)/A(w))-derived embryonic stem cells using a targeting construct that deleted exon 3, encoding all the known functional POMC-derived peptides including alpha MSH, from the Pomc gene. Although these Pomc-/- mice exhibited adrenal hypoplasia and obesity similar to the syndrome of POMC deficiency in children, their agouti coat color was only subtly altered. To further investigate the mechanism of hair pigmentation in the absence of POMC peptides, we studied wild-type (Pomc+/+), heterozygous (Pomc+/-), and homozygous (Pomc-/-) mice on a nonagouti (a/a) 129;B6 hybrid genetic background. All three genotypes had similar black fur pigmentation with yellow hairs behind the ears, around the nipples, and in the perianal area characteristic of inbred C57BL/6 mice. Histologic and electron paramagnetic resonance spectrometry examination demonstrated that hair follicles in back skin of Pomc-/- mice developed with normal structure and eumelanin pigmentation; corresponding molecular analyses, however, excluded local production of alpha MSH and ACTH because neither Pomc nor putative Pomc pseudogene mRNAs were detected in the skin. Thus, 129;B6 Pomc null mutant mice produce abundant eumelanin hair pigmentation despite their congenital absence of melanocortin ligands. These results suggest that either the mouse melanocortin receptor 1 has sufficient basal activity to trigger and sustain eumelanogenesis in vivo or that redundant nonmelanocortin pathway(s) compensate for the melanocortin deficiency. Whereas the latter implies feedback control of melanogenesis, it is also possible that the two mechanisms operate jointly in hair follicles.

Gamma-MSH, sodium metabolism, and salt-sensitive hypertension

Alpha-, beta-, and gamma-melanocyte stimulating hormones (MSHs) are melanotropin peptides that are derived from the ACTH/beta-endorphin prohormone proopiomelanocortin (POMC). They have been highly conserved through evolutionary development, although their functions in mammals have remained obscure. The identification in the last decade of a family of five membrane-spanning melanocortin receptors (MC-Rs), for which the melanotropins are the natural ligands, has permitted the characterization of a number of important actions of these peptides, although the physiological function(s) of gamma-MSH have remained elusive. Much evidence indicates that gamma-MSH stimulates sympathetic outflow and raises blood pressure through a central mechanism. However, this review focuses on newer cardiovascular and renal actions of the peptide, acting in most cases through the MC3-R. In rodents, a high-sodium diet (HSD) increases the pituitary abundance of POMC mRNA and of gamma-MSH content and results in a doubling of plasma gamma-MSH concentration. The peptide is natriuretic and acts through renal MC3-Rs, which are also upregulated by the HSD. Thus the system appears designed to participate in the integrated response to dietary sodium excess. Genetic or pharmacologic induction of gamma-MSH deficiency results in marked salt-sensitive hypertension that is corrected by the administration of the peptide, probably through a central site of action. Deletion of the MC3-R also produces salt-sensitive hypertension, which, however, is not corrected by infusion of the hormone. These observations in aggregate suggest the operation of a hormonal system important in blood pressure control and in the regulation of sodium excretion. The relationship of these two actions to each other and the significance of this system in humans are important questions for future research.

Subcellular pathways of beta-endorphin synthesis, processing, and release from immunocytes in inflammatory pain

The opioid peptide beta-endorphin (END) as well as mRNA for its precursor proopiomelanocortin (POMC) are found not only in the pituitary gland, but also within various types of immune cells infiltrating inflamed sc tissue. During stressful stimuli END is released and interacts with peripheral opioid receptors to inhibit pain. However, the subcellular pathways of POMC processing and END release have not yet been delineated in inflammatory cells. The aim of the present study was to examine the presence of POMC, carboxypeptidase E, the prohormone convertases 1 (PC1), and 2 (PC2), PC2-binding protein 7B2, and the release of END from inflammatory cells in rats. Using immunohistochemistry we detected END and POMC alone or colocalized with PC1, PC2, carboxypeptidase E, and 7B2 in macrophages/monocytes, granulocytes, and lymphocytes of the blood and within inflamed sc paw tissue. Immunoelectron microscopy revealed that END is localized within secretory granules packed in membranous structures in macrophages, monocytes, granulocytes, and lymphocytes. Finally, END is released by noradrenaline from immune cells in vitro. Taken together, our results indicate that immune cells express the entire machinery required for POMC processing into functionally active peptides such as END and are able to release these peptides from secretory granules.

Resistance of macrophages to Mycobacterium avium is induced by alpha2-adrenergic stimulation

The ability of macrophages to control the growth of microorganisms is increased by macrophage activation. Previously, it was shown that epinephrine activated mouse macrophages to resist the growth of Mycobacterium avium via alpha(2)-adrenergic stimulation. In the present study, we show that the alpha(2)-adrenergic agonist (alpha(2)-agonist) clonidine induced resistance to M. avium growth in the RAW264.7 mouse macrophage cell line. The ability of catecholamines to induce resistance to mycobacteria was specific to alpha(2)-adrenergic stimulation, as alpha(1)-, beta(1)-, and beta(2)-agonists had no effect. Receptor signaling through Gi proteins was required. A G-protein antagonist specific for the alpha subunits of the Go/Gi family blocked the increased resistance induced by clonidine, while a Gs-protein antagonist was without effect. Both nitric oxide (NO) production and superoxide (O(2)(-)) production were required for the increased resistance to M. avium growth induced by clonidine. Although NO production was required, clonidine did not increase the level of NO in M. avium-infected cells. Since NO and O(2)(-) interact to produce peroxynitrite (ONOO(-)), we examined whether ONOO(-) mediates the increased resistance to M. avium induced by clonidine. 5,10,15,20-Tetrakis(4-sulfonatophenyl)prophyrinato iron (III) chloride (FeTPPS), a specific scavenger of ONOO(-), inhibited the effect of clonidine on M. avium growth. Clonidine also increased the production of ONOO(-) in M. avium-infected RAW264.7 cells, as measured by the oxidation of 123-dihydrorhodamine and the production of nitrated tyrosine residues. We therefore conclude that alpha(2)-adrenergic stimulation activates macrophages to resist the growth of M. avium by enhancing the production of ONOO(-).

Intrapituitary adenoviral administration of 7B2 can extend life span and reverse endocrinological deficiencies in 7B2 null mice

The prohormone convertase PC2 requires the aid of a helper protein, known as 7B2, for production of active enzyme. Deletion of 7B2 results in a lethal phenotype resembling Cushing's disease. In this study, we have investigated the effect of a single low dose of recombinant adenovirus vector encoding 7B2 and delivered directly to the pituitary of 7B2 nulls on pituitary ACTH, plasma ACTH, corticosterone, alpha MSH and glucose, and survival time. We show that after injection of recombinant adenovirus encoding 27-kDa 7B2 into 7B2 nulls, transgene expression, as measured by RIA for 7B2, exhibits a transient elevation in the pituitary and blood, with a slight but significant elevation of PC2 activity in pituitaries of 7B2 nulls and a drop in the level of circulating ACTH concomitant with a small increase in circulating alpha MSH. The level of circulating blood glucose was increased, and that of corticosterone was decreased. Lastly, slight but significantly prolonged survival times were observed. These data showing partial rescue of 7B2 nulls support the idea that adenoviral administration of 7B2 will represent an effective means to study the role of this interesting neuroendocrine protein on endocrine function in vivo.

Loss of ACTH expression in cultured human corticotroph macroadenoma cells is consistent with loss of the POMC gene signal sequence

The proopiomelanocortin (POMC) gene is highly expressed in the pituitary gland where the resulting mRNA of 1200 base pairs (bp) gives rise to a full-length protein sequence. In peripheral tissues however both shorter and longer POMC variants have been described, these include for example placental tissue which contain 800 (truncated at the 5' end) and 1500 as well as the 1200 bp transcripts. The importance of the 800 bp transcript is unclear as the lack of a signal sequence renders the molecule to be non-functional. This transcript has not been previously demonstrated in the pituitary gland. In this report we show evidence of a 5' truncated POMC gene in human pituitary corticotroph macroadenoma cells (JE) maintained in primary culture for >1 year. The original tumour tissue and the derived cells during early passage (up to passage 4-5) immunostained for ACTH and in situ hybridisation confirmed the presence of the POMC gene in the cultured cells. These cells also secreted 15-40 pg/10(5) cells/24 h ACTH. In addition, as expected RT-PCR demonstrated the presence of all three POMC gene exons and is thus indicative of a full-length POMC gene. In late culture passages (passages 8-15) JE cells ceased to express ACTH and cell growth became very slow due presumably to cells reaching their Hayflick limit. ACTH immunostaining in these cells was undetectable and ACTH secretion was also at the detection limits of the assay and no greater than 10 pg/10(5) cells/24 h. ACTH precursor molecules were also undetectable. RT-PCR for the POMC gene in these late passage cells showed that only exon 3 was detectable, in contrast to early passage cells where all three exons were present. In summary we isolated in culture, human pituitary cells that possessed initially all three exons of the POMC gene and immunostained for ACTH. On further passaging these cells showed a loss of exons 1 and 2 in the POMC gene and a loss of ACTH immunostaining and secretion. We would like to suggest that the loss of ACTH peptide expression in these late passage cells is in part due to the loss of the POMC signal sequence. An alternative explanation for our findings is that there were originally two populations of corticotrophs in the cultures, one of which possessed the full-length POMC gene and the other only the 5' truncated POMC transcript and it is these latter cells which survived in culture. In either scenario this is the first report of the 5' truncated POMC gene occurring in pituitary cells.

Mortality in 7B2 null mice can be rescued by adrenalectomy: involvement of dopamine in ACTH hypersecretion

The serine protease prohormone convertase 2 (PC2), principally involved in the processing of polypeptide hormone precursors in neuroendocrine tissues, requires interaction with the neuroendocrine protein 7B2 to generate an enzymatically active form. 7B2 null mice express no PC2 activity and release large quantities of uncleaved ACTH, resulting in a lethal endocrine condition that resembles pituitary Cushing's (Westphal, C. H., Muller, L., Zhou, A., Bonner-Weir, S., Schambelan, M., Steiner, D. F., Lindberg, I. & Leder, P. (1999) Cell 96, 689). Here, we have compared the 7B2 and PC2 null mouse models to determine why the 7B2 null, but not the PC2 null, exhibits a lethal disease state. Both 7B2 and PC2 nulls contained highly elevated pituitary adrenocorticotropic hormone (ACTH); the neurointermediate lobe content of ACTH in 7B2 nulls was 13-fold higher than in WT mice; that of the PC2 null was 65-fold higher. However, circulating ACTH levels were much higher in the 7B2 null than in the PC2 null. Because hypothalamic inhibitory dopaminergic control represents the major influence on intermediate lobe proopiomelanocortin-derived peptide secretion, dopamine levels were measured, and they revealed that 7B2 null pituitaries contained only one-fourth of WT pituitary dopamine. Adrenalectomized 7B2 null animals survived past the usual time of death at 5 weeks; a month after adrenalectomy, they exhibited normal levels of pituitary dopamine, circulating ACTH, and corticosterone. Elevated corticosterone, therefore, seems to play a central role in the lethal phenotype of the 7B2 null, whereas a 7B2-mediated dopaminergic deficiency state may be involved in the actual ACTH hypersecretion phenomenon. Interestingly, adrenalectomized 7B2 nulls also developed unexpectedly severe obesity.

Corticotropin releasing hormone and proopiomelanocortin involvement in the cutaneous response to stress

The skin is a known target organ for the proopiomelanocortin (POMC)-derived neuropeptides alpha-melanocyte stimulating hormone (alpha-MSH), beta-endorphin, and ACTH and also a source of these peptides. Skin expression levels of the POMC gene and POMC/corticotropin releasing hormone (CRH) peptides are not static but are determined by such factors as the physiological changes associated with hair cycle (highest in anagen phase), ultraviolet radiation (UVR) exposure, immune cytokine release, or the presence of cutaneous pathology. Among the cytokines, the proinflammatory interleukin-1 produces important upregulation of cutaneous levels of POMC mRNA, POMC peptides, and MSH receptors; UVR also stimulates expression of all the components of the CRH/POMC system including expression of the corresponding receptors. Molecular characterization of the cutaneous POMC gene shows mRNA forms similar to those found in the pituitary, which are expressed together with shorter variants. The receptors for POMC peptides expressed in the skin are functional and include MC1, MC5 and mu-opiate, although most predominant are those of the MC1 class recognizing MSH and ACTH. Receptors for CRH are also present in the skin. Because expression of, for example, the MC1 receptor is stimulated in a similar dose-dependent manner by UVR, cytokines, MSH peptides or melanin precursors, actions of the ligand peptides represent a stochastic (predictable) nonspecific response to environmental/endogenous stresses. The powerful effects of POMC peptides and probably CRH on the skin pigmentary, immune, and adnexal systems are consistent with stress-neutralizing activity addressed at maintaining skin integrity to restrict disruptions of internal homeostasis. Hence, cutaneous expression of the CRH/POMC system is highly organized, encoding mediators and receptors similar to the hypothalamic-pituitary-adrenal (HPA) axis. This CRH/POMC skin system appears to generate a function analogous to the HPA axis, that in the skin is expressed as a highly localized response which neutralizes noxious stimuli and attendant immune reactions.

Spatiotemporal expression, distribution, and processing of POMC and POMC-derived peptides in murine skin

In murine skin, after depilation-induced anagen, there was a differential spatial and temporal expression of pro-opiomelanocortin (POMC) mRNA, of the POMC-derived peptides beta-endorphin, ACTH, beta-MSH, and alpha-MSH, and of the prohormone convertases PC1 and PC2 in epidermal and hair follicle keratinocytes and in the cells of sebaceous units. Using a combination of in situ hybridization histochemistry and immunohistochemistry, we found cell-specific variations in the expression of POMC mRNA that were consistent with immunoreactivities for POMC-derived peptides. Cells that contained POMC peptide immunoreactivity (IR) also expressed POMC mRNA, and where the IR increased there was a parallel increase in mRNA. The levels of PC1-IR and PC2-IR also showed cell-specific variations and were present in the same cells that contained the POMC peptides. Based on the cleavage specificities of these convertases and on the spatial and temporal expression of the convertases and of ACTH, beta-endorphin, beta-MSH, and alpha-MSH, we can infer that the activities of PC1 and PC2 are responsible for the cell-specific differential processing of POMC in murine skin.

Influence of acute and chronic treadmill exercise on rat brain POMC gene expression

PURPOSE AND METHODS

In situ hybridization using biotin-labeled POMC cRNA probes and integrated image pattern analysis were used to observe the effect of chronic (total 7 wk) and acute treadmill exercise (an initial speed of 15 m x min(-1) gradually increased to 35 m x min(-1) with 0 degrees, 20-25 min x d(-1) duration) on the changes of POMC mRNA expression in different areas of the rat brain.

RESULTS

Acute exercise performed after 7 wk of training resulted in a decrease in the expression of POMC mRNA in both the frontal cortex and hippocampal CA1 of the experimental rats. Three hours postexercise, the POMC mRNA indicator had not yet returned to normal expression levels in the frontal cortex, but hippocampal CA1 levels showed increases above normal levels 30 min postexercise. Expression levels in the hypothalamus were shown to be increased immediately after acute exercise and remained high even during remeasurement 3 h postexercise.

CONCLUSION

Changes in POMC gene expression in response to chronic and high-intensity acute exercise vary depending on the brain region examined.

Beta2-adrenergic receptor stimulation inhibits nitric oxide generation by Mycobacterium avium infected macrophages

Catecholamine regulation of nitric oxide (NO) production by IFNgamma-primed macrophages infected with Mycobacterium avium was investigated. Epinephrine treatment of IFNgamma-primed macrophages at the time of M. avium infection inhibited the anti-mycobacterial activity of the cells. The anti-mycobacterial activity of macrophages correlated with NO production. Using specific adrenergic receptor agonists, the abrogation of mycobacterial killing and decreased NO production by catecholamines was shown to be mediated via the beta2-adrenergic receptor. Elevation of intracellular cAMP levels mimicked the catecholamine-mediated inhibition of NO in both M. avium infected and LPS stimulated macrophages. Specific inhibitors of both adenylate cyclase and protein kinase A prevented the beta2-adrenoceptor-mediated inhibition of nitric oxide production. Beta2-adrenoreceptor stimulation at the time of M. avium infection of IFNgamma-primed macrophages also inhibited expression of iNOS mRNA. These observations show that catecholamine hormones can affect the outcome of macrophage-pathogen interactions and suggest that one result of sympathetic nervous system activation is the suppression of the capacity of macrophages to produce anti-microbial effector molecules.

An immunocytochemical approach to the study of beta-endorphin production in human keratinocytes using confocal microscopy

Proopiomelanocortin (POMC) is a protein that is posttranslationally processed to yield POMC peptides. The main site of POMC expression is the anterior pituitary lobe but many other sources have been identified. There is evidence that the skin produces POMC peptides, although their roles have not yet been defined. In the skin, regulation of POMC gene expression is known to be hair-cycle dependent, and it is localized to the sebaceous gland. In particular, beta-endorphin, a POMC peptide, has been shown to be modulated by TPA, IL-1 alpha, and ultraviolet radiation in keratinocytes. These results were obtained by examination of POMC mRNA levels using the Northern blot method; beta-endorphin protein production by the Western blot method on cultured cells; and immunocytochemistry for tissue preparations. This report represents an approach to use immunocytochemistry to quantify beta-endorphin production in cultured human keratinocytes. Additionally, we examined whether exposure to 20 mJ ultraviolet B radiation (UVB) and/or UVA could influence beta-endorphin production in these cells. Keratinocytes were grown in monolayers, in serum-free medium, fixed, and incubated with antiserum to whole synthetic beta-endorphin. Fluorescence microscopy was performed with a confocal laser scanning microscope. The integrated level of fluorescence was evaluated in n = 18 +/- 8 individual cells, and this was assumed to be proportional to beta-endorphin content. High variability was observed in the fluorescence intensity among cells. No significant differences between control and UVB- or UVA + UVB-treated cells was found. Similar results were produced by using brefeldin A, a compound that disrupts the secretory pathway, eliminating the possibility that the absence of a difference between beta-endorphin content in the treated and control cells was due to secretion of the peptide into the medium. We conclude that: (1) beta-endorphin or beta-endorphin-like peptides are produced in human keratinocytes and are readily detected by immunocytochemistry; (2) under the conditions tested, UVA and/or UVB did not increase beta-endorphin-like immunoreactivity in these cells.

Cutaneous expression of CRH and CRH-R. Is there a "skin stress response system?"

The classical neuroendocrine pathway for response to systemic stress is by hypothalamic release of corticotropin releasing hormone (CRH), subsequent activation of pituitary CRH receptors (CRH-R), and production and release of proopiomelanocortin (POMC) derived peptides. It has been proposed that an equivalent to the hypothalamic-pituitary-adrenal axis functions in mammalian skin, in response to local stress (see Reference 1). To further define such system we used immunocytochemistry, RP-HPLC separation, and RIA techniques, in rodent and human skin, and in cultured normal and malignant melanocytes and keratinocytes. Production of mRNA for CRH-R1 was documented in mouse and human skin using RT-PCR and Northern blot techniques; CRH binding sites and CRH-R1 protein were also identified. Addition of CRH to immortalized human keratinocytes, and to rodent and human melanoma cells induced rapid, specific, and dose-dependent increases in intracellular Ca2+. The latter were inhibited by the CRH antagonist alpha-helical-CRH(9-41) and by the depletion of extracellular calcium with EGTA. CRH production was enhanced by ultraviolet light radiation and forskolin (a stimulator for intracellular cAMP production), and inhibited by dexamethasone. Thus, evidence that skin cells, both produce CRH and express functional CRH-R1, supports the existence of a local CRH/CRH-R neuroendocrine pathway that may be activated within the context of a skin stress response system.

Enhanced expression of melanocortin-1 receptor (MC1-R) in normal human keratinocytes during differentiation: evidence for increased expression of POMC peptides near suprabasal layer of epidermis

Immunohistochemical staining of human skin specimen showed the stronger localization of proopiomelanocortin peptides near the suprabasal layer of the epidermis, where keratinocytes are mostly differentiated. To test the possibilities of whether the production of proopiomelanocortin peptides or their receptor-binding activity or both is increased during differentiation of keratinocytes, we treated the cells in culture with Ca2+ to induce their differentiation. The production of proopiomelanocortin peptides and its gene expression were not induced significantly, but the binding ability of melanocortin receptor, as well as its gene expression were stimulated by Ca2+. Ultraviolet B irradiation, an inducer of differentiation, stimulated both proopiomelanocortin production and melanocortin receptor expression. These data show that normal human keratinocytes express melanocortin receptor similar to melanocytes, and that it is induced during differentiation.

Glucocorticoids differentially control synthesis of acetylcholinesterase and butyrylcholinesterase in rat liver and brain

Mammalian organisms possess two cholinesterases: acetylcholinesterase (AChE, EC 3.1.1.7.) and butyrylcholinesterase (BuChE, EC 3.1.1.8.). A clear explanation for this dual expression of acetylcholine-hydrolyzing enzymes is still missing. Better knowledge on how these two enzymes respond to various physiological or pharmacological factors would importantly contribute to the understanding of their function. The aim of the present study is to elucidate glucocorticoid (GC) influences on the synthesis of AChE and BuChE in rat liver and brain. Female Wistar rats were treated with dexamethasone until body weight loss was greater than 15%, signaling full expression of a GC response. At this stage, liver and brain were isolated and AChE and BuChE activities were determined in their homogenates. A new approach, based on precise radiometric measurements of AChE and BuChE activities in the polysomal fractions, prepared under non-denaturing conditions, was used to study GC influences on the early stages of biosynthesis of both enzymes. We found a differential GC influence on AChE and BuChE. In brain, only BuChE activity was affected (-30%), while AChE remained practically unchanged. In liver, BuChE activity fell by 60%, while AChE lost only 18% of its control activity. In case of BuChE, decreased activities in the whole homogenates correlated with decreased activities in the polysomal fractions, suggesting that early stages of enzyme biosynthesis were primarily affected. On the other hand, decreased AChE activity in liver homogenates was not paralleled by a significant change at the level of polysomal AChE activity in this organ, suggesting that higher AChE turn-over is primarily responsible for the decreased activity in homogenate. These results, together with the GC-mediated elimination of the correlation between brain and liver BuChE activities, strongly support the proposal of Edwards and Brimijoin (J.A. Edwards, S. Brimijoin, Effects of hypophysectomy on acetylcholinesterase and butyrylcholinesterase in the rat, Biochem. Pharmacol. 32 (1983) 1183-1189) that BuChE is regulated by systemically acting factors, including various hormones, while regulation of AChE is primarily tissue-specific.

The neuroendocrine protein 7B2 is required for peptide hormone processing in vivo and provides a novel mechanism for pituitary Cushing's disease

The neuroendocrine protein 7B2 has been implicated in activation of prohormone convertase 2 (PC2), an important neuroendocrine precursor processing endoprotease. To test this hypothesis, we created a null mutation in 7B2 employing a novel transposon-facilitated technique and compared the phenotypes of 7B2 and PC2 nulls. 7B2 null mice have no demonstrable PC2 activity, are deficient in processing islet hormones, and display hypoglycemia, hyperproinsulinemia, and hypoglucagonemia. In contrast to the PC2 null phenotype, these mice show markedly elevated circulating ACTH and corticosterone levels, with adrenocortical expansion. They die before 9 weeks of severe Cushing's syndrome arising from pituitary intermediate lobe ACTH hypersecretion. We conclude that 7B2 is indeed required for activation of PC2 in vivo but has additional important functions in regulating pituitary hormone secretion.

Expression of proopiomelanocortin (POMC)-derived melanocyte-stimulating hormone (MSH) and adrenocorticotropic hormone (ACTH) peptides in skin of basal cell carcinoma patients

We proposed that local expression and production of proopiomelanocortin (POMC) peptides may play a role in human skin physiology and pathology, including the development and progression of skin cancers. Reverse transcription polymerase chain reaction (RT-PCR) and Northern blotting hybridization techniques were used to study gene expression. Reversed-phase (RP) high-pressure liquid chromatography (HPLC) separation with subsequent radioimmunoassays were used to identify alpha-melanocyte-stimulating hormone (alpha-MSH) and adrenocorticotropic hormone (ACTH) peptides. Immunocytochemistry (IHC) was used to localize ACTH, alpha-MSH, and beta-MSH antigens in skin. RT-PCR, RP-HPLC, and IHC analyses documented the expression of POMC mRNA and production of ACTH and alpha-MSH peptides in lesional and perilesional skin of basal cell carcinoma (BCC) patients and in cultured keratinocytes, which was accompanied by the expression of the MC1-R gene encoding the receptor activated by MSH and ACTH. Thirty specimens were analyzed by IHC. Immunoreactive alpha-MSH, beta-MSH, and ACTH were detected, in 21 of 21, in 11 of 20, and in 6 of 8 of lesional skin, and in 6 of 6, in 5 of 7, and in 6 of 8 perilesional skin specimens analyzed, respectively. Antigen distribution was heterogenous and present in BCC, epidermis, hair follicles, dermal mononuclear cells, and extracellular matrix. We conclude that messenger RNA for POMC, MC1-R, and the peptides MSH and ACTH are produced in skin of BCC patients. Because keratinocytes are a target for MSH and ACTH bioregulation, the production of these peptides is stimulated by UVB, and the peptides can act as immunosupressors, we suggest that MSH and ACTH may facilitate development of BCC.

Effects of alcohol on the synthesis and expression of hypothalamic peptides

Studies aimed at analyzing the deleterious effects of excess alcohol in the brain have revealed structural alterations that are often associated with functional and behavioral disturbances. Among the neuronal damage related to prolonged alcohol exposure, alterations in the synthesizing capabilities and levels of expression of neuroactive peptides have been increasingly reported. Actually, such changes frequently represent the sole repercussion of acute and short-term exposure to ethanol. This review gathers the existing data on the effects of ethanol exposure on the synthesis and expression of hypothalamic peptides. Amid those that can act both as neurotransmitters and neurohormones, we allude to vasopressin, corticotropin-releasing hormone, thyrotropin-releasing hormone and pro-opiomelanocortin and related peptides produced by paraventricular, supraoptic and arcuate neurons. With respect to peptides that act exclusively as neurotransmitters, we address the effects of alcohol on vasoactive intestinal polypeptide, gastrin-releasing peptide, somatostatin and vasopressin synthesized by suprachiasmatic neurons. Hypothalamic neurons that produce peptides that act as neurotransmitters are supposed to be modulated primarily by influences exerted by neuronal afferents, whereas those producing peptides that additionally act as neurohormones are also regulated by peripheral stimuli (e.g., plasma levels of circulating hormones, osmotic challenges). These peculiar features endue the hypothalamus with characteristics that are particularly propitious to enlighten the still cryptic mechanisms underlying the ethanol effects on protein synthesis.

Proopiomelanocortin (POMC) mRNA and POMC-derived peptides immunolocalization in the skin of Protopterus annectens, an African lungfish

Antisera against adrenocorticotropic hormone (ACTH), alpha-melanocyte stimulating hormone (alpha-MSH) and beta-endorphin were used to localize, by immunohistochemistry, proopiomelanocortin (POMC)-derived peptides in the skin excised from different regions of the African lungfish Protopterus annectens. Immunoreactivity was observed in the epidermis mainly in the germinal layer. Using human POMC cDNA as hybridization probe, POMC-like mRNA was identified in situ in epidermal cells. The demonstration in the same cells of POMC mRNA and POMC-related peptides immunoreactivity indicates a local production of opiate hormones.

Hair cycle-dependent production of ACTH in mouse skin

We investigated the functional determinants of the cutaneous expression of elements of the hypothalamic-pituitary-adrenal axis. In the present work, the presence of adrenocorticotropin (ACTH) peptide in skin of C57/BL6 mouse was demonstrated by reversed-phase HPLC analysis combined with specific radioimmunoassay. ACTH concentration that was low in telogen, increased during anagen in two steps: a rapid phase in anagen I, and a slower rise that reached its peak in anagen VI. Immunofluorescence localized the ACTH antigen to the basal layer of epidermis, outer root sheath of hair follicle and subcutaneous muscle of anagen VI skin. At physiological plasma concentration (10-9 M), ACTH selectively stimulated DNA synthesis in dermis, while pharmacological doses (10-7-10-6 M) inhibited DNA synthesis in both dermis and epidermis. In conclusion, we suggest that local production of ACTH may represent a regulatory element in the control of skin functions including hair growth.

Identification and sequencing of a putative variant of proopiomelanocortin in human epidermis and epidermal cells in culture

Proopiomelanocortin (POMC) is a precursor polypeptide for various bioactive peptides, including adrenocorticotropic hormone, alpha-, beta-, and gamma-melanotropin, beta-endorphin, and beta-lipotropin. Although the classical source of POMC is the pituitary, various studies indicate the expression of POMC in several nonpituitary tissues. In this study, in situ hybridization with anti-sense cRNA riboprobe was used to show expression of POMC mRNA in human epidermis and cultured human epidermal cells (melanocytes and keratinocytes). POMC mRNA was amplified by reverse transcriptase-polymerase chain reaction using anti-sense and sense primers designed from Exons 2 and 3 of POMC gene. A approximately 300 bp product was present in normal human skin, grafted human skin, and cultured normal human melanocytes and keratinocytes. By Southern analysis this product was hybridized specifically to the POMC cDNA. Sequence analysis of the reverse transcriptase polymerase chain reaction product from tissues or cells showed 85% homology to POMC cDNA from human, bovine, pig, and monkey sources. This suggests the existence of a putative isoform or variant of POMC mRNA in human epidermis.

Molecular cloning of the chicken melanocortin 2 (ACTH)-receptor gene

The chicken melanocortin 2-receptor (MC2-R) gene was isolated. It is found to be a single copy gene encoding a 357 amino acid protein, sharing 65.8-68.7% identity with mammalian counterparts. The chicken MC2-R mRNA is expressed in the adrenal and spleen, suggesting that the receptor mediates both endocrine and immunoregulatory functions of ACTH in the chicken. The amino acid sequence of the chicken MC2-R is collinear with those of other subtypes of MC-R, whereas all cloned mammalian MC2-Rs contain a gap in the third intracellular loop, suggesting that mammalian MC2-R molecules have evolved by lacking a part of the domain which determines the specificity of signal transduction in G-protein coupled receptors. Interestingly, the codon usage differs dramatically between MC1-R and MC2-R in the chicken; the GC-contents at the third codon position in MC1-R and MC2-R are 94.6 and 50.6%, respectively. It may reflect selective constraints on the usage of synonymous codons.

Cutaneous immunomodulation and coordination of skin stress responses by alpha-melanocyte-stimulating hormone

The capacity of the skin immune system to mount various types of immune responses is largely dependent on their ability to release and respond to different signals provided by immunoregulatory mediators such as cytokines. There is recent evidence that neuropeptides such as alpha-melanocyte-stimulating hormone (alpha MSH), upon stimulation, are released by epidermal cells including keratinocytes, Langerhans cells, and melanocytes as well as immunocompetent cells. Moreover, alpha MSH recently has been recognized as a potent immunomodulating agent, which inhibits the production and activity of immunoregulatory and proinflammatory cytokines such as IL-1, IL-2, interferon-gamma, downregulates the expression of costimulatory molecules (B7) on antigen-presenting cells; and recently turned out to be a potent inducer of inhibitory mediators such as cytokine synthesis inhibitory factor interleukin-10. Recently, it also was discovered that monocytes among the five known melanocortin (MC) receptors only express MC-1, which is specific for alpha MSH. The expression of MC-1 on monocytes is upregulated by mitogens, endotoxins, and proinflammatory cytokines. There is also recent evidence for the in vivo relevance of the immunosuppressing capacity of alpha MSH. Accordingly, in animals alpha MSH has been shown to inhibit the induction of contact hypersensitivity reactions and to induce hapten-specific tolerance. These findings indicate that, in addition to the cytokine network, neurohormones within the cutaneous microenvironment are a crucial element for the induction, elicitation, and regulation of cutaneous immune and inflammatory responses.