Ghrelin receptor expression and colocalization with anterior pituitary hormones using a GHSR-GFP mouse line

Metabolic hormones are integral regulators of female reproductive health and function

The female reproductive system is strongly influenced by nutrition and energy balance. It is well known that food restriction or energy depletion can induce suppression of reproductive processes, while overnutrition is associated with reproductive dysfunction. However, the intricate mechanisms through which nutritional inputs and metabolic health are integrated into the coordination of reproduction are still being defined. In this review, we describe evidence for essential contributions by hormones that are responsive to food intake or fuel stores. Key metabolic hormones-including insulin, the incretins (glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1), growth hormone, ghrelin, leptin, and adiponectin-signal throughout the hypothalamic-pituitary-gonadal axis to support or suppress reproduction. We synthesize current knowledge on how these multifaceted hormones interact with the brain, pituitary, and ovaries to regulate functioning of the female reproductive system, incorporating in vitro and in vivo data from animal models and humans. Metabolic hormones are involved in orchestrating reproductive processes in healthy states, but some also play a significant role in the pathophysiology or treatment strategies of female reproductive disorders. Further understanding of the complex interrelationships between metabolic health and female reproductive function has important implications for improving women's health overall.

Prolactin and Growth Hormone Signaling and Interlink Focused on the Mammosomatotroph Paradigm: A Comprehensive Review of the Literature

Prolactin (PRL) and growth hormone (GH) are peptide hormones that bind to the class 1 cytokine receptor superfamily, a highly conserved cell surface class of receptors. Both hormones control their own secretion via a negative autocrine loop in their own mammosomatotroph, lactotroph or somatotroph. In this regard, GH and PRL are regulated by similar signaling pathways involving cell growth and hormone secretion. Thus, GH and PRL dysregulation and pituitary neuroendocrine tumor (PitNET) development may have common pathogenic pathways. Based on cell linage, lactotroph and somatotroph PitNETs come from pituitary-specific POU-class homeodomain transcription factor (Pit-1). Mammosomatotroph and plurihormonal PitNETs are a unique subtype of PitNETs that arise from a single-cell population of Pit-1 lineage. In contrast, mixed somatotroph-lactotroph PitNETs are composed of two distinct cell populations: somatotrophs and lactotrophs. Morphologic features that distinguish indolent PitNETs from locally aggressive ones are still unidentified, and no single prognostic parameter can predict tumor aggressiveness or treatment response. In this review, we aim to explore the latest research on lactotroph and somatotroph PitNETs, the molecular mechanisms involved in PRL and GH axis regulation and the signaling pathways involved in their aggressiveness, particularly focused on mammosomatotroph and mixed subtypes. Finally, we summarize epidemiological, clinical, and radiological features of these exceptional tumors. We aim to shed light, from basic to clinical settings, on new perspectives and scientific gaps in this field.

The Impact of Laparoscopic Sleeve Gastrectomy on Thyroid Functions in Egyptian Patients with Obesity

BACKGROUND

Sleeve gastrectomy (SG) continues to be one of the most popular bariatric procedures all over the world. Thyroid-stimulating hormone (TSH) frequently shows a slight elevation in patients with obesity. The effect of SG on thyroid hormones has been rarely investigated.

AIM OF THE STUDY

This study aimed to assess the short-term effect of SG on thyroid functions in Egyptian patients with morbid obesity and the potential predictors of the postoperative thyroid functions.

PATIENTS AND METHODS

This study included patients undergoing SG at kasr al ainy hospitals. The patients underwent preoperative 3-, 6-, and 12-month postoperative analyses of the thyroid functions and other biochemical markers.

RESULTS

The study included 106 patients who showed significant improvement in thyroid functions at the follow-up assessment. Twelve-month TSH positively correlated with the 12-month measures of LDL and HbA1c. TSH change at 12-month follow-up (TSH) was inversely correlated to 12-month BMI and positively correlated to preoperative TSH and 12-month percentage of total weight loss (TWL%). Univariable linear regression analysis demonstrated that preoperative TSH (p < 0.001), 12-month TWL% (p = 0.042), 12-month HbA1c (p = 0.001), and 12-month LDL (p = 0.049) were significant predictors for the 12-month TSH levels. Multivariable analysis showed that only preoperative TSH levels (p < 0.001) and 12-month HbA1c levels (p = 0.021) could affect the 12-month TSH levels.

CONCLUSION

The current study supports the evidence of thyroid function improvement after sleeve gastrectomy. This improvement was affected by the amount of weight loss after surgery.

Hypothalamus and Post-Traumatic Stress Disorder: A Review

Humans have lived in a dynamic environment fraught with potential dangers for thousands of years. While fear and stress were crucial for the survival of our ancestors, today, they are mostly considered harmful factors, threatening both our physical and mental health. Trauma is a highly stressful, often life-threatening event or a series of events, such as sexual assault, war, natural disasters, burns, and car accidents. Trauma can cause pathological metaplasticity, leading to long-lasting behavioral changes and impairing an individual's ability to cope with future challenges. If an individual is vulnerable, a tremendously traumatic event may result in post-traumatic stress disorder (PTSD). The hypothalamus is critical in initiating hormonal responses to stressful stimuli via the hypothalamic-pituitary-adrenal (HPA) axis. Linked to the prefrontal cortex and limbic structures, especially the amygdala and hippocampus, the hypothalamus acts as a central hub, integrating physiological aspects of the stress response. Consequently, the hypothalamic functions have been attributed to the pathophysiology of PTSD. However, apart from the well-known role of the HPA axis, the hypothalamus may also play different roles in the development of PTSD through other pathways, including the hypothalamic-pituitary-thyroid (HPT) and hypothalamic-pituitary-gonadal (HPG) axes, as well as by secreting growth hormone, prolactin, dopamine, and oxytocin. This review aims to summarize the current evidence regarding the neuroendocrine functions of the hypothalamus, which are correlated with the development of PTSD. A better understanding of the role of the hypothalamus in PTSD could help develop better treatments for this debilitating condition.

The Role of Chicken Prolactin, Growth Hormone and Their Receptors in the Immune System

Prolactin (PRL) and growth hormone (GH) exhibit important roles in the immune system maintenance. In poultry, PRL mainly plays its roles in nesting, hatching, and reproduction, while GH is primarily responding to body weight, fat formation and feed conversion. In this review, we attempt to provide a critical overview of the relationship between PRL and GH, PRLR and GHR, and the immune response of poultry. We also propose a hypothesis that PRL, GH and their receptors might be used by viruses as viral receptors. This may provide new insights into the pathogenesis of viral infection and host immune response.

Effect of Growth Hormone Secretagogue Receptor Deletion on Growth, Pulsatile Growth Hormone Secretion, and Meal Pattern in Male and Female Mice

INTRODUCTION

While the vast majority of research investigating the role of ghrelin or its receptor, GHS-R1a, in growth, feeding, and metabolism has been conducted in male rodents, very little is known about sex differences in this system. Furthermore, the role of GHS-R1a signaling in the control of pulsatile GH secretion and its link with growth or metabolic parameters has never been characterized.

METHODS

We assessed the sex-specific contribution of GHS-R1a signaling in the activity of the GH/IGF-1 axis, metabolic parameters, and feeding behavior in adolescent (5-6 weeks old) or adult (10-19 weeks old) GHS-R KO (Ghsr-/-) and WT (Ghsr+/+) male and female mice.

RESULTS

Adult Ghsr-/- male and female mice displayed deficits in weight and linear growth that were correlated with reduced GH pituitary contents in males only. GHS-R1a deletion was associated with reduced meal frequency and increased meal intervals, as well as reduced hypothalamic GHRH and NPY mRNA in males, not females. In adult, GH release from Ghsr-/- mice pituitary explants ex vivo was reduced independently of the sex. However, in vivo pulsatile GH secretion decreased in adult but not adolescent Ghsr-/- females, while in males, GHS-R1a deletion was associated with reduction in pulsatile GH secretion during adolescence exclusively. In males, linear growth did not correlate with pulsatile GH secretion, but rather with ApEn, a measure that reflects irregularity of the rhythmic secretion. Fat mass, plasma leptin concentrations, or ambulatory activity did not predict differences in GH secretion.

DISCUSSION/CONCLUSION

These results point to a sex-dependent dimorphic effect of GHS-R1a signaling to modulate pulsatile GH secretion and meal pattern in mice with different compensatory mechanisms occurring in the hypothalamus of adult males and females after GHS-R1a deletion. Altogether, we show that GHS-R1a signaling plays a more critical role in the regulation of pulsatile GH secretion during adolescence in males and adulthood in females.

Ghrelin Gene Deletion Alters Pulsatile Growth Hormone Secretion in Adult Female Mice

Using preproghrelin-deficient mice (Ghrl-/-), we previously observed that preproghrelin modulates pulsatile growth hormone (GH) secretion in post-pubertal male mice. However, the role of ghrelin and its derived peptides in the regulation of growth parameters or feeding in females is unknown. We measured pulsatile GH secretion, growth, metabolic parameters and feeding behavior in adult Ghrl-/- and Ghrl+/+ male and female mice. We also assessed GH release from pituitary explants and hypothalamic growth hormone-releasing hormone (GHRH) expression and immunoreactivity. Body weight and body fat mass, linear growth, spontaneous food intake and food intake following a 48-h fast, GH pituitary contents and GH release from pituitary explants ex vivo, fasting glucose and glucose tolerance were not different among adult Ghrl-/- and Ghrl+/+ male or female mice. In vivo, pulsatile GH secretion was decreased, while approximate entropy, that quantified orderliness of secretion, was increased in adult Ghrl-/- females only, defining more irregular GH pattern. The number of neurons immunoreactive for GHRH visualized in the hypothalamic arcuate nucleus was increased in adult Ghrl-/- females, as compared to Ghrl+/+ females, whereas the expression of GHRH was not different amongst groups. Thus, these results point to sex-specific effects of preproghrelin gene deletion on pulsatile GH secretion, but not feeding, growth or metabolic parameters, in adult mice.

High Coexpression of the Ghrelin and LEAP2 Receptor GHSR With Pancreatic Polypeptide in Mouse and Human Islets

Islets represent an important site of direct action of the hormone ghrelin, with expression of the ghrelin receptor (growth hormone secretagogue receptor; GHSR) having been localized variably to alpha cells, beta cells, and/or somatostatin (SST)-secreting delta cells. To our knowledge, GHSR expression by pancreatic polypeptide (PP)-expressing gamma cells has not been specifically investigated. Here, histochemical analyses of Ghsr-IRES-Cre × Cre-dependent ROSA26-yellow fluorescent protein (YFP) reporter mice showed 85% of GHSR-expressing islet cells coexpress PP, 50% coexpress SST, and 47% coexpress PP + SST. Analysis of single-cell transcriptomic data from mouse pancreas revealed 95% of Ghsr-expressing cells coexpress Ppy, 100% coexpress Sst, and 95% coexpress Ppy + Sst. This expression was restricted to gamma-cell and delta-cell clusters. Analysis of several single-cell human pancreatic transcriptome data sets revealed 59% of GHSR-expressing cells coexpress PPY, 95% coexpress SST, and 57% coexpress PPY + SST. This expression was prominent in delta-cell and beta-cell clusters, also occurring in other clusters including gamma cells and alpha cells. GHSR expression levels were upregulated by type 2 diabetes mellitus in beta cells. In mice, plasma PP positively correlated with fat mass and with plasma levels of the endogenous GHSR antagonist/inverse agonist LEAP2. Plasma PP also elevated on LEAP2 and synthetic GHSR antagonist administration. These data suggest that in addition to delta cells, beta cells, and alpha cells, PP-expressing pancreatic cells likely represent important direct targets for LEAP2 and/or ghrelin both in mice and humans.

Contribution of Ghrelin to the Pathogenesis of Growth Hormone Deficiency

In this review we described the interactions between ghrelin and the growth hormone (GH)-insulin-like growth factor 1 (IGF-1) axis in children and adults with growth hormone deficiency (GHD). A possible involvement of these interactions in the pathogenesis of unexplained cases of GHD was suggested. Current research provides more and more details to the knowledge on the circadian rhythm of ghrelin. We gathered reports on the decreasing effect of Helicobacter pylori-related chronic gastritis on the number of ghrelin immunopositive cells and the consequent decrease in ghrelin serum concentration. The gastrointestinal tract microflora modification of the ghrelin action, by the mechanism of molecular mimicry, was also stressed. Moreover, the mutual relationships between ghrelin and the TSH-FT4/FT3 axis in growth and metabolic processes are described. It is to be recalled that FT4 and FT3 exert a permissive impact on IGF-1 action and, in turn, GH, in reaction mediated by IGF-1, enhances the monodeiodination of FT4 to FT3. Finally, we discussed the latest attempts to use the GH secretagogue receptor (GHS-R) analogues for possible diagnostic and therapeutic purposes.

Ghrelin-induced Food Intake, but not GH Secretion, Requires the Expression of the GH Receptor in the Brain of Male Mice

Ghrelin stimulates both GH secretion and food intake. The orexigenic action of ghrelin is mainly mediated by neurons that coexpress agouti-related protein (AgRP) and neuropeptide Y (NPY) in the arcuate nucleus of the hypothalamus (ARH). GH also stimulates food intake and, importantly, ARHAgRP/NPY neurons express GH receptor (GHR). Thus, ghrelin-induced GH secretion may contribute to the orexigenic effect of ghrelin. Here, we investigated the response to ghrelin in male mice carrying GHR ablation specifically in neurons (brain GHR knockout [KO] mice) or exclusively in ARHAgRP/NPY neurons (AgRP GHR KO mice). Although brain GHR KO mice showed normal ghrelin-induced increase in plasma GH levels, these mutants lacked the expected orexigenic response to ghrelin. Additionally, brain GHR KO mice displayed reduced hypothalamic levels of Npy and Ghsr mRNA and did not elicit ghrelin-induced c-Fos expression in the ARH. Furthermore, brain GHR KO mice exhibited a prominent reduction in AgRP fiber density in the ARH and paraventricular nucleus of the hypothalamus (PVH). In contrast, AgRP GHR KO mice showed no changes in the hypothalamic Npy and Ghsr mRNAs and conserved ghrelin-induced food intake and c-Fos expression in the ARH. AgRP GHR KO mice displayed a reduced AgRP fiber density (~16%) in the PVH, but this reduction was less than that observed in brain GHR KO mice (~61%). Our findings indicate that GHR signaling in the brain is required for the orexigenic effect of ghrelin, independently of GH action on ARHAgRP/NPY neurons.

The ups and downs of growth hormone secretagogue receptor signaling

The growth hormone secretagogue receptor (GHSR) has emerged as one of the most fascinating molecules from the perspective of neuroendocrine control. GHSR is mainly expressed in the pituitary and the brain, and plays key roles regulating not only growth hormone secretion but also food intake, adiposity, body weight, glucose homeostasis and other complex functions. Quite atypically, GHSR signaling displays a basal constitutive activity that can be up- or downregulated by two digestive system-derived hormones: the octanoylated-peptide ghrelin and the liver-expressed antimicrobial peptide 2 (LEAP2), which was recently recognized as an endogenous GHSR ligand. The existence of two ligands with contrary actions indicates that GHSR activity can be tightly regulated and that the receptor displays the capability to integrate such opposing inputs in order to provide a balanced intracellular signal. This article provides a summary of the current understanding of the biology of ghrelin, LEAP2 and GHSR and discusses the reconceptualization of the cellular and physiological implications of the ligand-regulated GHSR signaling, based on the latest findings.

Central Regulation of Metabolism by Growth Hormone

Growth hormone (GH) is secreted by the pituitary gland, and in addition to its classical functions of regulating height, protein synthesis, tissue growth, and cell proliferation, GH exerts profound effects on metabolism. In this regard, GH stimulates lipolysis in white adipose tissue and antagonizes insulin's effects on glycemic control. During the last decade, a wide distribution of GH-responsive neurons were identified in numerous brain areas, especially in hypothalamic nuclei, that control metabolism. The specific role of GH action in different neuronal populations is now starting to be uncovered, and so far, it indicates that the brain is an important target of GH for the regulation of food intake, energy expenditure, and glycemia and neuroendocrine changes, particularly in response to different forms of metabolic stress such as glucoprivation, food restriction, and physical exercise. The objective of the present review is to summarize the current knowledge about the potential role of GH action in the brain for the regulation of different metabolic aspects. The findings gathered here allow us to suggest that GH represents a hormonal factor that conveys homeostatic information to the brain to produce metabolic adjustments in order to promote energy homeostasis.

Ghrelin as a prominent endocrine factor in stress-induced obesity

Objectives: Ghrelin acts on a variety of central- and peripheral organs causing an orexigenic effect, conclusively followed by increased caloric intake. Recent studies have indicated that ghrelin's function as an orexigenic agent does not entirely reflect the full functional properties of the peptide. Specifically, ghrelin regulates stress-hormone synthesis and secretion therewith affecting the stress-axis. The role of stress in the development of obesity has been extensively studied. However, the orexigenic and underlying stress-regulatory effect of ghrelin has not yet been further considered in the development of stress-induced obesity.Methods: Therefore, this review aims to accentuate the potential of ghrelin as a factor in the pathological development of stress-induced obesity.Results: In this review we discuss (1) the ghrelin-mediated intracellular cascades and elucidate the overall bioactivation of the peptide, and (2) the mechanisms of ghrelin signalling and regulation within the central nervous system and the gastro-intestinal system.Discussion: These biological processes will be ultimately discussed in relation to the pathogenesis of stress-induced obesity.

Strong Positive Correlation between TSH and Ghrelin in Euthyroid Non-Growth Hormone-Deficient Children with Short Stature

The growth processes in children depend on the proper functioning of some hormones and growth factors. Recently, a positive correlation between ghrelin and TSH (thyroid stimulating hormone) in patients with hyper- and hypothyroidism was proved. Moreover, in hypothyroid rats with high ghrelin concentration, growth hormone (GH) and insulin-like growth factor I (IGF-I) secretion was suppressed. We analyzed these relationships in euthyroid prepubertal children with idiopathic short stature (ISS). The analysis comprised concentration of ghrelin, GH in stimulating tests and during the night, as well as IGF-I, TSH, free thyroxine (FT4) and free triiodothyronine (FT3) in 85 children with ISS (36 girls, 49 boys) aged 9.65 ± 3.02 years (mean ± SD). A strong positive correlation between ghrelin and TSH was confirmed (r = +0.44, p < 0.05). A higher ghrelin but lower nocturnal GH and lower IGF-I were observed in children with higher normal TSH concentration than those in children with lower normal TSH. Interestingly, alterations of TSH level were without any impact on FT4 and FT3 concentrations. Summing up, in ISS prepubertal euthyroid children, ghrelin and TSH secretion are closely related. On the other hand, the higher the TSH, the lower the nocturnal GH and IGF-I levels. The contribution of the above findings in deterioration of growth processes requires further studies.

Response of the expression of oxytocin neurons to ghrelin in female mice

Ghrelin is an orexigenic agonist that acts directly on neurons in the hypothalamus, controlling appetite and energy balance. Although its role in appetite-associated neurons has been described, the relationship between peripheral ghrelin stimulation and oxytocin expression in the paraventricular nucleus is not fully understood. We evaluated the suppressive function of ghrelin in oxytocin-positive paraventricular nucleus neurons in ovariectomized C57BL/6 mice 2 h after ghrelin injection. The results showed that, in intact mice, peripheral ghrelin stimulation activated estrogen receptor alpha-expressing neurons during the estrous cycle and that agouti-related peptide mRNA expression was remarkably increased. Agouti-related peptide neuron axons co-localized with oxytocin neurons in the paraventricular nucleus. Moreover, the response of oxytocin-positive paraventricular nucleus neurons to ghrelin was suppressed in the proestrus period, while ghrelin decreased the serum concentration of estradiol in the proestrus phase. These data suggest that ghrelin may suppress oxytocin-positive neuron expression via the arcuate nucleus agouti-related peptide circuit, with the possible influence of estradiol in the murine estrous cycle. Unraveling the mechanism of ghrelin-induced oxytocin expression in the hypothalamus paraventricular nucleus broadens the horizon for ghrelin-related appetite research.

Calorie restriction activates new adult born olfactory-bulb neurones in a ghrelin-dependent manner but acyl-ghrelin does not enhance subventricular zone neurogenesis

The ageing and degenerating brain show deficits in neural stem/progenitor cell (NSPC) plasticity that are accompanied by impairments in olfactory discrimination. Emerging evidence suggests that the gut hormone ghrelin plays an important role in protecting neurones, promoting synaptic plasticity and increasing hippocampal neurogenesis in the adult brain. In the present study, we investigated the role of ghrelin with respect to modulating adult subventricular zone (SVZ) NSPCs that give rise to new olfactory bulb (OB) neurones. We characterised the expression of the ghrelin receptor, growth hormone secretagogue receptor (GHSR), using an immunohistochemical approach in GHSR-eGFP reporter mice to show that GHSR is expressed in several regions, including the OB but not in the SVZ of the lateral ventricle. These data suggest that acyl-ghrelin does not mediate a direct effect on NSPC in the SVZ. Consistent with these findings, treatment with acyl-ghrelin or genetic silencing of GHSR did not alter NSPC proliferation within the SVZ. Similarly, using a bromodeoxyuridine pulse-chase approach, we show that peripheral treatment of adult rats with acyl-ghrelin did not increase the number of new adult-born neurones in the granule cell layer of the OB. These data demonstrate that acyl-ghrelin does not increase adult OB neurogenesis. Finally, we investigated whether elevating ghrelin indirectly, via calorie restriction (CR), regulated the activity of new adult-born cells in the OB. Overnight CR induced c-Fos expression in new adult-born OB cells but not in developmentally born cells, whereas neuronal activity was absent following re-feeding. These effects were not present in ghrelin^-/- mice, suggesting that adult-born cells are uniquely sensitive to changes in ghrelin mediated by fasting and re-feeding. In summary, ghrelin does not promote neurogenesis in the SVZ and OB; however, new adult-born OB cells are activated by CR in a ghrelin-dependent manner.

Linking Stress and Infertility: A Novel Role for Ghrelin

Infertility affects a remarkable one in four couples in developing countries. Psychological stress is a ubiquitous facet of life, and although stress affects us all at some point, prolonged or unmanageable stress may become harmful for some individuals, negatively impacting on their health, including fertility. For instance, women who struggle to conceive are twice as likely to suffer from emotional distress than fertile women. Assisted reproductive technology treatments place an additional physical, emotional, and financial burden of stress, particularly on women, who are often exposed to invasive techniques associated with treatment. Stress-reduction interventions can reduce negative affect and in some cases to improve in vitro fertilization outcomes. Although it has been well-established that stress negatively affects fertility in animal models, human research remains inconsistent due to individual differences and methodological flaws. Attempts to isolate single causal links between stress and infertility have not yet been successful due to their multifaceted etiologies. In this review, we will discuss the current literature in the field of stress-induced reproductive dysfunction based on animal and human models, and introduce a recently unexplored link between stress and infertility, the gut-derived hormone, ghrelin. We also present evidence from recent seminal studies demonstrating that ghrelin has a principal role in the stress response and reward processing, as well as in regulating reproductive function, and that these roles are tightly interlinked. Collectively, these data support the hypothesis that stress may negatively impact upon fertility at least in part by stimulating a dysregulation in ghrelin signaling.

Ghrelin-mediated inhibition of the TSH-stimulated function of differentiated human thyrocytes ex vivo

Ghrelin is a peptide hormone produced mainly in the gastrointestinal tract known to regulate several physiological functions including gut motility, adipose tissue accumulation and hunger sensation leading to increased bodyweight. Studies have found a correlation between the plasma levels of thyroid hormones and ghrelin, but an effect of ghrelin on the human thyroid has never been investigated even though ghrelin receptors are present in the thyroid. The present study shows a ghrelin-induced decrease in the thyroid-stimulating hormone (TSH)-induced production of thyroglobulin and mRNA expression of thyroperoxidase in a primary culture of human thyroid cells obtained from paranodular tissue. Accordingly, a trend was noted for an inhibition of TSH-stimulated expression of the sodium-iodine symporter and the TSH-receptor. Thus, this study suggests an effect of ghrelin on human thyrocytes and thereby emphasizes the relevance of examining whether ghrelin also influences the metabolic homeostasis through altered thyroid hormone production.

Ghrelin attenuates vascular calcification in diabetic patients with amputation

Vascular calcification is established to be a critical factor in diabetes mellitus, which causes cardiovascular and amputation complication of diabetic patients. OPG/RANKL/RANK axis serves as a regulatory role in vascular calcification. Ghrelin, an endogenous ligand of growth hormone secretagogue receptor (GHSR), has been reported to exhibit potent cardiovascular protective effects. However, the role of ghrelin in the regulation of diabetic vascular calcification is still elusive. Here, we reported the role of ghrelin and its relationship with OPG/RANKL/RANK system in patients with diabetic foot amputation. In vivo and in vitro investigations were performed. Sixty type 2 diabetic patients with foot amputation were enrolled in vivo investigation, and they were divided into three groups through Doppler ultrasound: mild stenosis group (n=20), moderate stenosis group (n=20), and severe stenosis/occlusion group (n=20). Morphological analysis results showed diffused calcium depositions in the anterior tibial artery of diabetic amputees. Compared with the mild and moderate stenosis group, the severe stenosis/occlusion group had more spotty calcium depositions in atherosclerotic plaques. Western blot analysis indicated the expressions of osteoprotegerin (OPG) and ghrelin were downregulated, while the expression of receptor activator of nuclear factor kappa B ligand (RANKL) was upregulated with the vascular stenosis aggravation. Pearson correlation analysis revealed a negative correlation between calcium content and ghrelin levels (r=-0.58, P<0.001), as well as the ghrelin levels and sRANKL levels (r=-0.57, P<0.001). Meanwhile, OPG levels were positively correlated with ghrelin levels (r=0.63, P<0.001). From in vitro investigation, we found that the high-glucose (HG), high-lipid (HL), and β-glycerophosphate (β-GP) considerably increased the total calcium content, ALP activity, and expression of osteogenic markers in vascular smooth muscle cells (VSMCs). Ghrelin blunted calcification in a dose-dependent manner. In addition, ghrelin upregulated OPG expression and downregulated RANKL expression in VSMC calcification when anti-OPG antibody and RANKL were performed. Collectively, we therefore conclude serum ghrelin level may be a predictor of diabetic vascular calcification. The possible mechanism may be related with OPG/RANKL signal.

[Ghrelin: a gastric hormone at the crossroad between growth and appetite regulation]

Ghrelin is a 28 amino acid peptide hormone synthesized within the gastrointestinal tract. Initially identified as the endogenous ligand of the GHS-R1a (Growth Hormone Secretagogue Receptor 1a), ghrelin is a powerful stimulator of growth hormone (GH) secretion. At the crossroad between nutrition, growth and long-term energy metabolism, ghrelin also plays a unique role as the first identified gastric hormone increasing appetite and adiposity. However, the role of the ghrelin/GHS-R system in the physiology of growth, feeding behaviour and energy homeostasis needs to be better understood. Utilization of pharmacological tools and complementary animal models with deficiency in preproghrelin, ghrelin-O-acyl-transferase (GOAT - the enzyme that acylates ghrelin -) or GHS-R in situations of chronic undernutrition or high fat diet gives a more precise overview of the role of ghrelin in the pathophysiology of eating and metabolic disorders.

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.

Combined Administration of Ghrelin and Corticotropin-Releasing Hormone in the Diagnosis of Cushing's Disease

BACKGROUND/AIMS

Exaggerated adrenocorticotropic hormone (ACTH) and cortisol responses to ghrelin in Cushing's disease (CD) have previously been reported, similarly to responses to corticotropin-releasing hormone (CRH). We assessed the ability of ghrelin to enhance ACTH and cortisol responses when added to CRH stimulation in CD patients.

METHODS

In 21 CD patients (18 females, 3 males; age 49.8 ± 10.2 years; BMI 29.8 ± 0.8) and 8 healthy subjects (7 females, 1 male; age 40.6 ± 5.3 years; BMI 29.9 ± 1.2), we administered (1) ghrelin 100 µg i.v. bolus, (2) CRH 100 µg i.v. bolus, and (3) ghrelin + CRH combination. ACTH and cortisol were analyzed by commercially available kits from samples taken at 0, 15, 30, 45, 60, 90 and 120 min. ACTH and cortisol responses were calculated as peak and area under the curve (AUC0-120 min).

RESULTS

ACTH and cortisol at baseline and stimulated with ghrelin and/or CRH (peak and AUC0-120 min) were significantly higher in CD patients compared to controls (p < 0.01). ACTH and cortisol responses to ghrelin or CRH were similar in CD patients. Combined ghrelin + CRH administration in CD patients produced the highest ACTH response (peak and AUC0-120 min) compared to ghrelin or CRH alone (p < 0.01). Cortisol responses after ghrelin + CRH were uncoupled with ACTH responses and similar to the response to ghrelin or CRH alone in both groups. ACTH and cortisol responses, during all three tests, were similar in CD patients with micro- or macroadenomas.

CONCLUSION

Ghrelin administration causes exaggerated ACTH and cortisol responses in CD patients compared to healthy controls. In combination with CRH, it additionally enhances ACTH secretion without further additive effect on cortisol output.

Klotho and the Growth Hormone/Insulin-Like Growth Factor 1 Axis: Novel Insights into Complex Interactions

The growth hormone (GH)/insulin-like growth factor (IGF)-1 axis is pivotal for many metabolic functions, including proper development and growth of bones, skeletal muscles, and adipose tissue. Defects in the axis' activity during childhood result in growth abnormalities, while increased secretion of GH from the pituitary results in acromegaly. In order to keep narrow physiologic concentration, GH and IGF-1 secretion and activity are tightly regulated by hypothalamic, pituitary, endocrine, paracrine, and autocrine factors. Klotho was first discovered as an aging-suppressor gene. Mice that do not express klotho die prematurely with multiple symptoms of aging, several of them are also characteristic of decreased GH/IGF-1 axis activity. Klotho is highly expressed in the brain, the kidney, and parathyroid and pituitary glands, but can also serve as a circulating hormone by its shedding, forming soluble klotho that can be detected in blood, cerebrospinal fluid, and urine. Several lines of evidence suggest an association between klotho levels and activity of the GH/IGF-1 axis: the GH-secreting cells in the anterior pituitary of klotho-deficient mice are hypotrophic; klotho levels are altered in subjects with pathologies of the GH/IGF-1 axis; and accumulating data indicate that klotho is a direct regulator of GH secretion. Thus, klotho seems to be a new player in the intricate regulation of the GH/IGF-1 axis.

Neuroendocrine Regulation of Growth Hormone Secretion

This article reviews the main findings that emerged in the intervening years since the previous volume on hormonal control of growth in the section on the endocrine system of the Handbook of Physiology concerning the intra- and extrahypothalamic neuronal networks connecting growth hormone releasing hormone (GHRH) and somatostatin hypophysiotropic neurons and the integration between regulators of food intake/metabolism and GH release. Among these findings, the discovery of ghrelin still raises many unanswered questions. One important event was the application of deconvolution analysis to the pulsatile patterns of GH secretion in different mammalian species, including Man, according to gender, hormonal environment and ageing. Concerning this last phenomenon, a great body of evidence now supports the role of an attenuation of the GHRH/GH/Insulin-like growth factor-1 (IGF-1) axis in the control of mammalian aging.

Effects of intracerebroventricular infusions of ghrelin on secretion of follicle-stimulating hormone in peripubertal female sheep

Reproduction depends on mechanisms responsible for the regulation of energy homeostasis and puberty is a developmental period when reproductive and somatic maturity are achieved. Ghrelin affects the activity of the hypothalamo–pituitary–gonadal axis under conditions of energy insufficiency. An in vivo model based on intracerebroventricular (i.c.v.) infusions was used to determine whether centrally administered acyl ghrelin affects transcriptional and translational activity of FSH in peripubertal lambs and whether ghrelin administration mimics the effects of short-term fasting. Standard-fed lambs received either Ringer–Lock (R-L) solution (120 µL h–1) or ghrelin (120 µL h–1, 100 µg day–1). Animals experiencing a short-term (72 h) fast were treated only with R-L solution. In each experimental group, i.c.v. infusions occurred for 3 consecutive days. Immunohistochemistry, in situ hybridisation and real-time reverse transcription quantitative polymerase chain reaction analyses revealed that short-term fasting, as well as exogenous acyl ghrelin administration to standard-fed peripubertal lambs, augmented FSHβ mRNA expression and immunoreactive FSH accumulation. In addition to the effects of ghrelin on FSH synthesis in standard-fed animals, effects on gonadotrophin release were also observed. Acyl ghrelin increased the pulse amplitude for gonadotrophin release, which resulted in an elevation in mean serum FSH concentrations. In conclusion, the present data suggest that ghrelin participates in an endocrine network that modulates gonadotrophic activity in peripubertal female sheep.

Short-term calorie restriction enhances adult hippocampal neurogenesis and remote fear memory in a Ghsr-dependent manner

The beneficial effects of calorie restriction (CR) have been described at both organismal and cellular levels in multiple organs. However, our understanding of the causal mediators of such hormesis is poorly understood, particularly in the context of higher brain function. Here, we show that the receptor for the orexigenic hormone acyl-ghrelin, the growth hormone secretagogue receptor (Ghsr), is enriched in the neurogenic niche of the hippocampal dentate gyrus (DG). Acute elevation of acyl-ghrelin levels by injection or by overnight CR, increased DG levels of the neurogenic transcription factor, Egr-1. Two weeks of CR increased the subsequent number of mature newborn neurons in the DG of adult wild-type but not Ghsr(-/-) mice. CR wild-type mice also showed improved remote contextual fear memory. Our findings suggest that Ghsr mediates the beneficial effects of CR on enhancing adult hippocampal neurogenesis and memory.

Octanoylated ghrelin attenuates angiogenesis induced by oxLDL in human coronary artery endothelial cells via the GHSR1a-mediated NF-κB pathway

OBJECTIVE

Low concentrations of oxidized low-density lipoprotein (oxLDL) promote the in vitro angiogenesis of endothelial cells and play an important role in plaque angiogenesis, which may cause plaque vulnerability and enhance the risk of intravascular thrombosis. The aim of this research was to investigate the effects of octanoylated ghrelin on oxLDL-induced angiogenesis and the underlying molecular mechanisms involved in this process.

MATERIALS/METHODS

Human coronary artery endothelial cells (HCAECs) were incubated with 5 μg/ml oxLDL and treated with various concentrations of octanoylated ghrelin (10(-9)-10(-6)M) with or without inhibitors for 24h. Cell proliferation, migration, and in vitro angiogenesis were analyzed by bromodeoxyuridine (BrdU) staining and BrdU enzyme-linked immunosorbent assay (ELISA), transwell assay, and tube formation on Matrigel, respectively. NF-κB (nuclear factor κB) expression was determined by Western-blot analysis.

RESULTS

Treatment with oxLDL at 5 μg/ml enhanced the proliferation, migration and tube formation of HCAECs. In contrast, pretreatment with octanoylated ghrelin significantly attenuated in vitro angiogenesis in oxLDL-induced HCAECs. In addition, Western blot analysis indicated that NF-κB expression was increased after oxLDL treatment, and that this effect was significantly reversed by pretreatment with octanoylated ghrelin. However, the NF-κB inhibitor PDTC or the GHSR1a inhibitor [D-Lys3]-GHRP-6 abolished the effects of octanoylated ghrelin on the inhibition of angiogenesis and NF-κB p65 expression induced by oxLDL.

CONCLUSIONS

These findings suggest that octanoylated ghrelin attenuates angiogenesis induced by oxLDL in HCAECs via the inhibition of GHSR1a-mediated NF-κB pathway. Furthermore, octanoylated ghrelin may promote the stability of vulnerable plaques by inhibiting plaque angiogenesis.

Ghrelin's Role in the Hypothalamic-Pituitary-Adrenal Axis Stress Response: Implications for Mood Disorders

Ghrelin is a stomach hormone normally associated with feeding behavior and energy homeostasis. Recent studies highlight that ghrelin targets the brain to regulate a diverse number of functions, including learning, memory, motivation, stress responses, anxiety, and mood. In this review, we discuss recent animal and human studies showing that ghrelin regulates the hypothalamic-pituitary-adrenal axis and affects anxiety and mood disorders, such as depression and fear. We address the neural sites of action through which ghrelin regulates the hypothalamic-pituitary-adrenal axis and associated stress-induced behaviors, including the centrally projecting Edinger-Westphal nucleus, the hippocampus, amygdala, locus coeruleus, and the ventral tegmental area. Stressors modulate many behaviors associated with motivation, fear, anxiety, depression, and appetite; therefore, we assess the potential role for ghrelin as a stress feedback signal that regulates these associated behaviors. Finally, we briefly discuss important areas for future research that will help us move closer to potential ghrelin-based therapies to treat stress responses and related disorders.

Neuroanatomical characterization of a growth hormone secretagogue receptor-green fluorescent protein reporter mouse

Growth hormone secretagogue receptor (GHSR) 1a is the only molecularly identified receptor for ghrelin, mediating ghrelin-related effects on eating, body weight, and blood glucose control, among others. The expression pattern of GHSR within the brain has been assessed previously by several neuroanatomical techniques. However, inherent limitations to these techniques and the lack of reliable anti-GHSR antibodies and reporter rodent models that identify GHSR-containing neurons have prevented a more comprehensive functional characterization of ghrelin-responsive neurons. Here we have systematically characterized the brain expression of an enhanced green fluorescence protein (eGFP) transgene controlled by the Ghsr promoter in a recently reported GHSR reporter mouse. Expression of eGFP in coronal brain sections was compared with GHSR mRNA expression detected in the same sections by in situ hybridization histochemistry. eGFP immunoreactivity was detected in several areas, including the prefrontal cortex, insular cortex, olfactory bulb, amygdala, and hippocampus, which showed no or low GHSR mRNA expression. In contrast, eGFP expression was low in several midbrain regions and in several hypothalamic nuclei, particularly the arcuate nucleus, where robust GHSR mRNA expression has been well-characterized. eGFP expression in several brainstem nuclei showed high to moderate degrees of colocalization with GHSR mRNA labeling. Further quantitative PCR and electrophysiological analyses of eGFP-labeled hippocampal cells confirmed faithful expression of eGFP within GHSR-containing, ghrelin-responsive neurons. In summary, the GHSR-eGFP reporter mouse model may be a useful tool for studying GHSR function, particularly within the brainstem and hippocampus; however, it underrepresents GHSR expression in nuclei within the hypothalamus and midbrain.

Ghrelin gene products, receptors, and GOAT enzyme: biological and pathophysiological insight

Ghrelin is a 28-amino acid acylated hormone, highly expressed in the stomach, which binds to its cognate receptor (GHSR1a) to regulate a plethora of relevant biological processes, including food intake, energy balance, hormonal secretions, learning, inflammation, etc. However, ghrelin is, in fact, the most notorious component of a complex, intricate regulatory system comprised of a growing number of alternative peptides (e.g. obestatin, unacylated ghrelin, and In1-ghrelin, etc.), known (GHSRs) and, necessarily unknown receptors, as well as modifying enzymes (e.g. ghrelin-O-acyl-transferase), which interact among them as well as with other regulatory systems in order to tightly modulate key (patho)-physiological processes. This multiplicity of functions and versatility of the ghrelin system arise from a dual, genetic and functional, complexity. Importantly, a growing body of evidence suggests that dysregulation in some of the components of the ghrelin system can lead to or influence the development and/or progression of highly concerning pathologies such as endocrine-related tumors, inflammatory/cardiovascular diseases, and neurodegeneration, wherein these altered components could be used as diagnostic, prognostic, or therapeutic targets. In this context, the aim of this review is to integrate and comprehensively analyze the multiple components and functions of the ghrelin system described to date in order to define and understand its biological and (patho)-physiological significance.

Ghrelin suppresses nocturnal secretion of luteinizing hormone (LH) and thyroid stimulating hormone (TSH) in patients with major depression

Major depression is associated with various endocrine disturbances. Apart from the well-known hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis, also the function of the hypothalamic-pituitary-gonadal (HPG) axis and of the hypothalamic-pituitary-thyroid (HPT) axis may be altered compared to healthy subjects. The orexigenic hormone ghrelin is involved in mood regulation and may have antidepressant effects. In addition, it has been shown to suppress secretion of luteinizing hormone (LH) and thyroid stimulating hormone (TSH) in healthy subjects. Aim of this study was therefore to test the effect of ghrelin on the activity of the HPG and HPT axis in patients with major depression. Therefore, secretion profiles of LH and TSH were determined in 14 unmedicated patients with major depression (7 women) twice, receiving 50 μg ghrelin or placebo at 2200, 2300, 0000, and 0100 h. LH secretion after ghrelin injection as assessed by the AUC (4.05 ± 1.18 mlIU min/ml) was significantly (P = 0.049) lower than after placebo injection (4.75 ± 1.33 mlIU min/ml) during the predefined intervention period (2220-0200 h). In addition, LH pulses occurred significantly (P = 0.045) less frequently after ghrelin injection (3.2 ± 1.4) than after placebo injection (3.9 ± 1.7). Mean TSH plasma levels were significantly lower at 0240 h and from 0320 until 0420 h after ghrelin injection than after placebo injection. In conclusion, ghrelin suppressed nocturnal secretion of LH and TSH in patients with major depression. However, these effects were weaker than previously shown in healthy subjects.

An eGFP-expressing subpopulation of growth hormone secretagogue receptor cells are distinct from kisspeptin, tyrosine hydroxylase, and RFamide-related peptide neurons in mice

Ghrelin acts on the growth hormone secretagogue receptor (GHSR) in the brain to elicit changes in physiological functions. It is associated with the neural control of appetite and metabolism, however central ghrelin also affects fertility. Central ghrelin injection in rats suppresses luteinizing hormone (LH) concentrations and pulse frequency. Although ghrelin suppresses LH and regulates kisspeptin mRNA in the anteroventral periventricular/periventricular nucleus (AVPV/PeN), there is no neuroanatomical evidence linking GHSR neural circuits to kisspeptin neurons. In this study, we first determined coexpression of GHSR and GnRH neurons using a GHSR-eGFP reporter mouse line. Using dual-label immunohistochemistry, we saw no coexpression. GHSR-eGFP expressing cells were present in the AVPV/PeN and over 90% of these expressed estrogen receptor-α (ERα). Despite this, we observed no evidence of GHSR-eGFP/kisspeptin coexpressing neurons in the AVPV/PeN. To further examine the phenotype of GHSR-eGFP cells in the AVPV/PeN, we determined coexpression with tyrosine hydroxylase (TH) and showed virtually no coexpression in the AVPV/PeN (<2%). We also observed no coexpression of GHSR-eGFP and RFamide-related peptide-3 (RFRP3) neurons in the dorsomedial hypothalamic nucleus. Importantly, we observed that approximately half of the GHSR-eGFP cells in the AVPV coexpressed Ghsr mRNA (as determined by in situ hybridization) so these data should be interpreted accordingly. Although ghrelin influences the hypothalamic reproductive axis, our data using a GHSR-eGFP reporter suggests ghrelin regulates neurons expressing ERα but does not directly act on GnRH, kisspeptin, TH, or RFRP3 neurons, as little or no GHSR-eGFP coexpression was observed.