Expression of cortistatin and MrgX2, a specific cortistatin receptor, in human neuroendocrine tissues and related tumours

Bioinformatic and gene expression analysis of the somatostatin/cortistatin gene family in the gilthead seabream (Sparus aurata)

Somatostatin (SST) and cortistatin (CST) are neuromodulators with distinct expression patterns and functions. While SST and CST have been extensively studied in mammalian central nervous system (CNS) and immune system, their roles in teleost fish remain poorly explored due to evolutionary emergence of multiple SST paralogous genes. This study aimed to identify SST isoforms in gilthead seabream (Sparus aurata) and assess their transcriptional levels. Phylogeny and synteny analyses reclassified the six SST genes and proteins as SST1, SST3, SST3-like, SST4, SST5, and SST6. The protein sequences showed high conservation, except for an additional region upstream of the SST3-like protein's leader region. Evolutionary differences were mainly due to specific amino acid residue changes in the mature peptide. Genetic analyses revealed constitutive expression of five genes (sst1, sst3, sst5, sst4 and sst6) in all studied organs, except for sst3 in the heart, liver, and blood. The highest expression of sst1, sst3, sst4 and sst6 genes occurred in the brain's forebrain, while sst5 was most expressed in the heart. However, sst4 exhibited very low basal expression across all analysed tissues. In vitro, λ-carrageenan and cantharidin upregulated sst6 transcription in head kidney leucocytes (HKLs), indicating a potential anti-inflammatory role similar to mammalian CST. Additionally, sst5 expression was downregulated during the innate cell-mediated cytotoxic response, suggesting a regulatory role. These findings provide insights into the SST/CST gene family in gilthead seabream, necessitating gene and protein reclassification, and underscore their significant neuroendocrine and immune system functions, relevant for teleost research.

Transcriptomic analysis identifies the neuropeptide cortistatin (CORT) as an inhibitor of temozolomide (TMZ) resistance by suppressing the NF-κB-MGMT signaling axis in human glioma

Glioma is a common tumor originating in the brain that has a high mortality rate. Temozolomide (TMZ) is the first-line treatment for high-grade gliomas. However, a large proportion of gliomas are resistant to TMZ, posing a great challenge to their treatment. In the study, the specific functions and mechanism(s) by which cortistatin (CORT) regulates TMZ resistance and glioma progression were evaluated. The decreased expression of CORT was detected in glioma tissues, and highly expressed CORT was associated with a better survival rate in patients with glioma. CORT overexpression notably decreased the capacity of glioma cells to proliferate and migrate in vitro and to form tumors in vivo. CORT overexpression also markedly suppressed the viability and enhanced the apoptosis of TMZ-resistant U251 cells by regulating MGMT, p21, and Puma expression. Importantly, CORT overexpression reduced the resistance of gliomas to TMZ in vivo. CORT expression was negatively correlated with MGMT expression in both glioma tissues and cells, and it was found that CORT inhibited NF-κB pathway activation in glioma cells, thereby inhibiting MGMT expression. In conclusion, CORT regulates glioma cell growth, migration, apoptosis, and TMZ resistance by weakening the activity of NF-κB/p65 and thereby regulating MGMT expression. The CORT/NF-κB/MGMT axis might be regarded as a molecular mechanism contributing to the resistance of glioma to TMZ. Our data also suggest that CORT regulates the viability and metastatic potential of glioma cells, independent of its effects on TMZ resistance, providing evidence of novel therapeutic targets for glioma that should be evaluated in further studies.

Histopathologic Features of Adrenal Cortical Carcinoma

Adrenal cortical carcinoma (ACC) is a rare and aggressive malignancy that poses challenging issues regarding the diagnostic workup. Indeed, no presurgical technique or clinical parameters can reliably distinguish between adrenal cortical adenomas, which are more frequent and have a favorable outcome, and ACC, and the final diagnosis largely relies on histopathologic analysis of the surgical specimen. However, even the pathologic assessment of malignancy in an adrenal cortical lesion is not straightforward and requires a combined evaluation of multiple histopathologic features. Starting from the Weiss score, which was developed in 1984, several histopathologic scoring systems have been designed to tackle the difficulties of ACC diagnosis. Dealing with specific histopathologic variants (eg, Liss-Weiss-Bisceglia scoring system for oncocytic ACC) or patient characteristics (eg, Wieneke index in the pediatric setting), these scores remarkably improved the diagnostic workup of ACC and its subtypes. Nevertheless, cases with misleading features or discordant correlations between pathologic findings and clinical behavior still occur. Owing to multicentric collaborative studies integrating morphologic features with ancillary immunohistochemical markers and molecular analysis, ACC has eventually emerged as a multifaceted, heterogenous malignancy, and, while innovative and promising approaches are currently being tested, the future clinical management of patients with ACC will mainly rely on personalized medicine and target-therapy protocols. At the dawn of the new Fifth World Health Organization classification of endocrine tumors, this review will tackle ACC from the pathologist's perspective, thus focusing on the main available diagnostic, prognostic, and predictive tissue-tethered features and biomarkers and providing relevant clinical and molecular correlates.

In vitro prediction of in vivo pseudo-allergenic response via MRGPRX2

In development of peptide therapeutics, rodents are commonly-used preclinical models when screening compounds for efficacy endpoints in the early stages of discovery projects. During the screening process, some peptides administered subcutaneously to rodents caused injection site reactions manifesting as localized swelling. Screening by postmortem evaluations of injection site swelling as a marker for local subcutaneous histamine release, were conducted in rats to select drug candidates without this adverse effect. Histological analysis of skin samples revealed that the injection site reactions were concurrent with mast cell degranulation, resulting in histamine release. Mast cell activation can be mediated by MRGPRX2, a GPCR that induces a pseudo-allergenic immune response. The present study demonstrates that a commercially-available cell-based MRGPRX2 assay reliably identifies compounds that induce histamine release or localized edema in ex vivo human and rodent skin samples. In vitro screening was subsequently implemented using the MRGPRX2 assay as a substitute for postmortem injection site evaluation, thus achieving a significant reduction in animal use. Thus, in cases where injection site reactions are encountered during in vivo screening, to enable faster screening during the early drug discovery process, an MRGPRX2 in vitro assay can be used as an efficient, more ethical tool with human translational value for the development of safer pharmacotherapies for patients.

δ-Cells: The Neighborhood Watch in the Islet Community

Somatostatin-secreting δ-cells have aroused great attention due to their powerful roles in coordination of islet insulin and glucagon secretion and maintenance of glucose homeostasis. δ-cells exhibit neuron-like morphology with projections which enable pan-islet somatostatin paracrine regulation despite their scarcity in the islets. The expression of a range of hormone and neurotransmitter receptors allows δ-cells to integrate paracrine, endocrine, neural and nutritional inputs, and provide rapid and precise feedback modulations on glucagon and insulin secretion from α- and β-cells, respectively. Interestingly, the paracrine tone of δ-cells can be effectively modified in response to factors released by neighboring cells in this interactive communication, such as insulin, urocortin 3 and γ-aminobutyric acid from β-cells, glucagon, glutamate and glucagon-like peptide-1 from α-cells. In the setting of diabetes, defects in δ-cell function lead to suboptimal insulin and glucagon outputs and lift the glycemic set-point. The interaction of δ-cells and non-δ-cells also becomes defective in diabetes, with reduces paracrine feedback to β-cells to exacerbate hyperglycemia or enhanced inhibition of α-cells, disabling counter-regulation, to cause hypoglycemia. Thus, it is possible to restore/optimize islet function in diabetes targeting somatostatin signaling, which could open novel avenues for the development of effective diabetic treatments.

A rare testicular tumor: primary carcinoid tumor

BACKGROUND

Primary carcinoid tumors are rare and constitute 0.23% of all testicular tumors. We report a case of primary carcinoid tumor of testicular localization, with a review of the literature.

CASE PRESENTATION

A 29-year-old man, without specific ascendants, consulted the urology department for progressive scrotal swelling of 6 months, associated with pain. After surgery, histology showed diffuse tumor proliferation composed of small round monotone cells with hyperchromatic nuclei evoking undifferentiated carcinoma. Immunohistochemistry showed that tumor cells were positive for chromogranin A and negative for placental alkaline phosphatase and α-fetoprotein.

CONCLUSION

Primary neuroendocrine carcinoma of the testis is a very rare malignant tumor. Immunohistochemistry contributes to its diagnosis in relation to other metastatic neuroendocrine carcinomas, carcinoid tumor teratomas, seminoma, and Sertoli cells.

Cortistatin regulates glucose-induced electrical activity and insulin secretion in mouse pancreatic beta-cells

Although there is growing evidence that cortistatin regulates several functions in different tissues, its role in the endocrine pancreas is not totally known. Here, we aim to study the effect of cortistatin on pancreatic beta-cells and glucose-stimulated insulin secretion (GSIS). Exposure of isolated mouse islets to cortistatin inhibited GSIS. This effect was prevented using a somatostatin receptor antagonist. Additionally, cortistatin hyperpolarized the membrane potential and reduced glucose-induced action potentials in isolated pancreatic beta-cells. Cortistatin did not modify ATP-dependent K⁺ (K_ATP) channel activity. In contrast, cortistatin increased the activity of a small conductance channel with characteristics of G protein-coupled inwardly rectifying K⁺ (GIRK) channels. The cortistatin effects on membrane potential and GSIS were largely reduced in the presence of a GIRK channel antagonist and by down-regulation of GIRK2 with small interfering RNA. Thus, cortistatin acts as an inhibitory signal for glucose-induced electrical activity and insulin secretion in the mouse pancreatic beta-cell.

International Union of Basic and Clinical Pharmacology. CV. Somatostatin Receptors: Structure, Function, Ligands, and New Nomenclature

Somatostatin, also known as somatotropin-release inhibitory factor, is a cyclopeptide that exerts potent inhibitory actions on hormone secretion and neuronal excitability. Its physiologic functions are mediated by five G protein-coupled receptors (GPCRs) called somatostatin receptor (SST)1-5. These five receptors share common structural features and signaling mechanisms but differ in their cellular and subcellular localization and mode of regulation. SST2 and SST5 receptors have evolved as primary targets for pharmacological treatment of pituitary adenomas and neuroendocrine tumors. In addition, SST2 is a prototypical GPCR for the development of peptide-based radiopharmaceuticals for diagnostic and therapeutic interventions. This review article summarizes findings published in the last 25 years on the physiology, pharmacology, and clinical applications related to SSTs. We also discuss potential future developments and propose a new nomenclature.

Circulating levels of cortistatin are correlated with metabolic parameters in patients with newly diagnosed type 2 diabetes mellitus

Cortistatin (CST) is a recently discovered cyclic neuropeptide with multiple bioactive effects. The aim of this study was to investigate the relationship between plasma CST and various metabolic markers in patients with newly diagnosed type 2 diabetes mellitus (T2DM). For this study, 60 patients with newly diagnosed T2DM and 38 age- and gender-matched healthy controls were recruited. Fasting plasma glucose (FPG), serum insulin and hemoglobin A_1c (HbA_1c) levels and a blood lipid profile were obtained with commercially available diagnostic reagents. CST plasma levels were determined using an enzyme immunoassay kit. The results showed that the plasma levels of CST were substantially lower in patients with newly diagnosed T2DM compared with the healthy controls. Plasma CST levels were positively correlated with high-density lipoprotein and negatively related to FPG, serum insulin, the homeostasis model assessment of insulin resistance (HOMA-IR) and HbA_1c in all subjects. Further analysis showed that CST levels were positively correlated with systolic blood pressure and negatively correlated with FPG, serum insulin, HOMA-IR and HbA_1c in patients with newly diagnosed T2DM. Moreover, logistic regression analyses indicated that plasma CST was correlated with newly diagnosed T2DM. In conclusion, patients with newly diagnosed T2DM had significantly lower plasma levels of CST than healthy controls, and plasma CST was associated with glucose metabolism and insulin resistance, indicating a potential role of CST in the development of T2DM.

Obesity- and gender-dependent role of endogenous somatostatin and cortistatin in the regulation of endocrine and metabolic homeostasis in mice

Somatostatin (SST) and cortistatin (CORT) regulate numerous endocrine secretions and their absence [knockout (KO)-models] causes important endocrine-metabolic alterations, including pituitary dysregulations. We have demonstrated that the metabolic phenotype of single or combined SST/CORT KO-models is not drastically altered under normal conditions. However, the biological actions of SST/CORT are conditioned by the metabolic-status (e.g. obesity). Therefore, we used male/female SST- and CORT-KO mice fed low-fat (LF) or high-fat (HF) diet to explore the interplay between SST/CORT and obesity in the control of relevant pituitary-axes and whole-body metabolism. Our results showed that the SST/CORT role in the control of GH/prolactin secretions is maintained under LF- and HF-diet conditions as SST-KOs presented higher GH/prolactin-levels, while CORT-KOs displayed higher GH- and lower prolactin-levels than controls under both diets. Moreover, the impact of lack of SST/CORT on the metabolic-function was gender- and diet-dependent. Particularly, SST-KOs were more sensitive to HF-diet, exhibiting altered growth and body-composition (fat/lean percentage) and impaired glucose/insulin-metabolism, especially in males. Conversely, only males CORT-KO under LF-diet conditions exhibited significant alterations, displaying higher glucose-levels and insulin-resistance. Altogether, these data demonstrate a tight interplay between SST/CORT-axis and the metabolic status in the control of endocrine/metabolic functions and unveil a clear dissociation of SST/CORT roles.

Cortistatin Is a Key Factor Regulating the Sex-Dependent Response of the GH and Stress Axes to Fasting in Mice

Cortistatin (CORT) shares high structural and functional similarities with somatostatin (SST) but displays unique sex-dependent pituitary actions. Indeed, although female CORT-knockout (CORT-KO) mice exhibit enhanced GH expression/secretion, Proopiomelanocortin expression, and circulating ACTH/corticosterone/ghrelin levels, male CORT-KO mice only display increased plasma GH/corticosterone levels. Changes in peripheral ghrelin and SST (rather than hypothalamic levels) seem to regulate GH/ACTH axes in CORT-KOs under fed conditions. Because changes in GH/ACTH axes during fasting provide important adaptive mechanisms, we sought to determine whether CORT absence influences GH/ACTH axes during fasting. Accordingly, fed and fasted male/female CORT-KO were compared with littermate controls. Fasting increased circulating GH levels in male/female controls but not in CORT-KO, suggesting that CORT can be a relevant regulator of GH secretion during fasting. However, GH levels were already higher in CORT-KO than in controls in fed state, which might preclude a further elevation in GH levels. Interestingly, although fasting-induced pituitary GH expression was elevated in both male/female controls, GH expression only increased in fasted female CORT-KOs, likely owing to specific changes observed in key factors controlling somatotrope responsiveness (ie, circulating ghrelin and IGF-1, and pituitary GHRH and ghrelin receptor expression). Fasting increased corticosterone levels in control and, most prominently, in CORT-KO mice, which might be associated with a desensitization to SST signaling and to an augmentation in CRH and ghrelin-signaling regulating corticotrope function. Altogether, these results provide compelling evidence that CORT plays a key, sex-dependent role in the regulation of the GH/ACTH axes in response to fasting.

Lulling immunity, pain, and stress to sleep with cortistatin

Cortistatin is a neuropeptide isolated from cortical brain regions, showing high structural homology and sharing many functions with somatostatin. However, cortistatin exerts unique functions in the central nervous and immune systems, including decreasing locomotor activity, inducing sleep-promoting effects, and deactivating inflammatory and T helper (TH )1/TH 17-driven responses in preclinical models of sepsis, arthritis, multiple sclerosis, and colitis. Besides its release by cortical and hippocampal interneurons, cortistatin is produced by macrophages, lymphocytes, and peripheral nociceptive neurons in response to inflammatory stimuli, supporting a physiological role of cortistatin in the immune and nociceptive systems. Cortistatin-deficient mice have been shown to have exacerbated nociceptive responses to neuropathic and inflammatory pain sensitization. However, a paradoxical effect has been observed in studies of immune disorders, in which, despite showing competent inflammatory/autoreactive responses, cortistatin-deficient mice were partially resistant to systemic autoimmunity and inflammation. This unexpected phenotype was associated with elevated circulating glucocorticoids and anxiety-like behavior. These findings support cortistatin as a novel multimodal therapeutic approach to treat autoimmunity and clinical pain and identify it as a key endogenous component of the neuroimmune system related to stress responses.

MAS and its related G protein-coupled receptors, Mrgprs

The Mas-related G protein-coupled receptors (Mrgprs or Mas-related genes) comprise a subfamily of receptors named after the first discovered member, Mas. For most Mrgprs, pruriception seems to be the major function based on the following observations: 1) they are relatively promiscuous in their ligand specificity with best affinities for itch-inducing substances; 2) they are expressed in sensory neurons and mast cells in the skin, the main cellular components of pruriception; and 3) they appear in evolution first in tetrapods, which have arms and legs necessary for scratching to remove parasites or other noxious substances from the skin before they create harm. Because parasites coevolved with hosts, each species faced different parasitic challenges, which may explain another striking observation, the multiple independent duplication and expansion events of Mrgpr genes in different species as a consequence of parallel adaptive evolution. Their predominant expression in dorsal root ganglia anticipates additional functions of Mrgprs in nociception. Some Mrgprs have endogenous ligands, such as β-alanine, alamandine, adenine, RF-amide peptides, or salusin-β. However, because the functions of these agonists are still elusive, the physiologic role of the respective Mrgprs needs to be clarified. The best studied Mrgpr is Mas itself. It was shown to be a receptor for angiotensin-1-7 and to exert mainly protective actions in cardiovascular and metabolic diseases. This review summarizes the current knowledge about Mrgprs, their evolution, their ligands, their possible physiologic functions, and their therapeutic potential.

Dietary fat alters the expression of cortistatin and ghrelin systems in the PBMCs of elderly subjects: putative implications in the postprandial inflammatory response

SCOPE

Dietary fat influences systemic inflammatory status, which determines the progression of age-associated diseases. Since somatostatin (SST), cortistatin (CORT), and ghrelin systems modulate inflammatory response, we aim to comprehensively characterize the presence and regulation of the components of these systems in the peripheral blood mononuclear cells (PMBCs), a subset of white blood cells placed at the crossroad between diet and inflammation, in response to diets with different fat composition, and during the postprandial phase in elderly subjects.

METHODS AND RESULTS

The applied nutrigenomic, inflammation-related PBMC-based approach revealed that the majority of components of SST/CORT and ghrelin systems are present in the human PBMCs. Particularly, CORT, SST/CORT receptors (sst2, sst3, sst5, and sst5TMD4), ghrelin, its acylating enzyme (GOAT), In1-ghrelin variant, and GHSR1b were detected in PBMCs. Their expression was altered in the long-term by diet composition, and in the short-term, during the postprandial phase. Of particular relevance is the postprandial elevation of CORT, sst2, and sst5 expression in PBMCs of subjects under n-3 PUFAs-enriched diet.

CONCLUSION

Our results suggest a potential relevant role of CORT/ssts and ghrelin systems in regulating PBMCs response to nutrient intake, which could help to explain the positive effects of n-3 PUFAs-enriched diets in reducing the inflammatory response.

Expression of Mas-related gene X2 on mast cells is upregulated in the skin of patients with severe chronic urticaria

BACKGROUND

Wheal reactions to intradermally injected neuropeptides, such as substance P (SP) and vasoactive intestinal peptide, are significantly larger and longer lasting in patients with chronic urticaria (CU) than in nonatopic control (NC) subjects. Mas-related gene X2 (MrgX2) has been identified as a receptor for basic neuropeptides, such as SP and vasoactive intestinal peptide. Mast cell (MC) responsiveness to eosinophil mediators contributes to the late-phase reaction of allergy.

OBJECTIVE

We sought to compare the frequency of MrgX2 expression in skin MCs from patients with CU and NC subjects and to identify the receptor for basic eosinophil granule proteins on human skin MCs.

METHODS

MrgX2 expression was investigated by using immunofluorescence in skin tissues from NC subjects and patients with severe CU and on skin-derived cultured MCs. MrgX2 expression in human MCs was reduced by using a lentiviral small hairpin RNA silencing technique. Ca(2+) influx was measured in CHO cells transfected with MrgX2 in response to eosinophil granule proteins. Histamine and prostaglandin D2 levels were measured by using enzyme immunoassays.

RESULTS

The number of MrgX2(+) skin MCs and the percentage of MrgX2(+) MCs in all MCs in patients with CU were significantly greater than those in NC subjects. Eosinophil infiltration in urticarial lesions was observed in 7 of 9 patients with CU. SP, major basic protein, and eosinophil peroxidase, but not eosinophil-derived neurotoxin, induced histamine release from human skin MCs through MrgX2.

CONCLUSION

MrgX2 might be a new target molecule for the treatment of wheal reactions in patients with severe CU.

Expression and distribution patterns of Mas-related gene receptor subtypes A-H in the mouse intestine: inflammation-induced changes

Mas-related gene (Mrg) receptors constitute a subfamily of G protein-coupled receptors that are implicated in nociception, and are as such considered potential targets for pain therapies. Furthermore, some Mrgs have been suggested to play roles in the regulation of inflammatory responses to non-immunological activation of mast cells and in mast cell-neuron communication. Except for MrgD, E and F, whose changed expression has been revealed during inflammation in the mouse intestine in our earlier studies, information concerning the remaining cloned mouse Mrg subtypes in the gastrointestinal tract during (patho) physiological conditions is lacking. Therefore, the present study aimed at identifying the presence and putative function of these remaining cloned Mrg subtypes (n = 19) in the (inflamed) mouse intestine. Using reverse transcriptase-PCR, quantitative-PCR and multiple immunofluorescence staining with commercial and newly custom-developed antibodies, we compared the ileum and the related dorsal root ganglia (DRG) of non-inflamed mice with those of two models of intestinal inflammation, i.e., intestinal schistosomiasis and 2,4,6-trinitrobenzene sulfonic acid-induced ileitis. In the non-inflamed ileum and DRG, the majority of the Mrg subtypes examined were sparsely expressed, showing a neuron-specific expression pattern. However, significant changes in the expression patterns of multiple Mrg subtypes were observed in the inflamed ileum; for instance, MrgA4, MrgB2and MrgB8 were expressed in a clearly increased number of enteric sensory neurons and in nerve fibers in the lamina propria, while de novo expression of MrgB10 was observed in enteric sensory neurons and in newly recruited mucosal mast cells (MMCs). The MrgB10 expressing MMCs were found to be in close contact with nerve fibers in the lamina propria. This is the first report on the expression of all cloned Mrg receptor subtypes in the (inflamed) mouse intestine. The observed changes in the expression and cellular localization of the Mrg subtypes suggest that these receptors are involved in the mediation of primary afferent responses, mast cell responses, and in neuroimmune communication during intestinal inflammation.

Cortistatin modulates the expression and release of corticotrophin releasing hormone in rat brain. Comparison with somatostatin and octreotide

Cortistatin (CST) is an endogenous neuropeptide characterized by remarkable structural and functional resemblance to somatostatin (SST), both peptides sharing the ability to bind and activate all five SST receptor subtypes. Evidence is also available showing that CST exerts biological activities independently from SST, perhaps via the activation of specific receptors that remain to be fully characterized at present. Here we have investigated the effects of CST on the gene expression and release of corticotrophin releasing hormone (CRH) from rat hypothalamic and hippocampal explants; moreover, we compared the effects of CST with those of SST and octreotide (OCT) in these models. We found that: (i) CST inhibits the expression and release of CRH from rat hypothalamic and hippocampal explants under basal conditions as well as after CRH stimulation by well known secretagogues; (ii) SST does not modify basal CRH secretion from the hypothalamus or the hippocampus, while it is able to reduce KCl-stimulated CRH release from both brain areas; (iii) OCT inhibits both basal and KCl-induced CRH secretion from rat hypothalamic explants, while it has no effect on CRH release from the hippocampus, either under basal conditions or after stimulation by high K(+) concentrations; (iv) at variance with CST; SST and OCT have not effect whatsoever on veratridine-induced CRH release from the hypothalamus. In conclusion the present findings provide in vitro evidence in support of the hypothesis that CST plays a role in the regulation of endocrine adaptive responses to stress.

Epigenetic control of somatostatin and cortistatin expression by β amyloid peptide

β Amyloid, present in senile plaques, has been related largely to neuronal loss in the brain of patients with Alzheimer's disease. However, how neurons respond to β amyloid insults is still poorly understood. Here we show that β amyloid increases somatostatin and cortistatin gene expression mainly through an increase in histone 3 lysine 4 methylation (H3K4me3), a modification associated with transcriptional activation. Somatostatin and cortistatin partially decreased β amyloid toxicity in primary cortical neurons in culture. Thus we suggest that neurons respond to β amyloid insults by releasing somatostatin and cortistatin, which will act as a protective agent against β amyloid toxicity. Our results suggest a relevant function for both neuropeptides against β amyloid toxicity, providing new insights into Alzheimer's disease.

Reflections on the theory of "silver bullet" octreotide tracers: implications for ligand-receptor interactions in the age of peptides, heterodimers, receptor mosaics, truncated receptors, and multifractal analysis

The classical attitude of Nuclear Medicine practitioners on matters of peptide-receptor interactions has maintained an intrinsic monogamic character since many years. New advances in the field of biochemistry and even in clinical Nuclear Medicine have challenged this type of thinking, which prompted me to work on this review. The central issue of this paper will be the use of somatostatin analogs, i.e., octreotide, in clinical imaging procedures as well as in relation to neuroendocirne tumors. Newly described characteristics of G-protein coupled receptors such as the formation of receptor mosaics will be discussed. A small section will enumerate the regulatory processes found in the cell membrane. Possible new interpretations, other than tumor detection, based on imaging procedures with somatostatin analogs will be presented. The readers will be taken to situations such as inflammation, nociception, mechanosensing, chemosensing, fibrosis, taste, and vascularity where somatostatin is involved. Thyroid-associated orbitopathy will be used as a model for the development of multi-agent therapeutics. The final graphical summary depicts the multifactorial properties of ligand binding.

Cortistatin modulates calcitonin gene-related peptide release from neuronal tissues of rat. Comparison with somatostatin

Cortistatin (CST) is an endogenous neuropeptide bearing strong structural and functional analogies with somatostatin (SST). Gene expression of CST and its putative receptor MrgX2 in dorsal root ganglia (DRG) neurons in man suggests the involvement of CST in pain transmission. In this study we have investigated the effects of CST and SST on calcitonin gene-related peptide (CGRP, the main neuropeptide mediator of pain transmission) from primary cultures of rat trigeminal neurons. Moreover, here for the first time we used organotypic cultures of rat brainstem to investigate the release of CGRP form nucleus caudalis as a model of pre-synaptic peptide release. In both experimental paradigm CGRP release was evaluated in the presence of CST or SST, with or without the addition of known secretagogues (namely high KCl concentrations, veratridine and capsaicin). We found that CST and SST do not modify basal CGRP secretion from trigeminal neurons, but both peptides were able to inhibit in a concentration-dependent manner the release of CGRP stimulated by KCl, veratridine or capsaicin. Likewise, in brainstem organotypic cultures CST and SST did not modify baseline CGRP secretion. Of the secretagogues used, capsaicin proved to be most effective compared to KCl and veratridine (8-fold vs 2-fold increase, respectively). Thereafter, CST and SST were tested on capsaicin-stimulated CGPR release only. Under these conditions, CST but not SST was able to inhibit in a significant manner pre-synaptic CGRP release from the brainstem, providing further evidence in support of a role for CST in pain transmission.

Role of somatostatins in gastroenteropancreatic neuroendocrine tumor development and therapy

The incidence and prevalence of gastroenteropancreatic neuroendocrine tumors (GEP-NETs) have increased in the past 20 years. GEP-NETs are heterogeneous tumors, in terms of clinical and biological features, that originate from the pancreas or the intestinal tract. Some GEP-NETs grow very slowly, some grow rapidly and do not cause symptoms, and others cause hormone hypersecretion and associated symptoms. Most GEP-NETs overexpress receptors for somatostatins. Somatostatins inhibit the release of many hormones and other secretory proteins; their effects are mediated by G protein-coupled receptors that are expressed in a tissue-specific manner. Most GEP-NETs overexpress the somatostatin receptor SSTR2; somatostatin analogues are the best therapeutic option for functional neuroendocrine tumors because they reduce hormone-related symptoms and also have antitumor effects. Long-acting formulations of somatostatin analogues stabilize tumor growth over long periods. The development of radioactive analogues for imaging and peptide receptor radiotherapy has improved the management of GEP-NETs. Peptide receptor radiotherapy has significant antitumor effects, increasing overall survival times of patients with tumors that express a high density of SSTRs, particularly SSTR2 and SSTR5. The multi-receptor somatostatin analogue SOM230 (pasireotide) and chimeric molecules that bind SSTR2 and the dopamine receptor D2 are also being developed to treat patients with GEP-NETs. Combinations of radioactive labeled and unlabeled somatostatin analogues and therapeutics that inhibit other signaling pathways, such as mammalian target of rapamycin (mTOR) and vascular endothelial growth factor, might be the most effective therapeutics for GEP-NETs.

Effect of cortistatin on tau phosphorylation at Ser262 site

The development of intraneuronal lesions as a result of the progressive deposition of hyperphosphorylated tau at specific brain regions (such as hippocampus and cortex) plays a key role in the pathological process of Alzheimer's disease. However, the mechanisms by which tau phosphorylation is regulated, mainly in the pathology found in the cortex, are still poorly understood. Here, we analyzed the effect of cortistatin, a cortical neuropeptide related to somatostatin, on tau phosphorylation at Ser262 in cultures of murine cortical neurons. Both somatostatin and cortistatin induce tau phosphorylation at Ser262, a site modified in Alzheimer's disease, although with different kinetics in cortex. The effect of cortistatin likely is mediated by heterodimeric receptors composed of somatostatin receptor subtypes 2 and 4 and also by protein kinase C signaling. Cortistatin-deficient mice show decreased tau phosphorylation at Ser262 in the cortex but not in other brain regions tested. Our results suggest an important role for cortistatin in the regulation of tau phosphorylation that may be associated with the pathophysiology of Alzheimer's disease in regions such as the cerebral cortex.

Somatostatin, cortistatin and their receptors in tumours

Somatostatin (SS) and its synthetic analogs have a role in the treatment of neuroendocrine tumours both in terms of symptoms control and antiproliferative activities. These effects are mediated by five SS receptors, widely expressed in both human neuroendocrine and non-neuroendocrine tumours, which were demonstrated to be diagnostically and therapeutically valuable targets. Cortistatin (CST), a brain cortex peptide, partially homologous to SS and having similar functions is also expressed in peripheral tissues and tumours. CST binds all SS receptors, and, differently from SS, also the ghrelin receptor GHSR1a and the CST specific receptor MrgX2. The expression profile of CST is mostly restricted to neuroendocrine tumours (gastrointestinal, pancreas, lung, parathyroid, thyroid, adrenal). In these tumours, CST probably acts via the SS or ghrelin receptor, the MrgX2 receptor being absent. Thus, in comparison to SS analogs, CST synthetic analogs may represent additional diagnostic/therapeutic tools in those tumours expressing the receptors for SS, for ghrelin or for both peptides.

Pharmacological profile of somatostatin and cortistatin receptors

Somatostatin (SRIF) and cortistatin (CST) are two endogenous peptides with high sequence similarities that act as hormones/neurotransmitters both in the CNS and the periphery; their genes although distinct result from gene duplication. Their receptors appear to be common, since the five known SRIF receptors (sst1-sst5) have similar subnanomolar affinity for SRIF and CST, whether the short (SRIF-14, CST-14, CST-17) or the long versions (SRIF-28, CST-29) of the peptides. Whether CST targets specific receptors not shared by SRIF, is still debated: MrgX2 has been described as a selective CST receptor, with submicromolar affinity for CST but devoid of affinity for SRIF; however the distribution of CST and MrgX2 is largely different, and there is no MrgX2 in rodents. A similar situation arises with the GHS receptor GHS-R1a, which displays some preferential affinity for CST over SRIF, but for which there is no evidence that it is activated by CST in vivo. In both cases, one may argue that submicromolar affinity is not the norm of a GPCR for its endogenous neuropeptide. On the other hand, all receptors known to bind SRIF have similar high affinity for CST and both peptides act as potent agonists at the sst1-sst5 receptors, whichever transduction pathway is considered. In addition, [(125)I][Tyr(10)]CST(14) labels sst1-sst5 receptors with subnanomolar affinity, and [(125)I][Tyr(10)]CST(14) binding in the brain is overlapping with that of [(125)I][Tyr(0)]SRIF(14). The functional differences reported that distinguish CST from SRIF, have not been explained convincingly and may relate to ligand-driven transductional selectivity, and other complicating factors such as receptor dimerisation, (homo or heterodimerisation), and/or the influence of accessory proteins (GIPs, RAMPS), which remain to be studied in more detail.

Endocrine actions of cortistatin: in vivo studies

Cortistatin (CST) shares high structural homology with somatostatin (SST) and binds all SST-receptors (SST-R) subtypes with similar affinity. However, CST actions, tissue expression patterns and regulation do not fully overlap with those of SST, and, moreover, CST, but not SST, also binds and activates proadrenomedullin N-terminal peptide receptor (MrgX2) and shows binding affinity to ghrelin receptor (GHS-R1a). Several studies performed to clarify the endocrine actions of CST, compared with SST, showed that, in humans, CST and SST share the same endocrine actions, i.e. inhibition of GH and insulin secretion in physiological conditions and in acromegaly. A similar inhibitory effect on PRL and ACTH secretion was shown in acromegaly, prolactinoma or in Cushing's disease. This identity of endocrine actions by CST and SST suggests that SST-R activation by CST overrides any other independent action of this peptide mediated by other receptors. Thus, in terms of endocrine actions, CST can well be considered a natural alternative to SST.

Gender-dependent role of endogenous somatostatin in regulating growth hormone-axis function in mice

It has been previously reported that male and female somatostatin (SST) knockout mice (Sst-/-) release more GH, compared with Sst+/+ mice, due to enhanced GH-secretory vesicle release. Endogenous SST may also regulate GH secretion by directly inhibiting GHRH-stimulated GH gene expression and/or by modulating hypothalamic GHRH input. To begin to explore these possibilities and to learn more about the gender-dependent role of SST in modulating GH-axis function, hypothalamic, pituitary, and liver components of the GH-axis were compared in male and female Sst+/+ and Sst-/- mice. Pituitary mRNA levels for GH and receptors for GHRH and ghrelin were increased in female Sst-/- mice, compared with Sst+/+ controls, and these changes were reflected by an increase in circulating GH and IGF-I. Elevated levels of IGF-I in female Sst-/- mice were associated with elevated hepatic mRNA levels for IGF-I, as well as for GH and prolactin receptors. Consistent with the role of GH/IGF-I in negative feedback regulation of hypothalamic function, GHRH mRNA levels were reduced in female Sst-/- mice, whereas cortistatin (CST) mRNA levels were unaltered. In contrast to the widespread impact of SST loss on GH-axis function in females, only circulating GH, hypothalamic CST, and hepatic prolactin receptor expression were up-regulated in Sst-/- male mice, compared with Sst+/+ controls. These results confirm and extend the sexually dimorphic role of SST on GH-axis regulation, and suggest that CST, a neuropeptide that acts through SST receptors to inhibit GH secretion, may serve a compensatory role in maintaining GH-axis function in Sst-/- male mice.

Brain-gut communication: cortistatin, somatostatin and ghrelin

Although cortistatin (CST) shares great structural homology with somatostatin (SST) and binds to all SST receptor subtypes with similar affinity, these neurohormones have divergent biological roles, as evidenced by their different patterns of tissue expression and biological actions. Moreover, CST, but not SST, can bind to the proadrenomedullin N-terminal peptide (PAMP) receptor MrgX2 and type 1a growth hormone secretagogue (GHS) receptor (GHSR-1a), also known as the 'ghrelin' receptor. These findings suggest that CST-specific actions could be mediated by the GHSR-1a and CST might represent a link between the ghrelin and the SST systems. Here, we review the data leading to this working hypothesis and discuss the in vitro, in vivo and clinical implications of potential SST-receptor-independent, GHSR-1a-mediated neuroendocrine and metabolic effects of CST.

Cortistatin as a therapeutic target in inflammation

Cortistatin (CST) is a recently discovered neuropeptide from the somatostatin gene family, named after its predominantly cortical expression and ability to depress cortical activity. CST shows many remarkable structural and functional similarities to its related neuropeptide somatostatin, or somatotropin release-inhibiting factor. However, the many physiological differences between CST and somatostatin are just as remarkable as the similarities. CST-29 has recently been shown to prevent inflammation in rodent models for human diseases, raising novel therapeutic properties to this neuropeptide. In this review, the authors address a new possible role for CST in the immune system and evaluate the possible therapeutic use of CST to treat disorders associated with inflammation.

Compensatory changes in the hippocampus of somatostatin knockout mice: upregulation of somatostatin receptor 2 and its function in the control of bursting activity and synaptic transmission

Somatostatin-14 (SRIF) co-localizes with gamma-aminobutyric acid (GABA) in the hippocampus and regulates neuronal excitability. A role of SRIF in the control of seizures has been proposed, although its exact contribution requires some clarification. In particular, SRIF knockout (KO) mice do not exhibit spontaneous seizures, indicating that compensatory changes may occur in KO. In the KO hippocampus, we examined whether specific SRIF receptors and/or the cognate peptide cortistatin-14 (CST) compensate for the absence of SRIF. We found increased levels of both sst2 receptors (sst2) and CST, and we explored the functional consequences of sst2 compensation on bursting activity and synaptic responses in hippocampal slices. Bursting was decreased by SRIF in wild-type (WT) mice, but it was not affected by either CST or sst2 agonist and antagonist. sst4 agonist increased bursting frequency in either WT or KO. In WT, but not in KO, its effects were blocked by agonizing or antagonizing sst2, suggesting that sst2 and sst4 are functionally coupled in the WT hippocampus. Bursting was reduced in KO as compared with WT and was increased upon application of sst2 antagonist, while SRIF, CST and sst2 agonist had no effect. At the synaptic level, we observed that in WT, SRIF decreased excitatory postsynaptic potentials which were, in contrast, increased by sst2 antagonist in KO. We conclude that sst2 compensates for SRIF absence and that its upregulation is responsible for reduced bursting and decreased excitatory transmission in KO mice. We suggest that a critical density of sst2 is needed to control hippocampal activity.

Ghrelin and cortistatin in lung cancer: expression of peptides and related receptors in human primary tumors and in vitro effect on the H345 small cell carcinoma cell line

Ghrelin, a natural GH secretagogue (GHS) acylated peptide, and cortistatin (CST), a natural SRIF-like peptide, interfere with neoplastic growth in different cancers. We tested forty-one lung carcinomas and the H345 small cell lung carcinoma (SCLC) cell line by RT-PCR to investigate the presence of ghrelin and CST and related receptors, including type 1a GHS receptor (GHS-R1a), all SRIF-receptor subtypes (sst 1-5) and MRGX2. Moreover, the presence of ghrelin and CST peptides was studied in both tumors and H345 cells. Ghrelin and CST mRNA were present in the majority of tested tumors, but ghrelin and CST proteins were revealed only in tumors with a neuroendocrine phenotype. All the receptors mRNA had a heterogeneous expression without correlation between ghrelin (or CST) and their receptor distribution. All the transcripts, but not GHS-R1a, were expressed in H345 cells. However, ghrelin and desacyl ghrelin induced in vitro a dose-dependent inhibition on the H345 cell proliferation and increased apoptosis. Conversely, neither CST nor SRIF affected H345 cell growth, despite the presence of their specific receptors. The anti-proliferative and the pro-apoptotic effects of ghrelin were consistent with binding experiments on H345 cell, where either acylated or des-acylated ghrelin recognized a common binding site. In conclusion, the present study indicates that: a) ghrelin and CST mRNAs are expressed in lung cancers, although some neuroendocrine tumors contain detectable amounts of the peptides; b) GHSR-1a mRNA is present exclusively in neuroendocrine tumors, whereas MRGX2 mRNA (but not peptide) is expressed in all histological types; c) both ghrelin forms inhibit H345 cell proliferation, both directly and enhancing apoptosis, despite the absence of GHS-R1a, whereas CST and its receptors do not interfere with cell growth.