Cortistatin as a Novel Multimodal Therapy for the Treatment of Parkinson's Disease

Parkinson's disease (PD) is a complex disorder characterized by the impairment of the dopaminergic nigrostriatal system. PD has duplicated its global burden in the last few years, becoming the leading neurological disability worldwide. Therefore, there is an urgent need to develop innovative approaches that target multifactorial underlying causes to potentially prevent or limit disease progression. Accumulating evidence suggests that neuroinflammatory responses may play a pivotal role in the neurodegenerative processes that occur during the development of PD. Cortistatin is a neuropeptide that has shown potent anti-inflammatory and immunoregulatory effects in preclinical models of autoimmune and neuroinflammatory disorders. The goal of this study was to explore the therapeutic potential of cortistatin in a well-established preclinical mouse model of PD induced by acute exposure to the neurotoxin 1-methil-4-phenyl1-1,2,3,6-tetrahydropyridine (MPTP). We observed that treatment with cortistatin mitigated the MPTP-induced loss of dopaminergic neurons in the substantia nigra and their connections to the striatum. Consequently, cortistatin administration improved the locomotor activity of animals intoxicated with MPTP. In addition, cortistatin diminished the presence and activation of glial cells in the affected brain regions of MPTP-treated mice, reduced the production of immune mediators, and promoted the expression of neurotrophic factors in the striatum. In an in vitro model of PD, treatment with cortistatin also demonstrated a reduction in the cell death of dopaminergic neurons that were exposed to the neurotoxin. Taken together, these findings suggest that cortistatin could emerge as a promising new therapeutic agent that combines anti-inflammatory and neuroprotective properties to regulate the progression of PD at multiple levels.

Serum Cortistatin Level in Type 2 Diabetes Mellitus and Its Relationship with Nonalcoholic Fatty Liver Disease

Purpose

To evaluate serum cortistatin (CST) levels in type 2 diabetes mellitus (T2DM) patients with or without non-alcoholic fatty liver disease (NAFLD) and to examine the relationship between CST and NAFLD.

Methods

A total of 90 T2DM patients, which included 56 NAFLD patients (referred to as DM+NAFLD group) and 34 patients without NAFLD (DM-only group), and 83 non-diabetes individuals that included 39 NAFLD patients (NAFLD-only group) and 44 without NAFLD that acted as the normal-control group (NC group). The differences in the serum CST levels between the groups were compared, and the correlations between CST and other variables were calculated by applying both correlational analysis and multiple linear regression analysis.

Results

The mean serum CST levels were significantly lower in the DM+NAFLD and DM groups than in the NC group (P < 0.05). In addition, the CST levels were lower in the DM group relative to that in the NAFLD group (P < 0.05). However, no statistical difference was noted in the serum CST between diabetic patients with and without NAFLD (P > 0.05). Similarly, in the non-diabetic group, the serum CST level was not significantly different between individuals with and without NAFLD (P > 0.05). Furthermore, the serum CST levels were negatively associated with the levels of total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), fasting plasma glucose (FPG), homeostasis model assessment-insulin resistance (HOMA-IR), and insulin cell function index (HOMA-β). Conversely, the serum CST levels were positively associated with high-density lipoprotein cholesterol (HDL-C). The data obtained through multiple linear regression implied that LDL-C and HOMA-β, but not HOMA-IR, were closely related to serum CST levels.

Conclusion

T2DM was related to decreased serum CST. However, serum CST was correlated with HOMA-β in T2DM patients, while HOMA-IR was not. There was no correlation between CST and NAFLD.

The Effect of Resveratrol in Sirt1/CST Pathway to Inhibit TNF-α Induced Inflammatory Response in Rat Primary Fibroblast-Like Synoviocytes

Rheumatoid arthritis has a significant impact on the life quality, but current pharmacological therapies have limitations. As a result, there is growing interest in exploring the potential of natural plant components to intervene in the development of rheumatoid arthritis. Resveratrol, a natural polyphenol and one of the main active components of the Chinese herbal medicine Polygonum cuspidatum, has emerged as a promising candidate for this purpose. In the present study, we investigated the role and mechanism of resveratrol in inhibiting inflammatory response in rat primary fibroblast-like synoviocytes. Tumor necrosis factor (TNF)-α was used to establish a model of inflammation, the Sirtuin1 selective inhibitor Selisistat (EX527) was used to inhibit Sirtuin1 activity, and small interfering RNA was used to silence cortistatin expression. The results showed that pre-treatment with resveratrol could time- and dose-dependently inhibit TNF-α induced cellular interleukin (IL)-1β and IL-6 secretion, and upregulate Sirtuin1 and cortistatin mRNA and protein expression in the range of 48 h, 100 µM. Selisistat (EX527) could attenuate resveratrol inhibited inflammatory response and upregulated cortistatin expression. Silencing cortistatin expression attenuated the effect of resveratrol on inhibiting inflammatory response, but did not affect its effect on upregulating Sirtuin1 expression. In conclusion, resveratrol effectively inhibited the TNF-α induced inflammatory response in fibroblast-like synoviocytes by a mechanism involving the Sirtuin1/cortistatin pathway.

Therapeutic Effect of a Latent Form of Cortistatin in Experimental Inflammatory and Fibrotic Disorders

Cortistatin is a cyclic neuropeptide that recently emerged as an attractive therapeutic factor for treating inflammatory, autoimmune, fibrotic, and pain disorders. Despite of its efficiency and apparent safety in experimental preclinical models, its short half-life in body fluids and its potential pleiotropic effects, due to its promiscuity for several receptors expressed in various cells and tissues, represent two major drawbacks for the clinical translation of cortistatin-based therapies. Therefore, the design of new strategies focused on increasing the stability, bioavailability, and target specificity of cortistatin are lately demanded by the industry. Here, we generated by molecular engineering a new cortistatin-based prodrug formulation that includes, beside the bioactive cortistatin, a molecular-shield provided by the latency-associated protein of the transforming growth factor-β1 and a cleavage site specifically recognized by metalloproteinases, which are abundant in inflammatory/fibrotic foci. Using different models of sepsis, inflammatory bowel disease, scleroderma, and pulmonary fibrosis, we demonstrated that this latent form of cortistatin was a highly effective protection against these severe disorders. Noteworthy, from a therapeutic point of view, is that latent cortistatin seems to require significantly lower doses and fewer administrations than naive cortistatin to reach the same efficacy. Finally, the metalloproteinase-cleavage site was essential for the latent molecule to exert its therapeutic action. In summary, latent cortistatin emerges as a promising innovative therapeutic tool for treating chronic diseases of different etiologies with difficult clinical solutions and as a starting point for a rational development of prodrugs based on the use of bioactive peptides.

Evaluation of a Novel DNA Vaccine Double Encoding Somatostatin and Cortistatin for Promoting the Growth of Mice

Animal growth traits are directly linked with the economics of livestock species. A somatostatin DNA vaccine has been developed to improve the growth of animals. However, the growth-promoting effect is still unsatisfying. The current study aimed to evaluate the effect of a novel eukaryotic dual expression vaccine known as pIRES-S/CST14-S/2SS, which encodes the genes obtained by fusing somatostatin (SS) and cortistatin (CST) into hepatitis B surface antigen (HBsAg). After transfection into GH3 cells with pIRES-S/CST14-S/2SS, green fluorescence signals were observed by fluorescence microscopy, suggesting the effective expression of CST and SS in GH3 cells using the IRES elements. Subsequently, both GH and PRL levels were found to be significantly lower in pIRES-S/CST14-S/2SS-treated cells as compared to the control group (p < 0.05). Furthermore, the antibody level, hormone secretion, and weight gain in the mice injected with novel recombinant plasmids were also evaluated. The anti-SS antibodies were detectable in all vaccine treated groups, resulting in significantly higher levels of GH secretion (p < 0.05). It is worth mentioning that pIRES-S/CST14-S/2SS (10 μg/100 μL) vaccinated mice exhibited a higher body weight gain in the second immunization period. This study increases the understanding of the relationship between somatostatin and cortistatin, and may help to develop an effective growth-promoting DNA vaccine in animals.

Cortistatin attenuates titanium particle-induced osteolysis through regulation of TNFR1-ROS-caspase-3 signaling in osteoblasts

Aseptic loosening is a major complication of prosthetic joint surgery and is associated with impaired osteoblast homeostasis. Cortistatin (CST) is a neuropeptide that protects against inflammatory conditions. In this study, we found that expression of CST was diminished in patients with prosthetic joint loosening and in titanium (Ti) particle-induced animal models. A Ti particle-induced calvarial osteolysis model was established in wild-type and CST gene knockout mice; CST deficiency enhanced, while exogenously added CST attenuated, the severity of Ti particle-mediated osteolysis. CST protected against inflammation as well as apoptosis and maintained the osteogenic function of MC3T3-E1 osteoblasts upon stimulation with Ti particles. Furthermore, CST antagonized reactive oxygen species production and suppressed caspase-3-associated apoptosis mediated by Ti particles in osteoblasts. Additionally, CST protects against Ti particle-induced osteolysis through tumor necrosis factor receptor 1. Taken together, CST might provide a therapeutic strategy for wear debris-induced inflammatory osteolysis.

Cortistatin protects against intervertebral disc degeneration through targeting mitochondrial ROS-dependent NLRP3 inflammasome activation

Background: Intervertebral disc (IVD) degeneration is a common degenerative disease that can lead to collapse or herniation of the nucleus pulposus (NP) and result in radiculopathy in patients.

Methods: NP tissue and cells were isolated from patients and mice, and the expression profile of cortistatin (CST) was analysed. In addition, ageing of the NP was compared between 6-month-old WT and CST-knockout (CST^-/-) mice. Furthermore, NP tissues and cells were cultured to validate the role of CST in TNF-α-induced IVD degeneration. Moreover, in vitro and in vivo experiments were performed to identify the potential role of CST in mitochondrial dysfunction, mitochondrial ROS generation and activation of the NLRP3 inflammasome during IVD degeneration. In addition, NF-κB signalling pathway activity was tested in NP tissues and cells from CST^-/- mice.

Results: The expression of CST in NP cells was diminished in the ageing- and TNF-α-induced IVD degeneration process. In addition, compared with WT mice, aged CST^-/- mice displayed accelerated metabolic imbalance and enhanced apoptosis, and these mice showed a disorganized NP tissue structure. Moreover, TNF-α-mediated catabolism and apoptosis were alleviated by exogenous CST treatment. Furthermore, CST inhibited mitochondrial dysfunction in NP cells through IVD degeneration and suppressed activation of the NLRP3 inflammasome. In vitro and ex vivo experiments indicated that increased NF-κB pathway activity might have been associated with the IVD degeneration observed in CST^-/- mice.

Conclusion: This study suggests the role of CST in mitochondrial ROS and activation of the NLRP3 inflammasome in IVD degeneration, which might shed light on therapeutic targets for IVD degeneration.

Serum Cortistatin Levels in Patients with Ocular Active and Ocular Inactive Behçet Disease

PURPOSE

To evaluate serum cortistatin (CST) levels in patients with ocular active and ocular inactive Behçet disease (BD) and its relationship with disease activity.

METHODS

24 BD patients with ocular active, 24 BD patients with ocular inactive patients and 24 healthy control subjects were included in the study.

RESULTS

In ocular active and ocular inactive BD patients and healthy control subjects, the mean serum CST levels were 4.38 ± 1.63ng/ml, 5.46 ± 1.81ng/ml and 7.56 ± 1.73ng/ml, respectively. ESR, serum CRP, CST levels and NLR were significantly different between the groups (p < 0.001 for all). The CST levels were similar between ocular active and inactive BD patient groups (p = 0.197). ESR, CRP and NLR were significantly higher in ocular active BD patients compared to ocular inactive BD patients and healthy control subjects (p < 0.05 for all).

CONCLUSION

Serum CST level was significantly lower in BD patients. CST may be a neuropeptide that plays a role in the pathogenesis of BD.

TrkB Signaling Influences Gene Expression in Cortistatin-Expressing Interneurons

Brain-derived neurotrophic factor (BDNF) signals through its cognate receptor tropomyosin receptor kinase B (TrkB) to promote the function of several classes of inhibitory interneurons. We previously reported that loss of BDNF-TrkB signaling in cortistatin (Cort)-expressing interneurons leads to behavioral hyperactivity and spontaneous seizures in mice. We performed bulk RNA sequencing (RNA-seq) from the cortex of mice with disruption of BDNF-TrkB signaling in cortistatin interneurons, and identified differential expression of genes important for excitatory neuron function. Using translating ribosome affinity purification and RNA-seq, we define a molecular profile for Cort-expressing inhibitory neurons and subsequently compare the translatome of normal and TrkB-depleted Cort neurons, revealing alterations in calcium signaling and axon development. Several of the genes enriched in Cort neurons and differentially expressed in TrkB-depleted neurons are also implicated in autism and epilepsy. Our findings highlight TrkB-dependent molecular pathways as critical for the maturation of inhibitory interneurons and support the hypothesis that loss of BDNF signaling in Cort interneurons leads to altered excitatory/inhibitory balance.

Evaluation of aqueous humor and serum cortistatin levels in diabetic patients with and without diabetic retinopathy

PURPOSE

To evaluate the aqueous humor and serum cortistatin levels in diabetic patients with and without diabetic retinopathy and its relationship with various metabolic markers that have been reported to be associated with diabetes mellitus.

METHODS

The current study included 20 diabetes mellitus patients with diabetic retinopathy, 20 diabetes mellitus patients without diabetic retinopathy, and 20 healthy control subjects with the same sex and age characteristics. Aqueous humor and serum cortistatin, fasting blood glucose, hemoglobinA1c, 25-hydroxyvitamin D levels, blood lipid profiles, and body mass index were measured in all subjects.

RESULTS

In diabetic patients with and without diabetic retinopathy and in healthy control subjects, the mean aqueous humor cortistatin levels were 25.55 ± 2.03, 27.71 ± 2.01, and 32.76 ± 3.43 ng/mL, respectively. Likewise, the mean serum cortistatin levels were 6.16 ± 1.08, 6.57 ± 1.00, and 7.56 ± 1.51 ng/mL, respectively. Aqueous humor cortistatin levels were decreased in diabetic patients with and without diabetic retinopathy when compared to healthy controls (p < 0.001). Although aqueous humor cortistatin levels tended to be reduced in diabetic patients with diabetic retinopathy, the difference was not statistically significant between diabetic patients with and without diabetic retinopathy (p = 0.147). Serum cortistatin levels were not statistically significant between diabetic patients with and without diabetic retinopathy and healthy control subjects (p = 0.166). Body mass index, fasting blood glucose, and hemoglobinA1c levels were significantly different between the groups (p < 0.05 for all parameters tested).

CONCLUSION

Aqueous humor cortistatin levels were decreased in diabetic patients with and without diabetic retinopathy. The results suggest that a local decrease in the amount of cortistatin may play a role in the pathogenesis of diabetic retinopathy.

Cortistatin inhibits arterial calcification in rats via GSK3β/β-catenin and protein kinase C signalling but not c-Jun N-terminal kinase signalling

AIM

Cortistatin (CST) is a newly discovered endogenous active peptide that exerts protective effects on the cardiovascular system. However, the relationship between CST and aortic calcification and the underlying mechanism remain obscure. Therefore, we investigated effects of CST on aortic calcification and its signalling pathways.

METHODS

Calcium content and alkaline phosphatase (ALP) activity were measured using the o-cresolphthalein colorimetric method and ALP assay kit respectively. Protein expression of smooth muscle (SM)-ɑ-actin, osteocalcin (OCN), β-catenin, glycogen synthase kinase 3β (GSK3β), p-GSK3β, protein kinase C (PKC), p-PKC, c-Jun N-terminal kinase (JNK) and p-JNK was determined using Western blotting.

RESULTS

In aorta from a rat vitamin D3 calcification model, CST abrogated calcium deposition and pathological damage, decreased the protein expression of OCN and β-catenin and increased SM-ɑ-actin expression. In a rat cultured vascular smooth muscular cell (VSMC) calcification model induced by β-glycerophosphate (β-GP), CST inhibited the increase in ALP activity, calcium content and OCN protein and the decrease in SM-α-actin expression. CST also inhibited the β-GP-induced increase in p-GSK3β and β-catenin protein (both P < .05). The inhibitory effects of CST on ALP activity, calcium deposition and β-catenin protein were abolished by pretreatment with lithium chloride, a GSK3β inhibitor. CST promoted the protein expression of p-PKC by 68.5% (P < .01), but not p-JNK. The ability of CST to attenuate β-GP-induced increase in ALP activity, calcium content and OCN expression in the VSMC model was abolished by pretreatment with the PKC inhibitor Go6976.

CONCLUSION

These results indicate that CST inhibits aortic calcification and osteogenic differentiation of VSMCs likely via the GSK3β/β-catenin and PKC signalling pathways, but not JNK signalling pathway.

Ultraviolet A radiation induces cortistatin overexpression and activation of somatostatin receptors in ARPE‑19 cells

Long-term exposure to ultraviolet (UV) radiation is associated with pathological alterations of the retinal pigment epithelium (RPE). It has been indicated that Cortistatin (CST) and somatostatin (SST) are able to inhibit the neurodegeneration of the RPE associated with diabetic retinopathy and retinal ischemia via activation of SST receptors (SSTRs). To the best of our knowledge, the present study indicated for the first time that treatment with UV‑A (30 and 60 min) causes an increase of CST expression, rather than SST, which was linked with the upregulation of STTR3,4,5 subtype receptor gene expression levels. The study revealed that: i) SST and CST mRNA expression were both detected under basal conditions in a human retinal pigment epithelial cell line (Arpe‑19); ii) SST expression remained constant from baseline to 1 h of UV‑A treatment; iii) CST mRNA expression levels were 80 times increased compared with time 0 and after 30 min of exposition to ultraviolet irradiation; iv) SSTR1, SSTR2 mRNA and low levels of SSTR4 were expressed in basal conditions, whereas SSTR3 and SSTR5 mRNA were not detected under the same conditions; and v) only SSTR3, SSTR4 and SSTR5 were overexpressed after UV‑A treatment, although in a different way. In conclusion, the findings provide reasonable evidence to support the pathophysiological role of the CST/SST/SSTRs system in the adaptive response of the RPE exposed to UV‑A radiation.

Berberine ameliorates collagen-induced arthritis in rats by suppressing Th17 cell responses via inducing cortistatin in the gut

Berberine, an isoquinoline alkaloid, has been reported to ameliorate various autoimmune diseases including rheumatoid arthritis by oral administration. However, its mechanism remains mysterious due to an extremely low bioavailability. The fact that berberine readily accumulates in the gut, the largest endocrine organ in the body, attracted us to explore its anti-arthritic mechanism in view of the induction of intestinal immunosuppressive neuropeptides. In this study, berberine (200 mg·kg^-1 , i.g.) was shown to ameliorate collagen-induced arthritis in rats, which was manifested by the reduction of clinical signs and joint destruction, as well as marked down-regulation of Th17 cell frequency and interleukin-17 level in blood. In contrast, an intravenous injection of berberine failed to affect arthritis in rats, implying that its anti-arthritic effect was gut-dependent. Further studies revealed that oral berberine selectively elevated the levels of cortistatin, of five gut-derived neuropeptides tested, in the intestines and sera of arthrititic rats. Antagonists of ghrelin/growth hormone secretagogue receptor 1 (a subtype of cortistatin receptor) almost completely abolished the ameliorative effect of berberine on arthritis and Th17 cell responses in rats. In vitro, berberine showed a moderate ability to promote the expression of cortistatin in nerve cells, which was strengthened when the nerve cells were cocultured with enteroendocrine cells to induce an autocrine/paracrine environment. In summary, oral berberine exerted anti-arthritic effect through inhibiting the Th17 cell response, which was closely associated with the induction of cortistatin generation from gut through augmenting autocrine/paracrine action between enteric nerve cells and endocrine cells.

Neuropeptide receptors as potential drug targets in the treatment of inflammatory conditions

Cross-talk between the nervous, endocrine and immune systems exists via regulator molecules, such as neuropeptides, hormones and cytokines. A number of neuropeptides have been implicated in the genesis of inflammation, such as tachykinins and calcitonin gene-related peptide. Development of their receptor antagonists could be a promising approach to anti-inflammatory pharmacotherapy. Anti-inflammatory neuropeptides, such as vasoactive intestinal peptide, pituitary adenylate cyclase-activating polypeptide, α-melanocyte-stimulating hormone, urocortin, adrenomedullin, somatostatin, cortistatin, ghrelin, galanin and opioid peptides, are also released and act on their own receptors on the neurons as well as on different inflammatory and immune cells. The aim of the present review is to summarize the most prominent data of preclinical animal studies concerning the main pharmacological effects of ligands acting on the neuropeptide receptors. Promising therapeutic impacts of these compounds as potential candidates for the development of novel types of anti-inflammatory drugs are also discussed.

Brain somatostatin receptor 2 mediates the dipsogenic effect of central somatostatin and cortistatin in rats: role in drinking behavior

Intracerebroventricular injection of stable somatostatin (SST) agonists stimulates food and water intake in rats. We investigated the receptor subtype(s) involved in the dipsogenic effect of intracerebroventricular injection of SST agonists, mechanisms of action, and role. In nonfasted and non-water-deprived male rats with chronic intracerebroventricular cannula, intake of water without food or food without water was monitored separately to avoid any interactions compared with intracerebroventricular vehicle. SST-14 and cortistatin (CST-14) (1 μg/rat icv) increased water intake by 3.1- and 2.7-fold, respectively, while both peptides did not alter food intake at 1 h postinjection in the light phase. By contrast, the stable pan-somatostatin agonist ODT8-SST (1 μg/rat icv) increased both water and food intake by 4.9- and 3.7-fold, respectively. S-346-011, a selective receptor 2 (sst2) agonist (1 μg/rat icv) induced water ingestion, while sst1 or sst4 agonist, injected under the same conditions, did not. The sst2 antagonist S-406-028 (1 μg/rat icv) prevented the 1-h water intake induced by intracerebroventricular ODT8-SST and CST-14. Losartan (100 μg/rat icv), an angiotensin receptor 1 (AT1) antagonist, completely blocked the water consumption induced by intracerebroventricular ODT8-SST, whereas intracerebroventricular injection of S-406-028 did not modify the intracerebroventricular ANG II-induced dipsogenic response. The sst2 antagonist reduced by 40% the increase of the 3-h water intake in the early dark phase. These data indicate that SST-14 and CST-14 interact with sst2 to exert a potent dipsogenic effect, which is mediated downstream by angiotensin-AT1 signaling. These data also indicate that sst2 activation by brain SST-14 and/or CST-14 may play an important role in the regulation of drinking behavior.

Cortistatin inhibits migration and proliferation of human vascular smooth muscle cells and decreases neointimal formation on carotid artery ligation

RATIONALE

Proliferation and migration of smooth muscle cells (SMCs) are key steps for the progression of atherosclerosis and restenosis. Cortistatin is a multifunctional neuropeptide belonging to the somatostatin family that exerts unique functions in the nervous and immune systems. Cortistatin is elevated in plasma of patients experiencing coronary heart disease and attenuates vascular calcification.

OBJECTIVE

To investigate the occurrence of vascular cortistatin and its effects on the proliferation and migration of SMCs in vitro and in vivo and to delimitate the receptors and signal transduction pathways governing its actions.

METHODS AND RESULTS

SMCs from mouse carotid and human aortic arteries and from human atherosclerotic plaques highly expressed cortistatin. Cortistatin expression positively correlated with the progression of arterial intima hyperplasia. Cortistatin inhibited platelet-derived growth factor-stimulated proliferation of human aortic SMCs via binding to somatostatin receptors (sst2 and sst5) and ghrelin receptor, induction of cAMP and p38-mitogen-activated protein kinase, and inhibition of Akt activity. Moreover, cortistatin impaired lamellipodia formation and migration of human aortic SMCs toward platelet-derived growth factor by inhibiting, in a ghrelin-receptor-dependent manner, Rac1 activation and cytosolic calcium increases. These effects on SMC proliferation and migration correlated with an inhibitory action of cortistatin on the neointimal formation in 2 models of carotid arterial ligation. Endogenous cortistatin seems to play a critical role in regulating SMC function because cortistatin-deficient mice developed higher neointimal hyperplasic lesions than wild-type mice.

CONCLUSIONS

Cortistatin emerges as a natural endogenous regulator of SMCs under pathological conditions and an attractive candidate for the pharmacological management of vascular diseases that course with neointimal lesion formation.

Activation of somatostatin 2 receptors in the brain and the periphery induces opposite changes in circulating ghrelin levels: functional implications

Somatostatin is an important modulator of neurotransmission in the central nervous system and acts as a potent inhibitor of hormone and exocrine secretion and regulator of cell proliferation in the periphery. These pleiotropic actions occur through interaction with five G protein-coupled somatostatin receptor subtypes (sst(1) (-) (5)) that are widely expressed in the brain and peripheral organs. The characterization of somatostatin's effects can be investigated by pharmacological or genetic approaches using newly developed selective sst agonists and antagonists and mice lacking specific sst subtypes. Recent evidence points toward a divergent action of somatostatin in the brain and in the periphery to regulate circulating levels of ghrelin, an orexigenic hormone produced by the endocrine X/A-like cells in the rat gastric mucosa. Somatostatin interacts with the sst(2) in the brain to induce an increase in basal ghrelin plasma levels and counteracts the visceral stress-related decrease in circulating ghrelin. By contrast, stimulation of peripheral somatostatin-sst(2) signaling results in the inhibition of basal ghrelin release and mediates the postoperative decrease in circulating ghrelin. The peripheral sst(2)-mediated reduction of plasma ghrelin is likely to involve a paracrine action of D cell-derived somatostatin acting on sst(2) bearing X/A-like ghrelin cells in the gastric mucosa. The other member of the somatostatin family, named cortistatin, in addition to binding to sst(1) (-) (5) also directly interacts with the ghrelin receptor and therefore may simultaneously modulate ghrelin release and actions at target sites bearing ghrelin receptors representing a link between the ghrelin and somatostatin systems.

Somatostatinergic systems: an update on brain functions in normal and pathological aging

Somatostatin is highly expressed in mammalian brain and is involved in many brain functions such as motor activity, sleep, sensory, and cognitive processes. Five somatostatin receptors have been described: sst(1), sst(2) (A and B), sst(3), sst(4), and sst(5), all belonging to the G-protein-coupled receptor family. During the recent years, numerous studies contributed to clarify the role of somatostatin systems, especially long-range somatostatinergic interneurons, in several functions they have been previously involved in. New advances have also been made on the alterations of somatostatinergic systems in several brain diseases and on the potential therapeutic target they represent in these pathologies.

Somatostatin: an endogenous antiepileptic

The neuropeptide somatostatin (SST) is highly expressed in brain regions associated with seizures. In hippocampus, SST expression and release is regulated by seizures, and SST-containing neurons within the hilus of the dentate gyrus are sensitive to seizure-induced death. In vivo and in vitro studies suggest that the loss of SST function in the dentate could contribute to epileptogenesis and seizure susceptibility. SST also has inhibitory actions in the CA1 and CA3 hippocampus indicating this peptide is an important homeostatic regulator throughout the hippocampus. In vivo studies show SST has robust antiepileptic properties with the major site of action being hippocampus. In rodents, somatostatin receptor subtype 2 (SST(2)) and SST(4) appear to mediate the majority of the antiepileptic actions of SST, with SST(2) predominate in rat and SST(4) in mouse. Thus SST receptors may be appropriate targets for new antiepileptic drugs (AEDs), although validation in human tissue is lacking.

Cortistatin increase of a potassium conductance in rat locus coeruleus in vitro

1. In this study we examined the effects of cortistatin, a putative endogenous ligand for somatostatin (SRIF) receptors, on the membrane properties of rat locus coeruleus (LC) neurones in vitro, by use of intracellular and whole cell patch clamp recording. We have compared the actions of cortistatin with those of SRIF and the SRIF analogue D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2 (CTOP). 2. When LC neurones were voltage clamped to -60 mV, application of cortistatin caused an outward current in all cells examined (n = 44), with a pEC50 of 6.62. SRIF also caused an outward current in all cells examined (n = 43), with a pEC50 of 6.93. 3. The outward currents caused by cortistatin in 2.5 mM extracellular K+ reversed polarity at -106 mV, very close to the predicted K+ reversal potential of -105 mV. Increasing extracellular K+ to 10.5 mM resulted in a shift of the reversal potential of +38 mV, a shift consistent with a K+ conductance. The conductance activated by cortistatin showed mild inward rectification. 4. Continuous application of a high concentration of SRIF (1 microM) resulted in a decrease of the outward current to a steady level of 49% of the maximum response, with a t1/2 of 131 s. Application of a high concentration of cortistatin (3 microM) during the desensitized portion of the SRIF response did not result in any further outward current. Continuous application of a high concentration of cortistatin (10 microM) resulted in a decrease of the outward current to a steady level of 42% of the maximum response with a t1/2 of 114 s. Application of a high concentration of SRIF (3 microM) during the desensitized portion of the cortistatin response produced only a small outward current. 5. Continuous application of cortistatin (3 microM) also resulted in a decrease of the outward current (by 43%, t1/2 of 136 s) and application of a high concentration of CTOP (10 microM) during the desensitized portion of the cortistatin response did not produce any outward current. Continuous application of a high concentration of CTOP (10 microM) resulted in a decrease of the outward current to a steady level of 70% of the maximum response with a t1/2 of 143 s. Application of a high concentration of cortistatin (3 microM) during the desensitized portion of the CTOP response did not result in any further outward current. 6. The actions of cortistatin (300 nM-10 microM) were not affected by the opioid antagonist naloxone (10 microM). Application of met-enkephalin during the desensitized portion of the response to a high concentration of cortistatin (3 microM) produced an outward current similar to that produced by metenkephalin application alone. 7. Thus cortistatin efficaciously activates an inwardly rectifying K+ conductance in LC neurones. These actions appear to be mediated by a population of SRIF receptors, at which CTOP is also an agonist. Cortistatin does not appear to be a ligand for mu-opioid receptors in rat LC neurons.

Cortistatin is expressed in a distinct subset of cortical interneurons

Cortistatin is a presumptive neuropeptide that shares 11 of its 14 amino acids with somatostatin. In contrast to somatostatin, administration of cortistatin into the rat brain ventricles specifically enhances slow wave sleep, apparently by antagonizing the effects of acetylcholine on cortical excitability. Here we show that preprocortistatin mRNA is expressed in a subset of GABAergic cells in the cortex and hippocampus that partially overlap with those containing somatostatin. A significant percentage of cortistatin-positive neurons is also positive for parvalbumin. In contrast, no colocalization was found between cortistatin and calretinin, cholecystokinin, or vasoactive intestinal peptide. During development there is a transient increase in cortistatin-expressing cells in the second postnatal week in all cortical areas and in the dentate gyrus. A transient expression of preprocortistatin mRNA in the hilar region at P16 is paralleled by electrophysiological changes in dentate granule cells. Together, these observations suggest mechanisms by which cortistatin may regulate cortical activity.