Cortistatin-14 mediates its anticonvulsant effects via sst2 and sst3 but not ghrelin receptors

Unraveling the Effects of GSK-3β Isoform Modulation against Limbic Seizures and in the 6 Hz Electrical Kindling Model for Epileptogenesis

Two closely related glycogen synthase kinase-3 (GSK-3) isoforms have been identified in mammals: GSK-3α and GSK-3β. GSK-3β is the most prominent in the central nervous system and was previously shown to control neuronal excitability. We previously demonstrated that indirubin and its structural analogue and the nonselective GSK-3 inhibitor BIO-acetoxime exerted anticonvulsant effects in acute seizure models in zebrafish, mice, and rats. We here examined for the first time the anticonvulsant effect of TCS2002, a specific and potent inhibitor of GSK-3β, in two models for limbic seizures: the pilocarpine rat model for focal seizures and the acute 6 Hz corneal mouse model for refractory seizures. Next, we additionally used the 6 Hz kindling model to establish differences in seizure susceptibility and seizure progression in mice that either overexpress human GSK-3β (GSK-3β OE) or lack GSK-3β (GSK-3β^-/-) in neurons. We demonstrate that TCS2002 exerts anticonvulsant actions against pilocarpine- and 6 Hz-evoked seizures. Compared to wild-type littermates, GSK-3β OE mice are less susceptible to seizures but are more rapidly kindled. Interestingly, compared to GSK-3β^+/+ mice, neuronal GSK-3β^-/- mice show increased susceptibility to 6 Hz-induced seizures. These contrasting observations suggest compensatory neurodevelopmental mechanisms that alter seizure susceptibility in GSK-3β OE and GSK-3β^-/- mice. Although the pronounced anticonvulsant effects of selective and acute GSK-3β inhibition in the 6 Hz model identify GSK-3β as a potential drug target for pharmacoresistant seizures, our data on the sustained disruption of GSK-3β activity in the transgenic mice suggest a role for GSK-3 in kindling and warrants further research into the long-term effects of selective pharmacological GSK-3β inhibition.

Anti-inflammatory effect of cortistatin in rat endotoxin-induced uveitis model

Purpose

To evaluate the anti-inflammatory effect of cortistatin (CST) in endotoxin-induced uveitis (EIU) model and to compare the results with corticosteroid treatment.

Methods

A total of 35 healthy Wistar albino rats were randomly divided into five groups. EIU was induced by a single subcutaneous injection of lipopolysaccharide (LPS). Group I received intraperitoneal (ip) normal saline (NS), Group II received ip 150 μg LPS plus NS, Group III received ip 150 μg LPS plus 250 μg/kg CST, Group IV received ip 150 μg LPS plus 1mg/kg dexamethasone, and Group V received ip 250 μg/kg CST only. The aqueous humor was collected 24 h after injection and the infiltrating cells were determined. Moreover, histopathological and immunohistochemical examinations were also performed.

Results

The clinical score and infiltrated cell count were reduced in Groups III and IV compared with Group II (P < 0.001). The pathological findings of Groups III and IV were significantly reduced compared with Group II (P < 0.001). These findings were similar between Groups III and IV (P = 1.000). Tumor necrosis factor-alpha (TNF-α) and interleukin 1 beta (IL-1β) immunoreactivity in the ciliary body of Group III and Group IV were significantly reduced compared with Group II (P < 0.001). TNF-α and IL-1β immunoreactivity in the ciliary body of Group III and Group IV were similar compared with Group I and Group V (range of P values was 0.539-0.958).

Conclusion

CST administration as a therapeutic agent might ameliorate the severity of intraocular inflammation in uveitis patients. In conclusion, effect of CST and dexamethasone in EIU model was comparable.

Identification of GSK-3 as a Potential Therapeutic Entry Point for Epilepsy

In view of the clinical need for new antiseizure drugs (ASDs) with novel modes of action, we used a zebrafish seizure model to screen the anticonvulsant activity of medicinal plants used by traditional healers in the Congo for the treatment of epilepsy, and identified a crude plant extract that inhibited pentylenetetrazol (PTZ)-induced seizures in zebrafish larvae. Zebrafish bioassay-guided fractionation of this anticonvulsant Fabaceae species, Indigofera arrecta, identified indirubin, a compound with known inhibitory activity of glycogen synthase kinase (GSK)-3, as the bioactive component. Indirubin, as well as the more potent and selective GSK-3 inhibitor 6-bromoindirubin-3'-oxime (BIO-acetoxime) were tested in zebrafish and rodent seizure assays. Both compounds revealed anticonvulsant activity in PTZ-treated zebrafish larvae, with electroencephalographic recordings revealing reduction of epileptiform discharges. Both indirubin and BIO-acetoxime also showed anticonvulsant activity in the pilocarpine rat model for limbic seizures and in the 6-Hz refractory seizure mouse model. Most interestingly, BIO-acetoxime also exhibited anticonvulsant actions in 6-Hz fully kindled mice. Our findings thus provide the first evidence for anticonvulsant activity of GSK-3 inhibition, thereby implicating GSK-3 as a potential therapeutic entry point for epilepsy. Our results also support the use of zebrafish bioassay-guided fractionation of antiepileptic medicinal plant extracts as an effective strategy for the discovery of new ASDs with novel mechanisms of action.

Cortistatin binds to TNF-α receptors and protects against osteoarthritis

Background

Osteoarthritis (OA) is a common degenerative disease, and tumor necrosis factor (TNF-α) is known to play a critical role in OA. Cortistatin (CST) is a neuropeptide discovered over 20  years ago, which plays a vital role in inflammatory reactions. However, it is unknown whether CST is involved in cartilage degeneration and OA development.

Methods

The interaction between CST and TNF-α receptors was investigated through Coimmunoprecipitation and Biotin-based solid-phase binding assay. Western blot, Real-time PCR, ELISA, immunofluorescence staining, nitrite production assay and DMMB assay of GAG were performed for the primary chondrocyte experiments. Surgically induced and spontaneous OA models were established and western blot, flow cytometry, Real-time PCR, ELISA, immunohistochemistry and fluorescence in vivo imaging were performed for in vivo experiments.

Findings

CST competitively bound to TNFR1 as well as TNFR2. CST suppressed proinflammatory function of TNF-α. Both spontaneous and surgically induced OA models indicated that deficiency of CST led to an accelerated OA-like phenotype, while exogenous CST attenuated OA development in vivo. Additionally, TNFR1- and TNFR2-knockout mice were used for analysis and indicated that TNFRs might be involved in the protective role of CST in OA. CST inhibited activation of the NF-κB signaling pathway in OA.

Interpretation

This study provides new insight into the pathogenesis and therapeutic strategy of cartilage degenerative diseases, including OA.

Fund

The National Natural Science Foundation of China, the Natural Science Foundation of Shandong Province, Key Research and Development Projects of Shandong Province and the Cross-disciplinary Fund of Shandong University.

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.

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.

Cortistatin-expressing interneurons require TrkB signaling to suppress neural hyper-excitability

Signaling of brain-derived neurotrophic factor (BDNF) via tropomyosin receptor kinase B (TrkB) plays a critical role in the maturation of cortical inhibition and controls expression of inhibitory interneuron markers, including the neuropeptide cortistatin (CST). CST is expressed exclusively in a subset of cortical and hippocampal GABAergic interneurons, where it has anticonvulsant effects and controls sleep slow-wave activity (SWA). We hypothesized that CST-expressing interneurons play a critical role in regulating excitatory/inhibitory balance, and that BDNF, signaling through TrkB receptors on CST-expressing interneurons, is required for this function. Ablation of CST-expressing cells caused generalized seizures and premature death during early postnatal development, demonstrating a critical role for these cells in providing inhibition. Mice in which TrkB was selectively deleted from CST-expressing interneurons were hyperactive, slept less and developed spontaneous seizures. Frequencies of spontaneous excitatory post-synaptic currents (sEPSCs) on CST-expressing interneurons were attenuated in these mice. These data suggest that BDNF, signaling through TrkB receptors on CST-expressing cells, promotes excitatory drive onto these cells. Loss of excitatory drive onto CST-expressing cells that lack TrkB receptors may contribute to observed hyperexcitability and epileptogenesis.

Centrally Administered Cortistation-14 Induces Antidepressant-Like Effects in Mice via Mediating Ghrelin and GABAA Receptor Signaling Pathway

Cortistatin-14 (CST-14), a recently discovered cyclic neuropeptide, can bind to all five cloned somatostatin receptors (SSTRs) and ghrelin receptor to exert its biological activities and co-exists with GABA within the cortex and hippocampus. However, the role of CST-14 in the control of depression processes is not still clarified. Here, we tested the behavioral effects of CST-14 in the in a variety of classical rodent models of depression [forced swimming test (FST), tail suspension test (TST) and novelty-suppressed feeding test]. In the models of depression, CST-14 produced antidepressant-like effects, and does not altered locomotor activity levels. And, we found that CST-14 mRNA and BDNF mRNA were significantly decreased in the hippocampus and cortex after mice exposed to stress. Further data show that i.c.v. administration of CST-14 produce rapid antidepressant effects, and does not altered locomotor activity levels. Then these antidepressant-like effects were significantly reversed by [D-Lys₃]GHRP-6 (ghrelin receptor antagonist), but not c-SOM (SSTRs antagonist). Meanwhile, the effects of some neurotransmitter blockers indicates that only GABA_A system, but not CRF1 receptor, α/β-adrenergic receptor, is involved in the antidepressant effect of CST-14. The effects of the mTOR inhibitor (rapamycin), the PI3K inhibitor (LY294002) and the p-ERK1/2 inhibitor (U0126) suggesting that the ERK/mTOR or PI3K/Akt/mTOR signaling pathway is not involved in the antidepressant effects of CST-14. Interestingly, intranasal administration of CST-14 led to reducing depressive-like behavior, and near-infrared fluorescent experiments showed the real-time in vivo bio-distribution in brain after intranasal infusion of Cy7.5-CST-14. Taken all together, the results of present study point to a role for CST-14 in the modulation of depression processes via the ghrelin and GABA_A receptor, and suggest cortistation may represent a novel strategy for the treatment of depression disorders.

Highlights:-

CST-14 and BDNF mRNA are decreased in hippocampus and cortex once mice exposed to stress.

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i.c.v. or intranasal administration of CST-14 produce rapid antidepressant effects.

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NIR fluorescence imaging detected the brain uptake and distribution after intranasal CST-14.

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Antidepressant effects of CST-14 were only related to ghrelin and GABA_A system.

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Co-injection of CST-14 and NPS produce antidepressant effect, and do not impair memory.

The ventromedial hypothalamic nucleus plays an important role in anxiolytic-like effect of neuropeptide S

Neuropeptide S (NPS), the endogenous neuropeptide ligand of NPSR, has been reported to regulate anxiety-related behavior involved in multiple brain regions, including amygdale, locus coeruleus and Barrington's nucleus. However, little research has been conducted on the anxiolytic-like behaviors of NPS on the hypothalamus, which was an important area in defensive behavior. Here, we investigated a role of hypothalamus in anxiolytic-like behaviors of NPS. We found that NPSR protein of mouse distributed mainly in the ventromedial hypothalamus (VMH). And in the single prolonged stress model (SPS), the results showed that NPS mRNA of the mice exposed to SPS was significantly higher than control, while NPSR mRNA was remarkable lower than control in hypothalamus. Further studies found that NPS intra-VMH infusion dose-dependently (1, 10 and 100pmol) induced anxiolytic effects, using elevated plus maze and open field tests. These anxiolytic effects could be blocked by NPSR antagonist (SHA68), but not by picrotoxin (a GABA_A receptor antagonist) and sacolfen (a GABA_B receptor antagonist). Meanwhile, our data showed that the expression of c-Fos was significantly increased in VMH after NPS delivered into the lateral ventricles. These results cast a new light on the hypothalamic nucleus in the anxiolytic-like effect of NPS system.

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.