The sigma-1 receptor enhances brain plasticity and functional recovery after experimental stroke

Activation of Sigma-1 Receptor by Cutamesine Attenuates Neuronal Apoptosis by Inhibiting Endoplasmic Reticulum Stress and Mitochondrial Dysfunction in a Rat Model of Asphyxia Cardiac Arrest

BACKGROUND

Global cerebral ischemic/reperfusion (I/R) injury after cardiac arrest (CA) is a major cause of mortality and morbidity in survivors of resuscitation. We utilized a rat model of asphyxia CA to explore the functional effects and mechanisms of Sigma-1 receptor (Sig-1R) activation in cerebral protection using the Sig-1R agonist cutamesine (SA-4503).

METHODS

After resuscitation, the surviving rats were randomly divided into three groups (n = 18 each): the cardiopulmonary resuscitation (CPR) group (0.9% saline at 1 mL/kg); the SA4503 low-dose group (1 mg/kg SA4503); and the SA4503 high-dose group (2.5 mg/kg SA4503). The neurological deficit scores were recorded, and the cerebral cortex was harvested for western blotting. Mitochondrial transmembrane potential, adenosine triphosphate (ATP) concentrations, calcium homeostasis, and mitochondrial ultrastructure were also studied.

RESULTS

The SA4503 treatment groups exhibited improved neurological outcomes compared with the CPR group. The protein levels of caspase-3 and the endoplasmic reticulum stress markers C/EBP homologous protein and caspase-12 were lower in the SA4503 treatment groups compared with the CPR group. SA4503 treatment also normalized mitochondrial membrane potential, tissue ATP concentrations, intracellular Ca overload, and upregulated Sig-1R protein level compared with the CPR group. The SA4503 high dose treatment showed significant cerebral protective effects compared with the SA4503 low dose treatment. The therapeutic effect of SA4503 was dose-dependent.

CONCLUSIONS

CA downregulated Sig-1R protein expression. Activating Sig-1R using SA4503 protected against global cerebral I/R injury in a rat model of asphyxia CA by alleviating endoplasmic reticulum stress and mitochondrial dysfunction and eventually inhibiting neuronal apoptosis.

Electroacupuncture Improves Neurobehavioral Function Through Targeting of SOX2-Mediated Axonal Regeneration by MicroRNA-132 After Ischemic Stroke

Our previous studies have shown that electroacupuncture (EA) enhances neurobehavioral functional recovery after ischemic stroke, however, the underlying regulatory mechanisms remain unclear. MicroRNAs (miRNAs) are abundant in the brain and are involved in post-transcriptional gene regulation. During cerebral ischemia reperfusion, miRNAs perform numerous biological functions in the central nervous system related to regeneration and repair of damaged nerves. Our previous studies also have shown that the expression of miRNA-132 (miR-132) is obviously down-regulated after stroke by middle cerebral artery occlusion (MCAO), which can be up-regulated by EA. This study aimed to identify whether up-regulation of miR-132 by EA improved the damaged nerves after stroke and to screen the potential target of miR-132. The results showed that EA up-regulated miR-132 thus suppressing SOX2 expression in vivo after MCAO, which obviously ameliorated neurobehavioral functional recovery. Moreover, our results also suggested that up-regulated miR-132 suppressed SOX2 in primary neurons after oxygen-glucose deprivation (OGD), which promoted neurite outgrowth. In conclusion, EA enhances neurobehavioral functional recovery against ischemic stroke through targeting of SOX2-mediated axonal regeneration by miR-132.

Dark Classics in Chemical Neuroscience: N, N-Dimethyltryptamine (DMT)

Though relatively obscure, N, N-dimethyltryptamine (DMT) is an important molecule in psychopharmacology as it is the archetype for all indole-containing serotonergic psychedelics. Its structure can be found embedded within those of better-known molecules such as lysergic acid diethylamide (LSD) and psilocybin. Unlike the latter two compounds, DMT is ubiquitous, being produced by a wide variety of plant and animal species. It is one of the principal psychoactive components of ayahuasca, a tisane made from various plant sources that has been used for centuries. Furthermore, DMT is one of the few psychedelic compounds produced endogenously by mammals, and its biological function in human physiology remains a mystery. In this review, we cover the synthesis of DMT as well as its pharmacology, metabolism, adverse effects, and potential use in medicine. Finally, we discuss the history of DMT in chemical neuroscience and why this underappreciated molecule is so important to the field of psychedelic science.

Sigma-1 receptor activation alleviates blood-brain barrier dysfunction in vascular dementia mice

Sigma-1 receptor (Sig-1R) activation has been shown to decrease infarct volume and enhance neuronal survival after brain ischemia-reperfusion (IR) in rodent models. The present study aims to investigate first the effect of Sig-1R activation on blood-brain barrier (BBB) disruption during experimental stroke. Male C57BL/6 mice were subjected to bilateral common carotid artery occlusion (BCCAO) for 15 min, and the worst BBB leakage was observed on the 7th day after brain IR. To confirm the BBB protective role of Sig-1R, mice were divided into five groups (sham group, BCCAO group, PRE084 group, BD1047 group, PRE084 and BD1047 group; 29-35 mice for each group), and treated with agonist PRE084 (1 mg/kg) and/or antagonist BD1047 (1 mg/kg) for 7 days intraperitoneally once a day after BCCAO. Interestingly, PRE084 administration significantly improved neurobehavioral performance as well as healing of neuron damage and white matter lesions. PRE084 also reduced the leakage of Evans blue and IgG and attenuated the disassembly of BBB structural proteins, while the neuroprotective and BBB protective functions of PRE084 were blocked by BD1047. Furthermore, in Sig-1R knockout (Sig-1R KO) mice, brain IR produced more serious IgG leakage and degradation of BBB structural proteins than in wild-type model mice. In addition, the protective effect of PRE084 against the BBB was lost in Sig-1R KO mice after brain IR. Finally, treatment with PRE084 significantly increased the expression of Sig-1R in brain microvascular endothelial cells of mice that were subjected to brain IR and increased translocation of Sig-1R to the cell plasmalemma. Thus, we identified a previously unexplored role of Sig-1R in alleviating BBB disruption in stroke processes and have demonstrated that reversing BBB rupture through Sig-1R activation may be another promising method for cerebral protection against IR injury.

Sigma-1 Receptor-Modulated Neuroinflammation in Neurological Diseases

A large body of evidence indicates that sigma-1 receptors (Sig-1R) are important drug targets for a number of neuropsychiatric disorders. Sig-1Rs are enriched in central nervous system (CNS). In addition to neurons, both cerebral microglia and astrocytes express Sig-1Rs. Activation of Sig-1Rs is known to elicit potent neuroprotective effects and promote neuronal survival via multiple mechanisms, including promoting mitochondrial functions, decreasing oxidative stress and regulating neuroimmnological functions. In this review article, we focus on the emerging role of Sig-1Rs in regulating neuroinflammation and discuss the recent advances on the Sig-1R-modulating neuroinflammation in the pathophysiology and therapy of neurodegenerative disorders.

SA4503, A Potent Sigma-1 Receptor Ligand, Ameliorates Synaptic Abnormalities and Cognitive Dysfunction in a Mouse Model of ATR-X Syndrome

α-thalassemia X-linked intellectual disability (ATR-X) syndrome is caused by mutations in ATRX. An ATR-X model mouse lacking Atrx exon 2 displays phenotypes that resemble symptoms in the human intellectual disability: cognitive defects and abnormal dendritic spine formation. We herein target activation of sigma-1 receptor (Sig-1R) that can induce potent neuroprotective and neuroregenerative effects by promoting the activity of neurotrophic factors, such as brain-derived neurotrophic factor (BDNF). We demonstrated that treatment with SA4503, a potent activator of Sig-1R, reverses axonal development and dendritic spine abnormalities in cultured cortical neurons from ATR-X model mice. Moreover, the SA4503 treatment rescued cognitive deficits exhibited by the ATR-X model mice. We further found that significant decreases in the BDNF-protein level in the medial prefrontal cortex of ATR-X model mice were recovered with treatment of SA4503. These results indicate that the rescue of dendritic spine abnormalities through the activation of Sig-1R has a potential for post-diagnostic therapy in ATR-X syndrome.

Cannabidiol enhances morphine antinociception, diminishes NMDA-mediated seizures and reduces stroke damage via the sigma 1 receptor

Cannabidiol (CBD), the major non-psychotomimetic compound present in the Cannabis sativa plant, exhibits therapeutic potential for various human diseases, including chronic neurodegenerative diseases, such as Alzheimer's and Parkinson's, ischemic stroke, epilepsy and other convulsive syndromes, neuropsychiatric disorders, neuropathic allodynia and certain types of cancer. CBD does not bind directly to endocannabinoid receptors 1 and 2, and despite research efforts, its specific targets remain to be fully identified. Notably, sigma 1 receptor (σ1R) antagonists inhibit glutamate N-methyl-D-aspartate acid receptor (NMDAR) activity and display positive effects on most of the aforesaid diseases. Thus, we investigated the effects of CBD on three animal models in which NMDAR overactivity plays a critical role: opioid analgesia attenuation, NMDA-induced convulsive syndrome and ischemic stroke. In an in vitro assay, CBD disrupted the regulatory association of σ1R with the NR1 subunit of NMDAR, an effect shared by σ1R antagonists, such as BD1063 and progesterone, and prevented by σ1R agonists, such as 4-IBP, PPCC and PRE084. The in vivo administration of CBD or BD1063 enhanced morphine-evoked supraspinal antinociception, alleviated NMDA-induced convulsive syndrome, and reduced the infarct size caused by permanent unilateral middle cerebral artery occlusion. These positive effects of CBD were reduced by the σ1R agonists PRE084 and PPCC, and absent in σ1R-/- mice. Thus, CBD displays antagonist-like activity toward σ1R to reduce the negative effects of NMDAR overactivity in the abovementioned experimental situations.

N, N-Dimethyltryptamine (DMT), an Endogenous Hallucinogen: Past, Present, and Future Research to Determine Its Role and Function

This report provides a historical overview of research concerning the endogenous hallucinogen N, N-dimethyltryptamine (DMT), focusing on data regarding its biosynthesis and metabolism in the brain and peripheral tissues, methods and results for DMT detection in body fluids and brain, new sites of action for DMT, and new data regarding its possible physiological and therapeutic roles. Research that further elaborates its consideration as a putative neurotransmitter is also addressed. Taking these studies together, the report proposes several new directions and experiments to ascertain the role of DMT in the brain, including brain mapping of enzymes responsible for the biosynthesis of DMT, further studies to elaborate its presence and role in the pineal gland, a reconsideration of binding site data, and new administration and imaging studies. The need to resolve the "natural" role of an endogenous hallucinogen from the effects observed from peripheral administration are also emphasized.

CRMP2-binding compound, edonerpic maleate, accelerates motor function recovery from brain damage

Brain damage such as stroke is a devastating neurological condition that may severely compromise patient quality of life. No effective medication-mediated intervention to accelerate rehabilitation has been established. We found that a small compound, edonerpic maleate, facilitated experience-driven synaptic glutamate AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic-acid) receptor delivery and resulted in the acceleration of motor function recovery after motor cortex cryoinjury in mice in a training-dependent manner through cortical reorganization. Edonerpic bound to collapsin-response-mediator-protein 2 (CRMP2) and failed to augment recovery in CRMP2-deficient mice. Edonerpic maleate enhanced motor function recovery from internal capsule hemorrhage in nonhuman primates. Thus, edonerpic maleate, a neural plasticity enhancer, could be a clinically potent small compound with which to accelerate rehabilitation after brain damage.

Neuroprotective dobutamine treatment upregulates superoxide dismutase 3, anti-oxidant and survival genes and attenuates genes mediating inflammation

Background

Labor subjects the fetus to an hypoxic episode and concomitant adrenomodullary catecholamine surge that may provide protection against the hypoxic insult. The beta1-adrenergic agonist dobutamine protects against hypoxia/aglycemia induced neuronal damage. We aimed to identify the associated protective biological processes involved.

Results

Hippocampal slices from 6 days old mice showed significant changes of gene expression comparing slices with or without dobutamine (50 mM) in the following two experimental paradigms: (1) control conditions versus lipopolysacharide (LPS) stimulation and (2) oxygen–glucose deprivation (OGD), versus combined LPS/OGD. Dobutamine depressed the inflammatory response by modifying the toll-like receptor-4 signalling pathways, including interferon regulatory factors and nuclear factor κ B activation in experimental paradigm 1. The anti-oxidant defense genes superoxide dismutase 3 showed an upregulation in the OGD paradigm while thioredoxin reductase was upregulated in LPS paradigm. The survival genes Bag-3, Tinf2, and TMBIM-1, were up-regulated in paradigm 1. Moreover, increased levels of SOD3 were verified on the protein level 24 h after OGD and control stimulation in cultures with or without preconditioning with LPS and dobutamine, respectively.

Conclusions

Neuroprotective treatment with dobutamine depresses expression of inflammatory mediators and promotes the defense against oxidative stress and depresses apoptotic genes in a model of neonatal brain hypoxia/ischemia interpreted as pharmacological preconditioning. We conclude that beta1-adrenoceptor activation might be an efficient strategy for identifying novel pharmacological targets for protection of the neonatal brain.

Electronic supplementary material

The online version of this article (10.1186/s12868-018-0415-2) contains supplementary material, which is available to authorized users.

STAT3 precedes HIF1α transcriptional responses to oxygen and oxygen and glucose deprivation in human brain pericytes

Brain pericytes are important to maintain vascular integrity of the neurovascular unit under both physiological and ischemic conditions. Ischemic stroke is known to induce an inflammatory and hypoxic response due to the lack of oxygen and glucose in the brain tissue. How this early response to ischemia is molecularly regulated in pericytes is largely unknown and may be of importance for future therapeutic targets. Here we evaluate the transcriptional responses in in vitro cultured human brain pericytes after oxygen and/or glucose deprivation. Hypoxia has been widely known to stabilise the transcription factor hypoxia inducible factor 1-alpha (HIF1α) and mediate the induction of hypoxic transcriptional programs after ischemia. However, we find that the transcription factors Jun Proto-Oncogene (c-JUN), Nuclear Factor Of Kappa Light Polypeptide Gene Enhancer In B-Cells (NFκB) and signal transducer and activator of transcription 3 (STAT3) bind genes regulated after 2hours (hs) of omitted glucose and oxygen before HIF1α. Potent HIF1α responses require 6hs of hypoxia to substantiate transcriptional regulation comparable to either c-JUN or STAT3. Phosphorylated STAT3 protein is at its highest after 5 min of oxygen and glucose (OGD) deprivation, whereas maximum HIF1α stabilisation requires 120 min. We show that STAT3 regulates angiogenic and metabolic pathways before HIF1α, suggesting that HIF1α is not the initiating trans-acting factor in the response of pericytes to ischemia.

Neuroendocrine Associations Underlying the Persistent Therapeutic Effects of Classic Serotonergic Psychedelics

Recent reports on the effects of psychedelic-assisted therapies for mood disorders and addiction, as well as the effects of psychedelics in the treatment of cluster headache, have demonstrated promising therapeutic results. In addition, the beneficial effects appear to persist well after limited exposure to the drugs, making them particularly appealing as treatments for chronic neuropsychiatric and headache disorders. Understanding the basis of the long-lasting effects, however, will be critical for the continued use and development of this drug class. Several mechanisms, including biological and psychological ones, have been suggested to explain the long-lasting effects of psychedelics. Actions on the neuroendocrine system are some such mechanisms that warrant further investigation in the study of persisting psychedelic effects. In this report, we review certain structural and functional neuroendocrinological pathologies associated with neuropsychiatric disorders and cluster headache. We then review the effects that psychedelic drugs have on those systems and provide preliminary support for potential long-term effects. The circadian biology of cluster headache is of particular relevance in this area. We also discuss methodologic considerations for future investigations of neuroendocrine system involvement in the therapeutic benefits of psychedelic drugs.

Enhancing endogenous capacity to repair a stroke-damaged brain: An evolving field for stroke research

Stroke represents a severe medical condition that causes stroke survivors to suffer from long-term and even lifelong disability. Over the past several decades, a vast majority of stroke research targets neuroprotection in the acute phase, while little work has been done to enhance stroke recovery at the later stage. Through reviewing current understanding of brain plasticity, stroke pathology, and emerging preclinical and clinical restorative approaches, this review aims to provide new insights to advance the research field for stroke recovery. Lifelong brain plasticity offers the long-lasting possibility to repair a stroke-damaged brain. Stroke impairs the structural and functional integrity of entire brain networks; the restorative approaches containing multi-components have great potential to maximize stroke recovery by rebuilding and normalizing the stroke-disrupted entire brain networks and brain functioning. The restorative window for stroke recovery is much longer than previously thought. The optimal time for brain repair appears to be at later stage of stroke rather than the earlier stage. It is expected that these new insights will advance our understanding of stroke recovery and assist in developing the next generation of restorative approaches for enhancing brain repair after stroke.

Discovery of N-cyclobutylaminoethoxyisoxazole derivatives as novel sigma-1 receptor ligands with neurite outgrowth efficacy in cells

Herein we reported a series of 14 novel derivatives based on the N-cyclobutylaminoethoxyisoxazole scaffold. In vitro binding studies of these compounds demonstrated their low nanomolar to subnanomolar potencies as σ1 receptor ligands, with moderate to excellent selectivity over the σ2 receptor as represented by compounds 17-30. The majority of the derivatives scored high (>4.7) in the CNS MPO appraisal system, indicating their high likelihood in penetrating the blood-brain barrier. A number of these compounds exhibited significant neurite outgrowth efficacy in N1E-115 neuronal cells and displayed excellent selectivity for σ1 receptors over the selected endogenous neurotransmitter transporters, such as DAT, NET and SERT. Among the mini-series, compound 28 (K i σ1 = 0.2 nM, K i σ2 = 198 nM, CNS MPO score = 5.4) emerged as a promising selective σ1 receptor ligand that warrants its further evaluation as a potential therapeutic for neurodegenerative diseases.

circHIPK2-mediated σ-1R promotes endoplasmic reticulum stress in human pulmonary fibroblasts exposed to silica

Silicosis is characterized by fibroblast accumulation and excessive deposition of extracellular matrix. Although the roles of SiO2-induced chemokines and cytokines released from alveolar macrophages have received significant attention, the direct effects of SiO2 on protein production and functional changes in pulmonary fibroblasts have been less extensively studied. Sigma-1 receptor, which has been associated with cell proliferation and migration in the central nervous system, is expressed in the lung, but its role in silicosis remains unknown. To elucidate the role of sigma-1 receptor in fibrosis induced by silica, both the upstream molecular mechanisms and the functional effects on cell proliferation and migration were investigated. Both molecular biological assays and pharmacological techniques, combined with functional experiments, such as migration and proliferation, were applied in human pulmonary fibroblasts from adults to analyze the molecular and functional changes induced by SiO2. SiO2 induced endoplasmic reticulum stress in association with enhanced expression of sigma-1 receptor. Endoplasmic reticulum stress promoted migration and proliferation of human pulmonary fibroblasts-adult exposed to SiO2, inducing the development of silicosis. Inhibition of sigma-1 receptor ameliorated endoplasmic reticulum stress and fibroblast functional changes induced by SiO2. circHIPK2 is involved in the regulation of sigma-1 receptor in human pulmonary fibroblasts-adult exposed to SiO2. Our study elucidated a link between SiO2-induced fibrosis and sigma-1 receptor signaling, thereby providing novel insight into the potential use of sigma-1 receptor/endoplasmic reticulum stress in the development of novel therapeutic strategies for silicosis treatment.

Sigma-1 receptor agonist increases axon outgrowth of hippocampal neurons via voltage-gated calcium ions channels

INTRODUCTION

Sigma-1 receptors (Sig-1Rs) are unique endoplasmic reticulum proteins that have been implicated in both neurodegenerative and ischemic diseases, such as Alzheimer's disease and stroke. Accumulating evidence has suggested that Sig-1R plays a role in neuroprotection and axon outgrowth. The underlying mechanisms of Sig-1R-mediated neuroprotection have been well elucidated. However, the mechanisms underlying the effects of Sig-1R on axon outgrowth are not fully understood.

METHODS

To clarify this issue, we utilized immunofluorescence to compare the axon lengths of cultured naïve hippocampal neurons before and after the application of the Sig-1R agonist, SA4503. Then, electrophysiology and immunofluorescence were used to examine voltage-gated calcium ion channel (VGCCs) currents in the cell membranes and growth cones.

RESULTS

We found that Sig-1R activation dramatically enhanced the axonal length of the naïve hippocampal neurons. Application of the Sig-1R antagonist NE100 and gene knockdown techniques both demonstrated the effects of Sig-1R. The growth-promoting effect of SA4503 was accompanied by the inhibition of voltage-gated Ca2+ influx and was recapitulated by incubating the neurons with the L-type, N-type, and P/Q-type VGCC blockers, nimodipine, MVIIA and ω-agatoxin IVA, respectively. This effect was unrelated to glial cells. The application of SA4503 transformed the growth cone morphologies from complicated to simple, which favored axon outgrowth.

CONCLUSION

Sig-1R activation can enhance axon outgrowth and may have a substantial influence on neurogenesis and neurodegenerative diseases.

Short term changes in the proteome of human cerebral organoids induced by 5-MeO-DMT

Dimethyltryptamines are entheogenic serotonin-like molecules present in traditional Amerindian medicine recently associated with cognitive gains, antidepressant effects, and changes in brain areas related to attention. Legal restrictions and the lack of adequate experimental models have limited the understanding of how such substances impact human brain metabolism. Here we used shotgun mass spectrometry to explore proteomic differences induced by 5-methoxy-N,N-dimethyltryptamine (5-MeO-DMT) on human cerebral organoids. Out of the 6,728 identified proteins, 934 were found differentially expressed in 5-MeO-DMT-treated cerebral organoids. In silico analysis reinforced previously reported anti-inflammatory actions of 5-MeO-DMT and revealed modulatory effects on proteins associated with long-term potentiation, the formation of dendritic spines, including those involved in cellular protrusion formation, microtubule dynamics, and cytoskeletal reorganization. Our data offer the first insight about molecular alterations caused by 5-MeO-DMT in human cerebral organoids.

An Increase of Sigma-1 Receptor in the Penumbra Neuron after Acute Ischemic Stroke

BACKGROUND

Penumbra salvage from infarction by early reperfusion within the time window is the target of acute ischemic stroke therapies. Although the penumbral imaging is potently usable in clinic trial, additional work needs to be performed to advancing the field with better-defined, evaluated, and validated imaging measures.

METHODS

Mice were subjected to permanent stroke by right middle cerebral artery (MCA) occlusion. Multimodel magnetic resonance imaging (MRI) method was assessed to define the penumbra as that brain region in which the perfusion and diffusion-weighted MR images are mismatched (perfusion-weighted imaging [PWI]-diffusion-weighted imaging [DWI] mismatch). MRI measurements were performed at 1 hour after MCA occlusion (MCAO). Sigma-1 receptor expression was assessed by immunoblotting and immunostaining in PWI-DWI-defined penumbra and core compared with sham or contralateral slice. Penumbral sigma-1 receptor identified the correlation with the neuron, astrocyte, and microglia by immuno-colocalization.

RESULTS

Sigma-1 receptor was significantly upregulated in penumbra or peri-infarct compared with sham and core tissue at 1 hour and 24 hours after MCAO. There was a colocalization of sigma-1 receptor and neuron in penumbra at 1 hour after stroke. Sigma-1 receptor is specifically increased in ischemic penumbral neuron at 1 hour after MCAO.

CONCLUSIONS

Sigma-1 receptor may act as an endogenous marker of penumbra after acute ischemic stroke.

The Sigma-1 Receptor Antagonist, S1RA, Reduces Stroke Damage, Ameliorates Post-Stroke Neurological Deficits and Suppresses the Overexpression of MMP-9

The glutamate N-methyl-D-aspartate receptor (NMDAR) plays an essential role in the excitotoxic neural damage that follows ischaemic stroke. Because the sigma-1 receptor (σ1R) can regulate NMDAR transmission, exogenous and putative endogenous regulators of σ1R have been investigated using animal models of ischaemic stroke. As both agonists and antagonists provide some neural protection, the selective involvement of σ1Rs in these effects has been questioned. The availability of S1RA (E-52862/MR309), a highly selective σ1R antagonist, prompted us to explore its therapeutic potential in an animal model of focal cerebral ischaemia. Mice were subjected to right middle cerebral artery occlusion (MCAO), and post-ischaemic infarct volume and neurological deficits were determined across a range of intervals after the stroke-inducing surgery. Intracerebroventricular or intravenous treatment with S1RA significantly reduced the cerebral infarct size and neurological deficits caused by permanent MCAO (pMCAO). Compared with the control/sham-operated mice, the neuroprotective effects of S1RA were observed when delivered up to 5 h prior to surgery and 3 h after ischaemic onset. Interestingly, neither mice with the genetic deletion of σ1R nor wild-type mice that were pre-treated with the σ1R agonist PRE084 showed beneficial effects after S1RA administration with regard to stroke infarction. S1RA-treated mice showed faster behavioural recovery from stroke; this finding complements the significant decreases in matrix metalloproteinase-9 (MMP-9) expression and reactive astrogliosis surrounding the infarcted cortex. Our data indicate that S1RA, via σ1R, holds promising potential for clinical application as a therapeutic agent for ischaemic stroke.

The SigmaR1 chaperone drives breast and colorectal cancer cell migration by tuning SK3-dependent Ca2+ homeostasis

The remodeling of calcium homeostasis contributes to the cancer hallmarks and the molecular mechanisms involved in calcium channel regulation in tumors remain to be characterized. Here, we report that SigmaR1, a stress-activated chaperone, is required to increase calcium influx by triggering the coupling between SK3, a Ca2+-activated K+ channel (KCNN3) and the voltage-independent calcium channel Orai1. We show that SigmaR1 physically binds SK3 in BC cells. Inhibition of SigmaR1 activity, either by molecular silencing or by the use of sigma ligand (igmesine), decreased SK3 current and Ca2+ entry in breast cancer (BC) and colorectal cancer (CRC) cells. Interestingly, SigmaR1 inhibition diminished SK3 and/or Orai1 levels in lipid nanodomains isolated from BC cells. Analyses of tissue microarray from CRC patients showed higher SigmaR1 expression levels in cancer samples and a correlation with tumor grade. Moreover, the exploration of a cohort of 4937 BC patients indicated that high expression of SigmaR1 and Orai1 channels was significantly correlated to a lower overall survival. As the SK3/Orai1 tandem drives invasive process in CRC and bone metastasis progression in BC, our results may inaugurate innovative therapeutic approaches targeting SigmaR1 to control the remodeling of Ca2+ homeostasis in epithelial cancers.

Sigma-1 Receptor Plays a Negative Modulation on N-type Calcium Channel

The sigma-1 receptor is a 223 amino acids molecular chaperone with a single transmembrane domain. It is resident to eukaryotic mitochondrial-associated endoplasmic reticulum and plasma membranes. By chaperone-mediated interactions with ion channels, G-protein coupled receptors and cell-signaling molecules, the sigma-1 receptor performs broad physiological and pharmacological functions. Despite sigma-1 receptors have been confirmed to regulate various types of ion channels, the relationship between the sigma-1 receptor and N-type Ca²⁺ channel is still unclear. Considering both sigma-1 receptors and N-type Ca²⁺ channels are involved in intracellular calcium homeostasis and neurotransmission, we undertake studies to explore the possible interaction between these two proteins. In the experiment, we confirmed the expression of the sigma-1 receptors and the N-type calcium channels in the cholinergic interneurons (ChIs) in rat striatum by using single-cell reverse transcription-polymerase chain reaction (scRT-PCR) and immunofluorescence staining. N-type Ca²⁺ currents recorded from ChIs in the brain slice of rat striatum was depressed when sigma-1 receptor agonists (SKF-10047 and Pre-084) were administrated. The inhibition was completely abolished by sigma-1 receptor antagonist (BD-1063). Co-expression of the sigma-1 receptors and the N-type calcium channels in Xenopus oocytes presented a decrease of N-type Ca²⁺ current amplitude with an increase of sigma-1 receptor expression. SKF-10047 could further depress N-type Ca²⁺ currents recorded from oocytes. The fluorescence resonance energy transfer (FRET) assays and co-immunoprecipitation (Co-IP) demonstrated that sigma-1 receptors and N-type Ca²⁺ channels formed a protein complex when they were co-expressed in HEK-293T (Human Embryonic Kidney -293T) cells. Our results revealed that the sigma-1 receptors played a negative modulation on N-type Ca²⁺ channels. The mechanism for the inhibition of sigma-1 receptors on N-type Ca²⁺ channels probably involved a chaperone-mediated direct interaction and agonist-induced conformational changes in the receptor-channel complexes on the cell surface.

Extracellular Matrix Modulation Is Driven by Experience-Dependent Plasticity During Stroke Recovery

Following stroke, complete cellular death in the ischemic brain area may ensue, with remaining brain areas undergoing tissue remodelling to various degrees. Experience-dependent brain plasticity exerted through an enriched environment (EE) promotes remodelling after central nervous system injury, such as stroke. Post-stroke tissue reorganization is modulated by growth inhibitory molecules differentially expressed within the ischemic hemisphere, like chondroitin sulfate proteoglycans found in perineuronal nets (PNNs). PNNs in the neocortex predominantly enwrap parvalbumin-containing GABAergic (PV/GABA) neurons, important in sensori-information processing. Here, we investigate how extracellular matrix (ECM) proteases and their inhibitors may participate in the regulation of PNN integrity during stroke recovery. Rats were subjected to photothrombotic stroke in the motor cortex, and functional deficits were assessed at 7 days of recovery. Sham and stroked rats were housed in either standard or EE conditions for 5 days, and infarct volumes were calculated. PNNs were visualized by immunohistochemistry and counted in the somatosensory cortex of both hemispheres. mRNA expression levels of ECM proteases and protease inhibitors were assessed by RT-qPCR and their activity analyzed by gel zymography. PNNs and protease activity were also studied in brains from stroke patients where similar results were observed. EE starting 2 days after stroke and continuing for 5 days stimulated behavioral recovery of limb-placement ability without affecting infarct size. EE promoted a decrease of PNNs around PV/GABA neurons and a concomitant modulation of the proteolytic activity and mRNA expression of ECM proteases and protease inhibitors in the somatosensory cortex. This study provides molecular targets for novel therapies that could support rehabilitation of stroke patients.

Soluble cpg15 from Astrocytes Ameliorates Neurite Outgrowth Recovery of Hippocampal Neurons after Mouse Cerebral Ischemia

The present study focuses on the function of cpg15, a neurotrophic factor, in ischemic neuronal recovery using transient global cerebral ischemic (TGI) mouse model and oxygen-glucose deprivation (OGD)-treated primary cultured cells. The results showed that expression of cpg15 proteins in astrocytes, predominantly the soluble form, was significantly increased in mouse hippocampus after TGI and in the cultured astrocytes after OGD. Addition of the medium from the cpg15-overexpressed astrocytic culture into the OGD-treated hippocampal neuronal cultures reduces the neuronal injury, whereas the recovery of neurite outgrowths of OGD-injured neurons was prevented when cpg15 in the OGD-treated astrocytes was knocked down, or the OGD-treated-astrocytic medium was immunoadsorbed by cpg15 antibody. Furthermore, lentivirus-delivered knockdown of cpg15 expression in mouse hippocampal astrocytes diminishes the dendritic branches and exacerbates injury of neurons in CA1 region after TGI. In addition, treatment with inhibitors of MEK1/2, PI3K, and TrkA decreases, whereas overexpression of p-CREB, but not dp-CREB, increases the expression of cpg15 in U118 or primary cultured astrocytes. Also, it is observed that the Flag-tagged soluble cpg15 from the astrocytes transfected with Flag-tagged cpg15-expressing plasmids adheres to the surface of neuronal bodies and the neurites. In conclusion, our results suggest that the soluble cpg15 from astrocytes induced by ischemia could ameliorate the recovery of the ischemic-injured hippocampal neurons via adhering to the surface of neurons. The upregulated expression of cpg15 in astrocytes may be activated via MAPK and PI3K signal pathways, and regulation of CREB phosphorylation.SIGNIFICANCE STATEMENT Neuronal plasticity plays a crucial role in the amelioration of neurological recovery of ischemic injured brain, which remains a challenge for clinic treatment of cerebral ischemia. cpg15 as a synaptic plasticity-related factor may participate in promoting the recovery process; however, the underlying mechanisms are still largely unknown. The objective of this study is to reveal the function and mechanism of neuronal-specific cpg15 expressed in astrocytes after ischemia induction, in promoting the recovery of injured neurons. Our findings provided new mechanistic insight into the neurological recovery, which might help develop novel therapeutic options for cerebral ischemia via astrocytic-targeting interference of gene expression.

The Role of Sigma 1 Receptor as a Neuroprotective Target in Glaucoma

The role of sigma 1 receptor (S1R) in glaucoma is emerging as a promising field of study. Glaucoma is an optic neuropathy that shares common pathogenic mechanisms with other neurodegenerative diseases such as Alzheimer's and Parkinson's disease . S1R modulates multiple cellular functions associated with neurodegeneration . These include Ca2+ ion homeostasis, endoplasmic reticulum (ER) and oxidative stress , survival signaling pathways, neurotrophin secretion, and glial activation. S1R may also have neurorestorative properties including enhancement of neuronal plasticity and neurite outgrowth. Recent studies using agonists for S1R within the eye provide hope that it could be a therapeutic target for glaucoma. Understanding the role of S1R in glaucoma may help us to stop the progression of this sight threatening disease.

Sigma-1 Receptors and Neurodegenerative Diseases: Towards a Hypothesis of Sigma-1 Receptors as Amplifiers of Neurodegeneration and Neuroprotection

Sigma-1 receptors are molecular chaperones that may act as pathological mediators and targets for novel therapeutic applications in neurodegenerative diseases. Accumulating evidence indicates that sigma-1 ligands can either directly or indirectly modulate multiple neurodegenerative processes, including excitotoxicity, calcium dysregulation, mitochondrial and endoplasmic reticulum dysfunction, inflammation, and astrogliosis. In addition, sigma-1 ligands may act as disease-modifying agents in the treatment for central nervous system (CNS) diseases by promoting the activity of neurotrophic factors and neural plasticity. Here, we summarize their neuroprotective and neurorestorative effects in different animal models of acute brain injury and chronic neurodegenerative diseases, and highlight their potential role in mitigating disease. Notably, current data suggest that sigma-1 receptor dysfunction worsens disease progression, whereas enhancement amplifies pre-existing functional mechanisms of neuroprotection and/or restoration to slow disease progression. Collectively, the data support a model of the sigma-1 receptor as an amplifier of intracellular signaling, and suggest future clinical applications of sigma-1 ligands as part of multi-therapy approaches to treat neurodegenerative diseases.

Sigma 1 Receptor and Ion Channel Dynamics in Cancer

SigmaR1 is a multitasking chaperone protein which has mainly been studied in CNS physiological and pathophysiological processes such as pain, memory, neurodegenerative diseases (amyotrophic lateral sclerosis , Parkinson's and Alzheimer's diseases, retinal neurodegeneration ), stroke and addiction . Strikingly, G-protein and ion channels are the main client protein fami lies of this atypical chaperone and the recent advances that have been performed for the last 10 years demonstrate that SigmaR1 is principally activated following tissue injury and disease development to promote cell survival. In this chapter, we synthesize the data enhancing our comprehension of the interaction between SigmaR1 and ion channels and the unexpected consequences of such functional coupling in cancer development. We also describe a model in which the pro-survival functions of SigmaR1 observed in CNS pathologies are hijacked by cancer cells to shape their electrical signature and behavior in response to the tumor microenvironment .

The sigma-1 receptor mediates the beneficial effects of pridopidine in a mouse model of Huntington disease

The tri-nucleotide repeat expansion underlying Huntington disease (HD) results in corticostriatal synaptic dysfunction and subsequent neurodegeneration of striatal medium spiny neurons (MSNs). HD is a devastating autosomal dominant disease with no disease-modifying treatments. Pridopidine, a postulated "dopamine stabilizer", has been shown to improve motor symptoms in clinical trials of HD. However, the target(s) and mechanism of action of pridopidine remain to be fully elucidated. As binding studies identified sigma-1 receptor (S1R) as a high-affinity receptor for pridopidine, we evaluated the relevance of S1R as a therapeutic target of pridopidine in HD. S1R is an endoplasmic reticulum - (ER) resident transmembrane protein and is regulated by ER calcium homeostasis, which is perturbed in HD. Consistent with ER calcium dysregulation, we observed striatal upregulation of S1R in aged YAC128 transgenic HD mice and HD patients. We previously demonstrated that dendritic MSN spines are lost in aged corticostriatal co-cultures from YAC128 mice. We report here that pridopidine and the chemically similar S1R agonist 3-PPP prevent MSN spine loss in aging YAC128 co-cultures. Spine protection was blocked by neuronal deletion of S1R. Pridopidine treatment suppressed supranormal ER Ca2+ release, restored ER calcium levels and reduced excessive store-operated calcium (SOC) entry in spines, which may account for its synaptoprotective effects. Normalization of ER Ca2+ levels by pridopidine was prevented by S1R deletion. To evaluate long-term effects of pridopidine, we analyzed expression profiles of calcium signaling genes. Pridopidine elevated striatal expression of calbindin and homer1a, whereas their striatal expression was reduced in aged Q175KI and YAC128 HD mouse models compared to WT. Pridopidine and 3-PPP are proposed to prevent calcium dysregulation and synaptic loss in a YAC128 corticostriatal co-culture model of HD. The actions of pridopidine were mediated by S1R and led to normalization of ER Ca2+ release, ER Ca2+ levels and spine SOC entry in YAC128 MSNs. This is a new potential mechanism of action for pridopidine, highlighting S1R as a potential target for HD therapy. Upregulation of striatal proteins that regulate calcium, including calbindin and homer1a, upon chronic therapy with pridopidine, may further contribute to long-term beneficial effects of pridopidine in HD.

Activation of σ1 and σ2 receptors by afobazole increases glial cell survival and prevents glial cell activation and nitrosative stress after ischemic stroke

Activation of sigma receptors at delayed time points has been shown to decrease injury following ischemic stroke. The mixed σ1/σ2 receptor agonist, 5-ethoxy-2-[2-(morpholino)-ethylthio]benzimidazole (afobazole), provides superior long-term outcomes compared to other σ ligands in the rat middle cerebral artery occlusion (MCAO) stroke model. Experiments using the MCAO model were carried out to determine the molecular mechanism involved in the beneficial effects of afobazole. Administration of afobazole (3 mg/kg) at delayed time points post-stroke significantly increased the number of microglia and astrocytes detected in the ipsilateral hemisphere at 96 h post-surgery. Morphological analysis of the microglia indicated that a greater number of these cells were found in the ramified resting state in MCAO animals treated with afobazole relative to MCAO vehicle controls. Similarly, fewer reactive astrocytes were detected in the injured hemisphere of afobazole-treated animals. Both the enhanced survival and reduced activation of glial cells were abolished by co-application of either a σ1 (BD-1063) or a σ2 (SM-21) receptor antagonist with afobazole. To gain further insight into the mechanisms by which afobazole lessens stroke injury, we probed the brain sections for markers of neuroinflammation (tumor necrosis factor α) and nitrosative stress (S-nitrosocysteine). Data show that afobazole significantly reduces S-nitrosocysteine levels, but does not alter tumor necrosis factor α expression 96 h after an ischemic stroke. Taken together our data indicate that afobazole acting via both σ1 and σ2 receptors decreases stroke injury by enhancing glial cell survival, blocking ischemia-induced glial cell activation, and decreasing nitrosative stress.

Sigma-1 receptors modulate neonatal Nav1.5 ion channels in breast cancer cell lines

The main aim of this study was to investigate a possible functional connection between sigma-1 receptors and voltage-gated sodium channels (VGSCs) in human breast cancer cells. The hypothesis was that sigma-1 drugs could alter the metastatic properties of breast cancer cells via the VGSC. Evidence was found for expression of sigma-1 receptor and neonatal Nav1.5 (nNav1.5) expression in both MDA-MB-231 and MDA-MB-468 cells. Sigma-1 drugs (SKF10047 and dimethyltryptamine) did not affect cell proliferation or migration but significantly reduced adhesion to the substrate. Silencing sigma-1 receptor expression by siRNA similarly reduced the adhesion. Blocking nNav1.5 activity with a polyclonal antibody (NESOpAb) targeting an extracellular region of nNav1.5 also reduced the adhesion in both cell lines. Importantly, the results of combined treatments with NESOpAb and a sigma-1 drug or sigma-1 siRNA suggested that both treatments targeted the same mechanism. The possibility was tested, therefore, that the sigma-1 receptor and the nNav1.5 channel formed a physical, functional complex. This suggestion was supported by the results of co-immunoprecipitation experiments. Furthermore, application of sigma-1 drugs to the cells reduced the surface expression of nNav1.5 protein, which could explain how sigma-1 receptor activation could alter the metastatic behaviour of breast cancer cells. Overall, these results are consistent with the idea of a sigma-1 protein behaving like either a "chaperone" or a regulatory subunit associated with nNav1.5.

Neuropharmacology of N,N-dimethyltryptamine

N,N-dimethyltryptamine (DMT) is an indole alkaloid widely found in plants and animals. It is best known for producing brief and intense psychedelic effects when ingested. Increasing evidence suggests that endogenous DMT plays important roles for a number of processes in the periphery and central nervous system, and may act as a neurotransmitter. This paper reviews the current literature of both the recreational use of DMT and its potential roles as an endogenous neurotransmitter. Pharmacokinetics, mechanisms of action in the periphery and central nervous system, clinical uses and adverse effects are also reviewed. DMT appears to have limited neurotoxicity and other adverse effects except for intense cardiovascular effects when administered intravenously in large doses. Because of its role in nervous system signaling, DMT may be a useful experimental tool in exploring how the brain works, and may also be a useful clinical tool for treatment of anxiety and psychosis.

Role of peripheral sigma-1 receptors in ischaemic pain: Potential interactions with ASIC and P2X receptors

BACKGROUND

The role of peripheral sigma-1 receptors (Sig-1Rs) in normal nociception and in pathologically induced pain conditions has not been thoroughly investigated. Since there is mounting evidence that Sig-1Rs modulate ischaemia-induced pathological conditions, we investigated the role of Sig-1Rs in ischaemia-induced mechanical allodynia (MA) and addressed their possible interaction with acid-sensing ion channels (ASICs) and P2X receptors at the ischaemic site.

METHODS

We used a rodent model of hindlimb thrombus-induced ischaemic pain (TIIP) to investigate their role. Western blot was performed to observe changes in Sig-1R expression in peripheral nervous tissues. MA was measured after intraplantar (i.pl.) injections of antagonists for the Sig-1, ASIC and P2X receptors in TIIP rats or agonists of each receptor in naïve rats.

RESULTS

Sig-1R expression significantly increased in skin, sciatic nerve and dorsal root ganglia at 3 days post-TIIP surgery. I.pl. injections of the Sig-1R antagonist, BD-1047 on post-operative days 0-3 significantly attenuated the development of MA during the induction phase, but had no effect on MA when given during the maintenance phase (days 3-6 post-surgery). BD-1047 synergistically increased amiloride (an ASICs blocker)- and TNP-ATP (a P2X antagonist)-induced analgesic effects in TIIP rats. In naïve rats, i.pl. injection of Sig-1R agonist PRE-084 alone did not produce MA; but it did induce MA when co-administered with either an acidic pH solution or a sub-effective dose of αβmeATP.

CONCLUSION

Peripheral Sig-1Rs contribute to the induction of ischaemia-induced MA via facilitation of ASICs and P2X receptors. Thus, peripheral Sig-1Rs represent a novel therapeutic target for the treatment of ischaemic pain.

The Sigma-1 Receptor as a Pluripotent Modulator in Living Systems

The sigma-1 receptor (Sig-1R) is an endoplasmic reticulum (ER) protein that resides specifically in the mitochondria-associated endoplasmic reticulum (ER) membrane (MAM), an interface between ER and mitochondria. In addition to being able to translocate to the plasma membrane (PM) to interact with ion channels and other receptors, Sig-1R also occurs at the nuclear envelope, where it recruits chromatin-remodeling factors to affect the transcription of genes. Sig-1Rs have also been reported to interact with other membranous or soluble proteins at other loci, including the cytosol, and to be involved in several central nervous system (CNS) diseases. Here, we propose that Sig-1R is a pluripotent modulator with resultant multiple functional manifestations in living systems.

Progesterone improves long-term functional and histological outcomes after permanent stroke in older rats

Previous studies have shown progesterone to be beneficial in animal models of central nervous system injury, but less is known about its longer-term sustained effects on recovery of function following stroke. We evaluated progesterone's effects on a panel of behavioral tests up to 8 weeks after permanent middle cerebral artery occlusion (pMCAO). Male Sprague-Dawley rats 12m.o. were subjected to pMCAO and, beginning 3h post-pMCAO, given intraperitoneal injections of progesterone (8mg/kg) or vehicle, followed by subcutaneous injections at 8h and then every 24h for 7 days, with tapering of the last 2 treatments. The rats were then tested on functional recovery at 3, 6 and 8 weeks post-stroke. We observed that progesterone-treated animals showed attenuation of infarct volume and improved functional outcomes at 8 weeks after stroke on grip strength, sensory neglect, motor coordination and spatial navigation tests. Progesterone treatments significantly improved motor deficits in the affected limb on a number of gait parameters. Glial fibrillary acidic protein expression was increased in the vehicle group and considerably lowered in the progesterone group at 8 weeks post-stroke. With repeated post-stroke testing, sensory neglect and some aspects of spatial learning performance showed spontaneous recovery, but on gait and grip-strength measres progesterone given only in the acute stage of stroke (first 7 days) showed sustained beneficial effects on all other measures of functional recovery up to 8 weeks post-stroke.

Stimulation of Sigma-1 Receptor Ameliorates Depressive-like Behaviors in CaMKIV Null Mice

Sigma-1 receptor (Sig-1R) is a molecular chaperone regulating calcium efflux from the neuronal endoplasmic reticulum to the mitochondria. Calcium/calmodulin-dependent protein kinase IV (CaMKIV) null mice exhibit depressive-like behaviors and impaired neurogenesis as assessed by bromodeoxyuridine (BrdU) incorporation into newborn cells of the hippocampal dentate gyrus (DG). Here, we demonstrate that chronic stimulation of Sig-1R by treatment with the agonist SA4503 or the SSRI fluvoxamine for 14 days improves depressive-like behaviors in CaMKIV null mice. By contrast, treatment with paroxetine, which lacks affinity for Sig-1R, did not alter these behaviors. Reduced numbers of BrdU-positive cells and decreased brain-derived neurotrophic factor (BDNF) mRNA expression and protein kinase B (Akt; Ser-473) phosphorylation seen in the DG of CaMKIV null mice were significantly rescued by chronic Sig-1R stimulation. Interestingly, reduced ATP production observed in the DG of CaMKIV null mice was improved by chronic Sig-1R stimulation. Such stimulation also improved hippocampal long-term potentiation (LTP) induction and maintenance, which are impaired in the DG of CaMKIV null mice. LTP rescue was closely associated with both increases in calcium/calmodulin-dependent protein kinase II (CaMKII) autophosphorylation and GluA1 (Ser-831) phosphorylation. Taken together, Sig-1R stimulation by SA4503 or fluvoxamine treatment increased hippocampal neurogenesis, which is closely associated with amelioration of depressive-like behaviors in CaMKIV null mice.

Rehabilitation and plasticity following stroke: Insights from rodent models

Ischemic injuries within the motor cortex result in functional deficits that may profoundly impact activities of daily living in patients. Current rehabilitation protocols achieve only limited recovery of motor abilities. The brain reorganizes spontaneously after injury, and it is believed that appropriately boosting these neuroplastic processes may restore function via recruitment of spared areas and pathways. Here I review studies on circuit reorganization, neuronal and glial plasticity and axonal sprouting following ischemic damage to the forelimb motor cortex, with a particular focus on rodent models. I discuss evidence pointing to compensatory take-over of lost functions by adjacent peri-lesional areas and the role of the contralesional hemisphere in recovery. One key issue is the need to distinguish "true" recovery (i.e. re-establishment of original movement patterns) from compensation in the assessment of post-stroke functional gains. I also consider the effects of physical rehabilitation, including robot-assisted therapy, and the potential mechanisms by which motor training induces recovery. Finally, I describe experimental approaches in which training is coupled with delivery of plasticizing drugs that render the remaining, undamaged pathways more sensitive to experience-dependent modifications. These combinatorial strategies hold promise for the definition of more effective rehabilitation paradigms that can be translated into clinical practice.

Sigma receptors [σRs]: biology in normal and diseased states

This review compares the biological and physiological function of Sigma receptors [σRs] and their potential therapeutic roles. Sigma receptors are widespread in the central nervous system and across multiple peripheral tissues. σRs consist of sigma receptor one (σ₁R) and sigma receptor two (σ₂R) and are expressed in numerous regions of the brain. The sigma receptor was originally proposed as a subtype of opioid receptors and was suggested to contribute to the delusions and psychoses induced by benzomorphans such as SKF-10047 and pentazocine. Later studies confirmed that σRs are non-opioid receptors (not an µ opioid receptor) and play a more diverse role in intracellular signaling, apoptosis and metabolic regulation. σ₁Rs are intracellular receptors acting as chaperone proteins that modulate Ca²⁺ signaling through the IP₃ receptor. They dynamically translocate inside cells, hence are transmembrane proteins. The σ₁R receptor, at the mitochondrial-associated endoplasmic reticulum membrane, is responsible for mitochondrial metabolic regulation and promotes mitochondrial energy depletion and apoptosis. Studies have demonstrated that they play a role as a modulator of ion channels (K⁺ channels; N-methyl-d-aspartate receptors [NMDAR]; inositol 1,3,5 triphosphate receptors) and regulate lipid transport and metabolism, neuritogenesis, cellular differentiation and myelination in the brain. σ₁R modulation of Ca²⁺ release, modulation of cardiac myocyte contractility and may have links to G-proteins. It has been proposed that σ₁Rs are intracellular signal transduction amplifiers. This review of the literature examines the mechanism of action of the σRs, their interaction with neurotransmitters, pharmacology, location and adverse effects mediated through them.

The effects of sigma (σ1) receptor-selective ligands on muscarinic receptor antagonist-induced cognitive deficits in mice

BACKGROUND AND PURPOSE

Cognitive deficits in patients with Alzheimer's disease, Parkinson's disease, traumatic brain injury and stroke often involve alterations in cholinergic signalling. Currently available therapeutic drugs provide only symptomatic relief. Therefore, novel therapeutic strategies are needed to retard and/or arrest the progressive loss of memory.

EXPERIMENTAL APPROACH

Scopolamine-induced memory impairment provides a rapid and reversible phenotypic screening paradigm for cognition enhancement drug discovery. Male C57BL/6J mice given scopolamine (1 mg·kg(-1) ) were used to evaluate the ability of LS-1-137, a novel sigma (σ1) receptor-selective agonist, to improve the cognitive deficits associated with muscarinic antagonist administration.

KEY RESULTS

LS-1-137 is a high-affinity (Ki = 3.2 nM) σ1 receptor agonist that is 80-fold selective for σ1, compared with σ2 receptors. LS-1-137 binds with low affinity at D2-like (D2, D3 and D4) dopamine and muscarinic receptors. LS-1-137 was found to partially reverse the learning deficits associated with scopolamine administration using a water maze test and an active avoidance task. LS-1-137 treatment was also found to trigger the release of brain-derived neurotrophic factor from rat astrocytes.

CONCLUSIONS AND IMPLICATIONS

The σ1 receptor-selective compound LS-1-137 may represent a novel candidate cognitive enhancer for the treatment of muscarinic receptor-dependent cognitive deficits.

Albumin induces excitatory synaptogenesis through astrocytic TGF-β/ALK5 signaling in a model of acquired epilepsy following blood-brain barrier dysfunction

Post-injury epilepsy (PIE) is a common complication following brain insults, including ischemic, and traumatic brain injuries. At present, there are no means to identify the patients at risk to develop PIE or to prevent its development. Seizures can occur months or years after the insult, do not respond to anti-seizure medications in over third of the patients, and are often associated with significant neuropsychiatric morbidities. We have previously established the critical role of blood-brain barrier dysfunction in PIE, demonstrating that exposure of brain tissue to extravasated serum albumin induces activation of inflammatory transforming growth factor beta (TGF-β) signaling in astrocytes and eventually seizures. However, the link between the acute astrocytic inflammatory responses and reorganization of neural networks that underlie recurrent spontaneous seizures remains unknown. Here we demonstrate in vitro and in vivo that activation of the astrocytic ALK5/TGF-β-pathway induces excitatory, but not inhibitory, synaptogenesis that precedes the appearance of seizures. Moreover, we show that treatment with SJN2511, a specific ALK5/TGF-β inhibitor, prevents synaptogenesis and epilepsy. Our findings point to astrocyte-mediated synaptogenesis as a key epileptogenic process and highlight the manipulation of the TGF-β-pathway as a potential strategy for the prevention of PIE.

Treatment with AMD3100 attenuates the microglial response and improves outcome after experimental stroke

Background

Recovery of lost neurological function after stroke is limited and dependent on multiple mechanisms including inflammatory processes. Selective pharmacological modulation of inflammation might be a promising approach to improve stroke outcome.

Methods

We used 1,1′-[1,4-phenylenebis(methylene)]bis[1,4,8,11-tetraazacyclotetradecane] (AMD3100), an antagonist to the C-X-C chemokine receptor type 4 (CXCR4) and potential allosteric agonist to CXCR7, administered to mice twice daily from day 2 after induction of photothrombosis (PT). In addition to functional outcome, the dynamics of post-stroke microglia response were monitored in vivo by 2-photon-laser-microscopy in heterozygous transgenic CX₃CR1-green fluorescent protein (GFP) mice (CX₃CR1^GFP/+) and complemented with analyses for fractalkine (FKN) and pro-inflammatory cytokines.

Results

We found a significantly enhanced recovery and modified microglia activation without affecting infarct size in mice treated with AMD3100 after PT. AMD3100 treatment significantly reduced the number of microglia in the peri-infarct area accompanied by stabilization of soma size and ramified cell morphology. Within the ischemic infarct core of AMD3100 treated wild-type mice we obtained significantly reduced levels of the endogenous CX₃CR1 ligand FKN and the pro-inflammatory cytokines interleukin (IL)-1β and IL-6. Interestingly, in CX₃CR1-deficient mice (homozygous transgenic CX₃CR1-GFP mice) subjected to PT, the levels of FKN were significantly lower compared to their wild-type littermates. Moreover, AMD3100 treatment did not induce any relevant changes of cytokine levels in CX₃CR1 deficient mice.

Conclusion

After AMD3100 treatment, attenuation of microglia activation contributes to enhanced recovery of lost neurological function in experimental stroke possibly due to a depression of FKN levels in the brain. We further hypothesize that this mechanism is dependent on a functional receptor CX₃CR1.

Ether modifications to 1-[2-(3,4-dimethoxyphenyl)ethyl]-4-(3-phenylpropyl)piperazine (SA4503): effects on binding affinity and selectivity for sigma receptors and monoamine transporters

Two series of novel ether analogs of the sigma (σ) receptor ligand 1-[2-(3,4-dimethoxyphenyl)ethyl]-4-(3-phenylpropyl)piperazine (SA4503) have been prepared. In one series, the alkyl portion of the 4-methoxy group was replaced with allyl, propyl, bromoethyl, benzyl, phenethyl, and phenylpropyl moieties. In the second series, the 3,4-dimethoxy was replaced with cyclic methylenedioxy, ethylenedioxy and propylenedioxy groups. These ligands, along with 4-O-des-methyl SA4503, were evaluated for σ1 and σ2 receptor affinity, and compared to SA4503 and several known ether analogs. SA4503 and a subset of ether analogs were also evaluated for dopamine transporter (DAT) and serotonin transporter (SERT) affinity. The highest σ1 receptor affinities, Ki values of 1.75-4.63 nM, were observed for 4-O-des-methyl SA4503, SA4503 and the methylenedioxy analog. As steric bulk increased, σ1 receptor affinity decreased, but only to a point. Allyl, propyl and bromoethyl substitutions gave σ1 receptor Ki values in the 20-30 nM range, while bulkier analogs having phenylalkyl, and Z- and E-iodoallyl, ether substitutions showed higher σ1 affinities, with Ki values in the 13-21 nM range. Most ligands studied exhibited comparable σ1 and σ2 affinities, resulting in little to no subtype selectivity. SA4503, the fluoroethyl analog and the methylenedioxy congener showed modest six- to fourteen-fold selectivity for σ1 sites. DAT and SERT interactions proved much more sensitive than σ receptor interactions to these structural modifications. For example, the benzyl congener (σ1Ki=20.8 nM; σ2Ki=16.4 nM) showed over 100-fold higher DAT affinity (Ki=121 nM) and 6-fold higher SERT affinity (Ki=128nM) than the parent SA4503 (DAT Ki=12650 nM; SERT Ki=760 nM). Thus, ether modifications to the SA4503 scaffold can provide polyfunctional ligands having a broader spectrum of possible pharmacological actions.

The involvement of the sigma-1 receptor in neurodegeneration and neurorestoration

The sigma-1 receptor (Sig-1R) is a single 25 kD polypeptide and a chaperone protein immersed in lipid rafts of the endoplasmic reticulum (ER) where it interacts with mitochondria at the mitochondria-associated ER membrane domain (MAM). Upon activation, the Sig-1R binds to the inositol trisphosphate receptor (IP3R), and modulates cellular calcium (Ca(2+)) homeostasis. Also, the activated Sig-1R modulates plasma membrane receptor and ion channel functions, and may regulate cellular excitability. Further, the Sig-1R promotes trafficking of lipids and proteins essential for neurotransmission, cell growth and motility. Activation of the Sig-1R provides neuroprotection and is neurorestorative in cellular and animal models of neurodegenerative diseases and brain ischaemia. Neuroprotection appears to be due to inhibition of cellular Ca(2+) toxicity and/or inflammation, and neurorestoration may include balancing abberant neurotransmission or stimulation of synaptogenesis, thus remodelling brain connectivity. Single nucleotide polymorphisms and mutations of the SIGMAR1 gene worsen outcome in Alzheimer's disease and myotrophic lateral sclerosis supporting a role of Sig-1R in neurodegenerative disease. The combined neuroprotective and neurorestorative actions of the Sig-1R, provide a broad therapeutic time window of Sig-1R agonists. The Sig-1R is therefore a strong therapeutic target for the development of new treatments for neurodegenerative diseases and stroke.

Role of sigma-1 receptors in neurodegenerative diseases

Neurodegenerative diseases with distinct genetic etiologies and pathological phenotypes appear to share common mechanisms of neuronal cellular dysfunction, including excitotoxicity, calcium dysregulation, oxidative damage, ER stress and mitochondrial dysfunction. Glial cells, including microglia and astrocytes, play an increasingly recognized role in both the promotion and prevention of neurodegeneration. Sigma receptors, particularly the sigma-1 receptor subtype, which are expressed in both neurons and glia of multiple regions within the central nervous system, are a unique class of intracellular proteins that can modulate many biological mechanisms associated with neurodegeneration. These receptors therefore represent compelling putative targets for pharmacologically treating neurodegenerative disorders. In this review, we provide an overview of the biological mechanisms frequently associated with neurodegeneration, and discuss how sigma-1 receptors may alter these mechanisms to preserve or restore neuronal function. In addition, we speculate on their therapeutic potential in the treatment of various neurodegenerative disorders.

Sigma-1 receptor chaperones in neurodegenerative and psychiatric disorders

INTRODUCTION

Sigma-1 receptors (Sig-1Rs) are molecular chaperones that reside mainly in the endoplasmic reticulum (ER) but exist also in the proximity of the plasma membrane. Sig-1Rs are highly expressed in the CNS and are involved in many cellular processes including cell differentiation, neuritogenesis, microglia activation, protein quality control, calcium-mediated ER stress and ion channel modulation. Disturbance in any of the above cellular processes can accelerate the progression of many neurological disorders; therefore, the Sig-1R has been implicated in several neurological diseases.

AREAS COVERED

This review broadly covers the functions of Sig-1Rs including several neurodegenerative disorders in humans and drug addiction-associated neurological disturbance in the case of HIV infection. We discuss how several Sig-1R ligands could be utilized in therapeutic approaches to treat those disorders.

EXPERT OPINION

Emerging understanding of the cellular functions of this unique transmembrane chaperone may lead to the use of new agents or broaden the use of certain available ligands as therapeutic targets in those neurological disorders.

σ1 receptors activate astrocytes via p38 MAPK phosphorylation leading to the development of mechanical allodynia in a mouse model of neuropathic pain

BACKGROUND AND PURPOSE

Spinal astrocytes have emerged as important mechanistic contributors to the genesis of mechanical allodynia (MA) in neuropathic pain. We recently demonstrated that the spinal sigma non-opioid intracellular receptor 1 (σ1 receptor) modulates p38 MAPK phosphorylation (p-p38), which plays a critical role in the induction of MA in neuropathic rats. However, the histological and physiological relationships among σ1, p-p38 and astrocyte activation is unclear.

EXPERIMENTAL APPROACH

We investigated: (i) the precise location of σ1 receptors and p-p38 in spinal dorsal horn; (ii) whether the inhibition of σ1 receptors or p38 modulates chronic constriction injury (CCI)-induced astrocyte activation; and (iii) whether this modulation of astrocyte activity is associated with MA development in CCI mice.

KEY RESULTS

The expression of σ1 receptors was significantly increased in astrocytes on day 3 following CCI surgery. Sustained intrathecal treatment with the σ1 antagonist, BD-1047, attenuated CCI-induced increase in GFAP-immunoreactive astrocytes, and the treatment combined with fluorocitrate, an astrocyte metabolic inhibitor, synergistically reduced the development of MA, but not thermal hyperalgesia. The number of p-p38-ir astrocytes and neurons, but not microglia was significantly increased. Interestingly, intrathecal BD-1047 attenuated the expression of p-p38 selectively in astrocytes but not in neurons. Moreover, intrathecal treatment with a p38 inhibitor attenuated the GFAP expression, and this treatment combined with fluorocitrate synergistically blocked the induction of MA.

CONCLUSIONS AND IMPLICATIONS

Spinal σ1 receptors are localized in astrocytes and blockade of σ1 receptors inhibits the pathological activation of astrocytes via modulation of p-p38, which ultimately prevents the development of MA in neuropathic mice.

Phase II trial of the Sigma-1 receptor agonist cutamesine (SA4503) for recovery enhancement after acute ischemic stroke

BACKGROUND AND PURPOSE

The σ-1 receptor (Sig-1R) agonist cutamesine (SA4503) enhanced functional recovery after experimental stroke with a treatment initiation window of 48 hours and chronic treatment for 28 days. We conducted a phase 2 clinical trial exploring the safety, tolerability, dose range, and functional effects of cutamesine in patients with ischemic stroke.

METHODS

Subjects were randomized between 48 and 72 hours after stroke to receive cutamesine 1 mg/d, 3 mg/d, or placebo for 28 days. Effects on safety and function were assessed at baseline, at end of treatment (day 28), and at end of follow-up (day 56).

RESULTS

In 60 patients, treatment with both cutamesine dosages was safe and well tolerated without significant differences in numbers of treatment emergent or serious adverse events. No significant effect was observed on the primary efficacy measure (change in National Institutes of Health Stroke Scale from baseline to day 56) or modified Rankin Scale and Barthel Index scores. Post hoc analysis of moderately and severely affected patients (baseline National Institutes of Health Stroke Scale, ≥7 and ≥10) showed greater National Institutes of Health Stroke Scale improvements in the 3 mg/d cutamesine group when compared with placebo (P=0.034 and P=0.038, respectively). A trend toward a higher proportion being able to complete a 10m timed walk was observed for cutamesine-treated subjects.

CONCLUSIONS

Cutamesine was safe and well tolerated at both dosage levels. Although no significant effects on functional end points were seen in the population as a whole, greater improvement in National Institutes of Health Stroke Scale scores among patients with greater pretreatment deficits seen in post hoc analysis warrants further investigation. Additional studies should focus on the patient population with moderate-to-severe stroke.

CLINICAL TRIAL REGISTRATION URL

http://www.clinicaltrials.gov/show/NCT00639249. Unique identifier: NCT00639249. The EudraCT number is 2007-004840-60 (https://www.clinicaltrialsregister.eu/ctr-search/trial/2007-004840-60/GB).

Variations in apolipoprotein D and sigma non-opioid intracellular receptor 1 genes with relation to risk, severity and outcome of ischemic stroke

BACKGROUND

In experimental studies, the apolipoprotein D (APOD) and the sigma receptor type 1 (SIGMAR1) have been related to processes of brain damage, repair and plasticity.

METHODS

We examined blood samples from 3081 ischemic stroke (IS) patients and 1595 control subjects regarding 10 single nucleotide polymorphisms (SNPs) in the APOD (chromosomal location 3q29) and SIGMAR1 (chromosomal location 9p13) genes to find possible associations with IS risk, IS severity (NIHSS-score) and recovery after IS (modified Rankin Scale, mRS, at 90 days). Simple/multiple logistic regression and Spearman's rho were utilized for the analyses.

RESULTS

Among the SNPs analyzed, rs7659 within the APOD gene showed a possible association with stroke risk (OR = 1.12; 95% CI: 1.01-1.25; P = 0.029) and stroke severity (NIHSS ≥ 16) (OR = 0.70; 95% CI: 0.54-0.92; P = 0.009) when controlling for age, sex and vascular risk factors for stroke. No SNP showed an association with stroke recovery (mRS).

CONCLUSIONS

We conclude that the SNP rs7659 within the APOD gene might be related to risk and severity of ischemic stroke in patients.

Pharmacological stimulation of sigma-1 receptors has neurorestorative effects in experimental parkinsonism

The sigma-1 receptor, an endoplasmic reticulum-associated molecular chaperone, is attracting great interest as a potential target for neuroprotective treatments. We provide the first evidence that pharmacological modulation of this protein produces functional neurorestoration in experimental parkinsonism. Mice with intrastriatal 6-hydroxydopamine lesions were treated daily with the selective sigma-1 receptor agonist, PRE-084, for 5 weeks. At the dose of 0.3 mg/kg/day, PRE-084 produced a gradual and significant improvement of spontaneous forelimb use. The behavioural recovery was paralleled by an increased density of dopaminergic fibres in the most denervated striatal regions, by a modest recovery of dopamine levels, and by an upregulation of neurotrophic factors (BDNF and GDNF) and their downstream effector pathways (extracellular signal regulated kinases 1/2 and Akt). No treatment-induced behavioural-histological restoration occurred in sigma-1 receptor knockout mice subjected to 6-hydroxydopamine lesions and treated with PRE-084. Immunoreactivity for the sigma-1 receptor protein was evident in both astrocytes and neurons in the substantia nigra and the striatum, and its intracellular distribution was modulated by PRE-084 (the treatment resulted in a wider intracellular distribution of the protein). Our results suggest that sigma-1 receptor regulates endogenous defence and plasticity mechanisms in experimental parkinsonism. Boosting the activity of this protein may have disease-modifying effects in Parkinson's disease.