Sigma1 (sigma 1) receptor agonists and neurosteroids attenuate B25-35-amyloid peptide-induced amnesia in mice through a common mechanism

Amylovis-201 is a new dual-target ligand, acting as an anti-amyloidogenic compound and a potent agonist of the σ 1 chaperone protein

The aggregation of Amyloid-β (Aβ) peptides is associated with neurodegeneration in Alzheimer's disease (AD). We previously identified novel naphtalene derivatives, including the lead compound Amylovis-201, able to form thermodynamically stable complexes with Aβ species, peptides and fibrils. As the drug showed a chemical scaffold coherent for an effective interaction with the σ 1 receptor chaperone and as σ 1 agonists are currently developed as potent neuroprotectants in AD, we investigated the pharmacological action of Amylovis-201 on the σ 1 receptor. We report that Amylovis-201 is a potent σ 1 agonist by several in silico, in vitro and in vivo assays and that its anti-amnesic and neuroprotective effects involve a pharmacological action at σ 1 receptors. Furthermore, we show for the first time that classical σ 1 receptor agonist (PRE-084), and antagonist (NE-100) are able to interact and disaggregate Aβ 25-35 fibrils. Interestingly, Amylovis-201 was the only compound inhibiting Aβ 25-35 aggregates formation. Our results therefore highlight a dual action of Amylovis-201 as anti-aggregating agent and σ 1 receptor agonist that could be highly effective in long-term treatment against neurodegeneration in AD.

The immunomodulatory effects of classical psychedelics: A systematic review of preclinical studies

Emerging evidence suggests that classical psychedelics possess immunomodulatory and anti-inflammatory properties; however, these effects are yet to be well-established. This systematic review aims to provide a timely and comprehensive overview of the immunomodulatory effects of classical psychedelics in preclinical studies. A systematic search was conducted on six databases, including CINAHL, EMBASE, MEDLINE, PsychINFO, Scopus, and Web of Science. Eligible studies targeting classical psychedelics for evaluation of their effects on inflammatory markers and immunomodulation have been included for analysis. Data was extracted from 40 out of 2822 eligible articles, and their risk of bias was assessed using the Systematic Review Center for Laboratory Animal Experimentation (SYRCLE) tool and Quality Assessment Tool for In Vitro Studies (QUIN). Studies examined 2,5-dimethoxy-4-iodoamphetamine (DOI; n = 18); psilocybin (4-PO-DMT; n = 9); N,N-dimethyltryptamine (DMT; n = 8); lysergic acid diethylamide (LSD; n = 6); 5-methoxy-N,N-dimethyltryptamine (5-MeO-DMT; n = 3); psilocin (4-HO-DMT; n = 3); and mescaline (n = 2). In 36 studies where inflammatory cytokine levels were measured following psychedelic administration, a decrease in at least one inflammatory cytokine was observed in 29 studies. Immune cell activity was assessed in 10 studies and findings were mixed, with an equal number of studies (n = 5 out of 10) reporting either an increase or decrease in immune cell activity. Classical psychedelics were found to alleviate pre-existing inflammation but promote inflammation when administered under normal physiological conditions. This information is anticipated to inform future clinical trials, exploring classical psychedelics' potential to alleviate inflammation in various pathologies.

Comprehensive Analysis of Age- and Sex-Related Expression of the Chaperone Protein Sigma-1R in the Mouse Brain

Sigma-1R (S1R) is a ubiquitously distributed protein highly expressed in the brain and liver. It acts as a ligand-inducible chaperone protein localized at the endoplasmic reticulum. S1R participates in several signaling pathways that oversee diverse cellular and neurological functions, such as calcium and proteome homeostasis, neuronal activity, memory, and emotional regulation. Despite its crucial functions, S1R expression profile in the brain with respect to age and sex remains elusive. To shed light on this matter, we assessed S1R distribution in the mouse brain across different developmental stages, including juvenile, early adult, and middle-aged mice. Using immunohistochemistry, we found that S1R is predominantly expressed in the hippocampus in juvenile mice, particularly in CA1 and CA3 regions. Notably, S1R is not expressed in the subgranular layer of the dentate gyrus of juvenile mice. We observed dynamic changes in S1R levels during development, with most brain regions showing either an abrupt or gradual decline as mice transition from juveniles to adults. Sexual dimorphism is observed before puberty in the hippocampus and hypothalamus and during adulthood in the hippocampus and cortex.

Emerging Therapeutic Potential of Fluoxetine on Cognitive Decline in Alzheimer's Disease: Systematic Review

Fluoxetine, a commonly prescribed medication for depression, has been studied in Alzheimer's disease (AD) patients for its effectiveness on cognitive symptoms. The aim of this systematic review is to investigate the therapeutic potential of fluoxetine in cognitive decline in AD, focusing on its anti-degenerative mechanisms of action and clinical implications. According to PRISMA, we searched MEDLINE, up to 1 April 2024, for animal and human studies examining the efficacy of fluoxetine with regard to the recovery of cognitive function in AD. Methodological quality was evaluated using the ARRIVE tool for animal AD studies and the Cochrane tool for clinical trials. In total, 22 studies were analyzed (19 animal AD studies and 3 clinical studies). Fluoxetine promoted neurogenesis and enhanced synaptic plasticity in preclinical models of AD, through a decrease in Aβ pathology and increase in BDNF, by activating diverse pathways (such as the DAF-16-mediated, TGF-beta1, ILK-AKT-GSK3beta, and CREB/p-CREB/BDNF). In addition, fluoxetine has anti-inflammatory properties/antioxidant effects via targeting antioxidant Nrf2/HO-1 and hindering TLR4/NLRP3 inflammasome. Only three clinical studies showed that fluoxetine ameliorated the cognitive performance of people with AD; however, several methodological issues limited the generalizability of these results. Overall, the high-quality preclinical evidence suggests that fluoxetine may have neuroprotective, antioxidant, and anti-inflammatory effects in AD animal models. While more high-quality clinical research is needed to fully understand the mechanisms underlying these effects, fluoxetine is a promising potential treatment for AD patients. If future clinical trials confirm its anti-degenerative and neuroprotective effects, fluoxetine could offer a new therapeutic approach for slowing down the progression of AD.

Convolamine, a tropane alkaloid extracted from Convolvulus plauricalis, is a potent sigma-1 receptor-positive modulator with cognitive and neuroprotective properties

BACKGROUND AND AIM

By using an in vivo phenotypic screening assay in zebrafish, we identified Convolamine, a tropane alkaloid from Convulvus plauricalis, as a positive modulator of the sigma-1 receptor (S1R). The wfs1abKO zebrafish larva, a model of Wolfram syndrome, exhibits an increased visual-motor response due to a mutation in Wolframin, a protein involved in endoplasmic reticulum-mitochondria communication. We previously reported that ligand activating S1R, restored the cellular and behavioral deficits in patient fibroblasts and zebrafish and mouse models.

EXPERIMENTAL PROCEDURES

We screened a library of 108 repurposing and natural compounds on zebrafish motor response.

KEY RESULTS

One hit, the tropane alkaloid Convolamine, restored normal mobility in wfs1abKO larvae without affecting wfs1abWT controls. They did not bind to the S1R agonist/antagonist binding site nor dissociated S1R from BiP, an S1R activity assay in vitro, but behaved as a positive modulator by shifting the IC50 value of the reference agonist PRE-084 to lower values. Convolamine restored learning in Wfs1∆Exon8 , Dizocilpine-treated, and Aβ25-35 -treated mice. These effects were observed at low ~1 mg/kg doses, not shared by Convolvine, the desmethyl metabolite, and blocked by an S1R antagonist.

CONCLUSION AND IMPLICATIONS

Convolamine therefore acts as an S1R positive modulator and this pharmacological action is relevant to the traditional use of Shankhpushpi in memory and cognitive protection.

Fluoroethylnormemantine (FENM) shows synergistic protection in combination with a sigma-1 receptor agonist in a mouse model of Alzheimer's disease

Fluoroethylnormemantine (FENM) is a Memantine derivative with anti-amnesic and neuroprotective activities showed in the Aβ25-35 pharmacological mouse model of Alzheimer's disease (AD). As AD is a complex multi-factorial neurodegenerative pathology, combination therapies relying on drugs acting through different pathways, have been suggested to more adequately address neuroprotection. As several agonists of the sigma-1 receptor (S1R), an intracellular chaperone, are presently in phase 2 or 3 clinical trials in neurodegenetrative diseases including AD, we examined the potentialities of S1R drug-based combinations with FENM, or Memantine. Aβ25-35-treated mice were treated with S1R agonists (PRE-084, Igmesine, Cutamesine) and/or FENM, or Memantine, during 7 days after intracerebroventricular administration of oligomerized Aβ25-35. Mice were then tested for spatial short-term memory on day 8 and non-spatial long-term memory on days 9-10, using the spontaneous alternation or passive avoidance tests, respectively. The FENM or Memantine combination with Donepezil, that non-selectively inhibits acetylcholinesterase and activates S1R, was also tested. The efficacy of combinations using maximal non-active or minimal active doses of S1R agonist or FENM was analyzed using calculations of the combination index, based on simple isobologram representation. Data showed that most of the FENM-based combinations led to synergistic protection against Aβ25-35-induced learning deficits, for both long- and short-term memory responses, with a higher efficiency on the latter. Memantine led to synergistic combination in short-term memory but poorly in long-term memory responses, with either PRE-084 or Donepezil. These study showed that drug combinations based on FENM and S1R agonists may lead to highly effective and synergistic protection in AD, particularly on short-term memory.

Mitochondrial cytochrome P450 1B1 is involved in pregnenolone synthesis in human brain cells

Neurosteroids, which are steroids synthesized by the nervous system, can exert neuromodulatory and neuroprotective effects via genomic and nongenomic pathways. The neurosteroid and major steroid precursor pregnenolone has therapeutical potential in various diseases, such as psychiatric and pain disorders, and may play important roles in myelination, neuroinflammation, neurotransmission, and neuroplasticity. Although pregnenolone is synthesized by CYP11A1 in peripheral steroidogenic organs, our recent study showed that pregnenolone must be synthesized by another mitochondrial cytochrome P450 (CYP450) enzyme other than CYP11A1 in human glial cells. Therefore, we sought to identify the CYP450 responsible for pregnenolone production in the human brain. Upon screening for CYP450s expressed in the human brain that have mitochondrial localization, we identified three enzyme candidates: CYP27A1, CYP1A1, and CYP1B1. We found that inhibition of CYP27A1 through inhibitors and siRNA knockdown did not negatively affect pregnenolone synthesis in human glial cells. Meanwhile, treatment of human glial cells with CYP1A1/CYP1B1 inhibitors significantly reduced pregnenolone production in the presence of 22(R)-hydroxycholesterol. We performed siRNA knockdown of CYP1A1 or CYP1B1 in human glial cells and found that only CYP1B1 knockdown significantly decreased pregnenolone production. Furthermore, overexpression of mitochondria-targeted CYP1B1 significantly increased pregnenolone production under basal conditions and in the presence of hydroxycholesterols and low-density lipoprotein. Inhibition of CYP1A1 and/or CYP1B1 via inhibitors or siRNA knockdown did not significantly reduce pregnenolone synthesis in human adrenal cortical cells, implying that CYP1B1 is not a major pregnenolone-producing enzyme in the periphery. These data suggest that mitochondrial CYP1B1 is involved in pregnenolone synthesis in human glial cells.

The Sigma Receptors in Alzheimer's Disease: New Potential Targets for Diagnosis and Therapy

Sigma (σ) receptors are a class of unique proteins with two subtypes: the sigma-1 (σ1) receptor which is situated at the mitochondria-associated endoplasmic reticulum (ER) membrane (MAM), and the sigma-2 (σ2) receptor, located in the ER-resident membrane. Increasing evidence indicates the involvement of both σ1 and σ2 receptors in the pathogenesis of Alzheimer's disease (AD), and thus these receptors represent two potentially effective biomarkers for emerging AD therapies. The availability of optimal radioligands for positron emission tomography (PET) neuroimaging of the σ1 and σ2 receptors in humans will provide tools to monitor AD progression and treatment outcomes. In this review, we first summarize the significance of both receptors in the pathophysiology of AD and highlight AD therapeutic strategies related to the σ1 and σ2 receptors. We then survey the potential PET radioligands, with an emphasis on the requirements of optimal radioligands for imaging the σ1 or σ2 receptors in humans. Finally, we discuss current challenges in the development of PET radioligands for the σ1 or σ2 receptors, and the opportunities for neuroimaging to elucidate the σ1 and σ2 receptors as novel biomarkers for early AD diagnosis, and for monitoring of disease progression and AD drug efficacy.

Sigma 1 receptor activation improves retinal structure and function in the RhoP23H/+ mouse model of autosomal dominant retinitis pigmentosa

Retinitis pigmentosa (RP) is a group of devastating inherited retinal diseases that leads to visual impairment and oftentimes complete blindness. Currently no cure exists for RP thus research into prolonging vision is imperative. Sigma 1 receptor (Sig1R) is a promising small molecule target that has neuroprotective benefits in retinas of rapidly-degenerating mouse models. It is not clear whether Sig1R activation can provide similar neuroprotective benefits in more slowly-progressing RP models. Here, we examined Sig1R-mediated effects in the slowly-progressing RhoP23H/+ mouse, a model of autosomal dominant RP. We characterized the retinal degeneration of the RhoP23H/+ mouse over a 10 month period using three in vivo methods: Optomotor Response (OMR), Electroretinogram (ERG), and Spectral Domain-Optical Coherence Tomography (SD-OCT). A slow retinal degeneration was observed in both male and female RhoP23H/+ mice when compared to wild type. The OMR, which reflects visual acuity, showed a gradual decline through 10 months. Interestingly, female mice had more reduction in visual acuity than males. ERG assessment showed a gradual decline in scotopic and photopic responses in RhoP23H/+ mice. To investigate the neuroprotective benefits of Sig1R activation in the RhoP23H/+ mouse model, mutant mice were treated with a high-specificity Sig1R ligand (+)-pentazocine ((+)-PTZ) 3x/week at 0.5 mg/kg and examined using OMR, ERG, SD-OCT. A significant retention of visual function was observed in males and females at 10 months of age, with treated females retaining ∼50% greater visual acuity than non-treated mutant females. ERG revealed significant retention of scotopic and photopic b-wave amplitudes at 6 months in male and female RhoP23H/+ mice treated with (+)-PTZ. Further, in vivo analysis by SD-OCT revealed a significant retention of outer nuclear layer (ONL) thickness in male and female treated RhoP23H/+ mice. Histological studies showed significant retention of IS/OS length (∼50%), ONL thickness, and number of rows of photoreceptor cell nuclei at 6 months in (+)-PTZ-treated mutant mice. Interestingly, electron microscopy revealed preservation of OS discs in (+)-PTZ treated mutant mice compared to non-treated. Taken collectively, the in vivo and in vitro data provide the first evidence that targeting Sig1R can rescue visual function and structure in the RhoP23H/+ mouse. These results are promising and provide a framework for future studies to investigate Sig1R as a potential therapeutic target in retinal degenerative disease.

Investigation of the Entry Pathway and Molecular Nature of σ1 Receptor Ligands

The σ1 receptor (σ1-R) is an enigmatic endoplasmic reticulum resident transmembrane protein implicated in a variety of central nervous system disorders and whose agonists have neuroprotective activity. In spite of σ1-R’s physio-pathological and pharmacological importance, two of the most important features required to fully understand σ1-R function, namely the receptor endogenous ligand(s) and the molecular mechanism of ligand access to the binding site, have not yet been unequivocally determined. In this work, we performed molecular dynamics (MD) simulations to help clarify the potential route of access of ligand(s) to the σ1-R binding site, on which discordant results had been reported in the literature. Further, we combined computational and experimental procedures (i.e., virtual screening (VS), electron density map fitting and fluorescence titration experiments) to provide indications about the nature of σ1-R endogenous ligand(s). Our MD simulations on human σ1-R suggested that ligands access the binding site through a cavity that opens on the protein surface in contact with the membrane, in agreement with previous experimental studies on σ1-R from Xenopus laevis. Additionally, steroids were found to be among the preferred σ1-R ligands predicted by VS, and 16,17-didehydroprogesterone was shown by fluorescence titration to bind human σ1-R, with significantly higher affinity than the prototypic σ1-R ligand pridopidine in the same essay. These results support the hypothesis that steroids are among the most important physiological σ1-R ligands.

Naringin enhances long-term potentiation and recovers learning and memory deficits of amyloid-beta induced Alzheimer's disease-like behavioral rat model

Alzheimer's disease (AD), as the most typical type of dementia, is a chronic neurodegenerative disorder characterized by progressive learning and memory impairment. It is known that the main causes of AD are the accumulation of β-amyloid (Aβ) plaques and neurofibrillary tangles (NFT) containing hyperphosphorylated tau protein. Naringin is a flavonoid from citrus fruits, especially in grapefruit, which has anti-inflammatory, antioxidant, anti-apoptotic, and neuroprotective activities. However, the effect of naringin in AD caused by Aβ has not been clearly studied, and there are few studies on the electrophysiological aspect. Thus, we investigated the ex vivo neuroprotective effect of naringin through the long-term potentiation (LTP) on organotypic hippocampal slice cultures. We evaluated the in vivo effects of naringin (100 mg/kg/day) orally treated for 20 days on learning, memory, and cognition which was impaired by bilateral CA1 subregion injection of Aβ. Cognitive behaviors were measured 2 weeks after Aβ injection using behavioral tests and the hippocampal expression of apoptotic and neurotrophic regulators were measured by immunoblotting. In hippocampal tissue slices, naringin dose-dependently increased the field excitatory postsynaptic potential (fEPSP) after theta burst stimulation and attenuated Aβ-induced blockade of fEPSP in the hippocampal CA1 area. In Aβ injected rats, naringin improved object recognition memory in the novel object test, avoidance memory in the passive avoidance test and spatial recognition memory in the Morris water maze test. In the hippocampus, naringin attenuated the Aβ-induced cyclooxygenase-2, Bax activation and Bcl-2, CREB, BDNF and TrkB inhibition. These results suggest that naringin has therapeutic potential to reduce neuronal inflammation and apoptosis induced by Aβ related with the BDNF/TrkB/CREB signaling.

Overview of Sigma-1R Subcellular Specific Biological Functions and Role in Neuroprotection

For the past several years, fundamental research on Sigma-1R (S1R) protein has unveiled its necessity for maintaining proper cellular homeostasis through modulation of calcium and lipid exchange between the endoplasmic reticulum (ER) and mitochondria, ER-stress response, and many other mechanisms. Most of these processes, such as ER-stress response and autophagy, have been associated with neuroprotective roles. In fact, improving these mechanisms using S1R agonists was beneficial in several brain disorders including neurodegenerative diseases. In this review, we will examine S1R subcellular localization and describe S1R-associated biological activity within these specific compartments, i.e., the Mitochondrion-Associated ER Membrane (MAM), ER-Lipid Droplet (ER-LD) interface, ER-Plasma Membreane (ER-PM) interface, and the Nuclear Envelope (NE). We also discussed how the dysregulation of these pathways contributes to neurodegenerative diseases, while highlighting the cellular mechanisms and key binding partners engaged in these processes.

Chaperone-Dependent Mechanisms as a Pharmacological Target for Neuroprotection

Modern pharmacotherapy of neurodegenerative diseases is predominantly symptomatic and does not allow vicious circles causing disease development to break. Protein misfolding is considered the most important pathogenetic factor of neurodegenerative diseases. Physiological mechanisms related to the function of chaperones, which contribute to the restoration of native conformation of functionally important proteins, evolved evolutionarily. These mechanisms can be considered promising for pharmacological regulation. Therefore, the aim of this review was to analyze the mechanisms of endoplasmic reticulum stress (ER stress) and unfolded protein response (UPR) in the pathogenesis of neurodegenerative diseases. Data on BiP and Sigma1R chaperones in clinical and experimental studies of Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and Huntington's disease are presented. The possibility of neuroprotective effect dependent on Sigma1R ligand activation in these diseases is also demonstrated. The interaction between Sigma1R and BiP-associated signaling in the neuroprotection is discussed. The performed analysis suggests the feasibility of pharmacological regulation of chaperone function, possibility of ligand activation of Sigma1R in order to achieve a neuroprotective effect, and the need for further studies of the conjugation of cellular mechanisms controlled by Sigma1R and BiP chaperones.

Role of amyloid beta (25-35) neurotoxicity in the ferroptosis and necroptosis as modalities of regulated cell death in Alzheimer's disease

Neuronal cell death as a prominent pathological feature contributes to cognitive decline and memory loss in Alzheimer's disease. We investigated the role of two forms of cell death pathways, ferroptosis and necroptosis, and their interactions following entorhinal cortex (EC) amyloidopathy. The Aβ_25-35 was bilaterally injected into the rat's EC, and Morris Water Maze was applied to determine spatial performance one week after Aβ injection. For evaluation of ferroptosis and necroptosis involvement in Aβ induced pathology, ferroptosis inhibitor, Ferrostatin (Fer-1), and necroptosis inhibitor, Necrostatin (Nec-1), were injected into the EC during training days of behavioral test. Our behavioral and histological assessment showed spatial learning and memory impairment, along with neuropathology changes such as cell survival and intracellular Aβ deposits in response to EC amyloidopathy, which were ameliorated by treatment with Fer-1 or Nec-1. The expression of ferroptosis key factors GPX4 and SLC7A11 were decreased and the level of TfR was increased following Aβ toxicity. Also, Necroptosis pathway related factors RIP1, RIP3, and MLKL were modulated by Aβ neurotoxicity. However, application of Fer-1 or Nec-1 could inhibit the hippocampal ferroptosis and necroptosis pathways due to EC amyloidopathy. Our data also demonstrated that Aβ-induced necroptosis suppressed by Fer-1, although Nec-1 had no effect on ferroptosis, indicating that ferroptosis pathway is upstream of necroptosis process in the Aβ neurotoxicity. Moreover, Aβ induced hippocampal mGLUR5 overexpression and reduced level of STIM1/2 recovered by Fer-1 or Nec-1. According to our findings ferroptosis and necroptosis pathways are involved in Aβ neurotoxicity through modulation of mGLUR5 and STIM1/2 signaling.

Study of neuroprotective activity of new acetylcholinesterase inhibitors TVA and TVS in experimental model of Alzheimer’s disease

Introduction: Alzheimer’s disease (AD) is a severe neurodegenerative disease characterized by loss of synaptic connection between neurons of the cortex and subcortical regions. The cholinergic deficit is a consistent and early finding in AD, hence acetylcholinesterase inhibitors (AChEIs) are used for symptomatic improvement of AD. Most of these therapeutic agents are hepatotoxic, leading to liver failure and other complications. Therefore, the study of new AChEIs with less toxic impact and better effectivity is a topical challenge. In view of this, we synthesized novel chemical compounds: TVA and TVS that possess AChEI activity and studied their neuroprotective effect in an experimental AD model.

Materials and methods: Studies were performed on white rats. Acute toxicity studies were performed by Karber’s method. AD was induced via bilateral intracerebroventricular administration of Aβ 25–35. Histopathological examinations were performed in the hippocampus and the entorhinal cortex. Liver tissue was additionally examined to monitor the hepatotoxicity of these compounds.

Results: Studies of the hippocampus showed that compared to control and TVA-treated groups, under the influence of TVS there were few morphological alterations. Experimental groups showed an increase in the glial cell count, compared to the intact animals. In comparison to the AD group, the increase in microglia was not that prominent under the action of the novel compounds. Under the influence of TVA and TVS, the entorhinal cortex was more susceptible to neuronal injury, although TVS protected pyramidal neurons. Also, the group treated with TVA had signs of acute liver damage, while under the influence of TVS there were no signs of liver changes.

Discussion: Histopathological examination showed that the neurodegenerative processes in the hippocampus, as well as in the entorhinal cortex, were significantly reduced under the influence of TVS, compared with the control group. At the same time, TVA had no significant effect on the protection of neuronal cells. Also, TVS was less toxic, and there was no sign of hepatotoxicity during the experiments.

Conclusion: These studies demonstrated that TVS possesses neuroprotective activity and reduces neuronal damage induced by Aβ.

Graphical abstract:

Endoplasmic Reticulum-Mitochondria Contacts Modulate Reactive Oxygen Species-Mediated Signaling and Oxidative Stress in Brain Disorders: The Key Role of Sigma-1 Receptor

Significance: Mitochondria-Associated Membranes (MAMs) are highly dynamic endoplasmic reticulum (ER)-mitochondria contact sites that, due to the transfer of lipids and Ca2+ between these organelles, modulate several physiologic processes, such as ER stress response, mitochondrial bioenergetics and fission/fusion events, autophagy, and inflammation. In addition, these contacts are implicated in the modulation of the cellular redox status since several MAMs-resident proteins are involved in the generation of reactive oxygen species (ROS), which can act as both signaling mediators and deleterious molecules, depending on their intracellular levels. Recent Advances: In the past few years, structural and functional alterations of MAMs have been associated with the pathophysiology of several neurodegenerative diseases that are closely associated with the impairment of several MAMs-associated events, including perturbation of the redox state on the accumulation of high ROS levels. Critical Issues: Inter-organelle contacts must be tightly regulated to preserve cellular functioning by maintaining Ca2+ and protein homeostasis, lipid metabolism, mitochondrial dynamics and energy production, as well as ROS signaling. Simultaneously, these contacts should avoid mitochondrial Ca2+ overload, which might lead to energetic deficits and deleterious ROS accumulation, culminating in oxidative stress-induced activation of apoptotic cell death pathways, which are common features of many neurodegenerative diseases. Future Directions: Given that Sig-1R is an ER resident chaperone that is highly enriched at the MAMs and that controls ER to mitochondria Ca2+ flux, as well as oxidative and ER stress responses, its potential as a therapeutic target for neurodegenerative diseases such as Amyotrophic Lateral Sclerosis, Alzheimer, Parkinson, and Huntington diseases should be further explored. Antioxid. Redox Signal. 37, 758-780.

Haloperidol Prevents Oxytosis/Ferroptosis by Targeting Lysosomal Ferrous Ions in a Manner Independent of Dopamine D2 and Sigma-1 Receptors

Haloperidol is a widely used antipsychotic agent that exerts antipsychotic effects through a strong antagonism of dopamine D2 receptors. In addition, haloperidol is classified as a sigma-1 receptor (S1R) antagonist that prevents endogenous oxidative stress in cultured cells. However, pharmacological activities of haloperidol against oxidative stress remain unclear. Oxytosis/ferroptosis are iron-dependent nonapoptotic oxidative cell deaths that are regarded as two names for the same cell death pathway and the potential physiological relevance of oxytosis/ferroptosis in multiple diseases is suggested. In the present study, the effects of haloperidol on oxytosis/ferroptosis were investigated in S1R-knockdown mouse hippocampal HT22 cells. The results indicate that haloperidol is a strong inhibitor of oxytosis/ferroptosis independent of S1R. Imaging of HT22 cells with a newly developed fluorescent probe showed that haloperidol was localized to late endosomes and lysosomes and reduced the accumulation of lysosomal ferrous ions, resulting in reduced production of intracellular reactive oxygen species and inhibition of cell death. These results indicate that haloperidol is useful not only as an antipsychotic agent but also as a neuroprotective agent against endogenous oxidative stress via distinct mechanisms. Furthermore, lysosome-targeting ferroptosis inhibitors could be useful for the treatment of various diseases, including cancers, ischemia-reperfusion injury, and neurodegenerative disorders, which have been associated with ferroptosis.

Antidepressive-like Behavior-Related Metabolomic Signatures of Sigma-1 Receptor Knockout Mice

Sigma-1 receptor (Sig1R) has been proposed as a therapeutic target for neurological, neurodegenerative, and psychiatric disorders, including depression and anxiety. Identifying metabolites that are affected by Sig1R absence and cross-referencing them with specific mood-related behaviors would be helpful for the development of new therapies for Sig1R-associated disorders. Here, we examined metabolic profiles in the blood and brains of male CD-1 background Sig1R knockout (KO) mice in adulthood and old age and correlated them with the assessment of depression- and anxiety-related behaviors. The most pronounced changes in the metabolic profile were observed in the plasma of adult Sig1R KO mice. In adult mice, the absence of Sig1R significantly influenced the amino acid, sphingolipid (sphingomyelin and ceramide (18:1)), and serotonin metabolic pathways. There were higher serotonin levels in plasma and brain tissue and higher histamine levels in the plasma of Sig1R KO mice than in their age-matched wild-type counterparts. This increase correlated with the reduced behavioral despair in the tail suspension test and lack of anhedonia in the sucrose preference test. Overall, these results suggest that Sig1R regulates behavior by altering serotonergic and histaminergic systems and the sphingolipid metabolic pathway.

Sigma-1 Receptors in Depression: Mechanism and Therapeutic Development

Depression is the most common type of neuropsychiatric illness and has increasingly become a major cause of disability. Unfortunately, the recent global pandemic of COVID-19 has dramatically increased the incidence of depression and has significantly increased the burden of mental health care worldwide. Since full remission of the clinical symptoms of depression has not been achieved with current treatments, there is a constant need to discover new compounds that meet the major clinical needs. Recently, the roles of sigma receptors, especially the sigma-1 receptor subtype, have attracted increasing attention as potential new targets and target-specific drugs due to their translocation property that produces a broad spectrum of biological functions. Even clinical first-line antidepressants with or without affinity for sigma-1 receptors have different pharmacological profiles. Thus, the regulatory role of sigma-1 receptors might be useful in treating these central nervous system (CNS) diseases. In addition, long-term mental stress disrupts the homeostasis in the CNS. In this review, we discuss the topical literature concerning sigma-1 receptor antidepressant mechanism of action in the regulation of intracellular proteostasis, calcium homeostasis and especially the dynamic Excitatory/Inhibitory (E/I) balance in the brain. Furthermore, based on these discoveries, we discuss sigma-1 receptor ligands with respect to their promise as targets for fast-onset action drugs in treating depression.

Impact of Two Neuronal Sigma-1 Receptor Modulators, PRE084 and DMT, on Neurogenesis and Neuroinflammation in an Aβ1-42-Injected, Wild-Type Mouse Model of AD

Alzheimer's disease (AD) is the most common form of dementia characterized by cognitive dysfunctions. Pharmacological interventions to slow the progression of AD are intensively studied. A potential direction targets neuronal sigma-1 receptors (S1Rs). S1R ligands are recognized as promising therapeutic agents that may alleviate symptom severity of AD, possibly via preventing amyloid-β-(Aβ-) induced neurotoxicity on the endoplasmic reticulum stress-associated pathways. Furthermore, S1Rs may also modulate adult neurogenesis, and the impairment of this process is reported to be associated with AD. We aimed to investigate the effects of two S1R agonists, dimethyltryptamine (DMT) and PRE084, in an Aβ-induced in vivo mouse model characterizing neurogenic and anti-neuroinflammatory symptoms of AD, and the modulatory effects of S1R agonists were analyzed by immunohistochemical methods and western blotting. DMT, binding moderately to S1R but with high affinity to 5-HT receptors, negatively influenced neurogenesis, possibly as a result of activating both receptors differently. In contrast, the highly selective S1R agonist PRE084 stimulated hippocampal cell proliferation and differentiation. Regarding neuroinflammation, DMT and PRE084 significantly reduced Aβ1-42-induced astrogliosis, but neither had remarkable effects on microglial activation. In summary, the highly selective S1R agonist PRE084 may be a promising therapeutic agent for AD. Further studies are required to clarify the multifaceted neurogenic and anti-neuroinflammatory roles of these agonists.

Activation of the sigma-1 receptor chaperone alleviates symptoms of Wolfram syndrome in preclinical models

The Wolfram syndrome is a rare autosomal recessive disease affecting many organs with life-threatening consequences; currently, no treatment is available. The disease is caused by mutations in the WSF1 gene, coding for the protein wolframin, an endoplasmic reticulum (ER) transmembrane protein involved in contacts between ER and mitochondria termed as mitochondria-associated ER membranes (MAMs). Inherited mutations usually reduce the protein's stability, altering its homeostasis and ultimately reducing ER to mitochondria calcium ion transfer, leading to mitochondrial dysfunction and cell death. In this study, we found that activation of the sigma-1 receptor (S1R), an ER-resident protein involved in calcium ion transfer, could counteract the functional alterations of MAMs due to wolframin deficiency. The S1R agonist PRE-084 restored calcium ion transfer and mitochondrial respiration in vitro, corrected the associated increased autophagy and mitophagy, and was able to alleviate the behavioral symptoms observed in zebrafish and mouse models of the disease. Our findings provide a potential therapeutic strategy for treating Wolfram syndrome by efficiently boosting MAM function using the ligand-operated S1R chaperone. Moreover, such strategy might also be relevant for other degenerative and mitochondrial diseases involving MAM dysfunction.

Fenfluramine modulates the anti-amnesic effects induced by sigma-1 receptor agonists and neuro(active)steroids in vivo

Fenfluramine (N-ethyl-α-methl-3-(trifluoromethyl)phenethylamine) is an anti-seizure medication (ASM) particularly effective in patients with Dravet syndrome, a severe treatment-resistant epileptic encephalopathy. Fenfluramine acts not only as neuronal serotonin (5-HT) releaser but also as a positive modulator of the sigma-1 receptor (S1R). We here examined the modulatory activity of Fenfluramine on the S1R-mediated anti-amnesic response in mice using combination analyses. Fenfluramine and Norfenfluramine, racemate and isomers, were combined with either the S1R agonist (PRE-084) or the S1R-acting neuro(active)steroids, pregnenolone sulfate (PREGS), Dehydroepiandrosterone sulfate (DHEAS), or progesterone. We report that Fenfluramine racemate or (+)-Fenfluramine, in the 0.1-1 mg/kg dose range, attenuated the dizocilpine-induced learning deficits in spontaneous alternation and passive avoidance, and showed low-dose synergies in combination with PRE-084. These effects were blocked by the S1R antagonist NE-100. Dehydroepiandrosterone sulfate or PREGS attenuated dizocilpine-induced learning deficits in the 5-20 mg/kg dose range. Co-treatments at low dose between steroids and Fenfluramine or (+)-Fenfluramine were synergistic. Progesterone blocked Fenfluramine effect. Finally, Fenfluramine and (+)-Fenfluramine effects were prevented by the 5-HT1A receptor antagonist WAY-100635 or 5-HT2A antagonist RS-127445, but not by the 5-HT1B/1D antagonist GR 127935 or the 5-HT2C antagonist SB 242084, confirming a 5-HT1A and 5-HT2A receptor involvement in the drug effect on memory. We therefore confirmed the positive modulation of Fenfluramine racemate or dextroisomer on S1R and showed that, in physiological conditions, the drug potentiated the low dose effects of neuro(active)steroids, endogenous S1R modulators. The latter are potent modulators of the excitatory/inhibitory balance in the brain, and their levels must be considered in the antiepileptic action of Fenfluramine.

Impact of ER Stress and ER-Mitochondrial Crosstalk in Huntington's Disease

Accumulation of misfolded proteins is a common phenomenon of several neurodegenerative diseases. The misfolding of proteins due to abnormal polyglutamine (PolyQ) expansions are linked to the development of PolyQ diseases including Huntington's disease (HD). Though the genetic basis of PolyQ repeats in HD remains prominent, the primary molecular basis mediated by PolyQ toxicity remains elusive. Accumulation of misfolded proteins in the ER or disruption of ER homeostasis causes ER stress and activates an evolutionarily conserved pathway called Unfolded protein response (UPR). Protein homeostasis disruption at organelle level involving UPR or ER stress response pathways are found to be linked to HD. Due to dynamic intricate connections between ER and mitochondria, proteins at ER-mitochondria contact sites (mitochondria associated ER membranes or MAMs) play a significant role in HD development. The current review aims at highlighting the most updated information about different UPR pathways and their involvement in HD disease progression. Moreover, the role of MAMs in HD progression has also been discussed. In the end, the review has focused on the therapeutic interventions responsible for ameliorating diseased states via modulating either ER stress response proteins or modulating the expression of ER-mitochondrial contact proteins.

Revisiting the sigma-1 receptor as a biological target to treat affective and cognitive disorders

Depression and cognitive disorders are diseases with complex and not-fully understood etiology. Unfortunately, the COVID-19 pandemic dramatically increased the prevalence of both conditions. Since the current treatments are inadequate in many patients, there is a constant need for discovering new compounds, which will be more effective in ameliorating depressive symptoms and treating cognitive decline. Proteins attracting much attention as potential targets for drugs treating these conditions are sigma-1 receptors. Sigma-1 receptors are multi-functional proteins localized in endoplasmic reticulum membranes, which play a crucial role in cellular signal transduction by interacting with receptors, ion channels, lipids, and kinases. Changes in their functions and expression may lead to various diseases, including depression or memory impairments. Thus, sigma-1 receptor modulation might be useful in treating these central nervous system diseases. Importantly, two sigma-1 receptor ligands entered clinical trials, showing that this compound group possesses therapeutic potential. Therefore, based on preclinical studies, this review discusses whether the sigma-1 receptor could be a promising target for drugs treating affective and cognitive disorders.

Brain-derived neurotrophic factor for high-throughput evaluation of selective Sigma-1 receptor ligands

The Sigma-1 receptor (S1R) is an endoplasmic reticulum (ER) chaperone protein that has been implicated in attenuating inflammatory stress-mediated brain injuries. Selective S1R agonists represent a new class of therapeutic agent for treating neuropsychiatric and neurodegenerative disorders, however, to date, no S1R ligand has been approved for therapeutic purposes. We used three potential methods on known and potential S1R ligands to develop an unambiguous high-throughput cell screen for S1R activity. We screened known and potential S1R ligands using radioligand binding and previously reported markers of S1R activity including BDNF release, modulation of IP3 mediated calcium release, and modulation of NGF-induced neurite sprouting. Here, we present results several prototypical S1R compounds and some compounds with the potential for drug repurposing. Using an in-situ ELISA approach we demonstrated that these compounds could stimulate S1R-mediated BDNF release, which is a valuable therapeutic property since BDNF plays a critical role in neuronal support. These compounds were classified as S1R agonists because the BDNF response was comparable to the prototypical agonist 4-PPBP and because it could be reversed by a S1R selective concentration of the antagonist BD1063. When modulation of IP3 mediated calcium response and NGF-induced neurite sprouting were used as a measure of S1R activation, we were unable to reproduce the published results and determined that they are not reliable measures for evaluating functional properties of S1R ligands.

AZP2006, a new promising treatment for Alzheimer's and related diseases

Progranulin (PGRN) is a protein with multiple functions including the regulation of neuroinflammation, neuronal survival, neurite and synapsis growth. Although the mechanisms of action of PGRN are currently unknown, its potential therapeutic application in treating neurodegenerative diseases is huge. Thus, strategies to increase PGRN levels in patients could provide an effective treatment. In the present study, we investigated the effects of AZP2006, a lysotropic molecule now in phase 2a clinical trial in Progressive Supranuclear Palsy patients, for its ability to increase PGRN level and promote neuroprotection. We showed for the first time the in vitro and in vivo neuroprotective effects of AZP2006 in neurons injured with Aβ1-42 and in two different pathological animal models of Alzheimer's disease (AD) and aging. Thus, the chronic treatment with AZP2006 was shown to reduce the loss of central synapses and neurons but also to dramatically decrease the massive neuroinflammation associated with the animal pathology. A deeper investigation showed that the beneficial effects of AZP2006 were associated with PGRN production. Also, AZP2006 binds to PSAP (the cofactor of PGRN) and inhibits TLR9 receptors normally responsible for proinflammation when activated. Altogether, these results showed the high potential of AZP2006 as a new putative treatment for AD and related diseases.

Association between Novel Object Recognition/Spontaneous Alternation Behavior and Emission of Ultrasonic Vocalizations in Rats: Possible Relevance to the Study of Memory

Rats emit ultrasonic vocalizations (USVs) in situations with emotional valence, and USVs have also been proposed as a marker for memories conditioned to those situations. This study investigated whether USV emissions can predict and/or be associated with the behavior of rats in tests that evaluate unconditioned memory. To this end, rats were subjected to “tickling”, a procedure of heterospecific play that has emotional valence and elicits the emission of USVs, and afterwards evaluated in the novel object recognition test (NOR) and in the single trial continuous spontaneous alternation behavior (SAB) test in a Y maze. The number of 22-kHz USVs (aversive) and 50-kHz USVs (appetitive) emitted in response to tickling and during NOR and SAB tests were scored, and the correlations among them and with rats’ behavior evaluated. Rats emitted 50-kHz USVs, but not 22-kHz USVs, during the NOR and SAB tests, and such calling behavior was not linked with the behavioral readouts indicative of memory function in either test. However, rats that prevalently emitted 22-kHz USVs in response to tickling displayed an impaired NOR performance. These findings suggest that measuring the emission of USVs could be of interest in studies of unconditioned memory, at least with regard to 22-kHz USVs.

An Emerging Role for Sigma-1 Receptors in the Treatment of Developmental and Epileptic Encephalopathies

Developmental and epileptic encephalopathies (DEEs) are complex conditions characterized primarily by seizures associated with neurodevelopmental and motor deficits. Recent evidence supports sigma-1 receptor modulation in both neuroprotection and antiseizure activity, suggesting that sigma-1 receptors may play a role in the pathogenesis of DEEs, and that targeting this receptor has the potential to positively impact both seizures and non-seizure outcomes in these disorders. Recent studies have demonstrated that the antiseizure medication fenfluramine, a serotonin-releasing drug that also acts as a positive modulator of sigma-1 receptors, reduces seizures and improves everyday executive functions (behavior, emotions, cognition) in patients with Dravet syndrome and Lennox-Gastaut syndrome. Here, we review the evidence for sigma-1 activity in reducing seizure frequency and promoting neuroprotection in the context of DEE pathophysiology and clinical presentation, using fenfluramine as a case example. Challenges and opportunities for future research include developing appropriate models for evaluating sigma-1 receptors in these syndromic epileptic conditions with multisystem involvement and complex clinical presentation.

Sigmar1's Molecular, Cellular, and Biological Functions in Regulating Cellular Pathophysiology

The Sigma 1 receptor (Sigmar1) is a ubiquitously expressed multifunctional inter-organelle signaling chaperone protein playing a diverse role in cellular survival. Recessive mutation in Sigmar1 have been identified as a causative gene for neuronal and neuromuscular disorder. Since the discovery over 40 years ago, Sigmar1 has been shown to contribute to numerous cellular functions, including ion channel regulation, protein quality control, endoplasmic reticulum-mitochondrial communication, lipid metabolism, mitochondrial function, autophagy activation, and involved in cellular survival. Alterations in Sigmar1’s subcellular localization, expression, and signaling has been implicated in the progression of a wide range of diseases, such as neurodegenerative diseases, ischemic brain injury, cardiovascular diseases, diabetic retinopathy, cancer, and drug addiction. The goal of this review is to summarize the current knowledge of Sigmar1 biology focusing the recent discoveries on Sigmar1’s molecular, cellular, pathophysiological, and biological functions.

Selective Pseudo-irreversible Butyrylcholinesterase Inhibitors Transferring Antioxidant Moieties to the Enzyme Show Pronounced Neuroprotective Efficacy In Vitro and In Vivo in an Alzheimer's Disease Mouse Model

A series of multitarget-directed ligands (MTDLs) was designed by functionalizing a pseudo-irreversible butyrylcholinesterase (BChE) inhibitor. The obtained hybrids were investigated in vitro regarding their hBChE and hAChE inhibition, their enzyme kinetics, and their antioxidant physicochemical properties (DPPH, ORAC, metal chelating). In addition, in vitro assays were applied to investigate antioxidant effects using murine hippocampal HT22 cells and immunomodulatory effects on the murine microglial N9 cell line. The MTDLs retained their antioxidative properties compared to the parent antioxidant-moieties in vitro and the inhibition of hBChE was maintained in the submicromolar range. Representative compounds were tested in a pharmacological Alzheimer's disease (AD) mouse model and demonstrated very high efficacy at doses as low as 0.1 mg/kg. The most promising compound was also tested in BChE^-/- mice and showed reduced efficacy. In vivo neuroprotection by BChE inhibition can be effectively enhanced by incorporation of structurally diverse antioxidant moieties.

Subcommissural Organ-Spondin-Derived Peptide Restores Memory in a Mouse Model of Alzheimer's Disease

Alzheimer’s disease (AD) is a devastating neurodegenerative disease that affects millions of older people worldwide and is characterized by a progressive deterioration of cognitive functions, including learning and memory. There are currently very few approved treatments (i.e., acetylcholinesterase inhibitors such as donepezil), all of which are limited to the symptomatic control of AD and are associated with side effects that may result in discontinuation of treatment. Therefore, there is an urgent need to develop disease-modifying treatments to prevent AD-induced cognitive deficits. Subcommissural organ (SCO)-spondin is a brain-specific glycoprotein produced during embryogenesis and has a substantial impact on neuronal development. In the current study, we sought to evaluate the protective effects of the linear (NX210) and cyclized (NX210c) forms of a SCO-spondin-derived peptide on learning and memory in a mouse model of AD. Mice received an intracerebroventricular injection of Aβ_25–35 oligomers and were subsequently treated with intraperitoneal injections of vehicle, NX210 or NX210c of different doses (ranging from 0.1 to 30 mg/kg) and therapy paradigms (early or late stand-alone treatments, combination with donepezil or second-line treatment). Cognitive function was evaluated using Y-Maze, step-through latency passive avoidance (STPA) and Morris water maze (MWM) tests for up to 4 months. Early stage daily treatment with NX210 and NX210c decreased the levels of common pathological markers and features of AD, including Aβ_1–42, phosphorylated-tau, inflammation, astrogliosis and lipid peroxidation. Meanwhile, use of these drugs increased the levels of synaptophysin and postsynaptic density protein 95. Regardless of the experimental paradigm used, NX210 and NX210c prevented Aβ_25–35-induced decrease in spontaneous alternations (Y-Maze) and step-through latency into the dark compartment (STPA), and Aβ_25–35-induced increase in time needed to locate the immersed platform during the learning phase and decrease in time spent in the target quadrant during the retention phase (MWM). Interestingly, this study provides the novel evidence that the native and oxidized cyclic forms of the SCO-spondin-derived peptide reduce pathological factors associated with AD and restore learning and memory at both early and late disease stages. Overall, this study sheds light on the therapeutic potential of this innovative disease-modifying peptide to restore memory function in patients with AD.

Differential effects of alkaloids on memory in rodents

Nicotinic acetylcholine receptors (nAChRs) play a critical role in the neuropharmacology of learning and memory. As such, naturally occurring alkaloids that regulate nAChR activity have gained interest for understanding and potentially improving memory function. In this study, we tested the acute effects of three known nicotinic alkaloids, nicotine, cotinine, and anatabine, in suppressing scopolamine-induced memory deficit in rodents by using two classic memory paradigms, Y-maze and novel object recognition (NOR) in mice and rats, respectively. We found that all compounds were able to suppress scopolamine-induced spatial memory deficit in the Y-maze spontaneous alternation paradigm. However, only nicotine was able to suppress the short-term object memory deficit in NOR, despite the higher doses of cotinine and anatabine used to account for their potential differences in nAChR activity. These results indicate that cotinine and anatabine can uniquely regulate short-term spatial memory, while nicotine seems to have more robust and general role in memory regulation in rodents. Thus, nAChR-activating alkaloids may possess distinct procognitive properties in rodents, depending on the memory types examined.

Sigma-1 Receptor (S1R) Interaction with Cholesterol: Mechanisms of S1R Activation and Its Role in Neurodegenerative Diseases

The sigma-1 receptor (S1R) is a 223 amino acid-long transmembrane endoplasmic reticulum (ER) protein. The S1R modulates the activity of multiple effector proteins, but its signaling functions are poorly understood. S1R is associated with cholesterol, and in our recent studies we demonstrated that S1R association with cholesterol induces the formation of S1R clusters. We propose that these S1R-cholesterol interactions enable the formation of cholesterol-enriched microdomains in the ER membrane. We hypothesize that a number of secreted and signaling proteins are recruited and retained in these microdomains. This hypothesis is consistent with the results of an unbiased screen for S1R-interacting partners, which we performed using the engineered ascorbate peroxidase 2 (APEX2) technology. We further propose that S1R agonists enable the disassembly of these cholesterol-enriched microdomains and the release of accumulated proteins such as ion channels, signaling receptors, and trophic factors from the ER. This hypothesis may explain the pleotropic signaling functions of the S1R, consistent with previously observed effects of S1R agonists in various experimental systems.

Bi-phasic dose response in the preclinical and clinical developments of sigma-1 receptor ligands for the treatment of neurodegenerative disorders

Introduction: The sigma-1 receptor (S1R) is attracting much attention for disease-modifying therapies in neurodegenerative diseases. It is a conserved protein, present in plasma and endoplasmic reticulum (ER) membranes and enriched in mitochondria-associated ER membranes (MAMs). It modulates ER-mitochondria Ca2+ transfer and ER stress pathways. Mitochondrial and MAM dysfunctions contribute to neurodegenerative processes in diseases such as Alzheimer, Parkinson, Huntington or Amyotrophic Lateral Sclerosis. Interestingly, the S1R can be activated by small druggable molecules and accumulating preclinical data suggest that S1R agonists are effective protectants in these neurodegenerative diseases.Area covered: In this review, we will present the data showing the high therapeutic potential of S1R drugs for the treatment of neurodegenerative diseases, focusing on pridopidine as a potent and selective S1R agonist under clinical development. Of particular interest is the bi-phasic (bell-shaped) dose-response effect, representing a common feature of all S1R agonists and described in numerous preclinical models in vitro, in vivo and in clinical trials.Expert opinion: S1R agonists modulate inter-organelles communication altered in neurodegenerative diseases and activate intracellular survival pathways. Research will continue growing in the future. The particular cellular nature of this chaperone protein must be better understood to facilitate the clinical developement of promising molecules.

Biosynthesis and signalling functions of central and peripheral nervous system neurosteroids in health and disease

Neurosteroids are steroid hormones synthesised de novo in the brain and peripheral nervous tissues. In contrast to adrenal steroid hormones that act on intracellular nuclear receptors, neurosteroids directly modulate plasma membrane ion channels and regulate intracellular signalling. This review provides an overview of the work that led to the discovery of neurosteroids, our current understanding of their intracellular biosynthetic machinery, and their roles in regulating the development and function of nervous tissue. Neurosteroids mediate signalling in the brain via multiple mechanisms. Here, we describe in detail their effects on GABA (inhibitory) and NMDA (excitatory) receptors, two signalling pathways of opposing function. Furthermore, emerging evidence points to altered neurosteroid function and signalling in neurological disease. This review focuses on neurodegenerative diseases associated with altered neurosteroid metabolism, mainly Niemann-Pick type C, multiple sclerosis and Alzheimer disease. Finally, we summarise the use of natural and synthetic neurosteroids as current and emerging therapeutics alongside their potential use as disease biomarkers.

Psychedelics in Psychiatry: Neuroplastic, Immunomodulatory, and Neurotransmitter Mechanisms

Mounting evidence suggests safety and efficacy of psychedelic compounds as potential novel therapeutics in psychiatry. Ketamine has been approved by the Food and Drug Administration in a new class of antidepressants, and 3,4-methylenedioxymethamphetamine (MDMA) is undergoing phase III clinical trials for post-traumatic stress disorder. Psilocybin and lysergic acid diethylamide (LSD) are being investigated in several phase II and phase I clinical trials. Hence, the concept of psychedelics as therapeutics may be incorporated into modern society. Here, we discuss the main known neurobiological therapeutic mechanisms of psychedelics, which are thought to be mediated by the effects of these compounds on the serotonergic (via 5-HT_2A and 5-HT_1A receptors) and glutamatergic [via N-methyl-d-aspartate (NMDA) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors] systems. We focus on 1) neuroplasticity mediated by the modulation of mammalian target of rapamycin-, brain-derived neurotrophic factor-, and early growth response-related pathways; 2) immunomodulation via effects on the hypothalamic-pituitary-adrenal axis, nuclear factor ĸB, and cytokines such as tumor necrosis factor-α and interleukin 1, 6, and 10 production and release; and 3) modulation of serotonergic, dopaminergic, glutamatergic, GABAergic, and norepinephrinergic receptors, transporters, and turnover systems. We discuss arising concerns and ways to assess potential neurobiological changes, dependence, and immunosuppression. Although larger cohorts are required to corroborate preliminary findings, the results obtained so far are promising and represent a critical opportunity for improvement of pharmacotherapies in psychiatry, an area that has seen limited therapeutic advancement in the last 20 years. Studies are underway that are trying to decouple the psychedelic effects from the therapeutic effects of these compounds. SIGNIFICANCE STATEMENT: Psychedelic compounds are emerging as potential novel therapeutics in psychiatry. However, understanding of molecular mechanisms mediating improvement remains limited. This paper reviews the available evidence concerning the effects of psychedelic compounds on pathways that modulate neuroplasticity, immunity, and neurotransmitter systems. This work aims to be a reference for psychiatrists who may soon be faced with the possibility of prescribing psychedelic compounds as medications, helping them assess which compound(s) and regimen could be most useful for decreasing specific psychiatric symptoms.

Sigma-1 receptor chaperones rescue nucleocytoplasmic transport deficit seen in cellular and Drosophila ALS/FTD models

In a subgroup of patients with amyotrophic lateral sclerosis (ALS)/Frontotemporal dementia (FTD), the (G4C2)-RNA repeat expansion from C9orf72 chromosome binds to the Ran-activating protein (RanGAP) at the nuclear pore, resulting in nucleocytoplasmic transport deficit and accumulation of Ran in the cytosol. Here, we found that the sigma-1 receptor (Sig-1R), a molecular chaperone, reverses the pathological effects of (G4C2)-RNA repeats in cell lines and in Drosophila. The Sig-1R colocalizes with RanGAP and nuclear pore proteins (Nups) and stabilizes the latter. Interestingly, Sig-1Rs directly bind (G4C2)-RNA repeats. Overexpression of Sig-1Rs rescues, whereas the Sig-1R knockout exacerbates, the (G4C2)-RNA repeats-induced aberrant cytoplasmic accumulation of Ran. In Drosophila, Sig-1R (but not the Sig-1R-E102Q mutant) overexpression reverses eye necrosis, climbing deficit, and firing discharge caused by (G4C2)-RNA repeats. These results on a molecular chaperone at the nuclear pore suggest that Sig-1Rs may benefit patients with C9orf72 ALS/FTD by chaperoning the nuclear pore assembly and sponging away deleterious (G4C2)-RNA repeats.

Disruption of Cholinergic Circuits as an Area for Targeted Drug Treatment of Alzheimer's Disease: In Vivo Assessment of Short-Term Plasticity in Rat Brain

The search for new therapeutics for the treatment of Alzheimer’s disease (AD) is still in progress. Aberrant pathways of synaptic transmission in basal forebrain cholinergic neural circuits are thought to be associated with the progression of AD. However, the effect of amyloid-beta (Aβ) on short-term plasticity (STP) of cholinergic circuits in the nucleus basalis magnocellularis (NBM) is largely unknown. STP assessment in rat brain cholinergic circuitry may indicate a new target for AD cholinergic therapeutics. Thus, we aimed to study in vivo electrophysiological patterns of synaptic activity in NBM-hippocampus and NBM-basolateral amygdala circuits associated with AD-like neurodegeneration. The extracellular single-unit recordings of responses from the hippocampal and basolateral amygdala neurons to high-frequency stimulation (HFS) of the NBM were performed after intracerebroventricular injection of Aβ 25–35. We found that after Aβ 25–35 exposure the number of hippocampal neurons exhibiting inhibitory responses to HFS of NBM is decreased. The reverse tendency was seen in the basolateral amygdala inhibitory neural populations, whereas the number of amygdala neurons with excitatory responses decreased. The low intensity of inhibitory and excitatory responses during HFS and post-stimulus period is probably due to the anomalous basal synaptic transmission and excitability of hippocampal and amygdala neurons. These functional changes were accompanied by structural alteration of hippocampal, amygdala, and NBM neurons. We have thus demonstrated that Aβ 25–35 induces STP disruption in NBM-hippocampus and NBM-basolateral amygdala circuits as manifested by unbalanced excitatory/inhibitory responses and their frequency. The results of this study may contribute to a better understanding of synaptic integrity. We believe that advancing our understanding of in vivo mechanisms of synaptic plasticity disruption in specific neural circuits could lead to effective drug searches for AD treatment.

Mitochondrial Movement and Number Deficits in Embryonic Cortical Neurons from 3xTg-AD Mice

Mitochondrial dysfunction is often found in Alzheimer's disease (AD) patients and animal models. Clinical severity of AD is linked to early deficiencies in cognitive function and brain metabolism, indicating that pathological changes may begin early in life. Previous studies showed decreased mitochondrial function in primary hippocampal neurons from triple-transgenic Alzheimer's disease (3xTg-AD) mice and mitochondrial movement and structure deficits in primary neurons exposed to amyloid-β oligomers. The present study characterized mitochondrial movement, number, and structure in 3xTg-AD primary cortical neurons and non-transgenic (nonTg) controls. We found a significant reduction in mitochondrial number and movement in 3xTg-AD primary cortical neurons with modest structural changes. Additionally, application of the sigma-1 receptor agonist, (+)SKF-10,047, markedly increased mitochondrial movement in both 3xTg-AD and nonTg primary cortical cultures after one hour of treatment. (+)SKF-10,047 also led to a trend of increased mitochondrial number in 3xTg-AD cultures. Embryonic mitochondrial movement and number deficits could be among the key steps in the early pathogenesis of AD that compromise cognitive or metabolic reserve, and amelioration of these deficits could be a promising area for further preclinical and clinical study.

PRE-084 as a tool to uncover potential therapeutic applications for selective sigma-1 receptor activation

The discovery of a highly selective putative sigma-1 (σ1) receptor agonist, PRE-084, has revealed the numerous potential uses of this receptor subtype as a therapeutic target. While much work has been devoted to determining the role of σ1 receptors in normal and pathophysiological states in the nervous system, recent work suggests that σ1 receptors may be important for modulating functions of other tissues. These discoveries have provided novel insights into σ1 receptor structure, function, and importance in multiple intracellular signaling mechanisms. These discoveries were made possible by σ1 receptor-selective agonists such as PRE-084. The chemical properties and pharmacological actions of PRE-084 will be reviewed here, along with the expanding list of potential therapeutic applications for selective activation of σ1 receptors.

Steroids and Alzheimer's Disease: Changes Associated with Pathology and Therapeutic Potential

Alzheimer's disease (AD) is a multifactorial age-related neurodegenerative disease that today has no effective treatment to prevent or slow its progression. Neuroactive steroids, including neurosteroids and sex steroids, have attracted attention as potential suitable candidates to alleviate AD pathology. Accumulating evidence shows that they exhibit pleiotropic neuroprotective properties that are relevant for AD. This review focuses on the relationship between selected neuroactive steroids and the main aspects of AD disease, pointing out contributions and gaps with reference to sex differences. We take into account the regulation of brain steroid concentrations associated with human AD pathology. Consideration is given to preclinical studies in AD models providing current knowledge on the neuroprotection offered by neuroactive (neuro)steroids on major AD pathogenic factors, such as amyloid-β (Aβ) and tau pathology, mitochondrial impairment, neuroinflammation, neurogenesis and memory loss. Stimulating endogenous steroid production opens a new steroid-based strategy to potentially overcome AD pathology. This article is part of a Special Issue entitled Steroids and the Nervous System.

Steroids and TRP Channels: A Close Relationship

Transient receptor potential (TRP) channels are remarkable transmembrane protein complexes that are essential for the physiology of the tissues in which they are expressed. They function as non-selective cation channels allowing for the signal transduction of several chemical, physical and thermal stimuli and modifying cell function. These channels play pivotal roles in the nervous and reproductive systems, kidney, pancreas, lung, bone, intestine, among others. TRP channels are finely modulated by different mechanisms: regulation of their function and/or by control of their expression or cellular/subcellular localization. These mechanisms are subject to being affected by several endogenously-produced compounds, some of which are of a lipidic nature such as steroids. Fascinatingly, steroids and TRP channels closely interplay to modulate several physiological events. Certain TRP channels are affected by the typical genomic long-term effects of steroids but others are also targets for non-genomic actions of some steroids that act as direct ligands of these receptors, as will be reviewed here.

[New therapeutic avenues for neurosteroids in psychiatric diseases]

Discovered in the eighties by Pr Baulieu and colleagues, neurosteroids are a class of neuroactive brain-born steroids, which comprises the steroid hormones, their biosynthesis precursors and their metabolites. They can act through genomic as well as non-genomic pathways. Genomic pathways, only triggered by the neurosteroid hormones, are, in the brain, the same as those largely described in the periphery: the binding of these steroid hormones to nuclear receptors leads to transcription regulations. On the other hand, their precursors and metabolites, such as pregnenolone (PREG), dehydroepiandrosterone (DHEA), their respective sulfate esters, pregnenolone sulfate (PREG-S) and DHEA sulfate (DHEA-S) and allopregnanolone (ALLOP), are defined as neurosteroids, but no corresponding nuclear receptors have been identified so far. In fact, they trigger non-genomic pathways which consist in (i) inhibitory ionotropic receptors, (ii) excitatory ionotropic receptors and (iii) the microtubular system. Hence, inhibitory neurosteroids, whose mostly studied representative is ALLOP, positively modulate, or directly activate, the ionotropic GABA-A receptors. In contrast, excitatory neurosteroids, represented by PREG-S, DHEA-S and DHEA, inhibit the GABA-A receptors, and activate, directly or indirectly, through the sigma-1 receptors, the NMDA glutamate receptors. Neurosteroids of the third group, the microtubular neurosteroids, are able to bind microtubule associated proteins, in particular MAP2, to promote microtubule assembly, neurite outgrowth and in fine structural neuroplasticity. So far, PREG, DHEA and progesterone are the three identified microtubular neurosteroids. The pharmacological properties of neurosteroids have led to specific investigations for assessing their therapeutic potentialities in psychiatric diseases, using validated animal models. In some cases, clinical trials were also performed. These studies showed that ALLOP, the main inhibitory neurosteroid, displayed clear-cut anxiolytic-like and antidepressant-like efficacy in animals. It has been subsequently developed as Brexanolone and tested with success in phase III of clinical trials for the treatment of post-partum depression. Although showing pro-cognitive properties in animals, the sulfated neurosteroids, PREG-S and DHEA-S, were, in contrast, never tested in clinical trials, probably due to their poor stability and proconvulsivant side effects. Their respective non-sulfated forms, PREG and DHEA, showed antidepressant and antipsychotic efficacies in clinical trials, but these drugs never reached the phase III of clinical development because their therapeutic uses would have led to an overproduction of active metabolites responsible for intolerable side effects. The alternative strategy which has been selected consists of the development of non-metabolizable synthetic derivatives of these natural steroids, which keep the same neuroactive properties as their parent molecules, but are devoid of any hormonal side effects. An example of such innovative drugs is MAP4343, a synthetic derivative of PREG, which exhibits potent antidepressant-like efficacy in validated animal models. It is currently tested in depressed patients.

Fenfluramine acts as a positive modulator of sigma-1 receptors

OBJECTIVE

Adjunctive fenfluramine hydrochloride, classically described as acting pharmacologically through a serotonergic mechanism, has demonstrated a unique and robust clinical response profile with regard to its magnitude, consistency, and durability of effect on seizure activity in patients with pharmacoresistant Dravet syndrome. Recent findings also support long-term improvements in executive functions (behavior, emotion, cognition) in these patients. The observed clinical profile is inconsistent with serotonergic activity alone, as other serotonergic medications have not been demonstrated to have these clinical effects. This study investigated a potential role for σ1 receptor activity in complementing fenfluramine's serotonergic pharmacology.

METHODS

Radioligand binding assays tested the affinity of fenfluramine for 47 receptors associated with seizures in the literature, including σ receptors. Cellular function assays tested fenfluramine and norfenfluramine (its major metabolite) activity at various receptors, including adrenergic, muscarinic, and serotonergic receptors. The σ1 receptor activity was assessed by the mouse vas deferens isometric twitch and by an assay of dissociation of the σ1 receptor from the endoplasmic reticulum stress protein binding immunoglobulin protein (BiP). In vivo mouse models assessed fenfluramine activity at σ1 receptors in ameliorating dizocilpine-induced learning deficits in spatial and nonspatial memory tasks, alone or in combination with the reference σ1 receptor agonist PRE-084.

RESULTS

Fenfluramine and norfenfluramine bound ≥30% to β2-adrenergic, muscarinic M1, serotonergic 5-HT1A, and σ receptors, as well as sodium channels, with a Ki between 266 nM (σ receptors) and 17.5 μM (β-adrenergic receptors). However, only σ1 receptor isometric twitch assays showed a positive functional response, with weak stimulation by fenfluramine and inhibition by norfenfluramine. Fenfluramine, but not the 5-HT2C agonist lorcaserin, showed a positive modulation of the PRE-084-induced dissociation of σ1 protein from BiP. Fenfluramine also showed dose-dependent antiamnesic effects against dizocilpine-induced learning deficits in spontaneous alternation and passive avoidance responses, which are models of σ1 activation. Moreover, low doses of fenfluramine synergistically potentiated the low-dose effect of PRE-084, confirming a positive modulatory effect at the σ1 receptor. Finally, all in vivo effects were blocked by the σ1 receptor antagonist NE-100.

SIGNIFICANCE

Fenfluramine demonstrated modulatory activity at σ1 receptors in vitro and in vivo in addition to its known serotonergic activity. These studies identify a possible new σ1 receptor mechanism underpinning fenfluramine's central nervous system effects, which may contribute to its antiseizure activity in Dravet syndrome and positive effects observed on executive functions in clinical studies.

Dual-Acting Cholinesterase-Human Cannabinoid Receptor 2 Ligands Show Pronounced Neuroprotection in Vitro and Overadditive and Disease-Modifying Neuroprotective Effects in Vivo

We have designed and synthesized a series of 14 hybrid molecules out of the cholinesterase (ChE) inhibitor tacrine and a benzimidazole-based human cannabinoid receptor subtype 2 (hCB2R) agonist and investigated them in vitro and in vivo. The compounds are potent ChE inhibitors, and for the most promising hybrids, the mechanism of human acetylcholinesterase (hAChE) inhibition as well as their ability to interfere with AChE-induced aggregation of β-amyloid (Aβ), and Aβ self-aggregation was assessed. All hybrids were evaluated for affinity and selectivity for hCB1R and hCB2R. To ensure that the hybrids retained their agonist character, the expression of cAMP-regulated genes was quantified, and potency and efficacy were determined. Additionally, the effects of the hybrids on microglia activation and neuroprotection on HT-22 cells were investigated. The most promising in vitro hybrids showed pronounced neuroprotection in an Alzheimer's mouse model at low dosage (0.1 mg/kg, i.p.), lacking hepatotoxicity even at high dose (3 mg/kg, i.p.).

Small-Molecule Modulators of Sigma1 and Sigma2/TMEM97 in the Context of Cancer: Foundational Concepts and Emerging Themes

There are two known subtypes of the so-called sigma receptors, Sigma1 and Sigma2. Sigma1 (encoded by the SIGMAR1 gene and also known as Sigma-1 receptor, S1R) is a unique pharmacologically regulated integral membrane chaperone or scaffolding protein that allosterically modulates the activity of its associated proteins. Sigma2, recently identified as transmembrane protein 97 (TMEM97), is an integral membrane protein implicated in cellular cholesterol homeostasis. A number of publications over the past two decades have suggested a role for both sigma proteins in tumor biology. Although there is currently no clinically used anti-cancer drug that targets Sigma1 or Sigma2/TMEM97, a growing body of evidence supports the potential of small-molecule compounds with affinity for these proteins, putative sigma ligands, as therapeutic agents to treat cancer. In preclinical models, these compounds have been reported to inhibit cancer cell proliferation, survival, adhesion, and migration; furthermore, they have been demonstrated to suppress tumor growth, to alleviate cancer-associated pain, and to exert immunomodulatory properties. Here, we will address the known knowns and the known unknowns of Sigma1 and Sigma2/TMEM97 ligand actions in the context of cancer. This review will highlight key discoveries and published evidence in support of a role for sigma proteins in cancer and will discuss several fundamental questions regarding the physiological roles of sigma proteins in cancer and sigma ligand mechanism of action.

Neuroprotection in non-transgenic and transgenic mouse models of Alzheimer's disease by positive modulation of σ1 receptors

The sigma-1 (σ1) receptor is an endoplasmic reticulum (ER) chaperone protein, enriched in mitochondria-associated membranes. Its activation triggers physiological responses to ER stress and modulate Ca2+ mobilization in mitochondria. Small σ1 agonist molecules activate the protein and act behaviorally as antidepressant, anti-amnesic and neuroprotective agents. Recently, several chemically unrelated molecules were shown to be σ1 receptor positive modulators (PMs), with some of them a clear demonstration of their allostericity. We here examined whether a σ1 PM also shows neuroprotective potentials in pharmacological and genetic models of Alzheimer's disease (AD). For this aim, we describe (±)-2-(3-chlorophenyl)-3,3,5,5-tetramethyl-2-oxo-[1,4,2]-oxazaphosphinane (OZP002) as a novel σ1 PM. OZP002 does not bind σ1 sites but induces σ1 effects in vivo and boosts σ1 agonist activity. OZP002 was antidepressant in the forced swim test and its effect was blocked by the σ1 antagonist NE-100 or in σ1 receptor knockout mice. It potentiated the antidepressant effect of the σ1 agonist igmesine. In mice tested for Y-maze alternation or passive avoidance, OZP002 prevented scopolamine-induced learning deficits, in a NE-100 sensitive manner. Pre-administered IP before an ICV injection of amyloid Aβ25-35 peptide, a pharmacological model of Alzheimer's disease, OZP002 prevented the learning deficits induced by the peptide after one week in the Y-maze, passive avoidance and novel object tests. Biochemical analyses of the mouse hippocampi showed that OZP002 significantly decreased Aβ25-35-induced increases in reactive oxygen species, lipid peroxidation, and increases in Bax, TNFα and IL-6 levels. Immunohistochemically, OZP002 prevented Aβ25-35-induced reactive astrogliosis and microgliosis in the hippocampus. It also alleviated Aβ25-35-induced decreases in synaptophysin level and choline acetyltransferase activity. Moreover, chronically administered in APPswe mice during 2 months, OZP002 prevented learning deficits (in all tests plus place learning in the water-maze) and increased biochemical markers. This study shows that σ1 PM with high neuropotective potential can be identified, combining pharmacological efficacy, selectivity and therapeutic safety, and identifies a novel promising compound, OZP002.

Trends in Sigma-1 Receptor Research: A 25-Year Bibliometric Analysis

Purpose: There are previous reviews focused on Sigma-1 receptor but no bibliometric studies examining this field as a whole. This article aims to present a global view of Sigma-1 receptor research and its intellectual structure.

Methods: We used bibliometric indicators of a basic nature as well as techniques for the visualization and analysis of networks of scientific information extracted from Scopus database.

Results: In total, 1,102 articles from 1992 to 2017 were identified. The growth in the production of articles is not constant over time, with periods of stagnation of approximately 5 years. Only 247 authors have five or more publications. The authors appear grouped in relatively independent clusters, thus suggesting a low level of collaborations between those dedicated to the Sigma-1 receptor. The United States was the country with the highest production followed by Japan and Germany. Spain, Japan, and Italy showed the highest per million inhabitants ratio. The highest citation/article ratio was reached in France, United States, and Canada. The leading institutions were the University of Münster, the National Institutes of Health, ESTEVE, and INSERM. The top authors in number of publications were Wünsch-B, Schepmann-D, and Maurice-T. Hayashi-T, Su-TP and Bowen-WD showed the highest citations per article. The article by Hayashi-T and Su-TP in Cell (2007) describing the Sigma-1 receptor as a chaperone protein is the top cited reference. Cluster labeling from author co-citation analysis shows that research has been focused on specific diseases such as addiction, neuroprotection and neurodegenerative diseases, psychiatric disorders, and pain. High-frequency terms in author keywords suggest that the research efforts in some areas such as neuroimaging, cocaine addiction or psychiatric disorders have declined over time, while others such as neurodegenerative diseases or pain are currently most popular.

Perspective: A greater involvement of the scientific community, with an increase in the scientific production related to Sigma-1, is desirable. Additional boost needed to improve research performance is likely to come from combining data from different laboratories to overcome the limitations of individual approaches. The resulting maps are a useful and attractive tool for the Sigma-1 receptor research community, as they reveal the main lines of exploration at a glance.

Blockade of the Sigma-1 Receptor Relieves Cognitive and Emotional Impairments Associated to Chronic Osteoarthritis Pain

Osteoarthritis is the most common musculoskeletal disease worldwide, often characterized by degradation of the articular cartilage, chronic joint pain and disability. Cognitive dysfunction, anxiety and depression are common comorbidities that impact the quality of life of these patients. In this study, we evaluated the involvement of sigma-1 receptor (σ1R) on the nociceptive, cognitive and emotional alterations associated with chronic osteoarthritis pain. Monosodium iodoacetate (MIA) was injected into the knee of Swiss-albino CD1 mice to induce osteoarthritis pain, which then received a repeated treatment with the σ1R antagonist E-52862 or its vehicle. Nociceptive responses and motor performance were assessed with the von Frey and the Catwalk gait tests. Cognitive alterations were evaluated using the novel object recognition task, anxiety-like behavior with the elevated plus maze and the zero-maze tests, whereas depressive-like responses were determined using the forced swimming test. We also studied the local effect of the σ1R antagonist on cartilage degradation, and its central effects on microglial reactivity in the medial prefrontal cortex. MIA induced mechanical allodynia and gait abnormalities that were prevented by the chronic treatment with the σ1R antagonist. E-52862 also reduced the memory impairment and the depressive-like behavior associated to osteoarthritis pain. Interestingly, the effect of E-52862 on depressive-like behavior was not accompanied by a modification of anxiety-like behavior. The pain-relieving effects of the σ1R antagonist were not due to a local effect on the articular cartilage, since E-52862 treatment did not modify the histological alterations of the knee joints. However, E-52862 induced central effects revealed by a reduction of the cortical microgliosis observed in mice with osteoarthritis pain. These findings show that σ1R antagonism inhibits mechanical hypersensitivity, cognitive deficits and depressive-like states associated with osteoarthritis pain in mice. These effects are associated with central modulation of glial activity but are unrelated to changes in cartilage degradation. Therefore, targeting the σ1R with E-52862 represents a promising pharmacological approach with effects on multiple aspects of chronic osteoarthritis pain that may go beyond the strict inhibition of nociception.