Sigma-1 receptor deficiency reduces MPTP-induced parkinsonism and death of dopaminergic neurons

SIGMAR1 variants in ALS-PD complex cases: a case report of a novel mutation and literature review

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease characterized by progressive degeneration of upper and lower motor neurons, with occasional involvement of the extrapyramidal system. Mutations in the sigma non-opioid intracellular receptor 1 (SIGMAR1) gene have been identified as one of the causes of ALS. Here, we present a case of a 49-year-old man diagnosed with ALS-Parkinson's disease (PD) complex. The patient exhibited bradykinesia and tremor, and whole-exome sequencing revealed homozygous mutations in the SIGMAR1 gene (c.446-2A > T). In addition, we conducted an investigation into the clinical and molecular phenotype of previously reported variants of SIGMAR1 associated with ALS. This case report aims to raise awareness among physicians regarding atypical phenotypes of amyotrophic lateral sclerosis and to encourage further research on the factors leading to SIGMAR1 mutations in patients.

Exploring the Association between Schizophrenia and Cardiovascular Diseases: Insights into the Role of Sigma 1 Receptor

Contemporary society is characterized by rapid changes. Various epidemiological, political and economic crises represent a burden to mental health of nowadays population, which may at least partially explain the increasing incidence of mental disorders, including schizophrenia. Schizophrenia is associated with premature mortality by at least 13-15 years. The leading cause of premature mortality in schizophrenia patients is high incidence of cardiovascular diseases. The specific-cause mortality risk for cardiovascular diseases in schizophrenia patients is more than twice higher as compared to the general population. Several factors are discussed as the factor of cardiovascular diseases development. Intensive efforts to identify possible link between schizophrenia and cardiovascular diseases are made. It seems that sigma 1 receptor may represent such link. By modulation of the activity of several neurotransmitter systems, including dopamine, glutamate, and GABA, sigma 1 receptor might play a role in pathophysiology of schizophrenia. Moreover, significant roles of sigma 1 receptor in cardiovascular system have been repeatedly reported. The detailed role of sigma 1 receptor in both schizophrenia and cardiovascular disorders development however remains unclear. The article presents an overview of current knowledge about the association between schizophrenia and cardiovascular diseases and proposes possible explanations with special emphasis on the role of the sigma 1 receptor.

Sigma-1 receptor and seizures

Over the last decade, sigma-1 receptor (Sig1R) has been recognized as a valid target for the treatment of seizure disorders and seizure-related comorbidities. Clinical trials with Sig1R ligands are underway testing therapies for the treatment of drug-resistant seizures, developmental and epileptic encephalopathies, and photosensitive epilepsy. However, the direct molecular mechanism by which Sig1R modulates seizures and the balance between excitatory and inhibitory pathways has not been fully elucidated. This review article aims to summarize existing knowledge of Sig1R and its involvement in seizures by focusing on the evidence obtained from Sig1R knockout animals and the anti-seizure effects of Sig1R ligands. In addition, this review article includes a discussion of the advantages and disadvantages of the use of existing compounds and describes the challenges and future perspectives on the use of Sig1R as a target for the treatment of seizure disorders.

The Missing Piece? A Case for Microglia's Prominent Role in the Therapeutic Action of Anesthetics, Ketamine, and Psychedelics

There is much excitement surrounding recent research of promising, mechanistically novel psychotherapeutics - psychedelic, anesthetic, and dissociative agents - as they have demonstrated surprising efficacy in treating central nervous system (CNS) disorders, such as mood disorders and addiction. However, the mechanisms by which these drugs provide such profound psychological benefits are still to be fully elucidated. Microglia, the CNS's resident innate immune cells, are emerging as a cellular target for psychiatric disorders because of their critical role in regulating neuroplasticity and the inflammatory environment of the brain. The following paper is a review of recent literature surrounding these neuropharmacological therapies and their demonstrated or hypothesized interactions with microglia. Through investigating the mechanism of action of psychedelics, such as psilocybin and lysergic acid diethylamide, ketamine, and propofol, we demonstrate a largely under-investigated role for microglia in much of the emerging research surrounding these pharmacological agents. Among others, we detail sigma-1 receptors, serotonergic and γ-aminobutyric acid signalling, and tryptophan metabolism as pathways through which these agents modulate microglial phagocytic activity and inflammatory mediator release, inducing their therapeutic effects. The current review includes a discussion on future directions in the field of microglial pharmacology and covers bidirectional implications of microglia and these novel pharmacological agents in aging and age-related disease, glial cell heterogeneity, and state-of-the-art methodologies in microglial research.

Blockage of TRPV4 Downregulates the Nuclear Factor-Kappa B Signaling Pathway to Inhibit Inflammatory Responses and Neuronal Death in Mice with Pilocarpine-Induced Status Epilepticus

The blockage of transient receptor potential vanilloid 4 (TRPV4) inhibits inflammation and reduces hippocampal neuronal injury in a pilocarpine-induced mouse model of temporal lobe epilepsy. However, the underlying mechanisms remain largely unclear. NF-κB signaling pathway is responsible for the inflammation and neuronal injury during epilepsy. Here, we explored whether TRPV4 blockage could affect the NF-κB pathway in mice with pilocarpine-induced status epilepticus (PISE). Application of a TRPV4 antagonist markedly attenuated the PISE-induced increase in hippocampal HMGB1, TLR4, phospho (p)-IκK (p-IκK), and p-IκBα protein levels, as well as those of cytoplasmic p-NF-κB p65 (p-p65) and nuclear NF-κB p65 and p50; in contrast, the application of GSK1016790A, a TRPV4 agonist, showed similar changes to PISE mice. Administration of the TLR4 antagonist TAK-242 or the NF-κB pathway inhibitor BAY 11-7082 led to a noticeable reduction in the hippocampal protein levels of cleaved IL-1β, IL-6 and TNF, as well as those of cytoplasmic p-p65 and nuclear p65 and p50 in GSK1016790A-injected mice. Finally, administration of either TAK-242 or BAY 11-7082 greatly increased neuronal survival in hippocampal CA1 and CA2/3 regions in GSK1016790A-injected mice. Therefore, TRPV4 activation increases HMGB1 and TLR4 expression, leading to IκK and IκBα phosphorylation and, consequently, NF-κB activation and nuclear translocation. The resulting increase in pro-inflammatory cytokine production is responsible for TRPV4 activation-induced neuronal injury. We conclude that blocking TRPV4 can downregulate HMGB1/TLR4/IκK/κBα/NF-κB signaling following PISE onset, an effect that may underlie the anti-inflammatory response and neuroprotective ability of TRPV4 blockage in mice with PISE.

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.

Sigma-1 Receptor as a Protective Factor for Diabetes-Associated Cognitive Dysfunction via Regulating Astrocytic Endoplasmic Reticulum-Mitochondrion Contact and Endoplasmic Reticulum Stress

The prevalence of diabetes-associated cognitive dysfunction (DACD) has increased to 13.5%. Dementia, as the most severe DACD, is the second leading cause of death in patients with diabetes mellitus. Hence, the potential mechanisms of DACD for slowing or halting its progression need to be urgently explored. Given that the sigma-1 receptor (Sig-1R), a chaperone protein located in the endoplasmic reticulum (ER)-mitochondrion contact membranes to regulate ER stress (ERS), is associated with cognitive outcomes in neurodegenerative diseases, this study aimed to investigate the role of astrocytic Sig-1R in DACD and its underlying mechanism. Here, we examined the levels of ERS and complement component 3/3a (C3/C3a) from primary astrocytes with different concentrations of glucose and treatment. Subsequently, HT22 neurons were cultured in different astrocyte-conditioned medium, and the expression of synaptic proteins was detected. We constructed type 1 diabetes mellitus (T1DM) model to evaluate the astrocytic Sig-1R mechanism on synapse and cognitive function changes. In vitro, high glucose concentration downregulated Sig-1R and aggravated ERS in astrocytes, resulting in synapse deficits. PRE-084, a high-affinity and selective Sig-1R agonist, inhibited astrocytic ERS and complement cascades and restored synaptic damage, while the Sig-1R antagonist displayed the opposite results. Moreover, C3a receptor antagonist (C3aRA) could mimic the effect of PRE-084 and exerted neuroprotective effects. In vivo, PRE-084 substantially reduced ER-mitochondrion contact, activation of ERS, and C3/C3a secretion in mice with T1DM. Additionally, the synaptic loss and neurobehavioral dysfunction of mice with T1DM were less pronounced in both the PRE-084 and C3aRA treatment groups. These findings demonstrated that Sig-1R activation reduced the astrocytic ER-mitochondrion contact, ERS activation, and complement-mediated synaptic damage in T1DM. This study suggested the mechanisms and potential therapeutic approaches for treating DACD.

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.

Sigma-1 Receptor in Retina: Neuroprotective Effects and Potential Mechanisms

Retinal degenerative diseases are the major factors leading to severe visual impairment and even irreversible blindness worldwide. The therapeutic approach for retinal degenerative diseases is one extremely urgent and hot spot in science research. The sigma-1 receptor is a novel, multifunctional ligand-mediated molecular chaperone residing in endoplasmic reticulum (ER) membranes and the ER-associated mitochondrial membrane (ER-MAM); it is widely distributed in numerous organs and tissues of various species, providing protective effects on a variety of degenerative diseases. Over three decades, considerable research has manifested the neuroprotective function of sigma-1 receptor in the retina and has attempted to explore the molecular mechanism of action. In the present review, we will discuss neuroprotective effects of the sigma-1 receptor in retinal degenerative diseases, mainly in aspects of the following: the localization in different types of retinal neurons, the interactions of sigma-1 receptors with other molecules, the correlated signaling pathways, the influence of sigma-1 receptors to cellular functions, and the potential therapeutic effects on retinal degenerative diseases.

Knocking Out Sigma-1 Receptors Reveals Diverse Health Problems

Sigma-1 receptor (Sig-1R) is a protein present in several organs such as brain, lung, and heart. In a cell, Sig-1R is mainly located across the membranes of the endoplasmic reticulum and more specifically at the mitochondria-associated membranes. Despite numerous studies showing that Sig-1R could be targeted to rescue several cellular mechanisms in different pathological conditions, less is known about its fundamental relevance. In this review, we report results from various studies and focus on the importance of Sig-1R in physiological conditions by comparing Sig-1R KO mice to wild-type mice in order to investigate the fundamental functions of Sig-1R. We note that the Sig-1R deletion induces cognitive, psychiatric, and motor dysfunctions, but also alters metabolism of heart. Finally, taken together, observations from different experiments demonstrate that those dysfunctions are correlated to poor regulation of ER and mitochondria metabolism altered by stress, which could occur with aging.

An open-like conformation of the sigma-1 receptor reveals its ligand entry pathway

The sigma-1 receptor (σ1R) is a non-opioid transmembrane receptor which has been implicated in many diseases, including neurodegenerative disorders and cancer. After more than forty years of research, substantial progress has been made in understanding this unique receptor, yet the molecular mechanism of its ligand entry pathway remains uncertain. Published structures of human σ1R reveal its homotrimeric organization of a cupin-fold β-barrel body that contains the ligand binding site, a carboxy-terminal V-shaped two-helix bundle, and a single amino-terminal transmembrane helix, while simulation studies have suggested a ligand entry pathway that is generated by conformational rearrangements of the cupin-fold domain. Here, we present multiple crystal structures, including an open-like conformation, of σ1R from Xenopus laevis. Together with functional binding analysis our data suggest that access to the σ1R ligand binding site is likely achieved by protein conformational changes that involve the carboxy-terminal two-helix bundle, rather than structural changes in the cupin-fold domain.

Allosteric Modulation of the Sigma-1 Receptor Elicits Antipsychotic-like Effects

Allosteric modulation represents an important approach in drug discovery because of its advantages in safety and selectivity. SOMCL-668 is the first selective and potent sigma-1 receptor allosteric modulator, discovered in our laboratory. The present work investigates the potential therapeutic effects of SOMCL-668 on phencyclidine (PCP)-induced schizophrenia-related behavior in mice and further elucidates underlying mechanisms for its antipsychotic-like effects. SOMCL-668 not only attenuated acute PCP-induced hyperactivity and PPI disruption, but also ameliorated social deficits and cognitive impairment induced by chronic PCP treatment. Pretreatment with the selective sigma-1 receptor antagonist BD1047 blocked the effects of SOMCL-668, indicating sigma-1 receptor-mediated responses. This was confirmed using sigma-1 receptor knockout mice, in which SOMCL-668 failed to ameliorate PPI disruption and hyperactivity induced by acute PCP and social deficits and cognitive impairment induced by chronic PCP treatment. Additionally, in vitro SOMCL-668 exerted positive modulation of sigma-1 receptor agonist-induced intrinsic plasticity in brain slices recorded by patch-clamp. Furthermore, in vivo lower dose of SOMCL-668 exerted positive modulation of improvement in social deficits and cognitive impairment induced by the selective sigma-1 agonist PRE084. Also, SOMCL-668 reversed chronic PCP-induced down-regulation in expression of frontal cortical p-AKT/AKT, p-CREB/CREB and BDNF in wide-type but not sigma-1 knockout mice. Moreover, administration of the PI3K/AKT inhibitor LY294002 abolished amelioration by SOMCL-668 of chronic PCP-induced schizophrenia-related behaviors by inhibition of BDNF expression. The present data provide initial, proof-of-concept evidence that allosteric modulation of the sigma-1 receptor may be a novel approach for the treatment of psychotic illness.

Reduced GFAP Expression in Bergmann Glial Cells in the Cerebellum of Sigma-1 Receptor Knockout Mice Determines the Neurobehavioral Outcomes after Traumatic Brain Injury

Neuroprotective effects of Sigma-1 receptor (S1R) ligands have been observed in multiple animal models of neurodegenerative diseases. Traumatic brain injury (TBI)-related neurodegeneration can induce long-lasting physical, cognitive, and behavioral disabilities. The aim of our study was to evaluate the role of S1R in the development of neurological deficits after TBI. Adult male wild-type CD-1 (WT) and S1R knockout (S1R-/-) mice were subjected to lateral fluid percussion injury, and behavioral and histological outcomes were assessed for up to 12 months postinjury. Neurological deficits and motor coordination impairment were less pronounced in S1R-/- mice with TBI than in WT mice with TBI 24 h after injury. TBI-induced short-term memory impairments were present in WT but not S1R-/- mice 7 months after injury. Compared to WT animals, S1R-/- mice exhibited better motor coordination and less pronounced despair behavior for up to 12 months postinjury. TBI induced astrocyte activation in the cortex of WT but not S1R-/- mice. S1R-/- mice presented a significantly reduced GFAP expression in Bergmann glial cells in the molecular layer of the cerebellum compared to WT mice. Our findings suggest that S1R deficiency reduces TBI-induced motor coordination impairments by reducing GFAP expression in Bergmann glial cells in the cerebellum.

Sigma-1 receptor regulates mitophagy in dopaminergic neurons and contributes to dopaminergic protection

Mitochondria are essential for neuronal survival and function, and mitochondrial dysfunction plays a critical role in the pathological development of Parkinson's disease (PD). Mitochondrial quality control is known to contribute to the survival of dopaminergic (DA) neurons, with mitophagy being a key regulator of the quality control system. In this study, we show that mitophagy is impaired in the substantia nigra pars compacta (SNc) of the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced mouse model of PD. Treatment with the sigma-1 receptor (Sig 1R) agonist 2-morpholin-4-ylethyl 1-phenylcyclohexane-1-carboxylate (PRE-084) reduced loss of DA neurons, restored motor ability and MPTP-induced damage to mitophagy activity in the SNc of PD-like mice. Additionally, knockdown of Sig 1R in SH-SY5Y DA cells inhibited mitophagy and enhanced 1-methyl-4-phenylpyridinium ion (MPP+) neurotoxicity, whereas application of the Sig 1R selective agonist SKF10047 promoted clearance of damaged mitochondria. Moreover, knockdown of Sig 1R in SH-SY5Y cells resulted in decreased levels of p-ULK1 (Unc-51 Like Autophagy Activating Kinase 1) (Ser555), p-TBK1 (TANK Binding Kinase 1) (Ser172), p-ubiquitin (Ub) (Ser65), Parkin recruitment, and stabilization of PTEN-induced putative kinase 1 (PINK1) in mitochondria. The present data provide the first evidence for potential roles of PINK1/Parkin in Sig 1R-modulated mitophagy in DA neurons.

Sigma1 Receptor Inhibits TRPC1-Mediated Ca2+ Entry That Promotes Dopaminergic Cell Death

Regulation of Ca2+ homeostasis is essential for neuronal function and its survival. Recent data suggest that TRPC1 function as the endogenous store-mediated Ca2+ entry channel in dopaminergic cells, and loss of TRPC1 function leads to neurodegeneration; however, its regulation is not fully identified. Here we provide evidence that the sigma 1 receptor contributes to the loss of dopaminergic cells by blocking TRPC1-mediated Ca2+ entry. Importantly, downregulation of sigma 1 receptor expression significantly decreased neurotoxin-induced loss of dopaminergic cells as measured by MTT assays and caspase activity was also inhibited. Importantly, sigma 1 receptor inhibited TRPC1-mediated Ca2+ entry and silencing of sigma 1 receptor significantly restored store-dependent Ca2+ influx. Although co-immunoprecipitation failed to show an interaction between the TRPC1 and sigma 1 receptor, store depletion promoted a decrease in the sigma 1 receptor-STIM1 association. Neurotoxin-induced loss of Ca2+ entry was significantly restored in cells that had decreased sigma 1 receptor expression. Furthermore, TRPC1 or STIM1 silencing inhibited store-mediated Ca2+ entry, which was further increased upon the downregulation of the sigma 1 receptor expression. TRPC1 silencing prevented the increased neuroprotection and caspase activity observed upon the downregulation of sigma 1 receptor. Finally, sigma 1 receptor activation also significantly decreased TRPC1-mediated Ca2+ entry and lead to an increase in neurodegeneration. In contrast, addition of sigma 1 receptor antagonist prevented neurotoxin-induced neurodegeneration and facilitated TRPC1-mediated Ca2+ influx. Together these results suggest that the sigma 1 receptor is involved in the inhibition of TRPC1- mediated Ca2+ entry, which leads to the degeneration in the dopaminergic cells, and prevention of sigma 1 receptor function could protect neuronal cell death as observed in Parkinson's disease.

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.

Sigma 1 receptor as a therapeutic target for amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is an adult disease causing a progressive loss of upper and lower motoneurons, muscle paralysis and early death. ALS has a poor prognosis of 3-5 years after diagnosis with no effective cure. The aetiopathogenic mechanisms involved include glutamate excitotoxicity, oxidative stress, protein misfolding, mitochondrial alterations, disrupted axonal transport and inflammation. Sigma non-opioid intracellular receptor 1 (sigma 1 receptor) is a protein expressed in motoneurons, mainly found in the endoplasmic reticulum (ER) on the mitochondria-associated ER membrane (MAM) or in close contact with cholinergic postsynaptic sites. MAMs are sites that allow the assembly of several complexes implicated in essential survival cell functions. The sigma 1 receptor modulates essential mechanisms for motoneuron survival including excitotoxicity, calcium homeostasis, ER stress and mitochondrial dysfunction. This review updates sigma 1 receptor mechanisms and its alterations in ALS, focusing on MAM modulation, which may constitute a novel target for therapeutic strategies. LINKED ARTICLES: This article is part of a themed issue on Neurochemistry in Japan. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.6/issuetoc.

Fetal growth restriction mice are more likely to exhibit depression-like behaviors due to stress-induced loss of dopaminergic neurons in the VTA

Fetal growth restriction (FGR) is a severe perinatal complication that can increase risk for mental illness. To investigate the mechanism by which FGR mice develop mental illness in adulthood, we established the FGR mouse model and the FGR mice did not display obvious depression-like behaviors, but after environmental stress exposure, FGR mice were more likely to exhibit depression-like behaviors than control mice. Moreover, FGR mice had significantly fewer dopaminergic neurons in the ventral tegmental area but no difference in serotoninergic neurons in the dorsal raphe. RNA-seq analysis showed that the downregulated genes in the midbrain of FGR mice were associated with many mental diseases and were especially involved in the regulation of NMDA-selective glutamate receptor (NMDAR) activity. Furthermore, the NMDAR antagonist memantine can relieve the stress-induced depression-like behaviors of FGR mice. In summary, our findings provide a theoretical basis for future research and treatment of FGR-related depression.

Development and characterization of an inducible Dicer conditional knockout mouse model of Parkinson's disease: validation of the antiparkinsonian effects of a sigma-1 receptor agonist and dihydromyricetin

Parkinson's disease (PD) is a common neurodegenerative disease characterized by motor impairment and progressive loss of dopamine (DA) neurons. At present, the acute application of neurotoxic drugs such as 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and 6-hydroxydopamine (6-OHDA) are commonly used to simulate the pathology of PD; however, it is difficult to induce the progressive pathogenesis of PD with these models. In this study, we employed DAT promoter-mediated Cre transgenic mice to establish tamoxifen-inducible Dicer conditional knockout (cKO) mice in an effort to mimic the progressive loss of DA neurons and the development of PD-like behavioral phenotypes. The results showed that Dicer cKO mice exhibited progressive loss of DA neurons in the substantia nigra (SN) following tamoxifen administration. Significant DA loss was observed 6 weeks after tamoxifen administration; accordingly, progressive motor function impairment was also observed. We also found that a significant neuroinflammatory response, as evidenced by microglial proliferation, another hallmark of PD pathogenesis, accompanied the loss of DA neurons. The acute application of levo-DOPA (L-DOPA) relieved the PD-like motor impairments in Dicer cKO mice to exert its antiparkinsonian action, indicating that the model can be used to evaluate the antiparkinsonian efficacy of PD drugs. To further elucidate the potential application of this novel PD animal model for PD drug development, we employed the powerful neuroprotective agent dihydromyricetin (DHM) (10 mg/kg) and the selective sigma-1 receptor agonist PRE-084 (1 mg/kg), both of which were previously shown to produce antiparkinsonian effects. The results indicated that the chronic administration of either DHM or PRE-084 attenuated the Dicer cKO-induced loss of DA neurons and motor impairments, although the two drugs acted through different mechanisms. These data indicate that the Dicer cKO mouse model may be a useful model for investigating the pathological development of PD and intervention-mediated changes. In conclusion, this transgenic mouse model appears to simulate the progressive pathogenesis of PD and may be a potentially useful model for PD drug discovery.

Generation of a Novel Mouse Model of Parkinson's Disease via Targeted Knockdown of Glutamate Transporter GLT-1 in the Substantia Nigra

Parkinson's disease (PD) is a common neurodegenerative disease that is characterized by pathological dopaminergic (DA) neuronal death and α-synuclein aggregation. Glutamate excitotoxicity is a well-established pathogenesis of PD that involves dysfunctional expression of glutamate transporters. Glutamate transporter-1 (GLT-1) is mainly responsible for clearance of glutamate at synapses, including DA synapses. However, the role of GLT-1 in the aberrant synaptic transmission in PD remains elusive. In the present study, we generated small-interfering RNAs (siRNAs) to knockdown GLT-1 expression in primary astrocytes, and we report that siRNA knockdown of astrocytic GLT-1 decreased postsynaptic density-95 (PSD-95) expression in neuron-astrocyte cocultures in vitro. Using adeno-associated viruses (AAVs) targeting GLT-1 short-hairpin RNA (shRNA) sequences with a glial fibrillary acidic protein (GFAP) promoter, we abolished astrocytic GLT-1 expression in the substantia nigra pars compacta (SNpc) of mice. We found that GLT-1 deficiency in the SNpc induced parkinsonian phenotypes in terms of progressive motor deficits and nigral DA neuronal death in mice. We also found that there were reactive astrocytes and microglia in the SNpc upon GLT-1 knockdown. Furthermore, we used RNA sequencing to determine altered gene expression patterns upon GLT-1 knockdown in the SNpc, which revealed that disrupted calcium signaling pathways may be responsible for GLT-1 deficiency-mediated DA neuronal death in the SNpc. Taken together, our findings provide evidence for a novel role of GLT-1 in parkinsonian phenotypes in mice, which may contribute to further elucidation of the mechanisms of PD pathogenesis.

Alterations of thyroidal status in brain regions and hypothalamo-pituitary-blood-thyroid-axis associated with dopaminergic depletion in substantia nigra and ROS formation in different brain regions after MPTP treatment in adult male mice

MPTP produces oxidative stress, damages niagrostriatal dopaminergic neurons and develops Parkinsonism in rodents. Due to paucity of information, the thyroidal status in brain regions and peripheral tissues during different post-treatment days in MPTP-induced mice had been executed in the present study. MPTP depleted tyrosine hydroxylase protein expressions that signify the dopaminergic neuronal damage in substantia nigra. MPTP elevated ROS formation differentially in brain regions (cerebral cortex, hippocampus, substantia nigra) with maximal elevation at hippocampus. The changes in thyroid hormone (T₄ and T₃) levels indicate that brain regions might combat the adverse situation by keeping the levels of thyroid hormones either unchanged or in the elevated conditions in the latter phases (day-3 and day-7), apart from the depletion of thyroid hormones in certain brain regions (T₄ in SN and hippocampus, T₃ in hippocampus) as the immediate (day-1) effects after MPTP treatment. MPTP caused alterations of cellular morphology, RNA:Protein ratio and TPO protein expression, concomitantly depleted TPO mRNA expression and elevated TSH levels in the thyroid gland. Although T₄ levels changed differentially, T₃ levels remained unaltered in thyroid gland throughout the post-treatment days. Results have been discussed mentioning the putative role of T₄ and TSH in apoptosis and/or proliferation/differentiation of thyrocytes. In blood, T₄ levels remained unchanged while the changes in T₃ and TSH levels did not signify the clinical feature of hypo/hyperthyroidism of animals. In the pituitary, both T₄ and T₃ levels remained elevated where TSH differentially altered (elevated followed by depletion) during post-treatment days. Notably, T₄, T₃ and TSH levels did not alter in hypothalamus except initial (day-1) depletion of the T₄ level. Therefore, the feedback control mechanism of hypothalamo-pituitary-blood-thyroid-axis failed to occur after MPTP treatment. Overall, MPTP altered thyroidal status in the brain and peripheral tissues while both events might occur in isolation as well.

The loss of dopaminergic neurons in DEC1 deficient mice potentially involves the decrease of PI3K/Akt/GSK3β signaling

Here we study the effects of differentiated embryonic chondrocyte gene 1(DEC1) deficiency on midbrain dopaminergic(DA) neurons in the substantia nigra pars compacta(SNpc) through behavioral, histological and molecular analysis. We have found that compared to the age-matched WT mice, DEC1 deficient mice show a decrease in locomotor activity and motor coordination, which shows the main features of Parkinson's disease(PD). But there is no significant difference in spatial learning and memory skills between WT and DEC1 KO mice. Compared to the age-matched WT mice, DEC1 deficient mice exhibit the loss of DA neurons in the SNpc and reduction of dopamine and its metabolites in the striatum. The activated caspase-3 and TH/TUNEL⁺ cells increase in the SNpc of 6- and 12-month-old DEC1 KO mice compared to those of the age-matched WT mice. But we haven't found any NeuN/TUNEL⁺ cell increase in the hippocampus of the above two types of mice at the age of 6 months. Furthermore, DEC1 deficiency leads to a significant inhibition of PI3K/Akt/GSK3β signaling pathway. Additionally, LiCl could rescue the DA neuron loss of midbrain in the 6-month-old DEC1 KO mice. Taken together, the loss of DA neurons in the DEC1 deficient mice potentially involves the downregulation of PI3K/Akt/GSK3β signaling.

Chaperone Sigma1R mediates the neuroprotective action of afobazole in the 6-OHDA model of Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disease with limited treatment options. Therefore, the identification of therapeutic targets is urgently needed. Previous studies have shown that the ligand activation of the sigma-1 chaperone (Sigma1R) promotes neuroprotection. The multitarget drug afobazole (5-ethoxy-2-[2-(morpholino)-ethylthio]benzimidazole dihydrochloride) was shown to interact with Sigma1Rs and prevent decreases in striatal dopamine in the 6-hydroxydopamine (6-OHDA)-induced parkinsonism model. The aim of the present study was to elucidate the role of Sigma1Rs in afobazole pharmacological activity. Using ICR mice we found that administration of afobazole (2.5 mg/kg, i.p.) or selective agonist of Sigma1R PRE-084 (1.0 mg/kg, i.p.) over 14 days normalizes motor disfunction and prevents decreases in dopamine in the 6-OHDA-lesioned striatum. Afobazole administration also prevents the loss of TH + neurons in the substantia nigra. The pre-administration of selective Sigma1R antagonist BD-1047 (3.0 mg/kg, i.p.) abolishes the activity of either afobazole or PRE-084, as determined using the rotarod test and the analysis of striatal dopamine content. The current study demonstrates the contribution of Sigma1Rs in the neuroprotective effect of afobazole in the 6-OHDA model of Parkinson's disease and defines the therapeutic perspective of Sigma1R agonists in the clinic.

The Roles of Intracellular Chaperone Proteins, Sigma Receptors, in Parkinson's Disease (PD) and Major Depressive Disorder (MDD)

Sigma receptors, including Sigma-1 receptors and Sigma-2 receptors, are highly expressed in the CNS. They are intracellular chaperone proteins. Sigma-1 receptors localize mainly at the mitochondria-associated endoplasmic reticulum (ER) membrane (MAM). Upon stimulation, they translocate from MAM to plasma membrane (PM) and nucleus, where they interact with many proteins and ion channels. Sigma-1 receptor could interact with itself to form oligomers, its oligomerization states affect its ability to interact with client proteins including ion channels and BiP. Sigma-1 receptor shows high affinity for many unrelated and structurally diverse ligands, but the mechanism for this diverse drug receptor interaction remains unknown. Sigma-1 receptors also directly bind many proteins including G protein-coupled receptors (GPCRs) and ion channels. In recent years, significant progress has been made in our understanding of roles of the Sigma-1 receptors in normal and pathological conditions, but more studies are still required for the Sigma-2 receptors. The physiological roles of Sigma-1 receptors in the CNS are discussed. They can modulate the activity of many ion channels including voltage-dependent ion channels including Ca²⁺, Na⁺, K⁺ channels and NMDAR, thus affecting neuronal excitability and synaptic activity. They are also involved in synaptic plasticity and learning and memory. Moreover, the activation of Sigma receptors protects neurons from death via the modulation of ER stress, neuroinflammation, and Ca²⁺ homeostasis. Evidences about the involvement of Sigma-1 receptors in Parkinson’s disease (PD) and Major Depressive Disorder (MDD) are also presented, indicating Sigma-1 receptors might be promising targets for pharmacologically treating PD and MDD.

TRPV4-induced inflammatory response is involved in neuronal death in pilocarpine model of temporal lobe epilepsy in mice

Activation of transient receptor potential vanilloid 4 (TRPV4) induces neuronal injury. TRPV4 activation enhances inflammatory response and promotes the proinflammatory cytokine release in various types of tissue and cells. Hyperneuroinflammation contributes to neuronal damage in epilepsy. Herein, we examined the contribution of neuroinflammation to TRPV4-induced neurotoxicity and its involvement in the inflammation and neuronal damage in pilocarpine model of temporal lobe epilepsy in mice. Icv. injection of TRPV4 agonist GSK1016790A (GSK1016790A-injected mice) increased ionized calcium binding adapter molecule-1 (Iba-1) and glial fibrillary acidic protein (GFAP) protein levels and Iba-1-positive (Iba-1⁺) and GFAP-positive (GFAP⁺) cells in hippocampi, which indicated TRPV4-induced microglial cell and astrocyte activation. The protein levels of nucleotide-binding oligomerization domain-like receptor pyrin domain containing 3 (NLRP3) inflammasome components NLRP3, apoptosis-related spotted protein (ASC) and cysteinyl aspartate-specific protease-1 (caspase-1) were increased in GSK1016790A-injected mice, which indicated NLRP3 inflammasome activation. GSK1016790A also increased proinflammatory cytokine IL-1β, TNF-α and IL-6 protein levels, which were blocked by caspase-1 inhibitor Ac-YVAD-cmk. GSK1016790A-induced neuronal death was attenuated by Ac-YVAD-cmk. Icv. injection of TRPV4-specific antagonist HC-067047 markedly increased the number of surviving cells 3 d post status epilepticus in pilocarpine model of temporal lobe epilepsy in mice (pilocarpine-induced status epilepticus, PISE). HC-067047 also markedly blocked the increase in Iba-1 and GFAP protein levels, as well as Iba-1⁺ and GFAP⁺ cells 3 d post-PISE. Finally, the increased protein levels of NLRP3, ASC and caspase-1 as well as IL-1β, TNF-α and IL-6 were markedly blocked by HC-067047. We conclude that TRPV4-induced neuronal death is mediated at least partially by enhancing the neuroinflammatory response, and this action is involved in neuronal injury following status epilepticus.

Pridopidine Induces Functional Neurorestoration Via the Sigma-1 Receptor in a Mouse Model of Parkinson's Disease

Pridopidine is a small molecule in clinical development for the treatment of Huntington's disease. It was recently found to have high binding affinity to the sigma-1 receptor, a chaperone protein involved in cellular defense mechanisms and neuroplasticity. Here, we have evaluated the neuroprotective and neurorestorative effects of pridopidine in a unilateral 6-hydroxydopamine (6-OHDA) lesion model of parkinsonism in mice. By 5 weeks of daily administration, a low dose of pridopidine (0.3 mg/kg) had significantly improved deficits in forelimb use (cylinder test, stepping test) and abolished the ipsilateral rotational bias typical of hemiparkinsonian animals. A higher dose of pridopidine (1 mg/kg) significantly improved only the rotational bias, with a trend towards improvement in forelimb use. The behavioral recovery induced by pridopidine 0.3 mg/kg was accompanied by a significant protection of nigral dopamine cell bodies, an increased dopaminergic fiber density in the striatum, and striatal upregulation of GDNF, BDNF, and phosphorylated ERK1/2. The beneficial effects of pridopidine 0.3 mg/kg were absent in 6-OHDA-lesioned mice lacking the sigma-1 receptor. Pharmacokinetic data confirmed that the effective dose of pridopidine reached brain concentrations sufficient to bind S1R. Our results are the first to show that pridopidine promotes functional neurorestoration in the damaged nigrostriatal system acting via the sigma-1 receptor.

Smilagenin Protects Dopaminergic Neurons in Chronic MPTP/Probenecid-Lesioned Parkinson's Disease Models

Current therapies for Parkinson’s disease (PD) only offer limited symptomatic alleviation but fail to hamper the progress of the disease. Thus, it is imperative to establish new approaches aiming at protecting or reversing neurodegeneration in PD. Recent work elucidates whether smilagenin (abbreviated SMI), a steroidal sapogenin from traditional Chinese medicinal herbs, can take neuroprotective effect on dopaminergic neurons in a chronic model of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) conjuncted with probenecid mice. We reported for the first time that SMI significantly improved the locomotor ability of chronic MPTP/probenecid–lesioned mice. SMI increased the tyrosine hydroxylase (TH) positive and Nissl positive neuron number in the substantia nigra pars compacta (SNpc), augmented striatal DA and its metabolites concentration and elevated striatal dopamine transporter density (DAT). In addition, dopamine receptor D2R not D1R was down-regulated by MPTP/probenecid and slightly raised by SMI prevention. What’s more, we discovered that SMI markedly elevated striatal glial cell line-derived neurotrophic factor (GDNF) and brain-derived neurotrophic factor (BDNF) protein levels in SMI prevented mice. And we found that SMI increased GDNF and BDNF mRNA level by promoting CREB phosphorylation in 1-methyl-4-phenylpyridimium (MPP⁺) treated SH-SY5Y cells. The results illustrated that SMI could prevent the impairment of dopaminergic neurons in chronic MPTP/probenecid-induced mouse model.

Gestational stress induced differential expression of HDAC2 in male rat offspring hippocampus during development

Accumulating evidence from preclinical and clinical studies indicates prenatal exposure to stress or excess glucocorticoids can affect offspring brain. HDAC2 is an important target of glucocorticoid. Here we detected HDAC2 expression in male offspring hippocampus from gestational restraint stressed rat during development and the relationship between HDAC2 expression and behaviors and neurogenesis in male offspring. Pregnant rats received restrained stress during the last week of pregnancy. Expressions of HDAC2 in offspring hippocampus were detected on postnatal 0 day (P0) and 60 days (P60). Neurogenesis was evaluated by Doublecortin (DCX) staining on P60. Anxiety-like behavior and cognition were detected in open field, elevated plus maze, novel object recognition test, and Barnes maze. We found that HDAC2 expression in the hippocampus of male prenatally stressed offspring (MPSO) was similar to the male control offspring on P0, but significantly lower on P60. Corresponding to the decreased expression of HDAC2 in MPSO hippocampus at P60, neurogenesis in the dentate gyrus of MPSO was significantly lower than the control male offspring. And MPSO also showed greater anxiety and poorer learning and memories abilities than control male offspring. These showed that HDAC2 could partly explain the effects of gestational stress on male offspring behaviors.

Structural basis for σ1 receptor ligand recognition

The σ₁ receptor is a poorly understood membrane protein expressed throughout the human body. Ligands targeting the σ₁ receptor are in clinical trials for treatment of Alzheimer's disease, ischemic stroke, and neuropathic pain. However, relatively little is known regarding the σ₁ receptor's molecular function. Here, we present crystal structures of human σ₁ receptor bound to the antagonists haloperidol and NE-100, and the agonist (+)-pentazocine, at crystallographic resolutions of 3.1 Å, 2.9 Å, and 3.1 Å, respectively. These structures reveal a unique binding pose for the agonist. The structures and accompanying molecular dynamics (MD) simulations identify agonist-induced structural rearrangements in the receptor. Additionally, we show that ligand binding to σ₁ is a multistep process that is rate limited by receptor conformational change. We used MD simulations to reconstruct a ligand binding pathway involving two major conformational changes. These data provide a framework for understanding the molecular basis for σ₁ agonism.

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.

The sigma-1 receptor as a regulator of dopamine neurotransmission: A potential therapeutic target for methamphetamine addiction

Methamphetamine (METH) abuse is a major public health issue around the world, yet there are currently no effective pharmacotherapies for the treatment of METH addiction. METH is a potent psychostimulant that increases extracellular dopamine levels by targeting the dopamine transporter (DAT) and alters neuronal activity in the reward centers of the brain. One promising therapeutic target for the treatment of METH addiction is the sigma-1 receptor (σ1R). The σ1R is an endoplasmic reticulum-localized chaperone protein that is activated by cellular stress, and, unique to this chaperone, its function can also be induced or inhibited by different ligands. Upon activation of this unique "chaperone receptor", the σ1R regulates a variety of cellular functions and possesses neuroprotective activity in the brain. Interestingly, a variety of σ1R ligands modulate dopamine neurotransmission and reduce the behavioral effects of METH in animal models of addictive behavior, suggesting that the σ1R may be a viable therapeutic target for the treatment of METH addiction. In this review, we provide background on METH and the σ1R as well as a literature review regarding the role of σ1Rs in modulating both dopamine neurotransmission and the effects of METH. We aim to highlight the complexities of σ1R pharmacology and function as well as the therapeutic potential of the σ1R as a target for the treatment of METH addiction.

Neuroprotective effect of gold nanoparticles composites in Parkinson's disease model

Parkinson's disease (PD) is second most common neurodegenerative disorder worldwide. Although drugs and surgery can relieve the symptoms of PD, these therapies are incapable of fundamentally treating the disease. For PD patients, over-expression of α-synuclein (SNCA) leads to the death of dopaminergic neurons. This process can be prevented by suppressing SNCA over-expression through RNA interference. Here, we successfully synthesized gold nanoparticles (GNP) composites (CTS@GNP-pDNA-NGF) via the combination of electrostatic adsorption and photochemical immobilization, which could load plasmid DNA (pDNA) and target specific cell types. GNP was transfected into cells via endocytosis to inhibiting the apoptosis of PC12 cells and dopaminergic neurons. Simultaneously, GNP composites are also used in PD models in vivo, and it can successfully cross the blood-brain barrier by contents of GNP in the mice brain. In general, all the works demonstrated that GNP composites have good therapeutic effects for PD models in vitro and in vivo.

Sigma-1 receptor knockout increases α-synuclein aggregation and phosphorylation with loss of dopaminergic neurons in substantia nigra

Sigma-1 receptor (σ1R) is expressed in dopaminergic neurons of substantia nigra. Here, we show that σ1R knockout (σ1R-/-) mice, at age 6-12 months, appeared with age-related loss of dopaminergic neurons and decline of motor coordination. Levels of α-synuclein (αSyn) oligomers and fibrillar αSyn in substantia nigra of σ1R-/- mice were age-dependently increased without the changes in αSyn monomers. The phosphorylation of αSyn monomers or oligomers in dopaminergic neurons was enhanced in σ1R-/- mice. Levels of phosphorylated eIF2a and C/EBP homologous protein expression were elevated in σ1R-/- mice with decline of proteasome activity. Inhibition of endoplasmic reticulum stress by salubrinal recovered the αSyn phosphorylation and proteasome activity and prevented early oligomerization of αSyn in σ1R-/- mice. Rifampicin reduced the late increase of αSyn oligomers in σ1R-/- mice. Rifampicin or salubrinal could reduce the loss of dopaminergic neurons in σ1R-/- mice and improved their motor coordination. The results indicate that the σ1R deficiency through enhanced aggregation and phosphorylation of αSyn causes the loss of dopaminergic neurons leading to the decline of motor coordination.

Dysregulation of Corticostriatal Connectivity in Huntington's Disease: A Role for Dopamine Modulation

Aberrant communication between striatum, the main information processing unit of the basal ganglia, and cerebral cortex plays a critical role in the emergence of Huntington’s disease (HD), a fatal monogenetic condition that typically strikes in the prime of life. Although both striatum and cortex undergo substantial cell loss over the course of HD, corticostriatal circuits become dysfunctional long before neurons die. Understanding the dysfunction is key to developing effective strategies for treating a progressively worsening triad of motor, cognitive, and psychiatric symptoms. Cortical output neurons drive striatal activity through the release of glutamate, an excitatory amino acid. Striatal outputs, in turn, release γ-amino butyric acid (GABA) and exert inhibitory control over downstream basal ganglia targets. Ample evidence from transgenic rodent models points to dysregulation of corticostriatal glutamate transmission along with corresponding changes in striatal GABA release as underlying factors in the HD behavioral phenotype. Another contributor is dysregulation of dopamine (DA), a modulator of both glutamate and GABA transmission. In fact, pharmacological manipulation of DA is the only currently available treatment for HD symptoms. Here, we review data from animal models and human patients to evaluate the role of DA in HD, including DA interactions with glutamate and GABA within the context of dysfunctional corticostriatal circuitry.

Loss of Sigma-1 Receptor Chaperone Promotes Astrocytosis and Enhances the Nrf2 Antioxidant Defense

Sigma-1 receptor (Sig-1R) functions as a chaperon that interacts with multiple proteins and lipids and is implicated in neurodegenerative and psychiatric diseases. Here, we used Sig-1R KO mice to examine brain expression profiles of astrocytes and ubiquitinated proteins, which are both hallmarks of central nervous system (CNS) pathologies. Our results showed that Sig-1R KO induces increased glial fibrillary acidic protein (GFAP) expression in primary neuron-glia cultures and in the whole brain of fetus mice with concomitantly increased accumulations of ubiquitinated proteins. Astrogliosis was also observed in the neuron-glia culture. Upon proteasome or autophagy inhibitor treatments, the pronounced ubiquitinated proteins were further increased in Sig-1R KO neurons, indicating that the Sig-1R regulates both protein degradation and quality control systems. We found that Nrf2 (nuclear factor erythroid 2-related factor 2), which functions to overcome the stress condition, was enhanced in the Sig-1R KO systems especially when cells were under stressful conditions. Mutation or deficiency of Sig-1Rs has been observed in neurodegenerative models. Our study identifies the critical roles of Sig-1R in CNS homeostasis and supports the idea that functional complementation pathways are triggered in the Sig-1R KO pathology.

Activation of Sigma-1 Receptor Alleviates Postpartum Estrogen Withdrawal-Induced "Depression" Through Restoring Hippocampal nNOS-NO-CREB Activities in Mice

Postpartum depression affects approximately 15 % of mothers; however, its pathological mechanisms still remain unclear. Ovariectomized adult mice received the administration of estrogen (E2) and progesterone with a subsequent alone E2, termed hormone-simulated pregnancy (HSP). Affective behaviors as assessed by forced swim and tail suspension tests, hippocampal neuronal nitric oxide synthase (nNOS), nitric oxide (NO), cyclic AMP (cAMP) response element binding protein (CREB) phosphorylation (phosphor-CREB), and neurosteroidogenesis were examined before E2 withdrawal (EW; HSP mice) and on days 2-4 (early-EW mice) and days 8-10 (late-EW mice) after EW. Depressive-like behaviors were observed in early-EW mice but not in late-EW mice. Levels of nNOS, NO, and phosphor-CREB were increased in HSP mice followed by a significant decline in early-EW mice with a subsequent restoration in late-EW mice. The treatment of early-EW mice with NO donor alleviated depressive-like behaviors and decline of phosphor-CREB. The nNOS inhibitor and NO scavenger caused depressive-like behaviors and reduced phosphor-CREB in HSP mice and late-EW mice. Notably, the levels of steroidogenic enzymes StAR and P450scc were elevated in late-EW mice. The sigma-1 receptor (σ1R) agonist could alleviate depressive-like behaviors and decline of nNOS-NO-CREB in early-EW mice. The pharmacological blockade or deficiency of σ1R in late-EW mice caused depressive-like behaviors with decline of nNOS-NO-CREB. The reduction of hippocampal brain-derived neurotrophic factor (BDNF) or N-methyl-D-aspartic acid (NMDA) receptor NR2B phosphorylation in early-EW mice could recover in late-EW mice, which was sensitive to the blockade of σ1R. The NMDA receptor agonist, but not TrkB receptor activator, could correct the decline of nNOS-NO-CREB in early-EW mice. The findings indicate that the activation of σ1R can alleviate postpartum "depression" through increasing nNOS-NO-CREB activities.

Sigma-1 (σ1) Receptor in Memory and Neurodegenerative Diseases

The sigma-1 (σ1) receptor has been associated with regulation of intracellular Ca2+ homeostasis, several cellular signaling pathways, and inter-organelle communication, in part through its chaperone activity. In vivo, agonists of the σ1 receptor enhance brain plasticity, with particularly well-described impact on learning and memory. Under pathological conditions, σ1 receptor agonists can induce cytoprotective responses. These protective responses comprise various complementary pathways that appear to be differentially engaged according to pathological mechanism. Recent studies have highlighted the efficacy of drugs that act through the σ1 receptor to mitigate symptoms associated with neurodegenerative disorders with distinct mechanisms of pathogenesis. Here, we will review genetic and pharmacological evidence of σ1 receptor engagement in learning and memory disorders, cognitive impairment, and neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, multiple sclerosis, and Huntington's 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.

Is the Enzyme ACMSD a Novel Therapeutic Target in Parkinson's Disease?

Several large genome wide association studies have identified a locus in close proximity to the gene encoding the enzyme aminocarboxymuconate-semialdehyde-decarboxylase (ACMSD) to be associated with the risk for Parkinson's disease (PD), tentatively suggesting that this enzyme might influence PD pathogenesis. Further support for this comes from the recent identification of a disease-segregating stop codon mutation in ACMSD in a family with Parkinsonism, and a missense mutation in the ACMSD gene predicted to disrupt enzyme function in an individual with typical PD. ACMSD is part of the kynurenine pathway, responsible for the catalytic breakdown of tryptophan into NAD+, generating several neuroactive metabolites in the process. The enzyme is located at a key branch-point of the pathway, limiting the production of the neurotoxin quinolinic acid, which has excitotoxic and inflammatory properties. In this review, we discuss the genetic findings in light of the functions of ACMSD and its potential involvement in PD pathogenesis.

MPTP Impairs Dopamine D1 Receptor-Mediated Survival of Newborn Neurons in Ventral Hippocampus to Cause Depressive-Like Behaviors in Adult Mice

Parkinson’s disease (PD) is characterized by motor symptoms with depression. We evaluated the influence of dopaminergic depletion on hippocampal neurogenesis process to explore mechanisms of depression production. Five consecutive days of 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) injection in mice (MPTP-mice) reduced dopaminergic fibers in hippocampal dentate gyrus (DG). MPTP-mice exhibited depressive-like behaviors later for 2–3 weeks. BrdU was injected 4 h after last-injection of MPTP. BrdU-positive (BrdU⁺) cells in dorsal (d-DG) and ventral (v-DG) DG were examined on day 1 (D1), 7 (D7), 14 (D14) and 21 (D21) after BrdU injection. Fewer D7-, D14- and D21-BrdU⁺ cells or BrdU⁺/NeuN⁺ cells, but not D1-BrdU⁺ cells, were found in v-DG of MPTP-mice than in controls. However, the number of BrdU⁺ cells in d-DG did not differ between the both. Loss of doublecortin-positive (DCX⁺) cells was observed in v-DG of MPTP-mice. Protein kinase A (PKA) and Ca²⁺/cAMP-response element binding protein (CREB) phosphorylation were reduced in v-DG of MPTP-mice, which were reversed by D1-like receptor (D1R) agonist SKF38393, but not D2R agonist quinpirole. The treatment of MPTP-mice with SKF38393 on days 2–7 after BrdU-injection reduced the loss of D7- and D21-BrdU⁺ cells in v-DG and improved the depressive-like behaviors; these changes were sensitive to PKA inhibitor H89. Moreover, the v-DG injection of SKF38393 in MPTP-mice could reduce the loss of D21-BrdU⁺ cells and relieve the depressive-like behaviors. In control mice, the blockade of D1R by SCH23390 caused the reduction of D21-BrdU⁺ cells in v-DG and the depressive-like behaviors. Our results indicate that MPTP-reduced dopaminergic depletion impairs the D1R-mediated early survival of newborn neurons in v-DG, producing depressive-like behaviors.

Dihydromyricetin protects neurons in an MPTP-induced model of Parkinson's disease by suppressing glycogen synthase kinase-3 beta activity

AIM

It is general believed that mitochondrial dysfunction and oxidative stress play critical roles in the pathology of Parkinson's disease (PD). Dihydromyricetin (DHM), a natural flavonoid extracted from Ampelopsis grossedentata, has recently been found to elicit potent anti-oxidative effects. In the present study, we explored the role of DHM in protecting dopaminergic neurons.

METHODS

Male C57BL/6 mice were intraperitoneally injected with 1-methyl4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) for 7 d to induce PD. Additionally, mice were treated with either 5 or 10 mg/kg DHM for a total of 13 d (3 d before the start of MPTP, during MPTP administration (7 d) and 3 d after the end of MPTP). For the saline or DHM alone treatment groups, mice were injected with saline or DHM for 13 d. On d 14, behavioral tests (locomotor activity, the rotarod test and the pole test) were administered. After the behavioral tests, the mice were sacrificed, and brain tissue was collected for immunofluorescence staining and Western blotting. In addition, MES23.5 cells were treated with MPP⁺ and DHM, and evaluated using cell viability assays, reactive oxygen species (ROS) measurements, apoptosis analysis and Western blotting.

RESULTS

DHM significantly attenuated MPTP-induced mouse behavioral impairments and dopaminergic neuron loss. In the MES23.5 cells, DHM attenuated MPP⁺-induced cell injury and ROS production in a dose-dependent manner. In addition, DHM increased glycogen synthase kinase-3 beta phosphorylation in a dose- and time-dependent manner, which may be associated with DHM-induced dopaminergic neuronal protection.

CONCLUSION

The present study demonstrated that DHM is a potent neuroprotective agent for DA neurons by modulating the Akt/GSK-3β pathway, which suggests that DHM may be a promising therapeutic candidate for PD.

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.

Postpartum estrogen withdrawal impairs hippocampal neurogenesis and causes depression- and anxiety-like behaviors in mice

Postpartum estrogen withdrawal is known to be a particularly vulnerable time for depressive symptoms. Ovariectomized adult mice (OVX-mice) treated with hormone-simulated pregnancy (HSP mice) followed by a subsequent estradiol benzoate (EB) withdrawal (EW mice) exhibited depression- and anxiety-like behaviors, as assessed by forced swim, tail suspension and elevated plus-maze, while HSP mice, OVX mice or EB-treated OVX mice (OVX/EB mice) did not. The survival and neurite growth of newborn neurons in hippocampal dentate gyrus were examined on day 5 after EW. Compared with controls, the numbers of 28-day-old BrdU(+) and BrdU(+)/NeuN(+) cells were increased in HSP mice but significantly decreased in EW mice; the numbers of 10-day-old BrdU(+) cells were increased in HSP mice and OVX/EB mice; and the density of DCX(+) fibers was reduced in EW mice and OVX mice. The phosphorylation of hippocampal NMDA receptor (NMDAr) NR2B subunit or Src was increased in HSP mice but decreased in EW mice. NMDAr agonist NMDA prevented the loss of 28-day-old BrdU(+) cells and the depression- and anxiety-like behaviors in EW mice. NR2B inhibitor Ro25-6981 or Src inhibitor dasatinib caused depression- and anxiety-like behaviors in HSP mice with the reduction of 28-day-old BrdU(+) cells. The hippocampal BDNF levels were reduced in EW mice and OVX mice. TrkB receptor inhibitor K252a reduced the density of DCX(+) fibers in HSP mice without the reduction of 28-day-old BrdU(+) cells, or the production of affective disorder. Collectively, these results indicate that postpartum estrogen withdrawal impairs hippocampal neurogenesis in mice that show depression- and anxiety-like behaviors.

Sigma-1 Receptor Antagonist BD1047 Reduces Mechanical Allodynia in a Rat Model of Bone Cancer Pain through the Inhibition of Spinal NR1 Phosphorylation and Microglia Activation

Previous studies have demonstrated that sigma-1 receptor plays important roles in the induction phase of rodent neuropathic pain; however, whether it is involved in bone cancer pain (BCP) and the underlying mechanisms remain elusive. The aim of this study was to examine the potential role of the spinal sigma-1 receptor in the development of bone cancer pain. Walker 256 mammary gland carcinoma cells were implanted into the intramedullary space of the right tibia of Sprague-Dawley rats to induce ongoing bone cancer-related pain behaviors; our findings indicated that, on days 7, 10, 14, and 21 after operation, the expression of sigma-1 receptor in the spinal cord was higher in BCP rats compared to the sham rats. Furthermore, intrathecal injection of 120 nmol of sigma-1 receptor antagonist BD1047 on days 5, 6, and 7 after operation attenuated mechanical allodynia as well as the associated induction of c-Fos and activation of microglial cells, NR1, and the subsequent Ca(2+)-dependent signals of BCP rats. These results suggest that sigma-1 receptor is involved in the development of bone cancer pain and that targeting sigma-1 receptor may be a new strategy for the treatment of bone cancer pain.