Mitochondrial fission drives neuronal metabolic burden to promote stress susceptibility in male mice.

Neurons are particularly susceptible to energy fluctuations in response to stress. Mitochondrial fission is highly regulated to generate ATP via oxidative phosphorylation; however, the role of a regulator of mitochondrial fission in neuronal energy metabolism and synaptic efficacy under chronic stress remains elusive. Here, we show that chronic stress promotes mitochondrial fission in the medial prefrontal cortex via activating dynamin-related protein 1 (Drp1), resulting in mitochondrial dysfunction in male mice. Both pharmacological inhibition and genetic reduction of Drp1 ameliorates the deficit of excitatory synaptic transmission and stress-related depressive-like behavior. In addition, enhancing Drp1 fission promotes stress susceptibility, which is alleviated by coenzyme Q10, which potentiates mitochondrial ATP production. Together, our findings unmask the role of Drp1-dependent mitochondrial fission in the deficits of neuronal metabolic burden and depressive-like behavior and provides medication basis for metabolism-related emotional disorders.

Cell type-specific NRBF2 orchestrates autophagic flux and adult hippocampal neurogenesis in chronic stress-induced depression.

Dysfunctional autophagy and impairment of adult hippocampal neurogenesis (AHN) each contribute to the pathogenesis of major depressive disorder (MDD). However, whether dysfunctional autophagy is linked to aberrant AHN underlying MDD remains unclear. Here we demonstrate that the expression of nuclear receptor binding factor 2 (NRBF2), a component of autophagy-associated PIK3C3/VPS34-containing phosphatidylinositol 3-kinase complex, is attenuated in the dentate gyrus (DG) under chronic stress. NRBF2 deficiency inhibits the activity of the VPS34 complex and impairs autophagic flux in adult neural stem cells (aNSCs). Moreover, loss of NRBF2 disrupts the neurogenesis-related protein network and causes exhaustion of aNSC pool, leading to the depression-like phenotype. Strikingly, overexpressing NRBF2 in aNSCs of the DG is sufficient to rescue impaired AHN and depression-like phenotype of mice. Our findings reveal a significant role of NRBF2-dependent autophagy in preventing chronic stress-induced AHN impairment and suggest the therapeutic potential of targeting NRBF2 in MDD treatment.

α-MSH-catabolic enzyme prolylcarboxypeptidase in nucleus accumbens shell ameliorates stress susceptibility in mice through regulating synaptic plasticity.

Emerging evidence demonstrates the vital role of synaptic transmission and structural remodeling in major depressive disorder. Activation of melanocortin receptors facilitates stress-induced emotional behavior. Prolylcarboxypeptidase (PRCP) is a serine protease, which splits the C-terminal amino acid of α-MSH and inactivates it. In this study, we asked whether PRCP, the endogenous enzyme of melanocortin system, might play a role in stress susceptibility via regulating synaptic adaptations. Mice were subjected to chronic social defeat stress (CSDS) or subthreshold social defeat stress (SSDS). Depressive-like behavior was assessed in SIT, SPT, TST and FST. Based on to behavioral assessments, mice were divided into the susceptible (SUS) and resilient (RES) groups. After social defeat stress, drug infusion or viral expression and behavioral tests, morphological and electrophysiological analysis were conducted in PFX-fixed and fresh brain slices containing the nucleus accumbens shell (NAcsh). We showed that PRCP was downregulated in NAcsh of susceptible mice. Administration of fluoxetine (20 mg·kg-1·d-1, i.p., for 2 weeks) ameliorated the depressive-like behavior, and restored the expression levels of PRCP in NAcsh of susceptible mice. Pharmacological or genetic inhibition of PRCP in NAcsh by microinjection of N-benzyloxycarbonyl-L-prolyl-L-prolinal (ZPP) or LV-shPRCP enhanced the excitatory synaptic transmission in NAcsh, facilitating stress susceptibility via central melanocortin receptors. On the contrary, overexpression of PRCP in NAcsh by microinjection of AAV-PRCP alleviated the depressive-like behavior and reversed the enhanced excitatory synaptic transmission, abnormal dendritogenesis and spinogenesis in NAcsh induced by chronic stress. Furthermore, chronic stress increased the level of CaMKIIα, a kinase closely related to synaptic plasticity, in NAcsh. The elevated level of CaMKIIα was reversed by overexpression of PRCP in NAcsh. Pharmacological inhibition of CaMKIIα in NAcsh alleviated stress susceptibility induced by PRCP knockdown. This study has revealed the essential role of PRCP in relieving stress susceptibility through melanocortin signaling-mediated synaptic plasticity in NAcsh.

BNIP3L/NIX-mediated mitophagy alleviates passive stress-coping behaviors induced by tumor necrosis factor-α.

Recent studies based on animal models of various neurological disorders have indicated that mitophagy, a selective autophagy that eliminates damaged and superfluous mitochondria through autophagic degradation, may be involved in various neurological diseases. As an important mechanism of cellular stress response, much less is known about the role of mitophagy in stress-related mood disorders. Here, we found that tumor necrosis factor-α (TNF-α), an inflammation cytokine that plays a particular role in stress responses, impaired the mitophagy in the medial prefrontal cortex (mPFC) via triggering degradation of an outer mitochondrial membrane protein, NIP3-like protein X (NIX). The deficits in the NIX-mediated mitophagy by TNF-α led to the accumulation of damaged mitochondria, which triggered synaptic defects and behavioral abnormalities. Genetic ablation of NIX in the excitatory neurons of mPFC caused passive coping behaviors to stress, and overexpression of NIX in the mPFC improved TNF-α-induced synaptic and behavioral abnormalities. Notably, ketamine, a rapid on-set and long-lasting antidepressant, reversed the TNF-α-induced behavioral abnormalities through activation of NIX-mediated mitophagy. Furthermore, the downregulation of NIX level was also observed in the blood of major depressive disorder patients and the mPFC tissue of animal models. Infliximab, a clinically used TNF-α antagonist, alleviated both chronic stress- and inflammation-induced behavioral abnormalities via restoring NIX level. Taken together, these results suggest that NIX-mediated mitophagy links inflammation signaling to passive coping behaviors to stress, which underlies the pathophysiology of stress-related emotional disorders.

A thalamic circuit facilitates stress susceptibility via melanocortin 4 receptor-mediated activation of nucleus accumbens shell.

AIMS: Central melanocortin 4 receptor (MC4R) has been reported to induce anhedonia via eliciting dysfunction of excitatory synapses. It is evident that metabolic signals are closely related to chronic stress-induced depression. Here, we investigated that a neural circuit is involved in melanocortin signaling contributing to susceptibility to stress. METHODS: Chronic social defeat stress (CSDS) was used to develop depressive-like behavior. Electrophysiologic and chemogenetic approaches were performed to evaluate the role of paraventricular thalamus (PVT) glutamatergic to nucleus accumbens shell (NAcsh) circuit in stress susceptibility. Pharmacological and genetic manipulations were applied to investigate the molecular mechanisms of melanocortin signaling in the circuit. RESULTS: CSDS increases the excitatory neurotransmission in NAcsh through MC4R signaling. The enhanced excitatory synaptic input in NAcsh is projected from PVT glutamatergic neurons. Moreover, chemogenetic manipulation of PVTGlu -NAcsh projection mediates the susceptibility to stress, which is dependent on MC4R signaling. Overall, these results reveal that the strengthened excitatory neurotransmission in NAcsh originates from PVT glutamatergic neurons, facilitating the susceptibility to stress through melanocortin signaling. CONCLUSIONS: Our results make a strong case for harnessing a thalamic circuit to reorganize excitatory synaptic transmission in relieving stress susceptibility and provide insights gained on metabolic underpinnings of protection against stress-induced depressive-like behavior.

Microglia-dependent excessive synaptic pruning leads to cortical underconnectivity and behavioral abnormality following chronic social defeat stress in mice.

Synapse loss in medial prefrontal cortex (mPFC) has been implicated in stress-related mood disorders, such as depression. However, the exact effect of synapse elimination in the depression and how it is triggered are largely unknown. Through repeated longitudinal imaging of mPFC in the living brain, we found both presynaptic and postsynaptic components were declined, together with the impairment of synapse remodeling and cross-synaptic signal transmission in the mPFC during chronic stress. Meanwhile, chronic stress also induced excessive microglia phagocytosis, leading to engulfment of excitatory synapses. Further investigation revealed that the elevated complement C3 during the stress acted as the tag of synapses to be eliminated by microglia. Besides, chronic stress induced a reduction of the connectivity between the mPFC and neighbor regions. C3 knockout mice displayed significant reduction of synaptic pruning and alleviation of disrupted functional connectivity in mPFC, resulting in more resilience to chronic stress. These results indicate that complement-mediated excessive microglia phagocytosis in adulthood induces synaptic dysfunction and cortical hypo-connectivity, leading to stress-related behavioral abnormality.

Repeated vagus nerve stimulation produces anxiolytic effects via upregulation of AMPAR function in centrolateral amygdala of male rats.

Repeated vagus nerve stimulation (rVNS) exerts anxiolytic effect by activation of noradrenergic pathway. Centrolateral amygdala (CeL), a lateral subdivision of central amygdala, receives noradrenergic inputs, and its neuronal activity is positively correlated to anxiolytic effect of benzodiazepines. The activation of ß-adrenergic receptors (ß-ARs) could enhance glutamatergic transmission in CeL. However, it is unclear whether the neurobiological mechanism of noradrenergic system in CeL mediates the anxiolytic effect induced by rVNS. Here, we find that rVNS treatment produces an anxiolytic effect in male rats by increasing the neuronal activity of CeL. Electrophysiology recording reveals that rVNS treatment enhances the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor (AMPAR)-mediated excitatory neurotransmission in CeL, which is mimicked by ß-ARs agonist isoproterenol or blocked by ß-ARs antagonist propranolol. Moreover, chemogenetic inhibition of CeL neurons or pharmacological inhibition of ß-ARs in CeL intercepts both enhanced glutamatergic neurotransmission and the anxiolytic effects by rVNS treatment. These results suggest that the amplified AMPAR trafficking in CeL via activation of ß-ARs is critical for the anxiolytic effects induced by rVNS treatment.

Transcription Factor TWIST1 Integrates Dendritic Remodeling and Chronic Stress to Promote Depressive-like Behaviors.

BACKGROUND: Deficiency in neuronal structural plasticity is involved in the development of major depressive disorder. TWIST1, a helix-loop-helix transcription factor that is essential for morphogenesis and organogenesis, is normally expressed at low levels in mature neurons. However, it is poorly understood what role TWIST1 plays in the brain and whether it is involved in the pathophysiology of depression. METHODS: Depressive-like behaviors in C57BL/6J mice were developed by chronic social defeat stress. Genetic and pharmacological approaches were used to investigate the role of the TWIST1-miR-214-PPAR-δ signaling pathway in depressive-like behaviors. Molecular biological and morphological studies were performed to define the molecular mechanisms downstream of TWIST1. RESULTS: The expression of TWIST1 was positively correlated with depressive behaviors in humans and mice. Chronic stress elevated TWIST1 expression in the medial prefrontal cortex of mice, which was reversed by fluoxetine treatment. While the overexpression of TWIST1 increased susceptibility to stress, the knockdown of TWIST1 prevented the defective morphogenesis of dendrites of pyramidal neurons in layer II/III of the medial prefrontal cortex and alleviated depressive-like behaviors. Mechanistically, this prodepressant property of TWIST1 was mediated, at least in part, through the repression of miR-214-PPAR-δ signaling and mitochondrial function, which was also mimicked by genetic and pharmacological inhibition of PPAR-δ. CONCLUSIONS: These results suggest that TWIST1 in the medial prefrontal cortex mediates chronic stress-induced dendritic remodeling and facilitates the occurrence of depressive-like behavior, providing new information for developing drug targets for depression therapy.

Angiotensin-Converting Enzyme Inhibitor Rapidly Ameliorates Depressive-Type Behaviors via Bradykinin-Dependent Activation of Mammalian Target of Rapamycin Complex 1.

BACKGROUND: Angiotensin-converting enzyme inhibitors (ACEIs) are widely prescribed antihypertensive agents. Intriguingly, case reports and clinical trials have indicated that ACEIs, including captopril and lisinopril, may have a rapid mood-elevating effect in certain patients, but few experimental studies have investigated their value as fast-onset antidepressants. METHODS: The present study consisted of a series of experiments using biochemical assays, immunohistochemistry, and behavioral techniques to examine the effect and mechanism of captopril on depressive-like behavior in 2 animal models, the chronic unpredictable stress model and the chronic social defeat stress model. RESULTS: Captopril (19.5 or 39 mg/kg, intraperitoneal injection) exerted rapid antidepressant activity in mice treated under the chronic unpredictable stress model and mice treated under the chronic social defeat stress model. Pharmacokinetic analysis revealed that captopril crossed the blood-brain barrier and that lisinopril, another ACEI with better blood-brain barrier permeability, exerted a faster and longer-lasting effect at a same molar equivalent dose. This antidepressant effect seemed to be independent of the renin-angiotensin system, but dependent on the bradykinin (BK) system, since the decreased BK detected in the stressed mice could be reversed by captopril. The hypofunction of the downstream effector of BK, Cdc42 (cell division control protein 42) homolog, contributed to the stress-induced loss of dendritic spines, which was rapidly reversed by captopril via activating the mTORC1 (mammalian target of rapamycin complex 1) pathway. CONCLUSIONS: Our findings indicate that the BK-dependent activation of mTORC1 may represent a promising mechanism underlying antidepressant pharmacology. Considering their affordability and availability, ACEIs may emerge as a novel fast-onset antidepressant, especially for patients with comorbid depression and hypertension.

A-Kinase Anchoring Protein 150 and Protein Kinase A Complex in the Basolateral Amygdala Contributes to Depressive-like Behaviors Induced by Chronic Restraint Stress.

BACKGROUND: The basolateral amygdala (BLA) has been widely implicated in the pathophysiology of major depressive disorder. A-kinase anchoring protein 150 (AKAP150) directs kinases and phosphatases to synaptic glutamate receptors, controlling synaptic transmission and plasticity. However, the role of the AKAP150 in the BLA in major depressive disorder remains poorly understood. METHODS: Depressive-like behaviors in C57BL/6J mice were developed by chronic restraint stress (CRS). Mice received either intra-BLA injection of lentivirus-expressing Akap5 short hairpin RNA or Ht-31, a peptide to disrupt the interaction of AKAP150 and protein kinase A (PKA), followed by depressive-like behavioral tests. Alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid glutamate receptor (AMPAR)-mediated miniature excitatory postsynaptic currents were recorded by whole-cell patch-clamp techniques. RESULTS: Chronic stress exposure induced depressive-like behaviors, which were accompanied by an increase in total and synaptic AKAP150 expression in the BLA. Accordingly, CRS facilitated the association of AKAP150 with PKA, but not of calcineurin in the BLA. Intra-BLA infusion of lentivirus-expressing Akap5 short hairpin RNA or Ht-31 prevented depressive-like behaviors and normalized phosphorylation of serine 845 and surface expression of AMPAR subunit 1 (GluA1) in the BLA of CRS mice. Finally, blockage of AKAP150-PKA complex signaling rescued the changes in AMPAR-mediated miniature excitatory postsynaptic currents in depressive-like mice. CONCLUSIONS: These results suggest that AKAP150-PKA directly modulates BLA neuronal synaptic strength, and that AKAP150-PKA-GluA1 streamline signaling complex is responsible for CRS-induced disruption of synaptic AMPAR-mediated transmission and depressive-like behaviors in mice.

Gephyrin Palmitoylation in Basolateral Amygdala Mediates the Anxiolytic Action of Benzodiazepine.

BACKGROUND: Benzodiazepines (BZDs) have been used to treat anxiety disorders for more than five decades as the allosteric modulator of the gamma-aminobutyric acid A receptor (GABAAR). Little is known about other mechanisms of BZDs. Here, we describe how the rapid stabilization of postsynaptic GABAAR is essential and sufficient for the anxiolytic effect of BZDs via a palmitoylation-dependent mechanism. METHODS: Palmitoylated proteins in the basolateral amygdala (BLA) of rats with different anxious states were assessed by a biotin exchange protocol. Both pharmacological and genetic approaches were used to investigate the role of palmitoylation in anxiety behavior. Electrophysiological recording, reverse transcription polymerase chain reaction, Western blotting, and coimmunoprecipitation were used to investigate the mechanisms. RESULTS: Highly anxious rats were accompanied by the deficiency of gephyrin palmitoylation and decreased the synaptic function of GABAAR in the BLA. We then identified that the dysfunction of DHHC12, a palmitoyl acyltransferase that specifically palmitoylates gephyrin, contributed to the high-anxious state. Furthermore, diazepam, as an anxiolytic drug targeting GABAARs, was found to increase gephyrin palmitoylation in the BLA via a GABAAR-dependent manner to activate DHHC12. The anxiolytic effect of diazepam was nearly abolished by the DHHC12 knockdown. Specifically, similar to the effect of BZD, the overexpression of DHHC12 in the BLA exerted a significant anxiolytic action, which was prevented by flumazenil. CONCLUSIONS: Our results support the view that the strength of inhibitory synapse was controlled by gephyrin palmitoylation in vivo and proposes a previously unknown palmitoylation-centered mode of BZD's action.

SAR405, a Highly Specific VPS34 Inhibitor, Disrupts Auditory Fear Memory Consolidation of Mice via Facilitation of Inhibitory Neurotransmission in Basolateral Amygdala.

BACKGROUND: Autophagy has been demonstrated to play an important role in memory deficits as well as the degradation of neurotransmitter receptors. SAR405 is a newly discovered inhibitor that can specifically inhibit vacuolar sorting protein 34 and prevent autophagosome biogenesis. However, the effects of SAR405 on memory processes remain largely unknown. METHODS: Western blotting, immunofluorescence, and transmission electron microscopy were used to assess the level of autophagy after fear conditioning and SAR405 treatment. Behavioral tests, biotinylation assay, electrophysiology, and co-immunoprecipitation were used to unravel the mechanisms of SAR405 in memory consolidation. RESULTS: SAR405 infusion into the basolateral amygdala impaired long-term memory through autophagy inhibition. Furthermore, the trafficking of gamma-aminobutyric acid type A receptors (GABAARs) following fear conditioning was disrupted by SAR405, and the decreased frequency and amplitude of miniature inhibitory postsynaptic currents induced by fear conditioning were also reversed by SAR405, suggesting that SAR405 disrupted memory consolidation through blockade of the downregulated inhibitory neurotransmission in basolateral amygdala. GABAAR-associated protein (GABARAP) and its interaction with GABAAR γ2 subunit were found to be upregulated after fear conditioning, and SAR405 could suppress this increased interaction. Moreover, disruption of the GABARAP-GABAAR binding by a trans-activating transcriptional activator-GABARAP inhibitory peptide blocked the decrease in surface expression of GABAARs and attenuated long-term memory. CONCLUSIONS: The present study suggests that SAR405 can prevent the memory consolidation via intervening autophagy and GABAAR trafficking and has a potential therapeutic value for disorders characterized by exaggerated fear memories, such as posttraumatic stress disorder.

Activity-Dependent Sulfhydration Signal Controls N-Methyl-D-Aspartate Subtype Glutamate Receptor-Dependent Synaptic Plasticity via Increasing d-Serine Availability.

AIMS: Reactive sulfur species, including hydrogen sulfide (H2S) and its oxydates, have been raised as novel redox signaling molecules. The present study aimed at examining whether endogenous sulfhydration signal is required for long-term potentiation (LTP), a cellular model for memory. RESULTS: In this study, we found that increased synaptic activity triggered sulfide generation and protein sulfhydration. Activity-triggered sulfide production was essential for N-methyl-D-aspartate subtype glutamate receptor (NMDAR)-dependent LTP via maintaining the availability of d-serine, a primary coagonist for synaptic NMDARs. Genetic knockdown of cystathionine ß-synthase, not cystathionine γ-lyase, impaired LTP. H2S increased NMDAR-dependent LTP via sulfhydration and disinhibition of serine racemase (SR), a main synthetase of d-serine. We found that polysulfides also increased NMDAR-dependent LTP and NMDAR activity. In aged rats, the level of H2S and SR sulfhydration decreased significantly. Exogenous supplement of H2S restored the sulfhydration of SR, followed by the improvement of age-related deficits in LTP. Furthermore, boost of H2S signal in vivo improves hippocampus-dependent memory. Innovation and Conclusion: Our results provide a direct evidence for the biological significance of endogenous sulfhydration signal in synaptic plasticity. Exogenous supplement of H2S could be considered as the new therapeutic approach for the treatment of neurocognitive dysfunction after aging. Antioxid. Redox Signal. 27, 398-414.

Dimethyl sulfide protects against oxidative stress and extends lifespan via a methionine sulfoxide reductase A-dependent catalytic mechanism.

Methionine (Met) sulfoxide reductase A (MsrA) is a key endogenous antioxidative enzyme with longevity benefits in animals. Only very few approaches have been reported to enhance MsrA function. Recent reports have indicated that the antioxidant capability of MsrA may involve a Met oxidase activity that facilities the reaction of Met with reactive oxygen species (ROS). Herein, we used a homology modeling approach to search the substrates for the oxidase activity of MsrA. We found that dimethyl sulfide (DMS), a main metabolite that produced by marine algae, emerged as a good substrate for MsrA-catalytic antioxidation. MsrA bounds to DMS and promoted its antioxidant capacity via facilitating the reaction of DMS with ROS through a sulfonium intermediate at residues Cys72, Tyr103, and Glu115, followed by the release of dimethyl sulfoxide (DMSO). DMS reduced the antimycin A-induced ROS generation in cultured PC12 cells and alleviated oxidative stress. Supplement of DMS exhibited cytoprotection and extended longevity in both Caenorhabditis elegans and Drosophila. MsrA knockdown abolished the cytoprotective effect and the longevity benefits of DMS. Furthermore, we found that the level of physiologic DMS was at the low micromolar range in different tissues of mammals and its level decreased after aging. This study opened a new window to elucidate the biological role of DMS and other low-molecular sulfides in the cytoprotection and aging.

AMPK Mediates Glucocorticoids Stress-Induced Downregulation of the Glucocorticoid Receptor in Cultured Rat Prefrontal Cortical Astrocytes.

Chronic stress induces altered energy metabolism and plays important roles in the etiology of depression, in which the glucocorticoid negative feedback is disrupted due to imbalanced glucocorticoid receptor (GR) functions. The mechanism underlying the dysregulation of GR by chronic stress remains elusive. In this study, we investigated the role of AMP-activated protein kinase (AMPK), the key enzyme regulating cellular energy metabolism, and related signaling pathways in chronic stress-induced GR dysregulation. In cultured rat cortical astrocytes, glucocorticoid treatment decreased the level, which was accompanied by the decreased expression of liver kinase B1 (LKB1) and reduced phosphorylation of AMPK. Glucocorticoid-induced effects were attenuated by glucocorticoid-inducible kinase 1 (SGK1) inhibitor GSK650394, which also inhibited glucocorticoid induced phosphorylation of Forkhead box O3a (FOXO3a). Furthermore, glucocorticoid-induced down-regulation of GR was mimicked by the inhibition of AMPK and abolished by the AMPK activators or the histone deacetylase 5 (HDAC5) inhibitors. In line with the role of AMPK in GR expression, AMPK activator metformin reversed glucocorticoid-induced reduction of AMPK phosphorylation and GR expression as well as behavioral alteration of rats. Taken together, these results suggest that chronic stress activates SGK1 and suppresses the expression of LKB1 via inhibitory phosphorylation of FOXO3a. Downregulated LKB1 contributes to reduced activation of AMPK, leading to the dephosphorylation of HDAC5 and the suppression of transcription of GR.

Potentiation of Surface Stability of AMPA Receptors by Sulfhydryl Compounds: A Redox-Independent Effect by Disrupting Palmitoylation.

Sulfhydryl compounds such as dithiothreitol (DTT) and ß-mercaptoethanol (ß-ME) are widely used as redox agents. Previous studies in our group and other laboratory have reported the effect of sulfhydryl compounds on the function of glutamate receptor, including plasticity. Most of these findings have focused on the N-methyl-D-aspartic acid receptor, in contrast, very little is known about the effect of sulfhydryl compounds on α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor (AMPAR). Here, we observed that DTT (100 µM), ß-ME (200 µM) and L-cysteine (200 µM) significantly elevated the surface expression of AMPARs via reducing their palmitoylation in rat hippocampal slices in vitro. Increased surface stability of AMPARs was not be correlated with the altered redox status, because the chemical entities containing mercapto group such as penicillamine (200 µM) and 2-mercapto-1-methylimidazole (200 µM) exhibited little effects on the surface expression of AMPARs. Computing results of Asp-His-His-Cys (DHHC) 3, the main enzyme for palmitoylation of AMPARs, indicated that only the alkyl mercaptans with chain-like configuration, such as DTT and ß-ME, can enter the pocket of DHHC3 and disrupt the catalytic activity via inhibiting DHHC3 auto-palmitoylation. Collectively, our findings indicate a novel redox-independent mechanism underlay the multiple effects of thiol reductants on synaptic function.

Hydrogen Sulfide Promotes Surface Insertion of Hippocampal AMPA Receptor GluR1 Subunit via Phosphorylating at Serine-831/Serine-845 Sites Through a Sulfhydration-Dependent Mechanism.

AIMS: Hydrogen sulfide (H2 S) has been widely accepted as a gas neuromodulator to regulate synaptic function. Herein, we set out to determine the effect of H2 S on α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor (AMPAR) and its mechanism. METHODS: BS(3) protein cross-linking, Western blot, patch clamp, and biotin-switch assay. RESULTS: Bath application of H2 S donor NaHS (50 and 100 µM) rapidly promoted surface insertion of hippocampal AMPAR GluR1 subunit. This effect can be abolished by dithiothreitol (DTT) and mimicked by Na2 S4 , indicating that a sulfhydration-dependent mechanism may be involved. NaHS increased APMAR-mediated EPSC and led to an elevation of GluR2-lacking AMPAR content. Notably, NaHS did not increase the sulfhydration of AMPAR subunits, but it significantly increased the phosphorylation of GluR1 at serine-831 and serine-845 sites. Postsynaptic signal pathways that control GluR1 phosphorylation, such as protein kinase A (PKA), protein kinase C, and calcium/calmodulin-dependent protein kinases II (CaMKII), were sulfhydrated, activated by NaHS, and these effects can be occluded by DTT. H2 S increased S-sulfhydration of protein phosphatase type 2A (PP2A), which may be partially involved in the activation of signal pathways. CONCLUSION: Our data suggest that H2 S promotes surface insertion of AMPARs via phosphorylation of GluR1, which depends on a sulfhydration-mediated mechanism.

Chronic administration tetrahydroxystilbene glucoside promotes hippocampal memory and synaptic plasticity and activates ERKs, CaMKII and SIRT1/miR-134 in vivo.

ETHNOPHARMACOLOGICAL RELEVANCE: Polygonum multiflorum Thunb is a traditional Chinese medicine with anti-aging effect. 2,3,5,4'-tetrahydroxystilbene-2-O-ß-D-glucoside (TSG) is generally considered as the main active component in Polygonum multiflorum Thunb. However, the effect of TSG on memory in adult is unclear till now. AIM OF STUDY: 2,3,5,4'-tetrahydroxystilbene-2-O-ß-D-glucoside (TSG) is a polyphenols compound from Polygonum multiflorum Thunb. The present study aimed to evaluate the effect of chronic administration of TSG on hippocampal memory in normal mice. MATERIALS AND METHODS: Behavioral test, electrophysiology and golgi staining were used to evaluate the effect of TSG on hippocampus-dependent memory and synaptic plasticity. Western blotting was used to determine the expression of ERK1/2, CaMKII, and SIRT1. Real-time quantitative PCR was explored to measure miR-134. RESULTS: It was found that TSG enhanced hippocampus-dependent contextual fear memory and novel object recognition, facilitated hippocampal LTP and increased dendrite spine density in the CA1 region of hippocampus. TSG obviously promoted the phosphorylations of ERK1/2, CaMKII, CREB and the expression of BDNF in the hippocampus, with upregulation of silent information regulator 1 (SIRT1) and downregulation of miR-134. CONCLUSIONS: Chronic administration of TSG promotes hippocampal memory in normal mice, suggesting that supplementary of TSG might serve as an enhancement of memory.

Sulfite triggers sustained calcium overload in cultured cortical neurons via a redox-dependent mechanism.

Sulfite is a compound commonly used as preservative in foods and pharmaceuticals. Many studies have examined the neurotoxicity of sulfite, but its effect on neuronal calcium homeostasis has not yet been reported. Here, we observed the effect of sulfite on the cytosolic free calcium concentration ([Ca(2+)]i) in cultured cortical neurons using Fura-2/AM based calcium imaging technique. Sulfite (250-1000µM) caused a sustained increase in [Ca(2+)]i in the neurons via a dose-dependent manner. In Ca(2+)-free solution, sulfite failed to increase [Ca(2+)]i. After the depletion of the intracellular calcium store, the effect of sulfite on the [Ca(2+)]i was largely abolished. Pharmacological inhibition of phospholipase C (PLC)-inositol 1,4,5-triphosphate (IP3) signaling pathway blocked sulfite-induced increase of [Ca(2+)]i. Interestingly, antioxidants such as trolox and dithiothreitol, abolished the increase of [Ca(2+)]i induced by sulfite. Exposure to sulfite triggered generation of sulfur- and oxygen-centered free radicals in neurons and increased oxidative stress both in the cultured cortical neurons and the prefrontal cortex of rats. Furthemore, sulfite decreased cell viability in cultured cortical neurons via a calcium-dependent manner. Thus, our current study suggests that the redox-dependent calcium overload triggered by sulfite in cortical neuronsmay be involved in its neurotoxicity.

HFS-Triggered AMPK Activation Phosphorylates GSK3ß and Induces E-LTP in Rat Hippocampus In Vivo.

BACKGROUND: The AMP-activated protein kinase (AMPK) is a sensor of cellular energy and nutrient status, with substantial amount of cross talk with other signaling pathways, including its phosphorylation by Akt, PKA, and GSK3ß. AIMS: Various signaling pathways and energy-consuming transport of glutamate receptors subunits are required in synaptic plasticity. However, it is unknown which energy sensors integrate the signaling pathways in these processes. In this article, we elucidated the role of AMPK activation and GSK3ß phosphorylation after HFS during the inducement of early-phase long-term potentiation (E-LTP). METHODS: Synaptic LTP in vivo was induced by high-frequency stimulation (HFS at 200 Hz at a 5-s interval). In addition, phosphorylation of AMPK and glycogen synthase kinase 3ß (GSK3ß) were measured using Western blotting. The amount of hippocampal AMP, ADP and ATP was measured by HPLC. RESULTS: We showed that the phosphorylation of AMPK and GSK3ß was significantly increased by HFS in vivo. HFS-induced AMPK activation occurred via increased (AMP + ADP)/ATP ratio and activation of Ca(2+) /calmodulin-dependent kinase kinase beta (CaMKKß). Pharmacological inhibition of AMPK by compound C (CC) prevented HFS-induced inhibitory phosphorylation of GSK3ß and the induction of LTP in dentate gyrus (DG) area in vivo. CONCLUSIONS: Our findings reveal that HFS-triggered AMPK activation phosphorylates GSK3ß and induces E-LTP in vivo.