Changes in synaptic proteins of the complex PSD-95/NMDA receptor/nNOS and mitochondrial dysfunction after levocabastine treatment

Nitric oxide generation is related to the activity of certain proteins located at synaptic sites. Previous findings show that NOS activity, nNOS protein expression, respiratory parameters and mitochondrial complex activities are altered in rat cerebral cortex by administration of levocabastine, an antagonist of histamine H1 and neurotensin NTS2 receptors. ATP provision by mitochondria may play an important role in the functional interaction between synaptic proteins NMDA receptor and PSD-95 with NO synthesis. In this context, our purpose was to evaluate the effect of levocabastine administration on protein expression of PSD-95, GluN2B and iNOS, as well as on mitochondrial ATP production. Male Wistar rats received a single (i.p.) dose of levocabastine (50 μg/kg) or saline solution (controls) and were decapitated 18 h later. Mitochondrial and synaptosomal membrane fractions were isolated from cerebral cortex by differential and sucrose gradient centrifugation. Expression of synaptic proteins was evaluated by Western blot assays in synaptosomal membrane fractions. Oxygen consumption, mitochondrial membrane potential and ATP production rate were determined in fresh crude mitochondrial fractions. After levocabastine treatment, protein expression of PSD-95, GluN2B and β-actin decreased 97, 45 and 55%, respectively, whereas that of iNOS enhanced 3.5-fold versus controls. In crude mitochondrial fractions levocabastine administration reduced roughly 15% respiratory control rate as assayed with malate-glutamate or succinate as substrates, decreased mitochondrial membrane potential (21%), and ATP production rates (57%). Results suggested that levocabastine administration induces alterations in synaptic proteins of the protein complex PSD-95/NMDA receptor/nNOS and in neuron cytoskeleton. Mitochondrial bioenergetics impairment may play a role in the functional link between synaptic proteins and NO synthesis.

Extinction vs. Abstinence: A Review of the Molecular and Circuit Consequences of Different Post-Cocaine Experiences

The intravenous cocaine self-administration model is widely used to characterize the neurobiology of cocaine seeking. When studies are aimed at understanding relapse to cocaine-seeking, a post-cocaine abstinence period is imposed, followed by “relapse” tests to assess the ability of drug-related stimuli (“primes”) to evoke the resumption of the instrumental response previously made to obtain cocaine. Here, we review the literature on the impact of post-cocaine abstinence procedures on neurobiology, finding that the prelimbic and infralimbic regions of the prefrontal cortex are recruited by extinction training, and are not part of the relapse circuitry when extinction training does not occur. Pairing cocaine infusions with discrete cues recruits the involvement of the NA, which together with the dorsal striatum, is a key part of the relapse circuit regardless of abstinence procedures. Differences in molecular adaptations in the NA core include increased expression of GluN1 and glutamate receptor signaling partners after extinction training. AMPA receptors and glutamate transporters are similarly affected by abstinence and extinction. Glutamate receptor antagonists show efficacy at reducing relapse following extinction and abstinence, with a modest increase in efficacy of compounds that restore glutamate homeostasis after extinction training. Imaging studies in humans reveal cocaine-induced adaptations that are similar to those produced after extinction training. Thus, while instrumental extinction training does not have face validity, its use does not produce adaptations distinct from human cocaine users.

Aberrant Synaptic PTEN in Symptomatic Alzheimer's Patients May Link Synaptic Depression to Network Failure

In Alzheimer’s disease (AD), Amyloid β (Aβ) impairs synaptic function by inhibiting long-term potentiation (LTP), and by facilitating long-term depression (LTD). There is now evidence from AD models that Aβ provokes this shift toward synaptic depression by triggering the access to and accumulation of PTEN in the postsynaptic terminal of hippocampal neurons. Here we quantified the PTEN in 196,138 individual excitatory dentate gyrus synapses from AD patients at different stages of the disease and from controls with no neuropathological findings. We detected a gradual increase of synaptic PTEN in AD brains as the disease progresses, in conjunction with a significant decrease in synaptic density. The synapses that remain in symptomatic AD patients are more likely to be smaller and exhibit fewer AMPA receptors (AMPARs). Hence, a high Aβ load appears to strongly compromise human hippocampal synapses, as reflected by an increase in PTEN, inducing a loss of AMPARs that may eventually provoke synaptic failure and loss.

Alcohol hangover induces nitric oxide metabolism changes by impairing NMDA receptor-PSD95-nNOS pathway

Alcohol hangover is defined as the combination of mental and physical symptoms experienced the day after a single episode of heavy drinking, starting when blood alcohol concentration approaches zero. We previously evidenced increments in free radical generation and an imbalance in antioxidant defences in non-synaptic mitochondria and synaptosomes during hangover. It is widely known that acute alcohol exposure induces changes in nitric oxide (NO) production and blocks the binding of glutamate to NMDAR in central nervous system. Our aim was to evaluate the residual effect of acute ethanol exposure (hangover) on NO metabolism and the role of NMDA receptor-PSD95-nNOS pathway in non-synaptic mitochondria and synaptosomes from mouse brain cortex. Results obtained for the synaptosomes fraction showed a 37% decrease in NO total content, a 36% decrease in NOS activity and a 19% decrease in nNOS protein expression. The in vitro addition of glutamate to synaptosomes produced a concentration-dependent enhancement of NO production which was significantly lower in samples from hangover mice than in controls for all the glutamate concentrations tested. A similar patter of response was observed for nNOS activity being decreased both in basal conditions and after glutamate addition. In addition, synaptosomes exhibited a 64% and 15% reduction in NMDA receptor subunit GluN2B and PSD-95 protein expression, respectively. Together with this, glutamate-induced calcium entry was significant decreased in synaptosomes from alcohol-treated mice. On the other hand, in non-synaptic mitochondria, no significant differences were observed in NO content, NOS activity or nNOS protein expression. The expression of iNOS remained unaltered in synaptosomes and non-synaptic mitochondria. Here we demonstrated that hangover effects on NO metabolism are strongly evidenced in synaptosomes probably due to a disruption in NMDAR/PSD-95/nNOS pathway.

A novel cell-penetrating peptide targeting calpain-cleavage of PSD-95 induced by excitotoxicity improves neurological outcome after stroke

Postsynaptic density protein-95 (PSD-95) is a multidomain protein critical to the assembly of signaling complexes at excitatory synapses, required for neuronal survival and function. However, calpain-processing challenges PSD-95 function after overactivation of excitatory glutamate receptors (excitotoxicity) in stroke, a leading cause of death, disability and dementia in need of efficient pharmacological treatments. A promising strategy is neuroprotection of the infarct penumbra, a potentially recoverable area, by promotion of survival signaling. Interference of PSD-95 processing induced by excitotoxicity might thus be a therapeutic target for stroke and other excitotoxicity-associated pathologies.

Methods: The nature and stability of PSD-95 calpain-fragments was analyzed using in vitro assays or excitotoxic conditions induced in rat primary neuronal cultures or a mouse model of stroke. We then sequenced PSD-95 cleavage-sites and rationally designed three cell-penetrating peptides (CPPs) containing these sequences. The peptides effects on PSD-95 stability and neuronal viability were investigated in the cultured neurons, subjected to acute or chronic excitotoxicity. We also analyzed the effect of one of these peptides in the mouse model of stroke by measuring infarct size and evaluating motor coordination and balance.

Results: Calpain cleaves three interdomain linker regions in PSD-95 and produces stable fragments corresponding to previously described PSD-95 supramodules (PDZ1-2 and P-S-G) as well as a truncated form SH3-GK. Peptide TP95₄₁₄, containing the cleavage site in the PDZ3-SH3 linker, is able to interfere PSD-95 downregulation and reduces neuronal death by excitotoxicity. Additionally, TP95₄₁₄ is delivered to mice cortex and, in a severe model of permanent ischemia, significantly improves the neurological outcome after brain damage.

Conclusions: Interference of excitotoxicity-induced PSD-95-processing with specific CPPs constitutes a novel and promising therapeutic approach for stroke treatment.

PSD-95 protects the pancreas against pathological damage through p38 MAPK signaling pathway in acute pancreatitis

Acute pancreatitis is one of the leading causes of gastrointestinal disorder-related hospitalizations, yet its pathogenesis remains to be fully elucidated. Postsynaptic density protein-95 (PSD-95) is closely associated with tissue inflammation and injury. We aimed to investigate the expression of PSD-95 in pancreatic acinar cells, and its function in regulating the inflammatory response and pancreatic pathological damage in acute pancreatitis. A mouse model of edematous acute pancreatitis was induced with caerulein and lipopolysaccharide in C57BL/6 mice. Tat-N-dimer was injected to inhibit the PSD-95 activity separately, or simultaneously with SB203580, inhibitor of p38 MAPK phosphorylation. Rat pancreatic acinar cells AR42J were cultured with 1 μM caerulein to build a cell model of acute pancreatitis. PSD-95-knockdown and negative control cell lines were constructed by lentiviral transfection of AR42J cells. Paraffin-embedded pancreatic tissue samples were processed for routine HE staining to evaluate the pathological changes of human and mouse pancreatic tissues. Serum amylase and inflammatory cytokine levels were detected with specific ELISA kits. Immunofluorescence, immunohistochemical, Western-blot, and qRT-PCR were used to detect the expression levels of PSD-95, p38, and phosphorylated p38. Our findings showed that PSD-95 is expressed in the pancreatic tissues of humans, C57BL/6 mice, and AR42J cells, primarily in the cytoplasm. PSD-95 expression increased at 2 h, reaching the peak at 6 h in mice and 12 h in AR42J cells. IL-6, IL-8, and TNF-α increased within 2 h of disease induction. The pancreatic histopathologic score was greater in the PSD-95 inhibition group compared with the control (P < 0.05), while it was lesser when phosphorylation of p38 MAPK was inhibited compared with the PSD-95 inhibition group (P < 0.05). Moreover, phosphorylation of p38 MAPK increased statistically after PSD-95 knocked-down. In conclusion, PSD-95 effectively influences the pathological damage of the pancreas in acute pancreatitis by affecting the phosphorylation of p38 MAPK.

Fructose Removal from the Diet Reverses Inflammation, Mitochondrial Dysfunction, and Oxidative Stress in Hippocampus

Young age is often characterized by high consumption of processed foods and fruit juices rich in fructose, which, besides inducing a tendency to become overweight, can promote alterations in brain function. The aim of this study was therefore to (a) clarify brain effects resulting from fructose consumption in juvenile age, a critical phase for brain development, and (b) verify whether these alterations can be rescued after removing fructose from the diet. Young rats were fed a fructose-rich or control diet for 3 weeks. Fructose-fed rats were then fed a control diet for a further 3 weeks. We evaluated mitochondrial bioenergetics by high-resolution respirometry in the hippocampus, a brain area that is critically involved in learning and memory. Glucose transporter-5, fructose and uric acid levels, oxidative status, and inflammatory and synaptic markers were investigated by Western blotting and spectrophotometric or enzyme-linked immunosorbent assays. A short-term fructose-rich diet induced mitochondrial dysfunction and oxidative stress, associated with an increased concentration of inflammatory markers and decreased Neurofilament-M and post-synaptic density protein 95. These alterations, except for increases in haptoglobin and nitrotyrosine, were recovered by returning to a control diet. Overall, our results point to the dangerous effects of excessive consumption of fructose in young age but also highlight the effect of partial recovery by switching back to a control diet.

PSD-95 in CA1 Area Regulates Spatial Choice Depending on Age

Cognitive processes that require spatial information rely on synaptic plasticity in the dorsal CA1 area (dCA1) of the hippocampus. Since the function of the hippocampus is impaired in aged individuals, it remains unknown how aged animals make spatial choices. Here, we used IntelliCage to study behavioral processes that support spatial choices of aged female mice living in a group. As a proxy of training-induced synaptic plasticity, we analyzed the morphology of dendritic spines and the expression of a synaptic scaffold protein, PSD-95. We observed that spatial choice training in young adult mice induced correlated shrinkage of dendritic spines and downregulation of PSD-95 in dCA1. Moreover, long-term depletion of PSD-95 by shRNA in dCA1 limited correct choices to a reward corner, while reward preference was intact. In contrast, old mice used behavioral strategies characterized by an increased tendency for perseverative visits and social interactions. This strategy resulted in a robust preference for the reward corner during the spatial choice task. Moreover, training decreased the correlation between PSD-95 expression and the size of dendritic spines. Furthermore, PSD-95 depletion did not impair place choice or reward preference in old mice. Thus, our data indicate that while young mice require PSD-95-dependent synaptic plasticity in dCA1 to make correct spatial choices, old animals observe cage mates and stick to a preferred corner to seek the reward. This strategy is resistant to the depletion of PSD-95 in the CA1 area. Overall, our study demonstrates that aged mice combine alternative behavioral and molecular strategies to approach and consume rewards in a complex environment.SIGNIFICANCE STATEMENT It remains poorly understood how aging affects behavioral and molecular processes that support cognitive functions. It is, however, essential to understand these processes to develop therapeutic interventions that support successful cognitive aging. Our data indicate that while young mice require PSD-95-dependent synaptic plasticity in dCA1 to make correct spatial choices (i.e., choices that require spatial information), old animals observe cage mates and stick to a preferred corner to seek the reward. This strategy is resistant to the depletion of PSD-95 in the CA1 area. Overall, our study demonstrates that aged mice combine alternative behavioral and molecular strategies to approach and consume rewards in a complex environment. Second, the contribution of PSD-95-dependent synaptic functions in spatial choice changes with age.

Prehabilitative exercise hastens recovery from isoflurane in diabetic and non-diabetic rats

Diabetes has been demonstrated to be one of the strongest predictors of risk for postoperative delirium and functional decline in older patients undergoing surgery. Exercise is often prescribed as a treatment for diabetic patients and regular physical activity is hypothesized to decrease the risk of postoperative cognitive impairments. Prior studies suggest that anesthetic emergence trajectories and recovery are predictive of risk for later postoperative cognitive impairments. Therapeutic strategies aimed at improving emergence and recovery from anesthesia may therefore be beneficial for diabetic patients. Wistar (n = 32) and Goto-Kakizaki (GK) type 2 diabetic (n = 32) rats between 3-4 months old underwent treadmill exercise for 30 min/day for ten days or remained inactive. Pre-anesthesia spontaneous alternation behavior was recorded with a Y-maze. Rats then received a 2-h exposure to 1.5-2 % isoflurane or oxygen only. The time to reach anesthetic emergence and post-anesthesia recovery behaviors was recorded for each rat. Postsynaptic density protein-95 (PSD-95), an important scaffolding protein required for synaptic plasticity, protein levels were quantified from hippocampus using western blot. Spontaneous alternation behavior (p = 0.044) and arm entries (p < 0.001) were decreased in GK rats. There was no difference between groups in emergence times from isoflurane, but exercise hastened the recovery time (p = 0.008) for both Wistar and GK rats. Following 10 days of exercise, both Wistar and GK rats show increased levels of PSD-95 in the hippocampus. Prehabilitation with moderate intensity exercise, even on a short timescale, is beneficial for recovery from isoflurane in rats, regardless of metabolic disease status.

From Hyposociability to Hypersociability-The Effects of PSD-95 Deficiency on the Dysfunctional Development of Social Behavior

Abnormal social behavior, including both hypo- and hypersociability, is often observed in neurodevelopmental disorders such as autism spectrum disorders. However, the mechanisms associated with these two distinct social behavior abnormalities remain unknown. Postsynaptic density protein-95 (PSD-95) is a highly abundant scaffolding protein in the excitatory synapses and an essential regulator of synaptic maturation by binding to NMDA and AMPA receptors. The DLG4 gene encodes PSD-95, and it is a risk gene for hypersocial behavior. Interestingly, PSD-95 knockout mice exhibit hyposociability during adolescence but hypersociability in adulthood. The adolescent hyposociability is accompanied with an NMDAR hyperfunction in the medial prefrontal cortex (mPFC), an essential part of the social brain for control of sociability. The maturation of mPFC development is delayed until young adults. However, how PSD-95 deficiency affects the functional maturation of mPFC and its connection with other social brain regions remains uncharacterized. It is especially unknown how PSD-95 knockout drives the switch of social behavior from hypo- to hyper-sociability during adolescent-to-adult development. We propose an NMDAR-dependent developmental switch of hypo- to hyper-sociability. PSD-95 deficiency disrupts NMDAR-mediated synaptic connectivity of mPFC and social brain during development in an age- and pathway-specific manner. By utilizing the PSD-95 deficiency mouse, the mechanisms contributing to both hypo- and hyper-sociability can be studied in the same model. This will allow us to assess both local and long-range connectivity of mPFC and examine how they are involved in the distinct impairments in social behavior and how changes in these connections may mature over time.

Neuroprotective Effects Against Cerebral Ischemic Injury Exerted by Dexmedetomidine via the HDAC5/NPAS4/MDM2/PSD-95 Axis

Numerous evidences have highlighted the efficient role of dexmedetomidine (DEX) in multi-organ protection. In the present study, the neuroprotective role of DEX on cerebral ischemic injury and the underlining signaling mechanisms were explored. In order to simulate cerebral ischemic injury, we performed middle cerebral artery occlusion in mice and oxygen-glucose deprivation in neurons. Immunohistochemistry, Western blot analysis, and RT-qPCR were used to examine expression of HDAC5, NPAS4, MDM2, and PSD-95 in hippocampus tissues of MCAO mice and OGD-treated neurons. MCAO mice received treatment with DEX and sh-PSD-95, followed by neurological function evaluation, behavioral test, infarct volume detection by TTC staining, and apoptosis by TUNEL staining. Additionally, gain- and loss-of-function approaches were conducted in OGD-treated neuron after DEX treatment. Cell viability and apoptosis were assessed with the application of CCK-8 and flow cytometry. The interaction between MDM2 and PSD-95 was evaluated using Co-IP assay, followed by ubiquitination of PSD-95 detection. As per the results, HDAC5 and MDM2 were abundantly expressed, while NPAS4 and PSD-95 were poorly expressed in hippocampus tissues of MCAO mice and OGD-treated neurons. DEX elevated viability, and reduced LDH leakage rate and apoptosis rate of OGD-treated neurons, which was reversed following the overexpression of HDAC5. Moreover, HDAC5 augmented MDM2 expression via NPAS4 inhibition. MDM2 induced PSD-95 ubiquitination and degradation. In MCAO mice, DEX improved neurological function and behaviors and decreased infarct volume and apoptosis, which was negated as a result of PSD-95 silencing. DEX plays a neuroprotective role against cerebral ischemic injury by disrupting MDM2-induced PSD-95 ubiquitination and degradation via HDAC5 and NPAS4.

Identification of Novel Fragments Binding to the PDZ1-2 Domain of PSD-95

Inhibition of PSD-95 has emerged as a promising strategy for the treatment of ischemic stroke, as shown with peptide-based compounds that target the PDZ domains of PSD-95. In contrast, developing potent and drug-like small molecules against the PSD-95 PDZ domains has so far been unsuccessful. Here, we explore the druggability of the PSD-95 PDZ1-2 domain and use fragment screening to investigate if this protein is prone to binding small molecules. We screened 2500 fragments by fluorescence polarization (FP) and validated the hits by surface plasmon resonance (SPR), including an inhibition counter-test, and found four promising fragments. Three ligand efficient fragments were shown by ¹ H,¹⁵ N HSQC NMR to bind in the small hydrophobic P⁰ pockets of PDZ1-2, and one of them underwent structure-activity relationship (SAR) studies. Overall, we demonstrate that fragment screening can successfully be applied to PDZ1-2 of PSD-95 and disclose novel fragments that can serve as starting points for optimization towards small-molecule PDZ domain inhibitors.

Astrocyte-secreted IL-33 mediates homeostatic synaptic plasticity in the adult hippocampus

Synaptic plasticity in the hippocampus is important for learning and memory formation. In particular, homeostatic synaptic plasticity enables neurons to restore their activity levels in response to chronic neuronal activity changes. While astrocytes modulate synaptic functions via the secretion of factors, the underlying molecular mechanisms remain unclear. Here, we show that suppression of hippocampal neuronal activity increases cytokine IL-33 release from astrocytes in the CA1 region. Activation of IL-33 and its neuronal ST2 receptor complex promotes functional excitatory synapse formation. Moreover, IL-33/ST2 signaling is important for the neuronal activity blockade-induced increase of CA1 excitatory synapses in vivo and spatial memory formation. This study suggests that astrocyte-secreted IL-33 acts as a negative feedback control signal to regulate hippocampal homeostatic synaptic plasticity.

Hippocampal synaptic plasticity is important for learning and memory formation. Homeostatic synaptic plasticity is a specific form of synaptic plasticity that is induced upon prolonged changes in neuronal activity to maintain network homeostasis. While astrocytes are important regulators of synaptic transmission and plasticity, it is largely unclear how they interact with neurons to regulate synaptic plasticity at the circuit level. Here, we show that neuronal activity blockade selectively increases the expression and secretion of IL-33 (interleukin-33) by astrocytes in the hippocampal cornu ammonis 1 (CA1) subregion. This IL-33 stimulates an increase in excitatory synapses and neurotransmission through the activation of neuronal IL-33 receptor complex and synaptic recruitment of the scaffold protein PSD-95. We found that acute administration of tetrodotoxin in hippocampal slices or inhibition of hippocampal CA1 excitatory neurons by optogenetic manipulation increases IL-33 expression in CA1 astrocytes. Furthermore, IL-33 administration in vivo promotes the formation of functional excitatory synapses in hippocampal CA1 neurons, whereas conditional knockout of IL-33 in CA1 astrocytes decreases the number of excitatory synapses therein. Importantly, blockade of IL-33 and its receptor signaling in vivo by intracerebroventricular administration of its decoy receptor inhibits homeostatic synaptic plasticity in CA1 pyramidal neurons and impairs spatial memory formation in mice. These results collectively reveal an important role of astrocytic IL-33 in mediating the negative-feedback signaling mechanism in homeostatic synaptic plasticity, providing insights into how astrocytes maintain hippocampal network homeostasis.

nNOS-mediated protein-protein interactions: promising targets for treating neurological and neuropsychiatric disorders

Neurological and neuropsychiatric disorders are one of the leading causes of disability worldwide and affect the health of billions of people. Nitric oxide (NO), a free gas with multitudinous bioactivities, is mainly produced from the oxidation of L-arginine by neuronal nitric oxide synthase (nNOS) in the brain. Inhibiting nNOS benefits a variety of neurological and neuropsychiatric disorders, including stroke, depression and anxiety disorders, post-traumatic stress disorder, Parkinson's disease, Alzheimer's disease, chronic pain, and drug addiction. Due to critical roles of nNOS in learning and memory and synaptic plasticity, direct inhibition of nNOS may cause severe side effects. Importantly, interactions of several proteins, including post-synaptic density 95 (PSD-95), carboxy-terminal PDZ ligand of nNOS (CAPON) and serotonin transporter (SERT), with the PSD/Disc-large/ZO-1 homologous (PDZ) domain of nNOS have been demonstrated to influence the subcellular distribution and activity of the enzyme in the brain. Therefore, it will be a preferable means to interfere with nNOS-mediated protein-protein interactions (PPIs), which do not lead to undesirable effects. Herein, we summarize the current literatures on nNOS-mediated PPIs involved in neurological and neuropsychiatric disorders, and the discovery of drugs targeting the PPIs, which is expected to provide potential targets for developing novel drugs and new strategy for the treatment of neurological and neuropsychiatric disorders.

Activation of CaMKII and GluR1 by the PSD-95-GluN2B Coupling-Dependent Phosphorylation of GluN2B in the Spinal Cord in a Rat Model of Type-2 Diabetic Neuropathic Pain

The mechanisms underlying type-2 diabetic neuropathic pain (DNP) are unclear. This study investigates the coupling of postsynaptic density-95 (PSD-95) to N-methyl-D-aspartate receptor subunit 2B (GluN2B), and the subsequent phosphorylation of GluN2B (Tyr1472-GluN2B) in the spinal cord in a rat model of type-2 DNP. Expression levels of PSD-95, Tyr1472-GluN2B, Ca2+/calmodulin-dependent protein kinase II (CaMKII) and its phosphorylated counterpart (Thr286-CaMKII), and α-amino-3-hydroxy-5-methyl-4-soxazole propionic acid receptor subtype 1 (GluR1) and its phosphorylated counterpart (Ser831-GluR1) were significantly increased versus controls in the spinal cord of type-2 DNP rats whereas the expression of total spinal GluN2B did not change. The intrathecal injection of Ro25-6981 (a specific antagonist of GluN2B) or Tat-NR2B9c (a mimetic peptide disrupting the interaction between PSD-95 and GluN2B) induced an antihyperalgesic effect and blocked the increased expression of Tyr1472-GluN2B, CaMKII, GluR1, Thr286-CaMKII, and Ser831-GluR1 in the spinal cords; the increase in spinal cord PSD-95 was not affected. These findings indicate that the PSD-95-GluN2B interaction may increase phosphorylation of GluN2B, and subsequently induce the expression of phosphorylation of CaMKII and GluR1 in the spinal cord of type-2 DNP rats. Targeting the interaction of PSD-95 with GluN2B may provide a new therapeutic strategy for type-2 DNP.

[Effects of Xiaotan Huayu Liqiao Formula on cognitive impairment in mice exposed to chronic intermittent hypoxia]

Objective: To investigate the improvement effects of Xiaotan Huayu Liqiao Formula on cognitive impairment in mice exposed to chronic intermittent hypoxia (CIH), and to explore the related mechanisms. Methods: Forty-eight male C57 BL/6 mice were randomly divided into four groups as Normoxia, CIH, Formula+CIH and Formula group. Mice were exposed to normoxia in the normoxia and formula group, or intermittent hypoxia in CIH or Formula+CIH group (in the chambers, mice were filled with 100% N₂ to produce FiO₂ of 9% for 1. 5 min. The FiO₂ gradually returned to 21% over the remainder of each cycle. The exposure cycle was repeated every 3 min, 8 h/day for 35 days). Mice were treated with Xiaotan Huayu Liqiao Formula at the dose of 26. 8 g/kg by intragastric administration before CIH exposure. Meanwhile, mice in CIH and normoxia group were given the same volume of normal saline. When the experiment lasts for 26-35 d, Morris water maze was used to detect cognitive dysfunction in mice. At the end of 35 days, Y-maze was performed in each group. After anesthesia, hippocampus was isolated for morphological observation and Western blot ananlysis. Nissl staining and electron microscopy were adopted to assess the neuronal damage in hippocampus, and Western blot was used to detect the levels of PSD-95 and synapsin expression. Results: Compared with normoxia group,the performance of CIH mice was significantly reduced in Morris water maze and Y-maze(P＜0. 01,P＜0. 01). Both the number of Nissl staining positive cells and the thickness of the postsynaptic density in hippocampus were significantly reduced. And, the levels of PSD-95 expression in hippocampus was also decreased in the CIH group(P＜0. 01), however, no significant change of synapsin expression was observed. Compared to CIH group, administration of Xiaotan Huayu Liqiao Formula markedly improved performance of mice in Morris water maze and Y-maze (P＜0. 01), increased Nissl staining positive cells and the thickness of the postsynaptic density and PSD-95 expression in hippocampus (P＜0. 01). Conclusion: Xiaotan Huayu Liqiao Formula could alleviate the structural and functional impairment of the postsynaptic dense area, and improved CIH-induced cognitive dysfunction.

Involvement of NMDAR/PSD-95/nNOS-NO-cGMP pathway in embryonic exposure to BPA induced learning and memory dysfunction of rats

Bisphenol A (BPA), can lead to learning and memory impairment, but the underlying mechanism is poorly understood. Researchers have indicated that the N-methyl-D-aspartate receptor (NMDAR)/postsynaptic density protein 95 (PSD-95)/neuronal nitric oxide synthase (nNOS)-nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) pathway greatly contributes to learning and memory process. Pregnant rats were exposed to 0, 0.05, 0.5, 5 and 50 mg/kg/day BPA via oral gavage from gestational day (GD) 5 to GD 19. Morris water maze, transmission electron microscope, western blot, real time PCR, biochemical analysis and ELISA were used to analyze the changes in behavior, synaptic ultrastructure, protein and gene expression of NMDAR, PSD-95, nNOS, together with nNOS activity, NO (Nitrate reductase method) and cGMP levels of the rat pups at different growth stages. Results of this research displayed that exposure to 0.5 mg/kg/day BPA could damage the spatial learning ability of rats at postnatal day (PND) 56. However, spatial memory ability could be affected by exposure to BPA at doses up to 5 mg/kg/day. Moreover, the thickness of the postsynaptic density decreased after exposure to BPA at doses of 5 and 50 mg/kg/day. Levels of NR1, NR2A, PSD-95 protein and mRNA were downregulated to some extent after exposure to BPA, whereas the expression of NR2B increased at GD 20 but decreased at PND 21 and 56. Contrarily, the nNOS expression along with the enzyme activity were promoted after exposure to BPA. Meanwhile, the NO and cGMP levels were suppressed at GD 20 but promoted at PND 21 and 56. In conclusion, these results demonstrated that NMDAR/PSD-95/nNOS-NO-cGMP pathway could be affected by embryonic exposure to BPA, which may involve in the spatial learning and memory dysfunction of rats in later life.

Rho Guanine Nucleotide Exchange Factor 4 (Arhgef4) Deficiency Enhances Spatial and Object Recognition Memory

Guanine nucleotide exchange factors (GEFs) play multiple functional roles in neurons. In a previous study, we reported that Arhgef4 (Rho guanine nucleotide exchange factor 4) functioned as a negative regulator of the excitatory synaptic function by sequestering postsynaptic density protein 95 (PSD-95). However, the role of Arhgef4 in behavior has not been examined. We performed comprehensive behavioral tests in knockout (KO) mice to investigate of the effects of Arhgef4 deficiency. We found that the expressed PSD-95 particle size was significantly increased in hippocampal neuronal cultures from Arhgef4 KO mice, which is consistent with the previous in vitro findings. Arhgef4 KO mice exhibited general motor activity and anxiety-like behavior comparable to those of the wild type littermates. However, spatial memory and object recognition memory were significantly enhanced in the Arhgef4 KO mice. Taken together, these data confirm the role of Arhgef4 as a negative synaptic regulator at the behavioral level.

Impairment of cognitive function induced by Shati/Nat8l overexpression in the prefrontal cortex of mice

A novel N-acetyltransferase, Shati/Nat8l, was identified in the brains of mice exposed to methamphetamine. Shati/Nat8l overexpression in the medial prefrontal cortex (mPFC) was found to attenuate methamphetamine-induced dependence. The mPFC is a brain region that plays an important role in cognitive function. However, the effect of Shati/Nat8l on cognition and memory has not yet been clarified. To understand the role of Shati/Nat8l in memory, we generated C57BL/6J mice with overexpressed Shati/Nat8l in the mPFC and performed memory-related experiments, including novel object-location and object-in-context tests. Furthermore, we used quantitative immunohistochemistry to assess the presynaptic and postsynaptic proteins, synaptophysin and postsynaptic density protein (PSD)-95, respectively. Shati/Nat8l overexpression in the mPFC impaired both novel object-location and object-in-context memory. Moreover, Shati/Nat8l overexpression in the mPFC reduced PSD-95 levels, but not synaptophysin levels in the mPFC. These results demonstrated that Shati/Nat8l overexpression in the mPFC is involved in location and contextual memory, and can affect the excitatory postsynaptic protein, PSD-95.

PSD-95 deficiency alters GABAergic inhibition in the prefrontal cortex

Postsynaptic Density Protein-95 (PSD-95) is a major scaffolding protein in the excitatory synapses in the brain and a critical regulator of synaptic maturation for NMDA and AMPA receptors. PSD-95 deficiency has been linked to cognitive and learning deficits implicated in neurodevelopmental disorders such as autism and schizophrenia. Previous studies have shown that PSD-95 deficiency causes a significant reduction in the excitatory response in the hippocampus. However, little is known about whether PSD-95 deficiency will affect gamma-aminobutyric acid (GABA)ergic inhibitory synapses. Using a PSD-95 transgenic mouse model (PSD-95^+/-), we studied how PSD-95 deficiency affects GABA_A receptor expression and function in the medial prefrontal cortex (mPFC) during adolescence. Our results showed a significant increase in the GABA_A receptor subunit α1. Correspondingly, there are increases in the frequency and amplitude in spontaneous inhibitory postsynaptic currents (sIPSCs) in pyramidal neurons in the mPFC of PSD-95^+/- mice, along with a significant increase in evoked IPSCs, leading to a dramatic shift in the excitatory-to-inhibitory balance in PSD-95 deficient mice. Furthermore, PSD-95 deficiency promotes inhibitory synapse function via upregulation and trafficking of NLGN2 and reduced GSK3β activity through tyr-216 phosphorylation. Our study provides novel insights on the effects of GABAergic transmission in the mPFC due to PSD-95 deficiency and its potential link with cognitive and learning deficits associated with neuropsychiatric disorders.

Morphological and functional abnormalities of hippocampus in APC1638T/1638T mice

In the present study, we examined morphology and function of hippocampus in the APC^1638T/1638T mouse. Expression levels of the APC mRNA and protein were both identical in the hippocampus of the APC^+/+ and APC^1638T/1638T mice. The dentate gyrus of the APC^1638T/1638T hippocampus was thicker, and has more densely-populated granule cells in the APC^1638T/1638T mouse hippocampus. Immunoelectron microscopy revealed co-localization of APC with alpha-amino-3- hydroxy-5-methyl- isoxazole-4-propionate receptor (AMPA-R) and with PSD-95 at post-synapse in the APC^+/+ hippocampus, while APC1638T was co-localized with neither AMPA-R nor PSD-95 in the APC^1638T/1638T hippocampus. By immunoprecipitation assay, full-length APC expressed in the APC ^+/+ mouse was co-immunoprecipitated with AMPA-R and PSD-95. In contrast, APC1638T expressed in the APC^1638T/1638T mouse was not co-immunoprecipitated with AMPA-R and PSD-95. In the hippocampal CA1 region of the APC^1638T/1638T mouse, c-Fos expression after electric foot shock was decreased compared with the APC^+/+ mouse. The present study showed some abnormalities on morphology of the hippocampus caused by a truncated APC (APC1638T). Also, our findings suggest that failure in APC binding to AMPA-R and PSD-95 may bring about less activities of hippocampal neurons in the APC^1638T/1638T mouse.

Quercetin attenuates diabetic neuropathic pain by inhibiting mTOR/p70S6K pathway-mediated changes of synaptic morphology and synaptic protein levels in spinal dorsal horn of db/db mice

Numerous studies indicate that the changes of synaptic morphology and synaptic protein levels in spinal dorsal horn neurons contributes to the development and maintenance of neuropathic pain. Quercetin, a bioflavonoid compound, has been shown to have analgesic effect in several pain models. However, the underlying mechanism for quercetin to allieviate pain is unclear. Therefore, in this study, we observed the effect of quercetin on diabetic neuropathic pain in db/db mice and explored the underlying mechanisms. Our results showed that chronic quercetin treatment alleviated thermal hyperalgesia in db/db mice. Moreover, quercetin administration significantly reduced the total dendritic length, the number of dendritic branches, and the dendritic spine density in the spinal dorsal horn neurons of db/db mice. Meanwhile, the up-regulated expressions of synaptic plasticity-associated proteins postsynaptic density protein 95 (PSD-95) and synaptophysin in spinal dorsal horn of db/db mice were decreased by quercetin treatment. In addition, quercetin treatment reduced the phosphorylated levels of mammalian target of rapamycin (mTOR) and p70 ribosomal S6 kinase (p70S6K) in spinal dorsal horn of db/db mice. These results demonstrate that quercetin may alleviate diabetic neuropathic pain by inhibiting mTOR/p70S6K pathway-mediated changes of synaptic morphology and synaptic protein levels in spinal dorsal horn neurons of db/db mice. These findings suggest that quercetin may be a promising therapeutic drug in neuropathic pain.

Mitigation of helium irradiation-induced brain injury by microglia depletion

Background

Cosmic radiation exposures have been found to elicit cognitive impairments involving a wide-range of underlying neuropathology including elevated oxidative stress, neural stem cell loss, and compromised neuronal architecture. Cognitive impairments have also been associated with sustained microglia activation following low dose exposure to helium ions. Space-relevant charged particles elicit neuroinflammation that persists long-term post-irradiation. Here, we investigated the potential neurocognitive benefits of microglia depletion following low dose whole body exposure to helium ions.

Methods

Adult mice were administered a dietary inhibitor (PLX5622) of colony stimulating factor-1 receptor (CSF1R) to deplete microglia 2 weeks after whole body helium irradiation (⁴He, 30 cGy, 400 MeV/n). Cohorts of mice maintained on a normal and PLX5622 diet were tested for cognitive function using seven independent behavioral tasks, microglial activation, hippocampal neuronal morphology, spine density, and electrophysiology properties 4–6 weeks later.

Results

PLX5622 treatment caused a rapid and near complete elimination of microglia in the brain within 3 days of treatment. Irradiated animals on normal diet exhibited a range of behavioral deficits involving the medial pre-frontal cortex and hippocampus and increased microglial activation. Animals on PLX5622 diet exhibited no radiation-induced cognitive deficits, and expression of resting and activated microglia were almost completely abolished, without any effects on the oligodendrocyte progenitors, throughout the brain. While PLX5622 treatment was found to attenuate radiation-induced increases in post-synaptic density protein 95 (PSD-95) puncta and to preserve mushroom type spine densities, other morphologic features of neurons and electrophysiologic measures of intrinsic excitability were relatively unaffected.

Conclusions

Our data suggest that microglia play a critical role in cosmic radiation-induced cognitive deficits in mice and, that approaches targeting microglial function are poised to provide considerable benefit to the brain exposed to charged particles.

CD40L Reverse Signaling Influences Dendrite Spine Morphology and Expression of PSD-95 and Rho Small GTPases

CD40-activated CD40L reverse signaling is a major physiological regulator of neural process growth from many kinds of developing neurons. Here we have investigated whether CD40L-reverse signaling also influences dendrite spine number and morphology in striatal medium spiny neurons (MSNs). Golgi preparations revealed no differences in the spine density, but because the dendrite arbors of MSNs were larger and branched in Cd40 ^-/- mice, the total number of spines was greater in Cd40 ^-/- mice. We also detected more mature spines compared with wild-type littermates. Western blot revealed that MSN cultures from Cd40 ^-/- mice had significantly less PSD-95 and there were changes in RhoA/B/C and Cdc42. Immunocytochemistry revealed that PSD-95 was clustered in spines in Cd40 ^-/- neurons compared with more diffuse labeling in Cd40 ^+/+ neurons. Activation of CD40L-reverse signaling with CD40-Fc prevented the changes observed in Cd40 ^-/- cultures. Our findings suggest that CD40L-reverse signaling influences dendrite spine morphology and related protein expression and distribution.

CD44 Can Compensate for IgSF11 Deficiency by Associating with the Scaffold Protein PSD-95 during Osteoclast Differentiation

Differentiation of osteoclasts, which are specialized multinucleated macrophages capable of bone resorption, is driven primarily by receptor activator of NF-κB ligand (RANKL). Additional signaling from cell surface receptors, such as cell adhesion molecules (CAMs), is also required for osteoclast maturation. Previously, we have demonstrated that immunoglobulin superfamily 11 (IgSF11), a member of the immunoglobulin-CAM (IgCAM) family, plays an important role in osteoclast differentiation through association with the scaffold protein postsynaptic density protein 95 (PSD-95). Here, we demonstrate that the osteoclast-expressed CAM CD44 can compensate for IgSF11 deficiency when cell-cell interaction conditions are suboptimal by associating with PSD-95. Impaired osteoclast differentiation in IgSF11-deficient (IgSF11^-/-) cultures was rescued by antibody-mediated stimulation of CD44 or by treatment with low-molecular-weight hyaluronan (LMW-HA), a CD44 ligand. Biochemical analysis revealed that PSD-95, which is required for osteoclast differentiation, associates with CD44 in osteoclasts regardless of the presence or absence of IgSF11. RNAi-mediated knockdown of PSD-95 abrogated the effects of either CD44 stimulation or LMW-HA treatment on osteoclast differentiation, suggesting that CD44, similar to IgSF11, is functionally associated with PSD-95 during osteoclast differentiation. Taken together, these results reveal that CD44 can compensate for IgSF11 deficiency in osteoclasts through association with PSD-95.