Immunohistochemical localization of Ca2+/calmodulin-dependent protein kinase II in rat brain and various tissues

Clinical and electrophysiological features of SCN8A variants causing episodic or chronic ataxia

BACKGROUND

Variants in SCN8A are associated with a spectrum of epilepsies and neurodevelopmental disorders. Ataxia as a predominant symptom of SCN8A variation has not been well studied. We set out to investigate disease mechanisms and genotype-phenotype correlations of SCN8A-related ataxia.

METHODS

We collected genetic and electro-clinical data of ten individuals from nine unrelated families carrying novel SCN8A variants associated with chronic progressive or episodic ataxia. Electrophysiological characterizations of these variants were performed in ND7/23 cells and cultured neurons.

FINDINGS

Variants associated with chronic progressive ataxia either decreased Na+ current densities and shifted activation curves towards more depolarized potentials (p.Asn995Asp, p.Lys1498Glu and p.Trp1266Cys) or resulted in a premature stop codon (p.Trp937Ter). Three variants (p.Arg847Gln and biallelic p.Arg191Trp/p.Asp1525Tyr) were associated with episodic ataxia causing loss-of-function by decreasing Na+ current densities or a hyperpolarizing shift of the inactivation curve. Two additional episodic ataxia-associated variants caused mixed gain- and loss-of function effects in ND7/23 cells and were further examined in primary murine hippocampal neuronal cultures. Neuronal firing in excitatory neurons was increased by p.Arg1629His, but decreased by p.Glu1201Lys. Neuronal firing in inhibitory neurons was decreased for both variants. No functional effect was observed for p.Arg1913Trp. In four individuals, treatment with sodium channel blockers exacerbated symptoms.

INTERPRETATION

We identified episodic or chronic ataxia as predominant phenotypes caused by variants in SCN8A. Genotype-phenotype correlations revealed a more pronounced loss-of-function effect for variants causing chronic ataxia. Sodium channel blockers should be avoided under these conditions.

FUNDING

BMBF, DFG, the Italian Ministry of Health, University of Tuebingen.

A comprehensive toxicological analysis of trans-fatty acids (TFAs) reveals a pro-apoptotic action specific to industrial TFAs counteracted by polyunsaturated FAs

trans-Fatty acids (TFAs) are unsaturated fatty acids containing at least one carbon-carbon double bond in trans configuration, which are classified into two groups according to their food source: industrial TFAs (iTFAs) and ruminant TFAs (rTFAs). Previous epidemiological evidence has demonstrated a preferential association of iTFAs, rather than rTFAs, with various diseases including cardiovascular diseases. However, it is still unknown how iTFAs exert their specific toxicity and what effective treatments are available to mitigate their toxicity. Here, we performed a comprehensive toxicological assessment of TFAs based on the toxicity mechanism that we established previously. We found that iTFAs including elaidic acid (EA), but not other types of fatty acids including rTFAs, had a strong pro-apoptotic effect upon treatment of extracellular ATP, a damage-associated molecular pattern that induces apoptosis through the apoptosis signal-regulating kinase 1 (ASK1)-p38 MAP kinase pathway. We also found that polyunsaturated fatty acids (PUFAs), such as docosahexaenoic acid (DHA), potently suppressed EA-dependent increase in ASK1 activation and apoptosis. These results demonstrate that iTFAs specifically exert toxicity by targeting ASK1, and that PUFAs serve as their effective suppressor. Our study provides a molecular basis for risk assessment of foods, and for new prevention and treatment strategies for TFA-related diseases.

Amelioration of Nicotine-Induced Conditioned Place Preference Behaviors in Mice by an FABP3 Inhibitor

We previously demonstrated that fatty acid-binding protein 3 null (FABP3−/−) mice exhibit resistance to nicotine-induced conditioned place preference (CPP). Here, we confirm that the FABP3 inhibitor, MF1 ((4-(2-(1-(2-chlorophenyl)-5-phenyl-1H-pyrazol-3-yl)phenoxy) butanoic acid), successfully reduces nicotine-induced CPP scores in mice. MF1 (0.3 or 1.0 mg/kg) was orally administered 30 min before nicotine, and CPP scores were assessed in the conditioning, withdrawal, and relapse phases. MF1 treatment decreased CPP scores in a dose-dependent manner. Failure of CPP induction by MF1 (1.0 mg/kg, p.o.) was associated with the inhibition of both CaMKII and ERK activation in the nucleus accumbens (NAc) and hippocampal CA1 regions. MF1 treatment reduced nicotine-induced increases in phosphorylated CaMKII and cAMP-response element-binding protein (CREB)-positive cells. Importantly, the increase in dopamine D2 receptor (D2R) levels following chronic nicotine exposure was inhibited by MF1 treatment. Moreover, the quinpirole (QNP)-induced increase in the level of CaMKII and ERK phosphorylation was significantly inhibited by MF1 treatment of cultured NAc slices from wild type (WT) mice; however, QNP treatment had no effect on CaMKII and ERK phosphorylation levels in the NAc of D2R null mice. Taken together, these results show that MF1 treatment suppressed D2R/FABP3 signaling, thereby preventing nicotine-induced CPP induction. Hence, MF1 can be used as a novel drug to block addiction to nicotine and other drugs by inhibiting the dopaminergic system.

The Anti-social Brain in Schizophrenia: A Role of CaMKII?

Current pharmacological therapy has limited effects on the cognitive impairments and negative symptoms associated with schizophrenia. Therefore, understanding the molecular underpinnings of this disorder is essential for the development of effective treatments. It appears that a reduction in calcium/calmodulin-dependent protein kinase II (α-CaMKII) activity is a common mechanism underlying the abnormal social behavior and cognitive deficits associated with schizophrenia. In addition, in a previous study social interaction with a partner of the same sex and weight increased the activity of α-CaMKII in rats. Here, we propose that boosting of CaMKII signaling, in a manner that counteracts this neuropsychiatric disease without disrupting the normal brain function, might ameliorate the abnormalities in social cognition and the negative symptoms of schizophrenia.

T-Type Ca2+ Enhancer SAK3 Activates CaMKII and Proteasome Activities in Lewy Body Dementia Mice Model

Lewy bodies are pathological characteristics of Lewy body dementia (LBD) and are composed of α-synuclein (α-Syn), which is mostly degraded via the ubiquitin–proteasome system. More importantly, 26S proteasomal activity decreases in the brain of LBD patients. We recently introduced a T-type calcium channel enhancer SAK3 (ethyl-8-methyl-2,4-dioxo-2-(piperidin-1-yl)- 2H-spiro[cyclopentane-1,3-imidazo [1,2-a]pyridin]-2-ene-3-carboxylate) for Alzheimer’s disease therapeutics. SAK3 enhanced the proteasome activity via CaMKII activation in amyloid precursor protein knock-in mice, promoting the degradation of amyloid-β plaques to improve cognition. At this point, we addressed whether SAK3 promotes the degradation of misfolded α-Syn and the aggregates in α-Syn preformed fibril (PFF)-injected mice. The mice were injected with α-Syn PFF in the dorsal striatum, and SAK3 (0.5 or 1.0 mg/kg) was administered orally for three months, either immediately or during the last month after injection. SAK3 significantly inhibited the accumulation of fibrilized phosphorylated-α-Syn in the substantia nigra. Accordingly, SAK3 significantly recovered mesencephalic dopamine neurons from cell death. Decreased α-Syn accumulation was closely associated with increased proteasome activity. Elevated CaMKII/Rpt-6 signaling possibly mediates the enhanced proteasome activity after SAK3 administration in the cortex and hippocampus. CaMKII/Rpt-6 activation also accounted for improved memory and cognition in α-Syn PFF-injected mice. These findings indicate that CaMKII/Rpt-6-dependent proteasomal activation by SAK3 recovers from α-Syn pathology in LBD.

Cav3.1 t-type calcium channel is critical for cell proliferation and survival in newly generated cells of the adult hippocampus

AIMS

Adult hippocampal neurogenesis plays an important role in neuronal plasticity and maintenance in mammals. Low-threshold voltage-gated T-type calcium channels produce calcium spikes that increase fast action potentials in newborn cells in the hippocampal dentate gyrus (DG); however, their role in adult hippocampal neurogenesis remains unclear. Here, we demonstrate impaired adult hippocampal neurogenesis in Cav3.1T-type calcium channel knockout mice.

METHODS AND RESULTS

Cav3.1T-type calcium channel was predominantly localized in neuronal progenitor cells of the mouse hippocampal DG. By counting the number of 5-bromo-2'-deoxyuridine-labeled cells, decreased proliferation and survival of newly generated cells were observed in the adult hippocampal DG in Cav3.1 knockout mice as compared to wild-type (WT) mice. Moreover, the degree of maturation of doublecortin-positive cells in Cav3.1 knockout mice was lower than that in WT mice, suggesting that Cav3.1 deletion may impair neuronal differentiation. Consistent with impaired hippocampal neurogenesis, Cav3.1 knockout mice showed decreased social interaction. Reduced phosphorylation levels of calcium/calmodulin-dependent protein kinase II and protein kinase B were closely associated with impaired hippocampal neurogenesis in Cav3.1 knockout mice. Moreover, the mRNA and protein expression levels of brain-derived neurotrophic factor, important for neurogenesis, were significantly decreased in Cav3.1 knockout mice. Finally, gene ontology analysis revealed alterations in genes related to the promotion of cell death/apoptosis and suppression of cell proliferation/neuronal differentiation pathways, including Bdnf.

CONCLUSION

These results suggest that the Cav3.1T-type calcium channel may be a key molecule required for cell proliferation, survival and neuronal differentiation in newly generated cells of the adult mouse hippocampus.

Impaired Acquisition of Nicotine-Induced Conditioned Place Preference in Fatty Acid-Binding Protein 3 Null Mice

Nicotine causes psychological dependence through its interactions with nicotinic acetylcholine receptors in the brain. We previously demonstrated that fatty acid-binding protein 3 (FABP3) colocalizes with dopamine D2 receptors (D2Rs) in the dorsal striatum, and FABP3 deficiency leads to impaired D2R function. Moreover, D2R null mice do not exhibit increased nicotine-induced conditioned place preference (CPP) following chronic nicotine administration. To investigate the role of FABP3 in nicotine-induced CPP, FABP3 knockout (FABP3^-/-) mice were evaluated using a CPP apparatus following consecutive nicotine administration (0.5 mg/kg) for 14 days. Importantly, nicotine-induced CPP was suppressed in the conditioning, withdrawal, and relapse phases in FABP3^-/- mice. To resolve the mechanisms underlying impaired nicotine-induced CPP in these mice, we assessed c-Fos expression and Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) and extracellular signal-regulated kinase (ERK) signaling in both dopamine D1 receptor (D1R)- and D2R-positive neurons in the nucleus accumbens (NAc). Notably, 64% of dopamine receptor-positive neurons in the mouse NAc expressed both D1R and D2R. Impaired nicotine-induced CPP was correlated with lack of responsiveness of both CaMKII and ERK phosphorylation. The number of D2R-positive neurons was increased in FABP3^-/- mice, while the number of D1R-positive neurons and the responsiveness of c-Fos expression to nicotine were decreased. The aberrant c-Fos expression was closely correlated with CaMKII but not ERK phosphorylation levels in the NAc of FABP3^-/- mice. Taken together, these results indicate that impaired D2R signaling due to lack of FABP3 may affect D1R and c-Fos signaling and underlie nicotine-induced CPP behaviors.

SAK3 Administration Improves Spine Abnormalities and Cognitive Deficits in AppNL-G-F/NL-G-F Knock-in Mice by Increasing Proteasome Activity through CaMKII/Rpt6 Signaling

Alzheimer's disease (AD) is the most common form of dementia and is characterized by neuropathological hallmarks consisting of accumulation of extracellular amyloid-β (Aβ) plaques and intracellular neurofibrillary tangles (NFT). Recently, we have identified a new AD therapeutic candidate, ethyl-8'-methyl-2',4-dioxo-2-(piperidin-1-yl)-2'H-spiro[cyclopentane-1,3'-imidazo [1,2-a] pyridin]-2-ene-3-carboxylate (SAK3), which ameliorates the AD-like pathology in AppNL-F/NL-F knock-in mice. However, the detailed mechanism underlying the therapeutic effects of SAK3 remains unclear. In this study, we found that SAK3 administration improved the reduced proteasome activity through the activation of CaMKII/Rpt6 signaling in AppNL-F/NL-F knock-in (NL-G-F) mice. Moreover, spine abnormalities observed in NL-G-F mice were significantly reversed by SAK3 administration. Along with this, cognitive impairments found in NL-G-F mice were markedly ameliorated by SAK3. In summary, our data suggest that SAK3 administration increases the activity of the proteasome via activation of the CaMKII/Rpt6 signaling pathway, contributing to improvements in spine abnormalities and cognitive deficits in NL-G-F mice. Overall, our findings suggest that SAK3 might be a new attractive drug candidate, representing a new mechanism for the treatment of AD pathology.

Cholinergic Grb2-Associated-Binding Protein 1 Regulates Cognitive Function

Grb2-associated-binding protein 1 (Gab1) is a docking/scaffolding molecule known to play an important role in cell growth and survival. Here, we report that Gab1 is decreased in cholinergic neurons in Alzheimer's disease (AD) patients and in a mouse model of AD. In mice, selective ablation of Gab1 in cholinergic neurons in the medial septum impaired learning and memory and hippocampal long-term potentiation. Gab1 ablation also inhibited SK channels, leading to an increase in firing in septal cholinergic neurons. Gab1 overexpression, on the other hand, improved cognitive function and restored hippocampal CaMKII autorphosphorylation in AD mice. These results suggest that Gab1 plays an important role in the pathophysiology of AD and may represent a novel therapeutic target for diseases involving cholinergic dysfunction.

Cognitive enhancer ST101 improves schizophrenia-like behaviors in neonatal ventral hippocampus-lesioned rats in association with improved CaMKII/PKC pathway

Atypical antipsychotics improve positive and negative symptoms but are not effective for treating cognitive impairments in patients with schizophrenia. We previously reported that cognitive impairments in neonatal ventral hippocampus (NVH)-lesioned rats show resistance to atypical antipsychotics risperidone and are associated with reduced calcium/calmodulin-dependent protein kinase II (CaMKII) and protein kinase C (PKC) signaling in memory-related regions. The cognitive enhancer ST101 (spiro[imi-dazo[1,2-a]pyridine-3,2-indan]-2(3H)-one) stimulates CaMKII activity in the hippocampus and medial prefrontal cortex (mPFC). We thus tested ST101 on cognitive impairments in NVH-lesioned rats. Chronic ST101 administration (0.1 and/or 0.5 mg/kg, p.o.) significantly improved deficits in prepulse inhibition (PPI), social interaction, and cognitive function in NVH-lesioned rats. ST101 administration (0.5 mg/kg, p.o.) significantly restored the decreased CaMKII autophosphorylation (Thr-286) in the mPFC and hippocampal CA1 regions of NVH-lesioned rats when assessed by immunohistochemistry. Chronic ST101 administration (0.1 mg/kg, p.o.) improved the decline in phosphorylation levels of CaMKII (Thr-286), PKCα (Ser-657), α-amino-3-hydroxy-5-methyl-4-isoxazol- propionic acid (AMPA)-type glutamate receptor subunit 1 (GluA1: Ser-831), and N-methyl-d-aspartate (NMDA) receptor subunit 1 (GluN1: Ser-896) in the mPFC and hippocampal CA1 regions. Taken together, these results suggest that ST101 improves schizophrenia-like behaviors and cognitive impairment by enhancing CaMKII/PKCα signaling in the mPFC and hippocampus in NVH-lesioned rats.

Combined citicoline and docosahexaenoic acid treatment improves cognitive dysfunction following transient brain ischemia

Phospholipids are structural components of cellular membranes that play important roles as precursors for various signaling pathways in modulating neuronal membrane function and maintenance of the intracellular environment. Phosphatidylcholine (PtdCho) is the most abundant cellular phospholipid. Citicoline and docosahexaenoic acid (DHA) are essential intermediates in the synthesis of PtdCho. Both PtdCho intermediates have independently shown neuroprotective effects in cerebral ischemia, but their combined effect is unknown. This study aimed to investigate the combined effect of oral citicoline and DHA treatment on improvement of cognitive deficits following cerebral ischemia using a 20-min bilateral common carotid artery occlusion (BCCAO) mouse model. BCCAO ischemic mice were treated for a total of 11 days with a combination of citicoline (40 mg/kg body weight/day) and DHA (300 mg/kg body weight/day) or each alone. Combined citicoline and DHA synergistically and significantly improved learning and memory ability of ischemic mice compared with either alone. Further, citicoline and DHA treatment significantly prevented neuronal cell death, and slightly increased DHA-containing PtdCho in the hippocampus, albeit not significantly. Taken together, these findings suggest that combined citicoline and DHA treatment may have synergistic benefits for partially improving memory deficits following transient brain ischemia.

Endothelium-Derived Semaphorin 3G Regulates Hippocampal Synaptic Structure and Plasticity via Neuropilin-2/PlexinA4

The proper interactions between blood vessels and neurons are critical for maintaining the strength of neural circuits and cognitive function. However, the precise molecular events underlying these interactions remain largely unknown. Here, we report that the selective knockout of semaphorin 3G (Sema3G) in endothelial cells impaired hippocampal-dependent memory and reduced dendritic spine density in CA1 neurons in mice; these effects were reversed after restoration of Sema3G levels in the hippocampus by AAV transfection. We further show that Sema3G increased excitatory synapse density via neuropilin-2/PlexinA4 signaling and through activation of Rac1. These results provide the first evidence that, in the central nervous system, endothelial Sema3G serves as a vascular-derived synaptic organizer that regulates synaptic plasticity and hippocampal-dependent memory. Our findings highlight the role of vascular endothelial cells in regulating cognitive function through intercellular communication with neurons in the hippocampus.

T-type calcium channel enhancer SAK3 produces anti-depressant-like effects by promoting adult hippocampal neurogenesis in olfactory bulbectomized mice

T-type calcium channels are involved in the pathophysiology of epilepsy, pain, and sleep. Recently, we developed a novel spiroimidazopyridine compound, SAK3 (ethyl 8'-methyl-2',4-dioxo-2-(piperidin-1-yl)-2'H-spiro[cyclopentane-1,3'-imidazo[1,2-a]pyridine]-2-ene-3-carboxylate), which enhances T-type calcium channel currents and improves memory deficits in olfactory bulbectomized (OBX) mice. Here, we demonstrated the anti-depressant effects of SAK3 in OBX mice. Chronic SAK3 administration (0.5 or 1.0 mg/kg, p.o.) improved depressive-like behaviors in OBX mice. The impaired adult neurogenesis in the hippocampal dentate gyrus (DG) that occurred 4 weeks after OBX administration was significantly restored by chronic SAK3 administration (0.5 or 1.0 mg/kg, p.o.). Additionally, SAK3 (0.5 mg/kg, p.o.) promoted the proliferation and survival of newborn cells in the naïve DG. Moreover, SAK3 administration (0.5 mg/kg, p.o.) antagonized the reduction of calcium/calmodulin-dependent protein kinase II (CaMKII) and CaMKIV phosphorylation levels, thereby rescuing the decreased levels of cAMP response element-binding protein (CREB)/brain derived neurotrophic factor (BDNF) signaling in the OBX DG. The effects of SAK3 were completely blocked by the T-type calcium channel selective blocker NNC 55-0396 (12.5 mg/kg, i.p.). Altogether, these results suggest that SAK3 improves depressive-like behaviors by promoting adult neurogenesis via T-type calcium channel stimulation in the hippocampus.

Ramelteon Improves Post-traumatic Stress Disorder-Like Behaviors Exhibited by Fatty Acid-Binding Protein 3 Null Mice

We previously reported that fatty acid-binding protein 3 (FABP3) knockout (Fabp3 ^-/-) mice exhibit abnormal dopamine-related behaviors such as enhanced dopamine D2 receptor antagonist-induced catalepsy behaviors. Here, we report that Fabp3 null mice exhibit cognitive deficits, hyperlocomotion and impaired fear extinction, and thus show post-traumatic stress disorder (PTSD)-like behaviors. Notably, chronic administration of ramelteon (1.0 mg/kg, p.o.), a melatonin receptor agonist, improved all PTSD-like behaviors tested in Fabp3 ^-/- mice. Relevant to mechanisms underlying impaired fear extinction, we observed significantly reduced levels of Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) autophosphorylation without changes in ERK phosphorylation in the anterior cingulate cortex (ACC). Inversely, CaMKII autophosphorylation increased in the basolateral amygdala (BLA) but remained relatively unchanged in hippocampus of Fabp3 ^-/- mice. Likewise, the number of c-Fos-positive neurons in BLA significantly increased after exposure to contextual fear conditions but remained unchanged in the central nucleus of the amygdala (CeA). Importantly, chronic ramelteon administration (1.0 mg/kg, p.o.) restored abnormal c-Fos expression and CaMKII autophosphorylation in the ACC and BLA of Fabp3 ^-/- mice. Finally, the melatonin receptor antagonist luzindole (2.5 mg/kg, i.p.) blocked ramelteon-dependent improvements. Taken together, Fabp3 ^-/- mice show PTSD-like behaviors, and ramelteon is a likely attractive candidate for PTSD therapy.

trans-Fatty acids promote proinflammatory signaling and cell death by stimulating the apoptosis signal-regulating kinase 1 (ASK1)-p38 pathway

Food-borne trans-fatty acids (TFAs) are mainly produced as byproducts during food manufacture. Recent epidemiological studies have revealed that TFA consumption is a major risk factor for various disorders, including atherosclerosis. However, the underlying mechanisms in this disease etiology are largely unknown. Here we have shown that TFAs potentiate activation of apoptosis signal-regulating kinase 1 (ASK1) induced by extracellular ATP, a damage-associated molecular pattern leaked from injured cells. Major food-associated TFAs such as elaidic acid (EA), linoelaidic acid, and trans-vaccenic acid, but not their corresponding cis isomers, dramatically enhanced extracellular ATP-induced apoptosis, accompanied by elevated activation of the ASK1-p38 pathway in a macrophage-like cell line, RAW264.7. Moreover, knocking out the ASK1-encoding gene abolished EA-mediated enhancement of apoptosis. We have reported previously that extracellular ATP induces apoptosis through the ASK1-p38 pathway activated by reactive oxygen species generated downstream of the P2X purinoceptor 7 (P2X₇). However, here we show that EA did not increase ATP-induced reactive oxygen species generation but, rather, augmented the effects of calcium/calmodulin-dependent kinase II-dependent ASK1 activation. These results demonstrate that TFAs promote extracellular ATP-induced apoptosis by targeting ASK1 and indicate novel TFA-associated pathways leading to inflammatory signal transduction and cell death that underlie the pathogenesis and progression of TFA-induced atherosclerosis. Our study thus provides insight into the pathogenic mechanisms of and proposes potential therapeutic targets for these TFA-related disorders.

Pharmacological properties of SAK3, a novel T-type voltage-gated Ca2+ channel enhancer

T-type voltage-gated Ca²⁺ channels (T-VGCCs) function in the pathophysiology of epilepsy, pain and sleep. However, their role in cognitive function remains unclear. We previously reported that the cognitive enhancer ST101, which stimulates T-VGCCs in rat cortical slices, was a potential Alzheimer's disease therapeutic. Here, we introduce a more potent T-VGCC enhancer, SAK3 (ethyl 8'-methyl-2',4-dioxo-2-(piperidin-1-yl)-2'H-spiro[cyclopentane-1,3'-imidazo [1,2-a]pyridin]-2-ene-3-carboxylate), and characterize its pharmacological properties in brain. Based on whole cell patch-clamp analysis, SAK3 (0.01-10 nM) significantly enhanced Cav3.1 currents in neuro2A cells ectopically expressing Cav3.1. SAK3 (0.1-10 nM nM) also enhanced Cav3.3 but not Cav3.2 currents in the transfected cells. Notably, Cav3.1 and Cav3.3 T-VGCCs were localized in cholinergic neurve systems in hippocampus and in the medial septum. Indeed, acute oral administration of SAK3 (0.5 mg/kg, p.o.), but not ST101 (0.5 mg/kg, p.o.) significantly enhanced acetylcholine (ACh) release in the hippocampal CA1 region of naïve mice. Moreover, acute SAK3 (0.5 mg/kg, p.o.) administration significantly enhanced hippocampal ACh levels in olfactory-bulbectomized (OBX) mice, rescuing impaired memory-related behaviors. Treatment of OBX mice with the T-VGCC-specific blocker NNC 55-0396 (12.5 mg/kg, i.p.) antagonized both enhanced ACh release and memory improvements elicited by SAK3 administration. We also observed that SAK3-induced ACh releases were significantly blocked in the hippocampus from Cav3.1 knockout (KO) mice. These findings suggest overall that T-VGCCs play a key role in cognition by enhancing hippocampal ACh release and that the cognitive enhancer SAK3 could be a candidate therapeutic in Alzheimer's disease.

Combined Memantine and Donepezil Treatment Improves Behavioral and Psychological Symptoms of Dementia-Like Behaviors in Olfactory Bulbectomized Mice

Memantine, an uncompetitive N-methyl-D-aspartate receptor antagonist, and the cholinesterase inhibitor, donepezil, are approved in most countries for treating moderate-to-severe Alzheimer's disease (AD). These drugs have different molecular targets; thus, it is expected that the effects of combined treatment would be synergistic. Some reports do show memantine/donepezil synergy in ameliorating cognition in AD model animals, but their combined effects on behavioral and psychological symptoms of dementia (BPSD)-like behaviors have not been addressed. Here, we investigate combined memantine/donepezil effects on cognitive impairment and BPSD-like behaviors in olfactory bulbectomized (OBX) mice. Interestingly, combined administration synergistically improved both depressive-like behaviors and impaired social interaction in OBX mice, whereas only weak synergistic effects on cognitive performance were seen. To address mechanisms underlying these effects, we used in vivo microdialysis study and observed impaired nicotine-induced serotonin (5-HT) release in OBX mouse hippocampus. Combined memantine/donepezil administration, but not single administration of either, significantly antagonized the decrease in nicotine-induced 5-HT release seen in OBX mouse hippocampus. Furthermore, decreased autophosphorylation of calcium/calmodulin dependent protein kinase II (CaMKII) was rescued in hippocampal CA1 and dentate gyrus of OBX mice by combined memantine/donepezil administration. These results suggest that improvement of BPSD-like behaviors by the co-administration of both drugs is in part mediated by enhanced 5-HT release and CaMKII activity in OBX mouse hippocampus.

Herbal formula GAPT prevents beta amyloid deposition induced Ca(2+)/Calmodulin-dependent protein kinase II and Ca(2+)/Calmodulin-dependent protein phosphatase 2B imbalance in APPV717I mice

Background

Synaptic dysfunction is one of the pathological characteristics of Alzheimer's disease (AD), which is directly related to the progressive decline of cognitive function. CaMKII and CaN have been found to play important roles in memory processes and synaptic transmission. So present study aimed to elucidate relationships between CaMKII, CaN and cognitive decline in APPV717I mice, and to reveal whether the cognitive improving effects of GAPT is conducted through rebalance CaMKII and CaN.

Methods

Three-month-old-male APPV717I mice were randomly divided into ten groups (n = 12 per group) and received intragastrically administrated vehicle, donepezil or different doses of herbal formula GAPT for 8 or 4 months. Three-month-old male C57BL/6 J mice was set as vehicle control.

Results

Immunohistochemistry analysis showed that there were CaMKII expression decrease in the CA1 region of APPV717I transgenic mice, while the CaMKII expression of donepezil or GAPT treated transgenic mice were all increased. And there were CaN expression increase in the brain cortex of APPV717I transgenic mice, while there were decrease of CaN expression in donepezil or GAPT treated transgenic group. Western blot analysis showed the similar expression pattern without significant difference.

Conclusion

GAPT extract have showed effectiveness in activating the expression of CaMKII and inhibiting the expression of CaN either before or after the formation of amyloid plaques in the brain of APPV717I transgenic mice, which may in certain way alleviated neuron synaptic dysfunction in AD.

Enhanced Store-Operated Calcium Entry Leads to Striatal Synaptic Loss in a Huntington's Disease Mouse Model

In Huntington's disease (HD), mutant Huntingtin (mHtt) protein causes striatal neuron dysfunction, synaptic loss, and eventual neurodegeneration. To understand the mechanisms responsible for synaptic loss in HD, we developed a corticostriatal coculture model that features age-dependent dendritic spine loss in striatal medium spiny neurons (MSNs) from YAC128 transgenic HD mice. Age-dependent spine loss was also observed in vivo in YAC128 MSNs. To understand the causes of spine loss in YAC128 MSNs, we performed a series of mechanistic studies. We previously discovered that mHtt protein binds to type 1 inositol (1,4,5)-trisphosphate receptor (InsP3R1) and increases its sensitivity to activation by InsP3. We now report that the resulting increase in steady-state InsP3R1 activity reduces endoplasmic reticulum (ER) Ca(2+) levels. Depletion of ER Ca(2+) leads to overactivation of the neuronal store-operated Ca(2+) entry (nSOC) pathway in YAC128 MSN spines. The synaptic nSOC pathway is controlled by the ER resident protein STIM2. We discovered that STIM2 expression is elevated in aged YAC128 striatal cultures and in YAC128 mouse striatum. Knock-down of InsP3R1 expression by antisense oligonucleotides or knock-down or knock-out of STIM2 resulted in normalization of nSOC and rescue of spine loss in YAC128 MSNs. The selective nSOC inhibitor EVP4593 was identified in our previous studies. We now demonstrate that EVP4593 reduces synaptic nSOC and rescues spine loss in YAC128 MSNs. Intraventricular delivery of EVP4593 in YAC128 mice rescued age-dependent striatal spine loss in vivo. Our results suggest EVP4593 and other inhibitors of the STIM2-dependent nSOC pathway as promising leads for HD therapeutic development.

SIGNIFICANCE STATEMENT

In Huntington's disease (HD) mutant Huntingtin (mHtt) causes early corticostriatal synaptic dysfunction and eventual neurodegeneration of medium spine neurons (MSNs) through poorly understood mechanisms. We report here that corticostriatal cocultures prepared from YAC128 HD mice feature age-dependent MSN spine loss, mirroring YAC128 MSN spine loss in vivo. This finding establishes a system for mechanistic studies of synaptic instability in HD. We use it to demonstrate that sensitization of type 1 inositol (1,4,5)-trisphosphate receptors by mHtt, which depletes endoplasmic reticulum calcium, contributes to synaptotoxic enhancement of STIM2-dependent store-operated calcium (SOC) entry. Treatment with EVP4593, a neuroprotective inhibitor of neuronal SOC channels, rescues YAC128 MSN spine loss both in vitro and in vivo. These results suggest that enhanced neuronal SOC causes synaptic loss in HD-afflicted MSNs.

Dehydroepiandrosterone administration improves memory deficits following transient brain ischemia through sigma-1 receptor stimulation

Dehydroepiandrosterone (DHEA) is the most abundant neurosteroid synthesized de novo in the central nervous system. Oral DHEA administration elicits neuroprotection and cognitive improvement, but mechanisms underlying these functions in cerebral ischemia have remained unclear. Since DHEA is the endogenous ligand for the sigma-1 receptor (σ1R), we determined whether oral DHEA administration prevents neuronal cell death and improves cognition via σ1R stimulation in brain ischemia using a 20-min bilateral common carotid artery occlusion (BCCAO) mouse model. Twenty-four hours after BCCAO ischemia, mice were administered DHEA (15 or 30mg/kg p.o.) daily for 11 consecutive days. Memory deficits following brain ischemia were improved by DHEA administration dose-dependently. Accordingly, DHEA administration significantly prevented neuronal cell death in the hippocampal CA1 region in BCCAO mice. Interestingly, DHEA administration rescued decreases in Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) autophosphorylation and phosphorylation of extracellular signal-regulated kinase (ERK) and protein kinase B (Akt) in the CA1 region. Moreover, DHEA administration significantly ameliorated decreases in adenosine 5'-triphosphate (ATP) levels and decreased σ1R expression levels in CA1 following BCCAO ischemia. Finally, co-treatment of mice with the σ1R antagonist NE-100 (1mg/kg, p.o.) blocked DHEA effects on memory improvement and neuroprotection in ischemic mice. Taken together, DHEA prevents neuronal cell death and activates CaMKII via σ1R stimulation, thereby improving cognitive deficits following brain ischemia.

Differential CaMKII regulation by voltage-gated calcium channels in the striatum

Calcium signaling regulates synaptic plasticity and many other functions in striatal medium spiny neurons to modulate basal ganglia function. Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) is a major calcium-dependent signaling protein that couples calcium entry to diverse cellular changes. CaMKII activation results in autophosphorylation at Thr286 and sustained calcium-independent CaMKII activity after calcium signals dissipate. However, little is known about the mechanisms regulating striatal CaMKII. To address this, mouse brain slices were treated with pharmacological modulators of calcium channels and punches of dorsal striatum were immunoblotted for CaMKII Thr286 autophosphorylation as an index of CaMKII activation. KCl depolarization increased levels of CaMKII autophosphorylation ~2-fold; this increase was blocked by an LTCC antagonist and was mimicked by treatment with pharmacological LTCC activators. The chelation of extracellular calcium robustly decreased basal CaMKII autophosphorylation within 5min and increased levels of total CaMKII in cytosolic fractions, in addition to decreasing the phosphorylation of CaMKII sites in the GluN2B subunit of NMDA receptors and the GluA1 subunit of AMPA receptors. We also found that the maintenance of basal levels of CaMKII autophosphorylation requires low-voltage gated T-type calcium channels, but not LTCCs or R-type calcium channels. Our findings indicate that CaMKII activity is dynamically regulated by multiple calcium channels in the striatum thus coupling calcium entry to key downstream substrates.

Nuclear Translocation of Calcium/Calmodulin-dependent Protein Kinase IIδ3 Promoted by Protein Phosphatase-1 Enhances Brain-derived Neurotrophic Factor Expression in Dopaminergic Neurons

We have reported previously that dopamine D2 receptor stimulation activates calcium/calmodulin-dependent protein kinase II (CaMKII) δ3, a CaMKII nuclear isoform, increasing BDNF gene expression. However, the mechanisms underlying that activity remained unclear. Here we report that CaMKIIδ3 is dephosphorylated at Ser(332) by protein phosphatase 1 (PP1), promoting CaMKIIδ3 nuclear translocation. Neuro-2a cells transfected with CaMKIIδ3 showed cytoplasmic and nuclear staining, but the staining was predominantly nuclear when CaMKIIδ3 was coexpressed with PP1. Indeed, PP1 and CaMKIIδ3 coexpression significantly increased nuclear CaMKII activity and enhanced BDNF expression. In support of this idea, chronic administration of the dopamine D2 receptor partial agonist aripiprazole increased PP1 activity and promoted nuclear CaMKIIδ3 translocation and BDNF expression in the rat brain substantia nigra. Moreover, aripiprazole treatment enhanced neurite extension and inhibited cell death in cultured dopaminergic neurons, effects blocked by PP1γ knockdown. Taken together, nuclear translocation of CaMKIIδ3 following dephosphorylation at Ser(332) by PP1 likely accounts for BDNF expression and subsequent neurite extension and survival of dopaminergic neurons.

Deficient Wnt signalling triggers striatal synaptic degeneration and impaired motor behaviour in adult mice

Synapse degeneration is an early and invariant feature of neurodegenerative diseases. Indeed, synapse loss occurs prior to neuronal degeneration and correlates with the symptom severity of these diseases. However, the molecular mechanisms that trigger synaptic loss remain poorly understood. Here we demonstrate that deficient Wnt signalling elicits synaptic degeneration in the adult striatum. Inducible expression of the secreted Wnt antagonist Dickkopf1 (Dkk1) in adult mice (iDkk1) decreases the number of cortico-striatal glutamatergic synapses and of D1 and D2 dopamine receptor clusters. Synapse loss occurs in the absence of axon retraction or cell death. The remaining excitatory terminals contain fewer synaptic vesicles and have a reduced probability of evoked transmitter release. IDkk1 mice show impaired motor coordination and are irresponsive to amphetamine. These studies identify Wnts as key endogenous regulators of synaptic maintenance and suggest that dysfunction in Wnt signalling contributes to synaptic degeneration at early stages in neurodegenerative diseases.

[Imaging monitoring method of CaMKII activity by immunohistochemical analysis in schizophrenic model rats]

Schizophrenia is characterized by various behavioral abnormalities including cognitive dysfunction. Neonatal ventral hippocampus (NVH)-lesioned rats had been known as neurodevelopmental animal model similar to schizophrenia. Previous observations indicate that postpubertal NVH-lesioned rats exhibit impairments in prepulse inhibition (PPI), spontaneous locomotion, social interaction behavior and working memory. Here, we document the neurochemical basis of those defects in NVH-lesioned rats. Since Ca²⁺/calmodulin-dependent protein kinase II (CaMKII), which is NMDA receptor downstream kinase, is essential for memory and learning acquisition, we developed a protocol to monitor the spatial changes in CaMKII autophosphorylation using immunohistochemical imaging of whole brain slices with anti-autophosphorylated CaMKII antibody in order to address mechanisms underlying impaired cognitive function in NVH-lesioned rats. Immunohistochemical analyses using anti-autophosphorylated CaMKII antibody revealed that CaMKII autophosphorylation was significantly reduced in the medial prefrontal cortex (mPFC) of NVH-lesioned rats compared with control animals. This immunohistochemical technique is useful to investigate temporal and special changes in CaMKII activity in rodent brain and to evaluate drugs to improve the cognitive impairment.

Presynaptic CaMKIIα modulates dopamine D3 receptor activation in striatonigral terminals of the rat brain in a Ca²⁺ dependent manner

CaMKIIα is expressed at high density in the nucleus accumbens where it binds to postsynaptic D3 receptors inhibiting their effects. In striatonigral projections, activation of presynaptic D3 receptors potentiates D1 receptor-induced stimulation of cAMP production and GABA release. In this study we examined whether the presynaptic effects of D3 receptor stimulation in the substantia nigra reticulata (SNr) are modulated by Ca²⁺ activation of CaMKIIα. In SNr synaptosomes two procedures that increase cytoplasmic Ca²⁺, ionomycin and K⁺-depolarization, blocked the additional stimulation of cAMP accumulation produced by coactivating D3 and D1 dopamine receptors. The selective CaMKIIα inhibitor KN-62 reversed the blockade produced by ionomycin and K⁺-depolarization. Incubation in either Ca²-free solutions or with the selective Ca²⁺ blocker nifedipine, also reversed the blocking effects of K⁺-depolarization. Immunoblot studies showed that K⁺-depolarization increased CaMKIIα phosphorylation in a KN-62 sensitive manner and promoted CaMKIIα binding to D3 receptors. In K⁺-depolarized tissues, D3 receptors potentiated D1 receptor-induced stimulation of [³H]GABA release only when CaMKIIα was blocked with KN-62. In the presence of this inhibitor, the selective D3 agonist PD 128,907 reduced the ED₅₀ for the D1 agonist SKF 38393 from 56 to 4 nM. KN-62 also enhanced the effects of dopamine on depolarization induced [³H]GABA release. KN-62 changed ED₅₀ for dopamine from 584 to 56 nM. KN-62 did not affect D1 and D4 receptor responses. These experiments show that in striatonigral projections, CaMKIIα inhibits the action of D3 receptors in a Ca²⁺ dependent manner blocking their modulatory effects on GABA release. These findings suggest a mechanism through which the frequency of action potential discharge in presynaptic terminals regulates dopamine effects.

Novel cognitive enhancer ST101 enhances acetylcholine release in mouse dorsal hippocampus through T-type voltage-gated calcium channel stimulation

We recently developed a novel cognitive enhancer, ST101 (spiro[imidazo[1,2-a]pyridine-3,2-indan]-2(3H)-one), that activates T-type voltage-gated calcium channels (VGCCs). Here, we address whether T-type VGCC activation with ST101 mediates its cognitive effects in vivo and the relevance of T-type VGCC activation to acetylcholine (ACh) release in the hippocampus. Acute intraperitoneal administration of ST101 (1 mg/kg, i.p.) improved memory-related behaviors in both olfactory bulbectomized (OBX) and scopolamine-treated mice. Effects of ST101 administration were abolished by both intraperitoneal and intracerebroventricular pre-administration of the T-type VGCC inhibitor mibefradil. Acute administration of ST101 enhanced basal and nicotine-induced ACh release in the dorsal hippocampus in both OBX and sham-treated mice. Enhanced ACh release was abolished by infusion with mibefradil (10 μM) but not with the L-type VGCC inhibitor nifedipine (10 μM). As expected, significantly reduced CaMKIIα, PKCα, and ERK phosphorylation was restored by acute ST101 administration in the OBX mouse hippocampal CA1 region. Enhancement of CaMKIIα and PKCα but not ERK phosphorylation was inhibited by mibefradil (20 mg/kg, i.p.) preadministration. Increased CaMKIIα and PKCα phosphorylation was confirmed by increased phosphorylation of GluR1, synapsin I, and NR1. Taken together, stimulation of T-type VGCCs is critical for the enhanced hippocampal ACh release and improved cognitive function seen following ST101 administration.

Influence of Maternal Exposure to 2,3,7,8-Tetrachlorodibenzo-p-dioxin on Socioemotional Behaviors in Offspring Rats

Effects of dioxins on cognitive functions were reported in previous studies conducted in humans and animals. In the present study, we investigated the influence of dioxin exposure during pregnancy on social interaction and on the activity of offspring, which are related to neurodevelopmental disturbances. In addition, we analyzed neurochemical alterations of the limbic system of rat brains to suggest one mechanism of dioxin effects on brain function. We believe that this manuscript is suitable for publication in "Environmental Health Insights" because it provides an interesting topic for a wide global audience. To clarify the relationships between maternal dioxin exposure and socioemotional functions of rat offspring, dams were given TCDD (1.0 μg/kg) on gestational day 15. Social interactions and forced swimming time were compared between TCDD-exposed and control offspring in each gender. Frequency and duration of locomotion were higher, and durations per one behavior of proximity and social contact were significantly lower in the exposed males, while only the duration of proximity was lower in the exposed females. Forced swimming time on the first day was significantly longer in the exposed males. In the limbic system of the rat brain, the levels and/or activity of CaMKIIα were decreased in males and were increased in females in the exposed offspring. These results suggest that prenatal TCDD exposure induces hyperactivity and socioemotional deficits, particularly in the male offspring due to alterations in CaMKIIα activity in the limbic system of the brain.

Genetic inhibition of CaMKII in dorsal striatal medium spiny neurons reduces functional excitatory synapses and enhances intrinsic excitability

Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) is abundant in striatal medium spiny neurons (MSNs). CaMKII is dynamically regulated by changes in dopamine signaling, as occurs in Parkinson's disease as well as addiction. Although CaMKII has been extensively studied in the hippocampus where it regulates excitatory synaptic transmission, relatively little is known about how it modulates neuronal function in the striatum. Therefore, we examined the impact of selectively overexpressing an EGFP-fused CaMKII inhibitory peptide (EAC3I) in striatal medium spiny neurons (MSNs) using a novel transgenic mouse model. EAC3I-expressing cells exhibited markedly decreased excitatory transmission, indicated by a decrease in the frequency of spontaneous excitatory postsynaptic currents (sEPSCs). This decrease was not accompanied by changes in the probability of release, levels of glutamate at the synapse, or changes in dendritic spine density. CaMKII regulation of the AMPA receptor subunit GluA1 is a major means by which the kinase regulates neuronal function in the hippocampus. We found that the decrease in striatal excitatory transmission seen in the EAC3I mice is mimicked by deletion of GluA1. Further, while CaMKII inhibition decreased excitatory transmission onto MSNs, it increased their intrinsic excitability. These data suggest that CaMKII plays a critical role in setting the excitability rheostat of striatal MSNs by coordinating excitatory synaptic drive and the resulting depolarization response.

Reduced calcium/calmodulin-dependent protein kinase II activity in the hippocampus is associated with impaired cognitive function in MPTP-treated mice

Parkinson's disease (PD) patients frequently reveal deficit in cognitive functions during the early stage in PD. The dopaminergic neurotoxin, MPTP-induced neurodegeneration causes an injury of the basal ganglia and is associated with PD-like behaviors. In this study, we demonstrated that deficits in cognitive functions in MPTP-treated mice were associated with reduced calcium/calmodulin-dependent protein kinase II (CaMKII) autophosphorylation and impaired long-term potentiation (LTP) induction in the hippocampal CA1 region. Mice were injected once a day for 5days with MPTP (25mg/kg i.p.). The impaired motor coordination was observed 1 or 2week after MPTP treatment as assessed by rota-rod and beam-walking tasks. In immunoblotting analyses, the levels of tyrosine hydroxylase protein and CaMKII autophosphorylation in the striatum were significantly decreased 1week after MPTP treatment. By contrast, deficits of cognitive functions were observed 3-4weeks after MPTP treatment as assessed by novel object recognition and passive avoidance tasks but not Y-maze task. Impaired LTP in the hippocampal CA1 region was also observed in MPTP-treated mice. Concomitant with impaired LTP induction, CaMKII autophosphorylation was significantly decreased 3weeks after MPTP treatment in the hippocampal CA1 region. Finally, the reduced CaMKII autophosphorylation was closely associated with reduced AMPA-type glutamate receptor subunit 1 (GluR1; Ser-831) phosphorylation in the hippocampal CA1 region of MPTP-treated mice. Taken together, decreased CaMKII activity with concomitant impaired LTP induction in the hippocampus likely account for the learning disability observed in MPTP-treated mice.

Sigma-1 receptor stimulation by dehydroepiandrosterone ameliorates cognitive impairment through activation of CaM kinase II, protein kinase C and extracellular signal-regulated kinase in olfactory bulbectomized mice

Dehydroepiandrosterone (DHEA) is one of the most abundant neurosteroids synthesized de novo in the CNS. We here found that sigma-1 receptor stimulation by DHEA improves cognitive function through phosphorylation of synaptic proteins in olfactory bulbectomized (OBX) mouse hippocampus. We have previously reported that calcium/calmodulin-dependent protein kinase II (CaMKII), protein kinase C (PKC) and extracellular signal-regulated kinase (ERK) were impaired in OBX mouse hippocampus. OBX mice were administered once a day for 7-8 days with DHEA (30 or 60 mg/kg p.o.) 10 days after operation. The spatial, cognitive and conditioned fear memories in OBX mice were significantly improved as assessed by Y-maze, novel object recognition and passive avoidance task, respectively. DHEA also improved impaired hippocampal long-term potentiation in OBX mice. Notably, DHEA treatment restored PKCα (Ser-657) autophosphorylation and NR1 (Ser-896) and myristoylated alanine-rich protein kinase C substrate (Ser-152/156) phosphorylation to the control levels in the hippocampal CA1 region. Likewise, DHEA treatment improved CaMKIIα (Thr-286) autophosphorylation and GluR1 (Ser-831) phosphorylation to the control levels in the CA1 region. Furthermore, DHEA treatment improved ERK and cAMP-responsive element-binding protein (Ser-133) phosphorylation to the control levels. Finally, NE-100, sigma-1 receptor antagonist, significantly inhibited the DHEA-induced improvement of memory-related behaviors and CaMKII, PKC and ERK phosphorylation in CA1 region. Taken together, sigma-1 receptor stimulation by DHEA ameliorates OBX-induced impairment in memory-related behaviors and long-term potentiation in the hippocampal CA1 region through activation of CaMKII, PKC and ERK.

Aberrant calcium/calmodulin-dependent protein kinase II (CaMKII) activity is associated with abnormal dendritic spine morphology in the ATRX mutant mouse brain

In humans, mutations in the gene encoding ATRX, a chromatin remodeling protein of the sucrose-nonfermenting 2 family, cause several mental retardation disorders, including α-thalassemia X-linked mental retardation syndrome. We generated ATRX mutant mice lacking exon 2 (ATRX(ΔE2) mice), a mutation that mimics exon 2 mutations seen in human patients and associated with milder forms of retardation. ATRX(ΔE2) mice exhibited abnormal dendritic spine formation in the medial prefrontal cortex (mPFC). Consistent with other mouse models of mental retardation, ATRX(ΔE2) mice exhibited longer and thinner dendritic spines compared with wild-type mice without changes in spine number. Interestingly, aberrant increased calcium/calmodulin-dependent protein kinase II (CaMKII) activity was observed in the mPFC of ATRX(ΔE2) mice. Increased CaMKII autophosphorylation and activity were associated with increased phosphorylation of the Rac1-guanine nucleotide exchange factors (GEFs) T-cell lymphoma invasion and metastasis 1 (Tiam1) and kalirin-7, known substrates of CaMKII. We confirmed increased phosphorylation of p21-activated kinases (PAKs) in mPFC extracts. Furthermore, reduced protein expression and activity of protein phosphatase 1 (PP1) was evident in the mPFC of ATRX(ΔE2) mice. In cultured cortical neurons, PP1 inhibition by okadaic acid increased CaMKII-dependent Tiam1 and kalirin-7 phosphorylation. Together, our data strongly suggest that aberrant CaMKII activation likely mediates abnormal spine formation in the mPFC. Such morphological changes plus elevated Rac1-GEF/PAK signaling seen in ATRX(ΔE2) mice may contribute to mental retardation syndromes seen in human patients.

Expression profiling of Ca(2+)/calmodulin-dependent signaling molecules in the rat dorsal and ventral hippocampus after acute lead exposure

The septal and temporal poles of the hippocampus differ markedly in their anatomical organization, but whether these distinct regions exhibit differential neurochemical profiles underlying lead (Pb(2+)) neurotoxicity remains to be determined. In the present study, we examined changes in the expression of Ca(2+)/calmodulin-dependent enzymes, including calpain, calcineurin, phospho-CaMKII (Thr286) and neuronal nitric oxide synthase (nNOS), in the rat dorsal and ventral hippocampus (DH and VH) after acute Pb(2+) exposure. Five days after Pb(2+) exposure, we observed constitutively active forms of calcineurin (45 kDa and 48 kDa) in ventral portions of the hippocampus, a result consistent with the observed calpain activation that is indicated by the breakdown of spectrin in this region. Our data demonstrate that nNOS expression is significantly higher in the ventral region of the hippocampus when compared to the dorsal region, whereas phosphorylation of CaMKII (Thr286) is less pronounced in the ventral portion of the hippocampus and more pronounced in dorsal regions after acute Pb(2+) exposure. Thus, it appears likely that the ventral region of hippocampus is more vulnerable to the neurotoxic effects of Pb(2+) than the dorsal region. Taken together, the present data suggest that acute lead exposure leads to differential expression patterns of Ca(2+)/calmodulin-dependent enzymes along the dorsoventral axis of the hippocampus.

Ca2+/calmodulin-dependent protein kinase II and protein kinase C activities mediate extracellular glucose-regulated hippocampal synaptic efficacy

To define how extracellular glucose levels affect synaptic efficacy and long-term potentiation (LTP), we evaluated electrophysiological and neurochemical properties in hippocampal CA1 regions following alterations in glucose levels in the ACSF. In rat hippocampal slices prepared in ACSF with 3.5mM glucose, fEPSPs generated by Schaffer collateral/commissural stimulation markedly increased when ACSF glucose levels were increased from 3.5 to 7.0mM. The paired-pulse facilitation reflecting presynaptic transmitter release efficacy was significantly suppressed by elevation to 7.0mM glucose because of potentiation of the input-output relationship (I/O relationship) of fEPSPs by single pulse stimulation. Prolonged potentiation of fEPSPs by elevation to 7.0mM glucose coincided with increased autophosphorylation both of Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) and protein kinase Cα (PKCα). The increased I/O relationship of fEPSPs was also associated with markedly increased synapsin I phosphorylation by CaMKII. Transmitter-evoked postsynaptic currents were also measured in CA1 neurons by electrophoretical application of NMDA and AMPA to the apical dendrites of pyramidal neurons. NMDA- and AMPA-evoked currents were significantly augmented by elevation to 7.0mM. Notably, high frequency stimulation of the Schaffer collateral/commissural pathway failed to induce LTP in the CA1 region at 3.5mM glucose but LTP was restored dose-dependently by increasing glucose levels to 7.0 and 10.0mM. LTP induction in the presence of 7.0mM glucose was closely associated with further increases in CaMKII autophosphorylation without changes in PKCα autophosphorylation. Taken together, CaMKII and PKC activation likely mediate potentiation of fEPSPs by elevated glucose levels, and CaMKII activity is also associated with LTP induction in the hippocampal CA1 region.

Planar polarity of multiciliated ependymal cells involves the anterior migration of basal bodies regulated by non-muscle myosin II

Motile cilia generate constant fluid flow over epithelial tissue, and thereby influence diverse physiological processes. Such functions of ciliated cells depend on the planar polarity of the cilia and on their basal bodies being oriented in the downstream direction of fluid flow. Recently, another type of basal body planar polarity, characterized by the anterior localization of the basal bodies in individual cells, was reported in the multiciliated ependymal cells that line the surface of brain ventricles. However, little is known about the cellular and molecular mechanisms by which this polarity is established. Here, we report in mice that basal bodies move in the apical cell membrane during differentiation to accumulate in the anterior region of ependymal cells. The planar cell polarity signaling pathway influences basal body orientation, but not their anterior migration, in the neonatal brain. Moreover, we show by pharmacological and genetic studies that non-muscle myosin II is a key regulator of this distribution of basal bodies. This study demonstrates that the orientation and distribution of basal bodies occur by distinct mechanisms.

Heart-type fatty acid binding protein regulates dopamine D2 receptor function in mouse brain

Fatty acid binding proteins (FABPs) are essential for energy production and long-chain polyunsaturated fatty acid-related signaling in the brain and other tissues. Of various FABPs, heart-type fatty acid binding protein (H-FABP, FABP3) is highly expressed in neurons of mature brain and plays a role in arachidonic acid incorporation into brain and heart cells. However, the precise function of H-FABP in brain remains unclear. We previously demonstrated that H-FABP is associated with the dopamine D(2) receptor long isoform (D2LR) in vitro. Here, we confirm that H-FABP binds to dopamine D(2) receptor (D2R) in brain extracts and colocalizes immunohistochemically with D2R in the dorsal striatum. We show that H-FABP is highly expressed in acetylcholinergic interneurons and terminals of glutamatergic neurons in the dorsal striatum of mouse brain but absent in dopamine neuron terminals and spines in the same region. H-FABP knock-out (KO) mice showed lower responsiveness to methamphetamine-induced sensitization and enhanced haloperidol-induced catalepsy compared with wild-type mice, indicative of D2R dysfunction. Consistent with the latter, aberrant increased acetylcholine (ACh) release and depolarization-induced glutamate (Glu) release were observed in the dorsal striatum of H-FABP KO mice. Furthermore, phosphorylation of CaMKII (Ca(2+)/calmodulin-dependent protein kinase II) and ERK (extracellular signal-regulated kinase) was significantly increased in the dorsal striatum. We confirmed elevated ERK phosphorylation following quinpirole-mediated D2R stimulation in H-FABP-overexpressing SHSY-5Y human neuroblastoma cells. Together, H-FABP is highly expressed in ACh interneurons and glutamatergic terminals, thereby regulating dopamine D2R function in the striatum.

Reduced expression of the ATRX gene, a chromatin-remodeling factor, causes hippocampal dysfunction in mice

Mutations of the ATRX gene, which encodes an ATP-dependent chromatin-remodeling factor, were identified in patients with α-thalassemia X-linked mental retardation (ATR-X) syndrome. There is a milder variant of ATR-X syndrome caused by mutations in the Exon 2 of the gene. To examine the impact of the Exon 2 mutation on neuronal development, we generated ATRX mutant (ATRX(ΔE2)) mice. Truncated ATRX protein was produced from the ATRX(ΔE2) mutant allele with reduced expression level. The ATRX(ΔE2) mice survived and reproduced normally. There was no significant difference in Morris water maze test between wild-type and ATRX(ΔE2) mice. In a contextual fear conditioning test, however, total freezing time was decreased in ATRX(ΔE2) mice compared to wild-type mice, suggesting that ATRX(ΔE2) mice have impaired contextual fear memory. ATRX(ΔE2) mice showed significantly reduced long-term potentiation in the hippocampal CA1 region evoked by high-frequency stimulation. Moreover, autophosphorylation of calcium-calmodulin-dependent kinase II (αCaMKII) and phosphorylation of glutamate receptor, ionotropic, AMPA 1 (GluR1) were decreased in the hippocampi of the ATRX(ΔE2) mice compared to wild-type mice. These findings suggest that ATRX(ΔE2) mice may have fear-associated learning impairment with the dysfunction of αCaMKII and GluR1. The ATRX(ΔE2) mice would be useful tools to investigate the role of the chromatin-remodeling factor in the pathogenesis of abnormal behaviors and learning impairment.

Comprehensive behavioral analysis of calcium/calmodulin-dependent protein kinase IV knockout mice

Calcium-calmodulin dependent protein kinase IV (CaMKIV) is a protein kinase that activates the transcription factor CREB, the cyclic AMP-response element binding protein. CREB is a key transcription factor in synaptic plasticity and memory consolidation. To elucidate the behavioral effects of CaMKIV deficiency, we subjected CaMKIV knockout (CaMKIV KO) mice to a battery of behavioral tests. CaMKIV KO had no significant effects on locomotor activity, motor coordination, social interaction, pain sensitivity, prepulse inhibition, attention, or depression-like behavior. Consistent with previous reports, CaMKIV KO mice exhibited impaired retention in a fear conditioning test 28 days after training. In contrast, however, CaMKIV KO mice did not show any testing performance deficits in passive avoidance, one of the most commonly used fear memory paradigms, 28 days after training, suggesting that remote fear memory is intact. CaMKIV KO mice exhibited intact spatial reference memory learning in the Barnes circular maze, and normal spatial working memory in an eight-arm radial maze. CaMKIV KO mice also showed mildly decreased anxiety-like behavior, suggesting that CaMKIV is involved in regulating emotional behavior. These findings indicate that CaMKIV might not be essential for fear memory or spatial memory, although it is possible that the activities of other neural mechanisms or signaling pathways compensate for the CaMKIV deficiency.

Platelet-activating factor-induced synaptic facilitation is associated with increased calcium/calmodulin-dependent protein kinase II, protein kinase C and extracellular signal-regulated kinase activities in the rat hippocampal CA1 region

Platelet-activating factor (PAF) is an important inflammatory lipid mediator affecting neural plasticity. In the present study, we demonstrated how PAF affects synaptic efficacy through activation of protein kinases in the rat hippocampal CA1 region. In cultured hippocampal neurons, 10 to 1000 nM PAF stimulated autophosphorylation of calcium/calmodulin-dependent protein kinase II (CaMKII) and phosphorylation of synapsin I and myristoylated alanine-rich protein kinase C substrate (MARCKS). In hippocampal CA1 slices, field excitatory postsynaptic potentials (fEPSPs) induced by stimulation of the Schaffer collateral/commissural pathways were significantly increased 10-50 min after exposure to 100 to 1000 nM PAF. Immunoblotting analysis showed that 100 nM PAF treatment for 10 or 50 min significantly and persistently increased CaMKII autophosphorylation in the hippocampal CA1 region. Increased protein kinase Calpha (PKCalpha) autophosphorylation was also seen at the same time point after PAF exposure. By contrast, extracellular signal-regulated kinase (ERK) phosphorylation was slightly but significantly increased at 10 min after PAF exposure. Consistent with increased CaMKII autophosphorylation, AMPA-type glutamate receptor subunit 1 (GluR1) (Ser-831) phosphorylation as a CaMKII postsynaptic substrate significantly increased after 10 or 50 min of treatment, whereas synapsin I (Ser-603) phosphorylation as a presynaptic substrate increased at 10 min in the hippocampal CA1 region. Phosphorylation of MARCKS (Ser-152/156) and NMDA receptor subunit 1 (NR1) (Ser-896) as PKCalpha substrates also significantly increased after 10 min but had not further increased by 50 min in the CA1 region. Increased of fEPSPs induced by PAF treatment completely and/or partly inhibited by KN93 and/or U0126 treatment. These results suggest that PAF induces synaptic facilitation through activation of CaMKII, PKC and ERK in the hippocampal CA1 region.

Nobiletin improves brain ischemia-induced learning and memory deficits through stimulation of CaMKII and CREB phosphorylation

Decreased cerebral blood flow causes cognitive impairments and neuronal injury in the progressive age-related neurodegenerative disorders such as Alzheimer's disease (AD) and vascular dementia. In the present study, we for the first time found that nobiletin, a novel leading compound for AD therapy, improved cerebral ischemia-induced memory deficits in vivo. Treatment with 50 mg/kg of nobiletin (i.p.) for the consecutive 7 days before and after brain ischemia significantly inhibited delayed neuronal death in the hippocampal CA1 neurons in a 20-min bilateral common carotid arteries occlusion (BCCAO) ischemia. However, the contextual memory assessed by passive avoidance task was not improved. On the other hand, a 5-min BCCAO-induced contextual memory deficit was significantly improved by the nobiletin treatment. In the 5-min BCCAO mice, Western blot analysis evidently showed that the levels of synaptic proteins, including calcium/calmodulin-dependent protein kinase II (CaMKII), microtubule-associated protein 2 (MAP2) and glutamate receptor 1 (GluR1), significantly decreased in the hippocampal CA1 region. The nobiletin treatment prevented the reduction in CaMKII, MAP2 and GluR1 protein levels in the hippocampal CA1 region, accompanied by restoration of both ERK and CREB phosphorylation and CaMKII autophosphorylation. Consistent with the restored CaMKII and ERK phosphorylation, an electrophysiological study showed that the impaired hippocampal long-term potentiation (LTP) observed in the 5-min ischemic mice was significantly improved by the nobiletin treatment. These findings suggest that the activation of CaMKII and ERK signaling in part mediates improvement of ischemia-induced learning and memory deficits by nobiletin.