Regulation of ERK1/2 mitogen-activated protein kinase by NMDA-receptor-induced seizure activity in cortical slices

Memantine ameliorates the impairment of social behaviors induced by a single social defeat stress as juveniles

Clinically, juveniles are more sensitive to stress than adults, and exposure to stress as juveniles prolongs psychiatric symptoms and causes treatment resistance. However, the efficacy of antidepressants for juveniles with psychiatric disorders is unknown. In the present study, we investigated whether the expression or development of impaired social behavior was attenuated by memantine, a NMDA receptor antagonist. In addition, we clarified the molecular mechanisms related to intracellular signal transduction through NMDA receptors and the ameliorating effect of memantine in mice with impaired social behavior. Acute administration of memantine before the social interaction test, but not before exposure to social defeat stress, attenuated social behavioral impairment. A single social defeat stress increased the phosphorylation of NMDA receptor subunit GluN2A and extracellular-signal-related kinase 1/2 (ERK1/2). Memantine inhibited the increase of phosphorylated GluN2A and ERK1/2 resulting from social interaction behavior. In both GluN2A deficient and pharmacological blockaded mice, social behavioral impairment was not observed in the social interaction test through regulation of ERK1/2 phosphorylation. These findings suggest that memantine ameliorates social behavioral impairment in mice exposed to a single social defeat stress as juveniles by regulating the NMDA receptor and subsequent ERK1/2 signaling activation. Memantine may constitute a novel therapeutic drug for stress-related psychiatric disorders in juveniles with adverse juvenile experiences.

Effects of rapamycin and curcumin on inflammation and oxidative stress in vitro and in vivo - in search of potential anti-epileptogenic strategies for temporal lobe epilepsy

Background

Previous studies in various rodent epilepsy models have suggested that mammalian target of rapamycin (mTOR) inhibition with rapamycin has anti-epileptogenic potential. Since treatment with rapamycin produces unwanted side effects, there is growing interest to study alternatives to rapamycin as anti-epileptogenic drugs. Therefore, we investigated curcumin, the main component of the natural spice turmeric. Curcumin is known to have anti-inflammatory and anti-oxidant effects and has been reported to inhibit the mTOR pathway. These properties make it a potential anti-epileptogenic compound and an alternative for rapamycin.

Methods

To study the anti-epileptogenic potential of curcumin compared to rapamycin, we first studied the effects of both compounds on mTOR activation, inflammation, and oxidative stress in vitro, using cell cultures of human fetal astrocytes and the neuronal cell line SH-SY5Y. Next, we investigated the effects of rapamycin and intracerebrally applied curcumin on status epilepticus (SE)—induced inflammation and oxidative stress in hippocampal tissue, during early stages of epileptogenesis in the post-electrical SE rat model for temporal lobe epilepsy (TLE).

Results

Rapamycin, but not curcumin, suppressed mTOR activation in cultured astrocytes. Instead, curcumin suppressed the mitogen-activated protein kinase (MAPK) pathway. Quantitative real-time PCR analysis revealed that curcumin, but not rapamycin, reduced the levels of inflammatory markers IL-6 and COX-2 in cultured astrocytes that were challenged with IL-1β. In SH-SY5Y cells, curcumin reduced reactive oxygen species (ROS) levels, suggesting anti-oxidant effects. In the post-SE rat model, however, treatment with rapamycin or curcumin did not suppress the expression of inflammatory and oxidative stress markers 1 week after SE.

Conclusions

These results indicate anti-inflammatory and anti-oxidant properties of curcumin, but not rapamycin, in vitro. Intracerebrally applied curcumin modified the MAPK pathway in vivo at 1 week after SE but failed to produce anti-inflammatory or anti-oxidant effects. Future studies should be directed to increasing the bioavailability of curcumin (or related compounds) in the brain to assess its anti-epileptogenic potential in vivo.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1247-9) contains supplementary material, which is available to authorized users.

Acamprosate in a mouse model of fragile X syndrome: modulation of spontaneous cortical activity, ERK1/2 activation, locomotor behavior, and anxiety

BACKGROUND

Fragile X Syndrome (FXS) occurs as a result of a silenced fragile X mental retardation 1 gene (FMR1) and subsequent loss of fragile X mental retardation protein (FMRP) expression. Loss of FMRP alters excitatory/inhibitory signaling balance, leading to increased neuronal hyperexcitability and altered behavior. Acamprosate (the calcium salt of N-acetylhomotaurinate), a drug FDA-approved for relapse prevention in the treatment of alcohol dependence in adults, is a novel agent with multiple mechanisms that may be beneficial for people with FXS. There are questions regarding the neuroactive effects of acamprosate and the significance of the molecule's calcium moiety. Therefore, the electrophysiological, cellular, molecular, and behavioral effects of acamprosate were assessed in the Fmr1^-/y (knock out; KO) mouse model of FXS controlling for the calcium salt in several experiments.

METHODS

Fmr1 KO mice and their wild-type (WT) littermates were utilized to assess acamprosate treatment on cortical UP state parameters, dendritic spine density, and seizure susceptibility. Brain extracellular-signal regulated kinase 1/2 (ERK1/2) activation was used to investigate this signaling molecule as a potential biomarker for treatment response. Additional adult mice were used to assess chronic acamprosate treatment and any potential effects of the calcium moiety using CaCl₂ treatment on behavior and nuclear ERK1/2 activation.

RESULTS

Acamprosate attenuated prolonged cortical UP state duration, decreased elevated ERK1/2 activation in brain tissue, and reduced nuclear ERK1/2 activation in the dentate gyrus in KO mice. Acamprosate treatment modified behavior in anxiety and locomotor tests in Fmr1 KO mice in which control-treated KO mice were shown to deviate from control-treated WT mice. Mice treated with CaCl₂ were not different from saline-treated mice in the adult behavior battery or nuclear ERK1/2 activation.

CONCLUSIONS

These data indicate that acamprosate, and not calcium, improves function reminiscent of reduced anxiety-like behavior and hyperactivity in Fmr1 KO mice and that acamprosate attenuates select electrophysiological and molecular dysregulation that may play a role in the pathophysiology of FXS. Differences between control-treated KO and WT mice were not evident in a recognition memory test or in examination of acoustic startle response/prepulse inhibition which impeded conclusions from being made about the treatment effects of acamprosate in these instances.

Initial analysis of peripheral lymphocytic extracellular signal related kinase activation in autism

BACKGROUND

Dysregulation of extracellular signal-related kinase (ERK) activity has been potentially implicated in the pathophysiology of autistic disorder (autism). ERK is part of a central intracellular signaling cascade responsible for a myriad of cellular functions. ERK is expressed in peripheral blood lymphocytes, and measurement of activated (phosphorylated) lymphocytic ERK is commonly executed in many areas of medicine. We sought to conduct the first study of ERK activation in humans with autism by utilizing a lymphocytic ERK activation assay. We hypothesized that ERK activation would be enhanced in peripheral blood lymphocytes from persons with autism compared to those of neurotypical control subjects.

METHOD

We conducted an initial study of peripheral lymphocyte ERK activation in 45 subjects with autism and 26 age- and gender-matched control subjects (total n = 71). ERK activation was measured using a lymphocyte counting method (primary outcome expressed as lymphocytes staining positive for cytosolic phosphorylated ERK divided by total cells counted) and additional Western blot analysis of whole cell phosphorylated ERK adjusted for total ERK present in the lymphocyte lysate sample.

RESULTS

Cytosolic/nuclear localization of pERK activated cells were increased by almost two-fold in the autism subject group compared to matched neurotypical control subjects (cell count ratio of 0.064 ± 0.044 versus 0.034 ± 0.031; p = 0.002). Elevated phosphorylated ERK levels in whole cell lysates also showed increased activated ERK in the autism group compared to controls (n = 54 total) in Western blot analysis.

CONCLUSIONS

The results of this first in human ERK activation study are consistent with enhanced peripheral lymphocytic ERK activation in autism, as well as suggesting that cellular compartmentalization of activated ERK may be altered in this disorder. Future work will be required to explore the impact of concomitant medication use and other subject characteristics such as level of cognitive functioning on ERK activation.

TRIAL REGISTRATION

Not applicable.

The expression and distribution of seizure-related and synaptic proteins in the insular cortex of rats genetically prone to audiogenic seizures

It is known that perirhinal/insular cortices participate in the transmission of sensory stimuli to the motor cortex, thus coordinating motor activity during seizures. In the present study we analysed seizure-related proteins, such as GABA, glutamate, ERK1/2 and the synaptic proteins in the insular cortex of Krushinsky-Molodkina (KM) rats genetically prone to audiogenic seizures (AGS). We compared seizure-naïve and seizure-experienced KM rats with control Wistar rats in order to distinguish whether seizure-related protein changes are associated with seizure event or representing an inhered pathological abnormality that determines predisposition to AGS. Our data demonstrated an increased level of vesicular glutamate transporter VGLUT2 in naïve and seizure-experienced KM rats, while glutamic acid decarboxylases GAD65 and GAD67 levels were unchanged. Evaluation of the synaptic proteins showed a decrease in SNAP-25 and upregulation of synapsin I phosphorylation in both groups of KM rats in comparison to Wistar rats. However, when phosphorylation level of ERK1/2 in naïve KM rats was significantly increased, several episodes of AGS diminished ERK1/2 activity. Obtained data indicate that changes in ERK1/2 phosphorylation status and glutamate release controlling synaptic proteins in the insular cortex of KM rats could contribute to the AGS susceptibility.

Contrasting features of ERK1/2 activity and synapsin I phosphorylation at the ERK1/2-dependent site in the rat brain in status epilepticus induced by kainic acid in vivo

Extracellular signal-regulated kinase 1/2 (ERK1/2) plays diverse roles in the central nervous system. Activation of ERK1/2 has been observed in various types of neuronal excitation, including seizure activity in vivo and in vitro. However, studies examining ERK1/2 activity and its substrate phosphorylation in parallel are scarce especially in seizure models. We have been studying the phosphorylation state of the presynaptic protein, synapsin I at ERK1/2-dependent and -independent sites in various types of seizure models and showed that ERK1/2-dependent phosphorylation of synapsin I was indeed under control of ERK1/2 activity in vivo. To further expand our study, here we examined the effects of prolonged seizure activity on ERK1/2 activity and synapsin I phosphorylation by using status epilepticus induced by kainic acid (KA-SE) in rats in vivo. In KA-SE, robust ERK1/2 activation was observed in the hippocampus, a representative limbic structure, with lesser activation in the parietal cortex, a representative non-limbic structure. In contrast, the phosphorylation level of synapsin I at ERK1/2-dependent phospho-site 4/5 was profoundly decreased, the extent of which was much larger in the hippocampus than in the parietal cortex. In addition, phosphorylation at other ERK1/2-independent phospho-sites in synapsin I also showed an even larger decrease. All these changes disappeared after recovery from KA-SE. These results indicate that the phosphorylation state of synapsin I is dynamically regulated by the balance between kinase and phosphatase activities. The contrasting features of robust ERK1/2 activation yet synapsin I dephosphorylation may be indicative of an irreversible pathological outcome of the epileptic state in vivo.