PI3Kγ deficiency enhances seizures severity and associated outcomes in a mouse model of convulsions induced by intrahippocampal injection of pilocarpine

PI3K, mTOR and GSK3 modulate cytokines' production in peripheral leukocyte in temporal lobe epilepsy

INTRODUCTION

Epilepsy is a common pathological condition that predisposes individuals to seizures, as well as cognitive and emotional dysfunctions. Different studies have demonstrated that inflammation contributes to the pathophysiology of epilepsy. Indeed, seizures change the peripheral inflammatory pattern, which, in turn, could contribute to seizures. However, the cause of the altered production of peripheral inflammatory mediators is not known. The PI3K/mTOR/GSK3β pathway is important for different physiological and pharmacological phenomena. Therefore, in the present study, we tested the hypothesis that the PI3K/mTOR/GSK3β pathway is deregulated in immune cells from patients with epilepsy and contributes to the abnormal production of inflammatory mediators.

METHODS

Patients with temporal lobe epilepsy presenting hippocampal sclerosis and controls aged between 18 and 65 years-old were selected for this study. Peripheral blood was collected for the isolation of peripheral mononuclear blood cells (PBMC). Cells were pre-incubated with different PI3K, mTOR and GSK-3 inhibitors for 30 min and further stimulated with phytohaemaglutinin (PHA) or vehicle for 24 h. The supernatant was used to evaluate the production of IL-1β, IL-6, IL-10, TNF e IL-12p70.

RESULTS

Non-selective inhibition of PI3K, as well as inhibition of PI3Kγ and GSK-3, reduced the levels of TNF and IL-10 in PHA-stimulated cells from TLE individuals. This stimulus increased the production of IL-12p70 only in cells from TLE individuals, while the inhibition of PI3K and mTOR enhanced the production of this cytokine. On the other hand, inhibition of GSK3 reduced the PHA-induced production of IL-12p70.

CONCLUSIONS

Herein we demonstrated that the production of cytokines by immune cells from patients with TLE differs from non-epileptic patients. This differential regulation may be associated with the altered activity and responsiveness of intracellular molecules, such as PI3K, mTOR and GSK-3, which, in turn, might contribute to the inflammatory state that exists in epilepsy and its pathogenesis.

Effects of Cerebrolysin on Hippocampal Neuronal Death After Pilocarpine-Induced Seizure

Epilepsy is one of the most common and severe brain diseases. The exact cause of epilepsy is unclear. Epilepsy often occurs following brain damage, such as traumatic brain injury (TBI) and ischemia. Cerebrolysin is a porcine brain peptide that is a unique neurotropic and neuroprotective agent. Cerebrolysin has been reported to increase neuroprotective effects after TBI, ischemia, and other CNS diseases. However, the effects of cerebrolysin on seizures are not known. Therefore, this study aimed to investigate the effects of neuropeptide cerebrolysin on neuronal death in the hippocampus after a seizure. To confirm the effects of cerebrolysin, we used a pilocarpine-induced seizure animal model. Cerebrolysin (2.5 ml/kg, i.p., once per day for 7 days) was immediately injected after a seizure induction. After 1 week, we obtained brain tissues and performed staining to histologically evaluate the potentially protective effects of cerebrolysin on seizure-induced neuronal death in the hippocampus. We found that cerebrolysin decreased hippocampal neuronal death after a seizure. In addition, an increase in brain-derived neurotrophic factor (BDNF) was confirmed through Western blot analysis to further support our hypothesis. Therefore, the present study suggests that the administration of cerebrolysin can be a useful therapeutic tool for preventing neuronal death after a seizure.

Phosphoinositide-3-Kinase γ Is Not a Predominant Regulator of ATP-Dependent Directed Microglial Process Motility or Experience-Dependent Ocular Dominance Plasticity

Microglia are dynamic cells whose extensive interactions with neurons and glia during development allow them to regulate neuronal development and function. The microglial P2Y12 receptor is crucial for microglial responsiveness to extracellular ATP and mediates numerous microglial functions, including ATP-dependent directional motility, microglia-neuron interactions, and experience-dependent synaptic plasticity. However, little is known about the downstream signaling effectors that mediate these diverse actions of P2Y12. Phosphoinositide-3-kinase γ (PI3Kγ), a lipid kinase activated downstream of G_i-protein-coupled receptors such as P2Y12, could translate localized extracellular ATP signals into directed microglial action and serve as a broad effector of P2Y12-dependent signaling. Here, we used pharmacological and genetic methods to manipulate P2Y12 and PI3Kγ signaling to determine whether inhibiting PI3Kγ phenocopied the loss of P2Y12 signaling in mouse microglia. While pan-inhibition of all PI3K activity substantially affected P2Y12-dependent microglial responses, our results suggest that PI3Kγ specifically is only a minor part of the P2Y12 signaling pathway. PI3Kγ was not required to maintain homeostatic microglial morphology or their dynamic surveillance in vivo Further, PI3Kγ was not strictly required for P2Y12-dependent microglial responses ex vivo or in vivo, although we did observe subtle deficits in the recruitment of microglial process toward sources of ATP. Finally, PI3Kγ was not required for ocular dominance plasticity, a P2Y12-dependent form of experience-dependent synaptic plasticity that occurs in the developing visual cortex. Overall, our results demonstrate that PI3Kγ is not the major mediator of P2Y12 function in microglia, but may have a role in amplifying or fine-tuning the chemotactic response.

A positive allosteric modulator of mGluR5 promotes neuroprotective effects in mouse models of Alzheimer's disease

Alzheimer's Disease (AD) is the most prevalent neurodegenerative disorder. Despite advances in the understanding of its pathophysiology, none of the available therapies prevents disease progression. Excess glutamate plays an important role in excitotoxicity by activating ionotropic receptors. However, the mechanisms modulating neuronal cell survival/death via metabotropic glutamate receptors (mGluRs) are not completely understood. Recent data indicates that CDPPB, a positive allosteric modulator of mGluR5, has neuroprotective effects. Thus, this work aimed to investigate CDPPB treatment effects on amyloid-β (Aβ) induced pathological alterations in vitro and in vivo and in a transgenic mouse model of AD (T41 mice). Aβ induced cell death in primary cultures of hippocampal neurons, which was prevented by CDPPB. Male C57BL/6 mice underwent stereotaxic surgery for unilateral intra-hippocampal Aβ injection, which induced memory deficits, neurodegeneration, neuronal viability reduction and decrease of doublecortin-positive cells, a marker of immature neurons and neuronal proliferation. Treatment with CDPPB for 8 days reversed neurodegeneration and doublecortin-positive cells loss and recovered memory function. Fourteen months old T41 mice presented cognitive deficits, neuronal viability reduction, gliosis and Aβ accumulation. Treatment with CDPPB for 28 days increased neuronal viability (32.2% increase in NeuN⁺ cells) and reduced gliosis in CA1 region (Iba-1⁺ area by 31.3% and GFAP⁺ area by 37.5%) in transgenic animals, without inducing hepatotoxicity. However, it did not reverse cognitive deficit. Despite a four-week treatment did not prevent memory loss in aged transgenic mice, CDPPB is protective against Aβ stimulus. Therefore, this drug represents a potential candidate for further investigations as AD treatment.

Anticonvulsant effect of cannabidiol in the pentylenetetrazole model: Pharmacological mechanisms, electroencephalographic profile, and brain cytokine levels

Cannabidiol (CBD), the main nonpsychotomimetic compound from Cannabis sativa, inhibits experimental seizures in animal models and alleviates certain types of intractable epilepsies in patients. Its pharmacological profile, however, is still uncertain. Here we tested the hypothesis that CBD anticonvulsant mechanisms are prevented by cannabinoid (CB₁ and CB₂) and vanilloid (TRPV1) receptor blockers. We also investigated its effects on electroencephalographic (EEG) activity and hippocampal cytokines in the pentylenetetrazole (PTZ) model. Pretreatment with CBD (60mg/kg) attenuated seizures induced by intraperitoneal, subcutaneous, and intravenous PTZ administration in mice. The effects were reversed by CB₁, CB₂, and TRPV1 selective antagonists (AM251, AM630, and SB366791, respectively). Additionally, CBD delayed seizure sensitization resulting from repeated PTZ administration (kindling). This cannabinoid also prevented PTZ-induced EEG activity and interleukin-6 increase in prefrontal cortex. In conclusion, the robust anticonvulsant effects of CBD may result from multiple pharmacological mechanisms, including facilitation of endocannabinoid signaling and TRPV1 mechanisms. These findings advance our understanding on CBD inhibition of seizures, EEG activity, and cytokine actions, with potential implications for the development of new treatments for certain epileptic syndromes.

TLR4 signal ablation attenuated neurological deficits by regulating microglial M1/M2 phenotype after traumatic brain injury in mice

Traumatic brain injury (TBI) initiates inflammatory responses that result in an enduring cascade of secondary neuronal loss and behavioural impairment. Toll-like receptor 4 (TLR4), predominantly expressed by microglia, recognizes damage-associated molecular patterns (DAMPs) and regulates inflammatory processes. Interestingly, the switch of microglial M1/M2 phenotypes after TBI is highly important regarding damage and restoration of neurological function. Therefore, we investigated the role and mechanisms of the TLR4 signalling pathway in regulating microglial M1/M2 phenotypes. Using a controlled cortical impact (CCI) model, we found that TLR4 knockout (KO) mice exhibited decreased infarct volumes and improved outcomes in behavioural tests. In addition, mice lacking TLR4 had higher expression of M2 phenotype biomarkers but lower expression of M1 phenotype biomarkers. Compared with microglia derived from wild-type (WT) mice, increased expression of M2 phenotype biomarkers and decreased expression of M1 phenotype biomarkers were also noted in primary cultures of microglia from TLR4 KO mice. In TLR4 KO mice, the expression levels of downstream signalling molecules of TLR4, such as active Rac-1 and phospho-AKT, were higher, while MyD88 and phospho-NF-κB p65 expression levels were lower than in WT mice. Our results demonstrate that the absence of TLR4 induces microglial polarization toward the M2 phenotype and promotes microglial migration and, in turn, alleviates the development of neuroinflammation, which indicates potential neuroprotective effects in the TBI mouse model. Furthermore, up-regulation of IL-4 expression in TLR4 KO mice could contribute to anti-inflammatory functions and promote microglial polarization toward the M2 phenotype, which might be mediated by active Rac-1 expression. Taken together, TLR4 deficiency contributes to regulating microglia to switch to the M2 phenotype, which ameliorates neurological impairment after TBI.

Cyclooxygenase-2 inhibitors differentially attenuate pentylenetetrazol-induced seizures and increase of pro- and anti-inflammatory cytokine levels in the cerebral cortex and hippocampus of mice

Seizures increase prostaglandin and cytokine levels in the brain. However, it remains to be determined whether cyclooxygenase-2 (COX-2) derived metabolites play a role in seizure-induced cytokine increase in the brain and whether anticonvulsant activity is shared by all COX-2 inhibitors. In this study we investigated whether three different COX-2 inhibitors alter pentylenetetrazol (PTZ)-induced seizures and increase of interleukin-1β (IL-1β), interleukin-6 (IL-6), interferon-γ (INF-γ), tumor necrosis factor-α (TNF-α) and interleukin-10 (IL-10) levels in the hippocampus and cerebral cortex of mice. Adult male albino Swiss mice received nimesulide, celecoxib or etoricoxib (0.2, 2 or 20mg/kg in 0.1% carboxymethylcellulose (CMC) in 5% Tween 80, p.o.). Sixty minutes thereafter the animals were injected with PTZ (50mg/kg, i.p.) and the latency to myoclonic jerks and to generalized tonic-clonic seizures were recorded. Twenty minutes after PTZ injection animals were killed and cytokine levels were measured. PTZ increased cytokine levels in the cerebral cortex and hippocampus. While celecoxib and nimesulide attenuated PTZ -induced increase of proinflammatory cytokines in the cerebral cortex, etoricoxib did not. Nimesulide was the only COX-2 inhibitors that attenuated PTZ-induced seizures. This effect coincided with an increase of IL-10 levels in the cerebral cortex and hippocampus, constituting circumstantial evidence that IL-10 increase may be involved in the anticonvulsant effect of nimesulide.

Postictal alterations induced by intrahippocampal injection of pilocarpine in C57BL/6 mice

Temporal lobe epilepsy (TLE) is the most common form of epilepsy in adults. The pilocarpine (PILO) experimental model of TLE portrays behavioral and pathophysiological changes in rodents that are very similar to those found in humans with TLE. However, this model is associated with an unfortunate high mortality rate. Studies have shown that intrahippocampal injection of PILO, while having a much smaller mortality rate, induces status epilepticus (SE) that secondarily leads to TLE. To the best of our knowledge, the present study was the first to evaluate the cognitive and histological alterations 72h after intrahippocampal microinjection of PILO in C57BL/6 mice. Seventy percent of mice developed status epilepticus (SE) after PILO administration, and all animals survived after SE. Seventy-two hours after SE, mice presented memory impairment in both Novel Object Recognition (recognition index - vehicle: 67.57±4.46% vs PILO: 52.33±3.29%) and Contextual Fear Conditioning (freezing time - vehicle: 203±20.43 vs PILO: 107.80±25.17s) tasks. Moreover, using Nissl and NeuN staining, we observed in PILO-treated mice a significant decrease in cell viability and an increase in neuronal loss in all three hippocampal regions analyzed, cornus ammonis (CA) 1, CA3, and dentate gyrus (DG), in comparison with the control group. Additionally, using Iba-1 staining, we observed in PILO-treated mice a significant increase in microglial proliferation in CA1, CA3, and DG of the hippocampus. Therefore, intrahippocampal PILO microinjection is an efficient route to induce SE and acute postictal epileptogenic-like alterations in C57BL/6 mice.

Neuroprotective effects of the anticancer drug NVP-BEZ235 (dactolisib) on amyloid-β 1-42 induced neurotoxicity and memory impairment

Alzheimer's Disease (AD) is a progressive neurodegenerative disease and the main cause of dementia. Substantial evidences indicate that there is over-activation of the PI3K/Akt/mTOR axis in AD. Therefore, the aim of the present study was to investigate the effects of NVP-BEZ235 (BEZ; dactolisib), a dual PI3K/mTOR inhibitor that is under phase I/II clinical trials for the treatment of some types of cancer, in hippocampal neuronal cultures stimulated with amyloid-β (Aβ) 1-42 and in mice injected with Aβ 1-42 in the hippocampus. In cell cultures, BEZ reduced neuronal death induced by Aβ. BEZ, but not rapamycin, a mTOR inhibitor, or LY294002, a PI3K inhibitor that also inhibits mTOR, reduced the memory impairment induced by Aβ. The effect induced by Aβ was also prevented in PI3Kγ(-/-) mice. Neuronal death and microgliosis induced by Aβ were reduced by BEZ. In addition, the compound increased IL-10 and TNF-α levels in the hippocampus. Finally, BEZ did not change the phosphorylation of Akt and p70s6K, suggesting that the involvement of PI3K and mTOR in the effects induced by BEZ remains controversial. Therefore, BEZ represents a potential strategy to prevent the pathological outcomes induced by Aβ and should be investigated in other models of neurodegenerative conditions.