The differential roles of PEA15 phosphorylations in reactive astrogliosis and astroglial apoptosis following status epilepticus

N-Formyl-Methionyl-Leucyl-Phenylalanine Plays a Neuroprotective and Anticonvulsant Role in Status Epilepticus Model

Status epilepticus (SE) is described as continuous and self-sustaining seizures, which triggers hippocampal neurodegeneration, inflammation, and gliosis. N-formyl peptide receptor (FPR) has been associated with inflammatory process. N-formyl-methionyl-leucyl-phenylalanine (fMLP) peptide plays an anti-inflammatory role, mediated by the activation of G-protein-coupled FPR. Here, we evaluated the influence of fMLP peptides on the behavior of limbic seizures, memory consolidation, and hippocampal neurodegeneration process. Male Wistar rats (Rattus norvegicus) received microinjections of pilocarpine in hippocampus (H-PILO, 1.2 mg/μL, 1 μL) followed by fMLP (1 mg/mL, 1 μL) or vehicle (VEH, saline 0.9%, 1 μL). During the 90 min of SE, epileptic seizures were analyzed according to the Racine's Scale. After 24 h of SE, memory impairment was assessed by the inhibitory avoidance test and the neurodegeneration process was evaluated in hippocampal areas. There was no change in latency and number of wet dog shake (WDS) after administration of fMLP. However, our results showed that the intrahippocampal infusion of fMLP reduced the severity of seizures, as well as the number of limbic seizures. In addition, fMLP infusion protected memory dysfunction followed by SE. Finally, the intrahippocampal administration of fMLP attenuated the process of neurodegeneration in both hippocampi. Taken together, our data suggest a new insight into the functional role of fMLP peptides, with important implications for their potential use as a therapeutic agent for the treatment of brain disorders, such as epilepsy. Schematic drawing on the neuroprotective and anticonvulsant role of fMLP during status epilepticus. Initially, a cannula was implanted in hippocampus and pilocarpine/saline was administered into the hippocampus followed by fMLP/saline (A-C). fMLP reduced seizure severity and neuronal death in the hippocampus, as well as protecting against memory deficit (D).

CDDO-Me Distinctly Regulates Regional Specific Astroglial Responses to Status Epilepticus via ERK1/2-Nrf2, PTEN-PI3K-AKT and NFκB Signaling Pathways

2-Cyano-3,12-dioxo-oleana-1,9(11)-dien-28-oic acid methyl ester (CDDO-Me) is a triterpenoid analogue of oleanolic acid. CDDO-Me shows anti-inflammatory and neuroprotective effects. Furthermore, CDDO-Me has antioxidant properties, since it activates nuclear factor-erythroid 2-related factor 2 (Nrf2), which is a key player of redox homeostasis. In the present study, we evaluated whether CDDO-Me affects astroglial responses to status epilepticus (SE, a prolonged seizure activity) in the rat hippocampus in order to understand the underlying mechanisms of reactive astrogliosis and astroglial apoptosis. Under physiological conditions, CDDO-Me increased Nrf2 expression in the hippocampus without altering activities (phosphorylations) of phosphatase and tensin homolog deleted on chromosome 10 (PTEN), phosphatidylinositol-3-kinase (PI3K), and AKT. CDDO-Me did not affect seizure activity in response to pilocarpine. However, CDDO-Me ameliorated reduced astroglial Nrf2 expression in the CA1 region and the molecular layer of the dentate gyrus (ML), and attenuated reactive astrogliosis and ML astroglial apoptosis following SE. In CA1 astrocytes, CDDO-Me inhibited the PI3K/AKT pathway by activating PTEN. In contrast, CDDO-ME resulted in extracellular signal-related kinases 1/2 (ERK1/2)-mediated Nrf2 upregulation in ML astrocytes. Furthermore, CDDO-Me decreased nuclear factor-κB (NFκB) phosphorylation in both CA1 and ML astrocytes. Therefore, our findings suggest that CDDO-Me may attenuate SE-induced reactive astrogliosis and astroglial apoptosis via regulation of ERK1/2-Nrf2, PTEN-PI3K-AKT, and NFκB signaling pathways.

Acetylcholinesterase inhibition ameliorates retinal neovascularization and glial activation in oxygen-induced retinopathy

AIM

To investigate whether inhibition of acetylcholinesterase (AChE) by donepezil ameliorate aberrant retinal neovascularization (RNV) and abnormal glial activation in oxygen-induced retinopathy (OIR).

METHODS

A mouse model of RNV was induced in postnatal day 7 (P7) mice by exposure to 75% oxygen. Donepezil was administrated to P12 mice by intraperitoneal injection. Expression and localization of AChE in mouse retinas were determined by immunofluorescence. RNV was evaluated by paraffin sectioning and hematoxylin and eosin (HE) staining. Activation of retinal Müller glial cells were examined by immunoblot of glial fibrillary acidic protein (GFAP). rMC-1, a retinal Müller cell line, was used for in vitro study. Expression of hypoxia-induced factor 1α (HIF-1α) and vascular endothelial growth factor (VEGF) were determined by Western-blot analysis, enzyme-linked immunosorbent assay (ELISA) or immunostaining.

RESULTS

Aberrant RNV and glial activation was observed after OIR. Of note, retinal AChE was mainly expressed by retinal Müller glial cells and markedly increased in OIR mice. Systemic administration of donepezil significantly reduced RNV and abnormal glial activation in mice with OIR. Moreover, ischemia-induced HIF-1α accumulation and VEGF upregulation in OIR mouse retinas and cultured rMC-1 were significantly inhibited by donepezil intervention.

CONCLUSION

AchE is implicated in RNV with OIR. Inhibition of AChE by donepeizl is likely to be a potential therapeutic approach for retinal neovascular diseases.

PKC, AKT and ERK1/2-Mediated Modulations of PARP1, NF-κB and PEA15 Activities Distinctly Regulate Regional Specific Astroglial Responses Following Status Epilepticus

Status epilepticus (SE, a prolonged seizure activity) leads to reactive astrogliosis and astroglial apoptosis in the regional specific manners, independent of hemodynamics. Poly(ADP-ribose) polymerase-1 (PARP1) activity is relevant to these distinct astroglial responses. Since various regulatory signaling molecules beyond PARP1 activity may be involved in the distinct astroglial response to SE, it is noteworthy to explore the roles of protein kinases in PARP1-mediated reactive astrogliosis and astroglial apoptosis following SE, albeit at a lesser extent. In the present study, inhibitions of protein kinase C (PKC), AKT and extracellular signal-related kinases 1/2 (ERK1/2), but not calcium/calmodulin-dependent protein kinase II (CaMKII), attenuated CA1 reactive astrogliosis accompanied by reducing PARP1 activity following SE, respectively. However, inhibition of AKT and ERK1/2 deteriorated SE-induced dentate astroglial loss concomitant with the diminished PARP1 activity. Following SE, PKC- and AKT inhibitors diminished phosphoprotein enriched in astrocytes of 15 kDa (PEA15)-S104 and -S116 phosphorylations in CA1 astrocytes, but not in dentate astrocytes, respectively. Inhibitors of PKC, AKT and ERK1/2 also abrogated SE-induced nuclear factor-κB (NF-κB)-S311 and -S468 phosphorylations in CA1 astrocytes. In contrast, both AKT and ERK1/2 inhibitors enhanced NF-κB-S468 phosphorylation in dentate astrocytes. Furthermore, PARP1 inhibitor aggravated dentate astroglial loss following SE. AKT inhibition deteriorated dentate astroglial loss and led to CA1 astroglial apoptosis following SE, which were ameliorated by AKT activation. These findings suggest that activities of PARP1, PEA15 and NF-κB may be distinctly regulated by PKC, AKT and ERK1/2, which may be involved in regional specific astroglial responses following SE.

Blockade of AMPA Receptor Regulates Mitochondrial Dynamics by Modulating ERK1/2 and PP1/PP2A-Mediated DRP1-S616 Phosphorylations in the Normal Rat Hippocampus

N-Methyl-D-aspartate receptor (NMDAR) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) activations induce fast and transient mitochondrial fragmentation under pathophysiological conditions. However, it is still unknown whether NMDAR or AMPAR activity contributes to mitochondrial dynamics under physiological conditions. In the present study, MK801 (a non-competitive NMDAR antagonist) did not affect mitochondrial length in hippocampal neurons as well as phosphorylation levels of dynamin-related protein 1 (DRP1)-serine (S) 616, extracellular-signal-regulated kinase 1/2 (ERK1/2), c-Jun N-terminal kinase (JNK), p38 mitogen-activated protein kinase (p38 MAPK) and AMPAR. In contrast, perampanel (a non-competitive AMPAR antagonist) elongated mitochondrial length in neurons concomitant with diminishing phosphorylations of DRP1-S616, ERK1/2, and JNK, but not p38 MAPK. Perampanel also reduced protein phosphatase (PP) 1, PP2A and PP2B phosphorylations, indicating activations of these PPs which were unaffected by MK801. U0126 (an ERK1/2 inhibitor) elongated mitochondrial length, accompanied by the reduced DRP1-S616 phosphorylation. SP600125 (a JNK inhibitor) did not influence mitochondrial length and DRP1 phosphorylations. Okadaic acid (a PP1/PP2A inhibitor) reduced mitochondrial length with the up-regulated DRP1-S616 phosphorylation, while CsA (a PP2B inhibitor) increased it with the elevated DRP1-S637 phosphorylation. Co-treatment of okadaic acid or CsA with perampanel attenuated the reductions in DRP1-S616 and -S637 phosphorylation without changing DRP1 expression level, respectively. GYKI 52466 (another non-competitive AMPAR antagonist) showed the similar effects of perampanel on phosphorylations of DRP1, ERK1/2, JNK, PPs, and GluR1 AMPAR subunits. Taken together, our findings suggest that a blockade of AMPAR may regulate the cooperation of ERK1/2- and PP1/PP2A for the modulation of DRP1 phosphorylations, which facilitate mitochondrial fusion.

Perampanel Affects Up-Stream Regulatory Signaling Pathways of GluA1 Phosphorylation in Normal and Epileptic Rats

To elucidate the pharmacological properties of perampanel [2-(2-oxo-1-phenyl-5-pyridin-2-yl-1,2-dihydropyridin-3-yl)benzonitrile, a novel non-competitive antagonist of AMPA receptor], we investigated its effects on the up-stream regulatory pathways of GluA1 phosphorylation including protein kinase C (PKC), Ca²⁺-calmodulin-dependent protein kinase II (CAMKII), protein kinase A (PKA), extracellular signal-regulated kinase 1/2 (ERK1/2), c-Jun N-terminal kinase (JNK), protein phosphatase (PP) 1, PP2A, and PP2B in normal and pilocarpine-induced epileptic rat model using Western blot analysis. In normal animals, perampanel affected GluA1 expression/phosphorylation, PKC, CAMKII, PKA, ERK1/2, JNK, and PPs activities. In epileptic rats, perampanel effectively inhibited spontaneous seizure activities. Perampanel enhanced phospho (p)-GluA1-S831 and -S845 ratios (phosphoprotein/total protein), while it reduced GluA1 expression. Perampanel also increased pCAMKII and pPKA ratios, which phosphorylate GluA1-S831 and -S845 site, respectively. Perampanel elevated pJNK and pPP2B ratios, which phosphorylates and dephosphorylates both GluA1-S831 and -S845 sits. Perampanel also increased pERK1/2 ratio in epileptic animals, while U0126 (an ERK1/2 inhibitor) did not affect pGluA1 ratios. Perampanel did not influence PKC, PP1, and PP2A expression levels and their phosphorylation ratios. In addition, perampanel did not have a detrimental impact on cognitive abilities of epileptic and normal rats in Morris water maze test. These findings suggest that perampanel may regulate AMPA receptor functionality via not only blockade of AMPA receptor but also the regulations of multiple molecules (CAMKII, PKA, JNK, and pPP2B)-mediated GluA1 phosphorylations without negative effects on cognition, although the effects of perampanel on PKC, PP1, and PP2A activities were different between normal and epileptic rats.

Astroglial role in the pathophysiology of status epilepticus: an overview

Status epilepticus is a medical emergency with elevated morbidity and mortality rates, and represents a leading cause of epilepsy-related deaths. Though status epilepticus can occur at any age, it manifests more likely in children and elderly people. Despite the common prevalence of epileptic disorders, a complete explanation for the mechanisms leading to development of self-limited or long lasting seizures (as in status epilepticus) are still lacking. Apart from neurons, research evidence suggests the involvement of immune and glial cells in epileptogenesis. Among glial cells, astrocytes represent an ideal target for the study of the pathophysiology of status epilepticus, due to their key role in homeostatic balance of the central nervous system. During status epilepticus, astroglial cells are activated by the presence of cytokines, damage associated molecular patterns and reactive oxygen species. The persistent activation of astrocytes leads to a decrease in glutamate clearance with a corresponding accumulation in the synaptic extracellular space, increasing the chance of neuronal excitotoxicity. Moreover, major alterations in astrocytic gap junction coupling, inflammation and receptor expression, facilitate the generation of seizures. Astrocytes are also involved in dysregulation of inhibitory transmission in the central nervous system and directly participate in ionic homeostatic alterations during status epilepticus. In the present review, we focus on the functional and structural changes in astrocytic activity that participate in the development and maintenance of status epilepticus, with special attention on concurrent inflammatory alterations. We also include potential astrocytic treatment targets for status epilepticus.