Roles of eukaryotic elongation factor 2 kinase (eEF2K) in neuronal plasticity, cognition, and Alzheimer disease

Linking KATP channel activation to p-AKT/mTORC1/eEF2/BDNF axis unravels Nicorandil's promise in countering acetaminophen-induced hepatic encephalopathy in mice

Nicorandil (NIC), an antianginal agent that acts both as an opener of adenosine triphosphate-sensitive potassium (KATP) channels and a nitric oxide donor, has demonstrated protective and curative effects in various diseases. The predominance of these mechanisms varies based on the dose of NIC and the specific organ affected. This study scrutinized the possible beneficial effects of NIC in acetaminophen (APAP)-induced hepatic encephalopathy (HE) model through highlighting the role of KATP channels in mediating these effects. Forty-eight mice were randomly subdivided into four groups: control (saline), APAP model (1 g/kg, i.p.), NIC treatment (15 mg/kg/day p.o. for 14 days), and glibenclamide (GLIB "KATP blocker", 5 mg/kg/day, p.o. 1 h before NIC for 14 days). NIC significantly mitigated APAP-induced liver injury, hyperammonemia, and cognitive deficits, as evidenced by reduced serum alanine aminotransferase, aspartate aminotransferase, ammonia levels, and improved performance in Y-maze and Morris Water Maze tests. Mechanistically, NIC suppressed hippocampal glutamate, activated phosphoserine 473 protein kinase B (p-AKT(Ser473))/mammalian target of rapamycin complex 1 (mTORC1) pathway, lessened the inactive phosphorylation of eukaryotic elongation factor 2 (eEF2), upsurged brain-derived neurotrophic factor (BDNF), leading to reduced neuroinflammation proved by nuclear factor-kappa B and tumor necrosis factor-alpha suppression. Histopathological analyses revealed improved liver and hippocampal morphology, while immunohistochemistry showed reduced astrocyte activation with NIC treatment. These effects were abolished by GLIB pre-treatment, indicating the crucial role of KATP channel. Accordingly, NIC could alleviate APAP-induced liver injury and HE mainly dependent on KATP channel opening, with resultant inhibition of glutamate signaling, activation of p-AKT/mTORC1/eEF2/BDNF trajectory, and abating hippocampal inflammation.

Eukaryotic Elongation Factor 2 Kinase EFK-1/eEF2K promotes starvation resistance by preventing oxidative damage in C. elegans

Cells and organisms frequently experience starvation. To survive, they mount an evolutionarily conserved stress response. A vital component in the mammalian starvation response is eukaryotic elongation factor 2 (eEF2) kinase (eEF2K), which suppresses translation in starvation by phosphorylating and inactivating the translation elongation driver eEF2. C. elegans EFK-1/eEF2K phosphorylates EEF-2/eEF2 on a conserved residue and is required for starvation survival, but how it promotes survival remains unclear. Surprisingly, we found that eEF2 phosphorylation is unchanged in starved C. elegans and EFK-1's kinase activity is dispensable for starvation survival, suggesting that efk-1 promotes survival via a noncanonical pathway. We show that efk-1 upregulates transcription of DNA repair pathways, nucleotide excision repair (NER) and base excision repair (BER), to promote starvation survival. Furthermore, efk-1 suppresses oxygen consumption and ROS production in starvation to prevent oxidative stress. Thus, efk-1 enables starvation survival by protecting animals from starvation-induced oxidative damage through an EEF-2-independent pathway.

Discovery of the therapeutic potential of naltriben against glutamate-induced neurotoxicity

Glutamate-induced neuronal death is associated with neurodegeneration including cerebral ischemia. Several μ-opioid receptor antagonists exhibit a neuroprotective activity and have been considered as a potential therapeutic option for neurodegenerative disorders. For the first time, our current study unveiled the neuroprotective activity of selective δ-opioid receptor antagonists. A potent, selective δ-opioid receptor antagonist naltriben, also known as a potent TRPM7 agonist, displayed the prominent protective effect against glutamate-induced toxicity through opioid receptor-independent, TRPM7-independent mechanisms in HT22 cells. Naltriben activated Nrf2 pathway, and alleviated glutamate-induced Ca2+ influx, ROS production, and apoptosis. Moreover, intraperitoneal administration of naltriben at 20 mg/kg greatly reduced the infarct volume in the subcortical photothrombotic ischemia mouse model in vivo. The neuroprotective activity of naltriben was enhanced by a longer pretreatment, indicating that like Nrf2 activators, naltriben also requires the cellular priming for its full protective effects. Together, these results suggested naltriben as a potential therapeutic agent in conditions related with glutamate-induced neurotoxicity.

Indole and Coumarin Derivatives Targeting EEF2K in Aβ Folding Reporter Cells

Misfolding and accumulation of amyloid-β (Aβ) in the brains of patients with Alzheimer's disease (AD) lead to neuronal loss through various mechanisms, including the downregulation of eukaryotic elongation factor 2 (EEF2) protein synthesis signaling. This study investigated the neuroprotective effects of indole and coumarin derivatives on Aβ folding and EEF2 signaling using SH-SY5Y cells expressing Aβ-green fluorescent protein (GFP) folding reporter. Among the tested compounds, two indole (NC009-1, -6) and two coumarin (LM-021, -036) derivatives effectively reduced Aβ misfolding and associated reactive oxygen species (ROS) production. Additionally, these compounds decreased acetylcholinesterase and caspase-3/-6 activities while promoting neurite outgrowth. NC009-1 increased active phosphorylation of extracellular-signal regulated kinase (ERK) (T202/Y204), leading to an increase in inactive eukaryotic elongation factor 2 kinase (EEF2K) phosphorylation (S366). LM-021 decreased the active phosphorylation of AMP-activated protein kinase (AMPK) (T172) and EEF2K (S398), while LM-036 exhibited dual effects, increasing inactive phosphorylation and decreasing active phosphorylation of EEF2K. These changes in EEF2K phosphorylation led to decreased EEF2K activity and a subsequent reduction in inactive phosphorylation of EEF2 (T56). This cascade further promoted the phosphorylation of transcription factor cAMP-response-element binding protein (CREB) (S133) and the expression of brain-derived neurotrophic factor (BDNF), and reduced BCL-2 associated X-protein (BAX)/B-cell lymphoma 2 (BCL2) ratio. Knockdown of EEF2 abolished the effects of NC009-1, LM-021, and LM-036 on CREB phosphorylation, BDNF expression, caspase-3 activity, and neurite outgrowth. These findings demonstrate that NC009-1, LM-021, and LM-036 exert their neuroprotective effects through modulation of EEF2K signaling, highlighting their potentials as therapeutic candidates for AD.

eEF-2K Deficiency Boosts the Virus-Specific Effector CD8+ T Cell Responses During Viral Infection

In this study, we revealed a critical role of eukaryotic elongation factor-2 kinase (eEF-2K), a negative regulator of protein synthesis, in regulating T cells during vaccinia virus (VACV) infection. We found that eEF-2K-deficient (eEF-2K⁻/⁻) mice exhibited a significantly higher proportion of VACV-specific effector CD8+ T cells without compromising the development of VACV-specific memory CD8+ T cells. RNA sequencing demonstrated that eEF-2K⁻/⁻ VACV-specific effector CD8+ T cells had enhanced functionality, which improves their capacity to combat viral infection during the effector phase. Moreover, we identified tumor necrosis factor receptor-associated factor 3 (TRAF3) as a critical mediator of the stronger antiviral response observed in eEF-2K⁻/⁻ effector CD8+ T cells. These findings suggest that targeting eEF-2K may provide a novel strategy to augmenting effector CD8+ T cell responses against viral infections.

Somatostatin: Linking Cognition and Alzheimer Disease to Therapeutic Targeting

Over 4 decades of research support the link between Alzheimer disease (AD) and somatostatin [somatotropin-releasing inhibitory factor (SRIF)]. SRIF and SRIF-expressing neurons play an essential role in brain function, modulating hippocampal activity and memory formation. Loss of SRIF and SRIF-expressing neurons in the brain rests at the center of a series of interdependent pathological events driven by amyloid-β peptide (Aβ), culminating in cognitive decline and dementia. The connection between the SRIF and AD further extends to the neuropsychiatric symptoms, seizure activity, and inflammation, whereas preclinical AD investigations show SRIF or SRIF receptor agonist administration capable of enhancing cognition. SRIF receptor subtype-4 activation in particular presents unique attributes, with the potential to mitigate learning and memory decline, reduce comorbid symptoms, and enhance enzymatic degradation of Aβ in the brain. Here, we review the links between SRIF and AD along with the therapeutic implications. SIGNIFICANCE STATEMENT: Somatostatin and somatostatin-expressing neurons in the brain are extensively involved in cognition. Loss of somatostatin and somatostatin-expressing neurons in Alzheimer disease rests at the center of a series of interdependent pathological events contributing to cognitive decline and dementia. Targeting somatostatin-mediated processes has significant therapeutic potential for the treatment of Alzheimer disease.

Reduction of eEF2 kinase alleviates the learning and memory impairment caused by acrylamide

BACKGROUND

The impact of acrylamide (ACR) on learning and memory has garnered considerable attention. However, the targets and mechanisms are still unclear.

RESULTS

Elongation factor 2 (eEF2) was significantly upregulated in the results of serum proteomics. Results from in vitro and in vivo experiments indicated a notable upregulation of Eukaryotic elongation factor 2 kinase (eEF2K), the sole kinase responsible for eEF2 phosphorylation, following exposure to ACR (P < 0.05). Subsequent in vitro experiments using eEF2K siRNA and in vivo experiments with eEF2K-knockout mice demonstrated significant improvements in abnormal indicators related to ACR-induced learning and memory deficits (P < 0.05). Proteomic analysis of the hippocampus revealed Lpcat1 as a crucial downstream protein regulated by eEF2K. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses indicated that eEF2K may play a role in the process of ACR-induced learning and memory impairment by affecting ether lipid metabolism.

CONCLUSIONS

In summary, eEF2K as a pivotal treatment target in the mechanisms underlying ACR-induced learning and memory impairment, and studies have shown that it provides robust evidence for potential clinical interventions targeting ACR-induced impairments.

An integrative view on the cell-type-specific mechanisms of ketamine's antidepressant actions

Over the past six decades, the use of ketamine has evolved from an anesthetic and recreational drug to the first non-monoaminergic antidepressant approved for treatment-resistant major depressive disorder (MDD). Subanesthetic doses of ketamine and its enantiomer (S)-ketamine (esketamine) directly bind to several neurotransmitter receptors [including N-methyl-d-aspartic acid receptor (NMDAR), κ and μ opioid receptor (KOR and MOR)] widely distributed in the brain and across different cell types, implicating several potential molecular mechanisms underlying the action of ketamine as an antidepressant. This review examines preclinical studies investigating cell-type-specific mechanisms underlying the effects of ketamine on behavior and synapses. Cell-type-specific approaches are crucial for disentangling the critical mechanisms involved in the therapeutic effect of ketamine.

Revealing eEF-2 kinase: recent structural insights into function

The α-kinase eukaryotic elongation factor 2 kinase (eEF-2K) regulates translational elongation by phosphorylating its ribosome-associated substrate, the GTPase eEF-2. eEF-2K is activated by calmodulin (CaM) through a distinctive mechanism unlike that in other CaM-dependent kinases (CAMK). We describe recent structural insights into this unique activation process and examine the effects of specific regulatory signals on this mechanism. We also highlight key unanswered questions to guide future structure-function studies. These include structural mechanisms which enable eEF-2K to interact with upstream/downstream partners and facilitate its integration of diverse inputs, including Ca2+ transients, phosphorylation mediated by energy/nutrient-sensing pathways, pH changes, and metabolites. Answering these questions is key to establishing how eEF-2K harmonizes translation with cellular requirements within the boundaries of its molecular landscape.

Preface: Special issue "Brain Proteostasis in Health and Disease"

This preface introduces the Journal of Neurochemistry Special Issue on Brain Proteostasis. Adequate control of protein homeostasis, or proteostasis, has been at the center stage of brain physiology, and its deregulation may contribute to brain diseases, including several neuropsychiatric and neurodegenerative conditions. Therefore, delineating the processes underlying protein synthesis, folding, stability, function, and degradation in brain cells is key to promoting brain function and identifying effective therapeutic options for neurological disorders. This special issue comprises four review articles and four original articles covering the roles of protein homeostasis in several mechanisms that are of relevance to sleep, depression, stroke, dementia, and COVID-19. Thus, these articles highlight different aspects of proteostasis regulation in the brain and present important evidence on this growing and exciting field.

In-Depth Proteomic Analysis of De Novo Proteome in a Mouse Model of Alzheimer's Disease

BACKGROUND

Alzheimer's disease (AD) is the most common dementia syndrome in the elderly characterized by synaptic failure and unique brain pathology. De novo protein synthesis is required for the maintenance of memory and synaptic plasticity. Mounting evidence links impaired neuronal protein synthesis capacity and overall protein synthesis deficits to AD pathogenesis. Meanwhile, identities of AD-associated dysregulation of "newly synthesized proteome" remain elusive.

OBJECTIVE

To investigate de novo proteome alterations in the hippocampus of aged Tg19959 AD model mice.

METHODS

In this study, we combined the bioorthogonal noncanonical amino acid tagging (BONCAT) method with the unbiased large-scale proteomic analysis in acute living brain slices (we name it "BONSPEC") to investigate de novo proteome alterations in the hippocampus of Tg19959 AD model mice. We further applied multiple bioinformatics methods to analyze in-depth the proteomics data.

RESULTS

In total, 1,742 proteins were detected across the 10 samples with the BONSPEC method. After exclusion of those only detected in less than half of the samples in both groups, 1,362 proteins were kept for further analysis. 37 proteins were differentially expressed (based on statistical analysis) between the WT and Tg19959 groups. Among them, 19 proteins were significantly decreased while 18 proteins were significantly increased in the hippocampi of Tg19959 mice compared to WT mice. The results suggest that proteins involved in synaptic function were enriched in de novo proteome of AD mice.

CONCLUSION

Our study could provide insights into the future investigation into the molecular signaling mechanisms underlying AD and related dementias (ADRDs).

eEF2 in the prefrontal cortex promotes excitatory synaptic transmission and social novelty behavior

Regulation of mRNA translation is essential for brain development and function. Translation elongation factor eEF2 acts as a molecular hub orchestrating various synaptic signals to protein synthesis control and participates in hippocampus-dependent cognitive functions. However, whether eEF2 regulates other behaviors in different brain regions has been unknown. Here, we construct a line of Eef2 heterozygous (HET) mice, which show a reduction in eEF2 and protein synthesis mainly in excitatory neurons of the prefrontal cortex. The mice also show lower spine density, reduced excitability, and AMPAR-mediated synaptic transmission in pyramidal neurons of the medial prefrontal cortex (mPFC). While HET mice exhibit normal learning and memory, they show defective social behavior and elevated anxiety. Knockdown of Eef2 in excitatory neurons of the mPFC specifically is sufficient to impair social novelty preference. Either chemogenetic activation of excitatory neurons in the mPFC or mPFC local infusion of the AMPAR potentiator PF-4778574 corrects the social novelty deficit of HET mice. Collectively, we identify a novel role for eEF2 in promoting prefrontal AMPAR-mediated synaptic transmission underlying social novelty behavior.

Homozygous knockout of eEF2K alleviates cognitive deficits in APP/PS1 Alzheimer’s disease model mice independent of brain amyloid β pathology

Maintenance of memory and synaptic plasticity depends on de novo protein synthesis, and accumulating evidence implicates a role of dysregulated mRNA translation in cognitive impairments associated with Alzheimer’s disease (AD). Accumulating evidence demonstrates hyper-phosphorylation of translation factor eukaryotic elongation factor 2 (eEF2) in the hippocampi of human AD patients as well as transgenic AD model mice. Phosphorylation of eEF2 (at the Thr 56 site) by its only known kinase, eEF2K, leads to inhibition of general protein synthesis. A recent study suggests that amyloid β (Aβ)-induced neurotoxicity could be associated with an interaction between eEF2 phosphorylation and the transcription factor nuclear erythroid 2-related factor (NRF2)-mediated antioxidant response. In this brief communication, we report that global homozygous knockout of the eEF2K gene alleviates deficits of long-term recognition and spatial learning in a mouse model of AD (APP/PS1). Moreover, eEF2K knockout does not alter brain Aβ pathology in APP/PS1 mice. The hippocampal NRF2 antioxidant response in the APP/PS1 mice, measured by expression levels of nicotinamide adenine dinucleotide plus hydrogen (NADPH) quinone oxidoreductase 1 (NQO1) and heme oxygenase-1 (HO-1), is ameliorated by suppression of eEF2K signaling. Together, the findings may contribute to our understanding of the molecular mechanisms underlying AD pathogenesis, indicating that suppression of eEF2K activity could be a beneficial therapeutic option for this devastating neurodegenerative disease.

The Brain's Microvascular Response to High Glycemia and to the Inhibition of Soluble Epoxide Hydrolase Is Sexually Dimorphic

Biological sex and a high glycemic diet (HGD) contribute to dementia, yet little is known about the operative molecular mechanisms. Our goal was to understand the differences between males and females in the multi-genomic response of the hippocampal microvasculature to the HGD, and whether there was vasculoprotection via the inhibition of soluble epoxide hydrolase (sEHI). Adult wild type mice fed high or low glycemic diets for 12 weeks, with or without an sEHI inhibitor (t-AUCB), had hippocampal microvessels isolated by laser-capture microdissection. Differential gene expression was determined by microarray and integrated multi-omic bioinformatic analyses. The HGD induced opposite effects in males and females: the HGD-upregulated genes were involved in neurodegeneration or neuroinflammation in males, whereas in females they downregulated the same pathways, favoring neuroprotection. In males, the HGD was associated with a greater number of clinical diseases than in females, the sEHI downregulated genes involved in neurodegenerative diseases to a greater extent with the HGD and compared to females. In females, the sEHI downregulated genes involved in endothelial cell functions to a greater extent with the LGD and compared to males. Our work has potentially important implications for sex-specific therapeutic targets for vascular dementia and cardiovascular diseases in males and females.

Bioactive human Alzheimer brain soluble Aβ: pathophysiology and therapeutic opportunities

The accumulation of amyloid-β protein (Aβ) plays an early role in the pathogenesis of Alzheimer's disease (AD). The precise mechanism of how Aβ accumulation leads to synaptic dysfunction and cognitive impairment remains unclear but is likely due to small soluble oligomers of Aβ (oAβ). Most studies have used chemical synthetic or cell-secreted Aβ oligomers to study their pathogenic mechanisms, but the Aβ derived from human AD brain tissue is less well characterized. Here we review updated knowledge on the extraction and characterization of bioactive human AD brain oAβ and the mechanisms by which they cause hippocampal synaptic dysfunction. Human AD brain-derived oAβ can impair hippocampal long-term potentiation (LTP) and enhance long-term depression (LTD). Many studies suggest that oAβ may directly disrupt neuronal NMDA receptors, AMPA receptors and metabotropic glutamate receptors (mGluRs). oAβ also impairs astrocytic synaptic functions, including glutamate uptake, D-serine release, and NMDA receptor function. We also discuss oAβ-induced neuronal hyperexcitation. These results may suggest a multi-target approach for the treatment of AD, including both oAβ neutralization and reversal of glutamate-mediated excitotoxicity.

Eukaryotic Extension Factor 2 Kinase may Affect the Occurrence and Development of Glioblastoma Through Immune Cell Infiltration

Glioblastoma (GBM) is one of the most common malignancies among primary brain tumors in adults, featuring a poor prognosis and a high recurrence rate. Eukaryotic elongation factor 2 kinase (eEF2K) is a calcium/calmodulin-dependent protein kinase that is involved in promoting tumor cell proliferation, migration, invasion, and survival. However, its expression level in GBM, its prognostic impact and correlation with immune infiltration are not yet known. In this study, we used The Cancer Genome Atlas (TCGA) database to explore the potential molecular mechanisms of eEF2K in GBM development and clinical prognosis in terms of gene expression, survival status, immune infiltration, and associated cellular pathways. We found that eEF2K expression levels were elevated in GBM, but eEF2K was not associated with the prognosis of GBM patients; eEF2K expression in GBM was associated with multiple immune cell infiltrations. These results show a statistical correlation between eEF2K expression and the development of GBM and immune cell infiltration, which helps us to understand the roles of eEF2K in GBM from different perspectives.

Translational control by ketamine and its implications for comorbid cognitive deficits in depressive disorders

Ketamine has shown antidepressant effects in patients with major depressive disorder (MDD) resistant to first-line treatments and approved for use in this patient population. Ketamine induces several forms of synaptic plasticity, which are proposed to underlie its antidepressant effects. However, the molecular mechanism of action directly responsible for ketamine's antidepressant effects remains under active investigation. It was recently demonstrated that the effectors of the mammalian target of rapamycin complex 1 (mTORC1) signalling pathway, namely, eukaryotic initiation factor 4E (eIF4E) binding proteins 1 and 2 (4E-BP1 and 4E-BP2), are central in mediating ketamine-induced synaptic plasticity and behavioural antidepressant-like effect. 4E-BPs are a family of messenger ribonucleic acid (mRNA) translation repressors inactivated by mTORC1. We observed that their expression in inhibitory interneurons mediates ketamine's effects in the forced swim and novelty suppressed feeding tests and the long-lasting inhibition of GABAergic neurotransmission in the hippocampus. In addition, another effector pathway that regulates translation elongation downstream of mTORC1, the eukaryotic elongation factor 2 kinase (eEF2K), has been implicated in ketamine's behavioural effects. We will discuss how ketamine's rapid antidepressant effect depends on the activation of neuronal mRNA translation through 4E-BP1/2 and eEF2K. Furthermore, given that these pathways also regulate cognitive functions, we will discuss the evidence of ketamine's effect on cognitive function in MDD. Overall, the data accrued from pre-clinical research have implicated the mRNA translation pathways in treating mood symptoms of MDD. However, it is yet unclear whether the pro-cognitive potential of subanesthetic ketamine in rodents also engages these pathways and whether such an effect is consistently observed in the treatment-resistant MDD population.