Effect of ceftriaxone on paired-pulse response and long-term potentiation of hippocampal dentate gyrus neurons in rats with Alzheimer-like disease

Ceftriaxone Modulates Ubiquitination of α-Amino-3-Hydroxy-5-Methyl-4-Isoxazole Propionic Acid Receptors to Improve Long-Term Potentiation Impairment Induced by Exogenous β-Amyloid in a Glutamate Transporter-1 Dependent Manner

Α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors (AMPARs) are crucial for properties of synaptic plasticity, such as long-term potentiation (LTP). LTP impairment can occur early in the onset of Alzheimer's disease (AD). The downregulation or decreased abundance of AMPAR expression in the postsynaptic membrane is closely associated with LTP impairment. Ceftriaxone (Cef) can improve LTP impairment in the early stages of AD in a mouse model. The purpose of this study was to explore the mechanism underlying this process from the aspects of AMPAR expression and ubiquitination degree. In this study, we found that β-amyloid (Aβ) treatment induced hippocampal LTP impairment and AMPAR downregulation and ubiquitination. Cef pretreatment ameliorated Aβ-induced hippocampal LTP impairment, reduced AMPAR ubiquitination, and increased AMPAR expression, especially in the plasma membrane, in Aβ-treated mice. Administration of USP46 siRNA and DHK (a specific blocker of glutamate transporter-1) significantly inhibited the above effects of Cef, suggesting a role for anti-AMPAR ubiquitination and upregulation of glutamate transporter-1 (GLT-1) in the Cef-induced improvements mentioned above. The above findings demonstrate that pretreatment with Cef effectively mitigated Aβ-induced impairment of hippocampal LTP by suppressing the ubiquitination process of AMPARs in a GLT-1-dependent manner. These results provide novel insights into the underlying mechanisms elucidating the anti-AD by Cef.

PS1/gamma-secretase acts as rogue chaperone of glutamate transporter EAAT2/GLT-1 in Alzheimer's disease

The recently discovered interaction between presenilin 1 (PS1), a catalytic subunit of γ-secretase responsible for the generation of amyloid-β(Aβ) peptides, and GLT-1, the major glutamate transporter in the brain (EAAT2 in the human) may provide a mechanistic link between two important pathological aspects of Alzheimer's disease (AD): abnormal Aβoccurrence and neuronal network hyperactivity. In the current study, we employed a FRET-based approach, fluorescence lifetime imaging microscopy (FLIM), to characterize the PS1/GLT-1 interaction in its native environment in the brain tissue of sporadic AD (sAD) patients. There was significantly less interaction between PS1 and GLT-1 in sAD brains, compared to tissue from patients with frontotemporal lobar degeneration (FTLD), or non-demented age-matched controls. Since PS1 has been shown to adopt pathogenic "closed" conformation in sAD but not in FTLD, we assessed the impact of changes in PS1 conformation on the interaction. Familial AD (fAD) PS1 mutations which induce a "closed" PS1 conformation similar to that in sAD brain and gamma-secretase modulators (GSMs) which induce a "relaxed" conformation, reduced and increased the interaction, respectively. This indicates that PS1 conformation seems to have a direct effect on the interaction with GLT-1. Furthermore, using biotinylation/streptavidin pull-down, western blotting, and cycloheximide chase assays, we determined that the presence of PS1 increased GLT-1 cell surface expression and GLT-1 homomultimer formation, but did not impact GLT-1 protein stability. Together, the current findings suggest that the newly described PS1/GLT-1 interaction endows PS1 with chaperone activity, modulating GLT-1 transport to the cell surface and stabilizing the dimeric-trimeric states of the protein. The diminished PS1/GLT-1 interaction suggests that these functions of the interaction may not work properly in AD.

Adolescent swimming exercise following maternal valproic acid treatment improves cognition and reduces stress-related symptoms in offspring mice: Role of sex and brain cytokines

Valproic acid (VPA) treatment during pregnancy is a risk factor for developing autism spectrum disorder, cognitive deficits, and stress-related disorders in children. No effective therapeutic strategies are currently approved to treat or manage core symptoms of autism. Active lifestyles and physical activity are closely associated with health and quality of life during childhood and adulthood. This study aimed to evaluate whether swimming exercise during adolescence can prevent the development of cognitive dysfunction and stress-related disorders in prenatally VPA-exposed mice offspring. Pregnant mice received VPA, afterwards, offspring were subjected to swimming exercise. We assessed neurobehavioral performances and inflammatory cytokines (interleukin-(IL)6, tumor-necrosis-factor-(TNF)α, interferon-(IFN)γ, and IL-17A) in the hippocampus and prefrontal cortex of offspring. Prenatal VPA treatment increased anxiety-and anhedonia-like behavior and decreased social behavior in male and female offspring. Prenatal VPA exposure also increased behavioral despair and reduced working and recognition memory in male offspring. Although prenatal VPA increased hippocampal IL-6 and IFN-γ, and prefrontal IFN-γ and IL-17 in males, it only increased hippocampal TNF-α and IFN-γ in female offspring. Adolescent exercise made VPA-treated male and female offspring resistant to anxiety-and anhedonia-like behavior in adulthood, whereas it only made VPA-exposed male offspring resistant to behavioral despair, social and cognitive deficits in adulthood. Exercise reduced hippocampal IL-6, TNF-α, IFN-γ, and IL-17, and prefrontal IFN-γ and IL-17 in VPA-treated male offspring, whereas it reduced hippocampal TNF-α and IFN-γ in VPA-treated female offspring. This study suggests that adolescent exercise may prevents the development of stress-related symptoms, cognitive deficits, and neuroinflammation in prenatally VPA-exposed offspring mice.

Zinc exacerbates tau-induced Alzheimer-like pathology in C57BL/6J mice

The pathogenesis of Alzheimer's disease (AD) is highly complex and multifactorial. Compared with Aβ, the pathological changes associated with tau are more related to the clinical symptoms and more indicative of the severity of AD. Studies have shown that the direct interaction between tau and Zn²⁺ plays an important role in tau toxicity, however, the mechanism by which Zn²⁺ contributes to tau-induced neurotoxicity is not fully understood. Our previous studies have found that Zn²⁺ bound to the third repeat unit of the microtubule-binding domain of tau (R3) with moderate affinity and induced R3 to form oligomers, thus increased the toxicity of R3 to nerve cells. Here, we demonstrated that Zn²⁺ binding to R3 (Zn²⁺+R3) significantly reduced cognitive ability and increased blood lipid and glucose levels of C57BL/6J mice. In addition, Zn²⁺+R3, not Zn²⁺ or R3 alone, markedly enhanced the endogenous Aβ and tau pathology and damaged the neurons of C57BL/6J mice. The study suggests that the main reason for the toxicity of Zn²⁺ may be the formation of Zn²⁺ and tau complex. Thus, preventing the combination of Zn²⁺ and tau may be a potential strategy for AD treatment. Furthermore, as the C57BL/6J mice injected with Zn²⁺+R3 complex showed behavioral deficits, deposition of Aβ plaques and tau tangles, and the death of neurons within 45 days. Thus, they can be considered as a fast sporadic AD or other tauopathies mouse model.

A Medicinal Chemistry Perspective on Excitatory Amino Acid Transporter 2 Dysfunction in Neurodegenerative Diseases

The excitatory amino acid transporter 2 (EAAT2) plays a key role in the clearance and recycling of glutamate - the major excitatory neurotransmitter in the mammalian brain. EAAT2 loss/dysfunction triggers a cascade of neurodegenerative events, comprising glutamatergic excitotoxicity and neuronal death. Nevertheless, our current knowledge regarding EAAT2 in neurodegenerative diseases, such as amyotrophic lateral sclerosis (ALS) and Alzheimer's disease (AD), is restricted to post-mortem analysis of brain tissue and experimental models. Thus, detecting EAAT2 in the living human brain might be crucial to improve diagnosis/therapy for ALS and AD. This perspective article describes the role of EAAT2 in physio/pathological processes and provides a structure-activity relationship of EAAT2-binders, bringing two perspectives: therapy (activators) and diagnosis (molecular imaging tools).

Melatonin treatment improves cognitive deficits by altering inflammatory and neurotrophic factors in the hippocampus of obese mice

Overweight and obesity are associated with an increased risk of developing dementia and cognitive deficits. Neuroinflammation is one of the most important mechanisms behind cognitive impairment in obese patients. In recent years, the neuroendocrine hormone melatonin has been suggested to have therapeutic effects for memory decline in several neuropsychiatric and neurological conditions. However, the effects of melatonin on cognitive function under obesity conditions still need to be clarified. The purpose of this study was to determine whether melatonin treatment can improve cognitive impairment in obese mice. To this end, male C57BL6 mice were treated with a high-fat diet (HFD) for 20 weeks to induce obesity. The animal received melatonin for 8 weeks. Cognitive functions were evaluated using the Y maze, object recognition test, and the Morris water maze. We measured inflammatory cytokines including tumor necrosis factor (TNF)-α, interferon (IFN)-γ, interleukin (IL)-17A, and brain-derived neurotrophic factor (BDNF) in the hippocampus of obese mice. Our results show that HFD-induced obesity significantly impaired working, spatial and recognition memory by increasing IFN-γ and IL-17A and decreasing BDNF levels in the hippocampus of mice. On the other hand, melatonin treatment effectively improved all cognitive impairments and reduced TNF-α, IFN-γ, and IL-17A and elevated BDNF levels in the hippocampus of obese mice. Taken together, this study suggests that melatonin treatment could have a beneficial role in the treatment of cognitive impairment in obesity.

EAAT2 as a therapeutic research target in Alzheimer's disease: A systematic review

Glutamate is the main excitatory neurotransmitter in the human central nervous system, responsible for a wide variety of normal physiological processes. Glutamatergic metabolism and its sequestration are tightly regulated in the normal human brain, and it has been demonstrated that dysregulation of the glutamatergic system can have wide-ranging effects both in acute brain injury and neurodegenerative diseases. The excitatory amino acid transporter 2 (EAAT2) is the dominant glutamatergic transporter in the human brain, responsible for efficient removal of glutamate from the synaptic cleft for recycling within glial cells. As such, it has a key role in maintaining excitatory-inhibitory homeostasis. Animal studies have demonstrated dysregulation or alterations of EAAT2 expression can have implications in neurodegenerative disorders. Despite extensive research into glutamatergic alterations in AD mouse models, there is a lack of studies examining the expression of EAAT2 within the AD human brain. In this systematic review, 29 articles were identified that either analyzed EAAT2 expression in the AD human brain or used a human-derived cell culture. Studies were inconclusive as to whether EAAT2 was upregulated or downregulated in AD. However, changes in localization and correlation between EAAT2 expression and symptomatology was noted. These findings implicate EAAT2 alterations as a key process in AD progression and highlight the need for further research into the characterization of EAAT2 processes in normal physiology and disease in human tissue and to identify compounds that can act as EAAT2 neuromodulators.

Discovery of novel α-carboline derivatives as glycogen synthase kinase-3β inhibitors for the treatment of Alzheimer's disease

Alzheimer's disease (AD) is a chronic and progressive neurodegenerative disease, characterized by irreversible cognitive impairment, memory loss, and behavioral disturbances, ultimately resulting in death. The critical roles of glycogen synthase kinase-3β (GSK-3β) in tau pathology have also received considerable attention. Based on molecular docking studies, a series of novel α-carboline derivatives were designed, synthesized, and evaluated as GSK-3β inhibitors for their various biological activities. Among them, compound ZCH-9 showed the most potent inhibitory activity against GSK-3β, with an IC₅₀ value of 1.71 ± 0.09 µM. The cytotoxicity assay showed that ZCH-9 had low cytotoxicity toward the cell lines SH-SY5Y, HepG2, and HL-7702. Moreover, Western blot analysis indicated that ZCH-9 effectively inhibited hyperphosphorylation of the tau protein in okadaic acid-treated SH-SY5Y cells. The binding mode between ZCH-9 and GSK-3β was analyzed and further clarified throughout the molecular dynamics simulations. In general, these results suggested that the α-carboline-based small-molecule compounds could serve as potential candidates targeting GSK-3β for the treatment of AD.

Early life GABAA blockade alters the synaptic plasticity and cognitive functions in male and female rats

Gamma-aminobutyric acid (GABA), the major inhibitory neurotransmitter in adults, has a critical contribution to balanced excitatory-inhibitory networks in the brain. Alteration in depolarizing action of GABA during early life is connected to a wide variety of neurodevelopmental disorders. Additionally, the effects of postnatal GABA blockade on neuronal synaptic plasticity are not known and therefore, we set out to determine whether postnatal exposure to bicuculline, a competitive antagonist of GABA_A receptors, affects electrophysiologic changes in hippocampal CA1 neurons later on. To this end, male and female Wistar rats received vehicle or bicuculline (300 μg/kg) on postnatal days (PNDs) 7, 9 and 11, and then underwent different behavioral and electrophysiological examinations in adulthood. Postnatal exposure to bicuculline did not affect basic synaptic transmission but led to a pronounced decrease in paired-pulse facilitation (PPF) in CA1 pyramidal neurons. Bicuculline treatment also attenuated the long-term potentiation (LTP) and long-term depression (LTD) of CA1 neurons accompanied by decreased theta-burst responses in male and female adult rats. These electrophysiology findings together with the reduced brain-derived neurotrophic factor (BDNF) levels in the hippocampus and prefrontal cortex reliably explain the disturbance in spatial reference and working memories of bicuculline-treated animals. This study suggests that postnatal GABA_A blockade deteriorates short- and long-term synaptic plasticity of hippocampal CA1 neurons and related encoding of spatial memory in adulthood.

Neonatal NMDA blockade alters the LTP, LTD and cognitive functions in male and female Wistar rats

There is compelling evidence that neonatal blockade of NMDA receptors by phencyclidine (PCP) is associated with cognitive impairment in adulthood but little is known about the effects of early life PCP treatment on synaptic function later in life. Here, we sought to determine whether early life exposure to PCP alters the electrophysiologic function of hippocampal CA1 neurons in adult rats. To this end, male and female Wistar rats received either saline or PCP (10 mg/kg) on postnatal days (PND) 7, 9, and 11, and then underwent separate behavioral and electrophysiology tests in adulthood. Neonatal PCP treatment did not alter basic synaptic transmission and had only a modest effect on frequency following (FF) capacity but significantly decreased the paired-pulse facilitation (PPF) in the Schaffer collateral (SC)-CA1 pathway. We found that PCP treatment significantly attenuated the long-term potentiation (LTP) and long-term depression (LTD) in CA1 neurons accompanied by pronounced alteration in complex response profile in adult rats. The electrophysiology data were comparable in male and female rats and reliably associated with impaired spatial reference and working memories in these animals. Overall, this study suggests that blockade of NMDA receptors during early life deteriorates the short-term and long-term synaptic plasticity and complex response profile of CA1 neurons in adulthood.

The role of glutamate transporter-1 in firing activity of locus coeruleus neurons and nociception in rats

Locus coeruleus (LC) is considered to be the main source of norepinephrine in the central nervous system (CNS) and plays important role in relieving pain in the body. Changes in the activity of synaptic excitatory amino acid transporters (EAATs) would be an applicable way to regulate synaptic transmission in the LC. In the present study, we examined the role of astrocytic glutamate transporter-1 (GLT1) in the firing activity of LC neurons and the sensation of pain in rats. Male Wistar rats were divided into three control (CNT), ceftriaxone (CFT) and dihydrokainic acid (DHK) groups. Animals were given intraperitoneal injections for nine consecutive days after which the electrophysiological and behavioral experiments were performed to determine the single-unit activity of LC neurons and pain sensation. Results of this study revealed that CFT as a well-known up-regulator of GLT1 expression decreases the latency of pain sensation in rats but inhibition of GLT1 activity by DHK showed no significant effects. Furthermore, the results obtained by single-unit recording from LC showed a significant decrease in evoked response in CFT group compared to the CNT group. Therefore, this study suggests that GLT1 might be considered as a potential therapeutic target for pain modulation in the future.

Antimicrobial therapy and the potential mechanisms in Alzheimer's disease

Alzheimer's disease treatments have been a heavily investigated research area, however, new drugs have failed one after another. Some scientists have begun to reposition drugs, including antimicrobial agents. Here, the treatment effects of nine antimicrobial agents on Alzheimer's disease and their possible therapeutic mechanisms are described to clarify their efficacy. In vivo and in vitro studies are quite encouraging and tend to demonstrate that antimicrobial therapy is effective in Alzheimer's disease. Nevertheless, unsatisfactory clinical efficacy, side effects, and insufficient knowledge have yet to be overcome. Further laboratory and clinical studies are required to recommend antimicrobial treatment regimens.

GLT-1 Knockdown Inhibits Ceftriaxone-Mediated Improvements on Cognitive Deficits, and GLT-1 and xCT Expression and Activity in APP/PS1 AD Mice

Objective

Glutamate transporter-1 (GLT-1) and system x_c^– mediate glutamate uptake and release, respectively. Ceftriaxone has been reported to upregulate GLT-1 expression and improve cognitive decline in APP/PS1 mice. The aim of the present study was to elucidate the role of GLT-1 in ceftriaxone-mediated improvement on cognitive deficits and associated changes in xCT (catalytic subunit of system x_c^–) expression and activity using GLT-1 knockdown APP/PS1 mice.

Methods

GLT-1 knockdown (GLT-1^±) mice were generated in C57BL/6J mice using the CRISPR/Cas9 technique and crossed to APP/PS1 mice to generate GLT-1^±APP/PS1 mice. The cognition was evaluated by novel object recognition and Morris water maze tests. GLT-1 and xCT expression, GLT-1 uptake for glutamate, and glutathione levels of hippocampus were assayed using Western blot and immunohistochemistry, ³H-glutamate, and glutathione assay kit, respectively.

Results

In comparison with wild-type mice, APP/PS1 mice exhibited significant cognitive deficits, represented with poor performance in novel object recognition and Morris water maze tests, downregulated GLT-1 expression and glutamate uptake. Ceftriaxone treatment significantly improved the above impairments in APP/PS1 mice, but had negligible impact in GLT-1^±APP/PS1 mice. The xCT expression increased in APP/PS1 and GLT-1^±APP/PS1 mice. This upregulation might be a compensatory change against the accumulated glutamate resulting from GLT-1 impairment. Ceftriaxone treatment restored xCT expression in APP/PS1 mice, but not in GLT-1^±APP/PS1 mice. Glutathione levels decreased in APP/PS1 mice in comparison to the wild-type group. After ceftriaxone administration, the decline in glutathione level was restored in APP/PS1 mice, but not in GLT-1^±APP/PS1 mice.

Conclusion

Ceftriaxone improves cognitive impairment of APP/PS1 mice by upregulating GLT-1-mediated uptake of glutamate and co-regulation of GLT-1 and xCT in APP/PS1 mice.