A synapsin Ⅰ cleavage fragment contributes to synaptic dysfunction in Alzheimer's disease

The GLP-1 agonist semaglutide ameliorates cognitive regression in P301S tauopathy mice model via autophagy/ACE2/SIRT1/FOXO1-Mediated Microglia Polarization

Tau hyper-phosphorylation has been recognized as an essential contributor to neurodegeneration in Alzheimer's disease (AD) and related tauopathies. In the last decade, tau hyper-phosphorylation has gained considerable concern in AD therapeutic development. Tauopathies are manifested with a broad spectrum of symptoms, from dementia to cognitive decline and motor impairments. Tau undergoes conformational changes and abnormal phosphorylation that mediate its detaching from microtubules, forming neurofibrillary tangles (NFTs). In the current study, a widely used P301S transgenic mice model of tauopathy was employed to evaluate the possible neuroprotective effects of semaglutide as an autophagy regulator through modifications of the brain renin-angiotensin system (RAS). Mice were divided into two groups according to their genotypes (wild type (Wt) and P301S), which were further subdivided to receive either vehicle (saline) or semaglutide (25 nmol/kg, i. p.), once every 2 days for 28 days. Current data suggest that semaglutide ameliorated the hyperactive pattern and alleviated the cognitive decline of P301S mice. It also hastened the autophagic flux through augmenting angiotensin-converting enzyme 2/sirtuin 1/forkhead box protein O1 signaling. Semaglutide also hindered the expression of phosphorylated adenosine monophosphate-activated protein kinase and phosphorylated glycogen synthase kinase-3 beta at serine 9, reducing the propagation of neuroinflammatory cytokines and oxidative reactions. Finally, semaglutide protected against hippocampal degeneration and reduced the immunoreactivity for total tau and ionized calcium-binding adapter molecule. Semaglutide showed promising neuroprotective implications in alleviating tauopathy-related AD's molecular and behavioral deficits through controlling autophagy and brain RAS.

Uncovering the intricacies of O-GlcNAc modification in cognitive impairment: New insights from regulation to therapeutic targeting

O-linked β-N-acetylglucosamine (O-GlcNAc) represents a post-translational modification that occurs on serine or threonine residues on various proteins. This conserved modification interacts with vital cellular pathways. Although O-GlcNAc is widely distributed throughout the body, it is particularly enriched in the brain, where most proteins are O-GlcNAcylated. Recent studies have established a causal link between O-GlcNAc regulation in the brain and alterations in neurophysiological function. Alterations in O-GlcNAc levels in the brain are associated with the pathogenesis of several neurogenic diseases that can lead to cognitive impairment. Remarkably, manipulation of O-GlcNAc levels demonstrated a protective effect on cognitive function. Although the precise molecular mechanism of O-GlcNAc modification in the nervous system remains elusive, its regulation is fundamental to multiple neural and cognitive functions, fluctuating levels during normal and pathological cognitive processes. In this review, we highlight the significant functional importance of O-GlcNAc modification in pathological cognitive impairments and the potential application of O-GlcNAc as a promising target for the intervention or amelioration of cognitive impairments.

Biomarkers of mature neuronal differentiation and related diseases

The nervous system regulates perception, cognition and behavioral responses by serving as the body's primary communication system for receiving, regulating and transmitting information. Neurons are the fundamental structures and units of the nervous system. Their differentiation and maturation processes rely on the expression of specific biomarkers. Neuron-specific intracellular markers can be used to determine the degree of neuronal maturation. Neuronal cytoskeletal proteins dictate the shape and structure of neurons, while synaptic plasticity and signaling processes are intricately associated with neuronal synaptic markers. Furthermore, abnormal expression levels of biomarkers can serve as diagnostic indicators for nervous system diseases. This article reviews the markers of mature neuronal differentiation and their relationship with nervous system diseases.

Role of astrocytes in Alzheimer's disease pathogenesis and the impact of exercise-induced remodeling

Alzheimer's disease (AD) is a prevalent and debilitating brain disorder that worsens progressively with age, characterized by cognitive decline and memory impairment. The accumulation of amyloid-beta (Aβ) leading to amyloid plaques and hyperphosphorylation of Tau, resulting in intracellular neurofibrillary tangles (NFTs), are primary pathological features of AD. Despite significant research investment and effort, therapies targeting Aβ and NFTs have proven limited in efficacy for treating or slowing AD progression. Consequently, there is a growing interest in non-invasive therapeutic strategies for AD prevention. Exercise, a low-cost and non-invasive intervention, has demonstrated promising neuroprotective potential in AD prevention. Astrocytes, among the most abundant glial cells in the brain, play essential roles in various physiological processes and are implicated in AD initiation and progression. Exercise delays pathological progression and mitigates cognitive dysfunction in AD by modulating astrocyte morphological and phenotypic changes and fostering crosstalk with other glial cells. This review aims to consolidate the current understanding of how exercise influences astrocyte dynamics in AD, with a focus on elucidating the molecular and cellular mechanisms underlying astrocyte remodeling. The review begins with an overview of the neuropathological changes observed in AD, followed by an examination of astrocyte dysfunction as a feature of the disease. Lastly, the review explores the potential therapeutic implications of exercise-induced astrocyte remodeling in the context of AD.

Effect of Kruppel-like factor 4 on PTZ-induced acute seizure mice

Kruppel-like factor 4 (Klf4) is a transcription factor that is involved in neuronal regeneration and the development of glutamatergic systems. However, it is unknown whether Klf4 is involved in acute seizure. To investigate the potential role of Klf4 in pentylenetetrazol (PTZ)-induced seizure, western blotting, immunofluorescence, behaviour test and electrophysiology were conducted in this study. We found that Klf4 protein and mRNA expression were increased in both the hippocampus (HP) and prefrontal cortex (PFC) after PTZ-induced seizure in mice. HP-specific knockout (KO) of Klf4 in mice decreased protein expression of Klf4 and the down-stream Klf4 target tumour protein 53 (TP53/P53). These molecular changes are accompanied by increased seizure latency, reduced immobility time in the forced swimming test and tail suspension test. Reduced hippocampal protein levels for synaptic proteins, including glutamate receptor 1 (GRIA1/GLUA1) and postsynaptic density protein 95 (DLG4/PSD95), were also observed after Klf4-KO, while increased mRNA levels of complement proteins were observed for complement component 1q subcomponent A (C1qa), complement component 1q subcomponent B (C1qb), complement component 1q subcomponent C (C1qc), complement component 3 (C3), complement component 4A (C4a) and complement component 4B (C4b). Moreover, c-Fos expression induced by PTZ was reduced by hippocampal conditional KO of Klf4. Electrophysiology showed that PTZ-induced action potential frequency was decreased by overexpression of Klf4. In conclusion, these findings suggest that Klf4 plays an important role in regulating PTZ-induced seizures and therefore constitutes a new molecular target that should be explored for the development of antiepileptic drugs.

Neuroprotection by Polyherbal Medicine Divya-Medha-Vati Against Scopolamine-Induced Cognitive Impairment Through Modulation of Oxidative Stress, Acetylcholine Activity, and Cell Signaling

Alzheimer disease is associated with cognitive impairments and neuronal damages. In this study, Scopolamine, a model drug used for the generation of Alzheimer-like symptoms induced cognitive dysfunction in C57BL/6 mice. It also elevated acetylcholine esterase (AcHE) activity, and reduced antioxidant (superoxide dismutase and catalase) activity in cortex tissue. Scop reduced neuronal density and increased pyknotic neurons in hippocampus tissue. In mouse neuroblastoma (Neuro2a) cells, Scop triggered a dose-dependent loss of cell viability and neurite outgrowth reduction. Scop-treated Neuro2a cells showed oxidative stress and reduction in mRNA expression for brain-derived neurotrophic factor (BDNF), nerve growth factor-1 (NGF-1), and Synapsin-1 (SYN-1) genes. Mice treated with Divya-Medha-Vati (DMV), an Ayurvedic polyherbal medicine showed protection against Scop-induced cognitive impairment (Morris Water Maze Escape Latency, and Elevated Plus Maze Transfer Latency). DMV protected against Scop-induced AcHE activity, and loss of antioxidant activities in the mice brain cortex while sustaining neuronal density in the hippocampus region. In the Neuro2a cells, DMV reduced Scop-induced loss of cell viability and neurite outgrowth loss. DMV protected the cells against induction of oxidative stress and promoted mRNA expression of BDNF, NGF-1, and SYN-1 genes. Phytochemical profiling of DMV showed the presence of Withanolide A, Withanolide B, Bacopaside II, Jujubogenin, Apigenin, Gallic acid, Caffeic acid, and Quercetin that are associated with antioxidant and neurostimulatory activities. In conclusion, the study showed that Divya-Medha-Vati was capable of promoting neuronal health and inhibiting Alzheimer-like cognitive dysfunction through enhanced antioxidant activities and modulation of neuronal activities.

AEP-cleaved DDX3X induces alternative RNA splicing events to mediate cancer cell adaptation in harsh microenvironments

Oxygen and nutrient deprivation are common features of solid tumors. Although abnormal alternative splicing (AS) has been found to be an important driving force in tumor pathogenesis and progression, the regulatory mechanisms of AS that underly the adaptation of cancer cells to harsh microenvironments remain unclear. Here, we found that hypoxia- and nutrient deprivation-induced asparagine endopeptidase (AEP) specifically cleaved DDX3X in a HIF1A-dependent manner. This cleavage yields truncated carboxyl-terminal DDX3X (tDDX3X-C), which translocates and aggregates in the nucleus. Unlike intact DDX3X, nuclear tDDX3X-C complexes with an array of splicing factors and induces AS events of many pre-mRNAs; for example, enhanced exon skipping (ES) in exon 2 of the classic tumor suppressor PRDM2 leads to a frameshift mutation of PRDM2. Intriguingly, the isoform ARRB1-Δexon 13 binds to glycolytic enzymes and regulates glycolysis. By utilizing in vitro assays, glioblastoma organoids, and animal models, we revealed that AEP/tDDX3X-C promoted tumor malignancy via these isoforms. More importantly, high AEP/tDDX3X-C/ARRB1-Δexon 13 in cancerous tissues was tightly associated with poor patient prognosis. Overall, our discovery of the effect of AEP-cleaved DDX3X switching on alternative RNA splicing events identifies a mechanism in which cancer cells adapt to oxygen and nutrient shortages and provides potential diagnostic and/or therapeutic targets.

Cholestanol accelerates α-synuclein aggregation and spreading by activating asparagine endopeptidase

Cerebrotendinous xanthomatosis (CTX), an autosomal recessive disorder characterized by high levels of cholestanol in the blood and accumulation of cholestanol in multiple tissues, especially the brain, often presents in parkinsonism. However, it remains unknown whether cholestanol plays a role in the pathogenesis of sporadic Parkinson's disease (PD). Here, we show that the levels of serum cholestanol in patients with sporadic PD are higher than those in control participants. Cholestanol activates the protease asparagine endopeptidase (AEP) and induces the fragmentation of α-synuclein (α-syn) and facilitates its aggregation. Furthermore, cholestanol promotes the spreading of α-syn pathology in a mouse model induced by intrastriatal injection of α-syn fibrils. KO of AEP or administration of an AEP inhibitor ameliorates α-syn pathology, degeneration of the nigrostriatal dopaminergic pathway, and PD-like motor symptoms. These results not only indicate that cholestanol contributes to the aggregation and spreading of α-syn by activating AEP but also reveal an opportunity for treating PD with AEP inhibitors.

Supraphysiologic doses of 17β-estradiol aggravate depression-like behaviors in ovariectomized mice possibly via regulating microglial responses and brain glycerophospholipid metabolism

BACKGROUND

17β-Estradiol (E2) is generally considered neuroprotective in humans. However, the current clinical use of estrogen replacement therapy (ERT) is based on the physiological dose of E2 to treat menopausal syndrome and has limited therapeutic efficacy. The efficacy and potential toxicity of superphysiological doses of ERT for menopausal neurodegeneration are unknown.

METHODS

In this study, we investigated the effect of E2 with a supraphysiologic dose (0.5 mg/kg, sE2) on the treatment of menopausal mouse models established by ovariectomy. We performed the open field, Y-maze spontaneous alternation, forced swim tests, and sucrose preference test to investigate behavioral alterations. Subsequently, the status of microglia and neurons was detected by immunohistochemistry, HE staining, and Nissl staining, respectively. Real-time PCR was used to detect neuroinflammatory cytokines in the hippocampus and cerebral cortex. Using mass spectrometry proteomics platform and LC-MS/ MS-based metabolomics platform, proteins and metabolites in brain tissues were extracted and analyzed. BV2 and HT22 cell lines and primary neurons and microglia were used to explore the underlying molecular mechanisms in vitro.

RESULTS

sE2 aggravated depression-like behavior in ovariectomized mice, caused microglia response, and increased proinflammatory cytokines in the cerebral cortex and hippocampus, as well as neuronal damage and glycerophospholipid metabolism imbalance. Subsequently, we demonstrated that sE2 induced the pro-inflammatory phenotype of microglia through ERα/NF-κB signaling pathway and downregulated the expression of cannabinoid receptor 1 in neuronal cells, which were important in the pathogenesis of depression.

CONCLUSION

These data suggest that sE2 may be nonhelpful or even detrimental to menopause-related depression, at least partly, by regulating microglial responses and glycerophospholipid metabolism.

Phrenic nerve stimulation mitigates hippocampal and brainstem inflammation in an ARDS model

Rationale: In porcine healthy-lung and moderate acute respiratory distress syndrome (ARDS) models, groups that received phrenic nerve stimulation (PNS) with mechanical ventilation (MV) showed lower hippocampal apoptosis, and microglia and astrocyte percentages than MV alone. Objectives: Explore whether PNS in combination with MV for 12 h leads to differences in hippocampal and brainstem tissue concentrations of inflammatory and synaptic markers compared to MV-only animals. Methods: Compare tissue concentrations of inflammatory markers (IL-1α, IL-1β, IL-6, IL-8, IL-10, IFN-γ, TNFα and GM-CSF), pre-synaptic markers (synapsin and synaptophysin) and post-synaptic markers (disc-large-homolog 4, N-methyl-D-aspartate receptors 2A and 2B) in the hippocampus and brainstem in three groups of mechanically ventilated pigs with injured lungs: MV only (MV), MV plus PNS every other breath (MV + PNS50%), and MV plus PNS every breath (MV + PNS100%). MV settings in volume control were tidal volume 8 ml/kg, and positive end-expiratory pressure 5 cmH₂O. Moderate ARDS was achieved by infusing oleic acid into the pulmonary artery. Measurements and Main Results: Hippocampal concentrations of GM-CSF, N-methyl-D-aspartate receptor 2B, and synaptophysin were greater in the MV + PNS100% group compared to the MV group, p = 0.0199, p = 0.0175, and p = 0.0479, respectively. The MV + PNS100% group had lower brainstem concentrations of IL-1β, and IL-8 than the MV group, p = 0.0194, and p = 0.0319, respectively; and greater brainstem concentrations of IFN-γ and N-methyl-D-aspartate receptor 2A than the MV group, p = 0.0329, and p = 0.0125, respectively. Conclusion: In a moderate-ARDS porcine model, MV is associated with hippocampal and brainstem inflammation, and phrenic nerve stimulation on every breath mitigates that inflammation.

Damaged mitochondria coincide with presynaptic vesicle loss and abnormalities in alzheimer's disease brain

Loss of synapses is the most robust pathological correlate of Alzheimer's disease (AD)-associated cognitive deficits, although the underlying mechanism remains incompletely understood. Synaptic terminals have abundant mitochondria which play an indispensable role in synaptic function through ATP provision and calcium buffering. Mitochondrial dysfunction is an early and prominent feature in AD which could contribute to synaptic deficits. Here, using electron microscopy, we examined synapses with a focus on mitochondrial deficits in presynaptic axonal terminals and dendritic spines in cortical biopsy samples from clinically diagnosed AD and age-matched non-AD control patients. Synaptic vesicle density within the presynaptic axon terminals was significantly decreased in AD cases which appeared largely due to significantly decreased reserve pool, but there were significantly more presynaptic axons containing enlarged synaptic vesicles or dense core vesicles in AD. Importantly, there was reduced number of mitochondria along with significantly increased damaged mitochondria in the presynapse of AD which correlated with changes in SV density. Mitochondria in the post-synaptic dendritic spines were also enlarged and damaged in the AD biopsy samples. This study provided evidence of presynaptic vesicle loss as synaptic deficits in AD and suggested that mitochondrial dysfunction in both pre- and post-synaptic compartments contribute to synaptic deficits in AD.

Long-term voluntary exercise inhibited AGE/RAGE and microglial activation and reduced the loss of dendritic spines in the hippocampi of APP/PS1 transgenic mice

Alzheimer's disease (AD) is closely related to hippocampal synapse loss, which can be alleviated by running exercise. However, further studies are needed to determine whether running exercise reduces synapse loss in the hippocampus in an AD model by regulating microglia. Ten-month-old male wild-type mice and APP/PS1 mice were randomly divided into control and running groups. All mice in the running groups were subjected to voluntary running exercise for four months. After the behavioral tests, immunohistochemistry, stereological methods, immunofluorescence staining, 3D reconstruction, western blotting and RNA-Seq were performed. Running exercise improved the spatial learning and memory abilities of APP/PS1 mice and increased the total number of dendritic spines, the levels of the PSD-95 and Synapsin Ia/b proteins, the colocalization of PSD-95 and neuronal dendrites (MAP-2) and the number of PSD-95-contacting astrocytes (GFAP) in the hippocampi of APP/PS1 mice. Moreover, running exercise reduced the relative expression of CD68 and Iba-1, the number of Iba-1⁺ microglia and the colocalization of PSD-95 and Iba-1⁺ microglia in the hippocampi of APP/PS1 mice. The RNA-Seq results showed that some differentially expressed genes (DEGs) related to the complement system (Cd59b, Serping1, Cfh, A2m, and Trem2) were upregulated in the hippocampi of APP/PS1 mice, while running exercise downregulated the C3 gene. At the protein level, running exercise also reduced the expression of advanced glycation end products (AGEs), receptor for advanced glycation end products (RAGE), C1q and C3 in the hippocampus and AGEs and RAGE in hippocampal microglia in APP/PS1 mice. Furthermore, the Col6a3, Scn5a, Cxcl5, Tdg and Clec4n genes were upregulated in the hippocampi of APP/PS1 mice but downregulated after running, and these genes were associated with the C3 and RAGE genes according to protein-protein interaction (PPI) analysis. These findings indicate that long-term voluntary exercise might protect hippocampal synapses and affect the function and activation of microglia, the AGE/RAGE signaling pathway in microglia and the C1q/C3 complement system in the hippocampus in APP/PS1 mice, and these effects may be related to the Col6a3, Scn5a, Cxcl5, Tdg and Clec4n genes. The current results provide an important basis for identifying targets for the prevention and treatment of AD.