Synapses and dendritic spines as pathogenic targets in Alzheimer's disease

Differential Expression of Disulfidptosis-Related Genes in Spinal Cord Injury and Their Role in the Immune Microenvironment

Spinal cord injury (SCI) often results in severe sensory, motor, and autonomic dysfunction, with limited treatment options due to complex underlying mechanisms. Disulfidptosis, a recently discovered form of cell death driven by disulfide bond accumulation, has been linked to various diseases, but its role in SCI remains unexplored. This study investigates the involvement of disulfidptosis-related genes (DRGs) in SCI to identify potential diagnostic markers and therapeutic targets. Using SCI datasets from the Gene Expression Omnibus (GEO), we conducted differential gene expression analysis, identifying key disulfidptosis-related differentially expressed genes (DRDEGs). Further analysis through gene set enrichment (GSEA) and Bayesian pathway enrichment highlighted significant involvement in pathways such as NF-κB, PI3K/Akt, and MAPK, with an emphasis on nephrin family interactions. Three core DRDEGs-HK2, Map3k8, and S100a6-were identified, and a diagnostic model built on these genes demonstrated strong predictive performance (AUC: 0.896 in training, 0.850 in validation). Additionally, real-time PCR (qRT-PCR) in an animal model validated the elevated expression of these DRDEGs in SCI samples. This research provides novel insights into disulfidptosis in SCI, suggesting these genes as promising targets for improved diagnostic and therapeutic strategies.

Maternal Exposure of SD Rats to Benzo[a]Pyrene Impairs Neurobehavior and Hippocampal Synaptic Ultrastructure in Offspring via Downregulating Synaptic-Associated Factors

Benzo[a]pyrene (B[a]P) is a carcinogenic contaminant widely present in the environment. Recently, increasing studies have paid attention to the developmental neurotoxicity of B[a]P in offspring in their early life stages; however, the underlying molecular mechanisms have not been clearly elucidated. In this study, we aimed to evaluate the effects of prenatal B[a]P exposure on neurobehavior of pups during their brain growth spurt (BGS) period and also explore the potential underlying mechanisms. Pregnant Sprague-Dawley (SD) rats were intraperitoneally exposed to 0, 10, 20, or 40 mg/kg-bw B[a]P for three consecutive days during embryonic days 17-19. The physiological development index of pups was observed, and a series of neurobehavioral tests assessing sensory and motor maturation were performed. The complexity of dendritic branches and the basal dendritic spine density of CA1 pyramidal neurons were examined using Golgi-Cox staining during PND 1-14. In addition, the mRNA and protein expression levels of hippocampal BDNF, SYP, Arc, PSD-95, DNMT1, and DNMT3a, and the level of 5-mC were detected using RT-qPCR, Western blotting, or immunohistochemical staining, respectively. We noted that prenatal B[a]P exposure induced body weight loss and neurobehavioral impairments in the early life stages. Furthermore, this study firstly revealed that maternal exposure to B[a]P impaired the dendritic arborization and complexity of pyramidal neurons in the hippocampus CA1 subfield in offspring during the early postnatal period, and the damage of B[a]P to basal dendritic spine density was also observed in a dose-dependent manner. Correspondingly, maternal exposure to B[a]P markedly reduced BDNF, Arc, SYP, and PSD-95 mRNA and protein levels in the offspring hippocampus. Meanwhile, the levels of hippocampal DNMT1, DNMT3a, and 5-mC significantly increased in the offspring prenatally exposed to B[a]P. In summary, this study firstly demonstrated that maternal B[a]P exposure induced neurobehavioral deficits by destroying the hippocampal synaptic ultrastructure, which was possibly associated with the downregulation of BDNF, Arc, SYP, and PSD95 in the hippocampus through increased DNMTs-mediated DNA methylation in offspring during the BGS period.

Neuronal and glial dysfunction, white matter hyperintensities and cognition in ageing and Alzheimer's disease

This cross-sectional study examined associations between multiple fluid biomarkers of neuronal and glial dysfunction (plasma neurofilament light chain, CSF growth-associated protein 43 and CSF soluble triggering receptor expressed on myeloid cells 2), total white matter hyperintensity volume and episodic memory and executive function performance in the context of Alzheimer's disease biomarker status. A total of 563 participants (mean age = 71.9 years, standard deviation = 7.2) from the Alzheimer's Disease Neuroimaging Initiative were classified by the amyloid-β/tau/neurodegeneration framework into no Alzheimer's disease pathology (n = 176), suspected non-Alzheimer's disease pathophysiology (n = 87) or Alzheimer's disease continuum (n = 300) groups. Participants completed baseline neuropsychological assessment, plasma/CSF biomarker collection and MRI. Analyses explored the relative contributions of biomarkers to episodic memory and executive function performance and whether relationships varied by amyloid-β/tau/neurodegeneration group status. Across all participants, neurofilament light chain (β ^ = -0.14, P < 0.001) and growth-associated protein 43 (β ^ = -0.13, P < 0.001) were the strongest biomarkers associated with episodic memory performance, such that greater levels were associated with worse episodic memory. There was a group by growth-associated protein 43 interaction with episodic memory: greater growth-associated protein 43 was associated with lower episodic memory performance in participants classified as Alzheimer's disease continuum relative to the no Alzheimer's disease pathology group (β ^ = -0.26, P < 0.001). No robust associations between biomarkers and executive function performance or between soluble triggering receptor expressed on myeloid cells 2, white matter hyperintensity volume and cognition were observed. Biomarkers of neuro-axonal injury and synaptic dysfunction may independently contribute to episodic memory performance across participants with differing amyloid-β/tau/neurodegeneration profiles. Growth-associated protein 43 may predict worse episodic memory performance in participants with greater Alzheimer's disease pathology. These biomarkers of neuronal dysfunction may serve as domain-specific cognitive correlates in the context of Alzheimer's disease biomarker status.

The role of inhibitory immune checkpoint receptors in the pathogenesis of Alzheimer's disease

There is mounting evidence that microglial cells have a key role in the pathogenesis of Alzheimer's disease (AD). In AD pathology, microglial cells not only are unable to remove β-amyloid (Aβ) plaques and invading pathogens but also are involved in synaptic pruning, chronic neuroinflammation, and neuronal degeneration. Microglial cells possess many different inhibitory immune checkpoint receptors, such as PD-1, LILRB2-4, Siglecs, and SIRPα receptors, which can be targeted by diverse cell membrane-bound and soluble ligand proteins to suppress the functions of microglia. Interestingly, in the brains of AD patients there are elevated levels of many of the inhibitory ligands acting via these inhibitory checkpoint receptors. For instance, Aβ oligomers, ApoE4, and fibronectin are able to stimulate the LILRB2-4 receptors. Increased deposition of sialoglycans, e.g., gangliosides, inhibits microglial function via Siglec receptors. AD pathology augments the accumulation of senescent cells, which are known to possess a high level of PD-L1 proteins, and thus, they can evade immune surveillance. A decrease in the expression of SIRPα receptor in microglia and its ligand CD47 in neurons enhances the phagocytic pruning of synapses in AD brains. Moreover, cerebral neurons contain inhibitory checkpoint receptors which can inhibit axonal growth, reduce synaptic plasticity, and impair learning and memory. It seems that inappropriate inhibitory immune checkpoint signaling impairs the functions of microglia and neurons thus promoting AD pathogenesis. KEY MESSAGES: Microglial cells have a major role in the pathogenesis of AD. A decline in immune activity of microglia promotes AD pathology. Microglial cells and neurons contain diverse inhibitory immune checkpoint receptors. The level of ligands for inhibitory checkpoint receptors is increased in AD pathology. Impaired signaling of inhibitory immune checkpoint receptors promotes AD pathology.

The effect of paeoniflorin on the rewarding effect of methamphetamine and the associated cognitive impairment in mice

Chronic exposure to methamphetamine (METH) has been suggested to cause METH use disorder and severe cognitive impairment. Paeoniflorin (PF) is a monoterpenoid glycoside with various beneficial effects, including anti-inflammatory, antioxidant and antidepressant. The current study was designed to investigate the effect of PF (30 mg/kg, i.p.) on the rewarding effect of METH (2.5 mg/kg, i.p.) and the associated cognitive impairment, using the animal model of conditioned place preference, new location reorganization test, new object reorganization test and Y-maze test. METH induced conditioned place preference, accompanied by increased expression of synapse-associated proteins in the ventral target areas (VTA) and nucleus accumbens (NAc). In addition, METH induced significant cognitive impairment and decreased the expression of synapse-associated proteins in the hippocampus (Hip). Administration of PF decreased the rewarding effect of METH and the expression of synapse-associated proteins in the VTA or NAc. PF was also effective to improve METH-induced cognitive impairment by upregulating the expression of synapse-associated proteins in the Hip. Therefore, PF could be a potential agent for the treatment of METH use disorder and the associated cognitive impairment.

Corilagin improves cognitive impairment in APP/PS1 mice by reducing Aβ generation and enhancing synaptic plasticity

Alzheimer's disease (AD) is closely associated with the neurotoxic effects of amyloid-β (Aβ), leading to synaptic damage, neuronal loss and cognitive dysfunction. Previous in vitro studies have demonstrated the potential of corilagin to counteract Aβ-induced oxidative stress, inflammatory injury, and β-site amyloid precursor protein cleaving enzyme-1 (BACE1) activity in Aβ production. However, the in vivo protective effects of corilagin on Alzheimer's disease remain unexplored. The purpose of this study was to investigate the protective effects of corilagin on APP/PS1 mice and the underlying mechanisms. The cognitive function of the mice was assessed by step-through passive avoidance and Morris water maze tests. Nissl staining was used to evaluate neuronal damage in the hippocampus. ELISA and Western blotting analyses were used to determine the associated protein expression. Transmission electron microscopy was utilized to observe the synaptic ultrastructure of hippocampal neurons. Golgi staining was applied to assess dendritic morphology and dendritic spine density in hippocampal pyramidal neurons. Immunohistochemistry and Western blotting were performed to examine the expression of synaptic-associated proteins. The results showed that corilagin improves learning and memory in APP/PS1 mice, reduces hippocampal neuron damage, inhibits BACE1 and reduces Aβ generation. It also improves synaptic plasticity and the expression of synaptic-associated proteins. Corilagin effectively reduces Aβ generation by inhibiting BACE1, ultimately reducing neuronal loss and enhancing synaptic plasticity to improve synaptic transmission. This study sheds light on the potential therapeutic role of corilagin in Alzheimer's disease.

Social isolation impairs cognition via Aβ-mediated synaptic dysfunction

Social isolation (SI) is a common phenomenon in the modern world, especially during the coronavirus disease 2019 pandemic, and causes lasting cognitive impairments and mental disorders. However, it is still unclear how SI alters molecules in the brain and induces behavioural dysfunctions. Here, we report that SI impairs cognitive function and induces depressive-like behaviours in C57BL/6 J mice, in addition to impairing synaptic plasticity and increasing the levels of APP cleavage-related enzymes, thereby promoting Aβ production. Moreover, we show that in APP/PS1 transgenic mice, SI accelerates pathological changes and behavioural deficits. Interestingly, downregulation of the expression of the BACE1 attenuates SI-induced Aβ toxicity and synaptic dysfunction. Furthermore, early intervention with BACE1 shRNA blocks SI-induced cognitive impairments. Together, our data strongly suggest that SI-induced upregulation of BACE1 expression mediates Aβ toxicity and induces behavioural deficits. Down-regulation of BACE1 may be a promising strategy for preventing SI-induced cognitive impairments.

Firing Alterations of Neurons in Alzheimer's Disease: Are They Merely a Consequence of Pathogenesis or a Pivotal Component of Disease Progression?

Alzheimer's disease (AD) is the most prevalent neurodegenerative disorder, yet its underlying causes remain elusive. The conventional perspective on disease pathogenesis attributes alterations in neuronal excitability to molecular changes resulting in synaptic dysfunction. Early hyperexcitability is succeeded by a progressive cessation of electrical activity in neurons, with amyloid beta (Aβ) oligomers and tau protein hyperphosphorylation identified as the initial events leading to hyperactivity. In addition to these key proteins, voltage-gated sodium and potassium channels play a decisive role in the altered electrical properties of neurons in AD. Impaired synaptic function and reduced neuronal plasticity contribute to a vicious cycle, resulting in a reduction in the number of synapses and synaptic proteins, impacting their transportation inside the neuron. An understanding of these neurophysiological alterations, combined with abnormalities in the morphology of brain cells, emerges as a crucial avenue for new treatment investigations. This review aims to delve into the detailed exploration of electrical neuronal alterations observed in different AD models affecting single neurons and neuronal networks.

Comparative proteomic analysis of cerebral cortex revealed neuroprotective mechanism of esculentoside A on Alzheimer's disease

Esculentoside A (EsA), isolated from phytolacca esculenta, is a saponin showing neuroprotective effect in the mouse models of Alzheimer's disease (AD). To investigate its action target and underlying mechanism, this study used the proteomics technique of isobaric tags for relative and absolute quantification (iTRAQ) to analyze the differentially expressed proteins (DEPs) in the cerebral cortex of EsA-treated and untreated triple-transgenic 3 × Tg-AD model mice. Proteomic comparison revealed 250, 436, and 903 DEPs in three group pairs, i.e. AD/Wild-type (WT), AD+5 mg/kg EsA/AD, AD+10 mg/kg EsA/AD, respectively. Among them 28 DEPs were commonly shared by three group pairs, and 25 of them showed reversed expression levels in the diseased group under the treatment of both doses of EsA. Bioinformatics analysis revealed that these DEPs were mainly linked to metabolism, synapses, apoptosis, learning and memory. EsA treatment restored the expression of these proteins, including amyloid precursor protein (APP), cathepsin B (Cstb), 4-aminobutyrate aminotransferase (Abat), 3-phosphoinositide-dependent protein kinase-1 (PDK1), carnitine palmitoyltransferase1 (Cpt1) and synaptotagmin 17 (Syt17), thereby ameliorated the spatial learning and memory of AD mice. Collectively, this study reveals for the first time the profound effect of EsA on the cerebral cortex of AD mice, which might be a potential therapeutic agent for the treatment of AD.

Controversial Past, Splendid Present, Unpredictable Future: A Brief Review of Alzheimer Disease History

Background: The concept of Alzheimer disease (AD)-since its histological discovery by Alzheimer to the present day-has undergone substantial modifications. Methods: We conducted a classical narrative review of this field with a bibliography selection (giving preference to Medline best match). Results: The following subjects are reviewed and discussed: Alzheimer's discovery, Kraepelin's creation of a new disease that was a rare condition until the 1970's, the growing interest and investment in AD as a major killer in a society with a large elderly population in the second half of the 20th century, the consolidation of the AD clinicopathological model, and the modern AD nosology based on the dominant amyloid hypothesis among many others. In the 21st century, the development of AD biomarkers has supported a novel biological definition of AD, although the proposed therapies have failed to cure this disease. The incidence of dementia/AD has shown a decrease in affluent countries (possibly due to control of risk factors), and mixed dementia has been established as the most frequent etiology in the oldest old. Conclusions: The current concept of AD lacks unanimity. Many hypotheses attempt to explain its complex physiopathology entwined with aging, and the dominant amyloid cascade has yielded poor therapeutic results. The reduction in the incidence of dementia/AD appears promising but it should be confirmed in the future. A reevaluation of the AD concept is also necessary.

Factors affecting the GABAergic synapse function in Alzheimer's disease: Focus on microRNAs

Alzheimer's disease (AD) is a progressive neurological disease characterized by the loss of cognitive function, confusion, and memory deficit. Accumulation of abnormal proteins, amyloid beta (Aß), and phosphorylated Tau (p-tau) forms plaques and tangles that deteriorate synapse function, resulting in neurodegeneration and cognitive decline in AD. The human brain is composed of different types of neurons and/or synapses that are functionally defective in AD. The GABAergic synapse, the most abundant inhibitory neuron in the human brain was found to be dysfunctional in AD and contributes to disrupting neurological function. This study explored the types of GABA receptors associated with neurological dysfunction and various biological and environmental factors that cause GABAergic neuron dysfunction in AD, such as Aβ, p-tau, aging, sex, astrocytes, microglia, APOE, mental disorder, diet, physical activity, and sleep. Furthermore, we explored the role of microRNAs (miRNAs) in the regulation of GABAergic synapse function in neurological disorders and AD states. We also discuss the molecular mechanisms underlying GABAergic synapse dysfunction with a focus on miR-27b, miR-30a, miR-190a/b, miR-33, miR-51, miR-129-5p, miR-376-3p, miR-376c, miR-30b and miR-502-3p. The purpose of our article is to highlight the recent research on miRNAs affecting the regulation of GABAergic synapse function and factors that contribute to the progression of AD.

Impairments in endogenous AMPA receptor dynamics correlates with learning deficits in Alzheimer's disease model mice

AMPA receptors (AMPARs) play a critical role in synaptic plasticity and learning and memory, and dysfunction or dysregulation of AMPARs could lead to various neurological and psychiatric disorders, such as Alzheimer's disease (AD). However, the dynamics and/or longitudinal changes of AMPARs in vivo during AD pathogenesis remain elusive. Here, employing 5xFAD SEP-GluA1 KI mice, we investigated endogenous AMPA receptor dynamics in a whisker deflection-associated Go/No-go learning paradigm. We found a significant increase in synaptosomal AMPA receptor subunits GluA1 in WT mice after learning, while no such changes were detected in 7-mo-old 5xFAD mice. Daily training led to an increase in endogenous spine surface GluA1 in Control mice, while this increase was absent in 5xFAD-KI mice which correlates with its learning defects in Go/No-go paradigm. Furthermore, we demonstrated that the onset of abnormal AMPAR dynamics corresponds temporally with microglia and astrocyte overactivation. Our results have shown that impairments in endogenous AMPA receptor dynamics play an important role in learning deficits in 5xFAD mice and AD pathogenesis.

Global trends and prospects about synaptic plasticity in Alzheimer's disease: a bibliometric analysis

Background and purpose

In recent years, synaptic plasticity disorders have been identified as one of the key pathogenic factors and the early pathological characteristics of Alzheimer's disease (AD). In this study, we tried to use bibliometric analysis to gain a systematic understanding about synaptic plasticity in Alzheimer's disease.

Methods

We extracted relevant publications from the Web of Science Core Collection (WoSCC) on August 29th, 2022. Then, we used CiteSpace, VOSviewer and other online bibliometric platforms to further analyze the obtained data.

Results

A total of 2,348 published articles and reviews about synaptic plasticity in AD from 2002 to 2022 were identified. During the past two decades, the overall trends of the numbers and citations of manuscripts were on the rise. The United States was the leading country with the largest number of publications which showed its crucial role in this field. The collaboration network analysis showed that the United States and China had the most frequent collaboration. In addition, Harvard University was the institution with the greatest number of publications and cited times. Among all authors, Selkoe DJ was the most influential author with the greatest cited times. The journal of Alzheimer's disease published the maximum number of documents in the field of synaptic plasticity in AD within 20 years. Furthermore, the results of keywords burst detection showed that the hot topics have shifted from the synaptic transmission, precursor protein and plaque formation to neuroinflammation, microglia and alpha synuclein.

Conclusion

This study analyzed 2,348 publications with 82,025 references covering the topic of synaptic plasticity in AD and presented the research trends. The results indicated that neuroinflammation, microglia and alpha synuclein were the current research hotspots, which implied the potential clinical applications to AD.

Identification of disulfidptosis-related genes and subgroups in Alzheimer's disease

Background

Alzheimer's disease (AD), a common neurological disorder, has no effective treatment due to its complex pathogenesis. Disulfidptosis, a newly discovered type of cell death, seems to be closely related to the occurrence of various diseases. In this study, through bioinformatics analysis, the expression and function of disulfidptosis-related genes (DRGs) in Alzheimer's disease were explored.

Methods

Differential analysis was performed on the gene expression matrix of AD, and the intersection of differentially expressed genes and disulfidptosis-related genes in AD was obtained. Hub genes were further screened using multiple machine learning methods, and a predictive model was constructed. Finally, 97 AD samples were divided into two subgroups based on hub genes.

Results

In this study, a total of 22 overlapping genes were identified, and 7 hub genes were further obtained through machine learning, including MYH9, IQGAP1, ACTN4, DSTN, ACTB, MYL6, and GYS1. Furthermore, the diagnostic capability was validated using external datasets and clinical samples. Based on these genes, a predictive model was constructed, with a large area under the curve (AUC = 0.8847), and the AUCs of the two external validation datasets were also higher than 0.7, indicating the high accuracy of the predictive model. Using unsupervised clustering based on hub genes, 97 AD samples were divided into Cluster1 (n = 24) and Cluster2 (n = 73), with most hub genes expressed at higher levels in Cluster2. Immune infiltration analysis revealed that Cluster2 had a higher level of immune infiltration and immune scores.

Conclusion

A close association between disulfidptosis and Alzheimer's disease was discovered in this study, and a predictive model was established to assess the risk of disulfidptosis subtype in AD patients. This study provides new perspectives for exploring biomarkers and potential therapeutic targets for Alzheimer's disease.

Ferulic Acid Improves Synaptic Plasticity and Cognitive Impairments by Alleviating the PP2B/DARPP-32/PP1 Axis-Mediated STEP Increase and Aβ Burden in Alzheimer's Disease

The burden of Alzheimer's disease, the most prevalent neurodegenerative disease, is increasing exponentially due to the increase in the elderly population worldwide. Synaptic plasticity is the basis of learning and memory, but it is impaired in AD. Uncovering the disease's underlying molecular pathogenic mechanisms involving synaptic plasticity could lead to the identification of targets for better disease management. Using primary neurons treated with Aβ and APP/PS1 animal models, we evaluated the effect of the phenolic compound ferulic acid (FA) on synaptic dysregulations. Aβ led to synaptic plasticity and cognitive impairments by increasing STEP activity and decreasing the phosphorylation of the GluN2B subunit of NMDA receptors, as well as decreasing other synaptic proteins, including PSD-95 and synapsin1. Interestingly, FA attenuated the Aβ-upregulated intracellular calcium and thus resulted in a decrease in PP2B-induced activation of DARPP-32, inhibiting PP1. This cascade event maintained STEP in its inactive state, thereby preventing the loss of GluN2B phosphorylation. This was accompanied by an increase in PSD-95 and synapsin1, improved LTP, and a decreased Aβ load, together leading to improved behavioral and cognitive functions in APP/PS1 mice treated with FA. This study provides insight into the potential use of FA as a therapeutic strategy in AD.

The effects of voluntary running exercise on the astrocytes of the medial prefrontal cortex in APP/PS1 mice

Pathological changes in the medial prefrontal cortex (mPFC) and astrocytes are closely associated with Alzheimer's disease (AD). Voluntary running has been found to effectively delay AD. However, the effects of voluntary running on mPFC astrocytes in AD are unclear. A total of 40 10-month-old male amyloid precursor protein/presenilin 1 (APP/PS1) mice and 40 wild-type (WT) mice were randomly divided into control and running groups, and the running groups underwent voluntary running for 3 months. Mouse cognition was assessed by the novel object recognition (NOR), Morris water maze (MWM), and Y maze tests. The effects of voluntary running on mPFC astrocytes were investigated using immunohistochemistry, immunofluorescence, western blotting, and stereology. APP/PS1 mice performed significantly worse than WT mice in the NOR, MWM, and Y maze tests, and voluntary running improved the performance of APP/PS1 mice in these tests. The total number of mPFC astrocytes was increased, cell bodies were enlarged, and protrusion number and length were increased in AD mice compared with WT mice, but there was no difference in component 3 (C3) levels in the mPFC (total mPFC level); however, C3 and S100B levels in astrocytes were increased in AD mice. Voluntary running reduced the total number of astrocytes and S100B levels in astrocytes and increased the density of PSD95⁺ puncta in direct contact with astrocyte protrusions in the APP/PS1 mouse mPFC. Three months of voluntary running inhibited astrocyte hyperplasia and S100B expression in astrocytes, increased the density of synapses in contact with astrocytes, and improved cognitive function in APP/PS1 mice.

The Multifaceted Role of WNT Signaling in Alzheimer's Disease Onset and Age-Related Progression

The evolutionary conserved WNT signaling pathway orchestrates numerous complex biological processes during development and is critical to the maintenance of tissue integrity and homeostasis in the adult. As it relates to the central nervous system, WNT signaling plays several roles as it relates to neurogenesis, synaptic formation, memory, and learning. Thus, dysfunction of this pathway is associated with multiple diseases and disorders, including several neurodegenerative disorders. Alzheimer's disease (AD) is characterized by several pathologies, synaptic dysfunction, and cognitive decline. In this review, we will discuss the various epidemiological, clinical, and animal studies that demonstrate a precise link between aberrant WNT signaling and AD-associated pathologies. In turn, we will discuss the manner in which WNT signaling influences multiple molecular, biochemical, and cellular pathways upstream of these end-point pathologies. Finally, we will discuss how merging tools and technologies can be used to generate next generation cellular models to dissect the relationship between WNT signaling and AD.

Geraniol improves passive avoidance memory and hippocampal synaptic plasticity deficits in a rat model of Alzheimer's disease

Alzheimer's disease (AD) is the most progressive and irreversible neurodegenerative disease that leads to synaptic loss and cognitive decline. The present study was designed to evaluate the effects of geraniol (GR), a valuable acyclic monoterpene alcohol, with protective and therapeutic effects, on passive avoidance memory, hippocampal synaptic plasticity, and amyloid-beta (Aβ) plaques formation in an AD rat model induced by intracerebroventricular (ICV) microinjection of Aβ_1-40. Seventy male Wistar rats were randomly into sham, control, control-GR (100 mg/kg; P.O. (orally), AD, GR-AD (100 mg/kg; P.O.; pretreatment), AD-GR (100 mg/kg; P.O.; treatment), and GR-AD-GR (100 mg/kg; P.O.; pretreatment & treatment). Administration of GR was continued for four consecutive weeks. Training for the passive avoidance test was carried out on the 36^th day and a memory retention test was performed 24 h later. On day 38, hippocampal synaptic plasticity (long-term potentiation; LTP) was recorded in perforant path-dentate gyrus (PP-DG) synapses to assess field excitatory postsynaptic potentials (fEPSPs) slope and population spike (PS) amplitude. Subsequently, Aβ plaques were identified in the hippocampus by Congo red staining. The results showed that Aβ microinjection increased passive avoidance memory impairment, suppressed of hippocampal LTP induction, and enhanced of Aβ plaque formation in the hippocampus. Interestingly, oral administration of GR improved passive avoidance memory deficit, ameliorated hippocampal LTP impairment, and reduced Aβ plaque accumulation in the Aβ-infused rats. The results suggest that GR mitigates Aβ-induced passive avoidance memory impairment, possibly through alleviation of hippocampal synaptic dysfunction and inhibition of Aβ plaque formation.

Deciphering the Tubulin Language: Molecular Determinants and Readout Mechanisms of the Tubulin Code in Neurons

Microtubules (MTs) are dynamic components of the cell cytoskeleton involved in several cellular functions, such as structural support, migration and intracellular trafficking. Despite their high similarity, MTs have functional heterogeneity that is generated by the incorporation into the MT lattice of different tubulin gene products and by their post-translational modifications (PTMs). Such regulations, besides modulating the tubulin composition of MTs, create on their surface a "biochemical code" that is translated, through the action of protein effectors, into specific MT-based functions. This code, known as "tubulin code", plays an important role in neuronal cells, whose highly specialized morphologies and activities depend on the correct functioning of the MT cytoskeleton and on its interplay with a myriad of MT-interacting proteins. In recent years, a growing number of mutations in genes encoding for tubulins, MT-interacting proteins and enzymes that post-translationally modify MTs, which are the main players of the tubulin code, have been linked to neurodegenerative processes or abnormalities in neural migration, differentiation and connectivity. Nevertheless, the exact molecular mechanisms through which the cell writes and, downstream, MT-interacting proteins decipher the tubulin code are still largely uncharted. The purpose of this review is to describe the molecular determinants and the readout mechanisms of the tubulin code, and briefly elucidate how they coordinate MT behavior during critical neuronal events, such as neuron migration, maturation and axonal transport.

Effect of a combined program of running exercise and environmental enrichment on memory function and neurogenesis markers in amyloid-beta-induced Alzheimer-like model

Objectives

It is urgent to develop non-pharmacological interventions or multifactor combination approaches to combat Alzheimer's disease (AD). The effect of exercise (EX) combined with environmental enrichment (EE) on behavioral phenotypes and neurogenesis markers in an Alzheimer-like rat model was investigated.

Materials and Methods

The groups consisted of AD, sham-operated, AD+EX, AD+EE, and AD+EX+EE. AD was produced by injection of amyloid-beta (1-42, 6 µg) intrahippocampally, and a daily treadmill for 3 consecutive weeks was used for EX animals. EE was a large cage (50× 50× 50 cm) containing differently shaped objects. Spatial learning and memory were evaluated in the Morris water maze (MWM), and a shuttle box was used to evaluate inhibitory avoidance memory. RT-PCR was performed to assess the expression of early neurogenesis markers, DCX, and Sox2 within the hippocampus.

Results

Pretreatment with exercise and EE, both individually and in combination, could provide protection from memory impairments in AD rats. Combined treatment led to a significantly more pronounced improvement in memory deficits of AD rats than either paradigm alone. Combination therapy with exercise and EE could also reverse the passive avoidance memory impairment and hippocampal DCX expression of AD rats to the control levels.

Conclusion

These data suggest that exercise in combination with cognitive engagement can provide a non-pharmacological and multidomain policy that may prevent or delay AD symptoms.

Golgi fragmentation - One of the earliest organelle phenotypes in Alzheimer's disease neurons

Alzheimer's disease (AD) is the most common cause of dementia, with no current cure. Consequently, alternative approaches focusing on early pathological events in specific neuronal populations, besides targeting the well-studied amyloid beta (Aβ) accumulations and Tau tangles, are needed. In this study, we have investigated disease phenotypes specific to glutamatergic forebrain neurons and mapped the timeline of their occurrence, by implementing familial and sporadic human induced pluripotent stem cell models as well as the 5xFAD mouse model. We recapitulated characteristic late AD phenotypes, such as increased Aβ secretion and Tau hyperphosphorylation, as well as previously well documented mitochondrial and synaptic deficits. Intriguingly, we identified Golgi fragmentation as one of the earliest AD phenotypes, indicating potential impairments in protein processing and post-translational modifications. Computational analysis of RNA sequencing data revealed differentially expressed genes involved in glycosylation and glycan patterns, whilst total glycan profiling revealed minor glycosylation differences. This indicates general robustness of glycosylation besides the observed fragmented morphology. Importantly, we identified that genetic variants in Sortilin-related receptor 1 (SORL1) associated with AD could aggravate the Golgi fragmentation and subsequent glycosylation changes. In summary, we identified Golgi fragmentation as one of the earliest disease phenotypes in AD neurons in various in vivo and in vitro complementary disease models, which can be exacerbated via additional risk variants in SORL1.

Prenatal benzo[a]pyrene exposure impairs hippocampal synaptic plasticity and cognitive function in SD rat offspring during adolescence and adulthood via HDAC2-mediated histone deacetylation

Benzo[a]pyrene (B[a]P) is a widespread carcinogenic pollutant in the environment. Although previous studies have demonstrated the neurodevelopmental toxicity of B[a]P, the precise mechanisms underlying the neurotoxic effects induced by prenatal B[a]P exposure remain largely unknown. In the present study, pregnant Sprague-Dawley (SD) rats were injected intraperitoneally with 0, 10, 20, or 40 mg/kg-bw of B[a]P for three consecutive days on embryonic days 17-19. The learning and memory abilities of offspring were determined by Morris Water Maze (MWM) test, while the number of dendritic branches and the density of dendritic spines in hippocampal CA1 and DG regions were evaluated by Golgi-Cox staining at PND 45 and PND 75. The mRNA expression of BDNF, PSD-95, and SYP in offspring hippocampus were detected by qRT-PCR, and the protein expression of BDNF, PSD-95, SYP, HDAC2, acH3K9, and acH3K14 were measured by Western blotting or immunohistochemistry. CHIP-PCR was performed to further detect the levels of acH3K9 and acH3K14 in the promoter regions of BDNF and PSD-95 genes. Our results showed that rats prenatally exposed to B[a]P exhibited impaired spatial learning and memory abilities and the number of dendritic branches and the density of dendritic spines in the hippocampal CA1 and DG regions were significantly reduced during adolescence and adulthood. The expression of HDAC2 protein was significantly upregulated, while acH3K9, acH3K14, BDNF, PSD-95, and SYP protein levels were significantly downregulated in the hippocampus of B[a]P- exposed rats. In addition, CHIP results showed that prenatal B[a]P exposure markedly decreased the level of acH3K9 and acH3K14 in the promoter region of BDNF and PSD-95 gene in the hippocampus of PND 45 and PND 75 offspring. All of the results suggest that prenatal B[a]P exposure impairs cognitive function and hippocampal synaptic plasticity of offspring in adolescence and adulthood, and HDAC2-mediated histone deacetylation plays a crucial role in these deficits.

CSF GAP-43 as a biomarker of synaptic dysfunction is associated with tau pathology in Alzheimer's disease

To test whether cerebrospinal fluid (CSF) growth-associated protein 43 (GAP-43) concentration is elevated in Alzheimer's disease (AD) dementia and its associations with other hallmarks of AD, we examined the CSF GAP-43 measurements of 787 participants (245 cognitively normal (CN), 415 individuals with mild cognitive impairment (MCI) and 127 individuals with AD dementia) from the Alzheimer's Disease Neuroimaging Initiative (ADNI) study. Associations were investigated between CSF GAP-43 and clinical diagnosis, Aβ/tau/neurodegeneration (AT(N)) status, CSF and blood biomarkers of AD, cognitive measurements and brain neuroimaging findings. CSF GAP-43 levels were increased in patients with AD dementia (mean, 6331.05 pg/ml) compared with the CN (mean, 5001.05 pg/ml) and MCI (mean, 5118.8 pg/ml) (P < 0.001) groups. CSF GAP-43 correlated with CSF phosphorylated tau 181(p-tau) (r = 0.768, P < 0.001), and had high diagnostic accuracy in differentiating tau positive status vs. tau negative status (area under the receiver operating characteristic curve, 0.8606). CSF GAP-43 was particularly elevated among individuals with tau positive status. High CSF GAP-43 was associated with longitudinal deterioration of cognitive scores and brain neuroimaging findings. CSF GAP-43 was associated with a clinical diagnosis of AD dementia and with an individual's tau status, cognitive measurements and findings from neuroimaging. This study implies that CSF GAP-43 as a biomarker of synaptic dysfunction could predict the disease progression of AD patients.

Moringa Oleifera Alleviates Aβ Burden and Improves Synaptic Plasticity and Cognitive Impairments in APP/PS1 Mice

Alzheimer's disease is a global public health problem and the most common form of dementia. Due to the failure of many single therapies targeting the two hallmarks, Aβ and Tau, and the multifactorial etiology of AD, there is now more and more interest in nutraceutical agents with multiple effects such as Moringa oleifera (MO) that have strong anti-oxidative, anti-inflammatory, anticholinesterase, and neuroprotective virtues. In this study, we treated APP/PS1 mice with a methanolic extract of MO for four months and evaluated its effect on AD-related pathology in these mice using a multitude of behavioral, biochemical, and histochemical tests. Our data revealed that MO improved behavioral deficits such as anxiety-like behavior and hyperactivity and cognitive, learning, and memory impairments. MO treatment abrogated the Aβ burden to wild-type control mice levels via decreasing BACE1 and AEP and upregulating IDE, NEP, and LRP1 protein levels. Moreover, MO improved synaptic plasticity by improving the decreased GluN2B phosphorylation, the synapse-related proteins PSD95 and synapsin1 levels, the quantity and quality of dendritic spines, and neurodegeneration in the treated mice. MO is a nutraceutical agent with promising therapeutic potential that can be used in the management of AD and other neurodegenerative diseases.

Estrogen deficiency exacerbates learning and memory deficits associated with glucose metabolism disorder in APP/PS1 double transgenic female mice

Alterations in glucose metabolism occur in the brain in the early stage of Alzheimer's disease (AD), and menopausal women have more severe metabolic dysfunction and are more prone to dementia than men. Although estrogen deficiency-induced changes in glucose metabolism have been previously studied in animal models, their molecular mechanisms in AD remain elusive. To investigate this issue, double transgenic (APP/PS1) female mice were subjected to bilateral ovariectomy at 3 months of age and were sacrificed 1 week, 1 month and 3 months after surgery to simulate early, middle and late postmenopause, respectively. Our analysis demonstrated that estrogen deficiency exacerbates learning and memory deficits in this mouse model of postmenopause. Estrogen deficiency impairs the function of mitochondria in glucose metabolism. It is possible that the occurrence of AD is associated with the aberrant mitochondrial ERβ-mediated IGF-1/IGF-1R/GSK-3β signaling pathway. In this study, we established a potential mechanism for the increased risk of AD in postmenopausal women and proposed a therapeutic target for AD due to postmenopause.

Methamphetamine induced neurotoxic diseases, molecular mechanism, and current treatment strategies

Methamphetamine (MA) is a extremely addictive psychostimulant drug with a significant abuse potential. Long-term MA exposure can induce neurotoxic effects through oxidative stress, mitochondrial functional impairment, endoplasmic reticulum stress, the activation of astrocytes and microglial cells, axonal transport barriers, autophagy, and apoptosis. However, the molecular and cellular mechanisms underlying MA-induced neurotoxicity remain unclear. MA abuse increases the chances of developing neurotoxic conditions such as Parkinson's disease (PD), Alzheimer's disease (AD) and other neurotoxic diseases. MA increases the risk of PD by increasing the expression of alpha-synuclein (ASYN). Furthermore, MA abuse is linked to high chances of developing AD and subsequent neurodegeneration due to biological variations in the brain region or genetic and epigenetic variations. To date, there is no Food and Drug Administration (FDA)-approved therapy for MA-induced neurotoxicity, although many studies are being conducted to develop effective therapeutic strategies. Most current studies are now focused on developing therapies to diminish the neurotoxic effects of MA, based on the underlying mechanism of neurotoxicity. This review article highlights current research on several therapeutic techniques targeting multiple pathways to reduce the neurotoxic effects of MA in the brain, as well as the putative mechanism of MA-induced neurotoxicity.

A Deep Learning-Based Workflow for Dendritic Spine Segmentation

The morphological analysis of dendritic spines is an important challenge for the neuroscientific community. Most state-of-the-art techniques rely on user-supervised algorithms to segment the spine surface, especially those designed for light microscopy images. Therefore, processing large dendritic branches is costly and time-consuming. Although deep learning (DL) models have become one of the most commonly used tools in image segmentation, they have not yet been successfully applied to this problem. In this article, we study the feasibility of using DL models to automatize spine segmentation from confocal microscopy images. Supervised learning is the most frequently used method for training DL models. This approach requires large data sets of high-quality segmented images (ground truth). As mentioned above, the segmentation of microscopy images is time-consuming and, therefore, in most cases, neuroanatomists only reconstruct relevant branches of the stack. Additionally, some parts of the dendritic shaft and spines are not segmented due to dyeing problems. In the context of this research, we tested the most successful architectures in the DL biomedical segmentation field. To build the ground truth, we used a large and high-quality data set, according to standards in the field. Nevertheless, this data set is not sufficient to train convolutional neural networks for accurate reconstructions. Therefore, we implemented an automatic preprocessing step and several training strategies to deal with the problems mentioned above. As shown by our results, our system produces a high-quality segmentation in most cases. Finally, we integrated several postprocessing user-supervised algorithms in a graphical user interface application to correct any possible artifacts.

Low-Dose Delta-9-Tetrahydrocannabinol as Beneficial Treatment for Aged APP/PS1 Mice

Studies on the effective and safe therapeutic dosage of delta-9-tetrahydrocannabinol (THC) for the treatment of Alzheimer’s disease (AD) have been sparse due to the concern about THC’s psychotropic activity. The present study focused on demonstrating the beneficial effect of low-dose THC treatment in preclinical AD models. The effect of THC on amyloid-β (Aβ) production was examined in N2a/AβPPswe cells. An in vivo study was conducted in aged APP/PS1 transgenic mice that received an intraperitoneal injection of THC at 0.02 and 0.2 mg/kg every other day for three months. The in vitro study showed that THC inhibited Aβ aggregation within a safe dose range. Results of the radial arm water maze (RAWM) test demonstrated that treatment with 0.02 and 0.2 mg/kg of THC for three months significantly improved the spatial learning performance of aged APP/PS1 mice in a dose-dependent manner. Results of protein analyses revealed that low-dose THC treatment significantly decreased the expression of Aβ oligomers, phospho-tau and total tau, and increased the expression of Aβ monomers and phospho-GSK-3β (Ser9) in the THC-treated brain tissues. In conclusion, treatment with THC at 0.2 and 0.02 mg/kg improved the spatial learning of aged APP/PS1 mice, suggesting low-dose THC is a safe and effective treatment for AD.

MicroRNA-455-5p/CPEB1 pathway mediates Aβ-related learning and memory deficits in a mouse model of Alzheimer's disease

Alzheimer's disease (AD), a common neurodegenerative disease, is the main cause of dementia, with cognitive decline as the core symptom observed during diagnosis. Synaptic loss may be the main cause of early cognitive dysfunction in AD, but the detailed mechanism is still unclear. In this study, we investigated the role of abnormal miR-455-5p/CPEB1 pathway in AD mouse model. We found that miR-455-5p was upregulated, while its downstream target, cytoplasmic polyadenylation element-binding 1 (CPEB1), was downregulated in the hippocampus of APP/PS1 mice at the age of 9 m. Abnormal miR-455-5p/CPEB1 pathway mediated cognitive deficits in APP/PS1 mice through suppressing α-Amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor expressions. And miR-455-5p suppression, CPEB1 overexpression or application of a peptide disrupting the miR-455-5p/CPEB1 interaction in CA1 of APP/PS1 mice rescued AD-like phenotypes in mice, including deficits in synaptic plasticity and memory. In conclusion, our results indicated that miRNA-455-5p/CPEB1 pathway mediated synaptic and memory deficits in Alzheimer's Disease through targeting on AMPARs, providing a potential therapeutic strategy for AD.

Running exercise protects spinophilin-immunoreactive puncta and neurons in the medial prefrontal cortex of APP/PS1 transgenic mice

The medial prefrontal cortex (mPFC) is thought to be closely associated with emotional processes, decision making, and memory. Previous studies have identified the prefrontal cortex as one of the most vulnerable brain regions in Alzheimer's disease (AD). Running exercise has widely been recognized as a simple and effective method of physical activity that enhances brain function and slows the progression of AD. However, the effect of exercise on the mPFC of AD is unclear. To address these issues, we investigated the effects of 4 months of exercise on the numbers of spinophilin-immunoreactive puncta and neurons in the mPFC of 12-month-old APPswe/PSEN1dE9 (APP/PS1) transgenic AD model mice using stereological methods. The spatial learning and memory abilities of mice were tested using the Morris water maze. Four months of running exercise delayed declines in spatial learning and memory abilities. The stereological results showed significantly lower numbers of spinophilin-immunoreactive puncta and neurons in the mPFC of APP/PS1 mice than in the wild-type control group. The numbers of spinophilin-immunoreactive puncta and neurons in the mPFC of running APP/PS1 mice were significantly greater than those in the APP/PS1 control mice. In addition, running-induced improvements in spatial learning and memory were significantly associated with running-induced increases in spinophilin-immunoreactive puncta and neurons numbers in the mPFC. Running exercise could delay the loss of spinophilin-immunoreactive puncta and neurons in the mPFC of APP/PS1 mice. This finding might provide an important structural basis for exercise-induced improvements in the spatial learning and memory abilities of individuals with AD.

Three-dimensional analysis of synaptic organization in the hippocampal CA1 field in Alzheimer's disease

Alzheimer's disease is the most common form of dementia, characterized by a persistent and progressive impairment of cognitive functions. Alzheimer's disease is typically associated with extracellular deposits of amyloid-β peptide and accumulation of abnormally phosphorylated tau protein inside neurons (amyloid-β and neurofibrillary pathologies). It has been proposed that these pathologies cause neuronal degeneration and synaptic alterations, which are thought to constitute the major neurobiological basis of cognitive dysfunction in Alzheimer's disease. The hippocampal formation is especially vulnerable in the early stages of Alzheimer's disease. However, the vast majority of electron microscopy studies have been performed in animal models. In the present study, we performed an extensive 3D study of the neuropil to investigate the synaptic organization in the stratum pyramidale and radiatum in the CA1 field of Alzheimer's disease cases with different stages of the disease, using focused ion beam/scanning electron microscopy (FIB/SEM). In cases with early stages of Alzheimer's disease, the synapse morphology looks normal and we observed no significant differences between control and Alzheimer's disease cases regarding the synaptic density, the ratio of excitatory and inhibitory synapses, or the spatial distribution of synapses. However, differences in the distribution of postsynaptic targets and synaptic shapes were found. Furthermore, a lower proportion of larger excitatory synapses in both strata were found in Alzheimer's disease cases. Individuals in late stages of the disease suffered the most severe synaptic alterations, including a decrease in synaptic density and morphological alterations of the remaining synapses. Since Alzheimer's disease cases show cortical atrophy, our data indicate a reduction in the total number (but not the density) of synapses at early stages of the disease, with this reduction being much more accentuated in subjects with late stages of Alzheimer's disease. The observed synaptic alterations may represent a structural basis for the progressive learning and memory dysfunctions seen in Alzheimer's disease cases.

Dysregulated gene-associated biomarkers for Alzheimer's disease and aging

Alzheimer’s disease (AD), the most common type of dementia, is a neurodegenerative disorder with a hidden onset, including difficult early detection and diagnosis. Nevertheless, the new crucial biomarkers for the diagnosis and pathogenesis of AD need to be explored further. Here, the common differentially expressed genes (DEGs) were identified through a comprehensive analysis of gene expression profiles from the Gene Expression Omnibus (GEO) database. Furthermore, Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway analyses revealed that these DEGs were mainly associated with biological processes, cellular components, and molecular functions, which are involved in multiple cellular functions. Next, we found that 9 of the 24 genes showed the same regulatory changes in the blood of patients with AD compared to those in the GEO database, and 2 of the 24 genes showed a significant correlation with Montreal Cognitive Assessment scores. Finally, we determined that mice with AD and elderly mice had the same regulatory changes in the identified DEGs in both the blood and hippocampus. Our study identified several potential core biomarkers of AD and aging, which could contribute to the early detection, differential diagnosis, treatment, and pathological analysis of AD.

Neuroligin-1 in brain and CSF of neurodegenerative disorders: investigation for synaptic biomarkers

Synaptic pathology is a central event in Alzheimer’s disease (AD) and other neurodegenerative conditions, and investigation of synaptic proteins can provide valuable tools to follow synaptic dysfunction and loss in these diseases. Neuroligin-1 (Nlgn1) is a postsynaptic cell adhesion protein, important for synapse stabilization and formation. Nlgn1 has been connected to cognitive disorders, and specifically to AD, as target of the synaptotoxic effect of amyloid-β (Aβ) oligomers and Aβ fibrils. To address changes in Nlgn1 expression in human brain, brain regions in different neurological disorders were examined by Western blot and mass spectrometry. Brain specimens from AD (n = 23), progressive supranuclear palsy (PSP, n = 11), corticobasal degeneration (CBD, n = 10), and Pick’s disease (PiD, n = 9) were included. Additionally, cerebrospinal fluid (CSF) samples of AD patients (n = 43) and non-demented controls (n = 42) were analysed. We found decreased levels of Nlgn1 in temporal and parietal cortex (~ 50–60% reductions) in AD brains compared with controls. In frontal grey matter the reduction was not seen for AD patients; however, in the same region, marked reduction was found for PiD (~ 77%), CBD (~ 66%) and to a lesser extent for PSP (~ 43%), which could clearly separate these tauopathies from controls. The Nlgn1 level was reduced in CSF from AD patients compared to controls, but with considerable overlap. The dramatic reduction of Nlgn1 seen in the brain extracts of tauopathies warrants further investigation regarding the potential use of Nlgn1 as a biomarker for these neurodegenerative diseases.

Fibroblast Growth Factor 9 Stimulates Neuronal Length Through NF-kB Signaling in Striatal Cell Huntington's Disease Models

Proper development of neuronal cells is important for brain functions, and impairment of neuronal development may lead to neuronal disorders, implying that improvement in neuronal development may be a therapeutic direction for these diseases. Huntington's disease (HD) is a neurodegenerative disease characterized by impairment of neuronal structures, ultimately leading to neuronal death and dysfunctions of the central nervous system. Based on previous studies, fibroblast growth factor 9 (FGF9) may provide neuroprotective functions in HD, and FGFs may enhance neuronal development and neurite outgrowth. However, whether FGF9 can provide neuronal protective functions through improvement of neuronal morphology in HD is still unclear. Here, we study the effects of FGF9 on neuronal length in HD and attempt to understand the related working mechanisms. Taking advantage of striatal cell lines from HD knock-in mice, we found that FGF9 increases total neuronal length and upregulates several structural and synaptic proteins under HD conditions. In addition, activation of nuclear factor kappa B (NF-kB) signaling by FGF9 was observed to be significant in HD cells, and blockage of NF-kB leads to suppression of these structural and synaptic proteins induced by FGF9, suggesting the involvement of NF-kB signaling in these effects of FGF9. Taken these results together, FGF9 may enhance total neuronal length through upregulation of NF-kB signaling, and this mechanism could serve as an important mechanism for neuroprotective functions of FGF9 in HD.

Synaptic basis of Alzheimer's disease: Focus on synaptic amyloid beta, P-tau and mitochondria

Alzheimer's disease (AD) is a progressive and synaptic failure disease. Despite the many years of research, AD still harbors many secrets. As more of the world's population grows older, researchers are striving to find greater information on disease progression and pathogenesis. Identifying and treating the markers of this disease, or better yet, preventing it all together, are the hopes of those investing in this field of study. Several years of research revealed that synaptic pathology and mitochondrial oxidative damage are early events in disease progression. Loss of synapses and synaptic damage are the best correlates of cognitive deficits found in AD patients. As the disease progresses, there are significant changes at the synapse. These changes can both shed greater light onto the progression of the disease and serve as markers and therapeutic targets. This article addresses the mechanisms of synaptic action, mitochondrial regulation/dysregulation, resulting synaptic changes caused by amyloid beta and phosphorylated tau in AD progression. This article also highlights recent developments of risk factors, genetics and ApoE4 involvement, factors related to synaptic damage and loss, mislocalization of amyloid beta and phosphorylated tau, mitophagy, microglial activation and synapse-based therapies in AD. Furthermore, impairments in LTD and reactivation of microglia are discussed.

PDE inhibition in distinct cell types to reclaim the balance of synaptic plasticity

Synapses are the functional units of the brain. They form specific contact points that drive neuronal communication and are highly plastic in their strength, density, and shape. A carefully orchestrated balance between synaptogenesis and synaptic pruning, i.e., the elimination of weak or redundant synapses, ensures adequate synaptic density. An imbalance between these two processes lies at the basis of multiple neuropathologies. Recent evidence has highlighted the importance of glia-neuron interactions in the synaptic unit, emphasized by glial phagocytosis of synapses and local excretion of inflammatory mediators. These findings warrant a closer look into the molecular basis of cell-signaling pathways in the different brain cells that are related to synaptic plasticity. In neurons, intracellular second messengers, such as cyclic guanosine or adenosine monophosphate (cGMP and cAMP, respectively), are known mediators of synaptic homeostasis and plasticity. Increased levels of these second messengers in glial cells slow down inflammation and neurodegenerative processes. These multi-faceted effects provide the opportunity to counteract excessive synapse loss by targeting cGMP and cAMP pathways in multiple cell types. Phosphodiesterases (PDEs) are specialized degraders of these second messengers, rendering them attractive targets to combat the detrimental effects of neurological disorders. Cellular and subcellular compartmentalization of the specific isoforms of PDEs leads to divergent downstream effects for these enzymes in the various central nervous system resident cell types. This review provides a detailed overview on the role of PDEs and their inhibition in the context of glia-neuron interactions in different neuropathologies characterized by synapse loss. In doing so, it provides a framework to support future research towards finding combinational therapy for specific neuropathologies.

Synaptic Loss in Alzheimer's Disease: Mechanistic Insights Provided by Two-Photon in vivo Imaging of Transgenic Mouse Models

Synapse loss is the strongest correlate for cognitive decline in Alzheimer's disease. The mechanisms underlying synapse loss have been extensively investigated using mouse models expressing genes with human familial Alzheimer's disease mutations. In this review, we summarize how multiphoton in vivo imaging has improved our understanding of synapse loss mechanisms associated with excessive amyloid in the living animal brain. We also discuss evidence obtained from these imaging studies for the role of cell-intrinsic calcium dyshomeostasis and cell-extrinsic activities of microglia, which are the immune cells of the brain, in mediating synapse loss.

PKA-Dependent Membrane Surface Recruitment of CI-AMPARs Is Crucial for BCP-Mediated Protection Against Post-acute Ischemic Stroke Cognitive Impairment

Post-acute ischemic stroke cognitive impairment frequently occurs and seriously affects patients daily activities. Recruitment of GluA2-containing Ca²⁺-impermeable AMPA receptors (CI-AMPARs) to hippocampal synaptic membrane surfaces was shown to trigger synaptic plasticity. Currently, the effect of CI-AMPAR trafficking on acute ischemic stroke remains poorly understood. β-Caryophyllene (BCP) has been shown to ameliorate cognitive impairment. However, the mechanism has not been characterized. In this study, a 60-min temporary middle cerebral artery occlusion (MCAO) model was established to simulate the pathology of acute ischemic stroke. BCP reduced neurologic deficits, cerebral infarct volume, and pathological damage in MCAO mice and caused CI-AMPARs to translocate to synaptic membranes in the hippocampus; surface expression of CI-AMPARs was also decreased in MCAO mice. Furthermore, this study also showed that BCP treatment significantly activated the cAMP/PKA pathway, which is consistent with the synaptic membrane expression of CI-AMPARs. To better understand the underlying mechanisms, the PKA inhibitor H-89 was used to study the role of BCP in MCAO mice. Interestingly, H-89 treatment significantly disrupted the BCP-mediated facilitation of CI-AMPAR translocation to the synaptic membrane surface and substantially attenuated BCP-induced protection against acute ischemic stroke. Additionally, inhibition the cAMP/PKA pathway not only reduced BCP-induced inhibition of AMPAR-mediated excitatory postsynaptic currents in the hippocampal CA1 region but also decreased the effect of BCP-mediated protection against post-acute ischemic stroke cognitive impairment. Taken together, these data indicate that PKA-dependent synaptic membrane surface recruitment of CI-AMPARs is crucial for the neuroprotective effect of BCP against acute ischemic stroke and protection against post-acute ischemic stroke cognitive impairment.

Insulin Resistance at the Crossroad of Alzheimer Disease Pathology: A Review

Insulin plays a major neuroprotective and trophic function for cerebral cell population, thus countering apoptosis, beta-amyloid toxicity, and oxidative stress; favoring neuronal survival; and enhancing memory and learning processes. Insulin resistance and impaired cerebral glucose metabolism are invariantly reported in Alzheimer's disease (AD) and other neurodegenerative processes. AD is a fatal neurodegenerative disorder in which progressive glucose hypometabolism parallels to cognitive impairment. Although AD may appear and progress in virtue of multifactorial nosogenic ingredients, multiple interperpetuative and interconnected vicious circles appear to drive disease pathophysiology. The disease is primarily a metabolic/energetic disorder in which amyloid accumulation may appear as a by-product of more proximal events, especially in the late-onset form. As a bridge between AD and type 2 diabetes, activation of c-Jun N-terminal kinase (JNK) pathway with the ensued serine phosphorylation of the insulin response substrate (IRS)-1/2 may be at the crossroads of insulin resistance and its subsequent dysmetabolic consequences. Central insulin axis bankruptcy translates in neuronal vulnerability and demise. As a link in the chain of pathogenic vicious circles, mitochondrial dysfunction, oxidative stress, and peripheral/central immune-inflammation are increasingly advocated as major pathology drivers. Pharmacological interventions addressed to preserve insulin axis physiology, mitochondrial biogenesis-integral functionality, and mitophagy of diseased organelles may attenuate the adjacent spillover of free radicals that further perpetuate mitochondrial damages and catalyze inflammation. Central and/or peripheral inflammation may account for a local flood of proinflammatory cytokines that along with astrogliosis amplify insulin resistance, mitochondrial dysfunction, and oxidative stress. All these elements are endogenous stressor, pro-senescent factors that contribute to JNK activation. Taken together, these evidences incite to identify novel multi-mechanistic approaches to succeed in ameliorating this pandemic affliction.

Connectome Signatures of Hyperexcitation in Cognitively Intact Middle-Aged Female APOE-ε4 Carriers

Synaptic dysfunction is hypothesized to be one of the earliest brain changes in Alzheimer's disease, leading to "hyperexcitability" in neuronal circuits. In this study, we evaluated a novel hyperexcitation indicator (HI) for each brain region using a hybrid resting-state structural connectome to probe connectome-level excitation-inhibition balance in cognitively intact middle-aged apolipoprotein E (APOE) ε4 carriers with noncarriers (16 male/22 female in each group). Regression with three-way interactions (sex, age, and APOE-ε4 carrier status) to assess the effect of APOE-ε4 on excitation-inhibition balance within each sex and across an age range of 40-60 years yielded a significant shift toward higher HI in female carriers compared with noncarriers (beginning at 50 years). Hyperexcitation was insignificant in the male group. Further, in female carriers the degree of hyperexcitation exhibited significant positive correlation with working memory performance (evaluated via a virtual Morris Water task) in three regions: the left pars triangularis, left hippocampus, and left isthmus of cingulate gyrus. Increased excitation of memory-related circuits may be evidence of compensatory recruitment of neuronal resources for memory-focused activities. In sum, our results are consistent with known Alzheimer's disease sex differences; in that female APOE-ε4 carriers have globally disrupted excitation-inhibition balance that may confer greater vulnerability to disease neuropathology.

Neuronal Plasticity: Neuronal Organization is Associated with Neurological Disorders

Stimuli from stressful events, attention in the classroom, and many other experiences affect the functionality of the brain by changing the structure or reorganizing the connections between neurons and their communication. Modification of the synaptic transmission is a vital mechanism for generating neural activity via internal or external stimuli. Neuronal plasticity is an important driving force in neuroscience research, as it is the basic process underlying learning and memory and is involved in many other functions including brain development and homeostasis, sensorial training, and recovery from brain injury. Indeed, neuronal plasticity has been explored in numerous studies, but it is still not clear how neuronal plasticity affects the physiology and morphology of the brain. Thus, unraveling the molecular mechanisms of neuronal plasticity is essential for understanding the operation of brain functions. In this timeline review, we discuss the molecular mechanisms underlying different forms of synaptic plasticity and their association with neurodegenerative/neurological disorders as a consequence of alterations in neuronal plasticity.

Early-Occurring Dendritic Spines Alterations in Mouse Models of Alzheimer's Disease Inform on Primary Causes of Neurodegeneration

The consensus that synaptic failure is the earliest cause of cognitive deterioration in Alzheimer’s disease (AD) has initially led to investigate structural (dendritic spines) and physiological (LTP) synaptic dysfunctions in mouse models of AD with established cognitive alterations. The challenge is now to track down ultra-early alterations in spines to uncover causes rather than disease’s symptoms. This review article pinpoints dysregulations of the postsynaptic density (PSD) protein network which alter the morphology and function of spines in pre- and early- symptomatic hAPP mouse models of AD, and, hence, inform on primary causes of neurodegeneration.

Acetylation of AMPA Receptors Regulates Receptor Trafficking and Rescues Memory Deficits in Alzheimer's Disease

In Alzheimer's disease (AD), decreases in the amount and synaptic localization of AMPA receptors (AMPARs) result in weakened synaptic activity and dysfunction in synaptic plasticity, leading to impairments in cognitive functions. We have previously found that AMPARs are subject to lysine acetylation, resulting in higher AMPAR stability and protein accumulation. Here we report that AMPAR acetylation was significantly reduced in AD and neurons with Aβ incubation. We identified p300 as the acetyltransferase responsible for AMPAR acetylation and found that enhancing GluA1 acetylation ameliorated Aβ-induced reductions in total and cell-surface AMPARs. Importantly, expression of acetylation mimetic GluA1 (GluA1-4KQ) in APP/PS1 mice rescued impairments in synaptic plasticity and memory. These findings indicate that Aβ-induced reduction in AMPAR acetylation and stability contributes to synaptopathy and memory deficiency in AD, suggesting that AMPAR acetylation may be an effective molecular target for AD therapeutics.

Fluid Biomarkers for Synaptic Dysfunction and Loss

Synapses are the site for brain communication where information is transmitted between neurons and stored for memory formation. Synaptic degeneration is a global and early pathogenic event in neurodegenerative disorders with reduced levels of pre- and postsynaptic proteins being recognized as a core feature of Alzheimer's disease (AD) pathophysiology. Together with AD, other neurodegenerative and neurodevelopmental disorders show altered synaptic homeostasis as an important pathogenic event, and due to that, they are commonly referred to as synaptopathies. The exact mechanisms of synapse dysfunction in the different diseases are not well understood and their study would help understanding the pathogenic role of synaptic degeneration, as well as differences and commonalities among them and highlight candidate synaptic biomarkers for specific disorders. The assessment of synaptic proteins in cerebrospinal fluid (CSF), which can reflect synaptic dysfunction in patients with cognitive disorders, is a keen area of interest. Substantial research efforts are now directed toward the investigation of CSF synaptic pathology to improve the diagnosis of neurodegenerative disorders at an early stage as well as to monitor clinical progression. In this review, we will first summarize the pathological events that lead to synapse loss and then discuss the available data on established (eg, neurogranin, SNAP-25, synaptotagmin-1, GAP-43, and α-syn) and emerging (eg, synaptic vesicle glycoprotein 2A and neuronal pentraxins) CSF biomarkers for synapse dysfunction, while highlighting possible utilities, disease specificity, and technical challenges for their detection.

Curdlan Prevents the Cognitive Deficits Induced by a High-Fat Diet in Mice via the Gut-Brain Axis

A high-fat (HF) diet is a major predisposing factor of neuroinflammation and cognitive deficits. Recently, changes in the gut microbiota have been associated with neuroinflammation and cognitive impairment, through the gut-brain axis. Curdlan, a bacterial polysaccharide widely used as food additive, has the potential to alter the composition of the microbiota and improve the gut-brain axis. However, the effects of curdlan against HF diet-induced neuroinflammation and cognitive decline have not been investigated. We aimed to evaluate the neuroprotective effect and mechanism of dietary curdlan supplementation against the obesity-associated cognitive decline observed in mice fed a HF diet. C57Bl/6J male mice were fed with either a control, HF, or HF with curdlan supplementation diets for 7 days (acute) or 15 weeks (chronic). We found that acute curdlan supplementation prevented the gut microbial composition shift induced by HF diet. Chronic curdlan supplementation prevented cognitive declines induced by HF diet. In addition, curdlan protected against the HF diet-induced abnormities in colonic permeability, hyperendotoxemia, and colonic inflammation. Furthermore, in the prefrontal cortex (PFC) and hippocampus, curdlan mitigated microgliosis, neuroinflammation, and synaptic impairments induced by a HF diet. Thus, curdlan—as a food additive and prebiotic—can prevent cognitive deficits induced by HF diet via the colon-brain axis.

Supplement of microbiota-accessible carbohydrates prevents neuroinflammation and cognitive decline by improving the gut microbiota-brain axis in diet-induced obese mice

Background

Western pattern diets induce neuroinflammation and impair cognitive behavior in humans and animals. Neuroinflammation and cognitive impairment have been associated with microbiota dysbiosis, through the gut-brain axis. Furthermore, microbiota-accessible carbohydrates (MACs) found in dietary fiber are important in shaping the microbial ecosystem and have the potential to improve the gut-brain-axis. However, the effects of MACs on neuroinflammation and cognition in an obese condition have not yet been investigated. The present study aimed to evaluate the effect of MACs on the microbiota-gut-brain axis and cognitive function in obese mice induced by a high-fat and fiber deficient (HF-FD) diet.

Methods

C57Bl/6 J male mice were fed with either a control HF-FD or a HF-MAC diet for 15 weeks. Moreover, an additional group was fed with the HF-MAC diet in combination with an antibiotic cocktail (HF-MAC + AB). Following the 15-week treatment, cognitive behavior was investigated; blood, cecum content, colon, and brain samples were collected to determine metabolic parameters, endotoxin, gut microbiota, colon, and brain pathology.

Results

We report MACs supplementation prevented HF-FD-induced cognitive impairment in nesting building and temporal order memory tests. MACs prevented gut microbiota dysbiosis, including increasing richness, α-diversity and composition shift, especially in Bacteroidetes and its lower taxa. Furthermore, MACs increased colonic mucus thickness, tight junction protein expression, reduced endotoxemia, and decreased colonic and systemic inflammation. In the hippocampus, MACs suppressed HF-FD-induced neuroglia activation and inflammation, improved insulin IRS-pAKT-pGSK3β-pTau synapse signaling, in addition to the synaptic ultrastructure and associated proteins. Furthermore, MACs’ effects on improving colon–cognitive parameters were eliminated by wide spectrum antibiotic microbiota ablation.

Conclusions

These results suggest that MACs improve cognitive impairments via the gut microbiota-brain axis induced by the consumption of an HF-FD. Supplemental MACs to combat obesity-related gut and brain dysfunction offer a promising approach to prevent neurodegenerative diseases associated with Westernized dietary patterns and obesity.

Collapsin Response Mediator Proteins: Novel Targets for Alzheimer's Disease

Numerous experimental and postmortem studies have increasingly reported dystrophic axons and dendrites, and alterations of dendritic spine morphology and density in the hippocampus as prominent changes in the early stages of Alzheimer's disease (AD). Furthermore, these alterations tend to correlate well with the progressive cognitive decline observed in AD. For these reasons, and because these neurite structures have a capacity to re-grow, re-establish lost connections, and are critical for learning and memory, there is compelling evidence to suggest that therapeutic interventions aimed at preventing their degradation or promoting their regrowth may hold tremendous promise in preventing the progression of AD. In this regard, collapsin response mediator proteins (CRMPs), a family of phosphoproteins playing a major role in axon guidance and dendritic growth, are especially interesting. The roles these proteins play in neurons and immune cells are reviewed here.

Disease-associated mutations in Niemann-Pick type C1 alter ER calcium signaling and neuronal plasticity

Niemann-Pick type C1 (NPC1) protein is essential for the transport of externally derived cholesterol from lysosomes to other organelles. Deficiency of NPC1 underlies the progressive NPC1 neurodegenerative disorder. Currently, there are no curative therapies for this fatal disease. Given the Ca2+ hypothesis of neurodegeneration, which posits that altered Ca2+ dynamics contribute to neuropathology, we tested if disease mutations in NPC1 alter Ca2+ signaling and neuronal plasticity. We determine that NPC1 inhibition or disease mutations potentiate store-operated Ca2+ entry (SOCE) due to a presenilin 1 (PSEN1)-dependent reduction in ER Ca2+ levels alongside elevated expression of the molecular SOCE components ORAI1 and STIM1. Associated with this dysfunctional Ca2+ signaling is destabilization of neuronal dendritic spines. Knockdown of PSEN1 or inhibition of the SREBP pathway restores Ca2+ homeostasis, corrects differential protein expression, reduces cholesterol accumulation, and rescues spine density. These findings highlight lysosomes as a crucial signaling platform responsible for tuning ER Ca2+ signaling, SOCE, and synaptic architecture in health and disease.

PI31 Is an Adaptor Protein for Proteasome Transport in Axons and Required for Synaptic Development

Protein degradation by the ubiquitin-proteasome system is critical for neuronal function. Neurons utilize microtubule-dependent molecular motors to allocate proteasomes to synapses, but how proteasomes are coupled to motors and how this is regulated to meet changing demand for protein breakdown remain largely unknown. We show that the conserved proteasome-binding protein PI31 serves as an adaptor to couple proteasomes with dynein light chain proteins (DYNLL1/2). The inactivation of PI31 inhibited proteasome motility in axons and disrupted synaptic proteostasis, structure, and function. Moreover, phosphorylation of PI31 by p38 MAPK enhanced binding to DYNLL1/2 and promoted the directional movement of proteasomes in axons, suggesting a mechanism to regulate loading of proteasomes onto motors. Inactivation of PI31 in mouse neurons attenuated proteasome movement in axons, indicating this process is conserved. Because mutations affecting PI31 activity are associated with human neurodegenerative diseases, impairment of PI31-mediated axonal transport of proteasomes may contribute to these disorders.

Mitochondrial Function, Dynamics, and Permeability Transition: A Complex Love Triangle as A Possible Target for the Treatment of Brain Aging and Alzheimer's Disease

Because of the failure of all amyloid-β directed treatment strategies for Alzheimer's disease (AD), the concept of mitochondrial dysfunction as a major pathomechanism of the cognitive decline in aging and AD has received substantial support. Accordingly, improving mitochondrial function as an alternative strategy for new drug development became of increasing interest and many different compounds have been identified which improve mitochondrial function in preclinical in vitro and in vivo experiments. However, very few if any have been investigated in clinical trials, representing a major drawback of the mitochondria directed drug development. To overcome these problems, we used a top-down approach by investigating several older antidementia drugs with clinical evidence of therapeutic efficacy. These include EGb761® (standardized ginkgo biloba extract), piracetam, and Dimebon. All improve experimentally many aspects of mitochondrial dysfunction including mitochondrial dynamics and also improve cognition and impaired neuronal plasticity, the functionally most relevant consequences of mitochondrial dysfunction. All partially inhibit opening events of the mitochondrial permeability transition pore (mPTP) which previously has mainly been discussed as a mechanism relevant for the induction of apoptosis. However, as more recent work suggests the mPTP as a master regulator of many mitochondrial functions, our data suggest the mPTP as a possible relevant drug target within the love triangle between mPTP regulation, mitochondrial dynamics, and mitochondrial function including regulation of neuronal plasticity. Drugs interfering with mPTP function will improve not only mitochondrial impairment in aging and AD but also will have beneficial effects on impaired neuronal plasticity, the pathomechanism which correlates best with functional deficits (cognition, behavior) in aging and AD.