Plaque-independent disruption of neural circuits in Alzheimer's disease mouse models

Rodent Models of Alzheimer's Disease: Past Misconceptions and Future Prospects

Alzheimer's disease (AD) is a progressive neurodegenerative disease with no effective treatments, not least due to the lack of authentic animal models. Typically, rodent models recapitulate the effects but not causes of AD, such as cholinergic neuron loss: lesioning of cholinergic neurons mimics the cognitive decline reminiscent of AD but not its neuropathology. Alternative models rely on the overexpression of genes associated with familial AD, such as amyloid precursor protein, or have genetically amplified expression of mutant tau. Yet transgenic rodent models poorly replicate the neuropathogenesis and protein overexpression patterns of sporadic AD. Seeding rodents with amyloid or tau facilitates the formation of these pathologies but cannot account for their initial accumulation. Intracerebral infusion of proinflammatory agents offer an alternative model, but these fail to replicate the cause of AD. A novel model is therefore needed, perhaps similar to those used for Parkinson's disease, namely adult wildtype rodents with neuron-specific (dopaminergic) lesions within the same vulnerable brainstem nuclei, 'the isodendritic core', which are the first to degenerate in AD. Site-selective targeting of these nuclei in adult rodents may recapitulate the initial neurodegenerative processes in AD to faithfully mimic its pathogenesis and progression, ultimately leading to presymptomatic biomarkers and preventative therapies.

Dopamine neuron degeneration in the Ventral Tegmental Area causes hippocampal hyperexcitability in experimental Alzheimer's Disease

Early and progressive dysfunctions of the dopaminergic system from the Ventral Tegmental Area (VTA) have been described in Alzheimer's Disease (AD). During the long pre-symptomatic phase, alterations in the function of Parvalbumin interneurons (PV-INs) are also observed, resulting in cortical hyperexcitability represented by subclinical epilepsy and aberrant gamma-oscillations. However, it is unknown whether the dopaminergic deficits contribute to brain hyperexcitability in AD. Here, using the Tg2576 mouse model of AD, we prove that reduced hippocampal dopaminergic innervation, due to VTA dopamine neuron degeneration, impairs PV-IN firing and gamma-waves, weakens the inhibition of pyramidal neurons and induces hippocampal hyperexcitability via lower D2-receptor-mediated activation of the CREB-pathway. These alterations coincide with reduced PV-IN numbers and Perineuronal Net density. Importantly, L-DOPA and the selective D2-receptor agonist quinpirole rescue p-CREB levels and improve the PV-IN-mediated inhibition, thus reducing hyperexcitability. Moreover, similarly to quinpirole, sumanirole - another D2-receptor agonist and a known anticonvulsant - not only increases p-CREB levels in PV-INs but also restores gamma-oscillations in Tg2576 mice. Conversely, blocking the dopaminergic transmission with sulpiride (a D2-like receptor antagonist) in WT mice reduces p-CREB levels in PV-INs, mimicking what occurs in Tg2576. Overall, these findings support the hypothesis that the VTA dopaminergic system integrity plays a key role in hippocampal PV-IN function and survival, disclosing a relevant contribution of the reduced dopaminergic tone to aberrant gamma-waves, hippocampal hyperexcitability and epileptiform activity in early AD.

Differential disruptions in population coding along the dorsal-ventral axis of CA1 in the APP/PS1 mouse model of Aβ pathology

Alzheimer's Disease (AD) is characterized by a range of behavioral alterations, including memory loss and psychiatric symptoms. While there is evidence that molecular pathologies, such as amyloid beta (Aβ), contribute to AD, it remains unclear how this histopathology gives rise to such disparate behavioral deficits. One hypothesis is that Aβ exerts differential effects on neuronal circuits across brain regions, depending on the neurophysiology and connectivity of different areas. To test this, we recorded from large neuronal populations in dorsal CA1 (dCA1) and ventral CA1 (vCA1), two hippocampal areas known to be structurally and functionally diverse, in the APP/PS1 mouse model of amyloidosis. Despite similar levels of Aβ pathology, dCA1 and vCA1 showed distinct disruptions in neuronal population activity as animals navigated a virtual reality environment. In dCA1, pairwise correlations and entropy, a measure of the diversity of activity patterns, were decreased in APP/PS1 mice relative to age-matched C57BL/6 controls. However, in vCA1, APP/PS1 mice had increased pair-wise correlations and entropy as compared to age matched controls. Finally, using maximum entropy models, we connected the microscopic features of population activity (correlations) to the macroscopic features of the population code (entropy). We found that the models' performance increased in predicting dCA1 activity, but decreased in predicting vCA1 activity, in APP/PS1 mice relative to the controls. Taken together, we found that Aβ exerts distinct effects across different hippocampal regions, suggesting that the various behavioral deficits of AD may reflect underlying heterogeneities in neuronal circuits and the different disruptions that Aβ pathology causes in those circuits.

Behavioral and Metabolic Effects of ABCG4 KO in the APPswe,Ind (J9) Mouse Model of Alzheimer's Disease

The pathogenesis of Alzheimer's disease (AD) is complex and involves an imbalance between production and clearance of amyloid-ß peptides (Aß), resulting in accumulation of Aß in senile plaques. Hypercholesterolemia is a major risk factor for developing AD, with cholesterol shown to accumulate in senile plaques and increase production of Aß. ABCG4 is a member of the ATP-binding cassette transporters predominantly expressed in the CNS and has been suggested to play a role in cholesterol and Aß efflux from the brain. In this study, we bred Abcg4 knockout (KO) with the APPSwe,Ind (J9) mouse model of AD to test the hypothesis that loss of Abcg4 would exacerbate the AD phenotype. Unexpectedly, no differences were observed in novel object recognition (NOR) and novel object placement (NOP) behavioral tests, or on histologic examinations of brain tissues for senile plaque numbers. Furthermore, clearance of radiolabeled Aß from the brains did not differ between Abcg4 KO and control mice. Metabolic testing by indirect calorimetry, glucose tolerance test (GTT), and insulin tolerance test (ITT) were also mostly similar between groups with only a few mild metabolic differences noted. Overall, these data suggest that the loss of ABCG4 did not exacerbate the AD phenotype.

Performance of SOBA-AD blood test in discriminating Alzheimer's disease patients from cognitively unimpaired controls in two independent cohorts

Amyloid-beta (Aβ) toxic oligomers are critical early players in the molecular pathology of Alzheimer's disease (AD). We have developed a Soluble Oligomer Binding Assay (SOBA-AD) for detection of these Aβ oligomers that contain α-sheet secondary structure that discriminates plasma samples from patients on the AD continuum from non-AD controls. We tested 265 plasma samples from two independent cohorts to investigate the performance of SOBA-AD. Testing was performed at two different sites, with different personnel, reagents, and instrumentation. Across two cohorts, SOBA-AD discriminated AD patients from cognitively unimpaired (CU) subjects with 100% sensitivity, > 95% specificity, and > 98% area under the curve (AUC) (95% CI 0.95-1.00). A SOBA-AD positive readout, reflecting α-sheet toxic oligomer burden, was found in AD patients, and not in controls, providing separation of the two populations, aside from 5 SOBA-AD positive controls. Based on an earlier SOBA-AD study, the Aβ oligomers detected in these CU subjects may represent preclinical cases of AD. The results presented here support the value of SOBA-AD as a promising blood-based tool for the detection and confirmation of AD.

Dynamic neuroinflammatory profiles predict Alzheimer's disease pathology in microglia-containing cerebral organoids

Neuroinflammation and the underlying dysregulated immune responses of microglia actively contribute to the progression and, likely, the initiation of Alzheimer's disease (AD). Fine-tuned therapeutic modulation of immune dysfunction to ameliorate disease cannot be achieved without the characterization of diverse microglial states that initiate unique, and sometimes contradictory, immune responses that evolve over time in chronic inflammatory environments. Because of the functional differences between human and murine microglia, untangling distinct, disease-relevant reactive states and their corresponding effects on pathology or neuronal health may not be possible without the use of human cells. In order to profile shifting microglial states in early AD and identify microglia-specific drivers of disease, we differentiated human induced pluripotent stem cells (iPSCs) carrying a familial AD PSEN2 mutation or its isogenic control into cerebral organoids and quantified the changes in cytokine concentrations over time with Luminex XMAP technology. We used partial least squares (PLS) modeling to build cytokine signatures predictive of disease and age to identify key differential patterns of cytokine expression that inform the overall organoid immune milieu and quantified the corresponding changes in protein pathology. AD organoids exhibited an overall reduction in cytokine secretion after an initial amplified immune response. We demonstrate that reduced synapse density observed in the AD organoids is prevented with microglial depletion. Crucially, these differential effects of dysregulated immune signaling occurred without the accumulation of pathological proteins. In this study, we used microglia-containing AD organoids to quantitatively characterize an evolving immune milieu, made up of a diverse of collection of activation patterns and immune responses, to identify how a dynamic, overall neuroinflammatory state negatively impacts neuronal health and the cell-specific contribution of microglia.

GDI2 deletion alleviates neurodegeneration and memory loss in the 5xFAD mice model of Alzheimer's disease

Accumulation of insoluble deposits of amyloid β-peptide (Aβ), derived from amyloid precursor protein (APP) processing, represents one of the major pathological hallmarks of Alzheimer's disease (AD). Perturbations in APP transport and hydrolysis could lead to increased Aβ production. However, the precise mechanisms underlying APP transport remain elusive. The GDP dissociation inhibitor2 (GDI2), a crucial regulator of Rab GTPase activity and intracellular vesicle and membrane trafficking, was investigated for its impact on AD pathogenesis through neuron-specific knockout of GDI2 in 5xFAD mice. Notably, deficiency of GDI2 significantly ameliorated cognitive impairment, prevented neuronal loss in the subiculum and cortical layer V, reduced senile plaques as well as astrocyte activation in 5xFAD mice. Conversely, increased activated microglia and phagocytosis were observed in GDI2 ko mice. Further investigation revealed that GDI2 knockout led to more APP co-localized with the ER rather than the Golgi apparatus and endosomes in SH-SY5Y cells, resulting in decreased Aβ production. Collectively, these findings suggest that GDI2 may regulate Aβ production by modulating APP intracellular transport and localization dynamics. In summary, our study identifies GDI2 as a pivotal regulator governing APP transport and process implicated in AD pathology; thus highlighting its potential as an attractive pharmacological target for future drug development against AD.

Cytokine expression patterns predict suppression of vulnerable neural circuits in a mouse model of Alzheimer's disease

Alzheimer's disease is a neurodegenerative disorder characterized by progressive amyloid plaque accumulation, tau tangle formation, neuroimmune dysregulation, synapse an neuron loss, and changes in neural circuit activation that lead to cognitive decline and dementia. Early molecular and cellular disease-instigating events occur 20 or more years prior to presentation of symptoms, making them difficult to study, and for many years amyloid-β, the aggregating peptide seeding amyloid plaques, was thought to be the toxic factor responsible for cognitive deficit. However, strategies targeting amyloid-β aggregation and deposition have largely failed to produce safe and effective therapies, and amyloid plaque levels poorly correlate with cognitive outcomes. However, a role still exists for amyloid-β in the variation in an individual's immune response to early, soluble forms of aggregates, and the downstream consequences of this immune response for aberrant cellular behaviors and creation of a detrimental tissue environment that harms neuron health and causes changes in neural circuit activation. Here, we perform functional magnetic resonance imaging of awake, unanesthetized Alzheimer's disease mice to map changes in functional connectivity over the course of disease progression, in comparison to wild-type littermates. In these same individual animals, we spatiotemporally profile the immune milieu by measuring cytokines, chemokines, and growth factors across various brain regions and over the course of disease progression from pre-pathology through established cognitive deficit. We identify specific signatures of immune activation predicting hyperactivity followed by suppression of intra- and then inter-regional functional connectivity in multiple disease-relevant brain regions, following the pattern of spread of amyloid pathology.

TARGETING SOLUBLE AMYLOID-BETA OLIGOMERS WITH A NOVEL NANOBODY

The classical amyloid cascade hypothesis postulates that the aggregation of amyloid plaques and the accumulation of intracellular hyperphosphorylated Tau tangles, together, lead to profound neuronal death. However, emerging research has demonstrated that soluble amyloid-β oligomers (SAβOs) accumulate early, prior to amyloid plaque formation. SAβOs induce memory impairment and disrupt cognitive function independent of amyloid-β plaques, and even in the absence of plaque formation. This work describes the development and characterization of a novel anti-SAβO (E3) nanobody generated from an alpaca immunized with SAβO. In-vitro assays and in-vivo studies using 5XFAD mice indicate that the fluorescein (FAM)-labeled E3 nanobody recognizes both SAβOs and amyloid-β plaques. The E3 nanobody traverses across the blood-brain barrier and binds to amyloid species in the brain of 5XFAD mice. Imaging of mouse brains reveals that SAβO and amyloid-β plaques are not only different in size, shape, and morphology, but also have a distinct spatial distribution in the brain. SAβOs are associated with neurons, while amyloid plaques reside in the extracellular matrix. The results of this study demonstrate that the SAβO nanobody can serve as a diagnostic agent with potential theragnostic applications in Alzheimer's disease.

A common molecular and cellular pathway in developing Alzheimer and cancer

Globally cancer and Alzheimer's disease (AD) are two major diseases and still, there is no clearly defined molecular mechanism. There is an opposite relation between cancer and AD which are the proportion of emerging cancer was importantly slower in AD patients, whereas slow emerging AD in patients with cancer. In cancer, regulation of cell mechanisms is interrupted by an increase in cell survival and proliferation, while on the contrary, AD is related to augmented neuronal death, that may be either produced by or associated with amyloid-β (Aβ) and tau deposition. Stated that the probability that disruption of mechanisms takes part in the regulation of cell survival/death and might be implicated in both diseases. The mechanism of actions such as DNA-methylation, genetic polymorphisms, or another mechanism of actions that induce alteration in the action of drugs with significant roles in resolving the finding to repair and live or die might take part in the pathogenesis of these two ailments. The functions of miRNA, p53, Pin1, the Wnt signaling pathway, PI3 KINASE/Akt/mTOR signaling pathway GRK2 signaling pathway, and the pathophysiological role of oxidative stress are presented in this review as potential candidates which hypothetically describe inverse relations between cancer and AD. Innovative materials almost mutual mechanisms in the aetiology of cancer and AD advocates novel treatment approaches. Among these treatment strategies, the most promising use treatment such as tyrosine kinase inhibitor, nilotinib, protein kinase C, and bexarotene.

Effect of gut microbiota-derived metabolites and extracellular vesicles on neurodegenerative disease in a gut-brain axis chip

A new perspective suggests that a dynamic bidirectional communication system, often referred to as the microbiome-gut-brain axis, exists among the gut, its microbiome, and the central nervous system (CNS). This system may influence brain health and various brain-related diseases, especially in the realms of neurodevelopmental and neurodegenerative conditions. However, the exact mechanism is not yet understood. Metabolites or extracellular vesicles derived from microbes in the gut have the capacity to traverse the intestinal epithelial barrier or blood-brain barrier, gaining access to the systemic circulation. This phenomenon can initiate the physiological responses that directly or indirectly impact the CNS and its function. However, reliable and controllable tools are required to demonstrate the causal effects of gut microbial-derived substances on neurogenesis and neurodegenerative diseases. The integration of microfluidics enhances scientific research by providing advanced in vitro engineering models. In this study, we investigated the impact of microbe-derived metabolites and exosomes on neurodevelopment and neurodegenerative disorders using human induced pluripotent stem cells (iPSCs)-derived neurons in a gut-brain axis chip. While strain-specific, our findings indicate that both microbial-derived metabolites and exosomes exert the significant effects on neural growth, maturation, and synaptic plasticity. Therefore, our results suggest that metabolites and exosomes derived from microbes hold promise as potential candidates and strategies for addressing neurodevelopmental and neurodegenerative disorders.

Nr4a2 blocks oAβ-mediated synaptic plasticity dysfunction and ameliorates spatial memory deficits in the APP Sw,Ind mouse

Alzheimer's disease AD is associated with disruptions in neuronal communication, especially in brain regions crucial for learning and memory, such as the hippocampus. The amyloid hypothesis suggests that the accumulation of amyloid-beta oligomers (oAβ) contributes to synaptic dysfunction by internalisation of synaptic AMPA receptors. Recently, it has been reported that Nr4a2, a member of the Nr4a family of orphan nuclear receptors, plays a role in hippocampal synaptic plasticity by regulating BDNF and synaptic AMPA receptors. Here, we demonstrate that oAβ inhibits activity-dependent Nr4a2 activation in hippocampal neurons, indicating a potential link between oAβ and Nr4a2 down-regulation. Furthermore, we have observed a reduction in Nr4a2 protein levels in postmortem hippocampal tissue samples from early AD stages. Pharmacological activation of Nr4a2 proves effective in preventing oAβ-mediated synaptic depression in the hippocampus. Notably, Nr4a2 overexpression in the hippocampus of AD mouse models ameliorates spatial learning and memory deficits. In conclusion, the findings suggest that oAβ may contribute to early cognitive impairment in AD by blocking Nr4a2 activation, leading to synaptic dysfunction. Thus, our results further support that Nr4a2 activation is a potential therapeutic target to mitigate oAβ-induced synaptic and cognitive impairments in the early stages of Alzheimer's disease.

Localized APP expression results in progressive network dysfunction by disorganizing spike timing

Progressive cognitive decline in Alzheimer's disease could either be caused by a spreading molecular pathology or by an initially focal pathology that causes aberrant neuronal activity in a larger network. To distinguish between these possibilities, we generated a mouse model with expression of mutant human amyloid precursor protein (APP) in only hippocampal CA3 cells. We found that performance in a hippocampus-dependent memory task was impaired in young adult and aged mutant mice. In both age groups, we then recorded from the CA1 region, which receives inputs from APP-expressing CA3 cells. We observed that theta oscillation frequency in CA1 was reduced along with disrupted relative timing of principal cells. Highly localized pathology limited to the presynaptic CA3 cells is thus sufficient to cause aberrant firing patterns in postsynaptic neuronal networks, which indicates that disease progression is not only from spreading pathology but also mediated by progressively advancing physiological dysfunction.

Loss of Direct Vascular Contact to Astrocytes in the Hippocampus as an Initial Event in Alzheimer's Disease. Evidence from Patients, In Vivo and In Vitro Experimental Models

Alzheimer's disease (AD) is characterized by the accumulation of aggregated amyloid peptides in the brain parenchyma and within the walls of cerebral vessels. The hippocampus-a complex brain structure with a pivotal role in learning and memory-is implicated in this disease. However, there is limited data on vascular changes during AD pathological degeneration in this susceptible structure, which has distinctive vascular traits. Our aim was to evaluate vascular alterations in the hippocampus of AD patients and PDAPP-J20 mice-a model of AD-and to determine the impact of Aβ40 and Aβ42 on endothelial cell activation. We found a loss of physical astrocyte-endothelium interaction in the hippocampus of individuals with AD as compared to non-AD donors, along with reduced vascular density. Astrocyte-endothelial interactions and levels of the tight junction protein occludin were altered early in PDAPP-J20 mice, preceding any signs of morphological changes or disruption of the blood-brain barrier in these mice. At later stages, PDAPP-J20 mice exhibited decreased vascular density in the hippocampus and leakage of fluorescent tracers, indicating dysfunction of the vasculature and the BBB. In vitro studies showed that soluble Aβ40 exposure in human brain microvascular endothelial cells (HBMEC) was sufficient to induce NFκB translocation to the nucleus, which may be linked with an observed reduction in occludin levels. The inhibition of the membrane receptor for advanced glycation end products (RAGE) prevented these changes in HBMEC. Additional results suggest that Aβ42 indirectly affects the endothelium by inducing astrocytic factors. Furthermore, our results from human and mouse brain samples provide evidence for the crucial involvement of the hippocampal vasculature in Alzheimer's disease.

Combination Therapy with Platelet-Rich Plasma and Epidermal Neural Crest Stem Cells Increases Treatment Efficacy in Vascular Dementia

This study aimed to evaluate the efficacy and treatment mechanism of platelet-rich plasma (PRP) and neural crest-derived epidermal stem cells (ESCs) in their administration alone and combination in vascular dementia (VaD) model by two-vessel occlusion (2VO). Methods. Sixty-six rats were divided into six groups: the control, sham, 2VO + vehicle, 2VO + PRP, 2VO + ESC, and 2VO + ESC + PRP. The treated groups received 1 million cells on days 4, 14, and 21 with or without 500 µl PRP (twice a week) after 2VO. The memory performance and anxiety were evaluated by behavioral tests including open field, passive avoidance, and Morris water maze. The basal-synaptic transmission (BST) and long-term potentiation (LTP) were assessed through field-potential recordings of the CA1. The mRNA expression levels of IGF-1, TGF-β1, PSD-95, and GSk-3β were measured in the rat hippocampus by quantitative reverse transcription polymerase chain reaction. Results. The results demonstrated impaired learning, memory, and synaptic plasticity in the 2VO rats, along with a significant decrease in the expression of IGF-1, TGF-β1, PSD-95, and upregulation of GSK-3β. Treatment with ESC alone and ESC + PRP showed similar improvements in spatial memory and LTP induction, with associated upregulation of PSD-95 and downregulation of GSK-3β. However, only the ESC + PRP group showed recovery in BST. Furthermore, combination therapy was more effective than PRP monotherapy for LTP and memory. Conclusions. The transplantation of ESC showed better effects than PRP alone, and combination therapy increased the treatment efficacy with the recovery of BST. This finding may be a clue for the combination therapy of ESC and PRP for VaD.

Critical thinking of Alzheimer's transgenic mouse model: current research and future perspective

Transgenic models are useful tools for studying the pathogenesis of and drug development for Alzheimer's Disease (AD). AD models are constructed usually using overexpression or knock-in of multiple pathogenic gene mutations from familial AD. Each transgenic model has its unique behavioral and pathological features. This review summarizes the research progress of transgenic mouse models, and their progress in the unique mechanism of amyloid-β oligomers, including the first transgenic mouse model built in China based on a single gene mutation (PSEN1 V97L) found in Chinese familial AD. We further summarized the preclinical findings of drugs using the models, and their future application in exploring the upstream mechanisms and multitarget drug development in AD.

Combined use of hair follicle stem cells and CEPO (carbamylated erythropoietin)-Fc in a rat model of chronic cerebral hypoperfusion: A behavioral, electrophysiological, and molecular study

BACKGROUND

In dementia, synaptic dysfunction appears before neuronal loss. Stem cell therapy could potentially provide a promising strategy for the treatment of dementia models. The carbamylated erythropoietin fusion protein (CEPO-Fc) has shown synaptotrophic effects. This study aimed to determine the efficiency of the combined use of hair follicle stem cells (HFSC) and CEPO-Fc in the basal synaptic transmission (BST) and long-term plasticity (LTP) of chronic cerebral hypoperfusion (CCH) rats.

METHODS

We divided 64 adult rats into control, sham, CCH+vehicle, CCH+CEPO, CCH+HFSC, and CCH+HFSC+CEPO groups. The CEPO-Fc was injected three times/week for 30 days. HFSC transplantation was done on days 4, 14, and 21 after surgery. The Morris water maze test and passive avoidance were used to assess memory. BST and LTP were assessed by a field-potential recording of the CA1 region. The hippocampal mRNA expression of IGF-1, TGF-β1, β1-Catenine, NR2B, PSD-95, and GSk-3β was evaluated by quantitative RT-PCR.

RESULTS

Following combination therapy, spatial memory retention, and BST showed significant improvement relative to HFSC and CEPO-Fc groups. These effects were also confirmed by recovered mRNA expression of β1-catenin, TGF-β1, and NR2B. GSK-3β expression was downregulated in all treatment groups. The upregulated PSD-95 was identified in HFSC and combination groups compared to the vehicle group.

CONCLUSIONS

These findings indicate that the combined use of HFSC and CEPO-Fc may be more advantageous for treating memory disruption in the CCH model than CEPO-Fc or HFSC alone. This type of combination therapy may hopefully lead to a new approach to treatment for dementia.

Probing neural circuit mechanisms in Alzheimer's disease using novel technologies

The study of Alzheimer's Disease (AD) has traditionally focused on neuropathological mechanisms that has guided therapies that attenuate neuropathological features. A new direction is emerging in AD research that focuses on the progressive loss of cognitive function due to disrupted neural circuit mechanisms. Evidence from humans and animal models of AD show that dysregulated circuits initiate a cascade of pathological events that culminate in functional loss of learning, memory, and other aspects of cognition. Recent progress in single-cell, spatial, and circuit omics informs this circuit-focused approach by determining the identities, locations, and circuitry of the specific cells affected by AD. Recently developed neuroscience tools allow for precise access to cell type-specific circuitry so that their functional roles in AD-related cognitive deficits and disease progression can be tested. An integrated systems-level understanding of AD-associated neural circuit mechanisms requires new multimodal and multi-scale interrogations that longitudinally measure and/or manipulate the ensemble properties of specific molecularly-defined neuron populations first susceptible to AD. These newly developed technological and conceptual advances present new opportunities for studying and treating circuits vulnerable in AD and represent the beginning of a new era for circuit-based AD research.

Saccharomyces cerevisiae as a research tool for RNA-mediated human disease

The budding yeast, Saccharomyces cerevisiae, has been used for decades as a powerful genetic tool to study a broad spectrum of biological topics. With its ease of use, economic utility, well-studied genome, and a highly conserved proteome across eukaryotes, it has become one of the most used model organisms. Due to these advantages, it has been used to study an array of complex human diseases. From broad, complex pathological conditions such as aging and neurodegenerative disease to newer uses such as SARS-CoV-2, yeast continues to offer new insights into how cellular processes are affected by disease and how affected pathways might be targeted in therapeutic settings. At the same time, the roles of RNA and RNA-based processes have become increasingly prominent in the pathology of many of these same human diseases, and yeast has been utilized to investigate these mechanisms, from aberrant RNA-binding proteins in amyotrophic lateral sclerosis to translation regulation in cancer. Here we review some of the important insights that yeast models have yielded into the molecular pathology of complex, RNA-based human diseases. This article is categorized under: RNA in Disease and Development > RNA in Disease.

Nicotinic Acetylcholine Receptor Dysfunction in Addiction and in Some Neurodegenerative and Neuropsychiatric Diseases

The cholinergic system plays an essential role in brain development, physiology, and pathophysiology. Herein, we review how specific alterations in this system, through genetic mutations or abnormal receptor function, can lead to aberrant neural circuitry that triggers disease. The review focuses on the nicotinic acetylcholine receptor (nAChR) and its role in addiction and in neurodegenerative and neuropsychiatric diseases and epilepsy. Cholinergic dysfunction is associated with inflammatory processes mainly through the involvement of α7 nAChRs expressed in brain and in peripheral immune cells. Evidence suggests that these neuroinflammatory processes trigger and aggravate pathological states. We discuss the preclinical evidence demonstrating the therapeutic potential of nAChR ligands in Alzheimer disease, Parkinson disease, schizophrenia spectrum disorders, and in autosomal dominant sleep-related hypermotor epilepsy. PubMed and Google Scholar bibliographic databases were searched with the keywords indicated below.

Behavioral and metabolic and effects of ABCG4 KO in the APPswe,Ind (J9) mouse model of Alzheimer's disease

The pathogenesis of Alzheimer's disease (AD) is complex and involves an imbalance between production and clearance of amyloid-ß peptides (Aß), resulting in accumulation of Aß in senile plaques. Hypercholesterolemia is a major risk factor for developing AD, with cholesterol shown to accumulate in senile plaques and increase production of Aß. ABCG4 is a member of the ATP-binding cassette transporters predominantly expressed in the CNS, and has been suggested to play a role in cholesterol and Aß efflux from the brain. In this study, we bred Abcg4 knockout (KO) with the APPSwe,Ind (J9) mouse model of AD to test the hypothesis that loss of Abcg4 would exacerbate the AD phenotype. Unexpectedly, no differences were observed in Novel object recognition (NOR) and Novel object placement (NOP) behavioral tests, or on histologic examinations of brain tissues for senile plaque numbers. Furthermore, clearance of radiolabeled Aß from the brains did not differ between Abcg4 KO and control mice. Metabolic testing by indirect calorimetry, glucose tolerance test (GTT) and insulin tolerance test (ITT), were also mostly similar between groups with only a few mild metabolic differences noted. Overall these data suggest that the loss of ABCG4 did not exacerbate the AD phenotype.

c-Abl tyrosine kinase down-regulation as target for memory improvement in Alzheimer's disease

Background

Growing evidence suggests that the non-receptor tyrosine kinase, c-Abl, plays a significant role in the pathogenesis of Alzheimer's disease (AD). Here, we analyzed the effect of c-Abl on the cognitive performance decline of APPSwe/PSEN1ΔE9 (APP/PS1) mouse model for AD.

Methods

We used the conditional genetic ablation of c-Abl in the brain (c-Abl-KO) and pharmacological treatment with neurotinib, a novel allosteric c-Abl inhibitor with high brain penetrance, imbued in rodent's chow.

Results

We found that APP/PS1/c-Abl-KO mice and APP/PS1 neurotinib-fed mice had improved performance in hippocampus-dependent tasks. In the object location and Barnes-maze tests, they recognized the displaced object and learned the location of the escape hole faster than APP/PS1 mice. Also, APP/PS1 neurotinib-fed mice required fewer trials to reach the learning criterion in the memory flexibility test. Accordingly, c-Abl absence and inhibition caused fewer amyloid plaques, reduced astrogliosis, and preserved neurons in the hippocampus.

Discussion

Our results further validate c-Abl as a target for AD, and the neurotinib, a novel c-Abl inhibitor, as a suitable preclinical candidate for AD therapies.

N-glycoproteomics of brain synapses and synaptic vesicles

At mammalian neuronal synapses, synaptic vesicle (SV) glycoproteins are essential for robust neurotransmission. Asparagine (N)-linked glycosylation is required for delivery of the major SV glycoproteins synaptophysin and SV2A to SVs. Despite this key role for N-glycosylation, the molecular compositions of SV N-glycans are largely unknown. In this study, we combined organelle isolation techniques and high-resolution mass spectrometry to characterize N-glycosylation at synapses and SVs from mouse brain. Detecting over 2,500 unique glycopeptides, we found that SVs harbor a distinct population of oligomannose and highly fucosylated N-glycans. Using complementary fluorescence methods, we identify at least one highly fucosylated N-glycan enriched in SVs compared with synaptosomes. High fucosylation was characteristic of SV proteins, plasma membrane proteins, and cell adhesion molecules with key roles in synaptic function and development. Our results define the N-glycoproteome of a specialized neuronal organelle and inform timely questions in the glycobiology of synaptic pruning and neuroinflammation.

Rapamycin restores peripheral blood flow in aged mice and in mouse models of atherosclerosis and Alzheimer's disease

Peripheral artery disease (PAD), defined as reduced blood flow to the lower limbs, is a serious disorder that can lead to loss of function in the lower extremities and even loss of limbs. One of the main risk factors for PAD is age, with up to 25% of adults over the age of 55 and up to 40% over the age of 80 presenting with some form of the disease. While age is the largest risk factor for PAD, other risk factors include atherosclerosis, smoking, hypertension, and diabetes. Furthermore, previous studies have suggested that the incidence of PAD is significantly increased in patients with Alzheimer's disease (AD). Attenuation of mTOR with rapamycin significantly improves cerebral blood flow and heart function in aged rodents as well as in mouse models of atherosclerosis, atherosclerosis-driven cognitive impairment, and AD. In this study, we show that rapamycin treatment improves peripheral blood flow in aged mice and in mouse models of atherosclerosis and AD. Inhibition of mTOR with rapamycin ameliorates deficits in baseline hind paw perfusion in aged mice and restores levels of blood flow to levels indistinguishable from those of young controls. Furthermore, rapamycin treatment ameliorates peripheral blood flow deficits in mouse models of atherosclerosis and AD. These data indicate that mTOR is causally involved in the reduction of blood flow to lower limbs associated with aging, atherosclerosis, and AD-like progression in model mice. Rapamycin or other mTOR inhibitors may have potential as interventions to treat peripheral artery disease and other peripheral circulation-related conditions.

Impairments of glutamatergic synaptic transmission in Alzheimer's disease

One of the hallmarks of Alzheimer's disease (AD) is structural cell damage and neuronal death in the brains of affected individuals. As these changes are irreversible, it is important to understand their origins and precursors in order to develop treatment strategies against AD. Here, we review evidence for AD-specific impairments of glutamatergic synaptic transmission by relating evidence from human AD subjects to functional studies in animal models of AD. The emerging picture is that early in the disease, the accumulation of toxic β-amyloid aggregates, particularly dimers and low molecular weight oligomers, disrupts glutamate reuptake, which leads to its extracellular accumulation causing neuronal depolarization. This drives the hyperactivation of neurons and might facilitate neuronal damage and degeneration through glutamate neurotoxicity.

Novel CYP1B1-RMDN2 Alzheimer's disease locus identified by genome-wide association analysis of cerebral tau deposition on PET

Determining the genetic architecture of Alzheimer's disease (AD) pathologies can enhance mechanistic understanding and inform precision medicine strategies. Here, we performed a genome-wide association study of cortical tau quantified by positron emission tomography in 3,136 participants from 12 independent studies. The CYP1B1-RMDN2 locus was associated with tau deposition. The most significant signal was at rs2113389, which explained 4.3% of the variation in cortical tau, while APOE4 rs429358 accounted for 3.6%. rs2113389 was associated with higher tau and faster cognitive decline. Additive effects, but no interactions, were observed between rs2113389 and diagnosis, APOE4 , and Aβ positivity. CYP1B1 expression was upregulated in AD. rs2113389 was associated with higher CYP1B1 expression and methylation levels. Mouse model studies provided additional functional evidence for a relationship between CYP1B1 and tau deposition but not Aβ. These results may provide insight into the genetic basis of cerebral tau and novel pathways for therapeutic development in AD.

Neuroprotective Effects of a Multi-Herbal Extract on Axonal and Synaptic Disruption in Vitro and Cognitive Impairment in Vivo

Background

Alzheimer's disease (AD) is a multifactorial disorder characterized by cognitive decline. Current available therapeutics for AD have limited clinical benefit. Therefore, preventive therapies for interrupting the development of AD are critically needed. Molecules targeting multifunction to interact with various pathlogical components have been considered to improve the therapeutic efficiency of AD. In particular, herbal medicines with multiplicity of actions produce cognitive benefits on AD. Bugu-M is a multi-herbal extract composed of Ganoderma lucidum (Antler form), Nelumbo nucifera Gaertn., Ziziphus jujuba Mill., and Dimocarpus longan, with the ability of its various components to confer resilience to cognitive deficits.

Objective

To evaluate the potential of Bugu-M on amyloid-β (Aβ) toxicity and its in vitro mechanisms and on in vivo cognitive function.

Methods

We illustrated the effect of Bugu-M on Aβ_25-35-evoked toxicity as well as its possible mechanisms to diminish the pathogenesis of AD in rat cortical neurons. For cognitive function studies, 2-month-old female 3×Tg-AD mice were administered 400 mg/kg Bugu-M for 30 days. Behavioral tests were performed to assess the efficacy of Bugu-M on cognitive impairment.

Results

In primary cortical neuronal cultures, Bugu-M mitigated Aβ-evoked toxicity by reducing cytoskeletal aberrations and axonal disruption, restoring presynaptic and postsynaptic protein expression, suppressing mitochondrial damage and apoptotic signaling, and reserving neurogenic and neurotrophic factors. Importantly, 30-day administration of Bugu-M effectively prevented development of cognitive impairment in 3-month-old female 3×Tg-AD mice.

Conclusion

Bugu-M might be beneficial in delaying the progression of AD, and thus warrants consideration for its preventive potential for AD.

Screening of BACE1 inhibitors with antiamyloidogenic activity: A study of flavonoids and flavonoid derivatives

Aggregates of β-amyloid peptide are found to occur in brains of AD patients and are formed upon sequential cleavage of the amyloid precursor protein by BACE1 and γ-secretase. Strategies inhibiting either peptide aggregation or the rate limiting enzyme BACE1 have been in demand for its implication in AD therapeutics. The present study is undertaken to mine compounds with dual ability. In this context, some natural compounds that were already predicted as BACE1 inhibitors by our group, were further tested for their activity as aggregation inhibitors. A pharmacophore model built with known antiamyloidogenic compounds was then applied for screening the natural compounds previously predicted as BACE1 inhibitors. Subsequently experimental validation by Thioflavin-T and Aβ-GFP assay filtered four compounds genistein, syringetin, tamarixetin and ZINC53276039. Out of them, ZINC53276039 showed promising antiamyloidogenic activity to act as a potent inhibitor of aggregation. Interestingly, our previous study revealed syringetin and ZINC53276039 to be good BACE1 inhibitors while tamarixetin to be a moderate BACE1 inhibitor. These good to moderate BACE1 inhibitors with moderate to reasonable antiamyloidogenic activity might show potency in reducing the amyloid load of AD brains.

SOBA: Development and testing of a soluble oligomer binding assay for detection of amyloidogenic toxic oligomers

The formation of toxic Amyloid β-peptide (Aβ) oligomers is one of the earliest events in the molecular pathology of Alzheimer's Disease (AD). These oligomers lead to a variety of downstream effects, including impaired neuronal signaling, neuroinflammation, tau phosphorylation, and neurodegeneration, and it is estimated that these events begin 10 to 20 y before the presentation of symptoms. Toxic Aβ oligomers contain a nonstandard protein structure, termed α-sheet, and designed α-sheet peptides target this main-chain structure in toxic oligomers independent of sequence. Here we show that a designed α-sheet peptide inhibits the deleterious effects on neuronal signaling and also serves as a capture agent in our soluble oligomer binding assay (SOBA). Pre-incubated synthetic α-sheet-containing Aβ oligomers produce strong SOBA signals, while monomeric and β-sheet protofibrillar Aβ do not. α-sheet containing oligomers were also present in cerebrospinal fluid (CSF) from an AD patient versus a noncognitively impaired control. For the detection of toxic oligomers in plasma, we developed a plate coating to increase the density of the capture peptide. The proof of concept was achieved by testing 379 banked human plasma samples. SOBA detected Aβ oligomers in patients on the AD continuum, including controls who later progressed to mild cognitive impairment. In addition, SOBA discriminated AD from other forms of dementia, yielding sensitivity and specificity of 99% relative to clinical and neuropathological diagnoses. To explore the broader potential of SOBA, we adapted the assay for a-synuclein oligomers and confirmed their presence in CSF from patients with Parkinson's disease and Lewy body dementia.

From synapses to circuits and back: Bridging levels of understanding in animal models of Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by behavioural changes that include memory loss and cognitive decline and is associated with the appearance of amyloid-β plaques and neurofibrillary tangles throughout the brain. Although aspects of the disease percolate across multiple levels of neuronal organization, from the cellular to the behavioural, it is increasingly clear that circuits are a critical junction between the cellular pathology and the behavioural phenotypes that bookend these levels of analyses. In this review, we discuss critical aspects of neural circuit research, beginning with synapses and progressing to network activity and how they influence our understanding of disease processed in AD.

Augmenting neurogenesis rescues memory impairments in Alzheimer's disease by restoring the memory-storing neurons

Hippocampal neurogenesis is impaired in Alzheimer's disease (AD) patients and familial Alzheimer's disease (FAD) mouse models. However, it is unknown whether new neurons play a causative role in memory deficits. Here, we show that immature neurons were actively recruited into the engram following a hippocampus-dependent task. However, their recruitment is severely deficient in FAD. Recruited immature neurons exhibited compromised spine density and altered transcript profile. Targeted augmentation of neurogenesis in FAD mice restored the number of new neurons in the engram, the dendritic spine density, and the transcription signature of both immature and mature neurons, ultimately leading to the rescue of memory. Chemogenetic inactivation of immature neurons following enhanced neurogenesis in AD, reversed mouse performance, and diminished memory. Notably, AD-linked App, ApoE, and Adam10 were of the top differentially expressed genes in the engram. Collectively, these observations suggest that defective neurogenesis contributes to memory failure in AD.

Based on molecular structures: Amyloid-β generation, clearance, toxicity and therapeutic strategies

Amyloid-β (Aβ) has long been considered as one of the most important pathogenic factors in Alzheimer’s disease (AD), but the specific pathogenic mechanism of Aβ is still not completely understood. In recent years, the development of structural biology technology has led to new understandings about Aβ molecular structures, Aβ generation and clearance from the brain and peripheral tissues, and its pathological toxicity. The purpose of the review is to discuss Aβ metabolism and toxicity, and the therapeutic strategy of AD based on the latest progress in molecular structures of Aβ. The Aβ structure at the atomic level has been analyzed, which provides a new and refined perspective to comprehend the role of Aβ in AD and to formulate therapeutic strategies of AD.

Urokinase-Type Plasminogen Activator Triggers Wingless/Int1-Independent Phosphorylation of the Low-Density Lipoprotein Receptor-Related Protein-6 in Cerebral Cortical Neurons

BACKGROUND

Urokinase-type plasminogen activator (uPA) is a serine proteinase found in excitatory synapses located in the II/III and V cortical layers. The synaptic release of uPA promotes the formation of synaptic contacts and the repair of synapses damaged by various forms of injury, and its abundance is decreased in the synapse of Alzheimer's disease (AD) patients. Inactivation of the Wingless/Int1 (Wnt)-β-catenin pathway plays a central role in the pathogenesis of AD. Soluble amyloid-β (Aβ) prevents the phosphorylation of the low-density lipoprotein receptor-related protein-6 (LRP6), and the resultant inactivation of the Wnt-β-catenin pathway prompts the amyloidogenic processing of the amyloid-β protein precursor (AβPP) and causes synaptic loss.

OBJECTIVE

To study the role of neuronal uPA in the pathogenesis of AD.

METHODS

We used in vitro cultures of murine cerebral cortical neurons, a murine neuroblastoma cell line transfected with the APP-695 Swedish mutation (N2asw), and mice deficient on either plasminogen, or uPA, or its receptor (uPAR).

RESULTS

We show that uPA activates the Wnt-β-catenin pathway in cerebral cortical neurons by triggering the phosphorylation of LRP6 via a plasmin-independent mechanism that does not require binding of Wnt ligands (Wnts). Our data indicate that uPA-induced activation of the Wnt-β-catenin pathway protects the synapse from the harmful effects of soluble Aβ and prevents the amyloidogenic processing of AβPP by inhibiting the expression of β-secretase 1 (BACE1) and the ensuing generation of Aβ 40 and Aβ 42 peptides.

CONCLUSION

uPA protects the synapse and antagonizes the inhibitory effect of soluble Aβ on the Wnt-β-catenin pathway by providing an alternative pathway for LRP6 phosphorylation and β-catenin stabilization.

VGLUT3 neurons in median raphe control the efficacy of spatial memory retrieval via ETV4 regulation of VGLUT3 transcription

The raphe nucleus is critical for feeding, rewarding and memory. However, how the heterogenous raphe neurons are molecularly and structurally organized to engage their divergent functions remains unknown. Here, we genetically target a subset of neurons expressing VGLUT3. VGLUT3 neurons control the efficacy of spatial memory retrieval by synapsing directly with parvalbumin-expressing GABA interneurons (PGIs) in the dentate gyrus. In a mouse model of Alzheimer's disease (AD mice), VGLUT3→PGIs synaptic transmission is impaired by ETV4 inhibition of VGLUT3 transcription. ETV4 binds to a promoter region of VGLUT3 and activates VGLUT3 transcription in VGLUT3 neurons. Strengthening VGLUT3→PGIs synaptic transmission by ETV4 activation of VGLUT3 transcription upscales the efficacy of spatial memory retrieval in AD mice. This study reports a novel circuit and molecular mechanism underlying the efficacy of spatial memory retrieval via ETV4 inhibition of VGLUT3 transcription and hence provides a promising target for therapeutic intervention of the disease progression.

Genetic and pharmacologic proteasome augmentation ameliorates Alzheimer's-like pathology in mouse and fly APP overexpression models

The proteasome has key roles in neuronal proteostasis, including the removal of misfolded and oxidized proteins, presynaptic protein turnover, and synaptic efficacy and plasticity. Proteasome dysfunction is a prominent feature of Alzheimer's disease (AD). We show that prevention of proteasome dysfunction by genetic manipulation delays mortality, cell death, and cognitive deficits in fly and cell culture AD models. We developed a transgenic mouse with neuronal-specific proteasome overexpression that, when crossed with an AD mouse model, showed reduced mortality and cognitive deficits. To establish translational relevance, we developed a set of TAT-based proteasome-activating peptidomimetics that stably penetrated the blood-brain barrier and enhanced 20S/26S proteasome activity. These agonists protected against cell death, cognitive decline, and mortality in cell culture, fly, and mouse AD models. The protective effects of proteasome overexpression appear to be driven, at least in part, by the proteasome's increased turnover of the amyloid precursor protein along with the prevention of overall proteostatic dysfunction.

Theta and gamma oscillatory dynamics in mouse models of Alzheimer's disease: A path to prospective therapeutic intervention

Understanding the neural basis of cognitive deficits, a key feature of Alzheimer's disease (AD), is imperative for achieving the therapy of the disease. Rhythmic oscillatory activities in neural systems are a fundamental mechanism for diverse brain functions, including cognition. In several neurological conditions like AD, aberrant neural oscillations have been shown to play a central role. Furthermore, manipulation of brain oscillations in animals has confirmed their impact on cognition and disease. In this article, we review the evidence from mouse models that shows how synchronized oscillatory activity is intricately linked to AD machinery. We primarily focus on recent reports showing abnormal oscillatory activities at theta and gamma frequencies in AD condition and their influence on cellular disturbances and cognitive impairments. A thorough comprehension of the role that neuronal oscillations play in AD pathology should pave the way to therapeutic interventions that can curb the disease.

Amyloid-β Oligomers: Multiple Moving Targets

Alzheimer’s Disease (AD) is a neurodegenerative disorder that is characterized clinically by progressive cognitive decline and pathologically by the β-sheet rich fibril plaque deposition of the amyloid-β (Aβ) peptide in the brain. While plaques are a hallmark of AD, plaque burden is not correlated with cognitive impairment. Instead, Aβ oligomers formed during the aggregation process represent the main agents of neurotoxicity, which occurs 10–20 years before patients begin to show symptoms. These oligomers are dynamic in nature and represented by a heterogeneous distribution of aggregates ranging from low- to high-molecular weight, some of which are toxic while others are not. A major difficulty in determining the pathological mechanism(s) of Aβ, developing reliable diagnostic markers for early-stage detection, as well as effective therapeutics for AD are the differentiation and characterization of oligomers formed throughout disease propagation based on their molecular features, effects on biological function, and relevance to disease propagation and pathology. Thus, it is critical to methodically identify the mechanisms of Aβ aggregation and toxicity, as well as describe the roles of different oligomers and aggregates in disease progression and molecular pathology. Here, we describe a variety of biophysical techniques used to isolate and characterize a range of Aβ oligomer populations, as well as discuss proposed mechanisms of toxicity and therapeutic interventions aimed at specific assemblies formed during the aggregation process. The approaches being used to map the misfolding and aggregation of Aβ are like what was done during the fundamental early studies, mapping protein folding pathways using combinations of biophysical techniques in concert with protein engineering. Such information is critical to the design and molecular engineering of future diagnostics and therapeutics for AD.

Brain cellular senescence in mouse models of Alzheimer's disease

The accumulation of senescent cells contributes to aging pathologies, including neurodegenerative diseases, and its selective removal improves physiological and cognitive function in wild-type mice as well as in Alzheimer's disease (AD) models. AD models recapitulate some, but not all components of disease and do so at different rates. Whether brain cellular senescence is recapitulated in some or all AD models and whether the emergence of cellular senescence in AD mouse models occurs before or after the expected onset of AD-like cognitive deficits in these models are not yet known. The goal of this study was to identify mouse models of AD and AD-related dementias that develop measurable markers of cellular senescence in brain and thus may be useful to study the role of cellular senescence in these conditions. We measured the levels of cellular senescence markers in the brains of P301S(PS19), P301L, hTau, and 3xTg-AD mice that model amyloidopathy and/or tauopathy in AD and related dementias and in wild-type, age-matched control mice for each strain. Expression of cellular senescence markers in brains of transgenic P301L and 3xTg-AD mice was largely indistinguishable from that in WT control age-matched mice. In contrast, markers of cellular senescence were differentially increased in brains of transgenic hTau and P301S(PS19) mice as compared to WT control mice before the onset of AD-like cognitive deficits. Taken together, our data suggest that P301S(PS19) and hTau mice may be useful models for the study of brain cellular senescence in tauopathies including, but not limited to, AD.

Sodium tanshinone IIA sulfonate improves cognitive impairment via regulating Aβ transportation in AD transgenic mouse model

Alzheimer's disease (AD) is a most common neurodegenerative disease. Sodium Tanshinone IIA Sulfonate (STS) has been reported to ameliorate AD pathology. However, the underlying mechanism is still unclear. In this study, AD transgenic mouse model (APP/PS1) was used to explore the potential mechanism of STS against AD. Morris water maze and Y-maze tests showed that administration of STS improved learning and memory abilities of APP/PS1 mice. STS reduced the levels of reactive oxygen species and malondialdehyde, while improved the activity of superoxide dismutase in both hippocampus and cortex in APP/PS1 mice. STS inhibited the activity of acetylcholinesterase, while improved the activity of choline acetyltransferase in APP/PS1 mice. In addition, STS elevated the protein expressions of neurotrophic factors and synapse-related proteins in both the hippocampus and cortex in APP/PS1 mice. At last, STS improved the protein expressions of glucose transporter 1 (GLUT1) and low-density lipoprotein receptor-related protein 1 (LRP1). These results indicated that the potential mechanism of STS on AD might be related to Aβ transportation function via GLUT1/LRP1 pathway. HIGHLIGHTS: STS improves cognitive impairment of APP/PS1 mice. STS ameliorates the oxidative stress damage and improves the cholinergic system. STS protects against neuronal dysfunction and enhances the synaptic plasticity. STS mediates the Aβ transportation of BMECs.

Calcium signaling in individual APP/PS1 mouse dentate gyrus astrocytes increases ex vivo with Aβ pathology and age without affecting astrocyte network activity

Astrocytes are critical for healthy brain function. In Alzheimer's disease, astrocytes become reactive, which affects their signaling properties. Here, we measured spontaneous calcium transients ex vivo in hippocampal astrocytes in brain slices containing the dentate gyrus of 6- (6M) and 9-month-old (9M) APPswe/PSEN1dE9 (APP/PS1) mice. We investigated the frequency and duration of calcium transients in relation to aging, amyloid-β (Aβ) pathology, and the proximity of the astrocyte to Aβ plaques. The 6M APP/PS1 astrocytes showed no change in spontaneous calcium-transient properties compared to wild-type (WT) astrocytes. 9M APP/PS1 astrocytes, however, showed more hyperactivity compared to WT, characterized by increased spontaneous calcium transients that were longer in duration. Our data also revealed an effect of aging, as 9M astrocytes overall showed an increase in calcium activity compared to 6M astrocytes. Subsequent calcium-wave analysis showed an increase in sequential calcium transients (i.e., calcium waves) in 9M astrocytes, suggesting increased network activity ex vivo. Further analysis using null models revealed that this network effect is caused by chance, due to the increased number of spontaneous transients. Our findings show that alterations in calcium signaling in individual hippocampal astrocytes of APP/PS1 mice are subject to both aging and Aβ pathology but these do not lead to a change in astrocyte network activity. These alterations in calcium dynamics of astrocytes may help to understand changes in neuronal physiology leading to cognitive decline and ultimately dementia.

Association of Hippocampal Subfield Volumes with Amyloid-Beta Deposition in Alzheimer's Disease

We investigated the relationship between hippocampal subfield volumes and cortical amyloid-beta (Aβ) deposition in Alzheimer’s disease (AD). Fifty participants (11 cognitively unimpaired [CU], 10 with mild cognitive impairment [MCI], and 29 with AD) who underwent 18F-florbetaben positron emission tomography, magnetic resonance imaging, and neuropsychological tests were enrolled. The hippocampal subfield volumes were obtained using an automated brain volumetry system with the Winterburn atlas and were compared among the diagnostic groups, and the correlations with the Aβ deposition and AD risk factors were determined. Patients with MCI and AD showed decreased volume in the stratum radiatum/lacunosum/moleculare (SRLM) of the cornu ammonis (CA)1 and CA4-dentate gyrus (DG) compared with the CU. Decreased SRLM and CA4-DG volumes were associated with an increased Aβ deposition in the global cortex (R = −0.459, p = 0.001; R = −0.393, p = 0.005, respectively). The SRLM and CA4-DG volumes aided in the distinction of AD from CU (areas under the receiver operating characteristic [AUROC] curve = 0.994 and 0.981, respectively, p < 0.001), and Aβ+ from Aβ− individuals (AUROC curve = 0.949 and 0.958, respectively, p < 0.001). Hippocampal subfield volumes demonstrated potential as imaging biomarkers in the diagnosis and detection of AD and Aβ deposition, respectively.

The Therapeutic and Diagnostic Potential of Amyloid β Oligomers Selective Antibodies to Treat Alzheimer's Disease

Improvements have been made in the diagnosis of Alzheimer’s disease (AD), manifesting mostly in the development of in vivo imaging methods that allow for the detection of pathological changes in AD by magnetic resonance imaging (MRI) and positron emission tomography (PET) scans. Many of these imaging methods, however, use agents that probe amyloid fibrils and plaques–species that do not correlate well with disease progression and are not present at the earliest stages of the disease. Amyloid β oligomers (AβOs), rather, are now widely accepted as the Aβ species most germane to AD onset and progression. Here we report evidence further supporting the role of AβOs as pathological instigators of AD and introduce promising anti-AβO diagnostic probes capable of distinguishing the 5xFAD mouse model from wild type mice by PET and MRI. In a developmental study, Aβ oligomers in 5xFAD mice were found to appear at 3 months of age, just prior to the onset of memory dysfunction, and spread as memory worsened. The increase of AβOs is prominent in the subiculum and correlates with concomitant development of reactive astrocytosis. The impact of these AβOs on memory is in harmony with findings that intraventricular injection of synthetic AβOs into wild type mice induced hippocampal dependent memory dysfunction within 24 h. Compelling support for the conclusion that endogenous AβOs cause memory loss was found in experiments showing that intranasal inoculation of AβO-selective antibodies into 5xFAD mice completely restored memory function, measured 30–40 days post-inoculation. These antibodies, which were modified to give MRI and PET imaging probes, were able to distinguish 5xFAD mice from wild type littermates. These results provide strong support for the role of AβOs in instigating memory loss and salient AD neuropathology, and they demonstrate that AβO selective antibodies have potential both for therapeutics and for diagnostics.

Disrupted neural correlates of anesthesia and sleep reveal early circuit dysfunctions in Alzheimer models

Dysregulated homeostasis of neural activity has been hypothesized to drive Alzheimer's disease (AD) pathogenesis. AD begins with a decades-long presymptomatic phase, but whether homeostatic mechanisms already begin failing during this silent phase is unknown. We show that before the onset of memory decline and sleep disturbances, familial AD (fAD) model mice display no deficits in CA1 mean firing rate (MFR) during active wakefulness. However, homeostatic down-regulation of CA1 MFR is disrupted during non-rapid eye movement (NREM) sleep and general anesthesia in fAD mouse models. The resultant hyperexcitability is attenuated by the mitochondrial dihydroorotate dehydrogenase (DHODH) enzyme inhibitor, which tunes MFR toward lower set-point values. Ex vivo fAD mutations impair downward MFR homeostasis, resulting in pathological MFR set points in response to anesthetic drug and inhibition blockade. Thus, firing rate dyshomeostasis of hippocampal circuits is masked during active wakefulness but surfaces during low-arousal brain states, representing an early failure of the silent disease stage.

Neurodegenerative Disorders of Alzheimer, Parkinsonism, Amyotrophic Lateral Sclerosis and Multiple Sclerosis: An Early Diagnostic Approach for Precision Treatment

Neurodegenerative diseases (NDs) are characterised by progressive dysfunction of synapses, neurons, glial cells and their networks. Neurodegenerative diseases can be classified according to primary clinical features (e.g., dementia, parkinsonism, or motor neuron disease), anatomic distribution of neurodegeneration (e.g., frontotemporal degenerations, extrapyramidal disorders, or spinocerebellar degenerations), or principal molecular abnormalities. The most common neurodegenerative disorders are amyloidosis, tauopathies, a-synucleinopathy, and TAR DNA-binding protein 43 (TDP-43) proteopathy. The protein abnormalities in these disorders have abnormal conformational properties along with altered cellular mechanisms, and they exhibit motor deficit, mitochondrial malfunction, dysfunctions in autophagic-lysosomal pathways, synaptic toxicity, and more emerging mechanisms such as the roles of stress granule pathways and liquid-phase transitions. Finally, for each ND, microglial cells have been reported to be implicated in neurodegeneration, in particular, because the microglial responses can shift from neuroprotective to a deleterious role. Growing experimental evidence suggests that abnormal protein conformers act as seed material for oligomerization, spreading from cell to cell through anatomically connected neuronal pathways, which may in part explain the specific anatomical patterns observed in brain autopsy sample. In this review, we mention the human pathology of select neurodegenerative disorders, focusing on how neurodegenerative disorders (i.e., Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and multiple sclerosis) represent a great healthcare problem worldwide and are becoming prevalent because of the increasing aged population. Despite many studies have focused on their etiopathology, the exact cause of these diseases is still largely unknown and until now with the only available option of symptomatic treatments. In this review, we aim to report the systematic and clinically correlated potential biomarker candidates. Although future studies are necessary for their use in early detection and progression in humans affected by NDs, the promising results obtained by several groups leads us to this idea that biomarkers could be used to design a potential therapeutic approach and preclinical clinical trials for the treatments of NDs.

Peering into the Brain through the Retrosplenial Cortex to Assess Cognitive Function of the Injured Brain

The retrosplenial cortex (RSC) is a posterior cortical area that has been drawing increasing interest in recent years, with a growing number of studies studying its contribution to cognitive and sensory functions. From an anatomical perspective, it has been established that the RSC is extensively and often reciprocally connected with the hippocampus, neocortex, and many midbrain regions. Functionally, the RSC is an important hub of the default-mode network. This endowment, with vast anatomical and functional connections, positions the RSC to play an important role in episodic memory, spatial and contextual learning, sensory-cognitive activities, and multi-modal sensory information processing and integration. Additionally, RSC dysfunction has been reported in cases of cognitive decline, particularly in Alzheimer's disease and stroke. We review the literature to examine whether the RSC can act as a cortical marker of persistent cognitive dysfunction after traumatic brain injury (TBI). Because the RSC is easily accessible at the brain's surface using in vivo techniques, we argue that studying RSC network activity post-TBI can shed light into the mechanisms of less-accessible brain regions, such as the hippocampus. There is a fundamental gap in the TBI field about the microscale alterations occurring post-trauma, and by studying the RSC's neuronal activity at the cellular level we will be able to design better therapeutic tools. Understanding how neuronal activity and interactions produce normal and abnormal activity in the injured brain is crucial to understanding cognitive dysfunction. By using this approach, we expect to gain valuable insights to better understand brain disorders like TBI.

Amyloid β structural polymorphism, associated toxicity and therapeutic strategies

A review of the multidisciplinary scientific literature reveals a large variety of amyloid-β (Aβ) oligomeric species, differing in molecular weight, conformation and morphology. These species, which may assemble via either on- or off-aggregation pathways, exhibit differences in stability, function and neurotoxicity, according to different experimental settings. The conformations of the different Aβ species are stabilized by intra- and inter-molecular hydrogen bonds and by electrostatic and hydrophobic interactions, all depending on the chemical and physical environment (e.g., solvent, ions, pH) and interactions with other molecules, such as lipids and proteins. This complexity and the lack of a complete understanding of the relationship between the different Aβ species and their toxicity is currently dictating the nature of the inhibitor (or inducer)-based approaches that are under development for interfering with (or inducing) the formation of specific species and Aβ oligomerization, and for interfering with the associated downstream neurotoxic effects. Here, we review the principles that underlie the involvement of different Aβ oligomeric species in neurodegeneration, both in vitro and in preclinical studies. In addition, we provide an overview of the existing inhibitors (or inducers) of Aβ oligomerization that serve as potential therapeutics for neurodegenerative diseases. The review, which covers the exciting studies that have been published in the past few years, comprises three main parts: 1) on- and off-fibrillar assembly mechanisms and Aβ structural polymorphism; 2) interactions of Aβ with other molecules and cell components that dictate the Aβ aggregation pathway; and 3) targeting the on-fibrillar Aβ assembly pathway as a therapeutic approach.

Down-regulation of cyclin D2 in amyloid β toxicity, inflammation, and Alzheimer's disease

In the current study, we analyzed the effects of the systemic inflammatory response (SIR) and amyloid β (Aβ) peptide on the expression of genes encoding cyclins and cyclin-dependent kinase (Cdk) in: (i) PC12 cells overexpressing human beta amyloid precursor protein (βAPP), wild-type (APPwt-PC12), or carrying the Swedish mutantion (APPsw-PC12); (ii) the murine hippocampus during SIR; and (iii) Alzheimer’s disease (AD) brain. In APPwt-PC12 expression of cyclin D2 (cD2) was exclusively reduced, and in APPsw-PC12 cyclins cD2 and also cA1 were down-regulated, but cA2, cB1, cB2, and cE1 were up-regulated. In the SIR cD2, cB2, cE1 were found to be significantly down-regulated and cD3, Cdk5, and Cdk7 were significantly up-regulated. Cyclin cD2 was also found to be down-regulated in AD neocortex and hippocampus. Our novel data indicate that Aβ peptide and inflammation both significantly decreased the expression of cD2, suggesting that Aβ peptides may also contribute to downregulation of cD2 in AD brain.

From Neurodevelopmental to Neurodegenerative Disorders: The Vascular Continuum

Structural and functional integrity of the cerebral vasculature ensures proper brain development and function, as well as healthy aging. The inability of the brain to store energy makes it exceptionally dependent on an adequate supply of oxygen and nutrients from the blood stream for matching colossal demands of neural and glial cells. Key vascular features including a dense vasculature, a tightly controlled environment, and the regulation of cerebral blood flow (CBF) all take part in brain health throughout life. As such, healthy brain development and aging are both ensured by the anatomical and functional interaction between the vascular and nervous systems that are established during brain development and maintained throughout the lifespan. During critical periods of brain development, vascular networks remodel until they can actively respond to increases in neural activity through neurovascular coupling, which makes the brain particularly vulnerable to neurovascular alterations. The brain vasculature has been strongly associated with the onset and/or progression of conditions associated with aging, and more recently with neurodevelopmental disorders. Our understanding of cerebrovascular contributions to neurological disorders is rapidly evolving, and increasing evidence shows that deficits in angiogenesis, CBF and the blood-brain barrier (BBB) are causally linked to cognitive impairment. Moreover, it is of utmost curiosity that although neurodevelopmental and neurodegenerative disorders express different clinical features at different stages of life, they share similar vascular abnormalities. In this review, we present an overview of vascular dysfunctions associated with neurodevelopmental (autism spectrum disorders, schizophrenia, Down Syndrome) and neurodegenerative (multiple sclerosis, Huntington's, Parkinson's, and Alzheimer's diseases) disorders, with a focus on impairments in angiogenesis, CBF and the BBB. Finally, we discuss the impact of early vascular impairments on the expression of neurodegenerative diseases.

Curcumin Complex Analogues as Near-Infrared Fluorescent Probes for Monitoring all Aβ Species in the Early Alzheimer's Disease Model

Aggregation of amyloid β-peptide (Aβ) is closely related to the pathology of Alzheimer's disease (AD). In this pathology, the beginning stage is characterized by excessive accumulation of Aβ monomers due to imbalanced Aβ in the process of clearance. The Aβ peptide exists in many forms such as soluble and insoluble Aβ species, both of which coexist during the progression of AD and contribute to AD pathology. Thus, probes capable of monitoring all Aβ species are highly desirable. While there are several fluorescent probes for detecting insoluble Aβ, it is still challenging to monitor all Aβ forms by using probes. Here, we describe a near-infrared fluorescent chemical probe, termed AD-1, developed through complexation of curcumin analogues with a stabilizer, which has good photophysical properties and shows high binding to all Aβ species in solution tests. Furthermore, AD-1 exhibited good blood-brain barrier penetrating ability and low cytotoxicity. More importantly, it was successfully applied to 4-month-young APP/PS1 mice imaging noninvasively.

Overexpression of wild-type human amyloid precursor protein alters GABAergic transmission

The function of the amyloid precursor protein (APP) is not fully understood, but its cleavage product amyloid beta (Aβ) together with neurofibrillary tangles constitute the hallmarks of Alzheimer's disease (AD). Yet, imbalance of excitatory and inhibitory neurotransmission accompanied by loss of synaptic functions, has been reported much earlier and independent of any detectable pathological markers. Recently, soluble APP fragments have been shown to bind to presynaptic GABA_B receptors (GABA_BRs), subsequently decreasing the probability of neurotransmitter release. In this body of work, we were able to show that overexpression of wild-type human APP in mice (hAPP_wt) causes early cognitive impairment, neuronal loss, and electrophysiological abnormalities in the absence of amyloid plaques and at very low levels of Aβ. hAPP_wt mice exhibited neuronal overexcitation that was evident in EEG and increased long-term potentiation (LTP). Overexpression of hAPP_wt did not alter GABAergic/glutamatergic receptor components or GABA production ability. Nonetheless, we detected a decrease of GABA but not glutamate that could be linked to soluble APP fragments, acting on presynaptic GABA_BRs and subsequently reducing GABA release. By using a specific presynaptic GABA_BR antagonist, we were able to rescue hyperexcitation in hAPP_wt animals. Our results provide evidence that APP plays a crucial role in regulating inhibitory neurotransmission.