Amyloid-β plaque formation and reactive gliosis are required for induction of cognitive deficits in App knock-in mouse models of Alzheimer's disease

Decreased plasma nicotinamide and altered NAD+ metabolism in glial cells surrounding Aβ plaques in a mouse model of Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease and a leading cause of senile dementia. Amyloid-β (Aβ) accumulation triggers chronic neuroinflammation, initiating AD pathogenesis. Recent clinical trials for anti-Aβ immunotherapy underscore that blood-based biomarkers have significant advantages and applicability over conventional diagnostics and are an unmet clinical need. To further advance ongoing clinical trials and identify novel therapeutic targets for AD, developing additional plasma biomarkers closely associated with pathogenic mechanisms downstream of Aβ accumulation is critically important. To identify plasma metabolites reflective of neuroinflammation caused by Aβ pathology, we performed untargeted metabolomic analyses of the plasma by capillary electrophoresis time-of-flight mass spectrometry (CE-TOFMS) and analyzed the potential roles of the identified metabolic changes in the brain neuroinflammatory response using the female App knock-in (AppNLGF) mouse model of Aβ amyloidosis. The CE-TOFMS analysis of plasma samples from female wild-type (WT) and AppNLGF mice revealed that plasma levels of nicotinamide, a nicotinamide adenine dinucleotide (NAD+) precursor, were decreased in AppNLGF mice, and altered metabolite profiles were enriched for nicotinate/nicotinamide metabolism. In AppNLGF mouse brains, NAD+ levels were unaltered, but mRNA levels of NAD+-synthesizing nicotinate phosphoribosyltransferase (Naprt) and NAD+-degrading Cd38 genes were increased. These enzymes were induced in reactive astrocytes and microglia surrounding Aβ plaques in the cortex and hippocampus of female AppNLGF mouse brains, suggesting neuroinflammation increases NAD+ metabolism. This study suggests plasma nicotinamide could be indicative of the neuroinflammatory response and that nicotinate and nicotinamide metabolism are potential therapeutic targets for AD, by targeting both neuroinflammation and neuroprotection.

Structural Variations of Prions and Prion-like Proteins Associated with Neurodegeneration

Neurodegeneration is becoming one of the leading causes of death worldwide as the population expands and grows older. There is a growing desire to understand the mechanisms behind prion proteins as well as the prion-like proteins that make up neurodegenerative diseases (NDs), including Alzheimer's disease (AD) and Parkinson's disease (PD). Both amyloid-β (Aβ) and hyperphosphorylated tau (p-tau) proteins behave in ways similar to those of the infectious form of the prion protein, PrPSc, such as aggregating, seeding, and replicating under not yet fully understood mechanisms, thus the designation of prion-like. This review aims to highlight the shared mechanisms between prion-like proteins and prion proteins in the structural variations associated with aggregation and disease development. These mechanisms largely focus on the dysregulation of protein homeostasis, self-replication, and protein aggregation, and this knowledge could contribute to diagnoses and treatments for the given NDs.

Associations of amyloid-β oligomers and plaques with neuropathology in the App NL-G-F mouse

Amyloid-β pathology and neurofibrillary tangles lead to glial activation and neurodegeneration in Alzheimer's disease. In this study, we investigated the relationships between the levels of amyloid-β oligomers, amyloid-β plaques, glial activation and markers related to neurodegeneration in the App NL-G-F triple mutation mouse line and in a knock-in line homozygous for the common human amyloid precursor protein (App hu mouse). The relationships between neuropathological features were characterized with immunohistochemistry and imaging mass cytometry. Markers assessing human amyloid-β proteins, microglial and astrocytic activation and neuronal and synaptic densities were used in mice between 2.5 and 12 months of age. We found that amyloid-β oligomers were abundant in the brains of App hu mice in the absence of classical amyloid-β plaques. These brains showed morphological changes consistent with astrocyte activation but no evidence of microglial activation or synaptic or neuronal pathology. In contrast, both high levels of amyloid-β oligomers and numerous plaques accumulated in App NL-G-F mice in association with substantial astrocytic and microglial activation. The increase in amyloid-β oligomers over time was more strongly correlated with astrocytic than with microglia activation. Spatial analyses suggested that activated microglia were more closely associated with amyloid-β oligomers than with amyloid-β plaques in App NL-G-F mice, which also showed age-dependent decreases in neuronal and synaptic density markers. A comparative study of the two models highlighted the dependence of glial and neuronal pathology on the nature and aggregation state of the amyloid-β peptide. Astrocyte activation and neuronal pathology appeared to be more strongly associated with amyloid-β oligomers than with amyloid-β plaques, although amyloid-β plaques were associated with microglia activation.

Modeling of age-related neurological disease: utility of zebrafish

Many age-related neurological diseases still lack effective treatments, making their understanding a critical and urgent issue in the globally aging society. To overcome this challenge, an animal model that accurately mimics these diseases is essential. To date, many mouse models have been developed to induce age-related neurological diseases through genetic manipulation or drug administration. These models help in understanding disease mechanisms and finding potential therapeutic targets. However, some age-related neurological diseases cannot be fully replicated in human pathology due to the different aspects between humans and mice. Although zebrafish has recently come into focus as a promising model for studying aging, there are few genetic zebrafish models of the age-related neurological disease. This review compares the aging phenotypes of humans, mice, and zebrafish, and provides an overview of age-related neurological diseases that can be mimicked in mouse models and those that cannot. We presented the possibility that reproducing human cerebral small vessel diseases during aging might be difficult in mice, and zebrafish has potential to be another animal model of such diseases due to their similarity of aging phenotype to humans.

A M1 muscarinic acetylcholine receptor-specific positive allosteric modulator VU0486846 reduces neurogliosis in female Alzheimer's mice

Alzheimer's disease (AD) is the most prevalent type of dementia, disproportionately affecting females, who make up nearly 60% of diagnosed cases. In AD patients, the accumulation of beta-amyloid (Aβ) in the brain triggers a neuroinflammatory response driven by neuroglia, worsening the condition. We have previously demonstrated that VU0486846, an orally available positive allosteric modulator (PAM) targeting M1 muscarinic acetylcholine receptors, enhances cognitive function and reduces Aβ pathology in female APPswe/PSEN1ΔE9 (APP/PS1) mice. However, it remained unclear whether these improvements were linked to a decrease in neuroglial activation. To investigate, we treated nine-month-old APP/PS1 and wildtype mice with VU0486846 for 8 weeks and analyzed brain slices for markers of microglial activation (ionized calcium binding adaptor molecule 1, Iba1) and astrocyte activation (Glial fibrillary acidic protein, GFAP). We find that VU0486846 reduces the presence of Iba1-positive microglia and GFAP-positive astrocytes in the hippocampus of female APP/PS1 mice and limits the recruitment of these cells to remaining Aβ plaques. This study sheds light on an additional mechanism through which novel M1 mAChR PAMs exhibit disease-modifying effects by reducing neuroglial activation and underscore the potential of these ligands for the treatment of AD, especially in females.

Genetically modified non-human primate models for research on neurodegenerative diseases

Neurodegenerative diseases (NDs) are a group of debilitating neurological disorders that primarily affect elderly populations and include Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), and amyotrophic lateral sclerosis (ALS). Currently, there are no therapies available that can delay, stop, or reverse the pathological progression of NDs in clinical settings. As the population ages, NDs are imposing a huge burden on public health systems and affected families. Animal models are important tools for preclinical investigations to understand disease pathogenesis and test potential treatments. While numerous rodent models of NDs have been developed to enhance our understanding of disease mechanisms, the limited success of translating findings from animal models to clinical practice suggests that there is still a need to bridge this translation gap. Old World non-human primates (NHPs), such as rhesus, cynomolgus, and vervet monkeys, are phylogenetically, physiologically, biochemically, and behaviorally most relevant to humans. This is particularly evident in the similarity of the structure and function of their central nervous systems, rendering such species uniquely valuable for neuroscience research. Recently, the development of several genetically modified NHP models of NDs has successfully recapitulated key pathologies and revealed novel mechanisms. This review focuses on the efficacy of NHPs in modeling NDs and the novel pathological insights gained, as well as the challenges associated with the generation of such models and the complexities involved in their subsequent analysis.

Inflammation as common link to progressive neurological diseases

Life expectancy has increased immensely over the past decades, bringing new challenges to the health systems as advanced age increases the predisposition for many diseases. One of those is the burden of neurologic disorders. While many hypotheses have been placed to explain aging mechanisms, it has been widely accepted that the increasing pro-inflammatory status with advanced age or "inflammaging" is a main determinant of biological aging. Furthermore, inflammaging is at the cornerstone of many age-related diseases and its involvement in neurologic disorders is an exciting hypothesis. Indeed, aging and neurologic disorders development in the elderly seem to share some basic pathways that fundamentally converge on inflammation. Peripheral inflammation significantly influences brain function and contributes to the development of neurological disorders, including Alzheimer's disease, Parkinson's disease, and multiple sclerosis. Understanding the role of inflammation in the pathogenesis of progressive neurological diseases is of crucial importance for developing effective treatments and interventions that can slow down or prevent disease progression, therefore, decreasing its social and economic burden.

Soluble epoxide hydrolase inhibitor blockage microglial cell activation in subnucleus caudalis in a persistent model of arthritis

Rheumatoid arthritis (RA) is a chronic condition characterized by pain and infiltration of immune cells into the joint. Immune cells can be activated, producing inflammatory cytokines, leading to continuously degenerative and inflammatory reactions and the temporomandibular joint (TMJ) can be affected by RA. In this scenario, novel targets are needed to increase treatment efficacy with minimized side effects. The epoxy-eicosatrienoic acids (EETs), are endogenous signaling molecules, playing important roles in diminishing inflammation and pain but are promptly metabolized by soluble epoxide hydrolase (sEH), generating less-bioactive acids.Therefore, sEH inhibitors is an interest therapeutic target to enhance the beneficial effect of natural EETs. TPPU is a potent sEH inhibitor that is capable of dampening EETs hydrolysis. Thus, we aimed to assess the impact of pharmacological sEH inhibition on a persistent model of albumin-induced arthritis in the TMJ, in two scenarios: first, as post-treatment, in an installed arthritic condition, and second, the protective role, in preventing the development of an arthritic condition. In addition, we investigate the influence of sEH inhibition on microglia cell activation in the trigeminal subnucleus caudalis (TSC) and in vitro experiments. Finally, we examined the astrocyte phenotype. Oral administration of TPPU, acts in multiple pathways, in a protective and reparative post-treatment, ameliorating the preservation of the TMJ morphology, reducing the hypernociception, with an immunosuppressive action reducing neutrophil and lymphocytes and pro-inflammatory cytokines in the TMJ of rats. In TSC, TPPU reduces the cytokine storm and attenuates the microglia activated P2X7/Cathepsin S/Fractalkine pathway and reduces the astrocyte activation and glutamate levels. Collectively, our findings revealed that sEH inhibition mitigates hypersensitive nociception through the regulation of microglia activation and astrocyte modulation, demonstrating the potential use of sEH inhibitors as immunoresolvents in the treatment of autoimmune disorders.

Alzheimer's Disease-Related Phospho-Tau181 Signals Are Localized to Demyelinated Axons of Parvalbumin-Positive GABAergic Interneurons in an App Knock-In Mouse Model of Amyloid-β Pathology

BACKGROUND

The tau protein phosphorylated at Thr181 (p-tau181) in cerebrospinal fluid and blood is a sensitive biomarker for Alzheimer's disease (AD). Increased p-tau181 levels correlate well with amyloid-β (Aβ) pathology and precede neurofibrillary tangle formation in the early stage of AD; however, the relationship between p-tau181 and Aβ-mediated pathology is less well understood. We recently reported that p-tau181 represents axonal abnormalities in mice with Aβ pathology (AppNLGF). However, from which neuronal subtype(s) these p-tau181-positive axons originate remains elusive.

OBJECTIVE

The main purpose of this study is to differentiate neuronal subtype(s) and elucidate damage associated with p-tau181-positive axons by immunohistochemical analysis of AppNLGF mice brains.

METHODS

Colocalization between p-tau181 and (1) unmyelinated axons positive for vesicular acetylcholine transporter or norepinephrine transporter and (2) myelinated axons positive for vesicular glutamate transporter, vesicular GABA transporter, or parvalbumin in the brains of 24-month-old AppNLGF and control mice without Aβ pathology were analyzed. The density of these axons was also compared.

RESULTS

Unmyelinated axons of cholinergic or noradrenergic neurons did not overlap with p-tau181. By contrast, p-tau181 signals colocalized with myelinated axons of parvalbumin-positive GABAergic interneurons but not of glutamatergic neurons. Interestingly, the density of unmyelinated axons was significantly decreased in AppNLGF mice, whereas that of glutamatergic, GABAergic, or p-tau181-positive axons was less affected. Instead, myelin sheaths surrounding p-tau181-positive axons were significantly reduced in AppNLGF mice.

CONCLUSION

This study demonstrates that p-tau181 signals colocalize with axons of parvalbumin-positive GABAergic interneurons with disrupted myelin sheaths in the brains of a mouse model of Aβ pathology.

Reduced Autophagy in Aged Trigeminal Neurons Causes Amyloid β Diffusion

The relationship between oral health and the development of Alzheimer's disease (AD) in the elderly is not yet well understood. In this regard, the association between aging or neurodegeneration of the trigeminal nervous system and the accumulation of amyloid-β(1-42) (Aβ₄₂) oligomers in the pathogenesis of AD is unknown. We focused on selective autophagy in the trigeminal mesencephalic nucleus (Vmes) and the diffusion of Aβ₄₂ oligomers with respect to aging of the trigeminal nervous system and whether the degeneration of Vmes neurons affects the diffusion of Aβ₄₂ oligomers. We used female 2- to 8-mo-old transgenic 3xTg-AD mice and App^NL-G-F knock-in mice and immunohistochemically examined aging-related changes in selective autophagy and Aβ₄₂ oligomer processing in the Vmes, which exhibits high amyloid-β (Aβ) expression. We induced degeneration of Vmes neurons by extracting the maxillary molars and examined the changes in Aβ₄₂ oligomer kinetics. Autophagosome-like membranes, which stained positive for Aβ, HO-1, and LC3B, were observed in Vmes neurons of 3xTg-AD mice, while there was weak immunoreactivity of the membranes for intraneuronal Aβ in App^NL-G-F mice. By contrast, there was strong immunopositivity for extracellular Aβ₄₂ oligomers with the formation of Aβ₄₂ oligomer clusters in App^NL-G-F mice. The expression of Rubicon, which indicates age-related deterioration of autophagy, increased the diffusion of Aβ₄₂ oligomer with the age of Vmes neurons. Tooth extraction increased the extracellular immunopositivity for Aβ₄₂ oligomers in App^NL-G-F mice. These results suggest that autophagy maintains homeostasis in Vmes neurons and that deterioration of autophagy due to aging or neurodegeneration leads to the diffusion of Aβ₄₂ oligomers into the extracellular space and possibly the development of AD.

Impaired episodic-like memory in a mouse model of Alzheimer's disease is associated with hyperactivity in prefrontal-hippocampal regions

Alzheimer's disease (AD) is a degenerative brain disorder with a long prodromal period. An APPNL-G-F knock-in mouse model is a preclinical model to study incipient pathologies during the early stages of AD. Despite behavioral tests revealing broad cognitive deficits in APPNL-G-F mice, detecting these impairments at the early disease phase has been challenging. In a cognitively demanding task that assessed episodic-like memory, 3-month-old wild-type mice could incidentally form and retrieve 'what-where-when' episodic associations of their past encounters. However, 3-month-old APPNL-G-F mice, corresponding to an early disease stage without prominent amyloid plaque pathology, displayed impairment in recalling 'what-where' information of past episodes. Episodic-like memory is also sensitive to the effect of age. Eight-month-old wild-type mice failed to retrieve conjunctive 'what-where-when' memories. This deficit was also observed in 8-month-old APPNL-G-F mice. c-Fos expression revealed that impaired memory retrieval in APPNL-G-F mice was accompanied by abnormal neuronal hyperactivity in the medial prefrontal cortex and CA1 dorsal hippocampus. These observations can be used for risk stratification during preclinical AD to detect and delay the progression into dementia.

The metal ion hypothesis of Alzheimer's disease and the anti-neuroinflammatory effect of metal chelators

Alzheimer's disease (AD), characterized by the β-amyloid protein (Aβ) deposition and tau hyperphosphorylation, is the most common dementia with uncertain etiology. The clinical trials of Aβ monoclonal antibody drugs have almost failed, giving rise to great attention on the other etiologic hypothesis regarding AD such as metal ions dysmetabolism and chronic neuroinflammation. Mounting evidence revealed that the metal ions (iron, copper, and zinc) were dysregulated in the susceptible brain regions of AD patients, which was highly associated with Aβ deposition, tau hyperphosphorylation, neuronal loss, as well as neuroinflammation. Further studies uncovered that iron, copper and zinc could not only enhance the production of Aβ but also directly bind to Aβ and tau to promote their aggregations. In addition, the accumulation of iron and copper could respectively promote ferroptosis and cuproptosis. Therefore, the metal ion chelators were recognized as promising agents for treating AD. This review comprehensively summarized the effects of metal ions on the Aβ dynamics and tau phosphorylation in the progression of AD. Furthermore, taking chronic neuroinflammation contributes to the progression of AD, we also provided a summary of the mechanisms concerning metal ions on neuroinflammation and highlighted the metal ion chelators may be potential agents to alleviate neuroinflammation under the condition of AD. Nevertheless, more investigations regarding metal ions on neuroinflammation should be taken into practice, and the effects of metal ion chelators on neuroinflammation should gain more attention. Running title: Metal chelators against neuroinflammation.

Caffeine protects against hippocampal alterations in type 2 diabetic rats via modulation of gliosis, inflammation and apoptosis

Type 2 diabetes (T2D) is implicated in the injury of several organs, including the brain resulting in neuronal damage, which may lead to cognitive impairment and dementia. Additionally, it is linked to inflammation, cytokine release, apoptosis and various degenerative conditions. Astrocytes and microglia might have a role in mediating these processes. Caffeine, a psychoactive beverage, has been shown to reduce the risk of cognitive and memory impairment. This study proposes anti-inflammatory and anti-apoptotic role of caffeine, which can be mediated via microglia/astrocyte activation and overexpression of pro-inflammatory molecules. T2D was induced in rats by feeding with high fat high sugar diet and injecting a single low dose streptozotocin (STZ) intraperitoneally. Other diabetic rats were given caffeine orally (in two doses) for 5 weeks, starting 1 week before STZ injection. Measurement of plasma cytokines, TNFα and IL6, was performed using enzyme-linked immunosorbent assay (ELISA) technique. After sacrificing animals, brains were obtained and processed for histological evaluation. Immunohistochemistry was also performed using the following primary antibodies, anti-astrocyte marker GFAP, anti-microglia marker CD11b and apoptotic marker (anti-cleaved caspase-3). There was upregulation of IL6 and TNF-α in diabetic rats. Additionally, histological evaluation of the hippocampus of diabetic rats revealed cellular degeneration. There was increased immunostaining of GFAP, CD11b and cleaved caspase-3 in diabetic rats. Pretreatment with caffeine to diabetic rats, resulted in improvement of structural changes and decrease in cytokine levels and immuno-markers, expression, and this was in a dose-dependent manner. In conclusion, caffeine had an ameliorative role in enhancing hippocampal degenerative changes in T2D.

Sex-split analysis of pathology and motor-behavioral outcomes in a mouse model of CLN8-Batten disease reveals an increased disease burden and trajectory in female Cln8mnd mice

BACKGROUND

CLN8-Batten disease (CLN8 disease) is a rare neurodegenerative disorder characterized phenotypically by progressive deterioration of motor and cognitive abilities, visual symptoms, epileptic seizures, and premature death. Mutations in CLN8 results in characteristic Batten disease symptoms and brain-wide pathology including accumulation of lysosomal storage material, gliosis, and neurodegeneration. Recent investigations of other subforms of Batten disease (CLN1, CLN3, CLN6) have emphasized the influence of biological sex on disease and treatment outcomes; however, little is known about sex differences in the CLN8 subtype. To determine the impact of sex on CLN8 disease burden and progression, we utilized a Cln8^mnd mouse model to measure the impact and progression of histopathological and behavioral outcomes between sexes.

RESULTS

Several notable sex differences were observed in the presentation of brain pathology, including Cln8^mnd female mice consistently presenting with greater GFAP⁺ astrocytosis and CD68⁺ microgliosis in the somatosensory cortex, ventral posteromedial/ventral posterolateral nuclei of the thalamus, striatum, and hippocampus when compared to Cln8^mnd male mice. Furthermore, sex differences in motor-behavioral assessments revealed Cln8^mnd female mice experience poorer motor performance and earlier death than their male counterparts. Cln8^mnd mice treated with an AAV9-mediated gene therapy were also examined to assess sex differences on therapeutics outcomes, which revealed no appreciable differences between the sexes when responding to the therapy.

CONCLUSIONS

Taken together, our results provide further evidence of biologic sex as a modifier of Batten disease progression and outcome, thus warranting consideration when conducting investigations and monitoring therapeutic impact.

Multifunctional Therapeutic Cyclodextrin-Appended Dendrimer Complex for Treatment of Systemic and Localized Amyloidosis

Amyloidosis pathologically proceeds via production of amyloidogenic proteins by organs, formation of protein aggregates through structural changes, and their deposition on tissues. A growing body of evidence demonstrates that amyloidosis generally develops through three critical pathological steps: (1) production of amyloid precursor proteins, (2) amyloid formation, and (3) amyloid deposition. However, no clinically effective therapy that is capable of targeting each pathological step of amyloidosis independently is currently available. Here, we combined therapeutic effects and developed a short hairpin RNA expression vector (shRNA) complex with a cyclodextrin-appended cationic dendrimer (CDE) as a novel multitarget therapeutic drug that is capable of simultaneously suppressing these three steps. We evaluated its therapeutic effects on systemic transthyretin (ATTR) amyloidosis and Alzheimer's disease (AD) as localized amyloidosis, by targeting TTR and amyloid β, respectively. CDE/shRNA exhibited RNAi effects to suppress amyloid protein production and also achieved both inhibition of amyloid formation and disruption of existing amyloid fibrils. The multitarget therapeutic effects of CDE/shRNA were confirmed by evaluating TTR deposition reduction in early- and late-onset human ATTR amyloidosis model rats and amyloid β deposition reduction in App^{NL-G-F/NL-G-F} AD model mice. Thus, the CDE/shRNA complex exhibits multifunctional therapeutic efficacy and may reveal novel strategies for establishing curative treatments for both systemic and localized amyloidosis.

β-secretase inhibition prevents structural spine plasticity deficits in AppNL-G-F mice

All clinical BACE1-inhibitor trials for the treatment of Alzheimer's Disease (AD) have failed due to insufficient efficacy or side effects like worsening of cognitive symptoms. However, the scientific evidence to date suggests that BACE1-inhibition could be an effective preventative measure if applied prior to the accumulation of amyloid-beta (Aβ)-peptide and resultant impairment of synaptic function. Preclinical studies have associated BACE1-inhibition-induced cognitive deficits with decreased dendritic spine density. Therefore, we investigated dose-dependent effects of BACE1-inhibition on hippocampal dendritic spine dynamics in an APP knock-in mouse line for the first time. We conducted in vivo two-photon microscopy in the stratum oriens layer of hippocampal CA1 neurons in 3.5-month-old App^NL-G-FGFP-M mice over 6 weeks to monitor the effect of potential preventive treatment with a high and low dose of the BACE1-inhibitor NB-360 on dendritic spine dynamics. Structural spine plasticity was severely impaired in untreated App^NL-G-FGFP-M mice, although spines were not yet showing signs of degeneration. Prolonged high-dose BACE1-inhibition significantly enhanced spine formation, improving spine dynamics in the AD mouse model. We conclude that in an early AD stage characterized by low Aβ-accumulation and no irreversible spine loss, BACE1-inhibition could hold the progressive synapse loss and cognitive decline by improving structural spine dynamics.

The Physiological Effects of Air Pollution: Particulate Matter, Physiology and Disease

Nine out of 10 people breathe air that does not meet World Health Organization pollution limits. Air pollutants include gasses and particulate matter and collectively are responsible for ~8 million annual deaths. Particulate matter is the most dangerous form of air pollution, causing inflammatory and oxidative tissue damage. A deeper understanding of the physiological effects of particulate matter is needed for effective disease prevention and treatment. This review will summarize the impact of particulate matter on physiological systems, and where possible will refer to apposite epidemiological and toxicological studies. By discussing a broad cross-section of available data, we hope this review appeals to a wide readership and provides some insight on the impacts of particulate matter on human health.

Inbred Mice Again at Stake: How the Cognitive Profile of the Wild-Type Mouse Background Discloses Pathogenic Effects of APP Mutations

Increasing efforts have been made in the last decades to increase the face validity of Alzheimer's disease (AD) mouse models. Main advancements have consisted in generating AD mutations closer to those identified in humans, enhancing genetic diversity of wild-type backgrounds, and choosing protocols much apt to reveal AD-like cognitive dysfunctions. Nevertheless, two aspects remain less considered: the cognitive specialization of inbred strains used as recipient backgrounds of mutations and the heuristic importance of studying destabilization of memory circuits in pre-symptomatic mice facing cognitive challenges. This article underscores the relevance of these behavioral/experimental aspects by reviewing data which show that (i) inbred mice differ in their innate predisposition to rely on episodic vs. procedural memory, which implicates differential sensitivity to mutations aimed at disrupting temporal lobe-dependent memory, and that (ii) investigating training-driven neural alterations in asymptomatic mutants unveils early synaptic damage, which considerably anticipates detection of AD first signs.

Z-Guggulsterone attenuates cognitive defects and decreases neuroinflammation in APPswe/PS1dE9 mice through inhibiting the TLR4 signaling pathway

Growing evidence indicates that inflammatory damage is implicated in the pathogenesis of Alzheimer's disease (AD). Z-Guggulsterone (Z-GS) is a natural steroid, which is extracted from Commiphora mukul and has anti-inflammatory effects in vivo and in vitro. In the present study, we investigated the disease-modifying effects of chronic Z-GS administration on the cognitive and neuropathological impairments in the transgenic mouse models of AD. We found that chronic Z-GS administration prevented learning and memory deficits in the APPswe/PS1dE9 mice. In addition, Z-GS treatment significantly decreased cerebral amyloid-β (Aβ) levels and plaque burden via inhibiting amyloid precursor protein (APP) processing by reducing beta-site APP cleaving enzyme 1 (BACE1) expression in the APPswe/PS1dE9 mice. We also found that Z-GS treatment markedly alleviated neuroinflammation and reduced synaptic defects in the APPswe/PS1dE9 mice. Furthermore, the activated TLR4/NF-κB signaling pathways in APPswe/PS1dE9 mice were remarkably inhibited by Z-GS treatment, which was achieved via suppressing the phosphorylation of JNK. Collectively, our data demonstrate that chronic Z-GS treatment restores cognitive defects and reverses multiple neuropathological impairments in the APPswe/PS1dE9 mice. This study provides novel insights into the neuroprotective effects and neurobiological mechanisms of Z-GS on AD, indicating that Z-GS is a promising disease-modifying agent for the treatment of AD.

Novel App knock-in mouse model shows key features of amyloid pathology and reveals profound metabolic dysregulation of microglia

BACKGROUND

Genetic mutations underlying familial Alzheimer's disease (AD) were identified decades ago, but the field is still in search of transformative therapies for patients. While mouse models based on overexpression of mutated transgenes have yielded key insights in mechanisms of disease, those models are subject to artifacts, including random genetic integration of the transgene, ectopic expression and non-physiological protein levels. The genetic engineering of novel mouse models using knock-in approaches addresses some of those limitations. With mounting evidence of the role played by microglia in AD, high-dimensional approaches to phenotype microglia in those models are critical to refine our understanding of the immune response in the brain.

METHODS

We engineered a novel App knock-in mouse model (AppSAA) using homologous recombination to introduce three disease-causing coding mutations (Swedish, Arctic and Austrian) to the mouse App gene. Amyloid-β pathology, neurodegeneration, glial responses, brain metabolism and behavioral phenotypes were characterized in heterozygous and homozygous AppSAA mice at different ages in brain and/ or biofluids. Wild type littermate mice were used as experimental controls. We used in situ imaging technologies to define the whole-brain distribution of amyloid plaques and compare it to other AD mouse models and human brain pathology. To further explore the microglial response to AD relevant pathology, we isolated microglia with fibrillar Aβ content from the brain and performed transcriptomics and metabolomics analyses and in vivo brain imaging to measure energy metabolism and microglial response. Finally, we also characterized the mice in various behavioral assays.

RESULTS

Leveraging multi-omics approaches, we discovered profound alteration of diverse lipids and metabolites as well as an exacerbated disease-associated transcriptomic response in microglia with high intracellular Aβ content. The AppSAA knock-in mouse model recapitulates key pathological features of AD such as a progressive accumulation of parenchymal amyloid plaques and vascular amyloid deposits, altered astroglial and microglial responses and elevation of CSF markers of neurodegeneration. Those observations were associated with increased TSPO and FDG-PET brain signals and a hyperactivity phenotype as the animals aged.

DISCUSSION

Our findings demonstrate that fibrillar Aβ in microglia is associated with lipid dyshomeostasis consistent with lysosomal dysfunction and foam cell phenotypes as well as profound immuno-metabolic perturbations, opening new avenues to further investigate metabolic pathways at play in microglia responding to AD-relevant pathogenesis. The in-depth characterization of pathological hallmarks of AD in this novel and open-access mouse model should serve as a resource for the scientific community to investigate disease-relevant biology.

The Roles of Long-Term Hyperhomocysteinemia and Micronutrient Supplementation in the AppNL–G–F Model of Alzheimer’s Disease

A causal contribution of hyperhomocysteinemia to cognitive decline and Alzheimer’s disease (AD), as well as potential prevention or mitigation of the pathology by dietary intervention, have frequently been subjects of controversy. In the present in vivo study, we attempted to further elucidate the impact of elevated homocysteine (HCys) and homocysteic acid (HCA) levels, induced by dietary B-vitamin deficiency, and micronutrient supplementation on AD-like pathology, which was simulated using the amyloid-based App^NL–G–F knock-in mouse model. For this purpose, cognitive assessment was complemented by analyses of ex vivo parameters in whole blood, serum, CSF, and brain tissues from the mice. Furthermore, neurotoxicity of HCys and HCA was assessed in a separate in vitro assay. In confirmation of our previous study, older App^NL–G–F mice also exhibited subtle phenotypic impairment and extensive cerebral amyloidosis, whereas dietary manipulations did not result in significant effects. As revealed by proximity extension assay-based proteome analysis, the App^NL–G–F genotype led to an upregulation of AD-characteristic neuronal markers. Hyperhomocysteinemia, in contrast, indicated mainly vascular effects. Overall, since there was an absence of a distinct phenotype despite both a significant amyloid-β burden and serum HCys elevation, the results in this study did not corroborate the pathological role of amyloid-β according to the “amyloid hypothesis,” nor of hyperhomocysteinemia on cognitive performance. Nevertheless, this study aided in further characterizing the App^NL–G–F model and in elucidating the role of HCys in diverse biological processes. The idea of AD prevention with the investigated micronutrients, however, was not supported, at least in this mouse model of the disease.

Assessments of prolonged effects of desflurane and sevoflurane on motor learning deficits in aged AppNL-G-F/NL-G-F mice

As the proportion of elderly in society increases, so do the number of older patients undergoing surgical procedures. This is concerning as exposure to anesthesia has been identified as a risk factor for Alzheimer's disease (AD). However, the causal relationship between clinical AD development and anesthesia remains conjectural. Preclinical studies have demonstrated that anesthesia, such as halothane, isoflurane, and sevoflurane, induces AD-like pathophysiological changes and cognitive impairments in transgenic mouse models of AD. Desflurane does not have these effects and is expected to have more potential for use in elderly patients, yet little is known about its effects, especially on non-cognitive functions, such as motor and emotional functions. Thus, we examined the postanesthetic effects of desflurane and sevoflurane on motor and emotional function in aged App^{NL-G-F/NL-G-F} (App-KI) mice. This is a recently developed transgenic mouse model of AD exhibiting amyloid β peptide (Aβ) amyloidosis and a neuroinflammatory response in an age-dependent manner without non-physiological amyloid precursor protein (APP) overexpression. Mice were subjected to a short behavioral test battery consisting of an elevated plus maze, a balance beam test, and a tail suspension test seven days after exposure to 8.0% desflurane for 6 h or 2.8% sevoflurane for 2 h. App-KI mice showed significant increments in the percentage of entry and time spent in open arms in the elevated plus maze, increments in the number of slips and latency to traverse for the balance beam test, increments in the limb clasping score, increments in immobile duration, and decrements in latency to first immobile episode for the tail suspension test compared to age-matched wild type (WT) controls. Desflurane- and sevoflurane-exposed App-KI mice showed a delayed decrement in the number of slips for each trial in the balance beam test, while air-treated App-KI mice rapidly improved their performance, and increased their clasping behavior in the tail suspension test. Furthermore, App-KI inhibited the change in membrane GluA3 following exposure to anesthetics in the cerebellum. These results suggest high validity of App-KI mice as an animal model of AD.

Common pathways in dementia and diabetic retinopathy: understanding the mechanisms of diabetes-related cognitive decline

Type 2 diabetes (T2D) is associated with multiple comorbidities, including diabetic retinopathy (DR) and cognitive decline, and T2D patients have a significantly higher risk of developing Alzheimer's disease (AD). Both DR and AD are characterized by a number of pathological mechanisms that coalesce around the neurovascular unit, including neuroinflammation and degeneration, vascular degeneration, and glial activation. Chronic hyperglycemia and insulin resistance also play a significant role, leading to activation of pathological mechanisms such as increased oxidative stress and the accumulation of advanced glycation end-products (AGEs). Understanding these common pathways and the degree to which they occur simultaneously in the brain and retina during diabetes will provide avenues to identify T2D patients at risk of cognitive decline.

MUTYH Actively Contributes to Microglial Activation and Impaired Neurogenesis in the Pathogenesis of Alzheimer's Disease

Oxidative stress is a major risk factor for Alzheimer's disease (AD), which is characterized by brain atrophy, amyloid plaques, neurofibrillary tangles, and loss of neurons. 8-Oxoguanine, a major oxidatively generated nucleobase highly accumulated in the AD brain, is known to cause neurodegeneration. In mammalian cells, several enzymes play essential roles in minimizing the 8-oxoguanine accumulation in DNA. MUTYH with adenine DNA glycosylase activity excises adenine inserted opposite 8-oxoguanine in DNA. MUTYH is reported to actively contribute to the neurodegenerative process in Parkinson and Huntington diseases and some mouse models of neurodegenerative diseases by accelerating neuronal dysfunction and microgliosis under oxidative conditions; however, whether or not MUTYH is involved in AD pathogenesis remains unclear. In the present study, we examined the contribution of MUTYH to the AD pathogenesis. Using postmortem human brains, we showed that various types of MUTYH transcripts and proteins are expressed in most hippocampal neurons and glia in both non-AD and AD brains. We further introduced MUTYH deficiency into App ^{NL-G-F/NL-G-F} knock-in AD model mice, which produce humanized toxic amyloid-β without the overexpression of APP protein, and investigated the effects of MUTYH deficiency on the behavior, pathology, gene expression, and neurogenesis. MUTYH deficiency improved memory impairment in App ^{NL-G-F/NL-G-F} mice, accompanied by reduced microgliosis. Gene expression profiling strongly suggested that MUTYH is involved in the microglial response pathways under AD pathology and contributes to the phagocytic activity of disease-associated microglia. We also found that MUTYH deficiency ameliorates impaired neurogenesis in the hippocampus, thus improving memory impairment. In conclusion, we propose that MUTYH, which is expressed in the hippocampus of AD patients as well as non-AD subjects, actively contributes to memory impairment by inducing microgliosis with poor neurogenesis in the preclinical AD phase and that MUTYH is a novel therapeutic target for AD, as its deficiency is highly beneficial for ameliorating AD pathogenesis.

Dynamic Role of Phospholipases A2 in Health and Diseases in the Central Nervous System

Phospholipids are major components in the lipid bilayer of cell membranes. These molecules are comprised of two acyl or alkyl groups and different phospho-base groups linked to the glycerol backbone. Over the years, substantial interest has focused on metabolism of phospholipids by phospholipases and the role of their metabolic products in mediating cell functions. The high levels of polyunsaturated fatty acids (PUFA) in the central nervous system (CNS) have led to studies centered on phospholipases A2 (PLA2s), enzymes responsible for cleaving the acyl groups at the sn-2 position of the phospholipids and resulting in production of PUFA and lysophospholipids. Among the many subtypes of PLA2s, studies have centered on three major types of PLA2s, namely, the calcium-dependent cytosolic cPLA2, the calcium-independent iPLA2 and the secretory sPLA2. These PLA2s are different in their molecular structures, cellular localization and, thus, production of lipid mediators with diverse functions. In the past, studies on specific role of PLA2 on cells in the CNS are limited, partly because of the complex cellular make-up of the nervous tissue. However, understanding of the molecular actions of these PLA2s have improved with recent advances in techniques for separation and isolation of specific cell types in the brain tissue as well as development of sensitive molecular tools for analyses of proteins and lipids. A major goal here is to summarize recent studies on the characteristics and dynamic roles of the three major types of PLA2s and their oxidative products towards brain health and neurological disorders.

Microglia and Astrocytes in Alzheimer's Disease in the Context of the Aberrant Copper Homeostasis Hypothesis

Evidence of copper's (Cu) involvement in Alzheimer's disease (AD) is available, but information on Cu involvement in microglia and astrocytes during the course of AD has yet to be structurally discussed. This review deals with this matter in an attempt to provide an updated discussion on the role of reactive glia challenged by excess labile Cu in a wide picture that embraces all the major processes identified as playing a role in toxicity induced by an imbalance of Cu in AD.

Widespread Reduced Density of Noradrenergic Locus Coeruleus Axons in the App Knock-In Mouse Model of Amyloid-β Amyloidosis

BACKGROUND

The locus coeruleus (LC), a brainstem nucleus comprising noradrenergic neurons, is one of the earliest regions affected by Alzheimer's disease (AD). Amyloid-β (Aβ) pathology in the cortex in AD is thought to exacerbate the age-related loss of LC neurons, which may lead to cortical tau pathology. However, mechanisms underlying LC neurodegeneration remain elusive.

OBJECTIVE

Here, we aimed to examine how noradrenergic neurons are affected by cortical Aβ pathology in AppNL-G-F/NL-G-F knock-in mice.

METHODS

The density of noradrenergic axons in LC-innervated regions and the LC neuron number were analyzed by an immunohistochemical method. To explore the potential mechanisms for LC degeneration, we also examined the occurrence of tau pathology in LC neurons, the association of reactive gliosis with LC neurons, and impaired trophic support in the brains of AppNL-G-F/NL-G-F mice.

RESULTS

We observed a significant reduction in the density of noradrenergic axons from the LC in aged AppNL-G-F/NL-G-F mice without neuron loss or tau pathology, which was not limited to areas near Aβ plaques. However, none of the factors known to be related to the maintenance of LC neurons (i.e., somatostatin/somatostatin receptor 2, brain-derived neurotrophic factor, nerve growth factor, and neurotrophin-3) were significantly reduced in AppNL-G-F/NL-G-F mice.

CONCLUSION

This study demonstrates that cortical Aβ pathology induces noradrenergic neurodegeneration, and further elucidation of the underlying mechanisms will reveal effective therapeutics to halt AD progression.

Prokineticin-2 prevents neuronal cell deaths in a model of traumatic brain injury

Prokineticin-2 (Prok2) is an important secreted protein likely involved in the pathogenesis of several acute and chronic neurological diseases through currently unidentified regulatory mechanisms. The initial mechanical injury of neurons by traumatic brain injury triggers multiple secondary responses including various cell death programs. One of these is ferroptosis, which is associated with dysregulation of iron and thiols and culminates in fatal lipid peroxidation. Here, we explore the regulatory role of Prok2 in neuronal ferroptosis in vitro and in vivo. We show that Prok2 prevents neuronal cell death by suppressing the biosynthesis of lipid peroxidation substrates, arachidonic acid-phospholipids, via accelerated F-box only protein 10 (Fbxo10)-driven ubiquitination, degradation of long-chain-fatty-acid-CoA ligase 4 (Acsl4), and inhibition of lipid peroxidation. Mice injected with adeno-associated virus-Prok2 before controlled cortical impact injury show reduced neuronal degeneration and improved motor and cognitive functions, which could be inhibited by Fbxo10 knockdown. Our study shows that Prok2 mediates neuronal cell deaths in traumatic brain injury via ferroptosis.

Comparison of memory, affective behavior, and neuropathology in APPNLGF knock-in mice to 5xFAD and APP/PS1 mice

Transgenic mouse models of Aβ amyloidosis generated by knock-in of a humanized Aβ sequence can offer some advantages over the transgenic models that overexpress amyloid precursor protein (APP). However, systematic comparison of memory, behavioral, and neuropathological phenotypes between these models has not been well documented. In this study, we compared memory and affective behavior in APP^NLGF mice, an APP knock-in model, to two widely used mouse models of Alzheimer's disease, 5xFAD and APP/PS1 mice, at 10 months of age. We found that, despite similar deficits in working memory, object recognition, and social recognition memory, APP^NLGF and 5xFAD mice but not APP/PS1 mice show compelling anxiety- and depressive-like behavior, and exhibited a marked impairment of social interaction. We quantified corticolimbic Aβ plaques, which were lowest in APP^NLGF, intermediate in APP/PS1, and highest in 5xFAD mice. Interestingly, analysis of plaque size revealed that plaques were largest in APP/PS1 mice, intermediate in 5xFAD mice, and smallest in APP^NLGF mice. Finally, we observed a significantly higher percentage of the area occupied by plaques in both 5xFAD and APP/PS1 relative to APP^NLGF mice. Overall, our findings suggest that the severity of Aβ neuropathology is not directly correlated with memory and affective behavior impairments between these three transgenic mouse models. Additionally, APP^NLGF may represent a valid mouse model for studying AD comorbid with anxiety and depression.

Retinal Thickness Changes Over Time in a Murine AD Model APP NL-F/NL-F

Background: Alzheimer's disease (AD) may present retinal changes before brain pathology, suggesting the retina as an accessible biomarker of AD. The present work is a diachronic study using spectral domain optical coherence tomography (SD-OCT) to determine the total retinal thickness and retinal nerve fiber layer (RNFL) thickness in an APP^{NL−F/NL−F} mouse model of AD at 6, 9, 12, 15, 17, and 20 months old compared to wild type (WT) animals.

Methods: Total retinal thickness and RNFL thickness were determined. The mean total retinal thickness was analyzed following the Early Treatment Diabetic Retinopathy Study sectors. RNFL was measured in six sectors of axonal ring scans around the optic nerve.

Results: In the APP^{NL−F/NL−F} group compared to WT animals, the total retinal thickness changes observed were the following: (i) At 6-months-old, a significant thinning in the outer temporal sector was observed; (ii) at 15-months-old a significant thinning in the inner temporal and in the inner and outer inferior retinal sectors was noticed; (iii) at 17-months-old, a significant thickening in the inferior and nasal sectors was found in both inner and outer rings; and (iv) at 20-months-old, a significant thinning in the inner ring of nasal, temporal, and inferior retina and in the outer ring of superior and temporal retina was seen. In RNFL thickness, there was significant thinning in the global analysis and in nasal and inner-temporal sectors at 6 months old. Thinning was also found in the supero-temporal and nasal sectors and global value at 20 months old.

Conclusions: In the APP^{NL−F/NL−F} AD model, the retinal thickness showed thinning, possibly produced by neurodegeneration alternating with thickening caused by deposits and neuroinflammation in some areas of the retina. These changes over time are similar to those observed in the human retina and could be a biomarker for AD. The APP^{NL−F/NL−F} AD model may help us better understand the different retinal changes during the progression of AD.

APP/PS1 Gene-Environment Noise Interaction Aggravates AD-like Neuropathology in Hippocampus Via Activation of the VDAC1 Positive Feedback Loop

BACKGROUND

Environmental risk factors, including environmental noise stress, and genetic factors, have been associated with the occurrence and development of Alzheimer's disease (AD). However, the exact role and mechanism of AD-like pathology induced by environment-gene interactions between environmental noise and APP/PS1 gene remain elusive.

METHODS

Herein, we investigated the impact of chronic noise exposure on AD-like neuropathology in APP/PS1 transgenic mice. The Morris water maze (MWM) task was conducted to evaluate AD-like changes. The hippocampal phosphorylated Tau, amyloid-β (Aβ), and neuroinflammation were assessed. We also assessed changes in positive feedback loop signaling of the voltage-dependent anion channel 1 (VDAC1) to explore the potential underlying mechanism linking AD-like neuropathology to noise-APP/PS1 interactions.

RESULTS

Long-term noise exposure significantly increased the escape latency and the number of platform crossings in the MWM task. The Aβ overproduction was induced in the hippocampus of APP/PS1 mice, along with the increase of Tau phosphorylation at Ser396 and Thr231 and the increase of the microglia and astrocytes markers expression. Moreover, the VDAC1-AKT (protein kinase B)-GSK3β (glycogen synthase kinase 3 beta)-VDAC1 signaling pathway was abnormally activated in the hippocampus of APP/PS1 mice after noise exposure.

CONCLUSION

Chronic noise exposure and APP/PS1 overexpression may synergistically exacerbate cognitive impairment and neuropathological changes that occur in AD. This interaction may be mediated by the positive feedback loop of the VDAC1-AKT-GSK3β-VDAC1 signaling pathway.

Gene-environment interaction promotes Alzheimer's risk as revealed by synergy of repeated mild traumatic brain injury and mouse App knock-in

There is a strong unmet need for translational progress towards Alzheimer's disease (AD) modifying therapy. Unfortunately, preclinical modeling of the disease has been disappointing, relying primarily on transgenic mouse overexpression of rare dominant mutations. Clinical manifestation of AD symptoms is known to reflect interaction between environmental and genetic risks. Mild traumatic brain injury (mTBI) is an environmental risk for dementia, including Alzheimer's, but there has been limited mechanistic analysis of mTBI contribution to AD. Here, we investigate the interplay between mTBI and Aβ precursor protein gene mutation in AD pathogenesis. We employed a knock-in (KI) model of AD that expresses the Aß-containing exons from human APP bearing the Swedish and Iberian mutations, namely AppNL-F/NL-F mice. Without environmental risk, this genetic variation yields minimal mouse symptomatology. Anesthetized 4-month-old KI mice and their age-matched wild type (WT) controls were subjected to repeated mild closed head injury (rmCHI), once daily for 14 days. Anesthetized, uninjured genotype- and age-matched mice were used as sham controls. At 3- and 8-months post-injury, amyloid-β, phospho-tau and Iba1 expression in the injured KI cortices were assessed. Our data reveal that rmCHI enhances accumulation of amyloid-β and hyperphosphorylated tau inclusions, as well as neuroinflammation in AppNL-F/NL-F mice. Furthermore, novel object recognition and Morris water maze tests demonstrated that rmCHI greatly exacerbates persistent cognitive deficits in APPNL-F/NL-F mice. Therefore, study of gene-environment interaction demonstrates that combining risk factors provides a more robust model for AD, and that repeated mTBI substantially accelerates AD pathology in a genetically susceptible situation.

Impact of Hyperhomocysteinemia and Different Dietary Interventions on Cognitive Performance in a Knock-in Mouse Model for Alzheimer's Disease

BACKGROUND

Hyperhomocysteinemia is considered a possible contributor to the complex pathology of Alzheimer's disease (AD). For years, researchers in this field have discussed the apparent detrimental effects of the endogenous amino acid homocysteine in the brain. In this study, the roles of hyperhomocysteinemia driven by vitamin B deficiency, as well as potentially beneficial dietary interventions, were investigated in the novel App^NL-G-F knock-in mouse model for AD, simulating an early stage of the disease.

METHODS

Urine and serum samples were analyzed using a validated LC-MS/MS method and the impact of different experimental diets on cognitive performance was studied in a comprehensive behavioral test battery. Finally, we analyzed brain samples immunohistochemically in order to assess amyloid-β (Aβ) plaque deposition.

RESULTS

Behavioral testing data indicated subtle cognitive deficits in App^NL-G-F compared to C57BL/6J wild type mice. Elevation of homocysteine and homocysteic acid, as well as counteracting dietary interventions, mostly did not result in significant effects on learning and memory performance, nor in a modified Aβ plaque deposition in 35-week-old App^NL-G-F mice.

CONCLUSION

Despite prominent Aβ plaque deposition, the App^NL-G-F model merely displays a very mild AD-like phenotype at the investigated age. Older App^NL-G-F mice should be tested in order to further investigate potential effects of hyperhomocysteinemia and dietary interventions.

Gut-Brain Axis: Role of Gut Microbiota on Neurological Disorders and How Probiotics/Prebiotics Beneficially Modulate Microbial and Immune Pathways to Improve Brain Functions

The gut microbiome acts as an integral part of the gastrointestinal tract (GIT) that has the largest and vulnerable surface with desirable features to observe foods, nutrients, and environmental factors, as well as to differentiate commensals, invading pathogens, and others. It is well-known that the gut has a strong connection with the central nervous system (CNS) in the context of health and disease. A healthy gut with diverse microbes is vital for normal brain functions and emotional behaviors. In addition, the CNS controls most aspects of the GI physiology. The molecular interaction between the gut/microbiome and CNS is complex and bidirectional, ensuring the maintenance of gut homeostasis and proper digestion. Besides this, several mechanisms have been proposed, including endocrine, neuronal, toll-like receptor, and metabolites-dependent pathways. Changes in the bidirectional relationship between the GIT and CNS are linked with the pathogenesis of gastrointestinal and neurological disorders; therefore, the microbiota/gut-and-brain axis is an emerging and widely accepted concept. In this review, we summarize the recent findings supporting the role of the gut microbiota and immune system on the maintenance of brain functions and the development of neurological disorders. In addition, we highlight the recent advances in improving of neurological diseases by probiotics/prebiotics/synbiotics and fecal microbiota transplantation via the concept of the gut-brain axis.

Subchronic administration of auranofin reduced amyloid-β plaque pathology in a transgenic APPNL-G-F/NL-G-F mouse model

Alzheimer's disease (AD) is the most common cause of dementia. Neuropathological processes, including the accumulation of amyloid-β (Aβ) plaques and neurofibrillary tangles, and neuroinflammation, lead to cognitive impairment at middle and eventually later stages of AD progression. Over the last decade, focused efforts have explored repurposed drug approaches for AD pathophysiological mechanisms. Recently, auranofin, an anti-inflammatory drug, was shown to have therapeutic potential in a number of diseases in addition to rheumatoid arthritis. Surprisingly, no data regarding the effects of auranofin on cognitive deficits in AD mice or the influence of auranofin on Aβ pathology and neuroinflammatory processes are available. In the present study, we used 14-month-old transgenic male APP^{NL-G-F/NL-G-F} mice to assess the effects of subchronic administration of auranofin at low doses (1 and 5 mg/kg, intraperitoneal) on spatial memory, Aβ pathology and the expression of cortical and hippocampal proteins (glial fibrillary acidic protein (GFAP), ionized calcium binding adaptor molecule-1 (Iba-1)) and proteins related to synaptic plasticity (glutamic acid decarboxylase 67 (GAD67), homer proteins homologue-1 (Homer-1)). The data demonstrated that auranofin significantly decreased Aβ deposition in the hippocampus and the number of Aβ plaques in the cingulate cortex, but it did not have memory-enhancing effects or induce changes in the expression of the studied proteins. Our current results highlight the importance of considering further pre-clinical research to investigate the possible beneficial effects of auranofin on the other pathological aspects of AD.

Amyloid β induces interneuron-specific changes in the hippocampus of APPNL-F mice

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by cognitive decline and amyloid-beta (Aβ) depositions generated by the proteolysis of amyloid precursor protein (APP) in the brain. In APPNL-F mice, APP gene was humanized and contains two familial AD mutations, and APP-unlike other mouse models of AD-is driven by the endogenous mouse APP promoter. Similar to people without apparent cognitive dysfunction but with heavy Aβ plaque load, we found no significant decline in the working memory of adult APPNL-F mice, but these mice showed decline in the expression of normal anxiety. Using immunohistochemistry and 3D block-face scanning electron microscopy, we found no changes in GABAA receptor positivity and size of somatic and dendritic synapses of hippocampal interneurons. We did not find alterations in the level of expression of perineuronal nets around parvalbumin (PV) interneurons or in the density of PV- or somatostatin-positive hippocampal interneurons. However, in contrast to other investigated cell types, PV interneuron axons were occasionally mildly dystrophic around Aβ plaques, and the synapses of PV-positive axon initial segment (AIS)-targeting interneurons were significantly enlarged. Our results suggest that PV interneurons are highly resistant to amyloidosis in APPNL-F mice and amyloid-induced increase in hippocampal pyramidal cell excitability may be compensated by PV-positive AIS-targeting cells. Mechanisms that make PV neurons more resilient could therefore be exploited in the treatment of AD for mitigating Aβ-related inflammatory effects on neurons.

Astaxanthin Ameliorated Parvalbumin-Positive Neuron Deficits and Alzheimer's Disease-Related Pathological Progression in the Hippocampus of AppNL-G-F/NL-G-F Mice

Growing evidence suggests that oxidative stress due to amyloid β (Aβ) accumulation is involved in Alzheimer's disease (AD) through the formation of amyloid plaque, which leads to hyperphosphorylation of tau, microglial activation, and cognitive deficits. The dysfunction or phenotypic loss of parvalbumin (PV)-positive neurons has been implicated in cognitive deficits. Astaxanthin is one of carotenoids and known as a highly potent antioxidant. We hypothesized that astaxanthin's antioxidant effects may prevent the onset of cognitive deficits in AD by preventing AD pathological processes associated with oxidative stress. In the present study, we investigated the effects of astaxanthin intake on the cognitive and pathological progression of AD in a mouse model of AD. The App^{NL-G-F/NL-G-F} mice were fed with or without astaxanthin from 5-to-6 weeks old, and cognitive functions were evaluated using a Barnes maze test at 6 months old. PV-positive neurons were investigated in the hippocampus. Aβ42 deposits, accumulation of microglia, and phosphorylated tau (pTau) were immunohistochemically analyzed in the hippocampus. The hippocampal anti-oxidant status was also investigated. The Barnes maze test indicated that astaxanthin significantly ameliorated memory deficits. Astaxanthin reduced Aβ42 deposition and pTau-positive areal fraction, while it increased PV-positive neuron density and microglial accumulation per unit fraction of Aβ42 deposition in the hippocampus. Furthermore, astaxanthin increased total glutathione (GSH) levels, although 4-hydroxy-2,3-trans-nonenal (4-HNE) protein adduct levels (oxidative stress marker) remained high in the astaxanthin supplemented mice. The results indicated that astaxanthin ameliorated memory deficits and significantly reversed AD pathological processes (Aβ42 deposition, pTau formation, GSH decrease, and PV-positive neuronal deficits). The elevated GSH levels and resultant recovery of PV-positive neuron density, as well as microglial activation, may prevent these pathological processes.