Experimental colitis in young Tg2576 mice accelerates the onset of an Alzheimer's-like clinical phenotype.

Systemic inflammation and neuroinflammation affect the natural course of the sporadic form of Alzheimer's disease (AD), as supported by epidemiological and preclinical data, and several epidemiological studies indicate a higher prevalence of AD in patients with inflammatory bowel disease. In this study, we explored whether colitis induced by dextran sulfate sodium (DSS) in young, presymptomatic/preplaque mice worsens and/or anticipates age-dependent cognitive impairment in Tg2576, a widely used mouse model of AD. We demonstrated that DSS colitis induced in young Tg2576 mice anticipates the onset age of learning and memory deficit in the Morris water maze test. To explore potential mechanisms behind the acceleration of cognitive decline in Tg2576 mice by DSS colitis, we focused on gut microbiota, systemic inflammation and neuroinflammation markers. We observed a Firmicutes/Bacteroidetes ratio change in Tg2576 DSS animals comparable to that of elderly Tg2576 mice, suggesting accelerated microbiota aging in Tg2576 DSS mice, a change not observed in C57BL6 DSS mice. We also observed substantial differences between Tg2576 and WT mice in several inflammation and neuroinflammation-related parameters as early as 3 months of age, well before plaque deposition, a picture which evolved rapidly (between 3 and 5.5 months of age) in contrast to Tg2576 and WT littermates not treated with DSS. In detail, following induction of DSS colitis, WT and Tg2576 mice exhibited contrasting features in the expression level of inflammation-evoked astrocyte-associated genes in the hippocampus. No changes in microglial features occurred in the hippocampus between the experimental groups, whereas a reduced glial fibrillary acidic protein immunoreactivity was observed in Tg2576 vs. WT mice. This finding may reflect an atrophic, "loss-of-function" profile, further exacerbated by DSS where a decreased of GFAP mRNA expression level was detected. In conclusion, we suggest that as-yet unidentified peripheral mediators evoked by DSS colitis and involving the gut-brain axis emphasize an astrocyte "loss-of-function" profile present in young Tg2576 mice, leading to impaired synaptic morphological and functional integrity as a very early sign of AD.

Genotype- and sex-specific changes in vital parameters during isoflurane anesthesia in a mouse model of Alzheimer's disease.

Background: The prevalence of neurodegenerative diseases is increasing as is life expectancy with Alzheimer's disease accounting for two-thirds of dementia cases globally. Whether general anesthesia and surgery worsen cognitive decline is still a matter of debate and most likely depending on the interplay of various influencing factors. In order to account for this complexity, Alzheimer's disease animal models have been developed. The Tg2576 model of Alzheimer's disease is a well-established mouse model exhibiting amyloidopathy and age-dependent sex-specific differences in Alzheimer's disease symptomology. Yet, data on anesthesia in this mouse model is scarce and a systematic comparison of vital parameters during anesthesia with wild-type animals is missing. In order to investigate the safety of general anesthesia and changes in vital parameters during general anesthesia in Tg2576 mice, we did a secondary analysis of vital parameters collected during general anesthesia in aged Tg2576 mice. Methods: After governmental approval (General Administration of the Free State of Bavaria, file number: 55.2-1-54-2532-149-11) 60 mice at 10-12 months of age were exposed to isoflurane (1.6 Vol%) for 120 min, data of 58 mice was analyzed. During general anesthesia, heart rate, respiratory rate, temperature, isoflurane concentration and fraction of inspired oxygen were monitored and collected. Data were analyzed using univariate and multivariate linear mixed regression models. Results: During general anesthesia, heart rate decreased in a sex-specific manner. Respiratory rate decreased and body temperature increased dependent on genotype. However, the changes were limited and all vital parameters stayed within physiological limits. Conclusion: Isoflurane anesthesia in the Tg2576 mouse model is safe and does not seem to influence experimental results by interacting with vital parameters. The present study provides information on appropriate anesthesia in order to advance research on anesthesia and AD and could contribute to improving laboratory animal welfare.

Dentate Gyrus Granule Cells Show Stability of BDNF Protein Expression in Mossy Fiber Axons with Age, and Resistance to Alzheimer's Disease Neuropathology in a Mouse Model.

Brain-derived neurotrophic factor (BDNF) is important in the development and maintenance of neurons and their plasticity. Hippocampal BDNF has been implicated in Alzheimer's disease (AD) because hippocampal levels in AD patients and AD animal models are often downregulated, suggesting that reduced BDNF contributes to AD. However, the location where hippocampal BDNF protein is most highly expressed, the mossy fiber (MF) axons of dentate gyrus granule cells (GCs), has been understudied, and not in controlled conditions. Therefore, we evaluated MF BDNF protein in the Tg2576 mouse model of AD. Tg2576 and wild-type (WT) mice of both sexes were examined at 2-3 months of age, when amyloid-ß (Aß) is present in neurons but plaques are absent, and 11-20 months of age, after plaque accumulation. As shown previously, WT mice exhibited high levels of MF BDNF protein. Interestingly, there was no significant decline with age in either the genotype or sex. Notably, MF BDNF protein was correlated with GC ΔFosB, a transcription factor that increases after 1-2 weeks of elevated neuronal activity. We also report the novel finding that Aß in GCs or the GC layer was minimal even at old ages. The results indicate that MF BDNF is stable in the Tg2576 mouse, and MF BDNF may remain unchanged due to increased GC neuronal activity, since BDNF expression is well known to be activity dependent. The resistance of GCs to long-term Aß accumulation provides an opportunity to understand how to protect vulnerable neurons from increased Aß levels and therefore has translational implications.

Transcriptomic Analysis in the Hippocampus and Retina of Tg2576 AD Mice Reveals Defective Mitochondrial Oxidative Phosphorylation and Recovery by Tau 12A12mAb Treatment.

Increasing evidence implicates decreased energy metabolism and mitochondrial dysfunctions among the earliest pathogenic events of Alzheimer's disease (AD). However, the molecular mechanisms underlying bioenergetic dysfunctions in AD remain, to date, largely unknown. In this work, we analyzed transcriptomic changes occurring in the hippocampus and retina of a Tg2576 AD mouse model and wild-type controls, evaluating their functional implications by gene set enrichment analysis. The results revealed that oxidative phosphorylation and mitochondrial-related pathways are significantly down-regulated in both tissues of Tg2576 mice, supporting the role of these processes in the pathogenesis of AD. In addition, we also analyzed transcriptomic changes occurring in Tg2576 mice treated with the 12A12 monoclonal antibody that neutralizes an AD-relevant tau-derived neurotoxic peptide in vivo. Our analysis showed that the mitochondrial alterations observed in AD mice were significantly reverted by treatment with 12A12mAb, supporting bioenergetic pathways as key mediators of its in vivo neuroprotective and anti-amyloidogenic effects. This study provides, for the first time, a comprehensive characterization of molecular events underlying the disrupted mitochondrial bioenergetics in AD pathology, laying the foundation for the future development of diagnostic and therapeutic tools.

Evidence for a protective effect of the loss of α4-containing nicotinic acetylcholine receptors on Aß-related neuropathology in Tg2576 mice.

Introduction: Loss of cholinergic neurons as well as α4ß2* (* = containing) nicotinic acetylcholine receptors (nAChRs) is a prominent feature of Alzheimer's disease (AD). Specifically, amyloid ß (Aß), the principal pathogenic factor of AD, is a high affinity ligand for nAChRs. Yet, the pathophysiological role of nAChRs in AD is not well established. Methods: In the present study, we have investigated the effects of the loss of α4* nAChRs on the histological alterations of the Tg2576 mouse model of AD (APPswe) crossing hemizygous APPswe mice with mice carrying the genetic inactivation of α4 nAChR subunit (α4KO). Results: A global decrease in Aß plaque load was observed in the forebrain of APPswe/α4KO mice in comparison with APPswe mice, that was particularly marked in neocortex of 15 month-old mice. At the same age, several alterations in synaptophysin immunoreactivity were observed in cortico-hippocampal regions of APPswe mice that were partially counteracted by α4KO. The analysis of the immunoreactivity of specific astroglia (glial fibrillary acidic protein, GFAP) and microglia (ionized calcium-binding adapter molecule, Iba1) markers showed an increase in the number as well as in the area occupied by these cells in APPswe mice that were partially counteracted by α4KO. Conclusion: Overall, the present histological study points to a detrimental role of α4* nAChRs that may be specific for Aß-related neuropathology.

Neuronal hyperexcitability in the Tg2576 mouse model of Alzheimer's disease - the influence of sleep and noradrenergic transmission.

The link between Alzheimer's disease (AD) and network hypersynchrony - manifesting as epileptic activities - received considerable attention in the past decade. However, several questions remain unanswered as to its mechanistic underpinnings. Therefore, our objectives were (1) to better characterise epileptic events in the Tg2576 mouse model throughout the sleep-wake cycle and disease progression via electrophysiological recordings and (2) to explore the involvement of noradrenergic transmission in this pathological hypersynchrony. Over and above confirming the previously described early presence and predominance of epileptic events during rapid-eye-movement (REM) sleep, we also show that these events do not worsen with age and are highly phase-locked to the section of the theta cycle during REM sleep where hippocampal pyramidal cells reach their highest firing probability. Finally, we reveal an antiepileptic mechanism of noradrenergic transmission via α1-adrenoreceptors that could explain the intriguing distribution of epileptic events over the sleep-wake cycle in this model, with potential therapeutic implications in the treatment of the epileptic events occurring in many AD patients.

Dysbiosis of Fecal Microbiota in Tg2576 Mice for Alzheimer's Disease during Pathological Constipation.

Tg2576 transgenic mice for Alzheimer's disease (AD) exhibited significant phenotypes for neuropathological constipation, but no research has been conducted on the association of the fecal microbiota with dysbiosis. The correlation between fecal microbiota composition and neuropathological constipation in Tg2576 mice was investigated by examining the profile of fecal microbiota and fecal microbiota transplantation (FMT) in 9-10-month-old Tg2576 mice with the AD phenotypes and constipation. Several constipation phenotypes, including stool parameters, colon length, and histopathological structures, were observed prominently in Tg2576 mice compared to the wild-type (WT) mice. The fecal microbiota of Tg2576 mice showed decreases in Bacteroidetes and increases in the Firmicutes and Proteobacteria populations at the phylum level. The FMT study showed that stool parameters, including weight, water content, and morphology, decreased remarkably in the FMT group transplanted with a fecal suspension of Tg2576 mice (TgFMT) compared to the FMT group transplanted with a fecal suspension of WT mice (WFMT). The distribution of myenteric neurons and the interstitial cells of Cajal (ICC), as well as the enteric nervous system (ENS) function, remained lower in the TgFMT group. These results suggest that the neuropathological constipation phenotypes of Tg2576 mice may be tightly linked to the dysbiosis of the fecal microbiota.

The VTA dopaminergic system as diagnostic and therapeutical target for Alzheimer's disease.

Neuropsychiatric symptoms (NPS) occur in nearly all patients with Alzheimer's Disease (AD). Most frequently they appear since the mild cognitive impairment (MCI) stage preceding clinical AD, and have a prognostic importance. Unfortunately, these symptoms also worsen the daily functioning of patients, increase caregiver stress and accelerate the disease progression from MCI to AD. Apathy and depression are the most common of these NPS, and much attention has been given in recent years to understand the biological mechanisms related to their appearance in AD. Although for many decades these symptoms have been known to be related to abnormalities of the dopaminergic ventral tegmental area (VTA), a direct association between deficits in the VTA and NPS in AD has never been investigated. Fortunately, this scenario is changing since recent studies using preclinical models of AD, and clinical studies in MCI and AD patients demonstrated a number of functional, structural and metabolic alterations affecting the VTA dopaminergic neurons and their mesocorticolimbic targets. These findings appear early, since the MCI stage, and seem to correlate with the appearance of NPS. Here, we provide an overview of the recent evidence directly linking the dopaminergic VTA with NPS in AD and propose a setting in which the precocious identification of dopaminergic deficits can be a helpful biomarker for early diagnosis. In this scenario, treatments of patients with dopaminergic drugs might slow down the disease progression and delay the impairment of daily living activities.

Natural Age-Related Slow-Wave Sleep Alterations Onset Prematurely in the Tg2576 Mouse Model of Alzheimer's Disease.

INTRODUCTION: Sleep insufficiency or decreased quality have been associated with Alzheimer's disease (AD) already in its preclinical stages. Whether such traits are also present in rodent models of the disease has been poorly addressed, somewhat disabling the preclinical exploration of sleep-based therapeutic interventions for AD. METHODS: We investigated age-dependent sleep-wake phenotype of a widely used mouse model of AD, the Tg2576 line. We implanted electroencephalography/electromyography headpieces into 6-month-old (plaque-free, n = 10) and 11-month-old (moderate plaque-burdened, n = 10) Tg2576 mice and age-matched wild-type (WT, 6 months old n = 10, 11 months old n = 10) mice and recorded vigilance states for 24 h. RESULTS: Tg2576 mice exhibited significantly increased wakefulness and decreased non-rapid eye movement sleep over a 24-h period compared to WT mice at 6 but not at 11 months of age. Concomitantly, power in the delta frequency was decreased in 6-month old Tg2576 mice in comparison to age-matched WT controls, rendering a reduced slow-wave energy phenotype in the young mutants. Lack of genotype-related differences over 24 h in the overall sleep-wake phenotype at 11 months of age appears to be the result of changes in sleep-wake characteristics accompanying the healthy aging of WT mice. CONCLUSION: Therefore, our results indicate that at the plaque-free disease stage, diminished sleep quality is present in Tg2576 mice which resembles aged healthy controls, suggesting an early-onset of sleep-wake deterioration in murine AD. Whether such disturbances in the natural patterns of sleep could in turn worsen disease progression warrants further exploration.

Increased KV2.1 Channel Clustering Underlies the Reduction of Delayed Rectifier K+ Currents in Hippocampal Neurons of the Tg2576 Alzheimer's Disease Mouse.

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by the progressive deterioration of cognitive functions. Cortical and hippocampal hyperexcitability intervenes in the pathological derangement of brain activity leading to cognitive decline. As key regulators of neuronal excitability, the voltage-gated K+ channels (KV) might play a crucial role in the AD pathophysiology. Among them, the KV2.1 channel, the main α subunit mediating the delayed rectifier K+ currents (IDR) and controlling the intrinsic excitability of pyramidal neurons, has been poorly examined in AD. In the present study, we investigated the KV2.1 protein expression and activity in hippocampal neurons from the Tg2576 mouse, a widely used transgenic model of AD. To this aim we performed whole-cell patch-clamp recordings, Western blotting, and immunofluorescence analyses. Our Western blotting results reveal that KV2.1 was overexpressed in the hippocampus of 3-month-old Tg2576 mice and in primary hippocampal neurons from Tg2576 mouse embryos compared with the WT counterparts. Electrophysiological experiments unveiled that the whole IDR were reduced in the Tg2576 primary neurons compared with the WT neurons, and that this reduction was due to the loss of the KV2.1 current component. Moreover, we found that the reduction of the KV2.1-mediated currents was due to increased channel clustering, and that glutamate, a stimulus inducing KV2.1 declustering, was able to restore the IDR to levels comparable to those of the WT neurons. These findings add new information about the dysregulation of ionic homeostasis in the Tg2576 AD mouse model and identify KV2.1 as a possible player in the AD-related alterations of neuronal excitability.

Anti-epileptogenic effects of synaptic vesicle protein 2A modulation in a mouse model of Alzheimer's disease.

OBJECTIVE: To assess the effects of synaptic vesicle protein 2A (SV2A) modulators brivaracetam and levetiracetam on amygdala kindling epileptogenesis in Tg2576 mice, a model of Alzheimer's disease which exhibits sensitivity to seizures. METHODS: First, aged Tg2576 mice (13-25 months; n = 17) were treated subcutaneously with either brivaracetam (10 mg/kg/day), levetiracetam (150 mg/kg/day) or vehicle via osmotic pumps for 28 days prior to, and during electrical amygdala kindling epileptogenesis. Next, we treated young (4-6 months; n = 24) Tg2576 mice with brivaracetam (10 mg/kg/day) or vehicle for 28 days and allowed one week's 'washout' before commencing kindling. Progression of seizure severity and duration were compared between treatment groups and wildtype mice (WT). RESULTS: In older Tg2576 mice, treatment with brivaracetam (p < 0.001) and levetiracetam (p < 0.05) before and during kindling significantly delayed the progression of seizure severity, compared to vehicle. Animals treated with brivaracetam required significantly more stimulations to reach the first class V (convulsive) seizure and had a lower mortality rate (p < 0.05) compared to those treated with vehicle. Young Tg2576 mice also exhibited increased susceptibility to kindling epileptogenesis compared to WT. Treatment with brivaracetam in younger animals only prior to kindling also delayed kindling acquisition compared to vehicle treatment, increasing the number of stimulations required to experience class V seizures (p < 0.05). SIGNIFICANCE: Brivaracetam treatment displayed marked anti-epileptogenic effects in both aged and young Tg2576 mice, including when treatment is ceased prior to initiating kindling. Targeting SV2A might represent a strategy for prevention of epilepsy in patients with Alzheimer's disease.

Single-Cell Transcriptional Profiling and Gene Regulatory Network Modeling in Tg2576 Mice Reveal Gender-Dependent Molecular Features Preceding Alzheimer-Like Pathologies.

Alzheimer's disease (AD) onset and progression is influenced by a complex interplay of several environmental and genetic factors, one of them gender. Pronounced gender differences have been observed both in the relative risk of developing AD and in clinical disease manifestations. A molecular level understanding of these gender disparities is still missing, but could provide important clues on cellular mechanisms modulating the disease and reveal new targets for gender-oriented disease-modifying precision therapies. We therefore present here a comprehensive single-cell analysis of disease-associated molecular gender differences in transcriptomics data from the neocortex, one of the brain regions most susceptible to AD, in one of the most widely used AD mouse models, the Tg2576 model. Cortical areas are also most commonly used in studies of post-mortem AD brains. To identify disease-linked molecular processes that occur before the onset of detectable neuropathology, we focused our analyses on an age with no detectable plaques and microgliosis. Cell-type specific alterations were investigated at the level of individual genes, pathways, and gene regulatory networks. The number of differentially expressed genes (DEGs) was not large enough to build context-specific gene regulatory networks for each individual cell type, and thus, we focused on the study of cell types with dominant changes and included analyses of changes across the combination of cell types. We observed significant disease-associated gender differences in cellular processes related to synapse organization and reactive oxygen species metabolism, and identified a limited set of transcription factors, including Egr1 and Klf6, as key regulators of many of the disease-associated and gender-dependent gene expression changes in the model. Overall, our analyses revealed significant cell-type specific gene expression changes in individual genes, pathways and sub-networks, including gender-specific and gender-dimorphic changes in both upstream transcription factors and their downstream targets, in the Tg2576 AD model before the onset of overt disease. This opens a window into molecular events that could determine gender-susceptibility to AD, and uncovers tractable target candidates for potential gender-specific precision medicine for AD.

Early derailment of firing properties in CA1 pyramidal cells of the ventral hippocampus in an Alzheimer's disease mouse model.

Gradual decline in cognitive and non-cognitive functions are considered clinical hallmarks of Alzheimer's Disease (AD). Post-mortem autoptic analysis shows the presence of amyloid ß deposits, neuroinflammation and severe brain atrophy. However, brain circuit alterations and cellular derailments, assessed in very early stages of AD, still remain elusive. The understanding of these early alterations is crucial to tackle defective mechanisms. In a previous study we proved that the Tg2576 mouse model of AD displays functional deficits in the dorsal hippocampus and relevant behavioural AD-related alterations. We had shown that these deficits in Tg2576 mice correlate with the precocious degeneration of dopamine (DA) neurons in the Ventral Tegmental Area (VTA) and can be restored by L-DOPA treatment. Due to the distinct functionality and connectivity of dorsal versus ventral hippocampus, here we investigated neuronal excitability and synaptic functionality in the ventral CA1 hippocampal sub-region of Tg2576 mice. We found an age-dependent alteration of cell excitability and firing in pyramidal neurons starting at 3 months of age, that correlates with reduced levels in the ventral CA1 of tyrosine hydroxylase - the rate-limiting enzyme of DA synthesis. Additionally, at odds with the dorsal hippocampus, we found no alterations in basal glutamatergic transmission and long-term plasticity of ventral neurons in 8-month old Tg2576 mice compared to age-matched controls. Last, we used computational analysis to model the early derailments of firing properties observed and hypothesize that the neuronal alterations found could depend on dysfunctional sodium and potassium conductances, leading to anticipated depolarization-block of action potential firing. The present study depicts that impairment of cell excitability and homeostatic control of firing in ventral CA1 pyramidal neurons is a prodromal feature in Tg2576 AD mice.

The Impact of the hAPP695SW Transgene and Associated Amyloid-ß Accumulation on Murine Hippocampal Biochemical Pathways.

BACKGROUND: Alzheimer's disease (AD) is a neurodegenerative disease characterized by the accumulation of amyloid-ß (Aß) peptide in the brain. OBJECTIVE: To gain a better insight into alterations in major biochemical pathways underlying AD. METHODS: We compared metabolomic profiles of hippocampal tissue of 20-month-old female Tg2576 mice expressing the familial AD-associated hAPP695SW transgene with their 20-month-old wild type female littermates. RESULTS: The hAPP695SW transgene causes overproduction and accumulation of Aß in the brain. Out of 180 annotated metabolites, 54 metabolites differed (30 higher and 24 lower in Tg2576 versus wild-type hippocampal tissue) and were linked to the amino acid, nucleic acid, glycerophospholipid, ceramide, and fatty acid metabolism. Our results point to 1) heightened metabolic activity as indicated by higher levels of urea, enhanced fatty acid ß-oxidation, and lower fatty acid levels; 2) enhanced redox regulation; and 3) an imbalance of neuro-excitatory and neuro-inhibitory metabolites in hippocampal tissue of aged hAPP695SW transgenic mice. CONCLUSION: Taken together, our results suggest that dysregulation of multiple metabolic pathways associated with a concomitant shift to an excitatory-inhibitory imbalance are contributing mechanisms of AD-related pathology in the Tg2576 mouse.

The Na+/Ca2+ Exchanger 3 Is Functionally Coupled With the NaV1.6 Voltage-Gated Channel and Promotes an Endoplasmic Reticulum Ca2+ Refilling in a Transgenic Model of Alzheimer's Disease.

The remodelling of neuronal ionic homeostasis by altered channels and transporters is a critical feature of the Alzheimer's disease (AD) pathogenesis. Different reports converge on the concept that the Na+/Ca2+ exchanger (NCX), as one of the main regulators of Na+ and Ca2+ concentrations and signalling, could exert a neuroprotective role in AD. The activity of NCX has been found to be increased in AD brains, where it seemed to correlate with an increased neuronal survival. Moreover, the enhancement of the NCX3 currents (INCX) in primary neurons treated with the neurotoxic amyloid ß 1-42 (Aß1-42) oligomers prevented the endoplasmic reticulum (ER) stress and neuronal death. The present study has been designed to investigate any possible modulation of the INCX, the functional interaction between NCX and the NaV1.6 channel, and their impact on the Ca2+ homeostasis in a transgenic in vitro model of AD, the primary hippocampal neurons from the Tg2576 mouse, which overproduce the Aß1-42 peptide. Electrophysiological studies, carried in the presence of siRNA and the isoform-selective NCX inhibitor KB-R7943, showed that the activity of a specific NCX isoform, NCX3, was upregulated in its reverse, Ca2+ influx mode of operation in the Tg2576 neurons. The enhanced NCX activity contributed, in turn, to increase the ER Ca2+ content, without affecting the cytosolic Ca2+ concentrations of the Tg2576 neurons. Interestingly, our experiments have also uncovered a functional coupling between NCX3 and the voltage-gated NaV1.6 channels. In particular, the increased NaV1.6 currents appeared to be responsible for the upregulation of the reverse mode of NCX3, since both TTX and the Streptomyces griseolus antibiotic anisomycin, by reducing the NaV1.6 currents, counteracted the increase of the INCX in the Tg2576 neurons. In agreement, our immunofluorescence analyses revealed that the NCX3/NaV1.6 co-expression was increased in the Tg2576 hippocampal neurons in comparison with the WT neurons. Collectively, these findings indicate that NCX3 might intervene in the Ca2+ remodelling occurring in the Tg2576 primary neurons thus emerging as a molecular target with a neuroprotective potential, and provide a new outcome of the NaV1.6 upregulation related to the modulation of the intracellular Ca2+ concentrations in AD neurons.

Reversing pathology in a preclinical model of Alzheimer's disease by hacking cerebrovascular neoangiogenesis with advanced cancer therapeutics.

BACKGROUND: Cognitive decline leading to dementia, accompanied by the accumulation of amyloid-beta (Aß) in neuritic plaques together with the appearance of neurofibrillary tangles (NFT) composed of hyperphosphorylated tau protein (tau), are previously noted hallmarks of Alzheimer's disease (AD). We previously discovered hypervascularity in brain specimens from AD patients and consistent with this observation, we demonstrated that overexpression of Aß drives cerebrovascular neoangiogenesis leading to hypervascularity and coincident tight-junction disruption and blood-brain barrier (BBB) leakiness in animal models of AD. We subsequently demonstrated that amyloid plaque burden and cerebrovascular pathogenesis subside when pro-angiogenic Aß levels are reduced. Based on these data, we propose a paradigm of AD etiology where, as a compensatory response to impaired cerebral blood flow (CBF), Aß triggers pathogenic cerebrovascular neoangiogenesis that underlies the conventional hallmarks of AD. Consequently, here we present evidence that repurposing anti-cancer drugs to modulate cerebrovascular neoangiogenesis, rather than directly targeting the amyloid cascade, may provide an effective treatment for AD and related vascular diseases of the brain. METHODS: We explored whether the anti-cancer drug, Axitinib, a small molecule tyrosine kinase inhibitor that targets vascular endothelial growth factor receptors (VEGFR) can inhibit aberrant cerebrovascular neoangiogenic changes, reduce Aß deposits and reverse cognitive decline in an animal model of AD. One month post-treatment with Axitinib, we employed a battery of tests to assess cognition and memory in aged Tg2576 AD mice and used molecular analysis to demonstrate reduction of amyloid plaques, BBB leakage, hypervascularity and associated disease pathology. FINDINGS: Targeting the pro-angiogenic pathway in AD using the cancer drug, Axitinib, dramatically reduced cerebrovascular neoangiogenesis, restored BBB integrity, resolved tight-junction pathogenesis, diminishes Aß depositions in plaques and effectively restores memory and cognitive performance in a preclinical mouse model of AD. INTERPRETATION: Modulation of neoangiogenesis, in an analogous approach to those used to treat aberrant vascularization in cancer and also in the wet form of age-related macular degeneration (AMD), provides an alternative therapeutic strategy for intervention in AD that warrants clinical investigation. FUNDING: None.

Myeloid Arginase 1 Insufficiency Exacerbates Amyloid-ß Associated Neurodegenerative Pathways and Glial Signatures in a Mouse Model of Alzheimer's Disease: A Targeted Transcriptome Analysis.

Brain myeloid cells, include infiltrating macrophages and resident microglia, play an essential role in responding to and inducing neurodegenerative diseases, such as Alzheimer's disease (AD). Genome-wide association studies (GWAS) implicate many AD casual and risk genes enriched in brain myeloid cells. Coordinated arginine metabolism through arginase 1 (Arg1) is critical for brain myeloid cells to perform biological functions, whereas dysregulated arginine metabolism disrupts them. Altered arginine metabolism is proposed as a new biomarker pathway for AD. We previously reported Arg1 deficiency in myeloid biased cells using lysozyme M (LysM) promoter-driven deletion worsened amyloidosis-related neuropathology and behavioral impairment. However, it remains unclear how Arg1 deficiency in these cells impacts the whole brain to promote amyloidosis. Herein, we aim to determine how Arg1 deficiency driven by LysM restriction during amyloidosis affects fundamental neurodegenerative pathways at the transcriptome level. By applying several bioinformatic tools and analyses, we found that amyloid-ß (Aß) stimulated transcriptomic signatures in autophagy-related pathways and myeloid cells' inflammatory response. At the same time, myeloid Arg1 deficiency during amyloidosis promoted gene signatures of lipid metabolism, myelination, and migration of myeloid cells. Focusing on Aß associated glial transcriptomic signatures, we found myeloid Arg1 deficiency up-regulated glial gene transcripts that positively correlated with Aß plaque burden. We also observed that Aß preferentially activated disease-associated microglial signatures to increase phagocytic response, whereas myeloid Arg1 deficiency selectively promoted homeostatic microglial signature that is non-phagocytic. These transcriptomic findings suggest a critical role for proper Arg1 function during normal and pathological challenges associated with amyloidosis. Furthermore, understanding pathways that govern Arg1 metabolism may provide new therapeutic opportunities to rebalance immune function and improve microglia/macrophage fitness.

Metabolic Profiling of Suprachiasmatic Nucleus Reveals Multifaceted Effects in an Alzheimer's Disease Mouse Model.

BACKGROUND: Circadian rhythm disturbance is commonly observed in Alzheimer's disease (AD). In mammals, these rhythms are orchestrated by the superchiasmatic nucleus (SCN). Our previous study in the Tg2576 AD mouse model suggests that inflammatory responses, most likely manifested by low GABA production, may be one of the underlying perpetrators for the changes in circadian rhythmicity and sleep disturbance in AD. However, the mechanistic connections between SCN dysfunction, GABA modulation, and inflammation in AD is not fully understood. OBJECTIVE: To reveal influences of amyloid pathology in Tg2576 mouse brain on metabolism in SCN and to identify key metabolic sensors that couple SCN dysfunction with GABA modulation and inflammation. METHODS: High resolution magic angle spinning (HR-MAS) NMR in conjunction with multivariate analysis was applied for metabolic profiling in SCN of control and Tg2576 female mice. Immunohistochemical analysis was used to detect neurons, astrocytes, expression of GABA transporter 1 (GAT1) and Bmal1. RESULTS: Metabolic profiling revealed significant metabolic deficits in SCN of Tg2576 mice. Reductions in glucose, glutamate, GABA, and glutamine provide hints toward an impaired GABAergic glucose oxidation and neurotransmitter cycling in SCN of AD mice. In addition, decreased redox co-factor NADPH and glutathione support a redox disbalance. Immunohistochemical examinations showed low expression of the core clock protein, Bmal1, especially in activated astrocytes. Moreover, decreased expression of GAT1 in astrocytes indicates low GABA recycling in this cell type. CONCLUSION: Our results suggest that redox disbalance and compromised GABA signaling are important denominators and connectors between neuroinflammation and clock dysfunction in AD.

Targeting autophagy as a therapeutic strategy to prevent dopamine neuron loss in early stages of Alzheimer disease.

Alzheimer disease (AD) is a neurodegenerative disorder for which no approved medication exists. AD is characterized by worsening cognitive and non-cognitive symptoms, and research in the AD field strives to identify very precocious brain alterations leading to an irreversible condition. Recently it has been demonstrated that several early AD symptoms are paralleled with degeneration of neurons producing dopamine (DA), a neurotransmitter involved in the regulation of cognitive and non-cognitive functions. Actually, we found that ventral tegmental area (VTA) DA neurons degenerate early in a validated AD mouse model (Tg2576). Here, we summarize new data showing how macroautophagy/autophagy impairment - due to enhanced activity of the ABL/c-Abl kinase - might cause the DA neuron loss. We also proved that nilotinib, an ABL inhibitor, restores autophagy flux, thus preventing VTA neurodegeneration. Most notably, from a clinical point of view, nilotinib, by preventing DA neuronal loss, preserves DA outflow in VTA-projecting areas, improving Tg2576 behavioral phenotypes. Our findings shed light on the mechanism involved in DA neurodegeneration, revealing that autophagy represents a viable therapeutic target in early AD.

Long-term ovarian hormone deprivation alters functional connectivity, brain neurochemical profile and white matter integrity in the Tg2576 amyloid mouse model of Alzheimer's disease.

Premenopausal bilateral ovariectomy is considered to be one of the risk factors of Alzheimer's disease (AD). However, the underlying mechanisms remain unclear. Here, we aimed to investigate long-term neurological consequences of ovariectomy in a rodent AD model, TG2576 (TG), and wild-type mice (WT) that underwent an ovariectomy or sham-operation, using in vivo MRI biomarkers. An increase in osmoregulation and energy metabolism biomarkers in the hypothalamus, a decrease in white matter integrity, and a decrease in the resting-state functional connectivity was observed in ovariectomized TG mice compared to sham-operated TG mice. In addition, we observed an increase in functional connectivity in ovariectomized WT mice compared to sham-operated WT mice. Furthermore, genotype (TG vs. WT) effects on imaging markers and GFAP immunoreactivity levels were observed, but there was no effect of interaction (Genotype × Surgery) on amyloid-beta-and GFAP immunoreactivity levels. Taken together, our results indicated that both genotype and ovariectomy alters imaging biomarkers associated with AD.