STAT3 ameliorates truncated tau-induced cognitive deficits

Proteolytic cleavage of tau by asparagine endopeptidase (AEP) creates tau-N368 fragments, which may drive the pathophysiology associated with synaptic dysfunction and memory deterioration in the brain of Alzheimer's disease patients. Nonetheless, the molecular mechanisms of truncated tau-induced cognitive deficits remain unclear. Evidence suggests that signal transduction and activator of transcription-3 (STAT3) is associated with modulating synaptic plasticity, cell apoptosis, and cognitive function. Using luciferase reporter assays, electrophoretic mobility shift assays, western blotting, and immunofluorescence, we found that human tau-N368 accumulation inhibited STAT3 activity by suppressing STAT3 translocation into the nucleus. Overexpression of STAT3 improved tau-N368-induced synaptic deficits and reduced neuronal loss, thereby improving the cognitive deficits in tau-N368 mice. Moreover, in tau-N368 mice, activation of STAT3 increased N-methyl-D-aspartic acid receptor levels, decreased Bcl-2 levels, reversed synaptic damage and neuronal loss, and thereby alleviated cognitive deficits caused by tau-N368. Taken together, STAT3 plays a critical role in truncated tau-related neuropathological changes. This indicates a new mechanism behind the effect of tau-N368 on synapses and memory deficits. STAT3 can be used as a new molecular target to treat tau-N368-induced protein pathology.

Epimedium Aqueous Extract Ameliorates Cerebral Ischemia/Reperfusion Injury through Inhibiting ROS/NLRP3-Mediated Pyroptosis

Cerebral ischemia/reperfusion causes exacerbated neuronal damage involving excessive neuroinflammation and oxidative stress. ROS is considered a signal molecule to activate NLRP3; thus, the ROS/NLRP3/pyroptosis axis plays a vital role in the pathogenesis of cerebral ischemia/reperfusion injury (CIRI). Therefore, targeting the inhibition of the ROS/NLRP3/pyroptosis axis may be a promising therapeutic tactic for CIRI. Epimedium (EP) contains many active ingredients (ICA, ICS II, and ICT), which have a wide range of pharmacological activities. However, whether EP can protect against CIRI remains unknown. Thus, in this study, we designed to investigate the effect and possible underlying mechanism of EP on CIRI. The results showed that treatment with EP dramatically mitigated brain damage in rats following CIRI, which was achieved by suppressing mitochondrial oxidative stress and neuroinflammation. Furthermore, we identified the ROS/NLRP3/pyroptosis axis as a vital process and NLRP3 as a vital target in EP-mediated protection. Most interestingly, the main compounds of EP directly bonded with NLRP3, as reflected by molecular docking, which indicated that NLRP3 might be a promising therapeutic target for EP-elicited cerebral protection. In conclusion, our findings illustrate that ICS II protects against neuron loss and neuroinflammation after CIRI by inhibiting ROS/NLRP3-mediated pyroptosis.

A Combination of Caffeine Supplementation and Enriched Environment in an Alzheimer's Disease Mouse Model

A variety of factors has been associated with healthy brain aging, and epidemiological studies suggest that physical activity and nutritional supplements such as caffeine may reduce the risk of developing dementia and, in particular, Alzheimer's disease (AD) in later life. Caffeine is known to act as a cognitive enhancer but has been also shown to positively affect exercise performance in endurance activities. We have previously observed that chronic oral caffeine supplementation and a treatment paradigm encompassing physical and cognitive stimulation by enriched environment (EE) housing can improve learning and memory performance and ameliorate hippocampal neuron loss in the Tg4-42 mouse model of AD. Here, we investigated whether these effects were synergistic. To that end, previous findings on individual treatments were complemented with unpublished, additional data and analyzed in depth by ANOVA followed by Bonferroni multiple comparison post tests. We further evaluated whether plasma neurofilament light chain levels reflect neuropathological and behavioral changes observed in the experimental groups. While a treatment combining physical activity and caffeine supplementation significantly improved learning and memory function compared to standard-housed vehicle-treated Tg4-42 in tasks such as the Morris water maze, no major additive effect outperforming the effects of the single interventions was observed.

DNA vaccines targeting amyloid-β oligomer ameliorate cognitive deficits of aged APP/PS1/tau triple-transgenic mouse models of Alzheimer's disease

The amyloid-β (Aβ) oligomer, rather than the Aβ monomer, is considered to be the primary initiator of Alzheimer’s disease. It was hypothesized that p(Aβ3–10)10-MT, the recombinant Aβ3–10 gene vaccine of the Aβ oligomer has the potential to treat Alzheimer’s disease. In this study, we intramuscularly injected the p(Aβ3–10)10-MT vaccine into the left hindlimb of APP/PS1/tau triple-transgenic mice, which are a model for Alzheimer’s disease. Our results showed that the p(Aβ3–10)10-MT vaccine effectively reduced Aβ oligomer levels and plaque deposition in the cerebral cortex and hippocampus, decreased the levels tau protein variants, reduced synaptic loss, protected synaptic function, reduced neuron loss, and ameliorated memory impairment without causing any cerebral hemorrhaging. Therefore, this novel DNA vaccine, which is safe and highly effective in mouse models of Alzheimer’s disease, holds a lot of promise for the treatment of Alzheimer’s disease in humans.

The association between neurodegeneration and local complement activation in the thalamus to progressive multiple sclerosis outcome

The extent of grey matter demyelination and neurodegeneration in the progressive multiple sclerosis (PMS) brains at post‐mortem associates with more severe disease. Regional tissue atrophy, especially affecting the cortical and deep grey matter, including the thalamus, is prognostic for poor outcomes. Microglial and complement activation are important in the pathogenesis and contribute to damaging processes that underlie tissue atrophy in PMS. We investigated the extent of pathology and innate immune activation in the thalamus in comparison to cortical grey and white matter in blocks from 21 cases of PMS and 10 matched controls. Using a digital pathology workflow, we show that the thalamus is invariably affected by demyelination and had a far higher proportion of active inflammatory lesions than forebrain cortical tissue blocks from the same cases. Lesions were larger and more frequent in the medial nuclei near the ventricular margin, whilst neuronal loss was greatest in the lateral thalamic nuclei. The extent of thalamic neuron loss was not associated with thalamic demyelination but correlated with the burden of white matter pathology in other forebrain areas (Spearman r = 0.79, p < 0.0001). Only thalamic neuronal loss, and not that seen in other forebrain cortical areas, correlated with disease duration (Spearman r = −0.58, p = 0.009) and age of death (Spearman r = −0.47, p = 0.045). Immunoreactivity for the complement pattern recognition molecule C1q, and products of complement activation (C4d, Bb and C3b) were elevated in thalamic lesions with an active inflammatory pathology. Complement regulatory protein, C1 inhibitor, was unchanged in expression. We conclude that active inflammatory demyelination, neuronal loss and local complement synthesis and activation in the thalamus, are important to the pathological and clinical disease outcomes of PMS.

A novel and accurate full-length HTT mouse model for Huntington's disease

Here, we report the generation and characterization of a novel Huntington's disease (HD) mouse model BAC226Q by using a bacterial artificial chromosome (BAC) system, expressing full-length human HTT with ~226 CAG-CAA repeats and containing endogenous human HTT promoter and regulatory elements. BAC226Q recapitulated a full-spectrum of age-dependent and progressive HD-like phenotypes without unwanted and erroneous phenotypes. BAC226Q mice developed normally, and gradually exhibited HD-like psychiatric and cognitive phenotypes at 2 months. From 3 to 4 months, BAC226Q mice showed robust progressive motor deficits. At 11 months, BAC226Q mice showed significant reduced life span, gradual weight loss and exhibited neuropathology including significant brain atrophy specific to striatum and cortex, striatal neuronal death, widespread huntingtin inclusions, and reactive pathology. Therefore, the novel BAC226Q mouse accurately recapitulating robust, age-dependent, progressive HD-like phenotypes will be a valuable tool for studying disease mechanisms, identifying biomarkers, and testing gene-targeting therapeutic approaches for HD.

Droplet Degeneration of Hippocampal and Cortical Neurons Signifies the Beginning of Neuritic Plaque Formation

BACKGROUND

Neuritic plaques contain neural and microglial elements, and amyloid-β protein (Aβ), but their pathogenesis remains unknown.

OBJECTIVE

Elucidate neuritic plaque pathogenesis.

METHODS

Histochemical visualization of hyperphosphorylated-tau positive (p-tau+) structures, microglia, Aβ, and iron.

RESULTS

Disintegration of large projection neurons in human hippocampus and neocortex presents as droplet degeneration: pretangle neurons break up into spheres of numerous p-tau+ droplets of various sizes, which marks the beginning of neuritic plaques. These droplet spheres develop in the absence of colocalized Aβ deposits but once formed become encased in diffuse Aβ with great specificity. In contrast, neurofibrillary tangles often do not colocalize with Aβ. Double-labelling for p-tau and microglia showed a lack of microglial activation or phagocytosis of p-tau+ degeneration droplets but revealed massive upregulation of ferritin in microglia suggesting presence of high levels of free iron. Perl's Prussian blue produced positive staining of microglia, droplet spheres, and Aβ plaque cores supporting the suggestion that droplet degeneration of pretangle neurons in the hippocampus and cortex represents ferroptosis, which is accompanied by the release of neuronal iron extracellularly.

CONCLUSION

Age-related iron accumulation and ferroptosis in the CNS likely trigger at least two endogenous mechanisms of neuroprotective iron sequestration and chelation, microglial ferritin expression and Aβ deposition, respectively, both contributing to the formation of neuritic plaques. Since neurofibrillary tangles and Aβ deposits colocalize infrequently, tangle formation likely does not involve release of neuronal iron extracellularly. In human brain, targeted deposition of Aβ occurs specifically in response to ongoing ferroptotic droplet degeneration thereby producing neuritic plaques.

Cerebrospinal fluid proteomics reveal potential protein targets of JiaWeiSiNiSan in preventing chronic psychological stress damage

CONTEXT

Chinese herbal formula JiaWeiSiNiSan (JWSNS) has been widely used to prevent stress-induced neuropsychiatric ailments in clinics and proven to have therapeutic anti-stress effects on rats. However, the mechanism remains unclear.

OBJECTIVE

Based on the proteomics of cerebrospinal fluid (CSF), this study explores the possible mechanism and target proteins of JiaWeiSiNiSan raising stress resilience and preventing stress damage.

MATERIALS AND METHODS

A 6-week Chronic Unpredictable Mild Stress (CUMS) model was applied on adult Wistar male rats to observe the effects of JWSNS on improving mental stress resilience. Tandem Mass Tag (TMT) proteomics and bioinformatics analysis were used to screen and analyze differentially expressed proteins (DEPs) in CSF. Parallel Reaction Monitoring (PRM) was used to validate target DEPs.

RESULTS

Significantly decreased sucrose preference, locomotion activity level and accuracy of T-maze, as well as increased immobility time, were observed in CUMS rats compared to CON rats while JWSNS improved above depression-like behaviours. The quantitative proteomics and bioinformatics analysis showed that JWSNS decreased the expression of Rps4x, HSP90AA1, Rps12, Uba1, Rsp14, Tuba1b in CUMS rats CSF (p < 0.05, FDR < 0.5). Immunofluorescence results showed that the number of BrdU/DCX positive cells (p < 0.01) and the relative number of neurons (p < 0.01) in the hippocampus dentate gyrus (DG) of the JSWNS group significantly increased, compared with the CUMS group.

CONCLUSIONS

JWSNS could increase mental stress resilience and prevent stress damage by regulating proteins in CSF. This study provides a scientific basis for further study on Chinese formulas preventing mental illness.

N-Truncated Aβ Starting at Position Four-Biochemical Features, Preclinical Models, and Potential as Drug Target in Alzheimer's Disease

The discussion of whether amyloid plaque Aβ is a valid drug target to fight Alzheimer’s disease (AD) has been a matter of scientific dispute for decades. This question can only be settled by successful clinical trials and the approval of disease-modifying drugs. However, many clinical trials with antibodies against different regions of the amyloid Aβ peptide have been discontinued, as they did not meet the clinical endpoints required. Recently, passive immunization of AD patients with Donanemab, an antibody directed against the N-terminus of pyroglutamate Aβ, showed beneficial effects in a phase II trial, supporting the concept that N-truncated Aβ is a relevant target for AD therapy. There is long-standing evidence that N-truncated Aβ variants are the main variants found in amyloid plaques besides full-length Aβ_1–42, t, therefore their role in triggering AD pathology and as targets for drug development are of interest. While the contribution of pyroglutamate Aβ_3–42 to AD pathology has been well studied in the past, the potential role of Aβ_4–42 has been largely neglected. The present review will therefore focus on Aβ_4–42 as a possible drug target based on human and mouse pathology, in vitro and in vivo toxicity, and anti-Aβ_4-X therapeutic effects in preclinical models.

Neuronal loss and microgliosis are restricted to the core of Aβ deposits in mouse models of Alzheimer's disease

Amyloid‐β (Aβ) deposits, pathologic tau, and neurodegeneration are major pathological hallmarks of Alzheimer's disease (AD). The relationship between neuronal loss and Aβ deposits is one of the fundamental questions in the pathogenesis of AD. However, this relationship is controversial. One main reason for the conflicting results may be the confounding effects of pathologic tau, which often coexists with Aβ deposits in the brains of AD patients. To clarify the relationship between neuronal loss and Aβ deposits, mouse models of AD, which develop abundant Aβ deposits in the aged brain without pathologic tau, were used to examine the co‐localization of NeuN‐positive neurons, NF‐H‐positive axons, MBP‐positive myelin sheaths, and Aβ deposits. Neuronal loss, as measured by decreased staining of the neuronal cell body, axon, and myelin sheath, as well as the IBA‐1‐positive microglia, was significantly increased in the core area of cerebral Aβ deposits, but not in adjacent areas. Furthermore, neuronal loss in the core area of cerebral Aβ deposits was correlated with Aβ deposit size. These results clearly indicate that neuronal loss is restricted to the core of Aβ deposits, and this restricted loss probably occurs because the Aβ deposit attracts microglia, which cluster in the core area where Aβ toxicity and neuroinflammation toxicity are restrained. These findings may contribute to our understanding of the relationship between neuronal loss and Aβ deposits in the absence of pathologic tau.

Characterization of a Mouse Model of Alzheimer's Disease Expressing Aβ4-42 and Human Mutant Tau

The relationship between the two most prominent neuropathological hallmarks of Alzheimer’s Disease (AD), extracellular amyloid-β (Aβ) deposits and intracellular accumulation of hyperphosphorylated tau in neurofibrillary tangles (NFT), remains at present not fully understood. A large body of evidence places Aβ upstream in the cascade of pathological events, triggering NFTs formation and the subsequent neuron loss. Extracellular Aβ deposits were indeed causative of an increased tau phosphorylation and accumulation in several transgenic models but the contribution of soluble Aβ peptides is still controversial. Among the different Aβ variants, the N-terminally truncated peptide Aβ_4–42 is among the most abundant. To understand whether soluble Aβ_4–42 peptides impact the onset or extent of tau pathology, we have crossed the homozygous Tg4–42 mouse model of AD, exclusively expressing Aβ_4–42 peptides, with the PS19 (P301S) tau transgenic model. Behavioral assessment showed that the resulting double-transgenic line presented a partial worsening of motor performance and spatial memory deficits in the aged group. While an increased loss of distal CA1 pyramidal neurons was detected in young mice, no significant alterations in hippocampal tau phosphorylation were observed in immunohistochemical analyses.

Combined treatment with valproic acid and estrogen has neuroprotective effects in ovariectomized mice with Alzheimer's disease

Postmenopausal women with Alzheimer’s disease (AD) exhibit dramatically reduced sensitivity to estrogen replacement therapy, which is though to be related to an estrogen receptor (ER)α/ERβ ratio imbalance arising from a significantly decreased level of ERs of the brain. The aim of our study was to investigate whether valproic acid (VPA) can enhance the beneficial effects of estrogen on cognitive function through restoration of ERα and ERβ expression in the brain. We removed the ovaries of female APP/PS1 mice to simulate the low estrogen levels present in postmenopausal women and then administered VPA (30 mg/kg, intraperitoneal injection, once daily), 17β-estradiol (E2) (2.4 μg, intraperitoneal injection, once daily), liquiritigenin (LG) (50 μg/kg, intragastric infusion, once daily), VPA + E2, or VPA + LG for 4 successive weeks. Compared with treatment with a single drug, treatment with VPA + E2 or VPA + LG significantly increased the level of glycogen synthase kinase 3β, increased the expression of estrogen receptor α, reduced the expression of small ubiquitin-like modifiers, and increased the level of estrogen receptor β. This resulted in enhanced sensitivity to estrogen therapy, reduced amyloid β aggregation, reduced abnormal phosphorylation of the tau protein, reduced neuronal loss, increased dendritic spine and postsynaptic density, and significantly alleviated memory loss and learning impairment in mice. This study was approved by the Chongqing Medical University Animal Protection and Ethics Committee, China on March 6, 2013.

Neuron Loss in Alzheimer's Disease: Translation in Transgenic Mouse Models

Transgenic mouse models represent an essential tool for the exploration of Alzheimer’s disease (AD) pathological mechanisms and the development of novel treatments, which at present provide only symptomatic and transient effects. While a variety of mouse models successfully reflects the main neuropathological hallmarks of AD, such as extracellular amyloid-β (Aβ) deposits, intracellular accumulation of Tau protein, the development of micro- and astrogliosis, as well as behavioral deficits, substantial neuron loss, as a key feature of the disease, seems to be more difficult to achieve. In this review, we summarize information on classic and more recent transgenic mouse models for AD, focusing in particular on loss of pyramidal, inter-, and cholinergic neurons. Although the cause of neuron loss in AD is still a matter of scientific debate, it seems to be linked to intraneuronal Aβ accumulation in several transgenic mouse models, especially in pyramidal neurons.

N-Terminal Truncated Aβ4-42 Is a Substrate for Neprilysin Degradation in vitro and in vivo

In sporadic Alzheimer's disease (AD), an imbalance between production and clearance of amyloid-β (Aβ) peptides seems to account for enhanced Aβ accumulation. The metalloprotease neprilysin (NEP) is an important Aβ degrading enzyme as shown by a variety of in vitro and in vivo studies. While the degradation of full-length Aβ peptides such as Aβ1-40 and Aβ1-42 is well established, it is less clear whether NEP is also capable of degrading N-terminally truncated Aβ species such as the common variant Aβ4-42. In the present report, we confirmed the degradation of Aβ4-x species by neprilysin using in vitro digestion and subsequent analysis using gel-based assays and mass spectrometry. By crossing Tg4-42 mice expressing only Aβ4-42 peptides with homozygous NEP-knock-out mice (NEP-/-), we were able to demonstrate that NEP deficiency increased hippocampal intraneuronal Aβ levels and aggravated neuron loss in the Tg4-42 transgenic mouse model of AD.

Reduced Acoustic Startle Response and Prepulse Inhibition in the Tg4-42 Model of Alzheimer's Disease

Sensorimotor deficits have been described in several neuropsychiatric disorders including Alzheimer’s disease. The aim of the present study was to evaluate possible sensorimotor gating deficits in the Tg4-42 mouse model of Alzheimer’s disease using the prepulse inhibition task (PPI). Previous studies indicated that the hippocampus is essentially involved in the regulation of PPI. We analyzed 7-month-old homozygous Tg4-42 mice as mice at this age display severe neuron loss especially in the CA1 region of the hippocampus. Our results revealed a reduced startle response and PPI in Tg4-42 mice. The observed deficits in startle response and PPI are likely due to altered sensory processing abilities rather than hearing deficits as Tg4-42 displayed intact hearing in the fear conditioning task. The present study demonstrates for the first time that sensorimotor gating is impaired in Tg4-42 mice. Analyzing startle response as well as the PPI may offer valuable measurements to assess the efficacy of therapeutic strategies in the future in this Alzheimer’s disease model.

Iron Exposure and the Cellular Mechanisms Linked to Neuron Degeneration in Adult Mice

Although the causal relationship between Alzheimer's disease (AD) and iron overload remains unclear, iron dyshomeostasis or improper transport mechanisms are speculated to lead to the accumulation of this neurotoxic metal in the hippocampal formation and other cerebral areas related to neurodegenerative diseases, resulting in the formation of reactive oxygen species (ROS) and, ultimately, cell death. In this study, exposure to high dietary iron (HDI) revealed no significant difference in the number of iron-positive cells and iron content in the cortex and hippocampal region between wild-type (WT) and APP/PS1 mice; however, compared with the control mice, the HDI-treated mice exhibited upregulated divalent metal transporter 1 (DMT1) and ferroportin (Fpn) expression, and downregulated transferrin receptor (TFR) expression. Importantly, we confirmed that there were significantly fewer NeuN-positive neurons in both APP/PS1 and WT mice given HDI, than in the respective controls. Moreover, this iron-induced neuron loss may involve increased ROS and oxidative mitochondria dysfunction, decreased DNA repair, and exacerbated apoptosis and autophagy. Although HDI administration might trigger protective antioxidant, anti-apoptosis, and autophagy signaling, especially in pathological conditions, these data clearly indicate that chronic iron exposure results in neuronal loss due to apoptosis, autophagy, and ferroptosis, hence increasing the risk for developing AD.

18F-FDG-PET Detects Drastic Changes in Brain Metabolism in the Tg4-42 Model of Alzheimer's Disease

The evaluation of new therapeutic strategies in Alzheimer’s disease (AD) relies heavily on in vivo imaging and suitable animal models that mimic the pathological changes seen in patients. ¹⁸F-Fluorodeoxyglucose (¹⁸F-FDG)-positron-emission tomography (PET) is a well-established non-invasive imaging tool for monitoring changes in cerebral brain glucose metabolism in vivo. ¹⁸F-FDG-PET is used as a functional biomarker for AD as patients show an early and progressive reduction of cerebral glucose metabolism. However, earlier studies in preclinical models of AD showed conflicting results. The aim of this study was the evaluation of cerebral glucose metabolism in the Tg4–42 mouse model of AD using ¹⁸F-FDG-PET/magnetic resonance imaging (MRI). Tg4–42 mice show an age-dependent reduction in glucose metabolism together with severe neuron loss and memory deficits. Similar to AD patients early decrease in ¹⁸F-FDG uptake was already detected in young (3 months) Tg4–42 mice. The altered glucose metabolism coupled with age- and disease related cognitive decline of Tg4–42 mice make it a well-suited model for preclinical testing of AD-relevant therapeutics.

Decrease of RyR2 in the prion infected cell line and in the brains of the scrapie infected mice models and the patients of human prion diseases

The levels of ryanodine receptors (RyRs) are usually increased in the brains of human Alzheimer disease (AD) and AD animal models. To evaluate the underlying alteration of brain RyRs in prion disease, scrapie infected cell line SMB-S15 and its infected mice were tested. RyR2 specific Western blots revealed markedly decreased RyR2 levels both in the cells and in the brains of infected mice. Assays of the brain samples of other scrapie (agents 139A and ME7) infected mice collected at different time-points during incubation period showed time-dependent decreases of RyR2. Immunofluorescent assays (IFA) verified that the expression of RyR2 locates predominantly in cytoplasm of SMB cells and overlapped with the neurons in the brain slices of mice. Furthermore, significant down-regulation of RyR2 was also detected in the postmortem cortical brains of the patients of various types of human prion diseases, including sporadic Creutzfeldt-Jakob disease (sCJD), fatal familial insomnia (FFI) and G114V-genetic CJD. Our data here propose the evidences of remarkably decreased brain RyR2 at terminal stages of both human prion diseases and prion infected rodent models. It also highlights that the therapeutic strategy with antagonist of RyRs in AD may not be suitable for prion disease.

Generation of Alzheimer's Disease Transgenic Zebrafish Expressing Human APP Mutation Under Control of Zebrafish appb Promotor

BACKGROUND

Amyloid peptide precursor (APP) as the precursor protein of peptide betaamyloid (β-amyloid, Aβ), which is thought to play a central role in the pathogenesis of Alzheimer's disease (AD), also has an important effect on the development and progression of AD. Through knocking-in APP gene in animals, numerous transgenic AD models have been set up for the investigation of the mechanisms behind AD pathogenesis and the screening of anti-AD drugs. However, there are some limitations to these models and here is a need for such an AD model that is economic as well as has satisfactory genetic homology with human.

METHODS

We generated a new AD transgenic model by knocking a mutant human APP gene (APPsw) in zebrafish with appb promoter of zebrafish to drive the expression of APPsw.

RESULTS

Fluorescent image and immunochemistry stain showed and RT-PCR and western blot assay confirmed that APPsw was successfully expressed in the brain, heart, eyes and vasculature of the transgenic zebrafish. Behavioral observation demonstrated that the transgenic zebrafish had AD-like symptoms. Histopathological observation found that there were cerebral β-amyloidosis and angiopathy (CAA), which induced neuron loss and enlarged pervascular space.

CONCLUSION

These results suggest that APPsw transgenic zebrafish well simulate the pathological characters of AD and can be used as an economic AD transgenic model. Furthermore, the new model suggested that APP can express in microvasculatures and cause the Aβ generation and deposition in cerebral vessel which further destroys cerebral vascular structure resulting in the development and/or the progress of AD.

Synergistic Effect on Neurodegeneration by N-Truncated Aβ4-42 and Pyroglutamate Aβ3-42 in a Mouse Model of Alzheimer's Disease

The N-terminally truncated pyroglutamate Aβ_3-42 (Aβ_pE3-42) and Aβ_4-42 peptides are known to be highly abundant in the brain of Alzheimer's disease (AD) patients. Both peptides show enhanced aggregation and neurotoxicity in comparison to full-length Aβ, suggesting that these amyloid peptides may play an important role in the pathogenesis of AD. The aim of the present work was to study the direct effect of the combination of Aβ_pE3-42 and Aβ_4-42 on ongoing AD-related neuron loss, pathology, and neurological deficits in transgenic mice. Bigenic mice were generated by crossing the established TBA42 and Tg4-42 mouse models expressing the N-truncated Aβ peptides Aβ_pE3-42 and Aβ_4-42, respectively. After generation of the bigenic mice, detailed phenotypical characterization was performed using either immunostainings to evaluate amyloid pathology or quantification of neuron numbers using design-based stereology. The elevated plus maze was used to study anxiety levels. In order to evaluate sensori-motor deficits, the inverted grid, the balance beam and the string suspension tasks were applied. We could demonstrate that co-expression of Aβ_pE3-42 and Aβ_4-42 accelerates neuron loss in the CA1 pyramidal layer of young bigenic mice as seen by reduced neuron numbers in comparison to single transgenic homozygous mice expressing either Aβ_pE3-42 or Aβ_4-42. This observation coincides with the robust intraneuronal Aβ accumulation observed in the bigenic mice. In addition, loss of anxiety and motor deficits were enhanced in an age-dependent manner. The sensori-motor deficits correlate with the abundant spinal cord pathology, as demonstrated by robust intracellular Aβ accumulation within motor neurons and extracellular Aβ deposition. Our observations demonstrate that a combination of Aβ_pE3-42 and Aβ_4-42 has a stronger effect on ongoing AD pathology than the peptides alone. Therefore, Aβ_pE3-42 and Aβ_4-42 might represent excellent potential therapeutic targets and diagnostic markers for AD.

Conditional Deletion of PDK1 in the Forebrain Causes Neuron Loss and Increased Apoptosis during Cortical Development

Decreased expression but increased activity of PDK1 has been observed in neurodegenerative disease. To study in vivo function of PDK1 in neuron survival during cortical development, we generate forebrain-specific PDK1 conditional knockout (cKO) mice. We demonstrate that PDK1 cKO mice display striking neuron loss and increased apoptosis. We report that PDK1 cKO mice exhibit deficits on several behavioral tasks. Moreover, PDK1 cKO mice show decreased activities for Akt and mTOR. These results highlight an essential role of endogenous PDK1 in the maintenance of neuronal survival during cortical development.

Hippocampal sclerosis, hippocampal neuron loss patterns and TDP-43 in the aged population

Hippocampal neuron loss is a common neuropathological feature in old age with various underlying etiologies. Hippocampal sclerosis of aging (HS-Aging) is neuropathologically characterized by severe CA1 neuronal loss and frequent presence of transactive response DNA-binding protein of 43 kDa (TDP-43) aggregations. Its etiology is unclear and currently no standardized approaches to measure HS-Aging exist. We developed a semi-quantitative protocol, which captures various hippocampal neuron loss patterns, and compared their occurrence in the context of HS-Aging, TDP-43, vascular and tau pathology in 672 brains (TDP-43 staining n = 642/672, 96%) donated for the population-based Cambridge City over-75s Cohort and the Cognitive Function and Ageing Study. HS-Aging was first evaluated independently from the protocol using the most common criteria defined in literature, and then described in detail through examination of neuron loss patterns and associated pathologies. 34 (5%) cases were identified, with a maximum of five pyramidal neurons in each of over half CA1 fields-of-view (x200 magnification), no vascular damage, no neuron loss in CA2-CA4, but consistent TDP-43 neuronal solid inclusions and neurites. We also report focal CA1 neuron loss with vascular pathology to affect predominantly CA1 bordering CA2 (Fisher's exact, P = 0.009), whereas neuron loss in the subicular end of CA1 was associated with TDP-43 inclusions (Fisher's exact, P < 0.001) and high Braak stage (Fisher's exact, P = 0.001). Hippocampal neuron loss in CA4-CA2 was not associated with TDP-43. We conclude that hippocampal neuron loss patterns are associated with different etiologies within CA1, and propose that these patterns can be used to form objective criteria for HS-Aging diagnosis. Finally, based on our results we hypothesize that neuron loss leading to HS-Aging starts from the subicular end of CA1 when it is associated with TDP-43 pathology, and that this neurodegenerative process is likely to be significantly more common than "end-stage" HS-Aging only.

Mild Traumatic Brain Injury Produces Neuron Loss That Can Be Rescued by Modulating Microglial Activation Using a CB2 Receptor Inverse Agonist

We have previously reported that mild TBI created by focal left-side cranial blast in mice produces widespread axonal injury, microglial activation, and a variety of functional deficits. We have also shown that these functional deficits are reduced by targeting microglia through their cannabinoid type-2 (CB2) receptors using 2-week daily administration of the CB2 inverse agonist SMM-189. CB2 inverse agonists stabilize the G-protein coupled CB2 receptor in an inactive conformation, leading to increased phosphorylation and nuclear translocation of the cAMP response element binding protein (CREB), and thus bias activated microglia from a pro-inflammatory M1 to a pro-healing M2 state. In the present study, we showed that SMM-189 boosts nuclear pCREB levels in microglia in several brain regions by 3 days after TBI, by using pCREB/CD68 double immunofluorescent labeling. Next, to better understand the basis of motor deficits and increased fearfulness after TBI, we used unbiased stereological methods to characterize neuronal loss in cortex, striatum, and basolateral amygdala (BLA) and assessed how neuronal loss was affected by SMM-189 treatment. Our stereological neuron counts revealed a 20% reduction in cortical and 30% reduction in striatal neurons bilaterally at 2-3 months post blast, with SMM-189 yielding about 50% rescue. Loss of BLA neurons was restricted to the blast side, with 33% of Thy1+ fear-suppressing pyramidal neurons and 47% of fear-suppressing parvalbuminergic (PARV) interneurons lost, and Thy1-negative fear-promoting pyramidal neurons not significantly affected. SMM-189 yielded 50-60% rescue of Thy1+ and PARV neuron loss in BLA. Thus, fearfulness after mild TBI may result from the loss of fear-suppressing neuron types in BLA, and SMM-189 may reduce fearfulness by their rescue. Overall, our findings indicate that SMM-189 rescues damaged neurons and thereby alleviates functional deficits resulting from TBI, apparently by selectively modulating microglia to the beneficial M2 state. CB2 inverse agonists thus represent a promising therapeutic approach for mitigating neuroinflammation and neurodegeneration.

Activation of neuronal defense mechanisms in response to pathogenic factors triggering induction of amyloidosis in Alzheimer's disease

We present a new model for etiology of Alzheimer's disease (AD) which postulates early involvement of specialized neuroprotective mechanisms in the pathology of AD. These neuroprotective mechanisms work in concert to regulate metabolic homeostasis in healthy neuronal cells, but contribute to the distinctive cytopathic phenotype of neuronal degeneration in AD. According to this model, two molecular/genetic hallmarks of AD, amyloid-β (Aβ) deposition and tau hyperphosphorylation, are associated with neuronal mechanisms for dissipating thermal energy associated with high levels of protein synthesis in highly temperature-sensitive neuronal cells. Development of effective methods of AD treatment will require a better understanding of how this neuronal defense system is activated in response to cytopathological triggers in sporadic AD. The cause and effect link between synthesis and processing of amyloid-β protein precursor (AβPP) and the AD terminal phenotype of neurofibrillary tangles and neuron loss involve the formation of Aβ peptides that accumulate as oligomers, cannot be controlled by neurons, and are toxic to the surrounding neuronal membranes. We analyze experimental and clinical studies that have investigated the correlation between phosphorylation of some transport proteins and increased synthesis of proteins in neurons. We also review the evidence related to the possibility that protein hyperphosphorylation may be a byproduct of energetic imbalances in AD cells associated with high levels of protein synthesis, and that activation of defense systems, through which energy-rich molecules are eliminated from the site of protein synthesis and are sequestered to the peripheral neuronal areas, may bring about some of the distinctive morphological features of AD.

Intracellular accumulation of amyloid-Beta - a predictor for synaptic dysfunction and neuron loss in Alzheimer's disease

Despite of long-standing evidence that beta-amyloid (Abeta) peptides have detrimental effects on synaptic function, the relationship between Abeta, synaptic and neuron loss is largely unclear. During the last years there is growing evidence that early intraneuronal accumulation of Abeta peptides is one of the key events leading to synaptic and neuronal dysfunction. Many studies have been carried out using transgenic mouse models of Alzheimer's disease (AD) which have been proven to be valuable model systems in modern AD research. The present review discusses the impact of intraneuronal Abeta accumulation on synaptic impairment and neuron loss and provides an overview of currently available AD mouse models showing these pathological alterations.

Age-related metabolite changes and volume loss in the hippocampus by magnetic resonance spectroscopy and imaging

Magnetic resonance imaging (MRI) studies have produced controversial results concerning the correlation of hippocampal volume loss with increasing age. The goals in this study were: 1) to test whether levels of N-acetyl aspartate (NAA, a neuron marker) change in the hippocampus during normal aging and 2) to determine the relationship between hippocampal NAA and volume changes. Proton magnetic resonance spectroscopic imaging (1H MRSI) and MRI were used to measure hippocampal metabolites and volumes in 24 healthy adults from 36 to 85 years of age. NAA/Cho decreased by 24% (r = 0.53, p = 0.01) and NAA/Cr by 26% (r = 0.61, p < 0.005) over the age range studied, whereas Cho/Cr remained stable, implying diminished NAA levels. Hippocampal volume shrank by 20% (r = 0.64, p < 0.05). In summary, aging effects must be considered in 1H MRSI brain studies. Furthermore, because NAA is considered a marker of neurons, these results provide stronger support for neuron loss in the aging hippocampus than volume measurements by MRI alone.