Investigating the Head Impact Force-Induced Evolution of Hyperphosphorylated Tau Proteins in Brain Tissue Through Mechanical Mesoscale Finite Element Simulation

For human heads that experienced repetitive subconcussive impacts,abnormal accumulation of hyperphosphorylated tau(p-tau)proteins was found in the postmortem brain tissue.To numerically understand the cause–effect relationship between the external force and the microscopic volume change of the p-tau protein,we created a mesoscale finite element model of the multilayer brain tissue containing microscopic voids representing the p-tau proteins.The model was applied under the loading boundary conditions obtained from a larger length scale simulation.A formerly developed internal state variable elastoplasticity model was implemented to describe the constitutive behaviors of gray and white matters,while the cerebrospinal fluid was assumed to be purely elastic.The effects of the initial sizes and distances of p-tau proteins located at four different brain regions(frontal,parietal,temporal and occipital lobes)on their volumetric evolutions were studied.It is concluded that both the initial sizes and distances of the proteins have more or less(depending on the specific brain region)influential effects on the growth or contraction rate of the p-tau protein.The p-tau proteins located within the brain tissue at the frontal and occipital lobes are more heavily affected by the frontal impact load compared with those at the parietal and temporal lobes.In summary,the modeling approach presented in this paper provides a strategy for mechanically studying the evolution of p-tau proteins in the brain tissue and gives insight into understanding the correlation between macroscopic force and microstructure change of the brain tissue.

Do tau-synaptic long-term depression interactions in the hippocampus play a pivotal role in the progression of Alzheimer’s disease?

Cognitive decline in Alzheimer’s disease correlates with the extent of tau pathology,in particular tau hyperphosphorylation that initially appears in the transentorhinal and related regions of the brain including the hippocampus.Recent evidence indicates that tau hyperphosphorylation caused by either amyloid-βor long-term depression,a form of synaptic weakening involved in learning and memory,share similar mechanisms.Studies from our group and others demonstrate that long-term depression-inducing low-frequency stimulation triggers tau phosphorylation at different residues in the hippocampus under different experimental conditions including aging.Conversely,certain forms of long-term depression at hippocampal glutamatergic synapses require endogenous tau,in particular,phosphorylation at residue Ser396.Elucidating the exact mechanisms of interaction between tau and long-term depression may help our understanding of the physiological and pathological functions of tau/tau(hyper)phosphorylation.We first summarize experimental evidence regarding tau-long-term depression interactions,followed by a discussion of possible mechanisms by which this interplay may influence the pathogenesis of Alzheimer’s disease.Finally,we conclude with some thoughts and perspectives on future research about these interactions.

P25/CDK5-mediated Tau Hyperphosphorylation in Both Ipsilateral and Contralateral Cerebra Contributes to Cognitive Deficits in Post-stroke Mice

Objective Post-stroke cognitive impairment(PSCI)develops in approximately one-third of stroke survivors and is associated with ingravescence.Nonetheless,the biochemical mechanisms underlying PSCI remain unclear.The study aimed to establish an ischemic mouse model by means of transient unilateral middle cerebral artery occlusions(MCAOs)and to explore the biochemical mechanisms of p25/cyclin-dependent kinase 5(CDK5)-mediated tau hyperphosphorylation on the PSCI behavior.Methods Cognitive behavior was investigated,followed by the detection of tau hyperphosphorylation,mobilization,activation of kinases and/or inhibition of phosphatases in the lateral and contralateral cerebrum of mice following ischemia in MACO mice.Finally,we treated HEK293/tau cells with oxygen-glucose deprivation(OGD)and a CDK5 inhibitor(Roscovitine)or a GSK3βinhibitor(LiCl)to the roles of CDK5 and GSK3βin mediating ischemia-reperfusion-induced tau phosphorylation.Results Ischemia induced cognitive impairments within 2 months,as well as causing tau hyperphosphorylation and its localization to neuronal somata in both ipsilateral and contralateral cerebra.Furthermore,p25 that promotes CDK5 hyperactivation had significantly higher expression in the mice with MCAO than in the shamoperation(control)group,while the expression levels of protein phosphatase 2(PP2A)and the phosphorylation level at Tyr307 were comparable between the two groups.In addition,the CDK5 inhibitor rescued tau from hyperphosphorylation induced by OGD.Conclusion These findings demonstrate that upregulation of CDK5 mediates tau hyperphosphorylation and localization in both ipsilateral and contralateral cerebra,contributing to the pathogenesis of PSCI.

Effect of Chronic Noise Exposure on Expression of N-Methyl-D-Aspartic Acid Receptor 2B and Tau Phosphorylation in Hippocampus of Rats

Objective To study the effect of chronic noise exposure on expression of N-methyI-D-aspartic acid receptor 2B （NR2B） and tau phosphorylation in hippocampus of rats. Methods Twenty-four male SD rats were divided in control group and chronic noise exposure group. NR2B expression and tau phosphorylation in hippocampus of rats were detected after chronic noise exposure （100 dB SPL white noise, 4 h/dx30d） and their mechanisms underlying neuronal apoptosis in hippocampus of rats with TUNEL staining. Results The NR2B expression decreased significantly after chronic noise exposure which resulted in tau hyperphosphorylation and neural apoptosis in hippocampus of rats. Immunohistochemistry showed that the tau hyperphosphorylation was most prominent in dentate gyrus （DG） and CA1 region of rat hippocampus. Conclusion The abnormality of neurotransmitter system, especially Glu and NR2B containing NMDA receptor, and tau hyperphosphorylation in hippocampus of rats, may play a role in chronic noise-induced neural apoptosis and cognition impairment.

Effect of p62 on tau hyperphosphorylation in a rat model of Alzheimer's disease

Tau hyperphosphorylation is a main cause of neuronal loss in Alzheimer＇s disease, which can be caused by many factors, including oxidative stress. The multifunctional protein p62, which exists in neurofibrillary tangles and causes aggregation of hyperphosphorylated tau, not only serves as a receptor in selective autophagy, but also regulates oxidative stress. However, whether p62 participates in oxidative stress-induced tau hyperphosphorylation remains unclear. In this study, we produced an Alzheimer＇s disease rat model by injecting 13-amyloid protein into the hippocampus and ^-galactose intraperitoneally. Hematoxylin-eosin staining was used for morphological analysis of brain tissue, and western blotting, immunohistochemistry and reverse transcription-PCR were employed to study p62 and autophagy related proteins, antioxidant defense system kelch-like ECH-associated protein 1-NF-E2-related factor 2 related proteins and hyperphosphorylated tau, respectively. The number of neurons in the brain decreased in Aizheimer＇s disease rats, and the autophagy related proteins Atg12-Atg5, microtubule-associated protein 1 light chain 3-phosphatidylethanolamine and Beclinl increased significantly, while p62 expression reduced. Expression of kelch-like ECH-associated protein 1 increased, NF-E2-related factor 2 protein and the downstream gene products of glutamate cysteine ligase catalytic subunit and glutamate cysteine ligase modulatory subunit decreased, and hyperphosphorylated tau increased. These findings demonstrate that autophagy levels increased and p62 levels decreased in the brains of Alzheimer＇s disease rats. Moreover, the anti-oxidative capability of the NF-E2-related factor 2-antioxidant response element pathway was decreased, which may be the cause of tau hyperphosphorylation in Alzheimer＇s disease brain tissue and the subsequent structural and functional damage to neurons.

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

The amyloid-β(Aβ)oligomer,rather than the Aβmonomer,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 Aβoligomer 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 Aβoligomer 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.

Toxicities of amyloid-beta and tau protein are reciprocally enhanced in the Drosophila model

Extracellular aggregation of amyloid-beta(Aβ)and intracellular tau tangles are two major pathogenic hallmarks and critical factors of Alzheimer’s disease.A linear interaction between Aβand tau protein has been characterized in several models.Aβinduces tau hyperphosphorylation through a complex mechanism;however,the master regulators involved in this linear process are still unclear.In our study with Drosophila melanogaster,we found that Aβregulated tau hyperphosphorylation and toxicity by activating c-Jun N-terminal kinase.Importantly,Aβtoxicity was dependent on tau hyperphosphorylation,and flies with hypophosphorylated tau were insulated against Aβ-induced toxicity.Strikingly,tau accumulation reciprocally interfered with Aβdegradation and correlated with the reduction in mRNA expression of genes encoding Aβ-degrading enzymes,including dNep1,dNep3,dMmp2,dNep4,and dIDE.Our results indicate that Aβand tau protein work synergistically to further accelerate Alzheimer’s disease progression and may be considered as a combined target for future development of Alzheimer’s disease therapeutics.

Icariin ameliorates memory deficits through regulating brain insulin signaling and glucose transporters in 3×Tg-AD mice

Icariin,a major prenylated flavonoid found in Epimedium spp.,is a bioactive constituent of Herba Epimedii and has been shown to exert neuroprotective effects in experimental models of Alzheimer’s disease.In this study,we investigated the neuroprotective mechanism of icariin in an APP/PS1/Tau triple-transgenic mouse model of Alzheimer’s disease.We performed behavioral tests,pathological examination,and western blot assay,and found that memory deficits of the model mice were obviously improved,neuronal and synaptic damage in the cerebral cortex was substantially mitigated,and amyloid-βaccumulation and tau hyperphosphorylation were considerably reduced after 5 months of intragastric administration of icariin at a dose of 60 mg/kg body weight per day.Furthermore,deficits of proteins in the insulin signaling pathway and their phosphorylation levels were significantly reversed,including the insulin receptor,insulin receptor substrate 1,phosphatidylinositol-3-kinase,protein kinase B,and glycogen synthase kinase 3β,and the levels of glucose transporter 1 and 3 were markedly increased.These findings suggest that icariin can improve learning and memory impairments in the mouse model of Alzheimer’s disease by regulating brain insulin signaling and glucose transporters,which lays the foundation for potential clinical application of icariin in the prevention and treatment of Alzheimer’s disease.

Lamotrigine protects against cognitive deficits,synapse and nerve cell damage,and hallmark neuropathologies in a mouse model of Alzheimer’s disease

Lamotrigine(LTG)is a widely used drug for the treatment of epilepsy.Emerging clinical evidence suggests that LTG may improve cognitive function in patients with Alzheimer’s disease.However,the underlying molecular mechanisms remain unclear.In this study,amyloid precursor protein/presenilin 1(APP/PS1)double transgenic mice were used as a model of Alzheimer’s disease.Five-month-old APP/PS1 mice were intragastrically administered 30 mg/kg LTG or vehicle once per day for 3 successive months.The cognitive functions of animals were assessed using Morris water maze.Hyperphosphorylated tau and markers of synapse and glial cells were detected by western blot assay.The cell damage in the brain was investigated using hematoxylin and eosin staining.The levels of amyloid-βand the concentrations of interleukin-1β,interleukin-6 and tumor necrosis factor-αin the brain were measured using enzyme-linked immunosorbent assay.Differentially expressed genes in the brain after LTG treatment were analyzed by high-throughput RNA sequencing and real-time polymerase chain reaction.We found that LTG substantially improved spatial cognitive deficits of APP/PS1 mice;alleviated damage to synapses and nerve cells in the brain;and reduced amyloid-βlevels,tau protein hyperphosphorylation,and inflammatory responses.High-throughput RNA sequencing revealed that the beneficial effects of LTG on Alzheimer’s disease-related neuropathologies may have been mediated by the regulation of Ptgds,Cd74,Map3k1,Fosb,and Spp1 expression in the brain.These findings revealed potential molecular mechanisms by which LTG treatment improved Alzheimer’s disease.Furthermore,these data indicate that LTG may be a promising therapeutic drug for Alzheimer’s disease.

A biomimetic upconversion nanoreactors for near-infrared driven H2 release to inhibit tauopathy in Alzheimer’s disease therapy

Abnormal hyperphosphorylation of tau protein is a principal pathological hallmark in the onset of neurodegenerative disorders,such as Alzheimer’s disease(AD),which can be induced by an excess of reactive oxygen species(ROS).As an antioxidant,hydrogen gas(H_(2))has the potential to mitigate AD by scavenging highly harmful ROS such as·OH.However,conventional administration methods of H_(2) face significant challenges in controlling H_(2) release on demand and fail to achieve effective accumulation at lesion sites.Herein,we report artificial nanoreactors that mimic natural photosynthesis to realize near-infrared(NIR)light-driven photocatalytic H_(2) evolution in situ.The nanoreactors are constructed by biocompatible crosslinked vesicles(CVs)encapsulating ascorbic acid and two photosensitizers,chlorophyll a(Chla)and indoline dye(Ind).In addition,platinum nanoparticles(Pt NPs)serve as photocatalysts and upconversion nanoparticles(UCNP)act as light-harvesting antennas in the nanoreacting system,and both attach to the surface of CVs.Under NIR irradiation,the nanoreactors release H_(2) in situ to scavenge local excess ROS and attenuate tau hyperphosphorylation in the AD mice model.Such NIR-triggered nanoreactors provide a proof-of-concept design for the great potential of hydrogen therapy against AD.

Natural polyphenols effects on protein aggregates in Alzheimer＇s and Parkinson＇s prion-like diseases

Alzheimer＇s and Parkinson＇s diseases are the most common neurodegenerative diseases. They are characterized by protein aggregates and so can be considered as prion-like disease. The major components of these deposits are amyloid peptide and tau for Alzheimer＇s disease, α-synuclein and synphilin-1 for Parkinson＇s disease. Drugs currently proposed to treat these pathologies do not prevent neurodegenerative processes and are mainly symptomatic therapies. Molecules inducing inhibition of aggregation or disaggregation of these proteins could have beneficial effects, especially if they have other beneficial effects for these diseases. Thus, several natural polyphenols, which have antioxidative, anti-inflammatory and neuroprotective properties, have been largely studied, for their effects on protein aggregates found in these diseases, notably in vitro. In this article, we propose to review the significant papers concerning the role of polyphenols on aggregation and disaggregation of amyloid peptide, tau, α-synuclein, synphilin-1, suggesting that these compounds could be useful in the treatments in Alzheimer＇s and Parkinson＇s diseases.

A novel transgenic mouse line with hippocampus-dominant and inducible expression of truncated human tau

Background Intraneuronal accumulation of hyperphosphorylated tau is a defining hallmark of Alzheimer’s disease(AD).However,mouse models imitating AD-exclusive neuronal tau pathologies are lacking.Methods We generated a new tet-on transgenic mouse model expressing truncated human tau N1-368(termed hTau368),a tau fragment increased in the brains of AD patients and aged mouse brains.Doxycycline(dox)was administered in drinking water to induce hTau368 expression.Immunostaining and Western blotting were performed to measure the tau level.RNA sequencing was performed to evaluate gene expression,and several behavioral tests were conducted to evaluate mouse cognitive functions,emotion and locomotion.Results Dox treatment for 1-2 months at a young age induced overt and reversible human tau accumulation in the brains of hTau368 transgenic mice,predominantly in the hippocampus.Meanwhile,the transgenic mice exhibited AD-like high level of tau phosphorylation,glial activation,loss of mature neurons,impaired hippocampal neurogenesis,synaptic degeneration and cognitive deficits.Conclusions This study developed a well-characterized and easy-to-use tool for the investigations and drug development for AD and other tauopathies.

Screening of treatment targets for Alzheimer's disease from the molecular mechanisms of impairment by β-amyloid aggregation and tau hyperphosphorylation

β-Amyloid （Aβ） over-expression and tau hyperphosphorylation are considered to be the central events in the pathogenesis of Alzheimer＇s disease （AD）.Studies on them may help elucidate the precise molecular pathogenesis of AD.Until now,although tau protein and Aβ remain the foci of AD research,the etiopathogenesis of AD and effective drugs for AD treatment are still largely unsolved.The present review was mainly focused on the molecular mechanism of Aβ aggregation-related impairment and the pathways leading to tau hyperphosphorylation,based on which some promising therapeutic targets for AD were also proposed.

Advances in the Pathogenesis of Alzheimer’s Disease:Focusing on Tau-Mediated Neurodegeneration

In addition to senile plaques and cerebral amyloid angiopathy,the hyperphosphorylation of tau protein and formation of intraneuronal neurofibrillary tangles(NFTs)represents another neuropathological hallmark in AD brain.Tau is a microtubule-associated protein and localizes predominantly in the axons of neurons with the primary function in maintaining microtubules stability.When the balance between tau phosphorylation and dephosphorylation is changed in favor of the former,tau is hyperphosphorylated and the level of the free tau fractions elevated.The hyperphosphorylation of tau protein and formation of NFTs represent a characteristic neuropathological feature in AD brain.We have discussed the role of Aβin AD in our previous review,this review focused on the recent advances in tau-mediated AD pathology,mainly including tau hyperphosphorylation,propagation of tau pathology and the relationship between tau and Aβ.

Associations of AT(N) biomarkers with neuropsychiatric symptoms in prechnical Alzheimer’s disease and cognitively unimpaired individuals

The development of in vivo biomarkers of Alzheimer's disease(AD)has advanced the diagnosis of AD from a clinical syndrome to a biological construct.The preclinical stage of AD continuum is defined by the identification of AD biomarkers crossing the pathological threshold in cognitively unimpaired individuals.While neuropsychiatric symptoms(NPS)are non-cognitive symptoms that are increasingly recognized as early manifestations of AD,the associations of NPS with AD pathophysiology in preclinical AD remain unclear.Here,we review the associations between NPS and AD biomarkers amyloid-(3(Aβ),tau and neurodegeneration in preclinical AD and cognitivelyunimpaired individuals in 19 eligible English-language publications(8 cross-sectional studies,10 longitudinal,1 both cross-sectional and longitudinal).The cross-sectional studies have consistently shown that NPS,particularly depressive and anxiety symptoms,are associated with higher Aβ.The longitudinal studies have suggested that greater NPS are associated with higher Aβ and cognitive decline in cognitively unimpaired subjects over time.However,most of the studies have either cross-sectionally or longitudinally shown no association between NPS and tau pathology.For the association of NPS and neurodegeneration,two studies have shown that the cerebrospinal fluid total-tau is linked to longitudinal increase in NPS and that the NPS may predict longitudinal metabolic decline in preclinical AD,respectively.However,evidence for the association between atrophy and NPS in preclinical AD is less consistent.Therefore,future longitudinal studies with well-designed methodologies and NPS measurements are required not only to determine the relationship among AT(N)biomarkers,NPS and cognitive decline,but also to elucidate the contribution of comorbid pathology to preclinical AD.