Tau Protein In Neurofibrillary Tangles Research Articles

Discovering correlates of off‐target 18F‐MK6240 signal in community‐dwelling adults

AbstractBackground18F‐MK6240 binds hyperphosphorylated tau protein in neurofibrillary tangles, a hallmark of Alzheimer’s disease(AD); however, the tracer may also bind to other similarly structured molecules, known as off‐target binding. Off‐target binding is inconsistent across individuals and can lead to biased quantitative assessment, making it difficult to accurately identify neurofibrillary tangle pathology. We examined variable off‐target binding by performing a correlation analysis with demographic factors, vascular risk, lifestyle factors, and co‐morbidities.MethodNinety‐five participants (65±3yrs; 67% women; 42/58% White/Black; 66% Hispanic; 12±4yrs education) in the Northern Manhattan Study of Metabolism and Mind(NOMEM) underwent 18F‐MK6240(90‐110min) and 18F‐Florbetaben(90‐110min) PET imaging and completed surveys, including age, sex, education, exercise levels, and medical history. Only visually‐determined amyloid‐negative participants were included to increase the likelihood that elevated tau PET signal was off‐target. Tau SUVR (cerebellar gray matter reference region) was calculated for composite Braak stages (I/II, III/IV, V/VI) and two known off‐target regions, the choroid plexus and the extra‐cerebral space around the brain. The extra‐cerebral mask was generated by dilating the gray/CSF boundary of the ANTs probability map and then subtracting the brain. Percent of variance explained (r2) from general linear models are reported between off‐target regions and factors of interest.ResultDescriptively, 18F‐MK6240 off‐target binding in choroid plexus was positively correlated with SUVR in Braak stage regions I/II (r2 = 0.37;p<0.001) and III/IV (r2 = 0.44;p<0.001) to a larger extent than V/VI (r2 = 0.21;p<0.001), while off‐target binding in the extra‐cerebral space was positively correlated with Braak stages I/II (r2 = 0.07;p<0.001) to a lesser extent than III/IV (r2 = 0.13;p<0.001) and V/VI (r2 = 0.18;p<0.001), suggesting that proximity of key AD regions to off‐target regions increases the likelihood of confounded signal. Off‐target binding in the choroid plexus was elevated amongst self‐identified Hispanic participants (r2 = 0.19;p<0.001). Extra‐cerebral off‐target binding was negatively associated with participant weight (r2 = 0.12;p<0.001).ConclusionExtra‐cerebral off‐target binding of 18F‐MK6240 may confound signal in key AD regions in amyloid‐negative participants. Off‐target binding should be accounted for regionally and methods for capturing extra‐cerebral signal are critical. Understanding the role of factors related to tracer distribution, including weight, and sociodemographic factors will enhance the quantification of 18F‐MK6240 for the early detection of neurofibrillary tangle pathology.

Discovering correlates of off‐target 18F‐MK6240 signal in community‐dwelling adults

AbstractBackground18F‐MK6240 binds hyperphosphorylated tau protein in neurofibrillary tangles, a hallmark of Alzheimer’s disease(AD); however, the tracer may also bind to other similarly structured molecules, known as off‐target binding. Off‐target binding is inconsistent across individuals and can lead to biased quantitative assessment, making it difficult to accurately identify neurofibrillary tangle pathology. We examined variable off‐target binding by performing a correlation analysis with demographic factors, vascular risk, lifestyle factors, and co‐morbidities.MethodsNinety‐five participants (65±3yrs; 67% women; 42/58% White/Black; 66% Hispanic; 12±4yrs education) in the Northern Manhattan Study of Metabolism and Mind(NOMEM) underwent 18F‐MK6240(90‐110min) and 18F‐Florbetaben(90‐110min) PET imaging and completed surveys, including age, sex, education, exercise levels, and medical history. Only visually‐determined amyloid‐negative participants were included to increase the likelihood that elevated tau PET signal was off‐target. Tau SUVR (cerebellar gray matter reference region) was calculated for composite Braak stages (I/II, III/IV, V/VI) and two known off‐target regions, the choroid plexus and the extra‐cerebral space around the brain. The extra‐cerebral mask was generated by dilating the gray/CSF boundary of the ANTs probability map and then subtracting the brain. Percent of variance explained (r2) from general linear models are reported between off‐target regions and factors of interest.ResultsDescriptively, 18F‐MK6240 off‐target binding in choroid plexus was positively correlated with SUVR in Braak stage regions I/II (r2 = 0.37;p<0.001) and III/IV (r2 = 0.44;p<0.001) to a larger extent than V/VI (r2 = 0.21;p<0.001), while off‐target binding in the extra‐cerebral space was positively correlated with Braak stages I/II (r2 = 0.07;p<0.001) to a lesser extent than III/IV (r2 = 0.13;p<0.001) and V/VI (r2 = 0.18;p<0.001), suggesting that proximity of key AD regions to off‐target regions increases the likelihood of confounded signal. Off‐target binding in the choroid plexus was elevated amongst self‐identified Hispanic participants (r2 = 0.19;p<0.001). Extra‐cerebral off‐target binding was negatively associated with participant weight (r2 = 0.12;p<0.001).ConclusionExtra‐cerebral off‐target binding of 18F‐MK6240 may confound signal in key AD regions in amyloid‐negative participants. Off‐target binding should be accounted for regionally and methods for capturing extra‐cerebral signal are critical. Understanding the role of factors related to tracer distribution, including weight, and sociodemographic factors will enhance the quantification of 18F‐MK6240 for the early detection of neurofibrillary tangle pathology.

Neuropsychiatric inventory questionnaire scores are predictive of dementia progression

AbstractBackgroundIn ageing adults, the most common form of dementia is Alzheimer’s disease (AD). AD pathogenesis involves the accumulation of beta‐amyloid (Aβ) protein aggregation in plaques and tau proteins in neurofibrillary tangles that are associated with a decreased number of synapses in the brain, altered neuronal function and cell death via neurotoxicity, as well as learning and memory deficits. Clinically, the presence and severity of neuropsychiatric symptoms that AD patients present with can be reliably measured by the Neuropsychiatric Inventory Questionnaire (NPIQ). This study aims to explore the association between baseline mental health and the severity of AD progression.MethodTo measure baseline mental health, NPIQ scores were used while the change in deq was used to represent the severity of AD progression within the TARCC cohort. deq is a homolog of d, a reliable latent dementia proxy that represents cognitive correlates of functional status and is specific for distinguishing cases with AD from other dementia‐related presentations. Most crucially, the deq homolog has been adjusted for equivalence across ethnicities. Using stratified analysis and structured equation models, the association between baseline mental health and change in was investigated.ResultThe first model exploring NPIQ and the change in deq was only adjusted for baseline deq; it showed NPIQ explaining 19% of the variance in delta deq and was statistically significant at p = 0.016 for Non‐Hispanic Whites. With the second model, age, sex, and education were adjusted for in addition to baseline deq. NPIQ was shown to explain 25% of the variance in delta deq while being statistically significant at p = 0.037 for Non‐Hispanic Whites. This model was replicated in the Alzheimer’s Disease Neuroimaging Initiative (ADNI) cohort; NPIQ was shown to be predictive for delta deq at p = 0.013.ConclusionIn Non‐Hispanic Whites, worse baseline mental health has been shown to predict increased severity and progression of AD. This makes it a clinical therapeutic target with the possible benefit of impacting the course of AD in patients. The fascinating interplay between mental health and its relationship to Alzheimer’s disease should be studied further with an additional focus on ethnicity.

Bioinformatic analysis of the SPs and NFTs proteomes unravel putative biomarker candidates for Alzheimer's disease.

Aging is the main risk factor for the appearance of age-related neurodegenerative diseases, including Alzheimer's disease (AD). AD is the most common form of dementia, characterized by the presence of senile plaques (SPs) and neurofibrillary tangles (NFTs), the main histopathological hallmarks in AD brains. The core of these deposits are predominantly amyloid fibrils in SPs and hyperphosphorylated Tau protein in NFTs, but other molecular components can be found associated with these pathological lesions. Herein, an extensive literature review was carried out to obtain the SPs and NFTs proteomes, followed by a bioinformatic analysis and further putative biomarker validation. For SPs, 857 proteins were recovered, and, for NFTs, 627 proteins of which 375 occur in both groups and represent the common proteome. Gene Ontology (GO) enrichment analysis permitted the identification of biological processes and the molecular functions most associated with these lesions. Analysis of the SPs and NFTs common proteins unraveled pathways and molecular targets linking both histopathological events. Further, validation of a putative phosphotarget arising from the in silico analysis was performed in serum-derived extracellular vesicles from AD patients. This bioinformatic approach contributed to the identification of putative molecular targets, valuable for AD diagnostic or therapeutic intervention.

Bioinformatic analysis of senile plaques and neurofibrillary tangles proteomes

AbstractBackgroundSenile plaques (SPs) and neurofibrillary tangles (NFTs) are the main histopathological hallmarks of Alzheimer’s disease (AD). Although these two deposits have main components, like amyloid fibrils in SPs and hyperphosphorylated tau protein in NFTs, the molecular composition underlying these lesions has not been completely unraveled. Hence, this work aims to characterize the SPs and NFTs proteomes’ by applying a bioinformatic analysis, to identify new possible biomarkers candidates for AD.MethodAn extensive literature research was carried out on Pubmed, using keywords that allowed the recovery of information regarding SPs and NFTs proteomes in AD brains. The data obtained was loaded and analysed on Cytoscape v3.8.2. For the Gene Ontology (GO) analysis, the plugins ClueGO v2.5.8 + CluePedia v1.5.8 were employed.ResultMore than 800 proteins were identified for SPs and more than 600 for the NFTs. GO analyses allowed the characterization of both proteomes at the biological process, molecular function, and cellular component levels. The top biological processes for SPs were related to cell development, secretion, and exocytosis, while for NFTs these were related to protein localization, vesicle‐mediated transport in synapse, and response to oxidative stress. Overlap of both proteomes revealed more than 300 proteins that represent interesting targets for AD. GO analyses revealed that these proteins are involved in biological processes like vesicle‐mediated transport in synapse and apoptotic signaling pathway. Additional experiments using antibody‐based methodologies need to be carried out to validate the potential of these candidates for AD.ConclusionThis study allowed the identification of several proteins, present in both SPs and NFTs, that can not only assist in unraveling pathways common to both histopathological hallmarks but also constitute possible biomarker candidates for AD diagnosis and/or therapeutics. To this end research was funded by a grant from the Alzheimer’s Association (2019‐AARG‐644347) and supported by iBiMED UIDB/04501/2020, FCT, COMPETE program, QREN, European Union. T.S.M. is supported by the FCT through the individual PhD grant (SFRH/BD/145979/2019). RV’s Fellowship Grant (IF/00286/2015).

Drug repurposing strategy for treating Alzheimer’s disease

AbstractBackgroundAlzheimer’s disease with a long preclinical period of ∼20 years is a chronic, insidious, and progressive neurodegenerative disease of old age. Neuropathologically AD is characterized by the presence of accumulated Amyloid‐beta in plaques (in extracellular spaces, and walls of blood vessels) and aggregated tau protein in neurofibrillary tangles. Drug repurposing is the search for new indications or molecular targets distinct from a drug’s acknowledged activity, pharmacological effect or binding specificities. With the ever‐increasing rates of termination of drugs in clinical trials, drug repositioning has risen as one of the effective solutions against the risk of drug failures.MethodA comprehensive literature search was performed in the Pub Med/Science direct/Google scholar/Plos one databases and connected papers to review relevant articles in English, using keywords ‘‘Drug repurposing and neurological disorder, drug repurposing and dementia, drug repurposing and Alzheimer 'disease. The research papers were scrutinized and studied thoroughly.ResultAccording to literature it has been found that some repurposed drugs i.e, Allopurinol, Bromocriptine, Bupropion, Raloxifene, Thalidomide, Zidovudine may have a potential to treat Alzheimer’s disease.ConclusionThe repurposing drug approach may be used to treat Alzheimer’s and these drugs are needed to studied further.

In‐silico and in‐vitro evaluation of imidazolone fused quinazolinone derivatives as anti‐amyloidal agents in Alzheimer’s

AbstractBackgroundAlzheimer’s disease with a long preclinical period of ∼20 years is a chronic, insidious, and progressive neurodegenerative disease of old age. Neuropathologically AD is characterized by the presence of accumulated Amyloid‐beta in plaques (in extracellular spaces, and walls of blood vessels) and aggregated tau protein in neurofibrillary tangles. Quinazolinone derivatives exhibit inhibition to β‐secretase as well as its core quinazoline moiety prevents the cholinergic system from pathological activities of Aβ by possessing significant amount of inhibition.MethodIn‐silico evaluation was based over computational approaches counting receptor and ligand preparation, grid formation, docking simulation, and its analysis followed by in‐vitro investigation via Thioflavin T‐amyloid binding assay and Protease (Trypsin) digestion assay.ResultThe computational approach provides us with two molecules A and B with higher estimated free energy of binding whereas for the justification of in‐vitro test results one molecule J with lower estimated free energy of binding from top ten docked scored molecules was selected. In‐vitro investigation of these three compounds reveals that compound A cause significant (p<0.005) reduction in fluorescence intensity of ThT as well as Aβ1‐42 peptides resistance to tryptic digestion, when compared with control. Compound B possess lesser amount of reduction (p<0.005) in both the assays as compared to compound A whereas, activity of Compound J was found to be almost negligible.ConclusionFrom the present study we found that our test compound A has shown significant results in modulating the Aβ aggregates i.e. Aβ fibrils. This study strongly suggests the further evaluation of this imidazolone fused quinazolinone derivative.

Drug Development for Alzheimer's Disease: Microglia Induced Neuroinflammation as a Target?

Alzheimer’s disease (AD) is one of the most common causes of dementia. Its pathogenesis is characterized by the aggregation of the amyloid-β (Aβ) protein in senile plaques and the hyperphosphorylated tau protein in neurofibrillary tangles in the brain. Current medications for AD can provide temporary help with the memory symptoms and other cognitive changes of patients, however, they are not able to stop or reverse the progression of AD. New medication discovery and the development of a cure for AD is urgently in need. In this review, we summarized drugs for AD treatments and their recent updates, and discussed the potential of microglia induced neuroinflammation as a target for anti-AD drug development.

Alzheimer's Disease-Associated Cerebrospinal Fluid (CSF) Biomarkers do not Correlate with CSF Volumes or CSF Production Rate.

Neuropathologically, Alzheimer's disease (AD) is characterized by accumulation of a 42 amino acid peptide called amyloid-β (Aβ42) in extracellular senile plaques together with intraneuronal inclusions of hyperphosphorylated tau protein in neurofibrillary tangles and neuronal degeneration. These changes are reflected in the cerebrospinal fluid (CSF), the volumes and production rates of which vary considerably between individuals, by reduced concentration of Aβ42, increased concentration of phosphorylated tau (P-tau) protein, and increased concentration of total tau (T-tau) protein, respectively. To examine the outstanding question if CSF concentrations of AD associated biomarkers are influenced by variations in CSF volumes, CSF production rate, and intracranial pressure in healthy individuals. CSF concentrations of Aβ42, P-tau, and T-tau, as well as a number of other AD-related CSF biomarkers were analyzed together with intracranial subarachnoid, ventricular, and spinal CSF volumes, as assessed by magnetic resonance imaging volumetric measurements, and CSF production rate in 19 cognitively normal healthy subjects (mean age 70.6, SD 3.6 years). Negative correlations were seen between the concentrations of three CSF biomarkers (albumin ratio, Aβ38, and Aβ40), and ventricular CSF volume, but apart from this finding, no significant correlations were observed. These results speak against inter-individual variations in CSF volume and production rate as important confounds in the AD biomarker research field.

New targets for the development of PET tracers for imaging neurodegeneration in Alzheimer disease.

The field of molecular imaging has experienced significant advances in the area of Alzheimer disease (AD), the most significant being the development of PET radiotracers for imaging β-amyloid burden in the brain of individuals at risk for or in the early stages of AD. More recent advances include the development of PET radiotracers for imaging aggregates of hyperphosphorylated tau protein in neurofibrillary tangles, a process that occurs late in the disease process. This article highlights advances in the neurobiology of AD and describes how PET can be used to study the mechanisms of neurodegeneration in AD.

CHARACTERIZATION OF THK5117 BINDING IN AD BRAIN TISSUE: IMPLICATION FOR DEVELOPMENT OF PET TAU IMAGING

Background: Averting and clearing the aberrant accumulation of tau proteins in neurofibrillary tangles is the current focus of therapeutic strategies in Alzheimer’s disease (AD).New approaches for direct targeting of tau demand safe, non-invasive methods to detect and quantify tau in vivo [1, 2]. To assess tau progression together with the induced brain pathology, we longitudinally applied MRI on a conditional bigenic mouse model of tauopathy, rTg4510, in which tau expression can be supressedwith doxycycline [3].We investigated four, clinically relevant, quantitative techniques: cerebral blood flow (CBF) using arterial spin labelling (ASL); aggregated protein detection using amide proton transfer (APT); microstructural diffusion using diffusion tensor imaging (DTI), which were compared with the established gold standard structural MRI. Methods: 19 rTg4510, and 8 wild-type(WT) littermatched mice were imaged at baseline (4.5 months) using a 9.4T scanner for ASL, DTI, APT and structural data using parameters previously described [4,5]. 10 rTg4510 were then treated orally with doxycycline hyclate (10mg/kg) and maintained on a doxycycline diet for the remainder of the study to supress tau expression. The doxycycline-treated rTg4510, untreated rTg4510 and WT groups were imaged again at 5.5 and 7.5 months for longitudinal ASL, DTI, APTand structural data. During imaging, anaesthesia was maintained using 1.5-2% isoflurane and 1L/min O 2. Results:At 4.5 months, prior to doxycycline treatment, we observed marked changes in CBF, ATP and diffusion in rTg4510s due to increased tau pathology in comparison toWT controls. This was most apparent in the CBF study. Following only one month of treatment to supress tau, (imaging at 5.5 months), CBF had returned to control levels. This pattern was also observed for APT and diffusion imaging and the trend continued through to 7.5 months. Conclusions: This study demonstrates the sensitivity of multi-parametric MRI to the regulation of tau-driven pathological processes and provides an opportunity to assess novel therapeutic strategies. These approaches could give insights into the early onset of tauopathies, at a time when non-invasive imaging biomarkers are urgently needed for understanding the progressive pathology. This is the first demonstration that suppression of tau expression can be observed with the clinically relevant MRI parameters CBF, ATP and diffusion.

Chapter Five - CSF in Alzheimer's Disease

Alzheimer's disease (AD) is a progressive brain amyloidosis that injures brain regions involved in memory consolidation and other cognitive functions. Neuropathologically, the disease is characterized by accumulation of a 42-amino acid protein called amyloid beta, and N-terminally truncated fragments thereof, in extracellular senile plaques together with intraneuronal inclusions of hyperphosphorylated tau protein in neurofibrillary tangles, and neuronal and axonal degeneration and loss. Clinical chemistry tests for these pathologies have been developed for use on cerebrospinal fluid samples. Here, we review what these markers have taught us on the disease process in AD and how they can be implemented in routine clinical chemistry. We also provide an update on new marker development and ongoing analytical standardization effort.

Postsynaptic dysfunction is associated with spatial and object recognition memory loss in a natural model of Alzheimer’s disease

Alzheimer's disease (AD) is an age-related neurodegenerative disorder associated with progressive memory loss, severe dementia, and hallmark neuropathological markers, such as deposition of amyloid-β (Aβ) peptides in senile plaques and accumulation of hyperphosphorylated tau proteins in neurofibrillary tangles. Recent evidence obtained from transgenic mouse models suggests that soluble, nonfibrillar Aβ oligomers may induce synaptic failure early in AD. Despite their undoubted value, these transgenic models rely on genetic manipulations that represent the inherited and familial, but not the most abundant, sporadic form of AD. A nontransgenic animal model that still develops hallmarks of AD would be an important step toward understanding how sporadic AD is initiated. Here we show that starting between 12 and 36 mo of age, the rodent Octodon degus naturally develops neuropathological signs of AD, such as accumulation of Aβ oligomers and phosphorylated tau proteins. Moreover, age-related changes in Aβ oligomers and tau phosphorylation levels are correlated with decreases in spatial and object recognition memory, postsynaptic function, and synaptic plasticity. These findings validate O. degus as a suitable natural model for studying how sporadic AD may be initiated.

Power tools for Alzheimer’s disease – an electrochemical preamp for Aβ

Power tools for Alzheimer’s disease – an electrochemical preamp for Aβ

14‐3‐3 protein beta isoform is associated with 3‐repeat tau neurofibrillary tangles in Alzheimer's disease

14-3-3 proteins play roles in phosphorylation of tau proteins in neurofibrillary tangles (NFT) in Alzheimer's disease (AD). Tau is phosphorylated at serine (pSer) and threonine (pThr) in NFT, and NFT morphology varies according to phosphorylated sites and tau isoform. The roles of 14-3-3 proteins in NFT morphology remain unknown. This study was performed to examine the relationships between 14 and 3-3 proteins and tau phosphorylation of NFT. NFT were labeled with Gallyas impregnation, tau and 14-3-3 immunohistochemistry in paraffin-embedded hippocampal sections from seven AD and three control brains. Anti-tau antisera included monoclonal antisera that recognize pSer262 (pSer262), pSer422 (pSer422), pSer202/pThr205 (AT8), Thr231 (AT180), three-repeat (RD3) and four-repeat (RD4) tau isoform. Anti-14-3-3 protein isoform antisera included polyclonal antisera to beta, gamma, zeta, epsilon, tau, mu and sigma isoforms and monoclonal antiserum to beta antiserum (H8-beta). NFT density was obtained by counting labeled NFT in cornu ammonis (CA) 1-CA4, subiculum and entorhinal cortex. H8-beta and zeta isoforms were strongly expressed in NFT. Regional densities of NFT positive for pSer262, AT8, AT180, and Gallyas impregnation were similar to RD3-positive NFT density with high densities in CA1 and entorhinal cortex. NFT positive for pSer422 showed a similar regional distribution to RD4-positive NFT with high NFT density in CA2-CA4. H8-beta-positive NFT showed a similar regional distribution to RD3-positive NFT. In contrast, zeta isoform-positive NFT showed no specific distribution. In conclusion, H8-beta isoform is associated with development of 3-repeats NFT but a role of 14-3-3 zeta isoform in NFT could not be specified.

Immunological demonstration of tau protein in neurofibrillary tangles of Alzheimer's disease

Neurofibrillary tangles are one of the neuropathological hallmark of Alzheimer's disease, described early as part of the pathological criteria of the disease. Ultrastuctural studies in the sixties showed their unusual features but their molecular composition was not unraveled before the mid-eighties. Initial biochemical studies suggested that they were composed of modified unidentified brain proteins, and several immunocytochemical studies suggested that they contained polypeptides cross-reactive with antibodies to cytoskeletal proteins. In 1985, we demonstrated that neurofibrillary tangles were immunolabelled by antibodies to the microtubule-associated protein tau and that antibodies raised to neurofibrillary tangles cross-reacted with tau proteins. These results were soon confirmed independently in several laboratories. Further studies were devoted to the analysis of tau post-translationnal modifications in the affected tissues and in cellular and animal models.

Emerging prospects for the disease-modifying treatment of Alzheimer's disease

The currently approved therapies for Alzheimer's disease (AD) in the US are designed to modify the function of specific neurotransmitter systems in the brain. While these palliative treatments can benefit some patients for a period of time, they do not halt the relentless cognitive and behavioral deterioration that characterize this neurodegenerative disorder. Consequently, much current research on AD is directed toward illuminating the disease process itself, particularly the abnormal accumulation of certain proteins in brain: the amyloid-β protein (Aβ) in senile plaques and cerebral blood vessels, and the tau protein in neurofibrillary tangles. Genetic, biochemical and pathologic evidence now favors a primary role of Aβ aggregation in the Alzheimer proteopathic cascade, and studies in mice indicate that lowering the amount of this protein in brain can be beneficial. Recently, Aβ-immunization therapy has emerged as a particularly promising therapeutic option for treating Alzheimer's disease, but unexpected treatment-related side-effects are an overriding issue. These adverse events were not anticipated from preclinical studies with rodents; hence, more biologically relevant models, such as nonhuman primates, are needed to test the safety and efficacy of novel therapies for Alzheimer's disease.

Drugs targeting Alzheimer's disease: some things old and some things new.

Enormous effort is now being devoted to developing drugs that slow neurodegeneration in Alzheimer's disease (AD), although insights into AD genetics and molecular pathogenesis only arose in the last 15 years. Acetylcholinesterase inhibitors that temporarily slow loss of cognitive function remain the only approved AD drugs. Discovery of mutations in three genes leading to severe early onset AD was critical in focusing attention on the role of amyloid peptides (Abeta) in neuronal cell death, and enhanced understanding of the biology of these peptides has led to an array of mechanism-based drug discovery strategies. These include inhibitors for Abeta-generating proteases, agents that prevent or reverse Abeta oligomerization, immunotherapies to reduce Abeta in brain and plasma, and drugs to modulate cholesterol-mediated effects on Abeta transport. Strategies are also underway to minimize toxic effects of Abeta fibrils on neurons, and these include antioxidants, blockers of glutamate-mediated excitotoxicity, and modulators of inflammatory responses within the brain. Although several approaches involve new agents for recently discovered targets, many are based on new applications of existing drugs such as statins and nonsteroidal anti-inflammatory drugs. Discovery of abnormally phosphorylated tau protein in neurofibrillary tangles in AD brain has led to strategies for identifying selective inhibitors of tau kinases and central nervous system/brain-permeable drugs that help maintain microtubule integrity. Clearly, a large gap exists between our understanding of the cellular cascades targeted in drug discovery and widespread failure of the nervous system that AD represents. Nevertheless, the pace of recent research clearly supports optimism that slowing progression of AD will soon be possible.

Transgenic mouse models with tau pathology to test therapeutic agents for Alzheimer's disease.

The deposit of two proteins in the brain characterizes Alzheimer's disease: deposits of beta-amyloid protein to form senile plaques and tau protein in neurofibrillary tangles. This review discusses transgenic animals overexpressing normal or mutated tau protein as well as kinases involved in tau hyperphosphorylation. These animals hold a great potential as tools to test the effects of forthcoming therapeutical agents for Alzheimer's disease.

Lysosomal Protease Inhibitors Induce Meganeurites and Tangle-like Structures in Entorhinohippocampal Regions Vulnerable to Alzheimer's Disease

Lysosomal protease inhibitors induce signs of human brain aging in rat hippocampal slices. The present studies tested if they (1) also cause neurofibrillary tangles and (2) reproduce regional patterns of pathology found in Alzheimer's disease (AD). Slices of hippocampus plus retrohippocampal cortex were prepared from rats at postnatal days 6–7 and maintained for 2–5 weeks. In agreement with earlier studies, 6- to 12-day infusions of selective (ZPAD) or generalized (chloroquine) inhibitors of lysosomal proteases generated meganeurites of the type found in aged human cortex. Surveys and quantitative analyses established that the meganeurites developed almost exclusively in AD vulnerable regions. Antibodies against the phosphorylated tau protein in neurofibrillary tangles labeled thick filaments running through neurons in the superficial layers of entorhinal cortex in 6-day ZPAD-treated slices. The general appearance of the stained structures resembled that of early stage tangles. More mature tangle-like profiles were found at a number of sites after longer incubations; these were threefold more frequent in the superficial (AD vulnerable) than in the deep layers of the entorhinal cortex. Immunoblots indicated that essentially all phosphorylated tau labeling in the slices involved ∼29-kDa fragments of the native isoforms. These findings establish that lysosomal dysfunction triggers the parallel formation of meganeurites and tangles with the regional distribution of both effects reflecting that for AD vulnerability.