Tau oligomers have been shown to transmit tau pathology from diseased neurons to healthy neurons through seeding, tau misfolding, and aggregation that is thought to play an influential role in the progression of Alzheimer's disease (AD) and related tauopathies.To develop a small molecule therapeutic for AD and related tauopathies, we have developed in vitro and cellular assays to select molecules inhibiting the first step in tau aggregation, the self-association of tau into oligomers.In vivo validation studies of an optimized lead compound were independently performed in the htau mouse model of tauopathy that expresses the human isoforms of tau without inherited tauopathy mutations that are irrelevant to AD. Treated mice did not show any adverse events related to the compound.The lead compound significantly reduced the level of self-associated tau and total and phosphorylated insoluble tau aggregates.The dose response was linear with respect to levels of compound in the brain.A confirmatory study was performed with male htau mice that gave consistent results.The results validated our screening approach by showing that targeting tau self-association can inhibit the entire tau aggregation pathway by using the selected and optimized lead compound whose activity translated from in vitro and cellular assays to an in vivo model of tau aggregation.

Tau oligomers form in neurons as tau redistributes from the axon to the cell body when tau protein loses its affinity to microtubules due to hyperphosphorylation during Alzheimer's disease and related tauopathies. Tau oligomers can accumulate in both the intracellular and extracellular spaces and have been shown to be toxic to neurons, reduce long-term potentiation (LTP) in mouse hippocampal slices, impair memory formation in wild type (w.t.) mice, and transmit tau pathology to neighboring neurons. Hence, tau oligomers have become a target for drug discovery using small molecule and antibody based approaches. Assays have been developed and used to select and optimize small molecules that inhibit tau monomer self-association. Here, we compare the chemical properties of our lead series to approved CNS drugs and other published molecules targeting tau. We also highlight in vivo studies testing the pharmacokinetics (PK) and safety of our lead compounds. The chemical properties of the molecules were compared based on their molecular weight, log of the partition coefficient (logP), polar surface area (PSA), and number of hydrogen bond donors and acceptors using graphical statistical software. PK analysis of plasma/brain compound levels was performed in mice. Compound safety was evaluated in a 5-day study in w.t. mice at 100 mg/kg using oral administration. The chemical profile of our lead series was more similar to that of FDA approved CNS drugs compared to tau aggregation inhibitors selected using tau fibril formation assays. Further, pharmacokinetic analyses showed that one of our lead series compounds readily penetrates the blood-brain-barrier. Our screening approach has enabled the selection of CNS drug-like molecules based on their chemical properties, and our lead compound showed CNS drug-like properties in mouse PK and safety studies. Targeting tau monomer self-association yields molecules with better CNS drug-like properties than published molecules selected using tau fibril formation assays.

Numerous studies have clearly demonstrated the role of tau oligomers in the initiation and progression of tau pathology in Alzheimer's disease (AD) and associated tauopathies. We have taken a highly differentiated approach to identify novel small molecule inhibitors of tau oligomer formation using proprietary AD relevant in vitro and cell assays, along with the htau mouse model. Here, we present recent progress in the identification of leads for in vivo efficacy and IND enabling studies. In vitro assays were developed to screen a compound library. Selected candidates identified in the primary screen were subjected to medicinal chemistry studies to identify potential lead compounds after characterization in secondary and cell based assays. A number of lead compounds were also tested in vivo to assess preliminary metabolic stability, pharmacokinetics, off-target activity and acute toxicity. An in vivo study in htau mice will be initiated using vehicle and three doses of a lead. A number of small molecule inhibitors of tau oligomerization with high potency, drug-like properties and with IC50’s in the nanomolar to micromolar range, have been identified. Preliminary metabolic stability using mouse liver microsomes showed a half-life in the range of hours for select compounds. In addition, certain compounds had a brain-plasma distribution of approximately 1:1 and were not toxic when administered daily by i.p. injection to wild type mice for 5 days. From an initial primary screen, we have performed lead optimization studies which have led to novel tau oligomerization inhibitors with improved properties.

Type 2 diabetes mellitus is characterized by the deposition of islet amyloid polypeptide (IAPP) as amyloid in islets, a process thought to be toxic to β-cells. To determine the feasibility of targeting these aggregates therapeutically, we vaccinated transgenic (Tg) mice that overexpress human IAPP and were fed a high-fat diet to promote their diabetic phenotype. Our findings indicate that prophylactic vaccination with IAPP and its derivative IAPP7-19-TT, protects wild-type female mice, but not males, from obesity-induced early mortality, and the derivative showed a strong trend for prolonging the lifespan of Tg females but not males. Furthermore, IAPP7-19-TT-immunized Tg females cleared a glucose bolus more efficiently than controls, while IAPP-immunized Tg females showed an impaired ability to clear a glucose bolus compared to their adjuvant injected Tg controls. Interestingly, IAPP or IAPP7-19-TT treatments had no effect on glucose clearance in Tg males. Overall, these beneficial effects of IAPP targeted immunization depend on Tg status, sex, and immunogen. Hence, future studies in this field should carefully consider these variables that clearly affect the therapeutic outcome. In conclusion, IAPP targeting immunotherapy may have benefits in patients with type 2 diabetes.

AD is a disorder with unknown aetiology. Tau oligomers may play a key role in the progression of AD pathology. They have been shown to be toxic to neurons, inhibit long term potentiation in hippocampal slices, impair the formation of associative fear memory in mice, induce synaptic dysfunction, and induce the propagation of tau pathology during disease progression. Hence targeting tau oligomers for drug discovery for the development of both symptom-modifying and disease-modifying therapeutics would be highly desirable. Our drug discovery platform has used a systematic approach to progress from screening for compounds, validating hits, testing tool compounds in situ, and conducting validation studies in an in vivo model. A highly diverse library of 100,000 drug-like small molecules was screened using a proximity based assay for detection of tau self-association. Hits were validated and dose response and neurocytotoxicity assays were performed. Medicinal chemistry analysis was used to select hits for secondary assays. Stably transfected cell lines were established for tau oligomer formation assays and acute toxicity of selected tool compounds was assessed in wild type mice. Proof-of-concept studies in the JNPL3 mouse model (Taconic) were initiated to demonstrate target engagement in vivo and to validate the screening approach. 57 drug-like molecules predicted to have good CNS penetration were selected from 11 chemical series and 19 singletons, and the most active hits were chosen as tool compounds. A tool compound was chosen for methods development for in vivo studies. An initial Pilot Validation Study with 34 JNPL3 mice showed that the tool compound was non-toxic and effective at reducing insoluble and phospho tau levels in a dose dependent manner. A larger scale study with 20 JNPL3 mice per cohort showed that the tool compound reduced phospho-tau levels at Ser202 and Thr231 sites, and reduced pathological 64kDa tau. Analysis of behavioral and histological results are under way. Methods have been developed to study small molecule tau aggregation inhibitors in vivo. Larger cohort sizes may be necessary to achieve statistical significance due to the variability of the JNPL3 phenotype. JULYGLOBAL: Ensure there is a space after the colon following Background, Methods, Results, Conclusions. 22, 2015

Antibodies or their derivatives as imaging probes for pathological tau protein have great potential, but have not been well studied. In particular, smaller, single-chain-variable antibody fragments (scFv's) are attractive for detecting tau lesions in live subjects. Here, we generated libraries of scFv's and identified numerous phospho-tau-selective scFv's. Peripheral injection of one of these scFv's consistently resulted in a strongin vivobrain signal in transgenic tauopathy mice, but not in wild-type or amyloid-β plaque mice. The parent tau antibody provided similar results, albeit with a weaker signal intensity. The imaging signal correlated very well with colocalization of the probe with intraneuronal tau aggregates. Both were associated with markers of endosomes, autophagosomes, and lysosomes, suggesting their interaction in these degradation pathways. Such specific antibody-derived imaging probes have great potential as diagnostic markers for Alzheimer's disease and related tauopathies.

Diagnostic imaging agents targeting amyloid-β (Aβ) in Alzheimer's disease (AD) are already in clinical use. Such tau probes are needed to monitor AD progression, the efficacy of tau-targeting therapies, and to identify Aβ negative tauopathies. Antibody-derived ligands are likely to provide excellent specificity for detecting tau lesions, and in particular smaller single chain variable antibody fragments (scFv's) are attractive for in vivo imaging of tau aggregates. Libraries of scFv's were generated from tau antibody hybridomas using phage display technology. Numerous phospho-tau (P-Ser396,404) selective scFv's were identified by ELISA and characterized further by immunoprecipitation, histology and Biacore. Subsequently, the diagnostic imaging utility for tauopathies was assessed for one of the scFv's and compared to its parent antibody using In Vivo Imaging System (IVIS) for proof of concept prior to PET studies. The scFv's showed strong selectivity for phospho-tau vs. non-phospho-tau epitope in ELISA, pulled down tau proteins from AD brains, and bound to pathological tau in AD and Pick's disease brain sections. The potential diagnostic imaging utility of one of these, with the best phospho-tau selectivity on Biacore (1x10 -8 M vs. 4x10 -3 M for non-phospho-tau), was characterized further by IVIS. Intracarotid or intravenous scFv injection led to a strong IVIS brain signal in transgenic tauopathy mice, that correlated nicely with scFv signal from brain tissue (r=0.97, p<0.0001, n=9), and brain tau pathology (r=0.94, p<0.0001, n=13). Importantly, limited signal was detected in wild-type mice. Similar findings were observed with the parent antibody (r=0.86, p=0.1, n=5 vs. r=0.75, p<0.062, n=11), although its IVIS signal appeared to be less but these differences need to be confirmed by comparing both probes in the same mice. Analyses of brain tissue collected 4-6 h after injection showed a partial to complete co-localization with stained intraneuronal tau aggregates in tg tauopathy mice but not in wt mice for both scFv and its parent antibody. Furthermore, both colocalized with markers of endosomes-autophagosomes-lysosomes, which are known to contain tau aggregates, suggesting that this interaction takes place in these degradation pathways. Tau scFv's are promising as novel diagnostic markers for AD and related tauopathies, and have therapeutic potential as well.

The aim of this program is to develop small molecule therapeutics for Alzheimer's disease (AD) and related tauopathies that inhibit the formation of tau oligomers. Recent advances in research at Oligomerix and in the AD field strongly support targeting tau oligomers for drug discovery for the development of both symptom modifying and disease modifying therapeutics. Tau oligomers are toxic to neurons, inhibit long term potentiation in hippocampal slices, impair the formation of associative fear memory in mice, and induce the propagation of tau pathology during disease progression. Tau oligomer specific antibody has been used in a mouse model of tauopathy to reduce the propagation of tau pathology and improve motor impairment and cognitive deficits validating tau oligomers as a target for drug development. A highly diverse library of 100,000 drug-like small molecules was screened using AlphaLISA for detection of tau self-association, hits were validated and dose response and neurocytotoxicity assays were performed. Medicinal chemistry analysis was used to select hits for secondary assays. Stably transfected cell lines were established for tau oligomer formation assays. Acute toxicity of selected tool compounds was assessed in wild type mice. Proof-of-concept studies in the JNPL3 mouse model (Taconic) were initiated to demonstrate target engagement in vivo and to validate the screening approach. About 60 drug-like molecules predicted to have good CNS penetration were selected from 11 chemical series and 19 singletons. The most active hits of 8 series were chosen as tool compounds and for lead development. Some of these compounds showed good dose response in the cell assay. The acute toxicity evaluation showed no effect on the wild type mice at high, medium and low doses. Studies of tau oligomer and larger aggregate formation in the JNPL3 mice are ongoing. Small molecule inhibitors of tau oligomer formation have been advanced to animal studies. This presentation focuses on the progress of the in vivo studies.

BACKGROUND:Tau is a microtubule stabilizing protein and is mainly expressed in neurons. Tau aggregation into oligomers and tangles is considered an important pathological event in tauopathies, such as frontotemporal dementia (FTD) and Alzheimer's disease (AD). Tauopathies are also associated with deficits in synaptic plasticity such as long-term potentiation (LTP), but the specific role of tau in the manifestation of these deficiencies is not well-understood. We examined long lasting forms of synaptic plasticity in JNPL3 (BL6) mice expressing mutant tau that is identified in some inherited FTDs.RESULTS:We found that aged (>12 months) JNPL3 (BL6) mice exhibit enhanced hippocampal late-phase (L-LTP), while young JNPL3 (BL6) mice (age 6 months) displayed normal L-LTP. This enhanced L-LTP in aged JNPL3 (BL6) mice was rescued with the GABAAR agonist, zolpidem, suggesting a loss of GABAergic function. Indeed, we found that mutant mice displayed a reduction in hippocampal GABAergic interneurons. Finally, we also found that expression of mutant tau led to severe sensorimotor-gating and hippocampus-dependent memory deficits in the aged JNPL3 (BL6) mice.CONCLUSIONS:We show for the first time that hippocampal GABAergic function is impaired by pathological tau protein, leading to altered synaptic plasticity and severe memory deficits. Increased understanding of the molecular mechanisms underlying the synaptic failure in AD and FTD is critical to identifying targets for therapies to restore cognitive deficiencies associated with tauopathies.

The impairment of axonal transport by overexpression or hyperphosphorylation of tau is well documented for in vitro conditions; however, only a few studies on this phenomenon have been conducted in vivo, using invasive procedures, and with contradictory results. Here we used the non-invasive, Manganese-Enhanced Magnetic Resonance Imaging technique (MEMRI), to study for the first time a pure model of tauopathy, the JNPL3 transgenic mouse line, which overexpresses a mutated (P301L) form of the human tau protein. We show progressive impairment in neuronal transport as tauopathy advances. These findings are further supported by a significant correlation between the severity of the impairment in neuronal transport assessed by MEMRI, and the degree of abnormal tau assessed by histology. Unlike conventional techniques that focus on axonal transport measurement, MEMRI can provide a global analysis of neuronal transport, i.e. from dendrites to axons and at the macroscopic scale of fiber tracts. Neuronal transport impairment has been shown to be a key pathogenic process in Alzheimer's disease and numerous other neurodegenerative disorders. Hence, MEMRI provides a promising set of functional biomarkers to be used during preclinical trials to facilitate the selection of new drugs aimed at restoring neuronal transport in neurodegenerative diseases.

Tau pathology is involved in multiple neurodegenerative disorders, for example in Alzheimer's disease, Parkinson's disease, and Frontotemporal dementia (FTD). Tau is a neuronal protein that binds microtubules and is thought to be involved in the stabilization of microtubules. Over 50 different mutations within the MAPT gene, the gene encoding for Tau, have been associated with inherited FTD. FTD is thought to involve deficits in the communication between neurons and in the mechanisms neuronal adaptation to experience, synaptic plasticity. The role of Tau in mechanisms of synaptic plasticity is not well-understood. To address this gap in the field, we have investigated synaptic plasticity and behavior in P301L mice, a mouse model for tau pathology that over-expresses human Tau protein carrying an inherited human mutation. Long-lasting forms of plasticity, late-phase long term potentiation (L-LTP) were examined in P301L (JNPL3) mice and age-matched controls by measuring field excitatory postsynaptic potentiation (fEPSP) in the CA1 hippocampal region after high frequency electrophysiological stimulation. Two behaviors associated with GABAergic function were assayed, prepulse inhibition of startle response (PPI) and susceptibility to epileptic seizures. GABAergic interneurons were stained using two markers; paravalbumin and somatostatin. By examining long-lasting forms of plasticity in aged (>18 months old) in hippocampal brain slices we found surprisingly enhanced L-LTP in P301L mice compared to age-matched controls. The enhanced L-LTP in P301L slices was rescued by treatment with a GABA agonist, Zolpidem. These results suggest a loss of GABAergic neurons in P301L mice. Next we examined PPI and susceptibility to epileptic seizures in P301L and control mice. We found an altered PPI response and differences in epileptic seizures grades. Finally, we stained GABAergic interneurons in the hippocampus using two markers that identify GABAergic cell types showing a decrease in GABAergic neurons in the hippocampal CA1 region. Our results suggest that GABAergic interneurons are more vulnerable to molecular lesions caused by pathological Tau, which may result in the selective loss of hippocampal GABAergic interneurons.The molecular mechanisms involved in this specific GABAergic loss remains to be resolved, but may help to explain the pathophysiological symptoms of diseases like FTD, which involve altered Tau function.

Neurodegenerative diseases such as Alzheimer's disease (AD), Parkinson's disease, Huntington's disease (HD) or amyotrophic lateral sclerosis (ALS) are all characterised histologically by the presence of deposits of misfolded proteins, tau and amyloid-β, α-synuclein, huntingtin or superoxide dismutase, respectively. Currently, these illnesses do not have any disease modifying treatment options. A novel therapeutic strategy that is being pursued is immunomodulation, which is using the body's immune system to target the self-proteins that are deposited. Most of these promising approaches are still in preclinical development while some have progressed to Phase III clinical trials. As new insights are gained, it is hoped that these immunotherapies will be effective tools at slowing the progression of these debilitating diseases.

Neurofibrillary tangles (NFTs) are one of the pathological hallmarks of Alzheimer's disease (AD) and are primarily composed of aggregates of hyperphosphorylated forms of the microtubule associated protein tau. It is likely that an imbalance of kinase and phosphatase activities leads to the abnormal phosphorylation of tau and subsequent aggregation. The wide ranging therapeutic approaches that are being developed include to inhibit tau kinases, to enhance phosphatase activity, to promote microtubule stability, and to reduce tau aggregate formation and/or enhance their clearance with small molecule drugs or by immunotherapeutic means. Most of these promising approaches are still in preclinical development whilst some have progressed to Phase II clinical trials. By pursuing these lines of study, a viable therapy for AD and related tauopathies may be obtained.

Immunotherapy holds great promise for Alzheimer's disease (AD) and other conformational disorders. Recent studies from our group have shown that immunization with an AD specific phospho-tau immunogen Tau379-408[P-Ser396,404] alleviates brain levels of aggregated tau and slows the progression of motor deficits or prevents cognitive impairments in two different tangle models (Asuni A. et al. J. Neurosci., 2007, Boutajangout A. et al., J. Neurosci., 2010). To assess potential epitope specificity and safety of this promising therapeutic effect, we are examining several tau epitopes. Here we assessed the efficacy of using a pseudo-phosphorylated tau immunogen. Homozygous JNPL3 mice were immunized with Tau379-408[E-Ser396, E-Ser404] in alum adjuvant (n = 13) or with adjuvant only (n = 7), starting at 2 months. Mice were tested on various sensorimotor tasks (rotarod, traverse beam, locomotor activity and grip strength) at 5 and 8 months of age. Antibody titers were determined and at 8 months their brains were processed for tau biochemistry and histology. The vaccine elicited a robust antibody response towards the immunogen, and its phosphorylated and non-phosphorylated analogs. Which is as expected since this region of the tau protein is highly immunogenic. The immunized mice had a 24% reduction in soluble PHF1/total tau ratio on western blots (p = 0.04), and a 42% reduction in PHF1 immunostaining in the dentate gyrus (p < 0.03), compared to alum-treated mice. Levels of sarkosyl insoluble human and total tau were highly variable in both groups and not significantly different. Biochemical and histological analyses with other antibodies and of other brain regions is underway. Disappointingly, potential improvements in motor function of the immunized mice could not be assessed since the animals did not develop overt signs of such impairments at the ages tested, in contrast to our previous observation in the same homozygous model (Asuni A. et al., J. Neurosci., 2007). Unfortunately, such changes in phenotype are commonly observed in transgenic mice. These findings indicate that immunological targeting using a pseudo-phosphorylated tau epitope can reduce pathological tau within the brain, further supporting the feasibility of tau immunotherapy.

Functional alterations of axonal transport have been suggested to occur in the early stages of Alzheimer's disease. In vitro studies have shown a deleterious effect of tauopathy on axonal transport. We hypothesized that Tract-Tracing-Manganese-Enhanced-MRI (TT-MEMRI) should detect early axonal transport impairments in a mouse model of tauopathy. Ten JNLP3 (P301L) transgenic mice (Tg) and 5 wild-type mice (WT) were imaged on a 7T magnet at 3 and 6 months of age, using a TT-MEMRI protocol with 9 imaging time points (1 prior to and 8 following nasal injection of MnCl2). Four regions of interest (ROI) were defined on MR images, corresponding to 4 consecutive areas of the olfactory system (glomerular and mitral cell layers, anterior and posterior part of the piriform cortex). In each ROI, the evolution of signal intensity profile, indicative of manganese propagation, was used to estimate the peak value (Pv) and time to peak (Pt) of the relative manganese concentration. By fitting to a one-dimensional flow-diffusion model, we calculated the 3 parameters expected to contribute to manganese propagation: the flow velocity, reflecting its active transport in neurons; the diffusion coefficient, reflecting its passive stochastic propagation in neurons; and the leakage rate, reflecting the clearance of manganese from the main olfactory fiber system, through ion channels, synapses, or collateral axons. A decrease of Pv and increase of Pt was observed in the older Tg mice compared to both age-matched WT (Fig. 1A) and young Tg mice. This decrease was significant in females (p < 0.05-0.01), who develop tauopathy earlier than males (Fig. 1B&C). Older Tg mice showed trends of increased diffusion and decreased leakage and velocity when compared to both old WT and young Tg mice. These 2 last parameters can contribute to the increase in Pt in the older Tg mice. This study provides the first in vivo evidence of impairment of axonal transport in a model of tauopathy, assessed non-invasively by TT-MEMRI. It also indicates that manganese propagation reflects not only active axonal transport but also passive diffusion and extra-neuronal leakage.

Recent studies have shown that immunotherapy clears amyloid beta (A) plaques and reduces A levels in mouse models of Alzheimer’s disease (AD), as well as in AD patients. Tangle pathology is also relevant for the neurodegeneration in AD, and our studies have shown that active immunization with an AD related phospho-tau peptide reduces aggregated tau within the brain and slows the progression of tauopathy-induced behavioural impairments. Thus, clearance of neurofibrillary tangles and/or their precursors may reduce synaptic and neuronal loss associated with AD and other tauopathies. So far the mechanisms involved in antibody-mediated clearance of tau pathology are yet to be elucidated. In this study we have used a mouse brain slice model to examine the uptake and localization of FITC labeled anti-tau antibodies. Confocal microscopy analysis showed that the FITC labelled anti-tau antibody co-stained with phosphorylated tau, had a perinuclear appearance and co-localised with markers of the endosomal/lysosomal pathway. Additionally, tau and FITC IgG were found together in an enriched lysosome fraction. In summary, antibody-mediated clearance of intracellular tau aggregates appears to occur via the lysosomal pathway.

Immunotherapy holds great promise for Alzheimer's disease (AD) and other conformational disorders. Recent studies from our group have shown that immunization with an AD specific phospho-tau immunogen Tau379-408[P-Ser396,404] could alleviate brain levels of aggregated tau and slow the progression of motor deficits or prevent cognitive impairments in two different tangle models (Asuni A. et al. J. Neurosci., 2007, Sigurdsson E.M. et al., ICAD Chicago, 2008). To assess potential epitope specificity and safety of this promising therapeutic effect, we are examining several tau epitopes. Here we assessed the efficacy of targeting a region within the microtubule binding site. Homozygous P301L mice were immunized with Tau260-264[P-Ser262] linked to a tetanus toxin helper T-cell epitope in alum adjuvant (n=8) or with adjuvant only (n=7), starting at 2 months. Mice were tested on various sensorimotor tasks (rotarod, traverse beam, locomotor activity) at 5 and 8 months of age. Antibody titers were determined and at 8 months their brains were processed for tau biochemistry and histology. The vaccine elicited a robust antibody response that was associated with a 64% reduction in PHF-1 tau staining (p=0.02) in the dentate gyrus of the right hemisphere but soluble PHF-1 tau levels were unaltered in the whole left hemisphere compared to controls. Analysis of other brain regions, of insoluble tau and with other tau antibodies is underway. The clearance of tau aggregates was accompanied with functional benefits as the control animals deteriorated in their performance on the rotarod (p=0.05) and the traverse beam (p=0.03) from 5 to 8 months of age, whereas the immunized mice performed equally well at both time points. Various locomotor activity measurements did not differ between the groups except that the 8 month old controls obtained a higher maximum velocity in the open field than treated littermates (p<0.01). Together with our previous results, these findings indicate that immunological targeting of various tau epitopes is a potential therapy for AD. However, a direct comparison of these different immunogens will be needed to assess their relative efficacy. Supported by: NIH grant AG032611, the Alzheimer's Drug Discovery Foundation and the Alzheimer's Association.

Cyclin-dependent kinase 5 (cdk5) has been implicated in Alzheimer's disease (AD) pathogenesis. Here, we demonstrate that overexpression of p25, an activator of cdk5, led to increased levels of BACE1 mRNA and protein in vitro and in vivo. A p25/cdk5 responsive region containing multiple sites for signal transducer and activator of transcription (STAT1/3) was identified in the BACE1 promoter. STAT3 interacts with the BACE1 promoter, and p25-overexpressing mice had elevated levels of pSTAT3 and BACE1, whereas cdk5-deficient mice had reduced levels. Furthermore, mice with a targeted mutation in the STAT3 cdk5 responsive site had lower levels of BACE1. Increased BACE levels in p25 overexpressing mice correlated with enhanced amyloidogenic processing that could be reversed by a cdk5 inhibitor. These data demonstrate a pathway by which p25/cdk5 increases the amyloidogenic processing of APP through STAT3-mediated transcriptional control of BACE1 that could have implications for AD pathogenesis.

In Alzheimer's disease, tau is hyperphosphorylated, which is thought to detach it from microtubules (MTs), induce MT destabilization, and promote aggregation. Using a previously described in vivo model, we investigated whether hyperphosphorylation impacts tau function in wild-type and transgenic mice. We found that after anesthesia-induced hypothermia, MT-free tau was hyperphosphorylated, which impaired its ability to bind MTs and promote MT assembly. MT-bound tau was more resistant to hyperphosphorylation compared with free tau and tau did not dissociate from MTs in wild-type mice. However, 3-repeat tau detached from MT in the transgenic mice. Surprisingly, dissociation of tau from MTs did not lead to overt depolymerization of tubulin, and there was no collapse, or disturbance of axonal MT networks. These results indicate that, in vivo, a subpopulation of tau bound to MTs does not easily dissociate under conditions that extensively phosphorylate tau. Tau remaining on the MTs under these conditions is sufficient to maintain MT network integrity.