Female gonadal hormone effects on microglial activation and functional outcomes in a mouse model of moderate traumatic brain injury.

AIM: To address the hypothesis that young, gonad-intact female mice have improved long-term recovery associated with decreased neuroinflammation compared to male mice. METHODS: Eight to ten week-old male, female, and ovariectomized (OVX) mice underwent closed cranial impact. Gonad-intact female mice were injured only in estrus state. After injury, between group differences were assessed using complementary immunohistochemical staining for microglial cells at 1 h, mRNA polymerase chain reaction for inflammatory markers at 1 h after injury, Rotarod over days 1-7, and water maze on days 28-31 after injury. RESULTS: Male mice had a greater area of injury (P = 0.0063), F4/80-positive cells (P = 0.032), and up regulation of inflammatory genes compared to female mice. Male and OVX mice had higher mortality after injury when compared to female mice (P = 0.043). No group differences were demonstrated in Rotarod latencies (P = 0.62). OVX mice demonstrated decreased water maze latencies compared to other groups (P = 0.049). CONCLUSION: Differences in mortality, long-term neurological recovery, and markers of neuroinflammation exist between female and male mice after moderate traumatic brain injury (MTBI). Unexpectedly, OVX mice have decreased long term neurological function after MTBI when compared to gonad intact male and female mice. As such, it can be concluded that the presence of female gonadal hormones may influence behavioural outcomes after MTBI, though mechanisms involved are unclear.

Neuroprotective pentapeptide CN-105 is associated with reduced sterile inflammation and improved functional outcomes in a traumatic brain injury murine model.

At present, there are no proven pharmacological treatments demonstrated to improve long term functional outcomes following traumatic brain injury(TBI). In the setting of non-penetrating TBI, sterile brain inflammatory responses are associated with the development of cerebral edema, intracranial hypertension, and secondary neuronal injury. There is increasing evidence that endogenous apolipoprotein E(apoE) modifies the neuroinflammatory response through its role in downregulating glial activation, however, the intact apoE holoprotein does not cross the blood-brain barrier due to its size. To address this limitation, we developed a small 5 amino acid apoE mimetic peptide(CN-105) that mimics the polar face of the apoE helical domain involved in receptor interactions. The goal of this study was to investigate the therapeutic potential of CN-105 in a murine model of closed head injury. Treatment with CN-105 was associated with a durable improvement in functional outcomes as assessed by Rotarod and Morris Water Maze and a reduction in positive Fluoro-Jade B stained injured neurons and microglial activation. Administration of CN-105 was also associated with reduction in mRNA expression of a subset of inflammatory and immune-related genes.

Apolipoprotein E mimetic peptide, CN-105, improves outcomes in ischemic stroke.

OBJECTIVE: At present, the absence of a pharmacological neuroprotectant represents an important unmet clinical need in the treatment of ischemic and traumatic brain injury. Recent evidence suggests that administration of apolipoprotein E mimetic therapies represent a viable therapeutic strategy in this setting. We investigate the neuroprotective and anti-inflammatory properties of the apolipoprotein E mimetic pentapeptide, CN-105, in a microglial cell line and murine model of ischemic stroke. METHODS: Ten to 13-week-old male C57/BL6 mice underwent transient middle cerebral artery occlusion and were randomly selected to receive CN-105 (0.1 mg/kg) in 100 µL volume or vehicle via tail vein injection at various time points. Survival, motor-sensory functional outcomes using rotarod test and 4-limb wire hanging test, infarct volume assessment using 2,3,5-Triphenyltetrazolium chloride staining method, and microglial activation in the contralateral hippocampus using F4/80 immunostaining were assessed at various time points. In vitro assessment of tumor necrosis factor-alpha secretion in a microglial cell line was performed, and phosphoproteomic analysis conducted to explore early mechanistic pathways of CN-105 in ischemic stroke. RESULTS: Mice receiving CN-105 demonstrated improved survival, improved functional outcomes, reduced infarct volume, and reduced microglial activation. CN-105 also suppressed inflammatory cytokines secretion in microglial cells in vitro. Phosphoproteomic signals suggest that CN-105 reduces proinflammatory pathways and lower oxidative stress. INTERPRETATION: CN-105 improves functional and histological outcomes in a murine model of ischemic stroke via modulation of neuroinflammatory pathways. Recent clinical trial of this compound has demonstrated favorable pharmacokinetic and safety profile, suggesting that CN-105 represents an attractive candidate for clinical translation.

Tau Protein Mediates APP Intracellular Domain (AICD)-Induced Alzheimer's-Like Pathological Features in Mice.

Amyloid precursor protein (APP) is cleaved by gamma-secretase to simultaneously generate amyloid beta (Aß) and APP Intracellular Domain (AICD) peptides. Aß plays a pivotal role in Alzheimer's disease (AD) pathogenesis but recent studies suggest that amyloid-independent mechanisms also contribute to the disease. We previously showed that AICD transgenic mice (AICD-Tg) exhibit AD-like features such as tau pathology, aberrant neuronal activity, memory deficits and neurodegeneration in an age-dependent manner. Since AD is a tauopathy and tau has been shown to mediate Aß-induced toxicity, we examined the role of tau in AICD-induced pathological features. We report that ablating endogenous tau protects AICD-Tg mice from deficits in adult neurogenesis, seizure severity, short-term memory deficits and neurodegeneration. Deletion of tau restored abnormal phosphorylation of NMDA receptors, which is likely to underlie hyperexcitability and associated excitotoxicity in AICD-Tg mice. Conversely, overexpression of wild-type human tau aggravated receptor phosphorylation, impaired adult neurogenesis, memory deficits and neurodegeneration. Our findings show that tau is essential for mediating the deleterious effects of AICD. Since tau also mediates Aß-induced toxic effects, our findings suggest that tau is a common downstream factor in both amyloid-dependent and-independent pathogenic mechanisms and therefore could be a more effective drug target for therapeutic intervention in AD.

Increased 4R-Tau Induces Pathological Changes in a Human-Tau Mouse Model.

Pathological evidence for selective four-repeat (4R) tau deposition in certain dementias and exon 10-positioned MAPT mutations together suggest a 4R-specific role in causing disease. However, direct assessments of 4R toxicity have not yet been accomplished in vivo. Increasing 4R-tau expression without change to total tau in human tau-expressing mice induced more severe seizures and nesting behavior abnormality, increased tau phosphorylation, and produced a shift toward oligomeric tau. Exon 10 skipping could also be accomplished in vivo, providing support for a 4R-tau targeted approach to target 4R-tau toxicity and, in cases of primary MAPT mutation, eliminate the disease-causing mutation.

Progesterone Improves Neurobehavioral Outcome in Models of Intracerebral Hemorrhage.

In models of acute brain injury, progesterone improves recovery through several mechanisms including modulation of neuroinflammation. Secondary injury from neuroinflammation is a potential therapeutic target after intracerebral hemorrhage (ICH). For potential translation of progesterone as a clinical acute ICH therapeutic, the present study sought to define efficacy of exogenous progesterone administration in ICH-relevant experimental paradigms. Young and aged C57BL/6 male, female, and ovariectomized (OVX) mice underwent left intrastriatal collagenase (0.05-0.075 U) or autologous whole blood (35 µl) injection. Progesterone at varying doses (4-16 mg/kg) was administered at 2, 5, 24, 48, and 72 h after injury. Rotarod and Morris water maze latencies were measured on days 1-7 and days 28-31 after injury, respectively. Hematoma volume, brain water content (cerebral edema), complementary immunohistochemistry, multiplex cytokine arrays, and inflammatory proteins were assessed at prespecified time points after injury. Progesterone (4 mg/kg) administration improved rotarod and water maze latencies (p < 0.01), and decreased cerebral edema (p < 0.05), microglial proliferation, and neuronal loss (p < 0.01) in young and aged male, young OVX, and aged female mice. Brain concentration of proinflammatory cytokines and Toll-like receptor-associated proteins were also decreased after progesterone (4 mg/kg) treatment (p < 0.01). Progesterone-treated young female mice showed no detectable effects. Exogenous progesterone improved short- and long-term neurobehavioral recovery and modulated neuroinflammation in male and OVX mice after ICH. Future studies should validate these findings, and address timing and length of administration before translation to clinical trial.

Opposing effects of traumatic brain injury on excitatory synaptic function in the lateral amygdala in the absence and presence of preinjury stress.

Traumatic brain injury (TBI) is a leading cause of death and disability among young adults and is highly prevalent among recently deployed military personnel. Survivors of TBI often experience cognitive and emotional deficits, suggesting that long-term effects of injury may disrupt neuronal function in critical brain regions, including the amygdala, which is involved in emotion and fear memory. Amygdala hyperexcitability has been reported in both TBI and posttraumatic stress disorder patients, yet little is known regarding the effects of combined stress and TBI on amygdala structure and function at the neuronal level. The present study seeks to determine how the long-term effects of preinjury foot-shock stress and TBI interact to influence synaptic plasticity in the lateral amygdala (LA) of adult male C57BL/6J mice by using whole-cell patch clamp electrophysiology 2-3 months postinjury. In the absence of stress, TBI resulted in a significant increase in membrane excitability and spontaneous excitatory postsynaptic currents (sEPSCs) in LA pyramidal-like neurons. Foot-shock stress in the absence of TBI also resulted in increased sEPSC activity. In contrast, when preinjury stress and TBI occurred in combination, sEPSC activity was significantly decreased compared with either condition alone. There were no significant differences in inhibitory activity or total dendritic length among any of the treatment groups. These results demonstrate that stress and TBI may be contributing to amygdala hyperexcitability via different mechanisms and that these pathways may counterbalance each other with respect to long-term pathophysiology in the LA.

Intravenous immunoglobulin G improves neurobehavioral and histological outcomes after traumatic brain injury in mice.

Intravenous immunoglobulin (IVIG) may improve neuroinflammation after traumatic brain injury (TBI). IVIG administration after TBI improved rotarod latencies over the first 7 days (p=0.039) and water maze latencies over 29-32 days (p=0.027), decreased F4/80-positive cells at 2 (p=0.001) and 7 days (p<0.001), decreased Fluoro-Jade B-positive cells (p=0.020), increased NeuN-positive cells (p=0.014), decreased IL-6 production at 4 (p=0.032) and 24h (p=0.023), and decreased blood-brain barrier breakdown by IgG extravasation (p=0.001) and brain edema (p=0.006); however, TNF-α concentration was unchanged. IVIG administration was associated with long-term neurobehavioral and histological improvement through modulation of neuroinflammation and blood-brain barrier permeability in a murine TBI model.

Anti-inflammatory effects of progesterone in lipopolysaccharide-stimulated BV-2 microglia.

Female sex is associated with improved outcome in experimental brain injury models, such as traumatic brain injury, ischemic stroke, and intracerebral hemorrhage. This implies female gonadal steroids may be neuroprotective. A mechanism for this may involve modulation of post-injury neuroinflammation. As the resident immunomodulatory cells in central nervous system, microglia are activated during acute brain injury and produce inflammatory mediators which contribute to secondary injury including proinflammatory cytokines, and nitric oxide (NO) and prostaglandin E2 (PGE2), mediated by inducible NO synthase (iNOS) and cyclooxygenase-2 (COX-2), respectively. We hypothesized that female gonadal steroids reduce microglia mediated neuroinflammation. In this study, the progesterone's effects on tumor necrosis factor alpha (TNF-α), iNOS, and COX-2 expression were investigated in lipopolysaccharide (LPS)-stimulated BV-2 microglia. Further, investigation included nuclear factor kappa B (NF-κB) and mitogen activated protein kinase (MAPK) pathways. LPS (30 ng/ml) upregulated TNF-α, iNOS, and COX-2 protein expression in BV-2 cells. Progesterone pretreatment attenuated LPS-stimulated TNF-α, iNOS, and COX-2 expression in a dose-dependent fashion. Progesterone suppressed LPS-induced NF-κB activation by decreasing inhibitory κBα and NF-κB p65 phosphorylation and p65 nuclear translocation. Progesterone decreased LPS-mediated phosphorylation of p38, c-Jun N-terminal kinase and extracellular regulated kinase MAPKs. These progesterone effects were inhibited by its antagonist mifepristone. In conclusion, progesterone exhibits pleiotropic anti-inflammatory effects in LPS-stimulated BV-2 microglia by down-regulating proinflammatory mediators corresponding to suppression of NF-κB and MAPK activation. This suggests progesterone may be used as a potential neurotherapeutic to treat inflammatory components of acute brain injury.

Amyloid-ß oligomers induce synaptic damage via Tau-dependent microtubule severing by TTLL6 and spastin.

Mislocalization and aggregation of Aß and Tau combined with loss of synapses and microtubules (MTs) are hallmarks of Alzheimer disease. We exposed mature primary neurons to Aß oligomers and analysed changes in the Tau/MT system. MT breakdown occurs in dendrites invaded by Tau (Tau missorting) and is mediated by spastin, an MT-severing enzyme. Spastin is recruited by MT polyglutamylation, induced by Tau missorting triggered translocalization of TTLL6 (Tubulin-Tyrosine-Ligase-Like-6) into dendrites. Consequences are spine loss and mitochondria and neurofilament mislocalization. Missorted Tau is not axonally derived, as shown by axonal retention of photoconvertible Dendra2-Tau, but newly synthesized. Recovery from Aß insult occurs after Aß oligomers lose their toxicity and requires the kinase MARK (Microtubule-Affinity-Regulating-Kinase). In neurons derived from Tau-knockout mice, MTs and synapses are resistant to Aß toxicity because TTLL6 mislocalization and MT polyglutamylation are prevented; hence no spastin recruitment and no MT breakdown occur, enabling faster recovery. Reintroduction of Tau re-establishes Aß-induced toxicity in TauKO neurons, which requires phosphorylation of Tau's KXGS motifs. Transgenic mice overexpressing Tau show TTLL6 translocalization into dendrites and decreased MT stability. The results provide a rationale for MT stabilization as a therapeutic approach.

Tumor necrosis factor α antagonism improves neurological recovery in murine intracerebral hemorrhage.

BACKGROUND: Intracerebral hemorrhage (ICH) is a devastating stroke subtype characterized by a prominent neuroinflammatory response. Antagonism of pro-inflammatory cytokines by specific antibodies represents a compelling therapeutic strategy to improve neurological outcome in patients after ICH. To test this hypothesis, the tumor necrosis factor alpha (TNF-α) antibody CNTO5048 was administered to mice after ICH induction, and histological and functional endpoints were assessed. METHODS: Using 10 to 12-week-old C57BL/6J male mice, ICH was induced by collagenase injection into the left basal ganglia. Brain TNF-α concentration, microglia activation/macrophage recruitment, hematoma volume, cerebral edema, and rotorod latency were assessed in mice treated with the TNF-α antibody, CNTO5048, or vehicle. RESULTS: After ICH induction, mice treated with CNTO5048 demonstrated reduction in microglial activation/macrophage recruitment compared to vehicle-treated animals, as assessed by unbiased stereology (P = 0.049). This reduction in F4/80-positive cells was associated with a reduction in cleaved caspase-3 (P = 0.046) and cerebral edema (P = 0.026) despite similar hematoma volumes, when compared to mice treated with vehicle control. Treatment with CNTO5048 after ICH induction was associated with a reduction in functional deficit when compared to mice treated with vehicle control, as assessed by rotorod latencies (P = 0.024). CONCLUSIONS: Post-injury treatment with the TNF-α antibody CNTO5048 results in less neuroinflammation and improved functional outcomes in a murine model of ICH.

Lacosamide improves outcome in a murine model of traumatic brain injury.

BACKGROUND: Use of antiepileptic drugs (AED's) is common in the neurocritical care setting. However, there remains a great deal of controversy regarding the optimal agent. Studies associating the prophylactic use of AED's with poor outcomes are heavily biased by the prevalent use of phenytoin, an agent highly associated with deleterious effects. In the current study, we evaluate lacosamide for neuroprotective properties in a murine model of closed head injury. METHODS: Mice were subjected to moderate closed head injury using a pneumatic impactor, and then treated with either low-dose (6 mg/kg) or high-dose (30 mg/kg) lacosamide or vehicle at 30 min post-injury, and twice daily for 3 days after injury. Motor and cognitive functional assessments were performed following injury using rotarod and Morris Water Maze, respectively. Neuronal injury and microglial activation were measured by flourojade-B, NeuN, and F4/80 staining at 1 and 7 days post-injury. Timm's staining was also performed to assess lacosamide effects on mossy fiber axonal sprouting. To evaluate possible mechanisms of lacosamide effects on the inflammatory response to injury, an RNA expression array was used to evaluate for alterations in differential gene expression patterns in injured mice following lacosamide or vehicle treatments. RESULTS: High-dose lacosamide was associated with improved functional outcome on both the rotarod and Morris Water Maze. High-dose lacosamide was also associated with a reduction of neuronal injury at 24 h post-injury. However, the reduction in neuronal loss observed early did not result in greater neuronal density at 31 days post-injury based on unbiased stereology of NeuN staining. High-dose lacosamide was also associated with a significant reduction in microglial activation at 7 days post-injury. The therapeutic effects of lacosamide are associated with a delay in injury-related changes in RNA expression of a subset of inflammatory mediator genes typically seen at 24 h post-injury. CONCLUSIONS: Administration of lacosamide improves functional performance, and reduces histological evidence of acute neuronal injury and neuroinflammation in a murine model of closed head injury. Lacosamide effects appear to be mediated via a reduction or delay in the acute inflammatory response to injury. Prior clinical and animal studies have found antiepileptic treatment following injury to be detrimental, though these studies are biased by the common use of older medications such as phenytoin. Our current results as well as prior work on levetiracetam suggest the newer AED's may be beneficial in the setting of acute brain injury.

TT-301 inhibits microglial activation and improves outcome after central nervous system injury in adult mice.

BACKGROUND: Microglial inhibition may reduce secondary tissue injury and improve functional outcome following acute brain injury. Utilizing clinically relevant murine models of traumatic brain injury and intracerebral hemorrhage, neuroinflammatory responses and functional outcome were examined in the presence of a potential microglial inhibitor, TT-301. METHODS: TT-301 or saline was administered following traumatic brain injury or intracerebral hemorrhage, and then for four subsequent days. The effect of TT-301 on neuroinflammatory responses and neuronal viability was assessed, as well as short-term vestibulomotor deficit (Rotorod) and long-term neurocognitive impairment (Morris water maze). Finally differential gene expression profiles of mice treated with TT-301 were compared with those of vehicle. RESULTS: Reduction in F4/80+ staining was demonstrated at 1 and 10 days, but not 28 days, after injury in mice treated with TT-301 (n = 6). These histologic findings were associated with improved neurologic function as assessed by Rotorod, which improved by 52.7% in the treated group by day 7, and Morris water maze latencies, which improved by 232.5% as a function of treatment (n = 12; P < 0.05). Similar benefit was demonstrated following intracerebral hemorrhage, in which treatment with TT-301 was associated with functional neurologic improvement of 39.6% improvement in Rotorod and a reduction in cerebral edema that was independent of hematoma volume (n = 12; P < 0.05). Differential gene expression was evaluated following treatment with TT-301, and hierarchical cluster analysis implicated involvement of the Janus kinase-Signal Transducer and Activator of Transcription pathway after administration of TT-301 (n = 3/group). CONCLUSIONS: Modulation of neuroinflammatory responses through TT-301 administration improved histologic and functional parameters in murine models of acute neurologic injury.

Statins improve outcome in murine models of intracranial hemorrhage and traumatic brain injury: a translational approach.

Traumatic brain injury (TBI) and intracerebral hemorrhage (ICH) are leading causes of neurological mortality and disability in the U.S. However, therapeutic options are limited and clinical management remains largely supportive. HMG-CoA reductase inhibitors (statins) have pleiotropic mechanisms of action in the setting of acute brain injury, and have been demonstrated to improve outcomes in preclinical models of ICH and TBI. To facilitate translation to clinical practice, we now characterize the optimal statin and dosing paradigm in murine models of ICH and TBI. In a preclinical model of TBI, mice received vehicle, simvastatin, and rosuvastatin at doses of 1 mg/kg and 5 mg/kg for 5 days after the impact. Immunohistochemistry, differential gene expression, and functional outcomes (rotarod and Morris water maze testing) were assessed to gauge treatment response. Following TBI, administration of rosuvastatin 1 mg/kg was associated with the greatest improvement in functional outcomes. Rosuvastatin treatment was associated with histological evidence of reduced neuronal degeneration at 24 h post-TBI, reduced microgliosis at day 7 post-TBI, and preserved neuronal density in the CA3 region at 35 days post-injury. Administration of rosuvastatin following TBI was also associated with downregulation of inflammatory gene expression in the brain. Following ICH, treatment with simvastatin 1 mg/kg was associated with the greatest improvement in functional outcomes, an effect that was independent of hemorrhage volume. Clinically relevant models of acute brain injury may be used to define variables such as optimal statin and dosing paradigms to facilitate the rational design of pilot clinical trials.

The apoE-mimetic peptide, COG1410, improves functional recovery in a murine model of intracerebral hemorrhage.

BACKGROUND: Apolipoprotein E has previously been demonstrated to modulate acute brain injury responses, and administration of COG1410, an apoE-mimetic peptide derived from the receptor-binding region of apoE, improves outcome in preclinical models of acute neurological injury. In the current study, we sought to establish the optimal dose and timing of peptide administration associated with improved functional outcome in a murine model of intracerebral hemorrhage (ICH). METHODS: Ten to twelve-week-old C57/BL6 male mice were injured by collagenase-induced ICH and randomly selected to receive either vehicle or one of four doses of COG1410 (0.5, 1, 2, or 4 mg/kg) via tail vein injection at 30 min after injury and then daily for 5 days. The injured mice were euthanized at various time points to assess inflammatory mediators, cerebral edema, and hematoma volume. Over the first 5 days following injury, vestibulomotor function was tested via Rotorod (RR) latency. After an optimal dose was demonstrated, a final cohort of animals was injured with ICH and randomly assigned to receive the first dose of COG1410 or vehicle at increasingly longer treatment initiation times after injury. The mice were then assessed for functional deficit via RR testing over the first 5 days following injury. RESULTS: The mice receiving 2 mg/kg of COG1410 after injury demonstrated reduced functional deficit, decreased brain concentrations of inflammatory proteins, and less cerebral edema, although hematoma volume did not vary. The improved RR performance was maintained when peptide administration was delayed for up to 2 h after ICH. CONCLUSIONS: COG1410 administered at a dose of 2 mg/kg within 2 h after injury improves functional recovery in a murine model of ICH.

Tau protein is required for amyloid {beta}-induced impairment of hippocampal long-term potentiation.

Amyloid ß (Aß) and tau protein are both implicated in memory impairment, mild cognitive impairment (MCI), and early Alzheimer's disease (AD), but whether and how they interact is unknown. Consequently, we asked whether tau protein is required for the robust phenomenon of Aß-induced impairment of hippocampal long-term potentiation (LTP), a widely accepted cellular model of memory. We used wild-type mice and mice with a genetic knock-out of tau protein and recorded field potentials in an acute slice preparation. We demonstrate that the absence of tau protein prevents Aß-induced impairment of LTP. Moreover, we show that Aß increases tau phosphorylation and that a specific inhibitor of the tau kinase glycogen synthase kinase 3 blocks the increased tau phosphorylation induced by Aß and prevents Aß-induced impairment of LTP in wild-type mice. Together, these findings show that tau protein is required for Aß to impair synaptic plasticity in the hippocampus and suggest that the Aß-induced impairment of LTP is mediated by tau phosphorylation. We conclude that preventing the interaction between Aß and tau could be a promising strategy for treating cognitive impairment in MCI and early AD.

Traumatic brain injury exacerbates neurodegenerative pathology: improvement with an apolipoprotein E-based therapeutic.

Cognitive impairment is common following traumatic brain injury (TBI), and neuroinflammatory mechanisms may predispose to the development of neurodegenerative disease. Apolipoprotein E (apoE) polymorphisms modify neuroinflammatory responses, and influence both outcome from acute brain injury and the risk of developing neurodegenerative disease. We demonstrate that TBI accelerates neurodegenerative pathology in double-transgenic animals expressing the common human apoE alleles and mutated amyloid precursor protein, and that pathology is exacerbated in the presence of the apoE4 allele. The administration of an apoE-mimetic peptide markedly reduced the development of neurodegenerative pathology in mice homozygous for apoE3 as well as apoE3/E4 heterozygotes. These results demonstrate that TBI accelerates the cardinal neuropathological features of neurodegenerative disease, and establishes the potential for apoE mimetic therapies in reducing pathology associated with neurodegeneration.

Tau deficiency leads to the upregulation of BAF-57, a protein involved in neuron-specific gene repression.

Although tau is mainly located in the cell cytoplasm, mostly bound to tubulin, it may also be found in the nucleus of neurons. Hence, we tested whether tau might play a role in regulating the expression of certain genes by comparing gene expression in mice containing or lacking the tau protein. Our results identified a significant difference in the expression of the smarce1 gene, which codes for the BAF-57 protein, a protein involved in the repression of neuron specific genes. These data suggest a role for tau in neuron maturation.

Tau-knockout mice show reduced GSK3-induced hippocampal degeneration and learning deficits.

It has been proposed that deregulation of neuronal glycogen synthase kinase 3 (GSK3) activity may be a key feature in Alzheimer disease pathogenesis. We have previously generated transgenic mice that overexpress GSK3beta in forebrain regions including dentate gyrus (DG), a region involved in learning and memory acquisition. We have found that GSK3 overexpression results in DG degeneration. To test whether tau protein modified by GSK3 plays a role in that neurodegeneration, we have brought GSK3 overexpressing mice to a tau knockout background. Our results indicate that the toxic effect of GSK3 overexpression is milder and slower in the absence of tau. Thus, we suggest that the hyperphosphorylated tau mediates, at least in part, the pathology observed in the brain of GSK3 overexpressing mice.