Methylene blue (MB, methylthioninium chloride) is a phenothiazine that crosses the blood brain barrier and acts as a redox cycler. Among its beneficial properties are its abilities to act as an antioxidant, to reduce tau protein aggregation and to improve energy metabolism. These actions are of particular interest for the treatment of neurodegenerative diseases with tau protein aggregates known as tauopathies. The present study examined the effects of MB in the P301S mouse model of tauopathy. Both 4 mg/kg MB (low dose) and 40 mg/kg MB (high dose) were administered in the diet ad libitum from 1 to 10 months of age. We assessed behavior, tau pathology, oxidative damage, inflammation and numbers of mitochondria. MB improved the behavioral abnormalities and reduced tau pathology, inflammation and oxidative damage in the P301S mice. These beneficial effects were associated with increased expression of genes regulated by NF-E2-related factor 2 (Nrf2)/antioxidant response element (ARE), which play an important role in antioxidant defenses, preventing protein aggregation, and reducing inflammation. The activation of Nrf2/ARE genes is neuroprotective in other transgenic mouse models of neurodegenerative diseases and it appears to be an important mediator of the neuroprotective effects of MB in P301S mice. Moreover, we used Nrf2 knock out fibroblasts to show that the upregulation of Nrf2/ARE genes by MB is Nrf2 dependent and not due to secondary effects of the compound. These findings provide further evidence that MB has important neuroprotective effects that may be beneficial in the treatment of human neurodegenerative diseases with tau pathology.
The peroxisome proliferator-activated receptor ? coactivator 1-? (PGC-1?) interacts with various transcription factors involved in energy metabolism and in the regulation of mitochondrial biogenesis. PGC-1? mRNA levels are reduced in a number of neurodegenerative diseases and contribute to disease pathogenesis, since increased levels ameliorate behavioral defects and neuropathology of Huntington's disease, Parkinson's disease, and amyotrophic lateral sclerosis. PGC-1? and its downstream targets are reduced both in postmortem brain tissue of patients with Alzheimer's disease (AD) and in transgenic mouse models of AD. Therefore, we investigated whether increased expression of PGC-1? would exert beneficial effects in the Tg19959 transgenic mouse model of AD; Tg19959 mice express the human amyloid precursor gene (APP) with 2 familial AD mutations and develop increased ?-amyloid levels, plaque deposition, and memory deficits by 2-3 mo of age. Rather than an improvement, the cross of the Tg19959 mice with mice overexpressing human PGC-1? exacerbated amyloid and tau accumulation. This was accompanied by an impairment of proteasome activity. PGC-1? overexpression induced mitochondrial abnormalities, neuronal cell death, and an exacerbation of behavioral hyperactivity in the Tg19959 mice. These findings show that PGC-1? overexpression exacerbates the neuropathological and behavioral deficits that occur in transgenic mice with mutations in APP that are associated with human AD.
A central question in Alzheimers disease (AD) research is what role ?-amyloid peptide (A?) plays in synaptic dysfunction. Synaptic activity increases A? secretion, potentially inhibiting synapses, but also decreases intraneuronal A?, protecting synapses. We now show that levels of secreted A? fall with time in culture in neurons of AD-transgenic mice, but not wild-type mice. Moreover, the ability of synaptic activity to elevate secreted A? and reduce intraneuronal A? becomes impaired in AD-transgenic but not wild-type neurons with time in culture. We demonstrate that synaptic activity promotes an increase in the A?-degrading protease neprilysin at the cell surface and a concomitant increase in colocalization with A?42. Remarkably, AD-transgenic but not wild-type neurons show reduced levels of neprilysin with time in culture. This impaired ability to secrete A? and reduce intraneuronal A? has important implications for the pathogenesis and treatment of AD.
Alzheimers disease, the most common neurodegenerative disease, is characterized by a progressive loss of synapses and accumulation of amyloid-beta (A?) peptides in the brain. Previous studies demonstrated that acute increase in synaptic activity in cultured hippocampal slices and mouse brains (Cirrito et al. Neuron 48: 913-922, 2005; Kamenetz et al. Neuron 37: 925-937, 2003) enhanced secretion of A?. Since synaptic activity promotes A? secretion, it could also affect the trafficking and processing of its precursor, the amyloid precursor protein (APP). Here, we describe a method to investigate the effect of acute synaptic activation on APP trafficking within dendrites.
?-Amyloid (A?) accumulation and aggregation are hallmarks of Alzheimers disease (AD). High-resolution three-dimensional (HR-3D) volumetric imaging allows for better analysis of fluorescence confocal microscopy and 3D visualization of A? pathology in brain. Early intraneuronal A? pathology was studied in AD transgenic mouse brains by HR-3D volumetric imaging. To better visualize and analyze the development of A? pathology, thioflavin S staining and immunofluorescence using antibodies against A?, fibrillar A?, and structural and synaptic neuronal proteins were performed in the brain tissue of Tg19959, wild-type, and Tg19959-YFP mice at different ages. Images obtained by confocal microscopy were reconstructed into three-dimensional volumetric datasets. Such volumetric imaging of CA1 hippocampus of AD transgenic mice showed intraneuronal onset of A?42 accumulation and fibrillization within cell bodies, neurites, and synapses before plaque formation. Notably, early fibrillar A? was evident within individual synaptic compartments, where it was associated with abnormal morphology. In dendrites, increasing intraneuronal thioflavin S correlated with decreases in neurofilament marker SMI32. Fibrillar A? aggregates could be seen piercing the cell membrane. These data support that A? fibrillization begins within AD vulnerable neurons, leading to disruption of cytoarchitecture and degeneration of spines and neurites. Thus, HR-3D volumetric image analysis allows for better visualization of intraneuronal A? pathology and provides new insights into plaque formation in AD.
Accumulation of ?-amyloid (A?) and loss of synapses are hallmarks of Alzheimers disease (AD). How synaptic activity relates to A? accumulation and loss of synapses is a current topic of major interest. Synaptic activation promotes A? secretion, and chronic reduction of synaptic activity reduced A? plaques in an AD transgenic mouse model. This suggested beneficial effects of reducing synaptic activity in AD. We now show that reduced synaptic activity causes detrimental effects on synapses and memory despite reducing plaques using two different models of chronic synaptic inhibition: deafferentation of the barrel cortex and administration of benzodiazepine. An interval of prolonged synaptic inhibition exacerbated loss of synaptophysin compared with synaptically more active brain in AD transgenic but not wild-type mice. Furthermore, an interval of benzodiazepine treatment, followed by a washout period, exacerbated memory impairment in AD transgenic mice. Exacerbation of synaptic and behavioral abnormalities occurred in the setting of reduced A? plaques but elevated intraneuronal A? immunoreactivity. These data support beneficial effects of synaptic activation on A?-related synaptic and behavioral impairment in AD.
The mammalian target of rapamycin (mTOR) is an evolutionarily conserved Ser/Thr protein kinase that plays a pivotal role in multiple fundamental biological processes, including synaptic plasticity. We explored the relationship between the mTOR pathway and ?-amyloid (A?)-induced synaptic dysfunction, which is considered to be critical in the pathogenesis of Alzheimers disease (AD).
The aberrant accumulation of aggregated beta-amyloid peptides (Abeta) as plaques is a hallmark of Alzheimers disease (AD) neuropathology and reduction of Abeta has become a leading direction of emerging experimental therapies for the disease. The mechanism(s) whereby Abeta is involved in the pathophysiology of the disease remain(s) poorly understood. Initially fibrils, and subsequently oligomers of extracellular Abeta have been viewed as the most important pathogenic form of Abeta in AD. More recently, the intraneuronal accumulation of Abeta has been described in the brain, although technical considerations and its relevance in AD have made this a controversial topic. Here, we review the emerging evidence linking intraneuronal Abeta accumulation to the development of synaptic pathology and plaques in AD, and discuss the implications of intraneuronal beta-amyloid for AD pathology, biology, diagnosis and therapy.
beta-Amyloid peptide accumulation plays a central role in the pathogenesis of Alzheimers disease. Aberrant beta-amyloid buildup in the brain has been shown to be present both in the extracellular space and within neurons. Synapses are important targets of beta-amyloid, and alterations in synapses better correlate with cognitive impairment than amyloid plaques or neurofibrillary tangles. The link between beta-amyloid and synapses became even tighter when it was discovered that beta-amyloid accumulates within synapses and that synaptic activity modulates beta-amyloid secretion. Currently, a central question in Alzheimers disease research is what role synaptic activity plays in the disease process, and how specifically beta-amyloid is involved in the synaptic dysfunction that characterizes the disease.
A central question in Alzheimers disease research is what role synaptic activity plays in the disease process. Synaptic activity has been shown to induce beta-amyloid peptide release into the extracellular space, and extracellular beta-amyloid has been shown to be toxic to synapses. We now provide evidence that the well established synaptotoxicity of extracellular beta-amyloid requires gamma-secretase processing of amyloid precursor protein. Recent evidence supports an important role for intraneuronal beta-amyloid in the pathogenesis of Alzheimers disease. We show that synaptic activity reduces intraneuronal beta-amyloid and protects against beta-amyloid-related synaptic alterations. We demonstrate that synaptic activity promotes the transport of the amyloid precursor protein to synapses using live cell imaging, and that the protease neprilysin is involved in reduction of intraneuronal beta-amyloid with synaptic activity.
Oxidative stress is one of the earliest events in the pathogenesis of Alzheimers disease (AD) and can markedly exacerbate amyloid pathology. Modulation of antioxidant and anti-inflammatory pathways represents an important approach for AD therapy. Synthetic triterpenoids have been found to facilitate antioxidant response and reduce inflammation in several models. We investigated the effect of the triterpenoid, 2-Cyano-3,12-Dioxooleana-1,9-Dien-28-Oic acid-MethylAmide (CDDO-MA) in Tg19959 mice, which carry the human amyloid precursor protein with two mutations. These mice develop memory impairments and amyloid plaques as early as 2-3 months of age. CDDO-MA was provided with chow (800 mg/kg) from 1 to 4 months of age. CDDO-MA significantly improved spatial memory retention and reduced plaque burden, Abeta42 levels, microgliosis, and oxidative stress in Tg19959 mice.
Peroxisome proliferator-activated receptors (PPARs) are ligand-mediated transcription factors, which control both lipid and energy metabolism and inflammation pathways. PPAR? agonists are effective in the treatment of metabolic diseases and, more recently, neurodegenerative diseases, in which they show promising neuroprotective effects. We studied the effects of the pan-PPAR agonist bezafibrate on tau pathology, inflammation, lipid metabolism and behavior in transgenic mice with the P301S human tau mutation, which causes familial frontotemporal lobar degeneration. Bezafibrate treatment significantly decreased tau hyperphosphorylation using AT8 staining and the number of MC1-positive neurons. Bezafibrate treatment also diminished microglial activation and expression of both inducible nitric oxide synthase and cyclooxygenase 2. Additionally, the drug differentially affected the brain and brown fat lipidome of control and P301S mice, preventing lipid vacuoles in brown fat. These effects were associated with behavioral improvement, as evidenced by reduced hyperactivity and disinhibition in the P301S mice. Bezafibrate therefore exerts neuroprotective effects in a mouse model of tauopathy, as shown by decreased tau pathology and behavioral improvement. Since bezafibrate was given to the mice before tau pathology had developed, our data suggest that bezafibrate exerts a preventive effect on both tau pathology and its behavioral consequences. Bezafibrate is therefore a promising agent for the treatment of neurodegenerative diseases associated with tau pathology.
Multiple lines of evidence have implicated ?-amyloid (A?) in the pathogenesis of Alzheimers disease (AD). However, the mechanism(s) whereby A? is involved in the disease process remains unclear. The dominant hypothesis in AD has been that A? initiates the disease via toxicity from secreted, extracellular A? aggregates. More recently, an alternative hypothesis has emerged focusing on a pool of A? that accumulates early on within AD vulnerable neurons of the brain. Although the topic of intraneuronal A? has been of major interest in the field, technical difficulties in detecting intraneuronal A? have also made this topic remarkably controversial. Here we review evidence pointing to the critical role of intraneuronal A? in AD and provide insights both into challenges faced in detecting intracellular A? and the prion-like properties of A?.
?-Amyloid (A?) plaques are a pathological hallmark of Alzheimers disease (AD) and multiple lines of evidence have linked A? with AD. However, synapse loss is known as the best pathological correlate of cognitive impairment in AD, and intraneuronal A? accumulation has been shown to precede plaque pathology. The progression of A? accumulation to synapse loss and plaque formation remains incomplete. The objective is to investigate the progression of intraneuronal A? accumulation in the brain.
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