Beta Amylod~Impaired transcription in Alzheimer's disease: key role in mitochondrial dysfunction and oxidative stress.

Alzheimer's disease (AD) is the major cause of dementia in the world. Abnormal extracellular accumulation of amyloid-β (Aβ) peptide and tau hyperphosphorylation, forming neurofibrillary tangles in the brain, are hallmarks of the disease. Oxidative stress, neuroinflammation, and mitochondrial and synaptic dysfunction are also observed in AD and often correlated to intracellular Aβ. This peptide results from the cleavage of the amyloid-β protein precursor by β- and γ-secretases and tends to be secreted after its production. However, secreted Aβ can be internalized by the interaction with membrane receptors, namely N-methyl-D-aspartate receptors, advanced glycation end products receptors, and/or alpha 7 nicotinic acetylcholine receptors. Inside the cell, Aβ interacts with several organelles, including mitochondria and nucleus, and there is growing evidence pointing to a possible role of Aβ in the regulation of gene transcription. Accordingly, transcriptional deregulation was observed in several AD models and human samples from AD patients through modified expression, phosphorylation levels, function, and subcellular localization of some transcription factors, resulting in the suppression of neuroprotective transcription both in the nucleus and the mitochondria. In this review we focus on key transcription regulators related with mitochondrial biogenesis and antioxidant defenses that seem to be altered in AD models and also on the role of intranuclear Aβ in the pathogenesis of the disease.

Beta Amyloid ~IFN-γ Production by Amyloid β-Specific Th1 Cells Promotes Microglial Activation and Increases Plaque Burden in a Mouse Model of Alzheimer's Disease.

Alzheimer's disease (AD) is characterized by the presence of amyloid-β (Aβ)-containing plaques, neurofibrillary tangles, and neuronal loss in the brain. Inflammatory changes, typified by activated microglia, particularly adjacent to Aβ plaques, are also a characteristic of the disease, but it is unclear whether these contribute to the pathogenesis of AD or are a consequence of the progressive neurodegenerative processes. Furthermore, the factors that drive the inflammation and neurodegeneration remain poorly understood. CNS-infiltrating T cells play a pivotal role in the pathogenesis of multiple sclerosis, but their role in the progression of AD is still unclear. In this study, we examined the role of Aβ-specific T cells on Aβ accumulation in transgenic mice that overexpress amyloid precursor protein and presenilin 1 (APP/PS1). We found significant infiltration of T cells in the brains of APP/PS1 mice, and a proportion of these cells secreted IFN-γ or IL-17. Aβ-specific CD4 T cells generated by immunization with Aβ and a TLR agonist and polarized in vitro to Th1-, Th2-, or IL-17-producing CD4(+) T cells, were adoptively transferred to APP/PS1 mice at 6 to 7 mo of age. Assessment of animals 5 wk later revealed that Th1 cells, but not Th2 or IL-17-producing CD4(+) T cells, increased microglial activation and Aβ deposition, and that these changes were associated with impaired cognitive function. The effects of Th1 cells were attenuated by treatment of the APP/PS1 mice with an anti-IFN-γ Ab. Our study suggests that release of IFN-γ from infiltrating Th1 cells significantly accelerates markers of diseases in an animal model of AD.

Beta Amylod~Dysregulation of Hypoxia-Inducible Factor by Presenilin/γ-Secretase Loss-of-Function Mutations.

Presenilin (PSEN) 1 and 2 are the catalytic components of the γ-secretase complex, which cleaves a variety of proteins, including the amyloid precursor protein (APP). Proteolysis of APP leads to the formation of the APP intracellular domain (AICD) and amyloid β that is crucially involved in the pathogenesis of Alzheimer's disease. Prolyl-4-hydroxylase-domain (PHD) proteins regulate the hypoxia-inducible factors (HIFs), the master regulators of the hypoxic response. We previously identified the FK506 binding protein 38 (FKBP38) as a negative regulator of PHD2. Genetic ablation of PSEN1/2 has been shown to increase FKBP38 protein levels. Therefore, we investigated the role of PSEN1/2 in the oxygen sensing pathway using a variety of genetically modified cell and mouse lines. Increased FKBP38 protein levels and decreased PHD2 protein levels were found in PSEN1/2-deficient mouse embryonic fibroblasts and in the cortex of forebrain-specific PSEN1/2 conditional double knock-out mice. Hypoxic HIF-1α protein accumulation and transcriptional activity were decreased, despite reduced PHD2 protein levels. Proteolytic γ-secretase function of PSEN1/2 was needed for proper HIF activation. Intriguingly, PSEN1/2 mutations identified in Alzheimer patients differentially affected the hypoxic response, involving the generation of AICD. Together, our results suggest a direct role for PSEN in the regulation of the oxygen sensing pathway via the APP/AICD cleavage cascade.

Beta Amyloid ~γ-Secretase Modulators: Can We Combine Potency with Safety?

γ-Secretase modulation has been proposed as a potential disease modifying anti-Alzheimer's approach. γ-Secretase modulators (GSMs) cause a product shift from the longer amyloid-beta (Aβ) peptide isoforms to shorter, more soluble, and less amyloidogenic isoforms, without inhibiting APP or Notch proteolytic processing. As such, modulating γ-secretase may avoid some of the adverse effects observed with γ-secretase inhibitors. Since the termination of the GSM tarenfurbil in 2008 due to negative phase III trial results, a considerable progress has been made towards more potent and better brain penetrable compounds. However, an analysis of their lipophilic efficiency indices indicates that their increased potency can be largely attributed to their increased lipophilicity. The need for early and chronic dosing with GSMs will require high-safety margins. This will be a challenge to achieve with the current, highly lipophilic GSMs. We will demonstrate that by focusing on the drug-like properties of GSMs, a combination of high in vitro potency and reduced lipophilicity can be achieved and does result in better tolerated compounds. The next hurdle will be to translate this knowledge into GSMs which are highly efficacious and safe in vivo.

Beta Amyloid ~PuF, an antimetastatic and developmental signaling protein, interacts with the Alzheimer's amyloid-beta precursor protein via a tissue-specific proximal regulatory element (PRE).

BACKGROUND: Alzheimer's disease (AD) is intimately tied to amyloid-beta (Abeta) peptide. Extraneuronal brain plaques consisting primarily of Abeta aggregates are a hallmark of AD. Intraneuronal Abeta subunits are strongly implicated in disease progression. Protein sequence mutations of the Abeta precursor protein (APP) account for a small proportion of AD cases, suggesting that regulation of the associated gene (APP) may play a more important role in AD etiology. The APP promoter possesses a novel 30 nucleotide sequence, or "proximal regulatory element" (PRE), at -76/-47, from the +1 transcription start site that confers cell type specificity. This PRE contains sequences that make it vulnerable to epigenetic modification and may present a viable target for drug studies. We examined PRE-nuclear protein interaction by gel electrophoretic mobility shift assay (EMSA) and PRE mutant EMSA. This was followed by functional studies of PRE mutant/reporter gene fusion clones.

Beta Amyloid~Encephalopathy: A Vicious Cascade following Forebrain Ischemia and Hypoxia.

Post ischemic/hypoxic encephalopathy is a progressive and widespread damage syndrome in human brain, which includes production of new ischemic foci as well as neurodegeneration associated with accumulation of amyloid protein (Aβ), which emerges within days after the primary ischemic or hypoxic ictus. Patients may suddenly suffer severe dementia and Parkinson's syndrome after a symptom-free period averaging 2 weeks following resuscitation. Death of neurons in the cortex, limbic system, globus pallidus (GP) and substantia nigra (SN) and damage to white matter are responsible. From experimental studies in animals evidence is obtained to reveal the mechanisms. Injured endothelia and activated platelets lead to secondary injury via thrombosis and vasoconstriction resulting in infarction and new foci of necrosis. Blood-brain barrier (BBB) breakdown allows penetration of blood-borne toxic substances into brain resulting in neuronal degeneration and enhanced inflammatory destruction. These secondary injuries happen within two weeks after moderate global ischemia. As these pathological changes cycle between the vascular and neuronal compartments, the damage expands and worsens. Aβ, β amyloid precursor protein (βAPP) and the inflammation mediator cyclooxygenase-2 (COX2) as well as γ-aminobutyric acid (GABA) system degeneration participate in producing secondary injury. Thus, implementing multi-targeted prophylaxis before or at the brain-at-risk stage is desirable. A combination of protecting endothelia, inhibiting platelet activity and improving cerebral circulation is a fundamental strategy to block this vicious cascade, thereby ameliorating or preventing the encephalopathy.

Beta Amyloid~Monoclonal antibodies selective for α-synuclein oligomers/protofibrils recognize brain pathology in Lewy body disorders and transgenic mice expressing the disease-causing A30P mutation.

Inclusions of intraneuronal alpha-synuclein (α-synuclein) can be detected in brains from patients with Parkinson's disease (PD) and dementia with Lewy bodies (DLB). The aggregation of α-synuclein is a central feature of the disease pathogenesis. Among the different α-synuclein species, large oligomers/protofibrils have particular neurotoxic properties and should therefore be suitable as both therapeutic and diagnostic targets. Two monoclonal antibodies, mAb38F and mAb38E2, with high affinity and strong selectivity for large α-synuclein oligomers were generated. These antibodies, which do not bind amyloid-beta or tau, recognize Lewy body pathology in brains from patients with PD and DLB and detect pathology earlier in α-synuclein transgenic mice than linear epitope antibodies. An oligomer selective sandwich-ELISA, based on mAb38F, was set up to analyze brain extracts of the transgenic mice. The overall levels of α-synuclein oligomers/protofibrils were found to increase with age in these mice, although the levels displayed a large interindividual variation. Upon subcellular fractionation higher levels of α-synuclein oligomers/protofibrils could be detected in the endoplasmic reticulum (ER) around the age when behavioural disturbances develop. In summary, our novel oligomer selective α-synuclein antibodies recognize relevant pathology and should be important tools to further explore the pathogenic mechanisms in Lewy body disorders. Moreover, they could be potential candidates both for immunotherapy and as reagents in an assay to assess a potential disease biomarker. © 2013 International Society for Neurochemistry, J. Neurochem. (2013) 10.1111/jnc.12175.

Beta Amyloid ~Age-Related Changes in Brain Extracellular Space Affect Processing of Amyloid-β Peptides in Alzheimer's Disease.

Alzheimer's disease is a neurodegenerative disease in which aging is not only a major risk factor but a major determinant of onset, course, and pathogenesis. The synthesis of amyloid-β (Aβ) peptides by neurons and their excretion into the extracellular space (ECS) is a core feature of AD that begins more than two decades before the onset of clinical symptoms. The ECS resembles a syncytium with the appearance in electron micrographs of continuous channels and lakes separating the outer membranes of the neurons, neuroglia, and vascular elements embedded in it. It consists primarily of a proteoglycan matrix through which circulates an interstitial fluid, derived in part from cerebrospinal fluid (CSF). The process by which Aβ accumulates in the ECS includes decreased production of CSF, matrix proteoglycans, and ECS volume, all of which become more severe with advancing age and lead to an age-related increase in the Aβ pool. Although the relationship between Aβ and the appearance of cognitive symptoms is uncertain, available data support a strong relationship between the toxicity of Aβ for neurons and the total Aβ burden, including the soluble and fibrillar Aβ, the Aβ42/Aβ40 ratio, and Aβ-proteoglycan reactivity. Proteoglycans have been shown to foster the formation of neurotoxic fibrillar Aβ42 and neuritic plaques that enhance neuronal and synaptic damage and eventual loss culminating in the onset and progression of dementia. As this process depends upon age-related events, it suggests that the successful control of AD lies in finding effective means of prevention.

Beta Amyloid~Aftins Increase Amyloid-β42, Lower Amyloid-β38, and Do Not Alter Amyloid-β40 Extracellular Production in vitro: Toward a Chemical Model of Alzheimer's Disease?

Increased production of amyloid-β (Aβ)42 peptide, derived from the amyloid-β protein precursor, and its subsequent aggregation into oligomers and plaques constitutes a hallmark of Alzheimer's disease (AD). We here report on a family of low molecular weight molecules, the Aftins (Amyloid-β Forty-Two Inducers), which, in cultured cells, dramatically affect the production of extracellular/secreted amyloid peptides. Aftins trigger β-secretase inhibitor and γ-secretase inhibitors (GSIs) sensitive, robust upregulation of Aβ42, and parallel down-regulation of Aβ38, while Aβ40 levels remain stable. In contrast, intracellular levels of these amyloids appear to remain stable. In terms of their effects on Aβ38/Aβ40/Aβ42 relative abundance, Aftins act opposite to γ-secretase modulators (GSMs). Aβ42 upregulation induced by Aftin-5 is unlikely to originate from reduced proteolytic degradation or diminished autophagy. Aftin-5 has little effects on mitochondrial functional parameters (swelling, transmembrane potential loss, cytochrome c release, oxygen consumption) but reversibly alters the ultrastructure of mitochondria. Aftins thus alter the Aβ levels in a fashion similar to that described in the brain of AD patients. Aftins therefore constitute new pharmacological tools to investigate this essential aspect of AD, in cell cultures, allowing (1) the detection of inhibitors of Aftin induced action (potential 'anti-AD compounds', including GSIs and GSMs) but also (2) the identification, in the human chemical exposome, of compounds that, like Aftins, might trigger sustained Aβ42 production and Aβ38 down-regulation (potential 'pro-AD compounds').

Beta Amyloid ~Impaired transcription in Alzheimer's disease: key role in mitochondrial dysfunction and oxidative stress.

Alzheimer's disease (AD) is the major cause of dementia in the world. Abnormal extracellular accumulation of amyloid-β (Aβ) peptide and tau hyperphosphorylation, forming neurofibrillary tangles in the brain, are hallmarks of the disease. Oxidative stress, neuroinflammation, and mitochondrial and synaptic dysfunction are also observed in AD and often correlated to intracellular Aβ. This peptide results from the cleavage of the amyloid-β protein precursor by β- and γ-secretases and tends to be secreted after its production. However, secreted Aβ can be internalized by the interaction with membrane receptors, namely N-methyl-D-aspartate receptors, advanced glycation end products receptors, and/or alpha 7 nicotinic acetylcholine receptors. Inside the cell, Aβ interacts with several organelles, including mitochondria and nucleus, and there is growing evidence pointing to a possible role of Aβ in the regulation of gene transcription. Accordingly, transcriptional deregulation was observed in several AD models and human samples from AD patients through modified expression, phosphorylation levels, function, and subcellular localization of some transcription factors, resulting in the suppression of neuroprotective transcription both in the nucleus and the mitochondria. In this review we focus on key transcription regulators related with mitochondrial biogenesis and antioxidant defenses that seem to be altered in AD models and also on the role of intranuclear Aβ in the pathogenesis of the disease.