105 research outputs found
Change in tau phosphorylation associated with neurodegeneration in the ME7 model of prion disease
No full textHyperphosphorylation of the microtubule-associated protein tau is a significant determinant in AD (Alzheimer's disease), where it is associated with disrupted axonal transport and probably causes synaptic dysfunction. Although less well studied, hyperphosphorylation has been observed in prion disease. We have investigated the expression of hyperphosphorylated tau in the hippocampus of mice infected with the ME7 prion agent. In ME7-infected animals, there is a selective loss of CA1 synapse, first discernable at 13 weeks of disease. There is a potential that dysfunctional axonal transport contributes to this synaptopathy. Thus investigating hyperphosphorylated tau that is dysfunctional in AD could illuminate whether and how they are significant in prion disease. We observed no differences in the levels of phosphorylated tau (using MC1, PHF-1 and CP13 antibodies) in detergent-soluble and detergent-insoluble fractions extracted from ME7- and NBH- (normal brain homogenate) treated animals across disease. In contrast, we observed an increase in phospho-tau staining for several epitopes using immunohistochemistry in ME7-infected hippocampal sections. Although the changes were not of the magnitude seen in AD tissue, clear differences for several phospho-tau species were seen in the CA1 and CA3 of ME7-treated animals (pSer(199-202)>pSer(214)>PHF-1 antibody). Temporally, these changes were restricted to animals at 20 weeks and none of the disease-related staining was associated with the axons or dendrites that hold CA1 synapses. These findings suggest that phosphorylation of tau at the epitopes examined does not underpin the early synaptic dysfunction. These data suggest that the changes in tau phosphorylation recorded here and observed by others relate to end-stage prion pathology when early dysfunctions have progressed to overt neuronal loss
Parkinson’s Disease and the “sunshine” vitamin
No full textAccrued evidence suggesting that hypovitaminosis D acts as a risk factor for developing Parkinson’s disease (PD) remains controversial. Herein we evaluated existing results, and outline several biological mechanisms by which the hypovitaminosis D-PD relationship may occur. We performed a meta-analysis, using data obtained from a search of PubMed from July 2002 to July 2012, for studies reporting serum vitamin D levels in PD and control patients.We found that in comparison to healthy individuals, those with PD had lower levels of serum vitamin D. Furthermore, we explore a number of potential associated biological mechanisms, including the actions of reactive nitrogen species (RNS), glutathione (GSH), and glial-derived neurotrophic factor (GDNF) in the brain. We also examine the roles of Nurr1 and VDR genes in PD. Although a unifying hypothesis remains challenging, there is evidence to demonstrate that supplementation with the vitamin can to have a positive effect on PD pathobiology. We surmise that hypovitaminosis D does act as a risk factor in the development of PD. However, the need for new epidemiological studies and further research around vitamin D metabolism is highlighted. Urgent efforts to correct vitamin D deficiency through supplementation are warranted as they may improve either motor and/or non-motor symptoms in PD
Biochemical evidence for the differential association of metabotropic glutamate receptors within synaptic complexes
No full textThe distribution of metabotropic glutamate (mGlu) receptors within the synapse is an important determinant of function. mGlu have been grouped together into three main sub-classes: Group I mGlu (1 and 5) are predominantly situated on the post-synaptic membrane, whereas Group III (4, 6, 7 and 8) are largely pre-synaptic. Group II mGlu (2 and 3) are distributed peripheral to the active zone, on both sides of the synaptic cleft. Methods based on a distinct pH-dependent extractability of the pre- and post-synaptic marker proteins can provide insight into the molecular organization of synaptic junctions [G.R. Phillips, J.K. Huang, Y. Wang, H. Tanaka, L. Shapiro, W. Zhang, W. Shan, K. Arndt, M. Frank, R.E. Gordon, M.A. Gawinowicz, Y. Zhao and D.R. Colman, The presynaptic particle web: ultrastructure, composition, dissolution and reconstitution, Neuron 32 (2001) 63–77]. We have applied such procedures to rat brain cortical synaptosomes to explore the biochemical evidence for the accepted localisations of metabotropic glutamate receptors. As shown previously a number of post-synaptic marker proteins remained detergent-insoluble at both pH 6 and pH 8. There was an increased extraction of a number of pre-synaptic plasma membrane and cytomatrix proteins consistent with dissolution of the pre-synaptic aspect of synaptic junctions at elevated pH. We similarly observed modest extraction of Group I mGlu at either pH consistent with their post-synaptic organization. However, we observed increased extractability of Group II mGlu at pH 8. The extractability of Group III mGlu was slightly increased at pH 8 but these receptors were largely refractory to extraction. We have also applied the approach to scaffolding proteins implicated in mGlu localisation to define the biochemical correlates of mGlu scaffolding.<br/
Differential molecular chaperone response associated with various mouse adapted scrapie strains
No full textPrionoses are a group of neurodegenerative diseases characterized by misfolding of cellular prion protein (PrP(C)) and accumulation of its diseases specific conformer PrP(Sc) in the brain and neuropathologically, they can be associated with presence or absence of PrP amyloid deposits. Functional molecular chaperones (MCs) that constitute the unfolded protein response include heat shock proteins and glucose-regulated protein families. They protect intracellular milieu against various stress conditions including accumulation of misfolded proteins and oxidative stress, typical of neurodegenerative diseases. Little is known about the role of MCs in pathogenesis of prionoses in mammalian prion model systems. In this study we characterized MCs response pattern in mice infected with various mouse adapted scrapie strains. Rather than uniform upregulation of MCs, we encountered two distinctly different patterns of MCs response distinguishing ME7 and 87V strains from 22L and 139A strains. ME7 and 87V strains are known for the induction of amyloid deposition in infected animals, while in mice infected with 22L and 139A strains amyloid deposits are absent. MCs response pattern similar to that associated with amyloidogenic ME7 and 87V strains was also observed in APPPS1-21 Alzheimer's transgenic mice, which represent an aggressive model of cerebral amyloidosis caused by ?-amyloid deposition. Our results highlight the probability that different mechanisms of MCs regulation exist driven by amyloidogenic and non-amyloidogenic nature of prion strains
Antioxidant peroxiredoxin 6 protein rescues toxicity due to oxidative stress and cellular hypoxia in vitro, and attenuates prion-related pathology in vivo
No full textProtein misfolding, mitochondrial dysfunction and oxidative stress are common pathomechanisms that underlie neurodegenerative diseases. In prion disease, central to these processes is the post-translational transformation of cellular prion protein (PrPc) to the aberrant conformationally altered isoform; PrPSc. This can trigger oxidative reactions and impair mitochondrial function by increasing levels of peroxynitrite, causing damage through formation of hydroxyl radicals or via nitration of tyrosine residues on proteins. The 6 member Peroxiredoxin (Prdx) family of redox proteins are thought to be critical protectors against oxidative stress via reduction of H2O2, hydroperoxides and peroxynitrite. In our in vitro studies cellular metabolism of SK-N-SH human neuroblastoma cells was significantly decreased in the presence of H2O2 (oxidative stressor) or CoCl2 (cellular hypoxia), but was rescued by treatment with exogenous Prdx6, suggesting that its protective action is in part mediated through a direct action. We also show that CoCl2-induced apoptosis was significantly decreased by treatment with exogenous Prdx6. We proposed a redox regulator role for Prdx6 in regulating and maintaining cellular homeostasis via its ability to control ROS levels that could otherwise accelerate the emergence of prion-related neuropathology. To confirm this, we established prion disease in mice with and without astrocyte-specific antioxidant protein Prdx6, and demonstrated that expression of Prdx6 protein in Prdx6 Tg ME7-animals reduced severity of the behavioural deficit, decreased neuropathology and increased survival time compared to Prdx6 KO ME7-animals. We conclude that antioxidant Prdx6 attenuates prion-related neuropathology, and propose that augmentation of endogenous Prdx6 protein represents an attractive adjunct therapeutic approach for neurodegenerative diseases
Prion Protein Misfolding at the Synapse
No full textThe synapse has emerged as a major target for the misfolding insults that underlie prion disease and many other proteinopathies (e.g., Alzheimer's disease (AD)). This common theme in the pathogenesis of these disorders indicates that analogous degenerative processes could be at play when increasing extracellular and/or intracellular accumulation of misfolded proteins leads to eventual cell loss. Similar therapeutic strategies may thus be effective in various central nervous system amyloidoses. Animal models of prion disease provide good evidence for specific synaptic degeneration within defined anatomical pathways of the hippocampus. Biochemical, histological, and electron microscopy studies have documented disintegrating synaptic structures during the early asymptomatic stage of disease, which has lead to the hypothesis that degenerative pathways are engaged locally at the synapse during an early key stage of neurodegeneration. Mirroring this, synapse loss precedes neuronal loss in early AD, and is more closely correlated with cognitive impairment than are plaques and tangles. As in other protein misfolding neurodegenerative disorders, it is likely that in prion disease, pathological prion protein conformers are present and actively participate in disease pathogenesis at the synapse. Despite this fundamental understanding, there has been little systematic study of the evidence for pathological accumulation of prion protein in either the presynaptic or postsynaptic specializations, or indeed the role of cellular pathways and synaptic proteins associated with these pathologies. This chapter will review key signaling pathways and processes implicated in biochemical changes that misfolded prion protein triggers at the synapse. Knowing what these changes are may well lead to new drug targets that would then enable us to prevent neuronal cell loss.</p
Pathogenic tau does not drive activation of the unfolded protein response
No full textThe unfolded protein response (UPR) is commonly associated with a range of neurodegenerative diseases, and targeting UPR components has been suggested as a therapeutic strategy. The UPR surveys protein folding within the endoplasmic reticulum (ER). However, many of the misfolded proteins that accumulate in neurodegeneration are localized such that they do not directly cause ER triggers that activate this pathway. Here, using a transgenic mouse model and primary cell cultures, along with qPCR, immunoblotting and immunohistochemistry, we tested whether UPR is induced in in vivo andin vitro murine models of tauopathy that are based on expression of mutant tauP301L. We found no evidence for UPR in the rTg4510 mouse model in which mutant tau is transgenically expressed under control oftetracycline-controlled transactivator protein (tTA). This observation was supported by results from acute experiments in which neuronal cultures expressed mutant tau and accumulated misfolded cytoplasmic tau aggregates, but exhibited no UPR activation. These results suggest that the UPR is not induced as a response to tau misfolding and aggregation, despite clear evidence for progressive cellular dysfunction and degeneration. We propose that caution is needed when evaluating the implied significance of the UPR as a critical determinant across major neurodegenerative diseases
Unaltered SNARE complex formation in an in vivo model of prion disease
No full textThe ME7 model of prion disease is a chronic slowly evolving model of neurodegeneration in which cell death is preceded by synaptic dysfunction. Previous studies in cell culture show that accumulation of misfolded prion inhibits the formation of the SNARE complexes involving synaptobrevin, syntaxin and SNAP-25 that play an essential role in neurotransmitter release. Such observations suggest that similar phenomenon may contribute to synaptic dysfunction observed in vivo. We have thus used detergent extraction of hippocampal tissue to investigate the status of SNARE complexes in the ME7 model. In the presence of increasing PrPSc deposition we failed to see a change in the amount of SNARE complexes directly extracted into SDS and resolved by SDS-PAGE. Conversely pre-extraction in Triton X-100, a treatment that promotes SNARE complexes ex vivo, demonstrated a modest reduction in hippocampal SNARE complexes when homogenates were made from tissue at late stage disease. This suggests that accumulated PrPSc, or perhaps fibrillar complexes formed of prion only inhibit SNARE complexes that are formed ex vivo following biochemical extraction. Thus the accumulation of PrPSc although deleterious to synaptic function in vivo, does not exert its synaptic effects by disrupting the formation of SNARE complexes that are core to transmitter releas
Antibody engineering for optimized immunotherapy in Alzheimer's disease
No full textThere are nearly 50 million people with Alzheimer's disease (AD) worldwide and currently no disease modifying treatment is available. AD is characterized by deposits of Amyloid-β (Aβ), neurofibrillary tangles, and neuroinflammation, and several drug discovery programmes studies have focussed on Aβ as therapeutic target. Active immunization and passive immunization against Aβ leads to the clearance of deposits in humans and transgenic mice expressing human Aβ but have failed to improve memory loss. This review will discuss the possible explanations for the lack of efficacy of Aβ immunotherapy, including the role of a pro-inflammatory response and subsequent vascular side effects, the binding site of therapeutic antibodies and the timing of the treatment. We further discuss how antibodies can be engineered for improved efficacy.</p
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