Berta Puig

Lipid Alterations in Lipid Rafts from Alzheimer's Disease Human Brain Cortex

Lipid rafts are membrane microdomains intimately associated with cell signaling. These biochemical microstructures are characterized by their high contents of sphingolipids, cholesterol and saturated fatty acids and a reduced content of polyunsaturated fatty acids (PUFA). Here, we have purified lipid rafts of human frontal brain cortex from normal and Alzheimers disease (AD) and characterized their biochemical lipid composition. The results revealed that lipid rafts from AD brains exhibit aberrant lipid profiles compared to healthy brains. In particular, lipid rafts from AD brains displayed abnormally low levels of n-3 long chain polyunsaturated fatty acids (LCPUFA, mainly 22:6n-3, docosahexaenoic acid) and monoenes (mainly 18:1n-9, oleic acid), as well as reduced unsaturation and peroxidability indexes. Also, multiple relationships between phospholipids and fatty acids were altered in AD lipid rafts. Importantly, no changes were observed in the mole percentage of lipid classes and fatty acids in rafts from normal brains throughout the lifespan (24-85 years). These indications point to the existence of homeostatic mechanisms preserving lipid raft status in normal frontal cortex. The disruption of such mechanisms in AD brains leads to a considerable increase in lipid raft order and viscosity, which may explain the alterations in lipid raft signaling observed in AD.

Brain protein preservation largely depends on the postmortem storage temperature: implications for study of proteins in human neurologic diseases and management of brain banks: a BrainNet Europe Study

The present study was designed to reveal protein modifications in control cases related with postmortem delay and temperature of storage in 3 paradigms in which the same postmortem tissue sample (frontal cortex) was frozen a short time after death or stored at 1°C, 4°C, or room temperature and then frozen at −80°C at different intervals. No evidence of protein degradation as revealed with monodimensional gel electrophoresis and Western blotting was observed in samples artificially stored at 1°C and then frozen at different intervals up to 50 hours after death. However, the levels of several proteins were modified in samples stored at 4°C and this effect was more marked in samples stored at room temperature. Two-dimensional gel electrophoresis and mass spectrometry further corroborated these observations and permitted the identification of other proteins vulnerable or resistant to postmortem delay. Finally, gel electrophoresis and Western blotting of sarkosyl-insoluble fractions in Alzheimer disease showed reduced intensity of phospho-tau-specific bands with postmortem delay with the effects being more dramatic when the brain samples were stored at room temperature for long periods. These results emphasize the necessity of reducing the body temperature after death to minimize protein degradation.

Lack of a-disintegrin-and-metalloproteinase ADAM10 leads to intracellular accumulation and loss of shedding of the cellular prion protein in vivo

BackgroundThe cellular prion protein (PrPC) fulfils several yet not completely understood physiological functions. Apart from these functions, it has the ability to misfold into a pathogenic scrapie form (PrPSc) leading to fatal transmissible spongiform encephalopathies. Proteolytic processing of PrPC generates N- and C-terminal fragments which play crucial roles both in the pathophysiology of prion diseases and in transducing physiological functions of PrPC. A-disintegrin-and-metalloproteinase 10 (ADAM10) has been proposed by cell culture experiments to be responsible for both shedding of PrPC and its α-cleavage. Here, we analyzed the role of ADAM10 in the proteolytic processing of PrPCin vivo.ResultsUsing neuron-specific Adam10 knockout mice, we show that ADAM10 is the sheddase of PrPC and that its absence in vivo leads to increased amounts and accumulation of PrPC in the early secretory pathway by affecting its posttranslational processing. Elevated PrPC levels do not induce apoptotic signalling via p53. Furthermore, we show that ADAM10 is not responsible for the α-cleavage of PrPC.ConclusionOur study elucidates the proteolytic processing of PrPC and proves a role of ADAM10 in shedding of PrPCin vivo. We suggest that ADAM10 is a mediator of PrPC homeostasis at the plasma membrane and, thus, might be a regulator of the multiple functions discussed for PrPC. Furthermore, identification of ADAM10 as the sheddase of PrPC opens the avenue to devising novel approaches for therapeutic interventions against prion diseases.

Deposition of hyperphosphorylated tau in cerebellum of PS1 E280A Alzheimer's disease.

Early‐onset familial Alzheimers disease (AD) caused by presenilin‐1 mutation E280A (PS1‐E280A) presents wide clinical and neuropathological variabilities. We characterized clinically and neuropathologically PS1‐E280A focusing in cerebellar involvement and compared it with early‐onset sporadic Alzheimers disease (EOSAD). Twelve E280A brains and 12 matched EOSAD brains were analyzed for beta‐amyloid and hyperphosphorylated tau (pTau) morphology, beta‐amyloid subspecies 1–40, 1–42 levels, pTau levels, and expression of stress kinases in frontal cortex and cerebellum. The data were correlated to clinical and genetic findings. We observed higher beta‐amyloid load, beta‐amyloid 1–42 and pTau concentrations in frontal cortex of PS1‐E280A compared with EOSAD. High beta‐amyloid load was found in the cerebellum of PS1‐E280A and EOSAD patients. In PS1‐E280A, beta‐amyloid localized to the molecular and Purkinje cell layers, whereas EOSAD showed them in Purkinje and granular cell layers. Surprisingly, 11 out of 12 PS1‐E280A patients showed deposition of pTau in the cerebellum. Also, seven out of 12 PS1‐E280A patients presented cerebellar ataxia. We conclude that deposition of beta‐amyloid in the cerebellum is prominent in early‐onset AD irrespective of genetic or sporadic origin. The presence of pTau in cerebellum in PS1‐E280A underscores the relevance of cerebellar involvement in AD and might be correlated to clinical phenotype.

Roles of endoproteolytic α‐cleavage and shedding of the prion protein in neurodegeneration

The cellular prion protein (PrPC) plays important roles in neurodegenerative diseases. First, it is the well‐established substrate for the conformational conversion into its pathogenic isoform (PrPSc) giving rise to progressive and fatal prion diseases. Moreover, several recent reports highlight important roles of PrPC in other neurodegenerative conditions such as Alzheimers disease. Since PrPC is subject to proteolytic processing, here we discuss the two main cleavage events under physiological conditions, α‐cleavage and shedding. We focus on how these cleavages and the resulting fragments may impact prion diseases as well as other neurodegenerative proteinopathies. Finally, we discuss the recently identified sheddase of PrPC, namely the metalloprotease ADAM10, with regard to therapeutic potential against neurodegenerative diseases.

The sheddase ADAM10 is a potent modulator of prion disease

The prion protein (PrPC) is highly expressed in the nervous system and critically involved in prion diseases where it misfolds into pathogenic PrPSc. Moreover, it has been suggested as a receptor mediating neurotoxicity in common neurodegenerative proteinopathies such as Alzheimers disease. PrPC is shed at the plasma membrane by the metalloprotease ADAM10, yet the impact of this on prion disease remains enigmatic. Employing conditional knockout mice, we show that depletion of ADAM10 in forebrain neurons leads to posttranslational increase of PrPC levels. Upon prion infection of these mice, clinical, biochemical, and morphological data reveal that lack of ADAM10 significantly reduces incubation times and increases PrPSc formation. In contrast, spatiotemporal analysis indicates that absence of shedding impairs spread of prion pathology. Our data support a dual role for ADAM10-mediated shedding and highlight the role of proteolytic processing in prion disease. DOI: http://dx.doi.org/10.7554/eLife.04260.001

The GPI-anchoring of PrP: Implications in sorting and pathogenesis

The cellular prion protein (PrPC) is an N-glycosylated GPI-anchored protein usually present in lipid rafts with numerous putative functions. When it changes its conformation to a pathological isoform (then referred to as PrPSc), it is an essential part of the prion, the agent causing fatal and transmissible neurodegenerative prion diseases. There is growing evidence that toxicity and neuronal damage on the one hand and propagation/infectivity on the other hand are two distinct processes of the disease and that the GPI-anchor attachment of PrPC and PrPSc plays an important role in protein localization and in neurotoxicity. Here we review how the signal sequence of the GPI-anchor matters in PrPC localization, how an altered cellular localization of PrPC or differences in GPI-anchor composition can affect prion infection, and we discuss through which mechanisms changes on the anchorage of PrPC can modify the disease process.

Active stress kinase p38 enhances and perpetuates abnormal tau phosphorylation and deposition in Pick’s disease

Abnormal tau hyperphosphorylation and deposition in Pick bodies is a major abnormality in Pick’s disease (PiD). This is associated with increased expression of the stress-activated protein kinase, p38 kinase, which has the capacity to phosphorylate tau in vitro. The present study has shown increased expression of phosphorylated p38 (p38-P), which does not cross-react with phospho-tau, in sarcosyl-insoluble fractions enriched in abnormal filaments, and hyperphosphorylated tau in the brain of two PiD cases obtained and processed with very short (less than 2xa0h) post-mortem delay. Immunohistochemical studies have shown p38-P co-localization in 90% of neurons with Pick bodies, whereas no positive cells are encountered in control brains processed in parallel. Moreover, p38-immunoprecipitated from sarcosyl-insoluble fractions in PiD brains is functionally active as it has the capacity to phosphorylate its specific substrate ATF-2. Combined biochemical, immunohistochemical and functional studies indicate that active p38 kinase is expressed in a very high percentage of Pick bodies, thus suggesting a critical role of this kinase in enhancing and perpetuating tau hyperphosphorylation in PiD.

Individual and regional variations of phospho-tau species in progressive supranuclear palsy

The purpose of this study was to learn about possible variations in phospho-tau profiles in terms of case-to-case differences, regional modifications and diversification of tau phosphorylation sites in five PSP cases with moderate to severe frontosubcortical dysfunction. Gel electrophoresis of sarkosyl-insoluble fractions and Western blotting with five anti-tau phospho-specific antibodies directed to phosphorylation sites Thr181, Ser202, Ser214, Ser396 and Ser422 were used to study four brain regions including frontal cortex, area 8, subcortical white matter of the frontal lobe, caudate/putamen: striatum, and basis pontis: pons. Although two bands of 66 and 62xa0kDa were observed in almost every region in each case, the intensity of the bands depends on the anti-tau phospho-specific antibody. More importantly, bands of 72, 50/55 and 37xa0kDa were commonly found in PSP brains, whereas other bands of about 60, 42, 33 and 29xa0kDa were irregularly observed. The pattern of bands differed slightly from one case to another and from one region to another. Moreover, the phospho-tau profile differed depending on the anti-tau phospho-specific antibody used. These data suggest that several species of tau are variably phosphorylated at a given time in a given region (and probably in a given cell), and that tau aggregates are composed of several phosphorylated truncated or cleaved tau molecules, in addition to phosphorylated complete tau isoforms.

N-Glycans and Glycosylphosphatidylinositol-Anchor Act on Polarized Sorting of Mouse PrP C in Madin-Darby Canine Kidney Cells

The cellular prion protein (PrPC) plays a fundamental role in prion disease. PrPC is a glycosylphosphatidylinositol (GPI)-anchored protein with two variably occupied N-glycosylation sites. In general, GPI-anchor and N-glycosylation direct proteins to apical membranes in polarized cells whereas the majority of mouse PrPC is found in basolateral membranes in polarized Madin-Darby canine kidney (MDCK) cells. In this study we have mutated the first, the second, and both N-glycosylation sites of PrPC and also replaced the GPI-anchor of PrPC by the Thy-1 GPI-anchor in order to investigate the role of these signals in sorting of PrPC in MDCK cells. Cell surface biotinylation experiments and confocal microscopy showed that lack of one N-linked oligosaccharide leads to loss of polarized sorting of PrPC. Exchange of the PrPC GPI-anchor for the one of Thy-1 redirects PrPC to the apical membrane. In conclusion, both N-glycosylation and GPI-anchor act on polarized sorting of PrPC, with the GPI-anchor being dominant over N-glycans.