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The role of LAMP-2 in AβPP processing and Aβ degradation; implications for Alzheimer’s Disease
Linköping University, Department of Clinical and Experimental Medicine, Division of Cell Biology. Linköping University, Faculty of Medicine and Health Sciences.
Linköping University, Department of Clinical and Experimental Medicine, Division of Neuro and Inflammation Science. Linköping University, Faculty of Medicine and Health Sciences. CBD Solutions, Stockholm, Sweden.
Neuroscience Research Australia and University of New South Wales, Sydney, Australia.
Clinical Neurochemistry Laboratory, Department of Neuroscience and Physiology, Sahlgrenska University Hospital, Mölndal, Sweden / UCL Institute of Neurology, Queen Square, London, United Kingdom.
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2015 (English)Manuscript (preprint) (Other academic)
Abstract [en]

Dysfunction in the lysosomal network, i.e., the endosomal, lysosomal and autophagy systems, are implicated in the pathways in Alzheimer’s disease brain pathology. This dysfunction is mirrored in the cerebrospinal fluid where a specific subset of lysosomal network proteins are found at elevated levels, lysosomal associated membrane protein-2 (LAMP-2) being one of the identified lysosomal proteins. Here we report that hippocampus and frontal cortex in Alzheimer’s disease cases have increased mRNA and protein expression of LAMP-2, and thus these brain areas are likely involved in the increased LAMP-2 levels seen in cerebrospinal fluid from Alzheimer’s disease patients. The increased LAMP-2 levels correlated with increased levels of β-amyloid1-42 (Aβ1-42). Oligomeric Aβ1-42 caused an upregulation of intracellular LAMP-2 in neuroblastoma cells, but did not trigger the release of LAMP-2 to the extracellular milieu, indicating that other cell types or mechanisms are responsible for the LAMP-2 release seen in cerebrospinal fluid. Overexpression of LAMP-2 in neuroblastoma cells caused a trend of reduction of secreted Aβ1-42 and changed the processing pattern of the Aβ precursor protein. These results indicate that Aβ1-42 mediated increase of LAMP-2 expression can act as a regulator of Aβ generation and secretion. LAMP-2 overexpression did not change the cellular uptake of extracellularly added Aβ1-42, but caused a delayed clearance of Aβ1-42. Whether the prolonged intracellular localization of Aβ1-42 in LAMP-2 overexpressing cells can change the transmission or degradation of Aβ remains to be investigated.

Place, publisher, year, edition, pages
2015.
Keyword [en]
AβPP processing, Alzheimer’s disease, β-amyloid, autophagy, LAMP-2, lysosome
National Category
Cell and Molecular Biology Chemical Sciences
Identifiers
URN: urn:nbn:se:liu:diva-122345OAI: oai:DiVA.org:liu-122345DiVA: diva2:865689
Available from: 2015-10-29 Created: 2015-10-29 Last updated: 2015-10-29Bibliographically approved
In thesis
1. Lysosomal network proteins as biomarkers and therapeutic targets in neurodegenerative disease
Open this publication in new window or tab >>Lysosomal network proteins as biomarkers and therapeutic targets in neurodegenerative disease
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The pre-symptomatic stage of neurodegenerative diseases such as Alzheimer’s disease (AD) and Parkinson’s disease (PD) occurs several decades before the clinical onset. Changes in the lysosomal network, i.e. the autophagosomal, endosomal and lysosomal vesicular system, are among the first alterations observed. There are currently no treatments to slow or cure neurodegenerative diseases, and there is a great need for discovery of treatment targets in cellular pathways where pathology pre-dates the neuronal death. It is also crucial to be able to diagnose neurodegenerative diseases earlier, both to enable early intervention treatment and aid in selecting clinical trial populations before the patient has widespread pathology.

This thesis aims at investigating the potential of lysosomal network proteins as biomarkers and therapeutic targets in neurodegenerative disease.

A targeted search for lysosomal network proteins was performed in cerebrospinal fluid (CSF) from AD patients, and seven proteins: early endosomal antigen 1 (EEA1), lysosomal-associated membrane proteins 1 and 2 (LAMP-1, LAMP-2), lysozyme, microtubule-associated protein 1 light chain 3 (LC3), Rab3 and Rab7, were elevated. The levels of EEA1, LAMP-1, LAMP-2, LC3, lysozyme and Rab3 were also measured in CSF from parkinsonian syndrome patients: PD, clinically diagnosed 4-repeat tauopathy, pathologically confirmed corticobasal degeneration (CBD) and pathologically confirmed progressive supranuclear palsy (PSP) patients. LAMP-1 and LAMP-2 were decreased in PD. LC3 and lysozyme levels were increased in 4-repeat tauopathy patients. EEA1 was decreased and lysozyme increased in PSP, and LAMP-1, LAMP-2, LC3 and lysozyme were increased in CBD. The lysosomal network proteins had different CSF protein profiles in all the parkinsonian syndromes, as well as in AD. It should be emphasized that only a select few of the lysosomal network proteins were observed to be changed, rather than a general change in lysosomal network proteins, which implicates the involvement of these seven proteins in specific pathological processes. The most interesting candidates, LAMP-2 and lysozyme, were selected for further study for their involvement in the pathology of AD.

Lysozyme was found to co-localise with Aβ plaques in AD patients and overexpression prolonged survival and improved the activity in a Drosophila model of AD. Lysozyme was found to alter the aggregation pathway of Aβ1-42, to counteract the formation of toxic Aβ species and to protect from Aβ1-42 induced cell toxicity. Aβ1-42 in turn was found to increase the expression of lysozyme in both neuronal and glial cells. These data suggest that lysozyme levels rise in AD as a compensatory response which is protective against Aβ associated toxicity.

LAMP-2 mRNA and protein were found increased in brain areas relevant for AD pathology and various cellular models showed complex involvement of LAMP-2 in Aβ related pathology, with extensive crosstalk between LAMP-2 and Aβ. Exposure to oligomeric Aβ1-42 caused an upregulation of LAMP-2 and in turn, overexpression of LAMP-2 caused a reduction in secreted levels of Aβ1-42, as well as changing the generation pattern of Aβ and affecting clearance and secretion of Aβ1-42. These data indicate that the increased levels of LAMP-2 in AD could be an attempt to regulate Aβ generation and secretion.

In summary, this thesis reports that utilising lysosomal network proteins as biomarkers and novel therapeutic targets for neurodegenerative diseases holds great promise.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2015. 58 p.
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1492
Keyword
Cerebrospinal fluid (CSF), biomarkers, therapeutic targets, neurodegeneration, Alzheimer’s disease (AD), Parkinson’s disease (PD), Corticobasal degeneration (CBD), Progressive supraneuclear palsy (PSP), Lysosomes, Endosomes, Autophagy, LAMP-2, Lysozyme
National Category
Neurosciences Neurology Cell and Molecular Biology
Identifiers
urn:nbn:se:liu:diva-122347 (URN)10.3384/diss.diva-122347 (DOI)978-91-7685-897-4 (print) (ISBN)
Public defence
2015-11-26, Eken, Campus US, Linköping, 09:00 (Swedish)
Opponent
Supervisors
Available from: 2015-10-29 Created: 2015-10-29 Last updated: 2015-10-30Bibliographically approved

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