Secretases as potential biomarkers and therapeutic target for Alzheimer’s disease
Alzheimer's disease (AD) is a neurodegenerative disorder characterized by a progressive loss of memory and cognition. The brain of AD patients is characterized by co-existence of amyloid plaques, extracellular protein deposits where the major component is the β-amyloid peptide (Aβ), and neurofi...
| Autor: | |
|---|---|
| Tipo de recurso: | tesis doctoral |
| Fecha de publicación: | 2018 |
| País: | España |
| Institución: | Universidad Miguel Hernández de Elche |
| Repositorio: | REDIUMH. Depósito Digital de la UMH |
| OAI Identifier: | oai:dspace.umh.es:11000/5096 |
| Acceso en línea: | http://hdl.handle.net/11000/5096 |
| Access Level: | acceso abierto |
| Palabra clave: | Neurobiologia molecular Bioquimica molecular Neurociencias CDU::6 - Ciencias aplicadas::61 - Medicina |
| Sumario: | Alzheimer's disease (AD) is a neurodegenerative disorder characterized by a progressive loss of memory and cognition. The brain of AD patients is characterized by co-existence of amyloid plaques, extracellular protein deposits where the major component is the β-amyloid peptide (Aβ), and neurofibrillary tangles (NFTs), composed of paired helical filaments of the microtubule-associated protein tau abnormally hyperphosphorylated (P-tau). The Aβ peptide is a small polypeptide generated by the proteolytic processing of a much larger transmembrane protein, the β-amyloid precursor protein (APP) through the successive action of two proteolytic enzymes, β-secretase and γ-secretase. γ-Secretase is an intramembranous multi-protein complex that cleaves more than 90 substrates, some of them with critical roles in neuronal function. Presenilin-1 (PS1) is the catalytic component of the γ-secretase complex. Our group has previously demonstrated the presence of PS1 in human cerebrospinal fluid (CSF) samples. Since the diagnosis for AD is mainly based on clinical symptoms, definition of an early biomarker for the disease is needed. Our present study further explores the potential of the levels of PS1 in human CSF as an early biomarker for AD. In this regard, we have analysed by Western blotting and sucrose gradients ultracentrifugation the levels of PS1 in CSF samples from symptomatic and asymptomatic genetically determined AD subjects (autosomal dominant AD: ADAD), from demented and non-demented Down Syndrome (DS) patients, from sporadic AD (sAD) and from mild cognitive impairment subjects (MCI), all compared to age-matched controls. We demonstrated an increase in high stable PS1 complexes and altered levels of CSF-PS1 in both symptomatic and asymptomatic ADAD subjects, in DS subjects with and without dementia and also in sAD and MCI subjects. We concluded that the occurrence of increased levels of high stable PS1 complexes in the CSF are more related to the brain pathological status than the occurrence of dementia and cognitive decline. Our results suggest that such increase is an early phenomenon associated to AD and may constitute an early and asymptomatic biomarker. Moreover, APP can undergo alternative processing pathways. Indeed, in the main pathway, the non-amyloidogenic pathway, APP is cleaved by α-secretase within the Aβ domain, precluding Aβ formation. We were also interested in characterize whether α- secretase ADAM10 (α-disintegrin and metalloprotease 10) is present in CSF. We found different ADAM10 species in human CSF. We identify by Western blotting two mature forms corresponding to the full length (ADAM10f) and the soluble form of ADAM10 (sADAM10), and also the immature form of the ADAM10 (proADAM10). In CSF samples from AD patients we found a significant decrease in mature forms, ADAM10f and sADAM10 compared to control CSF, while proADAM10 levels remained unaltered. Our data suggest the potential to explore decreased levels of mature forms of CSF-ADAM10 as a new and alternative biomarker for AD.Finally, we also extended our research on understanding the failure of γ-secretase inhibitors (GSI) as a therapy for AD. Most of the recently assayed AD therapies have not been successful to improve the condition of the patients. Some of these therapies aim to decrease the production of Aβ by inhibition of γ-secretase/PS1. Specifically, we addressed the possibility that GSIs can provoke a rebound effect, elevating the levels of the catalytic γ-secretase subunit, PS1. We performed in vitro experiments in which we obtained augments in PS1 after treatment with DAPT, a well-known GSI, or avagacestat, one of the first GSI that undergone clinical trials. We also performed in vivo experiments in which rats were sub-chronically treated with avagacestat. PS1 was increased in brain extracts from treated rats. In all the conditions, we found a rebound effect in PS1 as consequence of the γ-secretase inhibition. These results indicate that the rebound increase in PS1 in response to GSIs must be taken into consideration for the design of future therapeutic drugs. |
|---|