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Role of the 39-kDa receptor-associated protein (RAP) in Alzheimer's disease


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Hoang, T 2012 , 'Role of the 39-kDa receptor-associated protein (RAP) in Alzheimer's disease', Research Master thesis, University of Tasmania.

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Alzheimer’s disease (AD) is the most common form of dementia that gradually worsens over time and leads to death. AD is characterized by an accumulation of β-amyloid protein (Aβ) in the brain. Recently, the 39-kDa receptor-associated protein (RAP) has been implicated in the AD pathology. RAP is found mainly in endoplasmic reticulum (ER) and functions as a chaperone for the maturation and trafficking of the low density lipoprotein (LDL) receptor family. Polymorphisms in the RAP gene have been associated with an increased risk of AD. Two studies have shown that down-regulation of RAP expression exacerbates Aβ pathology in transgenic mouse models of AD, suggesting that RAP may have an important role in Aβ production and clearance. It has been also shown that RAP binds strongly to Aβ, leading to an inhibition of Aβ aggregation and neurotoxicity. Furthermore, a recent study has shown that the level of RAP expression is significantly decreased in the AD brain compared with healthy controls.

This study aimed to identify the region of RAP which binds to Aβ and the effect of RAP over-expression and treatment on APP metabolism and Aβ production. The possibility that Aβ can bind to RAP in the human CSF was also examined. To determine the Aβ-binding region on RAP, an in-vitro assay was established and validated to study Aβ-self association, based on the binding of biotin labelled Aβ42 to synthetic Aβ42 seeded in the wells of microplates. The Aβ-binding region on RAP was identified by measuring Aβ-self association in the presence of different RAP fragments. The results indicated that the Aβ-binding site was located between amino acid residues 206 and 216 of the RAP sequence in loop region between domains D2 and D3. To examine the effect of RAP on APP metabolism, two strategies were used. The first strategy involved over-expression of RAP in sweAPP-CHO and sweAPP-SH-SY5Y cells, after which the effect of RAP on APP processing and Aβ production was analysed. As a second strategy, the effect of RAP on APP metabolism was examined in primary cortical neurons derived from Tg2576 transgenic mice. The results showed that over-expression or treatment of RAP had no significant effect on the level of total APP. However, the levels of sAPPβ, C99 and Aβ were decreased and the production of C83 was significantly increased in RAP-transfected cells. The results suggest that RAP could decrease Aβ production by decreasing β-cleavage. Therefore, a decreased level of RAP in the brain could contribute to the pathogenesis of AD. Attempts to determine if Aβ can bind with RAP in the human CSF were not successful; the preliminary results, however, suggested that Clusterin/CLU is the main Aβ-binding protein in the human CSF. Taken together, these data suggest that RAP is a protective factor against Alzheimer’s disease.

Item Type: Thesis - Research Master
Authors/Creators:Hoang, T
Keywords: receptor-associated protein, RAP, Alzheimer's disease
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Copyright 2012 the author

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