Kidd, E and Good, M (2012-2014) The involvement of lipis raft proteins in the processing of amyloid precursor protein. BRACE. £132,432 (Cardiff Funding: £132,431)
Summary
β-Amyloid (Aβ) is cut out from a large protein, amyloid precursor protein (APP), by two enzymes, β-secretase and γ-secretase. The location of these events within the cell and how they are affected in Alzheimer’s disease (AD) is not well understood. Improving our understanding of Ab production is vital so that new therapies to reduce Aβ can be developed. We have been studying the importance of three proteins called caveolins-1, -2 and -3 to the conversion of APP to Aβ. These proteins are found in particular types of structures called lipid rafts which are regions of the outer layer of a cell (the cell membrane) containing high levels of cholesterol and fats. APP, β-secretase and γ-secretase are all found here. Caveolins may be important in AD as higher levels have been found in the brains of people suffering from AD than in people without AD. In our first pilot grant funded by BRACE, we have shown that reducing the levels of caveolin-1 in cells increases the production of Aβ suggesting that caveolins may keep APP and its enzymes apart in different compartments in the cell. Furthermore, we have also found that caveolin-3 and another lipid raft protein, flotillin-1, are both increased in cells with less caveolin-1. We now need to investigate the mechanisms behind these findings.
Hypothesis: We propose that caveolins control the location of APP in cells relative to β- and γ-secretase thus controlling the amount of Ab cells can make. To investigate further the interaction we have identified between flotillins and caveolins, we will firstly study the effects of increasing and decreasing the levels of the flotillin proteins on APP metabolism and caveolin protein levels in tumour cells which originated from brain cells. Then we will examine whether the effects of caveolins on Ab are dependent on the integrity of lipid rafts as caveolins are also found elsewhere in cells and have other functions. We will disrupt lipid rafts and look at the levels of caveolins and flotillins and APP metabolism and whether the consequences of changing caveolin levels are affected. Finally, we will perform key experiments in brain cells called neurones from a mouse model for AD which has higher levels of Aβ than normal and displays several features of AD seen in people. These cells represent a more physiologically relevant model of conditions likely to be present in AD. We will compare neurones from the mice with high levels of Ab with those from normal mice and measure levels of caveolins and flotillins. Then we will manipulate the amounts of caveolins and flotillins made by these cells and see how this affects APP and Aβ and whether the higher starting levels of Ab from the AD neurones make a difference to how these proteins interact. Importantly, this study will help to determine the pathophysiological relevance of our findings to the disease process and will facilitate the identification of therapeutic targets based around lipid rafts.