Mechanisms of cell death in Alzheimer´s disease: Role of presenilin fragments generated during apoptotsis

Alzheimers disease (AD) is the most common form of dementia with an incidence increasing with age. Today there is no treatment for this devastating disease and therefore it is of great importance to investigate the underlying mechanisms for the progressive neuronal degeneration, with the aim to find new targets for potential future drugs. Most AD-cases are sporadic with an unknown etiology, however in 5-10 % of the cases the genetic background is known. Three genes have been identified i.e amyloid precursor protein gene (APP), presenilin 1 gene (PS1) and presenilin 2 gene (PS2). Several mutations have been identified on these genes and linked to
families with AD. Gamma- and beta secretase cleavage of the APP protein leads to the release of beta-amyloid forming fibrils and plaques which accumulates in the brain during the progression of AD. The presenilins have been shown to play an important role for the gamma-secretase activity linking the function of these proteins together. In the present study we are investigating how the presenilins are processed during normal conditions and after the induction of apoptosis. Apoptosis is a form of controlled cell death occurring both during physiological and pathological conditions. Apoptotic cells have been detected in the AD-brain and therefore apoptosis is likely to be one of the cell death mechanisms involved in the neurodegeneration. Full-length presenilin is rapidly cleaved into N- and C-terminal fragments that form a functional heterodimer. The protease responsible for this cleavage has not been identified and is called presenilinase. Presenilins are also cleaved by caspases, a group of cysteine proteases activated during apoptosis. This cleavage results in the formation of alternative PS-fragments. The role of such fragments during the apoptotic process is presently unclear.
The project we propose for a 20 weeks diploma work is a continuation of this study with focus on the potential protective or toxic effect of alternative PS-fragments. For these studies we are using blastocyst lacking both PS1 and PS2. This PS null-background gives us the possibility to transfect these cells with PS1 fragments and study their effects on cell survival. Methods used include for example: cell culture, transfections, immunoblotting, toxicity assays and detection of apoptotic cells using confocal microscopy. The work is performed at Karolinska Institutet, Neurotec, Section for Experimental Geriatrics, Novum, Huddinge.