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Förslaget inkom 2006-09-25

Smac/Diablo and Omi/HtrA2 release from mitochondria during apoptosis in Alzheimer’s disease (AD)

Alzheimer's disease (AD) is a common neurodegenerative disease that leads to progressive dementia, resulting in amyloid- peptide (A) deposition in senile plaques and the formation of neurofibrillary tangles in the brain. Presenilin (PS) is an ~53 kDa integral membrane protein that spans the membrane 6-8 times. PS has two isoforms, PS1 and PS2, which was shown to increase their susceptibility to apoptosis. Mutations in the genes encoding PSs are known to cause early-onset familial AD. Previous studies show that PSs are primarily located in the endoplasmatic reticulum, cell membranes and in mitochondrial membranes. However the function of PSs in mitochondrial membranes is still unknown. It is believed that PS1 and PS2 constitute the catalytic subunit of the gamma-secretase responsible for the final step in Abeta biogenesis. X-linked inhibitor of apoptosis protein (XIAP) plays a crucial role in the regulation of apoptosis. XIAP binds to and inhibits caspases. The caspase-inhibitory activity of XIAP can be eliminated by Smac/DIABLO during apoptosis. When Smac is released from mitochondria into the cytosol; it interacts with the second and third BIR domains of XIAP and disrupts processed caspase-9 binding to XIAP; promoting caspase-3 activation, and potentiating apoptosis. In addition, in a recent study, Gupta et al demonstrated that the C-terminal of PS regulates Omi/HrtA2 activity. Omi/HrtA2 is a serine protease suggested to function as a sensor for unfolding stress proteins in Mt and inhibitor of IAPs. Upon apoptotic stimuli Omi/HtrA2 releases into the cytosol. Both Smac and Omi/HtrA2 release from mitochondria appears to be a general feature of apoptosis involving the mitochondrial pathway of cell death. The functional role of PS in Mt and its effect on Samc/DIABLO, Omi/HtrA2 and IAPs in AD are in some extent still unknown.
The functional role of PS in mitochondria and its effect on Samc/DIABLO, IAPs in AD are still unknown.

To study the effect of PS on Smac/DIABLO and Omi/HtrA2 release from mitochondria in Mouse Embryonic Fibroblasts (MEF), both wild type (wt) and presenilins knocked-out. PS is shown to regulate mitochondrial stress proteins through Omi/HtrA2 activity, this interaction is a potential target for blocking cell death induced by unfolded mitochondrial proteins. Therefore we will investigate whether the role of PS and PS mutations on Omi activity and its interaction to PSs in response to mitochondrial specific stress factors (H2O2, anti-mycin and 3-nitropropionic acid, 3-NP). In addition, we will investigate whether if PI3-kinase/Akt signalling pathway regulates Smac and Omi release in fibroblasts by using a PI3-inhibitor. Western blot, immunoprecipitation, cellular fractionation, flow cytometry and immunofluorescent staining (IFS) following confocal microscopy will be performed.

The mechanisms of cell death in the AD brain are not fully elucidated. However it is likely that several forms of cell death are involved. Several studies have shown an important role of PSs in this issue in different in vitro system. Here, we aim for an improved understanding of presenilin functions in mitochondria and its actions on cell death by in vitro studies. Furthermore, if the activity of Omi/HtrA2 can regulated by presenilins, the loss of activity or excess activity may cause mitochondrial dysfunction lead to neurodegentration. Thus, given the importance of presenilin, characterization of it and its associated proteins may provide important information and prove a useful targeting molecule in future AD therapy.


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