|M.Sc Student||Toidman Polina|
|Subject||The Role of ARTS in Neuronal Apoptosis|
|Department||Department of Medicine||Supervisor||PROFESSOR EMERITUS John Finberg|
|Full Thesis text|
ARTS is a 32 kDa pro-apoptotic member of the septin family. In many peripheral cell lines, ARTS localizes to the mitochondria and upon commencement of apoptotic stimuli it translocates to the cytosol and inhibits XIAP. Subsequently it translocates to the nucleus where its role is unknown. Its levels are regulated through ubiquitin-mediated protein degradation. It is known that ARTS is highly expressed in the brain, however its role in this organ is unclear. Therefore, the focus of this work was the characterization and investigation of neuronal ARTS expression in the rat brain and primary neuronal cultures.
We examined ARTS expression in vitro using primary neuronal cultures that were exposed to various insults. In vivo we used the Parkinson’s disease rat model of 6-hydroxydopamine injection into the left medial forebrain bundle. We assessed ARTS levels using Western blot analysis. ARTS cDNA sequence was obtained using RT-PCR technique. Proteosomal inhibition was performed using MG 132 and neuronal ARTS subcellular localization was determined using confocal microscopy.
We found that in primary neurons ARTS levels are upregulated as a result of trophic factor withdrawal but not as a result of Etoposide exposure. In vivo we did not find a significant difference in ARTS levels in the injected side in comparison with the control side of the brain after 3 or 7 days post injection. Moreover, when striatal ARTS levels were examined in rats with dopaminergic depletion, no difference was detected between the two sides. We also found that in rat primary neurons and brain regions, ARTS is expressed in a shorter form (25 kDa) that lacks part of the N terminal amino acid sequence in comparison with the full length ARTS in peripheral cells although, the full length mRNA sequence is found in neurons. Moreover, no additional ARTS variant appeared as a result of proteosome inhibition. Furthermore, it seems that in neurons ARTS levels are not regulated by cytosolic proteosome degradation, since we have found that in neurons this protein is localized mainly to the nucleus.
In summary, since ARTS form and subcellular localization is different in neurons than in peripheral tissues, it can not participate in the same signaling pathway and it can not be regulated by the same mechanism as the variant that is found in the peripheral tissues. Therefore, ARTS does not consistently behave as a pro-apoptotic protein, but may have additional physiological roles in the nervous system.