A proteomic study on the effect of polyphenolic extract from extra-virgin olive oil on a yeast model of aging

Saccharomyces cerevisiae can serve as a model to study the molecular mechanism underlying human neurodegenerative diseases and aging [1, 2]. In this study, a S. cerevisiae strain that express a glutamine repeat domain (103Q) of Huntingtin, the causing agent of protein misfolding leading to Huntington disease (HD), has been used for monitoring the effect of a polyphenol extracts from extra-virgin olive oil (EVOO) on neurodegeneration. In fact, it is well known that olive polyphenols such as tyrosol, hydroxytyrosol, and their complex derivatives exert a protective effect against oxidative damage, one of the main factors associated with age-related pathologies. At this purpose, the chronological aging of yeast strain 103Q, has been monitored in comparison with the wild type strain (GFP) by assessing the cell viability and the proteomic pattern. Polyphenols, after their extraction from EVOOs, have been introduced in the culture broth of both 103Q and GFP strains. Cells from both strains were harvested 6 (young), 15 (adult) and 26 (old cells) days after inoculation and the protein expression was evaluated in both strains by two-dimensional electrophoresis (2DE), consisting of a first dimension on an immobilized pH gradient 3-10 gel (Immobiline DryStrip gel, 18cm, GE Healthcare) and a second dimension through a 13% SDS-PAGE [3]. After electrophoresis, the silver stained gel was subjected to image analysis (by the PDquest software) and to mass spectrometry for protein identification. As a result, we found that polyphenols induce the expression of several proteins both in the neurodegeneration model (103Q) and in the controls (GFP). Until now, two spots were identified, one as "hypothetical protein AWRI1631_45230" [S. cerevisiae AWRI1631], and the other one as "YOR012W-like protein" [S. cerevisiae AWRI796], whose function is not known. Interestingly, in the system where huntingtin is expressed (103Q), we found a protein region, with a broad molecular weight (MW) around 22.2 kDa, and an isoelectric point (pI) of 3.8 which decreases after the administration of polyphenols. Ocampo and co-workers [2], during immunoblotting experiments performed to follow the induced 103Q expression and oligomerization, found the presence of degradation products at low molecular weight (about 35 kDa). With this in mind, we could speculate that the protein region showing the broad molecular weigh observed in our experiments may be a degradation product of the 103Q protein. Obviously, further studies should be carried out in order to validate this hypothesis. In conclusion, the results of the present study are very encouraging, and we can conclude that the yeast model of neurodegeneration proved to be a very promising system for the evaluation of antioxidant/nutraceutical substances efficacy towards neurodegenerative diseases. References: [1] Mortimer R.K., Johnston J.R. Life span of individual yeast cells. Nature. 1959; 183:1751-1752. [2] Ocampo A., Liu J. and Barrientos A. NAD salvage pathway proteins suppress proteotoxicity in yeast models of neurodegeneration by promoting the clearance of misfolded/oligomerized proteins. Hum Mol Genet. 2013;22:1699-1708. [3] S. Vincenzetti, A. Amici, S. Pucciarelli, A. Vita, D. Micozzi, F. M. Carpi, V. Polzonetti, P. Natalini, P. Polidori. A Proteomic Study on Donkey Milk. Biochem Anal Biochem. 2012; 1, 109.