Abstract

Aging is a multifactorial process that occurs in all biological organisms. The biological aspects of aging are evolutionary conserved across eukaryotes. Saccharomyces cerevisiae being a unicellular eukaryote has been used as a model organism to study aging. This unicellular eukaryote has a short lifespan, a fully sequenced genome and it is easy to manipulate genetically to make changes in metabolic pathways. Hence, it has been historically used to identify genes, metabolic pathways and chemical compounds that have influence on aging process. An extract from white willow bark (which is called PE21) was discovered in Dr. Vladimir Titorenko’s lab as the plant extract capable of extending the chronological lifespan (CLS) of Saccharomyces cerevisiae. Previous studies in the lab have shown that PE21 considerably alters the lipid composition of Saccharomyces cerevisiae. Lipids play crucial roles in many important pathways related to cellular signaling network, energy storage, membrane trafficking, membrane dynamics and apoptosis. Lipidomics is a relatively new research field that aims at characterizing lipid profiles. The characterization of lipids is a difficult process because of their diverse chemical and physical properties and due to lack of sensitive tools to study them. Only with the advent of mass spectrometry it became possible to characterize individual lipid species of various lipid classes. Herein, I have developed an optimized LC-MS/MS method to successfully identify and quantify many individual species of 10 different lipid classes of Saccharomyces cerevisiae. The developed method was used to analyze the effects of PE21 on the lipid composition of Saccharomyces cerevisiae. Our findings support previous studies, which stipulate that PE21 alters the lipid composition of yeast cells. PE21 markedly decreases the concentration of free fatty acids, thus it has been hypothesized that PE21 increases the CLS of yeast cells by decreasing the rate of liponecrosis known to be induced by free fatty acids. To further test this hypothesis, four single gene-deletion mutant strains differently affected in the metabolism of free fatty acids have been studied. More specifically, the lipid compositions and viabilities of such mutant strains were analyzed in yeast cultured in the presence or absence of PE21, and the results were compared to the results for wild-type strain.