Abstract

After budding yeast cells cultured in a nutrient-rich liquid medium with glucose ferment glucose to ethanol and then consume it as a carbon source, they enter the stationary phase of culturing and the process of their chronological aging begins. At that point, yeast cells in the culture arrest their cell cycle and enter a state of quiescence, also known as the G0 state. Shortly following such cell cycle arrest, the yeast culture begins to accumulate quiescent and non-quiescent cells. The Titorenko laboratory has recently used gradient centrifugation to purify the high- and low-density sub-populations quiescent and non-quiescent cells. They demonstrated that caloric
restriction, a robust aging-delaying (geroprotective) dietary intervention, decreases the concentrations of the neutral storage lipids triacylglycerols and increases the concentration of the mitochondrial membrane lipid cardiolipin in quiescent and non-quiescent cells. The studies described in my Thesis had the following two objectives. First, I sought to investigate how caloric restriction influences the concentrations of all lipid classes (not only triacylglycerols and cardiolipin concentrations) within the high- and low-density sub-populations of quiescent and nonquiescent yeast cells on different stages of the chronological aging process. My second objective was to compare the effects of caloric restriction, the tor1Δ mutation (a genetic geroprotective intervention) and lithocholic acid (a pharmacological geroprotective intervention) on the lipidomes
of the high- and low-density sub-populations of quiescent and non-quiescent yeast cells on different stages of chronological aging. To attain these objectives, I used liquid chromatography
coupled with tandem mass spectrometry quantitative lipidomics to assess the aging-associated changes in high- and low-density cells’ lipidomes. I provided the first evidence that caloric
restriction statistically significantly alters the concentrations of 18 different lipid classes through most of the chronological lifespan of high- and low-density cells. Caloric restriction decreased triacylglycerol concentration, increased free fatty acid concentration, raised ceramide concentration, and elevated phospholipid concentrations in high- and low-density cells through most of the chronological lifespan. My data also provided the first evidence that caloric restriction creates lipidomic patterns of chronologically aging high- and low-density cells that differ from the lipidomic patterns of these cells established by the tor1Δ mutation and lithocholic acid.