Eunyong Ahn, Ph.D. Thesis Seminar
Cellular metabolic demands change throughout the cell cycle. Nevertheless, a characterization of how metabolic fluxes adapt to the changing demands throughout the cell cycle is lacking. The rate of metabolic reactions and pathways in living cells, also referred to as metabolic flux, is not a directly measurable quantity. The most direct approach for quantifying intracellular metabolic flux is isotope tracing coupled with computational metabolic flux analysis. This has become a central technique in studies of cancer cellular metabolism. A fundamental limitation in our understanding of cellular metabolism is having no information on cell-cell variability in metabolic activity. Standard isotope tracing techniques are applied on a population of cells that are heterogeneous in terms of cell-cycle phase, providing no information on alterations in metabolic flux throughout the cell-cycle - practically aiming to estimate the ¡°average¡± flux through the cell population.
Here, we developed a temporal-fluxomics approach to derive a comprehensive and quantitative view of alterations in metabolic fluxes throughout the mammalian cell cycle. This is achieved by combining pulse-chase LC-MS based isotope tracing in synchronized cell populations with computational deconvolution and metabolic flux modelling. We find that TCA cycle fluxes are rewired as cells progress through the cell cycle with complementary oscillations of glucose versus glutamine-derived fluxes: Oxidation of glucose-derived flux peaks in late G1 phase while oxidative and reductive glutamine metabolism dominates S phase. These complementary flux oscillations maintain a constant production rate of reducing equivalents and oxidative phosphorylation flux throughout the cell cycle. The shift from glucose to glutamine oxidation in S phase plays an important role in cell cycle progression and cell proliferation.