Thesis of Julien Hurbain

Thesis  of Julien Hurbain - laboratoire PhLAM

Abstract :

Living cells such as mammalian cells in particular, are continuously exposed to multiple and varied types of stress. These stresses can perturb the cellular homeostasis and induce damages on the cellular components which could induce several types of diseases. It is particularly the case for a change of cellular redox state called oxidative stress induced by an excessive production or insufficient consumption of reactive oxygen species such as hydrogen peroxide (H2O2).
Cells have developed efficient defence mechanisms against oxidative stress that involve anti-oxidant systems such as glutathiones which reduce the oxidizing molecules, but also metabolic pathways such as Pentose Phosphate Pathway (PPP) and glycolysis. These metabolic pathways are known to reroute the carbon flux resources from the glycolysis toward the PPP which induces high NADPH recycling that is required for efficient detoxification rate of the anti-oxidant systems. It remains however unclear how regulatory mechanisms (i) contribute to such reallocation of metabolic flux resources during oxidative stress and (ii) give rise to observed adaptation profiles of intracellular H2O2 concentrations. In the thesis, the role of regulations in the metabolic response to oxidative stress is addressed using a comprehensive kinetic modeling framework. First, a model is built from a set of metabolomics and 13C labeling data, using conventional parameter estimation methods but also a novel metabolic flux analysis techniques based on a stochastic simulation algorithm. Systematic analysis of the model reveals that many metabolic inhibitions, especially on G6PD, PGI and GAPD, can favour flux rerouting for NADPH production. In particular, we show that all these regulations work in a dose-dependent and complementary manner, which explains some paradoxes and controversies, and is consistent with observed adaptation phenotypes. A more phenomenological model has also been developed to show how such adaptation phenotype could contribute to cell-fate heterogeneity, such as fractional killing, as a long-term outcome of oxidative stress.

Keywords : cell,stress,modeling,Regulation,Adaptation