No abstract

Fractional killing illustrates the cell propensity to display a heterogeneous fate response over a wide range of stimuli. The interplay between the nonlinear and stochastic dynamics of biochemical networks plays a fundamental role in shaping this probabilistic response and in reconciling requirements for heterogeneity and controllability of cell-fate decisions. The stress-induced fate choice between life and death depends on an early adaptation response which may contribute to fractional killing by amplifying small differences between cells. To test this hypothesis, we consider a stochastic modeling framework suited for comprehensive sensitivity analysis of dose response curve through the computation of a fractionality index. Combining bifurcation analysis and Langevin simulation, we show that adaptation dynamics enhances noise-induced cell-fate heterogeneity by shifting from a saddle-node to a saddle-collision transition scenario. The generality of this result is further assessed by a computational analysis of a detailed regulatory network model of apoptosis initiation and by a theoretical analysis of stochastic bifurcation mechanisms. Overall, the present study identifies a cooperative interplay between stochastic, adaptation and decision intracellular processes that could promote cell-fate heterogeneity in many contexts.

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Living cells use signaling and regulatory mechanisms to adapt to environmental stresses. In the case of oxidative stress due for instance to hydrogen peroxide exposure, the adaptation response relies on co-regulation of enzymes in both glycolysis and pentose phosphate pathways (PPP), so as to support PPP-dependent NADPH and redox homeostasis. To understand the regulatory logic underlying early oxidative stress response, available metabolomics and 13C fluxomics dataset are used to infer a probabilistic ensemble of kinetic models. Model ensemble properties of parameter distributions, transient dynamics, dose-response curves and loss-of-function phenotypes all highlights significant and cooperative effects of allosteric regulations of G6PD, PGI and GAPD in early oxidative response. Indeed, efficient flux rerouting into PPP is shown to require dose-dependent coordination between upregulated G6PD enzyme and increased G6P metabolite, the latter requiring fine-tuned inhibition of upper and lower glycolytic enzymes. This set of allosteric regulation also combines negative and positive feedback loops in a subtle manner prone to generate paradoxical perturbation phenotypes for instance related to 6PGD modulation.