Noisy-threshold control of cell death

Cellular responses to death-promoting stimuli typically proceed through a differentiated multistage process, involving a lag phase, extensive death, and potential adaptation. Deregulation of this chain of events is at the root of many diseases. Improper adaptation is particularly important because it allows cell sub-populations to survive even in the continuous presence of death conditions, which results, among others, in the eventual failure of many targeted anticancer therapies. Here, I show that these typical responses arise naturally from the interplay of intracellular variability with a threshold-based control mechanism that detects cellular changes in addition to just the cellular state itself. Implementation of this mechanism in a quantitative model for T-cell apoptosis, a prototypical example of programmed cell death, captures with exceptional accuracy experimental observations for different expression levels of the oncogene Bcl-xL and directly links adaptation with noise in an ATP threshold below which cells die. These results indicate that oncogenes like Bcl-xL, besides regulating absolute death values, can have a novel role as active controllers of cell-cell variability and the extent of adaptation.

💡 Research Summary

The paper proposes that the characteristic multistage response of cells to death‑inducing stimuli—comprising an initial lag phase, a rapid death burst, and a later adaptation phase—emerges naturally from the interplay between intracellular stochastic variability and a threshold‑based control system that senses not only the absolute state of the cell but also changes in that state. To test this hypothesis, the author builds a quantitative model of T‑cell apoptosis in which intracellular ATP concentration serves as the primary death determinant. ATP is modeled as a stochastic process (an Ornstein‑Uhlenbeck process) that fluctuates over time, while a death signal is triggered when ATP falls below a threshold θ. Crucially, θ is not fixed; it shifts linearly with the expression level of the anti‑apoptotic oncogene Bcl‑xL (θ = θ₀ – α·