The inherent capacity of somatic cells to switch their phenotypic status in response to damage stimuli in vivo might have a pivotal role in ageing and cancer. However, how the entry-exit mechanisms of phenotype reprogramming are established remains poorly understood. In an attempt to elucidate such mechanisms, we herein introduce a stochastic model of combined epigenetic regulation (ER)-gene regulatory network (GRN) to study the plastic phenotypic behaviours driven by ER heterogeneity. Furthermore, based on the existence of multiple scales, we formulate a method for stochastic model reduction, from which we derive an efficient hybrid simulation scheme that allows us to deal with such complex systems. Our analysis of the coupled system reveals a regime of tristability in which pluripotent stem-like and differentiated steady-states coexist with a third indecisive state. Crucially, ER heterogeneity of differentiation genes is for the most part responsible for conferring abnormal robustness to pluripotent stem-like states. We then formulate epigenetic heterogeneity-based strategies capable of unlocking and facilitating the transit from differentiation-refractory (pluripotent stem-like) to differentiation-primed epistates. The application of the hybrid numerical method validated the likelihood of such switching involving solely kinetic changes in epigenetic factors. Our results suggest that epigenetic heterogeneity regulates the mechanisms and kinetics of phenotypic robustness of cell fate reprogramming. The occurrence of tunable switches capable of modifying the nature of cell fate reprogramming from pathological to physiological might pave the way for new therapeutic strategies to regulate reparative reprogramming in ageing and cancer.
Author summaryCertain modifications of the structure and functioning of the protein/DNA complex 1 called chromatin can allow adult, fully differentiated cells to adopt a stem cell-like 2 pluripotent state in a purely epigenetic manner, not involving changes in the underlying 3 DNA sequence. Such reprogramming-like phenomena may constitute an innate 4 reparative route through which human tissues respond to injury and could also serve as 5 a novel regenerative strategy in human pathological situations in which tissue or organ 6 repair is impaired. However, it should be noted that in vivo reprogramming would be 7 capable of maintaining tissue homeostasis provided the acquisition of pluripotency 8 features is strictly transient and accompanied by an accurate replenishment of the 9 specific cell types being lost. Crucially, an excessive reprogramming to pluripotency in 10 the absence of controlled re-differentiation would impair the repair or the replacement of 11 damaged cells, thereby promoting pathological alterations of cell fate. A mechanistic 12 understanding of how the degree of chromatin plasticity dictates the reparative versus 13 pathological behaviour of in vivo reprogramming to rejuvenate aged tissues while 14 preventing tumorigenesis is urgently needed, including especially th...