Optimality Conditions for Cell-Fate Heterogeneity That Maximize the Effects of Growth Factors in PC12 Cells

Recently, the heterogeneity that arises from stochastic fate decisions has been reported for several types of cancer-derived cell lines and several types of clonal cells grown under constant environmental conditions. However, the relation between this stochasticity and the responsiveness to extracellular stimuli remains largely unknown. Here we focused on the fate decisions of the PC12 cell line, which was derived from rat pheochromocytoma, and is a model system to study differentiation into sympathetic neurons. Whereas epidermal growth factor (EGF) stimulates the proliferation of populations of PC12 cells, nerve growth factor (NGF) promotes the differentiation of neurites to neuron-like cells. We found that phenotypic heterogeneity increased with time at several surrounding serum concentrations, suggesting stochastic cell-fate decisions in single cells. We made a simple mathematical model assuming Markovian transitions of the cell fates, and estimated the transition rates based on Bayes' theorem. The model suggests that depending on the serum concentration, EGF (NGF) even directs differentiation (proliferation) at the single-cell level. The maximum effects of the growth factors were ensured when the transition rates were appropriately controlled by the serum concentration to produce a nonextremal, moderate amount of cell-fate heterogeneity. Our model was validated by the experimental finding that the means and variances of the local cell densities obey a power-law relationship. These results suggest that even when efficient responses to growth factors are observed at the population level, the growth factors stochastically direct the cell-fate decisions in different directions at the single-cell level.Author Summary: Elucidation of the mechanisms that regulate cell fate has become one of the primary goals of research in cell biology and regenerative medicine. Growth factors are often used to regulate cell fate. However, stochastic cellular responses to growth regulators have prevented precise control of cell fate. We report our investigation of the relationship between heterogeneity and responsiveness in cell fate decisions by both single cells and populations of cells. Our study involved PC12, a cultured cell line for which cell-fates are affected by exposure to growth factors and culture conditions. Computational methods using a mathematical model enabled us to determine the cell-fate decisions rate in single PC12 cells and analyze the population responses to growth factors from experimental data. Our findings reveal that growth factors control cell-fate decisions rate in single PC12 cells, and suggest distinct differences in the mechanisms of actions of growth factors under different culture conditions. In addition, we observed maximum effects of growth factors when a nonextremal, moderate amount of cell-fate heterogeneity exists. Our results give several insights into stochastic cell responses, including the effects of anticancer agents on cancer cells and the optimization of methods to induce the differentiation of stem cells.