Mutual interactions between telomere heterogeneity and cell culture growth dynamics shape stochasticity of cell aging

Mathematical modeling and computational simulations are often used to explain the stochastic nature of cell aging. The models published thus far are based on the molecular mechanisms of telomere biology and how they dictate the dynamics of cell culture proliferation. However, the influence of cell growth conditions on telomere dynamics has been widely overlooked. These conditions include interactions with surrounding cells through contact inhibition, gradual accumulation of non-dividing cells, culture propagation and other cell culture maintenance factors. In order to follow the intrinsic growth dynamics of normal human fibroblasts we employed the fluorescent dye DiI and FACS analysis which can distinguish cells that undergo different numbers of divisions within culture. We observed rapid generation of cell subpopulations undergoing from 0 to 9 divisions within growing cultures at each passage analyzed. These large differences in number of divisions among individual cells guarantee a strong impact on generation of telomere length heterogeneity in normal cell cultures and suggest that culture conditions should be included in future modeling of cell senescence.