Mathematical modeling of biochemical influences and live cell imaging of biophysical influences on adiposederived mesenchymal stem cell behavior

Slater, John H.Stem cell therapy holds promise in treating and curing diseases that currently do not have efficacious treatment options. However, the most efficient method of differentiating stem cells is unknown. Here, we present two novel approaches to capture temporal behavior of stem cells. First, we quantify biochemical influences by developing a mathematical model that captures the differentiation behavior of stem cells over the course of two weeks and describes differentiation behavior using rate constants. Our cell differentiation is congruent with the media formulation (e.g. statistically significant osteogenesis occurs in osteogenic media and statistically significant adipogenesis occurs in adipogenic media). We use two modeling methods, maximum likelihood and least squares to extrapolate differentiation rate constants. We disprove the equal rates hypothesis for differentiation rates and show that the presence of one differentiation marker influences the ability of cells to develop a contrasting differentiation marker. While the differentiation rates do not clearly describe trends between differentiation in varying media, comparing the ratio of the rates show the dynamics . By looking at the ratio of rates we are able to describe which phenotype will dominate by describing how quickly each population of stem cells positive for one marker becomes positive for both. This model provides a basis to compare differentiation as a function of different biochemical and biophysical cues in terms of rate constants. Next, we characterize biophysical influences of ASC behavior, particularly adhesion site dynamics, using hydrogel substrates with stiffness values congruent with bone and fat. We show that while the number of adhesions between cells on different substrates are not statistically significant, the size of adhesions developed on soft and stiff substrates are. We prove our hypothesis that stem cells on stiff substrates develop large, stable adhesions that their counterparts on soft substrates cannot. This implies that cells on stiff substrates may be able to bear greater forces across adhesions and activate signaling pathways that cannot be activated on soft substrates.University of Delaware, Department of Biomedical EngineeringM.S