Coupling of Chemical and Mechanical Sensing in Fibroblast Cells

Cells constantly sense their local chemical environment and make decisions based upon the information received. This chemosensing process, although stochastic on the individual cell level, exhibits highly regulated responses in multicellular organisms. Two key features, intercellular communication and first-responder cells, define this process. To understand the collective behavior induced by these two factors, we culture fibroblast cells inside a PDMS-on-glass channel, to which we deliver ATP solution, and study their calcium dynamics in response to the chemical stimulation. We demonstrate the existence of first-responder cells and how the presence of gap junctions influences the first step of the collective response, in that there are correlations in the response of neighboring cells. In addition, we investigate the effect of mechanical environment on a colony's response by studying cell responses when encapsulated in thin hydrogel films. By comparing the results from when the cells are cultured on glass to hydrogel-embedded cells, where intercellular communication is only possible via diffusing molecules, we find that (i) persistent calcium oscillations of individual cells occur only for cells embedded in hydrogel, and (ii) a colony of hydrogel-embedded cells show no synchronization. The fraction of a colony that responds to ATP increases with hydrogel elasticity and ATP concentration. For those cells that oscillate, we find that at high ATP concentration (>40 μM) cells inside a stiffer gel have fewer oscillations than those inside a softer gel. The distributions of oscillation periods have modes that are decreasing with increasing ATP concentration. Our observations and measurements highlight the role of mechanical environment for influencing spatial and temporal dynamics in cell colonies and tissues.