Forces Behind Cell Adhesion and Migration in Microgravity

Abstract

Cells sense and respond to their environment according to many factors, including gravity. Changes in the gravitational field during space exploration may alter cellular interactions. Our understanding of the fundamental mechanisms by which gravitational forces ultimately affect cell function, however, is limited. Based on our prior observations, human mesenchymal stem cells (hMSCs) adopt a more rounded morphology during simulated microgravity (clinorotation). We hypothesize that microgravity affects the cell-substrate forces, which in turn affects cell adhesion and motility. Therefore, we investigated the correlation between traction forces, spreading and chemotaxis. As an extension to our previously reported “clinochip” device, we developed a lab-on-a-chip device suitable for implementing traction force microscopy during clinorotation. The device contains a channel coated with an array of fluorescent beads embedded in a polyacrylamide substrate that can be processed to calculate cell-substrate traction forces. For our studies, we investigated both hMSCs and osteosarcoma cancer cells (143-B), because they represent highly regulated and deregulated cell states in the osteogenic lineage, respectively. Clinorotation speeds of 0, 30, and 75 rpm were examined, and cell shape, adhesion area, traction forces, and chemotactic migration were measured. Interestingly, results indicate that hMSCs exhibit a dose-dependent response to clinorotation speed based on a shift in the population distribution of cell shape and adhesion area, while osteosarcoma cells do not. These results suggest that a deregulated cell phenotype may possess distinct mechanosensing characteristics, which may be related to our measures of cell adhesion, traction and chemotaxis. Our results are among the first efforts to directly measure the physical interplay between the cell and its substrate during simulated microgravity. This will allow us to gain a deeper understanding of the cellular mechanisms that lead to tissue-level changes, such as atrophy and reduced bone mineral density, observed in astronauts.