The overall goal of this award is to understand at a fundamental level how neurons migrate and axons elongate as a function of the mechanical properties of the substrate. This research will be divided into three specific goals. First: measurement of neuron spreading and motility as a function of the stiffness of the substrate. Second: measurement of axon elongation, from neurite up to synapse formation, as a function of the substrate compliance. Third: tailoring of substrate compliance and chemical composition to direct axon elongation. The results of this research will yield a quantitative understanding of neuron development and axon outgrowth as a function of the mechanical properties of the substrate.
The knowledge acquired in this research will allow for precise tailoring of the mechanical properties of substrates to direct the growth of axons, which could be used for axon regeneration after trauma in the peripheral and central nervous system. This award will develop educational programs at the graduate, undergraduate, and high school levels. This proposal will implement international collaborations as well. At the graduate and undergraduate level a new course on Cell Mechanics will be developed. A summer cell mechanics research program will be developed for high school students. This program will introduce high school students to the interdisciplinary field of bioengineering with specific emphasis on the effect of substrate stiffness on cell mechanics and motility. Ongoing collaborations with Mexico will allow for a one week course on cell mechanics for undergraduate students.
1) Contrary to many cells that 'feel' the stiffness of the substrate, we have demonstrated that neurons from the central nervous system cannot sense differences in the mechanical properties of the substrate. We also showed that neurons from the peripheral nervous system can sense the mechanical properties of the substrate. 2) We have shown that neutrophils transmigrate through the endothelium as a function of the contractility of the endothelium, which is higher on stiffer substrates. This results could indicate that leukocytes transmigrate more on atherosclerotic lessions. 3) Similarly to 2, we showed that neutrophils transmigrate more when the endothelium is exposed to oxidized LDL. 4) We demonstrated that endothelial cells change morphology, cytoskeleton distribution, dynamics, stiffness, and traction forces when exposed to inflammatory signals. 5) Our results have demonstrated that some cells spread initially by attaching cellular blebs, but then these blebs inhibit the continuous spreading of the cell. Although others have reported on the effect of blebs on spreading, this is the first quantitative study of this effect. 6) Our results have demonstrated that neutrophils have a biphasic behavior as a function of substrate stiffness. Many have published work on how substrate stiffness affects cell behavior. Our work shows for the first time a biphasic behavior of cells.
