Macromolecular Crowding Directs Extracellular Matrix Organization and Mesenchymal Stem Cell Behavior.pdf

Macromolecular Crowding Directs Extracellular Matrix Organization and Mesenchymal Stem Cell Behavior Adam S. Zeiger1,2, Felicia C. Loe2,3,4, Ran Li5, Michael Raghunath2,3,6*, Krystyn J. Van Vliet1,2* 1 Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States of America, 2 Biosystems and Micromechanics Interdisciplinary Research Group (BioSyM), Singapore-MIT Alliance in Research and Technology (SMART), Singapore, Singapore, 3 Tissue Modulation Laboratory, Division of Bioengineering, Faculty of Engineering, National University of Singapore, Singapore, Singapore, 4 Graduate Programme in Science and Integrative Engineering (NGS), The National University of Singapore, Singapore, Singapore, 5 Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States of America, 6 Department of Biochemistry, Yong Loo Ling School of Medicine, Singapore, Singapore Abstract Microenvironments of biological cells are dominated in vivo by macromolecular crowding and resultant excluded volume effects. This feature is absent in dilute in vitro cell culture. Here, we induced macromolecular crowding in vitro by using synthetic macromolecular globules of nm-scale radius at physiological levels of fractional volume occupancy. We quantified the impact of induced crowding on the extracellular and intracellular protein organization of human mesenchymal stem cells (MSCs) via immunocytochemistry, atomic force microscopy (AFM), and AFM-enabled nanoindentation. Macromolecular crowding in extracellular culture media directly induced supramolecular assembly and alignment of extracellular matrix proteins deposited by cells, which in turn increased alignment of the intracellular actin cytoskeleton. The resulting cell- matrix reciprocity further affected adhesion, proliferation, and migration behavior of MSCs. Macromolecular crowding can thus aid the design of more physiologically rele