Effect of cyclic compression on cytoskeleton remolding and cell matrix interaction of hMSCs encapsulated in three dimensional Type I collage matrix

Abstract

Recently, potential of determining stem cell fate through mechanoregulation has been demonstrated. However, the underlying mechanism remains largely unknown. Previously, we developed a microencapsulation technique to entrap cells in a nanofibrous collagen meshwork for mechanoregulation study of human mesenchymal stem cells (hMSCs). And we demonstrated that hMSCs initially randomly distributed within the construct reoriented towards a loading direction upon compression. Cytoskeleton, being the major sub-cellular machinery supporting cell shape and motility, play a crucial role in sensing and responding mechanical signals. Therefore, a better understanding in changes of cytoskeleton and associated molecules upon mechanical loading is a prerequisite to rationalizing the loading regimes for tissue engineering. In current project, we hypothesize that hMSCs encapsulated in 3D collagen construct respond to cyclic compression by remodeling of cytoskeleton structures and alternating the interactions with collagen matrix. hMSCs collagen construct were cyclically compressed for 9 hours through micromanipulator based compression system. And constructs were harvested either immediately, 2 hours and 24 hours after compression, together with non-loading control group. Here, we report compression-induced novel changes in cytoskeleton. Firstly, omnidirectional filopodia-like structures together with stress fibers bucking were observed immediately after 9hrs compression. Secondly, actin patches were observed 2 hours after compression. Apart from exhibiting similar morphology with filopodia, the omnidirectional filopodia-like structures may share a similar function in interacting with ECM. Co-localization of the major membrane-bound matrix metalloproteinases MT1-MMP along the length of the filopodia-like structures was observed. And a local collagen digestion zone, characterized by the presence of collagenase cleaved collage, was found co-localizing at least partially with the filopodia-like structures around the cell. Another interesting observation is the complete disassembly of pre-existing stress fibers followed by formation by numerous actin patches 2 hours after compression. Stress fibers reformed in 24 hours after removal of the loading. Quantitative measurement of F:G actin ratio agrees with such disassembly and reassembly dynamics. Moreover, colocalization of actin branching protein Arp2/3 with the actin patches was found, suggest that mechanical loaded hMSCs were re-establishing actin cytoskeleton network from these nucleation centers. In future, first, whether creation of pericellular collagen digestion zone was mediated by MT1-MMP along the compression-induced filopodia like structures and what functions the digestion zone served will be investigated. And, second, whether completely disassembly of preexisting actin structure facilitated subsequent structural reestablishment or served as anther function will also be studied.