The Influence of Vimentin Intermediate Filaments on Human Mesenchymal Stem Cell Response to Physical Stimuli

Abstract

Mesenchymal stem cells (MSCs) are increasingly being investigated as a therapeutic cell population for a variety of diseases. However, these therapies are limited by an imperfect understanding of how MSCs interact with and respond to their physical environment. Cell response to external stimuli is mediated by the cytoskeleton. Of the cytoskeletal proteins, understanding of vimentin intermediate filaments’ influence on MSC behavior is still lacking, despite increasing evidence that they are involved in many cellular processes. In this work, we investigated the influence of vimentin intermediate filaments in modulating MSC characteristics and behavior by using lentiviral shRNA transduction to decrease vimentin levels in MSCs through RNA interference. First, the contribution of vimentin intermediate filaments to the deformability of MSCs within agarose hydrogels was examined. Vimentin-deficient MSCs were found to be less deformable than control cell populations and this resistance to deformation may be due to the compensatory role of actin microfilaments. Next, to determine how vimentin affects the ability of MSCs to interact with various microenvironments, we examined cell spreading on different extracellular matrix proteins, multiple substrate stiffness’, and in response to fluid shear stress. An intact vimentin network was found to be necessary for unimpaired spreading on fibronectin, but only on stiffer substrates. Further, vimentin appears to be involved in resisting cell area changes in response to low fluid shear stress. Vimentin’s physical interaction with focal adhesions, rather than an impact at the transcriptional or translational level, may contribute to the cell spreading response observed. Finally, in the third part of this work, we examined the influence of vimentin on chondrogenic differentiation of MSC populations. Unexpectedly, we found that vimentin may not be involved in chondrogenic differentiation in late stage chondrogenic cultures. Instead, the culture condition-dependent microenvironment may have a greater impact, particularly in gene expression of matrix degrading enzymes and the αV integrin subunit. Altogether, these studies indicate a role for vimentin in the MSC response to physical stimuli. Moreover, this work furthers the dialogue surrounding MSCs’ interaction with different environments, the understanding of which will be critical for the development and evaluation of cell-based therapies.