Abstract
Mesenchymal stem cell (MSC) differentiation is mediated by soluble and physical cues. In this study, we investigated differentiation-induced transformations in MSC cellular and nuclear biophysical properties and queried their role in mechanosensation. Our data show that nuclei in differentiated bovine and human MSCs stiffen and become resistant to deformation. This attenuated nuclear deformation was governed by restructuring of Lamin A/C and increased heterochromatin content. This change in nuclear stiffness sensitized MSCs to mechanical-loading-induced calcium signaling and differentiated marker expression. This sensitization was reversed when the 'stiff' differentiated nucleus was softened and was enhanced when the 'soft' undifferentiated nucleus was stiffened through pharmacologic treatment. Interestingly, dynamic loading of undifferentiated MSCs, in the absence of soluble differentiation factors, stiffened and condensed the nucleus, and increased mechanosensitivity more rapidly than soluble factors. These data suggest that the nucleus acts as a mechanostat to modulate cellular mechanosensation during differentiation.
Highlights
Mesenchymal stem cells (MSCs) are used in a variety of regenerative applications (Bianco et al, 2013)
From day 5 onward, there was no change in the nuclear aspect ratio (NAR) in differentiated MSCs (Diff) with scaffold stretch, while nuclear deformation persisted in undifferentiated MSCs (Ctrl, Figure 1b, c)
A similar effect, namely a reduction in nuclear deformation in response to stretch under differentiating conditions (Diff), was observed in both human bone marrow derived MSCs (Figure 1—figure supplement 2a–c) and in a human embryonic stem (ES) cell line (Figure 1—figure supplement 2d–e) treated
Summary
Mesenchymal stem cells (MSCs) are used in a variety of regenerative applications (Bianco et al, 2013). While considerable work has shown the importance of soluble differentiation factors in MSC lineage specification, recent studies have highlighted that physical signals from the microenvironment, including substrate stiffness (Engler et al, 2006), cell shape (McBeath et al, 2004), and dynamic mechanical cues (Huang et al, 2010a) can influence fate decisions. The manner in which soluble and physical cues are integrated to inform lineage specification and commitment is only just beginning to be understood (Guilak et al, 2009). One potentially confounding feature is that the physical properties of MSCs themselves likely change coincident with lineage specification, and such changes might alter cellular perception of super-imposed mechanical perturbations that arise from the microenvironment
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