Elsevier

Journal of Biomechanics

Volume 49, Issue 3, 8 February 2016, Pages 458-462
Journal of Biomechanics

Short communication
Aging enhances the vulnerability of mesenchymal stromal cells to uniaxial tensile strain-induced apoptosis

https://doi.org/10.1016/j.jbiomech.2015.11.053Get rights and content

Abstract

Mechanical priming can be employed in tissue engineering strategies to control the fate and differentiation pattern of mesenchymal stromal cells. This is relevant to regenerative medicine whereby mechanical cues can promote the regeneration of a specific tissue type from mesenchymal precursors. The ability of cells to respond to mechanical forces is dependent upon mechanotransduction pathways that involve membrane-associated proteins, such as integrins. During the aging process changes in the mechanotransduction machinery may influence how cells from aged individuals respond to mechanical priming.

In this study mesenchymal stromal cells were prepared from young adult and aged rats and exposed to uniaxial tensile strain at 5% and 10% for 3 days, or 2.5% for 7 days. Application of 5% tensile strain had no impact on cell viability. In contrast, application of 10% tensile strain evoked apoptosis and the strain-induced apoptosis was significantly higher in the mesenchymal stromal cells prepared from the aged rats. In parallel to the age-related difference in cellular responsiveness to strain, an age-related decrease in expression of α2 integrin and actin, and enhanced lipid peroxidation was observed.

This study demonstrates that mesenchymal stem cells from aged animals have an altered membrane environment, are more vulnerable to the pro-apoptotic effects of 10% tensile strain and less responsive to the pro-osteogenic effects of 2.5% tensile strain. Thus, it is essential to consider how aged cells respond to mechanical stimuli in order to identify optimal mechanical priming strategies that minimise cell loss, particularly if this approach is to be applied to an aged population.

Introduction

Mesenchymal stromal cells can be expanded in culture and mechanically primed towards specific lineages (Sonnaert et al., 2014). These cells are mechano-responsive and the application of mechanical stimuli has been demonstrated to control their differentiation (Kearney et al., 2010; Haugh et al., 2011).

Integrins are mechanosensitive proteins that activate downstream signalling to evoke a response to biophysical stimuli (Popov et al., 2011, Seong et al., 2013). In mesenchymal stem cells the α2 integrins anchor the cells to collagen I (Warstat et al., 2010) and regulate the osteogenic pathway (Kuo et al., 2012; Becerra-Bayona et al., 2012).

We have previously described how the application of cyclic uniaxial tensile strain can regulate the differentiation and viability of young adult rat mesenchymal stromal cells (Kearney et al., 2008, 2010; McMahon et al., 2008). With an increasingly aged population (Lutz et al., 2008) it is pertinent to examine how aged cells respond to biophysical stimuli. The aim of the current study was therefore to examine the effect of aging on the influence of tensile strain on the viability of aged mesenchymal stromal cells.

Section snippets

Culture of mesenchymal stromal cells

Mesenchymal stromal sells were prepared from 3-month old (250–300 g) and 22-month old (700–750 g) Wistar rats (Charles River (UK)), as previously described (Dominici et al., 2006). Animals were sacrificed by CO2 asphyxiation and cervical dislocation in accordance with European guidelines (86/609/EEC). The epiphyses of the femur and tibia were cut and the marrow was flushed out with Dulbecco’s modified Eagle’s medium supplemented with 10% foetal bovine serum (Gibco BRL, Dublin), 100 U/ml

Expression of α2 integrin in rat MSCs is decreased with age

A significant age-related reduction in expression of the α2 subunit of integrin was observed (Fig. 1(a)); (p<0.001, Student’s t-test, n=5). Distribution of α2 integrin in the plasma membrane was localised in dense regions around the membrane indicative of focal adhesion complex formations. Western immunoblot detected α2 integrin expression bands at 165 kDa and a significant 25% decrease in the expression of α2 integrin was observed in MSCs isolated from aged rats (p<0.05, Student’s t-test, n=4).

Expression of actin in MSCs is decreased with age

Discussion

The results of this study demonstrate an age-related reduction in the expression of α2 integrin and actin, in parallel with an age-related increase in lipid peroxidation. The data also demonstrate that MSCs from aged rats are more vulnerable to an induction of apoptosis following exposure to 10% strain. The lower tensile strain of 2.5% is able to evoke osteogenesis (Kearney et al., 2010) and this strain-mediated enhancement of osteogenesis is more pronounced in MSC isolated from young, compared

Conflicts of interest statement

None.

Acknowledgements

This work was funded by Science Foundation Ireland (08/RFP/ENM1361). KMcK was a recipient of a Trinity College Award.

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