Mechanical stimuli differentially control stem cell behavior: morphology, proliferation, and differentiation

Abstract

Mesenchymal stem cell (MSC) therapy has demonstrated applications in vascular regenerative medicine. Although blood vessels exist in a mechanically dynamic environment, there has been no rigorous, systematic analysis of mechanical stimulation on stem cell differentiation. We hypothesize that mechanical stimuli, relevant to the vasculature, can differentiate MSCs toward smooth muscle (SMCs) and endothelial cells (ECs). This was tested using a unique experimental platform to differentially apply various mechanical stimuli in parallel. Three forces, cyclic stretch, cyclic pressure, and laminar shear stress, were applied independently to mimic several vascular physiologic conditions. Experiments were conducted using subconfluent MSCs for 5 days and demonstrated significant effects on morphology and proliferation depending upon the type, magnitude, frequency, and duration of applied stimulation. We have defined thresholds of cyclic stretch that potentiate SMC protein expression, but did not find EC protein expression under any condition tested. However, a second set of experiments performed at confluence and aimed to elicit the temporal gene expression response of a select magnitude of each stimulus revealed that EC gene expression can be increased with cyclic pressure and shear stress in a cell-contact-dependent manner. Further, these MSCs also appear to express genes from multiple lineages simultaneously which may warrant further investigation into post-transcriptional mechanisms for controlling protein expression. To our knowledge, this is the first systematic examination of the effects of mechanical stimulation on MSCs and has implications for the understanding of stem cell biology, as well as potential bioreactor designs for tissue engineering and cell therapy applications.

The role of mechanical stimuli in the vascular differentiation of mesenchymal stem cells

“…For example, bone-marrow-derived MSCs from a number of species are able to differentiate into endothelial-like cells when they are stimulated through physiological shear stress conditions (Engelmayr et al, 2006;Bai et al, 2010;Huang et al, 2010;Maul et al, 2011;Dong et al, 2009;Kim et al, 2011). Likewise, MSCs derived from human adipose tissue (hASCs) (Bassaneze et al, 2010;Zhang et al, 2011;Shojaei et al, 2013) and MSCs from other sources, such as amniotic fluid cells ) and human placenta (Wu et al, 2008), have also been shown to differentiate into endothelial-like cells under shear stress (see Table 1 for a summary).…”

“…Parallel-plate chambers are constructed by sandwiching a silicone gasket between the plate chamber and a glass slide that is seeded with cells. A peristaltic pump then drives the medium through the chamber in order to generate a 2D laminar shear stress on the cells (Wang et al, 2005;Wu et al, 2008;Bai et al, 2010;Maul et al, 2011). Orbital shakers (or rotating disks) rotate the medium-coated disk so that the medium flows concentrically, thus generating laminar or turbulent shear stress over cells that are seeded onto the bottom of the disk (Fischer et al, 2009;Zhang et al, 2009;Bassaneze et al, 2010).…”

“…Cyclic strain has also been used to induce other types of differentiation, such as differentiation into skeletal muscle cells (Haghighipour et al, 2012), neuron-like cells (Leong et al, 2012) and osteogenic lineages. It is worth noting that cyclic strain alone can evoke considerable expression of SMC markers, as well as upregulation of the osteoinductor bone morphogenic protein 2 (BMP-2) and the early matrix protein osteopontin (OPN) (Maul et al, 2011). In recent work, the role of cyclic strain intensity on MSC differentiation was investigated.…”

“…In vitro, both of these two mechanical cues can be replicated by different models, such as using a parallel-plate chamber for shear stress and a longitudinal stretch system for cyclic strain (see Box 1). MSCs are highly responsive to their mechanical environment, and different types of forces applied to the same MSC population result in divergent outcomes (Maul et al, 2011). Therefore, in this Commentary, we will summarize the available literature that describes a role for mechanical forces in the differentiation of MSCs into vascular cells and discuss different means to maintain differentiation.…”

Numerical modeling of cell differentiation and proliferation in force-induced substrates via encapsulated magnetic nanoparticles

“…This mutually dependent relationship between cells and their surrounding matrices is often referred to as dynamic reciprocity [13]. Consequently, besides other cell reactions [38,39,41], cells may respond to changes in their mechanical environment, such as changes in matrix rigidity, by undergoing differentiation and/or proliferation [13,43]. For instance, experiments have demonstrated that for soft matrices that resembling brain tissue (0.1-1 kPa) SCs differentiate to neurogenic cells, for intermediate matrices that mimicking cartilage tissue (20-25 kPa) they differentiate into chondrogenic cells, and comparatively hard matrices that mimic the tissue of collagenous bone (30-45 kPa) they differentiate into osteogenic cells [13,26,40,55].…”