Engineering the geometrical shape of mesenchymal stromal cells through defined cyclic stretch regimens

Abstract

Stem cells have been predicted to improve disease outcomes and patient lives. Steering stem cell fate - through controlling cell shape - may substantially accelerate progress towards this goal. As mesenchymal stromal cells (MSCs) are continuously exposed in vivo to a dynamically changing biomechanical environment, we hypothesized that exogenous forces can be applied for engineering a variety of significantly different MSC shapes. We applied specific cyclic stretch regimens to human MSCs and quantitatively measured the resulting cell shape, alignment, and expression of smooth muscle (SMC) differentiation markers, as those have been associated with elongated morphology. As proof of principle, a range of different shapes, alignments, and correlating SMC marker levels were generated by varying strain, length, and repetition of stretch. However, the major determinant of biomechanically engineering cellular shape was the repetition of a chosen stretch regimen, indicating that the engineered shape and associated differentiation were complex non-linear processes relying on sustained biomechanical stimulation. Thus, forces are key regulators of stem cell shape and the targeted engineering of specific MSC shapes through biomechanical forces represents a novel mechanobiology concept that could exploit naturally occurring in vivo forces for improving stem cell fate in clinical regenerative therapies.

Shaping the Cell and the Future: Recent Advancements in Biophysical Aspects Relevant to Regenerative Medicine

“…Indeed, our group showed in a recent study that MSCs exhibit a specific baseline morphology that is associated with the biomaterial type and nanoscale stiffness of a given biomaterial surface [19] and one can intentionally generate a desired baseline shape using this concept. Moreover, our group demonstrated in Walters et al [24] that defined changes in externally applied biomechanical forces also prompt a subsequent, defined change in MSC shape. By applying various regimens of cyclic tensional forces we were able to engineer distinctly different MSC shapes.…”

“…Cell behavior can be dictated by microenvironmental biophysical cues including (1) mechanical forces such as compression, tension, and shear forces, (2) substrate properties such as biomaterial type, ligand presentation, surface topography, viscoelasticity, and stiffness, or (3) biochemical cues such as autocrine and paracrine signals [19,24,31,[36][37][38][39]. Collectively, such cues can ultimately lead to a specific differentiation behavior of cells such as MSCs [38].…”

“…We refer the biologically interested reader to [19] and the mathematically interested reader to the ImageJ homepage [50,51] and specifically to the "Analyze" menu section "set measurements", which details the mathematical calculations. In the context of quantifying MSC shape, we advocate using a defined panel of shape descriptors such as those introduced in our previous studies [18,19,24]. Other programs like MetaMorph [52] provide additional, albeit proprietary means for quantifying cell morphology and cell networks.…”

“…Scion Image (property of Scion Corporation), ImageJ [50,51] or Fiji [53], an ImageJ-based package with a rich set of tools and plugin focused on scientific image analysis, can potentially be used for such analyses [18,19,24]. Another option is CellProfiler, a Python based system [54].…”

“…Hence, studies have begun to increasingly and successfully use quantitative approaches to access morphological parameters and to correlate them to biological parameters and cell fate outcome. For example, our group has used a semi-automated high-throughput method for calculating a specific panel of shape descriptors [18,19,24], which was used to describe MSC shape in correlation to biophysical stimuli such as biomaterial type and nanoscale surface stiffness, as well as in response to externally applied biomechanical forces [19,24] (Figure 1). Therefore, quantitation of cellular morphology is useful for understanding the effects of different microenvironmental or biophysical stimuli on cells and for helping to define a morphological fingerprint for cells [20,25].…”