Elsevier

Journal of Biomechanics

Volume 43, Issue 1, 5 January 2010, Pages 55-62
Journal of Biomechanics

Intrinsic extracellular matrix properties regulate stem cell differentiation

https://doi.org/10.1016/j.jbiomech.2009.09.009Get rights and content

Abstract

One of the recent paradigm shifts in stem cell biology has been the discovery that stem cells can begin to differentiate into mature tissue cells when exposed to intrinsic properties of the extracellular matrix (ECM), such as matrix structure, elasticity, and composition. These parameters are known to modulate the forces a cell can exert upon its matrix. Mechano-sensitive pathways subsequently convert these biophysical cues into biochemical signals that commit the cell to a specific lineage. Just as with well-studied growth factors, ECM parameters are extremely dynamic and are spatially- and temporally-controlled during development, suggesting that they play a morphogenetic role in guiding differentiation and arrangement of cells. Our ability to dynamically regulate the stem cell niche as the body does is likely a critical requirement for developing differentiated cells from stem cells for therapeutic applications. Here, we present the emergence of stem cell mechanobiology and its future challenges with new biomimetic, three-dimensional scaffolds that are being used therapeutically to treat disease.

Introduction

Stem cell differentiation has traditionally employed cocktails of various growth factors, but differentiation has recently become increasingly linked to mechanobiological concepts such as cell-generated physical forces. These forces originate from myosin bundles sliding along actin filaments and are transmitted to the extracellular matrix (ECM), a three-dimensional fibrillar protein scaffold which surrounds and anchors cells. Transduction of these signals employs a vast array of adhesive proteins that assemble together to mechanically link the extracellular and intracellular worlds. Cells rely on ECM resistance much in the way that an electrical current requires the wire's internal resistance to permit the movement of charge: cells pull against matrix and “feel” the resistance to deformation by the adjacent environment, which provides feedback via mechanically-sensitive proteins along this connection. Though the molecular details require further exploration, the intention of this review is to provide insight into what, where, and when a stem cell senses its ECM cues, how they induce differentiation, and how such cues can be incorporated into new, three-dimensional scaffolds to treat disease.

A sound understanding of the interplay between development and ECM expression provides a starting point for tackling stem cell differentiation. ECM is composed predominantly of three major structural proteins, i.e. collagen, fibronectin, and laminin, as well as a host of elastin, fibrillin, tenascin, glycosaminoglycans, and proteoglycans. Each of these has a very specific distribution and assembly pattern in the body (Hay, 1991) that could contribute to certain developmental processes, especially given that the onset of matrix expression coincides with the late morula stage (Eyal-Giladi, 1995) just before the emergence of pluripotent embryonic stem cells (ESCs) and the first cell movements. For example, the matrix protein fibronectin regulates cell migration during the rearrangement process called gastrulation (Darribere and Schwarzbauer, 2000), which occurs just as stem cell fate is being decided and the body plan and axis is being established. Moreover, interactions between specific germ layers and matrix proteins, e.g. mesendoderm morphogenesis and the synergy site of fibronectin (Davidson et al., 2002), also suggest a link between intrinsic matrix properties and differentiation. On the other hand, adult stem cells, such as bone-marrow-derived mesenchymal stem cells (MSCs), are multipotent meaning that they can mature into a specific subset of cells. Though they may not have temporally-changing matrix as with ESCs, they are known to migrate from the marrow to a variety of tissues with different matrix compositions (Pittenger et al., 1999), providing good cause to examine their susceptibility to matrix variation. Both cell types sit in contrast with lineage-specific progenitor cells, which can only become a single cell type and thus may behave more closely to that adult cell type; therefore, we will limit our discussion to stem cells with multi-lineage potential.

For both embryonic and adult stem cells, ECM properties, including (1) structural (Dalby et al., 2007; McBeath et al., 2004), (2) biochemical (Helen et al., unpublished; Ott et al., 2008), and (3) mechanical (Engler et al., 2006; McBeath et al., 2004; Ruiz and Chen, 2008) cues, develop in concert. Here we will present a discussion of several of these mechanisms and how they regulate differentiation. Stem cells are surprisingly sensitive in vitro to these stimuli, especially with respect to how these cues change cell-generated forces or how forces influence the presentation of these properties. We will discuss how new materials have enabled the separation of these variables, which are often coupled matrix parameters in the body. Our review will only focus on stem cells, and we would refer the reader to the rich literature regarding cell–ECM interactions and the signaling that it induces in mature cells for a broader treatment of the subject (see (Butcher et al., 2009; Geiger et al., 2001; Nelson and Bissell, 2006; Schwartz, 2001; Schwartz and DeSimone, 2008; Vogel and Sheetz, 2006) among others), including many of the reviews within this special issue.

Section snippets

Matrix structure and organization

In vivo, matrix is first secreted by cells and subsequently assembled into a fibrillar network by their integrins which attach to the cell-binding regions of matrix, e.g. the Arginine–Glycine–Aspartic acid (or RGD) on fibronectin. Upon binding, clusters containing multiple bound integrins are pulled apart such that matrix proteins are unwound to reveal self-association domains, permitting homotypic binding, e.g. fibronectin–fibronectin (Mao and Schwarzbauer, 2005). In the absence of certain

Matrix chemistry

Biochemical regulation of stem cell fate is not limited to soluble ligands; the composition of matrix can regulate cells via differential integrin binding to adhesion sites – such as those shown in Fig. 1A—demonstrating a second mechanism to alter cell fate: ECM composition. For example, acellular tissue explants, having a distinct matrix composition, can interact with a specific subset of integrins on the MSC surface and direct a portion of the cell population to become beating cardiomyocytes

Mechanical properties of the matrix

Many observations in modern cell biology have been performed on rigid glass coverslips, often coated with a thin layer of ECM as in Fig. 1B. However, such thin coatings do not recapitulate the normal mechanical environment of most cell types (Engler et al., 2004c) and can lead to de-differentiation or loss of function in cells (Engler et al., 2008). The correct mechanical properties of a cell niche vary as much as 300-fold from soft brain tissue (0.1 kiloPascal or kPa; a unit of elasticity, E)

Designing matrix for the third dimension: microenvironment in context

Most of these ECM-based stimuli mentioned above were studied individually, and any given cue, whether growth factors or ECM structure, elasticity, or composition, does not appear to be sufficient to promote full differentiation relative to mature adult cells but results only in precursors to those cell types. Thus, MSCs grown on a gel of muscle elasticity, EM, become spindle-shaped and express only early muscle markers (Fig. 2A (Engler et al., 2006; Rowlands et al., 2008)); they cannot fuse

Designing for the future

Stem cells are exquisitely sensitive to the intrinsic properties of their extracellular matrix, and as illustrated here, one of the key differentiation mediators is the mechanical interaction between the cell and its matrix. These mechanobiological relationships and the cell pathways they modulate need to be better understood in order to manipulate stem cell differentiation for in vitro and clinical applications. In order to properly separate these variables and understand their individual

Conflict of interest statement

None

Acknowledgements

The authors would like to thank Nikolaj Gadegaard for the image of the PMMA semi-disordered substrate in Fig. 1. The authors would also like to acknowledge Jennifer Edwards and Fergal O’Brien (Department of Anatomy, Royal College of Surgeons, Ireland) for the confocal images of cells in large and small diameter porous scaffolds in Fig. 4, respectively. The authors additionally acknowledge funding from AHA 0865150F (to AJE), UCSD-RI-324G-ENGLER (to AJE), and the Foreign and Commonwealth Office

References (82)

  • A.J. Engler et al.

    Surface probe measurements of the elasticity of sectioned tissue, thin gels and polyelectrolyte multilayer films: correlations between substrate stiffness and cell adhesion

    Surf. Sci.

    (2004)
  • A.J. Engler et al.

    Matrix elasticity directs stem cell lineage specification

    Cell

    (2006)
  • M.W. Hayman et al.

    Growth of human stem cell-derived neurons on solid three-dimensional polymers

    J. Biochem. Biophys. Methods

    (2005)
  • A. Katsumi et al.

    Integrin activation and matrix binding mediate cellular responses to mechanical stretch

    J. Biol. Chem.

    (2005)
  • C.M. Lo et al.

    Cell movement is guided by the rigidity of the substrate

    Biophys. J.

    (2000)
  • Y. Mao et al.

    Fibronectin fibrillogenesis, a cell-mediated matrix assembly process

    Matrix Biol.

    (2005)
  • M.M. Martino et al.

    Controlling integrin specificity and stem cell differentiation in 2D and 3D environments through regulation of fibronectin domain stability

    Biomaterials

    (2009)
  • R. McBeath et al.

    Cell Shape, cytoskeletal tension, and RhoA regulate stem cell lineage commitment

    Dev. Cell

    (2004)
  • U. Muller et al.

    Mechanisms that regulate mechanosensory hair cell differentiation

    Trends Cell Biol.

    (2001)
  • F.J. O’Brien et al.

    The effect of pore size on cell adhesion in collagen-GAG scaffolds

    Biomaterials

    (2005)
  • M.J. Paszek et al.

    Tensional homeostasis and the malignant phenotype

    Cancer Cell

    (2005)
  • T. Rozario et al.

    The physical state of fibronectin matrix differentially regulates morphogenetic movements in vivo

    Dev. Biol.

    (2009)
  • M.A. Schwartz

    Integrin signaling revisited

    Trends Cell Biol.

    (2001)
  • M.A. Schwartz et al.

    Cell adhesion receptors in mechanotransduction

    Curr. Opinion Cell Biol.

    (2008)
  • C.A. Simmons et al.

    Cyclic strain enhances matrix mineralization by adult human mesenchymal stem cells via the extracellular signal-regulated kinase (ERK1/2) signaling pathway

    J. Biomech.

    (2003)
  • R. Adhikari et al.

    Correlation between molecular architecture, morphology, and deformation behaviour of styrene/butadiene block copolymers

    Macromol. Chem. Phys.

    (2003)
  • M.F. Berry et al.

    Mesenchymal stem cell injection after myocardial infarction improves myocardial compliance

    Am. J. Physiol. Heart Circ. Physiol.

    (2006)
  • A.M. Bratt-Leal et al.

    Engineering the embryoid body microenvironment to direct embryonic stem cell differentiation

    Biotechnol. Prog.

    (2009)
  • J.A. Burdick et al.

    Review: engineered microenvironments for controlled stem cell differentiation

    Tissue Eng. Part A

    (2008)
  • D.T. Butcher et al.

    A tense situation: forcing tumour progression

    Nat. Rev. Cancer

    (2009)
  • Chen, J.-H., Liu, C., You, L., Simmons, C.A., (this issue). Boning up on Wolff's Law: Mechanical regulation of the...
  • A.M. Collinsworth et al.

    Apparent elastic modulus and hysteresis of skeletal muscle cells throughout differentiation

    Am. J. Physiol. Cell Physiol.

    (2002)
  • E. Cukierman et al.

    Taking cell–matrix adhesions to the third dimension

    Science

    (2001)
  • M.J. Dalby et al.

    The control of human mesenchymal cell differentiation using nanoscale symmetry and disorder

    Nat. Mater.

    (2007)
  • N. Datta et al.

    In vitro generated extracellular matrix and fluid shear stress synergistically enhance 3D osteoblastic differentiation

    Proc. Natl. Acad. Sci. USA

    (2006)
  • A. del Rio et al.

    Stretching single talin rod molecules activates vinculin binding

    Science

    (2009)
  • D.E. Discher et al.

    Tissue cells feel and respond to the stiffness of their substrate

    Science

    (2005)
  • A.J. Engler et al.

    Embryonic cardiomyocytes beat best on a matrix with heart-like elasticity: scar-like rigidity inhibits beating

    J. Cell Sci.

    (2008)
  • A.J. Engler et al.

    A novel mode of cell detachment from fibrillar fibronectin matrix under shear

    J. Cell Sci.

    (2009)
  • A.J. Engler et al.

    Myotubes differentiate optimally on substrates with tissue-like stiffness: pathological implications for soft or stiff microenvironments

    J. Cell Biol.

    (2004)
  • Erickson, I.E., Huang, A.H., Sengupta, S., Kestle, S., Burdick, J., Mauck, R.L., in press. Macromer density influences...
  • Cited by (0)

    View full text