Matrix elasticity directs stem cell lineage specification.
TL;DR: Naive mesenchymal stem cells are shown here to specify lineage and commit to phenotypes with extreme sensitivity to tissue-level elasticity, consistent with the elasticity-insensitive commitment of differentiated cell types.
About: This article is published in Cell.The article was published on 2006-08-25 and is currently open access. It has received 12204 citations till now. The article focuses on the topics: Mesenchymal stem cell differentiation & Stem cell fate determination.
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TL;DR: YAP/TAZ are identified as sensors and mediators of mechanical cues instructed by the cellular microenvironment and are functionally required for differentiation of mesenchymal stem cells induced by ECM stiffness and for survival of endothelial cells regulated by cell geometry.
Abstract: Cells perceive their microenvironment not only through soluble signals but also through physical and mechanical cues, such as extracellular matrix (ECM) stiffness or confined adhesiveness. By mechanotransduction systems, cells translate these stimuli into biochemical signals controlling multiple aspects of cell behaviour, including growth, differentiation and cancer malignant progression, but how rigidity mechanosensing is ultimately linked to activity of nuclear transcription factors remains poorly understood. Here we report the identification of the Yorkie-homologues YAP (Yes-associated protein) and TAZ (transcriptional coactivator with PDZ-binding motif, also known as WWTR1) as nuclear relays of mechanical signals exerted by ECM rigidity and cell shape. This regulation requires Rho GTPase activity and tension of the actomyosin cytoskeleton, but is independent of the Hippo/LATS cascade. Crucially, YAP/TAZ are functionally required for differentiation of mesenchymal stem cells induced by ECM stiffness and for survival of endothelial cells regulated by cell geometry; conversely, expression of activated YAP overrules physical constraints in dictating cell behaviour. These findings identify YAP/TAZ as sensors and mediators of mechanical cues instructed by the cellular microenvironment.
4,120 citations
TL;DR: Reduction of lysyl oxidase-mediated collagen crosslinking prevented MMTV-Neu-induced fibrosis, decreased focal adhesions and PI3K activity, impeded malignancy, and lowered tumor incidence, and data show how collagenCrosslinking can modulate tissue fibrosis and stiffness to force focal adhesion, growth factor signaling and breast malignancies.
3,396 citations
TL;DR: The extracellular matrix and ECM proteins are important in phenomena as diverse as developmental patterning, stem cell niches, cancer, and genetic diseases and these properties need to be incorporated into considerations of the functions of the ECM.
Abstract: The extracellular matrix (ECM) and ECM proteins are important in phenomena as diverse as developmental patterning, stem cell niches, cancer, and genetic diseases. The ECM has many effects beyond providing structural support. ECM proteins typically include multiple, independently folded domains whose sequences and arrangement are highly conserved. Some of these domains bind adhesion receptors such as integrins that mediate cell-matrix adhesion and also transduce signals into cells. However, ECM proteins also bind soluble growth factors and regulate their distribution, activation, and presentation to cells. As organized, solid-phase ligands, ECM proteins can integrate complex, multivalent signals to cells in a spatially patterned and regulated fashion. These properties need to be incorporated into considerations of the functions of the ECM.
2,858 citations
TL;DR: The functional requirements, and types, of materials used in developing state of the art of scaffolds for tissue engineering applications are described and where future research and direction is required are described.
2,648 citations
TL;DR: This Review discusses how different mechanisms interact and can be integrated to exert fine control in time and space over the drug presentation, and collects experimental release data from the literature and presents quantitative comparisons between different systems to provide guidelines for the rational design of hydrogel delivery systems.
Abstract: Hydrogel delivery systems can leverage therapeutically beneficial outcomes of drug delivery and have found clinical use. Hydrogels can provide spatial and temporal control over the release of various therapeutic agents, including small-molecule drugs, macromolecular drugs and cells. Owing to their tunable physical properties, controllable degradability and capability to protect labile drugs from degradation, hydrogels serve as a platform in which various physiochemical interactions with the encapsulated drugs control their release. In this Review, we cover multiscale mechanisms underlying the design of hydrogel drug delivery systems, focusing on physical and chemical properties of the hydrogel network and the hydrogel-drug interactions across the network, mesh, and molecular (or atomistic) scales. We discuss how different mechanisms interact and can be integrated to exert fine control in time and space over the drug presentation. We also collect experimental release data from the literature, review clinical translation to date of these systems, and present quantitative comparisons between different systems to provide guidelines for the rational design of hydrogel delivery systems.
2,457 citations
References
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TL;DR: The atomic force microscope was employed to investigate the extension and retraction dynamics of protruding and stable edges of motile 3T3 fibroblasts in culture, and data are consistent with the notion that extension preferentially occurs in regions of lower cortical tension.
Abstract: The atomic force microscope (AFM) was employed to investigate the extension and retraction dynamics of protruding and stable edges of motile 3T3 fibroblasts in culture. Such dynamics closely paralleled the results of earlier studies employing video microscopy that indicated that the AFM force-mapping technique does not appreciably perturb these dynamics. Force scans permitted height determinations of active and stable edges. Whereas the profiles of active edges are flat with average heights of 0.4–0.8 μm, stable edges smoothly ascend to 2–3 μm within about 6 μm of the edge. In the region of the leading edge, the height fluctuates up to 50% (SD) of the mean value, much more than the stable edge; this fluctuation presumably reflects differences in underlying cytoskeletal activity. In addition, force mapping yields an estimate of the local Young’s modulus or modulus of elasticity (E, the cortical stiffness). This stiffness will be related to “cortical tension,” can be accurately calculated for the stable edges, and is ≈12 kPa in this case. The thinness of the leading edge precludes accurate estimation of the E values, but within 4 μm of the margin it is considerably smaller than that for stable edges, which have an upper limit of 3–5 kPa. Although blebbing cannot absolutely be ruled out as a mechanism of extension, the data are consistent with an actin polymerization and/or myosin motor mechanism in which the average material properties of the extending margin would be nearly constant to the edge. Because the leading edge is softer than the stable edge, these data also are consistent with the notion that extension preferentially occurs in regions of lower cortical tension.
429 citations
"Matrix elasticity directs stem cell..." refers background or methods in this paper
...…probe (Veeco; Santa Barbara, CA) with a constant, ksp 60 pN/nm. Force-indentation profiles were obtained immediately adjacent to a cell, and each indentation profile was fit up to the point at which probe indentation into the secreted matrix stopped with a Hertz cone model (Rotsch et al., 1999)....
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...Neuron-specific cytoskeletal markers such as nestin, an early commitment marker, and b3 tubulin, expressed in immature neurons, as well as the mature marker neurofilament light chain (NFL) (Lariviere and Julien, 2004) and the early/midadhesion protein NCAM (Rutishauser, 1984), are all upregulated....
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TL;DR: It is concluded that the resting state of Fn fibrils does not contain Fn molecules with crossed-over arms, and that the several-fold extensibility of Fnfibrils involves the unfolding of type III modules, which could imply that Fn might play a significant role in mechanotransduction processes.
Abstract: Whether mechanically unfolded fibronectin (Fn) is present within native extracellular matrix fibrils is controversial. Fn extensibility under the influence of cell traction forces has been proposed to originate either from the force-induced lengthening of an initially compact, folded quaternary structure as is found in solution (quaternary structure model, where the dimeric arms of Fn cross each other), or from the force-induced unfolding of type III modules (unfolding model). Clarification of this issue is central to our understanding of the structural arrangement of Fn within fibrils, the mechanism of fibrillogenesis, and whether cryptic sites, which are exposed by partial protein unfolding, can be exposed by cell-derived force. In order to differentiate between these two models, two fluorescence resonance energy transfer schemes to label plasma Fn were applied, with sensitivity to either compact-to-extended conformation (arm separation) without loss of secondary structure or compact-to-unfolded conformation. Fluorescence resonance energy transfer studies revealed that a significant fraction of fibrillar Fn within a three-dimensional human fibroblast matrix is partially unfolded. Complete relaxation of Fn fibrils led to a refolding of Fn. The compactly folded quaternary structure with crossed Fn arms, however, was never detected within extracellular matrix fibrils. We conclude that the resting state of Fn fibrils does not contain Fn molecules with crossed-over arms, and that the several-fold extensibility of Fn fibrils involves the unfolding of type III modules. This could imply that Fn might play a significant role in mechanotransduction processes.
425 citations
TL;DR: The ability of cultured rat MSC to undergo in vitro osteogenesis, chondrogenesis, and adipogenesis is confirmed, demonstrating differentiation of these cells to three mesenchymal cell fates, and changes in morphology upon addition of the chemical induction medium were caused by rapid disruption of the actin cytoskeleton.
Abstract: Bone marrow stromal cells (MSC), which represent a population of multipotential mesenchymal stem cells, have been reported to undergo rapid and robust transformation into neuron-like phenotypes in vitro following treatment with chemical induction medium including dimethyl sulfoxide (DMSO; Woodbury et al. [2002] J. Neurosci. Res. 96:908). In this study, we confirmed the ability of cultured rat MSC to undergo in vitro osteogenesis, chondrogenesis, and adipogenesis, demonstrating differentiation of these cells to three mesenchymal cell fates. We then evaluated the potential for in vitro neuronal differentiation of these MSC, finding that changes in morphology upon addition of the chemical induction medium were caused by rapid disruption of the actin cytoskeleton. Retraction of the cytoplasm left behind long processes, which, although strikingly resembling neurites, showed essentially no motility and no further elaboration during time-lapse studies. Similar neurite-like processes were induced by treating MSC with DMSO only or with actin filament-depolymerizing agents. Although process formation was accompanied by rapid expression of some neuronal and glial markers, the absence of other essential neuronal proteins pointed toward aberrantly induced gene expression rather than toward a sequence of gene expression as is required for neurogenesis. Moreover, rat dermal fibroblasts responded to neuronal induction by forming similar processes and expressing similar markers. These studies do not rule out the possibility that MSC can differentiate into neurons; however, we do want to caution that in vitro differentiation protocols may have unexpected, misleading effects. A dissection of molecular signaling and commitment events may be necessary to verify the ability of MSC transdifferentiation to neuronal lineages.
408 citations
"Matrix elasticity directs stem cell..." refers background in this paper
...…Sweeney,1 and Dennis E. Discher1,2,3,4,* 1Pennsylvania Muscle Institute 2School of Engineering and Applied Science 3Cell & Molecular Biology Graduate Group 4Physics Graduate Group University of Pennsylvania, Philadelphia, PA 19104, USA *Contact: discher@seas.upenn.edu DOI 10.1016/j.cell.2006.06.044...
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...…densities after 1 week in culture approach those of primary neurons on matrigel-coated gels (Flanagan et al., 2002), and the dynamics of outward extension with branching is clearly opposite to DMSO-induced retraction of the cell body that can leave pseudoextensions behind (Neuhuber et al., 2004)....
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...…to induce reversible branching in stem cells (Dinsmore et al., 1996; Woodbury et al., 2002), but DMSO also causes fibroblasts to appear ‘‘branched,’’ and this appears due to cytoskeletal disruption with centripetal retraction of the cell body that leaves extensions attached (Neuhuber et al., 2004)....
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TL;DR: The results indicate that TNF regulates RUNX2 expression at multiple levels including destabilization of mRNA and suppression of transcription, which may decrease osteoblast differentiation and inhibit bone formation in TNF excess states.
398 citations
"Matrix elasticity directs stem cell..." refers background in this paper
...On the stiffest, osteogenic matrices, MSCs upregulate the transcription factor CBFa1 (Figure 3A; open arrow), which is a crucial early marker of osteogenesis (Gilbert et al., 2002)....
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TL;DR: In this paper, the intrinsic strain fluctuations of living cells using a tracer correlation technique along with a theoretical framework for interpreting such data in heterogeneous media with nonthermal driving are reported.
Abstract: We report the first measurements of the intrinsic strain fluctuations of living cells using a recently developed tracer correlation technique along with a theoretical framework for interpreting such data in heterogeneous media with nonthermal driving. The fluctuations' spatial and temporal correlations indicate that the cytoskeleton can be treated as a course-grained continuum with power-law rheology, driven by a spatially random stress tensor field. Combined with recent cell rheology results, our data imply that intracellular stress fluctuations have a nearly $1/{\ensuremath{\omega}}^{2}$ power spectrum, as expected for a continuum with a slowly evolving internal prestress.
384 citations