Cell Contractility Facilitates Alignment of Cells and Tissues to Static Uniaxial Stretch.
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ABSTRACT:
SUBMITTER: Rens EG
PROVIDER: S-EPMC5340096 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Anisotropic geometries are critical for eliciting cell alignment to dictate tissue microarchitectures and biological functions. Current fabrication techniques are complex and utilize toxic solvents, hampering their applications for translational research. Here, we present a novel simple, solvent-free, and reproducible method via uniaxial stretching for incorporating anisotropic topographies on bioresorbable films with ambitions to realize stem cell alignment control. Uniaxial stretching of poly(?-caprolactone) (PCL) films resulted in a three-dimensional micro-ridge/groove topography (inter-ridge-distance: ~6 ?m; ridge-length: ~90 ?m; ridge-depth: 200-900 nm) with uniform distribution and controllable orientation by the direction of stretch on the whole film surface. When stretch temperature (Ts) and draw ratio (DR) were increased, the inter-ridge-distance was reduced and ridge-length increased. Through modification of hydrolysis, increased surface hydrophilicity was achieved, while maintaining the morphology of PCL ridge/grooves. Upon seeding human mesenchymal stem cells (hMSCs) on uniaxial-stretched PCL (UX-PCL) films, aligned hMSC organization was obtained. Compared to unstretched films, hMSCs on UX-PCL had larger increase in cellular alignment (>85%) and elongation, without indication of cytotoxicity or reduction in cellular proliferation. This aligned hMSC organization was homogenous and stably maintained with controlled orientation along the ridges on the whole UX-PCL surface for over 2 weeks. Moreover, the hMSCs on UX-PCL had a higher level of myogenic genes' expression than that on the unstretched films. We conclude that uniaxial stretching has potential in patterning film topography with anisotropic structures. The UX-PCL in conjunction with hMSCs could be used as "basic units" to create tissue constructs with microscale control of cellular alignment and elongation for tissue engineering applications.
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Project description:Cells select from a diverse repertoire of migration strategies. Recent developments in tunable biomaterials have helped identify how extracellular matrix properties influence migration, however, many settings lack the fibrous architecture characteristic of native tissues. To investigate migration in fibrous contexts, we independently varied the alignment and stiffness of synthetic 3D fiber matrices and identified two phenotypically distinct migration modes. In contrast to stiff matrices where cells migrated continuously in a traditional mesenchymal fashion, cells in deformable matrices stretched matrix fibers to store elastic energy; subsequent adhesion failure triggered sudden matrix recoil and rapid cell translocation. Across a variety of cell types, traction force measurements revealed a relationship between cell contractility and the matrix stiffness where this migration mode occurred optimally. Given the prevalence of fibrous tissues, an understanding of how matrix structure and mechanics influences migration could improve strategies to recruit repair cells to wound sites or inhibit cancer metastasis.
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Project description:Background/purposeMechanical stretch plays a key role in promoting proliferation and differentiation of bone marrow mesenchymal stem cells (BMSCs) in distraction osteogenesis (DO). A better understanding of how the extracellular biomechanical stimulation is transferred to intracellular signal expression will benefit DO. Focal adhesion kinase (FAK) is a key factor in integrin signaling pathway. However, little is known about the effect of integrin-FAK signaling during the process of stretch induced osteogenic differentiation of BMSCs.Materials and methodsA specific short hairpin RNAs (shRNAs) lentiviral expression vector was used to silence Fak gene and a well-established in vitro uniaxial dynamic stretching device was applied to stimulate DO. Fak silencing was confirmed by fluorescence microscopy and the detection of Fak mRNA and FAK, p-FAK protein expression. Alkaline phosphatase (ALP) activity, expression of osteogenic differentiation markers - runt-related transcription factor 2 (RUNX2/Runx2) and alkaline phosphatase (Alp) together with integrin upstream signal transduction molecules integrin beta-1 (ITGB1/Itgb1) and downstream signal transduction molecules integrin-linked kinase (ILK) were detected after the stretch.ResultsThe results showed that mechanical stretch in control groups significantly induced the osteogenic differentiation of BMSCs with increased ALP activity, expression of RUNX2/Runx2 and Alp, together with upregulated ITGB1/Itgb1 and ILK, which all vanished in Fak silencing group.ConclusionSilencing of the Fak gene inhibited the osteogenic differentiation of rat BMSCs induced by in vitro mechanical stretch through integrin signaling pathway.
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Project description:Many of the properties of graphene are tied to its lattice structure, allowing for tuning of charge carrier dynamics through mechanical strain. The graphene electromechanical coupling yields very large pseudomagnetic fields for small strain fields, up to hundreds of Tesla, which offer new scientific opportunities unattainable with ordinary laboratory magnets. Significant challenges exist in investigation of pseudomagnetic fields, limited by the nonplanar graphene geometries in existing demonstrations and the lack of a viable approach to controlling the distribution and intensity of the pseudomagnetic field. Here we reveal a facile and effective mechanism to achieve programmable extreme pseudomagnetic fields with uniform distributions in a planar graphene sheet over a large area by a simple uniaxial stretch. We achieve this by patterning the planar graphene geometry and graphene-based heterostructures with a shape function to engineer a desired strain gradient. Our method is geometrical, opening up new fertile opportunities of strain engineering of electronic properties of 2D materials in general.
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Project description:Endothelial cell (EC) alignment to directional flow or stretch supports anti-inflammatory functions, but mechanisms controlling polarized structural adaptation in response to physical cues remain unclear. This study aimed to determine whether factors associated with early actin edge ruffling implicated in cell polarization are prerequisite for stress fiber (SF) reorientation in response to cyclic uniaxial stretch. Time-lapse analysis of EGFP-actin in confluent ECs showed that onset of either cyclic uniaxial or equibiaxial stretch caused a non-directional increase in edge ruffling. Edge activity was concentrated in a direction perpendicular to the stretch axis after 60 min, consistent with the direction of SF alignment. Rho-kinase inhibition caused reorientation of both stretch-induced edge ruffling and SF alignment parallel to the stretch axis. Arp2/3 inhibition attenuated stretch-induced cell elongation and disrupted polarized edge dynamics and microtubule organizing center reorientation, but it had no effect on the extent of SF reorientation. Disrupting localization of p21-activated kinase (PAK) did not prevent stretch-induced SF reorientation, suggesting that this Rac effector is not critical in regulating stretch-induced cytoskeletal remodeling. Overall, these results suggest that directional edge ruffling is not a primary mechanism that guides SF reorientation in response to stretch; the two events are coincident but not causal.
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Project description:The ability of cells to orient in response to mechanical stimuli is essential to embryonic development, cell migration, mechanotransduction, and other critical physiologic functions in a range of organs. Endothelial cells, fibroblasts, mesenchymal stem cells, and osteoblasts all orient perpendicular to an applied cyclic stretch when plated on stretchable elastic substrates, suggesting a common underlying mechanism. However, many of these same cells orient parallel to stretch in vivo and in 3D culture, and a compelling explanation for the different orientation responses in 2D and 3D has remained elusive. Here, we conducted a series of experiments designed specifically to test the hypothesis that differences in strains transverse to the primary loading direction give rise to the different alignment patterns observed in 2D and 3D cyclic stretch experiments ("strain avoidance"). We found that, in static or low-frequency stretch conditions, cell alignment in fibroblast-populated collagen gels correlated with the presence or absence of a restraining boundary condition rather than with compaction strains. Cyclic stretch could induce perpendicular alignment in 3D culture but only at frequencies an order of magnitude greater than reported to induce perpendicular alignment in 2D. We modified a published model of stress fiber dynamics and were able to reproduce our experimental findings across all conditions tested as well as published data from 2D cyclic stretch experiments. These experimental and model results suggest an explanation for the apparently contradictory alignment responses of cells subjected to cyclic stretch on 2D membranes and in 3D gels.
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Project description:Mechanical cues in the cellular environment play important roles in guiding various cell behaviors, such as cell alignment, migration, and differentiation. Previous studies investigated mechanical stretch guided cell alignment pre-dominantly with cyclic stretching whereby an external force is applied to stretch the substrate dynamically (i.e., cyclically) while the cells are attached onto the substrate. In contrast, we created a static pre-stretched anisotropic surface in which the cells were seeded subsequent to stretching the substrate. We hypothesized that the cell senses the physical environment through a more active mechanism, namely, even without external forces the cell can actively apply traction and sense an increased stiffness in the stretched direction and align in that direction. To test our hypothesis, we quantified the extent of pre-stretch induced anisotropy by employing the theory of small deformation superimposed on large and predicted the effective stiffness in the stretch direction as well as its perpendicular direction. We showed mesenchymal stem cells (MSC) aligned in the pre-stretched direction, and the cell alignment and morphology were dependent on the pre-stretch magnitude. In addition, the pre-stretched surface demonstrated an ability to promote early myoblast differentiation of the MSC. This study is the first report on MSC alignment on a statically pre-stretched surface. The cell orientation induced by the pre-stretch induced anisotropy could provide insight into tissue engineering applications involving cells that aligned in vivo in the absence of dynamic mechanical stimuli.
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