Preparation of decellularized biphasic hierarchical myotendinous junction extracellular matrix for muscle regeneration

Muscle injury and defect affect people's quality of life, and effective treatment is lacking. Herein, we generated a scaffold to obtain decellularized porcine Achilles tendon myotendinous junction (D-MTJ) extracellular matrix (ECM) with well-preserved native biphasic hierarchical structure, biological composition, and excellent mechanical properties for muscle regeneration. The combined use of potassium chloride, potassium iodide, Triton-X 100, and sodium-dodecyl sulfate (SDS) can completely remove the main immunogenicity, while maintaining the major biological components and microstructure. The specific biomechanics of D-MTJ is comparable to the native muscle-tendon physiological conditions. Additionally, the D-MTJ ECM scaffold induced minimal immunological reaction (histology analysis) through rat subcutaneous implantation. Moreover, in vitro, muscle satellite cells adhered, proliferated, and infiltrated into the D-MTJ scaffold, and myofiber-like cell differentiation was observed as shown by increased expression of myogenesis-related genes during culture. In vivo, newly formed myofibers were observed in a muscle defect model with D-MTJ orthotopic transplantation, while the control group presented mostly with fibrous tissue deposition. Additionally, the number of Myod and MyHC-positive cells in the ECM scaffold group was higher at day 30. We preliminary explored the mechanisms underlying D-MTJ-mediated muscle regeneration, which may be attributed to its specific biphasic hierarchical structure, bio-components, and attractiveness for myogenesis cells. In conclusion, our findings suggest the D-MTJ ECM scaffold prepared in this study is a promising choice for muscle regeneration.

STATEMENT OF SIGNIFICANCE

This study is the first to use decellularization technology obtaining the specifically decellularized myotendinous junction (D-MTJ) with well-preserved biphasic hierarchical structure and constituents, excellent mechanical properties and good biocompatibility. The D-MTJ was further proved to be efficient for muscle regeneration in vitro and in vivo, and the underlying mechanisms may be attributed to its specifically structure and constituents, improved myogenesis and good preservation of repair-related factors. Our study may provide basis for the decellularization of other biphasic hierarchical tissues and a platform for further studies on muscle fiber and tendon integrations in vitro.

Disentangling Membrane Dynamics and Cell Migration; Differential Influences of F-actin and Cell-Matrix Adhesions

Cell migration is heavily interconnected with plasma membrane protrusion and retraction (collectively termed “membrane dynamics”). This makes it difficult to distinguish regulatory mechanisms that differentially influence migration and membrane dynamics. Yet such distinctions may be valuable given evidence that cancer cell invasion in 3D may be better predicted by 2D membrane dynamics than by 2D cell migration, implying a degree of functional independence between these processes. Here, we applied multi-scale single cell imaging and a systematic statistical approach to disentangle regulatory associations underlying either migration or membrane dynamics. This revealed preferential correlations between membrane dynamics and F-actin features, contrasting with an enrichment of links between cell migration and adhesion complex properties. These correlative linkages were often non-linear and therefore context-dependent, strengthening or weakening with spontaneous heterogeneity in cell behavior. More broadly, we observed that slow moving cells tend to increase in area, while fast moving cells tend to shrink, and that the size of dynamic membrane domains is independent of cell area. Overall, we define macromolecular features preferentially associated with either cell migration or membrane dynamics, enabling more specific interrogation and targeting of these processes in future.

Podosome reformation in macrophages: assays and analysis

Podosomes are multifunctional organelles of invasive cells that combine several key abilities including cell-matrix adhesion, extracellular matrix degradation, and mechanosensing. In combination with their high turnover rates that allow quick adaptation to the pericellular environment, podosomes are likely to play important roles during invasive migration of cells. Primary human macrophages constitutively form numerous podosomes and are thus an ideal system for the quantitative study of podosome dynamics. This protocol describes assays for the study of podosome dynamics, namely, reformation of podosomes, in fixed and living cells, with subsequent software-based analyses allowing the extraction of quantitative parameters such as the number of podosomes per cell, podosome density, and half times for podosome disruption and reformation. Moreover, we describe the preparation of podosome-enriched cell fractions and their analysis by immunoblotting.

An optical method to quantify the density of ligands for cell adhesion receptors in three-dimensional matrices

The three-dimensional matrix that surrounds cells is an important insoluble regulator of cell phenotypes. Examples of such insoluble surfaces are the extracellular matrix (ECM), ECM analogues and synthetic polymeric biomaterials. Cell-matrix interactions are mediated by cell adhesion receptors that bind to chemical entities (adhesion ligands) on the surface of the matrix. There are currently no established methods to obtain quantitative estimates of the density of adhesion ligands recognized by specific cell adhesion receptors. This article presents a new optical-based methodology for measuring ligands of adhesion receptors on three-dimensional matrices. The study also provides preliminary quantitative results for the density of adhesion ligands of integrins alpha(1)beta(1) and alpha(2)beta(1) on the surface of collagen-based scaffolds, similar to biomaterials that are used clinically to induce regeneration in injured skin and peripheral nerves. Preliminary estimates of the surface density of the ligands of these two major collagen-binding receptors are 5775 +/- 2064 ligands microm(-2) for ligands of alpha(1)beta(1) and 17 084 +/- 5353 ligands microm(-2) for ligands of alpha(2)beta(1). The proposed methodology can be used to quantify the surface chemistry of insoluble surfaces that possess biological activity, such as native tissue ECM and biomaterials, and therefore can be used in cell biology, biomaterials science and regenerative medical studies for quantitative description of a matrix and its effects on cells.

Hyaluronan-dependent pericellular matrix

Hyaluronan is a multifunctional glycosaminoglycan that forms the structural basis of the pericellular matrix. Hyaluronan is extruded directly through the plasma membrane by one of three hyaluronan synthases and anchored to the cell surface by the synthase or cell surface receptors such as CD44 or RHAMM. Aggregating proteoglycans and other hyaluronan-binding proteins, contribute to the material and biological properties of the matrix and regulate cell and tissue function. The pericellular matrix plays multiple complex roles in cell adhesion/de-adhesion, and cell shape changes associated with proliferation and locomotion. Time-lapse studies show that pericellular matrix formation facilitates cell detachment and mitotic cell rounding. Hyaluronan crosslinking occurs through various proteins, such as tenascin, TSG-6, inter-alpha-trypsin inhibitor, pentraxin and TSP-1. This creates higher order levels of structured hyaluronan that may regulate inflammation and other biological processes. Microvillous or filopodial membrane protrusions are created by active hyaluronan synthesis, and form the scaffold of hyaluronan coats in certain cells. The importance of the pericellular matrix in cellular mechanotransduction and the response to mechanical strain are also discussed.

Modeling dermal granulation tissue with the linear fibroblast-populated collagen matrix: A comparison with the round matrix model

BACKGROUND

Wound contraction typically is not symmetrical; for example, a square-shaped wound will not yield a square scar. Interestingly, the round fibroblast-populated collagen matrix has been used as a model of wound contraction, even though contraction in this model is mostly symmetrical.

OBJECTIVE

We wanted to compare the round versus linear fibroblast-populated collagen matrix to see which would be a better model of dermal granulation tissue.

METHODS

Gross and microscopic morphology, contraction kinetics, cytoskeletal architecture, and apoptotic and proliferative indices were compared between the round versus the linear fibroblast-populated collagen matrix. A rat excisional wound model was used as an in vivo standard of healing.

RESULTS

The rate of contraction was similar between the two models, although the mode of contraction was grossly asymmetric in the linear while remaining symmetric in the round model. Cellular survival and proliferation were both dependent on matrix attachment in both models; this was analogous to the attachment-dependence of granulation tissue. In the attached (restrained) condition, the level of cellular organization was higher in the linear than in the round matrix; the tissue architecture of the linear matrix, moreover, mimicked that of the excisional wound model.

CONCLUSION

The round versus linear fibroblast-populated collagen matrix displayed a similar proliferative and survival response to matrix attachment. The latter model, however, demonstrated tissue organization with attachment and asymmetrical contraction after detachment analogous to that of the in vivo wound model. The linear fibroblast-populated collagen matrix appears to be the better model of dermal granulation tissue.

The extracellular matrix protein betaIG-H3 is expressed at myotendinous junctions and supports muscle cell adhesion

Molecules of the extracellular matrix (ECM) play important roles in the development and maintenance of myotendinous junctions (MTJs), specialized regions of muscle to bone union. In this report we provide evidence that skeletal muscle cells synthesize the collagen- and fibronectin-binding ECM protein betaIG-H3 and that betaIG-H3 is localized to MTJs. In situ hybridization experiments revealed that during E16.5-E18.5 of murine development, betaIG-H3 RNA transcripts were expressed where developing skeletal muscle fibers contact primordial cartilage and bone. Immunohistochemical analysis verified that the betaIG-H3 protein itself localized distinctively at MTJs, and ultrastructural analysis suggested that betaIG-H3 associates with extracellular fibers and the surface of cells. In vitro, recombinant betaIG-H3 functioned as an adhesion substratum for skeletal muscle cells. Adhesion was significantly reduced by anti-integrin alpha7 and beta1 antibodies, suggesting that betaIG-H3 binds to skeletal muscle cells via alpha7beta1 integrin. Localization of betaIG-H3 to the termini of skeletal muscle fibers and the binding of betaIG-H3 to cells and to molecules of the ECM suggests that betaIG-H3 may play an organizational and structural role in developing MTJs, linking skeletal muscle to components of the ECM.

Plasma membrane-cell wall connections: roles in mitosis and cytokinesis revealed by plasmolysis of Tradescantia virginiana leaf epidermal cells

Tradescantia virginiana leaf epidermal cells were plasmolysed by sequential treatment with 0.8 M and 0.3 M sucrose. Plasmolysis revealed adhesion of the plasma membrane to the cell wall at sites coinciding with cytoskeletal arrays involved in the polarisation of cells undergoing asymmetric divisions--cortical actin patch--and in the establishment and maintenance of the division site--preprophase band of microtubules and filamentous (F) actin. The majority of cells retained adhesions at the actin patch throughout mitosis. However, only approximately 13% of cells formed or retained attachments at the site of the preprophase band. After the breakdown of the nuclear envelope, plasmolysis had a dramatic effect on spindle orientation, cell plate formation, and the plane of cytokinesis. Spindles were rotated at abnormal angles including tilted into the plane of the epidermis. Cell plates formed but were quickly replaced by vacuole-like intercellular compartments containing no Tinopal-stainable cell wall material. This compartment usually opened to the apoplast at one side, and cytokinesis was completed by the furrow extending across the protoplast. This atypical cytokinesis was facilitated by a phragmoplast containing microtubules and F-actin. Progression of the furrow was unaffected by 25 micrograms of cytochalasin B per ml but inhibited by 10 microM oryzalin. Phragmoplasts were contorted and misguided and cytokinesis prolonged, indicating severe disruption to the guidance mechanisms controlling phragmoplast expansion. These results are discussed in terms of cytoskeleton-plasma membrane-cell wall connections that could be important to the localisation of plasma membrane molecules defining the cortical division site and hence providing positional information to the cytokinetic apparatus, and/or for providing an anchor for cytoplasmic F-actin necessary to generate tension on the phragmoplast and facilitate its directed, planar expansion.