Dynamics of extracellular matrix production and turnover in tissue engineered cardiovascular structures

Appropriate matrix formation, turnover and remodeling in tissue-engineered small diameter vascular conduits are crucial requirements for their long-term patency and function. This complex process requires the deposition and accumulation of extracellular matrix molecules as well as the remodeling of this extracellular matrix (ECM) by matrix metalloproteinases (MMPs) and their endogenous inhibitors (TIMPs). In this study, we have investigated the dynamics of ECM production and the activity of MMPs and TIMPs in long-term tissue-engineered vascular conduits using quantitative ECM analysis, substrate gel electrophoresis, radiometric enzyme assays and Western blot analyses. Over a time period of 169 days in vivo, levels of elastin and proteoglycans/glycosaminoglycans in tissue-engineered constructs came to approximate those of their native tissue counter parts. The kinetics of collagen deposition and remodeling, however, apparently require a much longer time period. Through the use of substrate gel electrophoresis, proteolytic bands whose molecular weight was consistent with their identification as the active form of MMP-2 (approximately 64--66 kDa) were detected in all native and tissue-engineered samples. Additional proteolytic bands migrating at approximately 72 kDa representing the latent form of MMP-2 were detected in tissue-engineered samples at time points from 5 throughout 55 days. Radiometric assays of MMP-1 activity demonstrated no significant differences between the native and tissue-engineered samples. This study determines the dynamics of ECM production and turnover in a long-term tissue-engineered vascular tissue and highlights the importance of ECM remodeling in the development of successful tissue-engineered vascular structures.     

Dynamic compressive loading of image-guided tissue engineered meniscal constructs

This study investigated the hypothesis that dynamic compression loading enhances tissue formation and increases mechanical properties of anatomically shaped tissue engineered menisci. Bovine meniscal fibrochondrocytes were seeded in 2%w/v alginate, crosslinked with CaSO(4), injected into μCT based molds, and post crosslinked with CaCl(2). Samples were loaded via a custom bioreactor with loading platens specifically designed to load anatomically shaped constructs in unconfined compression. Based on the results of finite element simulations, constructs were loaded under sinusoidal displacement to yield physiological strain levels. Constructs were loaded 3 times a week for 1 h followed by 1 h of rest and loaded again for 1 h. Constructs were dynamically loaded for up to 6 weeks. After 2 weeks of culture, loaded samples had 2-3.2 fold increases in the extracellular matrix (ECM) content and 1.8-2.5 fold increases in the compressive modulus compared with static controls. After 6 weeks of loading, glycosaminoglycan (GAG) content and compressive modulus both decreased compared with 2 week cultures by 2.3-2.7 and 1.5-1.7 fold, respectively, whereas collagen content increased by 1.8-2.2 fold. Prolonged loading of engineered constructs could have altered alginate scaffold degradation rate and/or initiated a catabolic cellular response, indicated by significantly decreased ECM retention at 6 weeks compared with 2 weeks. However, the data indicates that dynamic loading had a strikingly positive effect on ECM accumulation and mechanical properties in short term culture.     

Anti-adhesive molecules of the extracellular matrix.

The prototype extracellular matrix glycoproteins had been identified on the basis of their activity in promoting cell adhesion and spreading. Recently, more and more evidence is accumulating that the reverse effect of extracellular matrix proteins, namely the inhibition of cell adhesion and spreading, may be equally important for proper cell function during morphogenesis and development. Several anti-adhesive proteins have been described and their mechanisms of action are being investigated.     

Comparative study of cellular and extracellular matrix composition of native and tissue engineered heart valves.

Tissue engineering of heart valves utilizes biodegradable or metabolizable scaffolds for remodeling by seeded autologous cells. The aim of this study was to determine and compare extracellular matrix (ECM) formations, cellular phenotypes and cell location of native and tissue engineered (TE) valve leaflets. Ovine carotid arteries, ovine and porcine hearts were obtained from slaughterhouses. Cells were isolated from carotid arteries and dissected ovine, porcine and TE leaflets. TE constructs were fabricated from decellularized porcine pulmonary valves, seeded ovine arterial cells and subsequent 16 days dynamic in vitro culture using a pulsatile bioreactor. Native and TE valves were studied by histology (hematoxylin-eosin, resorcin-fuchsin, Movat pentachrome), NIR femtosecond multiphoton laser scanning microscopy and scanning electron microscopy (SEM). Cells of native and TE tissues were identified and localized by immunohistochemistry. Arterial, valvular and re-isolated TE-construct cells were processed for immunocytochemistry and Western blotting. ECM analysis and SEM revealed characteristical and comparable structures in native and TE leaflets. Most cells in native leaflets stained strongly positive for vimentin. Cells positive to alpha-smooth muscle actin (alpha-SMA), myosin and calponin were only found at the ventricular (inflow) side of ovine aortic and porcine pulmonary valve leaflets. Cells from TE constructs had a strong expression of vimentin, alpha-SMA, myosin, calponin and h-caldesmon throughout the entire leaflet. Comparable ECM formation and endothelial cell lining of native and TE leaflets could be demonstrated. However, immunostaining revealed significant differences between valvular cell phenotypes of native and TE leaflets. These results may be essential for further cardiovascular tissue engineering efforts.     

Binding of extracellular matrix molecules by probiotic bacteria

AIMS: The aim of this study was to investigate extracellular matrix (ECM) and mucin binding of selected bacterial isolates with probiotic features in comparison with commercially used probiotic bacteria. METHODS AND RESULTS: ECM molecules were immobilized in microtitre plates (mucin and fetuin) or on the surface of latex beads. Porcine mucin was bound by all 13 probiotic strains tested with important inter-strain differences; however, fetuin binding was similar (weak) for all 14 strains tested. Strongly positive (three) binding of bovine fibrinogen was expressed by strains from fermented food (Lactobacillus rhamnosus GG, L. casei Shirota and L. johnsonii La1) as well as by L. casei L.c., Lactobacillus sp. 2I3 and by L. plantarum LP. The other strains expressed moderate (2) or weakly positive (1) binding of bovine fibrinogen. Strongly positive (3) binding of porcine fibronectin was observed only with two strains; however, all other strains also bound this molecule. Bovine lactoferrin was bound to a higher extent than transferrins. SIGNIFICANCE AND IMPACT OF THE STUDY: Some animal strains (at least L. casei L.c. and Lactobacillus sp. 2I3) are comparable with the commercially used strains with respect to their ECM binding ability. As this feature is important for probiotic bacteria to be able to colonize intestine, these strains should be considered for their wider use in fermented feed (or probiotic preparations) for animals.     

Adipose tissue engineering with cells in engineered matrices

Tissue engineering has shown promise for the development of constructs to facilitate large volume soft tissue augmentation in reconstructive and cosmetic plastic surgery. This article reviews the key progress to date in the field of adipose tissue engineering. In order to effectively design a soft tissue substitute, it is critical to understand the native tissue environment and function. As such, the basic physiology of adipose tissue is described and the process of adipogenesis is discussed. In this article, we have focused on tissue engineering using a cell-seeded scaffold approach, where engineered extracellular matrix substitutes are seeded with exogenous cells that may contribute to the regenerative response. The strengths and limitations of each of the possible cell sources for adipose tissue engineering, including adipose-derived stem cells, are detailed. We briefly highlight some of the results from the major studies to date, involving a range of synthetic and naturally derived scaffolds. While these studies have shown that adipose tissue regeneration is possible, more research is required to develop optimized constructs that will facilitate safe, predictable, and long-term augmentation in clinical applications.     

Adipose tissue engineering with cells in engineered matrices

Tissue engineering has shown promise for the development of constructs to facilitate large volume soft tissue augmentation in reconstructive and cosmetic plastic surgery. This article reviews the key progress to date in the field of adipose tissue engineering. In order to effectively design a soft tissue substitute, it is critical to understand the native tissue environment and function. As such, the basic physiology of adipose tissue is described and the process of adipogenesis is discussed. In this article, we have focused on tissue engineering using a cell-seeded scaffold approach, where engineered extracellular matrix substitutes are seeded with exogenous cells that may contribute to the regenerative response. The strengths and limitations of each of the possible cell sources for adipose tissue engineering, including adipose-derived stem cells, are detailed. We briefly highlight some of the results from the major studies to date, involving a range of synthetic and naturally derived scaffolds. While these studies have shown that adipose tissue regeneration is possible, more research is required to develop optimized constructs that will facilitate safe, predictable and long-term augmentation in clinical applications.Key words: tissue engineering, regenerative medicine, adipose tissue, adipose-derived stem cells, adipogenesis, cell culture, scaffolds, cell-biomaterial interactions     

Amine functionalization of cholecyst-derived extracellular matrix with generation 1 PAMAM dendrimer

A method to functionalize cholecyst-derived extracellular matrix (CEM) with free amine groups was established in an attempt to improve its potential for tethering of bioactive molecules. CEM was incorporated with Generation-1 polyamidoamine (G1 PAMAM) dendrimer by using N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide and N-hydroxysuccinimide cross-linking system. The nature of incorporation of PAMAM dendrimer was evaluated using shrink temperature measurements, Fourier transform infrared (FTIR) assessment, ninhydrin assay, and swellability. The effects of PAMAM incorporation on mechanical and degradation properties of CEM were evaluated using a uniaxial mechanical test and collagenase degradation assay, respectively. Ninhydrin assay and FTIR assessment confirmed the presence of increasing free amine groups with increasing quantity of PAMAM in dendrimer-incorporated CEM (DENCEM) scaffolds. The amount of dendrimer used was found to be critical in controlling scaffold degradation, shrink temperature, and free amine content. Cell culture studies showed that fibroblasts seeded on DENCEM maintained their metabolic activity and ability to proliferate in vitro. In addition, fluorescence cell staining and scanning electron microscopy analysis of cell-seeded DENCEM showed preservation of normal fibroblast morphology and phenotype.     

Reciprocal interactions between cells and extracellular matrix during remodeling of tissue constructs

Cells remodel extracellular matrix during tissue development and wound healing. Similar processes occur when cells compress and stiffen collagen gels. An important task for cell biologists, biophysicists, and tissue engineers is to guide these remodeling processes to produce tissue constructs that mimic the structure and mechanical properties of natural tissues. This requires an understanding of the mechanisms by which this remodeling occurs. Quantitative measurements of the contractile force developed by cells and the extent of compression and stiffening of the matrix describe the results of the remodeling processes. Not only do forces exerted by cells influence the structure of the matrix but also external forces exerted on the matrix can modulate the structure and orientation of the cells. The mechanisms of these processes remain largely unknown, but recent studies of the regulation of myosin-dependent contractile force and of cell protrusion driven by actin polymerization provide clues about the regulation of cellular functions during remodeling.     

Three-dimensional culture of human meniscal cells: Extracellular matrix and proteoglycan production

Background  

The meniscus is a complex tissue whose cell biology has only recently begun to be explored. Published models rely upon initial culture in the presence of added growth factors. The aim of this study was to test a three-dimensional (3D) collagen sponge microenvironment (without added growth factors) for its ability to provide a microenvironment supportive for meniscal cell extracellular matrix (ECM) production, and to test the responsiveness of cells cultured in this manner to transforming growth factor-β (TGF-β).     

Modulation of tissue transglutaminase in tubular epithelial cells alters extracellular matrix levels: A potential mechanism of tissue scarring

The up-regulation and trafficking of tissue transglutaminase (TG2) by tubular epithelial cells (TEC) has been implicated in the development of kidney scarring. TG2 catalyses the crosslinking of proteins via the formation of highly stable ε(γ-glutamyl) lysine bonds. We have proposed that TG2 may contribute to kidney scarring by accelerating extracellular matrix (ECM) deposition and by stabilising the ECM against proteolytic decay.To investigate this, we have studied ECM metabolism in Opossum kidney (OK) TEC induced to over-express TG2 by stable transfection and in tubular cells isolated from TG2 knockout mice.Increasing the expression of TG2 led to increased extracellular TG2 activity (p < 0.05), elevated ε(γ-glutamyl) lysine crosslinking in the ECM and higher levels of ECM collagen per cell by ³H-proline labelling. Immunofluorescence demonstrated that this was attributable to increased collagen III and IV levels. Higher TG2 levels were associated with an accelerated collagen deposition rate and a reduced ECM breakdown by matrix metalloproteinases (MMPs).In contrast, a lack of TG2 was associated with reduced ε(γ-glutamyl) lysine crosslinking in the ECM, causing reduced ECM collagen levels and lower ECM per cell.We report that TG2 contributes to ECM accumulation primarily by accelerating collagen deposition, but also by altering the susceptibility of the tubular ECM to decay. These findings support a role for TG2 in the expansion of the ECM associated with kidney scarring.     

Mathematical modelling of extracellular matrix dynamics using discrete cells: fiber orientation and tissue regeneration.

Matrix orientation plays a crucial role in determining the severity of scar tissue after dermal wounding. We present a model framework which allows us to examine the interaction of many of the factors involved in orientation and alignment. Within this framework, cells are considered as discrete objects, while the matrix is modelled as a continuum. Using numerical simulations, we investigate the effect on alignment of changing cell properties and of varying cell interactions with collagen and fibrin.     

Quantitative characterization of binding of small molecules to extracellular matrix

Extracellular matrix (ECM) is a major tissue component that, besides its cell support function, is implicated in cell-cell signaling, wound repair, cell adhesion, and other cell and tissue functions. For small molecules acting in tissues, including chemicals, signaling peptides, effectors, inhibitors, and other man-made and physiological compounds, non-specific binding to ECM is a critical phenomenon affecting their disposition. We describe here a method for a quantitative characterization of the ECM binding, using a solidified ECM layer incubated with medium containing studied small molecules. Working conditions of Matrigel, a commercial basement membrane preparation, were optimized in terms of the protein concentration, surface area, gel layer thickness, solidification time, and mixing speed. The release of proteins from the solidified layer into the buffer was monitored and taken into account. Two major proteins, laminin and collagen IV, dissolve at different rates. The Matrigel stability data, obtained under varying incubation conditions and gentle mixing, can also be useful in other ECM-related research. The experimental binding data, averaged over all binding sites, were analyzed assuming a fast linear binding. The binding constants were determined for 10 small organic molecules for both dissolved proteins and the solidified layer. The binding constants tend to increase with lipophilicity of the compounds, as characterized by the 1-octanol/water partition coefficients.     

Substrate-dependent differences in production of extracellular matrix molecules by squamous carcinoma cells and diploid fibroblasts

Two human squamous carcinoma cell lines and human diploid fibroblasts were examined for the production of extracellular matrix (ECM) molecules including fibronectin (FN), laminin (LN), and thrombospondin (TSP) when grown on a number of different substrates. The substrates used included glass, plastic, collagen (gelatin), and DEAE-dextran. Levels of TSP as indicated by enzyme-linked immunosorbent assay did not vary significantly as a function of substrate. In contrast, LN levels in the culture medium were significantly decreased when the cells were grown on DEAE-dextran or collagen-linked dextran as compared to the other substrates. FN levels were slightly lower in the culture medium of the cells grown on DEAE-dextran. Biosynthetic labeling followed by immunoprecipitation indicated that the reduction in LN was due, in part, to decreased biosynthesis. Previous studies have indicated that LN influences the behavior of epithelial cells in culture and that the cells, themselves, are a major source of the LN. The differences in LN production noted here indicate that the production of this ECM component is influenced by the substratum on which the cells are grown. These differences could contribute to alterations in biological properties that are known to be influenced by the substratum.     

Interactions of the extracellular matrix proteoglycans decorin and biglycan with C1q and collectins

Decorin and biglycan are closely related abundant extracellular matrix proteoglycans that have been shown to bind to C1q. Given the overall structural similarities between C1q and mannose-binding lectin (MBL), the two key recognition molecules of the classical and the lectin complement pathways, respectively, we have examined functional consequences of the interaction of C1q and MBL with decorin and biglycan. Recombinant forms of human decorin and biglycan bound C1q via both collagen and globular domains and inhibited the classical pathway. Decorin also bound C1 without activating complement. Furthermore, decorin and biglycan bound efficiently to MBL, but only biglycan could inhibit activation of the lectin pathway. Other members of the collectin family, including human surfactant protein D, bovine collectin-43, and conglutinin also showed binding to decorin and biglycan. Decorin and biglycan strongly inhibited C1q binding to human endothelial cells and U937 cells, and biglycan suppressed C1q-induced MCP-1 and IL-8 production by human endothelial cells. In conclusion, decorin and biglycan act as inhibitors of activation of the complement cascade, cellular interactions, and proinflammatory cytokine production mediated by C1q. These two proteoglycans are likely to down-regulate proinflammatory effects mediated by C1q, and possibly also the collectins, at the tissue level.     

Binding of Streptococcus mutans to extracellular matrix molecules and fibrinogen

We have determined the ability of Streptococcus mutans cells to bind to extracellular matrix (ECM) molecules and fibrinogen. S. mutans cells were found to bind fibronectin, laminin, collagen type I, and fibrinogen. An isogenic S. mutans strain with a defect in the expression of the major surface protein of S. mutans, antigen I/II, possessed a reduced ability to bind fibronectin, collagen, and fibrinogen but not laminin, suggesting that antigen I/II contributes during pathological processes to the interaction of S. mutans cells with fibronectin, collagen type I, and fibrinogen.