Growth factor regulation of smooth muscle actin expression and contraction of human articular chondrocytes and meniscal cells in a collagen-GAG matrix

Combining TGF-β1 and Mechanical Anchoring to Enhance Collagen Fiber Formation and Alignment in Tissue-Engineered Menisci

Recapitulating the collagen fiber structure of native menisci is one of the major challenges in the development of tissue-engineered menisci. Native collagen fibers are developed by the complex interplay of biochemical and biomechanical signals. In this study, we optimized glucose and transforming growth factor-β1 (TGF-β1) concentrations in combination with mechanical anchoring to balance contributions of proteoglycan synthesis and contractile behavior in collagen fiber assembly. Glucose had a profound effect on the final dimensions of collagen-based constructs. TGF-β1 influenced construct contraction rate and glycosaminoglycan (GAG) production with two half-maximal effective concentration (EC₅₀) ranges, which are 0.23 to 0.28 and 0.53 to 1.71 ng/mL, respectively. At concentrations less than the EC₅₀, for the GAG production and contraction rate, TGF-β1 treatment resulted in less organized collagen fibers. At concentrations greater than the EC₅₀, TGF-β1 led to dense, disorganized collagen fibers. Between the two EC₅₀ values, collagen fiber diameter and length increased. The effects of TGF-β1 on fiber development were enhanced by mechanical anchoring, leading to peaks in fiber diameter, length, and alignment index. Fiber diameter and length increased from 7.9 ± 1.4 and 148.7 ± 16.4 to 17.5 ± 2.1 and 262.0 ± 13.0 μm, respectively. The alignment index reached 1.31, comparable to that of native tissue, 1.40. These enhancements in fiber architecture resulted in significant increases in tensile modulus and ultimate tensile stress (UTS) by 1.6- and 1.4-fold. Correlation analysis showed that tensile modulus and UTS strongly correlated with collagen fiber length, diameter, and alignment, while compressive modulus correlated with GAG content. These outcomes highlight the need for optimization of both biochemical and biomechanical cues in the culture environment for enhancing fiber development within tissue-engineered constructs.

The Role of Fibrosis in Osteoarthritis Progression

Osteoarthritis (OA) is a chronic degenerative joint disease where the main characteristics include cartilage degeneration and synovial membrane inflammation. These changes in the knee joint eventually dampen the function of the joint and restrict joint movement, which eventually leads to a stage where total joint replacement is the only treatment option. While much is still unknown about the pathogenesis and progression mechanism of OA, joint fibrosis can be a critical issue for better understanding this disease. Synovial fibrosis and the generation of fibrocartilage are the two main fibrosis-related characteristics that can be found in OA. However, these two processes remain mostly misunderstood. In this review, we focus on the fibrosis process in OA, especially in the cartilage and the synovium tissue, which are the main tissues involved in OA.

Vitreous Proteomics Provides New Insights into Antivascular Endothelial Growth Factor Therapy for Pathologic Myopia Choroid Neovascularization

This study aimed to investigate the protein expression profile of vitreous humor (VH) from pathologic myopic retinoschisis (PMRS) patients with or without intravitreal antivascular endothelial growth factor (anti-VEGF) therapy. VH samples from PMRS patients were subjected to proteomic analysis. Clinical data, including visual acuity, refractive error, and axial length, were recorded, and the fundus optical coherence tomography was performed. Seven PMRS patients were enrolled: 3 PMRS patients as control group, 3 PMRS patients with coexisting choroidal neovascularization (CNV) who developed retinoschisis aggravation after multiple intravitreal conbercept (IVC) injections, and one PMRS patient with coexisting CNV without leakage CNV (CNV-). A total of 310 differentially expressed proteins were identified in these VH samples. The expression of 28 proteins, related to cellular adhesion, protease inhibitors, proangiogenic factors, and antiangiogenic factors, was significantly downregulated in the IVC-treated eyes than in control- and CNV-eyes. α-smooth muscle actin (α-SMA) expression was significantly upregulated in the IVC-treated eyes. Furthermore, the expression of αA-crystallin and fibrillin-1 was significantly upregulated in both IVC and CNV-eyes than in control eyes. These suggest that multiple IVC injections may increase the VH αSMA concentration, which may contribute to posterior hyaloid membrane or retinal inner limiting membrane contraction. Label-free proteomics is an efficient method to provide further insight into the pathogenesis of vitreoretinal diseases.

[Effects of staurosporine on the contraction of self-assembled constructs of goat temporomandibular joint disc cells]

OBJECTIVE

The effects of the staurosporine on contraction of self-assembled constructs and extracellular matrix syntheses of goat temporomandibular joint discs were investigated.

METHODS

Goat temporomandibular joint disc cells were isolated and cultured to P3, and 5.5×10⁶ cells were combined with different concentrations of staurosporine (0, 0.1, 1, 10, 100 nmol·L⁻¹) in agarose wells and cultured for one week. The samples were frozen and sectioned. Safranin-O,  Picro-sirius red and immunohistochemical staining were performed to observe the distributions of the extracellular matrix and the expression of alpha-smooth muscle actin (α-SMA). Enzyme linked immunosorbent assay (ELISA) and Blyscan kits were utilized to quan--titatively detect the contents of type Ⅰ collagen (ColⅠ) and glycosaminoglycans (GAGs).

RESULTS

Each group of goat temporo-mandibular joint disc cells in the agarose wells were gathered to self-assemble into a disc-shaped base for 4 hours and then to gradually contract into a round shape. The Picro-sirius red staining was strong and indicated collagen distribution. The Safranin-O staining observed GAGs throughout the entire construct. The expression of ColⅠ was strongly posi-tive in the staurosporine groups; however, the expression of α-SMA was weak. ColⅠ and GAGs contents in the stau-rosporine groups were greater than that of the control group, especially in the 10 nmol·L⁻¹ group (P<0.01).

CONCLUSIONS

Staurosporine has a certain effect on the shrinkage of self-assembled constructs; however, such effect is not prominent. Staurosporine contributes to the construction synthesis of extracellular matrix.

Biochemical Stimulus-Based Strategies for Meniscus Tissue Engineering and Regeneration

Meniscus injuries are very common and still pose a challenge for the orthopedic surgeon. Meniscus injuries in the inner two-thirds of the meniscus remain incurable. Tissue-engineered meniscus strategies seem to offer a new approach for treating meniscus injuries with a combination of seed cells, scaffolds, and biochemical or biomechanical stimulation. Cell- or scaffold-based strategies play a pivotal role in meniscus regeneration. Similarly, biochemical and biomechanical stimulation are also important. Seed cells and scaffolds can be used to construct a tissue-engineered tissue; however, stimulation to enhance tissue maturation and remodeling is still needed. Such stimulation can be biomechanical or biochemical, but this review focuses only on biochemical stimulation. Growth factors (GFs) are one of the most important forms of biochemical stimulation. Frequently used GFs always play a critical role in normal limb development and growth. Further understanding of the functional mechanism of GFs will help scientists to design the best therapy strategies. In this review, we summarize some of the most important GFs in tissue-engineered menisci, as well as other types of biological stimulation.

Complex coacervation in charge complementary biopolymers: Electrostatic versus surface patch binding

In this review, a number of systems are described to demonstrate the effect of polyelectrolyte chain stiffness (persistence length) on the coacervation phenomena, after we briefly review the field. We consider two specific types of complexation/coacervation: in the first type, DNA is used as a fixed substrate binding to flexible polyions such as gelatin A, bovine serum albumin and chitosan (large persistence length polyelectrolyte binding to low persistence length biopolymer), and in the second case, different substrates such as gelatin A, bovine serum albumin, and chitosan were made to bind to a polyion gelatin B (low persistence length substrate binding to comparable persistence length polyion). Polyelectrolyte chain flexibility was found to have remarkable effect on the polyelectrolyte-protein complex coacervation. The competitive interplay of electrostatic versus surface patch binding (SPB) leading to associative interaction followed by complex coacervation between these biopolymers is elucidated. We modelled the SPB interaction in terms of linear combination of attractive and repulsive Coulombic forces with respect to the solution ionic strength. The aforesaid interactions were established via a universal phase diagram, considering the persistence length of polyion as the sole independent variable.

Advances and Prospects in Tissue-Engineered Meniscal Scaffolds for Meniscus Regeneration

The meniscus plays a crucial role in maintaining knee joint homoeostasis. Meniscal lesions are relatively common in the knee joint and are typically categorized into various types. However, it is difficult for inner avascular meniscal lesions to self-heal. Untreated meniscal lesions lead to meniscal extrusions in the long-term and gradually trigger the development of knee osteoarthritis (OA). The relationship between meniscal lesions and knee OA is complex. Partial meniscectomy, which is the primary method to treat a meniscal injury, only relieves short-term pain; however, it does not prevent the development of knee OA. Similarly, other current therapeutic strategies have intrinsic limitations in clinical practice. Tissue engineering technology will probably address this challenge by reconstructing a meniscus possessing an integrated configuration with competent biomechanical capacity. This review describes normal structure and biomechanical characteristics of the meniscus, discusses the relationship between meniscal lesions and knee OA, and summarizes the classifications and corresponding treatment strategies for meniscal lesions to understand meniscal regeneration from physiological and pathological perspectives. Last, we present current advances in meniscal scaffolds and provide a number of prospects that will potentially benefit the development of meniscal regeneration methods.

Overexpression of TGF-β via rAAV-Mediated Gene Transfer Promotes the Healing of Human Meniscal Lesions Ex Vivo on Explanted Menisci

BACKGROUND

Direct application of therapeutic gene vectors derived from the adeno-associated virus (AAV) might be beneficial to improve the healing of meniscal tears.

PURPOSE

To test the ability of recombinant AAV (rAAV) to overexpress the potent transforming growth factor-β (TGF-β) in primary cultures of human meniscal fibrochondrocytes, in human meniscal explants, and in experimental human meniscal lesions as a new tool to enhance meniscal repair.

STUDY DESIGN

Controlled laboratory study.

METHODS

The effects of the candidate treatment on the proliferative and metabolic activities of meniscal cells were monitored in vitro for up to 21 days and in situ in intact and injured human menisci for up to 15 days using biochemical, immunohistochemical, histological, and histomorphometric analyses.

RESULTS

Efficient production of TGF-β via rAAV was achieved in vitro and in situ, both in the intact and injured meniscus. Application of the rAAV TGF-β vector stimulated the levels of cell proliferation and matrix synthesis (type I collagen) compared with control gene transfer in all systems tested, especially in situ in regions of poor healing capacity and in sites of meniscal injury. No adverse effects of the candidate treatment were observed at the level of osseous differentiation, as tested by immunodetection of type X collagen. Most remarkably, a significant reduction of the amplitude of meniscal tears was noted after TGF-β treatment, an effect that was associated with increased expression levels of the α-smooth muscle actin contractile marker.

CONCLUSION

Overexpression of TGF-β via rAAV gene transfer is capable of modulating the reparative activities of human meniscal cells, allowing for the healing of meniscal lesions by convenient injection in sites of injury.

CLINICAL RELEVANCE

Direct gene-based approaches using rAAV have strong potential to develop new therapeutic options that aim at treating human meniscal defects.

Why menisci show higher healing rate when repaired during ACL reconstruction? Growth factors release can be the explanation

PURPOSE

Healing rate of meniscus repair is higher when the suture is associated with anterior cruciate ligament reconstruction. A possible explanation can be a different pattern of release of growth factors between anterior cruciate ligament reconstruction and isolated meniscus surgery. Hypothesis of this study is that the concentrations of bFGF, TGF-β and platelet-derived growth factor (PDGF) in joint fluid, immediately after single-bundle anterior cruciate ligament reconstruction and arthroscopic partial meniscectomy, can be different.

METHODS

Twenty consecutive patients underwent partial medial meniscectomy and twenty consecutive patients underwent single-bundle anterior cruciate ligament reconstruction with hamstring grafts were enrolled in the study. Thirty minutes after the end of the surgical procedure, a sample of joint fluid, as well of venous blood, was collected from all the patients. Concentrations of growth factors were determined by enzyme-linked immunosorbent assay.

RESULTS

The peripheral blood concentration of TGF-β, bFGF and PDGF was comparable between partial meniscectomy and anterior cruciate ligament reconstruction groups. No differences between the two surgical techniques were also found in term of TGF-β and bFGF joint fluid concentration, whereas joint PDGF concentration of anterior cruciate ligament reconstruction patients was significantly higher than the one found in partial meniscectomy patients.

CONCLUSIONS

A significant growth factors release was detected in the knee joint during arthroscopic surgery. PDGF concentration was significantly higher in anterior cruciate ligament reconstructed knee than in the meniscectomy group. PDGF can play an important role enhancing the healing response of meniscus suture and can be one of the biological reasons of the higher meniscal healing rate in anterior cruciate ligament reconstructed knee.

Hypoxia enhances chondrogenic differentiation of human adipose tissue-derived stromal cells in scaffold-free and scaffold systems

Human adipose-derived stromal cells (hASCs) possess the potential for chondrogenic differentiation. Recent studies imply that this differentiation process may be enhanced by culturing the cells in low oxygen tension in combination with three-dimensional (3D) scaffolds. We report the evaluation of the chondrogenic potential of hASC pellets in 5 and 21% O2 and as cell-scaffold constructs using a collagen I/III scaffold with chemical induction using TGF-β3. hASCs from four human donors were cultured both in a micromass pellet system and in 3D collagen I/III scaffolds in either 5 or 21% O2. Chondrogenesis was evaluated by quantitative gene expression analysis of aggrecan, SOX9, collagen I, II and X and histological evaluation with H&E and toluidine blue staining. Induced pellets cultured in 5% O2 showed increased peripheral cellularity and matrix deposition compared with 21% O2. Induced pellets cultured in 5% O2 had increased control-adjusted gene expression of aggrecan, SOX9 and collagen I and decreased collagen X compared with 21% O2 cultures. Induced pellets had higher gene expression of aggrecan, SOX9, collagen I, II and X and increased ratios of collagen II/I and collagen II/X compared with controls. As for pellets, scaffold cultures showed cellularity and matrix deposition organized in a zonal manner as a function of the oxygen tension, with a cartilage-like morphology and matrix deposition peripherally in the 5% O2 group and a more centrally located matrix in the 21% O2 group. There were no differences in histology and gene expressions between pellet and scaffold cultures. Five percent O2 in combination with chondrogenic culture medium stimulated chondrogenic differentiation of hASCs in vitro. We observed similar patterns of differentiation and matrix disposition in pellet and scaffold cultures.

The effect of IGF-I on anatomically shaped tissue-engineered menisci

This study investigates the effect of insulin-like growth factor (IGF)-I on the development of anatomically-shaped alginate menisci seeded with meniscal fibrochondrocytes. To accomplish this, bovine meniscal fibrochondrocytes were seeded into 2% w/v alginate, crosslinked with calcium sulfate, and injected into anatomical molds derived from microcomputed tomography scans. The meniscal constructs were then cultured for up to 4 weeks with or without 100 ng/mL IGF-I supplemented in the media. Histological, immunohistological, biochemical, and mechanical analyses were performed to characterize tissue development, accumulation and localization of extracellular matrix, and mechanical properties. After 4 weeks of culture, IGF-I treatment significantly improved mechanical and biochemical properties, while maintaining DNA content, with a 26-fold increase in glycosaminoglycan (GAG) content and 10-fold increase in collagen content compared to 0-week controls, and a 3-fold increase in the equilibrium modulus at 2 weeks compared to controls. IGF-I-treated menisci had ∼60% of the GAG content of native tissue and the compressive equilibrium modulus matched native properties by 2 weeks of culture. Further, IGF-I-treated menisci developed a distinct surface layer similar to native tissue with elongated cells and collagen fibers aligned parallel to the surface, the presence of types I and II collagen, and accumulation of lubricin. This study demonstrates that IGF-I treatment can greatly increase the mechanical and biochemical properties of engineered tissues and aid in the development of a distinct surface zone similar to the superficial zone of native menisci.

Engineering biomaterials to integrate and heal: the biocompatibility paradigm shifts

This article focuses on one of the major failure routes of implanted medical devices, the foreign body reaction (FBR)--that is, the phagocytic attack and encapsulation by the body of the so-called "biocompatible" biomaterials comprising the devices. We then review strategies currently under development that might lead to biomaterial constructs that will harmoniously heal and integrate into the body. We discuss in detail emerging strategies to inhibit the FBR by engineering biomaterials that elicit more biologically pertinent responses.

CD34 and SMA expression of superficial zone cells in the normal and pathological human meniscus

The aim of this study was to evaluate histological changes in torn (0.5-27 weeks after injury) and osteoarthritic (OA) knee menisci versus normal menisci after PAS-AB, SAF-O-FG, and immunostaining for CD34, CD31, and smooth muscle actin (SMA). Cell layers in the superficial zone and the cell density in the deep zone of the menisci were counted. In the superficial zone of normal menisci, cells expressing CD34 were demonstrated. CD34(+) CD31(-) cells were absent in OA menisci and disappeared in torn menisci as a function of time. In contrast, an increase of SMA(+) cells combined with an increase of cell layers was observed in the superficial zone of torn menisci. SMA(+) cells were absent in normal and OA menisci. The predominant tissue type in torn menisci evolved from fibrocartilage-like to fibrous-like tissue as a function of time, whereas in OA menisci it became cartilage-like. The response of the superficial zone was reflected by the decrease of CD34(+) and the increase of SMA(+) cells in torn menisci and the transformation of a fibrous-like into a cartilage-like surface layer in OA menisci. These results potentially illustrate the contribution of CD34(+) cells to the homeostasis of meniscus tissue.

Advances in meniscal tissue engineering

Meniscal tears are the most common knee injuries and have a poor ability of healing. In the last few decades, several techniques have been increasingly used to optimize meniscal healing. Current research efforts of tissue engineering try to combine cell-based therapy, growth factors, gene therapy, and reabsorbable scaffolds to promote healing of meniscal defects. Preliminary studies did not allow to draw definitive conclusions on the use of these techniques for routine management of meniscal lesions. We performed a review of the available literature on current techniques of tissue engineering for the management of meniscal tears.

The knee meniscus: structure-function, pathophysiology, current repair techniques, and prospects for regeneration

Extensive scientific investigations in recent decades have established the anatomical, biomechanical, and functional importance that the meniscus holds within the knee joint. As a vital part of the joint, it acts to prevent the deterioration and degeneration of articular cartilage, and the onset and development of osteoarthritis. For this reason, research into meniscus repair has been the recipient of particular interest from the orthopedic and bioengineering communities. Current repair techniques are only effective in treating lesions located in the peripheral vascularized region of the meniscus. Healing lesions found in the inner avascular region, which functions under a highly demanding mechanical environment, is considered to be a significant challenge. An adequate treatment approach has yet to be established, though many attempts have been undertaken. The current primary method for treatment is partial meniscectomy, which commonly results in the progressive development of osteoarthritis. This drawback has shifted research interest toward the fields of biomaterials and bioengineering, where it is hoped that meniscal deterioration can be tackled with the help of tissue engineering. So far, different approaches and strategies have contributed to the in vitro generation of meniscus constructs, which are capable of restoring meniscal lesions to some extent, both functionally as well as anatomically. The selection of the appropriate cell source (autologous, allogeneic, or xenogeneic cells, or stem cells) is undoubtedly regarded as key to successful meniscal tissue engineering. Furthermore, a large variation of scaffolds for tissue engineering have been proposed and produced in experimental and clinical studies, although a few problems with these (e.g., byproducts of degradation, stress shielding) have shifted research interest toward new strategies (e.g., scaffoldless approaches, self-assembly). A large number of different chemical (e.g., TGF-β1, C-ABC) and mechanical stimuli (e.g., direct compression, hydrostatic pressure) have also been investigated, both in terms of encouraging functional tissue formation, as well as in differentiating stem cells. Even though the problems accompanying meniscus tissue engineering research are considerable, we are undoubtedly in the dawn of a new era, whereby recent advances in biology, engineering, and medicine are leading to the successful treatment of meniscal lesions.

Next generation of electrosprayed fibers for tissue regeneration

Electrospinning is a widely established polymer-processing technology that allows generation of fibers (in nanometer to micrometer size) that can be collected to form nonwoven structures. By choosing suitable process parameters and appropriate solvent systems, fiber size can be controlled. Since the technology allows the possibility of tailoring the mechanical properties and biological properties, there has been a significant effort to adapt the technology in tissue regeneration and drug delivery. This review focuses on recent developments in adapting this technology for tissue regeneration applications. In particular, different configurations of nozzles and collector plates are summarized from the view of cell seeding and distribution. Further developments in obtaining thick layers of tissues and thin layered membranes are discussed. Recent advances in porous structure spatial architecture parameters such as pore size, fiber size, fiber stiffness, and matrix turnover are summarized. In addition, possibility of developing simple three-dimensional models using electrosprayed fibers that can be utilized in routine cell culture studies is described.

Three-dimensional scaffold of electrosprayed fibers with large pore size for tissue regeneration

The regeneration of tissues using biodegradable porous scaffolds has been intensely investigated. Since electrospinning can produce scaffolds mimicking nanofibrous architecture found in the body, it has recently gained widespread attention. However, a major problem is the lack of pore size necessary for infiltration of cells into the layers below the surface, restricting cell colonization to the surfaces only. This study describes a novel twist to the traditional electrospinning technology: specifically, collector plates are designed which allow the formation of very thin layers with pore sizes suitable for cell infiltration. The thin samples could be handled without mechanically damaging the structure and could be transferred into cell culture. These thin layers were stacked layer-by-layer to develop thick structures. Thirty day cultures of fibroblasts show attachment and spreading of cells in every layer. This concept is useful in regenerating thick tissues with uniformly distributed cells and others in in vitro cell culture.

Investigation of the regenerative capacity of an acellular porcine medial meniscus for tissue engineering applications

Previously, we have described the development of an acellular porcine meniscal scaffold. The aims of this study were to determine the immunocompatibility of the scaffold and capacity for cellular attachment and infiltration to gain insight into its potential for meniscal repair and replacement. Porcine menisci were decellularized by exposing the tissue to freeze-thaw cycles, incubation in hypotonic tris buffer, 0.1% (w/v) sodium dodecyl sulfate in hypotonic buffer plus protease inhibitors, nucleases, hypertonic buffer followed by disinfection using 0.1% (v/v) peracetic, and final washing in phosphate-buffered saline. In vivo immunocompatibility was assessed after implantation of the acellular meniscal scaffold subcutaneously into galactosyltransferase knockout mice for 3 months in comparison to fresh and acellular tissue treated with α-galactosidase (negative control). The cellular infiltrates in the explants were assessed by histology and characterized using monoclonal antibodies against: CD3, CD4, CD34, F4/80, and C3c. Static culture was used to assess the potential of acellular porcine meniscal scaffold to support the attachment and infiltration of primary human dermal fibroblasts and primary porcine meniscal cells in vitro. The explants were surrounded by capsules that were more pronounced for the fresh meniscal tissue compared to the acellular tissues. Cellular infiltrates compromised mononuclear phagocytes, CD34-positive cells, and nonlabeled fibroblastic cells. T-lymphocytes were sparse in all explanted tissue types and there was no evidence of C3c deposition. The analysis revealed an absence of a specific immune response to all of the implanted tissues. Acellular porcine meniscus was shown to be capable of supporting the attachment and infiltration of primary human fibroblasts and primary porcine meniscal cells. In conclusion, acellular porcine meniscal tissue exhibits excellent immunocompatibility and potential for cellular regeneration in the longer term.

Chondrocytes and meniscal fibrochondrocytes differentially process aggrecan during de novo extracellular matrix assembly

Aggrecan is an extracellular matrix molecule that contributes to the mechanical properties of articular cartilage and meniscal fibrocartilage, but the abundance and processing of aggrecan in these tissues are different. The objective of this study was to compare patterns of aggrecan processing by chondrocytes and meniscal fibrochondrocytes in tissue explants and cell-agarose constructs. The effects of transforming growth factor-beta 1 (TGF-beta1) stimulation on aggrecan deposition and processing were examined, and construct mechanical properties were measured. Fibrochondrocytes synthesized and retained less proteoglycans than did chondrocytes in tissue explants and agarose constructs. In chondrocyte constructs, TGF-beta1 induced the accumulation of a 120-kDa aggrecan species previously detected in mature bovine cartilage. Fibrochondrocyte-seeded constructs contained high-molecular-weight aggrecan but lacked aggrecanase-generated fragments found in native, immature meniscus. In addition, reflecting the lesser matrix accumulation, fibrochondrocyte constructs had significantly lower compression moduli than did chondrocyte constructs. These cell type-specific differences in aggrecan synthesis, retention, and processing may have implications for the development of functional engineered tissue grafts.

rAAV-mediated overexpression of FGF-2 promotes cell proliferation, survival, and alpha-SMA expression in human meniscal lesions

Meniscal tears are a common problem in sports medicine. Direct application of therapeutic vectors derived from the adeno-associated virus might be beneficial to enhance meniscal repair. We tested the hypothesis that overexpression of fibroblast growth factor 2 (FGF-2) through recombinant adeno-associated virus (rAAV) vectors leads to detectable metabolic changes in human meniscal fibrochondrocytes and in human meniscal defects. rAAV-mediated gene transfer was investigated for its ability to promote FGF-2 secretion in human meniscal fibrochondrocytes in vitro, in intact human meniscal explants in situ, and in experimentally created human meniscal lesions. Effects of the treatment on cell proliferation and survival, extracellular matrix synthesis, and expression of the alpha-smooth muscle actin (alpha-SMA) contractile marker were monitored using biochemical, immunohistochemical, histological, and histomorphometric analyses. Efficient production of FGF-2 through rAAV could be achieved in vitro and in situ, both in the intact and injured meniscus. Application of the candidate FGF-2 vector allowed for enhanced cell proliferation and survival compared with control transduction, in particular in areas with poor healing capacity and in sites of injury, consistent with the mitogenic activities of the growth factor. Remarkably, a significant reduction of the amplitude of meniscal tears was noted after FGF-2 treatment, with increased levels of alpha-SMA expression. In contrast, there was no significant stimulation of synthesis of the major extracellular matrix components when the candidate vector was applied and instead, a decrease in the matrix/DNA contents was reported, in good agreement with the properties of FGF-2. Such a direct gene-based approach may have value in options aiming at treating human meniscal defects.

Comparison of chondrogenic potential in equine mesenchymal stromal cells derived from adipose tissue and bone marrow

OBJECTIVE

To compare the chondrogenic potential of adult equine mesenchymal stem cells derived from bone marrow (MSCs) or adipose tissue (ASCs).

STUDY DESIGN

In vitro experimental study.

ANIMALS

Adult Thoroughbred horses (n=11).

METHODS

BM (5 horses; mean [+/-SD] age, 4+/-1.4 years) or adipose tissue (6 horses; mean age, 3.5+/-1.1 years) samples were obtained. Cryopreserved MSCs and ASCs were used for pellet cultures in stromal medium (C) or induced into chondrogenesis+/-transforming growth factor-3 (TGFbeta(3)) and bone morphogenic factor-6 (BMP-6). Pellets harvested after 3, 7, 14, and 21 days were examined for cross-sectional size and tissue composition (hematoxylin and eosin), glycosaminoglycan (GAG) staining (Alcian blue), collagen type II immunohistochemistry, and by transmission electron microscopy. Pellet GAG and total DNA content were measured using dimethylmethylene blue and Hoechst DNA assays.

RESULTS

Collagen type II synthesis was predominantly observed in MSC pellets from Day 7 onward. Unlike ASC cultures, MSC pellets had hyaline-like matrix by Day 14. GAG deposition occurred earlier in MSC cultures compared with ASC cultures and growth factors enhanced both MSC GAG concentrations (P<.0001) and MSC pellet size (P<.004) after 2 weeks in culture.

CONCLUSION

Equine MSCs have superior chondrogenic potential compared with ASCs and the equine ASC growth factor response suggests possible differences compared with other species.

CLINICAL RELEVANCE

Elucidation of equine ASC and MSC receptor profiles will enhance the use of these cells in regenerative cartilage repair.

TGFbeta affects collagen cross-linking independent of chondrocyte phenotype but strongly depending on physical environment

Transforming growth factor beta (TGFbeta) is often used in cartilage tissue engineering to increase matrix formation by cells with various phenotypes. However, adverse effects of TGFbeta, such as extensive crosslinking in cultured fibroblasts, have also been reported. Our goal was to study effects of TGFbeta on collagen cross-linking and evaluating the role of cellular phenotype and physical environment. We therefore used four different cell populations in two very different physical environments: primary and expanded chondrocytes and fibroblasts embedded in alginate gel and attached to tissue culture plastic. Matrix production, collagen cross-linking, and alpha-smooth muscle actin (alphaSMA) were analyzed during 4 weeks with or without 2.5 ng/ mL TGFbeta2. TGFbeta2 did not affect collagen deposition by primary cells. In expanded cells, TGFbeta2 increased collagen deposition. Chondrocytes and fibroblasts in monolayer produced more collagen cross-links with TGFbeta2. In alginate, primary and expanded cells displayed an unexpected decrease in collagen cross-linking with TGFbeta2. alphaSMA was not present in alginate cultures and barely upregulated by TGFbeta2. Organized alphaSMA fibers were present in all monolayer cultures and became more pronounced with TGFbeta2. This study demonstrates that the physical environment determined by the substrate used co-determines the response of cells to TGFbeta. The presence of mechanical stress, determined with alphaSMA-staining, is probably responsible for the increase in collagen cross-linking upon addition of TGFbeta.

The stress relaxation characteristics of composite matrices etched to produce nanoscale surface features

Many synthetic and xenogenic natural matrices have been explored in tissue regeneration, however, they lack either mechanical strength or cell colonization characteristics found in natural tissue. Moreover natural matrices such as small intestinal submucosa (SIS) lack sample to sample homogeneity, leading to unpredictable clinical outcomes. This work explored a novel fabrication technique by blending together the useful characteristics of synthetic and natural polymers to form a composite structure by using a NaOH etching process that produces nanoscale surface features. The composite scaffold was formed by sandwiching a thin layer of PLGA between porous layers of gelatin-chitosan. The etching process increased the surface roughness of PLGA membrane, allowing easy spreading of the hydrophilic gelatin-chitosan solution on its hydrophobic surface and reducing the scaffold thickness by nearly 50% than otherwise. The viscoelastic properties of the scaffold, an area of mechanical analysis which remains largely unexplored in tissue regeneration was assessed. Stress relaxation experiments of the "ramp and hold" type performed at variable ranges of temperature (25 degrees C and 37 degrees C), loading rates (3.125% s(-1) and 12.5% s(-1)) and relaxation times (60 s, 100 s and 200 s) found stress relaxation to be sensitive to temperature and the loading rate but less dependent on the relaxation time. Stress relaxation behavior of the composite matrix was compared with SIS structures at 25 degrees C (hydrated), 3.125% s(-1) loading rate and 100 s relaxation time which showed that the synthetic matrix was found to be strain softening as compared to the strain hardening behavior exhibited by SIS. Popularly used quasi-linear viscoelastic (QLV) model to describe biomechanics of soft tissues was utilized. The QLV model predicted the loading behavior with an average error of 3%. The parameters of the QLV model predicted using nonlinear regression analysis appear to be in concurrence with soft tissues.

Cell colonization in degradable 3D porous matrices

Cell colonization is an important in a wide variety of biological processes and applications including vascularization, wound healing, tissue engineering, stem cell differentiation and biosensors. During colonization porous 3D structures are used to support and guide the ingrowth of cells into the matrix. In this review, we summarize our understanding of various factors affecting cell colonization in three-dimensional environment. The structural, biological and degradation properties of the matrix all play key roles during colonization. Further, specific scaffold properties such as porosity, pore size, fiber thickness, topography and scaffold stiffness as well as important cell material interactions such as cell adhesion and mechanotransduction also influence colonization.

Genetically enhanced engineering of meniscus tissue using ex vivo delivery of transforming growth factor-beta 1 complementary deoxyribonucleic acid

To investigate the use of a scaffold seeded with genetically modified meniscal cells or mesenchymal stem cells (MSCs) for the healing of meniscal lesions, primary meniscus cells and bone marrow-derived MSCs were isolated from bovine calves and transduced with first-generation adenoviral vectors encoding green fluorescent protein, luciferase, or transforming growth factor (TGF)-beta1 complementary deoxyribonucleic acid (cDNA). The genetically modified cells were seeded in type I collagen-glycosaminoglycan (GAG) matrices and transplanted into tears of the avascular zone of bovine menisci. After 3 weeks of in vitro culture, constructs and repair tissues were analyzed histologically, biochemically, and using reverse transcriptase polymerase chain reaction. Recombinant adenovirus readily transduced meniscal cells and MSCs, and transgene expression remained high after the cells were incorporated into collagen-GAG matrices. Transfer of TGF-beta1 cDNA increased cellularitiy and the synthesis of GAG/DNA [microg/microg]. It also led to stronger staining for proteoglycans and type II collagen and enhanced expression of meniscal genes. Transplantation of the TGF-beta1 transduced constructs into meniscal lesions of the avascular zone resulted in filling of the lesions with repair tissue after 3 weeks of in vitro culture. These results indicate that TGF-beta1 cDNA delivery may affect cell-based meniscus repair approaches in vivo.

Cartilaginous deposits in subchondral bone in regions of exposed bone in osteoarthritis of the human knee: histomorphometric study of PRG4 distribution in osteoarthritic cartilage

The objective of this study was to identify and characterize cartilaginous deposits aggregates in the subchondral bone in areas of the human osteoarthritic knee with exposed bone. A specific aim was to determine the distribution of the joint lubrication molecule, lubricin/superficial zone protein [referred to by its gene, proteoglycan4 (PRG4)], in these cartilaginous deposits and in osteoarthritic cartilage. This work was carried out in the context of assessing the potential contribution of these chondrocyte aggregates for joint resurfacing in certain cartilage repair procedures. The discarded bone cuts of femoral condyles and tibial plateaus were collected from 11 patients with advanced osteoarthritis (OA) of the knee during total knee arthroplasty; 9 women and 2 men with a mean age of 68 years. Sections of paraffin-embedded tissue were stained with Safranin-O, and with antibodies to type II collagen, alpha-smooth muscle actin (SMA), and PRG4. Chondrocyte aggregates were found in the subchondral bone of regions of exposed bone in sections from five individuals. The average diameter of cartilaginous aggregates was 152 microm, and the average depth of the aggregates below the surface was about 475 microm. Most aggregates were fibrocartilaginous and stained positive for type II collagen. Of interest was the finding that the cartilaginous deposits and osteoarthritic cartilage contained PRG4. Only a small percentage of chondrocytes stained positive for SMA. Cartilaginous deposits containing chondrocyte aggregates exist in subchondral bone in regions of exposed bone in some patients with advanced OA of the knee. These cells may be able to contribute to the resurfacing of the joint in certain cartilage repair procedures.

The effect of growth factor treatment on meniscal chondrocyte proliferation and differentiation on polyglycolic acid scaffolds

The aim of this investigation was to determine the effect of growth factor treatment on ovine meniscal chondrocyte (OMC) proliferation in vitro and on the production of matrix proteins by OMCs grown within a polyglycolic acid (PGA) scaffold. Analysis of 72-h monolayer cultures using the mean transit time (MTT) assay revealed a greater increase in OMC numbers in the presence of platelet-derived growth factor (PDGF)-AB, PDGF-BB, insulin-like growth factor (IGF)-I, transforming growth factor-beta1 (TGF-beta1) and basic fibroblast growth factor (bFGF) than in untreated controls. In contrast, IGF-II and bone morphogenetic protein-2 had no effect on OMC proliferation at the concentrations tested. The growth factors that elicited the greatest proliferative response (PDGF-AB, PDGF-BB, TGF-beta1, and IGF-I) were subsequently tested for their ability to enhance OMC proliferation and differentiation within PGA scaffolds. Biochemical analysis revealed less glycosaminoglycan (GAG) production in the presence of all growth factors tested compared to untreated control samples. In contrast, all of the growth factors increased collagen type I production by OMCs within the scaffolds at day 20, and all except PDGF-BB resulted in an increase at day 39, when compared to appropriate control samples. With the exception of IGF-I, none of the growth factors tested had any significant effect on collagen type II production. Histological staining of sections from OMC-PGA scaffolds did not reveal any difference in GAG or collagen production between the treatment groups. However, immunohistochemical analysis demonstrated an increase in collagen type I expression and a decrease in collagen type II at day 39 in all growth factortreated constructs, concomitant with a high infiltration of cells. This suggests that PDGF-AB, PDGF-BB, TGF-beta1, and IGF-1 may be useful in future tissue engineering studies for promoting meniscal cell proliferation and differentiation within scaffolds.

Characterization of emulsified chitosan–PLGA matrices formed using controlled-rate freezing and lyophilization technique

This study evaluated the formation of chitosan-50:50 poly-lactic-co-glycolic acid (PLGA) blend matrices using controlled-rate freezing and lyophilization technique (CRFLT). An emulsion system was used in the presence of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), a cellular component, as a stabilizer. Blended scaffolds showed an open pore morphology and homogenous interdispersion of PLGA and chitosan. Forming emulsions after dissolving PLGA in chloroform, benzene, or methylene chloride indicated better emulsion stability with benzene and chloroform. Scaffolds formed by freezing at -20, -78, and -196 degrees C from these emulsions showed significant influence of the solvent and freezing temperature on the microarchitecture of the scaffold. By controlling the concentration of chitosan, scaffolds with greater than 90% porosity were attained. Since the two polymers degrade by different mechanisms, formed scaffolds were analyzed for degradation characteristics for 4 weeks in presence of 10 mg/L lysozyme. These results showed no significant difference in the weight loss and dimension changes, as all scaffolds showed significant (a) weight loss and (b) nearly 60% reduction in volume. Further, pH of the incubation media decreased in all the samples. When cellular activity of green fluorescence protein-transfected smooth muscle cells was analyzed, no apparent cytotoxicity was observed. However, the cell spreading area decreased. In summary, these results show promising potential in tissue engineering and drug delivery applications.

Three-dimensional cell colonization in a sulfate rich environment

Glycosaminoglycans (GAGs) have been explored for regenerating various tissues due to their involvement in diverse bioregulatory activity. However, understanding their influence on cell colonization in three-dimension (3-D) has been difficult due to variation in their molecular weight, degree of sulfation, and lack of in vitro models. This research focused on developing an in vitro model and evaluating the influence of MW (5, 10, and 500 kDa) of negatively charged dextran sulfate (DS), a semisynthetic GAG analog, on cell colonization. DS was combined with chitosan, a positively charged polymer in solution and porous 3-D matrices were formed inside 24-well plates using controlled rate freezing and lyophilization technique by two schemes: (i) chitosan structures were formed and then allowed to react with DS; (ii) DS was reacted with chitosan in solution and then matrices were formed. Scanning electron microscopy analysis showed that forming matrices after reacting DS with chitosan was more suitable for tissue regeneration. Analysis for the quantity and stability of DS by toluidine blue assay indicated significant presence of DS in the 3-D matrices even after seven days of incubation in phosphate buffered saline solution. Matrices formed by reacting 4% 5 kDa, 2% 10 kDa and 1% 500 kDa DS solution with chitosan had optimum porosity and mechanical stability. Next, 25,000 fibroblasts per matrix were seeded onto 3-D matrices and analyzed for proliferation by MTT-formazan assay, cytoskeletal organization by actin staining, and histological analysis by H/E staining. These results showed that cell growth was better on low MW containing 2-D membranes but high MW DS containing 3-D matrix supported cell growth similar to chitosan. Also, cells showed peripheral actin distribution in 3-D matrices. Analysis of fibronectin binding by ELISA showed negligible binding to all the DS-containing matrices, unlike chitosan. In summary, results show cell colonization on negatively charged matrices, similar to chitosan.

Alpha-smooth muscle actin expression and structure integrity in chondrogenesis of human mesenchymal stem cells

The expression of alpha-smooth muscle actin (SMA) by human mesenchymal stem cells (hMSCs) during chondrogenesis was investigated by the use of pellet culture. Undifferentiated hMSCs expressed low but detectable amounts of SMA and the addition of transforming growth factor beta1 (TGF-beta1) to the culture medium increased SMA expression in a dose-dependent manner. Differentiation in pellet culture was rapidly induced in the presence of TGF-beta1 and was accompanied by the development of annular layers at the surface of the pellet. These peripheral layers lacked expression of glycosaminoglycan and type II collagen during early differentiation. Progress in differentiation increased the synthesis of glycosaminoglycan and type II collagen and the expression of SMA in these layers. Double-staining for type II collagen and SMA by immunofluorescence demonstrated the differentiation of hMSCs into cells positive for these two proteins. The addition of cytochalasin D, a potent inhibitor of the polymerization of actin microfilaments, caused damage to the structural integrity and surface smoothness of the chondrogenic pellets. The SMA-positive cells in the peripheral layers of the chondrogenic pellets mimic those within the superficial layer of articular cartilage and are speculated to play a major role in cartilage development and maintenance.

TGF-beta1 drives partial myofibroblastic differentiation in chondromyxoid fibroma of bone

Chondromyxoid fibroma (CMF) is a rare benign cartilaginous bone tumour with a lobular architecture containing stellate and myofibroblast-like spindle cells. The aim of this study was to investigate the presence, spatial distribution, and extent of myoid differentiation in CMF and to evaluate a possible causative role for TGF-beta1 signalling, which is known to promote smooth muscle actin (SMA) expression. Twenty cases were studied for immunoreactivity for muscle-specific actin (MSA), SMA, desmin, h-caldesmon, calponin, TGF-beta1, and plasminogen activator inhibitor type 1 (PAI-1). The extent of myofibroblastic differentiation was further investigated ultrastructurally, including immuno-electron microscopy using antibodies against MSA and SMA, focusing upon the different cell types in CMF. The expression of potential genes driving this process was quantified by Q-RT-PCR (TGF-beta1, fibronectin, its EDA splice variant, and PAI-1). Tumour cells, especially those with a spindled morphology, showed diffuse immunoreactivity for MSA, SMA, TGF-beta1, and PAI-1, while desmin, h-caldesmon, and calponin were absent. Ultrastructurally, neoplastic cells showed the presence of myofilaments and rare dense bodies, which were more prominent in spindle cells and less so in chondroblast-like cells. Immuno-electron microscopy confirmed the actin nature of these myofilaments. No fibronexus was identified. The functional activity of TGF-beta1 was demonstrated by the identification of PAI-1, a related downstream molecule both immunohistochemically as well as by Q-RT-PCR. There was a linear correlation between TGF-beta1 and PAI-1 expression. Fibronectin-EDA levels were low. We have therefore substantiated the presence of morphological, immunohistochemical, and immuno-electron microscopic partial myofibroblastic differentiation in CMF, driven by TGF-beta1 signalling.

Culturing of skin fibroblasts in a thin PLGA-collagen hybrid mesh

A thin biodegradable hybrid mesh of synthetic poly(DL-lactic-co-glycolic acid) (PLGA) and naturally derived collagen was used for three-dimensional culture of human skin fibroblasts. The hybrid mesh was constructed by forming web-like collagen microsponges in the openings of a PLGA knitted mesh. The behaviors of the fibroblasts on the hybrid mesh and PLGA knitted mesh were compared. The efficiency of cell seeding was much higher and the cells grew more quickly in the hybrid mesh than in the PLGA mesh. The fibroblasts in the PLGA mesh grew from the peripheral PLGA fibers toward the centers of the openings, while those in the hybrid mesh also grew from the collagen microsponges in the openings of the mesh resulting in a more homogenous growth. The proliferated cells and secreted extracellular matrices were more uniformly distributed in the hybrid mesh than in the PLGA mesh. Histological staining of in vitro cultured fibroblast/mesh implants indicated that the fibroblasts were distributed throughout the hybrid mesh and formed a uniform layer of dermal tissue having almost the same thickness as that of the hybrid mesh. However, the tissue formed in the PLGA mesh was thick adjacent to the PLGA fibers and thin in the center of the openings. Fibroblasts cultured in the hybrid mesh were implanted in the back of nude mouse. Dermal tissues were formed after 2 weeks and became epithelialized after 4 weeks. The results indicate that the web-like collagen microsponges formed in the openings of the PLGA knitted mesh increased the efficiency of cell seeding, improved cell distribution, and therefore facilitated rapid formation of dermal tissue having a uniform thickness. PLGA-collagen hybrid mesh may be useful for skin tissue engineering.

Tissue engineering of cartilage using a hybrid scaffold of synthetic polymer and collagen

A biodegradable hybrid scaffold of synthetic polymer, poly (DL-lactic-co-glycolic acid) (PLGA), and naturally derived polymer, collagen, was prepared by forming collagen microsponges in the pores of PLGA sponge. This was then used as the three-dimensional scaffold for tissue engineering of bovine articular cartilage, both in vitro and in vivo. In vitro studies show that hybridization with collagen facilitated cell seeding in the sponge and raised seeding efficiency. Chondrocytes adhered to the collagen microsponges, where they proliferated and secreted extracellular matrices with time, filling the space within the sponge. Hematoxylin and eosin staining revealed that most of the chondrocytes after 4 weeks of culture, and almost all cell types after 6 weeks of culture, maintained their phenotypically rounded morphology. While new tissue formed, the scaffold degraded and lost almost 36.9% of its original weight after 10 weeks. Subcutaneous implantation studies in nude mice demonstrated more homogeneous tissue formation in hybrid sponge than in PLGA sponge. The new tissue formed maintained the original shape of the hybrid sponge. The synthetic PLGA sponge, serving as a skeleton, facilitated easy formation into desired shapes and provided appropriate mechanical strength to define the ultimate shape of engineered tissue. Incorporation of collagen microsponges facilitated cell seeding and homogeneous cell distribution and created a favorable environment for cellular differentiation. The hybrid sponge could therefore represent a promising candidate as a three-dimensional scaffold for articular cartilage tissue engineering.

Combined effects of growth factors and static mechanical compression on meniscus explant biosynthesis

OBJECTIVE

To compare the actions of fibroblast growth factor-basic (bFGF), insulin-like growth factor-I (IGF-I), platelet derived growth factor-AB (PDGF-AB), and transforming growth factor-beta 1 (TGF-beta1) on bovine meniscus tissue explants with and without static mechanical compression.

DESIGN

Meniscus tissue explants were cultured in a serum-free environment supplemented with an individual growth factor (1) over a range of concentrations for 4 days, (2) at a single concentration for 2-14 days, and (3) at a single concentration for 4 days coupled with graded levels of static compression. Explants were analyzed for accumulation of newly synthesized proteoglycan and total protein as measured by 35S-sulfate and 3H-proline incorporation, respectively.

RESULTS

Over the range of chosen concentrations, TGF-beta1 was the most potent stimulator of both protein and proteoglycan production, whereas bFGF was the least effective stimulator. Over a 2-week period for all four growth factors, the stimulation of proteoglycan production was sustained while there was no stimulation of protein production during this period. The superposition of static mechanical compression inhibited matrix production in the presence of each anabolic factor, with comparable inhibition relative to uncompressed controls for all factors.

CONCLUSIONS

The growth factors chosen exhibited an anabolic effect on the meniscus tissue explants, encouraging matrix production and deposition. The addition of static mechanical compression produced comparable relative inhibition of matrix production for each growth factor, suggesting that static compression and growth factors may modulate meniscal fibrochondrocyte biosynthesis via distinct pathways.

Expression of α-Smooth Muscle Actin by and Contraction of Cells Derived from Synovium

Cells derived from synovium have drawn interest as donor cells for articular cartilage tissue engineering because they have been implicated in certain cartilage repair processes in vivo and the chondrogenic potential of the cells has been demonstrated in vitro. Studies have demonstrated that several other types of musculoskeletal connective tissue cells--including chondrocytes, fibrochondrocytes, ligament fibroblasts and osteoblasts, and mesenchymal stem cells can express the gene for the contractile actin isoform, alpha-smooth muscle actin (SMA), and can contract analogs of extracellular matrix in vitro. Although the physiological roles of SMA-enabled contraction of these cells have yet to be established, cell-mediated contraction of scaffolds employed for tissue engineering can alter the pore diameter of the matrix and distort its overall shape, and thus needs to be addressed. Toward this goal, the objective of this study was to investigate the expression of SMA by synovial cells and to evaluate their contraction of collagen-glycosaminoglycan (GAG) scaffolds. Synovial membranes obtained from the knees (stifle joints) of six adult dogs were evaluated for the presence of SMA by immunohistochemistry. Cells isolated from the synovial tissue were expanded through seven passages in monolayer culture, with samples from each passage allocated for Western blot analysis of SMA. Cells from passage 4 were seeded into porous type I collagen-GAG matrices and cultured for 4 weeks. Synovial cell-mediated contraction of the scaffolds was determined by measuring the diameters of the cell-seeded scaffolds and nonseeded controls every other day. Synovium-derived cells cultured as micropellets or in collagen-GAG matrices were incubated in chondrogenic medium with and without fetal bovine serum and evaluated for chondrogenesis by type II collagen immunohistochemistry. Immunohistochemistry revealed the presence of SMA in some cells (less than 10% of the cells) in the intimal layer of synovium from four of the five animals analyzed. Western blot analysis demonstrated a regular increase in the amount of SMA in the synovium-derived cells with passage number. Synovial cell-mediated contraction of the collagen-GAG scaffolds reached a value of 43% of the original diameter after 4 weeks, comparable to that found with other musculoskeletal cell types. Incubation of micropellet cultures of synovium-derived cells with chondrogenic medium revealed trace amounts of type II collagen production by immunohistochemistry. The findings of this study indicate that control of SMA-enabled contraction may be important when employing synovial cells for cartilage repair procedures, and warrant further investigation into the physiological role of SMA expression in synovial cells.

Tissue engineering of the meniscus

Meniscus lesions are among the most frequent injuries in orthopaedic practice and they will inevitably lead to degeneration of the knee articular cartilage. The fibro-cartilage-like tissue of the meniscus is notorious for its limited regenerative capacity. Tissue engineering could offer new treatment modalities for repair of meniscus tears and eventually will enable the replacement of a whole meniscus by a tissue-engineered construct. Many questions remain to be answered before the final goal, a tissue-engineered meniscus is available for clinical implementation. These questions are related to the selection of an optimal cell type, the source of the cells, the need to use growth factor(s) and the type of scaffold that can be used for stimulation of differentiation of cells into tissues with optimal phenotypes. Particularly in a loaded, highly complex environment of the knee, optimal mechanical properties of such a scaffold seem to be of utmost importance. With respect to cells, autologous meniscus cells seems the optimal cell source for tissue engineering of meniscus tissue, but their availability is limited. Therefore research should be stimulated to investigate the suitability of other cell sources for the creation of meniscus tissue. Bone marrow stroma cells could be useful since it is well known that they can differentiate into bone and cartilage cells. With respect to growth factors, TGF-beta could be a suitable growth factor to stimulate cells into a fibroblastic phenotype but the problems of TGF-beta introduced into a joint environment should then be solved. Polyurethane scaffolds with optimal mechanical properties and with optimal interconnective macro-porosity have been shown to facilitate ingrowth and differentiation of tissue into fibro-cartilage. However, even these materials cannot prevent cartilage degeneration in animal models. Surface modification and/or seeding of cells into the scaffolds before implantation may offer a solution for this problem in the future.This review focuses on a number of specific questions; what is the status of the development of procedures for lesion healing and how far are we from replacing the entire meniscus by a (tissue-engineered) prosthesis. Subquestions related to the type of scaffold used are: is the degree of tissue ingrowth and differentiation related to the initial mechanical properties and if so, what is the influence of those properties on the subsequent remodelling of the tissue into fibro-cartilage; what is the ideal pore geometry and what is the optimal degradation period to allow biological remodelling of the tissue in the scaffold. Finally, we will finish with our latest results of the effect of tear reconstruction and the insertion of prostheses on articular cartilage degradation.

Contractile forces generated by articular chondrocytes in collagen-glycosaminoglycan matrices

The objective of the study was to directly measure the force of contraction of adult articular chondrocytes and to examine their contractile behavior in collagen-glycosaminoglycan analogs of extracellular matrix by live cell imaging in vitro. The contractile forces generated by passages 2 and 3 adult canine articular chondrocytes were measured using a cell force monitor. The contractile behavior of the cells was also directly imaged as they were cultured in collagen-glycosaminoglycan scaffolds. Passage 2 cells seeded in a collagen-glycosaminoglycan scaffold were capable of generating a force of 0.3 nN/cell. Chondrocytes subcultured through a third passage generated a force twice that level, paralleling the increase in the alpha-smooth muscle actin (SMA) content of the cells as demonstrated by Western blot analysis. Treatment of passage 3 cells with staurosporine reduced the force of contraction by approximately one-half, reflecting the effects of this agent in reducing the SMA content of the cells and disrupting the microfilaments. These values compare with 1 nN previously reported for lapine dermal fibroblasts of passage 5-7, using the same apparatus. Direct live cell imaging documented the contractile behavior of the articular chondrocytes in the collagen-glycosaminoglycan matrix in the time frame in which the force was directly measured in the cell force monitor. This imaging demonstrated how the cells acted individually and in unison to buckle the collagen struts making up the matrix. Adult articular chondrocytes are capable of generating a SMA-enabled force of contraction sufficient to model extracellular matrix molecules.

The use of a novel PLGA fiber/collagen composite web as a scaffold for engineering of articular cartilage tissue with adjustable thickness

It has been a great challenge to make the thickness of engineered cartilage adjustable to cover the range of both partial-thickness and full-thickness articular cartilage defects. We developed a novel kind of composite web scaffold that could be used for tissue enginnering of articular cartilage with the thickness adjustable between 200 microm and 8 mm. The composite web showed a unique structure having web-like collagen microsponges formed in the openings of a mechanically strong knitted mesh of poly(lactic-co-glycolic acid). The knitted mesh served as a skeleton reinforcing the composite web, while the web-like collagen microsponges facilitated cell seeding, cell distribution, and tissue formation. Bovine chondrocytes cultured in the composite web showed a spatially even distribution, maintained their natural morphology, and produced cartilaginous extracellular matrices such as type II collagen and aggrecan. The thickness of the implant can be simply adjusted by laminating or rolling the web sheets. Not only did the histological structure of the engineered cartilage patches match the bovine native articular cartilage, but also their dynamic complex modulus, structural stiffness, and phase lag reached 37.8, 57.0, and 86.3% of those of native bovine articular cartilage, respectively. The composite web could be an important scaffold for tissue engineering.

Mechanical characterization of collagen fibers and scaffolds for tissue engineering

Engineered tissues must utilize scaffolding biomaterials that support desired cellular functions and possess or can develop appropriate mechanical characteristics. This study assessed properties of collagen as a scaffolding biomaterial for ligament replacements. Mechanical properties of extruded bovine achilles tendon collagen fibers were significantly affected by fiber diameter, with smaller fibers displaying higher tangent moduli and peak stresses. Mechanical properties of 125 micrometer-diameter extruded fibers (tangent modulus of 359.6+/-28.4MPa; peak stress of 36.0+/-5.4MPa) were similar to properties reported for human ligaments. Scaffolds of extruded fibers did not exhibit viscoelastic creep properties similar to natural ligaments. Collagen fibers from rat tail tendon (a well-studied comparison material) displayed characteristic strain-softening behavior, and scaffolds of rat tail fibers demonstrated a non-intuitive relationship between tangent modulus and specimen length. Composite scaffolds (extruded collagen fibers cast within a gel of Type I rat tail tendon collagen) were maintained with and without fibroblasts under standard culture conditions for 25 days; cell-incorporated scaffolds displayed significantly higher tangent moduli and peak stresses than those without cells. Because tissue-engineered products must possess appropriate mechanical as well as biological/chemical properties, data from this study should help enable the development of improved tissue analogues.

Effects of selected growth factors on porcine meniscus in chemically defined medium

Some evidence shows that selected growth factors can increase proteoglycan synthesis and that fibrin clot aids in the repair of meniscal tears. A significant (P<.05) dose-dependent stimulation of proteoglycan synthesis was found with platelet-derived growth factor AB (PDGF-[AB]), transforming growth factor-beta1 and bone morphogenetic protein-7 (osteogenic protein-I). In separate experiments, a significant increase in cellularity was found in the deep and superficial aspects of the explants treated with PDGF-(AB) compared with those treated with basal medium alone. The current study provides data as to which growth factors might prove most useful in the maintenance and repair of menisci.

Motile chondrocytes from newborn calf: migration properties and synthesis of collagen II

OBJECTIVE

To determine whether differentiated chondrocytes are motile.

DESIGN

Calf articular chondrocytes isolated from six animals were cultured in spinner flasks and removed on days 3 and 7. Boyden chamber assays and time-lapse videomicroscopy were performed to monitor and quantify cell migration. A novel method for selectively harvesting and metabolically labeling the migrated cells was developed, based on cell movement to the underside of the Boyden chamber membranes. The 3H-collagen synthesized by these cells was purified and analyzed by SDS-PAGE and autoradiography either before or after cyanogen bromide cleavage.

RESULTS

In Boyden chambers, locomotion of day 3 chondrocytes on fibronectin-coated membranes was approximately 3-fold higher than on bovine serum albumin-coated controls (39+/-15 vs 12+/-8 cells/mm(2), respectively (P=0.005)). Insulin-like growth factor-I (IGF-I, 10 ng/ml) was chemotactic, increasing motility to 87+/-16 cells/mm(-) (difference from fibronectin alone: P=0.0003). A similar response was observed for day 7 cells, but IGF-I activation was not as pronounced (P=0.055). The collagen patterns produced by the migrated cells closely resembled those of standard collagen type II, without any evidence of collagen I production. In videotracking experiments, motile cells attached on fibronectin exhibited typical lamellipodia and filopodia, and approximately 30% of attached cells were motile (speed >1 micro m/h and directional persistence >1h). Typical cell path lengths were 30-50 micro m, substantially greater than a full cell length displacement.

CONCLUSION

A population of well-differentiated chondrocytes capable of matrix (COL II) synthesis are motile in vitro. This original finding opens new avenues to study the potential of motile cells for cartilage repair.

Transforming growth factor-beta 1-mediated collagen gel contraction by cardiac fibroblasts

OBJECTIVE

Myofibroblasts and transforming growth factor-beta(1) (TGF-beta(1)) are key elements of cardiac tissue fibrosis development. The aim of this study was to determine whether the ability of TGF-beta(1) to affect the contractile activity of cardiac fibroblasts depends on their differentiation into myofibroblasts.

METHODS

Cardiac fibroblasts (from male adult Wistar rats) from passage two were cultured to confluency and incubated on a hydrated collagen gel with and without TGF-beta(1) (0, 20, 40, 100, 200, 400 or 600 pmol/L) for one, two and three days in a Dulbecco's Modified Eagle's Medium without foetal bovine serum.

RESULTS

TGF-beta(1) dose-dependently increased the contraction of collagen gel mediated by cardiac fibroblasts, reaching a maximal effect at 100 pmol/L TGF-beta(1). TGF-beta(1) also stimulated 3(H)-thymidine incorporation and total protein content in cardiac fibroblasts in the collagen gel lattice. TGF-beta(1) dose-dependently induced an increase in beta-smooth muscle actin, a marker of myofibroblasts. The TGF-beta(1)-induced reduction of area of the collagen gel was negatively correlated to the TGF-beta(1)-evoked appearance of a-smooth muscle actin in the collagen gel matrix.

CONCLUSION

Our data demonstrate that TGF-beta(1) increased the contractile activity of adult rat cardiac fibroblasts and their ability to differentiate into myofibroblasts. Because contractile activity was correlated with differentiation, the influence of TGF-beta(1) on cardiac fibroblast-induced collagen gel contraction might depend on the promotion of myofibroblast differentiation.

Altered response of vascular smooth muscle cells to exogenous biochemical stimulation in two- and three-dimensional culture

Removal of vascular smooth muscle cells (SMC) from their native environment alters the biochemical and mechanical signals responsible for maintaining normal cell function, causing a shift from a quiescent, contractile phenotype to a more proliferative, synthetic state. We examined the effect on SMC function of culture on two-dimensional (2D) substrates and in three-dimensional (3D) collagen Type I gels, including the effect of exogenous biochemical stimulation on gel compaction, cell proliferation, and expression of the contractile protein smooth muscle alpha-actin (SMA) in these systems. Embedding of SMC in 3D collagen matrices caused a marked decrease in both cell proliferation and expression of SMA. The presence of the extracellular matrix modulated cellular responses to platelet-derived growth factor BB, heparin, transforming growth factor-beta1, and endothelial cell-conditioned medium. Cell proliferation and SMA expression were shown to be inversely related, while gel compaction and SMA expression were not correlated. Taken together, these results show that SMC phenotype and function can be modulated using biochemical stimulation in vitro, but that the effects produced are dependent on the nature of the extracellular matrix. These findings have implications for the study of vascular biology in vitro, as well as for the development of engineered vascular tissues.

Regulation of smooth muscle actin expression and contraction in adult human mesenchymal stem cells

Prior studies have demonstrated the expression of a contractile actin isoform, alpha-smooth muscle actin, in bone marrow stromal cells. One objective of the current study was to correlate contractility with alpha-smooth muscle actin expression in human bone marrow stroma-derived mesenchymal stem cells. A second objective was to determine the effects of transforming growth factor-beta1, platelet derived growth factor-BB, and a microfilament-modifying agent on alpha-smooth muscle actin expression and alpha-smooth muscle actin-enabled contraction. Adult human bone marrow stromal cells were passaged in monolayer and their inducibility to chondrocytic, osteoblastic, and adipogenic phenotypes was demonstrated. Western blot analysis was employed along with densitometry to quantify the alpha-smooth muscle actin content of the cells and their contractility was evaluated by their contraction of a type I collagen-glycosaminoglycan sponge-like matrix into which they were seeded. Transforming growth factor-beta1 (1 ng/ml) significantly increased and platelet-derived growth factor-BB (10 ng/ml) decreased alpha-smooth muscle actin expression and the contractility of the cells. Cytochalasin D also blocked cell contraction. There was a notably high correlation of cell-mediated contraction normalized to the DNA content of the matrices with alpha-smooth muscle actin content of the cells by linear regression analysis (R(2) = 0.88). These findings lay the groundwork for considering the role of alpha-smooth muscle actin-enabled contraction in mesenchymal stem cells and in their connective tissue cell progeny.