An in vitro model for the pathological degradation of articular cartilage in osteoarthritis.

The objective of this study was to develop an in vitro cartilage degradation model that emulates the damage seen in early-stage osteoarthritis. To this end, cartilage explants were collagenase-treated to induce enzymatic degradation of collagen fibers and proteoglycans at the articular surface. To assess changes in mechanical properties, intact and degraded cartilage explants were subjected to a series of confined compression creep tests.

Characterization of total and active matrix metalloproteinases-1, -3, and -13 synthesized and secreted by anterior cruciate ligament fibroblasts in three-dimensional collagen gels.

Anterior cruciate ligament (ACL) injury and subsequent reconstructive surgery is increasing with an estimated 200,000 reconstructions performed yearly in the United States. Current treatment requires reconstruction with autograft or allograft tissue with inherent disadvantages. The development of tissue-engineered ligament replacements or scaffolds may provide an alternative treatment method minimizing these issues.

A Comparative Study of Fibronectin Cleavage by MMP-1, -3, -13, and -14.

Fibronectin fragments are important for synovial inflammation and the progression of arthritis, and thus, identifying potential enzymatic pathways that generate these fragments is of vital importance. The objective of this study was to determine the cleavage efficiency of fibronectin by matrix metalloproteinases (MMP-1, MMP-3, MMP-13, and MMP-14). Intact human plasma fibronectin was co-incubated with activated MMPs in neutral or acidic pH for up to 24 hours at 37 °C.

Quantitation of estrogen receptors and relaxin binding in human anterior cruciate ligament fibroblasts.

The significantly higher incidence of anterior cruciate ligament (ACL) injuries in collegiate women compared with men may result from relative ligament laxity. Differences in estrogen and relaxin activity, similar to that seen in pregnancy, may account for this. We quantified estrogen receptors by flow cytometry and relaxin receptors by radioligand binding assay in human ACL cells and compared the presence of these receptors in males and females.

Canine ACL fibroblast integrin expression and cell alignment in response to cyclic tensile strain in three-dimensional collagen gels.

Tissue-engineered ligament substitutes have the potential to become an alternative graft source for ligament reconstruction. If this approach is to become viable, one must first understand and define the mechanisms responsible for creation, maintenance, and remodeling of the native anterior cruciate ligament. It is well accepted that mechanical load alters fibroblast phenotypic expression in a variety of cell sources; however, the mechanosensitive pathways responsible for alteration in matrix production, remodeling, and alignment are unknown.

Effect of cyclic strain and plating matrix on cell proliferation and integrin expression by ligament fibroblasts.

The role of cell surface integrins in cell migration, proliferation, and attachment to matrix molecules is well known. Integrin-matrix interactions have been implicated in mechanotransduction and load transmission from the outside to the inside of the cell. In this study, the effect of cyclic strain on the cell proliferation, attachment, and expression of integrin subunits beta1, beta3, and alpha5 was determined in anterior cruciate ligament (ACL) and medial collateral ligament (MCL) fibroblasts grown on polystyrene, Type I collagen, laminin, elastin, and fibronectin.

Effects of hepatocyte growth factor and platelet-derived growth factor on the repair of meniscal defects in vitro.

Injuries to the avascular region of the meniscus occur frequently and may be difficult to repair. This study was designed to determine whether growth factors could diffuse from a collagen sponge or a collagen gel into meniscal tissue and stimulate healing of defects using an in vitro model. The diffusion of platelet-derived growth factor (PDGF) from the collagen carriers into the medium was rapid with approximately 50% being released from the collagen sponge within the first hour.

Characterization of sulfate, proline, and glucose transport systems in anterior cruciate and medial collateral ligament cells.

The present study was undertaken to define the nature of key transport processes for sodium, glucose, proline, and sulfate in primary culture of canine anterior cruciate ligament (ACL) and medial collateral ligament (MCL) cells. Uptake studies using radiolabeled isotopes were performed and Na,K-ATPase activity was determined in cell lysates. At 25 degrees C both ACL and MCL cells showed a significant uptake of 86Rb.

Maturational differences in superficial and deep zone articular chondrocytes.

To examine whether differences in chondrocytes from skeletally immature versus adult individuals are important in cartilage healing, repair, or tissue engineering, superficial zone chondrocytes (SZC, from within 100 microm of the articular surface) and deep zone chondrocytes (DZC, from 30%-45% of the deepest un-mineralized part of articular cartilage) were harvested from immature (1-4 months) and young adult (18-36 months) steers and compared. Cell size, matrix gene expression and protein levels, integrin levels, and chemotactic ability were measured in cells maintained in micromass culture for up to 7 days. Regardless of age, SZC were smaller, had a lower type II to type I collagen gene expression ratio, and higher gene expression of SZ proteins than their DZC counterparts.

The effect of mechanical load on integrin subunits alpha5 and beta1 in chondrocytes from mature and immature cartilage explants.

Articular cartilage is subjected to cyclic compressive stresses during joint loading. There is increasing experimental evidence that this loading is essential for the chondrocytes to maintain the functionality of the cartilage extracellular matrix (ECM) and that members of the integrin family of transmembrane receptors may play an important role in signal mechanotransduction between the ECM and chondrocytes. Of particular interest are the integrin subunits alpha5 and beta1, which are known to form the receptor for fibronectin, an important ECM protein, and to be involved in mechanotransduction as well as in the regulation of cytokine production.

Time, stress, and location dependent chondrocyte death and collagen damage in cyclically loaded articular cartilage.

We investigated the effect of light (0.1 MPa), moderate (1 MPa) or heavy (5 MPa) cyclical stresses applied continuously or intermittently for 0 to 72 h on cell death and collagen damage in adult bovine cartilage explants. No increase in cell death was observed in the cartilage loaded with a continuous cyclic stress at 0.