Inhibition of matrix metalloproteinases enhances in vitro repair of the meniscus

In vitro inhibition of compression-induced catabolic gene expression in meniscal explants following treatment with IL-1 receptor antagonist

BACKGROUND

Damage to the knee meniscus may result in tears that are difficult or unable to heal, and are often treated by partial removal of the damaged tissue. In vitro, 20% dynamic compressive strains on meniscal tissue explants have resulted in an increase in the release of sulfated glycosaminoglycans (GAG) and nitric oxide (NO) from the tissue explants and increased expression of matrix metalloproteinases (MMP) and interleukin-1α (IL-1α). The objective of this study was to explore the efficacy of IL-1 blockade on the expression of a wide range of genes, as well as NO and GAG release, following dynamic compression of porcine meniscal explants.

METHODS

Explants were dynamically compressed for 2 h at 1 Hz to 0, 10, or 20% strain with and without a pre-treatment of 500 ng/ml interleukin-1 receptor antagonist (IL-1RA). Relative changes in gene expression of IL-1α, MMP-1, -3, -13, A Disintegrin and Metalloproteinase with ThromboSpondin 4 (ADAMTS-4), ADAMTS-5, iNOS, aggrecan, and COX-2, as well as changes in NO and GAG release, were measured with standard biochemical assays.

RESULTS

Expression of IL-1α, MMP-3, MMP-13, and ADAMTS-4 in superficial explants was significantly downregulated at 20% dynamic strain compared to 10% strain following treatment with IL-1RA. GAG and NO release were not significantly influenced by IL-1RA treatment.

CONCLUSIONS

Treatment of meniscal explants with IL-1RA inhibited the expression of many catabolic genes following a single bout of high dynamic strain. IL-1RA may therefore be a potential therapy option during the acute phase of meniscal tear or meniscectomy treatment.

Integrin α5β1 facilitates cancer cell invasion through enhanced contractile forces

Cell migration through connective tissue, or cell invasion, is a fundamental biomechanical process during metastasis formation. Cell invasion usually requires cell adhesion to the extracellular matrix through integrins. In some tumors, increased integrin expression is associated with increased malignancy and metastasis formation. Here, we have studied the invasion of cancer cells with different α5β1 integrin expression levels into loose and dense 3D collagen fiber matrices. Using a cell sorter, we isolated from parental MDA-MB-231 breast cancer cells two subcell lines expressing either high or low amounts of α5β1 integrins (α5β1(high) or α5β1(low) cells, respectively). α5β1(high) cells showed threefold increased cell invasiveness compared to α5β1(low) cells. Similar results were obtained for 786-O kidney and T24 bladder carcinoma cells, and cells in which the α5 integrin subunit was knocked down using specific siRNA. Knockdown of the collagen receptor integrin subunit α2 also reduced invasiveness, but to a lesser degree than knockdown of integrin subunit α5. Fourier transform traction microscopy revealed that the α5β1(high) cells generated sevenfold greater contractile forces than α5β1(low) cells. Cell invasiveness was reduced after addition of the myosin light chain kinase inhibitor ML-7 in α5β1(high) cells, but not in α5β1(low) cells, suggesting that α5β1 integrins enhance cell invasion through enhanced transmission and generation of contractile forces.

The effects of adipokines on cartilage and meniscus catabolism

Obesity is one of the primary risk factors for osteoarthritis. Increased adiposity is associated not only with alterations in joint loading, but also with increased systemic and joint concentrations of adipose tissue-derived cytokines, or "adipokines", that promote a state of chronic, low-grade inflammation that may act in concert with other cytokines in the joint to increase joint degeneration. However, the direct effect of adipokines, such as leptin, visfatin, and interleukin-6 (IL-6), on joint tissues, such as articular cartilage and meniscus, are not fully understood. In this study, we examined the hypothesis that these adipokines act synergistically with interleukin-1 (IL-1) to increase catabolism and the production of proinflammatory mediators in cartilage and meniscus. Explants of porcine cartilage and meniscus were treated with physiologically relevant concentrations of leptin, IL-6, or visfatin, alone or in combination with IL-1. Visfatin and IL-1 promoted the catabolic degradation of both cartilage and meniscus, as evidenced by increased metalloproteinase activity, nitric oxide production, and proteoglycan release. However, leptin or IL-6 at physiologic concentrations had no effect on the breakdown of these tissues. These findings suggest that the effects of obesity-induced osteoarthritis may not be through a direct effect of leptin or IL-6 on cartilaginous tissues, but support a potential role for increased visfatin levels in this regard. These data provide an important first step in understanding the role of adipokines in regulating cartilage and meniscus metabolism; however, these adipokines may have different effects in the context of the whole joint and must be evaluated further.

Maturation state-dependent alterations in meniscus integration: implications for scaffold design and tissue engineering

The knee meniscus is a crucial component of the knee that functions to stabilize the joint, distribute load, and maintain congruency. Meniscus tears and degeneration are common, and natural healing is limited. Notably, few children present with meniscus injuries and other related fibrocartilaginous tissues heal regeneratively in immature animals and in the fetus. In this work, we evaluated fetal, juvenile, and adult bovine meniscus properties and repair capacity in vitro. Although no changes in cell behavior (migration and proliferation) were noted with age, drastic alterations in the density and distribution of the major components of meniscus tissue (proteoglycan, collagen, and DNA) occurred with development. Coincident with these marked tissue changes, the in vitro healing capacity of the tissue decreased with age. Fetal and juvenile meniscus formed a robust repair over 8 weeks on both a histological and mechanical basis, despite a lack of vascular supply. In contrast, adult meniscus did not integrate over this period. However, integration was improved significantly with the addition of the growth factor transforming growth factor-beta 3. Finally, to evaluate engineered scaffold integration in the context of aging, we monitored cellular infiltration from native tissue into engineered nanofibrous constructs. Our findings suggest that maturation processes that enable load bearing in the adult limit endogenous healing potential and identify new metrics for the development of tissue-engineered meniscus implants.

Dynamic loading enhances integrative meniscal repair in the presence of interleukin-1

OBJECTIVE

Meniscal tears are a common knee injury and increased levels of interleukin-1 (IL-1) have been measured in injured and degenerated joints. Studies have shown that IL-1 decreases the shear strength, cell accumulation, and tissue formation in meniscal repair interfaces. While mechanical stress and IL-1 modulate meniscal biosynthesis and degradation, the effects of dynamic loading on meniscal repair are unknown. The purpose of this study was to determine the effects of mechanical compression on meniscal repair under normal and inflammatory conditions.

EXPERIMENTAL DESIGN

Explants were harvested from porcine medial menisci. To simulate a full-thickness defect, a central core was removed and reinserted. Explants were loaded for 4h/day at 1 Hz and 0%-26% strain for 14 days in the presence of 0 or 100 pg/mL of IL-1. Media were assessed for matrix metalloproteinase (MMP) activity, aggrecanase activity, sulfated glycosaminoglycan (S-GAG) release, and nitric oxide (NO) production. After 14 days, biomechanical testing and histological analyses were performed.

RESULTS

IL-1 increased MMP activity, S-GAG release, and NO production, while decreasing the shear strength and tissue repair in the interface. Dynamic loading antagonized IL-1-mediated inhibition of repair at all strain amplitudes. Neither IL-1 treatment nor strain altered aggrecanase activity. Additionally, strain alone did not alter meniscal healing, except at the highest strain magnitude (26%), a level that enhanced the strength of repair.

CONCLUSIONS

Dynamic loading blocked the catabolic effects of IL-1 on meniscal repair, suggesting that joint loading through physical therapy may be beneficial in promoting healing of meniscal lesions under inflammatory conditions.

Vinculin facilitates cell invasion into three-dimensional collagen matrices

The cytoskeletal protein vinculin contributes to the mechanical link of the contractile actomyosin cytoskeleton to the extracellular matrix (ECM) through integrin receptors. In addition, vinculin modulates the dynamics of cell adhesions and is associated with decreased cell motility on two-dimensional ECM substrates. The effect of vinculin on cell invasion through dense three-dimensional ECM gels is unknown. Here, we report how vinculin expression affects cell invasion into three-dimensional collagen matrices. Cell motility was investigated in vinculin knockout and vinculin expressing wild-type mouse embryonic fibroblasts. Vinculin knockout cells were 2-fold more motile on two-dimensional collagen-coated substrates compared with wild-type cells, but 3-fold less invasive in 2.4 mg/ml three-dimensional collagen matrices. Vinculin knockout cells were softer and remodeled their cytoskeleton more dynamically, which is consistent with their enhanced two-dimensional motility but does not explain their reduced three-dimensional invasiveness. Importantly, vinculin-expressing cells adhered more strongly to collagen and generated 3-fold higher traction forces compared with vinculin knockout cells. Moreover, vinculin-expressing cells were able to migrate into dense (5.8 mg/ml) three-dimensional collagen matrices that were impenetrable for vinculin knockout cells. These findings suggest that vinculin facilitates three-dimensional matrix invasion through up-regulation or enhanced transmission of traction forces that are needed to overcome the steric hindrance of ECMs.

Aggrecanolysis and in vitro matrix degradation in the immature bovine meniscus: mechanisms and functional implications

Introduction

Little is known about endogenous or cytokine-stimulated aggrecan catabolism in the meniscal fibrocartilage of the knee. The objectives of this study were to characterize the structure, distribution, and processing of aggrecan in menisci from immature bovines, and to identify mechanisms of extracellular matrix degradation that lead to changes in the mechanical properties of meniscal fibrocartilage.

Methods

Aggrecanase activity in the native immature bovine meniscus was examined by immunolocalization of the aggrecan NITEGE neoepitope. To investigate mechanisms of cytokine-induced aggrecan catabolism in this tissue, explants were treated with interleukin-1α (IL-1) in the absence or presence of selective or broad spectrum metalloproteinase inhibitors. The sulfated glycosaminoglycan (sGAG) and collagen contents of explants and culture media were quantified by biochemical methods, and aggrecan catabolism was examined by Western analysis of aggrecan fragments. The mechanical properties of explants were determined by dynamic compression and shear tests.

Results

The aggrecanase-generated NITEGE neoepitope was preferentially localized in the middle and outer regions of freshly isolated immature bovine menisci, where sGAG density was lowest and blood vessels were present. In vitro treatment of explants with IL-1 triggered the accumulation of NITEGE in the inner and middle regions. Middle region explants stimulated with IL-1 exhibited substantial decreases in sGAG content, collagen content, and mechanical properties. A broad spectrum metalloproteinase inhibitor significantly reduced sGAG loss, abrogated collagen degradation, and preserved tissue mechanical properties. In contrast, an inhibitor selective for ADAMTS-4 and ADAMTS-5 was least effective at blocking IL-1-induced matrix catabolism and loss of mechanical properties.

Conclusions

Aggrecanase-mediated aggrecanolysis, typical of degenerative articular cartilage, may play a physiologic role in the development of the immature bovine meniscus. IL-1-induced release of sGAG and loss of mechanical properties can be ascribed primarily to the activity of MMPs or aggrecanases other than ADAMTS-4 and ADAMTS-5. These results may have implications for the clinical management of osteoarthritis.

Tumor necrosis factor alpha-dependent aggrecan cleavage and release of glycosaminoglycans in the meniscus is mediated by nitrous oxide-independent aggrecanase activity in vitro

Introduction

Little is known about factors that induce meniscus damage. Since joint inflammation appears to be a causative factor for meniscal destruction, we investigated the influence of tumor necrosis factor (TNFα) on glycosaminoglycan (GAG) release and aggrecan cleavage in an in vitro model.

Methods

Meniscal explant disks (3 mm diameter × 1 mm thickness) were isolated from 2-year-old cattle. After 3 days of TNFα-treatment GAG release (DMMB assay), biosynthetic activity (sulfate incorporation), nitric oxide (NO) production (Griess assay), gene expression of matrix-degrading enzymes (quantitative RT-PCR, zymography), and immunostaining of the aggrecan fragment NITEGE were determined.

Results

TNFα induced release of GAG as well as production of NO in a dose-dependent manner, while sulfate incorporation was decreased. TNFα increased matrix metalloproteinase (MMP)-3 and a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS)-4 mRNA expression, whereas collagen type I was decreased, and aggrecan, collagen type II as well as MMP-1, -2, -13 and ADAMTS-5 were variably affected. Zymography also showed a TNFα-dependent increase in MMP-3 expression, but pre-dominantly in the pro-form. TNFα-dependent formation of the aggrecanase-specific aggrecan neoepitope NITEGE was induced. Tissue inhibitor of metalloproteinases (TIMP)-3, but not TIMP-1 or -2 inhibited TNFα-dependent GAG release and NITEGE production, whereas inhibition of TNFα-dependent NO generation with the NO-synthetase inhibitor L-NMMA failed to inhibit GAG release and NITEGE production.

Conclusions

Our study shows that aggrecanase activity (a) is responsible for early TNFα-dependent aggrecan cleavage and GAG release in the meniscus and (b) might be involved in meniscal degeneration. Additionally, the meniscus is a TNFα-dependent source for MMP-3. However, the TNFα-dependent NO production seems not to be involved in release of proteoglycans under the given circumstances.