Madhu Bhargava

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 0.1 MPa for up to 72 h. Cell death occurred in the uppermost superficial tangential zone (STZ) of explants after loading for 1 h at 1 MPa, and reached a maximum depth of 61 ± 23 μm by 6 h (at the rate of 9 ± 6 μm/h). At 5 MPa, cell death occurred in the STZ after as little as 1 min (30 cycles) of loading, and reached a maximum depth of 70 ± 2 μm by 60 min (47 ± 8 μm/h). When an intermittent (with 2 s on, 2 s off) stress of 5 MPa was applied, cell death appeared in the STZ after 2 min (30 cycles) and increased to a depth of 63 ± 2 μm at 60 min (45 ± 11 μm/h). No significant differences were observed between the continuous and intermittent loading conditions. Both collagenase‐cleaved and denatured collagen fibers were found in the STZ of explants loaded at 1 and 5 MPa. We concluded that load‐induced cell death depends on load duration and magnitude, and that the chondrocytes in the STZ are more vulnerable to load‐induced injury than those in the middle and deep zones.

QUANTITATION OF ESTROGEN RECEPTORS AND RELAXIN BINDING IN HUMAN ANTERIOR CRUCIATE LIGAMENT FIBROBLASTS

SummaryThe 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. ACL stumps were harvested from seven males and eight females with acute ACL injuries. The tissue was placed in M199 cell culture medium. Outgrowth cultures were obtained, and passage 2 cells were used for all studies. Estrogen receptor determination was performed using flow cytometry. Relaxin binding was performed in ACL cells derived from five female and male patients using I125-labeled relaxin. Estrogen receptors were identified by flow cytometry in 4 to 10% of ACL cells. Mean fluorescence of cells expressing estrogen receptors was approximately twice that of controls, with no significant differences between males and females. Relaxin studies showed low-level binding of I125-relaxin-labeled ACL cells. Relaxin binding was present in four out of five female ACL cells versus one out of five male ACL cells.

Mechanical load inhibits IL-1 induced matrix degradation in articular cartilage

OBJECTIVE Osteoarthritis is a disease process of cellular degradation of articular cartilage caused by mechanical loads and inflammatory cytokines. We studied the cellular response in native cartilage subjected to a mechanical load administered simultaneously with an inflammatory cytokine interleukin-1 (IL-1), hypothesizing that the combination of load and cytokine would result in accelerated extracellular matrix (ECM) degradation. METHODS Mature bovine articular cartilage was loaded for 3 days (stimulation) with 0.2 and 0.5 MPa stresses, with and without IL-1 (IL-1alpha, 10 ng/ml), followed by 3 days of no stimulation (recovery). Aggrecan and collagen loss were measured as well as aggrecan cleavage using monoclonal antibodies AF-28 and BC-3 for cleavage by aggrecanases (ADAMTS) and matrix metalloproteinases (MMPs), respectively. RESULTS Incubation with IL-1 caused aggrecan cleavage by aggrecanases and MMPs during the 3 days of stimulation. A load of 0.5 MPa inhibited the IL-1-induced aggrecan loss while no inhibition was found for the 0.2 MPa stress. There was no collagen loss during the treatments but upon load and IL-1 removal proteoglycan and collagen loss increased. Load itself under these conditions was found to have no effect when compared to the unloaded controls. CONCLUSIONS A mechanical load of sufficient magnitude can inhibit ECM degradation by chondrocytes when stimulated by IL-1. The molecular mechanisms involved in this process are not clear but probably involve altered mechanochemical signal transduction between the ECM and chondrocyte.

EFFECTS OF HEPATOCYTE GROWTH FACTOR AND PLATELET-DERIVED GROWTH FACTOR ON THE REPAIR OF MENISCAL DEFECTS IN VITRO

SummaryInjuries 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. After 5 d of incubation, 8% of the PDGF was present in the meniscus, 11% in the collagen sponge, and 62% had been released into the medium. Similar results were obtained when a collagen gel was used as a carrier. Histological evaluation of the meniscal explants after 2 wk in culture revealed extensive proteoglycan staining in the areas surrounding defects treated with either hepatocyte growth factor (HGF) or PDGF compared with controls without growth factor. The HGF-PDGF treatment resulted in alignment and migration of meniscal cells toward the defect, which was not observed in untreated controls. At 3–7 d, increased number of cells were observed in defects treated with collagen gels (but not the sponge) with PDGF-HGF. At 4 wk, combined HGF-PDGF treatment resulted in the formation of tissue with birefringence by polarized microscopy, suggestive of organized collagen. The data suggest that use of specific PDGF-HGF may enhance the repair of meniscal injuries.

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. Changes in extracellular matrix structure and composition were determined using biochemical and histological approaches. Our results show that collagenase-induced degradation increased the amount of deformation experienced by the cartilage explants under compression. An increase in apparent permeability as well as a decrease in instantaneous and aggregate moduli was measured following collagenase treatment. Histological analysis of degraded explants revealed the presence of surface fibrillation, proteoglycan depletion in the superficial and intermediate zones and loss of the lamina splendens. Collagen cleavage was confirmed by the Col II-3/4Cshort antibody. Degraded specimens experienced a significant decrease in proteoglycan content but maintained total collagen content. Repetitive testing of degraded samples resulted in the gradual collapse of the articular surface and the compaction of the superficial zone. Taken together, our data demonstrates that enzymatic degradation with collagenase can be used to emulate changes seen in early-stage osteoarthritis. Further, our in vitro model provides information on cartilage mechanics and insights on how matrix changes can affect cartilages functional properties. More importantly, our model can be applied to develop and test treatment options for tissue repair.

Mechanical Loading of Articular Cartilage Reduces IL-1-Induced Enzyme Expression

Objective: Exposure of articular cartilage to interleukin-1 (IL-1) results in increased synthesis of matrix degrading enzymes. Previously mechanical load applied together with IL-1 stimulation was found to reduce aggrecan cleavage by ADAMTS-4 and 5 and MMP-1, -3, -9, and -13 and reduce proteoglycan loss from the extracellular matrix. To further delineate the inhibition mechanism the gene expression of ADAMTS-4 and 5; MMP-1, -3, -9, and -13; and TIMP-1, -2, and -3 were measured. Design: Mature bovine articular cartilage was stimulated with a 0.5 MPa compressive stress and 10 ng/ml of IL-1α for 3 days and then allowed to recover without stimulation for 1 additional day. The media was assayed for proteoglycan content on a daily basis, while chondrocyte gene expression (mRNA) was measured during stimulation and 1 day of recovery. Results: Mechanical load alone did not change the gene expression for ADAMTS, MMP, or TIMP. IL-1 caused an increase in gene expression for all enzymes after 1 day of stimulation while not affecting the TIMP levels. Load applied together with IL-1 decreased the expression levels of ADAMTS-4 and -5 and MMP-1 and -3 and increased TIMP-3 expression. Conclusions: A mechanical load appears to modify cartilage degradation by IL-1 at the cellular level by reducing mRNA.

Activation of MKK3/6, SAPK, and ATF-2/c-jun in ACL fibroblasts grown in 3 dimension collagen gels in response to application of cyclic strain.

Signal transduction pathways involved in response to cyclic tensile strain and strain deprivation in anterior cruciate ligament (ACL) fibroblasts grown in 3D collagen gels were investigated. Application of cyclic tensile strain resulted in significant activation (phosphorylation) of MKK3/6, SAPK and their downstream target transcription factors, ATF‐2 and c‐jun, while strain deprivation resulted in a decrease in these kinases and transcription factors. These data suggest that ACL fibroblasts cultured in 3D collagen gels respond to the mechanical environment and provide a useful system for determination of the molecular mechanisms involved in the regulation of proliferation and matrix turnover by mechanical load.

Inhibitory Effect of Mechanical Load on IL-1 Induced Cartilage Degradation Is Mediated by Interferon-Gamma and IL-1 Receptor 1

Matrix remodeling in articular cartilage is regulated by the elevation and activation of aggrecanases (ADAMTS-4 and ADAMTS-5) and matrix metalloproteinases (MMPs) [2–4, 7–9, 10]. Several recent studies from our and other groups have shown that mechanical loading can counteract interleukin 1 (IL-1) induced pro-inflammatory and catabolic events by down-regulating aggrecanases, MMPs, and pro-inflammatory genes [1, 3, 5, 6], but the molecular mechanism is not clear. Many previous studies have shown that the regulation of pro-inflammatory effect of IL-1 come from several aspects: anti-inflammatory cytokines (TGF-β, IL-10, IL-6 and interferon γ), IL-1 receptor related proteins (IL-1R1, IL-1R2, and IL-1Ra) as well as a family of intracellular inhibitory protein called Suppressor Of Cytokine Signaling (SOCS.) SOCS1 and SOCS3 are especially important, since they can inhibit both MAPK and NF-κB pathways induced by IL-1 [12]. The objective of this study was to determine whether mechanical load affected anti-inflammatory mediators along with anti-catabolic events.Copyright

Development of an In Vitro Cartilage Degradation Model to Emulate Early-Stage Osteoarthritis

Osteoarthritis (OA) is a disease characterized by the degeneration of articular cartilage. Disease progression is associated with the irreversible cleavage of the collagen network, surface fibrillation and loss of proteoglycans from the extracellular matrix.1, 2 These matrix changes increase surface porosity and matrix permeability, which diminish the cartilage’s ability to resist joint compressive loading. In this study, we developed an in vitro degradation model to emulate the damage that occurs in early OA in order to study how damage affects the tissue’s biomechanical function.Copyright