Membrane type-1 matrix metalloproteinase is induced following cyclic compression of in vitro grown bovine chondrocytes

Mechanical stimulation enhances integration in an in vitro model of cartilage repair

PURPOSE

(1) To characterize the effects of mechanical stimulation on the integration of a tissue-engineered construct in terms of histology, biochemistry and biomechanical properties; (2) to identify whether cells of the implant or host tissue were critical to implant integration; and (3) to study cells believed to be involved in lateral integration of tissue-engineered cartilage to host cartilage. We hypothesized that mechanical stimulation would enhance the integration of the repair implant with host cartilage in an in vitro integration model.

METHODS

Articular cartilage was harvested from 6- to 9-month-old bovine metacarpal-phalangeal joints. Constructs composed of tissue-engineered cartilage implanted into host cartilage were placed in spinner bioreactors and maintained on a magnetic stir plate at either 0 (static control) or 90 (experimental) rotations per minute (RPM). The constructs from both the static and spinner bioreactors were harvested after either 2 or 4 weeks of culture and evaluated histologically, biochemically, biomechanically and for gene expression.

RESULTS

The extent and strength of integration between tissue-engineered cartilage and native cartilage improved significantly with both time and mechanical stimulation. Integration did not occur if the implant was not viable. The presence of stimulation led to a significant increase in collagen content in the integration zone between host and implant at 2 weeks. The gene profile of cells in the integration zone differs from host cartilage demonstrating an increase in the expression of membrane type 1 matrix metalloproteinase (MT1-MMP), aggrecan and type II collagen.

CONCLUSIONS

This study shows that the integration of in vitro tissue-engineered implants with host tissue improves with mechanical stimulation. The findings of this study suggests that consideration should be given to implementing early loading (mechanical stimulation) into future in vivo studies investigating the long-term viability and integration of tissue-engineered cartilage for the treatment of cartilage injuries. This could simply be done through the use of continuous passive motion (CPM) in the post-operative period or through a more complex and structured rehabilitation program with a gradual increase in forces across the joint over time.

Mechanotransduction in primary human osteoarthritic chondrocytes is mediated by metabolism of energy, lipids, and amino acids

Chondrocytes are the sole cell type found in articular cartilage and are repeatedly subjected to mechanical loading in vivo. We hypothesized that physiological dynamic compression results in changes in energy metabolism to produce proteins for maintenance of the pericellular and extracellular matrices. The objective of this study was to develop an in-depth understanding for the short term (<30min) chondrocyte response to sub-injurious, physiological compression by analyzing metabolomic profiles for human chondrocytes harvested from femoral heads of osteoarthritic donors. Cell-seeded agarose constructs were randomly assigned to experimental groups, and dynamic compression was applied for 0, 15, or 30min. Following dynamic compression, metabolites were extracted and detected by HPLC-MS. Untargeted analyzes examined changes in global metabolomics profiles and targeted analysis examined the expression of specific metabolites related to central energy metabolism. We identified hundreds of metabolites that were regulated by applied compression, and we report the detection of 16 molecules not found in existing metabolite databases. We observed patient-specific mechanotransduction with aging dependence. Targeted studies found a transient increase in the ratio of NADP+ to NADPH and an initial decrease in the ratio of GDP to GTP, suggesting a flux of energy into the TCA cycle. By characterizing metabolomics profiles of primary chondrocytes in response to applied dynamic compression, this study provides insight into how OA chondrocytes respond to mechanical load. These results are consistent with increases in glycolytic energy utilization by mechanically induced signaling, and add substantial new data to a complex picture of how chondrocytes transduce mechanical loads.

The mechanical microenvironment of high concentration agarose for applying deformation to primary chondrocytes

Cartilage and chondrocytes experience loading that causes alterations in chondrocyte biological activity. In vivo chondrocytes are surrounded by a pericellular matrix with a stiffness of ~25-200kPa. Understanding the mechanical loading environment of the chondrocyte is of substantial interest for understanding chondrocyte mechanotransduction. The first objective of this study was to analyze the spatial variability of applied mechanical deformations in physiologically stiff agarose on cellular and sub-cellular length scales. Fluorescent microspheres were embedded in physiologically stiff agarose hydrogels. Microsphere positions were measured via confocal microscopy and used to calculate displacement and strain fields as a function of spatial position. The second objective was to assess the feasibility of encapsulating primary human chondrocytes in physiologically stiff agarose. The third objective was to determine if primary human chondrocytes could deform in high-stiffness agarose gels. Primary human chondrocyte viability was assessed using live-dead imaging following 24 and 72h in tissue culture. Chondrocyte shape was measured before and after application of 10% compression. These data indicate that (1) displacement and strain precision are ~1% and 6.5% respectively, (2) high-stiffness agarose gels can maintain primary human chondrocyte viability of >95%, and (3) compression of chondrocytes in 4.5% agarose can induce shape changes indicative of cellular compression. Overall, these results demonstrate the feasibility of using high-concentration agarose for applying in vitro compression to chondrocytes as a model for understanding how chondrocytes respond to in vivo loading.

Modulation of the proliferation and matrix synthesis of chondrocytes by dynamic compression on genipin-crosslinked chitosan/collagen scaffolds

Dynamic compression is an important physical stimulus for the physiology of chondrocyte and articular cartilage tissue engineering. In this study, modulation of chondrocyte behaviors in chitosan/collagen scaffolds with different mechanical properties under free-swelling or dynamic compression conditions was investigated. Rabbit chondrocytes were seeded in chitosan/collagen scaffolds crosslinked by genipin (GP) with different concentrations, and then cultured for 3 days prior to cyclic compression of 40% strain, 0.1 Hz, and 30 min/day for 2 weeks. The results showed that the cell proliferation was increased with increasing genipin concentrations and dynamic compression. On the other hand, although total glycosaminoglycans (GAGs) deposition was enhanced by dynamic compression under certain conditions, e.g. the GP0.5 chitosan/collagen scaffolds for 1 week of compression culture, normalized GAGs deposition per cell was decreased by dynamic compression. Our results suggest that while several studies suggest that dynamic compression benefits articular cartilage tissue engineering, many factors including scaffold types and compression conditions determine the outcome of dynamic compression culture.

Integration of tissue-engineered cartilage with host cartilage: an in vitro model

BACKGROUND

We developed a tissue-engineered biphasic cartilage bone substitute construct which has been shown to integrate with host cartilage and differs from autologous osteochondral transfer in which integration with host cartilage does not occur.

QUESTIONS/PURPOSES

(1) Develop a reproducible in vitro model to study the mechanisms regulating tissue-engineered cartilage integration with host cartilage, (2) compare the integrative properties of tissue-engineered cartilage with autologous cartilage and (3) determine if chondrocytes from the in-vitro formed cartilage migrate across the integration site.

METHODS

A biphasic construct was placed into host bovine osteochondral explant and cultured for up to 8 weeks (n = 6 at each time point). Autologous osteochondral implants served as controls (n = 6 at each time point). Integration was evaluated histologically, ultrastructurally, biochemically and biomechanically. Chondrocytes used to form cartilage in vitro were labeled with carboxyfluorescein diacetate which allowed evaluation of cell migration into host cartilage.

RESULTS

Histologic assessment demonstrated that tissue-engineered cartilage integrated over time, unlike autologous osteochondral implant controls. Biochemically there was an increase in collagen content of the tissue-engineered implant over time but was well below that for native cartilage. Integration strength increased between 4 and 8 weeks as determined by a pushout test. Fluorescent cells were detected in the host cartilage up to 1.5 mm from the interface demonstrating chondrocyte migration.

CONCLUSIONS

Tissue-engineered cartilage demonstrated improved integration over time in contrast to autologous osteochondral implants. Integration extent and strength increased with culture duration. There was chondrocyte migration from tissue-engineered cartilage to host cartilage.

CLINICAL RELEVANCE

This in vitro integration model will allow study of the mechanism(s) regulating cartilage integration. Understanding this process will facilitate enhancement of cartilage repair strategies for the treatment of chondral injuries.

Proteases involved in cartilage matrix degradation in osteoarthritis

Osteoarthritis is a common joint disease for which there are currently no disease-modifying drugs available. Degradation of the cartilage extracellular matrix is a central feature of the disease and is widely thought to be mediated by proteinases that degrade structural components of the matrix, primarily aggrecan and collagen. Studies on transgenic mice have confirmed the central role of Adamalysin with Thrombospondin Motifs 5 (ADAMTS-5) in aggrecan degradation, and the collagenolytic matrix metalloproteinase MMP-13 in collagen degradation. This review discusses recent advances in current understanding of the mechanisms regulating expression of these key enzymes, as well as reviewing the roles of other proteinases in cartilage destruction. This article is part of a Special Issue entitled: Proteolysis 50 years after the discovery of lysosome.

Calcium regulates cyclic compression-induced early changes in chondrocytes during in vitro cartilage tissue formation

A single application of cyclic compression (1kPa, 1Hz, 30min) to bioengineered cartilage results in improved tissue formation through sequential catabolic and anabolic changes mediated via cell shape changes that are regulated by α5β1 integrin and membrane-type metalloprotease (MT1-MMP). To determine if calcium was involved in this process, the role of calcium in regulating cell shape changes, MT1-MMP expression and integrin activity in response to mechanical stimulation was examined. Stimulation-induced changes in cell shape and MT1-MMP expression were abolished by chelation of extracellular calcium, and this effect was reversed by re-introduction of calcium. Spreading was inhibited by blocking stretch-activated channels (with gadolinium), while retraction was prevented by blocking the L-Type voltage-gated channel (with nifedipine); both compounds inhibited MT1-MMP upregulation. Calcium A23187 ionophore restored cellular response further supporting a role for these channels. Calcium regulated the integrin-mediated signalling pathway, which was facilitated through Src kinase. Both calcium- and integrin-mediated pathways converged on ERK-MAPK in response to stimulation. While both integrins and calcium signalling mediate chondrocyte mechanotransduction, calcium appears to play the major regulatory role. Understanding the underlying molecular mechanisms involved in chondrocyte mechanotransduction may lead to the development of improved bioengineered cartilage.

Hind limb unloading of mice modulates gene expression at the protein and mRNA level in mesenchymal bone cells

Background

We investigated the extent, modalities and reversibility of changes at cellular level in the expression of genes and proteins occurring upon Hind limb unloading (HU) in the tibiae of young C57BL/6J male mice. We focused on the effects of HU in chondrogenic, osteogenic, and marrow mesenchymal cells.

Methods

We analyzed for expression of genes and proteins at two time points after HU (7 and 14 days), and at 14 days after recovery from HU. Levels of mRNAs were tested by in situ hybridization. Protein levels were tested by immunohistochemistry. We studied genes involved in osteogenesis (alkaline phosphatase (AP), osteocalcin (OC), bonesialoprotein (BSP), membrane type1 matrix metalloproteinase (MT1-MMP)), in extracellular matrix (ECM) formation (procollagenases (BMP1), procollagenase enhancer proteins (PCOLCE)) and remodeling (metalloproteinase-9 (MMP9), RECK), and in bone homeostasis (Stro-1, CXCL12, CXCR4, CD146).

Results

We report the following patterns and timing of changes in gene expression induced by HU: 1) transient or stable down modulations of differentiation-associated genes (AP, OC), genes of matrix formation, maturation and remodelling, (BMP1, PCOLCEs MMP9) in osteogenic, chondrogenic and bone marrow cells; 2) up modulation of MT1-MMP in these same cells, and uncoupling of its expression from that of AP; 3) transient down modulation of the osteoblast specific expression of BSP; 4) for genes involved in bone homeostasis, up modulation in bone marrow cells at distal epiphysis for CXCR4, down modulation of CXCL12, and transient increases in osteoblasts and marrow cells for Stro1. 14 days after limb reloading expression returned to control levels for most genes and proteins in most cell types, except AP in all cells, and CXCL12, only in bone marrow.

Conclusions

HU induces the coordinated modulation of gene expression in different mesenchymal cell types and microenvironments of tibia. HU also induces specific patterns of expression for homeostasis related genes and modulation of mRNAs and proteins for ECM deposition, maturation and remodeling which may be key factors for bone maintenance.

Improved bioengineered cartilage tissue formation following cyclic compression is dependent on upregulation of MT1-MMP

The generation of bioengineered cartilage tissue suitable for transplantation is a potential therapy to treat damaged cartilage. We have shown previously that the physical and biomechanical properties of bioengineered cartilage can be improved by the application of 30 min of cyclic compression by a mechanism involving sequential upregulation of gene and protein levels of membrane type-1 matrix metalloproteinase (MT1-MMP) and MMP-13. In the current study, we demonstrated that MT1-MMP is critical to this response, as blocking the upregulation of MT1-MMP prevented the improvement in tissue formation. MT1-MMP seems to act by inducing tissue remodeling as evidenced by the presence of aggrecan degradation products by Western blot analysis and increased release of matrix molecules into the media. Release of these molecules was diminished when MT1-MMP upregulation was prevented. This matrix degradation was likely due to MT1-MMP, as under conditions where MMP-13 expression is maintained (stimulation in the presence of MT1-MMP siRNA) the release of these matrix molecules into the media was still prevented. It also appears that MT1-MMP does not regulate MMP-13 gene expression, as MT1-MMP-siRNA pretreatment had no effect on MMP-13 expression following mechanical stimulation. Further analysis of the anabolic genes and proteins involved in mechanically stimulated cartilage will lead to better understanding of the mechanism(s) underlying tissue formation yielding improved bioengineered cartilage.

EGR-1 decoy ODNs inhibit vascular smooth muscle cell proliferation and neointimal hyperplasia of balloon-injured arteries in rat

AIMS

Early growth response factor-1 (EGR-1) plays a master regulatory role in multiple cardiovascular pathological processes, such as atherosclerosis and restenosis. For investigating the possibility of using "decoy" strategy to prevent and cure vascular hyperplasia disease, we synthesized the double-stranded, cis-element, decoy oligodeoxynucleotides (ODNs) targeting EGR-1.

MAIN METHODS

EGR-1 decoy ODNs were transfected into the balloon-injured arteria carotis of rat as well as primary cultures of vascular smooth muscle cells (VSMC). Changes in the thickness of the arterial intima were evaluated by hematoxylin-eosin (HE) staining. VSMC proliferation, DNA synthesis, cell cycle and apoptosis were observed via MTT assay, bromodeoxyuridine (BrdU) incorporation and flow cytometry (FCM). Changes in the expression of EGR-1, and cell cycle related genes, were detected by reverse transcriptase polymerase chain reaction (PT-PCR) and western blot.

KEY FINDINGS

As a result of specific binding to EGR-1 protein, transfected EGR-1 decoy ODNs can reduce EGR-1 promoter affinity, hamper the transcriptional activation of EGR-1-dependent genes, block cell cycle progression of VSMCs, and inhibit neointimal hyperplasia.

SIGNIFICANCE

Through regulating the cell cycle progression and transcription of target gene, this new "decoy" strategy targeting EGR-1 provides further experimental evidence demonstrating the effectiveness of gene therapy in the treatment of restenosis following percutaneous coronary interventions.

Analysing the role of endogenous matrix molecules in the development of osteoarthritis

Osteoarthritis (OA) is the most common form of arthritis worldwide. In this condition, damage to the extracellular matrix (ECM) of cartilage occurs, resulting in joint destruction. Factors mediating cartilage damage include mechanical injury, cytokine and superoxide release on a background of genetic susceptibility and obesity. Studies of arthritic cartilage show increased production of ECM molecules including type II collagen, cartilage oligomeric matrix protein, fibronectin (FN) and fibromodulin. Recent reports suggest that ECM proteins may become endogenous catabolic factors during joint damage. Activation of pro-inflammatory pathways by ECM proteins has led to their description as damage-associated molecular patterns (DAMPs). The ECM proteins involved include fibromodulin, which activates the complement pathway and may promote the persistence of joint inflammation. Fragmentation of type II collagen, FN and hyaluronan reveals cryptic epitopes that stimulate proteolytic enzymes including matrix metalloproteinases and aggrecanases (ADAMTSs - a disintegrin and metalloproteinase with thrombospondin type 1 motifs). Proteolytic fragments also stimulate the release of nitric oxide, chemokines and cytokines and activation of the MAP kinases. Reports are emerging that the receptors for the fragments described involve interaction with integrins and toll-like receptors. In this review the contribution of endogenous ECM molecules to joint destruction will be discussed. A deeper understanding of the pathways stimulated by endogenous ligands could offer potential avenues for novel therapies in the future.

Mechanical stretch regulates the expression of matrix metalloproteinase in rheumatoid arthritis fibroblast-like synoviocytes

Mechanical stretch plays a crucial role in articular joints. In rheumatoid arthritis (RA), it is well known that fibroblast-like synoviocytes (FLS) produce matrix metalloproteinases (MMPs), resulting in local invasion into and degradation of bone and cartilage. We sought to examine whether mechanical stretch regulates the expression and underlying signal pathways of MMP secretion (MMP-1, -3, -13) in RA-FLS. FLS were grown on elastic silicone membrane in an equibiaxial strain apparatus and were exposed to 6% mechanical stretch (equivalent to gentle stretch exercise) for 15 min and 75 min, respectively. Semiquantitative PCR and real-time PCR were used to measure and analyze gene expression. Protein levels were determined by Western blotting. The results showed that 15 min of mechanical stretch inhibited MMP-1 and MMP-13 mRNA and protein level. However, the degree of inhibition by 75 min of stretch in expression of MMP-1 and MMP-13 was lower compared with 15 min stretch groups. The mRNA expression of ERK-1, ets-1 and citied-2 were increased by 6% mechanical stretch under both time points, however c-jun and c-fos mRNA level were affected differently after 15 min and 75 min mechanical stretch compared to control group. There were no significant changes on MMP-3 and ets-2 mRNA level under both 6% mechanical stretch time points. In the presence of pro-inflammatory cytokines (IL-1beta and TNF-alpha), the stretch also reduced the mRNA expression of MMP-1 and MMP-13. In short, our results showed that gentle mechanical strain affects MMP-1 and MMP-13 expression, potentially through the ERK-1-ets-1-cited-2-c-jun signaling pathway.