Aggrecan synthesized by mature bovine chondrocytes suspended in alginate. Identification of two distinct metabolic matrix pools

Nuclear Factor-κB Decoy Oligodeoxynucleotide Attenuates Cartilage Resorption In Vitro

BACKGROUND

Cartilage harvest and transplantation is a common surgery using costal, auricular, and septal cartilage for craniofacial reconstruction. However, absorption and warping of the cartilage grafts can occur due to inflammatory factors associated with wound healing. Transcription factor nuclear factor-κB (NF-κB) is activated by the various stimulation such as interleukin-1 (IL-1), and plays a central role in the transactivation of this inflammatory cytokine gene. Inhibition of NF-κB may have anti-inflammatory effects. The aim of this study was to explore the potential of an NF-κB decoy oligodeoxynucleotide (Decoy) as a chondroprotective agent.

MATERIALS AND METHODS

Safe and efficacious concentrations of Decoy were assessed using rabbit nasal septal chondrocytes (rNSChs) and assays for cytotoxicity, proteoglycan (PG) synthesis, and PG turnover were carried out. The efficacious concentration of Decoy determined from the rNSChs was then applied to human nasal septal cartilage (hNSC) in vitro and analyzed for PG turnover, the levels of inflammatory markers, and catabolic enzymes in explant-conditioned culture medium.

RESULTS

Over the range of Decoy conditions and concentrations, no inhibition of PG synthesis or cytotoxicity was observed. Decoy at 10 μM effectively inhibited PG degradation in the hNSC explant, prolonging PG half-life by 63% and decreasing matrix metalloprotease 3 (MMP-3) by 70.7% (p = 0.027).

CONCLUSIONS

Decoy may be considered a novel chondroprotective therapeutic agent in cartilage transplantation due to its ability to inhibit cartilage degradation due to inflammation cytokines.

Cytokine Inhibitors Upregulate Extracellular Matrix Anabolism of Human Intervertebral Discs under Alginate Beads and Alginate-Embedded Explant Cultures

We investigated the effects of the cytokine inhibitors IL-1 receptor antagonist (IL-1Ra) and soluble tumor necrosis factor receptor-1 (sTNFR1) on the extracellular matrix metabolism of human intervertebral discs (IVDs) and the roles of IL-1β and TNF in the homeostasis of IVD cells. The 1.2% alginate beads and the explants obtained from 35 human lumbar discs were treated with cytokine inhibitors. Extracellular matrix metabolism was evaluated by proteoglycan (PG) and collagen syntheses and IL-1β, TNF, and IL-6 expressions after three days of culture in the presence or absence of IL-1Ra, sTNFR1, and cycloheximide. Simultaneous treatment with IL-1Ra and sTNFR1 stimulated PG and collagen syntheses in the NP and AF cells and explants. The IL-1β concentration was significantly correlated to the relative increase in PG synthesis in AF explants after simultaneous cytokine inhibitor treatment. The relative increase in PG synthesis induced by simultaneous cytokine treatment was significantly higher in an advanced grade of MRI. Expressions of IL-1β and TNF were upregulated by each cytokine inhibitor, and simultaneous treatment suppressed IL-1β and TNF productions. In conclusion, IL-1Ra and sTNFR1 have the potential to increase PG and collagen synthesis in IVDs. IL-1β and TNF have a feedback pathway to maintain optimal expression, resulting in the control of homeostasis in IVD explants.

Application of Alginate Hydrogels for Next-Generation Articular Cartilage Regeneration

The articular cartilage has insufficient intrinsic healing abilities, and articular cartilage injuries often progress to osteoarthritis. Alginate-based scaffolds are attractive biomaterials for cartilage repair and regeneration, allowing for the delivery of cells and therapeutic drugs and gene sequences. In light of the heterogeneity of findings reporting the benefits of using alginate for cartilage regeneration, a better understanding of alginate-based systems is needed in order to improve the approaches aiming to enhance cartilage regeneration with this compound. This review provides an in-depth evaluation of the literature, focusing on the manipulation of alginate as a tool to support the processes involved in cartilage healing in order to demonstrate how such a material, used as a direct compound or combined with cell and gene therapy and with scaffold-guided gene transfer procedures, may assist cartilage regeneration in an optimal manner for future applications in patients.

Polyethylene glycol diacrylate scaffold filled with cell-laden methacrylamide gelatin/alginate hydrogels used for cartilage repair

Natural cartilage tissue has excellent mechanical properties and has certain cellular components. At this stage, it is a great challenge to produce cartilage scaffolds with excellent mechanical properties, biocompatibility, and biodegradability. Hydrogels are commonly used in tissue engineering because of their excellent biocompatibility; however, the mechanical properties of commonly used hydrogels are difficult to meet the requirements of making cartilage scaffolds. The mechanical properties of high concentration polyethylene glycol diacrylate (PEGDA) hydrogel are similar to those of natural cartilage, but its biocompatibility is poor. Low concentration hydrogel has better biocompatibility, but its mechanical properties are poor. In this study, two different hydrogels were combined to produce cartilage scaffolds with good mechanical properties and strong biocompatibility. First, the PEGDA grid scaffold was printed with light curing 3D printing technology, and then the low concentration GelMA/Alginate hydrogel with chondral cells was filled into the PEGDA grid scaffold. After a series of cell experiments, the filling hydrogel with the best biocompatibility was screened out, and finally the filled hydrogel with cells and excellent biocompatibility was obtained. Cartilage tissue engineering scaffolds with certain mechanical properties were found to have a tendency of cartilage formation in in vitro culture. Compared with the scaffold obtained by using a single hydrogel, this molding method can produce a tissue engineering scaffold with excellent mechanical properties on the premise of ensuring biocompatibility, which has a certain potential application value in the field of cartilage tissue engineering.

Phenotypic Characterization of Immortalized Chondrocytes from a Desbuquois Dysplasia Type 1 Mouse Model: A Tool for Studying Defects in Glycosaminoglycan Biosynthesis

The complexity of skeletal pathologies makes use of in vivo models essential to elucidate the pathogenesis of the diseases; nevertheless, chondrocyte and osteoblast cell lines provide relevant information on the underlying disease mechanisms. Due to the limitations of primary chondrocytes, immortalized cells represent a unique tool to overcome this problem since they grow very easily for several passages. However, in the immortalization procedure the cells might lose the original phenotype; thus, these cell lines should be deeply characterized before their use. We immortalized primary chondrocytes from a Cant1 knock-out mouse, an animal model of Desbuquois dysplasia type 1, with a plasmid expressing the SV40 large and small T antigen. This cell line, based on morphological and biochemical parameters, showed preservation of the chondrocyte phenotype. In addition reduced proteoglycan synthesis and oversulfation of glycosaminoglycan chains were demonstrated, as already observed in primary chondrocytes from the Cant1 knock-out mouse. In conclusion, immortalized Cant1 knock-out chondrocytes maintained the disease phenotype observed in primary cells validating the in vitro model and providing an additional tool to further study the proteoglycan biosynthesis defect. The same approach might be extended to other cartilage disorders.

Holistic Approach of Swiss Fetal Progenitor Cell Banking: Optimizing Safe and Sustainable Substrates for Regenerative Medicine and Biotechnology

Safety, quality, and regulatory-driven iterative optimization of therapeutic cell source selection has constituted the core developmental bedrock for primary fetal progenitor cell (FPC) therapy in Switzerland throughout three decades. Customized Fetal Transplantation Programs were pragmatically devised as straightforward workflows for tissue procurement, traceability maximization, safety, consistency, and robustness of cultured progeny cellular materials. Whole-cell bioprocessing standardization has provided plethoric insights into the adequate conjugation of modern biotechnological advances with current restraining legislative, ethical, and regulatory frameworks. Pioneer translational advances in cutaneous and musculoskeletal regenerative medicine continuously demonstrate the therapeutic potential of FPCs. Extensive technical and clinical hindsight was gathered by managing pediatric burns and geriatric ulcers in Switzerland. Concomitant industrial transposition of dermal FPC banking, following good manufacturing practices, demonstrated the extensive potential of their therapeutic value. Furthermore, in extenso, exponential revalorization of Swiss FPC technology may be achieved via the renewal of integrative model frameworks. Consideration of both longitudinal and transversal aspects of simultaneous fetal tissue differential processing allows for a better understanding of the quasi-infinite expansion potential within multi-tiered primary FPC banking. Multiple fetal tissues (e.g., skin, cartilage, tendon, muscle, bone, lung) may be simultaneously harvested and processed for adherent cell cultures, establishing a unique model for sustainable therapeutic cellular material supply chains. Here, we integrated fundamental, preclinical, clinical, and industrial developments embodying the scientific advances supported by Swiss FPC banking and we focused on advances made to date for FPCs that may be derived from a single organ donation. A renewed model of single organ donation bioprocessing is proposed, achieving sustained standards and potential production of billions of affordable and efficient therapeutic doses. Thereby, the aim is to validate the core therapeutic value proposition, to increase awareness and use of standardized protocols for translational regenerative medicine, potentially impacting millions of patients suffering from cutaneous and musculoskeletal diseases. Alternative applications of FPC banking include biopharmaceutical therapeutic product manufacturing, thereby indirectly and synergistically enhancing the power of modern therapeutic armamentariums. It is hypothesized that a single qualifying fetal organ donation is sufficient to sustain decades of scientific, medical, and industrial developments, as technological optimization and standardization enable high efficiency.

Modeling the Human Bone-Tumor Niche: Reducing and Replacing the Need for Animal Data

Bone is the most common site for cancer metastasis. Understanding the interactions within the complex, heterogeneous bone-tumor microenvironment is essential for the development of new therapeutics. Various animal models of tumor-induced bone disease are routinely used to provide valuable information on the relationship between cancer cells and the skeleton. However, new model systems exist that offer an alternative approach to the use of animals and might more accurately reveal the cellular interactions occurring within the human bone-tumor niche. This review highlights replacement models that mimic the bone microenvironment and where cancer metastases and tumor growth might be assessed alongside bone turnover. Such culture models include the use of calcified regions of animal tissue and scaffolds made from bone mineral hydroxyapatite, synthetic polymers that can be manipulated during manufacture to create structures resembling trabecular bone surfaces, gel composites that can be modified for stiffness and porosity to resemble conditions in the tumor-bone microenvironment. Possibly the most accurate model system involves the use of fresh human bone samples, which can be cultured ex vivo in the presence of human tumor cells and demonstrate similar cancer cell-bone cell interactions as described in vivo. In addition, the use of mathematical modeling and computational biology approaches provide an alternative to preliminary animal testing. The use of such models offers the capacity to mimic significant elements of the human bone-tumor environment, and complement, refine, or replace the use of preclinical models. © 2020 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Cartilage protective and anti-analgesic effects of ALM16 on monosodium iodoacetate induced osteoarthritis in rats

Background

Osteoarthritis (OA) is an age-related joint disease with characteristics that involve the progressive degradation of articular cartilage and resulting chronic pain. Previously, we reported that Astragalus membranaceus and Lithospermum erythrorhizon showed significant anti-inflammatory and anti-osteoarthritis activities. The objective of this study was to examine the protective effects of ALM16, a new herbal mixture (7:3) of ethanol extracts of A. membranaceus and L. erythrorhizon, against OA in in vitro and in vivo models.

Methods

The levels of matrix metalloproteinase (MMP)-1, −3 and − 13 and glycosaminoglycan (GAG) in interleukin (IL)-1β or ALM16 treated SW1353 cells were determined using an enzyme-linked immunosorbent and quantitative kit, respectively. In vivo, the anti-analgesic and anti-inflammatory activities of ALM16 were assessed via the acetic acid-induced writhing response and in a carrageenan-induced paw edema model in ICR mice, respectively. In addition, the chondroprotective effects of ALM16 were analyzed using a single-intra-articular injection of monosodium iodoacetate (MIA) in the right knee joint of Wister/ST rat. All samples were orally administered daily for 2 weeks starting 1 week after the MIA injection. The paw withdrawal threshold (PWT) in MIA-injected rats was measured by the von Frey test using the up-down method. Histopathological changes of the cartilage in OA rats were analyzed by hematoxylin and eosin (H&E) staining.

Results

ALM16 remarkably reduced the GAG degradation and MMP levels in IL-1β treated SW1353 cells. ALM16 markedly decreased the thickness of the paw edema and writhing response in a dose-dependent manner in mice. In the MIA-induced OA rat model, ALM16 significantly reduced the PWT compared to the control group. In particular, from histological observations, ALM16 showed clear improvement of OA lesions, such as the loss of necrotic chondrocytes and cartilage erosion of more than 200 mg/kg b.w., comparable to or better than a positive drug control (JOINS™^, 200 mg/kg) in the cartilage of MIA-OA rats.

Conclusions

Our results demonstrate that ALM16 has a strong chondroprotective effect against the OA model in vitro and in vivo, likely attributed to its anti-inflammatory activity and inhibition of MMP production.

Biomaterials for articular cartilage tissue engineering: Learning from biology

Articular cartilage is commonly described as a tissue that is made of up to 80% water, is devoid of blood vessels, nerves, and lymphatics, and is populated by only one cell type, the chondrocyte. At first glance, an easy tissue for clinicians to repair and for scientists to reproduce in a laboratory. Yet, chondral and osteochondral defects currently remain an open challenge in orthopedics and tissue engineering of the musculoskeletal system, without considering osteoarthritis. Why do we fail in repairing and regenerating articular cartilage? Behind its simple and homogenous appearance, articular cartilage hides a heterogeneous composition, a high level of organisation and specific biomechanical properties that, taken together, make articular cartilage a unique material that we are not yet able to repair or reproduce with high fidelity. This review highlights the available therapies for cartilage repair and retraces the research on different biomaterials developed for tissue engineering strategies. Their potential to recreate the structure, including composition and organisation, as well as the function of articular cartilage, intended as cell microenvironment and mechanically competent replacement, is described. A perspective of the limitations of the current research is given in the light of the emerging technologies supporting tissue engineering of articular cartilage.

STATEMENT OF SIGNIFICANCE

The mechanical properties of articular tissue reflect its functionally organised composition and the recreation of its structure challenges the success of in vitro and in vivo reproduction of the native cartilage. Tissue engineering and biomaterials science have revolutionised the way scientists approach the challenge of articular cartilage repair and regeneration by introducing the concept of the interdisciplinary approach. The clinical translation of the current approaches are not yet fully successful, but promising results are expected from the emerging and developing new generation technologies.

Articular cartilage: from formation to tissue engineering

Hyaline cartilage is the nonlinear, inhomogeneous, anisotropic, poro-viscoelastic connective tissue that serves as friction-reducing and load-bearing cushion in synovial joints and is vital for mammalian skeletal movements. Due to its avascular nature, low cell density, low proliferative activity and the tendency of chondrocytes to de-differentiate, cartilage cannot regenerate after injury, wear and tear, or degeneration through common diseases such as osteoarthritis. Therefore severe damage usually requires surgical intervention. Current clinical strategies to generate new tissue include debridement, microfracture, autologous chondrocyte transplantation, and mosaicplasty. While articular cartilage was predicted to be one of the first tissues to be successfully engineered, it proved to be challenging to reproduce the complex architecture and biomechanical properties of the native tissue. Despite significant research efforts, only a limited number of studies have evolved up to the clinical trial stage. This review article summarizes the current state of cartilage tissue engineering in the context of relevant biological aspects, such as the formation and growth of hyaline cartilage, its composition, structure and biomechanical properties. Special attention is given to materials development, scaffold designs, fabrication methods, and template-cell interactions, which are of great importance to the structure and functionality of the engineered tissue.

Bridging the Gap: From 2D Cell Culture to 3D Microengineered Extracellular Matrices

Historically the culture of mammalian cells in the laboratory has been performed on planar substrates with media cocktails that are optimized to maintain phenotype. However, it is becoming increasingly clear that much of biology discerned from 2D studies does not translate well to the 3D microenvironment. Over the last several decades, 2D and 3D microengineering approaches have been developed that better recapitulate the complex architecture and properties of in vivo tissue. Inspired by the infrastructure of the microelectronics industry, lithographic patterning approaches have taken center stage because of the ease in which cell-sized features can be engineered on surfaces and within a broad range of biocompatible materials. Patterning and templating techniques enable precise control over extracellular matrix properties including: composition, mechanics, geometry, cell-cell contact, and diffusion. In this review article we explore how the field of engineered extracellular matrices has evolved with the development of new hydrogel chemistry and the maturation of micro- and nano- fabrication. Guided by the spatiotemporal regulation of cell state in developing tissues, techniques for micropatterning in 2D, pseudo-3D systems, and patterning within 3D hydrogels will be discussed in the context of translating the information gained from 2D systems to synthetic engineered 3D tissues.

An enzyme-sensitive PEG hydrogel based on aggrecan catabolism for cartilage tissue engineering

A new cartilage-specific degradable hydrogel based on photoclickable thiol-ene poly(ethylene glycol) (PEG) hydrogels is presented. The hydrogel crosslinks are composed of the peptide, CRDTEGE-ARGSVIDRC, derived from the aggrecanase-cleavable site in aggrecan. This new hydrogel is evaluated for use in cartilage tissue engineering by encapsulating bovine chondrocytes from different cell sources (skeletally immature (juvenile) and mature (adult) donors and adult cells stimulated with proinflammatory lipopolysaccharide (LPS)) and culturing for 12 weeks. Regardless of cell source, a twofold decrease in compressive modulus is observed by 12 weeks, but without significant hydrogel swelling indicating limited bulk degradation. For juvenile cells, a connected matrix rich in aggrecan and collagen II, but minimal collagens I and X is observed. For adult cells, less matrix, but similar quality, is deposited. Aggrecanase activity is elevated, although without accelerating bulk hydrogel degradation. LPS further decreases matrix production, but does not affect aggrecanase activity. In contrast, matrix deposition in the nondegradable hydrogels consists of aggrecan and collagens I, II, and X, indicative of hypertrophic cartilage. Lastly, no inflammatory response in chondrocytes is observed by the aggrecanase-sensitive hydrogels. Overall, it is demonstrated that this new aggrecanase-sensitive hydrogel, which is degradable by chondrocytes and promotes a hyaline-like engineered cartilage, is promising for cartilage regeneration.

Transcription factor Mohawk and the pathogenesis of human anterior cruciate ligament degradation

OBJECTIVE

To investigate the expression and function of Mohawk (MKX) in human adult anterior cruciate ligament (ACL) tissue and ligament cells from normal and osteoarthritis (OA)-affected knees.

METHODS

Knee joints were obtained at autopsy (within 24-48 hours postmortem) from 13 donors with normal knees (mean ± SD age 36.9 ± 11.0 years), 16 donors with knee OA (age 79.7 ± 11.4 years), and 8 aging donors without knee OA (age 76.9 ± 12.9 years). All cartilage surfaces were graded macroscopically. MKX expression was analyzed by immunohistochemistry and quantitative polymerase chain reaction. ACL-derived cells were used to study regulation of MKX expression by interleukin-1β (IL-1β). MKX was knocked down with small interfering RNA (siRNA) to analyze the function of MKX in extracellular matrix (ECM) production and differentiation in ACL-derived cells.

RESULTS

The expression of MKX was significantly decreased in ACL-derived cells from OA knees compared with normal knees. Consistent with this finding, immunohistochemistry analysis showed that MKX-positive cells were significantly reduced in ACL tissue from OA donors, in particular in cells located in disorientated fibers. In ACL-derived cells, IL-1β strongly suppressed MKX expression and reduced expression of the ligament ECM genes COL1A1 and TNXB. In contrast, SOX9, a chondrocyte master transcription factor, was up-regulated by IL-1β treatment. Importantly, knockdown of MKX expression with siRNA up-regulated SOX9 expression in ACL-derived cells, whereas the expression of COL1A1 and TNXB was reduced.

CONCLUSION

Reduced expression of MKX is a feature of degenerated ACL in OA-affected joints, and this may be mediated in part by IL-1β. MKX appears necessary to maintain the tissue-specific cellular differentiation status and ECM production in adult human tendons and ligaments.

Transplantation of goat bone marrow stromal cells to the degenerating intervertebral disc in a goat disc injury model

STUDY DESIGN

In vivo randomized controlled study in the goat intervertebral disc (IVD) injury model.

OBJECTIVE

To define the effects of allogeneic bone marrow-derived stromal cell injected into the degenerating goat IVDs.

SUMMARY OF BACKGROUND DATA

Transplantation of bone marrow stromal cells to the degenerating disc has been suggested as a means to correct the biologic incompetence of the disc. However, large animal models with IVDs similar in shape and size to those of humans are needed to define the efficacy and safety of this approach.

METHODS

Goat IVD degeneration was induced by stabbing with a #15 blade. One month after disc injury, the injured discs were randomly selected to receive goat bone marrow-derived stromal cell (suspended in hydrogel), saline (control), or hydrogel (control) injections. Three and 6 months after stem cell transplantation, goats were euthanized and the IVD were examined for biochemical content and tissue morphology. MR images at 3- and 6-month time points were also examined.

RESULTS

The goat large animal model shows early degenerative changes following disc injury. Degenerating IVDs injected with bone marrow stromal cells showed significantly increased proteoglycan (PG) accumulation within their nucleus pulposus (NP) region. However, collagen content, MRI grade and histology did not show statistically significant differences between the cell-treated and control IVDs.

CONCLUSIONS

Following transplantation of bone marrow stromal cells, NP tissue contained more PG than control discs. Although this result was promising, the rate and severity of degeneration in this goat disc injury were modest, suggesting that a more severe injury and a larger sample size is indicated for future studies to better define the utility of cell therapies in this model.

Characterization of TIMP-3 in human articular talar cartilage

Tissue inhibitor of matrix metalloproteinase 3 (TIMP-3) is an inhibitor of matrix degradation; however, little else is known about the role(s) of this protein in articular cartilage. In this study we compared levels of TIMP-3 in human knee and ankle cartilages and in normal and degraded cartilages. In addition, our studies focused on the compartmentalization of TIMP-3 in human adult articular cartilage matrix, identification of its potential binding partners, and determining the effects of cytokines on its matrix compartment deposition. We extracted TIMP-3 from cartilage and found that while TIMP-3 was localized throughout the matrix, it was predominately associated with the chondrocyte. We also found that more TIMP-3 was extracted from normal compared to degraded cartilage and more in ankle than knee cartilage suggesting the potential of this inhibitor as a protective agent. Our data suggest that TIMP-3 interacts with heparan sulfate and heparan sulfate proteoglycans and to a lesser extent with heparin and chondroitin sulfate. Stimulation with Interleukin-1β and osteogenic protein-1 decreased while tumor necrosis factor alpha and transforming growth factor beta increased TIMP-3 protein levels; however, TIMP-3 mRNA was not significantly affected by any of these treatments. These characteristics indicate the chondroprotective nature of TIMP-3 and its potential as a therapeutic agent for osteoarthritis.

Preservation of the chondrocyte's pericellular matrix improves cell-induced cartilage formation

The extracellular matrix surrounding chondrocytes within a chondron is likely to affect the metabolic activity of these cells. In this study we investigated this by analyzing protein synthesis by intact chondrons obtained from different types of cartilage and compared this with chondrocytes. Chondrons and chondrocytes from goats from different cartilage sources (articular cartilage, nucleus pulposus, and annulus fibrosus) were cultured for 0, 7, 18, and 25 days in alginate beads. Real-time polymerase chain reaction analyses indicated that the gene expression of Col2a1 was consistently higher by the chondrons compared with the chondrocytes and the Col1a1 gene expression was consistently lower. Western blotting revealed that Type II collagen extracted from the chondrons was cross-linked. No Type I collagen could be extracted. The amount of proteoglycans was higher for the chondrons from articular cartilage and nucleus pulposus compared with the chondrocytes, but no differences were found between chondrons and chondrocytes from annulus fibrosus. The expression of both Mmp2 and Mmp9 was higher by the chondrocytes from articular cartilage and nucleus pulposus compared with the chondrons, whereas no differences were found with the annulus fibrosus cells. Gene expression of Mmp13 increased strongly by the chondrocytes (>50-fold), but not by the chondrons. Taken together, our data suggest that preserving the pericellular matrix has a positive effect on cell-induced cartilage production.

Association between the expression of aggrecan and the distribution of aggrecan gene variable number of tandem repeats with symptomatic lumbar disc herniation in Chinese Han of Northern China

STUDY DESIGN

Case-control study.

OBJECTIVE

To examine the association between the expression of aggrecan and the aggrecan gene variable number of tandem repeats (VNTR) polymorphism with symptomatic lumbar disc herniation (LDH) in Chinese Han of Northern China.

SUMMARY OF BACKGROUND DATA

Aggrecan fragments have been found in human degenerated discs, and an association between the aggrecan VNTR polymorphism and intervertebral disc degeneration has been previously reported in middle-aged Finnish men. However, the relationship between the munity of symptomatic LDH with the expression of aggrecan and aggrecan gene VNTR has not been well studied.

METHODS

The disease group consisted of 70 patients already diagnosed with symptomatic LDH. The control group consisted of 14 patients restricted to spinal trauma and 113 healthy blood donors without symptoms of LDH who were not diagnosed with LDH. Disc tissue samples were obtained from surgical operations, and blood samples were donated from all participants. The aggrecan expression in isolated tissues was assessed by Western blot using specific antibodies. The aggrecan gene VNTR region was analyzed by polymerase chain reaction.

RESULTS

The aggrecan expression positive rate of control group was statistically and significantly higher (P < 0.001) than that of the disease group. Moreover, there was a statistically significant higher frequency of allele 25 or allele 21 in disease group compared with controls (P(A25) = 0.003416 and P(A21) = 0.000716). Compared with the participants with 2 alleles > 25 repeats, subjects with 1 or 2 alleles < or = 25 repeats statistically and significantly overrepresented the disease group without the expression of aggrecan (P < 0.001).

CONCLUSION

The findings suggest a relation between aggrecan and symptomatic LDH, where symptomatic LDH has a lower tendency of allele repeats. In addition, this study observed an association between the distribution of aggrecan gene VNTR polymorphism and the expression of aggrecan in symptomatic LDH.

Metabolic activity of osteoarthritic knees correlates with BMI

Osteoarthritis of the knee has consistently been linked to obesity, defined as a body mass index (BMI) >30kg/m(2). It has been hypothesized that obesity may lead to osteoarthritis through increased joint pressure, accumulated microtrauma, and disruption of normal chondrocyte metabolism. These changes in chondrocyte metabolism have not been thoroughly investigated, and it is the purpose of this study to identify a relationship between BMI and altered chondrocyte metabolism in osteoarthritic tissue. Articular cartilage was harvested from the femoral condyles of patients after total knee arthroplasty, and analyzed in explant and alginate models. Glycosaminoglycan (GAG) content was measured using a dimethylmethylene blue assay and normalized to DNA content using a PicoGreen(R) assay. Studies have reported GAGs to be a reliable measurement of chondrocyte metabolism and osteoarthritis progression. Our results show a significant linear relationship of increasing BMI and increasing GAG content in both alginate and explant models (p<0.001 and p=0.001). Obese (BMI>/=30kg/m(2)) and non-obese (BMI<30kg/m(2)) comparisons also demonstrated significant differences with higher GAG/DNA content in obese individuals compared to non-obese (p=0.001 and p=0.015). The study results reveal significant relationships between GAG content and BMI in this population of osteoarthritic patients. The significant difference in GAG content between the obese and non-obese patients supports the connection between osteoarthritis and obesity previously reported. Higher patient BMI (>30kg/m(2)) may be similar to dynamic compression injuries which cause increased GAG synthesis in response to cartilage damage.

Development and characterization of a human articular cartilage-derived chondrocyte cell line that retains chondrocyte phenotype

Chondrocytes, the only cell type present in articular cartilage, regulate tissue homeostasis by a fine balance of metabolism that includes both anabolic and catabolic activities. Therefore, the biology of chondrocytes is critical for understanding cartilage metabolism. One major limitation when studying primary chondrocytes in culture is their loss of phenotype. To overcome this hurdle, limited attempts have been made to develop human chondrocyte cell lines that retain the phenotype for use as a good surrogate model. In this study, we report a novel approach to the establishment and characterization of human articular cartilage-derived chondrocyte cell lines. Adenoviral infection followed by culture of chondrocytes in 3-dimensional matrix within 48 h post-infection maintained the phenotype prior to clonal selection. Cells were then placed in culture either as monolayer, or in 3-dimensional matrix of alginate or agarose. The clones were characterized by their basal gene expression profile of chondrocyte markers. Based on type II collagen expression, 21 clones were analyzed for gene expression following treatment with IL-1 or BMP-7 and compared to similarly stimulated primary chondrocytes. This resulted in selection of two clones that retained the chondrocyte phenotype as evidenced by expression of type II collagen and other extra-cellular matrix molecules. In addition, one clone (AL-4-17) showed similar responses as primary chondrocytes when treated with IL-1 or BMP-7. In summary, this report provides a novel procedure to develop human articular cartilage-derived chondrocyte cell lines, which preserve important characteristics of articular chondrocytes and represent a useful model to study chondrocyte biology.

Primary bovine intervertebral disc cells transduced with adenovirus overexpressing 12 BMPs and Sox9 maintain appropriate phenotype

OBJECTIVE

To confirm that primary intervertebral disc cells cultured in monolayer transduced with adenovirus maintained their phenotype, hence is an appropriate system to test gene therapy agents.

DESIGN

Adult bovine nucleus pulposus and anulus fibrosus cells cultured in monolayer were transduced with adenoviruses expressing human bone morphogenetic proteins (AdBMPs) or Sox9 (AdSox9), or green fluorescence protein (AdGFP, as control). Chondrocyte phenotypic markers (e.g., type II collagen and aggrecan) and the chondrocyte hypertrophy marker (type X collagen) were measured 6 days after viral transduction by reverse-transcription polymerase chain reaction.

RESULTS

Primary nucleus pulposus and anulus fibrosus cells transduced with AdBMPs, AdSox9, or adenovirus-expressing green fluorescence protein only (AdGFP, as control) continue to express healthy chondrocyte phenotypic markers and showed no evidence of the expression of the chondrocyte hypertrophy marker (type X collagen gene). Thus, we have shown that bovine nucleus pulposus and anulus fibrosus cells transduced with adenovirus overexpressing 12 different bone morphogenetic proteins or Sox9 maintain their phenotype in short-term culture.

CONCLUSIONS

In this study, primary bovine intervertebral disc cells transduced with adenovirus overexpressing 12 bone morphogenetic proteins or Sox9 preserved their phenotype in short-term culture. These cells did not express the type X collagen gene, an undesirable chondrocyte hypertrophic gene that could lead to ossification. Therefore, low-passage intervertebral disc cells cultured in monolayer is an appropriate culture system to test therapeutic genes. We further suggest that these cells may also be appropriate for engineering tissues or for cell therapy for degenerative disc diseases.

Molecular and phenotypic modulations of primary and immortalized canine chondrocytes in different culture systems

This study was conducted to determine physiological and functional features of primary and immortalized canine chondrocytes. Chondrocytes were immortalized by introducing the catalytic component of human telomerase namely human telomerase reverse transcriptase (hTERT). Primary chondrocytes lost their characteristic phenotype and growth properties whereas the immortalized cells remained polygonal with rapid growth rate. The expression of chondrocyte-specific markers decreased many-fold whereas that of chondrocyte-non-specific gene increased in primary chondrocytes. The immortalized cells did not express chondrocyte-specific genes in monolayers. Both primary and immortalized cells were encapsulated in alginate microspheres to construct three-dimensional (3D) culture system. As the primary chondrocytes, also the telomerase-transfected cells adopted a chondrocyte-specific gene expression pattern in alginate culture. Thus, the expression of telomerase represents possibility to expand chondrocytes without limitation while maintaining the chondrocyte-specific phenotype in 3D cultures. Use of such cells provides a standardized tool for testing different tissue engineering applications in canine model.

Aggrecan modulation of growth plate morphogenesis

Chick and mouse embryos with heritable deficiencies of aggrecan exhibit severe dwarfism and premature death, demonstrating the essential involvement of aggrecan in development. The aggrecan-deficient nanomelic (nm) chick mutant E12 fully formed growth plate (GP) is devoid of matrix and exhibits markedly altered cytoarchitecture, proliferative capacity, and degree of cell death. While differentiation of chondroblasts to pre-hypertrophic chondrocytes (IHH expression) is normal up to E6, the extended periosteum expression pattern of PTCH (a downstream effector of IHH) indicates altered propagation of IHH signaling, as well as accelerated down-regulation of FGFR3 expression, decreased BrdU incorporation and higher levels of ERK phosphorylation, all indicating early effects on FGF signaling. By E7 reduced IHH expression and premature expression of COL10A1 foreshadow the acceleration of hypertrophy observed at E12. By E8, exacerbated co-expression of IHH and COL10A1 lead to delayed separation and establishment of the two GPs in each element. By E9, increased numbers of cells express P-SMAD1/5/8, indicating altered BMP signaling. These results indicate that the IHH, FGF and BMP signaling pathways are altered from the very beginning of GP formation in the absence of aggrecan, thereby inducing premature hypertrophic chondrocyte maturation, leading to the nanomelic long bone growth disorder.

Extracellular matrix stability of primary mammalian chondrocytes and intervertebral disc cells cultured in alginate-based microbead hydrogels

Three-dimensional alginate constructs are widely used as carrier systems for transplantable cells. In the present study, we evaluated the chondrogenic matrix stability of primary rat chondrocytes and intervertebral disc (IVD) cells cultured in three different alginate-based microbead matrices to determine the influence of microenvironment on the cellular and metabolic behaviors of chondrogenic cells confined in alginate microbeads. Cells entrapped in calcium, strontium, or barium ion gelled microbeads were monitored with the live/dead dual fluorescent cell viability assay kit and the 1,9-dimethylmethylene blue (DMB) assay designed to evaluate sulfated glycosaminoglycan (s-GAG) production. Expression of chondrogenic extracellular matrix (ECM) synthesis was further evaluated by semiquantitative RT-PCR of sox9, type II collagen, and aggrecan mRNAs. Results indicate that Ca and Sr alginate maintained significantly higher population of living cells compared to Ba alginate (p < 0.05). Production of s-GAG was similarly higher in Ca and Sr alginate microbead cultures compared to Ba alginate microbeads. Although there was no significant difference between strontium and calcium up to day 14 of culture, Sr alginate showed remarkably improved cellular and metabolic activities on long-term cultures, with chondrocytes expressing as much as 31% and 44% greater s-GAG compared to calcium and barium constructs, respectively, while IVD cells expressed 63% and 74% greater s-GAG compared to calcium and barium constructs, respectively, on day 28. These findings indicate that Sr alginate represent a significant improvement over Ca- and Ba alginate microbeads for the maintenance of chondrogenic phenotype of primary chondrocytes and IVD cells.

Isolation and in vitro chondrogenic potential of human foetal spine cells

Cell therapy for nucleus pulposus (NP) regeneration is an attractive treatment for early disc degeneration as shown by studies using autologous NP cells or stem cells. Another potential source of cells is foetal cells. We investigated the feasibility of isolating foetal cells from human foetal spine tissues and assessed their chondrogenic potential in alginate bead cultures. Histology and immunohistochemistry of foetal tissues showed that the structure and the matrix composition (aggrecan, type I and II collagen) of foetal intervertebral disc (IVD) were similar to adult IVD. Isolated foetal cells were cultured in monolayer in basic media supplemented with 10% Fetal Bovine Serum (FBS) and from each foetal tissue donation, a cell bank of foetal spine cells at passage 2 was established and was composed of around 2000 vials of 5 million cells. Gene expression and immunohistochemistry of foetal spine cells cultured in alginate beads during 28 days showed that cells were able to produce aggrecan and type II collagen and very low level of type I and type X collagen, indicating chondrogenic differentiation. However variability in matrix synthesis was observed between donors. In conclusion, foetal cells could be isolated from human foetal spine tissues and since these cells showed chondrogenic potential, they could be a potential cell source for IVD regeneration.

Synergistic effect of chondroitin sulfate and cyclic pressure on biochemical and morphological properties of chondrocytes from articular cartilage

OBJECTIVE

To investigate the synergistic effect of chondroitin sulfate (CS) and cyclic pressure on the biochemical and morphological properties of chondrocytes isolated from articular cartilage and cultured in alginate matrix.

METHODS

The chondrocytes obtained from articular cartilage of goat femoropatellar joint were isolated and cultured in alginate matrix. The cells were exposed to CS (100 microg/ml) along with cyclic pressure of 1.2 MPa and 2.4 MPa and biochemical analysis of DNA, proteoglycan, collagen and protease activity was carried out in different matrix fractions, i.e., cellular matrix (CM) and further removed matrix (FRM) and in culture medium. The morphological studies of chondrocytes were carried out using transmission electron microscopy (TEM).

RESULTS

The treatment of chondrocytes with CS along with cyclic pressure increased the rate of cell proliferation relative to control (without load and in the absence of CS) and CS alone (P<0.001). The proteoglycan content in CM increased in the presence of CS alone (P<0.05) as well as CS with cyclic pressure (P<0.001). The specific activity of protease in CM and FRM decreased in the presence of CS with cyclic pressure relative to control (P<0.001). The TEM images showed abundant CM, improved cell morphology and matrix organization in the presence of CS and cyclic load treatment.

CONCLUSIONS

The results of this study suggested that in the presence of CS along with cyclic loading, the cellular ability to utilize and incorporate exogenous CS as extracellular matrix improved, as compared to CS alone.

Immortalized mouse articular cartilage cell lines retain chondrocyte phenotype and respond to both anabolic factor BMP-2 and pro-inflammatory factor IL-1

Articular cartilage chondrocytes help in the maintenance of tissue homeostasis and function of the articular joint. Study of primary chondrocytes in culture provides information closely related to in vivo functions of these cells. Limitations in the primary culture of chondrocytes have lead to the development of cells lines that serve as good surrogate models for the study of chondrocyte biology. In this study, we report the establishment and characterization of chondrocyte cell lines, MM-Sv/HP and MM-Sv/HP-2 from mouse articular cartilage. Cells were isolated from mouse femoral head articular cartilage, immortalized and maintained in culture through numerous passages. The morphology of the cells was from fibroblastic to polygonal in nature. Gene expression studies using quantitative PCR (Q-PCR) were performed on cells in monolayer culture and cells embedded in a three-dimensional alginate matrix. Stimulation of cells in monolayer culture with anabolic factor, BMP-2, resulted in increased gene expression of the extracellular matrix molecules, aggrecan and type II collagen and their regulator transcription factor, Sox9. Treatment by pro-inflammatory IL-1 resulted in increased gene expression of catabolic effectors including Aggrecanases (ADAMTS4, ADAMTS5), MMP-13 and nitric oxide synthase (Nos2). Cells in alginate treated with BMP-2 resulted in increased synthesis of proteoglycan which was released into the conditioned media on IL-1 stimulation. Western analysis of conditioned media showed the presence of Aggrecanase-cleaved aggrecan fragments. In summary, MM-Sv/HP and MM-Sv/HP-2 show preservation of important characteristics of articular chondrocytes as examined under multiple culture conditions and would provide a useful reagent in the study of chondrocyte biology.

Effect of osteogenic protein-1 on the matrix metabolism of bovine tendon cells

Tendon rupture is a common sports injury in adults. However, the mechanical properties of repair tissue are inferior to those of normal tissue. To accelerate tendon healing, an in vivo approach using growth factors has been applied and has shown evidence for the efficacy of biological stimulation of the repair process. Recombinant human osteogenic protein-1 (rhOP-1) has been shown to be effective in stimulating matrix production by various connective tissues. To test the effect of rhOP-1 on the matrix metabolism of tendon cells in vitro, bovine tendon cells were cultured in monolayer with various doses of rhOP-1 for 7 days. The addition of rhOP-1 to cell culture media resulted in significant increases in cell proliferation, DNA content, and the synthesis of proteoglycans (PGs) and collagen, compared to control cultures. The relative percentage of large PGs in the OP-1 culture was higher than that in the control culture. In conclusion, we show for the first time that rhOP-1 stimulates the proliferation of tendon cells and their ability to synthesize and accumulate PGs and collagen in their extracellular matrix. These biological properties may be used in the tissue-engineering of tendon tissues.

Adhesive properties of laminated alginate gels for tissue engineering of layered structures

A significant challenge in tissue engineering is the creation of tissues with stratified morphology or embedded microstructures. This study investigated methods to fabricate composite gels from separately deposited alginate layers and examined the effects of processing methods on the mechanics of adhesion. Laminated alginate gels were created through a three step process which included: treatment of the interfaces with citrate; annealing of the gels to allow for molecular rearrangement of the alginate chains; and exposure to a CaCl(2) to crosslink the alginate sheets. Process variables included volume and concentration of applied citrate, annealing time, incubation time in CaCl(2), and CaCl(2) concentration. Laminated sheets were tested in lap-shear geometry to characterize failure phenomena and mechanical properties. The site of failure within the gel depended on the integrity of the interface, with weaker gels delaminating and gels with mechanical properties similar to that of bulk gels failing randomly throughout the thickness. Citrate volume, citrate concentration, CaCl(2) incubation time, and CaCl(2) concentration altered the mechanical properties of the laminated alginate sheets, while annealing time had little effect on all measured parameters. This study demonstrates the integration of separately fabricated alginate layers to create mechanically or chemically anisotropic or heterogeneous structures.

Comparative effects of bone morphogenetic proteins and Sox9 overexpression on matrix accumulation by bovine anulus fibrosus cells: implications for anular repair

STUDY DESIGN

An in vitro biologic study comparing the effects of a series of bone morphogenetic proteins (BMPs) and Sox9 on the extracellular matrix accumulation by bovine anulus fibrosus (AF) cells.

OBJECTIVE

To compare the effects of adenoviral-mediated overexpression of various BMPs and Sox9 on extracellular matrix accumulation by AF cells in vitro.

SUMMARY OF BACKGROUND DATA

Repair of the disrupted AF, which is perceived to be a potential therapy to diminish nucleus pulposus (NP) herniation, may also offer a treatment strategy for severe symptomatic degenerative disc disease. To date, no systematic comparison of a large group of growth factors in the AF has been published. In this study, we compared the effects of the adenoviral-mediated overexpression of 12 BMPs and Sox9 on extracellular matrix production by AF cells.

METHODS

Adult monolayer-cultured bovine AF cells were transduced with adenoviral vectors containing human BMP and green fluorescence protein (GFP) genes (AdBMPs), or Sox9 and GFP genes (AdSox9), or GFP gene alone (AdGFP, as negative control). Proteoglycan and collagen accumulation, and cell proliferation were measured for each of the treatment groups 6 days after viral transduction.

RESULTS

AF cells transduced with BMP-2, -3, -5, -7, -8, -12, -13, -14, and -15, and Sox9 accumulated significantly more collagen than AF cells transduced with AdGFP (control). AF cells transduced with AdBMP-2, -4, -7, -10, -12, and -13, and AdSox9 accumulated significantly more proteoglycans than AF cells transduced with AdGFP.

CONCLUSION

We have demonstrated the relative effectiveness of 12 different BMPs and Sox9 on the stimulation of proteoglycan and/or collagen accumulation by AF cells. This study is the first to compare the relative effectiveness of various BMPs and Sox9 on extracellular matrix accumulation by AF. This information should prove useful to those seeking to develop a strategy for repair of the AF in humans.

Aggrecanases and aggrecanase-generated fragments in the human intervertebral disc at early and advanced stages of disc degeneration

STUDY DESIGN

A comparative study of aggrecanases and aggrecan fragmentation profile in the human intervertebral disc at early and advanced stages of disc degeneration.

OBJECTIVE

To determine differences in the content of the aggrecanases and the profile of aggrecan fragmentation in early and advanced stages of disc degeneration using cadaveric human intervertebral discs.

SUMMARY OF BACKGROUND DATA

Aggrecanases and aggrecanase-generated aggrecan fragments have been found in human degenerated discs. However, the association between the grade of disc degeneration and the content of the aggrecanases and the profile of aggrecan fragments has not been well studied.

METHODS

A total of 108 cadaveric donor spines were assessed by MRI T2 imaging and graded based on the Thompson scale. Twelve donor spines (average age, 63 years), each specifically exhibiting 2 different stages (Grade 2 and Grade 4) of disc degeneration at different disc levels, were included in this study. After harvesting the preselected discs, tissue samples were obtained from the center of the nucleus pulposus (NP) and the middle zone of the anulus fibrosus (AF). The amount of the aggrecanases, specifically ADAMTS-4 and ADAMTS-5, and the pattern of aggrecan fragmentation in the isolated tissues were assessed by western blot using specific antibodies.

RESULTS

In both NP and the AF tissues, the amount of ADAMTS-4 detected was higher in disc tissues with a higher level of degeneration (Grade 4) than in Grade 2 disc tissues with a lower level of degeneration. However, the amount of ADAMTS-5 detected did not differ between the 2 disc tissue grades. The aggrecan fragmentation analysis of these samples demonstrated the presence of aggrecanase-mediated fragmentation in both groups; however, there was no apparent difference in the aggrecan fragmentation profile between discs at early and advanced stages of disc degeneration.

CONCLUSION

Aggrecanases are involved in aggrecanolysis at both the early and advanced stages of disc degeneration. The aggrecan fragmentation profile analysis demonstrates the involvement of aggrecanases, as well as that of matrix metalloproteinases and/or cathepsins, during disc degeneration.

Matrix replenishment by intervertebral disc cells after chemonucleolysis in vitro with chondroitinase ABC and chymopapain

BACKGROUND CONTEXT

One of the advantages of chemonucleolysis for the treatment of a herniated intervertebral disc is the potential for the disc to self-repair. It has been suggested that the enzymes used for chemonucleolysis differentially affect the potential of the disc cells to promote repair.

PURPOSE

To test the ability of nucleus pulposus and anulus fibrosus cells to repair the extracellular matrix degraded in vitro by either chondroitinase ABC or chymopapain.

STUDY DESIGN

An alginate cell culture system was used to monitor the progress of matrix repair after chemonucleolysis in vitro.

METHODS

Rabbit nucleus pulposus or anulus fibrosus cells precultured for 10 days in alginate gel were briefly exposed to low concentrations of chondroitinase ABC or chymopapain and then returned to normal culture conditions for up to 4 weeks. At each time point, the contents of DNA and matrix macromolecules and proteoglycan synthesis were measured.

RESULTS

The DNA content of enzyme-treated alginate beads during the following 4 weeks of culture was higher in the chondroitinase ABC group than in the chymopapain group (NP, p<.01, and AF, p<.05). The content of proteoglycan in beads containing nucleus pulposus and anulus fibrosus cells in the chondroitinase ABC group was higher than that in the chymopapain group (NP and AF, p<.001). The rate of proteoglycan synthesis and the content of collagen did not, however, differ between those two groups.

CONCLUSIONS

Intervertebral disc cells exposed to chondroitinase ABC reestablish a matrix richer in proteoglycan than cells exposed to chymopapain. This may be because of differences in the substrate spectrum of each enzyme. Although these results cannot be translated directly to the in vivo situation, they suggest the possibility that cells in discs subjected to chondroitinase ABC-induced chemonucleolysis retain a greater ability to replenish their extracellular matrix with proteoglycans than cells in discs exposed to chymopapain.

Soluble signalling factors derived from differentiated cartilage tissue affect chondrogenic differentiation of rat adult marrow stromal cells

BACKGROUND

Chondral defects show lack of proper regeneration whereas osteochondral lesions display limited regeneration capacity. Latter is probably due to immigration of chondroprogenitor cells from the subchondral bone. Known chondroprogenitor cells for cartilage tissues are multi-potent adult marrow stromal or mesenchymal stem cells (MSCs). In vitro chondrogenic differentiation of these precursor cells usually require cues from growth and signalling factors provided in vivo by surrounding tissues and cells. We hypothesise that signalling factors secreted by differentiated cartilage tissue can initiate and maintain chondrogenic differentiation status of MSCs.

METHODS

To study such paracrine communication between allogenic rat articular cartilage and rat MSCs embedded in alginate beads a novel coculture system without addition of external growth factors has been established.

RESULTS

Impact of cartilage on differentiating MSCs was observed at two different time points. Firstly, sustained expression of Sox9 was observed at an early stage which indicated induction of chondrogenic differentiation. Secondly, late stage repression of collagen X indicated pre-hypertrophic arrest of differentiation. In the culture supernatant we have identified vascular endothelial growth factor alpha (VEGF-164 alpha), matrix metalloproteinase (MMP) -13 and tissue inhibitors of MMPs (TIMP-1 and TIMP-2) which could be traced back either to the cartilage explant or to the MSCs under the influence of cartilage.

CONCLUSION

The identified factors might be involved in regulation of collagen X gene and protein expression and therefore, may have an impact on the control and regulation of MSCs differentiation.

In vitro culture of enzymatically isolated chondrons: a possible model for the initiation of osteoarthritis

The aim of this study was to assess whether enzymatically isolated chondrons from normal adult articular cartilage could be used as a model for the onset of osteoarthritis, by comparison with mechanically extracted chondrons from osteoarthritic cartilage. Enzymatically isolated chondrons (EC) were cultured for 4 weeks in alginate beads and agarose gel constructs. Samples were collected at days 1 and 2, and weekly thereafter. Samples were immunolabelled for types II and VI collagen, keratan sulphate and fibronectin and imaged using confocal microscopy. Mechanically extracted chondrons (MC) were isolated, immunohistochemically stained for type VI collagen and examined by confocal microscopy. In culture, EC showed the following characteristics: swelling of the chondron capsule, cell division within the capsule and remodelling of the pericellular microenvironment. This was followed by chondrocyte migration through gaps in the chondron capsule. Four types of cell clusters formed over time in both alginate beads and agarose constructs. Cells within clusters exhibited quite distinct morphologies and also differed in their patterns of matrix deposition. These differences in behaviour may be due to the origin of the chondrocytes in the intact tissue. The behaviour of EC in culture paralleled the range of morphologies observed in MC, which presented as single and double chondrons and large chondron clusters. This preliminary study indicates that EC in culture share similar structural characteristics with MC isolated from osteoarthritic cartilage, confirming that some processes that occur in osteoarthritis, such as pericellular remodelling, take place in EC cultures. The study of EC in culture may therefore provide an additional tool to investigate the mechanisms operating during the initial stages of osteoarthritis. Further investigation of specific osteoarthritic phenotype markers will, however, be required in order to validate the value of this model.

Alginate Encapsulation Impacts the Insulin-like Growth Factor-I System of Monolayer-Expanded Equine Articular Chondrocytes and Cell Response to Interleukin-1β

Alginate hydrogel culture has been shown to reestablish chondrocytic phenotype following monolayer expansion; however, previous studies have not adequately addressed how culture conditions affect the signaling systems responsible for chondrocyte metabolic activity. Here we investigate whether chondrocyte culture history influences the insulin-like growth factor-I (IGF-I) signaling system and its regulation by interleukin-1 (IL-1). Articular chondrocytes (ACs) from equine stifle joints were expanded by serial passage and were either encapsulated in alginate beads or maintained in monolayer culture for 10 days. Alginate-derived cells (ADCs) and monolayer-derived cells (MDCs) were then plated at high density, stimulated with IL-1beta (1 and 10 ng/mL) or IGF-I (50 ng/mL) for 48 h, and assayed for levels of type I IGF receptor (IGF-IR), IGF binding proteins (IGFBPs), and endogenously secreted IGF-I. Intermediate alginate culture yielded relatively low IGF-IR levels that increased in response to IL-1beta, whereas higher receptor levels on MDCs were reduced by cytokine. MDCs also secreted substantially more IGFBP-2, the predominant binding protein in conditioned media (CM), though IL-1beta suppressed levels for both cell populations. Concentrations of autocrine/paracrine IGF-I paralleled IGFBP-2 secretion. Disparate basal levels of IGF-IR and IGFBP-2, but not IGF-I, were attributed to relative transcript expression. Systemic differences coincided with varied effects of IL-1beta and IGF-I on cell growth and type I collagen expression. We conclude that culture strategy impacts the IGF-I signaling system of ACs, potentially altering their capacity to mediate cartilage repair. Consideration of hormonal regulators may be an essential element to improve chondrocyte culture protocols used in tissue engineering applications.

Microenvironment regulation of PRG4 phenotype of chondrocytes

Articular cartilage is a heterogeneous tissue with superficial (S), middle (M), and deep (D) zones. Chondrocytes in the S zone secrete the lubricating PRG4 protein, while chondrocytes from the M and D zones are more specialized in producing large amounts of the glycosaminoglycan (GAG) component of the extracellular matrix. Soluble and insoluble chemicals and mechanical stimuli regulate cartilage development, growth, and homeostasis; however, the mechanisms of regulation responsible for the distinct PRG4-positive and negative phenotypes of chondrocytes are unknown. The objective of this study was to determine if interaction between S and M chondrocytes regulates chondrocyte phenotype, as determined by coculture in monolayer at different ratios of S:M (100:0, 75:25, 50:50, 25:75, 0:100) and at different densities (240,000, 120,000, 60,000, and 30,000 cells/cm(2)), and by measurement of PRG4 secretion and expression, and GAG accumulation. Coculture of S and M cells resulted in significant up-regulation in PRG4 secretion and the percentage of cells expressing PRG4, with simultaneous down-regulation of GAG accumulation. Tracking M cells with PKH67 dye in coculture revealed that they maintained a PRG4-negative phenotype, and proliferated less than S cells. Taken together, these results indicate that the up-regulated PRG4 expression in coculture is a result of preferential proliferation of PRG4-expressing S cells. This finding may have practical implications for generating a large number of phenotypically normal S cells, which can be limited in source, for tissue engineering applications.

Proinflammatory cytokines stimulate the expression of nerve growth factor by human intervertebral disc cells

STUDY DESIGN

In vitro studies of the effects of proinflammatory cytokines on the production of nerve growth factor (NGF) by human intervertebral disc (IVD) cells.

OBJECTIVE

To determine the constitutive expression and production of NGF and the effect of cytokines on the expression of NGF by human IVD cells.

SUMMARY OF THE BACKGROUND DATA

NGF may play a role in the collateral sprouting of sensory axons, neural survival, and regulation of nociceptive sensory neurons. NGF is known to be up-regulated by proinflammatory cytokines.

METHODS

The presence of NGF protein was analyzed by immunohistochemistry using human IVD cells obtained from cadaveric human spines with no known disc disease (MRI Thompson grades 2-4). The effects of interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) on NGF production and mRNA expression of NGF by IVD cells were examined. The expression of NGF receptors, trkA and p75, was also assessed immunohistochemically.

RESULTS

Cadaveric anulus fibrosus (AF) and nucleus pulposus (NP) cells cultured in vitro in monolayer and in alginate beads positively stained with an anti-NGF antibody. The constitutive production of NGF protein in IVD cells was low (NP) or not detectable (AF). The expression of NGF mRNA was detectable in both cell types. IL-1beta and TNF-alpha up-regulated the NGF mRNA expression and the secretion of NGF protein into the media. TrkA was immunolocalized in AF and NP cells.

CONCLUSION

Our results demonstrate, for the first time, that human AF and NP cells constitutively express NGF protein and mRNA, and that the proinflammatory cytokines IL-1beta and TNF-alpha stimulate the production of NGF. The precise role of NGF produced by IVD cells in the generation of discogenic pain or on the metabolism of IVD cells, especially under certain physiologic conditions in which cytokines are up-regulated, needs to be clarified in future experimentation.

The expression of NG2 proteoglycan in the human intervertebral disc

STUDY DESIGN

Immunohistochemical and biochemical analyses of NG2 proteoglycan in the human intervertebral disc.

OBJECTIVE

To determine if the human intervertebral disc expresses NG2 proteoglycan.

SUMMARY OF BACKGROUND DATA

In the nervous system, NG2 has been reported to play an important role as an interactive extracellular matrix component and membrane receptor for growth factors. NG2 is also found in non-neuronal tissues, such as cartilage and bone; however, the expression of NG2 within the human intervertebral disc is unknown.

METHODS

NG2 expression in the intervertebral disc was examined through Western blotting, reverse transcriptase polymerase chain reaction, and immunohistochemistry. Confocal microscopy was used to assess the spatial association of NG2 with type VI collagen. To reveal changes in the content of NG2 with disc degeneration, Western blot analysis was used to assess the relative content of NG2 in human intervertebral disc tissues with varying degrees of degeneration.

RESULTS

NG2 was clearly identified in cells from both the anulus fibrosus and nucleus pulposus, and colocalized with both type VI collagen and beta-integrin, located in the inner area of the cell-associated matrix. Throughout the anterior and posterior regions of the disc tissues, most cells were confirmed to be NG2 positive. Cells expressed NG2 messenger ribonucleic acid, and Western blot confirmed the presence of the core protein of the NG2 protein, 250 kDa. A study comparing the different grades of disc degeneration showed that the content of NG2 was elevated in disc tissues in an advanced stage of degeneration compared to tissues in an early stage of degeneration.

CONCLUSIONS

Although the biologic role of NG2 remains to be elucidated, the colocalization of NG2 with type VI collagen in the pericellular area suggests that NG2 may play an important role in cell-matrix interactions. The high level of NG2 expression in advanced degeneration also suggests an important role of NG2 in the loss of disc integrity.

Platelet-rich plasma stimulates porcine articular chondrocyte proliferation and matrix biosynthesis

OBJECTIVE

Platelet-rich plasma (PRP) is a fraction of plasma that contains high levels of multiple growth factors. The purpose of this study was to examine the effects of PRP on cell proliferation and matrix synthesis by porcine chondrocytes cultured in alginate beads, conditions that promote the retention of the chondrocytic phenotype, in order to determine the plausibility of using this plasma-derived material for engineering cartilage.

DESIGN

PRP and platelet-poor plasma (PPP) were prepared from adult porcine blood. Adult porcine chondrocytes were cultured in the presence of 10% PRP, 10% PPP or 10% fetal bovine serum (FBS) for 3 days. Cell proliferation, proteoglycan (PG) and collagen synthesis were quantified, and the structure of newly synthesized PG and collagen was characterized.

RESULTS

Treatment with 10% PRP resulted in a small but significant increase in DNA content (+11%, vs FBS; P<0.01; vs PPP; P<0.001). PG and collagen syntheses by the PRP-treated chondrocytes were markedly higher than those by chondrocytes treated by FBS or PPP (PG; PRP: +115% vs FBS; +151% vs PPP, both P<0.0001, collagen; PRP: +163% vs FBS; +163% vs PPP, both P<0.0001). Biochemical analyses revealed that treatment with PRP growth factors did not markedly affect the types of PGs and collagens produced by porcine chondrocytes, suggesting that the cells remained phenotypically stable in the presence of PRP.

CONCLUSION

PRP isolated from autologous blood may be useful as a source of anabolic growth factors for stimulating chondrocytes to engineer cartilage tissue.

Stem cell-based tissue engineering with silk biomaterials

Silks are naturally occurring polymers that have been used clinically as sutures for centuries. When naturally extruded from insects or worms, silk is composed of a filament core protein, termed fibroin, and a glue-like coating consisting of sericin proteins. In recent years, silk fibroin has been increasingly studied for new biomedical applications due to the biocompatibility, slow degradability and remarkable mechanical properties of the material. In addition, the ability to now control molecular structure and morphology through versatile processability and surface modification options have expanded the utility for this protein in a range of biomaterial and tissue-engineering applications. Silk fibroin in various formats (films, fibers, nets, meshes, membranes, yarns, and sponges) has been shown to support stem cell adhesion, proliferation, and differentiation in vitro and promote tissue repair in vivo. In particular, stem cell-based tissue engineering using 3D silk fibroin scaffolds has expanded the use of silk-based biomaterials as promising scaffolds for engineering a range of skeletal tissues like bone, ligament, and cartilage, as well as connective tissues like skin. To date fibroin from Bombyx mori silkworm has been the dominant source for silk-based biomaterials studied. However, silk fibroins from spiders and those formed via genetic engineering or the modification of native silk fibroin sequence chemistries are beginning to provide new options to further expand the utility of silk fibroin-based materials for medical applications.

[Ankle chondrocytes are more resistant to Interleukin-1 than chondrocytes derived from the knee]

BACKGROUND

The incidence of degenerative changes and osteoarthritis is lower in the ankle than in the knee joints. This cannot be explained exclusively with differences in anatomy and biomechanical properties of these two synovial joints. Previous studies have indicated distinct differences in the biochemical composition of the extracellular matrix of articular cartilage from knee and ankle joints. The aim of this study was to identify potential metabolic differences between knee and ankle joint chondrocytes using isolated cells to distinguish the secondary effects of the resident extracellular matrix from the primary matrix-independent effects of cellular differentiation.

METHOD

Isolated knee and ankle chondrocytes from the same human donor were cultured in alginate beads and subsequently exposed to a three-day pulse of the catabolic cytokine interleukin-1 (IL-1) as a model of an inflammatory episode. The metabolism of proteoglycans (PG's) was analyzed as expressed changes in 35S-sulfate incorporation into glycosaminoglycans (GAG's).

RESULTS

The presence of IL-1 induced an inhibition of PG synthesis in knee and ankle articular chondrocytes. The 50% inhibitory concentration (IC50) of IL-1 was about 5 times lower for knee than for ankle chondrocytes.

CONCLUSION

Ankle chondrocytes are more resistant to IL-1 induced inhibition of PG synthesis than chondrocytes from the knee.