Chondrocyte apoptosis induced by aggrecan G1 domain as a result of decreased cell adhesion

Combined single-cell RNA sequencing and mendelian randomization to identify biomarkers associated with necrotic apoptosis in intervertebral disc degeneration

BACKGROUND

Intervertebral disc degeneration (IDD) is associated with back pain; back pain is a world-wide contributor to poor quality of life, while necroptosis has the characteristics of necroptosis and apoptosis, however, its role in IDD is still unclear. Therefore, the aim of this study was to identify biomarkers associated with necroptosis in IDD.

PURPOSE

To explore biomarkers associated with necroptosis in IDD, reveal the pathogenesis of IDD, as well as provide new directions for the diagnosis and treatment of this disease.

STUDY DESIGN/SETTINGS

Retrospective cohort study. Our study employs scRNA-seq coupled with MR analysis to investigate the causal relationship between necroptosis and IDD, laying a foundational groundwork for unveiling the intricate pathogenic mechanisms of this condition.

METHODS

Data quality control and normalisation was executed in single-cell dataset, GSE205535. Then, different cell types were obtained by cell annotation through marker genes. Subsequently, chi-square test was employed to assess the distribution difference of different cell types between IDD and control to screen key cells. AUCell was applied to calculate necroptosis-related genes (NRGs) scores of all cell types, further key cells were divided into high and low NRGs groups according to the median AUC scores of different cell types. Afterwards, the differentially expressed genes (DEGs) within the two score groups were screened. Then, the genes that had causal relationship with IDD were selected as biomarkers by univariate and multivariate Mendelian randomization (MR) analysis. Finally, the expression of biomarkers in different cell types and pseudo-time analysis was analyzed separately.

RESULTS

In GSE205535, 16 different cell populations identified by UMAP cluster analysis were further annotated to 8 cell types using maker genes. Afterwards, 53 DEGs were screened between the high and low NRGs groups. In addition, 9 genes with causal relationship with IDD were obtained by univariate MR analysis, further multivariate MR analysis proved that NT5E and TMEM158 had a direct causal relationship with IDD, which were used as biomarkers in this study. This study not only found that the expression levels of NT5E and TMEM158 were higher in IDD group, but also found that fibrochondrocytes and inflammatory chondrocytes were the key cells of NT5E and TMEM158, respectively. In the end, the biomarkers had the same expression trend in the quasi-time series, and both of them from high to low and then increased.

CONCLUSION

NT5E and TMEM158, as biomarkers of necroptotic apoptotic IDD, were causally associated with IDD.

CLINICAL SIGNIFICANCE

The understanding of chondrocytes as key cells provides new perspectives for deeper elucidation of the pathogenesis of IDD, improved diagnostic methods, and the development of more effective treatments. These findings are expected to provide a more accurate and personalised approach to clinical diagnosis and treatment, thereby improving the prognosis and quality of life of patients with IDD.

V3: an enigmatic isoform of the proteoglycan versican

V3 is an isoform of the extracellular matrix (ECM) proteoglycan (PG) versican generated through alternative splicing of the versican gene such that the two major exons coding for sequences in the protein core that support chondroitin sulfate (CS) glycosaminoglycan (GAG) chain attachment are excluded. Thus, versican V3 isoform carries no GAGs. A survey of PubMed reveals only 50 publications specifically on V3 versican, so it is a very understudied member of the versican family, partly because to date there are no antibodies that can distinguish V3 from the CS-carrying isoforms of versican, that is, to facilitate functional and mechanistic studies. However, a number of in vitro and in vivo studies have identified the expression of the V3 transcript during different phases of development and in disease, and selective overexpression of V3 has shown dramatic phenotypic effects in "gain and loss of function" studies in experimental models. Thus, we thought it would be useful and instructive to discuss the discovery, characterization, and the putative biological importance of the enigmatic V3 isoform of versican.

The synthesis and secretion of versican isoform V3 by mammalian cells: A role for N-linked glycosylation

Versican is a large extracellular matrix (ECM) chondroitin sulfate (CS) proteoglycan found in most soft tissues, which is encoded by the VCAN gene. At least four major isoforms (V0, V1, V2, and V3) are generated via alternative splicing. The isoforms of versican are expressed and accumulate in various tissues during development and disease, where they contribute to ECM structure, cell growth and migration, and immune regulation, among their many functions. While several studies have identified the mRNA transcript for the V3 isoform in a number of tissues, little is known about the synthesis, secretion, and targeting of the V3 protein. In this study, we used lentiviral generation of doxycycline-inducible rat V3 with a C-terminal tag in stable NIH 3T3 cell lines and demonstrated that V3 is processed through the classical secretory pathway. We further show that N-linked glycosylation is required for efficient secretion and solubility of the protein. By site-directed mutagenesis, we identified amino acids 57 and 330 as the active N-linked glycosylation sites on V3 when expressed in this cell type. Furthermore, exon deletion constructs of V3 revealed that exons 11-13, which code for portions of the carboxy region of the protein (G3 domain), are essential for V3 processing and secretion. Once secreted, the V3 protein associates with hyaluronan along the cell surface and within the surrounding ECM. These results establish critical parameters for the processing, solubility, and targeting of the V3 isoform by mammalian cells and establishes a role for V3 in the organization of hyaluronan.

Endothelial dysfunction induces atherosclerosis: increased aggrecan expression promotes apoptosis in vascular smooth muscle cells

Endothelial dysfunction-induced lipid retention is an early feature of atherosclerotic lesion formation. Apoptosis of vascular smooth muscle cells (VSMCs) is one of the major modulating factors of atherogenesis, which accelerates atherosclerosis progression by causing plaque destabilization and rupture. However, the mechanism underlying VSMC apoptosis mediated by endothelial dysfunction in relation to atherosclerosis remains elusive. In this study, we reveal differential expression of several genes related to lipid retention and apoptosis, in conjunction with atherosclerosis, by utilizing a genetic mouse model of endothelial nitric oxide synthase (eNOS) deficiency manifesting endothelial dysfunction. Moreover, eNOS deficiency led to the enhanced susceptibility against pro-apoptotic insult in VSMCs. In particular, the expression of aggrecan, a major proteoglycan, was elevated in aortic tissue of eNOS deficient mice compared to wild type mice, and administration of aggrecan induced apoptosis in VSMCs. This suggests that eNOS deficiency may elevate aggrecan expression, which promotes apoptosis in VSMC, thereby contributing to atherosclerosis progression. These results may facilitate the development of novel approaches for improving the diagnosis or treatment of atherosclerosis.

3D printed biofunctionalized scaffolds for microfracture repair of cartilage defects

While articular cartilage defects affect millions of people worldwide from adolescents to adults, the repair of articular cartilage defects still remains challenging due to the limited endogenous regeneration of the tissue and poor integration with implants. In this study, we developed a 3D-printed scaffold functionalized with aggrecan that supports the cellular fraction of bone marrow released from microfracture, a widely used clinical procedure, and demonstrated tremendous improvement of regenerated cartilage tissue quality and joint function in a lapine model. Optical coherence tomography (OCT) revealed doubled thickness of the regenerated cartilage tissue in the group treated with our aggrecan functionalized scaffold compared to standard microfracture treatment. H&E staining showed 366 ± 95 chondrocytes present in the unit area of cartilage layer with the support of bioactive scaffold, while conventional microfracture group showed only 112 ± 26 chondrocytes. The expression of type II collagen appeared almost 10 times higher with our approach compared to normal microfracture, indicating the potential to overcome the fibro-cartilage formation associated with the current microfracture approach. The therapeutic effect was also evaluated at joint function level. The mobility was evaluated using a modified Basso, Beattie and Bresnahan (BBB) scale. While the defect control group showed no movement improvement over the course of study, all experimental groups showed a trend of increasing scores over time. The present work developed an effective method to regenerate critical articular defects by combining a 3D-printed therapeutic scaffold with the microfracture surgical procedure. This biofunctionalized acellular scaffold has great potential to be applied as a supplement for traditional microfracture to improve the quality of cartilage regeneration in a cost and labor effective way.

PFKFB3 modulates glycolytic metabolism and alleviates endoplasmic reticulum stress in human osteoarthritis cartilage

Glycolytic disorder has been demonstrated to be a major cause of osteoarthritis (OA) and chondrocyte dysfunction. The present work aimed to investigate the expression and role of the glycolytic regulator 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 3 (PFKFB3) in OA cartilage. It was found that PFKFB3 expression was down-regulated in human OA cartilage tissues and in tumour necrosis factor (TNF)-α- or interleukin (IL)-1β-stimulated human chondrocytes. The glycolytic metabolism appeared as glucose utilization and adenosine triphosphate (ATP) generation, and lactate production was stunted in OA cartilage. However, the impaired glycolytic process in OA cartilage was improved by PFKFB3 overexpression, which was confirmed in TNF-α- or IL-1β-treated chondrocytes. Furthermore, the expressions of endoplasmic reticulum (ER) stress-associated genes including PERK, ATF3, IRE1, phosphorylated eIF2α (p-eIF2α) and MMP13 were enhanced in OA cartilage explants, while they were decreased by AdPFKFB3 transfection. PFKFB3 also modulated the expressions of PERK, ATF3, IRE1, p-eIF2α and MMP13 in tunicamycin-exposed chondrocytes. Additionally, PFKFB3 improved the cell viability of OA cartilage explants and chondrocytes through the PI3K/Akt/C/EBP homologous protein (CHOP) signalling pathway. The transfection of AdPFKFB3 also significantly reduced caspase 3 activation and promoted aggrecan and type II collagen expressions in OA cartilage explants and chondrocytes. In all, this study characterizes a novel role of PFKFB3 in glycolytic metabolism and ER stress of OA cartilage explants and chondrocytes. The study might provide a potential target for OA prevention or therapy.

RNA-seq analysis of clinical-grade osteochondral allografts reveals activation of early response genes

Preservation of osteochondral allografts used for transplantation is critical to ensure favorable outcomes for patients after surgical treatment of cartilage defects. To study the biological effects of protocols currently used for cartilage storage, we investigated differences in gene expression between stored allograft cartilage and fresh cartilage from living donors using high throughput molecular screening strategies. We applied next generation RNA sequencing (RNA-seq) and real-time reverse transcription quantitative polymerase chain reaction (RT-qPCR) to assess genome-wide differences in mRNA expression between stored allograft cartilage and fresh cartilage tissue from living donors. Gene ontology analysis was used to characterize biological pathways associated with differentially expressed genes. Our studies establish reduced levels of mRNAs encoding cartilage related extracellular matrix (ECM) proteins (i.e., COL1A1, COL2A1, COL10A1, ACAN, DCN, HAPLN1, TNC, and COMP) in stored cartilage. These changes occur concomitantly with increased expression of "early response genes" that encode transcription factors mediating stress/cytoprotective responses (i.e., EGR1, EGR2, EGR3, MYC, FOS, FOSB, FOSL1, FOSL2, JUN, JUNB, and JUND). The elevated expression of "early response genes" and reduced levels of ECM-related mRNAs in stored cartilage allografts suggests that tissue viability may be maintained by a cytoprotective program that reduces cell metabolic activity. These findings have potential implications for future studies focused on quality assessment and clinical optimization of osteochondral allografts used for cartilage transplantation. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1950-1959, 2016.

The effect of vascular endothelial growth factor on aggrecan and type II collagen expression in rat articular chondrocytes

The expression of vascular endothelial growth factor (VEGF) directly correlates with the Mankin score and the degree of cartilage destruction. The biological activity of VEGF on articular cartilage remains unknown, so this study was performed to investigate the effect of VEGF on aggrecan and type II collagen expression in vitro. We carried out this study at the Center Laboratory of Renmin Hospital at Wuhan University. Rat articular chondrocytes were cultured in a monolayer. Then, the experiment was divided into 4 groups: group A (control group), without any disposal; group B, treated with 10 ng/ml VEGF; group C, treated with 10 ng/ml IL-1β; and group D, treated with 10 ng/ml VEGF + 10 ng/ml IL-1β. After 48 h, messenger RNA (mRNA) expression of aggrecan and type II collagen was evaluated by real-time polymerase chain reaction (real-Time PCR), and protein expression of aggrecan and type II collagen was detected by Western blotting. VEGF was found to significantly inhibit the expression of aggrecan and type II collagen at the gene and protein levels. These findings suggest that VEGF may result in degeneration of articular cartilage by inhibiting the synthesis and expression of aggrecan and type II collagen.

The effect of hyaluronic acid on IL-1beta-induced chondrocyte apoptosis in a rat model of osteoarthritis

The purpose of this article was to study the effect of hyaluronic acid (HA) on chondrocyte apoptosis in a rat osteoarthritis in vitro model (exposure to IL-1beta) and explore its mechanism. A rat in vitro model of osteoarthritis (OA) was established using 10 ng/mL IL-1beta as a modulating and chondrocyte apoptosis inducing agent. Different doses of HA (10, 20, and 40 microg/mL) were added 1 h prior to the addition of IL-1beta to a monolayer culture of freshly isolated juvenile rat chondrocytes. The ratio of apoptotic cell death was surveyed by Annexin V-FITC and propidium iodide double-labeling FACS analysis. The mitochondrial membrane potential of chondrocytes was evaluated by rhodamine-123 fluorescence. The mitochondrial function was evaluated through detecting the ATP production by a luciferase assay. The reverse transcription polymerase chain reaction (RT-PCR) was performed to measure mRNA expression levels of inducible oxide synthase (iNOS). HA could inhibit IL-1beta-induced chondrocyte apoptosis in our cell culture model system. It was showed that addition of HA to the medium was able in a dose-dependent way to reduce the impairment of the mitochondrial membrane potential and to restore mitochondrial ATP production. This study shows that HA could suppress in a dose-dependent way chondrocyte apoptosis in our IL-1beta-induced osteoarthritis model. The suppression of inflammatory cytokine activity within the joint might be one important mechanism of the clinical action of intraarticular injection of HA in the treatment of OA.

Chondrocyte apoptosis: implications for osteochondral allograft transplantation

Osteochondral allograft transplantation is a useful technique to manage larger articular cartilage injuries. One factor that may compromise the effectiveness of this procedure is chondrocyte cell death that occurs during the storage, preparation, and implantation of the osteochondral grafts. Loss of viable chondrocytes may negatively affect osteochondral edge integration and long-term function. A better understanding of the mechanisms responsible for chondrocyte loss could lead to interventions designed to decrease cell death and improve results. Recent studies indicate that apoptosis, or programmed cell death, is responsible for much of the chondrocyte death associated with osteochondral allograft transplantation. Theoretically, some of these cells can be rescued by blocking important apoptotic mediators. We review the role of apoptosis in cartilage degeneration, focusing on apoptosis associated with osteochondral transplantation. We also review the pathways thought to be responsible for regulating chondrocyte apoptosis, as well as experiments testing inhibitors of the apoptotic pathway. These data suggest that key contributors to the apoptotic process can be manipulated to enhance chondrocyte survival. This knowledge may lead to better surgical outcomes for osteochondral transplantation.

Extracellular granzymes: current perspectives

Granzyme A (GrA) and granzyme B (GrB) play key roles in the induction of target cell death induced by cytotoxic lymphocytes. Whilst these roles have been extensively studied, it is becoming apparent that both granzymes also possess extracellular activities. Soluble granzymes are found extracellularly in normal plasma and are elevated in a number of diseases, ranging from viral and bacterial infections to autoimmune diseases. Here, we discuss the current knowledge of extracellular granzyme substrates, inhibitors and functions; and the pathological consequences of extracellular granzymes in disease. In addition, we provide new evidence for the role of glycosaminoglycan-binding sites of granzymes in extracellular matrix remodeling.

Neurocan-GFP fusion protein: a new approach to detect hyaluronan on tissue sections and living cells

Hyaluronan is an unsulfated glycosaminoglycan (GAG) that is ubiquitously expressed in the extracellular matrix (ECM) of all vertebrates, where hyaluronan rich matrices constitute a particular permissive environment for the development of complex biological structures and also for tumor progression. Because of its conserved structure and ubiquitous expression, antibodies for its histochemical detection cannot be produced. We have engineered a fusion protein, neurocan-GFP, and expressed it as a secreted molecule in mammalian cells. Neurocan-GFP fusion protein specifically binds to hyaluronan and directly visualizes hyaluronan on tissue sections, revealing a very detailed picture of hyaluronan distribution. The fluorescent fusion protein can be used in combination with antibodies and nuclear markers for double or triple staining. In addition, it is suitable to visualize hyaluronan on living cells by time-lapse video microscopy. The successful production and application of the neurocan-GFP fusion protein opens up new perspectives for using GFP fusion proteins as detection tools in histological and cytological studies complementing conventional antibody and biotin/avidin techniques.

The globular domains of PG-M/versican modulate the proliferation-apoptosis equilibrium and invasive capabilities of tumor cells

To dissect the role of the globular domains of PGM/versican--a large hyaluronan binding proteoglycan (PG) enriched in tumor lesions--we have stably transduced a human leiomyosarcoma cell line with either the G1 or G3 domain of the PG and subsequently assayed the effect of this manipulation on several cellular processes in vitro and in vivo. G1- and G3-overexpressing cells were found to exhibit an enhanced growth that was more accentuated in the absence of serum components and was seen both when cells were cultured on ECM substrates and in the absence of ECM anchorage. Accordingly, if inoculated subcutaneously into nude mice, G1 transfectants formed larger tumor masses than control cells at the site of implantation, albeit after a certain latency period. Upon binding to cell surface CD44, proliferation of G1-, but not G3-, overexpressing cells were dose dependently inhibited by exogenous hyaluronan (HA) or HA fragments. G1- and G3-transduced cells did not differ in their intrinsic ability to adhere and migrate on various purified ECM components, whereas G1-overproducing sarcoma cells were more invasive than the corresponding G3 mutants, and their locomotion was perturbed by exogenous HA. The augmented anchorage-independent growth exhibited solely by G1-transduced was largely ascribable to a reduced apoptotic rate, thereby indicating a shift in the proliferation--apoptosis equilibrium of the cells toward the former. In fact, G1-overexpressing cells appeared resistant to both cytotoxic drug-induced and Fas-dependent programmed cell death, and this resistance implicated mitochondrial apoptotic genes. The results indicate that the terminal domains of versican may differentially control propagation of tumor cells and diversely modulate their responses to environmental HA.

The effect of hyaluronan on CD44-mediated survival of normal and hydroxyl radical-damaged chondrocytes

OBJECTIVE

To identify the CD44-receptor-mediated effects of 5-7 x 10(5)MW hyaluronan (HA, Hyalgan) on cell viability in normal and damaged human chondrocyte primary cultures isolated from articular cartilage.

DESIGN

Primary cultures of human chondrocytes were established from normal articular biopsies and expanded to the second culture passage. The dose-response effects of HA on the viability of normal cultures were identified. Chondrocytes were then treated with either hypoxanthine (2 mM) and xanthine oxidase (20-60 mU), or with activated polymorphonuclear leukocytes (PMNs) to induce injury. Damaged and control cells were then treated with 5-7 x 10(5)HA in the previously identified optimal dose of 0.05 mg/ml. Viability was assessed at specific time periods for the chemically and PMN-damaged cells. To identify if HA effects were mediated by the CD44 receptor, chondrocytes were incubated with anti-CD44 antibody at saturating concentrations (5 microg/ml for 100,000 cells) to produce a maximum inhibition of HA binding. Cells were evaluated using the MTT viability assay, histology, electron microscopy and immunohistochemistry.

RESULTS

Direct addition of HA (optimal dose, 0.5 mg/ml) significantly increased cell survival in normal chondrocyte primary cultures (P<0.05). Similarly, addition of this same dose of HA to cultures of free radical-damaged chondrocytes, restored the viability to baseline conditions. Cell viability rates dropped significantly (P<0.05) when CD44 receptor binding was inhibited, indicating that cell growth was mediated by the CD44 receptor.

CONCLUSIONS

HA (0.5 mg/ml of 5-7 x 10(5)) significantly increased the viability of normal human chondrocytes in primary culture and restored cell viability to near normal levels after oxidative cell injury.

Structure and function of aggrecan

Aggrecan is the major proteoglycan in the articular cartilage. This molecule is important in the proper functioning of articular cartilage because it provides a hydrated gel structure (via its interaction with hyaluronan and link protein) that endows the cartilage with load-bearing properties. It is also crucial in chondroskeletal morphogenesis during development. Aggrecan is a multimodular molecule expressed by chondrocytes. Its core protein is composed of three globular domains (G1, G2, and G3) and a large extended region (CS) between G2 and G3 for glycosaminoglycan chain attachment. G1 comprises the amino terminus of the core protein. This domain has the same structural motif as link protein. Functionally, the G1 domain interacts with hyaluronan acid and link protein, forming stable ternary complexes in the extracellular matrix. G2 is homologous to the tandem repeats of G1 and of link protein and is involved in product processing. G3 makes up the carboxyl terminus of the core protein. It enhances glycosaminoglycan modification and product secretion. Aggrecan plays an important role in mediating chondrocyte-chondrocyte and chondrocyte-matrix interactions through its ability to bind hyaluronan.

Effect of material geometry on cartilagenous tissue formation in vitro

The effect of material geometry, as defined by average pore size, on chondrocyte phenotype and cartilagenous tissue formation in vitro was examined. Bovine articular chondrocytes were plated on porous titanium alloy (Ti6Al4V) discs of different average pore sizes (13, 43, and 68 microm) and grown in culture for 4 weeks. Chondrocyte phenotype was maintained as indicated by the synthesis of large proteoglycans (Kav +/- SD: 13 microm = 0.28 +/- 0.01; 43 microm = 0.29 +/- 0.01; 68 microm = 0.27 +/- 0.02) and type II collagen. Light microscopical examination of histological sections of the composites showed that cartilagenous tissue had formed on all discs. The cartilagenous tissue on the discs of the smallest average pore size (13 microm) was significantly thicker than the tissue on the discs of larger average pore sizes and also had greater amounts of proteoglycan [mean glycosaminoglycan content +/- SD microg/disc): 13 microm = 246.9 +/- 7.8; 43 microm = 190.4 +/- 10.2; 68 microm = 156.6 +/- 25.8, p = 0.002] and DNA [mean DNA content +/- SD microg/disc): 13 microm = 12.5 +/- 0.6; 43 microm = 8.3 +/- 0.2; 68 microm = 9.3 +/- 0.9, p = 0.0008]. However, the amount of proteoglycan accumulated per cell was similar in the tissues generated on the discs of different average pore sizes. In contrast, the amount of collagen in the cartilagenous tissues showed no significant differences between the different pore sizes, but the amount of collagen accumulated per cell was less in the tissue formed on the smallest pore size disc (13 microm) as compared with the tissue formed on the discs of the larger pore sizes [mean hydroxyproline content/DNA (microg/microg) +/- SD: 13 microm = 1.56 +/- 0.2; 43 microm = 2.19 +/- 0.2; 68 microm = 2.3 +/- 0.3]. These results suggest that material geometry, as defined by pore size, can affect the amount and composition of the cartilagenous tissue that forms.

Chondrocyte phenotype and cell survival are regulated by culture conditions and by specific cytokines through the expression of Sox-9 transcription factor

OBJECTIVE

To investigate the effects of culture conditions, serum and specific cytokines such as insulin-like growth factor (IGF) 1 and interleukin (IL) 1alpha on phenotype and cell survival in cultures of Syrian hamster embryonic chondrocyte-like cells (DES4(+).2).

METHODS

Proteins and RNA extracted from subconfluent and confluent early- and late-passage DES4(+).2 cells cultured in the presence or absence of serum and IL-1alpha or IGF-1 or both cytokines together were analysed for the expression of chondrocyte-specific genes and for the chondrogenic transcription factor Sox-9 by Western and Northern blotting. Apoptosis was assessed by agarose gel electrophoresis of labelled low-molecular weight DNA extracted from DES4(+).2 cells and another Syrian hamster embryonic chondrocyte-like cell line, 10W(+).1, cultured under the different conditions and treatments.

RESULTS

Early passage DES4(+).2 cells expressed chondrocyte-specific molecules such as collagen types alpha1(II) and alpha1(IX), aggrecan, biglycan and link protein and collagen types alpha1(I) and alpha1(X) mRNAs, suggesting a prehypertrophic chondrocyte-like phenotype. The expression of all genes investigated was cell density- and serum-dependent and was low to undetectable in cell populations from later passages. Early-passage DES4(+).2 and 10W(+).1 cells survived when cultured at low cell density, but died by apoptosis when cultured at high cell density in the absence of serum or IGF-1. IGF-1 and IL-1alpha had opposite and antagonistic effects on the chondrocyte phenotype and survival. Whereas IL-1alpha acting alone suppressed cartilage-specific gene expression without significantly affecting cell survival, IGF-1 increased the steady-state mRNA levels and relieved the IL-1alpha-induced suppression of all the chondrocyte-specific genes investigated; it also enhanced chondrocyte survival. Suppression of the chondrocyte phenotype by the inflammatory cytokine IL-1alpha correlated with marked down-regulation of the transcription factor Sox-9, which was relieved by IGF-1. The expression of the Sox9 gene was closely correlated with the expression of the chondrocyte-specific genes under all conditions and treatments.

CONCLUSIONS

The results suggest that the effects of cartilage anabolic and catabolic cytokines IGF-1 and IL-1alpha on the expression of the chondrocyte phenotype are mediated by Sox-9. As Sox-9 appears to be essential for matrix production, the potent effect of IL-1alpha in suppressing Sox-9 expression may limit the ability of cartilage to repair during inflammatory joint diseases.

Anti-Fas-induced apoptosis in chondrocytes reduced by hyaluronan: evidence for CD44 and CD54 (intercellular adhesion molecule 1) invovement

OBJECTIVE

To investigate the in vitro effect of therapeutic hyaluronan (HA) of 500-730 kd on anti-Fas-induced apoptosis of chondrocytes from osteoarthritis (OA) patients, and to assess its mechanism of action by analyzing the role of the 2 HA receptors, CD44 and CD54 (intercellular adhesion molecule 1 [ICAM-1]).

METHODS

Chondrocytes isolated from human OA knee cartilage were cultured and the effect of HA on both spontaneous and anti-Fas-induced apoptosis was evaluated. Apoptosis was analyzed by JAM test (for quantitative analysis of fragmented DNA), cell death detection immunoassay (for quantitative analysis of oligonucleosome), TUNEL assay, and electron microscopy. Blocking experiments with anti-CD44 and anti-CD54 alone or in combination were performed to investigate the HA mechanism of action.

RESULTS

Both quantitative tests demonstrated that anti-Fas significantly induced apoptosis of isolated OA chondrocytes. HA at 1,000 microg/ml significantly reduced the anti-Fas-induced apoptosis of chondrocytes but did not affect spontaneous chondrocyte apoptosis. These data were also confirmed by TUNEL staining and by electron microscopy morphologic evaluation. The antiapoptotic effects of HA on anti-FAS-induced chondrocyte apoptosis were significantly decreased by both anti-CD44 (mean +/- SD 57 +/- 12% inhibition) and anti-ICAM-1 (31 +/- 22% inhibition). The mixture of the 2 antibodies had an additive effect, since the rate of inhibition increased to 87 +/- 13%.

CONCLUSION

These data demonstrate that 500-730-kd HA exerts an antiapoptotic effect on anti-FAS-induced chondrocyte apoptosis by binding its specific receptors (CD44 and ICAM-1). Furthermore, this HA fraction may be able to slow down chondrocyte apoptosis in OA by regulating the processes of cartilage matrix degradation.

Anti-Fas-induced apoptosis in chondrocytes reduced by hyaluronan: evidence for CD44 and CD54 (intercellular adhesion molecule 1) invovement

OBJECTIVE

To investigate the in vitro effect of therapeutic hyaluronan (HA) of 500-730 kd on anti-Fas-induced apoptosis of chondrocytes from osteoarthritis (OA) patients, and to assess its mechanism of action by analyzing the role of the 2 HA receptors, CD44 and CD54 (intercellular adhesion molecule 1 [ICAM-1]).

METHODS

Chondrocytes isolated from human OA knee cartilage were cultured and the effect of HA on both spontaneous and anti-Fas-induced apoptosis was evaluated. Apoptosis was analyzed by JAM test (for quantitative analysis of fragmented DNA), cell death detection immunoassay (for quantitative analysis of oligonucleosome), TUNEL assay, and electron microscopy. Blocking experiments with anti-CD44 and anti-CD54 alone or in combination were performed to investigate the HA mechanism of action.

RESULTS

Both quantitative tests demonstrated that anti-Fas significantly induced apoptosis of isolated OA chondrocytes. HA at 1,000 microg/ml significantly reduced the anti-Fas-induced apoptosis of chondrocytes but did not affect spontaneous chondrocyte apoptosis. These data were also confirmed by TUNEL staining and by electron microscopy morphologic evaluation. The antiapoptotic effects of HA on anti-FAS-induced chondrocyte apoptosis were significantly decreased by both anti-CD44 (mean +/- SD 57 +/- 12% inhibition) and anti-ICAM-1 (31 +/- 22% inhibition). The mixture of the 2 antibodies had an additive effect, since the rate of inhibition increased to 87 +/- 13%.

CONCLUSION

These data demonstrate that 500-730-kd HA exerts an antiapoptotic effect on anti-FAS-induced chondrocyte apoptosis by binding its specific receptors (CD44 and ICAM-1). Furthermore, this HA fraction may be able to slow down chondrocyte apoptosis in OA by regulating the processes of cartilage matrix degradation.

Roles of aggrecan domains in biosynthesis, modification by glycosaminoglycans and product secretion

Aggrecan is a member of the chondroitin sulphate (CS) proteoglycan family, which also includes versican/PG-M, neurocan and brevican. Members of this family exhibit structural similarity: a G1 domain at the N-terminus and a G3 domain at the C-terminus, with a central sequence for modification by CS chains. A unique feature of aggrecan is the insertion of three additional domains, an inter-globular domain (IGD), a G2 domain and a keratan sulphate (KS) domain (sequence modified by KS chains), between the G1 domain and the CS domain (sequence modified by CS chains). The G1 and G3 domains have been implicated in product secretion, but G2, although structurally similar to the tandem repeats of G1, performs an unknown function. To define the functions of each aggrecan domain in product processing, we cloned and expressed these domains in various combinations in COS-7 cells. The results indicated that the G3 domain enhanced product secretion, alone or in combination with the KS or CS domain, and promoted glycosaminoglycan (GAG) chain attachment. Constructs containing the G1 domain were not secreted. Addition of a CS domain sequence to G1 reduced this inhibition, but GAG chain attachment was still decreased. The potential GAG chain attachment site in the IGD was occupied by GAGs, and IGD product was secreted efficiently. The KS domain was modified by GAG chains and secreted. Finally, the G2 domain was expressed but not secreted, and inhibited secretion of the IGD when expressed as an IGD-G2 combination.

Versican modulates embryonic chondrocyte morphology via the epidermal growth factor-like motifs in G3

This investigation was designed to characterize the effect of the extracellular matrix molecule versican on chondrocyte morphology, using the well-studied chondrocyte cell culture system. When cultured chondrocytes reverted or "dedifferentiated" to a fibroblast-like morphology, we found that versican expression was significantly enhanced. Transfection of chondrocytes, isolated from embryonic chicken sterna, with a chicken miniversican construct accelerated the reversion process, while expression of an antisense construct inhibited it. A mutant miniversican lacking two epidermal growth factor-like motifs (versicanDeltaEGF) promoted differentiation, as shown by morphological changes and changes in the expression of other extracellular matrix molecules. A truncated versican mutant, the G3DeltaEGF, a G3 domain lacking its two epidermal growth factor-like motifs, also enhanced differentiation. This effect is related to G3DeltaEGF-induced change in cytoskeleton, since transfected cells exhibited misassembly of actin filaments. This article thus provides the first evidence that versican modulates chondrocyte morphology via changes in cytoskeletal structure, and may imply that extracellular matrix molecules play an important role in cell differentiation.

Ryudocan expression by luteinized granulosa cells is associated with the process of follicle atresia

OBJECTIVE

To evaluate the presence of ryudocan in follicular fluid (FF) and its possible correlation with FF E(2) and P, and to study the levels of ryudocan in granulosa-lutein cells stimulated with hCG.

DESIGN

Controlled clinical study and in vitro experiment.

SETTING

University teaching hospital.

PATIENT(S)

One hundred seven patients undergoing IVF.

INTERVENTION(S)

The FF and granulosa-lutein cells were aspirated from follicles 34 hours after an ovulatory gonadotropin bolus.

MAIN OUTCOME MEASURE(S)

FF ryudocan, E(2), and P levels as well as hCG-mediated induction of ryudocan.

RESULT(S)

Ryudocan was abundant in the FF; the concentration of ryudocan in human FF was estimated to be 305.5 +/- 200.8 ng/mL (mean +/- SD). Atretic follicles had higher concentrations of ryudocan (559.1 +/- 156.5 ng/mL). FF ryudocan levels were inversely correlated with FF E(2) (r = -0.5023) and P concentrations (r = -0.4459). A detectable amount of ryudocan was found in pooled granulosa-lutein cells. Ryudocan production was augmented by surge levels of hCG.

CONCLUSION(S)

Ryudocan is expressed in luteinized granulosa cells in vitro. The higher concentrations of ryudocan in FF of atretic follicles suggest an involvement of ryudocan in the process of atresia.

Modulation of extracellular matrix adhesiveness by neurocan and identification of its molecular basis

Neurocan is one of the major chondroitin sulfate proteoglycans of perinatal rodent brain. HEK-293 cells producing neurocan recombinantly show changes in their behavior. The expression of full-length neurocan led to a detachment of the secreting cells and the formation of floating spheroids. This occurred in the continuous presence of 10% fetal bovine serum in the culture medium. Cells secreting fragments of neurocan-containing chondroitin sulfate chains and the C-terminal domain of the molecule showed a similar behavior, whereas cells expressing fragments of neurocan-containing chondroitin sulfate chains but lacking parts of the C-terminal domain did not show spheroid formation. Cells secreting the hyaluronan-binding N-terminal domain of neurocan showed an enhanced adhesiveness. When untransfected HEK-293 cells were plated on a surface conditioned by spheroid-forming cells, they also formed spheroids. This effect could be abolished by chondroitinase treatment of the conditioned surface. The observations indicate that the ability of the chondroitin sulfate proteoglycan neurocan to modulate the adhesive character of extracellular matrices is dependent on the structural integrity of the C-terminal domain of the core protein.

The roles of matrix molecules in mediating chondrocyte aggregation, attachment, and spreading

The most abundant macromolecules in cartilage are hyaluronan, collagen, aggrecan, and link protein, which are believed to play roles in maintaining a unique three-dimensional network for a functional joint. This study was designed to investigate the roles of the major extracellular molecules in mediating chondrocyte-matrix interactions. We employed specific approaches to remove components individually or in combination: hyaluronan was digested with hyaluronidase; type II collagen was digested with collagenase; aggrecan expression was inhibited with antisense and beta-xyloside approaches; and link protein expression was inhibited with antisense oligonucleotides. Digestion of hyaluronan induced chondrocyte attachment to tissue culture plates, collagen-coated plates, and fibroblast-like chondrocyte cultures, and induced chondrocyte aggregation. Treated chondrocytes exhibited a fibroblast-like morphology, and the effects of hyaluronidase were dose-dependent. Conversely, the effect of collagenase on chondrocyte adhesion and aggregation was far less pronounced. Treatment with Arg-Gly-Asp peptide inhibited chondrocyte-collagen interaction. Chondrocyte attachment was enhanced by antisense oligonucleotides complementary to aggrecan and link protein and by beta-xyloside treatment. Nevertheless, hyaluronan seems to predominate over the other molecules in mediating chondrocyte-matrix interactions.

Tandem repeats are involved in G1 domain inhibition of versican expression and secretion and the G3 domain enhances glycosaminoglycan modification and product secretion via the complement-binding protein-like motif

The large aggregating chondroitin sulfate proteoglycans, including aggrecan, versican (PG-M), neurocan, and brevican, are characterized by N-terminal and C-terminal globular (or selectin-like) domains known as the G1 and G3 domains, respectively. For this study, we generated a series of expression constructs containing various combinations of chicken versican/PG-M domains and a leading peptide of link protein in order to examine the roles of the G1 and G3 domains in versican function. In transfection studies, we observed that the presence of the G1 domain was sufficient to inhibit product secretion, while the G3 domain enhanced this process. We also demonstrated that the G1 domain inhibited the attachment of glycosaminoglycan chains to the core proteins, while the G3 domain enhanced this process. Further studies revealed that inhibition of secretion by G1 was mediated by its two tandem repeats, while G3's promotion of glycosaminoglycan chain attachment was apparently dependent on G3's complement-binding protein (CBP)-like motif. The modulatory effects of these two molecular domains may contribute to versican's biological activities.

beta-Integrin-collagen interaction reduces chondrocyte apoptosis

We have observed that the spent culture media in suspended chondrocyte cultures is essential for the survival of the cells, since complete change of the spent media induces severe programmed cell death (apoptosis). Moreover, we showed that extracellular matrix (ECM) molecules in the culture media provide vital chondrocyte-matrix interactions; when media are changed, cells are deprived of matrix molecules and undergo apoptosis. In this paper we report that interaction with collagen, a ubiquitous extracellular matrix molecule, is essential for chondrocyte survival. Such an interaction causes chondrocyte aggregation and reduces the level of chondrocyte apoptosis. Hyaluronan, an abundant ECM molecule, can influence the effects of collagen by preventing chondrocyte aggregation. Degradation of hyaluronan with hyaluronidase results in chondrocyte aggregation, and this reduces the level of chondrocyte apoptosis. Experiments with an antibody to integrin beta1 suggest that the collagen-chondrocyte interactions are mediated through integrin beta1, and these interactions may protect chondrocytes from apoptosis. We hypothesize that hyaluronan binds aggrecan and link protein, forming stable ternary complexes, which interact with the chondrocyte surface, perhaps via CD44, and thus maintains a stable chondrocyte-matrix network.