Microenvironment regulation of extracellular signal-regulated kinase activity in chondrocytes: effects of culture configuration,interleukin-1, and compressive stress

OBJECTIVE: To compare extracellular signal-regulated kinase (ERK) activity in response to interleukin-1 (IL-1) in chondrocytes under various culture configurations designed for the study of cartilage biology and repair, and also in response to dynamic load for chondrocytes in cartilage. METHODS: Isolated bovine articular chondrocytes were maintained in serum-supplemented medium under 4 culture configurations: high-density monolayer, attached to a cut surface of cartilage, within tissue-engineered constructs, or within intact cartilage explants. Samples were subjected to a change of medium with or without IL-1. Cartilage explants were also subjected to dynamic compression. RESULTS: In chondrocyte monolayers, both basal and IL-1-stimulated ERK activities were similarly elevated at 0.5 hours after medium change, diminishing by 74% after 16 hours. In contrast, chondrocytes in other culture configurations exhibited lower basal levels of ERK activity and a moderate activation of ERK in response to IL-1 that was sustained over the 16-hour treatment time. The dynamic component of loading of cartilage explants led to a 5-fold activation of ERK, compared with free-swelling controls, that was indistinguishable from the effects of IL-1. CONCLUSION: ERK signaling in response to IL-1 in chondrocyte monolayers exhibited a pattern that was distinct from that in other culture systems, suggesting that the extracellular matrix plays an important regulatory role in modulating the response to extracellular stimuli. Since IL-1 and dynamic loading have distinct effects on chondrocyte biosynthesis, signaling pathways other than ERK participate in the chondrocyte responses to these stimuli.     

Biology of articular cartilage repair--present status and prospects

The cartilage response to injury differs from the classic wound healing because of two important features of the cartilage structure; lack of vascular system and rich matrix preventing chondrocyte from migration to the injury site. Three distinct types of cartilage injuries can be identified based on the depth of injury and the repair response: microdamage, chondral injury, and osteochondral injury. There have been numerous attempts to repair cartilage injury, however their results have reinforced that articular cartilage has limited potential to repair itself. However, current research is helping to clarify the mechanism of cartilage injury and repair based on its gene expression. Biology, gene therapy, and tissue engineering may provide a breakthrough to treat cartilage injury.     

Inhibition of integrative cartilage repair by proteoglycan 4 in synovial fluid

OBJECTIVE: To determine the effects of the articular cartilage surface, as well as synovial fluid (SF) and its components, specifically proteoglycan 4 (PRG4) and hyaluronic acid (HA), on integrative cartilage repair in vitro. METHODS: Blocks of calf articular cartilage were harvested, some with the articular surface intact and others without. Some of the latter types of blocks were pretreated with trypsin, and then with bovine serum albumin, SF, PRG4, or HA. Immunolocalization of PRG4 on cartilage surfaces was performed after treatment. Pairs of similarly treated cartilage blocks were incubated in partial apposition for 2 weeks in medium supplemented with serum and (3)H-proline. Following culture, mechanical integration between apposed cartilage blocks was assessed by measuring adhesive strength, and protein biosynthesis and deposition were determined by incorporated (3)H-proline. RESULTS: Samples with articular surfaces in apposition exhibited little integrative repair compared with samples with cut surfaces in apposition. PRG4 was immunolocalized at the articular cartilage surface, but not in deeper, cut surfaces (without treatment). Cartilage samples treated with trypsin and then with SF or PRG4 exhibited an inhibition of integrative repair and positive immunostaining for PRG4 at treated surfaces compared with normal cut cartilage samples, while samples treated with HA exhibited neither inhibited integrative repair nor PRG4 at the tissue surfaces. Deposition of newly synthesized protein was relatively similar under conditions in which integration differed significantly. CONCLUSION: These results support the concept that PRG4 in SF, which normally contributes to cartilage lubrication, can inhibit integrative cartilage repair. This has the desirable effect of preventing fusion of apposing surfaces of articulating cartilage, but has the undesirable effect of inhibiting integrative repair.     

Biologic effects of an interleukin-1 receptor antagonist protein on interleukin-1-stimulated cartilage erosion and chondrocyte responsiveness

Recombinant human interleukin-1 alpha (IL-1 alpha) and recombinant human IL-1 beta stimulate matrix proteoglycan degradation and inhibit glycosaminoglycan synthesis in bovine nasal cartilage explants. A 17-kd human recombinant IL-1 receptor antagonist protein (IRAP) caused a concentration-dependent (0.2-200 ng/ml) suppression of the effects of IL-1 alpha and IL-1 beta in cartilage organ cultures. IRAP inhibited the binding of radiolabeled IL-1 alpha to rabbit articular chondrocytes. Matrix metalloproteinase (collagenase, gelatinase, and stromelysin) and prostanoid production by IL-1-activated rabbit articular chondrocytes was also suppressed by IRAP. These results could have potential significance in the development of a new antiarthritis therapy based on an IRAP.     

Fibronectin synthesis in superficial and deep layers of normal articular cartilage

Objective. To study the distribution and synthesis of fibronectin (FN) in superficial and deep layers of normal articular cartilage. Methods. Superficial and deep bovine and human articular cartilage slices were used to extract and quantitate FN by radioimmunoassay. Chondrocytes were also isolated by collagenase digestion for FN extraction and culture. Superficial and deep cartilage explants were cultured with and without stimulation by cytokines. Quantitation of newly synthesized FN was carried out by incubation with ³⁵S-methionine. FN was purified on gelatin-agarose columns and further characterized by polyacrylamide gel electrophoresis. FN messenger RNA (mRNA) was quantitated by Northern blot analysis. Results. Freshly isolated bovine chondrocytes from deep cartilage contained 2.3 ± 0.2 times more FN than was found in superficial cells (P < 0.025). Deep cartilage explants contained 1.2 times more FN than was found in superficial tissue. Explants obtained from deep cartilage synthesized 2.4 times more FN per cell than did superficial tissues (P < 0.01). FN synthesis as a fraction of total protein synthesis was significantly greater in deep explants (P < 0.01) compared with superficial tissues. Isolated deep chondrocytes in culture synthesized 1.89 ± 0.33-fold more FN than did superficial cells (P < 0.05). Cytokine-stimulated superficial cartilage explants failed to respond in terms of FN synthesis. FN mRNA quantitation showed no significant differences between superficial and deep populations. Conclusion. Since FN plays a major role in cell adhesion to damaged cartilage surfaces, our results suggest that modulation of FN synthesis near the articular surface of cartilage may be one of the factors that impede pannus invasion following an inflammatory insult to the joint.     

Cell-based cartilage repair: illusion or solution for osteoarthritis

PURPOSE OF REVIEW: Regeneration of damaged articular cartilage remains one of the most challenging problems in orthopedic surgery. Distinct surgical procedures were developed for the repair of focal cartilage defects and this review will focus on recent aspects of cell-based healing approaches that aim to achieve restoration of normal joint function by regenerating hyaline cartilage. RECENT FINDINGS: Surgical techniques are rapidly developing, and include resorbable biomaterials and expanded human mesenchymal stem cells to avoid disadvantages conferred by periosteal flaps and autologous chondrocytes. While expansion of mesenchymal stem cells seems to be safe and applicable, some concern exists about the stability of mesenchymal stem cells set to path to become chondrocytes, since common in-vitro protocols of chondrogenesis induce a program related to endochondral ossification which may finally yield only transient cartilage. SUMMERY: Bone marrow-stimulating techniques and autologous chondrocyte transplantation confer pain relief to the patients, and are superior to no treatment. Similar in their clinical outcome, they induce fibrocartilaginous repair tissue which may mature towards hyaline cartilage over time. Gained knowledge in the regulation of chondrogenesis, the role of host cell recruitment, transplanted cells, defect-filling materials and the influence of factors from subchondral bone will help to improve surgical procedures to allow their application to larger defects and patients with advanced signs of osteoarthritis.     

Surgical approaches to the repair of cartilage defects

Traumatic defects in articular cartilage are common in the young athletic population. They may occur in association with other injuries to the knee, particularly anterior cruciate ligament disruption. We understand that both theoretically and clinically, these defects may lead to an increased incidence of ongoing painful symptoms in the short term and degenerative joint disease in the long term. The orthopedic surgeon has several options to deal with theses injuries. The choice is dependent on the size and position of the lesion in the knee and any associated pathology. The most commonly practised methods aim to evoke a ‘repair’ response of fibrocartilage formation. This often helps in the short term, but the fibrocartilage degenerates over time, resulting in the return of symptoms. These ‘repair’ methods can be classified as: 1. Marrow stimulation techniques– these include abrasion chondroplasty, subchondral drilling and microfracture techniques. 2. Scaffold induced repair techniques. More recently, attempts to ‘re‐generate’ normal articular cartilage have been introduced to clinical practice. These are: 1. Mosaicplasty– autogenous osteochondral plug transplantation. 2. Autologous chondrocyte implantation (ACI)– this involves the harvest and culturing of autologous chondrocytes and then re‐implantation via injection under a periosteal or porcine collagen patch. The newest technology allow implantation of the collagen patch which has had chondrocytes cultured within its structure. The results of these autologous chondrocyte implantation show encouraging short to medium term results clinically. 3. Some orthopaedic centres have recently been advocating ‘articular cartilage paste grafting’– this is a simple technique based upon the theory that a paste of autogenous articular cartilage and subchondral bone should contain chondrocytes, stem cells and growth factors in its own scaffold. Orthopedic surgeons await with interest the outcome of pre‐clinical work in examining the use of growth factors, scaffold technology and gene therapy in helping with the clinical problem of articular cartilage defects.     

Interleukin 17 induced nitric oxide suppresses matrix synthesis and protects cartilage from matrix breakdown

OBJECTIVE: To investigate the role of nitric oxide (NO) in basal and cytokine induced cartilage matrix breakdown and synthesis across different species and in chondrocytes cultured as isolated cells or as tissue explants. METHODS: Articular cartilage from bovine, porcine, or human joints was cultured as explants in serum-free media. Explants or monolayer cultures of primary chondrocytes were treated with cytokines in the absence or presence of inhibitors [antibodies to leukemia inhibitory factor (anti-LIF) or tumor necrosis factor-alpha, dexamethasone, or inhibitors of aggrecanase or NO synthase]. NO production and matrix breakdown and synthesis were measured. RESULTS: At low concentrations, a novel interleukin 17 (IL-17) family member induced matrix breakdown without altering NO production. Treatment of articular cartilage explants with dexamethasone or anti-LIF blocked NO production by IL-17, but not by IL-1alpha. Inhibition of NO production in cytokine treated cartilage explants enhanced matrix breakdown and partially overcame suppression of matrix synthesis. In isolated chondrocytes, inhibition of NO production decreased expression of gelatinase and increased expression of stromelysin. CONCLUSION: Endogenous NO serves a dual function in cartilage: to protect the tissue from matrix breakdown and to mediate suppression of proteoglycan synthesis by cytokines. Despite the similarities in biological function between IL-I and IL-17, their downstream signaling pathways are distinct and appear to be affected by extracellular matrix degradation.     

Effects of ovariectomy and estrogen therapy on type II collagen degradation and structural integrity of articular cartilage in rats: implications of the time of initiation

OBJECTIVE: To investigate how the time of initiation influences the effects of estrogen therapy on type II collagen (CII) turnover and the structural integrity of articular cartilage in ovariectomized rats and to determine whether estrogen exerts direct effects on the catabolic function of chondrocytes ex vivo. METHODS: A total of 46 Sprague-Dawley rats were distributed into 1 of the following treatment groups: 1) ovariectomy, 2) ovariectomy plus early estrogen therapy, 3) ovariectomy plus delayed estrogen therapy, or 4) sham operation. Cartilage turnover was estimated by measuring the serum levels of C-telopeptide of type II collagen (CTX-II). Cartilage lesions at week 9 were quantified using a published scoring technique. The presence of the CTX-II epitope in articular cartilage was assessed by immunohistochemistry. The effects of estrogen (1-100 nM) on chondrocytes were investigated in bovine cartilage explants subjected to catabolic cytokines (tumor necrosis factor alpha [TNFalpha] and oncostatin M [OSM]). RESULTS: In ovariectomized rats, estrogen therapy evoked significant decreases in serum CTX-II independently of the time of initiation; yet, delayed initiation resulted in diminished efficacy in terms of preventing cartilage lesions. CTX-II fragments were present in articular cartilage, colocalizing with early lesions at the cartilage surface. In untreated animals, the early relative increases in serum CTX-II were proportional to the severity of cartilage lesions at week 9 (r = 0.73, P < 0.01). Estrogen significantly and dose-dependently countered CTX-II release from TNFalpha plus OSM-stimulated cartilage explants ex vivo. CONCLUSION: Our results suggest that estrogen counters the acceleration of CII degradation and related structural alterations, and these benefits can be maximized by early initiation after menopause. The protective effect of estrogen seems to involve direct inhibition of the catabolic function of chondrocytes.     

Repair function in organ cultured human cartilage. Replacement of enzymatically removed proteoglycans during longterm organ culture

The effect of enzymatic removal of proteoglycans (PG) from the extracellular matrix of human articular cartilage on subsequent PG metabolism of the remaining chondrocytes was investigated for periods of up to 12 weeks. Chondrocytes resynthesized normally aggregated PG but these macromolecules failed to stabilize in the intercellular matrix of the organ cultured explants and consequently diffused into the nutrient medium. After being in culture for about 2 months the chondrocytes no longer compensated for this PG loss and ceased to synthesize these biopolymers. A shift towards hyaluronic acid synthesis--as seen in dedifferentiated chondrocyte cultures--was not observed during the culture period. In this model some attempts at repair were demonstrated.     

Microenvironment regulation of extracellular signal–regulated kinase activity in chondrocytes: Effects of culture configuration,interleukin‐1, and compressive stress

Objective

To compare extracellular signal–regulated kinase (ERK) activity in response to interleukin‐1 (IL‐1) in chondrocytes under various culture configurations designed for the study of cartilage biology and repair, and also in response to dynamic load for chondrocytes in cartilage.

Methods

Isolated bovine articular chondrocytes were maintained in serum‐supplemented medium under 4 culture configurations: high‐density monolayer, attached to a cut surface of cartilage, within tissue‐engineered constructs, or within intact cartilage explants. Samples were subjected to a change of medium with or without IL‐1. Cartilage explants were also subjected to dynamic compression.

Results

In chondrocyte monolayers, both basal and IL‐1–stimulated ERK activities were similarly elevated at 0.5 hours after medium change, diminishing by 74% after 16 hours. In contrast, chondrocytes in other culture configurations exhibited lower basal levels of ERK activity and a moderate activation of ERK in response to IL‐1 that was sustained over the 16‐hour treatment time. The dynamic component of loading of cartilage explants led to a 5‐fold activation of ERK, compared with free‐swelling controls, that was indistinguishable from the effects of IL‐1.

Conclusion

ERK signaling in response to IL‐1 in chondrocyte monolayers exhibited a pattern that was distinct from that in other culture systems, suggesting that the extracellular matrix plays an important regulatory role in modulating the response to extracellular stimuli. Since IL‐1 and dynamic loading have distinct effects on chondrocyte biosynthesis, signaling pathways other than ERK participate in the chondrocyte responses to these stimuli.

     

Effects of methotrexate on normal articular cartilage in vitro and in vivo

OBJECTIVE—Methotrexate (MTX) has become the disease modifying drug of choice for the treatment of rheumatoid arthritis (RA). Direct effects of MTX on articular cartilage in vivo and in vitro were studied to determine possible adverse effects of the drug.
METHODS—For in vitro experiments, adult bovine articular cartilage explants were cultured in the presence of MTX (0 to 100 µM), and effects on DNA and matrix metabolism were studied. For in vivo studies, 48 adult female rabbits were treated with MTX (30 mg/kg/week intramuscularly) or placebo, respectively, for up to 12 weeks, and effects on the cartilage of the femoral condyles were assessed.
RESULTS—In vitro, MTX dose dependently increased the uptake of [³H]-thymidine, and decreased incorporation of [³H]-d-uridine into chondrocytes with a half maximal effect at 0.03 µM, suggesting inhibition of thymidylate-synthetase activity by the drug. MTX also dose dependently reduced the proportion of chondrocytes in S-phase, as determined by flow cytometry. MTX did not affect LDH release from chondrocytes or the proportion of viable cells, nor did it change the rate of protein synthesis, proteoglycan synthesis, proteoglycan breakdown, or the hydrodynamic size of newly synthesised proteoglycans. In vivo, MTX did not appreciably affect proteoglycan synthesis of the chondrocytes, proteoglycan content of the cartilage matrix, density of the chondrocyte population, or histological integrity of the cartilage.
CONCLUSIONS—The data suggest the absence of major adverse effects by MTX on articular cartilage proteoglycan metabolism. Chondrocyte DNA metabolism seems to be changed by MTX only in concentrations and exposition periods clearly exceeding those found in synovial fluid of RA patients receiving the commonly prescribed doses of the drug.

Keywords: methotrexate; articular cartilage; rheumatoid arthritis     

大骨节病患者关节软骨细胞凋亡及相关调控因子Bcl-2表达分布的特点

目的　探讨大骨节病患者关节软骨细胞凋亡及相关调控因子 Bcl- 2表达分布的特点。方法　采用脱氧核糖核酸末端转移酶介导的脱氧核糖核酸缺口标记法 (TUNEL氏法 )检测凋亡阳性细胞 ,利用单克隆抗体免疫组化检测 Bcl- 2在关节软骨中的表达。结果　 1TU NEL法染色的大骨节病儿童关节软骨凋亡阳性细胞数较正常关节软骨增多 ,且主要分布在中层。 2大骨节病儿童关节软骨 Bcl- 2的表达显著高于正常关节软骨中的表达 ,以表层最多 ,其次为中层 ;成人晚期大骨节病患者剥蚀的关节软骨表层 Bcl- 2的表达聚集在软骨细胞团中。结论　大骨节病患者关节软骨细胞凋亡及相关调控因子 Bcl- 2表达较正常人显著增多。     

Muscle derived,cell based ex vivo gene therapy for treatment of full thickness articular cartilage defects

OBJECTIVE: To evaluate the effectiveness of transplanted allogeneic muscle derived cells (MDC) embedded in collagen gels for the treatment of full thickness articular cartilage defects, to compare the results to those from chondrocyte transplantation, and to evaluate the feasibility of MDC based ex vivo gene therapy for cartilage repair. METHODS: Rabbit MDC and chondrocytes were transduced with a retrovirus encoding for the beta-galactosidase gene (LacZ). The cells were embedded in type I collagen gels, and the cell proliferation and transgene expression were investigated in vitro. In vivo, collagen gels containing transduced cells were grafted to the experimental full thickness osteochondral defects. The repaired tissues were evaluated histologically and histochemically, and collagen typing of the tissue was performed. RESULTS: The MDC and chondrocyte cell numbers at 4 weeks of culture were 305 +/- 25% and 199 +/- 25% of the initial cell number, respectively. The initial percentages of LacZ positive cells in the MDC and chondrocyte groups were 95.4 +/- 1.9% and 93.4 +/- 3.4%, and after 4 weeks of culture they were 84.2 +/- 3.9% and 76.9 +/- 4.3%, respectively. In vivo, although grafted cells were found in the defects only up to 4 weeks after transplantation, the repaired tissues in the MDC and chondrocyte groups were similarly better histologically than control groups. Repaired tissues in the MDC group were mainly composed of type II collagen, as in the chondrocyte group. CONCLUSION: Allogeneic MDC could be used for full thickness articular cartilage repair as both a gene delivery vehicle and a cell source for tissue repair.     

Synthesis of proteoglycan 4 by chondrocyte subpopulations in cartilage explants, monolayer cultures, and resurfaced cartilage cultures

OBJECTIVE: To quantify the levels of proteoglycan 4 (PRG4) expression by subpopulations of chondrocytes from superficial, middle, and deep layers of normal bovine calf cartilage in various culture systems. METHODS: Bovine calf articular cartilage discs or isolated cells were used in 1 of 3 systems of chondrocyte culture: explant, monolayer, or transplant, for 1-9 days. PRG4 expression was quantified by enzyme-linked immunosorbent assay of spent medium and localized by immunohistochemistry at the articular surface and within chondrocytes in explants and cultured cells. RESULTS: Superficial chondrocytes secreted much more PRG4 than did middle and deep chondrocytes in all cultures. The pattern of PRG4 secretion into superficial culture medium varied with the duration of culture, decreasing with time in explant culture (from approximately 25 microg/cm(2)/day on days 0-1 to approximately 3 microg/cm(2)/day on days 5-9), while increasing in monolayer culture (from approximately 1 pg/cell/day on days 0-1 to approximately 7 pg/cell/day on days 7-9) and tending to increase in transplant culture (reaching approximately 2 microg/cm(2)/day by days 7-9). In all of the culture systems, inclusion of ascorbic acid stimulated PRG4 secretion, and the source of PRG4 was immunolocalized to superficial cells. CONCLUSION: The results described here indicate that the phenotype of PRG4 secretion by chondrocytes in culture is generally maintained, in that PRG4 is expressed to a much greater degree by chondrocytes from the superficial zone than by those from the middle and deep zones. The marked up-regulation of PRG4 synthesis by ascorbic acid may have implications for cartilage homeostasis and prevention of osteoarthritic disease. Transplanting specialized cells that secrete PRG4 to a surface may impart functional lubrication and be generally applicable to many tissues in the body.