Phenotypic differences in murine chondrocyte cell lines derived from mature articular cartilage

OBJECTIVE: To obtain well characterized immortalized murine chondrocyte cell lines. The cell lines were obtained from mature articular chondrocytes, instead of embryonal cells which are used in most other studies. METHODS: Pieces of articular cartilage were cut from murine patellae and femoral heads. Chondrocytes were isolated by digestion with collagenase. These cells were cultured in monolayer and immortalized by transfection of the SV40 large T antigen gene. To preserve the differentiated phenotype, the resulting clones were cultured in three-dimensional carriers, alginate beads. The phenotypes of the cells were characterized using the following parameters: Cell morphology (light microscopy), messenger RNA (RT-PCR) and protein (immunohistochemistry) levels of extracellular matrix molecules. Moreover, responsiveness to interleukin-1(IL-1) was determined by measuring production of proteoglycans ((35)S-sulfate incorporation) and of nitric oxide (Griess reaction). RESULTS: Sixteen clones were obtained, ten (P1 to P10) derived from patellar cartilage, and six (H1 to H6) from femoral head cartilage. In seven cell lines (P2, P5, H1, H3, H4, H5, H6) high production of type II collagen corresponded with high levels of mRNA of type II collagen (and prevalence of the IIB type) and with high IL-1-induced suppression of proteoglycan synthesis. Like intact murine articular cartilage, all cell lines produced type I and type X collagens, but mRNA levels of both types of collagen were never higher in the cell lines as compared with intact cartilage. CONCLUSION: Our results demonstrate that it is possible to immortalize mature murine articular chondrocytes. Each of the obtained chondrocyte cell lines appeared to have a stable phenotype. Both relatively differentiated and relatively dedifferentiated chondrocyte cell lines could be identified.     

低氧环境对小鼠未成熟关节透明软骨细胞培养的影响

目的研究低氧和低氧模拟化合物氯化钴对小鼠未成熟关节透明软骨细胞氧感应基因和细胞表型的影响。方法经酶消化分离出小鼠未成熟关节透明软骨细胞，分别在21％氧、2％氧和150μmol/L氯化钴条件下培养一定时间。通过倒置显微镜、透射电镜和扫描电镜观察细胞形态学变化。应用定量PCR和Western Blot检测葡萄糖转运体-1（GLUT-1）、葡萄糖转运体-3（GLUT-3）、磷酸果糖激酶-1（PGK-1）和低氧诱导因子-1α（HIF—1α）的表达。应用定量PCR观察软骨细胞表型改变。应用四甲基偶氮唑盐法（MTT）检测低氧及氯化钴对软骨细胞活性的影响。用葡萄糖检测试剂盒测葡萄糖摄取量。结果不同培养条件下软骨细胞形态无明显差异。2％氧和氯化钴可增加GLUT-1、GLUT-3及PGK-1mRNA表达。2％氧和氯化钴可促进GLUT-1、GLUT-3和HIF—1α蛋白表达。低氧和氯化钴促进细胞活性，增加葡萄糖摄取并促进细胞外基质合成。结论软骨细胞能通过调节氧感应基因适应低氧环境，HIF—1α可能起关键作用。低氧能在一定程度上增加软骨细胞活性和细胞外基质合成。模拟体内氧环境培养细胞能更好地了解软骨细胞特性。     

Prostaglandin E2 inhibits BMP signaling and delays chondrocyte maturation

While cyclooxygenases are important in endochondral bone formation during fracture healing, mechanisms involved in prostaglandin E2 (PGE2) regulation of chondrocyte maturation are incompletely understood. The present study was undertaken to determine if PGE2 effects on chondrocyte differentiation are related to modulation of the bone morphogenetic protein (BMP) signaling pathway. In primary murine sternal chondrocytes, PGE2 differentially regulated genes involved in differentiation. PGE2 induced type II collagen and MMP-13, had minimal effects on alkaline phosphatase, and inhibited the expression of the maturational marker, type X collagen. In BMP-2–treated cultures, PGE2 blocked the induction of type X collagen. All four EP receptors were expressed in chondrocytes and tended to be inhibited by BMP-2 treatment. RCJ3.1C5.18 chondrocytes transfected with the protein kinase A (PKA) responsive reporter, CRE-luciferase, showed luciferase induction following exposure to PGE2, consistent with activation of PKA signaling and the presence of the EP2 and EP4 receptors. Both PGE2 and the PKA agonist, dibutyryl cAMP, blocked the induction of the BMP-responsive reporter, 12XSBE, by BMP-2 in RCJ3.1C5.18 chondrocytes. In contrast, PGE2 increased the ability of TGF-β to activate the TGF-β-responsive reporter, 4XSBE. Finally, PGE2 down-regulated BMP-mediated phosphorylation of Smads 1, 5, and 8 in RCJ3.1C5.18 cells and in primary murine sternal chondrocytes. Altogether, the findings show that PGE2 regulates chondrocyte maturation in part by targeting BMP/Smad signaling and suggest an important role for PGE2 in endochondral bone formation. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 27: 785–792, 2009     

Optimizing CO2 normalizes pH and enhances chondrocyte viability during cold storage

Fresh osteochondral allografts are an important treatment option for the repair of full‐thickness articular cartilage defects. Viable chondrocytes within the transplanted tissue are considered important to maintaining matrix integrity. The purpose of this study is to determine whether an increase in pH decreases chondrocyte viability during cold storage and whether equilibration of Dulbecco's modified Eagle's medium (DMEM) in 5% CO₂ normalizes pH and increases chondrocyte survival during storage at 4°C. Freshly isolated bovine articular chondrocytes cultured in alginate beads were stored for up to 5 days at 4°C or 37°C in DMEM exposed to ambient air or in DMEM equilibrated with 5% CO₂. Chondrocyte viability was determined by flow cytometry. Physiologic pH was maintained when DMEM was equilibrated with 5% CO₂, while pH increased in ambient air. After 5 days of storage at 4°C, chondrocyte necrosis was higher when stored in ambient air than if equilibrated with 5% CO₂. No decrease in chondrocyte viability was observed with storage at 37°C. In addition, chondrocyte viability in bovine cartilage osteochondral cores was examined after storage for 14 days at 4°C in DMEM with and without HEPES, and with and without 5% CO₂. Under these conditions, the superficial layer of chondrocytes was more viable when stored in DMEM with HEPES or DMEM equilibrated with 5% CO₂ than when stored in DMEM in ambient air. This data shows that an increase in pH decreased bovine chondrocyte viability when refrigerated at 4°C in DMEM, and that optimization of CO₂ normalized pH and improved chondrocyte viability during cold storage in DMEM. © 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 26:643–650, 2008     

Effects of individual control of pH and hypoxia in chondrocyte culture

Effects of oxygen tension (pO₂) and pH on gene and protein expression and metabolic activity of human chondrocytes were independently assessed. Chondrocytes were cultured under a range of pH (6.4–7.4) and different pO₂ (5 and 20%) during 5 days in a bioreactor. Effects on gene expression, DNA content, protein expression, and metabolic activity were determined. Linear regression analysis showed that gene expression of type I collagen (COL1), SOX9, and VEGF is significantly lower at acidic pH, while expression of aggrecan, type II collagen, and HIF1A is pH‐independent. Higher protein levels of VEGF were found under low pO₂. Acidic pH severely lowered VEGF release into medium, glucose consumption, and lactate production. Extracellular pH proved to more potently influence cell function than oxygen tension, the latter showing down‐regulation of COL1 gene expression and up‐regulation of VEGF protein under hypoxia. Hypoxic culture inhibits COL1 mRNA expression pH‐dependently, while expression of SOX9 is largely hypoxia independent, but pH dependent. Expression of HIF1A and VEGF revealed divergent pH dependencies. Subtle fluctuations in extracellular pH and oxygen tension clearly influence chondrocyte metabolism and marker expression. Sophisticated pH and oxygen control not only allows study of (patho)physiological changes, but also opens new venues in cartilage tissue engineering. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:537–545, 2010     

Alterations in structural macromolecules and chondrocyte deformations in lapine retropatellar cartilage 9 weeks after anterior cruciate ligament transection

The structural integrity and mechanical environment of the articular cartilage matrix directly affect chondrocyte deformations. Rabbit models of early osteoarthritis at 9 weeks following anterior cruciate ligament transection (ACLT) have been shown to alter the deformation behavior of superficial zone chondrocytes in mechanically loaded articular cartilage. However, it is not fully understood whether these changes in cell mechanics are caused by changes in structural macromolecules in the extracellular matrix. Therefore, the purpose of this study was to characterize the proteoglycan content, collagen content, and collagen orientation at 9 weeks post ACLT using microscopic techniques, and relate these changes to the altered cell mechanics observed upon mechanical loading of cartilage. At 9 weeks following ACLT, collagen orientation was significantly (p < 0.05) altered and proteoglycan content was significantly (p < 0.05) reduced in the superficial zone cartilage matrix. These structural changes either in the extracellular or pericellular matrix (ECM and PCM) were also correlated significantly (p < 0.05) with chondrocyte width and height changes, thereby suggesting that chondrocyte deformation response to mechanical compression in early OA changes primarily because of alterations in matrix structure. However, compared to the normal group, proteoglycan content in the PCM from the ACLT group decreased less than that in the surrounding ECM. Therefore, PCM could play a key role to protect excessive chondrocyte deformations in the ACLT group. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:342–350, 2018.     

Abnormal human chondrocyte morphology is related to increased levels of cell‐associated IL‐1β and disruption to pericellular collagen type VI

Early osteoarthritis (OA) is poorly understood, but abnormal chondrocyte morphology might be important. We studied IL‐1β and pericellular collagen type VI in morphologically normal and abnormal chondrocytes. In situ chondrocytes within explants from nondegenerate (grade 0/1) areas of human tibial plateaus (n = 21) were fluorescently labeled and visualized [2‐photon laser scanning microscopy (2PLSM)]. Normal chondrocytes exhibited a “smooth” membrane surface, whereas abnormal cells were defined as demonstrating ≥1 cytoplasmic process. Abnormal chondrocytes were further classified by number and average length of cytoplasmic processes/cell. IL‐1β or collagen type VI associated with single chondrocytes were visualized by fluorescence immuno‐histochemistry and confocal laser scanning microscopy (CLSM). Fluorescence was quantified as the number of positive voxels (i.e., 3D pixels with fluorescence above baseline)/cell. IL‐1β‐associated fluorescence increased between normal and all abnormal cells in the superficial (99.7 ± 29.8 [11 (72)] vs. 784 ± 382 [15 (132)]; p = 0.04, positive voxels/cell) and deep zones (66.5 ± 29.4 [9 (64)] vs. 795 ± 224 [9 (56)]; p = 0.006). There was a correlation (r² = 0.988) between the number of processes/cell (0–5) and IL‐1β, and an increase particularly with short processes (≤5 µm; p = 0.022). Collagen type VI coverage and thickness decreased (p < 0.001 and p = 0.005, respectively) with development of processes. Abnormal chondrocytes in macroscopically nondegenerate cartilage demonstrated a marked increase in IL‐1β and loss of pericellular type VI collagen, changes that could lead to cartilage degeneration. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:1507–1514, 2010     

Transient hypoxia improves matrix properties in tissue engineered cartilage

Adult articular cartilage is a hypoxic tissue, with oxygen tension ranging from <10% at the cartilage surface to <1% in the deepest layers. In addition to spatial gradients, cartilage development is also associated with temporal changes in oxygen tension. However, a vast majority of cartilage tissue engineering protocols involves cultivation of chondrocytes or their progenitors under ambient oxygen concentration (21% O₂), that is, significantly above physiological levels in either developing or adult cartilage. Our study was designed to test the hypothesis that transient hypoxia followed by normoxic conditions results in improved quality of engineered cartilaginous ECM. To this end, we systematically compared the effects of normoxia (21% O₂ for 28 days), hypoxia (5% O₂ for 28 days) and transient hypoxia—reoxygenation (5% O₂ for 7 days and 21% O₂ for 21 days) on the matrix composition and expression of the chondrogenic genes in cartilage constructs engineered in vitro. We demonstrated that reoxygenation had the most effect on the expression of cartilaginous genes including COL2A1, ACAN, and SOX9 and increased tissue concentrations of amounts of glycosaminoglycans and type II collagen. The equilibrium Young's moduli of tissues grown under transient hypoxia (510.01 ± 28.15 kPa) and under normoxic conditions (417.60 ± 68.46 kPa) were significantly higher than those measured under hypoxic conditions (279.61 ± 20.52 kPa). These data suggest that the cultivation protocols utilizing transient hypoxia with reoxygenation have high potential for efficient cartilage tissue engineering, but need further optimization in order to achieve higher mechanical functionality of engineered constructs. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 31: 544–553, 2013     

Outcome of combined autologous chondrocyte implantation and anterior cruciate ligament reconstruction

Background:

Instability of the knee joint, after anterior cruciate ligament (ACL) injury, is contraindication to osteochondral defect repair. This prospective study is to investigate the role of combined autologous chondrocyte implantation (ACI) with ACL reconstruction.

Materials and Methods:

Three independent groups of patients with previous ACL injuries undergoing ACI were identified and prospectively followed up. The first group had ACI in combination with ACL reconstruction (combined group); the 2^nd group consisted of individuals who had an ACI procedure having had a previously successful ACL reconstruction (ACL first group); and the third group included patients who had an ACI procedure to a clinically stable knee with documented nonreconstructed ACL disruption (No ACL group). Their outcomes were assessed using the modified cincinnati rating system, the Bentley functional (BF) rating system (BF) and a visual analog scale (VAS).

Results:

At a mean followup of 64.24 months for the ACL first group, 63 months for combined group and 78.33 months for the No ACL group; 60% of ACL first patients, 72.73% of combined group and 83.33% of the No ACL group felt their outcome was better following surgery. There was no significant difference demonstrated in BF and VAS between the combined and ACL first groups. Results revealed a significant affect of osteochondral defect size on outcome measures.

Conclusion:

The study confirms that ACI in combination with ACL reconstruction is a viable option with similar outcomes as those patients who have had the procedures staged.     

Effects of hypoxia on glucose transport in primary equine chondrocytes in vitro and evidence of reduced GLUT1 gene expression in pathologic cartilage in vivo

Articular chondrocytes exist in an environment lacking in oxygen and nutrients due to the avascular nature of cartilage. The main source of metabolic energy is glucose, which is taken up by glucose transporters (GLUTs). In diseased joints, oxygen tensions and glucose availability alter as a result of inflammation and changes in vascularisation. Accordingly, in this study we examined the effects of hypoxia and the hypoxia mimetic cobalt chloride (CoCl₂) on glucose transport in equine chondrocytes and compared expression of the hypoxia responsive GLUT1 gene in normal and diseased cartilage. Monolayers of equine chondrocytes were exposed to 20% O₂, 1% O₂, CoCl₂ (75 µM), or a combination of 1% O₂ and CoCl₂. Glucose uptake was measured using 2‐deoxy‐D‐[2,6‐³H] glucose. GLUT1 protein and mRNA expression were determined by FACS analysis and qPCR, respectively. GLUT1 mRNA expression in normal and diseased cartilage was analyzed using explants derived from normal, OA, and OCD cartilage. Chondrocytes under hypoxic conditions exhibited a significantly increased glucose uptake as well as upregulated GLUT1 protein expression. GLUT1 mRNA expression significantly increased in combined hypoxia‐CoCl₂ treatment. Analysis of clinical samples indicated a significant reduction in GLUT1 mRNA in OA samples. In OCD samples GLUT1 expression also decreased but did not reach statistical significance. The increase in glucose uptake and GLUT1 expression under hypoxic conditions confirms that hypoxia alters the metabolic requirements of chondrocytes. The altered GLUT1 mRNA expression in diseased cartilage with significance in OA suggests that reduced GLUT1 may contribute to the failure of OA cartilage repair. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 27: 529–535, 2009     

Honokiol,a low molecular weight natural product,prevents inflammatory response and cartilage matrix degradation in human osteoarthritis chondrocytes

Proinflammatory cytokine interleukin‐1β (IL‐1β) stimulates several mediators of cartilage degradation and plays an important role in the pathogenesis of osteoarthritis (OA). Honokiol, a low molecular weight natural product isolated from the Magnolia officinalis, has been shown to possess anti‐inflammatory effect. Here, we used an in vitro model of cartilage inflammation to investigate the therapeutic potential of honokiol in OA. Human OA chondrocytes were cultured and pretreated with honokiol (2.5–10 µM) with or without IL‐1β (10 ng/ml). Nitric oxide (NO) production was quantified by Griess reagent. Prostaglandin (PG)E₂, metalloproteinase‐13 (MMP‐13), and interleukin‐6 (IL‐6) productions were quantified by enzyme‐linked immunosorbent assay. The expressions of collagen II, cyclooxygenase‐2 (COX‐2), inducible nitric oxide synthase (iNOS), and nuclear factor κB (NF‐κB)‐related signaling molecules were determined by Western blotting. Our data showed that IL‐1β markedly stimulated the expressions of iNOS and COX‐2 and the productions of NO, PGE₂, and IL‐6, which could be significantly reversed by honokiol. Honokiol could also suppress the IL‐1β‐triggered activation of IKK/IκBα/NF‐κB signaling pathway. Moreover, honokiol significantly inhibited the IL‐1β‐induced MMP‐13 production and collagen II reduction. Taken together, the present study suggests that honokiol may have a chondroprotective effect and may be a potential therapeutic choice in the treatment of OA patients. © 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:573–580, 2014.     

Femoral epiphyseal cartilage matrix changes at predilection sites of equine osteochondrosis: Quantitative MRI,second‐harmonic microscopy,and histological findings

Osteochondrosis is an ischemic chondronecrosis of epiphyseal growth cartilage that results in focal failure of endochondral ossification and osteochondritis dissecans at specific sites in the epiphyses of humans and animals, including horses. The upstream events leading to the focal ischemia remain unknown. The epiphyseal growth cartilage matrix is composed of proteoglycan and collagen macromolecules and encases its vascular tree in canals. The matrix undergoes major dynamic changes in early life that could weaken it biomechanically and predispose it to focal trauma and vascular failure. Subregions in neonatal foal femoral epiphyses (n = 10 osteochondrosis predisposed; n = 6 control) were assessed for proteoglycan and collagen structure/content employing 3T quantitative MRI (3T qMRI: T1ρ and T2 maps). Site‐matched validations were made with histology, immunohistochemistry, and second‐harmonic microscopy. Growth cartilage T1ρ and T2 relaxation times were significantly increased (p < 0.002) within the proximal third of the trochlea, a site predisposed to osteochondrosis, when compared with other regions. However, this was observed in both control and osteochondrosis predisposed specimens. Microscopic evaluation of this region revealed an expansive area with low proteoglycan content and a hypertrophic‐like appearance on second‐harmonic microscopy. We speculate that this matrix structure and composition, though physiological, may weaken the epiphyseal growth cartilage biomechanically in focal regions and could enhance the risk of vascular failure with trauma leading to osteochondrosis. However, additional investigations are now required to confirm this. 3T qMRI will be useful for future non‐invasive longitudinal studies to track the osteochondrosis disease trajectory in animals and humans. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1743–1752, 2016.     

Glucosamine modulates chondrocyte proliferation, matrix synthesis, and gene expression

OBJECTIVE: To investigate the effects of glucosamine (GlcN) on chondrocyte proliferation, matrix production, and gene expression for providing insights into the biochemical basis of its reported beneficial effects in osteoarthritis (OA). METHODS: Dose-dependent effect of GlcN on cell morphology, proliferation, cartilage matrix production and gene expression was examined by incubating primary bovine chondrocytes with various amounts of GlcN in monolayers (2D) and in cell-laden hydrogels (3D constructs). Histology, immunofluorescent staining and biochemical analyses were used to determine the effect of GlcN on cartilage matrix production in 3D constructs. The impact of GlcN on gene expression was evaluated with real-time polymerase chain reaction (PCR). RESULTS: GlcN concentration and culture conditions significantly affected the cell behavior. Quantitative detection of matrix production in cell-laden hydrogels indicated a relatively narrow window of GlcN concentration that promotes matrix production (while limiting cellular proliferation, but not cell viability). Notably, GlcN enhanced cartilage specific matrix components, aggrecan and collagen type II, in a dose-dependent manner up to 2 mM but the effect was lost by 15 mM. Additionally, GlcN treatment up-regulated transforming growth factor-beta1 (TGF-beta1) mRNA levels. CONCLUSION: Results indicate that culture conditions play a significant role in determining the effect of GlcN on chondrocytes, explaining both the previously reported beneficial and deleterious effects of this sugar. The ability of GlcN to alter TGF-beta1 signaling provides a biochemical mechanism for GlcN activity on chondrocytes that up to now has remained elusive. The observed anabolic effect of optimal GlcN concentrations on chondrocytes may be useful in formulating effective cartilage repair strategies.     

Choosing the right chondrocyte cell line: Focus on nitric oxide

Nitric oxide (NO) has been considered a catabolic factor that contributes to OA pathology by inducing chondrocytes apoptosis, matrix metalloproteinases synthesis, and pro‐inflammatory cytokines expression. Thus, the research on NO regulation in chondrocytes represents a relevant field which needs to be explored in depth. However, to date, only the murine ATDC‐5 cell line and primary chondrocytes are well‐established cells to study NO production in cartilage tissues. The goal of this study is to determine whether two commonly used human chondrocytic cell lines: SW‐1353 and T/C‐28a2 cell lines are good models to examine lipopolysaccharide and/or pro‐inflammatory cytokine‐driven NO release and iNOS expression. To this aim, we carefully examined NO production and iNOS protein expression in human T/C‐28a2 and SW‐1353 chondrocytes stimulated with LPS and interleukin (IL)‐1 alone or in combination. We also use ATDC‐5 cells as a positive control for NO production. NO accumulation has been determined by colorimetric Griess reaction, whereas NOS type II expression was determined by Western Blot analysis. Our results clearly demonstrated that neither human T/C‐28a2 nor SW‐1353 chondrocytes showed a detectable increase in NO production or iNOS expression after bacterial endotoxin or cytokines challenge with IL‐1. Our study demonstrated that T/C‐28a2 and SW‐1353 human cell lines are not suitable for studying NO release and iNOS expression confirming that ATDC5 and human primary cultured chondrocytes are the best in vitro cell system to study the actions derived from this mediator. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 33:1784–1788, 2015.