Isolation of a plasma membrane-enriched fraction from collagenase-suspended rachitic rat growth plate chondrocytes

An attempt was made to concentrate plasma membranes of homogenized chondrocytes isolated by collagenase digestion of rachitic rat epiphyseal growth plate cartilage. This study reports the characterization of enzymes in the plasma membrane of isolated chondrocytes and their comparison with extracellular matrix vesicle components. The plasma membraneenriched fractions that were obtained showed a sevenfold increase in 5′-nucleotidase and a 15-fold increase in alkaline phosphatase, both of which are regarded as plasma membrane markers. SDS-polyacrylamide gel electrophoretic profiles of proteins extracted from membrane fractions contained several major protein bands also seen in isolated matrix vesicles. These studies indicate the usefulness of concentrating plasma membrane components from isolated chondrocytes, after the chondrocytes have been enzymatically freed from investing matrix and other stromal components by collagenase.     

Requirement of mitogen-activated protein kinase for collagenase production by the fibronectin fragment in human articular chondrocytes in culture

Fibronectin fragments have been shown to up-regulate matrix metalloproteinase production in chondrocytes. We investigated the roles of mitogen-activated protein kinase (MAPK) pathways activated by the COOH-terminal heparin-binding fibronectin fragment (HBFN-f) in collagenase production by human chondrocytes in culture. In articular cartilage explant culture, HBFN-f stimulated type II collagen cleavage by collagenase in association with increased secretion of MMP-1 and MMP-13. In human articular chondrocytes, HBFN-f induced the collagenases with activation of the extracellular signal-regulated kinase (ERK), p38, and the c-Jun NH₂-terminal kinase (JNK). PD98059 that inhibits the ERK pathway blocked HBFN-f-stimulated production of MMP-1 and MMP-13 in explant culture. SB203580 at 1µM, the concentration that inhibits p38 only, partially suppressed HBFN-f-induced collagenase production, whereas at 10µM, the inhibitor that blocks both p38 and JNK almost completely inhibited collagenase induction. PD98059 and SB203580 individually blocked HBFN-f-increased cleavage of type II collagen in the explant culture, although 10µM SB203580 strongly inhibited the collagen cleavage compared with 1µM of the inhibitor. These results indicate that collagenase production leading to type II collagen cleavage in cartilage explants requires ERK, p38, and JNK.     

Cartilage regeneration in SCID mice using a highly organized three-dimensional alginate scaffold

Tissue engineering for cartilage regeneration provides an alternative to surgery for degenerative osteoarthritis. Recently, a highly organized three-dimensional (3D) alginate scaffold was prepared using a microfluidic device; this scaffold is effective for chondrocyte culture in vitro. The performance of this scaffold was further demonstrated; an alginate scaffold seeded with porcine chondrocytes was implanted in the dorsal subcutaneous site of SCID mice. The recipients were sacrificed at 2, 4, and 6 weeks after transplantation. The grafted implants retrieved from the subcutaneous site were analyzed with histologic examinations. Real-time PCR was used to identify the gene expression patterns of the chondrocytes. The hematoxylin and eosin staining showed that the chondrocytes survived normally in SCID mice; cartilage-like structures were formed after 4 weeks implantation. Immunohistochemical staining revealed cells secreted type II collagen, produced glycosaminoglycans (proved by alcian blue stain), and maintained the expression of S-100. On the other hand, the cells were negative for type I and type X collagen staining. PCR showed that the mRNA expressions of aggrecan and type II collagen were up-regulated at weeks two and four, while type I and type X collagen were down-regulated during the study period. In summary, this highly organized 3D alginate scaffold provided a suitable environment and maintained functional phenotypes for chondrocytes in this animal study.     

透明质酸修饰壳聚糖/pDNA纳米微球的制备及体外转染软骨细胞

目的 以透明质酸(HA)修饰基因载体壳聚糖(CS)纳米微球,制作一种新型的HA/CS/pDNA基因转染系统,观察其结构特征及体外对软骨细胞的转染能力.方法 将不同比例的HA和CS与负载增强型绿色荧光蛋白基因(EGFP)的质粒DNA(pDNA)以复凝聚法制成纳米微球,以扫描电镜检测纳米微球形态,Zeta电位粒度分析仪测定其粒径、表面电位;凝胶电泳阻滞实验观察CS和pDNA的结合力;体外转染兔关节软骨细胞,以流式细胞仪及荧光显微镜检测转染效率.结果 HA/CS/pDNA纳米微球多呈球形,粒径为(223±51)nm,表面Zeta电位为(17.4±6.1)mV,可有效保护pDNA免受 DNaseⅠ的降解.体外转染实验证明HA/CS/pDNA纳米微球能介导pEGFP转染软骨细胞并在细胞内表达绿色荧光蛋白,转染率达(15.450±0.404)%,比裸pDNA组和CS/pDNA组有更高的转染效率(P<0.05).结论 复凝聚法制备的HA/CS/pDNA纳米微球是一种有效的新型非病毒基因转染系统,对软骨细胞有着潜在的靶向基因转染能力.

Abstract：

Objective To prepare hyaluronic acid (HA)-modified chitosan (CS)/pDNA (HA/CS/pDNA) nanoparticles as novel gene vectors, study their structural characteristics and gene transfection efficiency for chondrocytes in vitro in rabbits. Methods The HA/CS/pDNA nanoparticles were prepared by a DNA (pDNA), which load enhanced green fluorescent protein (EGFP) gene. The morphology of the nanoparticles was observed under the transmission electron microscopy. The sizes and zeta-potentials of the nanoparticles were measured by a Marven-nano laser diffractometer. The binding of pDNA was evaluated by agarose gel electrophoresis analysis. The gene transfection experiments in vitro were performed with the chondrocytes of rabbits. The gene transfection efficiency was measured by using flow cytometry and under the fluorescence microscopy. Results HA/CS/pDNA nanoparticles were mainly spherical, with an average size of (223±51) nm, and zeta-potential of (17.4±6.1) mV. The agarose gel electrophoresis analysis confirmed that they could effectively protect pDNA from degradation against DNase I. Gene transfection in vitro proved that HA/CS/pDNA nanoparticles could be efficiently transfected into chondrocytes of rabbits, the expression of green fluorescent proteins was observed under the fluorescent microscopy, and the transfection efficiency reached as high as (15.450±0.404)%, significantly higher than that of the naked pDNA or the CS/pDNA nanoparticles (P<0.05). Conclusion HA/CS/pDNA nanoparticles were an effective novel non-viral gene transfer vector, which possessed the potential targeting transfection ability on chondrocytes.     

微小RNAs在骨与软骨组织中的调节作用

目的对微小RNAs(microRNAs,miRNAs)在骨与软骨组织中的调控作用和作用机制作一综述。方法广泛查阅近年来有关miRNAs在骨与软骨组织的调控作用及作用机制的文献,进行总结与分析。结果 miRNAs是近年来骨关节疾病研究的热点,越来越多研究显示其在骨与软骨组织形成和代谢过程中,对于细胞分化、细胞基质分泌等方面发挥重要的调控作用,但确切机制尚不清楚。结论 通过对miRNAs在骨与软骨组织中的调控作用及作用机制的研究,可能为了解退行性骨关节疾病开辟新的领域。     

益节健片对体外软骨细胞影响实验研究

目的探讨益节健片对关节炎兔软骨细胞增殖、凋亡的影响。方法从兔关节中获取软骨细胞;通过检测不同浓度中培养软骨细胞的四氮唑蓝（MTT）值,使用不同的样品浓度;分别对凋亡软骨细胞进行干预培养;采用形态学观察等方法评价样品对软骨细胞凋亡状态的影响。结果益节健片在低浓度下（0．40mg／ml）对兔软骨细胞无直接促进增殖作用,在〉0．40mg／ml时,会对免软骨细胞有一定抑制作用（P〈0．05或P〈0．01）;益节健片不能缓解硝普钠对兔软骨细胞的损伤作用（P〈0．01）。结论益节健片对关节实验性骨关节炎软骨退变无直接保护作用。     

Heterogeneous nanomechanical properties of superficial and zonal regions of articular cartilage of the rabbit proximal radius condyle by atomic force microscopy

Articular chondrocytes have been thought to reside in a homogenous matrix. The physical characteristics of the intercellular matrix of articular cartilage are not well characterized, especially at a nanoscopic scale. The present work tested the hypothesis that the nanomechanical properties of the intercellular matrices of articular cartilage in both the articulating surface and various cellular zones are non-homogeneous. Nanoindentation by atomic force microscopy was applied to the geometric center of the medial, lateral and groove regions of the superficial zone of the rabbit proximal radius cartilage, and then the intercellular matrices of chondrocytes from the superficial to calcifying zones in 40 μm increments. The elastic modulus of the articular surface of the medial condyle (1.46±0.11 MPa) was significantly higher than the lateral condyle (1.18±0.10 MPa), and the groove (0.96±0.07 MPa). There is a significant gradient increase in Young’s moduli from the superficial zone (0.52±0.05 MPa) to calcifying zone (1.69±0.12 MPa). Thus, the nanomechanical properties of the intercellular matrices of the articulating surface are region-specific and likely related to articular function. Heterogeneous biophysical properties of intercellular matrices along the depth from the superficial to calcifying zones suggest that chondrocytes likely reside in a heterogeneous matrix.     

Induction of apoptosis of articular chondrocytes and suppression of articular cartilage proteoglycan synthesis by heat shock

We investigated cellular and matrix responses of articular cartilage to heat shock. Rat articular cartilage was pretreated at 37 degrees C for 24 h before being exposed to 48 degrees C for 10 min and subsequently incubated at 37 degrees C for 1, 2, 4, 7, 10, and 14 days. Following heat shock, a terminal deoxynucleotidyl transferase nick end labeling assay showed that articular chondrocyte apoptosis appeared at day 1, peaked at day 7, and declined by day 14. Analysis by transmission electron microscopy confirmed that the chondrocytes had characteristic morphological features of apoptosis; immunohistochemical staining revealed that caspase-3 activity in chondrocytes increased, 3-B-3-positive articular chondrocytes decreased in number, and the expression of 3-B-3 native epitope in articular chondrocytes was reduced. Safranin-O staining revealed that depletion of proteoglycans in the matrix was not found in any group. Morphological and biochemical evidence from this study suggested that heat shock at 48 degrees C induced articular chondrocyte apoptosis and suppressed proteoglycan synthesis of articular cartilage in vitro. This study thus provides evidence of the onset of osteoarthritis induced by heat shock and a basis for choosing a temperature at which malignant bone tumor cells can be killed with minimal damage to articular cartilage.     

Insulin-like growth factor-I diminishes the activation status and expression of the small GTPase Cdc42 in articular chondrocytes.

Insulin-like growth factor-I (IGF-I) is an important anabolic growth factor in the maintenance of articular cartilage phenotypic expression. Chondrocyte morphology is also tightly linked to phenotype. The small G-protein Cdc42 plays a key role in regulation of cell morphology and phenotypic expression in several cell types and, we show here, in articular chondrocytes. The purpose of these studies was to investigate possible links between the intracellular signaling pathways of IGF-I and Cdc42 in articular chondrocytes. Treatment of chondrocytes with IGF-I resulted in a rapid and sustained decrease in the activation state (decreased GTP-bound) of Cdc42. Nucleotide exchange and hydrolysis experiments suggest that the decreased activation occurs through increased hydrolysis. Transient expression of dominant-negative Cdc42(T17N) allowed for enhanced expression of normal chondrocyte phenotype as determined by increased mRNA expression of collagen type II (Coll II) with decreased matrix metalloproteinase-3 (MMP-3) expression. The results of these studies suggest a novel link between IGF-I and Cdc42 signaling pathways. Further, an additional mechanism for the regulation of chondrocyte phenotype is defined through the IGF-I induced down-regulation of Cdc42 activation.