Functionalization of dynamic culture surfaces with a cartilage extracellular matrix extract enhances chondrocyte phenotype against dedifferentiation

Culture on silicone rubber surfaces has been shown to partially overcome the chondrocyte dedifferentiation characteristic of standard culture on rigid polystyrene. These methods typically involve functionalization of culture surfaces with proteins. Collagen type I is often used, but more cartilage-specific proteins may be more appropriate for chondrocytes. To explore this hypothesis, a twofold experimental design was applied. First, chondrocytes were cultured in rigid Petri dishes coated with silicone rubber ("static silicone" or SS culture) functionalized with either cartilage extracellular matrix (ECM) extract or collagen type I. Second, chondrocytes were cultured on monotonically expanded high extension silicone rubber dishes ("continuous expansion" or CE culture) functionalized with ECM extract and compared to cells grown in SS culture. There were no differential effects of surface functionalization with the ECM extract vs. collagen type I on chondrocyte morphology, viability, proliferation or apoptosis in SS culture. However, chondrocyte growth on the ECM extract was associated with significantly reduced collagen types I and X gene expression and significantly increased glycosaminoglycan (GAG) secretion. After 3 passages (P3) on ECM-coated SS culture, chondrocyte phenotype and GAG secretion was enhanced compared to cells passaged on collagen type I. Pellet cultures from P3 SS culture displayed enhanced collagen type II content when ECM extract was used for functionalization rather than collagen type I. In CE culture with ECM functionalization, chondrocyte dedifferentiation was significantly inhibited vs. SS cultures, as evidenced by both gene expression and pellet cultures. Functionalization of extendable culture surfaces with cartilage ECM extract therefore supports enhanced preservation of chondrocyte phenotype.     

Human chondrocyte proliferation and matrix synthesis cultured in Atelocollagen gel

To evaluate the potential of Atelocollagen gel as a carrier for chondrocyte transplantation, histological and biochemical characteristics of the chondrocytes in gel culture were compared with those in conventional monolayer cultures. Articular chondrocytes from 20 patients were isolated by enzyme digestion, embedded in Atelocollagen gel, and cultured for up to 4 weeks. The effects on proliferation, morphological changes, and synthesis of proteoglycans were analyzed by cell counts, light and electron microscopy, and measurement of isomers of chondroitin sulfates. Chondrocytes embedded in the Atelocollagen gel gradually proliferated and produced chondroitin 6-sulfate, maintaining the chondrocyte phenotype for up to 4 weeks. In contrast, although monolayer chondrocytes increased in number, most could be characterized as being fibroblast-like cells with a reduced capability of producing chondroitin 6-sulfate. The results suggest that Atelocollagen gel permitted a gradual proliferation and matrix synthesis of chondrocytes and maintaining its phenotype. Atelocollagen gel represents an important carrier for the clinical application of cultured chondrocyte transplantation for repair of cartilage defects.     

Self-assembled octapeptide scaffolds for in vitro chondrocyte culture

Nature has evolved a variety of creative approaches to many aspects of materials synthesis and microstructural control. Molecular self-assembly is a simple and efficient way to fabricate complex nanostructures such as hydrogels. We have recently investigated the gelation properties of a series of ionic-complementary peptides based on the alternation of non-polar hydrophobic and polar hydrophilic residues. In this work we focus on one specific octapeptide, FEFEFKFK (F, phenylalanine; E, glutamic acid; K, lysine). This peptide was shown to self-assemble in solution and form β-sheet-rich nanofibres which, above a critical gelation concentration, entangle to form a self-supporting hydrogel. The fibre morphology of the hydrogel was analysed using transmission electron microscopy and cryo-scanning electron microscopy illustrating a dense fibrillar network of nanometer size fibres. Oscillatory rheology results show that the hydrogel possesses visco-elastic properties. Bovine chondrocytes were used to assess the biocompatibility of the scaffolds over 21 days under two-dimensional (2-D) and three-dimensional (3-D) cell culture conditions, particularly looking at cell morphology, proliferation and matrix deposition. 2-D culture resulted in cell viability and collagen type I deposition. In 3-D culture the mechanically stable gel was shown to support the viability of cells, the retention of cell morphology and collagen type II deposition. Subsequently the scaffold may serve as a template for cartilage tissue engineering.     

Modulation of chondrocyte phenotype via baculovirus-mediated growth factor expression

Baculovirus has emerged as a new gene delivery vector thanks to a number of advantages. This study demonstrated that baculovirus conferred efficient gene delivery and mediated expression of growth factors (TGF-beta1, IGF-1 and BMP-2) to therapeutic levels in rabbit chondrocytes. Interestingly, the cellular response to growth factor stimulation was dependent on the cell passage. The highly de-differentiated passage 5 (P5) chondrocytes failed to respond to the stimulation by either growth factor. The de-differentiated P3 cells also failed to maintain the chondrocyte phenotype, but baculovirus-mediated BMP-2 expression remarkably reversed the de-differentiation and enhanced the aggrecan and collagen II production in 2D and 3D cultures, as evidenced by cell morphology, histological staining and gene expression analyses. Baculovirus-mediated TGF-beta1 expression modestly enhanced the cartilage-specific matrix production, although to a lesser extent. Intriguingly, IGF-1, a well-known chondroinductive protein, failed to stimulate the P3 cells likely due to the loss of IGF-1 receptor expression. In summary, this study proved for the first time the potentials of baculovirus in modulating the differentiation status of chondrocytes in the context of cartilage tissue engineering, but also highlighted the importance of selecting appropriate cell passage and growth factor for genetic manipulation.     

Behaviour of epiphyseal mouse chondrocyte populations in monolayer culture

Summary Growth and dedifferentiation of a heterogeneous mouse chondrocyte population, prepared from epiphyses of mouse embryos (day 17 of gestation), were studied in primary monolayer culture. At different times of culture, light and electron microscopic investigations were carried out and the change of collagen types was shown by immunofluorescence microscopy. During the first four days in culture, chondrocytes express their typical phenotype. Round or polygonal cells are embedded in a metachromatically staining matrix and produce type II collagen. After four to eight days in vitro most of the chondrocytes lose their matrix capsule and alter to fibroblast-like cells. Simultaneously, a switch of collagen synthesis to type III and type I collagen occurs, whereas the type II collagen synthesis is stopped. Altered cells and transitional stages have intracellular glycogen like typical chondrocytes, but show phagocytosis and indications of cell migration like fibroblasts. It is proposed that these cells, originating from a subpopulation of epiphyseal cartilage, are able to differentiate and dedifferentiate in vitro.     

Role of apoptosis inhibition in various chondrocyte culture systems

Apoptosis may limit the utility of cell-based therapies for articular cartilage disorders. We tested the hypothesis that chondrocyte apoptosis can be reduced by optimizing the conditions employed to expand chondrocyte numbers in culture. Chondrocyte apoptosis was examined in monolayer and suspension culture, in the presence of fetal bovine serum (FBS) or autologous serum, and for culture periods of 2 or 4 days. The effect of these variables was assessed by measuring cell viability, Annexin V labeling and mitochondrial membrane potential. After 2 days of culture, the greatest increase in viable cell number (3.7-fold) occurred in monolayer cultures with autologous serum. After 4 days of culture, the greatest increase in cell number (9.0-fold) occurred in monolayer cultures supplemented with FBS. By Annexin V staining, the proportion of cells undergoing apoptosis after 2 days was not affected by the type of serum used or by culture in monolayer versus suspension. After 4 days of culture, the proportion of apoptotic cells was significantly reduced (35% to 13%, p<0.02) in suspension cultures with autologous serum. Apoptosis assessed by loss of mitochondrial membrane potential was decreased in the presence of autologous serum. These data suggest that suspension culture with autologous serum is useful in simultaneously maintaining cell proliferation and minimizing apoptosis in cultured human articular chondrocytes.     

Retaining zonal chondrocyte phenotype by means of novel growth environments

The loss of phenotype in articular chondrocytes expanded in monolayer has been established as a possible contributor to the deficiencies associated with in vitro cartilage engineering and autologous cell transplantation procedures. We cultured zonal articular chondrocytes on tissue culture plastic, collagen II-coated polystyrene, and aggrecan-coated polystyrene in an effort to find a surface that can either prevent or slow the loss of phenotype. In addition, we encapsulated passaged cells in agarose to examine the effect of three-dimensional culture on redifferentiating zonal chondrocytes. We used real-time polymerase chain reaction to measure the relative gene expression levels of collagen I and II, aggrecan, and superficial zone protein over relevant passages (P0-P4). Results showed that tissue culture plastic and the collagen II-coated surface induced rapid loss of phenotype in zonal articular chondrocytes. The aggrecan-coated surface had a less detrimental effect on the chondrocytic phenotype of seeded cells, inducing gene expression characteristics comparable to those of agarose-encapsulated cells. Furthermore, when chondrocytes that had been previously passaged on a collagen II surface were placed on an aggrecan surface, the zonal cells showed a dramatic change in gene expression from fibroblastic to chondrocytic. These results indicate that a culture environment using aggrecan as a substratum or agarose as a scaffold is crucial to the development of phenotypically correct articular cartilage.     

改良分步消化法培养原代软骨细胞

背景：胰蛋白酶和细菌胶原酶结合使用消化关节软骨基质获得大量纯度高的软骨细胞的方法步骤繁琐、过程复杂,容易污染,但更好的简单易行、安全可靠的方法至今少有报道。 目的：采用改良分步消化法进行软骨细胞培养,以获取大量纯净的软骨细胞。 方法：将新西兰白兔6只随机分2组,酶消化法组运用酶消化法分两步获取原代软骨细胞,对照组用传统法进行原代软骨细胞培养。培养1周后观察两组培养的软骨细胞的生长状态,并进行细胞鉴定、计数,评估改良后的方法对细胞的影响。 结果与结论：酶消化法组采用0.2%Ⅱ型胶原酶消化软骨细胞,与对照组相比,可将6 h以上的消化时间缩短至3 h。两组原代软骨细胞培养24 h均多呈圆形,悬浮状态,48 h后贴壁,培养1周后,两组软骨细胞可铺满培养瓶底。结果证实,采用改良分步消化法进行软骨细胞培养,在缩短了消化时间的同时其细胞生长及形态变化均无改变,可以顺利获取大量纯净的软骨细胞。     

Three-dimensional microenvironments retain chondrocyte phenotypes during proliferation culture

Although autologous chondrocyte implantation has already been in clinical use, chondrocyte dedifferentiation is problematic during proliferation culture. We attempted a three-dimensional (3D) collagen gel culture under chondrocyte proliferation with repeated passaging to prevent the chondrocytes dedifferentiation. Human auricular chondrocytes were cultured in 3D or conventional monolayer conditions, which reached a 1000-fold increase in cell numbers at passages 3 and 4, respectively. During multiplication, the chondrocytes in 3D culture showed greater suppression of collagen type I (COL1) and preservation of collagen type II (COL2) than those in monolayer. Tissue-engineered cartilage made of 3D cells also abundantly accumulated COL2 or proteoglycan and possessed favorable mechanical properties. The advantage of 3D cells may result from the similarity of microenvironments in cell-to-matrix adhesion or cell-to-cell contacts with that of native cartilage. The up-regulation of integrins and down-regulation of cadherins in the 3D cells mimicked the expression pattern of native cartilage, rather than that of monolayer cells. The silencing of integrin beta1 and Ob-cadherin expression by small interfering ribonucleic acid in the cultured chondrocytes led to the promotion of dedifferentiation and redifferentiation, respectively, indicating that the 3D collagen gel culture provided sufficient cell preparation and reduced chondrocyte dedifferentiation, which is regarded as a feasible strategy in autologous chondrocyte implantation.     

A modified cell culture method for autologous chondrocyte transplantation

Autologous chondrocyte transplantation (ACT) is a promising method to treat chondral and osteochondral defects. This study introduced a modified method for cell culture in ACT. Porcine chondrocytes were cultured for 3 weeks under low hydrostatic pressure at 250 Pa. The results showed that the dry weight of the cartilage-like membrane in the loading group was 3.0 times more than the control group (no loading) (p < 0.01), and cell numbers were significantly increased by 3.1 times (p < 0.01) after a 3-week culture. Compared with the fresh tissue sample, the mRNA expression of collagen II was not statistically different and the mRNA of aggrecan was only slightly decreased by 19%. These data suggest that the hydrostatic pressure at this level significantly increased the cell numbers and biosynthesis of cultured chondrocytes.     

Bovine chondrocyte behaviour in three-dimensional type I collagen gel in terms of gel contraction, proliferation and gene expression

This study evaluated the in vitro behaviour of bovine chondrocytes seeded in collagen gels, promising recently reported scaffolds for the treatment of full-thickness cartilage defects. To determine how chondrocytes respond to a collagen gel environment, 2 x 10(6) chondrocytes isolated from fetal, calf and adult bovine cartilage were seeded within type I collagen gels and grown for 12 days in both attached and floating (detached from the culture dish after polymerisation) conditions. Monolayer cultures were performed in parallel. All chondrocytes contracted floating gels to 55% of the initial size, by day 12. Contraction was dependent on initial cell density and inhibited by the presence of dihydrocytochalasin B as previously observed with fibroblasts. Gene expression was determined using conventional and real-time PCR. The chondrocyte phenotype was better maintained in floating gels compared to attached gels and monolayers. This was demonstrated by comparing the ratio of COL2A1/ COL1A2 mRNA and also of alpha10/alpha11 integrin mRNA. A strong up-regulation of MMP13 expression was measured at day 12 in floating gels. The composition of cartilage-like tissue obtained by growing chondrocytes in a collagen gel varied depending on the floating or attached conditions and initial cell density. It is thus important to consider these parameters when using this culture system in order to prepare a well-defined implant for cartilage repair.     

Matrix-mixed culture: new methodology for chondrocyte culture and preparation of cartilage transplants

For cartilage engineering a variety of biomaterials were applied for 3-dimensional chondrocyte embedding and transplantation. In order to find a suitable carrier for the in vitro culture of chondrocytes and the subsequent preparation of cartilage transplants we investigated the feasibility of a combination of the well-established matrices fibrin and alginate. In this work human articular chondrocytes were embedded and cultured either in alginate, a mixture of alginate and fibrin, or in a fibrin gel after the extraction of the alginate component (porous fibrin gel) over a period of 30 days. Histomorphological analysis, electron microscopy, and immunohistochemistry were performed to evaluate the phenotypic changes of the chondrocytes, as well as the quality of the newly formed cartilaginous matrix. Our experiments showed that a mixture of 0.6% alginate with 4.5% fibrin promoted sufficient chondrocyte proliferation and differentiation, resulting in the formation of a specific cartilage matrix. Alginate served as a temporary supportive matrix component during in vitro culture and can be easily removed prior to transplantation. The presented tissue engineering method on the basis of a mixed alginate-fibrin carrier offers the opportunity to create stable cartilage transplants for reconstructive surgery.     

Instability of the myofibroblast phenotype in culture

Myofibroblasts are cells that have features of both smooth muscle cells and fibroblasts. Myofibroblasts from rat granulation tissue were studied using a coordinated biochemical and morphological approach. These myofibroblasts were maintained in culture for more than 17 passages. After establishing that these cells were indeed myofibroblasts by immunohistochemical and ultrastructural criteria, their biochemical parameters and phenotypic stability were studied. Rat dermal fibroblasts grown under similar conditions served as controls. Biochemically, it was found that both cells produced similar types of procollagens, namely collagens I and III, in similar proportions at or near a 1:1 ratio. However, myofibroblasts at early passage produced threefold more procollagens than did fibroblasts at the same stage of passage, while similar quantities were produced in each at late passage. These observations for procollagens were confirmed by separate studies for collagens, as measured by hydroxyproline determinations. Such differences were also reflected ultrastructurally. Secretory vesicles were identified in myofibroblasts at early stage, but not at late stage of passaging. No such vesicles were seen in fibroblasts at any stage of passage. In conclusion, myofibroblasts are active secretory variants of fibroblasts which have an unstable phenotype in culture and become indistinguishable from fibroblasts at late passage.     

Characteristics of a scaffold-free articular chondrocyte plate grown in rotational culture

We investigated whether articular chondrocytes could form three-dimensional tissue-engineered cartilage in a rotational culture system without a scaffold. A suspension of chondrocytes derived from Japanese white rabbits was inoculated into a mold. Eight hours later, the cell suspension in the mold showed cell aggregation, forming a chondrocyte plate. The mold was removed, and the plate was cultured under static conditions. After 7 days of primary static culture, the plate was cultured under dynamic conditions, using rotational culture. After 2-3 weeks of rotational culture, the chondrocyte plate maintained a constant form and was considered stable enough to be handled with surgical pincers. Conversely, after 3 weeks of static culture, the plate gradually changed into an arch over that time. Histological and immunohistochemical evaluations indicated that the plate had cartilaginous qualities in terms of cell distribution and organization and the production of glycosaminoglycans and type II collagen in rotational cultures. Chondron units were detected with scanning electron microscopy. In contrast, a plate cultivated in static culture for 3 weeks was irregular in shape, and histological analysis indicated irregularly accumulated glycosaminoglycans. TUNEL-positive cells had increased significantly in the central region in 3-week static cultures, compared with those in 3-week rotational cultures. In this study, cartilaginous tissue in a scaffold-free environment has been produced. Significantly rotational cultures produce a construct, which is stable enough to be handled with surgical forceps after only 2 weeks of rotational culture. This system should be useful for implantation in the future.     

鲑鱼降钙素新型注射用温度敏感原位凝胶系统的构建及评价

目的构建鲑鱼降钙素新型注射用温度敏感原位凝胶系统并对其胶凝特性和降血钙效应进行评价。方法以泊洛沙姆F127为主要基质材料,复合使用泊洛沙姆F68,制备鲑鱼降钙素注射用温度敏感原位凝胶给药系统,以胶凝温度、胶凝时间、流变学、质构特性为考察指标,对该凝胶系统性质进行评价;采用大鼠眼眶取血,钙显色法监测体内血清钙离子浓度,对该凝胶系统降血钙效应进行研究。结果所制备的鲑鱼降钙素注射用温度敏感原位凝胶的胶凝温度为(35.3±1.3)℃,胶凝时间为(108.3±5.5)s,在25℃条件下为流动的液体,原位凝胶的黏度和黏滞力极低,方便注射给药,当温度增至37℃时能够迅速发生相转变,黏度和黏滞力等质构特性数据显著增加,成为具有一定胶凝强度的半固体;大鼠降血钙效应结果显示,该给药系统具有明显的缓释作用,其24 h时血钙浓度明显低于普通注射剂组,相对于普通注射剂的药理活性为138.6%。结论温度敏感原位凝胶用于鲑鱼降钙素的注射给药,是一种很有潜力的递送系统。     

Fabrication of micropatterned thermosensitive gel with highly-ordered honeycomb surface and inverse opal structure

Thermosensitive poly(N-isopropylacrylamide) gels with highly-ordered honeycome surface and inverse opal structure were successfully fabricated by several microfabrication methods using closely packed silica beads as a template. The gels are able to reversibly change the shapes and sizes of the pores with swelling-deswelling by temperature changes. In particular, regular buckling was induced due to compression with swelling. Such a thermoregulation of surface topography might be useful for design of functional surfaces with tunable physical properties.     

Development of PDMS microbioreactor with well-defined and homogenous culture environment for chondrocyte 3-D culture

Perfusion cell culture is believed to provide a stable culture environment due to the continuous supply of nutrients and removal of waste. However, the culture scales used in most cases were large, where the culture conditions can not be regarded as homogenous because of chemical gradients. To improve this, the concept of miniaturization is applied to 3-D cell culture. In this study, a simple perfusion microbioreactor was developed based on mass transport simulation to find out the reasonable culture scales with relatively lower chemical gradients. Besides, PDMS surface was treated with surfactant solution to reduce non-specific serum protein adsorption, which keeps the culture conditions steady. Chondrocyte 3-D culture using the proposed microbioreactors was compared with similar perfusion culture with a larger culture scale. Results showed that surfactant-treated PDMS surface could reduce serum protein adsorption by 85% over the native one. Also, microbioreactors were proved to provide a stable culture environment (e.g. pH) over the culture period. Cell culture scale of 200 μm thick culture construct was justified to have relatively lower chemical gradients than the larger scale perfusion culture. As a whole, the proposed culture system is capable of providing a well-defined and homogenous culture environment.     

星形胶质细胞在凝胶环境下的三维培养

目的:制备不同浓度的三维琼脂糖凝胶以进行星形胶质细胞的体外培养,从而寻找适合细胞生长的理想环境。方法:分别制备1%、2%、3%的琼脂糖凝胶,利用纳米压痕仪测量其弹性模量。星形胶质细胞在凝胶中培养1、3、5、7 d,观察细胞活性以及细胞骨架的变化。结果:随着凝胶浓度的增加,琼脂糖凝胶弹性模量逐渐增加。2%的琼脂糖凝胶的弹性模量最接近筛板组织的弹性模量;在2%、3%琼脂糖凝胶环境下,细胞活性具有较高水平。随着细胞在凝胶中培养的时间增加,星形胶质细胞的突起逐渐伸出,细胞从球形向梭形或星形转变,更接近细胞真实的生长状态。结论:2%琼脂糖凝胶最接近星形胶质细胞在体内的生长环境,细胞成活率较高,是细胞体外三维培养的理想环境。 【关键词】星形胶质细胞;琼脂糖凝胶;三维培养;力学特性