Immunohistochemical profile of basic fibroblast growth factor and heparan sulphate in adult rat mandibular condylar cartilage

Cell fate mediators Notch and Twist in mouse mandibular condylar cartilage

OBJECTIVE

The objectives of this study were to examine if Twist and Notch 1 are present in the mandibular condylar cartilage (MCC) and whether their gene expression can be altered by exogenous FGF-2 and TGF-β2.

DESIGN

Half-heads from CD-1 mice pups harvested at embryonic day 17 (E17) were fixed, decalcified, and sectioned in the sagittal plane for immunohistochemical detection of Notch and Twist using confocal microscopy. Other mandibular condyles and adjacent ramus from E17 mice were cultured in serum-free DMEM containing 0, 3, or 30 ng/mL of FGF-2 (10-12 condyles per treatment group). This experimental design was repeated with medium containing 0, 3, or 30 ng/mL of TGF-β2. After 3 days of culture, the pooled RNA from each group was extracted for examination of Notch and Twist gene expression using quantitative real-time RT-PCR.

RESULTS

Immunohistochemical examination revealed that Notch and Twist were localized to the prechondroblastic and upper chondroblastic layers of the cartilage. Exogenous FGF-2 up-regulated Notch 1, Twist 1 and Twist 2 gene expression in MCC explants from E17 mice, whilst TGF-β2 had the opposite effect.

CONCLUSIONS

The gene expression data demonstrate that MCC explants are sensitive to growth factors known to affect Notch and Twist in other tissues. The subset of cells in which Twist and Notch immunoreactivity was found is suggestive of a role for FGF-2 and TGF-β2 as regulators of cell differentiation of the bipotent MCC cell population, consistent with the role of Notch and Twist as downstream mediators of these growth factors in other tissues.

Recombinant adeno-associated virus serotype 2 (rAAV2)-An efficient vector for gene delivery in condylar cartilage, glenoid fossa and TMJ disc in an experimental study in vivo

OBJECTIVE

To elaborate whether rAAV2 can be used for future TMJ gene therapy, we examined the infection efficiencies of rAAV2 in vitro, and the transgene expression pattern mediated by rAAV2 in glenoid fossa, TMJ disc and condylar cartilage in vivo.

MATERIALS AND METHODS

Different dosages of rAAV2-eGFP (MOI: 5 x 10(4), 1 x 10(4), 5 x 10(3)) were applied to primary cultured condylar chondrocytes of rats. Infection efficiencies were analysed by FACSCalitur at different time points. Vastatin, a molecule not naturally expressed in TMJ, was used as a reporter for detection of rAAV2 mediated transgene expression in vivo. Thirty SD rats were injected with either rAAV2-sec-Vastatin (experimental group) or rAAV2-eGFP (control group) into both sides of TMJ. They were sacrificed at the indicated time (7, 14, 21, 30 and 60 days of injection) and the TMJ samples were collected for RT-PCR and immunostaining analysis.

RESULTS

High dosage (MOI 5 x 10(4)) of rAAV2-eGFP can achieve desirable transduction efficiencies in vitro after 5 days. Transgene expression of rAAV-sec-Vastatin persisted for about 21 days in glenoid fossa, around 7 days in TMJ disc and at least 60 days in condylar cartilage in vivo. In condylar cartilage, transgene expression was found in the proliferative layer and chondroblast layer (day 7), chondrocyte layer (day 14), pre-hypertrophic and hypertrophic layer (day 21), hypertrophic layer and deep hypertrophic layer (day 30 and 60).

CONCLUSION

Recombinant AAV2 could be considered as a promising vector for gene therapy in TMJ which can mediate therapeutic gene expression in glenoid fossa, articular disc and condylar cartilage in vivo.

Interplay of mechanical loading and growth factors in the mandibular condyle

The mandibular condyle is an important growth site in the developing mandible. The growth of the condyle is known to be highly adaptable to functional factors. This property is exploited in orthodontics for the treatment of class II malocclusions and mandibular asymmetries. However, there is an ongoing debate on the efficacy of functional appliances. The comparison of experimental studies is complicated by the lack of detailed analyses of the load distribution within the condyle. In spite of this, there is a large body of evidence showing that mechanical manipulation of the condyle induces metabolic changes, and changes in the expression of growth factors and other signalling molecules. This review aims to give an overview of the role of growth factors in the condyle with special emphasis on their responsiveness to mechanical perturbation.

Regulatory effects of FGF-2 on the growth of mandibular condyles and femoral heads from newborn rats

The secondary cartilage of the mandibular condyle is considered to be adaptive to functional factors. In the last decades, growth factors have also been shown to be potent regulators of cartilage metabolism. Moreover, it has been suggested that growth factors may differentially regulate the growth of primary and secondary cartilages. However, only a few studies have made a direct comparison of the effects of growth factors on both cartilages. Therefore, the aim here was to compare the effects of FGF-2 on secondary cartilage of the mandibular condyle and primary cartilage of the femoral head from 4-day-old rats in vitro. Cartilages were cultured for 1, 7 and 14 days with 0 and 100 ng/mL FGF-2. We evaluated the effects of FGF-2 on growth, tissue organisation, DNA and glycosaminoglycan (GAG) synthesis and GAG and collagen content. With FGF-2, the morphology of the mandibular condyles changed and the GAG and collagen contents were reduced. However, the growth of the mandibular condyles was not affected. On the contrary, the growth of the femoral heads was strongly reduced due to an inhibition of chondrocyte hypertrophy. In both cartilages, FGF-2 stimulated DNA synthesis in short-term cultures and reduced it in long-term cultures. In conclusion, FGF-2 had a larger effect on the metabolism of the mandibular condyles as compared to the femoral heads. However, the growth of the femoral heads was strongly reduced while that of the mandibular condyles was not affected.

In vitro analysis of matrix proteins and growth factors in dedifferentiating human chondrocytes for tissue-engineered cartilage

CONCLUSIONS

With ongoing culture and dedifferentiation of chondrocytes, significant changes in the expression patterns of various collagens and the insulin-like growth factor (IGF) receptor were detected. The latter could play an important role in the differentiation of human chondrocytes.

OBJECTIVE

Tissue engineering represents a promising method for the construction of autologous chondrogenic grafts for reconstructive surgery. So far, little is known about the expression of markers for cell proliferation and differentiation in cultured chondrocytes.

MATERIAL AND METHODS

Human chondrocytes were isolated from septal cartilage (n=5) and held in primary cell culture. Cells were harvested after 24 h and 6 days. Proliferation was analyzed using an Alamar Blue assay. The differentiation of the cells was investigated using bright field microscopy, the expression patterns of various proteins using immunohistochemistry and the expression of distinct genes using a microarray technique.

RESULTS

The chondrocytes showed strong proliferation (Day 0: 16.7+/-0.7 fluorescent units; Day 5: 52.4+/-2.2 fluorescent units) from the third day of cell culture in medium without growth factors. From this point onwards, a dedifferentiation of the chondrocytes could be observed. In cell culture, the chondrocytes expressed collagen 1 and 10 without expression of collagen 3. After 6 days of cell culture, they expressed collagen 2. The chondrocytes showed constant low expression of the fibroblast growth factor-2 receptor, but constant high expression of vascular endothelial growth factor, matrix metalloproteinase (MMP)2 and MMP9. The cells never expressed the epidermal growth factor receptor. The proportion of IGF receptor-expressing cells diminished significantly during cell culture.

Primary and secondary cartilages of the neonatal rat: the femoral head and the mandibular condyle

Primary and secondary cartilages differ in embryonic origin and in histological organization, and are generally considered to have a different mode of growth. However, few studies have directly compared the two types of cartilage of the same animal at the same age. Therefore, we analysed several histological and biochemical differences between secondary cartilage of the mandibular condyle and primary cartilage of the femoral head of 4-d-old rats. We evaluated the tissue organization, the level of DNA and glycosaminoglycan (GAG) synthesis, and the GAG and collagen content. The expression of collagen types I, II and III and of receptors for insulin-like growth factor (IGF)-I, fibroblast growth factor (FGF), and transforming growth factor (TGF)-beta were investigated by immunohistochemistry. The ex vivo DNA and GAG synthesis as well as the GAG content of femoral heads were much higher than that of mandibular condyles. Mandibular condyles expressed both collagen types I and II, while femoral heads expressed only type II collagen. In the mandibular condyles, receptors for IGF-I, FGF, and TGF-beta were observed mainly in the superficial layers, whereas they were found throughout the entire femoral head. In conclusion, major differences were found between both types of cartilage, which might be related to their specific functional demands.

New Chondrocyte Genes Discovered by Representational Difference Analysis of Chondroinduced Human Fibroblasts

This report includes a review of the potential for gene expression analyses to provide new information for solving problems in skeletal repair and regeneration. It focuses on two approaches: high-throughput gene array methods and representational difference analysis (RDA). The principles underlying these methods are presented with experimental tutorials and some applications. Second, this report includes a review of results from applying both approaches to an in vitro model of postnatal chondroinduction by demineralized bone powder (DBP). Human dermal fibroblasts (hDFs) cultured with DBP acquire a chondroblast phenotype and express cartilage-specific matrix proteins after 7 days. We used cDNA macroarrays and RDA to identify the genes that were altered prior to expression of the chondroblast phenotype, i.e., after only 3 days' culture with DBP. Using a strategy of data management and reduction based upon biological functions, we reported several functional families of genes (cytoskeletal elements, protein synthesis/trafficking, and matrix molecules and their modifiers) that are upregulated during chondroinduction of hDFs. Together with histological and biochemical evidence of the chondroblast phenotype, the gene expression patterns indicate that there are specific stages of induced chondrocyte differentiation in this experimental system. Third, this report includes a new study, in which DBP-regulated genes were used as a data base to derive new information on the cell biology of chondrocytes. The objective was to determine whether a set of genes expressed during induction of chondrocyte differentiation is also expressed by mature articular chondrocytes. Our search of the literature for 59 of the DBP-regulated genes disclosed that expression of 20 of them (33%) had been documented in mature cartilage or chondrocytes. Of the 39 genes not previously documented in cartilage, 11 were tested by RT-PCR and all were found to be expressed in freshly isolated adult human chondrocytes. This review and these new data show how the strategy of high-throughput methods and functional data reduction can expand our knowledge of chondrocyte cell biology.

Lateral functional shift of the mandible: Part II. Effects on gene expression in condylar cartilage

There is considerable evidence that proliferation and growth in the mandibular condylar cartilage (MCC) might be altered after a change in the postural position of the mandible. However, almost nothing is known about the molecular basis of this response. Using semiquantitative reverse-transcription polymerase chain reaction, we examined the expression of insulin-like growth factor-1 (Igf-1), fibroblast growth factor-2 (Fgf-2), and their receptors (Igf-1r, Fgfr1, Fgfr2, and Fgfr3) in the MCC of 28 day-old rats at 3, 7, and 14 days after placing intraoral appliances designed to produce a lateral functional shift of the mandible. This shift resulted in a transverse rotation of the mandible so that the condyle on the side away from the shift was distracted anteriorly (ie, protruded) from the glenoid fossa, while the contralateral condyle remained in place or moved slightly posteriorly (ie, nonprotruded). Gene expression for 5 of the 6 genes studied was significantly different (P <.05) between the protruded and the nonprotruded sides. In nearly every instance at the 3- and 7-day intervals, mRNA expression on the protruded side compared with age-matched controls was altered in the opposite direction from the nonprotruded side. Especially on the protruded side, the most pronounced differences from the control were evident at 3 and 7 days. In general, the changes in gene expression preceded the alterations in proliferative activity documented previously. These data suggest that alterations in the mRNA expression of Igf-1, Fgf-2, and their receptors might underlie in part changes in MCC proliferative activity after alteration in mandibular posture.

Chondromodulin-I expression in rat articular cartilage

The localization and expression of chondromodulin-I (ChM-I), an angiogenesis inhibitor, in the rat articular cartilage during maturation from 2 to 10 weeks of age were examined by immunohistochemistry, Western blot analysis and ribonuclease protection assay, and the results were compared with those in the epiphyseal cartilage. ChM-I was found to be diffusely immunostained in the inter-territorial space of the cartilage matrix from the intermediate to the deep layers at the immature stage. As the articular cartilage matured, the immunoreactivity was localized around the hypertrophic chondrocytes in the deep layer and the immunoreactivity became weak after maturation. In contrast, the ChM-I immunoreactivity was intense in the epiphyseal cartilage at all ages examined. ChM-I was detected by Western blotting as a broad band or occasionally as a cluster of multiple bands (approximately 25 kDa) in both the articular and the epiphyseal cartilage. The intensity of the bands decreased gradually with age in the articular cartilage, but was unchanged in the epiphyseal cartilage at all ages. Ribonuclease protection assay revealed that ChM-I mRNA also decreased gradually with age in the articular cartilage in parallel with the maturation of the articular cartilage, while no decrease in ChM-I mRNA was found in the epiphyseal cartilage. The expression of ChM-I mRNA in the articular cartilage was less than that in the epiphyseal cartilage at all ages. The decrease in amount of ChM-I in the mature articular cartilage suggests that ChM-I plays a more important role in the maintenance of avascularity in the immature articular cartilage than in the mature one. The avascular condition may be preserved by angiogenic inhibitors or mechanisms other than ChM-I in the mature articular cartilage.

Regulation of cell proliferation in rat mandibular condylar cartilage in explant culture by insulin-like growth factor-1 and fibroblast growth factor-2

Insulin-like growth factor-1 (IGF-1) and fibroblast growth factor-2 (FGF-2) regulate the proliferation and differentiation of growth-plate chondrocytes, but surprisingly little is known of the mechanisms underlying growth regulation in secondary cartilages such as the mandibular condylar. The aims here were to investigate whether IGF-1 and FGF-2 receptors are present in mandibular condylar cartilage in vivo from 28-day-old male Sprague-Dawley rats (by immunohistochemistry), how proliferation in that cartilage responds to increasing concentrations of exogenous IGF-1 or FGF-2 in explant culture (by [3H]thymidine incorporation), and whether the expression of these growth factors and their receptors in the cartilage changes during the transition to puberty (quantitative reverse transcriptase-polymerase chain reaction). Immunoreactivity for receptors (R) for IGF-1 and FGF-2 (IGF-1R, FGFR1, and FGFR3) was most pronounced in chondroblasts and hypertrophic chondrocytes, while FGFR2 immunoreactivity was strongest in the articular and prechondroblastic zones. The proliferative response elicited by exogenous IGF-1 was considerably greater than that induced by FGF-2, although the threshold concentration for a significant response was lower for FGF-2. In the transition from prepuberty (31 days) to the beginning of late puberty (42 days), a pronounced trend of increasing IGF-1 and decreasing FGF-2 gene expression was evident. Of the receptors, only FGFR2 and FGFR3 expression increased. These data provide evidence that proliferation in the mandibular condylar cartilage might be regulated in part by IGF-1 and FGF-2, and that expression of these genes changes considerably at puberty. The data also suggest that mechanisms governing proliferation in mandibular condylar cartilage might have as much in common with those regulating cranial sutures as those regulating growth-plate.

Distribution of fibroblast growth factors (FGFR-1 and -3) and platelet-derived growth factor receptors (PDGFR) in the rat mandibular condyle during growth

OBJECTIVES

To elucidate the role of the fibroblast growth factors 1 and 3 (FGFR-1, -3) and the platelet derived growth factor (PDGFR) in the growth of the mandibular condylar cartilage in the rat.

SETTING AND SAMPLE POPULATION

Institute of Dentistry and Department of Biostatistics, University of Turku, Turku, Finland. The material consisted of 1- to 21-day-old Long-Evans/Turku rats (total of 24 animals, three in each age group).

DESIGN

An immunohistological in vivo study combined with histomorphometry and biostatistical analysis.

EXPERIMENTAL VARIABLE

The animals were killed with an overdose of carbon dioxide and thereafter decapitated. Heads were fixed in 4% paraformaldehyde, decalcified in 12.5% ethylenediaminetetraacetic acid, cut sagittally into two halves and sectioned sagittally at 6 microns. In order to detect FGFR-1, -3 and PDGFR the sections were treated with H2O2/methanol (1:100), after which FGFR-1 and PDGFR monoclonal and FGFR-3 polyclonal antibodies were applied. The reaction products were visualized by using the Vectastain ABC Elite Kit using peroxidase substrate kit DAB as substrate. Negative and positive controls were also prepared. The sections were counterstained with hematoxylin.

OUTCOME MEASURE

In order to measure the depth of the cell layer labeled with FGF-1, -3 and PDGF receptors, the condylar head was divided into four regions: anterior, superior, posterosuperior and posterior. The measurements were made perpendicular to the articular surface using a computerized image analysis system, the images being acquired by means of a microscope connected to a CCD camera. The mean of five equally distributed measurements of each region was used to indicate the depth of the cell layers secreting the receptors. Regression analysis was used to evaluate the association between the depth of the labeled cell layer in relation to total depth of the condylar head, as a function of age.

RESULTS

Our results show that the depth of the cell layer labeled for FGFR-1, -3 and PDGFR increase significantly as a function of age in the mandibular condylar head of rats.

CONCLUSION

Increase in the cell layer labeled for FGFR-1, -3 and PDGFR occurs during the stage when the articular function of the mandibular condyle intensifies. FGFR-1, -3 and PDGFR evidently have an important role in the growth regulation of the condylar cartilage during the most rapid growth period in the rat.

Interaction of chondrocytes, extracellular matrix and growth factors: relevance for articular cartilage tissue engineering

The abundant extracellular matrix of articular cartilage has to be maintained by a limited number of chondrocytes. Vice versa, the extracellular matrix has an important role in the regulation of chondrocyte function.

OBJECTIVE

In this review we discuss the role of the extracellular matrix in the regulation of chondrocyte function and the relevance for cartilage tissue engineering. To reach this goal the international literature on this subject has been searched with a major focus on the last 5 years.

RESULTS

Structural matrix macromolecules (e.g. collagen, hyaluronate), but also growth factors (e.g. IGF-I, TGF beta) entrapped in the matrix and released under specific conditions affect chondrocyte behavior. These factors communicate with the chondrocyte via specific membrane receptors. In this way there is a close interaction between the extracellular and intracellular milieu. Articular cartilage has a limited capacity of intrinsic repair, which has resulted in the development of tissue engineering approaches to repair damaged cartilage. Successful application of scaffolds has to take into account the important role of both soluble and insoluble matrix-derived factors in cartilage homeostasis.

CONCLUSION

Functional tissue engineering will only be realized when the scaffolds used will provide cartilage cells with the correct extracellular signals.