Rapid expression of collagen type X gene of non-hypertrophic chondrocytes in the grafted chick periosteum demonstrated by in situ hybridization

Preparation and Evaluation of Tibia- and Calvarium-Derived Decellularized Periosteum Scaffolds

The periosteum plays a key role in bone regeneration and an artificial bionic material is urgently required. The periostea on the tibia and skull differ with respect to the types of cells, microstructure, and components, leading to different biological functions and biomechanical properties. We aimed to prepare decellularized periosteum scaffolds derived from different origins and evaluate their angiogenic and osteogenic activities. Histological assessment of α-smooth muscle actin, bone morphogenetic protein-2, and alkaline phosphatase in tibial and calvarial periosteum tissues provided preliminary information on their differing angiogenic and osteogenic properties. We developed decellularization protocols to completely remove the periosteum cellular components and for good maintenance of the hierarchical multilayer structures and components of the extracellular matrix (ECM) with no cytotoxicity. Moreover, using a chicken egg chorioallantoic membrane assay and a nude mouse implantation model, we found that tibia-derived periosteum ECM had superior osteogenic activity and calvarium-derived ECM had good angiogenic activity. The preliminary mechanisms of differing activities were then evaluated by osteogenesis- and angiogenesis-related gene expression in human umbilical vein endothelial cell- and MC-3T3 cell-seeded ECM scaffolds. Thus, this study provides periosteum biomaterials that are derived from specific tissues and have different functional properties and structures, for use in bone regeneration.

Regulation of chondrocyte differentiation level via co-culture with osteoblasts

The close apposition of osteoblasts and chondrocytes in bone and their interaction during bone development and regeneration suggest that they may each regulate the other's growth and differentiation. In these studies, osteoblasts and chondrocytes were co-cultured in vitro, with both direct and indirect contact. Proliferation of the co-cultured chondrocytes was enhanced using soluble factors produced from the osteoblasts, and the differentiation level of the osteoblasts influenced the differentiation level of the chondrocytes. In addition, the chondrocytes regulated differentiation of the co-cultured osteoblasts using soluble factors and direct contact. These data support the possibility of direct, reciprocal instructive interactions between chondrocytes and osteoblasts in a variety of normal processes and further suggest that it may be necessary to account for this signaling in the regeneration of complex tissues comprising cartilage and mineralized tissue.

Species Specificity of Ectopic Bone Formation Using Periosteum-Derived Mesenchymal Progenitor Cells

To investigate novel cell-based bone-engineering approaches using rabbit as a preclinical animal model, we compared the osteogenic potential of rabbit periosteum-derived cells (RPDCs) and human periosteum-derived cells (HPDCs) in vitro and in vivo. Adherent periosteal cells from both species were expanded in vitro and subsequently treated with osteogenic medium or bone morphogenetic protein 6 (BMP6). Alkaline phosphatase (ALP) activity was measured, and alizarin red staining was performed to evaluate osteogenic differentiation. In vivo ectopic bone formation was assessed by seeding 5x10(6) periosteal cells, grown in osteogenic conditions, in a Collagraft carrier and subsequent implantation subcutaneously in athymic mice. In vitro, growth analysis indicated that RPDCs expanded faster and were smaller than HPDCs under the same culture conditions. Osteogenic medium did not affect the ALP activity of HPDCs or RPDCs. In contrast, BMP6 stimulated ALP activity in cultured RPDCs and HPDCs but at different rates. In vivo, HPDCs gave rise to extensive bone formation, whereas RPDCs failed to make bone. In vivo, cell tracking revealed that engraftment and survival of HPDCs and RPDCs after 8 weeks in the implant were limited. Some HPDCs were incorporated into the newly formed bone. RPDCs and HPDCs displayed distinct growth characteristics and osteogenic differentiation capacity in vitro and in vivo under the culture conditions used. Our data indicate potential limitations of use of the rabbit as a preclinical model for cell-based treatments for bone repair.

Abnormal craniofacial development and expression patterns of extracellular matrix components in transgenic Del1 mice harboring a deletion mutation in the type II collagen gene

OBJECTIVE

To analyze the effect of a type II collagen mutation on craniofacial development in transgenic Del1 mice.

DESIGN

Samples from homozygous (+/+) and heterozygous (+/-) transgenic Del1 mice harboring mutations in the type II collagen gene as well as non-transgenic (-/-) littermates were collected at days 12.5, 14.5, 16.5 and 18.5 of gestation. The cartilaginous and bony elements of the craniofacial skeleton were analyzed after staining with alcian blue, alizarin red S and von Kossa. The expression patterns of type II, IX and X collagens and aggrecan were analyzed by immunohistochemistry and in situ hybridization.

RESULTS

Several abnormalities were observed in the craniofacial skeleton of transgenic Del1 mice. These include an overall retardation of chondrogenesis and osteogenesis in Del1 +/+ mice, and to a lesser extent also in Del1+/- mice. Characteristic findings in Del1 +/+ mice included a reduced anterioposterior length, a smaller size of the mandible, a palatal cleft and a downward bending snout. We also detected retarded ossification of calvarial bones in Del1 +/+ and +/- mice when compared with Del1 -/- mice. A surprising finding was the presence of both type II and X collagens and their mRNAs in the periosteum of the cranial base.

CONCLUSION

The present study confirms the important role of type II collagen mutation in craniofacial development and growth. In addition to affecting endochondral ossification, the type II collagen mutation also disturbs intramembranous ossification in the developing craniofacial skeleton.

Expression of type I, type II, and type X collagen genes during altered endochondral ossification in the femoral epiphysis of osteosclerotic (oc/oc) mice

The osteosclerotic (oc/oc) mouse, a genetically distinct murine mutation that has a functional defect in its osteoclasts, also has rickets and shows an altered endochondral ossification in the epiphyseal growth plate. The disorder is morphologically characterized by an abnormal extension of hypertrophic cartilage at 10 days after birth, which is later (21 days after birth) incorporated into the metaphyseal woven bone without breakdown of the cartilage matrix following vascular invasion of chondrocyte lacunae. In situ hybridization revealed that the extending hypertrophic chondrocytes expressed type I and type II collagen mRNA, as well as that of type X collagen and that the osteoblasts in the metaphysis expressed type II and type X collagen mRNA, in addition to type I collagen mRNA. The topographic distribution of the signals suggests a possible co-expression of each collagen gene in the individual cells. Immunohistochemically, an overlapping deposition of type I, type II, and type X collagen was observed in both the extending cartilage and metaphyseal bony trabeculae. Such aberrant gene expression and synthesis of collagen indicate that pathologic ossification takes place in the epiphyseal/metaphyseal junction of oc/oc mouse femur in different way than in normal endochondral ossification. This abnormality is probably not due to a developmental disorder in the epiphyseal plate but to the failure in conversion of cartilage into bone, since the epiphyseal plate otherwise appeared normal, showing orderly stratified zones with a proper expression of cartilage-specific genes.

The expression of types X and VI collagen and fibrillin in rat mandibular condylar cartilage. Response to mastication forces

Types X and VI collagen and fibrillin were localized by in situ hybridization and immunohistochemical methods in the mandibular condyles of rats, and the response of these molecules to post-weaning diets of soft food, ordinary pellets, or hardened pellets was studied. Type X collagen was synthesized, particularly in conditions of soft food consistency, by cells in the perichondrium-periosteum and in the bone and by cells at the erosion front between cartilage and bone. Type X collagen synthesis diminished under higher compression forces due to mastication and with increasing age. Type VI collagen and fibrillin were synthesized by cells in the perichondrium-periosteum and by chondrocytes and by stromal osteoblasts and were not modified by higher mechanical forces. In contrast to previous findings in the growth plate of long bones, type X collagen in the mandibular condyle was not synthesized by hypertrophic chondrocytes but was associated with cells of the osteoblastic rather than the chondroblastic phenotype.

Effects of X-ray irradiation on terminal differentiation and cartilage matrix calcification of rabbit growth plate chondrocytes in culture

The retardation of long bone growth caused by irradiation is thought to be closely related to the impairment of growth plate function, but its mechanism remains unclear. In this study, we examined the effects of irradiation on the terminal differentiation of growth plate chondrocytes and on calcification. Chondrocytes were isolated from the growth plate of the ribs of four-week-old rabbits and inoculated at a high density on a type-I collagen-coated dish. Following logarithmic proliferation, they reached confluence (premature chondrocytes), then matured (mature chondrocytes), and became hypertrophied (hypertrophic chondrocytes). 10 Gy or less irradiation of the premature chondrocytes potently inhibited the terminal differentiation and matrix mineralization. Irradiation inhibited chondrocyte hypertrophy and suppressed alkaline phosphatase induction and the expression of type-X collagen without changing the protein composition profile of any other cell layer. Premature cells had the highest radiosensitivity. The sensitivity was decreased as the cells differentiated; the effects of irradiation on hypertrophic chondrocytes with terminal differentiation-related phenotypes were reduced. This study showed that 10 Gy or less irradiation of growth plate chondrocytes impaired terminal differentiation and mineralization. Since chondroclasts and bone marrow cells invade only to the mineralized cartilage, the induction of calcification in cartilage matrices is one of the most important steps in endochondral ossification. Therefore, it is conceivable that the damage in the growth plate induced by irradiation could account for the subsequent abnormal bone and skeletal growth.

Co-expression of collagen types II and X mRNAs in newly formed hypertrophic chondrocytes of the embryonic chick vertebral body demonstrated by double-fluorescence in situ hybridization

Collagen types II and X mRNAs have been demonstrated simultaneously in newly formed hypertrophic chondrocytes of embryonic chick vertebral cartilage using a double-fluorescence in situ hybridization technique. Digoxigenin- and biotin-labelled type-specific collagen II and X cDNA probes were used. In the embryonic chick vertebra at stage 45, two different fluorescence signals (Fluorescein isothiocyanate and Rhodamine)--one for collagen type II mRNA, the other for type X mRNA--showed differential distribution of the two collagen mRNAs in the proliferating and hypertrophic chondrocyte zones. Several layers of newly formed hypertrophic chondrocytes expressing both collagen types II and X genes were identified in the same section as two different fluorescent colour signals. Low levels of fluorescent signals for collagen type II mRNA were also detected in the hypertrophic chondrocyte zone. Cytological identification of maturing chondrocyte phenotypes, expressing collagen mRNAs, is easier in sections processed by non-radioactive in situ hybridization than in those subjected to radioactive in situ hybridization using 3H-labelled cDNA probes. This study demonstrates that double-fluorescence in situ hybridization is a useful tool for simultaneously detecting the expression of two collagen genes in the same chondrocyte population.