The complete primary structure of the long form of mouse alpha 1(IX) collagen chain and its expression during limb development

Origin of cardiac fibroblasts and the role of periostin

Cardiac fibroblasts are the most populous nonmyocyte cell type within the mature heart and are required for extracellular matrix synthesis and deposition, generation of the cardiac skeleton, and to electrically insulate the atria from the ventricles. Significantly, cardiac fibroblasts have also been shown to play an important role in cardiomyocyte growth and expansion of the ventricular chambers during heart development. Although there are currently no cardiac fibroblast-restricted molecular markers, it is generally envisaged that the majority of the cardiac fibroblasts are derived from the proepicardium via epithelial-to-mesenchymal transformation. However, still relatively little is known about when and where the cardiac fibroblasts cells are generated, the lineage of each cell, and how cardiac fibroblasts move to reside in their final position throughout all four cardiac chambers. In this review, we summarize the present understanding regarding the function of Periostin, a useful marker of the noncardiomyocyte lineages, and its role during cardiac morphogenesis. Characterization of the cardiac fibroblast lineage and identification of the signals that maintain, expand and regulate their differentiation will be required to improve our understanding of cardiac function in both normal and pathophysiological states.

Identification of novel gene expression in healing fracture callus tissue by DNA microarray

Fracture healing requires controlled expression of thousands of genes. Only a small fraction of these genes have been isolated and fewer yet have been shown to play a direct role in fracture healing. The purpose of this study was threefold: (1) to develop a reproducible open femur model of fracture healing that produces consistent fracture calluses for subsequent RNA extraction, (2) to use this model to determine temporal expression patterns of known and unknown genes using DNA microarray expression profiling, and (3) to identify and validate novel gene expression in fracture healing. In the initial arm of the study, a total of 56 wild-type C57BL/6 mice were used. An open, stabilized diaphyseal femur fracture was created. Animals were killed at 1, 5, 7, 10, 14, 21, and 35 days after surgery and the femurs were harvested for analysis. At each time point, fractures were radiographed and sectioned for histologic analyses. Tissue from fracture callus at all stages following fracture yielded reproducibly large amounts of mRNA. Expression profiling revealed that genes cluster by function in a manner similar to the histologic stages of fracture healing. Based on the expression profiling of fracture tissue, temporal expression patterns of several genes known to be involved in fracture healing were verified. Novel expression of multiple genes in fracture callous tissue was also revealed including leptin and leptin receptor. In order to test whether leptin signaling is required for fracture repair, mice deficient in leptin or its receptor were fractured using the same model. Fracture calluses of mice deficient in both leptin or leptin receptor are larger than wild-type mice fractures, likely due to a delay in mineralization, revealing a previously unrecognized role of leptin signaling in fracture healing. This novel model of murine fracture repair is useful in examining both global changes in gene expression as well as individual signaling pathways, which can be used to identify specific molecular mechanisms of fracture healing.

Effect of β-alanyl-L-histidinato zinc on the differentiation of C2C12 cells

Although beta-alanyl-L-histidinato zinc (AHZ) can promote osteoblast differentiation, the molecular mechanism responsible is not fully understood. The purpose of this study was to determine the effect of AHZ on undifferentiating mesenchymal cells. C2C12, a typical pluripotential mesenchymal cell line, was used. The cells were cultured in 5% serum-containing medium to induce differentiation, either with or without the addition of AHZ. Cell lineage was determined by immunostaining of type II myosin heavy chains, alkaline phosphatase (ALPase) activity, mRNA expression of cellular phenotype-specific markers using semi-quantitative reverse transcriptase-polymerase chain reaction, and core binding factor alpha1/runt-related transcription factor-2 (Cbfa1/Runx2) protein synthesis using Western blot analysis. C2C12 cells cultured in the presence of AHZ were strongly inhibited from developing into myoblasts, and showed high ALPase activity that was approximately double that in the vehicle. The expression of mRNA for Cbfa1/Runx2, ALPase, Sox9 and type X collagen was increased markedly by the AHZ-stimulated medium, whereas that of desmin and MyoD mRNA was drastically decreased. AHZ increased Cbfa1/Runx2 protein expression substantially. These results provide clear evidence that AHZ converts the differentiation pathway of C2C12 cells to the osteoblast and/or chondroblast lineage.

Effect of enamel matrix derivative on the differentiation of C2C12 cells

BACKGROUND

Although enamel matrix derivative (EMD) can initiate de novo cementum and bone formation by stimulating and inducing differentiation of mesenchymal cells in the periodontal ligament, the molecular mechanism of this phenomenon is not fully understood. The purpose of this study was to determine the effect of EMD on the differentiation of pluripotential mesenchymal cells.

METHODS

A typical pluripotential mesenchymal cell line, C2C12, was used to clarify the effect of EMD on cell differentiation. The cells were cultured in 5% serum-containing medium to induce cell differentiation, either with or without the addition of EMD. Differentiation to myoblasts was analyzed by immunostaining of desmin and type II myosin heavy chains. Osteoblast differentiation was evaluated by measuring alkaline phosphatase (ALPase) activity. Furthermore, to verify the cell lineage after culture with EMD, mRNA expression of cellular phenotype-specific markers characterizing osteoblasts (ALPase and osteocalcin), chondroblasts (type X collagen), myoblasts (desmin and MyoD), and adipocytes (lipoprotein lipase) was studied using semiquantitative reverse transcription-polymerase chain reaction.

RESULTS

C2C12 cells cultured in differentiation medium without EMD altered their phenotype to myoblasts, exhibiting positive reactions to desmin and myosin heavy chains by immunological analysis. However, the cells cultured in the presence of EMD were strongly inhibited from developing into myoblasts, and showed high ALPase activity that was approximately 2 to 4 times greater than that of the vehicle. The mRNA expression of ALPase, osteocalcin, and type X collagen was increased markedly by the EMD-stimulated medium, whereas the expression of desmin, MyoD, and lipoprotein lipase was drastically decreased.

CONCLUSIONS

Our study provides clear evidence that EMD converts the differentiation pathway of C2C12 cells into the osteoblast and/or chondroblast lineage.

p21Cip-1/SDI-1/WAF-1 gene is involved in chondrogenic differentiation of ATDC5 cells in vitro

Development of skeletal cartilage is characterized with coupling growth arrest and cell differentiation. Here, to understand the cyclin-dependent kinase inhibitors involved in the progression of chondrogenic differentiation, we examined changes in the expression levels of cyclin-dependent kinase inhibitor members using mouse ATDC5 prechondrocytes as a widely used in vitro model of cartilage differentiation. Up-regulation of p21 and p27 mRNA was observed following a decrease in growth rate of prechondrocytes, and both transcripts subsequently accumulated during chondrogenic differentiation; p15, p18, and p19 mRNA, in contrast, did not change during differentiation. Only the up-regulation of p21 mRNA during differentiation was prevented by the continuous treatment of early chondrogenic inhibitor, parathyroid hormone, indicating a close correlation between differentiation and p21 induction in ATDC5 cells. Therefore, to examine the role of p21 during chondrogenesis, we established stable cell lines overexpressing full-length p21 antisense RNA in ATDC5. The reduction of endogenous p21 in these cell lines caused inhibition of early chondrogenic differentiation in ATDC5, indicating that p21 gene plays an important role in this process of the cells in vitro. Furthermore, the level of p21 protein and p21.CDK2 complexes transiently increased during differentiation, but not in undifferentiated cells, leading to a decrease in CDK2-associated kinase. However, differentiation-dependent expressed p21 protein was degraded by a proteasome-dependent pathway. Thus, the progression of chondrogenic differentiation requires down-regulation of CDK2-associated kinase with an increase in p21 protein and subsequent degradation of this protein by a proteasomal pathway.

HOXB7 overexpression promotes differentiation of C3H10T1/2 cells to smooth muscle cells

The presence of immature smooth muscle cells and ectopic tissues such as fully-formed bone in atherosclerotic lesions, may result from recapitulation of embryonic mechanisms in the artery wall. We hypothesized that expression of homeobox genes is triggered in atherogenesis and that these regulate proliferation and differentiation of multipotential progenitor cells along one or more specific lineages. We identified expression of the homeobox gene HOXB7 in clones of bovine aortic medial cells previously shown to be multipotent. HOXB7 was subsequently detected in human atherosclerotic plaques by RT-PCR and in situ hybridization. Expression was localized to areas adjacent to calcification and scattered in media and neointima, which may be reflective of a role in either osteoblastic or smooth muscle cell differentiation. To differentiate between these possibilities, we overexpressed HOXB7 in C3H10T1/2 cells, a multipotent cell line able to differentiate into vascular smooth muscle cells (SMC), as well as osteogenic and chondrogenic lineages. Results showed that overexpression of HOXB7 increased proliferation 3.5-fold, and induced an SMC-like cell morphology. In addition, expression of the early SMC markers calponin and SM22alpha increased 4-fold and 3-fold respectively by semi-quantitative RT-PCR. Expression of the intermediate SMC marker smooth muscle myosin heavy chain (SM-MHC) did not change. No increase in osteogenic or chondrogenic differentiation was detected, neither in the C3H10T1/2 cells nor in M2 cells, a bone marrow stromal cell line used to confirm this result. These findings suggest that HOXB7 plays a role in expansion of immature cell populations or dedifferentiation of mature cells.

Multipotency of a bone marrow stromal cell line, TBR31-2, established from ts-SV40 T antigen gene transgenic mice

Bone marrow is believed to contain multipotential stromal stem cells which can differentiate into osteoblasts, chondrocytes, adipocytes, and myoblasts (Prockop, D. J. Science 276, 71-74, 1997). Therefore, characterization and identification of the stem-like cell within the stromal cells are important to understand bone marrow function in relation to the hematopoietic microenvironment, and repair/regeneration of tissue defects. TBR31-2 cell, a bone marrow stromal cell line established from bone marrow of transgenic mice harboring temperature-sensitive (ts) simian virus (SV) 40T-antigen gene for immortality, is induced toward both adipocytic and osteogenic cells under conditions of the inactivation of T-antigen (Okuyama, R., Yanai, N., Obinata, M. Exp. Cell Res. 218, 424-429, 1995). In this work, using a semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) analysis, mRNA expressions of tissue-specific differentiation markers for adipocyte (lipoprotein lipase), osteoblast (type I collagen and osteocalcin), chondrocyte (type II and X collagen), and muscle cell (desmin) were examined during a long-term culture of the cell. In addition, histochemical studies showed the appearance of adipocytic, osteoblastic, chondrocytic, and muscle cells during this long-term culture. Thus, TBR31-2, which has characteristics of an undifferentiated cell, has the potential to express the multipotential cell lineages. These results indicated that a multipotential progenitor cell including potential to differentiate into a muscle cell and which is situated in the mesenchymal cell lineage was first obtained.

A short isoform of Col9a1 supports alveolar bone repair

Bone wound created in intramembranous alveolar bone heals without the formation of cartilage precursor tissue. However, the expression of cartilage collagen mRNAs has been suggested. In this report, we examined the expression and the potential role of type IX collagen in bone restoration and remodeling. The sequence specific polymerase chain reaction demonstrated the exclusive expression of short transcriptional isoform of alpha1(IX) collagen (Col9a1) in alveolar bone wound healing, while the long isoform of Col9a1 transcript was absent. Type IX collagen was immunolocalized in the preliminary matrix organized in granulation tissue before trabecular bone formation in tooth extraction socket. In Col9a1-null mutant mice, there were considerable variations in alveolar bone wound healing with the absence of or abnormally organized trabecular bone. Occasionally, unusual apposition of cortical-bone-like layers in bone marrow space was observed. The Col9a1-null mice indicated no growth retardation, and their facial and long bones maintained the normal size and shape. However, the primary spongiosa region of adult Col9a1 mutant mice showed an abnormal trabecular bone structure associated with abnormal immunostaining with the hypertrophic cartilage specific type X collagen antibody. These data suggest that type IX collagen short transcriptional variant is involved in the restoration and remodeling processes of trabecular bone.

Developmental regulation of mRNA species for types II, IX and XI collagens during mouse embryogenesis

Several techniques were used to study the co-ordination of mRNA levels for five constituent chains of cartilage collagen fibrils during mouse development. Short cDNA clones were first constructed for mouse and human alpha3(IX) and for mouse proalpha1(XI) collagen mRNA species. Northern analysis of developing mouse embryos revealed that the mRNA species for alpha1, alpha2 and alpha3 chains of type IX collagen peaked earlier than those for proalpha1(II) and proalpha1(XI) collagen chains. Quantification of these mRNA species by slot-blot hybridization confirmed this developmental regulation: the mRNA ratios for type II/type IX/type XI collagens changed from 5.7:1:0.6 (at embryonic day 12.5) to 10.6:1:0.9 (in newborn mice). However, the genes coding for the three chains of type IX collagen seemed to be under more co-ordinated regulation during mouse development. In addition to high mRNA levels in cartilages and the eye, low levels of type IX collagen transcripts were identified in brain and skin of newborn mouse using RNase protection and reverse transcriptase-PCR assays. Finally, hybridization in situ revealed identical tissue distributions of the three type IX collagen mRNA species during early chondrogenesis but somewhat more widespread expression of the alpha1(IX) and alpha3(IX) mRNA species during endochondral ossification at day 16.5 of embryonic development. These results suggest a relatively tight co-ordination of the alpha1(IX), alpha2(IX), and alpha3(IX) collagen mRNA species in chondrocytes, but a lack of co-ordination in several non-cartilaginous tissues.

Chondrogenic differentiation of clonal mouse embryonic cell line ATDC5 in vitro: differentiation-dependent gene expression of parathyroid hormone (PTH)/PTH-related peptide receptor

The regulatory role of parathyroid hormone (PTH)/PTH-related peptide (PTHrP) signaling has been implicated in embryonic skeletal development. Here, we studied chondrogenic differentiation of the mouse embryonal carcinoma-derived clonal cell line ATDC5 as a model of chondrogenesis in the early stages of endochondral bone development. ATDC5 cells retain the properties of chondroprogenitor cells, and rapidly proliferate in the presence of 5% FBS. Insulin (10 micrograms/ml) induced chondrogenic differentiation of the cells in a postconfluent phase through a cellular condensation process, resulting in the formation of cartilage nodules, as evidenced by expression of type II collagen and aggrecan genes. We found that differentiated cultures of ATDC5 cells abundantly expressed the high affinity receptor for PTH (Mr approximately 80 kD; Kd = 3.9 nM; 3.2 x 10(5) sites/cell). The receptors on differentiated cells were functionally active, as evidenced by a PTH-dependent activation of adenylate cyclase. Specific binding of PTH to cells markedly increased with the formation of cartilage nodules, while undifferentiated cells failed to show specific binding of PTH. Northern blot analysis indicated that expression of the PTH/PTHrP receptor gene became detectable at the early stage of chondrogenesis of ATDC5 cells, preceding induction of aggrecan gene expression. Expression of the PTH/PTHrP receptor gene was undetectable in undifferentiated cells. The level of PTH/PTHrP receptor mRNA was markedly elevated parallel to that of type II collagen mRNA. These lines of evidence suggest that the expression of functional PTH/PTHrP receptor is associated with the onset of chondrogenesis. In addition, activation of the receptor by exogenous PTH or PTHrP significantly interfered with cellular condensation and the subsequent formation of cartilage nodules, suggesting a novel site of PTHrP action.