Biomedical subjects

Reem A Kanaan

Publications and source records attributed to Reem A Kanaan.

5 recordsLinked to original sources

PubMed2007

Connective tissue growth factor (CTGF) acts as a downstream mediator of TGF-beta1 to induce mesenchymal cell condensation.

Mesenchymal cell (MC) condensation or the aggregation of MCs precedes chondrocyte differentiation and is required for subsequent cartilage formation during endochondral ossification. In this study, we used micromass cultures of C3H10T1/2 cells as an in vitro model system for studying MC condensation and the events important for this process. Transforming growth factor beta1 (TGF-beta1) served as the initiator of MC condensation in our model system and we were interested in determining whether CTGF functions as a downstream mediator of TGF-beta1. CTGF is a matricellular protein that has been found to be expressed in MC condensations and in the perichondrium. Micromass cultures of C3H10T1/2 cells condensed under TGF-beta1 stimulation concomitant with dramatic up-regulation of CTGF mRNA and protein levels. CTGF silencing by either CTGF siRNA or CTGF antisense oligonucleotide approaches showed that TGF-beta1-induced condensation was CTGF dependent. Furthermore, silencing of CTGF expression resulted in significant reductions in cell proliferation and migration, events that are crucial during MC condensation. In addition, up-regulation of Fibronectin (FN) and suppression of Sox9 expression by TGF-beta1 was also found to be mediated by CTGF. Immunofluorescence of developing mouse vertebrae showed that CTGF, TGF-beta1 and FN were co-expressed in condensations of MCs, while Sox9 expression was low at this stage. During subsequent chondrogenesis, Sox9 expression was high in chondrocytes while CTGF expression was limited to the perichondrium. Thus, CTGF is an essential downstream mediator of TGF-beta1-induced MC condensation through its effects on cell proliferation and migration. CTGF is also involved in up-regulating FN and suppressing Sox9 expression during TGF-beta1 induced MC condensation.

Animals↗

PubMed2006

The role of connective tissue growth factor in skeletal growth and development.

Connective tissue growth factor (CTGF) is a secreted, extracellular matrix-associated protein that regulates diverse cellular functions in different cell types. CTGF gene belongs to a larger CCN gene family that also includes Cyr61 and NOV. It modulates many cellular functions, including proliferation, migration, adhesion, and extracellular matrix production, and it is involved in many biological and pathological processes. CTGF has special importance in skeletal development. During Meckel's cartilage development, CTGF acts as a down-stream molecule of TGFbeta to stimulate cell-cell interactions and the expression of condensation-associated genes. CTGF promotes endochondral ossification and articular cartilage regeneration. During the healing of experimental bone fracture, CTGF was expressed in periosteal cells and hypertrophic chondrocytes. It promotes the proliferation of chondrocytes and osteoblasts. CTGF is a down-stream mediator for prostaglandin E2 (PGE2) in osteoblast-induced proliferation. It also regulates signaling through the Wnt pathway, in accord with its ability to bind to the Wnt co-receptor LDL receptor-related protein 6 (LRP6). Constitutive expression of CTGF was shown to inhibit both BMP-9- and Wnt3A-induced osteogenic differentiation.

Animals↗

PubMed2006

Transforming growth factor beta1, bone connection.

Transforming Growth Factor beta1 (TGF beta1) exerts its functions both during embryogenesis, and in adult organism. TGF beta1 regulates cell proliferation, differentiation, motility and apoptosis. TGF beta1 is the most abundant growth factor in human bone. It is implicated in the pathogenesis of several bone diseases such as otosclerosis. During embryonic development, TGF beta1 plays a role in the migration of cells to the site of future skeletogenesis, the epithelial-mesenchymal interaction, and the formation of cellular condensations which dictates the general shape of the future skeletal elements. It also influences normal skeleton development by playing a critical role in inducing mesenchymal cell differentiation to either chondrocytes or osteoblasts. During Adult life, TGF beta1 has an influence on the maintenance of normal skeleton by playing a critical role on bone-forming cell namely, the osteoblast. TGF beta1 affects osteoblast differentiation, matrix formation, and mineralization. In MC3T3-E1 osteoblast-like cell line TGF beta1 inhibited the expression of the Runx2 and osteocalcin osteoblast differentiation markers. It interacts with many will known pathways in osteoblasts biology, such as Prostaglandin E2, Parathyroid hormone related peptide and Wnt-beta-catenin pathways. TGF beta1 exerts effects on osteocytes too. Treatment of pre-osteocytes with TGF alpha1 decreased cell death. Studied performed on osteoclast revealed that it inhibits both their proliferation and activity. This review briefly discusses the relation between this cytokine and the skeleton development and maintenance.

Animals↗

PubMed2003

Expression of connective tissue growth factor in bone: its role in osteoblast proliferation and differentiation in vitro and bone formation in vivo.

Connective tissue growth factor (CTGF) is a secreted, extracellular matrix-associated signaling protein that regulates diverse cellular functions. In vivo, CTGF is expressed in many tissues with highest levels in the kidney and brain. The purpose of this study was twofold; first, to localize CTGF in normal bone in vivo during growth and repair, and second, to examine CTGF expression and function in primary osteoblast cultures in vitro and test its effect on bone formation in vivo. Northern and Western blot analyses confirmed that CTGF is expressed in normal long bones during the period of growth or modeling. In situ hybridization and immunohistochemical analysis demonstrated intense staining for CTGF mRNA and protein in osteoblasts lining metaphyseal trabeculae. Examination of CTGF expression in the fracture callus demonstrated that it was primarily localized in osteoblasts lining active, osteogenic surfaces. In primary osteoblast cultures, CTGF mRNA levels demonstrated a bimodal pattern of expression, being high during the peak of the proliferative period, abating as the cells became confluent, and increasing to peak levels and remaining high during mineralization. This pattern suggests that CTGF may play a role in osteoblast proliferation and differentiation as previously demonstrated for fibroblasts and chondrocytes. Treatment of primary osteoblast cultures with anti-CTGF neutralizing antibody caused a dose-dependent inhibition of nodule formation and mineralization. Treatment of primary osteoblast cultures with recombinant CTGF (rCTGF) caused an increase in cell proliferation, alkaline phosphatase activity, and calcium deposition, thereby establishing a functional connection between CTGF and osteoblast differentiation. In vivo delivery of rCTGF into the femoral marrow cavity induced osteogenesis that was associated with increased angiogenesis. This study clearly shows that CTGF is important for osteoblast development and function both in vitro and in vivo.

Animals↗

PubMed2003

Anti-osteoactivin antibody inhibits osteoblast differentiation and function in vitro.

Osteoactivin (OA) is a novel protein identified by mRNA differential display using bone from osteopetrotic versus normal rats. Bioinformatic analysis showed that OA cDNA has an open reading frame of 1716 bp encoding a protein of 572 aa, the first 21 aa constitute a signal peptide. OA sequence analysis also demonstrated 13 putative N-glycosylation sites suggestive of a heavily glycosylated protein. In this study, we localized OA protein in primary osteoblast culture by immunofluorescent staining and Western blot analysis. Primary osteoblast cultures pass through three stages: proliferation from day 1 to 7, matrix formation from day 7 to 14, and matrix mineralization from day 14 to 21. OA protein was detected at all stages examined, with maximal expression at 3 weeks when osteoblasts are terminally differentiated. Using the Chariot transfection reagent as a vehicle to deliver anti-OA antibody into the cells, we demonstrated that anti-OA antibody significantly inhibited osteoblast differentiation markers, including alkaline phosphatase activity, nodule formation, osteocalcin production, and calcium deposition, without affecting cell proliferation or viability. These data suggest that OA is an osteoblast-related protein that plays an important role in the regulation of osteoblast differentiation and function.

Alkaline Phosphatase↗