Physiological role of bone morphogenetic proteins in osteogenesis.
Explore the source record for details and available documents.
Animals↗
Biomedical subjects
Fumitaka Kugimiya
Publications and source records attributed to Fumitaka Kugimiya.
Mechanism of osteogenic induction by FK506 via BMP/Smad pathways.
FK506 is an immunosuppressant that exerts effects by binding to FK506-binding protein 12 (FKBP12). Recently, FK506 has also been reported to promote osteogenic differentiation when administered locally or in vitro in combination with bone morphogenetic proteins (BMPs), although the underlying mechanism remains unclarified. The present study initially showed that FK506 alone at a higher concentration (1muM) induced osteogenic differentiation of mesenchymal cell lines, which was suppressed by adenoviral introduction of Smad6. FK506 rapidly activates the BMP-dependent Smads in the absence of BMPs, and the activation was blocked by Smad6. Overexpression of FKBP12, which was reported to block the ligand-independent activation of BMP type I receptor A (BMPRIA), suppressed Smad signaling induced by FK506, but not that induced by BMP2. BMPRIA and FKBP12 bound to each other, and this binding was suppressed by FK506. These data suggest that FK506 promotes osteogenic differentiation by activating BMP receptors through interacting with FKBP12.
Animals↗
Involvement of endogenous bone morphogenetic protein (BMP) 2 and BMP6 in bone formation.
Although accumulated evidence has shown the bone anabolic effects of bone morphogenetic proteins (BMPs) that were exogenously applied in vitro and in vivo, the roles of endogenous BMPs during bone formation remain to be clarified. This study initially investigated expression patterns of BMPs in the mouse long bone and found that BMP2 and BMP6 were the main subtypes expressed in hypertrophic chondrocytes that induce endochondral bone formation. We then examined the involvement of the combination of these BMPs in bone formation in vivo by generating the compound-deficient mice (Bmp2+/-;Bmp6-/-). Under physiological conditions, these mice exhibited moderate growth retardation compared with the wild-type (WT) littermates during the observation period up to 52 weeks of age. Both the fetal and adult compound-deficient mice showed a reduction in the trabecular bone volume with suppressed bone formation, but normal bone resorption, whereas the single deficient mice (Bmp2+/- or Bmp6-/-) did not. When a fracture was created at the femoral midshaft and the bone healing was analyzed, the endochondral bone formation, but not intramembranous bone formation, was impaired by the compound deficiency. In the cultures of bone marrow cells, however, there was no difference in osteogenic differentiation between WT and compound-deficient cells in the presence or absence of the exogenous BMP2. We thus concluded that endogenous BMP2 and BMP6 cooperatively play pivotal roles in bone formation under both physiological and pathological conditions.
Animals↗
The canonical Wnt signaling pathway promotes chondrocyte differentiation in a Sox9-dependent manner.
To better understand the role of the canonical Wnt signaling pathway in cartilage development, we adenovirally expressed a constitutively active (ca) or a dominant negative (dn) form of lymphoid enhancer factor-1 (LEF-1), the main nuclear effector of the pathway, in undifferentiated mesenchymal cells, chondrogenic cells, and primary chondrocytes, and examined the expression of markers for chondrogenic differentiation and hypertrophy. caLEF-1 and LiCl, an activator of the canonical pathway, promoted both chondrogenic differentiation and hypertrophy, whereas dnLEF-1 and the gene silencing of beta-catenin suppressed LiCl-promoted effects. To investigate whether these effects were dependent on Sox9, a master regulator of cartilage development, we stimulated Sox9-deficient ES cells with the pathway. caLEF-1 and LiCl promoted both chondrogenic differentiation and hypertrophy in wild-type, but not in Sox9-deficient, cells. The response of Sox9-deficient cells was restored by the adenoviral expression of Sox9. Thus, the canonical Wnt signaling pathway promotes chondrocyte differentiation in a Sox9-dependent manner.
Animals↗
Mutation in cGMP-dependent protein kinase II causes dwarfism in a rat mutant KMI through uncoupling of proliferation and differentiation of chondrocytes.
Explore the source record for details and available documents.
Animals↗
Involvement of cyclic guanosine monophosphate-dependent protein kinase II in chondrocyte hypertrophy during endochondral ossification.
During vertebrate skeletal development, the appendicular skeleton forms through endochondral ossification, which involves the intricately regulated multistep differentiation of mesenchymal cells. During this process, mesenchymal condensations initially differentiate into chondrocytes. Then chondrocytes in the center further differentiate into hypertrophic chondrocytes. Hypertrophic chondrocytes express a number of osteogenic factors and induce bone formation. Although numerous studies have provided novel insights into the regulation and function of cartilage development, little is known about the intracellular signaling pathways regulating chondrocyte hypertrophy. Recent study revealed that cyclic guanosine monophosphate (cGMP)-dependent protein kinase II (cGKII) coupled the stop of proliferation and the start of hypertrophic differentiation of chondrocytes. Herein, we review the molecular mechanism of regulation of chondrocyte hypertrophy by cGKII and the interaction between cGKII and other signaling pathways.
Journal Article↗
Cyclic GMP-dependent protein kinase II is a molecular switch from proliferation to hypertrophic differentiation of chondrocytes.
The Komeda miniature rat Ishikawa (KMI) is a naturally occurring mutant caused by an autosomal recessive mutation mri, which exhibits longitudinal growth retardation. Here we identified the mri mutation as a deletion in the rat gene encoding cGMP-dependent protein kinase type II (cGKII). KMIs showed an expanded growth plate and impaired bone healing with abnormal accumulation of postmitotic but nonhypertrophic chondrocytes. Ex vivo culture of KMI chondrocytes reproduced the differentiation impairment, which was restored by introducing the adenovirus-mediated cGKII gene. The expression of Sox9, an inhibitory regulator of hypertrophic differentiation, persisted in the nuclei of postmitotic chondrocytes of the KMI growth plate. Transfection experiments in culture systems revealed that cGKII attenuated the Sox9 functions to induce the chondrogenic differentiation and to inhibit the hypertrophic differentiation of chondrocytes. This attenuation of Sox9 was due to the cGKII inhibition of nuclear entry of Sox9. The impaired differentiation of cultured KMI chondrocytes was restored by the silencing of Sox9 through RNA interference. Hence, the present study for the first time shed light on a novel role of cGKII as a molecular switch, coupling the cessation of proliferation and the start of hypertrophic differentiation of chondrocytes through attenuation of Sox9 function.
Animals↗
[BMP and bone formation].
Bone Morphogenetic Proteins (BMPs) are secreted proteins that represent a group of the transforming growth factor-beta. BMPs were identified as molecules that induce ectopic bone formation in muscles of mice. The homo- or heterodimetric BMP proteins, which bind to serine/threonine protein-kinase receptor and activate smad and p38MAPK signal transductions, function as potent osteogenic factors. In vivo, it is not clear which BMPs play crucial roles in regulating osteogenesis. Clinical uses of rhBMP-2 and rhBMP-7 have been performed, but we need numerous rhBMPs, which is very expensive, to induce osteogenesis in humans.
Animals↗
[Regulation of chondrogenesis by PTH/PTHrP signaling].
During endo chondral bone development, parathyroid hormone-related peptide(PTHrP)is expressed by the perichondrial cells and proliferating chondrocytes in the periarticular region. PTHrP mRNA expression is increased by Indian Hedgehog(Ihh), which is expressed by prehypertrophic and hypertrophic chondrocytes. PTHrP acts directly on columnar proliferating chondrocytes to prevent hypertrophic differentiation. This prevention indirectly results in less Ihh signaling by decreasing the number of prehypertrophic and hypertrophic chondrocytes expressing Ihh. This negative feedback loop serves to regulate the balance of differentiation and proliferation of growth plate chondrocytes. Gs, cAMP, Sox9 and CREB seem to act downstream of PTHrP, while Patched, smoothened, Gli appear to act downstream of Ihh.
English Abstract↗