The P2X7 nucleotide receptor is an ATP-gated ion channel expressed widely in cells of hematopoietic origin. Our purpose was to explore the involvement of the P2X7 receptor in bone development and remodeling by characterizing the phenotype of mice genetically modified to disrupt the P2X7 receptor [knockout (KO)]. Femoral length did not differ between KO and wild-type (WT) littermates at 2 or 9 months of age, indicating that the P2X7 receptor does not regulate longitudinal bone growth. However, KO mice displayed significant reduction in total and cortical bone content and periosteal circumference in femurs, and reduced periosteal bone formation and increased trabecular bone resorption in tibias. Patch clamp recording confirmed expression of functional P2X7 receptors in osteoclasts from WT but not KO mice. Osteoclasts were present in vivo and formed in cultures of bone marrow from KO mice, indicating that this receptor is not essential for fusion of osteoclast precursors. Functional P2X7 receptors were also found in osteoblasts from WT but not KO mice, suggesting a direct role in bone formation. P2X7 receptor KO mice demonstrate a unique skeletal phenotype that involves deficient periosteal bone formation together with excessive trabecular bone resorption. Thus, the P2X7 receptor represents a novel therapeutic target for the management of skeletal disorders such as osteoporosis.

Members of the transforming growth factor-␤ (TGF-␤)superfamily of growth and differentiation factors have been identified in a wide variety of organisms, ranging from invertebrates to mammals. Bone morphogenetic proteins (BMPs) constitute a subgroup of proteins belonging to the TGF-␤ superfamily. BMPs were initially identified by their ability to induce endochondral bone formation at ectopic sites, suggesting a critical role for this family in development and regeneration of the skeleton. They are also expressed at a variety of nonskeletal sites during development, suggesting possible extraskeletal roles for these proteins. We cloned a novel member of the BMP family that is expressed at high levels in the placenta and the prostate and that we have designated as prostate-derived factor (PDF). Based on cDNA sequence analysis, the predicted PDF protein contains two cysteines in addition to the seven conserved cysteines that are the hallmark of the members of the TGF-␤ superfamily. In addition, Northern blot hybridization to poly(A) ؉ RNA showed low levels of expression in the kidney and pancreas. We further characterized the expression of this member of the BMP family by in situ hybridization and immunohistochemistry. These results show high expression in the terminal villae of the placenta. The expression of the protein as visualized by immunohistochemistry shows an expression pattern identical to that of the message in the terminal villae of the placenta. In day 18 rat embryos, protein expression was also seen in the skin and in the cartilaginous tissue of developing skeleton. Orchidectomy and dihydrotestosterone treatment of rats revealed that PDF expression is regulated by androgens in the prostate. In addition, subcutaneous implantation of recombinant PDF induced cartilage formation and the early stages of endochondral bone formation. These data indicate that PDF has a functional relationship to the BMPs.

We have previously described osteoblast/osteocyte factor 45 (OF45), a novel bone-specific extracellular matrix protein, and demonstrated that its expression is tightly linked to mineralization and bone formation. In this report, we have cloned and characterized the mouse OF45 cDNA and genomic region. Mouse OF45 (also called MEPE) was similar to its rat orthologue in that its expression was increased during mineralization in osteoblast cultures and the protein was highly expressed within the osteocytes that are imbedded within bone. To further determine the role of OF45 in bone metabolism, we generated a targeted mouse line deficient in this protein. Ablation of OF45 resulted in increased bone mass. In fact, disruption of only a single allele of OF45 caused significantly increased bone mass. In addition, knockout mice were resistant to aging-associated trabecular bone loss. Cancellous bone histomorphometry revealed that the increased bone mass was the result of increased osteoblast number and osteoblast activity with unaltered osteoclast number and osteoclast surface in knockout animals. Consistent with the bone histomorphometric results, we also determined that OF45 knockout osteoblasts produced significantly more mineralized nodules in ex vivo cell cultures than did wild type osteoblasts. Osteoclastogenesis and bone resorption in ex vivo cultures was unaffected by OF45 mutation. We conclude that OF45 plays an inhibitory role in bone formation in mouse.The constant modulation of the balance between skeletal strength and mineral availability in bone is effected by competing cell types in response to physiological needs. Osteoblasts produce, organize, and mineralize bone matrix in forming bone. Osteoclasts break down matrix by forming a lytic pocket in which bone is degraded and calcium is released. The generation and activity of these cell types is tightly regulated to provide equilibrium between formation and resorption and, thereby, an appropriate balance of strength and mineral release. Under certain conditions, such as aging, postmenopausal estrogen deficiency, or some pathophysiological states, there can exist an imbalance between bone resorption and bone formation. As a result, skeletal mass and strength are compromised and osteoporotic fractures can occur in the afflicted individuals.Bone is produced by the organization and mineralization of the extracellular matrix produced by osteoblasts. The major component of the extracellular matrix of these cells is Type I collagen, which functions as a scaffold for new bone. In addition, non-collagenous matrix proteins have been identified that influence the operations of bone turnover, formation, and repair. These proteins are generally acidic and highly posttranslationally modified by phosphorylation, glycosylation, or sulfation (1).Targeted deletion of extracellular matrix genes in mice has been a useful method to determine the in vivo functions of several matrix proteins. For example, osteocalcin is an abundant gamma carboxyl glutamic acid-containing bone matrix...

Bone is accrued and maintained primarily through the coupled actions of bone-forming osteoblasts and bone-resorbing osteoclasts. Cumulative in vitro studies indicated that proline-rich tyrosine kinase 2 (PYK2) is a positive mediator of osteoclast function and activity. However, our investigation of PYK2؊/؊ mice did not reveal evidence supporting an essential function for PYK2 in osteoclasts either in vivo or in culture. We find that PYK2؊/؊ mice have high bone mass resulting from an unexpected increase in bone formation. Consistent with the in vivo findings, mouse bone marrow cultures show that PYK2 deficiency enhances differentiation and activity of osteoprogenitor cells, as does expressing a PYK2-specific short hairpin RNA or dominantly interfering proteins in human mesenchymal stem cells. Furthermore, the daily administration of a small-molecule PYK2 inhibitor increases bone formation and protects against bone loss in ovariectomized rats, an established preclinical model of postmenopausal osteoporosis. In summary, we find that PYK2 regulates the differentiation of early osteoprogenitor cells across species and that inhibitors of the PYK2 have potential as a bone anabolic approach for the treatment of osteoporosis.human mesenchymal stem cell ͉ osteoclast ͉ osteoblast P roline-rich tyrosine kinase 2 (PYK2) and focal adhesion kinase (FAK) are nonreceptor tyrosine kinases, and together they constitute the focal adhesion kinase subfamily (1). Unlike FAK, PYK2 expression is relatively restricted, with highest levels in the brain and the hematopoietic system. PYK2Ϫ/Ϫ mice have been described previously and appear normally developed (2, 3). Characterization of the immune system of PYK2Ϫ/Ϫ animals revealed the absence of marginal zone B cells along and abnormal T cell-independent type II responses (2), as well as altered macrophage morphology, adhesion, and migration (3).Although PYK2 is expressed in both bone-forming osteoblasts and bone-resorbing osteoclasts, the skeletal phenotype of PYK2Ϫ/Ϫ mice has not been described. In vitro studies pointed to a positive role for PYK2 in osteoclast maturation and bone resorption. PYK2 localizes to the podosomes of osteoclasts (4), and, upon integrin binding, cell attachment, and actin ring formation, PYK2 associates with a variety of proteins including p130 CAS (5), Src (4), Cbl (6), integrins (4), gelsolin (7), and paxillin (8). Antisense depletion of PYK2 (9), but not the expression of a kinase inactive dominant negative mutant (10), blocked osteoclast spreading and bone resorption, indicating that PYK2 catalytic activity may be dispensable. The in vitro effects of bone anabolic stimuli suggested that PYK2 might have a positive role in osteoblasts as well. Treatment of osteoblast cells with fluoroaluminate led to increased PYK2 autophosphorylation, Src association, and kinase activity (11) and was associated with increased cell attachment and spreading (12). Likewise, in an anabolic model of mechanical loading, PYK2 autophosphorylation and kinase activity were stimulated in o...

Developed a simple esterification route to obtain lignin derivatives with tunable Tg's and low E-factor reactions.