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BACKGROUND: It has been established that skeletal growth is stunted in lead-exposed children. Because chondrogenesis is a seminal step during skeletal development, elucidating the impact of Pb on this process is the first step toward understanding the mechanism of Pb toxicity in the skeleton. OBJECTIVES: The aim of this study was to test the hypothesis that Pb alters chondrogenic commitment of mesenchymal cells and to assess the effects of Pb on various signaling pathways. METHODS: We assessed the influence of Pb on chondrogenesis in murine limb bud mesenchymal cells (MSCs) using nodule formation assays and gene analyses. The effects of Pb on transforming growth factor-[beta] (TGF-[beta]) and bone morphogenetic protein (BMP) signaling was studied using luciferase-based reporters and Western analyses, and luciferase-based assays were used to study cyclic adenosine monophosphate response element binding protein (CREB), [beta]-catenin, AP-1, and nuclear factor-kappa B (NF-[kappa]B) signaling. We also used an ectopic bone formation assay to determine how Pb affects chondrogenesis in vivo. RESULTS: Pb-exposed MSCs showed enhanced basal and TGF-[beta]/BMP induction of chondrogenesis, evidenced by enhanced nodule formation and up-regulation of Sox-9, type 2 collagen, and aggrecan, all key markers of chondrogenesis. We observed enhanced chondrogenesis during ectopic bone formation in mice preexposed to Pb via drinking water. In MSCs, Pb enhanced TGF-[beta] but inhibited BMP-2 signaling, as measured by luciferase reporter assays and Western analyses of Smad phosphorylation. Although Pb had no effect on basal CREB or Wnt/[beta]-catenin pathway activity, it induced NF[kappa]B signaling and inhibited AP-1 signaling. CONCLUSIONS: The in vitro and in vivo induction of chondrogenesis by Pb likely involves modulation and integration of multiple signaling pathways including TGF-[beta], BMP, AP-1, and NF[kappa]B. KEY WORDS: BMP signaling, chondrogenesis, lead, mesenchymal stem cells, TGF-[beta] signaling. Environ Health Perspect 115:1276-1282 (2007). doi:10.1289/ehp.10028 available via http://dx.doi.org/ [Online 3 July 2007], In spite of effort to reduce human exposure, lead toxicity continues to be a major environmental health concern in the United States and in other industrial countries. Although recent research [...]

The article discusses a controlled laboratory study on the effect of upper extremity assistance in patients with post-hip fracture during a sit-to-stand task (STS). Participants in the study include 28 elderly subjects, who were independent ambulators. The analysis of variance models were used to assess the lower extremity force applications. A decrease in the side-to-side symmetry of lower extremity during a STS task had been observed.

The skeletal system is an important target for lead toxicity. One of the impacts of lead in the skeleton, the inhibition of axial bone development, is likely due to its effect on the normal progression of chondrocyte maturation that is central to the process of endochondral ossification. Since little is known about the effect of lead on chondrocyte function/maturation, its impact on (1) growth factor-induced proliferation, (2) expression of maturation-specific markers type X collagen and BMP-6, and (3) the activity of AP-1 and NF-κB was examined in chick growth plate and sternal chondrocyte models. Exposure to lead alone (1–30 μM) resulted in a dose-dependent inhibition of thymidine incorporation in growth plate chondrocytes. Lead also blunted the stimulation of thymidine incorporation by parathyroid hormone-related peptide (PTHrP) and transforming growth factor-β1 (TGF-β1), two critical regulators of chondrocyte maturation. Lead (1 and 10 μM), TGF-β1 (3 ng/ml) and PTHrP (10−7 M) all significantly inhibited the expression of type X collagen, a marker of chondrocyte terminal differentiation. However, when in combination, lead completely reversed the inhibition of type X collagen by PTHrP and TGF-β1. The effect of lead on BMP-6, an inducer of terminal differentiation, was also examined. Independently, lead and TGF-β1 were without effect on BMP-6 expression, but PTHrP significantly suppressed it. Comparatively, lead did not alter PTHrP-mediated suppression of BMP-6, but in combination with TGF-β1, BMP-6 expression was increased 3-fold. To determine if lead effects on signaling might play a role in facilitating these events, the impact of lead on NF-κB and AP-1 signaling was assessed using luciferase reporter constructs in sternal chondrocytes. Lead had no effect on the AP-1 reporter, but it dose-dependently inhibited the NF-κB reporter. PTHrP, which signals through AP-1, did not activate the NF-κB reporter and did not affect inhibition of this reporter by lead. In contrast, PTHrP activation of the AP-1 reporter was dose-dependently enhanced by lead. These findings, which establish that chondrocytes are important targets for lead toxicity, suggest that the effects of lead on bone growth are derived from its impact on the modulation of chondrocyte maturation by growth factors and second messenger signaling responses. [Copyright &y& Elsevier]

Aseptic loosening of prosthetic implants remains a serious orthopaedic problem and the greatest limitation to total joint arthroplasty. Central to the etiology of aseptic loosening is periprosthetic osteolysis at the bone–implant interface, which is caused by wear debris-induced inflammation. This inflammation produces the critical osteoclast differentiation factor RANKL, which directly stimulates osteoclastogenesis and osteoclastic bone resorption. A dominant factor known to counteract this process is the natural RANKL receptor antagonist protein OPG. Here we explore the potential of ex vivo OPG gene therapy for aseptic loosening by evaluating the efficacy of stably transfected fibroblast-like synoviocytes (FLS) expressing OPG in preventing wear debris-induced osteoclastogenesis, in a mouse calvaria model. Although the stably transfected fibroblasts produced small amounts of OPG (0.3 ng/ml/72 h/106 cells), this protein was very effective in preventing osteoclastic resorption as determined in a bone wafer assay. More importantly, implantation of 107 FLS–OPG, together with 30 mg of Ti wear debris, onto the calvaria of mice, completely inhibited osteoclastogenesis 3 days after surgery. Animals given FLS–LacZ control cells, which persisted for 3 days as determined by X-gal staining, together with the Ti particles, had a 6-fold increase in osteoclastogenesis compared to controls without Ti. This increased osteoclastogenesis was completely inhibited by the FLS–OPG, as osteoclast numbers in the calvaria of these animals were similar to that seen in the SHAM controls. [Copyright &y& Elsevier]

Osteoid osteoma is a benign bone forming neoplasm that is characterized by its small size (less than 2 cm), self-limited growth, and the tendency to cause extensive reactive changes in the adjacent tissue. The lesion classically presents with severe pain at night that is dramatically relieved by NSAIDs. The tumor has been shown to express very high levels of prostaglandins, particularly PGE2 and PGI2. The high local levels of these prostaglandins are presumed to be the cause of the intense pain seen in patients with this lesion. One generally accepted form of treatment is the prolonged use of NSAIDs. Since the cyclooxygenases are thought to be the source of these prostaglandins, and the central target of NSAIDs, we evaluated the expression of cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2) in osteoid osteoma tissues from patients following surgery. In the 12 specimens examined we found that the tumor osteoblasts had strong immunohistochemical staining for COX-2, while the staining in the surrounding host osteoblasts in the reactive bone was scant. Significant COX-1 staining was also detected in both tumor and host osteoblasts. For comparison we examined the COX expression in human fracture callus, fibrous dysplasia, osteoblastoma, osteofibrous dysplasia, and myositis ossificans. With the exception of fracture callus, very limited amounts of COX-2 could be detected in these tissues. Taken together, we conclude that the increased production of prostaglandins by osteoid osteomas implicates that COX-2 is one of the mediators of this condition. These findings suggest that the newly selective COX-2 inhibitors could be used to more safely treat osteoid osteomas. [Copyright &y& Elsevier]