Tooth eruption depends on the presence of osteoclasts to create an eruption pathway through the alveolar bone. In diseases where osteoclast formation, or function is reduced, such as the various ...types of osteopetrosis, tooth eruption is affected. Diseases in which osteoclast formation or activity is increased, such as familiar expansile osteolysis and Paget's disease, are associated with dental abnormalities such as root resorption and premature tooth loss. Less is known about the origin of the dental problems in these conditions as there are no rodent models of these diseases as yet. In this short review, the genes currently known to be mutated in human osteoclast diseases will be reviewed and, where known, the effect of osteoclast dysfunction on dental development described. It will focus on human conditions and only mention rodent disease where no clear data in the human are available.
Conflicting results have been reported on the detection of paramyxovirus transcripts in Paget's disease, and a possible explanation is differences in the sensitivity of RT‐PCR methods for detecting ...virus. In a blinded study, we found no evidence to suggest that laboratories that failed to detect viral transcripts had less sensitive RT‐PCR assays, and we did not detect measles or distemper transcripts in Paget's samples using the most sensitive assays evaluated.
Introduction: There is conflicting evidence on the possible role of persistent paramyxovirus infection in Paget's disease of bone (PDB). Some workers have detected measles virus (MV) or canine distemper virus (CDV) transcripts in cells and tissues from patients with PDB, but others have failed to confirm this finding. A possible explanation might be differences in the sensitivity of RT‐PCR methods for detecting virus. Here we performed a blinded comparison of the sensitivity of different RT‐PCR–based techniques for MV and CDV detection in different laboratories and used the most sensitive assays to screen for evidence of viral transcripts in bone and blood samples derived from patients with PDB.
Materials and Methods: Participating laboratories analyzed samples spiked with known amounts of MV and CDV transcripts and control samples that did not contain viral nucleic acids. All analyses were performed on a blinded basis.
Results: The limit of detection for CDV was 1000 viral transcripts in three laboratories (Aberdeen, Belfast, and Liverpool) and 10,000 transcripts in another laboratory (Manchester). The limit of detection for MV was 16 transcripts in one laboratory (NIBSC), 1000 transcripts in two laboratories (Aberdeen and Belfast), and 10,000 transcripts in two laboratories (Liverpool and Manchester). An assay previously used by a U.S.‐based group to detect MV transcripts in PDB had a sensitivity of 1000 transcripts. One laboratory (Manchester) detected CDV transcripts in a negative control and in two samples that had been spiked with MV. None of the other laboratories had false‐positive results for MV or CDV, and no evidence of viral transcripts was found on analysis of 12 PDB samples using the most sensitive RT‐PCR assays for MV and CDV.
Conclusions: We found that RT‐PCR assays used by different laboratories differed in their sensitivity to detect CDV and MV transcripts but found no evidence to suggest that laboratories that previously failed to detect viral transcripts had less sensitive RT‐PCR assays than those that detected viral transcripts. False‐positive results were observed with one laboratory, and we failed to detect paramyxovirus transcripts in PDB samples using the most sensitive assays evaluated. Our results show that failure of some laboratories to detect viral transcripts is unlikely to be caused by problems with assay sensitivity and highlight the fact that contamination can be an issue when searching for pathogens by sensitive RT‐PCR–based techniques.
Endothelial nitric oxide synthase (eNOS) has long been held responsible for NO production by mechanically stimulated osteoblasts, but this has recently been disputed. We investigated whether one of ...the three known NOS isoforms is essential for NO production by mechanically stimulated osteoblasts in vitro and revisited the bone phenotype of the eNOS
−/−
mouse. Osteoblasts, obtained as outgrowths from mouse calvaria or long bones of wild-type (WT), eNOS
−/−
, inducible NOS
−/−
(iNOS
−/−
), or neuronal NOS
−/−
(nNOS
−/−
) mice, were subjected to mechanical stimulation by means of pulsating fluid flow (PFF); and NO production was determined. Tibiae and femora from 8-week-old mice were subjected to μCT and three-point bending tests. Deletion of single NOS isoforms did not lead to significant upregulation of alternate isoforms in cultured osteoblasts from WT, eNOS
−/−
, iNOS
−/−
, or nNOS
−/−
mice. Expression of eNOS mRNA in osteoblasts was below our detection limit, and no differences in growth between WT and eNOS
−/−
osteoblasts were found. PFF increased NO production by approximately fourfold in WT and eNOS
−/−
osteoblasts and significantly stimulated NO production in iNOS
−/−
and nNOS
−/−
osteoblasts. Tibiae and femora from WT and eNOS
−/−
mice showed no difference in bone volume and architecture or in mechanical parameters. Our data suggest that mechanical stimuli can enhance NO production by cultured osteoblasts singly deficient for each known NOS isoform and that lack of eNOS does not significantly affect bone mass and strength at 8 weeks of age. Our data challenge the notion that eNOS is a key effector of mechanically induced bone maintenance.
Nitric oxide (NO) is produced by NO synthase (NOS) and plays an important role in the regulation of bone cell function. The endothelial NOS isoform is essential for normal osteoblast function, ...whereas the inducible NOS isoform acts as a mediator of cytokine effects in bone. The role of the neuronal isoform of NOS (nNOS) in bone has been studied little thus far. Therefore, we investigated the role of nNOS in bone metabolism by studying mice with targeted inactivation of the nNOS gene. Bone mineral density (BMD) was significantly higher in nNOS knockout (KO) mice compared with wild-type controls, particularly the trabecular BMD (P < 0.01). The difference in BMD between nNOS KO and control mice was confirmed by histomorphometric analysis, which showed a 67% increase in trabecular bone volume in nNOS KO mice when compared with controls (P < 0.001). This was accompanied by reduced bone remodeling, with a significant reduction in osteoblast numbers and bone formation surfaces and a reduction in osteoclast numbers and bone resorption surfaces. Osteoblasts from nNOS KO mice, however, showed increased levels of alkaline phosphatase and no defects in proliferation or bone nodule formation in vitro, whereas osteoclastogenesis was increased in nNOS KO bone marrow cultures. These studies indicate that nNOS plays a hitherto unrecognized but important physiological role as a stimulator of bone turnover. The low level of nNOS expression in bone and the in vitro behavior of nNOS KO bone cells indicate that these actions are indirect and possibly mediated by a neurogenic relay.
It has recently been suggested that bisphosphonates may have direct antitumor effects in vivo, in addition to their therapeutic antiresorptive properties. Bisphosphonates can inhibit proliferation ...and cause apoptosis in human myeloma cells in vitro. In macrophages, bisphosphonate-induced apoptosis was recently found to be a result of inhibition of the mevalonate (MVA) pathway. The aim of this study was to determine whether bisphosphonates also affect human myeloma cells in vitro by inhibiting the MVA pathway. Incadronate and mevastatin (a known inhibitor of the MVA pathway) caused apoptosis in JJN-3 myeloma cells and inhibited cell proliferation. Geranylgeraniol and farnesol prevented incadronate-induced apoptosis and had a partial effect on cell cycle arrest. MVA and geranylgeraniol prevented mevastatin-induced apoptosis and inhibition of proliferation and completely prevented the effect of mevastatin on the cell cycle. These observations demonstrate that incadronate-induced apoptosis in human myeloma cells in vitro is the result of inhibition of the MVA pathway.
Bisphosphonates are the important class of antiresorptive drugs used in the treatment of metabolic bone diseases. Although their molecular mechanism of action has not been fully elucidated, recent ...studies have shown that the nitrogen‐containing bisphosphonates can inhibit protein prenylation in macrophages in vitro. In this study, we show that the nitrogen‐containing bisphosphonates risedronate, zoledronate, ibandronate, alendronate, and pamidronate (but not the non nitrogen‐containing bisphosphonates clodronate, etidronate, and tiludronate) prevent the incorporation of 14Cmevalonate into prenylated (farnesylated and geranylgeranylated) proteins in purified rabbit osteoclasts. The inhibitory effect of nitrogen‐containing bisphosphonates on bone resorption is likely to result largely from the loss of geranylgeranylated proteins rather than loss of farnesylated proteins in osteoclasts, because concentrations of GGTI‐298 (a specific inhibitor of geranylgeranyl transferase I) that inhibited protein geranylgeranylation in purified rabbit osteoclasts prevented osteoclast formation in murine bone marrow cultures, disrupted the osteoclast cytoskeleton, inhibited bone resorption, and induced apoptosis in isolated chick and rabbit osteoclasts in vitro. By contrast, concentrations of FTI‐277 (a specific inhibitor of farnesyl transferase) that prevented protein farnesylation in purified rabbit osteoclasts had little effect on osteoclast morphology or apoptosis and did not inhibit bone resorption. These results therefore show the molecular mechanism of action of nitrogen‐containing bisphosphonate drugs in osteoclasts and highlight the fundamental importance of geranylgeranylated proteins in osteoclast formation and function.
The 5' untranslated region of the proto-oncogene c-myc contains an internal ribosome entry segment (IRES) (Nanbru et al., 1997; Stoneley et al., 1998) and thus c-myc protein synthesis can be ...initiated by a cap-independent as well as a cap-dependent mechanism (Stoneley et al., 2000). In cell lines derived from patients with multiple myeloma (MM) there is aberrant translational regulation of c-myc and this correlates with a C-T mutation in the c-myc-IRES (Paulin et al., 1996). RNA derived from the mutant IRES displays enhanced binding of protein factors (Paulin et al., 1998). Here we show that the same mutation is present in 42% of bone marrow samples obtained from patients with MM, but was not present in any of 21 controls demonstrating a strong correlation between this mutation and the disease. In a tissue culture based assay, the mutant version of the c-myc-IRES was more active in all cell types tested, but showed the greatest activity in a cell line derived from a patient with MM. Our data demonstrate that a single mutation in the c-myc-IRES is sufficient to cause enhanced initiation of translation via internal ribosome entry and represents a novel mechanism of oncogenesis.
Bone Research Protocols Helfrich, Miep H; Ralston, Stuart H
2003, 2003., 2008-02-01, Letnik:
80
eBook
The past decade has witnessed the discovery of many genes with profound effects on bone. In Bone Research Protocols, recognized authorities with extensive hands-on experience present a wide-ranging ...catalog of laboratory techniques that will help researchers to investigate the mechanisms by which these genes affect bone mass and strength. Described in step-by-step detail, these readily reproducible methods cover such topics as the isolation and culture of bone cells, the preparation of bone tissue for histological and ultrastructural analysis, methods for the measurement of bone strength and for mechanical studies, and how to use digital imaging techniques in the analysis of bone. Though in vitro methods receive central attention, there are also protocols for in vivo analyses of bone formation and resorption. State-of-the-art and highly practical, Bone Research Protocols offers both beginning and advanced laboratory researchers a major compendium of well-established techniques for studying bone cell function and metabolism.
Vesicular trafficking is crucial for bone resorption by osteoclasts, in particular for formation of the ruffled border membrane and for removal of the resultant bone degradation products by ...transcytosis. These processes are regulated by Rab family GTPases, whose activity is dependent on post-translational prenylation by Rab geranylgeranyl transferase (RGGT). Specific pharmacological inhibition of RGGT inhibits bone resorption in vitro and in vivo, illustrating the importance of Rab prenylation for osteoclast function. The gunmetal (gm/gm) mouse bears a mutation in the catalytic subunit of RGGT, causing a loss of 80% of the activity of this enzyme and hence hypoprenylation of several Rabs in melanocytes, platelets and cytotoxic T cells. We have now found that prenylation of several Rab proteins is also defective in gm/gm osteoclasts. Moreover, while osteoclast formation and cytoskeletal polarization occurs normally, gm/gm osteoclasts exhibit a substantial reduction in resorptive activity in vitro compared with osteoclasts from +/gm mice, which do not have a prenylation defect. Surprisingly, rather than the osteosclerosis that would be expected to result from defective osteoclast function in vivo, gm/gm mice exhibited a slightly lower bone mass than +/gm mice, indicating that defects in other cell types, such as osteoblasts, in which hypoprenylation of Rabs was also detected, may contribute to the phenotype. However, gm/gm mice were partially protected from ovariectomy-induced bone loss, suggesting that levels of Rab prenylation in gm/gm osteoclasts may be sufficient to maintain normal physiological levels of activity, but not pathological levels of bone resorption in vivo.
Nitrogen-containing bisphosphonate drugs inhibit bone resorption by inhibiting FPP synthase and thereby preventing the synthesis of isoprenoid lipids required for protein prenylation in ...bone-resorbing osteoclasts. NE10790 is a phosphonocarboxylate analogue of the potent bisphosphonate risedronate and is a weak anti-resorptive agent. Although NE10790 was a poor inhibitor of FPP synthase, it did inhibit prenylation in J774 macrophages and osteoclasts, but only of proteins of molecular mass ∼22–26 kDa, the prenylation of which was not affected by peptidomimetic inhibitors of either farnesyl transferase (FTI-277) or geranylgeranyl transferase I (GGTI-298). These 22–26-kDa proteins were shown to be geranylgeranylated by labelling J774 cells with 3Hgeranylgeraniol. Furthermore, NE10790 inhibited incorporation of 14Cmevalonic acid into Rab6, but not into H-Ras or Rap1, proteins that are modified by FTase and GGTase I, respectively. These data demonstrate that NE10790 selectively prevents Rab prenylation in intact cells. In accord, NE10790 inhibited the activity of recombinant Rab GGTase in vitro, but did not affect the activity of recombinant FTase or GGTase I. NE10790 therefore appears to be the first specific inhibitor of Rab GGTase to be identified. In contrast to risedronate, NE10790 inhibited bone resorption in vitro without markedly affecting osteoclast number or the F-actin “ring” structure in polarized osteoclasts. However, NE10790 did alter osteoclast morphology, causing the formation of large intracellular vacuoles and protrusion of the basolateral membrane into large, “domed” structures that lacked microvilli. The anti-resorptive activity of NE10790 is thus likely due to disruption of Rab-dependent intracellular membrane trafficking in osteoclasts.
PDF
