Role In Osteoclast Activation Research Articles

Genetic Analysis in a Familial Case With High Bone Mineral Density Suggests Additive Effects at Two Loci.

ABSTRACTOsteoporosis is the most common bone disease, characterized by a low bone mineral density (BMD) and increased risk of fracture. At the other end of the BMD spectrum, some individuals present strong, fracture‐resistant, bones. Both osteoporosis and high BMD are heritable and their genetic architecture encompasses polygenic inheritance of common variants and some cases of monogenic highly penetrant variants in causal genes. We have investigated the genetics of high BMD in a family segregating this trait in an apparently Mendelian dominant pattern. We searched for rare causal variants by whole‐exome sequencing in three affected and three nonaffected family members. Using this approach, we have identified 38 rare coding variants present in the proband and absent in the three individuals with normal BMD. Although we have found four variants shared by the three affected members of the family, we have not been able to relate any of these to the high‐BMD phenotype. In contrast, we have identified missense variants in two genes, VAV3 and ADGRE5, each shared by two of out of three affected members, whose loss of function fits with the phenotype of the family. In particular, the proband, a woman displaying the highest BMD (sum Z‐score = 7), carries both variants, whereas the other two affected members carry one each. VAV3 encodes a guanine‐nucleotide‐exchange factor with an important role in osteoclast activation and function. Although no previous cases of VAV3 mutations have been reported in humans, Vav3 knockout (KO) mice display dense bones, similarly to the high‐BMD phenotype present in our family. The ADGRE5 gene encodes an adhesion G protein‐coupled receptor expressed in osteoclasts whose KO mouse displays increased trabecular bone volume. Combined, these mouse and human data highlight VAV3 and ADGRE5 as novel putative high‐BMD genes with additive effects, and potential therapeutic targets for osteoporosis. © 2022 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

OSTEOPROTEGERIN (OPG) AND SOLUBLE RECEPTOR ACTIVATOR OF NUCLEAR FACTOR KAPPA B LIGAND (S-RANKL) IN PATIENTS WITH RHEUMATOID ARTHRITIS

Background: Rheumatoid arthritis (RA) is a chronic inflammatory disease that may result in debilitating joint deformities with destruction of bone and cartilage. Inflammation is still considered the pivotal inducer of both components of joint damage. A mechanism of bone destruction that could be dissociated from inflammation was proposed in which osteoclasts activation play a prominent role in bone resorption. RANKL and its natural decoy receptor, osteoprotegerin (OPG), play key roles in osteoclast activation. Objective: To evaluate osteoprotegrin (OPG) and soluble RANKL (s-RANKL) level in serum of rheumatoid arthritis patients, and to correlate their levels in serum to disease activity and radiological findings (bone loss). Patients and methods: Fifty five rheumatoid arthritis patients were included in the study. They were classified according to disease activity into 2 groups: The first group was active RA group, and the second was inactive RA group. In addition, RA group was classified according to bone erosions into 2 groups: The first group was RA group with bone erosions and the second group was RA group without bone erosions. The study included 25 healthy individuals of matched age and sex as a control group. All participants were exposed to complete clinical examination, radiological examination, and full laboratory evaluation including osteoclast activity markers (OPG/ RANKL ratio), inflammation markers (ESR, CRP and DAS-28 score), immunological markers (RF and anti-CCP), biochemical markers (calcium, phosphorus and alkaline phosphatase) and complete blood picture (CBC). Results: OPG/ RANKL ratio was significantly lower in RA group compared to control group. OPG/RANKL ratio was significantly lower in active RA group compared to inactive RA group. OPG/ RANKL ratio was significantly lower in RA group with bone erosion compared to RA group without bone erosions. OPG/ RANKL ratio showed significant negative correlation with both disease duration (in all RA groups) and inflammatory markers (in some not all RA groups). OPG/ RANKL ratio did not correlate with biochemical markers in all RA groups. Conclusion: OPG/ RANKL ratio could be used to monitor joint damage (bone erosions) progression in patients with RA. Progression of joint damage (bone erosions) due to osteoclast over activity could, at least in part, be dissociated from inflammation. Therefore, targeting OPG/ RANKL ratio may be effective in preventing bone damage in RA patients.

PENINGKATAN SEL OSTEOBLAST MANDIBULA TIKUS WISTAR JANTAN SETELAH PEMBERIAN FERMENTASI TEH KOMBUCHA

Osteoblasts are bone-forming cells to grow and play a role in regulation of bone metabolism, including alveolar bone. Imbalance of osteoblasts number in bone formation may lead loss of bone mass, which is causes osteoporosis. Reactive Oxygen Species (ROS) is an oxidant that take important roles in osteoclast activation, osteoclastogenesis and activation of osteoblasts inhibition. Kombucha tea has antioxidant effects. This study was conducted to determine Kombucha tea fermented on 14 days make the osteoblasts in the mandibular bone of male wistar rat more numerous.This research was a purely experimental method with Randomized Post Test Control Group Design. Subjects consisted of ten of three – month male wistar rats were divided into 2 groups. Control group received aquadest for 30 days, on the other hand the treatment group were treated by 8 ml of Kombucha tea for 30 days. On the 31st day, rats were euthanized for tissue sampling and histological preparation of mandibular bone and subjected for HE staining. The test results based on comparison between the control group and treatment group with independent t-test showed that there were significant differences in osteoblasts number in mandibular bone of wistar rats (p<0.05). Kombucha tea contain epicatechin gallate (ECG) that stimulate osteoblasts differentiation and inhibit induction of Receptor Activator Of Nuclear Factor-κB Ligand (RANKL). Further more, Epigallocatechin gallate (EGCG) and theaflavin (TF) detoxify molecules of ROS and enhance osteoblastogenesis. This study concluded that administration of Kombucha tea fermented on 14 days make osteoblasts in the mandibular bone of wistar rat more numerous.

The RANKL expression and osteoclast in alveolar bone of rat diabetic model at different mechanical force application

Background: Diabetes is a serious and important public health problem, especially in relation to dental treatment. Because of its complications in periodontal tissue, diabetes can be contraindicated in patients undergoing orthodontic treatment. The receptor activator of nuclear factor-κb ligand (RANKL) is an essential cytokine inducing osteoclastogenesis. Osteoblasts produce this cytokine which has been suggested to play an integral role in osteoclast activation during bone remodeling of orthodontic tooth movement. Purpose: The aim of this study was to determine the correlation between RANKL expression of osteoblast and the number of osteoclasts in the alveolar bone of diabetic rat models at different mechanical force application. Methods: This study used animal subjects, white rats (Rattus norvegicus) of the Wistar strain (n=24) divided into six groups. The mechanical force to which they were subjected ranged between 10, 20, and 30 gramforce (grf). The animal models with diabetes were injected with a stratified dose of Streptozotocin. An orthodontic appliance was inserted in both the maxillary incisors for seven days. The tissue was subjected to histological analysis of osteoclasts and immunohistochemistry analysis of RANKL expression on the pressure and tension side of the alveolar bone. Results: The results of this study showed that the increase in mechanical force produced a rise in RANKL expression and osteoclast number on the pressure and tension side of the alveolar bone of diabetic rat models. Conclusion: There was a correlation between the RANKL of osteoblast and osteoclast numbers in the alveolar bone of diabetic models with different mechanical force application.

Amyloid β Peptide Enhances RANKL-Induced Osteoclast Activation through NF-κB, ERK, and Calcium Oscillation Signaling.

Osteoporosis and Alzheimer’s disease (AD) are common chronic degenerative disorders which are strongly associated with advanced age. We have previously demonstrated that amyloid beta peptide (Aβ), one of the pathological hallmarks of AD, accumulated abnormally in osteoporotic bone specimens in addition to having an activation effect on osteoclast (Bone 2014,61:164-75). However, the underlying molecular mechanisms remain unclear. Activation of NF-κB, extracellular signal-regulated kinase (ERK) phosphorylates, and calcium oscillation signaling pathways by receptor activator NF-κB ligand (RANKL) plays a pivotal role in osteoclast activation. Targeting this signaling to modulate osteoclast function has been a promising strategy for osteoclast-related diseases. In this study, we investigated the effects of Aβ on RANKL-induced osteoclast signaling pathways in vitro. In mouse bone marrow monocytes (BMMs), Aβ exerted no effect on RANKL-induced osteoclastogenesis but promoted osteoclastic bone resorption. In molecular levels, Aβ enhanced NF-κB activity and IκB-α degradation, activated ERK phosphorylation and stimulated calcium oscillation, thus leading to upregulation of NFAT-c1 expression during osteoclast activation. Taken together, our data demonstrate that Aβ enhances RANKL-induced osteoclast activation through IκB-α degradation, ERK phosphorylation, and calcium oscillation signaling pathways and that Aβ may be a promising agent in the treatment of osteoclast-related disease such as osteoporosis.

Associations between OPG and RANKL polymorphisms, vertebral fractures, and abdominal aortic calcification in community-dwelling older subjects: the Sao Paulo Ageing & Health Study (SPAH)

Osteoprotegerin (OPG) and RANKL play an important role in osteoclast activation and differentiation as well as in vascular calcification. At present, there are no studies of OPG or RANKL gene polymorphisms in Brazilian older populations. The aim of this study was to evaluate OPG/RANKL polymorphism and their association with vertebral fractures (VFs) and aortic calcification. Eight hundred subjects (497 women/303 men) were genotyped for the OPG 1181G>C (rs2073618), 163C>T (rs3102735), 245T>G (rs3134069), and 209G>A (rs3134070) and RANKL A>G (rs2277438) single-nucleotide polymorphisms (SNPs). VFs were evaluated by spine radiography (Genant's method). Aortic calcification was quantified using Kauppila's method. The isolated genotype analyses and single-allele frequency data showed association of OPG 163C, 245G, and 209A alleles with presence of VFs (P < 0.05). Multiple logistic regression of subjects with absence of VFs vs. those with VFs (grades II/III) revealed only OPG 209A homozygosity as a risk factor for higher-grade VFs (odds ratio (OR) = 4.17, 95% CI 1.03-16.93, P = 0.046). Regarding aortic calcification, the isolated genotype analysis frequency data revealed a significant association of OPG 1181G, 163C, 245G, and 209A alleles with absent aortic calcification (P < 0.05). Multiple logistic regression data confirmed that the OPG 209A allele was protective for aortic calcification (OR = 0.63, 95% CI 0.45-0.88, P = 0.007) and the OPG 1181C allele was a risk factor for aortic calcification (OR = 1.26, 95% CI 1.00-1.58, P = 0.046). This study showed that the OPG 209AA genotype was a risk factor for higher-grade VFs, the OPG 209A allele was protective for aortic calcification, and the OPG 1181C was a risk factor for aortic calcification, supporting the involvement of OPG polymorphisms in the analyzed phenotypes and the concept that the related pathogenesis is multifactorial.

Anabolic bone formation via a site-specific bone-targeting delivery system by interfering with semaphorin 4D expression.

Semaphorins have been recently targeted as new molecules directly implicated in the cell-cell communication that occurs between osteoclasts and osteoblasts. Overexpression of certain semaphorins, such as semaphorin4D (sema4D), is found in an osteoporotic phenotype and plays a key role in osteoclast activity by suppressing osteoblast maturation, thus significantly altering the bone modeling cycle. In the present study, we fabricate a site-specific bone-targeting drug-delivery system from polymeric nanoparticles with the incorporation of siRNA interference molecule for sema4D and demonstrate their cellular uptake and intracellular trafficking within osteoclasts, thus preventing the suppression of osteoblast activity. We then demonstrate in an osteoporotic animal model induced by ovariectomy that weekly intravenous injections led to a significantly greater number of active osteoblasts at the bone surface, resulting in higher bone volume in compromised animals. The findings from the present study demonstrate a novel and promising site-specific therapeutic option for the treatment of osteoporosis via interference of the sema4D-plexin cell communication pathway between osteoclasts and osteoblasts.

A Novel Bruton′s Tyrosine Kinase Inhibitor CC-292 In Combination With The Proteasome Inhibitor Carfilzomib Iimpacts Multiple Myeloma Bone Microenviroment With Resultant Anti-Myeloma Activity

A member of the Tec family kinases, Bruton's tyrosine kinase (Btk) modulates B-cell development and activation, and plays an important role in antibody production. Interestingly, Btk and Tec (the other Tec kinase family) regulate osteoclast (OC) differentiation via Receptor Activator of Nuclear Factor κ B (RANK) signaling. Moreover, OCs derived from X-linked agammaglobulinemia (XLA) patients who harbor Btk null mutations have impaired function.Here we show that a potent and specific Btk inhibitor, CC-292 inhibits OC function in multiple myeloma (MM) patients. CC-292 is a highly selective, covalent Btk inhibitor. OC derived from MM patient monocytes were assayed with or without CC-292. Interestingly, OC function was significantly inhibited in the presence of CC-292 (100 nM and 1000 nM) as demonstrated by pit formation assay. However, mRNA expression for TRAP and Cathepsin K, two OC differentiation markers were increased in the presence of CC-292 suggesting that CC-292 inhibits OC function without inhibiting OC differentiation.OC sealing zone contributes to OC bone resorption function. Given the role of c-Src and Proline-rich tyrosine Kinase 2 (Pyk2) signaling in sealing zone formation and OC function we next evaluated CC-292's effect on Pyk2 and c-Src. Pyk2 plays a role in OC activation and localizes to the sealing zone in OC. RANK signaling activates c-Src, which phosphorylates Pyk2. Moreover c-Src controls OC bone resorption by regulating actin organization via cortactin. Interestingly, CC-292 (100 nM) inhibited c-Src total protein, c-Src phosphorylation and Pyk2 phosphorylation. Furthermore, CC-292 (100 nM) inhibited cortactin protein and mRNA expression, and upregulated c-Cbl protein (E3 ubiquitin ligase for c-Src) expression in OC derived from MM patient monocytes with resultant inhibition of OC sealing zone formation. However, at the same low doses (100 nM) CC-292 did not show any direct in vitro effect against MM cell viability.Because carfilzomib, a proteasome inhibitor that binds irreversibly to its target, has potent anti-MM activity and also inhibits OC resorptive activity, we studied CC-292 in combination with carfilzomib. Our data suggests that carfilzomib (1.25 nM) has no impact on OC sealing zone formation but inhibits OC differentiation. CC-292 (100 nM) in combination with carfilzomib (1.25 nM) inhibited not only sealing zone formation but also OC differentiation, resulting in stronger suppression of OC function than carfilzomib alone.The combination of CC-292 (30mg/kg p.o. for 5 days per week for 6 weeks) and carfilzomib (3 mg/kg i.v. x 2 days per week for 4 weeks and 2 mg/kg i.v. x 2 days per week for 2 weeks) significantly inhibited tumor burden and myeloma cell numbers in a diffuse NOD-SCID MM model. The calvarial cells derived from these mice treated with CC-292 alone, carfilzomib alone or the combination showed higher osteocalcin mRNA (osteoblast differentiation marker) expression. A specific bone resorption marker, carboxy-terminal telopeptide collagen crosslinks (CTX) in mouse serum was significantly inhibited in CC-292 and CC-292 in combination with carfilzomib treatment groups in comparison with control mice. Furthermore, 3D microCT reconstructions showed increase in cancellous bone volume in lumbar vertebrae in mice treated with CC-292 or carfilzomib, while the combination treatment resulted in an increase in cancellous bone volume in an additive manner.These data demonstrate that the novel BTK inhibitor CC-292 inhibits OC function through inhibition of OC sealing zone formation. Moreover, CC-292 in combination with carfilzomib augments effects against the bone microenvironment with resultant anti-MM activity. Disclosures:Arastu-Kapur:Onyx Pharmaceuticals, Inc.: Employment. Evans:Celgene Avilomics Research: Employment, Equity Ownership. Singh:Celgene Avilomics Research: Employment, Equity Ownership. Kirk:Onyx Pharmaceuticals, Inc.: Employment. Westlin:Celgene Avilomics Research: Employment, Equity Ownership. Raje:Celgene: Consultancy; Millenium: Consultancy; Onyx: Consultancy; Amgen: Consultancy; Acetylon: Research Funding; Eli Lilly: Research Funding.

Expression of osteoblast and osteoclast regulatory genes in the bone marrow microenvironment in multiple myeloma: only up-regulation of Wnt inhibitors SFRP3 and DKK1 is associated with lytic bone disease

Multiple myeloma (MM) lytic bone disease (LBD) is caused by osteoclast activation and osteoblast inhibition. RANK/RANKL/OPG play central roles in osteoclast activation and Wnt inhibitor DKK1 in osteoblast inhibition. The role of other Wnt inhibitors is less clear. We evaluated gene expression of osteoclast regulators (RANK, RANKL, OPG, TRAIL, MIP1A), Wnt inhibitors (DKK1, SFRP2, SFRP3, sclerostin, WIF1) and osteoblast transcription factors (RUNX2, osterix) by quantitative reverse transcriptase polymerase chain reaction (RT-PCR) in the bone marrow (BM) microenvironment using snap-frozen BM biopsies, thereby achieving minimal post-sampling manipulation, and gene expression profiling (GEP) data, reflecting the in vivo situation. We analyzed 110 biopsies from newly diagnosed patients with MM and monoclonal gammopathy of unknown significance (MGUS) and healthy volunteers. LBD was evaluated using standard radiographs and the bone resorption marker CTX-1. Protein levels were evaluated by enzyme-linked immunosorbent assay (ELISA) and immunohistochemistry. Among Wnt inhibitors, only SFRP3 and DKK1 were significantly overexpressed in advanced LBD, correlating with protein levels. SFRP3 correlated with CTX-1. Our findings support osteoblast inhibition as the driving force behind MM LBD.

P2RY12 and its role in osteoclast activity and bone remodeling

P2RY12 and its role in osteoclast activity and bone remodeling

Serum Levels of Total-RANKL in Multiple Myeloma

BackgroundReceptor activator of nuclear factor-κB ligand (RANKL) plays a key role in osteoclast activation in myeloma bone disease. The increased expression of RANKL in the bone marrow microenvironment was demonstrated in several studies, but there are only rare data on circulating RANKL levels in patients with multiple myeloma (MM). Patients and MethodsIn the current study, we investigated the clinical significance of serum RANKL levels, using an enzyme-linked immunosorbent assay test that detects both free and osteoprotegerin (OPG)-bound RANKL (total-RANKL, tRANKL) in patients with newly diagnosed MM (n = 93) and monoclonal gammopathy of undetermined significance (MGUS; n = 20) compared with healthy controls (n = 20). ResultsCirculating serum tRANKL was significantly elevated in patients with MM compared with controls (P < .001) or MGUS (P < .001). Furthermore, tRANKL levels were higher in smoldering MM versus MGUS (P = .031) and in symptomatic versus smoldering MM (P < .001). Serum tRANKL increased parallel to International Staging System stages I to III (P = .004) and correlated with the presence of lytic bone lesions (P < .001). Total-RANKL was a prognostic factor for overall survival in symptomatic MM (P = .043). A significantly longer progression-free survival was observed in patients with a > 50% decrease in tRANKL levels after 3 months of combined chemotherapy and bisphosphonate treatment. ConclusionOur study demonstrates for the first time that serum tRANKL reflects advanced disease, lytic bone destruction, and poor prognosis in MM.

Myeloma Cell Expression of Candidate Genes for Osteolytic Bone Disease - Over-Expression of DKK1 Correlates with Clinical Bone Involvment.

The etiology of the osteolytic bone disease (OBD) in multiple myeloma (MM) is not fully understood but seems to involve interactions between myeloma cells and the bone marrow microenvironment. Over-expression of the osteoclast activation cytokine, receptor activator of nuclear factor-κB ligand (RANKL), and decreased expression of the inhibitor of RANKL, called osteoprotegerin (OPG), is believed to be important. Macrophage inflammatory proteins are also reported to play a role in osteoclast activation. Recently, the role of osteoblast inactivation in OBD has come into focus, especially the importance of over expression of dickkopf 1 (DKK1), an inhibitor of the Wnt signalling pathway that induces osteoblastogenesis and osteoblast activation.Micro array profiling studies in MM have also introduced other candidate genes. Besides DKK1, over expression of CKS2, PSME2 and DHFR have been reported.We examined 9 candidate genes involved in OBD: RANKL, RANK, OPG, MIP1α, PTHrp, DKK1, CKS2, PSME2 and DHFR. Bone marrow (BM) aspirates from 170 newly diagnosed, un-treated MM patients and from 9 healthy volunteers were collected over a period of 12 years. Median age in the MM group was 62 years (33–83 years), male/ female ratio 1:1.25. 62 % of the patients had advanced disease at diagnosis (Durie Salmon stage III), 30 % of the patients had no, 28% limited, and 42 % advanced bone lesions.The immune phenotype of the myeloma cells were characterised by flowcytometry and afterwards used in fluorescence activated cell sorting (FACS) of the myeloma cells using a FACS Aria (Becton Dickinson immune systems) to ≥98% purity.For global amplification 100 PCs were FACS-sorted directly to PCR tubes, followed by global reverse transcription (RT)-PCR, generating a cDNA archive. By using a polyadenylating step we generated a 5′-oligo(dT)-transcript-poly(A)-3′ cDNA, that is finally amplified by PCR using a sequence independent X-(dT) 24 primer.Gene expression of the analysed genes and a housekeeping gene (β-actin) were performed by real-time quantitative polymerase chain reaction (RQ-PCR), using specific designed oligo primers and Taqman probes.Only over-expression of DKK1 in highly purified plasma cells was correlated to the degree of OBD in the studied population. We found expression of DKK1 in myeloma cells in about 42 % (71/170) of the samples. Expression of DKK1 correlated (p<0,002) to OBD, and the DKK1 expression levels were observed to increase with more advanced bone disease.No, or only a small percentage of the PC expressed RANK, RANKL, OPG, MIP1α or PTHrp1. CKS2, PSME2 and DHFR were expressed in varied degrees, but we observedno correlation to either OBD or disease stage of disease.In conclsion, our data showed a close connection between over-expression of DKK1 and OBD, whereas we were not able to confirm any correlation between OBD and myeloma cell expression of the genes CKS2, PSME2 and DHFR. We found no evidence for myeloma cell expression of RANKL, RANK, OPG, MIP1α, and PTHrp.

The ratio of circulating osteoprotegerin to RANKL in early rheumatoid arthritis predicts later joint destruction

Rheumatoid arthritis (RA) is a chronic inflammatory disease that may result in debilitating joint deformities with destruction of bone and cartilage. Inflammation is still considered the pivotal inducer of both components of joint damage. Results of recent animal studies suggested a prominent contribution of osteoclastic bone resorption that could be dissociated from inflammation. RANKL and its natural decoy receptor, osteoprotegerin (OPG), play key roles in osteoclast activation. In a group of patients with early RA not treated with disease-modifying drugs, we tested the hypothesis that osteoclast activation, reflected by the serum OPG:RANKL ratio at baseline, is negatively associated with progression of bone damage, independent of inflammation. OPG and RANKL levels, together with a parameter of inflammation (first-year time-averaged erythrocyte sedimentation rate [tESR]), were measured in 92 patients with newly diagnosed early active RA who were participants in a randomized study. The tESR and the OPG:RANKL ratio were evaluated for the ability to predict 5-year radiographic progression of joint damage. The first-year tESR and the OPG:RANKL ratio, as measured at baseline, independently predicted 5-year radiographic progression of joint damage (both P < or = 0.001). Progression of radiographic damage was greatest in patients with a high tESR and a low OPG:RANKL ratio and was lowest in patients with a low tESR and a high OPG:RANKL ratio. This study in patients with early untreated RA is the first to confirm the findings in animal models of arthritis, that radiographic progression of the bone component of joint destruction is dependent on both inflammation (tESR) and osteoclast activation (the OPG:RANKL ratio).

Soluble receptor activator of nuclear factor κB ligand–osteoprotegerin ratio predicts survival in multiple myeloma: proposal for a novel prognostic index

AbstractInteraction between receptor activator of nuclear factor κB ligand (RANKL) and RANK/osteoprotegerin (OPG) plays a dominant role in osteoclast activation and possibly in plasma cell survival in multiple myeloma (MM). We measured soluble RANKL (sRANKL), OPG, and bone remodeling markers in 121 patients with newly diagnosed MM to evaluate their role in bone disease and survival. Serum levels of sRANKL were elevated in patients with MM and correlated with bone disease. The sRANKL/OPG ratio was also increased and correlated with markers of bone resorption, osteolytic lesions, and markers of disease activity. The sRANKL/OPG ratio, C-reactive protein (CRP), and β2-microglobulin were the only independent prognostic factors predicting survival in multivariate analysis. We generated a prognostic index based on these factors that divided our patients into 3 risk groups. The low-risk group had a 96% probability of survival at 5 years, whereas the intermediate-risk and the high-risk groups had probabilities of survival of 52% and 0%, respectively. Not only do these results confirm for the first time in humans the importance of sRANKL/OPG in the development of bone disease, they also highlight the role of this pathway in the biology of plasma cell growth as reflected by its influence on survival.

HIV infection--a risk factor for osteoporosis.

Osteopenia and osteoporosis have recently been described as complications of antiretroviral therapy in HIV-infected patients. The advent of highly active antiretroviral therapy in conjunction with improved standard antiviral and antibiotic regimens has dramatically changed the clinical course of HIV infection, resulting in prolonged survival. The pathogenesis and role of each individual medication are poorly understood. Avascular necrosis has also been described in AIDS patients receiving or not receiving antiretroviral therapy. This article is a clinically focused review of the literature on osteopenia, osteoporosis, and mineral metabolism related to HIV infection. In patients with HIV infection, the risks of osteopenia and osteoporosis are not very clear. The suggested risk factors for the development of osteopenia are use of protease inhibitors, longer duration of HIV infection, high viral load, high lactate levels, low bicarbonate levels, raised alkaline phosphatase level, and lower body weight before antiretroviral therapy. There have also been a few case reports of pathologic fractures in AIDS patients with antiretroviral therapy-induced osteopenia and osteoporosis. The underlying mechanism triggering bone loss in HIV-infected patients is unknown. The proinflammatory cytokines tumor necrosis factor and interleukin-6 have been found to be constitutionally produced in increased amounts in HIV-positive individuals, and they may have a role in osteoclast activation and resorption. Serum markers of bone formation are decreased and resorption is increased in patients with advanced clinical disease. Hypocalcemia, hypercalcemia, and abnormalities of the parathyroid hormone axis have been described in HIV infection. Histomorphometric analyses have shown altered bone remodeling in HIV-infected patients when compared with controls. Patients with known risk factors for osteoporosis-advancing age, low body weight, and prolonged duration of HIV infection-and those receiving protease inhibitor treatment should be considered for dual x-ray absorptiometry imaging. If bone mineral density is osteopenic or osteoporotic, then the patient should also be screened for other known medical causes of osteoporosis and consider treatment with a bisphosphonate or, if hypogonadal, testosterone replacement under close monitoring.

Adenosine triphosphate stimulates human osteoclast activity via upregulation of osteoblast-expressed receptor activator of nuclear factor-κB ligand

Nucleotides such as adenosine triphosphate (ATP) and uridine triphosphate (UTP) exist in the extracellular environment where they are agonists at P2 receptors. Both P2Y G-protein-coupled receptors and P2X ligand-gated ion channels are expressed by osteoblasts and osteoclasts, reflected in the diverse nucleotide-induced effects reported to occur in bone. Previous reports have implicated ATP as a proresorptive agent; however, these studies were unable to determine whether ATP mediated its actions directly on osteoclasts, or indirectly via osteoblasts. The development of techniques to generate human osteoclasts in vitro has allowed us to further investigate the intriguing role of extracellular nucleotides with regard to osteoclast activity. This study reports that nearly all P2-receptor-subtype mRNAs were expressed throughout human osteoclast development, and provides evidence for functional P2 receptor expression by these cells. In cultures of human osteoclasts alone, neither ATP nor UTP affected the quantity of resorption by these cells; however, in cocultures of osteoblast-like UMR-106 cells and human osteoclasts, ATP, but not UTP, greatly enhanced resorption, indicating a role for osteoblasts in mediating the proresorptive effects of ATP. Furthermore, ATP, but not UTP, elevated receptor activator of nuclear factor-κB ligand (RANKL) mRNA and protein expression by UMR-106 cells. These data are consistent with observations that UMR-106 cells predominantly express P2Y 1 with low expression of P2Y 2, thereby explaining the response to ATP and not UTP, and further substantiating the involvement of osteoblasts in ATP-induced effects on osteoclasts. These results significantly advance our understanding of the role of P2 receptors in bone, and indicate that local-acting ATP may play a pivotal role in osteoclast activation at bone-resorbing sites by inducing elevated expression of RANKL.