Human osteoclasts and osteoclast-like cells synthesize and release high basal and inflammatory stimulated levels of the potent chemokine interleukin-8

Kaposi sarcoma is a therapeutic target for vitamin D3receptor agonist

Kaposi sarcoma (KS) is responsive to a number of different steroid hormones, such as glucocorticoids and retinoids. An active metabolite of vitamin D, 1α,25 dihydroxyvitamin D3, was used to study the effect of this steroid hormone in KS. Steroid hormones exert their effect through their cognate nuclear receptors, which for vitamin D metabolites is the vitamin D receptor (VDR). It was first shown that KS cell lines and primary tumor tissue express high levels of VDR, whereas endothelial cells had minimal expression and fibroblasts had no expression. Second, KS cell growth was inhibited by VDR agonist 1α,25 dihydroxyvitamin D3 with a 50% inhibitory concentration of 5 × 10 −8 mol/L, whereas endothelial cells and fibroblast cells showed no response. Studies on the mechanism of KS tumor growth inhibition by 1α,25 dihydroxyvitamin D3 showed that production of autocrine growth factors interleukin (IL)-6 and IL-8 was reduced in a dose-dependent manner, whereas no effect was observed on vascular endothelial growth factor and basic fibroblast growth factor. Transcription initiated at the IL-6 promoter was repressed by VDR agonist. The DNA sequences required to mediate this repression were localized to nucleotides −225/−110 in the 5′-flanking region. The antitumor activity of VDR agonists was also confirmed in KS tumor xenograft and after topical application in patients with KS. 1α,25 Dihydroxyvitamin D3 and its analogs may thus be candidates for clinical development in KS.

Cytokine production and bone remodeling in patients wearing overdentures on oral implants

The stability of titanium dental implants is determined by osseointegration. Bone is a dynamic tissue continuously remodeled through resorption and formation, processes controlled by local cytokine production. This study investigated osseotropic cytokine expression in gingival mucosa, in the intraforamina and inferior first molar zones, during rehabilitation with implant-retained overdentures. Specimens were taken from six patients prior to placement of implants in the intraforamina bone; at connection of healing abutments; and 4, 8, and 12 months after prosthetic anchorage. Through semi-quantitative reverse-transcriptase polymerase chain-reaction, the following constitutively expressed cytokines were found at first surgical stage: interleukin-1, -6, and -8; small amounts of interleukin-11; stem cell factor; and transforming growth factor-beta1, -beta2, and -beta3. From the connection of healing abutments to 12 months after prosthetic anchorage, transforming growth factor-beta1, -beta2, and -beta3 were markedly higher than initial values. Expression of interleukin-6 and -8 decreased 8 months after prosthetic anchorage, while that of interleukin-1 increased at 12 months. In cultured gingival fibroblasts, modulation of cytokine secretion was also time-dependent. Cell culture supernatants influenced osteoclast-like multinucleated cell formation in long-term human marrow culture or osteoblast function, depending on the cytokine profile produced. These results are consistent with functional contributions of cytokines to osseointegration and minimization of posterior edentulous zone bone resorption.

Human chondrocytes express functional chemokine receptors and release matrix-degrading enzymes in response to C-X-C and C-C chemokines

OBJECTIVE

Human chondrocytes produce different C-X-C and C-C chemokines under basal conditions and upon activation with proinflammatory cytokines. We investigated whether human chondrocytes also have chemokine receptors and examined the effects of chemokines on chondrocyte activity.

METHODS

The expression of chemokine receptors was determined by immunochemical analysis of frozen sections from normal and osteoarthritic cartilage and by flow cytometry of isolated cells. The messenger RNA expression for chemokine receptors was studied by reverse transcriptase-polymerase chain reaction. Isolated chondrocytes were stimulated with different chemokines, and the responses were evaluated by assaying the release of matrix metalloprotease 3 (MMP-3) and of the lysosomal enzyme N-acetyl-beta-D-glucosaminidase in the supernatants.

RESULTS

A wide variety of chemokine receptors (CCR-1, CCR-2, CCR-3, CCR-5, CXCR-1, and CXCR-2) was detected on human chondrocytes. Interaction of these receptors with the corresponding ligands induced the release of MMP-3. This response was abrogated by pretreatment of the cells with Bordetella pertussis toxin, demonstrating involvement of G proteins of the Gi type. The response decreased in the presence of cycloheximide, indicating dependence on protein synthesis. Chemokines also induced the exocytosis of N-acetyl-beta-D-glucosaminidase, which was prevented by receptor blockage with anti-CCR-3 and by treatment with B pertussis toxin. Chondrocytes obtained from osteoarthritic tissue showed an increased expression of CCR-3 and possibly of CXCR-1, and an augmented release of matrix-degrading enzymes compared with chondrocytes from normal donors.

CONCLUSION

Our findings suggest the existence in human chondrocytes of a novel catabolic pathway, primed by chemokines and their receptors, that leads to the breakdown of cartilage matrix components.

Expression of osteoclast differentiation signals by stromal elements of giant cell tumors

The mechanisms by which primary tumors of the bone cause bone destruction have not been elucidated. Unlike most other lytic bone tumors, osteoclastomas, otherwise known as giant cell tumors (GCT), contain osteoclast-like cells within the tumor stroma. A new member of the TNF-ligand superfamily member, osteoclast differentiation factor (ODF/OPGL/RANKL/TRANCE), was recently identified. ODF was shown to directly stimulate osteoclastogenesis, in the presence of M-CSF. In this study, the expression of ODF was examined in a number of tumor samples associated with bone lysis in vivo. In addition, we investigated expression of the ODF receptor on osteoclast precursors, RANK, as well as the ODF inhibitor osteoprotegerin (OPG), and another TNF-ligand superfamily member, TRAIL, previously shown to abrogate the inhibitory effects of OPG. We report here the novel finding that GCT stromal cells contain abundant ODF mRNA, whereas the giant cell population exclusively expresses RANK mRNA. These results are consistent with the osteoclast-mediated bone destruction by these tumors. We also report the expression of OPG and TRAIL mRNA in GCT samples. A comparison with other lytic and nonlytic tumors of bone showed that GCT express more ODF and TRAIL mRNA relative to OPG mRNA. In addition, GCT were found to express a number of cytokines previously reported to play central roles in osteoclastogenesis, namely, IL-1, -6, -11, -17, as well as TNF-alpha. Importantly, GCT were also found to express high levels of M-CSF mRNA, a cytokine shown to be an essential cofactor of ODF, and a survival factor for mature and developing osteoclasts. Furthermore, expression of these molecules by stromal cells isolated from GCT continued in vitro. Thus GCT constitutively express all of the signals that are currently understood to be necessary for the differentiation of osteoclasts from precursor cells.

Estrogen's bone-protective effects may involve differential IL-1 receptor regulation in human osteoclast-like cells

Declining estrogen levels during the first postmenopausal decade lead to rapid bone loss and increased fracture risk that can be reversed by estrogen replacement therapy. The bone-protective effects of estrogen may involve suppression of inflammatory cytokines that promote osteoclastogenesis and bone resorption, such as IL-1, TNF-alpha, and IL-6. We investigated whether estrogen modulates IL-1 actions on human osteoclasts (OCs) and other bone cell types. Isolated human OCs and primary bone marrow-derived OC-like cells expressed both the signaling (IL-1RI) and decoy (IL-1RII) IL-1 receptors, whereas only IL-1RI was detected in osteoblasts. IL-1RII/IL-1RI mRNA ratios and release of soluble IL-1RII (sIL-1RII) were lower in OC-like cells derived from women in the late postmenopausal period compared with younger women, but were unrelated to male donor age, suggesting that estrogen might play a role in regulating IL-1 receptor levels in vivo. Estrogen directly reduced in vitro OC-like cell IL-1RI mRNA levels while increasing IL-1RII mRNA levels and sIL-1RII release. These estrogenic events were associated with inhibited IL-1-mediated cytokine (IL-8) mRNA induction and cell survival, i.e., increased apoptosis. In contrast, estrogen did not alter IL-1R levels or IL-1 responsiveness in primary human osteoblasts or bone marrow stromal cells. We conclude that one novel mechanism by which estrogen exerts bone-protective effects may include a selective modulation of IL-1R isoform levels in OC or OC-like cells, thereby reducing their IL-1 responsiveness and cell survival. Conversely, this restraint on IL-1 actions may be lost as estrogen levels decline in aging women, contributing to an enhanced OC-mediated postmenopausal bone loss.

Macrophage-inflammatory protein-1alpha regulates preosteoclast differentiation in vitro

A validated in vitro system was used to investigate the nature of osteoclast-inducing growth factors (OGF) present in fetal rat calvarial conditioned medium (RCCM). Evidence is presented here that macrophage inflammatory protein-1alpha (MIP-1alpha), a member of the C-C chemokine family, is an essential factor for the induction of osteoclast differentiation in this system. Specific polyclonal antibodies against MIP-1alpha significantly inhibited development of TRAP-positive osteoclast precursors and multinucleated osteoclasts induced by RCCM. Anti-MIP-1alpha antibody treatment was accompanied by an increase in the number of macrophage-like cells, suggesting that bone-derived MIP-1alpha is involved in the direction of preosteoclast formation with an inhibitory action on progenitor cell proliferation. Reverse-phase HPLC of RCCM resolved multiple fractions with OGF activity. OGF fractions separated at low acetonitrile (AcN) concentrations (</=15%) did not bind heparin and were not blocked in their bioactivity by the anti-MIP-1alpha antibody. However, OGF fractions eluted at higher AcN concentrations (30-70%) showed heparin-binding activity and were inhibited in their bioactivity by the anti-MIP-1alpha antibody. Western blotting of RCCM with the anti-MIP-1alpha antibody revealed a distinct band with a molecular mass of around 8-14 kDa corresponding to MIP-1alpha. Recombinant rat MIP-1alpha dose dependently stimulated formation of mononuclear osteoclast precursors with maximum stimulation at 50 ng/ml, though it could not fully mimic RCCM activity. These results identify MIP-1alpha as a candidate responsible for bone-derived OGF bioactivity and confirm that chemokines play an important role in the process of osteoclast recruitment and differentiation.