Induction of chondrogenesis with a RANKL-binding peptide, WP9QY, in vitro and in vivo in a rabbit model.

WP9QY (W9) is a receptor activator of nuclear factor-κB ligand (RANKL)-binding peptide that inhibits osteoclastogenesis by blunting the RANKL-RANK interaction, and also increases osteoblastogenesis via RANKL reverse signaling. W9 has dual effects on osteoclasts and osteoblasts; however, it is unknown whether the peptide has an effect on chondrocytes. Here, we report that W9 induces proliferation and differentiation of chondrocytes in vitro and repairs full-thickness articular cartilage defects in vivo. W9 stimulated chondrocyte differentiation in a two-dimensional (2D) culture of human mesenchymal stem cells (hMSCs), and transforming growth factor ß3 (TGF-ß3) showed synergistic effects with W9 on chondrogenesis. W9 enlarged the size of 3D pellet cultures of hMSCs and produced chondrocyte-specific matrices, especially in combined treatment with TGF-ß3. The peptide also stimulated proliferation of hMSCs with induction of expression of chondrogenesis-related genes. Several RANKL inhibitors had no effect on chondrocytic differentiation. RANKL-knockdown experiments showed that W9 did not induce chondrogenesis through RANKL, but did induce osteoblastogenesis through RANKL. Intraarticular injection of W9 resulted in significant repair of full-thickness articular cartilage defects in rabbits. Taken together, these results suggest that W9 ameliorates the articular cartilage defects by increasing the volume of cartilaginous matrices with accompanying induction of proliferation and differentiation of chondrocytes via mechanisms independent of RANKL inhibition and RANKL reverse signaling. Since no pharmaceuticals are clinically available for treatment of cartilage damage such as osteoarthritis, our findings demonstrate the potential of W9 to address the unmet medical needs.

Osteoclast differentiation by RANKL and OPG signaling pathways.

INTRODUCTION: In bone tissue, bone resorption by osteoclasts and bone formation by osteoblasts are repeated continuously. Osteoclasts are multinucleated cells that derive from monocyte-/macrophage-lineage cells and resorb bone. In contrast, osteoblasts mediate osteoclastogenesis by expressing receptor activator of nuclear factor-kappa B ligand (RANKL), which is expressed as a membrane-associated cytokine. Osteoprotegerin (OPG) is a soluble RANKL decoy receptor that is predominantly produced by osteoblasts and which prevents osteoclast formation and osteoclastic bone resorption by inhibiting the RANKL-RANKL receptor interaction. MATERIALS AND METHODS: In this review, we would like to summarize our experimental results on signal transduction that regulates the expression of RANKL and OPG. RESULTS: Using OPG gene-deficient mice, we have demonstrated that OPG and sclerostin produced by osteocytes play an important role in the maintenance of cortical and alveolar bone. In addition, it was shown that osteoclast-derived leukemia inhibitory factor (LIF) reduces the expression of sclerostin in osteocytes and promotes bone formation. WP9QY (W9) is a peptide that was designed to be structurally similar to one of the cysteine-rich TNF-receptortype-I domains. Addition of the W9 peptide to bone marrow culture simultaneously inhibited osteoclast differentiation and stimulated osteoblastic cell proliferation. An anti-sialic acid-binding immunoglobulin-like lectin 15 (Siglec-15) antibody inhibited multinucleated osteoclast formation induced by RANKL and macrophage colony-stimulating factor (M-CSF). Pit-forming activity of osteoclasts was also inhibited by the anti-Siglec-15 antibody. In addition, anti-Siglec-15 antibody treatment stimulated the appearance of osteoblasts in cultures of mouse bone marrow cells in the presence of RANKL and M-CSF. CONCLUSIONS: Bone mass loss depends on the RANK-RANKL-OPG system, which is a major regulatory system of osteoclast differentiation induction, activation, and survival.

Treatment of OPG-deficient mice with WP9QY, a RANKL-binding peptide, recovers alveolar bone loss by suppressing osteoclastogenesis and enhancing osteoblastogenesis.

Osteoblasts express two key molecules for osteoclast differentiation, receptor activator of NF-κB ligand (RANKL) and osteoprotegerin (OPG), a soluble decoy receptor for RANKL. RANKL induces osteoclastogenesis, while OPG inhibits it by blocking the binding of RANKL to RANK, a cellular receptor of RANKL. OPG-deficient (OPG-/-) mice exhibit severe alveolar bone loss with enhanced bone resorption. WP9QY (W9) peptide binds to RANKL and blocks RANKL-induced osteoclastogenesis. W9 is also reported to stimulate bone formation in vivo. Here, we show that treatment with W9 restores alveolar bone loss in OPG-/-mice by suppressing osteoclastogenesis and enhancing osteoblastogenesis. Administration of W9 or risedronate, a bisphosphonate, to OPG-/-mice significantly decreased the osteoclast number in the alveolar bone. Interestingly, treatment with W9, but not risedronate, enhanced Wnt/ß-catenin signaling and induced alveolar bone formation in OPG-/-mice. Expression of sclerostin, an inhibitor of Wnt/ß-catenin signaling, was significantly lower in tibiae of OPG-/-mice than in wild-type mice. Treatment with risedronate recovered sclerostin expression in OPG-/-mice, while W9 treatment further suppressed sclerostin expression. Histomorphometric analysis confirmed that bone formation-related parameters in OPG-/-mice, such as osteoblast number, osteoblast surface and osteoid surface, were increased by W9 administration but not by risedronate administration. These results suggest that treatment of OPG-/-mice with W9 suppressed osteoclastogenesis by inhibiting RANKL signaling and enhanced osteoblastogenesis by attenuating sclerostin expression in the alveolar bone. Taken together, W9 may be a useful drug to prevent alveolar bone loss in periodontitis.

Stimulation of bone formation in cortical bone of mice treated with a receptor activator of nuclear factor-κB ligand (RANKL)-binding peptide that possesses osteoclastogenesis inhibitory activity.

To date, parathyroid hormone is the only clinically available bone anabolic drug. The major difficulty in the development of such drugs is the lack of clarification of the mechanisms regulating osteoblast differentiation and bone formation. Here, we report a peptide (W9) known to abrogate osteoclast differentiation in vivo via blocking receptor activator of nuclear factor-κB ligand (RANKL)-RANK signaling that we surprisingly found exhibits a bone anabolic effect in vivo. Subcutaneous administration of W9 three times/day for 5 days significantly augmented bone mineral density in mouse cortical bone. Histomorphometric analysis showed a decrease in osteoclastogenesis in the distal femoral metaphysis and a significant increase in bone formation in the femoral diaphysis. Our findings suggest that W9 exerts bone anabolic activity. To clarify the mechanisms involved in this activity, we investigated the effects of W9 on osteoblast differentiation/mineralization in MC3T3-E1 (E1) cells. W9 markedly increased alkaline phosphatase (a marker enzyme of osteoblasts) activity and mineralization as shown by alizarin red staining. Gene expression of several osteogenesis-related factors was increased in W9-treated E1 cells. Addition of W9 activated p38 MAPK and Smad1/5/8 in E1 cells, and W9 showed osteogenesis stimulatory activity synergistically with BMP-2 in vitro and ectopic bone formation. Knockdown of RANKL expression in E1 cells reduced the effect of W9. Furthermore, W9 showed a weak effect on RANKL-deficient osteoblasts in alkaline phosphatase assay. Taken together, our findings suggest that this peptide may be useful for the treatment of bone diseases, and W9 achieves its bone anabolic activity through RANKL on osteoblasts accompanied by production of several autocrine factors.

Increased bone mass in mice after single injection of anti-receptor activator of nuclear factor-kappaB ligand-neutralizing antibody: evidence for bone anabolic effect of parathyroid hormone in mice with few osteoclasts.

Receptor activator of nuclear factor-κB ligand (RANKL) is a pivotal osteoclast differentiation factor. To investigate the effect of RANKL inhibition in normal mice, we prepared an anti-mouse RANKL-neutralizing monoclonal antibody (Mab, clone OYC1) and established a new mouse model with high bone mass induced by administration of OYC1. A single subcutaneous injection of 5 mg/kg OYC1 in normal mice significantly augmented the bone mineral density in the distal femoral metaphysis from day 2 to day 28. The OYC1 treatment markedly reduced the serum level of tartrate-resistant acid phosphatase-5b (TRAP-5b, a marker for osteoclasts) on day 1, and this level was undetectable from day 3 to day 28. The serum level of alkaline phosphatase (a marker for osteoblasts) declined significantly following the reduction of TRAP-5b. Histological analysis revealed few osteoclasts in femurs of the treated mice on day 4, and both osteoclasts and osteoblasts were markedly diminished on day 14. Daily injection of parathyroid hormone for 2 weeks increased the bone mineral density in trabecular and cortical bone by stimulating bone formation in the OYC1-treated mice. These results suggest that parathyroid hormone exerted its bone anabolic activity in mice with few osteoclasts. The mouse anti-RANKL neutralizing antibody OYC1 may be a useful tool to investigate unknown functions of RANKL in vivo.

Establishment of a new murine model of hypercalcemia with anorexia by overexpression of soluble receptor activator of NF-κB ligand using an adenovirus vector.

Hypercalcemia is a significant complication of certain human malignancies that is primarily caused by the release of calcium from bone due to marked bone resorption by osteoclast activation. Osteoclast differentiation and activation is mediated by receptor activator of NF-κB ligand (RANKL). Transgenic mice overexpressing murine soluble RANKL (sRANKL) that we generated previously exhibited severe osteoporosis accompanied with enhanced osteoclastogenesis, but never exhibited hypercalcemia. To analyze the relationship between serum concentration of sRANKL and hypercalcemia and generate a simple and quick hypercalcemia model, an adenovirus vector harboring murine sRANKL cDNA (Ad-sRANKL) was injected i.p. into male C57BL/6 mice. Sera were collected to measure the levels of sRANKL, calcium and biochemical markers of bone turnover. Food intake and body weight were measured every 3 or 4 days. All the mice were killed 2 weeks after the injection, and femurs were collected to measure bone structure and bone mineral density (BMD). Serum sRANKL and calcium increased, peaking on day 7. Food intake and body weight significantly declined on day 7. These results indicated that the mice had anorexia as a symptom of hypercalcemia. Increases in bone resorption and formation markers with a marked decrease in BMD were observed on day 14. These results reflect accelerated bone formation following activation of osteoclasts, indicating coupling between bone formation and resorption. In conclusion, a new murine model of hypercalcemia with anorexia was established by overexpressing sRANKL. This model would be useful for studies of hypercalcemia and coupling between bone formation and resorption.

Suppressive effect of a traditional Japanese medicine, Hachimi-jio-gan (Ba-Wei-Di-Huang-Wan), on the hyperresponsiveness to IL-18 in autoimmune MRL/MPJ-lpr/lpr mice.

Oral administration of Hachimi-jio-gan (HMG, Ba-Wei-Di-Huang-Wan), a traditional Japanese herbal medicine, for several weeks, ameliorates some autoimmune symptoms of MRL/lpr mice. In the short time treatment for 9 days, hyperresponsiveness of mesenteric lymph node (MLN) cells to interleukin (IL)-18 manifested by the proliferation or the production of interferon (IFN)-gamma was significantly suppressed. Additionally, the treatment with HMG suppressed the expressions of IL-18Ralpha and IL-18Rbeta mRNA in CD45R(-) T cells, and also the expression of IL-18Ralpha mRNA in unpurified whole cells. Although the short treatment with HMG had no effect on the mRNA expressions of IL-10, IL-12 and IL-18, or the phosphorelated signal transducer and activator transcription (STAT)4 protein level in CD45R(-) MLN cells, the IL-4 mRNA expression or the phosphorelated STAT6 protein level were up-regulated by HMG, and the IL-4 mRNA up-regulation was clearer in whole cells than CD45R(-) cells. Furthermore, the treatment with HMG promoted the mRNA expression of invariant Valpha14 TCR that is uniquely expressed on NKT cells. Valpha14 NKT cells can produce large amount of IL-4 and play a crucial role in controlling the development of MRL/lpr mouse autoimmune disease. Therefore, these results suggested that HMG reduced the hyperresponsiveness of MRL/lpr mouse MLN cells to IL-18 through the reduction of IL-18Rs caused by Valpha14 NKT cell-produced IL-4, and consequently HMG suppressed the development of MRL/lpr autoimmune diseases.

Participation of contrasting changes in IL-10 and IL-12 production in the reduction of Th1-predominance by Hachimi-jio-gan in autoimmune MRL/MP-lpr/lpr mice.

Hachimi-jio-gan (Chinese name: Ba-Wei-Di-Huang-Wan, HMG), a traditional Japanese herbal medicine, has been used for disorders accompanying aging. Our previous studies suggested that HMG ameliorated Thl-predominant autoimmune diseases in MRL/lpr mice through inhibition of IL-12 production. In the present study, the oral administration of HMG down-regulated phosphorylated STAT4 and up-regulated phosphorylated STAT6 in CD4 T cells. In the T cells, IL-12Rbeta1 and IL-12Rbeta2 mRNA expression levels were suppressed. In antigen-presenting cells (CD45R- MHC class II+ cells) which control Th1 and Th2 immune responses, the total cell number and the percentage of cells expressing co-stimulatory molecules decreased in the HMG-treated group. In addition, the levels of IL-12 and 18 mRNA expression increased and conversely, IL-10 mRNA expression decreased. Further, the production of IL-10 was up-regulated and that of IL-12 was down-regulated by HMG in the presence of anti-CD40 antibody. These results suggest that the opposite effects on IL-10 production and, IL-12 or IL-18 production in antigen-presenting cells of oral administration of HMG are due a decline in IL-12R expression, and consequently, amelioration of MRL/lpr autoimmune diseases occurs through the suppression of Th1 predominance via STAT4/STAT6 signaling.