No abstract

Aging-related bone loss and osteoporosis affect millions of patients worldwide. Chronic inflammation associated with aging and arthritis promotes bone resorption and impairs bone formation. Here we show that Wnt4 attenuated bone loss in osteoporosis and skeletal aging by inhibiting nuclear factor-kappa B (NF-κB) via non-canonical Wnt signaling. Transgenic mice expressing Wnt4 from osteoblasts were significantly protected from bone loss and chronic inflammation induced by ovariectomy, tumor necrosis factor or natural aging. In addition to promoting bone formation, Wnt4 could inhibit osteoclast formation and bone resorption. Mechanistically, Wnt4 inhibited transforming growth factor beta-activated kinase 1-mediated NF-κB activation in macrophages and osteoclast precursors independent of β-catenin. Moreover, recombinant Wnt4 proteins were able to alleviate osteoporotic bone loss and inflammation by inhibiting NF-κB in vivo. Taken together, our results suggest that Wnt4 might be used as a therapeutic agent for treating osteoporosis by attenuating NF-κB.

Primary human oral keratinocytes were transformed by transfection with recombinant human papillomavirus type 16 (HPV-16) DNA, and two transformed cell lines named human oral keratinocytes-16A and -16B (HOK-16A and HOK-16B) were established. While normal cells and cells transfected with vector only exhibited a limited lifespan, the HOK-16A and HOK-16B lines demonstrated immortality and altered morphology from their normal counterpart. The HOK-16A and HOK-16B lines contained approximately 40 and approximately 25 copies of intact HPV-16 DNA as integrated form per cell respectively, and both cell lines expressed several viral specific poly(A+) RNAs. Notably these cell lines also overexpressed cellular myc proto-oncogene in comparison with the normal counterpart. However, the immortalized cell lines were not able to produce tumors in nude mice, indicating that the cells are partially transformed. The HOK-16A and HOK-16B lines are, therefore, useful for investigating the multistep molecular events of oral carcinogenesis.

The ability to penetrate tissue is an important virulence factor for pathogenic spirochetes. Previous studies have recognized the role of motility in allowing pathogenic spirochetes to invade tissues and migrate to sites favorable for bacterial proliferation. However, the nature of the movements, whether they are random or controlled by chemotaxis systems, has yet to be established. In this study, we addressed the role of motility and chemotaxis in tissue penetration by the periodontal disease-associated oral spirochete Treponema denticola using an oral epithelial cell line-based experimental approach. Wild-type T. denticola ATCC 35405 was found to penetrate the tissue layers effectively, whereas a nonmotile mutant was unable to overcome the tissue barrier. Interestingly, the chemotaxis mutants also showed impaired tissue penetration. A cheA mutant that is motile but lacks the central kinase of the chemotaxis pathway showed only about 2 to 3% of the wild-type penetration rate. The two known chemoreceptors of T. denticola, DmcA and DmcB, also appear to be involved in the invasion process. The dmc mutants were actively motile but exhibited reduced tissue penetration of about 30 and 10% of the wild-type behavior, respectively. These data suggest that not only motility but also chemotaxis is involved in the tissue penetration by T. denticola.

Drug-induced osteonecrosis of the jaw (ONJ) is a detrimental intraoral lesion that often occurs after dental-related interventions in patients undergoing treatment with bisphosphonates or denosumab, the neutralizing human anti-receptor activator of NF-κB ligand (RANKL) antibody (Ab). The cause of ONJ by these drugs has been speculated to their direct effects on osteoclasts. However, the extent to which osteoclasts contribute to ONJ pathogenesis remains controversial. Herein, by using a tooth-extraction mouse model with i.v. administration of mouse anti-RANKL Ab or the bisphosphonate zoledronate (ZOL), we show that unresorbed bone due to impaired formation or suppressed functions of osteoclasts, respectively, is associated with ONJ development. After tooth extraction, ONJ-like lesions developed 50% in the anti-RANKL Ab-treated mice and 30% in the ZOL-treated mice. Nonviable and unresorbed bone was found more in anti-RANKL Ab-treated mice compared with mice receiving ZOL. All mice receiving anti-RANKL Ab had an undetectable tartrate-resistant acid phosphatase (TRAP) level in the serum and no TRAP-positive osteoclasts at the extracted sockets, whereas ZOL-treated mice had a decreased TRAP level without altering the numbers of TRAP-positive osteoclasts. Interestingly, the absence of newly formed woven bone in the extracted sockets was evident in ONJ-like lesions from both anti-RANKL Ab- and ZOL-treated mice. Our study suggests that the lack of osteoclasts' bone-resorptive functions by these drugs and suppression of woven bone formation after dental trauma may be associated with ONJ development.