Cathepsin K-deficient osteocytes prevent lactation-induced bone loss and parathyroid hormone suppression.

Lactation induces bone loss to provide sufficient calcium in the milk, a process that involves osteoclastic bone resorption but also osteocytes and perilacunar resorption. The exact mechanisms by which osteocytes contribute to bone loss remain elusive. Osteocytes express genes required in osteoclasts for bone resorption, including cathepsin K (Ctsk), and lactation elevates their expression. We show that Ctsk deletion in osteocytes prevented the increase in osteocyte lacunar area seen during lactation, as well as the effects of lactation to increase osteoclast numbers and decrease trabecular bone volume, cortical thickness and mechanical properties. In addition, Ctsk deletion in osteocytes increased bone Parathyroid Hormone related Peptide (PTHrP), prevented the decrease in serum Parathyroid Hormone (PTH) induced by lactation, but amplified the increase in serum 1,25(OH)2D. The net result of these changes is to maintain serum and milk calcium levels in the normal range, ensuring normal offspring skeletal development. Our studies confirm the fundamental role of osteocytic perilacunar remodeling in physiological states of lactation and provides genetic evidence that osteocyte-derived Ctsk contributes not only to osteocyte perilacunar remodeling, but also to the regulation of PTH, PTHrP, 1,25-Dyhydroxyvitamin D (1,25(OH)2D), osteoclastogenesis and bone loss in response to the high calcium demand associated with lactation.

Irisin Mediates Effects on Bone and Fat via αV Integrin Receptors.

Irisin is secreted by muscle, increases with exercise, and mediates certain favorable effects of physical activity. In particular, irisin has been shown to have beneficial effects in adipose tissues, brain, and bone. However, the skeletal response to exercise is less clear, and the receptor for irisin has not been identified. Here we show that irisin binds to proteins of the αV class of integrins, and biophysical studies identify interacting surfaces between irisin and αV/ß5 integrin. Chemical inhibition of the αV integrins blocks signaling and function by irisin in osteocytes and fat cells. Irisin increases both osteocytic survival and production of sclerostin, a local modulator of bone remodeling. Genetic ablation of FNDC5 (or irisin) completely blocks osteocytic osteolysis induced by ovariectomy, preventing bone loss and supporting an important role of irisin in skeletal remodeling. Identification of the irisin receptor should greatly facilitate our understanding of irisin's function in exercise and human health.

The association between TNF-α 238A/G and 308A/G polymorphisms and juvenile idiopathic arthritis: An updated PRISMA-compliant meta-analysis.

OBJECTIVE: A previous meta-analysis concluded that TNF-α 238A/G and TNF-α 308A/G polymorphisms were not associated with the risk of juvenile idiopathic arthritis (JIA) in the overall population or Caucasian subjects. With the publication of a fair number of studies on the association between TNF-α polymorphisms and JIA in recent years, we conducted this updated meta-analysis to make a more accurate evaluation of such relationship. METHODS: We adopted PubMed, EMBASE, ISI Web of Science and CNKI to identify observational studies that addressed the association between TNF-α polymorphisms and risk for JIA. The allelic effect of variant A for the risk of JIA was expressed as odds ratio (OR) along with the associated 95% confidence interval (95% CI). Meta-analyses were performed by pooling ORs and 95%CI from included studies using RevMan 5.3 software. The stratified-analysis based on ethnicity was performed to confirm the ethnicity-dependent effect on the relationship. RESULTS: A total of 15 case-control studies including 2845 patients in JIA groups and 4771 patients in control groups were included in our study. The findings indicated a statistically significant association between the A allele of the TNF-alpha 238A/G polymorphism and the decreased JIA risk in Caucasians (P = .0002). The study in Iranian showed similar results (P = .0002) whereas the studies in other ethnicities failed to replicate this finding: Han (P = .29), Mexican (P = .64) and Turkish population (P = .32). TNF-α 308A/G was not statistically associated with JIA in overall subjects or Caucasians. CONCLUSION: Our study confirmed the protective role of the A allele in TNF-α 238A/G but not TNF-α 308A/G against the occurrence of JIA in the Caucasian population. To exactly validate the correlation between TNF-α polymorphisms and JIA in other ethnic backgrounds, additional studies are required.

Boldine Ameliorates Estrogen Deficiency-Induced Bone Loss via Inhibiting Bone Resorption.

Osteoporosis is an enormous health problem caused by the imbalance between bone resorption and bone formation. The current therapeutic strategies for osteoporosis still have some limitations. Boldine, an alkaloid isolated from Peumus boldus, has been shown to have antioxidant and anti-inflammatory effects in vivo. For the first time, we discover that boldine has a protective effect for the estrogen deficiency-induced bone loss in mice. According to the Micro-CT and histomorphometry assays, boldine conducts this protective effect through inhibiting bone resorption without affecting bone formation in vivo. Moreover, we showed that boldine can inhibit receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclast formation via impairing the AKT signaling pathways, while SC79 (an AKT agonist) partially rescue this effect. In conclusion, our results suggest that boldine can prevent estrogen deficiency-induced osteoporosis by inhibiting osteoclastogenesis. Thus, boldine may be served as a novel therapeutic agent for anti-osteoporotic therapy.

Sophocarpine attenuates wear particle-induced implant loosening by inhibiting osteoclastogenesis and bone resorption via suppression of the NF-κB signalling pathway in a rat model.

BACKGROUND AND PURPOSE: Aseptic prosthesis loosening, caused by wear particles, is one of the most common causes of arthroplasty failure. Extensive and over-activated osteoclast formation and physiological functioning are regarded as the mechanism of prosthesis loosening. Therapeutic modalities based on inhibiting osteoclast formation and bone resorption have been confirmed to be an effective way of preventing aseptic prosthesis loosening. In this study, we have investigated the effects of sophocarpine (SPC, derived from Sophora flavescens) on preventing implant loosening and further explored the underlying mechanisms. EXPERIMENTAL APPROACH: The effects of SPC in inhibiting osteoclastogenesis and bone resorption were evaluated in osteoclast formation, induced in vitro by the receptor activator of NF-κB ligand (RANKL). A rat femoral particle-induced peri-implant osteolysis model was established. Subsequently, micro-CT, histology, mechanical testing and bone turnover were used to assess the effects of SPC in preventing implant loosening. KEY RESULTS: In vitro, we found that SPC suppressed osteoclast formation, bone resorption, F-actin ring formation and osteoclast-associated gene expression by inhibiting NF-κB signalling, specifically by targeting IκB kinases. Our in vivo study showed that SPC prevented particle-induced prosthesis loosening by inhibiting osteoclast formation, resulting in reduced periprosthetic bone loss, diminished pseudomembrane formation, improved bone-implant contact, reduced bone resorption-related turnover and enhanced stability of implants. Inhibition of NF-κB signalling by SPC was confirmed in vivo. CONCLUSION AND IMPLICATIONS: SPC can prevent implant loosening through inhibiting osteoclast formation and bone resorption. Thus, SPC might be a novel therapeutic agent to prevent prosthesis loosening and for osteolytic diseases.