The mitochondrial sirtuin 3 (SIRT3) is involved in suppressing the onset of multiple pathologies, including cardiovascular disease, fatty liver, age-related hearing loss, and breast cancer. But a physiological role of SIRT3 in bone metabolism is not known. Here we show that SIRT3 is a key regulatory molecule to maintain bone homeostasis. Mice deficient in SIRT3 exhibited severe osteopenia owing to increased numbers of osteoclasts. Osteoclast precursors from Sirt3−/− mice underwent increased osteoclastogenesis in response to receptor activator of nuclear factor-κB ligand (RANKL), an essential cytokine for osteoclast differentiation. SIRT3 expression from RANKL induction depended on the transcription coactivator PGC-1β (peroxisome proliferator-activated receptor-γ co-activator-1β) and the nuclear receptor ERRα (estrogen receptor-related receptor α), and that SIRT3 inhibited the differentiation by interfering with the RANKL-induced expression of PGC-1β. Thus an auto-regulatory feedback mechanism operates to induce its own inhibitor SIRT3 by PGC-1β. Moreover, Sirt3−/− osteoclast precursors reduced AMP-activated protein kinase (AMPK) phosphorylation through down-regulating the expression of AMPK. Our results suggest that a mitochondrial SIRT3 is an intrinsic inhibitor for RANKL-mediated osteoclastogenesis.

Coexisting Hashimoto's thyroiditis in patients with papillary thyroid carcinoma was identified as a negative independent predictive factor for central lymph node metastasis.

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Osteoclast cells (OCs) are differentiated from bone marrow-derived macrophages (BMMs) by activation of receptor activator of nuclear factor κB (NF-κB) ligand (RANKL). Activation of NADPH oxidase (Nox) isozymes is involved in RANKL-dependent OC differentiation, implicating Nox isozymes as therapeutic targets for treatment of osteoporosis. Here, we show that a novel pyrazole derivative, Ewha-18278 has high inhibitory potency on Nox isozymes. Blocking the activity of Nox with Ewha-18278 inhibited the responses of BMMs to RANKL, including reactive oxygen species (ROS) generation, activation of mitogen-activated protein (MAP) kinases and NF-κB, and OC differentiation. To evaluate the anti-osteoporotic function of Ewha-18278, the derivative was applied to estrogen-deficient ovariectomized (OVX) ddY mice. Oral administration of Ewha-18278 (10 mg/kg/daily, 4 weeks) into the mice recovered bone mineral density, trabecular bone volume, trabecular bone length, number and thickness, compared to control OVX ddY mice. Moreover, treatment of OVX ddY mice with Ewha-18278 increased bone strength by increasing cortical bone thickness. We provide that Ewha-18278 displayed Nox inhibition and blocked the RANKL-dependent cell signaling cascade leading to reduced differentiation of OCs. Our results implicate Ewha-18278 as a novel therapeutic agent for the treatment of osteoporosis.

Although Toll-like receptors (TLRs) have been implicated in the regulation of stem cell functions, their role in osteogenic differentiation of adipose-derived stromal cells (ASCs) has not been reported. We found that ASCs express a restricted subset of TLRs, including TLR1-TLR5, and that TLR agonists such as Pam3CSK4 (TLR1/2 agonist), polyinosinic:polycytidylic acid (TLR3 agonist), lipopolysaccharide (TLR4 agonist), and flagellin (TLR5 agonist), but not R848 (TLR7/8 agonist), consistently induced osteogenic differentiation in murine-derived ASCs, which coincided with the TLR expression pattern of ASCs. Cytokine expression profiles induced by TLR agonists and results from subsequent functional assays indicated that interleukin-6 (IL-6) together with soluble IL-6 receptor (sIL-6R) enhanced osteogenic differentiation of ASCs by activating STAT3. Small interfering RNA (siRNA)-mediated STAT3-silencing blunted osteogenesis and the expression of osteogenic markers, whereas STAT3 overexpression resulted in an increase in osteogenesis. Consistently, STAT3 inhibitor treatment reduced osteogenesis, STAT3 phosphorylation, and expression of osteogenic markers including osterix. Chromatin immunoprecipitation (ChIP) assays indicated that STAT3 binding to the STAT3-binding sites on the osterix promoter increased during IL-6-stimulated osteogenesis. Our results thus establish TLRs as novel regulators of ASCs which signal through IL-6/STAT3 pathway and induce osterix expression as a part of the osteogenesis.