Pharmacologically targeting fatty acid synthase-mediated de novo lipogenesis alleviates osteolytic bone loss...

Pharmacologically targeting fatty acid synthase-mediated de novo lipogenesis alleviates osteolytic bone loss by directly inhibiting osteoclastogenesis through suppression of STAT3 palmitoylation and ROS signaling

AUTHORS

Chunmei Xiu, Lei Zhang, Chenxi Zhang, Yuannan Zhang, Xi Luo, Ziyi Zhang, Hangkai Zhao, Kaizhong Ji, Zhiyuan Chen, Guangxu He, Jianquan Chen

ABSTRACT

Aberrant increases in osteoclast formation and/or activity are the underlying cause of bone loss in a variety of osteolytic diseases. Fatty acid synthase (Fasn)-mediated de novo lipogenesis (DNL) is one of the major lipid metabolic pathways and has been shown to play critical roles in diverse physiological and pathological processes. However, little is known about its role in osteoclastogenesis. Here, we investigate the direct role of DNL in osteoclastogenesis and its therapeutic potential in osteolytic diseases. We found that Fasn expression and DNL levels are upregulated during receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclastogenesis. Inhibition of Fasn by shRNA knockdown or its pharmacological inhibitors (ASC40 and trans-C75) impairs osteoclast differentiation in vitro. Mechanistically, pharmacological inhibition of Fasn suppresses RANKL-induced c-Fos/NFATc1 expression and thus osteoclastogenesis partly by disrupting STAT3 palmitoylation, while promoting ROS scavenging to impair mitogen-activated protein kinase (MAPK) signaling. Finally, the therapeutic potential of ASC40 for the treatment of osteolytic bone loss is tested in two mouse models of osteolytic diseases, i.e. ovariectomy (OVX)-induced osteoporosis and titanium nanoparticle-induced calvarial osteolysis. The results show that ASC40 significantly attenuates bone loss and osteoclastogenesis in both models. In conclusion, our results demonstrate that Fasn-mediated DNL is a novel positive regulator of osteoclastogenesis and may serve as a promising therapeutic target for the treatment of osteoclast-driven osteolytic bone diseases.

Aberrant NSUN2-mediated m5C modification of exosomal LncRNA MALAT1 induced RANKL-mediated bone destruction in multiple myeloma

AUTHORS

Manya Yu, Zhiguo Cai, Jie Zhang, Yanyu Zhang, Jiaqi Fu, Xing Cui

ABSTRACT

The impact of exosome-mediated crosstalk between multiple myeloma (MM) cells and osteoclasts (OCs) on bone lesions remains to be investigated. Here, we identified NSUN2 and YBX1-mediated m5C modifications upregulated LncRNA MALAT1 expression in MM cells, which could be transported to OCs via exosomes and promote bone lesions. Methodologically, RNA-seq was carried out to detect the cargoes of exosomes. TRAP staining and WB were used to evaluate osteoclastogenesis in vitro. Micro-CT and bone histomorphometric analyses were performed to identify bone destruction in vivo. RNA pull-down, RIP, MeRIP, and luciferase reporter assays were used to test the interactions between molecules. The clinical features of MALAT1, NSUN2 and YBX1 were verified through public datasets and clinicopathological data analyses. Mechanistically, MALAT1 was the highest expressed lncRNA in U266 exosomes and could be transported to RAW264.7 cells. MALAT1 could enhance the differentiation of RAW264.7 cells into OCs by stimulating RANKL expression and its downstream AKT and MAPKs signaling pathways via a ceRNA mechanism. Additionally, MALAT1 could be modified by NSUN2, an m5C methyltransferase, which in turn stabilized MALAT1 through the “reader” YBX1. Clinical studies indicated a notable positive correlation between MALAT1, NSUN2, YBX1 levels and bone destruction features, as well as with RANKL expression.

Temporal patterns of osteoclast formation and activity following withdrawal of RANKL inhibition

AUTHORS

Albert S Kim, Victoria E Taylor, Ariel Castro-Martinez, Suraj Dhakal, Amjad Zamerli, Sindhu Mohanty, Ya Xiao, Marija K Simic, Jinchen Wen, Ryan Chai, Peter I Croucher, Jacqueline R Center, Christian M Girgis, Michelle M McDonald

ABSTRACT

Rebound bone loss following denosumab discontinuation is an important clinical challenge. Current treatment strategies to prevent this fail to suppress the rise and overshoot in osteoclast-mediated bone resorption. In this study, we use a murine model of denosumab treatment and discontinuation to show the temporal changes in osteoclast formation and activity during RANKL inhibition and withdrawal. We show that the cellular processes that drive the formation of osteoclasts and subsequent bone resorption following withdrawal of RANKL inhibition precede the rebound bone loss. Furthermore, a rise in serum TRAP and RANKL levels is detected before markers of bone turnover used in current clinical practice. These mechanistic advances may provide insight into a more defined window of opportunity to intervene with sequential therapy following denosumab discontinuation.

Piperlongumine, a Piper longum-derived amide alkaloid, protects mice from ovariectomy-induced osteoporosis by inhibiting osteoclastogenesis via suppression of p38 and JNK signaling†

AUTHORS

Na Luo, Lei Zhang, Chunmei Xiu, Xi Luo, Siyuan Hu, Kaizhong Ji, Qingbai Li, Jianquan Chen

ABSTRACT

Postmenopausal osteoporosis (PMOP) is a metabolic bone disease that results from overproduction and hyperactivation of osteoclasts caused by insufficient estrogen in women after menopause. Current therapeutic strategies are mainly focused on treating PMOP patients who have already developed severe bone loss or even osteoporotic fractures. Obviously, a better strategy is to prevent PMOP from occurring in the first place. However, such reagents are largely lacking. Piperlongumine (PLM), an amide alkaloid extracted from long pepper Piper longum, exhibits the anti-osteoclastogenic effect in normal bone marrow macrophages (BMMs) and the protective effect against osteolysis induced by titanium particles in mice. This study examined the preventive effect of PLM on PMOP and explored the potential mechanism of this effect using both ovariectomized mice and their primary cells. The result showed that PLM (5 and 10 mg kg−1) administered daily for 6 weeks ameliorated ovariectomy-induced bone loss and osteoclast formation in mice. Further cell experiments showed that PLM directly suppressed osteoclast formation, F-actin ring formation, and osteoclastic resorption pit formation in BMMs derived from osteoporotic mice, but did not obviously affect osteogenic differentiation of bone marrow stromal cells (BMSCs) from these mice. Western blot analysis revealed that PLM attenuated maximal activation of p38 and JNK pathways by RANKL stimulation without affecting acute activation of NF-κB, AKT, and ERK signaling. Furthermore, PLM inhibited expression of key osteoclastogenic transcription factors NFATc1/c-Fos and their target genes (Dcstamp, Atp6v0d2, Acp5, and Oscar). Taken together, our findings suggest that PLM inhibits osteoclast formation and function by suppressing RANKL-induced activation of the p38/JNK-cFos/NFATc1 signaling cascade, thereby preventing ovariectomy-induced osteoporosis in mice. Thus, PLM can potentially be used as an anti-resorption drug or dietary supplement for the prevention of PMOP.

Sexual dimorphism of osteoclast reliance on mitochondrial oxidation of energy substrates in the mouse

AUTHORS

Chao Song, Arianna Valeri, Fangfang Song, Xing Ji, Xueyang Liao, Tyler Marmo, Rebecca Seeley, Jared Rutter, and Fanxin Long

ABSTRACT

Osteoclasts specialize in bone resorption and are critical for bone remodeling. Previous studies have shown that osteoclasts possess abundant mitochondria and derive most energy through oxidative phosphorylation (OXPHOS). However, the energy substrates fueling OXPHOS in osteoclasts remain to be fully defined. Here, we showed that osteoclast differentiation was coupled with increased oxidation of glucose, glutamine, and oleate. Transcriptomic analyses with RNA sequencing revealed marked upregulation of genes participating in OXPHOS and mitochondrial fatty acid oxidation, during osteoclast differentiation. Increased mitochondrial oxidation of long-chain fatty acids was required for osteoclast differentiation in vitro. However, blocking fatty acid oxidation in vivo, by deletion of carnitine palmitoyltransferase 1a (Cpt1a) in osteoclast progenitors, impaired osteoclast formation only in the female mice. The Cpt1a-deficient females were further protected from osteoclast activation by a high-fat diet. The males, on the contrary, exhibited normal bone resorption despite Cpt1a deletion, regardless of the dietary fat content. Moreover, concurrent deletion of mitochondrial pyruvate carrier 1 and Cpt1a, blocking mitochondrial oxidation of both glucose and fatty acids in the osteoclast lineage, failed to impede bone resorption in the males. The study therefore uncovers a female-specific dependence on mitochondrial oxidation of fatty acids and glucose in osteoclasts in vivo.

Dlk2 interacts with Syap1 to activate Akt signaling pathway during osteoclast formation

AUTHORS

Xinwei Chen, Xuzhuo Chen, Rui Chao, Yexin Wang, Yi Mao, Baoting Fan, Yaosheng Zhang, Weifeng Xu, An Qin & Shanyong Zhang

ABSTRACT

Excessive osteoclast formation and bone resorption are related to osteolytic diseases. Delta drosophila homolog-like 2 (Dlk2), a member of the epidermal growth factor (EGF)-like superfamily, reportedly regulates adipocyte differentiation, but its roles in bone homeostasis are unclear. In this study, we demonstrated that Dlk2 deletion in osteoclasts significantly inhibited osteoclast formation in vitro and contributed to a high-bone-mass phenotype in vivo. Importantly, Dlk2 was shown to interact with synapse-associated protein 1 (Syap1), which regulates Akt phosphorylation at Ser473. Dlk2 deletion inhibited Syap1-mediated activation of the AktSer473, ERK1/2 and p38 signaling cascades. Additionally, Dlk2 deficiency exhibits increased bone mass in ovariectomized mice. Our results reveal the important roles of the Dlk2-Syap1 signaling pathway in osteoclast differentiation and osteoclast-related bone disorders.