Disuse osteoporosis is a metabolic bone disease resulted from skeletal unloading (e.g., during extended bed rest, limb immobilization, and spaceflight), and the slow and insufficient bone recovery during re-ambulation remains an unresolved medical challenge. Here, we demonstrated that loading-induced increase in bone architecture/strength was suppressed in skeletons previously exposed to unloading. This reduction in bone mechanosensitivity was directly associated with attenuated osteocytic Ca2+ oscillatory dynamics. The unloading-induced compromised osteocytic Ca2+ response to reloading resulted from the HIF-1α/PDK1 axis-mediated increase in glycolysis, and a subsequent reduction in ATP synthesis. HIF-1α also transcriptionally induced substantial glutaminase 2 expression and thereby glutamine addiction in osteocytes. Inhibition of glycolysis by blocking PDK1 or glutamine supplementation restored the mechanosensitivity in those skeletons with previous unloading by fueling the tricarboxylic acid cycle and rescuing subsequent Ca2+ oscillations in osteocytes. Thus, we provide a mechanistic insight into disuse-induced deterioration of bone mechanosensitivity and a promising therapeutic approach to accelerate bone recovery after long-duration disuse.
Xiyu Liu, Zedong Yan, Jing Cai, Dan Wang, Yongqing Yang, Yuanjun Ding, Xi Shao, Xiaoxia Hao, Erping Luo, X. Edward Guo, Peng Luo, Liangliang Shen, Da Jing
The various functions of the skeleton are influenced by extracellular cues, hormones and neurotransmitters. One type of neuronal regulation favors bone mass accrual by inhibiting sympathetic nervous system activity. This observation raises questions about the transcriptional mechanisms regulating catecholamine synthesis. Using a combination of genetic and pharmacological studies we have found that the histone deacetylase SIRT1 is a transcriptional modulator of the neuronal control of bone mass. Neuronal SIRT1 reduced bone mass by increasing SNS signaling. SIRT1 did so by increasing expression of monoamine oxidase A (MAO-A), a SIRT1 target that reduces brain serotonin levels by inducing its catabolism, and by suppressing Tph2 expression and serotonin synthesis in the brainstem. SIRT1 upregulated brain catecholamine synthesis indirectly through serotonin but did not directly affect Dbh expression in the locus coeruleus. These results help understand skeletal changes associated with SSRIs and may have implications for treating skeletal and metabolic diseases.
Na Luo, Ioanna Mosialou, Mattia Capulli, Brygida Bisikirska, Chyuan-Sheng Lin, Yung-yu Huang, Peter Timothy Shyu, X. Edward Guo, Aris Economides, J. John Mann, Stavroula Kousteni
Osteolytic bone disease is a hallmark of multiple myeloma (MM). A significant fraction (~20%) of MM patients do not develop osteolytic lesions (OL). The molecular basis for the absence of bone disease in MM is not understood. We combined PET-CT and gene expression profiling (GEP) of purified bone marrow (BM) CD138+ MM cells from 512 newly diagnosed MM patients to reveal that elevated expression of cystatin M/E (CST6) was significantly associated with the absence of OL in MM. An enzyme-linked immunosorbent assay revealed a strong correlation between CST6 levels in BM serum/plasma and CST6 mRNA expression. Both recombinant CST6 protein and BM serum from patients with high CST6 significantly inhibited the activity of the osteoclast-specific protease cathepsin K, and blocked osteoclast differentiation and function. Recombinant CST6 inhibited bone destruction in ex vivo and in vivo myeloma models. Single cell RNA-sequencing identified that CST6 attenuates polarization of monocytes to osteoclast precursors. Furthermore, CST6 protein blocks osteoclast differentiation by suppressing cathepsin-mediated cleavage of NF-κB/p100 and TRAF3 following RANKL stimulation. Secretion by MM cells of CST6, an inhibitor of osteoclast differentiation and function, suppresses osteolytic bone disease in MM and probably other diseases associated with osteoclast-mediated bone loss.
Dongzheng Gai, Jin-Ran Chen, James P. Stewart, Intawat Nookaew, Hasem Habelhah, Cody Ashby, Fumou Sun, Yan Cheng, Can Li, Hongwei Xu, Bailu Peng, Tarun K. Garg, Carolina Schinke, Sharmilan Thanendrarajan, Maurizio Zangari, Fangping Chen, Bart Barlogie, Frits van Rhee, Guido Tricot, John D. Shaughnessy Jr, Fenghuang Zhan
Fibrodysplasia ossificans progressiva (FOP) is a rare genetic disorder whose most debilitating pathology is progressive and cumulative heterotopic ossification (HO) of skeletal muscles, ligaments, tendons, and fascia. FOP is caused by mutations in the type I BMP receptor gene ACVR1, which enable ACVR1 to utilize its natural antagonist, Activin A, as an agonistic ligand. The physiological relevance of this property is underscored by the fact that HO in FOP is exquisitely dependent on activation of FOP-mutant ACVR1 by Activin A, an effect countered by inhibition of Activin A via monoclonal antibody treatment. Hence, we surmised that ACVR1 antibodies that block activation of ACVR1 by ligand should also inhibit HO in FOP and provide an additional therapeutic option for this condition. Therefore, we generated ACVR1 monoclonal antibodies that block ACVR1’s activation by its ligands. Surprisingly, in vivo, these ACVR1 antibodies stimulate HO and activate signaling of FOP-mutant ACVR1. This property is restricted to FOP-mutant ACVR1 and results from ACVR1 antibody-mediated dimerization of ACVR1. Conversely, wild type ACVR1 is inhibited by ACVR1 antibodies. These results uncover an additional novel property of FOP-mutant ACVR1 and indicate that ACVR1 antibodies should not be considered as therapeutics for FOP.
Senem Aykul, Lily Huang, Lili Wang, Nanditha M. Das, Sandra Reisman, Yonaton Ray, Qian Zhang, Nyanza J. Rothman, Kalyan C. Nannuru, Vishal Kamat, Susannah Brydges, Luca Troncone, Laura Johnsen, Paul B. Yu, Sergio Fazio, John Lees-Shepard, Kevin Schutz, Andrew J. Murphy, Aris N. Economides, Vincent Idone, Sarah J. Hatsell
Bone metastases are frequent complications of malignant melanoma leading to reduced quality of life and significant morbidity. Regulation of immune cells by the gut microbiome influences cancer progression, but the role of the microbiome in tumor growth in bone is unknown. Using intracardiac or intratibial injections of B16-F10 melanoma cells in mice we showed that gut microbiome depletion by broad-spectrum antibiotics accelerated intraosseous tumor growth and osteolysis. Microbiome depletion blunted melanoma-induced expansion of intestinal natural killer (NK) cells and T helper 1 (Th1) cells and their migration from the gut to tumor bearing bones. Demonstrating the functional relevance of immune cell trafficking from the gut to the bone marrow (BM) in bone metastasis, blockade of S1P-mediated NK and Th1 cells intestinal egress, or inhibition of their CXCR3/CXCL9-mediated influx into the BM prevented expansion of BM NK and Th1 cells and accelerated tumor growth and osteolysis. Using a mouse model, this study revealed mechanisms of microbiota-mediated gut-bone crosstalk that are relevant to the immunological restraint of melanoma metastasis and tumor growth in bone. Microbiome modifications induced by antibiotics might have negative clinical consequences in melanoma patients.
Subhashis Pal, Daniel S. Perrien, Tetsuya Yumoto, Roberta Faccio, Andreea Stoica, Jonathan Adams, Craig M. Coopersmith, Rheinallt M. Jones, M. Neale Weitzmann, Roberto Pacifici
Fibrodysplasia ossificans progressiva (FOP) is a rare genetic disease characterized by progressive and catastrophic heterotopic ossification (HO) of skeletal muscle and associated soft tissues. FOP is caused by dominantly acting mutations in the gene encoding the bone morphogenetic protein (BMP) type I receptor, ACVR1 (ALK2), the most prevalent of which results in an arginine to histidine substitution at position 206[ACVR1(R206H)]. The fundamental pathological consequence of FOP-causing ACVR1 receptor mutations is to enable activin A to initiate canonical BMP signaling in fibro-adipogenic progenitors (FAPs), which drives HO. We developed a monoclonal blocking antibody (JAB0505) to the extracellular domain of ACVR1 and tested its effect on HO in two independent FOP mouse models. Although JAB0505 inhibited BMP-dependent gene expression in wild-type and ACVR1(R206H)-overexpressing cell lines, JAB0505 treatment profoundly exacerbated injury-induced HO. JAB0505-treated mice exhibited multiple, distinct foci of heterotopic lesions, suggesting an atypically broad anatomical domain of FAP recruitment to endochondral ossification. This was accompanied by dysregulated FAP population growth and an abnormally sustained immunological reaction following muscle injury. JAB0505 drove injury-induced HO in the absence of activin A, indicating that JAB0505 has receptor agonist activity. These data raise serious safety and efficacy concerns for the use of bivalent anti-ACVR1 antibodies to treat patients with FOP.
John B. Lees-Shepard, Sean J. Stoessel, Julian T. Chandler, Keith Bouchard, Patricia Bento, Lorraine N. Apuzzo, Parvathi Madhavi Devarakonda, Jeffrey W. Hunter, David J. Goldhamer
Rheumatoid arthritis (RA) is characterized by chronic synovial inflammation with aberrant epigenetic alterations, eventually leading to joint destruction. However, the epigenetic regulatory mechanisms underlying RA pathogenesis remain largely unknown. Here we showed that Ubiquitin-like containing PHD and RING finger domains 1 (UHRF1) is a central epigenetic regulator that suppressively orchestrates multiple pathogeneses in RA. UHRF1 expression was remarkably up-regulated in synovial fibroblasts (SF) from arthritis model mice and RA patients. Mice with SF-specific Uhrf1 conditional knockout showed more severe arthritic phenotypes than littermate control. Uhrf1-deficient SF also exhibited enhanced apoptosis resistance and up-regulated expression of several cytokines including Ccl20. In RA patients, DAS28, CRP, and Th17 accumulation as well as apoptosis resistance were negatively correlated with UHRF1 expression in synovium. Finally, Ryuvidine administration that stabilizes UHRF1 ameliorated arthritis pathogeneses in a mouse model of RA. This study demonstrated that UHRF1 expressed in RA SF can contribute to negative feedback mechanisms that suppress multiple pathogenic events in arthritis, suggesting that targeting UHRF1 could be one of the therapeutic strategies for RA.
Noritaka Saeki, Kazuki Inoue, Maky Ideta-Otsuka, Kunihiko Watamori, Shinichi Mizuki, Katsuto Takenaka, Katsuhide Igarashi, Hiromasa Miura, Shu Takeda, Yuuki Imai
Cellular senescence plays an important role in human diseases, including osteoporosis and osteoarthritis. Senescent cells (SCs) produce the senescence-associated secretory phenotype to affect the function of neighboring cells and SCs themselves. Delayed fracture healing is common in the elderly and is accompanied by reduced mesenchymal progenitor cells (MPCs). However, the contribution of cellular senescence to fracture healing in the aged has not to our knowledge been studied. Here, we used C57BL/6J 4-month-old young and 20-month-old aged mice and demonstrated a rapid increase in SCs in the fracture callus of aged mice. The senolytic drugs dasatinib plus quercetin enhanced fracture healing in aged mice. Aged callus SCs inhibited the growth and proliferation of callus-derived MPCs (CaMPCs) and expressed high levels of TGF-β1. TGF-β–neutralizing Ab prevented the inhibitory effects of aged callus SCs on CaMPCs and promoted fracture healing in aged mice, which was associated with increased CaMPCs and proliferating cells. Thus, fracture triggered a significant cellular senescence in the callus cells of aged mice, which inhibited MPCs by expressing TGF-β1. Short-term administration of dasatinib plus quercetin depleted callus SCs and accelerated fracture healing in aged mice. Senolytic drugs represent a promising therapy, while TGF-β1 signaling is a molecular mechanism for fractures in the elderly via SCs.
Jiatong Liu, Jun Zhang, Xi Lin, Brendan F. Boyce, Hengwei Zhang, Lianping Xing
Through their ability to regulate gene expression in most organs, glucocorticoid hormones influence numerous physiological processes and therefore are key regulators of organismal homeostasis. In bone, glucocorticoid hormones inhibit the expression of the hormone Osteocalcin for poorly understood reasons. Here we show that in a classical endocrine feedback loop, osteocalcin in return enhances the biosynthesis of glucocorticoid but also mineralocorticoid hormones (adrenal steroidogenesis) in rodents and primates. Conversely, inactivating osteocalcin signalling in adrenal glands significantly impairs adrenal growth and steroidogenesis in mice. Embryo-made osteocalcin is necessary for normal Sf1 expression in foetal adrenal cells and adrenal cell steroidogenic differentiation, it therefore determines the number of steroidogenic cells present in adrenal glands of adult animals. Embryonic not postnatal osteocalcin also governs adrenal growth, adrenal steroidogenesis, blood pressure, electrolyte equilibrium and the rise of circulating corticosterone during the acute stress response in adult offspring. This osteocalcin-dependent regulation of adrenal development and steroidogenesis occurs even in the absence of a functional of hypothalamus-pituitary-adrenal axis; this explains why osteocalcin administration during pregnancy promotes adrenal growth and steroidogenesis and improves survival of adrenocorticotropic hormone signalling-deficient animals. This study reveals that a bone-derived, embryonic hormone influences lifelong adrenal functions and organismal homeostasis in the mouse.
Vijay K. Yadav, Julian M. Berger, Parminder Singh, Perumal Nagarajan, Gerard Karsenty
Therapeutics targeting osteoclasts are commonly used treatments for bone metastasis; however, whether and how osteoclasts regulate pre-metastatic niche and bone tropism is largely unknown. In this study, we report that osteoclast precursors (OPs) can function as a pre-metastatic niche component that facilitates breast cancer (BCa) bone metastasis at early stages. At the molecular level, unbiased GPCR ligand/agonist screening in BCa cells suggested that R-spondin 2 (RSPO2) and RANKL, through interacting with their receptor LGR4, promoted osteoclastic pre-metastatic niche formation and enhanced BCa bone metastasis. This was achieved by RSPO2/RANKL-LGR4 signal modulating WNT inhibitor DKK1 through Gαq and β-catenin signaling. DKK1 directly facilitated OP recruitment through suppressing its receptor low-density lipoprotein-related receptors 5 (LRP5) but not LRP6, upregulating Rnasek expression via inhibiting canonical WNT signaling. In clinical samples, RSPO2, LGR4 and DKK1 expression showed positive correlation with BCa bone metastasis. Furthermore, soluble LGR4 extracellular domain (ECD) protein, acting as a decoy receptor for RSPO2 and RANKL, significantly alleviated bone metastasis and osteolytic lesions in mouse bone metastasis model. These findings provide unique insights into the functional role of OPs as key components of pre-metastatic niche for BCa bone metastasis, indicate RSPO2/RANKL-LGR4 signaling as a promising target for inhibiting BCa bone metastasis.
Zhiying Yue, Xin Niu, Zengjin Yuan, Qin Qin, Wenhao Jiang, Liang He, Jingduo Gao, Yi Ding, Yanxi Liu, Ziwei Xu, Zhenxi Li, Zhengfeng Yang, Rong Li, Xiwen Xue, Yankun Gao, Fei Yue, Xiang H.-F. Zhang, Guohong Hu, Yi Wang, Yi Li, Geng Chen, Stefan Siwko, Alison Gartland, Ning Wang, Jianru Xiao, Mingyao Liu, Jian Luo