The periosteum, a thin tissue that covers almost the entire bone surface, accounts for more than 80% of human bone mass and is essential for bone regeneration. Its osteogenic and bone regenerative abilities are well studied, but much is unknown about the periosteum. In this study, we found that macrophage-lineage cells recruit periosteum-derived cells (PDCs) for cortical bone formation. Knockout of colony stimulating factor-1 eliminated macrophage-lineage cells and resulted in loss of PDCs with impaired periosteal bone formation. Moreover, macrophage-lineage TRAP+ cells induced transcriptional expression of periostin and recruitment of PDCs to the periosteal surface through secretion of platelet-derived growth factor-BB (PDGF-BB), where the recruited PDCs underwent osteoblast differentiation coupled with type H vessel formation. We also found that subsets of Nestin+ and LepR+ PDCs possess multipotent and self-renewal abilities and contribute to cortical bone formation. Nestin+ PDCs are found primarily during bone development, whereas LepR+ PDCs are essential for bone homeostasis in adult mice. Importantly, conditional knockout of Pdgfrβ (platelet-derived growth factor receptor beta) in LepR+ cells impaired periosteal bone formation and regeneration. These findings uncover the essential role of periosteal macrophage-lineage cells in regulating periosteum homeostasis and regeneration.
Bo Gao, Ruoxian Deng, Yu Chai, Hao Chen, Bo Hu, Xiao Wang, Shouan Zhu, Yong Cao, Shuangfei Ni, Mei Wan, Liu Yang, Zhuojing Luo, Xu Cao
Bone osteogenic sarcoma has a poor prognosis as the exact cell of origin and the signaling pathways underling tumor formation remain undefined. Here, we report an osteogenic tumor mouse model based on the conditional knockout of liver kinase b1 (Lkb1; also known as Stk11) in Cathepsin K (Ctsk)-Cre expressing cells. Lineage tracing studies demonstrated that Ctsk-Cre could label a population of periosteal cells. The cells functioned as mesenchymal progenitors with regard to markers and functional properties. LKB1 deficiency increased proliferation and osteoblast differentiation of Ctsk+ periosteal cells, while downregulation of mTORC1 activity, using Raptor genetic mouse model or mTORC1 inhibitor treatment, ameliorated tumor progression of Ctsk-Cre Lkb1fllfl mice. Xenograft mouse models, using human osteosarcoma cell lines, also demonstrated that LKB1 deficiency promoted tumor formation, while mTOR inhibition suppressed xenograft tumor growth. In summary, we identified periosteum-derived Ctsk-Cre expressing cells as a cell of origin for osteogenic tumor and suggested the LKB1-mTORC1 pathway as a promising target for treatment of osteogenic tumor.
Yujiao Han, Heng Feng, Jun Sun, Xiaoting Liang, Zhuo Wang, Wenhui Xing, Qinggang Dai, Yang Yang, Anjia Han, Zhanying Wei, Qing Bi, Hongbin Ji, Tiebang Kang, Weiguo Zou
Joint pain is the defining symptom of osteoarthritis (OA) but its origin and mechanisms remain unclear. Here, we investigated an unprecedented role of osteoclast-initiated subchondral bone remodeling in sensory innervation for OA pain. We show that osteoclasts secrete NETRIN1 to induce sensory nerve axonal growth in subchondral bone. Reduction of osteoclast formation by knockout of receptor activator of nuclear factor kappa-B ligand (Rankl) in osteocytes inhibited the growth of sensory nerves into subchondral bone, DRG neuron hyperexcitability, and behavioral measures of pain hypersensitivity in OA mice. Moreover, we demonstrated a possible role for NETRIN1 secreted by osteoclasts during aberrant subchondral bone remodeling in inducing sensory innervation and OA pain through its receptor DCC (deleted in colorectal cancer). Importantly, knockout of Netrin1 in tartrate-resistant acid phosphatase (TRAP) positive osteoclasts or knockdown of Dcc reduces OA pain behavior. In particular, inhibition of osteoclast activity by alendronate modifies aberrant subchondral bone remodeling and reduces innervation and pain behavior at the early stage of OA. These results suggest that intervention of the axonal guidance molecules (e.g. NETRIN1) derived from aberrant subchondral bone remodeling may have therapeutic potential for OA pain.
Shouan Zhu, Jianxi Zhu, Gehua Zhen, Yihe Hu, Senbo An, Yusheng Li, Qin Zheng, Zhiyong Chen, Ya Yang, Mei Wan, Richard Leroy Skolasky, Yong Cao, Tianding Wu, Bo Gao, Mi Yang, Manman Gao, Julia Kuliwaba, Shuangfei Ni, Lei Wang, Chuanlong Wu, David Findlay, Holger K. Eltzschig, Hong Wei Ouyang, Janet Crane, Feng-Quan Zhou, Yun Guan, Xinzhong Dong, Xu Cao
Notch signaling critically controls cell fate decisions in mammals, both during embryogenesis and in adults. In the skeleton, Notch suppresses osteoblast differentiation and sustains bone marrow mesenchymal progenitors during postnatal life. Stabilizing mutations of Notch2 cause the Hajdu-Cheney syndrome characterized by early onset osteoporosis in humans, but the mechanism whereby Notch inhibits bone accretion is not fully understood. Here we report that activation of Notch signaling by either Jagged1 or Notch2 intracellular domain suppresses glucose metabolism and osteoblast differentiation in primary cultures of bone marrow mesenchymal progenitors. Importantly, deletion of Notch2 in the limb mesenchyme increases both glycolysis and bone formation in the long bones of postnatal mice, whereas pharmacological reduction of glycolysis abrogates the excessive bone formation. Mechanistically, Notch reduces the expression of glycolytic and mitochondrial Complex I genes, resulting in a decease in mitochondrial respiration, superoxide production and Ampk activity. Forced activation of Ampk restores glycolysis in the face of Notch signaling. Thus, suppression of glucose metabolism contributes to the mechanism whereby Notch restricts osteoblastogenesis from bone marrow mesenchymal progenitors.
Seung-Yon Lee, Fanxin Long
Hyperphosphatemic familial tumoral calcinosis (HFTC)/hyperostosis-hyperphosphatemia syndrome (HHS) is an autosomal recessive disorder of ectopic calcification due to deficiency of or resistance to intact fibroblast growth factor 23 (iFGF23). Inactivating mutations in FGF23, N-acetylgalactosaminyltransferase 3 (GALNT3), or KLOTHO have been reported to cause HFTC/HHS. We present the first identified case of autoimmune hyperphosphatemic tumoral calcinosis in an 8-year-old boy. In addition to the classical clinical and biochemical features of hyperphosphatemic tumoral calcinosis, the patient exhibited markedly elevated intact and C-terminal FGF23 levels suggestive of FGF23 resistance. However, no mutations in FGF23, KLOTHO, or fibroblast growth factor receptor 1 (FGFR1) were identified. He subsequently developed type 1 diabetes mellitus, which raised the possibility of an autoimmune cause for hyperphosphatemic tumoral calcinosis. Luciferase immunoprecipitation systems revealed significantly elevated FGF23 autoantibodies without detectable FGFR1 or KLOTHO autoantibodies. Using an in vitro FGF23 functional assay, the FGF23 autoantibodies in the patient’s plasma blocked downstream signaling via the MAPK/ERK signaling pathway in a dose-dependent manner. Thus, this report describes the first case of autoimmune hyperphosphatemic tumoral calcinosis with pathogenic autoantibodies targeting FGF23. Identification of this pathophysiology extends the etiologic spectrum of hyperphosphatemic tumoral calcinosis and suggests that immunomodulatory therapy may be an effective treatment.
Mary Scott Roberts, Peter D. Burbelo, Daniela Egli-Spichtig, Farzana Perwad, Christopher J. Romero, Shoji Ichikawa, Emily G. Farrow, Michael J. Econs, Lori C. Guthrie, Michael T. Collins, Rachel I. Gafni
BACKGROUND. Evidence from rodent studies indicates that the sympathetic nervous system (SNS) regulates bone metabolism, principally via β2-adrenergic receptors (β2-ARs). Given conflicting human data, we used multiple approaches to evaluate the role of the SNS in regulating human bone metabolism. METHODS. (1) Bone biopsies were obtained from 19 young and 19 old women for assessment of ADRB1, ADRB2, and ADRB3 mRNA expression; (2) the relationship of β-blocker use to bone microarchitecture was assessed by high resolution-peripheral quantitative computed tomography in a population sample of 248 subjects; and (3) 155 postmenopausal women were randomized to one of five treatment groups for 20 weeks: placebo; propranolol, 20 mg twice a day (BID); propranolol, 40 mg BID; atenolol, 50 mg/d; and nebivolol, 5 mg/d. We took advantage of the β1-AR selectivity gradient of these drugs (propranolol [non-selective] << atenolol [relatively β1-AR selective] < nebivolol [highly β1-AR selective]) to define the β-AR selectivity for SNS effects on bone. RESULTS. (1) ADRB1and ADRB2, but not ADRB3, were expressed in human bone; (2) patients treated clinically with β1-AR selective blockers had better bone microarchitecture than non-users; and (3) relative to placebo, atenolol and nebivolol, but not propranolol, reduced the bone resorption marker serum C-telopeptide of type I collagen (by 19.5% and 20.6%, respectively; P < 0.01) and increased ultra-distal radius BMD (by 3.6% and 2.9%; P < 0.01 and P < 0.05, respectively). CONCLUSIONS. These three independent lines of evidence strongly support a role for adrenergic signaling in regulating bone metabolism in humans, principally via β1-ARs. TRIAL REGISTRATION. ClinicalTrials.gov NCT02467400. FUNDING. This research was supported by NIH grants AG004875, AR027065, and the Mayo Clinic CTSA (UL1 TR002377).
Sundeep Khosla, Matthew T. Drake, Tammie L. Volkman, Brianne S. Thicke, Sara J. Achenbach, Elizabeth J. Atkinson, Michael J. Joyner, Clifford J. Rosen, David G. Monroe, Joshua N. Farr
The biological activity of 24R,25-dihydroxyvitamin D3 [24R,25(OH)2D3] remains controversial, but it has been suggested that it contributes to fracture healing. Cyp24a1–/– mice, synthesizing no 24R,25(OH)2D3, show suboptimal endochondral ossification during fracture repair, with smaller callus and reduced stiffness. These defects were corrected by 24R,25(OH)2D3 treatment, but not by 1,25-dihydroxyvitamin D3. Microarrays with Cyp24a1–/– callus mRNA identified FAM57B2 as a mediator of the 24R,25(OH)2D3 effect. FAM57B2 produced lactosylceramide (LacCer) upon specific binding of 24R,25(OH)2D3. Fam57b inactivation in chondrocytes (Col2-Cre Fam57bfl/fl) phenocopied the callus formation defect of Cyp24a1–/– mice. LacCer or 24R,25(OH)2D3 injections restored callus volume, stiffness, and mineralized cartilage area in Cyp24a1-null mice, but only LacCer rescued Col2-Cre Fam57bfl/fl mice. Gene expression in callus tissue suggested that the 24R,25(OH)2D3/FAM57B2 cascade affects cartilage maturation. We describe a previously unrecognized pathway influencing endochondral ossification during bone repair through LacCer production upon binding of 24R,25(OH)2D3 to FAM57B2. Our results identify potential new approaches to ameliorate fracture healing.
Corine Martineau, Roy Pascal Naja, Abdallah Husseini, Bachar Hamade, Martin Kaufmann, Omar Akhouayri, Alice Arabian, Glenville Jones, René St-Arnaud
In the brain, the ventral hypothalamus (VHT) regulates energy and bone metabolism. Whether this regulation uses the same or different neuronal circuits is unknown. Alteration of AP1 signaling in the VHT increases energy expenditure, glucose utilization, and bone density, yet the specific neurons responsible for each or all of these phenotypes are not identified. Using neuron-specific genetically targeted AP1 alterations as a tool in adult mice, we found that AgRP- or POMC- expressing neurons, predominantly present in the arcuate nucleus (ARC) within the VHT, stimulate whole body energy expenditure, glucose utilization and bone formation and density, although their effects on bone resorption differed. In contrast, AP1 alterations in Steroidogenic factor 1 (SF1)-expressing neurons, present in the ventromedial hypothalamus (VMH), increase energy, but decrease bone density, suggesting that these effects are independent. Altered AP1 signaling also increased the levels of the neuromediator galanin in the hypothalamus and global galanin deletion, VHT galanin silencing using shRNA, or pharmacological galanin receptor blockade, counteracted the observed effects on energy and bone. Thus, AP1 antagonism reveals that AgRP- and POMC- expressing neurons can stimulate body metabolism and increase bone density, with galanin acting as a central downstream effector. The results obtained with SF1-expressing neurons, however, indicate that bone homeostasis is not always dictated by the global energy status, and vice versa.
Anna Idelevich, Kazusa Sato, Kenichi Nagano, Glenn Rowe, Francesca Gori, Roland Baron
Coupling is the process that links bone resorption to bone formation in a temporally and spatially coordinated manner within the remodeling cycle. Several lines of evidence point to the critical roles of osteoclast-derived coupling factors in the regulation of osteoblast performance. Here, we used a fractionated secretomic approach and identified the axon-guidance molecule SLIT3 as a clastokine that stimulated osteoblast migration and proliferation by activating β-catenin. SLIT3 also inhibited bone resorption by suppressing osteoclast differentiation in an autocrine manner. Mice deficient in Slit3 or its receptor, Robo1, exhibited osteopenic phenotypes due to a decrease in bone formation and increase in bone resorption. Mice lacking Slit3 specifically in osteoclasts had low bone mass, whereas mice with either neuron-specific Slit3 deletion or osteoblast-specific Slit3 deletion had normal bone mass, thereby indicating the importance of SLIT3 as a local determinant of bone metabolism. In postmenopausal women, higher circulating SLIT3 levels were associated with increased bone mass. Notably, injection of a truncated recombinant SLIT3 markedly rescued bone loss after an ovariectomy. Thus, these results indicate that SLIT3 plays an osteoprotective role by synchronously stimulating bone formation and inhibiting bone resorption, making it a potential therapeutic target for metabolic bone diseases.
Beom-Jun Kim, Young-Sun Lee, Sun-Young Lee, Wook-Young Baek, Young Jin Choi, Sung Ah Moon, Seung Hun Lee, Jung-Eun Kim, Eun-Ju Chang, Eun-Young Kim, Jin Yoon, Seung-Whan Kim, Sung Ho Ryu, Sun-Kyeong Lee, Joseph A. Lorenzo, Seong Hee Ahn, Hyeonmok Kim, Ki-Up Lee, Ghi Su Kim, Jung-Min Koh
Genetic forms of vitamin D–dependent rickets (VDDRs) are due to mutations impairing activation of vitamin D or decreasing vitamin D receptor responsiveness. Here we describe two unrelated patients with early-onset rickets, reduced serum levels of the vitamin D metabolites 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D, and deficient responsiveness to parent and activated forms of vitamin D. Neither patient had a mutation in any genes known to cause VDDR, however, using whole exome sequence analysis we identified a recurrent de novo missense mutation c.902T>C (p.I301T) in CYP3A4 in both subjects that alters the conformation of substrate-recognition-site 4 (SRS-4). In vitro, the mutant CYP3A4 oxidized 1,25-dihydroxyvitamin D with 10-fold greater activity than wild-type CYP3A4 and 2-fold greater activity than CYP24A1, the principal inactivator of vitamin D metabolites. As CYP3A4 mutations have not previously been linked to rickets, these findings provide new insight into vitamin D metabolism, and demonstrate that accelerated inactivation of vitamin D metabolites represents a previously undescribed mechanism for vitamin D deficiency.
Jeffrey D. Roizen, Dong Li, Lauren O'Lear, Muhammad K. Javaid, Nicholas J. Shaw, Peter R. Ebeling, Hanh H. Nguyen, Christine P. Rodda, Kenneth E. Thummel, Tom D Thacher, Hakon Hakonarson, Michael A. Levine