Bone biology
Abstract
Adolescent idiopathic scoliosis (AIS) is the most common form of spinal deformity affecting millions of adolescents worldwide, but it lacks a defined theory of etiopathogenesis. As such, treatment of AIS is limited to bracing and/or invasive surgery post onset. Pre-onset diagnosis or preventive treatment remains unavailable. Here we performed a genetic analysis of a large multi-center AIS cohort and identified disease-causing and predisposing variants of SLC6A9 in multi-generation families, trios, and sporadic patients. Variants of SLC6A9, which encodes glycine transporter 1 (GLYT1), reduced glycine uptake activity in cells, leading to an increased extracellular glycine level and aberrant glycinergic neurotransmission. Slc6a9 mutant zebrafish exhibited discoordination of spinal neural activities and pronounced lateral spinal curvature, a phenotype resembling human patients. The penetrance and severity of curvature was sensitive to the dosage of functional glyt1. Administration of a glycine receptor antagonist or a clinically-used glycine neutralizer (sodium benzoate) partially rescued the phenotype. Our results indicate a neuropathic origin for “idiopathic” scoliosis, involving the dysfunction of synaptic neurotransmission and central pattern generators (CPGs), potentially a common cause of AIS. Our work further suggests avenues for early diagnosis and intervention of AIS in preadolescents.
Authors
Xiaolu Wang, Ming Yue, Jason Pui Yin Cheung, Prudence Wing Hang Cheung, Yanhui Fan, Meicheng Wu, Xiaojun Wang, Sen Zhao, Anas M. Khanshour, Jonathan J. Rios, Zheyi Chen, Xiwei Wang, Wenwei Tu, Danny Chan, Qiuju Yuan, Dajiang Qin, Guixing Qiu, Zhihong Wu, Jianguo Zhang, Shiro Ikegawa, Nan Wu, Carol A. Wise, Yong Hu, Keith Dipp Kei Luk, You-Qiang Song, Bo Gao
Abstract
Brain vascular calcification is a prevalent age-related condition often accompanying neurodegenerative and neuroinflammatory diseases. The pathogenesis of large vessel calcifications in peripheral tissue is well-studied, but microvascular calcification in the brain remains poorly understood. Here, we report that elevated platelet-derived growth factor BB (PDGF-BB) from bone preosteoclasts contribute to cerebrovascular calcification in male mice. Aged male mice exhibited higher serum PDGF-BB levels and a significantly higher incidence of brain calcification compared to young mice, mainly in the thalamus. Transgenic mice with preosteoclast-specific Pdgfb overexpression exhibited elevation of serum PDGF-BB levels and recapitulated age-associated thalamic calcification. Conversely, mice with preosteoclast-specific Pdgfb deletion displayed diminished age-associated thalamic calcification. In an ex vivo cerebral microvascular culture system, PDGF-BB dose-dependently promoted vascular calcification. Analysis of osteogenic gene array and single-cell RNA sequencing revealed that PDGF-BB upregulates multiple osteogenic differentiation genes and the phosphate transporter Slc20a1 in cerebral microvessels. Mechanistically, PDGF-BB stimulated the phosphorylation of its receptor PDGFRβ (pPDGFRβ) and ERK (p-ERK), leading to the activation of RUNX2. This activation, in turn, induced the transcription of the osteoblast differentiation genes in pericytes and upregulated Slc20a1 in astrocytes. Thus, bone-derived PDGF-BB induces brain vascular calcification by activating the pPDGFRβ/p-ERK/RUNX2 signaling cascade in cerebrovascular cells.
Authors
Jiekang Wang, Ching-Lien Fang, Kathleen Noller, Zhiliang Wei, Guanqiao Liu, Ke Shen, Kangping Song, Xu Cao, Mei Wan
Abstract
Authors
Kara N. Thomas, Destani D. Derrico, Michael C. Golding
Abstract
Renal osteodystrophy (ROD) is a disorder of bone metabolism that affects virtually all patients with chronic kidney disease (CKD), and is associated with adverse clinical outcomes including fractures, cardiovascular events and death. In the present study, we showed that hepatocyte nuclear factor 4 alpha (HNF4α), a transcription factor mostly expressed in the liver, is also expressed in bone, and that osseous HNF4α expression was dramatically reduced in patients and mice with ROD. Osteoblast-specific deletion of Hnf4α resulted in impaired osteogenesis in cells and mice. Using multi-omics analyses of bones and cells lacking or overexpressing Hnf4α1 and Hnf4α2, we showed that HNF4α2 is the main osseous Hnf4α isoform that regulates osteogenesis, cell metabolism, and cell death. As a result, osteoblast-specific overexpression of Hnf4α2 prevented bone loss in mice with CKD. Our results showed that HNF4α2 is a transcriptional regulator of osteogenesis, implicated in the development of ROD.
Authors
Marta Martinez-Calle, Guillaume Courbon, Bridget Hunt-Tobey, Connor Francis, Jadeah J. Spindler, Xueyan Wang, Luciene M. dos Reis, Carolina Steller Wagner Martins, Isidro B. Salusky, Hartmut H. Malluche, Thomas L. Nickolas, Rosa M.A. Moyses, Aline Martin, Valentin David
Abstract
Cutaneous Skeletal Hypophosphatemia Syndrome (CSHS) is a mosaic RASopathy characterized by the association of dysplastic skeletal lesions, congenital skin nevi of epidermal and/or melanocytic origin, and fibroblast growth factor-23 (FGF23)-mediated hypophosphatemia. The primary physiological source of circulating FGF23 is bone cells. However, several reports have suggested skin lesions as the source of excess FGF23 in CSHS. Consequently, without convincing evidence of efficacy, many patients with CSHS have undergone painful removal of cutaneous lesions in an effort to normalize blood phosphate levels.This study aims to elucidate whether the source of FGF23 excess in CSHS is RAS mutation-bearing bone or skin lesions. Towards this end, we analyzed the expression and activity of Fgf23 in two mouse models expressing similar HRAS/Hras activating mutations in a mosaic-like fashion in either bone or epidermal tissue. We found that HRAS hyperactivity in bone, not skin, caused excess of bioactive intact FGF23, hypophosphatemia and osteomalacia. Our findings support RAS-mutated dysplastic bone as the primary source of physiologically active FGF23 excess in patients with CSHS. This evidence informs the care of patients with CSHS, arguing against the practice of nevi removal to decrease circulating, physiologically active FGF23.
Authors
Diana Ovejero, Zachary Michel, Christophe Cataisson, Amanda Saikali, Rebeca Galisteo, Stuart H. Yuspa, Michael T. Collins, Luis F. de Castro
Abstract
IL-17A (IL-17), a driver of the inflammatory phase of fracture repair, is produced locally by several cell lineages including γδ T cells and Th17 cells. However, the origin and relevance for fracture repair of these T cells are unknown. Here we show that fractures rapidly expanded callus γδ T cells, which led to increased gut permeability by promoting systemic inflammation. When the microbiota contained the Th17 cell-inducing taxa segmented filamentous bacteria (SFB), activation of γδ T cells was followed by expansion of intestinal Th17 cells, their migration to the callus, and improvement of fracture repair. Mechanistically, fractures increased the S1P-receptor-1 (S1PR1) mediated egress of Th17 cells from the intestine and enhanced their homing to the callus through a CCL20 mediated mechanism. Fracture repair was impaired by deletion of γδ T cells, depletion of the microbiome by antibiotics, blockade of Th17 cell egress from the gut or antibody neutralization of Th17 cell influx into the callus. These findings demonstrated the relevance of the microbiome and T cell trafficking for fracture repair. Modifications of microbiome composition via Th17 cell-inducing bacteriotherapy and avoidance of broad-spectrum antibiotics may represent novel therapeutic strategies to optimize fracture healing.
Authors
Hamid Y. Dar, Daniel S. Perrien, Subhashis Pal, Andreea Stoica, Sasidhar Uppuganti, Jeffry S. Nyman, Rheinallt M. Jones, M. Neale Weitzmann, Roberto Pacifici
Abstract
The renal actions of parathyroid hormone (PTH) promote 1,25-vitamin D generation; however, the signaling mechanisms that control PTH-dependent vitamin D activation remain unknown. Here we demonstrated that Salt Inducible Kinases (SIKs) orchestrated renal 1,25-vitamin D production downstream of PTH signaling. PTH inhibited SIK cellular activity by cAMP-dependent PKA phosphorylation. Whole tissue and single cell transcriptomics demonstrated that both PTH and pharmacologic SIK inhibitors regulated a vitamin D gene module in the proximal tubule. SIK inhibitors increased 1,25-vitamin D production and renal Cyp27b1 mRNA expression in mice and in human embryonic stem cell-derived kidney organoids. Global- and kidney-specific Sik2/Sik3 mutant mice showed Cyp27b1 upregulation, elevated serum 1,25-vitamin D, and PTH-independent hypercalcemia. The SIK substrate CRTC2 showed PTH and SIK inhibitor-inducible binding to key Cyp27b1 regulatory enhancers in the kidney, which were also required for SIK inhibitors to increase Cyp27b1 in vivo. Lastly, in a podocyte injury model of chronic kidney disease-mineral bone disorder (CKD-MBD), SIK inhibitor treatment stimulated renal Cyp27b1 expression and 1,25-vitamin D production. Together, these results demonstrated a PTH/SIK/CRTC signaling axis in the kidney that controls Cyp27b1 expression and 1,25-vitamin D synthesis. These findings indicate that SIK inhibitors might be helpful to stimulate 1,25-vitamin D production in CKD-MBD.
Authors
Sung-Hee Yoon, Mark B. Meyer, Carlos Arevalo Rivas, Murat Tekguc, Chengcheng Zhang, Jialiang S. Wang, Christian D. Castro Andrade, Katelyn E. Strauss, Tadatoshi Sato, Nancy Benkusky, Seong Min Lee, Rebecca Berdeaux, Marc Foretz, Thomas B. Sundberg, Ramnik J. Xavier, Charles H. Adelmann, Daniel J. Brooks, Anthony Anselmo, Ruslan I. Sadreyev, Ivy A. Rosales, David E. Fisher, Navin Gupta, Ryuji Morizane, Anna Greka, J. Wesley Pike, Michael Mannstadt, Marc N. Wein
Abstract
Clearance of senescent cells (SnCs) can prevent several age-related pathologies, including bone loss. However, the local versus systemic roles of SnCs in mediating tissue dysfunction remain unclear. Thus, we developed a mouse model (p16-LOX-ATTAC) that allows for inducible SnC elimination (senolysis) in a cell-specific manner and compared the effects of local versus systemic senolysis during aging using bone as a prototype tissue. Specific removal of Sn osteocytes prevented age-related bone loss at the spine, but not the femur, by improving bone formation without affecting osteoclasts or marrow adipocytes. By contrast, systemic senolysis prevented bone loss at the spine and femur and not only improved bone formation, but also reduced osteoclasts and marrow adipocytes. Transplantation of SnCs into the peritoneal cavity of young mice caused bone loss and also induced senescence in distant host osteocytes. Collectively, our findings provide the first proof-of-concept evidence that local senolysis has health benefits in the context of aging, but importantly, local senolysis only partially replicates the benefits of systemic senolysis. Further, we establish that SnCs, through their SASP, lead to senescence in distant cells. Therefore, our study indicates that optimizing senolytic drugs may require systemic instead of local SnC targeting to extend healthy aging.
Authors
Joshua N. Farr, Dominik Saul, Madison L. Doolittle, Japneet Kaur, Jennifer L. Rowsey, Stephanie J. Vos, Mitchell N. Froemming, Anthony B. Lagnado, Yi Zhu, Megan M. Weivoda, Yuji Ikeno, Robert J. Pignolo, Laura J. Niedernhofer, Paul D. Robbins, Diana Jurk, João F. Passos, Nathan K. LeBrasseur, Tamara Tchkonia, James L. Kirkland, David G. Monroe, Sundeep Khosla
Abstract
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.
Authors
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
Abstract
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.
Authors
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
Copyright © 2024 American Society for Clinical Investigation
ISSN: 0021-9738 (print), 1558-8238 (online)