Bone biology
Endothelial BMAL1 decline during aging leads to bone loss by destabilizing extracellular fibrillin-1
Abstract
The occurrence of aging is intricately associated with alterations in circadian rhythms that coincide with stem cell exhaustion. Nonetheless, the extent to which the circadian system governs skeletal aging remains inadequately understood. Here, we noticed that skeletal aging in male mice was accompanied by a decline in a core circadian protein, BMAL1, especially in bone marrow endothelial cells (ECs). Using male mice with endothelial KO of aryl hydrocarbon receptor nuclear translocator–like protein 1 (Bmal1), we ascertained that endothelial BMAL1 in bone played a crucial role in ensuring the stability of an extracellular structural component, fibrillin-1 (FBN1), through regulation of the equilibrium between the extracellular matrix (ECM) proteases thrombospondin type 1 domain–containing protein 4 (THSD4) and metalloproteinase with thrombospondin motifs 4 (ADAMTS4), which promote FBN1 assembly and breakdown, respectively. The decline of endothelial BMAL1 during aging prompted excessive breakdown of FBN1, leading to persistent activation of TGF-β/SMAD3 signaling and exhaustion of bone marrow mesenchymal stem cells. Meanwhile, the free TGF-β could promote osteoclast formation. Further analysis revealed that activation of ADAMTS4 in ECs lacking BMAL1 was stimulated by TGF-β/SMAD3 signaling through an ECM-positive feedback mechanism, whereas THSD4 was under direct transcriptional control by endothelial BMAL1. Our investigation has elucidated the etiology of bone aging in male mice by defining the role of ECs in upholding the equilibrium within the ECM, consequently coordinating osteogenic and osteoclastic activities and retarding skeletal aging.
Authors
Ying Yin, Qingming Tang, Jingxi Yang, Shiqi Gui, Yifan Zhang, Yufeng Shen, Xin Zhou, Shaoling Yu, Guangjin Chen, Jiwei Sun, Zhenshuo Han, Luoying Zhang, Lili Chen
Abstract
Local immunoinflammatory events instruct skeletal stem cells (SSCs) to repair/regenerate bone after injury, but mechanisms are incompletely understood. We hypothesized that specialized Regulatory T (Treg) cells are necessary for bone repair and interact directly with SSCs through organ-specific messages. Both in human patients with bone fracture and mouse model of bone injury, we identified a bone injury-responding Treg subpopulation with bone-repair capacity marked by CCR8. Local production of CCL1 induced a massive migration of CCR8+ Treg cells from periphery to the injury site. Depending on secretion of progranulin (PGRN), a protein encoded by the granulin (Grn) gene, CCR8+ Treg cells supported the accumulation and osteogenic differentiation of SSCs, and thereby bone repair. Mechanistically, we revealed that CCL1 enhanced expression level of basic leucine zipper ATF-like transcription factor (BATF) in CCR8+ Treg cells, which bound to Grn promoter and increased Grn translational output and then PGRN secretion. Together, our work provides a new perspective in osteoimmunology and highlights possible ways of manipulating Treg cell signaling to enhance bone repair and regeneration.
Authors
Ruiying Chen, Xiaomeng Zhang, Bin Li, Maurizio S. Tonetti, Yijie Yang, Yuan Li, Beilei Liu, Shujiao Qian, Yingxin Gu, Qingwen Wang, Kairui Mao, Hao Cheng, Hongchang Lai, Junyu Shi
Abstract
Translation of mRNA to protein is tightly regulated by tRNAs, which are subject to various chemical modifications that maintain the structure, stability and function. Deficiency of tRNA N7-methylguanosine (m7G) modification in patients causes a type of primordial dwarfism, but the underlying mechanism remains unknown. Here we report the loss of m7G rewires cellular metabolism, leading to the pathogenesis of primordial dwarfism. Conditional deletion of the catalytic enzyme Mettl1 or missense mutation of the scaffold protein Wdr4 severely impaired endochondral bone formation and bone mass accrual. Mechanistically, Mettl1 knockout decreased abundance of m7G-modified tRNAs and inhibited translation of mRNAs relating to cytoskeleton and Rho GTPase signaling. Meanwhile, Mettl1 knockout enhanced cellular energy metabolism despite of incompetent proliferation and osteogenic commitment. Further exploration revealed that impaired Rho GTPase signaling upregulated branched-chain amino acid transaminase 1 (BCAT1) level that rewired cell metabolism and restricted intracellular α-ketoglutarate (αKG). Supplementation of αKG ameliorated the skeletal defect of Mettl1-deficient mice. In addition to the selective translation of metabolism-related mRNAs, we further revealed that Mettl1 knockout globally regulated translation via integrated stress response (ISR) and mammalian target of rapamycin complex 1 (mTORC1) signaling. Restoring translation either by targeting ISR or mTORC1 aggravated bone defects of Mettl1-deficient mice. Overall, our study unveils a critical role of m7G tRNA modification in bone development by regulating cellular metabolism, and indicates that suspension of translation initiation as quality control mechanism in response to tRNA dysregulation.
Authors
Qiwen Li, Shuang Jiang, Kexin Lei, Hui Han, Yaqian Chen, Weimin Lin, Qiuchan Xiong, Xingying Qi, Xinyan Gan, Rui Sheng, Yuan Wang, Yarong Zhang, Jieyi Ma, Tao Li, Shuibin Lin, Chenchen Zhou, Demeng Chen, Quan Yuan
Abstract
The periosteum contains skeletal stem/progenitor cells that contribute to bone fracture healing. However, the in vivo identity of periosteal skeletal stem cells (P-SSCs) remains unclear, and membrane protein markers of P-SSCs that facilitate tissue engineering are needed. Here, we identified integral membrane protein 2A (Itm2a) enriched in SSCs using single-cell transcriptomics. Itm2a+ P-SSCs displayed clonal multipotency and self-renewal and sat at the apex of their differentiation hierarchy. Lineage-tracing experiments showed that Itm2a selectively labeled the periosteum and that Itm2a+ cells were preferentially located in the outer fibrous layer of the periosteum. The Itm2a+ cells rarely expressed CD34 or Osx, but expressed periosteal markers such as Ctsk, CD51, PDGFRA, Sca1, and Gli1. Itm2a+ P-SSCs contributed to osteoblasts, chondrocytes, and marrow stromal cells upon injury. Genetic lineage tracing using dual recombinases showed that Itm2a and Prrx1 lineage cells generated spatially separated subsets of chondrocytes and osteoblasts during fracture healing. Bone morphogenetic protein 2 (Bmp2) deficiency or ablation of Itm2a+ P-SSCs resulted in defects in fracture healing. ITM2A+ P-SSCs were also present in the human periosteum. Thus, our study identified a membrane protein marker that labels P-SSCs, providing an attractive target for drug and cellular therapy for skeletal disorders.
Authors
Wenhui Xing, Heng Feng, Bo Jiang, Bo Gao, Jiping Liu, Zaiqi Xie, Yazhuo Zhang, Xuye Hu, Jun Sun, Matthew B. Greenblatt, Bo O. Zhou, Weiguo Zou
Abstract
Chronic low back pain (LBP) can severely affect daily physical activity. Aberrant osteoclast-mediated resorption leads to porous endplates for the sensory innervation to cause LBP. Here, we report that the expression of proton-activated chloride (PAC) channel is induced during osteoclast differentiation in the porous endplates via a RANKL-NFATc1 signaling pathway. Extracellular acidosis evokes robust PAC currents in osteoclasts. An acidic environment of porous endplates and elevated PAC activation-enhanced osteoclast fusion provoke LBP. Further, we find that genetic knockout of PAC gene Pacc1 significantly reduces endplate porosity and spinal pain in a mouse LBP model, but it does not affect bone development or homeostasis of bone mass in adult mice. Moreover, both osteoclast bone resorptive compartment environment and PAC traffic from the plasma membrane to endosomes to form an intracellular organelle Cl channel have low pH around 5.0. The low pH environment activates PAC channel to increase sialyltransferase St3gal1 expression and sialylation of TLR2 in initiation of osteoclast fusion. Aberrant osteoclast-mediated resorption is also found in most skeletal disorders, including osteoarthritis, ankylosing spondylitis, rheumatoid arthritis, heterotopic ossification, enthesopathy. Thus, elevated Pacc1 expression and PAC activity could be a potential therapeutic target for LBP and osteoclast-associated pain.
Authors
Peng Xue, Weixin Zhang, Mengxi Shen, Junhua Yang, Jiachen Chu, Shenyu Wang, Mei Wan, Junying Zheng, Zhaozhu Qiu, Xu Cao
Abstract
Osteogenesis imperfecta (OI) type V is the second most common form of OI, distinguished by hyperplastic callus formation and calcification of the interosseous membranes in addition to bone fragility. It is caused by a recurrent, dominant pathogenic variant (c.-14C>T) in IFITM5. Here, we generated a conditional Rosa26 knock-in mouse model to study the mechanistic consequences of the recurrent mutation. Expression of the mutant Ifitm5 in osteo-chondroprogenitor or chondrogenic cells resulted in low bone mass and growth retardation. Mutant limbs showed impaired endochondral ossification, cartilage overgrowth, and abnormal growth plate architecture. The cartilage phenotype correlates with the pathology reported in OI type V patients. Surprisingly, expression of mutant Ifitm5 in mature osteoblasts caused no obvious skeletal abnormalities. In contrast, earlier expression in osteo-chondroprogenitors was associated with increase in the skeletal progenitor population within the periosteum. Lineage tracing showed that chondrogenic cells expressing the mutant Ifitm5 showed decreased differentiation into osteoblastic cells in diaphyseal bone. Moreover, mutant IFITM5 disrupts early skeletal homeostasis in part by activating ERK signaling and downstream SOX9 protein, and inhibition of these pathways partially rescued the phenotype in mutant animals. These data identify the contribution of a signaling defect altering osteo-chondroprogenitor differentiation as a driver in the pathogenesis of OI type V.
Authors
Ronit Marom, I-Wen Song, Emily C. Busse, Megan E. Washington, Ava S. Berrier, Vittoria C. Rossi, Laura Ortinau, Youngjae Jeong, Ming-Ming Jiang, Brian C. Dawson, Mary Adeyeye, Carolina Leynes, Caressa D. Lietman, Bridget M. Stroup, Dominyka Batkovskyte, Mahim Jain, Yuqing Chen, Racel Cela, Alexis Castellon, Alyssa A. Tran, Isabel Lorenzo, D. Nicole Meyers, Shixia Huang, Alicia Turner, Vinitha Shenava, Maegen Wallace, Eric Orwoll, Dongsu Park, Catherine G. Ambrose, Sandesh C.S. Nagamani, Jason D. Heaney, Brendan H. Lee
Abstract
Cells expressing features of senescence, including upregulation of p21 and p16, appear transiently following tissue injury, yet the properties of these cells or how they contrast with age-induced senescent cells remains unclear. Here, we used skeletal injury as a model and identified the rapid appearance following fracture of p21+ cells expressing senescence markers, mainly as osteochondroprogenitors (OCHs) and neutrophils. Targeted genetic clearance of p21+ cells suppressed senescence-associated signatures within the fracture callus and accelerated fracture healing. By contrast, p21+ cell clearance did not alter bone loss due to aging; conversely, p16+ cell clearance, known to alleviate skeletal aging, did not affect fracture healing. Following fracture, p21+ neutrophils were enriched in signaling pathways known to induce paracrine stromal senescence, while p21+ OCHs were highly enriched in senescence-associated secretory phenotype factors known to impair bone formation. Further analysis revealed an injury-specific stem cell-like OCH subset that was p21+ and highly inflammatory, with a similar inflammatory mesenchymal population (fibro-adipogenic progenitors) evident following muscle injury. Thus, intercommunicating senescent-like neutrophils and mesenchymal progenitor cells were key regulators of tissue repair in bone and potentially across tissues. Moreover, our findings established contextual roles of p21+ vs p16+ senescent/senescent-like cells that may be leveraged for therapeutic opportunities.
Authors
Dominik Saul, Madison L. Doolittle, Jennifer L. Rowsey, Mitchell N. Froemming, Robyn L. Kosinsky, Stephanie J. Vos, Ming Ruan, Nathan K. LeBrasseur, Abhishek Chandra, Robert J. Pignolo, João F. Passos, Joshua N. Farr, David G. Monroe, Sundeep Khosla
Abstract
Gender affirming hormone therapy (GAHT) is often prescribed to transgender (TG) adolescents to alleviate gender dysphoria, but the impact of GAHT on the growing skeleton is unclear. We found GAHT to improve trabecular bone structure via increased bone formation in young male mice and not to affect trabecular structure in female mice. GAHT modified gut microbiome composition in both male and female mice. However, fecal microbiota transfers (FMT) revealed that GAHT-shaped gut microbiome was a communicable regulator of bone structure and turnover in male, but not in female mice. Mediation analysis identified two species of Bacteroides as significant contributors to the skeletal effects of GAHT in male mice, with Bacteroides supplementation phenocopying the effects of GAHT on bone. Bacteroides have the capacity to expand Treg populations in the gut. Accordingly, GAHT expanded intestinal regulatory T cells (Tregs) and stimulated their homing to the bone marrow (BM) in male but not in female mice. Attesting to the functional relevance of Tregs, pharmacological blockade of Treg expansion prevented GAHT-induced bone anabolism. In summary, in male mice GAHT stimulated bone formation and improved trabecular structure by promoting Treg expansion via a microbiome-mediated effect. In female mice GAHT neither improved nor impaired trabecular structure.
Authors
Subhashis Pal, Xochitl Morgan, Hamid Y. Dar, Camilo Anthony Gacasan, Sanchiti Patil, Andreea Stoica, Yi-Juan Hu, M. Neale Weitzmann, Rheinallt M. Jones, Roberto Pacifici
Abstract
Elevated bone resorption and diminished bone formation have been recognized as the primary features of glucocorticoid-associated skeletal disorders. However, the direct effects of excess glucocorticoids on bone turnover remains unclear. Here, we explored the outcomes of exogenous glucocorticoid treatment on bone loss and delayed fracture healing in mice and found that reduced bone turnover was a dominant feature, resulting in a net loss of bone mass. The primary effect of glucocorticoids on osteogenic differentiation was not inhibitory; instead, they cooperated with macrophages to facilitate osteogenesis. Impaired local nutrient status, notably, obstructed fatty acid transportation, was a key factor contributing to glucocorticoid-induced impairment of bone turnover in vivo. Furthermore, fatty acid oxidation in macrophages fueled the ability of glucocorticoid-liganded receptors to enter the nucleus and then promoted the expression of Bmp2, a key cytokine that facilitates osteogenesis. Metabolic reprogramming by localized fatty acid delivery partly rescued glucocorticoid-induced pathology by restoring a healthier immune-metabolic milieu. These data provide insights into the multifactorial metabolic mechanisms by which glucocorticoids generate skeletal disorders, thus suggesting possible therapeutic avenues.
Authors
Xu Li, Tongzhou Liang, Bingyang Dai, Liang Chang, Yuan Zhang, Shiwen Hu, Jiaxin Guo, Shunxiang Xu, Lizhen Zheng, Hao Yao, Hong Lian, Yu Nie, Ye Li, Xuan He, Zhi Yao, Wenxue Tong, Xinluan Wang, Dick Ho Kiu Chow, Jiankun Xu, Ling Qin
Abstract
Given the leading cause of disability worldwide, low back pain (LBP) is recognized as a pivotal socio-economic challenge to the aging population, which is importantly attributed to intervertebral disc degeneration (IVDD). Elastic nucleus pulposus (NP) tissue is essential for the maintenance of IVD structural and functional integrity. The accumulation of senescent NP cells with inflammatory hypersecretory phenotype due to aging and other damaged factors is a distinctive hallmark of IVDD initiation and progression. In this study, we revealed a mechanism of IVDD progression in which aberrant genomic DNA damage promoted NP cell inflammatory senescence via activation of the cGAS-STING axis but not AIM2 inflammasome assembly. ATR deficiency destroyed genomic integrity and led to cytosolic mislocalization of genomic DNA, which acted as a powerful driver of cGAS-STING axis-dependent inflammatory phenotype acquisition during NP cell senescence. Mechanically, the disassembly of ATR-TRIM56 complex with the enzyme activity liberation of USP5 and TRIM25 drove change in ATR ubiquitination, with ATR switching from K63-linked modification to K48-linked modification, promoting ubiquitin-proteasome-dependent dynamic instability of ATR protein during NP cell senescent progression. Importantly, an engineered extracellular vesicle (EV)-based strategy for delivering ATR-overexpressing plasmid cargo efficiently diminished DNA damage-associated NP cell senescence and substantially mitigated IVDD progression, indicating promising targets and efficient approaches for ameliorating the impact of IVDD.
Authors
Weifeng Zhang, Gaocai Li, Xingyu Zhou, Huaizhen Liang, Bide Tong, Di Wu, Kevin Yang, Yu Song, Bingjin Wang, Zhiwei Liao, Liang Ma, Wencan Ke, Xiaoguang Zhang, Jie Lei, Chunchi Lei, Xiaobo Feng, Kun Wang, Kangcheng Zhao, Cao Yang
Copyright © 2024 American Society for Clinical Investigation
ISSN: 0021-9738 (print), 1558-8238 (online)