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Metzger CE, Moore RC, Pirkle AS, Tak LY, Rau J, Bryan JA, Stefanov A, Allen MR, Hook MA. A moderate spinal contusion injury in rats alters bone turnover both below and above the level of injury with sex-based differences apparent in long-term recovery. Bone Rep 2024; 21:101761. [PMID: 38646090 PMCID: PMC11033081 DOI: 10.1016/j.bonr.2024.101761] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/29/2024] [Accepted: 04/07/2024] [Indexed: 04/23/2024] Open
Abstract
Spinal cord injury (SCI) leads to significant sublesional bone loss and high fracture rates. While loss of mechanical loading plays a significant role in SCI-induced bone loss, animal studies have demonstrated mechanical loading alone does not fully account for loss of bone following SCI. Indeed, we have shown that bone loss occurs below the level of an incomplete moderate contusion SCI, despite the resumption of weight-bearing and stepping. As systemic factors could also impact bone after SCI, bone alterations may also be present in bone sites above the level of injury. To examine this, we assessed bone microarchitecture and bone turnover in the supralesional humerus in male and female rats at two different ages following a moderate contusion injury in both sub-chronic (30 days) and chronic (180 days) time points after injury. At the 30-day timepoint, we found that both young and adult male SCI rats had decrements in trabecular bone volume at the supralesional proximal humerus (PH), while female SCI rats were not different from age-matched shams. At the 180-day timepoint, there were no statistical differences between SCI and sham groups, irrespective of age or sex, at the supralesional proximal humerus. At the 30-day timepoint, all SCI rats had lower BFR and higher osteoclast-covered trabecular surfaces in the proximal humerus compared to age-matched sham groups generally matching the pattern of SCI-induced changes in bone turnover seen in the sublesional proximal tibia. However, at the 180-day timepoint, only male SCI rats had lower BFR at the supralesional proximal humerus while female SCI rats had higher or no different BFR than their age-matched counterparts. Overall, this preclinical study demonstrates that a moderate contusion SCI leads to alterations in bone turnover above the level of injury within 30-days of injury; however male SCI rats maintained lower BFR in the supralesional humerus into long-term recovery. These data further highlight that bone loss after SCI is not driven solely by disuse. Additionally, these data allude to potential systemic factors exerting influence on bone following SCI and highlight the need to consider treatments for SCI-induced bone loss that impact both sublesional and systemic factors.
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Affiliation(s)
- Corinne E. Metzger
- Department of Anatomy, Cell Biology, and Physiology, Indiana University School of Medicine, Indianapolis, IN, United States of America
| | - Robert C. Moore
- Department of Anatomy, Cell Biology, and Physiology, Indiana University School of Medicine, Indianapolis, IN, United States of America
| | - Alexander S. Pirkle
- Department of Anatomy, Cell Biology, and Physiology, Indiana University School of Medicine, Indianapolis, IN, United States of America
| | - Landon Y. Tak
- Department of Anatomy, Cell Biology, and Physiology, Indiana University School of Medicine, Indianapolis, IN, United States of America
| | - Josephina Rau
- Department of Neuroscience and Experimental Therapeutics, Texas A&M University School of Medicine, Bryan, TX, United States of America
| | - Jessica A. Bryan
- Department of Neuroscience and Experimental Therapeutics, Texas A&M University School of Medicine, Bryan, TX, United States of America
| | - Alexander Stefanov
- Department of Neuroscience and Experimental Therapeutics, Texas A&M University School of Medicine, Bryan, TX, United States of America
| | - Matthew R. Allen
- Department of Anatomy, Cell Biology, and Physiology, Indiana University School of Medicine, Indianapolis, IN, United States of America
| | - Michelle A. Hook
- Department of Neuroscience and Experimental Therapeutics, Texas A&M University School of Medicine, Bryan, TX, United States of America
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Miura T, Etani Y, Noguchi T, Hirao M, Takami K, Goshima A, Kurihara T, Fukuda Y, Ochiai N, Kanamoto T, Nakata K, Okada S, Ebina K. Iguratimod suppresses sclerostin and receptor activator of NF-κB ligand production via the extracellular signal-regulated kinase/early growth response protein 1/tumor necrosis factor alpha pathway in osteocytes and ameliorates disuse osteoporosis in mice. Bone 2024; 181:117026. [PMID: 38325651 DOI: 10.1016/j.bone.2024.117026] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/22/2023] [Revised: 01/07/2024] [Accepted: 01/28/2024] [Indexed: 02/09/2024]
Abstract
Disuse osteoporosis is a prevalent complication among patients afflicted with rheumatoid arthritis (RA). Although reports have shown that the antirheumatic drug iguratimod (IGU) ameliorates osteoporosis in RA patients, details regarding its effects on osteocytes remain unclear. The current study examined the effects of IGU on osteocytes using a mouse model of disuse-induced osteoporosis, the pathology of which crucially involves osteocytes. A reduction in distal femur bone mass was achieved after 3 weeks of hindlimb unloading in mice, which was subsequently reversed by intraperitoneal IGU treatment (30 mg/kg; five times per week). Histology revealed that hindlimb-unloaded (HLU) mice had significantly increased osteoclast number and sclerostin-positive osteocyte rates, which were suppressed by IGU treatment. Moreover, HLU mice exhibited a significant decrease in osteocalcin-positive cells, which was attenuated by IGU treatment. In vitro, IGU suppressed the gene expression of receptor activator of NF-κB ligand (RANKL) and sclerostin in MLO-Y4 and Saos-2 cells, which inhibited osteoclast differentiation of mouse bone marrow cells in cocultures. Although IGU did not affect the nuclear translocation or transcriptional activity of NF-κB, RNA sequencing revealed that IGU downregulated the expression of early growth response protein 1 (EGR1) in osteocytes. HLU mice showed significantly increased EGR1- and tumor necrosis factor alpha (TNFα)-positive osteocyte rates, which were decreased by IGU treatment. EGR1 overexpression enhanced the gene expression of TNFα, RANKL, and sclerostin in osteocytes, which was suppressed by IGU. Contrarily, small interfering RNA-mediated suppression of EGR1 downregulated RANKL and sclerostin gene expression. These findings indicate that IGU inhibits the expression of EGR1, which may downregulate TNFα and consequently RANKL and sclerostin in osteocytes. These mechanisms suggest that IGU could potentially be used as a treatment option for disuse osteoporosis by targeting osteocytes.
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Affiliation(s)
- Taihei Miura
- Department of Orthopaedic Surgery, Osaka University Graduate School of Medicine, 2-2 Yamada-oka, Suita, Osaka 565-0871, Japan
| | - Yuki Etani
- Department of Musculoskeletal Regenerative Medicine, Osaka University Graduate School of Medicine, 2-2 Yamada-oka, Suita, Osaka 565-0871, Japan
| | - Takaaki Noguchi
- Department of Orthopaedic Surgery, Osaka University Graduate School of Medicine, 2-2 Yamada-oka, Suita, Osaka 565-0871, Japan
| | - Makoto Hirao
- Department of Orthopaedic Surgery, National Hospital Organization Osaka Minami Medical Center, 2-1 Kidohigashimachi, Kawachinagano, Osaka 586-8521, Japan
| | - Kenji Takami
- Department of Orthopaedic Surgery, Nippon Life Hospital, 2-1-54 Enokojima, Nishi-ku, Osaka, Osaka 550-0006, Japan
| | - Atsushi Goshima
- Department of Orthopaedic Surgery, Osaka Rosai Hospital, 1179-3 Nagasone-cho, Kita-ku, Sakai, Osaka 591-8025, Japan
| | - Takuya Kurihara
- Department of Orthopaedic Surgery, Osaka University Graduate School of Medicine, 2-2 Yamada-oka, Suita, Osaka 565-0871, Japan
| | - Yuji Fukuda
- Department of Orthopaedic Surgery, Osaka University Graduate School of Medicine, 2-2 Yamada-oka, Suita, Osaka 565-0871, Japan
| | - Nagahiro Ochiai
- Department of Musculoskeletal Regenerative Medicine, Osaka University Graduate School of Medicine, 2-2 Yamada-oka, Suita, Osaka 565-0871, Japan
| | - Takashi Kanamoto
- Department of Health and Sport Sciences, Osaka University Graduate School of Medicine, 2-2 Yamada-oka, Suita, Osaka 565-0871, Japan
| | - Ken Nakata
- Department of Health and Sport Sciences, Osaka University Graduate School of Medicine, 2-2 Yamada-oka, Suita, Osaka 565-0871, Japan
| | - Seiji Okada
- Department of Orthopaedic Surgery, Osaka University Graduate School of Medicine, 2-2 Yamada-oka, Suita, Osaka 565-0871, Japan
| | - Kosuke Ebina
- Department of Orthopaedic Surgery, Osaka University Graduate School of Medicine, 2-2 Yamada-oka, Suita, Osaka 565-0871, Japan; Department of Musculoskeletal Regenerative Medicine, Osaka University Graduate School of Medicine, 2-2 Yamada-oka, Suita, Osaka 565-0871, Japan.
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3
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Meas SJ, Daire GM, Friedman MA, DeNapoli R, Ghosh P, Farr JN, Donahue HJ. A comparison of bone microarchitectural and transcriptomic changes in murine long bones in response to hindlimb unloading and aging. Bone 2024; 179:116973. [PMID: 37996046 DOI: 10.1016/j.bone.2023.116973] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/17/2023] [Revised: 11/15/2023] [Accepted: 11/16/2023] [Indexed: 11/25/2023]
Abstract
Age- and disuse-related bone loss both result in decreases in bone mineral density, cortical thickness, and trabecular thickness and connectivity. Disuse induces changes in the balance of bone formation and bone resorption like those seen with aging. There is a need to experimentally compare these two mechanisms at a structural and transcriptomic level to better understand how they may be similar or different. Bone microarchitecture and biomechanical properties were compared between 6- and 22-month-old C57BL/6 J male control mice and 6-month-old mice that were hindlimb unloaded (HLU) for 3 weeks. Epiphyseal trabecular bone was the compartment most affected by HLU and demonstrated an intermediate bone phenotype between age-matched controls and aged controls. RNA extracted from whole-bone marrow-flushed tibiae was sequenced and analyzed. Differential gene expression analysis additionally included 4-month-old male mice unloaded for 3 weeks compared to age-matched controls. Gene ontology analysis demonstrated that there were age-dependent differences in differentially expressed genes in young adult mice. Genes related to downregulation of cellular processes were most affected in 4-month-old mice after disuse whereas those related to mitochondrial function were most affected in 6-month-old mice. Cell-cycle transition was downregulated with aging. A publicly available dataset (GSE169292) from 3-month female C57BL/6 N mice unloaded for 7 days was included in ingenuity pathway analysis (IPA) with the other datasets. IPA was used to identify the leading canonical pathways and upstream regulators in each HLU age group. IPA identified "Senescence Pathway" as the second leading canonical pathway enriched in mice exposed to HLU. HLU induced activation of the senescence pathway in 3-month and 4-month-old mice but inhibited it in 6-month-old mice. In conclusion, we demonstrate that hindlimb unloading and aging initiate similar changes in bone microarchitecture and gene expression. However, aging is responsible for more significant transcriptome and tissue-level changes compared to hindlimb unloading.
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Affiliation(s)
- Steven J Meas
- Virginia Commonwealth University, Richmond, VA 23284, USA.
| | | | | | | | - Preetam Ghosh
- Virginia Commonwealth University, Richmond, VA 23284, USA.
| | - Joshua N Farr
- Mayo Clinic College of Medicine, Rochester, MN 55905, USA.
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Deng W, Cao Z, Dong R, Yan Y, Jiang Q. Irisin inhibits CCK-8-induced TNF-α production via integrin αVβ5-NF-κB signaling pathways in Nile tilapia (Oreochromis niloticus). FISH & SHELLFISH IMMUNOLOGY 2024; 144:109245. [PMID: 38000652 DOI: 10.1016/j.fsi.2023.109245] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/25/2023] [Revised: 11/02/2023] [Accepted: 11/20/2023] [Indexed: 11/26/2023]
Abstract
Irisin, a secreted myokine generated by fibronectin type III domain-containing protein 5, has recently shown the potential to alleviate inflammation. Cholecystokinin-octapeptide (CCK-8) is closely associated with the inflammatory factor TNF-α, a central cytokine in inflammatory reactions. However, the interactions between irisin and CCK-8 in regulating TNF-α production and the underlying mechanism have not yet been elucidated. In the present study, irisin treatment inhibited the basal and the CCK-8-induced TNF-α production in vivo. Additionally, neutralizing circulating irisin using an irisin antiserum significantly augmented the CCK-8-induced stimulation of TNF-α levels. Moreover, the incubation of head kidney cells with irisin or CCK-8 has opposite effects on TNF-α secretion. Notably, irisin treatment inhibited basal and CCK-8-stimulated TNF-α release and gene transcription in head kidney cells. Mechanistically, the inhibitory actions of irisin on basal and CCK-8-induced TNF-α production could be negated by co-administered with the selective integrin αVβ5 inhibitor cilengitide. In addition, the inhibitory effect of irisin on basal and CCK-8-triggered TNF-α production could be abolished by the inhibition of the nuclear factor-kappa B (NF-κB) signaling pathway. Furthermore, irisin impeded CCK-8-induced phosphorylation and degradation of IκBα, simultaneously inhibiting NF-κB phosphorylation, preventing its translocation into the nucleus, and suppressing its DNA-binding activity induced by CCK-8. Collectively, these results suggest that the inhibitory effect of irisin on TNF-α production caused by CCK-8 is mediated via the integrin αVβ5-NF-κB signaling pathways in tilapia.
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Affiliation(s)
- Wenjun Deng
- Key Laboratory of Bio-resources and Eco-environment of Ministry of Education, College of Life Sciences, Sichuan University, Chengdu, PR China
| | - Zhikai Cao
- Key Laboratory of Bio-resources and Eco-environment of Ministry of Education, College of Life Sciences, Sichuan University, Chengdu, PR China
| | - Rui Dong
- Key Laboratory of Bio-resources and Eco-environment of Ministry of Education, College of Life Sciences, Sichuan University, Chengdu, PR China
| | - Yisha Yan
- Key Laboratory of Bio-resources and Eco-environment of Ministry of Education, College of Life Sciences, Sichuan University, Chengdu, PR China
| | - Quan Jiang
- Key Laboratory of Bio-resources and Eco-environment of Ministry of Education, College of Life Sciences, Sichuan University, Chengdu, PR China.
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5
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Meas SJ, Daire GM, Friedman MA, DeNapoli R, Ghosh P, Farr JN, Donahue HJ. Hindlimb Unloading Induces Bone Microarchitectural and Transcriptomic Changes in Murine Long Bones in an Age-Dependent Manner. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.10.09.561510. [PMID: 37873408 PMCID: PMC10592678 DOI: 10.1101/2023.10.09.561510] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/25/2023]
Abstract
Age and disuse-related bone loss both result in decreases in bone mineral density, cortical thickness, and trabecular thickness and connectivity. Disuse induces physiological changes in bone like those seen with aging. Bone microarchitecture and biomechanical properties were compared between 6- and 22-month-old C57BL/6J male control mice and 6-month-old mice that were hindlimb unloaded (HLU) for 3 weeks. Epiphyseal trabecular bone was the compartment most affected by HLU and demonstrated an intermediate bone phenotype between age-matched controls and aged controls. RNA extracted from whole-bone marrow-flushed tibiae was sequenced and analyzed. Differential gene expression analysis additionally included 4-month-old male mice unloaded for 3 weeks compared to age-matched controls. Gene ontology analysis demonstrated that there were age-dependent differences in differentially expressed genes. Genes related to downregulation of cellular processes were most affected in 4-month-old mice after disuse whereas those related to mitochondrial function were most affected in 6- month-old mice. Cell-cycle transition was downregulated with aging. A publicly available dataset (GSE169292) from 3-month female C57BL/6N mice unloaded for 7 days was included in ingenuity pathway analysis with the other datasets. IPA was used to identify the leading canonical pathways and upstream regulators in each HLU age group. IPA identified "Senescence Pathway" as the second leading canonical pathway enriched in mice exposed to HLU. HLU induced activation of the senescence pathway in 3- month and 4-month-old mice but inhibited it in 6-month-old mice. In conclusion, we demonstrate that hindlimb unloading and aging initiate similar changes in bone microarchitecture and gene expression. However, aging is responsible for more significant transcriptome and tissue-level changes compared to hindlimb unloading. Highlights Epiphyseal trabecular bone is most susceptible to hindlimb unloading.Hindlimb unloaded limbs resemble an intermediate phenotype between age-matched and aged controls.Hindlimb unloading induces gene expression changes that are age dependent and may lead to inflammation and/or mitochondrial dysfunction depending on context.Younger mice (3-4 months) activate the senescence pathway upon hindlimb unloading, whereas skeletally mature (6 months) mice inhibit it.
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6
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Liu S, Cui F, Ning K, Wang Z, Fu P, Wang D, Xu H. Role of irisin in physiology and pathology. Front Endocrinol (Lausanne) 2022; 13:962968. [PMID: 36225200 PMCID: PMC9549367 DOI: 10.3389/fendo.2022.962968] [Citation(s) in RCA: 18] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/07/2022] [Accepted: 09/07/2022] [Indexed: 01/10/2023] Open
Abstract
Irisin, out-membrane part of fibronectin type III domain-containing 5 protein (FNDC5), was activated by Peroxisome proliferator-activated receptor γ (PPARγ) coactivator-1α (PGC-1α) during physical exercise in skeletal muscle tissues. Most studies have reported that the concentration of irisin is highly associated with health status. For instance, the level of irisin is significantly lower in patients with obesity, osteoporosis/fractures, muscle atrophy, Alzheimer's disease, and cardiovascular diseases (CVDs) but higher in patients with cancer. Irisin can bind to its receptor integrin αV/β5 to induce browning of white fat, maintain glucose stability, keep bone homeostasis, and alleviate cardiac injury. However, it is unclear whether it works by directly binding to its receptors to regulate muscle regeneration, promote neurogenesis, keep liver glucose homeostasis, and inhibit cancer development. Supplementation of recombinant irisin or exercise-activated irisin might be a successful strategy to fight obesity, osteoporosis, muscle atrophy, liver injury, and CVDs in one go. Here, we summarize the publications of FNDC5/irisin from PubMed/Medline, Scopus, and Web of Science until March 2022, and we review the role of FNDC5/irisin in physiology and pathology.
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Affiliation(s)
- Shiqiang Liu
- Key Laboratory for Space Bioscience and Biotechnology, School of Life Sciences, Northwestern Polytechnical University, Xi’an, China
| | - Fengqi Cui
- Key Laboratory for Space Bioscience and Biotechnology, School of Life Sciences, Northwestern Polytechnical University, Xi’an, China
| | - Kaiting Ning
- Key Laboratory for Space Bioscience and Biotechnology, School of Life Sciences, Northwestern Polytechnical University, Xi’an, China
| | - Zhen Wang
- Xi’an International Medical Center Hospital Affiliated to Northwest University, Xi’an, China
| | - Pengyu Fu
- Department of Physical Education, Northwestern Polytechnical University, Xi’an, China
| | - Dongen Wang
- Key Laboratory for Space Bioscience and Biotechnology, School of Life Sciences, Northwestern Polytechnical University, Xi’an, China
| | - Huiyun Xu
- Key Laboratory for Space Bioscience and Biotechnology, School of Life Sciences, Northwestern Polytechnical University, Xi’an, China
- Research Center of Special Environmental Biomechanics and Medical Engineering, Northwestern Polytechnical University, Xi’an, China
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Chen T, Peng Y, Hu W, Shi H, Li P, Que Y, Qiu J, Qiu X, Gao B, Zhou H, Chen Y, Zhu Y, Li S, Liang A, Gao W, Huang D. Irisin enhances chondrogenic differentiation of human mesenchymal stem cells via Rap1/PI3K/AKT axis. Stem Cell Res Ther 2022; 13:392. [PMID: 35922833 PMCID: PMC9351134 DOI: 10.1186/s13287-022-03092-8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2022] [Accepted: 04/17/2022] [Indexed: 12/11/2022] Open
Abstract
Background Human mesenchymal stem cells (hMSCs) have been proven to have inherent chondrogenic differentiation potential, which appears to be used in cartilage regeneration. Increasing evidence suggests that irisin enhances osteoblast differentiation of MSCs, but little is known about its potential on chondrogenic differentiation. Methods In the study, we investigated the effects of irisin on chondrogenic differentiation of hMSCs using a high-density pellet culture system. The cartilage pellets were evaluated by morphology, and the metabolism of cartilage matrix was detected by qPCR, western blot and immunohistochemistry. Next, RNA-seq was performed to explore the underlying mechanism. Furthermore, using the transduction of plasmid, miRNAs mimics and inhibitor, the activation of Rap1/PI3K/AKT axis, the expression level of SIPA1L2, and the functional verification of miR-125b-5p were detected on day 7 of chondrogenic differentiation of hMSCs. Results Compared with the controls, we found that irisin treatment could significantly enhance the chondrogenic differentiation of hMSCs, enlarge the induced-cartilage tissue and up-regulate the expression levels of cartilage markers. RNA-seq indicated that irisin activated the Rap1 and PI3K/AKT signaling pathway, and the lower expression level of SIPA1L2 and the higher expression level of miR-125b-5p were found in irisin-treated group. Further, we found that irisin treatment could up-regulate the expression level of miR-125b-5p, targeting SIPA1L2 and consequently activating the Rap1/PI3K/AKT axis on the process of chondrogenic differentiation of hMSCs. Conclusions Collectively, our study reveals that irisin can enhance chondrogenic differentiation of hMSCs via the Rap1/PI3K/AKT pathway, suggesting that irisin possesses prospects in cartilage regeneration. Supplementary Information The online version contains supplementary material available at 10.1186/s13287-022-03092-8.
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Affiliation(s)
- Taiqiu Chen
- Department of Orthopedics, Sun Yat-Sen Memorial Hospital of Sun Yat-Sen University, #107 West Yan Jiang Road, Guangzhou, Guangdong, China
| | - Yan Peng
- Department of Orthopedics, Sun Yat-Sen Memorial Hospital of Sun Yat-Sen University, #107 West Yan Jiang Road, Guangzhou, Guangdong, China
| | - Wenjun Hu
- Department of Orthopedics, Sun Yat-Sen Memorial Hospital of Sun Yat-Sen University, #107 West Yan Jiang Road, Guangzhou, Guangdong, China
| | - Huihong Shi
- Department of Orthopedics, Sun Yat-Sen Memorial Hospital of Sun Yat-Sen University, #107 West Yan Jiang Road, Guangzhou, Guangdong, China
| | - Pengfei Li
- Department of Orthopedics, Sun Yat-Sen Memorial Hospital of Sun Yat-Sen University, #107 West Yan Jiang Road, Guangzhou, Guangdong, China
| | - Yichen Que
- Department of Orthopedics, Sun Yat-Sen Memorial Hospital of Sun Yat-Sen University, #107 West Yan Jiang Road, Guangzhou, Guangdong, China
| | - Jincheng Qiu
- Department of Orthopedics, Sun Yat-Sen Memorial Hospital of Sun Yat-Sen University, #107 West Yan Jiang Road, Guangzhou, Guangdong, China
| | - Xianjian Qiu
- Department of Orthopedics, Sun Yat-Sen Memorial Hospital of Sun Yat-Sen University, #107 West Yan Jiang Road, Guangzhou, Guangdong, China
| | - Bo Gao
- Department of Orthopedics, Sun Yat-Sen Memorial Hospital of Sun Yat-Sen University, #107 West Yan Jiang Road, Guangzhou, Guangdong, China
| | - Hang Zhou
- Department of Orthopedics, Sun Yat-Sen Memorial Hospital of Sun Yat-Sen University, #107 West Yan Jiang Road, Guangzhou, Guangdong, China
| | - Yanbo Chen
- Department of Orthopedics, Sun Yat-Sen Memorial Hospital of Sun Yat-Sen University, #107 West Yan Jiang Road, Guangzhou, Guangdong, China
| | - Yuanxin Zhu
- Department of Orthopedics, Sun Yat-Sen Memorial Hospital of Sun Yat-Sen University, #107 West Yan Jiang Road, Guangzhou, Guangdong, China
| | - Shaoguang Li
- Department of Orthopedics, Sun Yat-Sen Memorial Hospital of Sun Yat-Sen University, #107 West Yan Jiang Road, Guangzhou, Guangdong, China
| | - Anjing Liang
- Department of Orthopedics, Sun Yat-Sen Memorial Hospital of Sun Yat-Sen University, #107 West Yan Jiang Road, Guangzhou, Guangdong, China
| | - Wenjie Gao
- Department of Orthopedics, Sun Yat-Sen Memorial Hospital of Sun Yat-Sen University, #107 West Yan Jiang Road, Guangzhou, Guangdong, China.
| | - Dongsheng Huang
- Department of Orthopedics, Sun Yat-Sen Memorial Hospital of Sun Yat-Sen University, #107 West Yan Jiang Road, Guangzhou, Guangdong, China.
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Buettmann EG, Goldscheitter GM, Hoppock GA, Friedman MA, Suva LJ, Donahue HJ. Similarities Between Disuse and Age-Induced Bone Loss. J Bone Miner Res 2022; 37:1417-1434. [PMID: 35773785 PMCID: PMC9378610 DOI: 10.1002/jbmr.4643] [Citation(s) in RCA: 19] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/22/2021] [Revised: 06/17/2022] [Accepted: 06/24/2022] [Indexed: 11/07/2022]
Abstract
Disuse and aging are known risk factors associated with low bone mass and quality deterioration, resulting in increased fracture risk. Indeed, current and emerging evidence implicate a large number of shared skeletal manifestations between disuse and aging scenarios. This review provides a detailed overview of current preclinical models of musculoskeletal disuse and the clinical scenarios they seek to recapitulate. We also explore and summarize the major similarities between bone loss after extreme disuse and advanced aging at multiple length scales, including at the organ/tissue, cellular, and molecular level. Specifically, shared structural and material alterations of bone loss are presented between disuse and aging, including preferential loss of bone at cancellous sites, cortical thinning, and loss of bone strength due to enhanced fragility. At the cellular level bone loss is accompanied, during disuse and aging, by increased bone resorption, decreased formation, and enhanced adipogenesis due to altered gap junction intercellular communication, WNT/β-catenin and RANKL/OPG signaling. Major differences between extreme short-term disuse and aging are discussed, including anatomical specificity, differences in bone turnover rates, periosteal modeling, and the influence of subject sex and genetic variability. The examination also identifies potential shared mechanisms underlying bone loss in aging and disuse that warrant further study such as collagen cross-linking, advanced glycation end products/receptor for advanced glycation end products (AGE-RAGE) signaling, reactive oxygen species (ROS) and nuclear factor κB (NF-κB) signaling, cellular senescence, and altered lacunar-canalicular connectivity (mechanosensation). Understanding the shared structural alterations, changes in bone cell function, and molecular mechanisms common to both extreme disuse and aging are paramount to discovering therapies to combat both age-related and disuse-induced osteoporosis. © 2022 American Society for Bone and Mineral Research (ASBMR).
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Affiliation(s)
- Evan G Buettmann
- Department of Biomedical Engineering, Virginia Commonwealth University, Richmond, VA, USA
| | - Galen M Goldscheitter
- Department of Biomedical Engineering, Virginia Commonwealth University, Richmond, VA, USA
| | - Gabriel A Hoppock
- Department of Biomedical Engineering, Virginia Commonwealth University, Richmond, VA, USA
| | - Michael A Friedman
- Department of Biomedical Engineering, Virginia Commonwealth University, Richmond, VA, USA
| | - Larry J Suva
- Department of Veterinary Physiology and Pharmacology, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX, USA
| | - Henry J Donahue
- Department of Biomedical Engineering, Virginia Commonwealth University, Richmond, VA, USA
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9
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Irisin Ameliorates Intervertebral Disc Degeneration by Activating LATS/YAP/CTGF Signaling. OXIDATIVE MEDICINE AND CELLULAR LONGEVITY 2022; 2022:9684062. [PMID: 35915608 PMCID: PMC9338732 DOI: 10.1155/2022/9684062] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/10/2022] [Accepted: 07/05/2022] [Indexed: 12/30/2022]
Abstract
Unbalanced metabolism of an extracellular matrix (ECM) in nucleus pulposus cells (NPCs) is widely acknowledged as the primary cause of intervertebral disc degeneration (IDD). Irisin, a novel myokine, is cleaved from fibronectin type III domain-containing 5 (FNDC5) and has recently been proven to regulate the metabolism of ECM. However, little is known about its potential on NPCs and the development of IDD. Therefore, this study sought to examine the protective effects and molecular mechanism of irisin on IDD in vivo and in vitro. Decreased expression levels of FNDC5 and anabolism markers (COL2A1 and ACAN) but increased levels of catabolism markers (ADAMTS4) were found in degenerative nucleus pulposus (NP) tissues. In a punctured-induced rat IDD model, irisin treatment was found to significantly slow the development of IDD, and in TNF-α-stimulated NPCs, irisin treatment partly reversed the disorder of ECM metabolism. In mechanism, RNA-seq results suggested that irisin treatment affected the Hippo signaling pathway. Further studies revealed that with irisin treatment, the phosphorylation levels of key factors (LATS and YAP) were downregulated, while the expression level of CTGF was upregulated. Moreover, CTGF knockdown partially eliminated the protective effects of irisin on the metabolism of ECM in NPCs, including inhibiting the anabolism and promoting the catabolism. Taken together, this study demonstrated that the expression levels of FNDC5 were decreased in degenerative NP tissues, while irisin treatment promoted the anabolism, inhibited the catabolism of the ECM in NPCs, and delayed the progression of IDD via LATS/YAP/CTGF signaling. These results shed light on the protective actions of irisin on NPCs, leading to the development of a novel therapeutic target for treating IDD.
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10
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Man J, Graham T, Squires-Donelly G, Laslett AL. The effects of microgravity on bone structure and function. NPJ Microgravity 2022; 8:9. [PMID: 35383182 PMCID: PMC8983659 DOI: 10.1038/s41526-022-00194-8] [Citation(s) in RCA: 33] [Impact Index Per Article: 16.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2021] [Accepted: 03/04/2022] [Indexed: 12/22/2022] Open
Abstract
Humans are spending an increasing amount of time in space, where exposure to conditions of microgravity causes 1-2% bone loss per month in astronauts. Through data collected from astronauts, as well as animal and cellular experiments conducted in space, it is evident that microgravity induces skeletal deconditioning in weight-bearing bones. This review identifies contentions in current literature describing the effect of microgravity on non-weight-bearing bones, different bone compartments, as well as the skeletal recovery process in human and animal spaceflight data. Experiments in space are not readily available, and experimental designs are often limited due to logistical and technical reasons. This review introduces a plethora of on-ground research that elucidate the intricate process of bone loss, utilising technology that simulates microgravity. Observations from these studies are largely congruent to data obtained from spaceflight experiments, while offering more insights behind the molecular mechanisms leading to microgravity-induced bone loss. These insights are discussed herein, as well as how that knowledge has contributed to studies of current therapeutic agents. This review also points out discrepancies in existing data, highlighting knowledge gaps in our current understanding. Further dissection of the exact mechanisms of microgravity-induced bone loss will enable the development of more effective preventative and therapeutic measures to protect against bone loss, both in space and possibly on ground.
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Affiliation(s)
- Joey Man
- Commonwealth Scientific and Industrial Research Organisation (CSIRO) Manufacturing, Clayton, Victoria, 3168, Australia.
- Australian Regenerative Medicine Institute, Monash University, Melbourne, Victoria, 3800, Australia.
- Space Technology Future Science Platform, Commonwealth Scientific and Industrial Research Organisation (CSIRO), Clayton, Victoria, 3168, Australia.
| | - Taylor Graham
- Commonwealth Scientific and Industrial Research Organisation (CSIRO) Manufacturing, Clayton, Victoria, 3168, Australia
- Australian Regenerative Medicine Institute, Monash University, Melbourne, Victoria, 3800, Australia
| | - Georgina Squires-Donelly
- Commonwealth Scientific and Industrial Research Organisation (CSIRO) Manufacturing, Clayton, Victoria, 3168, Australia
- Australian Regenerative Medicine Institute, Monash University, Melbourne, Victoria, 3800, Australia
| | - Andrew L Laslett
- Commonwealth Scientific and Industrial Research Organisation (CSIRO) Manufacturing, Clayton, Victoria, 3168, Australia.
- Australian Regenerative Medicine Institute, Monash University, Melbourne, Victoria, 3800, Australia.
- Space Technology Future Science Platform, Commonwealth Scientific and Industrial Research Organisation (CSIRO), Clayton, Victoria, 3168, Australia.
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11
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Dolan CP, Imholt F, Yang TJ, Bokhari R, Gregory J, Yan M, Qureshi O, Zimmel K, Sherman KM, Falck A, Yu L, Leininger E, Brunauer R, Suva LJ, Gaddy D, Dawson LA, Muneoka K. Mouse Digit Tip Regeneration Is Mechanical Load Dependent. J Bone Miner Res 2022; 37:312-322. [PMID: 34783092 PMCID: PMC9400037 DOI: 10.1002/jbmr.4470] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/08/2021] [Revised: 10/12/2021] [Accepted: 11/08/2021] [Indexed: 12/15/2022]
Abstract
Amputation of the mouse digit tip results in blastema-mediated regeneration. In this model, new bone regenerates de novo to lengthen the amputated stump bone, resulting in a functional replacement of the terminal phalangeal element along with associated non-skeletal tissues. Physiological examples of bone repair, such as distraction osteogenesis and fracture repair, are well known to require mechanical loading. However, the role of mechanical loading during mammalian digit tip regeneration is unknown. In this study, we demonstrate that reducing mechanical loading inhibits blastema formation by attenuating bone resorption and wound closure, resulting in the complete inhibition of digit regeneration. Mechanical unloading effects on wound healing and regeneration are completely reversible when mechanical loading is restored. Mechanical unloading after blastema formation results in a reduced rate of de novo bone formation, demonstrating mechanical load dependence of the bone regenerative response. Moreover, enhancing the wound-healing response of mechanically unloaded digits with the cyanoacrylate tissue adhesive Dermabond improves wound closure and partially rescues digit tip regeneration. Taken together, these results demonstrate that mammalian digit tip regeneration is mechanical load-dependent. Given that human fingertip regeneration shares many characteristics with the mouse digit tip, these results identify mechanical load as a previously unappreciated requirement for de novo bone regeneration in humans. © 2021 American Society for Bone and Mineral Research (ASBMR).
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Affiliation(s)
- Connor P Dolan
- Department of Veterinary Physiology and Pharmacology, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX, USA.,DoD-VA Extremity Trauma and Amputation Center of Excellence, Bethesda, MD, USA.,Department of Surgery, Uniformed Services University of the Health Sciences and Walter Reed National Military Medical Center, Bethesda, MD, USA
| | - Felisha Imholt
- Department of Veterinary Physiology and Pharmacology, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX, USA
| | - Tae-Jung Yang
- Department of Veterinary Physiology and Pharmacology, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX, USA
| | - Rihana Bokhari
- Department of Veterinary Physiology and Pharmacology, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX, USA
| | - Joshua Gregory
- Department of Veterinary Physiology and Pharmacology, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX, USA
| | - Mingquan Yan
- Department of Veterinary Physiology and Pharmacology, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX, USA
| | - Osama Qureshi
- Department of Veterinary Physiology and Pharmacology, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX, USA
| | - Katherine Zimmel
- Department of Veterinary Physiology and Pharmacology, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX, USA
| | - Kirby M Sherman
- Department of Veterinary Physiology and Pharmacology, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX, USA
| | - Alyssa Falck
- Department of Veterinary Integrative Biosciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX, USA
| | - Ling Yu
- Department of Veterinary Physiology and Pharmacology, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX, USA
| | - Eric Leininger
- Department of Cell and Molecular Biology, School of Science and Engineering, Tulane University, New Orleans, LA, USA
| | - Regina Brunauer
- Department of Veterinary Physiology and Pharmacology, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX, USA
| | - Larry J Suva
- Department of Veterinary Physiology and Pharmacology, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX, USA
| | - Dana Gaddy
- Department of Veterinary Integrative Biosciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX, USA
| | - Lindsay A Dawson
- Department of Veterinary Physiology and Pharmacology, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX, USA
| | - Ken Muneoka
- Department of Veterinary Physiology and Pharmacology, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX, USA.,Department of Cell and Molecular Biology, School of Science and Engineering, Tulane University, New Orleans, LA, USA
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12
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Zhao R. Irisin at the crossroads of inter-organ communications: Challenge and implications. Front Endocrinol (Lausanne) 2022; 13:989135. [PMID: 36267573 PMCID: PMC9578559 DOI: 10.3389/fendo.2022.989135] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/08/2022] [Accepted: 09/20/2022] [Indexed: 12/02/2022] Open
Abstract
The physiological functions of organs are intercommunicated occurring through secreted molecules. That exercise can improve the physiological function of organs or tissues is believed by secreting myokines from muscle to target remote organs. However, the underlying mechanism how exercise regulates the inter-organ communications remains incompletely understood yet. A recently identified myokine-irisin, primarily found in muscle and adipose and subsequently extending to bone, heart, liver and brain, provides a new molecular evidence for the inter-organ communications. It is secreted under the regulation of exercise and mediates the intercommunications between exercise and organs. To best our understanding of the regulatory mechanism, this review discusses the recent evidence involving the potential molecular pathways of the inter-organ communications, and the interactions between signalings and irisin in regulating the impact of exercise on organ functions are also discussed.
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13
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Pereira LJ, Andrade EF, Barroso LC, Lima RRD, Macari S, Paiva SM, Silva TA. Irisin effects on bone: systematic review with meta-analysis of preclinical studies and prospects for oral health. Braz Oral Res 2022; 36:e055. [DOI: 10.1590/1807-3107bor-2022.vol36.0055] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2020] [Accepted: 01/26/2022] [Indexed: 12/24/2022] Open
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14
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Abstract
PURPOSE OF REVIEW In this review, we provide an overview of what is currently known about the impacts of mechanical stimuli on metastatic tumor-induced bone disease (TIBD). Further, we focus on the role of the osteocyte, the skeleton's primary mechanosensory cell, which is central to the skeleton's mechanoresponse, sensing and integrating local mechanical stimuli, and then controlling the downstream remodeling balance as appropriate. RECENT FINDINGS Exercise and controlled mechanical loading have anabolic effects on bone tissue in models of bone metastasis. They also have anti-tumorigenic properties, in part due to offsetting the vicious cycle of osteolytic bone loss as well as regulating inflammatory signals. The impacts of metastatic cancer on the mechanosensory function of osteocytes remains unclear. Increased mechanical stimuli are a potential method for mitigating TIBD.
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Affiliation(s)
- Blayne A Sarazin
- Department of Mechanical Engineering, University of Colorado, 427 UCB, Boulder, CO, 80309, USA
| | - Claire L Ihle
- Department of Pathology, University of Colorado Anschutz Medical Campus, Aurora, CO, 80045, USA
| | - Philip Owens
- Department of Pathology, University of Colorado Anschutz Medical Campus, Aurora, CO, 80045, USA
- Department of Veterans Affairs, Research Service, Eastern Colorado Health Care System, Aurora, CO, 80045, USA
| | - Maureen E Lynch
- Department of Mechanical Engineering, University of Colorado, 427 UCB, Boulder, CO, 80309, USA.
- Biofrontiers Institute, University of Colorado, Boulder, CO, 80309, USA.
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15
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Kornel A, Den Hartogh DJ, Klentrou P, Tsiani E. Role of the Myokine Irisin on Bone Homeostasis: Review of the Current Evidence. Int J Mol Sci 2021; 22:9136. [PMID: 34502045 PMCID: PMC8430535 DOI: 10.3390/ijms22179136] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2021] [Revised: 08/16/2021] [Accepted: 08/19/2021] [Indexed: 02/07/2023] Open
Abstract
Bone is a highly dynamic tissue that is constantly adapting to micro-changes to facilitate movement. When the balance between bone building and resorption shifts more towards bone resorption, the result is reduced bone density and mineralization, as seen in osteoporosis or osteopenia. Current treatment strategies aimed to improve bone homeostasis and turnover are lacking in efficacy, resulting in the search for new preventative and nutraceutical treatment options. The myokine irisin, since its discovery in 2012, has been shown to play an important role in many tissues including muscle, adipose, and bone. Evidence indicate that irisin is associated with increased bone formation and decreased bone resorption, leading to reduced risk of osteoporosis in post-menopausal women. In addition, low serum irisin levels have been found in individuals with osteoporosis and osteopenia. Irisin targets key signaling proteins, promoting osteoblastogenesis and reducing osteoclastogenesis. The present review summarizes the existing evidence regarding the effects of irisin on bone homeostasis.
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Affiliation(s)
- Amanda Kornel
- Department of Health Sciences, Faculty of Applied Health Sciences, Brock University, St. Catharines, ON L2S 3A1, Canada; (A.K.); (D.J.D.H.)
| | - Danja J. Den Hartogh
- Department of Health Sciences, Faculty of Applied Health Sciences, Brock University, St. Catharines, ON L2S 3A1, Canada; (A.K.); (D.J.D.H.)
- Centre for Bone and Muscle Health, Brock University, St. Catharines, ON L2S 3A1, Canada;
| | - Panagiota Klentrou
- Centre for Bone and Muscle Health, Brock University, St. Catharines, ON L2S 3A1, Canada;
- Department of Kinesiology, Brock University, St. Catharines, ON L2S 3A1, Canada
| | - Evangelia Tsiani
- Department of Health Sciences, Faculty of Applied Health Sciences, Brock University, St. Catharines, ON L2S 3A1, Canada; (A.K.); (D.J.D.H.)
- Centre for Bone and Muscle Health, Brock University, St. Catharines, ON L2S 3A1, Canada;
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16
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Liu L, Guo J, Chen X, Tong X, Xu J, Zou J. The Role of Irisin in Exercise-Mediated Bone Health. Front Cell Dev Biol 2021; 9:668759. [PMID: 34017836 PMCID: PMC8129548 DOI: 10.3389/fcell.2021.668759] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2021] [Accepted: 04/06/2021] [Indexed: 11/13/2022] Open
Abstract
Exercise training promotes physical and bone health, and is the first choice of non-drug strategies that help to improve the prognosis and complications of many chronic diseases. Irisin is a newly discovered peptide hormone that modulates energy metabolism and skeletal muscle mass. Here, we discuss the role of irisin in bone metabolism via exercise-induced mechanical forces regulation. In addition, the role of irisin in pathological bone loss and other chronic diseases is also reviewed. Notably, irisin appears to be a key determinant of bone mineral status and thus may serve as a novel biomarker for bone metabolism. Interestingly, the secretion of irisin appears to be mediated by different forms of exercise and pathological conditions such as diabetes, obesity, and inflammation. Understanding the mechanism by which irisin is regulated and how it regulates skeletal metabolism via osteoclast and osteoblast activities will be an important step toward applying new knowledge of irisin to the treatment and prevention of bone diseases such as osteolysis and other chronic disorders.
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Affiliation(s)
- Lifei Liu
- School of Kinesiology, Shanghai University of Sport, Shanghai, China.,Department of Rehabilitation, The People's Hospital of Liaoning Province, Shenyang, China
| | - Jianmin Guo
- School of Kinesiology, Shanghai University of Sport, Shanghai, China
| | - Xi Chen
- School of Sports Science, Wenzhou Medical University, Wenzhou, China
| | - Xiaoyang Tong
- School of Kinesiology, Shanghai University of Sport, Shanghai, China
| | - Jiake Xu
- School of Biomedical Sciences, University of Western Australia, Perth, WA, Australia
| | - Jun Zou
- School of Kinesiology, Shanghai University of Sport, Shanghai, China
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17
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The Pathophysiology of Osteoporosis after Spinal Cord Injury. Int J Mol Sci 2021; 22:ijms22063057. [PMID: 33802713 PMCID: PMC8002377 DOI: 10.3390/ijms22063057] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2021] [Revised: 03/15/2021] [Accepted: 03/15/2021] [Indexed: 12/12/2022] Open
Abstract
Spinal cord injury (SCI) affects approximately 300,000 people in the United States. Most individuals who sustain severe SCI also develop subsequent osteoporosis. However, beyond immobilization-related lack of long bone loading, multiple mechanisms of SCI-related bone density loss are incompletely understood. Recent findings suggest neuronal impairment and disability may lead to an upregulation of receptor activator of nuclear factor-κB ligand (RANKL), which promotes bone resorption. Disruption of Wnt signaling and dysregulation of RANKL may also contribute to the pathogenesis of SCI-related osteoporosis. Estrogenic effects may protect bones from resorption by decreasing the upregulation of RANKL. This review will discuss the current proposed physiological and cellular mechanisms explaining osteoporosis associated with SCI. In addition, we will discuss emerging pharmacological and physiological treatment strategies, including the promising effects of estrogen on cellular protection.
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