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Sampei C, Kato K, Arasaki Y, Kimura Y, Konno T, Otsuka K, Kohara Y, Noda M, Ezura Y, Hayata T. Gprc5a is a novel parathyroid hormone-inducible gene and negatively regulates osteoblast proliferation and differentiation. J Cell Physiol 2024; 239:e31297. [PMID: 38769895 DOI: 10.1002/jcp.31297] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2023] [Revised: 04/18/2024] [Accepted: 05/02/2024] [Indexed: 05/22/2024]
Abstract
Teriparatide is a peptide derived from a parathyroid hormone (PTH) and an osteoporosis therapeutic drug with potent bone formation-promoting activity. To identify novel druggable genes that act downstream of PTH signaling and are potentially involved in bone formation, we screened PTH target genes in mouse osteoblast-like MC3T3-E1 cells. Here we show that Gprc5a, encoding an orphan G protein-coupled receptor, is a novel PTH-inducible gene and negatively regulates osteoblast proliferation and differentiation. PTH treatment induced Gprc5a expression in MC3T3-E1 cells, rat osteosarcoma ROS17/2.8 cells, and mouse femurs. Induction of Gprc5a expression by PTH occurred in the absence of protein synthesis and was mediated primarily via the cAMP pathway, suggesting that Gprc5a is a direct target of PTH signaling. Interestingly, Gprc5a expression was induced additively by co-treatment with PTH and 1α, 25-dihydroxyvitamin D3 (calcitriol), or retinoic acid in MC3T3-E1 cells. Reporter analysis of a 1 kb fragment of human GPRC5A promoter revealed that the promoter fragment showed responsiveness to PTH via the cAMP response element, suggesting that GPRC5A is also a PTH-inducible gene in humans. Gprc5a knockdown promoted cell viability and proliferation, as demonstrated by MTT and BrdU assays. Gprc5a knockdown also promoted osteoblast differentiation, as indicated by gene expression analysis and mineralization assay. Mechanistic studies showed that Gprc5a interacted with BMPR1A and suppressed BMP signaling induced by BMP-2 and constitutively active BMP receptors, ALK2 (ACVR1) Q207D and ALK3 (BMPR1A) Q233D. Thus, our results suggest that Gprc5a is a novel gene induced by PTH that acts in an inhibitory manner on both cell proliferation and osteoblast differentiation and is a candidate for drug targets for osteoporosis.
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Affiliation(s)
- Chisato Sampei
- Department of Molecular Pharmacology, Graduate School of Pharmaceutical Sciences and Faculty of Pharmaceutical Science, Tokyo University of Science, Noda, Chiba, Japan
| | - Kosuke Kato
- Department of Molecular Pharmacology, Graduate School of Pharmaceutical Sciences and Faculty of Pharmaceutical Science, Tokyo University of Science, Noda, Chiba, Japan
| | - Yasuhiro Arasaki
- Department of Molecular Pharmacology, Graduate School of Pharmaceutical Sciences and Faculty of Pharmaceutical Science, Tokyo University of Science, Noda, Chiba, Japan
| | - Yuta Kimura
- Department of Molecular Pharmacology, Graduate School of Pharmaceutical Sciences and Faculty of Pharmaceutical Science, Tokyo University of Science, Noda, Chiba, Japan
| | - Takuto Konno
- Department of Molecular Pharmacology, Graduate School of Pharmaceutical Sciences and Faculty of Pharmaceutical Science, Tokyo University of Science, Noda, Chiba, Japan
| | - Kanon Otsuka
- Department of Molecular Pharmacology, Graduate School of Pharmaceutical Sciences and Faculty of Pharmaceutical Science, Tokyo University of Science, Noda, Chiba, Japan
| | - Yukihiro Kohara
- Department of Molecular Pharmacology, Graduate School of Pharmaceutical Sciences and Faculty of Pharmaceutical Science, Tokyo University of Science, Noda, Chiba, Japan
| | - Masaki Noda
- Department of Molecular Pharmacology, Medical Research Institute, Tokyo Medical and Dental University (TMDU), Bunkyo-ku, Tokyo, Japan
- Center for Stem Cell and Regenerative Medicine, Tokyo Medical and Dental University, Bunkyo-ku, Tokyo, Japan
| | - Yoichi Ezura
- Department of Molecular Pharmacology, Medical Research Institute, Tokyo Medical and Dental University (TMDU), Bunkyo-ku, Tokyo, Japan
- Department of Joint Surgery and Sports Medicine, Tokyo Medical and Dental University, Bunkyo-ku, Tokyo, Japan
- Department of Occupational Therapy, Faculty of Health and Medical Science, Teikyo Heisei University, Toshima-ku, Japan
| | - Tadayoshi Hayata
- Department of Molecular Pharmacology, Graduate School of Pharmaceutical Sciences and Faculty of Pharmaceutical Science, Tokyo University of Science, Noda, Chiba, Japan
- Department of Molecular Pharmacology, Medical Research Institute, Tokyo Medical and Dental University (TMDU), Bunkyo-ku, Tokyo, Japan
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Clark AR, Mauntel TC, Goldman SM, Dearth CL. Repurposing existing products to accelerate injury recovery (REPAIR) of military relevant musculoskeletal conditions. Front Bioeng Biotechnol 2023; 10:1105599. [PMID: 36698630 PMCID: PMC9868163 DOI: 10.3389/fbioe.2022.1105599] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2022] [Accepted: 12/21/2022] [Indexed: 01/11/2023] Open
Abstract
Musculoskeletal injuries (MSKIs) are a great hindrance to the readiness of the United States Armed Forces through lost duty time and reduced operational capabilities. While most musculoskeletal injuries result in return-to-duty/activity with no (functional) limitations, the healing process is often long. Long healing times coupled with the high frequency of musculoskeletal injuries make them a primary cause of lost/limited duty days. Thus, there exists an urgent, clinically unmet need for interventions to expedite tissue healing kinetics following musculoskeletal injuries to lessen their impact on military readiness and society as a whole. There exist several treatments with regulatory approval for other indications that have pro-regenerative/healing properties, but few have an approved indication for treating musculoskeletal injuries. With the immediate need for treatment options for musculoskeletal injuries, we propose a paradigm of Repurposing Existing Products to Accelerate Injury Recovery (REPAIR). Developing treatments via repurposing existing therapeutics for other indications has shown monumental advantages in both cost effectiveness and reduced time to bring to market compared to novel candidates. Thus, undertaking the needed research efforts to evaluate the effectiveness of promising REPAIR-themed candidates has the potential to enable near-term solutions for optimizing musculoskeletal injuries recovery, thereby addressing a top priority within the United States. Armed Forces. Herein, the REPAIR paradigm is presented, including example targets of opportunity as well as practical considerations for potential technical solutions for the translation of existing therapeutics into clinical practice for musculoskeletal injuries.
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Affiliation(s)
- Andrew R. Clark
- Research and Surveillance Division, DoD-VA Extremity Trauma and Amputation Center of Excellence, Bethesda, MD, United States,Department of Surgery, Uniformed Services University of the Health Sciences—Walter Reed National Military Medical Center, Bethesda, MD, United States
| | - Timothy C Mauntel
- Research and Surveillance Division, DoD-VA Extremity Trauma and Amputation Center of Excellence, Bethesda, MD, United States,Department of Surgery, Uniformed Services University of the Health Sciences—Walter Reed National Military Medical Center, Bethesda, MD, United States,Womack Army Medical Center, Fort Bragg, NC, United States
| | - Stephen M Goldman
- Research and Surveillance Division, DoD-VA Extremity Trauma and Amputation Center of Excellence, Bethesda, MD, United States,Department of Surgery, Uniformed Services University of the Health Sciences—Walter Reed National Military Medical Center, Bethesda, MD, United States
| | - Christopher L. Dearth
- Research and Surveillance Division, DoD-VA Extremity Trauma and Amputation Center of Excellence, Bethesda, MD, United States,Department of Surgery, Uniformed Services University of the Health Sciences—Walter Reed National Military Medical Center, Bethesda, MD, United States,*Correspondence: Christopher L. Dearth,
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Correlation Between Traumatic Brain Injuries and Callus Formation in Long bone Fractures. Indian J Orthop 2022; 56:837-846. [PMID: 35547339 PMCID: PMC9043063 DOI: 10.1007/s43465-021-00594-0] [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: 10/10/2021] [Accepted: 12/13/2021] [Indexed: 02/04/2023]
Abstract
INTRODUCTION Orthopaedic aphorism teaches that fractures of long bones when associated with head injuries frequently heal with excessive callus and at a faster rate than normal. However, the evidence on this subject is flimsy and the aphorism remains unsubstantiated. Numerous studies have been conducted evaluating the possible humoral and other factors involved leading to excess callus formation in patients with a head injury. This study was designed to evaluate the effects of a traumatic head injury on bone healing in adults with a diaphyseal fracture of the lower limb. METHODS Fiveteen patients with a closed fracture of tibia or femur and associated head injury (cases) and 15 patients with a closed fracture of tibia or femur without an associated head injury (controls) were included in the study. All patients were evaluated in terms of various serum parameters, including IL-6, growth hormone, PTH, LDH, prolactin levels, and ALP. Head injuries were graded as mild, moderate, or severe. Ventilatory support if required was noted. Serum prolactin was repeated at 5 weeks. Patients were followed up with serial radiographs, and the volume of callus formed was calculated and compared. RESULTS The mean value of growth hormone, interleukin-6 levels, and prolactin levels at 5 weeks were found to be higher in patients with head injuries, and the difference was highly significant (p = 0.001). The severity of head injury also correlated proportionately with the spike in IL-6 levels. There was more pronounced callus formation in patients with head injury group when compared to the controls. This difference was significant at all intervals. DISCUSSION There was higher volume of callus noted at the end of 6 months in patients with severe head injury (GCS < 7) when compared to patients with moderate head injury (GCS > 7). The patients with severe head injury were naturally under ventilator support for a prolonged period compared to those with moderate head injury. It was thus indiscernible if the excess callus observed is due to the humoral cascade or as an effect of prolonged ventilation. Patients with head injuries show elevated parathyroid hormone levels, growth hormone levels at the time of injury, and elevated prolactin levels 5 weeks after the trauma-all of which might contribute to enhanced osteogenesis. Interleukin-6 levels are also elevated and the levels correlate to severity of head injury. CONCLUSION Head injury triggers a humoral cascade invloving interleukin-6, parathyroid hormoe, growth hormone, and prolactin that contributes to enhanced fracture healing.
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Xu X, Wei W, Xu J, Huang J, Li L, Han T, Qi J, Sun C, Li Y, Jiang W. The association of minerals intake in three meals with cancer and all-cause mortality: the U.S. National Health and Nutrition Examination Survey, 2003-2014. BMC Cancer 2021; 21:912. [PMID: 34380458 PMCID: PMC8359108 DOI: 10.1186/s12885-021-08643-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2020] [Accepted: 07/22/2021] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Intake time of diet has recently been demonstrated to be associated with the internal clock and circadian pattern. However, whether and how the intake time of minerals would influence the natural course of cancer was largely unknown. METHODS This study aimed to assess the association of mineral intake at different periods with cancer and all-cause mortality. A total of 27,455 participants aged 18-85 years old in the National Health and Nutrition Examination Survey were recruited. The main exposures were the mineral intakes in the morning, afternoon and evening, which were categorized into quintiles, respectively. The main outcomes were mortality of cancer and all causes. RESULTS During the 178,182 person-years of follow-up, 2680 deaths, including 601 deaths due to cancer, were documented. After adjusting for potential confounders, compared to the participants who were in the lowest quintile(quintile-1) of mineral intakes at dinner, the participants in the highest quintile intake(quintile-5) of dietary potassium, calcium and magnesium had lower mortality risks of cancer (HRpotassium = 0.72, 95% CI:0.55-0.94, P for trend = 0.023; HRcalcium = 0.74, 95% CI:0.57-0.98, P for trend = 0.05; HRmagnesium = 0.75, 95% CI:0.56-0.99, P for trend = 0.037) and all-cause (HRpotassium = 0.83, 95% CI:0.73-0.94, P for trend = 0.012; HRcalcium = 0.87, 95% CI:0.76-0.99, P for trend = 0.025; HRmagnesium = 0.85, 95% CI:0.74-0.97, P for trend = 0.011; HRcopper = 0.80, 95%CI: 0.68-0.94, P for trend = 0.012). Further, equivalently replacing 10% of dietary potassium, calcium and magnesium consumed in the morning with those in the evening were associated with lower mortality risk of cancer (HRpotassium = 0.94, 95%CI:0.91-0.97; HRcalcium = 0.95, 95%CI:0.92-0.98; HRmagnesium = 0.95, 95%CI: 0.92-0.98). CONCLUSIONS This study demonstrated that the optimal intake time of potassium, calcium and magnesium for reducing the risk of cancer and all-cause mortality was in the evening.
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Affiliation(s)
- Xiaoqing Xu
- Department of Nutrition and Food Hygiene, the National Key Discipline, School of Public Health, Harbin Medical University, 157 Baojian Road, Harbin, People's Republic of China, 150081
| | - Wei Wei
- Department of Nutrition and Food Hygiene, the National Key Discipline, School of Public Health, Harbin Medical University, 157 Baojian Road, Harbin, People's Republic of China, 150081
| | - Jiaxu Xu
- Department of Nutrition and Food Hygiene, the National Key Discipline, School of Public Health, Harbin Medical University, 157 Baojian Road, Harbin, People's Republic of China, 150081
| | - Jiaxin Huang
- Department of Postgraduate, Harbin Medical University Cancer Hospital, No.150, Haping Road, Nangang District, Harbin, People's Republic of China
| | - Li Li
- Department of Nutrition and Food Hygiene, the National Key Discipline, School of Public Health, Harbin Medical University, 157 Baojian Road, Harbin, People's Republic of China, 150081
| | - Tianshu Han
- Department of Nutrition and Food Hygiene, the National Key Discipline, School of Public Health, Harbin Medical University, 157 Baojian Road, Harbin, People's Republic of China, 150081
- Department of Endocrinology, The Second Affiliated Hospital of Harbin Medical University, Harbin, People's Republic of China
| | - Jiayue Qi
- Department of Nutrition and Food Hygiene, the National Key Discipline, School of Public Health, Harbin Medical University, 157 Baojian Road, Harbin, People's Republic of China, 150081
| | - Changhao Sun
- Department of Nutrition and Food Hygiene, the National Key Discipline, School of Public Health, Harbin Medical University, 157 Baojian Road, Harbin, People's Republic of China, 150081
| | - Ying Li
- Department of Nutrition and Food Hygiene, the National Key Discipline, School of Public Health, Harbin Medical University, 157 Baojian Road, Harbin, People's Republic of China, 150081.
| | - Wenbo Jiang
- Department of Nutrition and Food Hygiene, the National Key Discipline, School of Public Health, Harbin Medical University, 157 Baojian Road, Harbin, People's Republic of China, 150081.
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Rocha T, Cavalcanti AS, Leal AC, Dias RB, da Costa RS, Ribeiro GDO, Guimarães JAM, Duarte MEL. PTH 1-34 improves devitalized allogenic bone graft healing in a murine femoral critical size defect. Injury 2021; 52 Suppl 3:S3-S12. [PMID: 34088469 DOI: 10.1016/j.injury.2021.03.063] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/07/2020] [Revised: 03/24/2021] [Accepted: 03/26/2021] [Indexed: 02/02/2023]
Abstract
The treatment of large segmental defects of long bones resulting from trauma, infection, or bone tumor resections is a major challenge for orthopedic surgeons. The reconstruction of bone defects with acellular allografts can be used as an osteoconductive approach. However, devitalized allografts are associated with high rates of clinical failure as a result of poor intrinsic osteoinduction properties and a lack of further remodeling. Nevertheless, evidence suggests that due to its anabolic properties, teriparatide (PTH1-34) could be effective as an adjuvant therapy for massive allograft healing. Therefore, our goal was to investigate in a murine critical-sized defect model whether the intermittent administration of PTH1-34 improves the incorporation and revitalization of acellular structural bone allografts. Thus, a 2.5-mm critical-sized defect was established in the right femur of C57BL/6 mice, followed by the reconstruction with a devitalized cortical structural allograft. A titanium micro locking plate was applied to the anterior femoral surface and secured in place with self-tapping locking screws. Subsequently, daily doses of PTH1-34 (30, and 40 µg/kg) or saline were administered to the mice for 14 days after surgery. The mice were maintained without PTH1-34 therapy for an additional 7 days before being euthanized at 3 weeks post-surgery. Bone graft consolidation was assessed on radiographic images and by histomorphometric analysis. Additionally, to determine the frequency of osteoprogenitor cells in the bone marrow and their in vitro osteogenic capacity, stromal cells were isolated from the bone marrow of animals treated with 30 or 40 µg/kg/day of PTH1-34 following the same protocol used for the experimental animals. Our results suggest that intermittent PTH1-34 treatment at 30 µg/kg/day after femoral allograft reconstruction surgery accelerated the healing process as evidenced by new bone formation induced on endosteal and periosteal surfaces, enhanced revitalization of allogeneic graft, and increased frequency and osteogenic capacity of bone marrow stromal cells (BMSC). These findings should encourage further studies aimed at investigating the potential therapeutic use of intermittent PTH1-34, specifically with regards to the optimal dosing regimen in clinically challenging orthopedic scenarios.
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Affiliation(s)
- Tito Rocha
- Trauma Center, National Institute of Traumatology and Orthopedics, Rio de Janeiro 20940-070, Brazil.
| | - Amanda S Cavalcanti
- Research Division, National Institute of Traumatology and Orthopedics, Rio de Janeiro 20940-070, Brazil.
| | - Ana Carolina Leal
- Research Division, National Institute of Traumatology and Orthopedics, Rio de Janeiro 20940-070, Brazil.
| | - Rhayra B Dias
- Research Division, National Institute of Traumatology and Orthopedics, Rio de Janeiro 20940-070, Brazil.
| | - Rafaela Sartore da Costa
- Research Division, National Institute of Traumatology and Orthopedics, Rio de Janeiro 20940-070, Brazil.
| | | | - João Antonio Matheus Guimarães
- Trauma Center, National Institute of Traumatology and Orthopedics, Rio de Janeiro 20940-070, Brazil; Research Division, National Institute of Traumatology and Orthopedics, Rio de Janeiro 20940-070, Brazil.
| | - Maria Eugênia Leite Duarte
- Research Division, National Institute of Traumatology and Orthopedics, Rio de Janeiro 20940-070, Brazil.
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Pathak JL, Bravenboer N, Klein-Nulend J. The Osteocyte as the New Discovery of Therapeutic Options in Rare Bone Diseases. Front Endocrinol (Lausanne) 2020; 11:405. [PMID: 32733380 PMCID: PMC7360678 DOI: 10.3389/fendo.2020.00405] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/10/2020] [Accepted: 05/20/2020] [Indexed: 01/18/2023] Open
Abstract
Osteocytes are the most abundant (~95%) cells in bone with the longest half-life (~25 years) in humans. In the past osteocytes have been regarded as vestigial cells in bone, since they are buried inside the tough bone matrix. However, during the last 30 years it has become clear that osteocytes are as important as bone forming osteoblasts and bone resorbing osteoclasts in maintaining bone homeostasis. The osteocyte cell body and dendritic processes reside in bone in a complex lacuno-canalicular system, which allows the direct networking of osteocytes to their neighboring osteocytes, osteoblasts, osteoclasts, bone marrow, blood vessels, and nerves. Mechanosensing of osteocytes translates the applied mechanical force on bone to cellular signaling and regulation of bone adaptation. The osteocyte lacuno-canalicular system is highly efficient in transferring external mechanical force on bone to the osteocyte cell body and dendritic processes via displacement of fluid in the lacuno-canalicular space. Osteocyte mechanotransduction regulates the formation and function of the osteoblasts and osteoclasts to maintain bone homeostasis. Osteocytes produce a variety of proteins and signaling molecules such as sclerostin, cathepsin K, Wnts, DKK1, DMP1, IGF1, and RANKL/OPG to regulate osteoblast and osteoclast activity. Various genetic abnormality-associated rare bone diseases are related to disrupted osteocyte functions, including sclerosteosis, van Buchem disease, hypophosphatemic rickets, and WNT1 and plastin3 mutation-related disorders. Meticulous studies during the last 15 years on disrupted osteocyte function in rare bone diseases guided for the development of various novel therapeutic agents to treat bone diseases. Studies on genetic, molecular, and cellular mechanisms of sclerosteosis and van Buchem disease revealed a role for sclerostin in bone homeostasis, which led to the development of the sclerostin antibody to treat osteoporosis and other bone degenerative diseases. The mechanism of many other rare bone diseases and the role of the osteocyte in the development of such conditions still needs to be investigated. In this review, we mainly discuss the knowledge obtained during the last 30 years on the role of the osteocyte in rare bone diseases. We speculate about future research directions to develop novel therapeutic drugs targeting osteocyte functions to treat both common and rare bone diseases.
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Affiliation(s)
- Janak L. Pathak
- Key Laboratory of Oral Medicine, Guangzhou Institute of Oral Disease, Affiliated Stomatology Hospital of Guangzhou Medical University, Guangzhou, China
| | - Nathalie Bravenboer
- Department of Clinical Chemistry, Amsterdam University Medical Centers, Amsterdam Movement Sciences, Vrije Universiteit Amsterdam, Amsterdam, Netherlands
| | - Jenneke Klein-Nulend
- Key Laboratory of Oral Medicine, Guangzhou Institute of Oral Disease, Affiliated Stomatology Hospital of Guangzhou Medical University, Guangzhou, China
- Department of Oral Cell Biology, Academic Centre for Dentistry Amsterdam, Amsterdam Movement Sciences, University of Amsterdam and Vrije Universiteit Amsterdam, Amsterdam, Netherlands
- *Correspondence: Jenneke Klein-Nulend
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Takahashi A, Mulati M, Saito M, Numata H, Kobayashi Y, Ochi H, Sato S, Kaldis P, Okawa A, Inose H. Loss of cyclin-dependent kinase 1 impairs bone formation, but does not affect the bone-anabolic effects of parathyroid hormone. J Biol Chem 2018; 293:19387-19399. [PMID: 30366983 DOI: 10.1074/jbc.ra118.004834] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2018] [Revised: 10/02/2018] [Indexed: 12/31/2022] Open
Abstract
Bone mass is maintained by a balance between osteoblast-mediated bone formation and osteoclast-mediated bone resorption. Although recent genetic studies have uncovered various mechanisms that regulate osteoblast differentiation, the molecular basis of osteoblast proliferation remains unclear. Here, using an osteoblast-specific loss-of-function mouse model, we demonstrate that cyclin-dependent kinase 1 (Cdk1) regulates osteoblast proliferation and differentiation. Quantitative RT-PCR analyses revealed that Cdk1 is highly expressed in bone and is down-regulated upon osteoblast differentiation. We also noted that Cdk1 is dispensable for the bone-anabolic effects of parathyroid hormone (PTH). Cdk1 deletion in osteoblasts led to osteoporosis in adult mice due to low bone formation, but did not affect osteoclast formation in vivo Cdk1 overexpression in osteoblasts promoted proliferation, and conversely, Cdk1 knockdown inhibited osteoblast proliferation and promoted differentiation. Of note, we provide direct evidence that PTH's bone-anabolic effects occur without enhancing osteoblast proliferation in vivo Furthermore, we found that Cdk1 expression in osteoblasts is essential for bone fracture repair. These findings may help reduce the risk of nonunion after bone fracture and identify patients at higher risk for nonresponse to PTH treatment. Collectively, our results indicate that Cdk1 is essential for osteoblast proliferation and that it functions as a molecular switch that shifts osteoblast proliferation to maturation. We therefore conclude that Cdk1 plays an important role in bone formation.
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Affiliation(s)
- Akira Takahashi
- From the Department of Orthopedics, Graduate School, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8519, Japan
| | - Mieradili Mulati
- From the Department of Orthopedics, Graduate School, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8519, Japan
| | - Masanori Saito
- From the Department of Orthopedics, Graduate School, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8519, Japan
| | - Hoashi Numata
- From the Department of Orthopedics, Graduate School, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8519, Japan
| | - Yutaka Kobayashi
- From the Department of Orthopedics, Graduate School, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8519, Japan
| | - Hiroki Ochi
- the Department of Physiology and Cell Biology, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8519, Japan
| | - Shingo Sato
- the Department of Physiology and Cell Biology, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8519, Japan
| | - Philipp Kaldis
- the Institute of Molecular and Cell Biology (IMCB), Agency for Science, Technology, and Research (A*STAR), Singapore 138673, Republic of Singapore, and.,the Department of Biochemistry, National University of Singapore (NUS), Singapore 117597, Republic of Singapore
| | - Atsushi Okawa
- From the Department of Orthopedics, Graduate School, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8519, Japan
| | - Hiroyuki Inose
- From the Department of Orthopedics, Graduate School, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8519, Japan,
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Müller WEG, Wang X, Schröder HC. New Target Sites for Treatment of Osteoporosis. PROGRESS IN MOLECULAR AND SUBCELLULAR BIOLOGY 2017; 55:187-219. [PMID: 28238039 DOI: 10.1007/978-3-319-51284-6_6] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
In the last few years, much progress has been achieved in the discovery of new drug target sites for treatment of osteoporotic disorders, one of the main challenging diseases with a large burden for the public health systems. Among these new agents promoting bone formation, shifting the impaired equilibrium between bone anabolism and bone catabolism in the direction of bone synthesis are inorganic polymers, in particular inorganic polyphosphates that show strong stimulatory effects on the expression of bone anabolic marker proteins and hydroxyapatite formation. The bone-forming activity of these polymers can even be enhanced by combination with certain small molecules like quercetin, or if given as functionally active particles with certain divalent cations like strontium ions even showing by itself biological activity. This chapter summarizes recent developments in the search and development of novel anti-osteoporotic agents, with a particular focus on therapeutic approaches based on the potential application of inorganic polymers and combinations.
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Affiliation(s)
- Werner E G Müller
- ERC Advanced Investigator Group, Institute for Physiological Chemistry, University Medical Center of the Johannes Gutenberg University, Duesbergweg 6, 55128, Mainz, Germany. .,NanotecMARIN GmbH, Duesbergweg 6, 55128, Mainz, Germany.
| | - Xiaohong Wang
- ERC Advanced Investigator Group, Institute for Physiological Chemistry, University Medical Center of the Johannes Gutenberg University, Duesbergweg 6, 55128, Mainz, Germany.,NanotecMARIN GmbH, Duesbergweg 6, 55128, Mainz, Germany
| | - Heinz C Schröder
- ERC Advanced Investigator Group, Institute for Physiological Chemistry, University Medical Center of the Johannes Gutenberg University, Duesbergweg 6, 55128, Mainz, Germany.,NanotecMARIN GmbH, Duesbergweg 6, 55128, Mainz, Germany
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9
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Shirakawa J, Harada H, Noda M, Ezura Y. PTH-Induced Osteoblast Proliferation Requires Upregulation of the Ubiquitin-Specific Peptidase 2 (Usp2) Expression. Calcif Tissue Int 2016; 98:306-15. [PMID: 26643174 DOI: 10.1007/s00223-015-0083-5] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/09/2015] [Accepted: 11/06/2015] [Indexed: 12/11/2022]
Abstract
Osteoporosis is a common disease that increases individual's fragility fracture risk. PTH is the only therapeutic agent for severe osteoporosis that requires anabolic action of bone formation. Although a part of the PTH actions is explained by increased proliferation of osteoblastic precursor cells, the mechanisms involved in the proliferation of osteoblastic cells by PTH have not been clarified yet. Therefore, in this study, we investigated the effects of PTH on gene expression in the cultured osteoblastic MC3T3-E1 cells, and found that the ubiquitin-specific peptidase 2 (Usp2) may be one of the direct target genes of PTHR signaling. Usp2 is a deubiquitination enzyme targeting various factors including CyclinD1 in cancer cells and PTH receptor 1 in osteoblasts. We confirmed that consistent induction of Usp2 expression peaked at 1 h by PTH1-34 (teriparatide) in MC3T3-E1 cells and primary calvarial osteoblasts. Among the three known splicing variants of the Usp2, we found the isoforms 1 and 2 are predominantly expressed in osteoblasts. Live-imaging analysis of the Fucci-transgenic mouse-derived primary osteoblasts indeed demonstrated that Usp2 is required for the PTH1-34-induced osteoblast proliferation. Western blotting analysis of the CyclinD1 indicated that Usp2 knock-down influences the paradoxical changes of CyclinD1 protein levels in this condition. Our data indicate that Usp2 is required for the PTH1-34-induced proliferation of osteoblasts.
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Affiliation(s)
- Jumpei Shirakawa
- Department of Molecular Pharmacology, Medical Research Institute, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo, Tokyo, 113-8510, Japan
- Global COE Program, Tokyo Medical and Dental University, Tokyo, Japan
- Department of Oral and Maxillofacial Surgery, Tokyo Medical and Dental University, Tokyo, Japan
| | - Hiroyuki Harada
- Department of Oral and Maxillofacial Surgery, Tokyo Medical and Dental University, Tokyo, Japan
| | - Masaki Noda
- Department of Molecular Pharmacology, Medical Research Institute, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo, Tokyo, 113-8510, Japan.
- Global COE Program, Tokyo Medical and Dental University, Tokyo, Japan.
| | - Yoichi Ezura
- Department of Molecular Pharmacology, Medical Research Institute, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo, Tokyo, 113-8510, Japan.
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10
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Silva BC, Bilezikian JP. Parathyroid hormone: anabolic and catabolic actions on the skeleton. Curr Opin Pharmacol 2015; 22:41-50. [PMID: 25854704 DOI: 10.1016/j.coph.2015.03.005] [Citation(s) in RCA: 312] [Impact Index Per Article: 34.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2015] [Accepted: 03/24/2015] [Indexed: 12/16/2022]
Abstract
Parathyroid hormone (PTH) is essential for the maintenance of calcium homeostasis through, in part, its actions to regulate bone remodeling. While PTH stimulates both bone formation and bone resorption, the duration and periodicity of exposure to PTH governs the net effect on bone mass, that is whether it is catabolic or anabolic. PTH receptor signaling in osteoblasts and osteocytes can increase the RANKL/OPG ratio, increasing both osteoclast recruitment and osteoclast activity, and thereby stimulating bone resorption. In contrast, PTH-induced bone formation is explained, at least in part, by its ability to downregulate SOST/sclerostin expression in osteocytes, permitting the anabolic Wnt signaling pathway to proceed. The two modes of administration of PTH, that is, continuous vs. intermittent, can regulate, in bone cells, different sets of genes; alternatively, the same sets of genes exposed to PTH in sustained vs. transient way, will favor bone resorption or bone formation, respectively. This article reviews the effects of PTH on bone cells that lead to these dual catabolic and anabolic actions on the skeleton.
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Affiliation(s)
- Barbara C Silva
- Santa Casa de Belo Horizonte and Felicio Rocho Hospital, Division of Endocrinology, Brazil
| | - John P Bilezikian
- Metabolic Bone Diseases Unit, Division of Endocrinology, Department of Medicine, College of Physicians and Surgeons, Columbia University, United States.
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11
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Li X, Garcia J, Lu J, Iriana S, Kalajzic I, Rowe D, Demer LL, Tintut Y. Roles of parathyroid hormone (PTH) receptor and reactive oxygen species in hyperlipidemia-induced PTH resistance in preosteoblasts. J Cell Biochem 2014; 115:179-88. [PMID: 24038594 DOI: 10.1002/jcb.24648] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2013] [Accepted: 08/13/2013] [Indexed: 11/08/2022]
Abstract
Bioactive lipids initiate inflammatory reactions leading to pathogenesis of atherosclerosis. Evidence shows that they also contribute to bone loss by inhibiting parathyroid hormone receptor (PTH1R) expression and differentiation of osteoblasts. We previously demonstrated that bone anabolic effects of PTH(1-34) are blunted in hyperlipidemic mice and that these PTH effects are restored by antioxidants. However, it is not clear which osteoblastic cell developmental stage is targeted by bioactive lipids. To investigate the effects of hyperlipidemia at the cellular level, hyperlipidemic Ldlr(-/-) mice were bred with Col3.6GFPtpz mice, in which preosteoblasts/osteoblasts carry a topaz fluorescent label, and with Col2.3GFPcyan mice, in which more mature osteoblasts/osteocytes carry a cyan fluorescent label. Histological analyses of trabecular bone surfaces in femoral as well as calvarial bones showed that intermittent PTH(1-34) increased fluorescence intensity in WT-Tpz mice, but not in Tpz-Ldlr(-/-) mice. In contrast, PTH(1-34) did not alter fluorescence intensity in femoral cortical envelopes of either WT-Cyan or Ldlr(-/-)-Cyan mice. To test the mechanism of PTH1R downregulation, preosteoblastic MC3T3-E1 cells were treated with bioactive lipids and the antioxidant Trolox. Results showed that inhibitory effects of PTH1R levels by bioactive lipids were rescued by pretreatment with Trolox. The inhibitory effects on expression of PTH1R as well as on PTH-induced osteoblastic genes were mimicked by xanthine/xanthine oxidase, a known generator of reactive oxygen species. These findings suggest an important role of the preosteoblastic development stage as the target and downregulation of PTH receptor expression mediated by intracellular oxidant stress as a mechanism in hyperlipidemia-induced PTH resistance.
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Affiliation(s)
- Xin Li
- Department of Medicine, University of California, Los Angeles, California
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12
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Fischer J, Aulmann A, Dexheimer V, Grossner T, Richter W. Intermittent PTHrP(1-34) exposure augments chondrogenesis and reduces hypertrophy of mesenchymal stromal cells. Stem Cells Dev 2014; 23:2513-23. [PMID: 24836507 DOI: 10.1089/scd.2014.0101] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Phenotype instability and premature hypertrophy prevent the use of human mesenchymal stromal cells (MSCs) for cartilage regeneration. Aim of this study was to investigate whether intermittent supplementation of parathyroid hormone-related protein (PTHrP), as opposed to constant treatment, can beneficially influence MSC chondrogenesis and to explore molecular mechanisms below catabolic and anabolic responses. Human MSCs subjected to chondrogenic induction in high-density culture received PTHrP(1-34), forskolin, dbcAMP, or PTHrP(7-34) either constantly or via 6-h pulses (three times weekly), before proteoglycan, collagen type II, and X deposition; gene expression; and alkaline phosphatase (ALP) activity were assessed. While constant application of PTHrP(1-34) suppressed chondrogenesis of MSCs, pulsed application significantly increased collagen type 2 (COL2A1) gene expression and the collagen type II, proteoglycan, and DNA content of pellets after 6 weeks. Collagen type 10 (COL10A1) gene expression was little affected but Indian hedgehog (IHH) expression and ALP activity were significantly downregulated by pulsed PTHrP. A faster response to PTHrP exposure was recorded for ALP activity over COL2A1 regulation, suggesting that signal duration is critical for catabolic versus anabolic reactions. Stimulation of cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA) signaling by forskolin reproduced major effects of both treatment modes, whereas application of PTHrP(7-34) capable of protein kinase C (PKC) signaling was ineffective. Pulsed PTHrP exposure of MSCs stimulated chondrogenesis and reduced endochondral differentiation apparently uncoupling chondrogenic matrix deposition from hypertrophic marker expression. cAMP/PKA was the major signaling pathway triggering the opposing effects of both treatment modes. Intermittent application of PTHrP represents an important novel means to improve chondrogenesis of MSCs and may be considered as a supporting clinical-treatment mode for MSC-based cartilage defect regeneration.
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Affiliation(s)
- Jennifer Fischer
- Research Center for Experimental Orthopaedics, Orthopaedic University Hospital Heidelberg , Heidelberg, Germany
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13
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Rochefort GY. The osteocyte as a therapeutic target in the treatment of osteoporosis. Ther Adv Musculoskelet Dis 2014; 6:79-91. [PMID: 24891879 DOI: 10.1177/1759720x14523500] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Osteoporosis is characterized by a low bone-mineral density associated with skeletal fractures. The decrease in bone-mineral density is the consequence of an unbalanced bone-remodeling process, with higher bone resorption than bone formation. The orchestration of the bone-remodeling process is under the control of the most abundant cell in bone, the osteocyte. Functioning as an endocrine cell, osteocytes are also a source of soluble factors that not only target cells on the bone surface, but also target distant organs. Therefore, any drugs targeting the osteocyte functions and signaling pathways will have a major impact on the bone-remodeling process. This review discusses potential advances in drug therapy for osteoporosis, including novel osteocyte-related antiresorptive and anabolic agents that may become available in the coming years.
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Affiliation(s)
- Gaël Y Rochefort
- EA 2496, Faculté de Chirurgie Dentaire, Université Paris Descartes, 1 rue Maurice Arnoux, 92120 Montrouge, France
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14
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Tintut Y, Demer LL. Effects of bioactive lipids and lipoproteins on bone. Trends Endocrinol Metab 2014; 25:53-9. [PMID: 24183940 PMCID: PMC3946677 DOI: 10.1016/j.tem.2013.10.001] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/15/2013] [Revised: 09/30/2013] [Accepted: 10/02/2013] [Indexed: 12/11/2022]
Abstract
Although epidemiological studies from the past two decades show a link between atherosclerotic vascular disease and bone loss, that is independent of age, the mechanism is still unclear. This review focuses on evidence that suggests a role for atherogenic lipids and lipoproteins in the pathogenesis of bone loss, including direct effects of these bioactive lipids/lipoproteins on bone cells, inhibiting osteoblastic differentiation and promoting osteoclastic differentiation. It also addresses recent evidence that suggests that bioactive lipids blunt the effects of bone anabolic agents such as teriparatide and bone morphogenetic proteins. Systemic and intracellular oxidant stress and inflammation are implicated in mediating the effects of bioactive lipids/lipoproteins.
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Affiliation(s)
- Yin Tintut
- Division of Cardiology, Department of Medicine, University of California, Los Angeles, CA 90095, USA.
| | - Linda L Demer
- Division of Cardiology, Department of Medicine, University of California, Los Angeles, CA 90095, USA; Department of Physiology, University of California, Los Angeles, CA 90095, USA; Department of Bioengineering, University of California, Los Angeles, CA 90095, USA
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15
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Dogaki Y, Lee SY, Niikura T, Koga T, Okumachi E, Nishida K, Kuroda R, Kurosaka M. Effects of parathyroid hormone 1-34 on osteogenic and chondrogenic differentiation of human fracture haematoma-derived cells in vitro. J Tissue Eng Regen Med 2013; 10:E365-E371. [PMID: 24039091 DOI: 10.1002/term.1818] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2013] [Revised: 05/31/2013] [Accepted: 07/26/2013] [Indexed: 11/10/2022]
Abstract
Parathyroid hormone (PTH) 1-34 has been shown to accelerate fracture healing. Previously, we reported that progenitor cells with osteogenic and chondrogenic potential exist in human fracture haematoma, suggesting that the fracture haematoma-derived progenitor cells (HCs) contribute to fracture healing. However, there has been no study investigating the effect of PTH on HCs. We investigated the effect of pulsatile and continuous PTH treatment on human fracture HCs in vitro. HCs were isolated from seven patients. The HCs were divided into four groups: growth medium; control [osteogenic medium (OM) without PTH]; PTH-C (OM with continuous PTH); and PTH-P (OM with pulsatile PTH) groups. Osteogenic differentiation potential and proliferation of HCs were compared among the four groups. For chondrogenesis, the HCs were divided into two groups: control [chondrogenic medium (CM) without PTH]; and PTH-C (CM with continuous PTH) groups, and chondrogenic differentiation potential was analysed. PTH treatment did not affect cell proliferation, regardless of the mode of administration. Osteogenic activity was also not significantly affected by continuous PTH treatment but significantly inhibited by pulsatile PTH treatment. Conversely, chondrogenic differentiation was significantly inhibited by continuous PTH treatment. Our results revealed that PTH treatment on HCs, either continuous or pulsatile, does not exhibit any positive effect, and indicates that exogenous PTH administration after fracture has no effect on HCs. PTH may not have a positive effect at the fracture site during the early stage of fracture healing in which haematoma formation occurs. Copyright © 2013 John Wiley & Sons, Ltd.
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Affiliation(s)
- Yoshihiro Dogaki
- Department of Orthopaedic Surgery, Kobe University Graduate School of Medicine, Kobe, Japan
| | - Sang Yang Lee
- Department of Orthopaedic Surgery, Kobe University Graduate School of Medicine, Kobe, Japan.
| | - Takahiro Niikura
- Department of Orthopaedic Surgery, Kobe University Graduate School of Medicine, Kobe, Japan
| | - Takaaki Koga
- Department of Orthopaedic Surgery, Kobe University Graduate School of Medicine, Kobe, Japan
| | - Etsuko Okumachi
- Department of Orthopaedic Surgery, Kobe University Graduate School of Medicine, Kobe, Japan
| | - Kotaro Nishida
- Department of Orthopaedic Surgery, Kobe University Graduate School of Medicine, Kobe, Japan
| | - Ryosuke Kuroda
- Department of Orthopaedic Surgery, Kobe University Graduate School of Medicine, Kobe, Japan
| | - Masahiro Kurosaka
- Department of Orthopaedic Surgery, Kobe University Graduate School of Medicine, Kobe, Japan
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16
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Sharma S, Mahalingam CD, Das V, Jamal S, Levi E, Rishi AK, Datta NS. Cell cycle and apoptosis regulatory protein (CARP)-1 is expressed in osteoblasts and regulated by PTH. Biochem Biophys Res Commun 2013; 436:607-12. [PMID: 23764399 DOI: 10.1016/j.bbrc.2013.05.136] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2013] [Accepted: 05/30/2013] [Indexed: 10/26/2022]
Abstract
Bone mass is dependent on osteoblast proliferation, differentiation and life-span of osteoblasts. Parathyroid hormone (PTH) controls osteoblast cell cycle regulatory proteins and suppresses mature osteoblasts apoptosis. Intermittent administration of PTH increases bone mass but the mechanism of action are complex and incompletely understood. Cell Cycle and Apoptosis Regulatory Protein (CARP)-1 (aka CCAR1) is a novel transducer of signaling by diverse agents including cell growth and differentiation factors. To gain further insight into the molecular mechanism, we investigated involvement of CARP-1 in PTH signaling in osteoblasts. Immunostaining studies revealed presence of CARP-1 in osteoblasts and osteocytes, while a minimal to absent levels were noted in the chondrocytes of femora from 10 to 12-week old mice. Treatment of 7-day differentiated MC3T3-E1 clone-4 (MC-4) mouse osteoblastic cells and primary calvarial osteoblasts with PTH for 30min to 5h followed by Western blot analysis showed 2- to 3-fold down-regulation of CARP-1 protein expression in a dose- and time-dependent manner compared to the respective vehicle treated control cells. H-89, a Protein Kinase A (PKA) inhibitor, suppressed PTH action on CARP-1 protein expression indicating PKA-dependent mechanism. PMA, a Protein Kinase C (PKC) agonist, mimicked PTH action, and the PKC inhibitor, GF109203X, partially blocked PTH-dependent downregulation of CARP-1, implying involvement of PKC. U0126, a Mitogen-Activated Protein Kinase (MAPK) Kinase (MEK) inhibitor, failed to interfere with CARP-1 suppression by PTH. In contrast, SB203580, p38 inhibitor, attenuated PTH down-regulation of CARP-1 suggesting that PTH utilized an Extracellular Signal Regulated Kinase (ERK)-independent but p38 dependent pathway to regulate CARP-1 protein expression in osteoblasts. Immunofluorescence staining of differentiated osteoblasts further revealed nuclear to cytoplasmic translocation of CARP-1 protein following PTH treatment. Collectively, our studies identified CARP-1 for the first time in osteoblasts and suggest its potential role in PTH signaling and bone anabolic action.
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Affiliation(s)
- Sonali Sharma
- Department of Internal Medicine/Endocrinology, Wayne State University School of Medicine, Detroit, MI 48201, USA
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17
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Bidwell JP, Childress P, Alvarez MB, Hood M, He Y, Pavalko FM, Kacena MA, Yang FC. Nmp4/CIZ closes the parathyroid hormone anabolic window. Crit Rev Eukaryot Gene Expr 2012; 22:205-18. [PMID: 23140162 DOI: 10.1615/critreveukargeneexpr.v22.i3.40] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Chronic degenerative diseases are increasing with the aging U.S. population. One consequence of this phenomenon is the need for long-term osteoporosis therapies. Parathyroid hormone (PTH), the only FDA-approved treatment that adds bone to the aged skeleton, loses its potency within two years of initial treatment but the mechanism regulating its limited "anabolic window" is unknown. We have discovered that disabling the nucleocytoplasmic shuttling transcription factor nuclear matrix protein 4/cas interacting zinc finger protein (Nmp4/CIZ) in mice extends the PTH bone-forming capacity. Nmp4 was discovered during our search for nuclear matrix transcription factors that couple this hormone's impact on osteoblast cytoskeletal and nuclear organization with its anabolic capacity. CIZ was independently discovered as a protein that associates with the focal adhesion-associated mechanosensor p130Cas. The Nmp4/CIZ-knockout (KO) skeletal phenotype exhibits a modestly enhanced bone mineral density but manifests an exaggerated response to both PTH and to BMP2 and is resistant to disuse-induced bone loss. The cellular basis of the global Nmp4/CIZ-KO skeletal phenotype remains to be elucidated but may involve an expansion of the bone marrow osteoprogenitor population along with modestly enhanced osteoblast and osteoclast activities supporting anabolic bone turnover. As a shuttling Cys(2)His(2) zinc finger protein, Nmp4/CIZ acts as a repressive transcription factor perhaps associated with epigenetic remodeling complexes, but the functional significance of its interaction with p130Cas is not known. Despite numerous remaining questions, Nmp4/CIZ provides insights into how the anabolic window is regulated, and itself may provide an adjuvant therapy target for the treatment of osteoporosis by extending PTH anabolic efficacy.
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Affiliation(s)
- Joseph P Bidwell
- Department of Anatomy and Cell Biology, Indiana University School of Medicine, Indianapolis, IN 46202, USA.
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18
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He Y, Childress P, Hood M, Alvarez M, Kacena MA, Hanlon M, McKee B, Bidwell JP, Yang FC. Nmp4/CIZ suppresses the parathyroid hormone anabolic window by restricting mesenchymal stem cell and osteoprogenitor frequency. Stem Cells Dev 2012; 22:492-500. [PMID: 22873745 DOI: 10.1089/scd.2012.0308] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Parathyroid hormone (PTH) anabolic osteoporosis therapy is intrinsically limited by unknown mechanisms. We previously showed that disabling the transcription factor Nmp4/CIZ in mice expanded this anabolic window while modestly elevating bone resorption. This enhanced bone formation requires a lag period to materialize. Wild-type (WT) and Nmp4-knockout (KO) mice exhibited equivalent PTH-induced increases in bone at 2 weeks of treatment, but by 7 weeks, the null mice showed more new bone. At 3-week treatment, serum osteocalcin, a bone formation marker, peaked in WT mice, but continued to increase in null mice. To determine if 3 weeks is the time when the addition of new bone diverges and to investigate its cellular basis, we treated 10-week-old null and WT animals with human PTH (1-34) (30 μg/kg/day) or vehicle before analyzing femoral trabecular architecture and bone marrow (BM) and peripheral blood phenotypic cell profiles. PTH-treated Nmp4-KO mice gained over 2-fold more femoral trabecular bone than WT by 3 weeks. There was no difference between genotypes in BM cellularity or profiles of several blood elements. However, the KO mice exhibited a significant elevation in CFU-F cells, CFU-F(Alk)(Phos+) cells (osteoprogenitors), and a higher percentage of CFU-F(Alk)(Phos+) cells/CFU-F cells consistent with an increase in CD45-/CD146+/CD105+/nestin+ mesenchymal stem cell frequency. Null BM exhibited a 2-fold enhancement in CD8+ T cells known to support osteoprogenitor differentiation and a 1.6-fold increase in CFU-GM colonies (osteoclast progenitors). We propose that Nmp4/CIZ limits the PTH anabolic window by restricting the number of BM stem, progenitor, and blood cells that support anabolic bone remodeling.
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Affiliation(s)
- Yongzheng He
- Department of Pediatrics, Indiana University School of Medicine, Indianapolis 46202, USA
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19
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Alvarez MB, Childress P, Philip BK, Gerard-O'Riley R, Hanlon M, Herbert BS, Robling AG, Pavalko FM, Bidwell JP. Immortalization and characterization of osteoblast cell lines generated from wild-type and Nmp4-null mouse bone marrow stromal cells using murine telomerase reverse transcriptase (mTERT). J Cell Physiol 2012; 227:1873-82. [PMID: 21732358 DOI: 10.1002/jcp.22915] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Intermittent parathyroid hormone (PTH) adds new bone to the osteoporotic skeleton; the transcription factor Nmp4/CIZ represses PTH-induced bone formation in mice and as a consequence is a potential drug target for improving hormone clinical efficacy. To explore the impact of Nmp4/CIZ on osteoblast phenotype, we immortalized bone marrow stromal cells from wildtype (WT) and Nmp4-knockout (KO) mice using murine telomerase reverse transcriptase. Clonal lines were initially chosen based on their positive staining for alkaline phosphatase and capacity for mineralization. Disabling Nmp4/CIZ had no gross impact on osteoblast phenotype development. WT and KO clones exhibited identical sustained growth, reduced population doubling times, extended maintenance of the mature osteoblast phenotype, and competency for differentiating toward the osteoblast and adipocyte lineages. Additional screening of the immortalized cells for PTH-responsiveness permitted further studies with single WT and KO clones. We recently demonstrated that PTH-induced c-fos femoral mRNA expression is enhanced in Nmp4-KO mice and in the present study we observed that hormone stimulated either an equivalent or modestly enhanced increase in c-fos mRNA expression in both primary null and KO clone cells depending on PTH concentration. The null primary osteoblasts and KO clone cells exhibited a transiently enhanced response to bone morphogenetic protein 2 (BMP2). The clones exhibited lower and higher expressions of the PTH receptor (Pthr1) and the BMP2 receptor (Bmpr1a, Alk3), respectively, as compared to primary cells. These immortalized cell lines will provide a valuable tool for disentangling the complex functional roles underlying Nmp4/CIZ regulation of bone anabolism.
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Affiliation(s)
- Marta B Alvarez
- Department of Anatomy & Cell Biology, Indiana University School of Medicine (IUSM), Indianapolis, IN 46202, USA
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20
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Silva BC, Costa AG, Cusano NE, Kousteni S, Bilezikian JP. Catabolic and anabolic actions of parathyroid hormone on the skeleton. J Endocrinol Invest 2011; 34:801-10. [PMID: 21946081 PMCID: PMC4315330 DOI: 10.3275/7925] [Citation(s) in RCA: 79] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
PTH, an 84-amino acid peptide hormone synthesized by the parathyroid glands, is essential for the maintenance of calcium homeostasis.While in its traditional metabolic role, PTH helps to maintain the serum calcium concentration within narrow, normal limits and participates as a determinant of bone remodeling, more specific actions, described as catabolic and anabolic are also well known. Clinically, the catabolic effect of PTH is best represented by primary hyperparathyroidism (PHPT), while the osteoanabolic effect of PTH is best seen when PTH or its biological amino-terminal fragment [PTH(1-34)] is used as a therapy for osteoporosis. These dual functions of PTH are unmasked under very specific pathological (PHPT) or therapeutic conditions. At the cellular level, PTH favors bone resorption, mostly by affecting the receptor activator of nuclear factor κ-B (RANK) ligand (RANKL)-osteoprotegerin- RANK system, leading to an increase in osteoclast formation and activity. Increased bone formation due to PTH therapy is explained best by its ability to enhance osteoblastogenesis and/or osteoblast survival. The PTH-induced bone formation is mediated, in part, by a decrease in SOST/sclerostin expression in osteocytes. This review focuses on the dual anabolic and catabolic actions of PTH on bone, situations where one is enhanced over the other, and the cellular and molecular mechanisms by which these actions are mediated.
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Affiliation(s)
- B C Silva
- Metabolic Bone Diseases Unit, Division of Endocrinology, Department of Medicine, College of Physicians and Surgeons, Columbia University, USA
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21
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Lossdörfer S, Abuduwali N, Jäger A. Bone Morphogenetic Protein-7 Modifies the Effects of Insulin-Like Growth Factors and Intermittent Parathyroid Hormone (1-34) on Human Periodontal Ligament Cell Physiology In Vitro. J Periodontol 2011; 82:900-8. [DOI: 10.1902/jop.2010.100572] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
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22
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Lossdörfer S, Götz W, Jäger A. PTH(1-34)-induced changes in RANKL and OPG expression by human PDL cells modify osteoclast biology in a co-culture model with RAW 264.7 cells. Clin Oral Investig 2010; 15:941-52. [PMID: 20697756 DOI: 10.1007/s00784-010-0456-0] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2009] [Accepted: 07/27/2010] [Indexed: 01/08/2023]
Abstract
Parathyroid hormone (PTH) is widely accepted as an anabolic agent when administered intermittently. Here, we explored the influence of intermittent PTH(1-34) on the expression of local factors by human periodontal ligament (PDL) cells that modify osteoclast biology. This approach aimed at a further elucidation of the role of the hormone and of PDL cells in the regulation of periodontal tissue homeostasis and of repair processes. In a co-culture model of mature PDL cells and RAW 264.7 cells, intermittent PTH(1-34) induced an increased gene expression for tartrate-resistant acid phosphatase (+84%), cathepsin K (+56%), and vitronectin-receptor (+56%); and an enhanced resorptive activity of differentiated osteoclasts (+154%). These findings were correlated with a reduction of the osteoprotegerin (OPG)/receptor activator of nuclear factor kappaB ligand (RANKL) ratio in the presence of PTH(1-34; -44%). Similar results were obtained when RAW cells were cultured with the conditioned medium of PTH(1-34)-stimulated PDL cells. In contrast, when less mature PDL cells were co-cultured with RAW cells, PTH(1-34) induced an inhibition of osteoclastic differentiation (TRAP, -35%; cathepsin K, -28%; vitronectin-receptor, -35%), a reduction of the resorbed substrate area (-77%) and an increase of the OPG/RANKL ratio (+11%). The conditioned medium of PTH(1-34)-pretreated less mature PDL cells led to a down-regulation of the number and activity of multinucleated cells. These data indicate that intermittent PTH(1-34) modifies the expression of membrane-bound and secreted factors by PDL cells which then in turn alter osteoclast biology. The PDL cell response to PTH(1-34) is specific in terms of cell maturation and the mechanism involved.
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Affiliation(s)
- Stefan Lossdörfer
- Department of Orthodontics, Dental Clinic, University of Bonn, Welschnonnenstr. 17, 53111 Bonn, Germany.
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23
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Balic A, Aguila HL, Caimano MJ, Francone VP, Mina M. Characterization of stem and progenitor cells in the dental pulp of erupted and unerupted murine molars. Bone 2010; 46:1639-51. [PMID: 20193787 PMCID: PMC2881695 DOI: 10.1016/j.bone.2010.02.019] [Citation(s) in RCA: 76] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/02/2009] [Revised: 02/12/2010] [Accepted: 02/18/2010] [Indexed: 12/15/2022]
Abstract
In the past few years there have been significant advances in the identification of putative stem cells also referred to as "mesenchymal stem cells" (MSC) in dental tissues including the dental pulp. It is thought that MSC in dental pulp share certain similarities with MSC isolated from other tissues. However, cells in dental pulp are still poorly characterized. This study focused on the characterization of progenitor and stem cells in dental pulps of erupted and unerupted mice molars. Our study showed that dental pulps from unerupted molars contain a significant number of cells expressing CD90+/CD45-, CD117+/CD45-, Sca-1+/CD45- and little if any CD45+ cells. Our in vitro functional studies showed that dental pulp cells from unerupted molars displayed extensive osteo-dentinogenic potential but were unable to differentiate into chondrocytes and adipocytes. Dental pulps from erupted molars displayed a reduced number of cells, contained a higher percentage of CD45+ and a lower percentage of cells expressing CD90+/CD45-, CD117+/CD45- as compared to unerupted molars. In vitro functional assays demonstrated the ability of a small fraction of cells to differentiate into odontoblasts, osteoblasts, adipocytes and chondrocytes. There was a significant reduction in the osteo-dentinogenic potential of the pulp cells derived from erupted molars compared to unerupted molars. Furthermore, the adipogenic and chondrogenic differentiation of pulp cells from erupted molars was dependent on a long induction period and were infrequent. Based on these findings we propose that the dental pulp of the erupted molars contain a small population of multipotent cells, whereas the dental pulp of the unerupted molars does not contain multipotent cells but is enriched in osteo-dentinogenic progenitors engaged in the formation of coronal and radicular odontoblasts.
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Affiliation(s)
- Anamaria Balic
- Department of Craniofacial Sciences, School of Dental Medicine, University of Connecticut Health Center, Farmington, CT
| | - H. Leonardo Aguila
- Department of Immunology, School of Medicine, University of Connecticut Health Center, Farmington, CT
| | - Melissa J. Caimano
- Department of Medicine, School of Medicine, University of Connecticut Health Center, Farmington, CT
| | - Victor P. Francone
- Department of Neuroscience, School of Medicine, University of Connecticut Health Center, Farmington, CT
| | - Mina Mina
- Department of Craniofacial Sciences, School of Dental Medicine, University of Connecticut Health Center, Farmington, CT
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24
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Abstract
The striking clinical benefit of PTH in osteoporosis began a new era of skeletal anabolic agents. Several studies have been performed, new studies are emerging out and yet controversies remain on PTH anabolic action in bone. This review focuses on the molecular aspects of PTH and PTHrP signaling in light of old players and recent advances in understanding the control of osteoblast proliferation, differentiation and function.
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Affiliation(s)
- Nabanita S Datta
- Division Endocrinology, Department Internal Medicine, Wayne State University School of Medicine, 421 East Canfield Avenue, Detroit, Michigan 48201, USA.
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25
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Yoshida T, Clark MF, Stern PH. The small GTPase RhoA is crucial for MC3T3-E1 osteoblastic cell survival. J Cell Biochem 2009; 106:896-902. [PMID: 19184980 DOI: 10.1002/jcb.22059] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Prolongation of cell survival through prevention of apoptosis is considered to be a significant factor leading to anabolic responses in bone. The current studies were carried out to determine the role of the small GTPase, RhoA, in osteoblast apoptosis, since RhoA has been found to be critical for cell survival in other tissues. We investigated the effects of inhibitors and activators of RhoA signaling on osteoblast apoptosis. In addition, we assessed the relationship of this pathway to parathyroid hormone (PTH) effects on apoptotic signaling and cell survival. RhoA is activated by geranylgeranylation, which promotes its membrane anchoring. In serum-starved MC3T3-E1 osteoblastic cells, inhibition of geranylgeranylation with geranylgeranyl transferase I inhibitors increased activity of caspase-3, a component step in the apoptosis cascade, and increased cell death. Dominant negative RhoA and Y27632, an inhibitor of the RhoA effector Rho kinase, also increased caspase-3 activity. A geranylgeranyl group donor, geranylgeraniol, antagonized the effect of the geranylgeranyl transferase I inhibitor GGTI-2166, but could not overcome the effect of the Rho kinase inhibitor. PTH 1-34, a potent anti-apoptotic agent, completely antagonized the stimulatory effects of GGTI-2166, dominant negative RhoA, and Y27632, on caspase-3 activity. The results suggest that RhoA signaling is essential for osteoblastic cell survival but that the survival effects of PTH 1-34 are independent of this pathway.
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Affiliation(s)
- Tomohiko Yoshida
- Department of Molecular Pharmacology and Biological Chemistry, Northwestern University Feinberg School of Medicine, Chicago, Illinois 60611, USA
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26
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Gautschi OP, Cadosch D, Frey SP, Skirving AP, Filgueira L, Zellweger R. Serum-mediated osteogenic effect in traumatic brain-injured patients. ANZ J Surg 2009; 79:449-55. [DOI: 10.1111/j.1445-2197.2008.04803.x] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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27
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Yang C, Frei H, Burt HM, Rossi F. Effects of continuous and pulsatile PTH treatments on rat bone marrow stromal cells. Biochem Biophys Res Commun 2009; 380:791-6. [DOI: 10.1016/j.bbrc.2009.01.167] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2009] [Accepted: 01/26/2009] [Indexed: 12/01/2022]
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28
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Ogita M, Rached MT, Dworakowski E, Bilezikian JP, Kousteni S. Differentiation and proliferation of periosteal osteoblast progenitors are differentially regulated by estrogens and intermittent parathyroid hormone administration. Endocrinology 2008; 149:5713-23. [PMID: 18617606 PMCID: PMC2584601 DOI: 10.1210/en.2008-0369] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The periosteum is now widely recognized as a homeostatic and therapeutic target for actions of sex steroids and intermittent PTH administration. The mechanisms by which estrogens suppress but PTH promotes periosteal expansion are not known. In this report, we show that intermittent PTH(1-34) promotes differentiation of periosteal osteoblast precursors as evidenced by the stimulation of the expression or activity of alkaline phosphatase as well as of targets of the bone morphogenetic protein 2 (BMP-2) and Wnt pathways. In contrast, 17beta-estradiol (E2) had no effect by itself. However, it attenuated PTH- or BMP-2-induced differentiation of primary periosteal osteoblast progenitors. Administration of intermittent PTH to ovariectomized mice induced rapid phosphorylation of the BMP-2 target Smad1/5/8 in the periosteum. A replacement dose of E2 had no effect by itself but suppressed PTH-induced phosphorylation of Smad1/5/8. In contrast to its effects to stimulate periosteal osteoblast differentiation, PTH promoted and subsequently suppressed proliferation of periosteal osteoblast progenitors in vitro and in vivo. E2 promoted proliferation and attenuated the antiproliferative effect of PTH. Both hormones protected periosteal osteoblasts from apoptosis induced by various proapoptotic agents. These observations suggest that the different effects of PTH and estrogens on the periosteum result from opposing actions on the recruitment of early periosteal osteoblast progenitors. Intermittent PTH promotes osteoblast differentiation from periosteum-derived mesenchymal progenitors through ERK-, BMP-, and Wnt-dependent signaling pathways. Estrogens promote proliferation of early osteoblast progenitors but inhibit their differentiation by osteogenic agents such as PTH or BMP-2.
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Affiliation(s)
- Mami Ogita
- Department of Medicine, Columbia University, New York, New York 10032, USA
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29
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Abstract
Continuous exposure to parathyroid hormone (PTH) is associated with catabolic effects, whereas intermittent exposure to low doses of PTH is associated with anabolic effects. By controlling osteoblast function, PTH increases bone formation on cancellous, endocortical, and periosteal bone surfaces. In general, PTH does not affect the replication of uncommitted osteoblast progenitors but suppresses proliferation of committed osteoprogenitors. Intermittent PTH promotes osteoblast differentiation, in part, by its ability to promote exit from the cell cycle, to activate Wnt signaling in osteoblasts, and to inhibit the Wnt antagonist sclerostin in osteocytes. Insulin-like growth factor-1 is also required for the actions of PTH to increase osteoblast numbers. Intermittent PTH prolongs osteoblast survival in rodents by mechanisms that involve activation and proteolytic degradation of Runx2. PTH's ability to orchestrate a dynamic range of signaling cascades that determine osteoblast fate may explain both its catabolic and beneficial actions on the skeleton.
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Affiliation(s)
- Stavroula Kousteni
- Department of Medicine, College of Physicians and Surgeons, Columbia University, 630 West 168th Street, New York, NY 10032, USA
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30
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Abstract
Studies during the last decade demonstrated that apoptosis is as important as mitosis for the growth and maintenance of the skeleton and provided information on the significance and molecular regulation of apoptosis of bone cells. It is now known that: (1) all osteoclasts die by apoptosis after completing a bone resorption cycle; (2) the majority of osteoblasts also die, whereas the remainder become lining cells or osteocytes; and (3) osteocytes, although long-living cells, also can die prematurely. Furthermore, mounting evidence indicates that systemic hormones, local growth factors, cytokines, and pharmacological agents, as well as mechanical forces regulate the rate of bone cell apoptosis. This chapter summarizes the methods developed in the last few years to examine apoptosis of cultured bone cells and identify the signaling pathways and molecules involved in apoptosis regulation by diverse skeletal stimuli.
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Affiliation(s)
- Teresita Bellido
- Division of Endocrinology & Metabolism and Center for Osteoporosis and Metabolic Bone Diseases, University of Arkansas for Medical Sciences, Little Rock, AR, USA
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31
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Duque G. As a matter of fat: New perspectives on the understanding of age-related bone loss. ACTA ACUST UNITED AC 2007. [DOI: 10.1138/20070257] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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32
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Yang J, Shah R, Robling AG, Templeton E, Yang H, Tracey KJ, Bidwell JP. HMGB1 is a bone-active cytokine. J Cell Physiol 2007; 214:730-9. [PMID: 17786958 DOI: 10.1002/jcp.21268] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
High mobility group box 1 (HMGB1) is a chromatin protein that acts as an immunomodulatory cytokine upon active release from myeloid cells. HMGB1 is also an alarmin, an endogenous molecule released by dying cells that acts to initiate tissue repair. We have previously reported that osteoclasts and osteoblasts release HMGB1 and release by the latter is regulated by parathyroid hormone (PTH), an agent of bone remodeling. A recent study suggests that HMGB1 acts as a chemotactic agent to osteoclasts and osteoblasts during endochondral ossification. To explore the potential impact of HMGB1 in the bone microenvironment and its mechanism of release by osseous cells, we characterized the effects of recombinant protein (rHMGB1) on multiple murine bone cell preparations that together exhibit the various cell phenotypes present in bone. We also inquired whether apoptotic bone cells release HMGB1. rHMGB1 enhanced the RANKL/OPG steady state mRNA ratio and dramatically augmented the release of tumor necrosis factor-alpha (TNFalpha) and interleukin-6 (IL6) in osteoblastogenic bone marrow stromal cell (BMSC) cultures but not in the calvarial-derived MC3T3-E1 cells. Interestingly, rHMGB1 promoted GSK-3beta phosphorylation in MC3T3-E1 cells but not in BMSCs. Apoptotic bone cells released HMGB1, including MLO-Y4 osteocyte-like cells. MLO-Y4 release of HMGB1 was coincident with caspase-3 cleavage. Furthermore, the anti-apoptotic action of PTH on MC3T3-E1 cells correlated with the observed decrease in HMGB1 release. Our data suggest that apoptotic bone cells release HMGB1, that within the marrow HMGB1 is a bone resorption signal, and that intramembraneous and endochondral osteoblasts exhibit differential responses to this cytokine.
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Affiliation(s)
- Jieping Yang
- Department of Anatomy & Cell Biology, Indiana University School of Medicine, Indianapolis, Indiana 46202, USA
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