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Yorgan T, David JP, Amling M, Schinke T. The high bone mass phenotype of Lrp5-mutant mice is not affected by megakaryocyte depletion. Biochem Biophys Res Commun 2018; 497:659-666. [PMID: 29454962 DOI: 10.1016/j.bbrc.2018.02.127] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2018] [Accepted: 02/14/2018] [Indexed: 11/18/2022]
Abstract
Bone remodeling is a continuously ongoing process mediated by bone-resorbing osteoclasts and bone-forming osteoblasts. One key regulator of bone formation is the putative Wnt co-receptor Lrp5, where activating mutations in the extracellular domain cause increased bone formation in mice and humans. We have previously reported that megakaryocyte numbers are increased the bone marrow of mice carrying a high bone mass mutation (HBM) of Lrp5 (Lrp5G170V). Since megakaryocytes can promote bone formation, we addressed the question, if the bone remodeling phenotype of Lrp5G170V mice is affected by megakaryocyte depletion. For that purpose we took advantage of a mouse model carrying a mutation of the Mpl gene, encoding the thrombopoietin receptor. These mice (Mplhlb219) were crossed with Lrp5G170V mice to generate animals carrying both mutations in a homozygous state. Using μCT, undecalcified histology and bone-specific histomorphometry of 12 weeks old littermates we observed that megakaryocyte number was remarkably decreased in Mplhlb219/Lrp5G170V mice, yet the high bone mass phenotype of Lrp5G170V mice was not significantly affected by the homozygous Mpl mutation. Finally, when we analyzed 24 weeks old wildtype and Mplhlb219 mice we did not observe a statistically significant alteration of bone remodeling in the latter ones. Taken together, our results demonstrate that an increased number of bone marrow megakaryocytes does not contribute to the increased bone formation caused by Lrp5 activation.
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Affiliation(s)
- Timur Yorgan
- Department of Osteology and Biomechanics, University Medical Center Hamburg Eppendorf, Hamburg 20246, Germany
| | - Jean-Pierre David
- Department of Osteology and Biomechanics, University Medical Center Hamburg Eppendorf, Hamburg 20246, Germany
| | - Michael Amling
- Department of Osteology and Biomechanics, University Medical Center Hamburg Eppendorf, Hamburg 20246, Germany
| | - Thorsten Schinke
- Department of Osteology and Biomechanics, University Medical Center Hamburg Eppendorf, Hamburg 20246, Germany.
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Meijome TE, Ekwealor JTB, Hooker RA, Cheng YH, Ciovacco WA, Balamohan SM, Srinivasan TL, Chitteti BR, Eleniste PP, Horowitz MC, Srour EF, Bruzzaniti A, Fuchs RK, Kacena MA. C-Mpl Is Expressed on Osteoblasts and Osteoclasts and Is Important in Regulating Skeletal Homeostasis. J Cell Biochem 2015; 117:959-69. [PMID: 26375403 DOI: 10.1002/jcb.25380] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2015] [Accepted: 09/14/2015] [Indexed: 11/10/2022]
Abstract
C-Mpl is the receptor for thrombopoietin (TPO), the main megakaryocyte (MK) growth factor, and c-Mpl is believed to be expressed on cells of the hematopoietic lineage. As MKs have been shown to enhance bone formation, it may be expected that mice in which c-Mpl was globally knocked out (c-Mpl(-/-) mice) would have decreased bone mass because they have fewer MKs. Instead, c-Mpl(-/-) mice have a higher bone mass than WT controls. Using c-Mpl(-/-) mice we investigated the basis for this discrepancy and discovered that c-Mpl is expressed on both osteoblasts (OBs) and osteoclasts (OCs), an unexpected finding that prompted us to examine further how c-Mpl regulates bone. Static and dynamic bone histomorphometry parameters suggest that c-Mpl deficiency results in a net gain in bone volume with increases in OBs and OCs. In vitro, a higher percentage of c-Mpl(-/-) OBs were in active phases of the cell cycle, leading to an increased number of OBs. No difference in OB differentiation was observed in vitro as examined by real-time PCR and functional assays. In co-culture systems, which allow for the interaction between OBs and OC progenitors, c-Mpl(-/-) OBs enhanced osteoclastogenesis. Two of the major signaling pathways by which OBs regulate osteoclastogenesis, MCSF/OPG/RANKL and EphrinB2-EphB2/B4, were unaffected in c-Mpl(-/-) OBs. These data provide new findings for the role of MKs and c-Mpl expression in bone and may provide insight into the homeostatic regulation of bone mass as well as bone loss diseases such as osteoporosis.
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Affiliation(s)
- Tomas E Meijome
- Department of Orthopaedic Surgery, Indiana University School of Medicine, Indiana, Indianapolis
| | - Jenna T B Ekwealor
- Department of Orthopaedic Surgery, Indiana University School of Medicine, Indiana, Indianapolis
| | - R Adam Hooker
- Department of Orthopaedic Surgery, Indiana University School of Medicine, Indiana, Indianapolis
| | - Ying-Hua Cheng
- Department of Orthopaedic Surgery, Indiana University School of Medicine, Indiana, Indianapolis
| | - Wendy A Ciovacco
- Department of Orthopaedic Surgery, Indiana University School of Medicine, Indiana, Indianapolis.,Department of Orthopaedics and Rehabilitation, Yale University School of Medicine, New Haven, Connecticut
| | - Sanjeev M Balamohan
- Department of Orthopaedic Surgery, Indiana University School of Medicine, Indiana, Indianapolis
| | - Trishya L Srinivasan
- Department of Orthopaedic Surgery, Indiana University School of Medicine, Indiana, Indianapolis
| | | | - Pierre P Eleniste
- Department of Oral Biology, Indiana University School of Dentistry, Indiana, Indianapolis
| | - Mark C Horowitz
- Department of Orthopaedics and Rehabilitation, Yale University School of Medicine, New Haven, Connecticut
| | - Edward F Srour
- Department of Medicine, Indiana University School of Medicine, Indiana, Indianapolis
| | - Angela Bruzzaniti
- Department of Oral Biology, Indiana University School of Dentistry, Indiana, Indianapolis
| | - Robyn K Fuchs
- Department of Physical Therapy, Indiana University School of Health and Rehabilitation Sciences, Indiana, Indianapolis
| | - Melissa A Kacena
- Department of Orthopaedic Surgery, Indiana University School of Medicine, Indiana, Indianapolis.,Department of Orthopaedics and Rehabilitation, Yale University School of Medicine, New Haven, Connecticut
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Bethel M, Barnes CLT, Taylor AF, Cheng YH, Chitteti BR, Horowitz MC, Bruzzaniti A, Srour EF, Kacena MA. A novel role for thrombopoietin in regulating osteoclast development in humans and mice. J Cell Physiol 2015; 230:2142-51. [PMID: 25656774 DOI: 10.1002/jcp.24943] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2015] [Accepted: 01/23/2015] [Indexed: 11/10/2022]
Abstract
Emerging data suggest that megakaryocytes (MKs) play a significant role in skeletal homeostasis. Indeed, osteosclerosis observed in several MK-related disorders may be a result of increased numbers of MKs. In support of this idea, we have previously demonstrated that MKs increase osteoblast (OB) proliferation by a direct cell-cell contact mechanism and that MKs also inhibit osteoclast (OC) formation. As MKs and OCs are derived from the same hematopoietic precursor, in these osteoclastogenesis studies we examined the role of the main MK growth factor, thrombopoietin (TPO) on OC formation and bone resorption. Here we show that TPO directly increases OC formation and differentiation in vitro. Specifically, we demonstrate the TPO receptor (c-mpl or CD110) is expressed on cells of the OC lineage, c-mpl is required for TPO to enhance OC formation in vitro, and TPO activates the mitogen-activated protein kinases, Janus kinase/signal transducer and activator of transcription, and nuclear factor-kappaB signaling pathways, but does not activate the PI3K/AKT pathway. Further, we found TPO enhances OC resorption in CD14+CD110+ human OC progenitors derived from peripheral blood mononuclear cells, and further separating OC progenitors based on CD110 expression enriches for mature OC development. The regulation of OCs by TPO highlights a novel therapeutic target for bone loss diseases and may be important to consider in the numerous hematologic disorders associated with alterations in TPO/c-mpl signaling as well as in patients suffering from bone disorders.
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Affiliation(s)
- Monique Bethel
- Department of Orthopaedic Surgery, Indiana University School of Medicine, Indianapolis, Indiana
| | - Calvin L T Barnes
- Department of Orthopaedics and Rehabilitation, Yale University School of Medicine, New Haven, Connecticut
| | - Amanda F Taylor
- Department of Orthopaedic Surgery, Indiana University School of Medicine, Indianapolis, Indiana
| | - Ying-Hua Cheng
- Department of Orthopaedic Surgery, Indiana University School of Medicine, Indianapolis, Indiana
| | | | - Mark C Horowitz
- Department of Orthopaedics and Rehabilitation, Yale University School of Medicine, New Haven, Connecticut
| | - Angela Bruzzaniti
- Department of Oral Biology, Indiana University School of Dentistry, Indianapolis, Indiana.,Department of Anatomy and Cell Biology, Indiana University School of Medicine, Indianapolis, Indiana
| | - Edward F Srour
- Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana.,Department of Pediatrics, Indiana University School of Medicine, Indianapolis, Indiana.,Department of Microbiology and Immunology, Indiana University School of Medicine, Indianapolis, Indiana
| | - Melissa A Kacena
- Department of Orthopaedic Surgery, Indiana University School of Medicine, Indianapolis, Indiana.,Department of Orthopaedics and Rehabilitation, Yale University School of Medicine, New Haven, Connecticut.,Department of Anatomy and Cell Biology, Indiana University School of Medicine, Indianapolis, Indiana
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