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Zhou YH, Zhu JY, Guo Y, Tang HN, Wang F, Iqbal J, Wu HX, Hu N, Xiao F, Wang T, Li L, Zhou HD. Notch1 is a marker for in situ resting osteocytes in a 3-dimensional gel culture model. Connect Tissue Res 2023; 64:491-504. [PMID: 37227119 DOI: 10.1080/03008207.2023.2217271] [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: 12/06/2022] [Accepted: 05/16/2023] [Indexed: 05/26/2023]
Abstract
PURPOSE Osteocytes in vivo exhibit different functional states, but no specific marker to distinguish these is currently available. MATERIALS AND METHODS To simulate the differentiation process of pre-osteoblasts to osteocytes in vitro, MC3T3-E1 cells were cultured on type I collagen gel and a three-dimensional (3D) culture system was established. The Notch expression of osteocyte-like cells in 3D culture system was compared with that of in situ osteocytes in bone tissues. RESULTS Immunohistochemistry demonstrated that Notch1 was not detected in "resting" in situ osteocytes, but was detected in normal cultured osteocyte-like cell line MLO-Y4. Osteocytes obtained from conventional osteogenic-induced osteoblasts and long-term cultured MLO-Y4 cells could not replicate the Notch1 expression pattern from in situ osteocytes. From day 14-35 of osteogenic induction, osteoblasts in 3D culture system gradually migrated into the gel to form canaliculus-like structures similar to bone canaliculus. On day 35, stellate-shaped osteocyte-like cells were observed, and expression of DMP1 and SOST, but not Runx2, was detected. Notch1 was not detected by immunohistochemistry, and Notch1 mRNA level was not significantly different from that of in situ osteocytes. In MC3T3-E1 cells, down-regulation of Notch2 increased Notch1, Notch downstream genes (β-catenin and Nfatc1), and Dmp1. In MLO-Y4 cells, Notch2 decreased after Notch1 siRNA transfection. Downregulation of Notch1 or Notch2 decreased Nfatc1, β-catenin, and Dmp1, and increased Sost. CONCLUSIONS We established "resting state" osteocytes using an in vitro 3D model. Notch1 can be a useful marker to help differentiate the functional states of osteocytes (activated vs. resting state).
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Affiliation(s)
- Ying-Hui Zhou
- National Clinical Research Center for Metabolic Diseases, Hunan Provincial Key Laboratory for Metabolic Bone Diseases, Department of Metabolism and Endocrinology, The Second Xiangya Hospital of Central South University, Changsha, Hunan, China
- Department of Stomatology, the Second Xiangya Hospital of Central South University, Changsha, Hunan, China
| | - Jia-Yu Zhu
- National Clinical Research Center for Metabolic Diseases, Hunan Provincial Key Laboratory for Metabolic Bone Diseases, Department of Metabolism and Endocrinology, The Second Xiangya Hospital of Central South University, Changsha, Hunan, China
- Department of Pathology, School of Basic Medical Sciences, Xinjiang Medical University, Urumqi, Xinjiang, China
| | - Yue Guo
- National Clinical Research Center for Metabolic Diseases, Hunan Provincial Key Laboratory for Metabolic Bone Diseases, Department of Metabolism and Endocrinology, The Second Xiangya Hospital of Central South University, Changsha, Hunan, China
- Department of Stomatology, the Second Xiangya Hospital of Central South University, Changsha, Hunan, China
| | - Hao-Neng Tang
- Department of Laboratory Medicine, The Second Xiangya Hospital of Central South University, Changsha, Hunan, China
| | - Fang Wang
- Departments of Endocrinology and Metabolism, Heping Hospital Affiliated to Changzhi Medical College, Changzhi, Shanxi, China
| | - Junaid Iqbal
- National Clinical Research Center for Metabolic Diseases, Hunan Provincial Key Laboratory for Metabolic Bone Diseases, Department of Metabolism and Endocrinology, The Second Xiangya Hospital of Central South University, Changsha, Hunan, China
| | - Hui-Xuan Wu
- National Clinical Research Center for Metabolic Diseases, Hunan Provincial Key Laboratory for Metabolic Bone Diseases, Department of Metabolism and Endocrinology, The Second Xiangya Hospital of Central South University, Changsha, Hunan, China
| | - Nan Hu
- National Clinical Research Center for Metabolic Diseases, Hunan Provincial Key Laboratory for Metabolic Bone Diseases, Department of Metabolism and Endocrinology, The Second Xiangya Hospital of Central South University, Changsha, Hunan, China
| | - Fen Xiao
- National Clinical Research Center for Metabolic Diseases, Hunan Provincial Key Laboratory for Metabolic Bone Diseases, Department of Metabolism and Endocrinology, The Second Xiangya Hospital of Central South University, Changsha, Hunan, China
| | - Ting Wang
- National Clinical Research Center for Metabolic Diseases, Hunan Provincial Key Laboratory for Metabolic Bone Diseases, Department of Metabolism and Endocrinology, The Second Xiangya Hospital of Central South University, Changsha, Hunan, China
| | - Long Li
- National Clinical Research Center for Metabolic Diseases, Hunan Provincial Key Laboratory for Metabolic Bone Diseases, Department of Metabolism and Endocrinology, The Second Xiangya Hospital of Central South University, Changsha, Hunan, China
| | - Hou-De Zhou
- National Clinical Research Center for Metabolic Diseases, Hunan Provincial Key Laboratory for Metabolic Bone Diseases, Department of Metabolism and Endocrinology, The Second Xiangya Hospital of Central South University, Changsha, Hunan, China
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Abstract
Although osteoblasts and osteocytes are descended from the same lineage, they each have unique and essential roles in bone. Targeting gene deletion to osteoblasts and osteocytes using the Cre/loxP system has greatly increased our current understanding of how these cells function. Additionally, the use of the Cre/loxP system in conjunction with cell-specific reporters has enabled lineage tracing of these bone cells both in vivo and ex vivo. However, concerns have been raised regarding the specificity of the promoters used and the resulting off-target effects on cells within and outside of the bone. In this review, we have summarized the main mouse models that have been used to determine the functions of specific genes in osteoblasts and osteocytes. We discuss the expression patterns and specificity of the different promoter fragments during osteoblast to osteocyte differentiation in vivo. We also highlight how their expression in non-skeletal tissues may complicate the interpretation of study results. A thorough understanding of when and where these promoters are activated will enable improved study design and greater confidence in data interpretation.
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Affiliation(s)
- Y Kitase
- Indiana Center for Musculoskeletal Health, Department of Anatomy, Cell Biology and Physiology, School of Medicine, Indiana University, Indianapolis, IN 46202, United States of America
| | - M Prideaux
- Indiana Center for Musculoskeletal Health, Department of Anatomy, Cell Biology and Physiology, School of Medicine, Indiana University, Indianapolis, IN 46202, United States of America.
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Shao J, Zhou Y, Xiao Y. The regulatory roles of Notch in osteocyte differentiation via the crosstalk with canonical Wnt pathways during the transition of osteoblasts to osteocytes. Bone 2018; 108:165-178. [PMID: 29331299 DOI: 10.1016/j.bone.2018.01.010] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/11/2017] [Revised: 01/05/2018] [Accepted: 01/09/2018] [Indexed: 12/17/2022]
Abstract
Osteocytes comprise more than 90% of the cells in bone and are differentiated from osteoblasts via an unknown mechanism. Recently, it was shown that Notch signaling plays an important role in osteocyte functions. To gain insights into the mechanisms underlying the functions of Notch in regulating the transition of osteoblasts to osteocytes, we performed a luciferase assay by cloning the proximal E11 and dentin matrix acidic phosphoprotein 1 (DMP1) promotor regions into pGluc-Basic 2 vectors, which were subsequently transfected into the IDG-SW3 (osteocytes), MC3T3 (osteoblasts) and 293T (non-osteoblastic cells) cell lines. Two approaches were used to activate Notch signaling in vitro. One was a Notch1 extracellular antibody-coated cell culture plate, and the other was transfection of a Hairy/Enhancer of Split 1 (Hes1) overexpression vector. The interaction between the Notch and Wnt signaling pathways was probed by assessing the expression of a series of phosphorylated proteins involved in the cascade of both signaling pathways. Our data suggested that Notch signaling regulates E11 expression through Hes1 activity, while Hes1 solely did not initiate the expression of DMP1. The regulatory function of E11 by Hes1 was not observed in the 293T cell line, indicating a cell context-dependent manner of the Notch signaling pathway. Additionally, we found that Notch inhibited Wnt signaling at the late differentiation stage of osteocytes by both directly repressing phosphorylated Akt and preventing the nuclear aggregation of β-catenin. These findings provide profound understandings of Notch's regulatory function in osteocyte differentiation.
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Affiliation(s)
- Jin Shao
- Institute of Health and Biomedical Innovation, Queensland University of Technology, Brisbane, QLD 4059, Australia; The Australia-China Centre for Tissue Engineering and Regenerative Medicine (ACCTERM), Queensland University of Technology, Brisbane, QLD 4059, Australia
| | - Yinghong Zhou
- Institute of Health and Biomedical Innovation, Queensland University of Technology, Brisbane, QLD 4059, Australia; The Australia-China Centre for Tissue Engineering and Regenerative Medicine (ACCTERM), Queensland University of Technology, Brisbane, QLD 4059, Australia
| | - Yin Xiao
- Institute of Health and Biomedical Innovation, Queensland University of Technology, Brisbane, QLD 4059, Australia; The Australia-China Centre for Tissue Engineering and Regenerative Medicine (ACCTERM), Queensland University of Technology, Brisbane, QLD 4059, Australia.
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Zanotti S, Canalis E. Parathyroid hormone inhibits Notch signaling in osteoblasts and osteocytes. Bone 2017; 103:159-167. [PMID: 28676438 PMCID: PMC5568480 DOI: 10.1016/j.bone.2017.06.027] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/30/2017] [Revised: 06/28/2017] [Accepted: 06/30/2017] [Indexed: 10/19/2022]
Abstract
Parathyroid hormone (PTH) and Notch receptors regulate bone formation by governing the function of osteoblastic cells. To determine whether PTH interacts with Notch signaling as a way to control osteoblast function, we tested the effects of PTH on Notch activity in osteoblast- and osteocyte-enriched cultures. Notch signaling was activated in osteoblast-enriched cells from wild-type C57BL/6J mice following exposure to the Notch ligand Delta-like (Dll)1 or by the transient transfection of the Notch intracellular domain (NICD), the transcriptionally active fragment of Notch1. To induce Notch signaling in osteocyte-enriched cultures, a murine model of Notch2 gain-of-function was used. PTH opposed the stimulatory effects of Dll1 on Hey1, Hey2 and HeyL mRNA levels in osteoblast-enriched cells and suppressed the expression of selected Notch target genes in osteocyte-enriched cultures, either under basal conditions or in the context of Notch2 gain-of-function. Induction of Notch signaling in osteocytes did not alter the inhibitory effect of PTH on Sost expression, but reduced the stimulation of Tnfsf11 mRNA levels by PTH. In agreement with these in vitro observations, male mice administered with PTH displayed suppressed Hey1 and HeyL expression in parietal bones. Transactivation experiments with a Notch reporter construct and electrophoretic mobility shift assays in osteoblast-enriched cells suggest that PTH acts by decreasing the capacity of Rbpjκ to bind to DNA. In conclusion, downregulation of Notch in osteoblasts and osteocytes may represent a mechanism contributing to the anabolic effects of PTH in bone.
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Affiliation(s)
- Stefano Zanotti
- Departments of Orthopaedic Surgery and Medicine, UConn Musculoskeletal Institute, UConn Health, Farmington, CT 06030-5456, USA.
| | - Ernesto Canalis
- Departments of Orthopaedic Surgery and Medicine, UConn Musculoskeletal Institute, UConn Health, Farmington, CT 06030-5456, USA
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