title: Gdf5 progenitors give rise to fibrocartilage cells that mineralize via hedgehog signaling to form the zonal enthesis.
abstract: The sequence of events that leads to the formation of a functionally graded enthesis is not clearly defined. The current study demonstrates that clonal expansion of Gdf5 progenitors contributes to linear growth of the enthesis. Prior to mineralization, Col1+ cells in the enthesis appose Col2+ cells of the underlying primary cartilage. At the onset of enthesis mineralization, cells at the base of the enthesis express alkaline phosphatase, Indian hedgehog, and ColX as they mineralize. The mineralization front then extends towards the tendon midsubstance as cells above the front become encapsulated in mineralized fibrocartilage over time. The hedgehog (Hh) pathway regulates this process, as Hh-responsive Gli1+ cells within the developing enthesis mature from unmineralized to mineralized fibrochondrocytes in response to activated signaling. Hh signaling is required for mineralization, as tissue-specific deletion of its obligate transducer Smoothened in the developing tendon and enthesis cells leads to significant reductions in the apposition of mineralized fibrocartilage. Together, these findings provide a spatiotemporal map of events - from expansion of the embryonic progenitor pool to synthesis of the collagen template and finally mineralization of this template - that leads to the formation of the mature zonal enthesis. These results can inform future tendon-to-bone repair strategies to create a mechanically functional enthesis in which tendon collagen fibers are anchored to bone through mineralized fibrocartilage.
authors.affiliation: Center for Regenerative Medicine and Skeletal Development, School of Dental Medicine, University of Connecticut Health Center, United States. Electronic address: dyment@uchc.edu.
authors.forename: Nathaniel A
authors.initials: NA
authors.lastname: Dyment
authors.affiliation: Biomedical Engineering Program, College of Engineering and Applied Science, University of Cincinnati, United States.
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Breidenbach
authors.affiliation: Department of Orthopaedic Surgery, Washington University in St. Louis, United States.
authors.forename: Andrea G
authors.initials: AG
authors.lastname: Schwartz
authors.affiliation: Center for Regenerative Medicine and Skeletal Development, School of Dental Medicine, University of Connecticut Health Center, United States.
authors.forename: Ryan P
authors.initials: RP
authors.lastname: Russell
authors.affiliation: Division of Developmental Biology, Cincinnati Children's Hospital Medical Center, United States.
authors.forename: Lindsey
authors.initials: L
authors.lastname: Aschbacher-Smith
authors.affiliation: Division of Developmental Biology, Cincinnati Children's Hospital Medical Center, United States.
authors.forename: Han
authors.initials: H
authors.lastname: Liu
authors.affiliation: Department of Orthopaedic Surgery, Nippon Medical School Hospital, Tokyo, Japan.
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Hagiwara
authors.affiliation: Division of Developmental Biology, Cincinnati Children's Hospital Medical Center, United States.
authors.forename: Rulang
authors.initials: R
authors.lastname: Jiang
authors.affiliation: Department of Orthopaedic Surgery, Washington University in St. Louis, United States.
authors.forename: Stavros
authors.initials: S
authors.lastname: Thomopoulos
authors.affiliation: Biomedical Engineering Program, College of Engineering and Applied Science, University of Cincinnati, United States.
authors.forename: David L
authors.initials: DL
authors.lastname: Butler
authors.affiliation: Center for Regenerative Medicine and Skeletal Development, School of Dental Medicine, University of Connecticut Health Center, United States.
authors.forename: David W
authors.initials: DW
authors.lastname: Rowe
mesh_terms: D000818:Animals; D001853:Bone Marrow / Q000473:pathology; D001862:Bone Resorption / Q000473:pathology / Q000503:physiopathology; D001842:Bone and Bones / Q000502:physiology; D002113:Calcification, Physiologic; D002454:Cell Differentiation; D019902:Chondrocytes / Q000378:metabolism; D002999:Clone Cells; D003094:Collagen / Q000378:metabolism; D004838:Epiphyses / Q000473:pathology; D051445:Fibrocartilage / Q000166:cytology*; D055428:Growth Differentiation Factor 5 / Q000378:metabolism*; D053823:Hedgehog Proteins / Q000378:metabolism*; D019426:Integrases / Q000378:metabolism; D051741:Kruppel-Like Transcription Factors / Q000378:metabolism; D051379:Mice; D008903:Minerals / Q000378:metabolism*; D008954:Models, Biological; D010010:Osteoclasts / Q000378:metabolism; D010329:Patella / Q000502:physiology; D015398:Signal Transduction; D013194:Staining and Labeling; D013234:Stem Cells / Q000166:cytology* / Q000378:metabolism; D013710:Tendons / Q000502:physiology; D000071676:Zinc Finger Protein GLI1
chemical_list: C498520:Gli1 protein, mouse; D055428:Growth Differentiation Factor 5; D053823:Hedgehog Proteins; D051741:Kruppel-Like Transcription Factors; D008903:Minerals; D000071676:Zinc Finger Protein GLI1; D003094:Collagen; C045073:Cre recombinase; D019426:Integrases
keywords: Alkaline phosphatase; Collagen; Enthesis; Fibrocartilage; GDF5; Growth; Hedgehog signaling; Lineage tracing; Maturation; Mineralization; Mouse