title: Mechanical activation of mammalian target of rapamycin pathway is required for cartilage development.
abstract: Mechanical stress regulates development by modulating cell signaling and gene expression. However, the cytoplasmic components mediating mechanotransduction remain unclear. In this study, elimination of muscle contraction during chicken embryonic development resulted in a reduction in the activity of mammalian target of rapamycin (mTOR) in the cartilaginous growth plate. Inhibition of mTOR activity led to significant inhibition of chondrocyte proliferation, cartilage tissue growth, and expression of chondrogenic genes, including Indian hedgehog (Ihh), a critical mediator of mechanotransduction. Conversely, cyclic loading (1 Hz, 5% matrix deformation) of embryonic chicken growth plate chondrocytes in 3-dimensional (3D) collagen scaffolding induced sustained activation of mTOR. Mechanical activation of mTOR occurred in serum-free medium, indicating that it is independent of growth factor or nutrients. Treatment of chondrocytes with Rapa abolished mechanical activation of cell proliferation and Ihh gene expression. Cyclic loading of chondroprogenitor cells deficient in SH2-containing protein tyrosine phosphatase 2 (Shp2) further enhanced mechanical activation of mTOR, cell proliferation, and chondrogenic gene expression. This result suggests that Shp2 is an antagonist of mechanotransduction through inhibition of mTOR activity. Our data demonstrate that mechanical activation of mTOR is necessary for cell proliferation, chondrogenesis, and cartilage growth during bone development, and that mTOR is an essential mechanotransduction component modulated by Shp2 in the cytoplasm.
authors.affiliation: Cell and Molecular Biology Laboratory, Department of Orthopaedics, Alpert Medical School of Brown University/Rhode Island Hospital, Providence, Rhode Island, USA; and.
authors.forename: Yingjie
authors.initials: Y
authors.lastname: Guan
authors.affiliation: Cell and Molecular Biology Laboratory, Department of Orthopaedics, Alpert Medical School of Brown University/Rhode Island Hospital, Providence, Rhode Island, USA; and Department of Orthopaedics, Affiliated Hospital of Medical College of Qingdao University, Qingdao, China.
authors.forename: Xu
authors.initials: X
authors.lastname: Yang
authors.affiliation: Cell and Molecular Biology Laboratory, Department of Orthopaedics, Alpert Medical School of Brown University/Rhode Island Hospital, Providence, Rhode Island, USA; and.
authors.forename: Wentian
authors.initials: W
authors.lastname: Yang
authors.affiliation: Cell and Molecular Biology Laboratory, Department of Orthopaedics, Alpert Medical School of Brown University/Rhode Island Hospital, Providence, Rhode Island, USA; and.
authors.forename: Cherie
authors.initials: C
authors.lastname: Charbonneau
authors.affiliation: Cell and Molecular Biology Laboratory, Department of Orthopaedics, Alpert Medical School of Brown University/Rhode Island Hospital, Providence, Rhode Island, USA; and qian_chen@brown.edu.
authors.forename: Qian
authors.initials: Q
authors.lastname: Chen
mesh_terms: D000818:Animals; D002356:Cartilage / Q000196:embryology / Q000378:metabolism*; D049109:Cell Proliferation; D002642:Chick Embryo; D019902:Chondrocytes / Q000166:cytology / Q000378:metabolism* / Q000502:physiology; D020219:Chondrogenesis; D053823:Hedgehog Proteins / Q000235:genetics / Q000378:metabolism; D040542:Mechanotransduction, Cellular; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11 / Q000235:genetics / Q000378:metabolism; D013314:Stress, Mechanical; D058570:TOR Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*
chemical_list: D053823:Hedgehog Proteins; D058570:TOR Serine-Threonine Kinases; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11
keywords: Shp2; chondrocyte; mTOR; mechanotransduction