title: Load regulates bone formation and Sclerostin expression through a TGFβ-dependent mechanism.
abstract: Bone continually adapts to meet changing physical and biological demands. Osteoblasts, osteoclasts, and osteocytes cooperate to integrate these physical and biochemical cues to maintain bone homeostasis. Although TGFβ acts on all three of these cell types to maintain bone homeostasis, the extent to which it participates in the adaptation of bone to mechanical load is unknown. Here, we investigated the role of the TGFβ pathway in load-induced bone formation and the regulation of Sclerostin, a mechanosensitive antagonist of bone anabolism. We found that mechanical load rapidly represses the net activity of the TGFβ pathway in osteocytes, resulting in reduced phosphorylation and activity of key downstream effectors, Smad2 and Smad3. Loss of TGFβ sensitivity compromises the anabolic response of bone to mechanical load, demonstrating that the mechanosensitive regulation of TGFβ signaling is essential for load-induced bone formation. Furthermore, sensitivity to TGFβ is required for the mechanosensitive regulation of Sclerostin, which is induced by TGFβ in a Smad3-dependent manner. Together, our results show that physical cues maintain bone homeostasis through the TGFβ pathway to regulate Sclerostin expression and the deposition of new bone.
authors: Graduate Program in Oral and Craniofacial Sciences, University of California San Francisco, San Francisco, California, United States of America.
authors: Jacqueline
authors: J
authors: Nguyen
authors: Simon Y
authors: SY
authors: Tang
authors: Daniel
authors: D
authors: Nguyen
authors: Tamara
authors: T
authors: Alliston
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D045744:Cell Line, Tumor; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D006023:Glycoproteins / Q000235:genetics* / Q000378:metabolism; D036341:Intercellular Signaling Peptides and Proteins; D008156:Luciferases; D008297:Male; D040542:Mechanotransduction, Cellular / Q000235:genetics*; D051379:Mice; D008822:Mice, Transgenic; D010006:Osteoblasts / Q000166:cytology / Q000000981:diagnostic imaging / Q000378:metabolism*; D010010:Osteoclasts / Q000166:cytology / Q000000981:diagnostic imaging / Q000378:metabolism*; D010011:Osteocytes / Q000166:cytology / Q000000981:diagnostic imaging / Q000378:metabolism*; D010012:Osteogenesis / Q000235:genetics; D010766:Phosphorylation; D051899:Smad2 Protein / Q000235:genetics / Q000378:metabolism; D051900:Smad3 Protein / Q000235:genetics / Q000378:metabolism; D013977:Tibia / Q000166:cytology / Q000000981:diagnostic imaging / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000235:genetics* / Q000378:metabolism; D016474:Weight-Bearing; D055114:X-Ray Microtomography
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D006023:Glycoproteins; D036341:Intercellular Signaling Peptides and Proteins; D051899:Smad2 Protein; C497783:Smad2 protein, mouse; D051900:Smad3 Protein; C497791:Smad3 protein, mouse; C486030:Sost protein, mouse; D016212:Transforming Growth Factor beta; D008156:Luciferases