Non-canonical Wnt signaling and N-cadherin related beta-catenin signaling play a role in mechanically induced osteogenic cell fate.
BACKGROUND
Understanding how the mechanical microenvironment influences cell fate, and more importantly, by what molecular mechanisms, will enhance not only the knowledge of mesenchymal stem cell biology but also the field of regenerative medicine. Mechanical stimuli, specifically loading induced oscillatory fluid flow, plays a vital role in promoting healthy bone development, homeostasis and morphology. Recent studies suggest that such loading induced fluid flow has the potential to regulate osteogenic differentiation via the upregulation of multiple osteogenic genes; however, the molecular mechanisms involved in the transduction of a physical signal into altered cell fate have yet to be determined.


RESULTS
Using immuno-staining, western blot analysis and luciferase assays, we demonstrate the oscillatory fluid flow regulates beta-catenin nuclear translocation and gene transcription. Additionally, real time RT-PCR analysis suggests that flow induces Wnt5a and Ror2 upregulation, both of which are essential for activating the small GTPase, RhoA, upon flow exposure. Furthermore, although beta-catenin phosphorylation is not altered by flow, its association with N-cadherin is, indicating that flow-induced beta-catenin signaling is initiated by adherens junction signaling.


CONCLUSIONS
We propose that the mechanical microenvironment of bone has the potential to regulate osteogenic differentiation by initiating multiple key molecular pathways that are essential for such lineage commitment. Specifically, non-canonical Wnt5a signaling involving Ror2 and RhoA as well as N-cadherin mediated beta-catenin signaling are necessary for mechanically induced osteogenic differentiation.
Arnsdorf
Emily J
EJ
Bone and Joint R&D Center, VA Palo Alto Health Care System, Palo Alto, California, United States of America. emily.arnsdorf@gmail.com
Tummala
Padmaja
P
Jacobs
Christopher R
CR
D022005:Adherens Junctions / Q000378:metabolism; D000818:Animals; D001483:Base Sequence; D001696:Biomechanical Phenomena; D015820:Cadherins / Q000378:metabolism*; D002454:Cell Differentiation; D002460:Cell Line; D059630:Mesenchymal Stem Cells / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D008954:Models, Biological; D010012:Osteogenesis / Q000502:physiology*; D034741:RNA, Small Interfering / Q000235:genetics; D020794:Receptor Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D057050:Receptor Tyrosine Kinase-like Orphan Receptors; D015398:Signal Transduction; D013314:Stress, Mechanical; D051153:Wnt Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D000071818:Wnt-5a Protein; D051176:beta Catenin / Q000378:metabolism*; D020741:rho GTP-Binding Proteins / Q000378:metabolism; D020742:rhoA GTP-Binding Protein
C495267:CTNNB1 protein, mouse; D015820:Cadherins; C489083:Cdh2 protein, mouse; D034741:RNA, Small Interfering; D051153:Wnt Proteins; D000071818:Wnt-5a Protein; C438615:Wnt5a protein, mouse; D051176:beta Catenin; D020794:Receptor Protein-Tyrosine Kinases; D057050:Receptor Tyrosine Kinase-like Orphan Receptors; C477010:Ror2 protein, mouse; C526380:RhoA protein, mouse; D020741:rho GTP-Binding Proteins; D020742:rhoA GTP-Binding Protein