title: TGFbeta/Activin/Nodal pathway in inhibition of human embryonic stem cell differentiation by mechanical strain.
abstract: Cyclic biaxial mechanical strain has been reported to inhibit human embryonic stem cell differentiation without selecting against survival of differentiated or undifferentiated cells. We show that TGFbeta/Activin/Nodal signaling plays a crucial role in repression of human embryonic stem cell (hESC) differentiation under mechanical strain. Strain-induced transcription of TGFbeta1, Activin A, and Nodal, and upregulated Similar to Mothers Against Decapentaplegic homolog (Smad)2/3 phosphorylation in undifferentiated hESC. TGFbeta/Activin/Nodal receptor inhibitor SB431542 stimulated differentiation of hESCs cultured under biaxial strain. Exogenous addition of TGFbeta1, Activin A, or Nodal alone was insufficient to stimulate hESC self-renewal to replicate behavior of hESCs in presence of strain. However, exogenous TGFbeta1 and Activin A in combination partially replicated the self-renewing phenotype induced by strain but when combined with strain did not further stimulate self-renewal. In presence of mechanical strain, addition of a neutralizing antibody to TGFbeta1 promoted hESC differentiation whereas inhibition of Activin A by Follistatin promoted hESC differentiation to a lesser extent. Together, these findings show that TGFbeta superfamily activation of Smad2/3 is required for repression of spontaneous differentiation under strain and suggest that strain may induce autocrine or paracrine signaling through TGFbeta superfamily ligands.
authors.affiliation: Department of Chemical and Biological Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
authors.forename: Somen
authors.initials: S
authors.lastname: Saha
authors.forename: Lin
authors.initials: L
authors.lastname: Ji
authors.forename: Juan J
authors.initials: JJ
authors.lastname: de Pablo
authors.forename: Sean P
authors.initials: SP
authors.lastname: Palecek
mesh_terms: D028341:Activins / Q000378:metabolism*; D017209:Apoptosis / Q000502:physiology; D002454:Cell Differentiation / Q000502:physiology; D002470:Cell Survival; D002478:Cells, Cultured; D004548:Elasticity; D053595:Embryonic Stem Cells / Q000166:cytology* / Q000502:physiology*; D006801:Humans; D040542:Mechanotransduction, Cellular / Q000502:physiology*; D055457:Nodal Protein; D033081:Shear Strength; D015398:Signal Transduction / Q000502:physiology*; D013314:Stress, Mechanical; D016212:Transforming Growth Factor beta / Q000378:metabolism*
chemical_list: C526007:NODAL protein, human; D055457:Nodal Protein; D016212:Transforming Growth Factor beta; D028341:Activins