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Lingtao You, Friedrich E. Kruse; Differential Effect of Activin A and BMP-7 on Myofibroblast Differentiation and the Role of the Smad Signaling Pathway. Invest. Ophthalmol. Vis. Sci. 2002;43(1):72-81.
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purpose. To investigate myofibroblast differentiation and signal transduction
induced by TGF-β family members activin A and bone morphogenetic
methods. Transcription of activin and receptors (ActR) for activin A and BMP-7
was detected by RT-PCR. Levels of marker proteins for differentiation
and phosphorylation of similar to mothers against decapentaplegics
(Smads) were quantified by Western blot analysis in response to BMP-7,
activin A and follistatin. Transfection with antisense Smad2/3 was
performed to evaluate signal transduction.
results. Activin A and receptors (ActR-I, ActR-IB, ActR-II) are transcribed in
corneal fibroblasts. Compared with TGF-β1 or serum, activin A but not
BMP-7 increased α-smooth muscle (SM) actin and actin-binding proteins
such as SM myosin, α-actinin, and vinculin. Talin, paxillin, and
desmin were not induced and vimentin was downregulated by activin.
Activin also induced extracellular matrix proteins fibronectin and
integrin β1. Activin-dependent accumulation of proteins was blocked
by follistatin. Regarding signal transduction, activin A induced
phosphorylation of Smad 2, and BMP-7 induced Smad 1, both of which were
inhibited by follistatin. Transfection with antisense Smad 2/3
prevented activin-induced expression and accumulation of α-SM actin.
conclusions. TGF-β proteins have different functions in the cornea. Activin A and
TGF-β1, but not BMP-7, are regulators of corneal keratocyte
differentiation and may play a role during myofibroblast
transdifferentiation. Smad 2/3 signal transduction seems to be
important in the regulation of muscle-specific genes. Further
investigation of Smad signaling may help to better understand the
function of TGF-β family members in the cornea.
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