Differential effect of activin A and BMP-7 on myofibroblast differentiation and the role of the Smad signaling pathway.
OBJECTIVE
To investigate myofibroblast differentiation and signal transduction induced by TGF-beta family members activin A and bone morphogenetic protein (BMP)-7.


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-beta1 or serum, activin A but not BMP-7 increased alpha-smooth muscle (SM) actin and actin-binding proteins such as SM myosin, alpha-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 beta1. 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 alpha-SM actin.


CONCLUSIONS
TGF-beta proteins have different functions in the cornea. Activin A and TGF-beta1, 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-beta family members in the cornea.
You
Lingtao
L
Department of Ophthalmology, University of Heidelberg Medical School, Heidelberg, Germany.
Kruse
Friedrich E
FE
D028341:Activins / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D015152:Blotting, Northern; D015153:Blotting, Western; D055419:Bone Morphogenetic Protein 7; D019485:Bone Morphogenetic Proteins / Q000494:pharmacology*; D002454:Cell Differentiation / Q000187:drug effects; D002478:Cells, Cultured; D003315:Cornea / Q000166:cytology* / Q000378:metabolism; D017931:DNA Primers / Q000737:chemistry; D004268:DNA-Binding Proteins / Q000502:physiology*; D015536:Down-Regulation; D016326:Extracellular Matrix Proteins / Q000378:metabolism; D005347:Fibroblasts / Q000378:metabolism*; D038681:Follistatin; D006801:Humans; D028322:Inhibin-beta Subunits / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D008840:Microfilament Proteins / Q000378:metabolism; D010766:Phosphorylation; D011233:Precipitin Tests; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D051899:Smad2 Protein; D051900:Smad3 Protein; D015534:Trans-Activators / Q000502:physiology*; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000494:pharmacology
C525819:BMP7 protein, human; D055419:Bone Morphogenetic Protein 7; D019485:Bone Morphogenetic Proteins; D017931:DNA Primers; D004268:DNA-Binding Proteins; D016326:Extracellular Matrix Proteins; D038681:Follistatin; D008840:Microfilament Proteins; C497782:SMAD2 protein, human; C497790:SMAD3 protein, human; D051899:Smad2 Protein; D051900:Smad3 Protein; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; C422405:activin A; D028341:Activins; D028322:Inhibin-beta Subunits