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James Wright Spurlin, Peter Y Lwigale; BMP-3 is a novel antagonist to TGFβ-2 mediated myofibroblast differentiation in embryonic keratocytes. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):1301.
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© ARVO (1962-2015); The Authors (2016-present)
Embryonic corneas heal scar free and show a transient expression of alpha smooth muscle actin (αSMA). We sought to elucidate the mechanistic regulation of the myofibroblast phenotype transition during scar free corneal regeneration.
Differential expression of BMPs was screened during various stages of embryonic cornea regeneration via RT-PCR. Spatiotemporal expression of TGFβ-2 and BMP-3 mRNA was identified in sections of regenerating embryonic corneas by in situ hybridization. The temporal response of keratocytes to TGF-β and BMP signaling in regenerating corneas were determined by immunostaining for pSMAD2 and pSMAD1/5/8 respectively. Primary cultures of embryonic keratocytes were treated with BMP-3; a novel antagonist to TGFβ mediated myofibroblast differentiation. To determine the effect of BMP-3 on TGFβ in embryonic keratocytes, the number of αSMA-positive cells was analyzed in primary cultures treated with BMP-3 and/or TGFβ-2. The activity of TGFβ in the presence BMP-3 was assayed by measuring the transcript levels of downstream target genes of TGFβ via qPCR.
Robust expression of TGFβ-2 and BMP-3 was identified in regenerating embryonic corneal stroma and epithelium, respectively. Nuclear localization of pSMAD2 and pSMAD1/5/8 respectively correlated with the expression and down regulation of αSMA. In vitro, BMP-3 was identified as a potent antagonist to the induction of myofibroblast phenotype in primary embryonic keratocytes. Interestingly, transcript analysis indicated that BMP-3 does not inhibit TGFβ mediated expression of αSMA. However, cells treated with BMP-3 expressed low levels of focal adhesion components and assumed a spherical morphology.
These data build a mechanistic model for embryonic cornea regeneration, by which TGFβ mediated myofibroblast differentiation is negatively regulated by BMP-3. While BMP-3 does not directly inhibit TGFβ-2 activity, focal adhesion appears to be abrogated by BMP-3, which may prevent myofibroblast maturation.
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