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G. S. Zode, R. J. Wordinger; Interaction Between BMP-4, TGF-β2, and Gremlin Modulates Extracellular Matrix Proteins in ONH Astrocytes and LC Cells. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3676. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
The characteristic cupping of the optic nerve head (ONH) in glaucoma is associated with elevated TGF-β2 and increased synthesis and deposition of extracellular matrix (ECM) proteins. We hypothesize that in glaucoma, elevated TGF-β2 in the ONH induces gremlin expression that blocks endogenous bone morphogenetic protein 4 (BMP) antagonism of TGF-β2 signaling. This results in unopposed TGF-β2 action and subsequent upregulation of ECM synthesis and deposition. The purpose of this initial study was to demonstrate that A) BMP-4 inhibits TGF-β2 stimulated ECM synthesis and deposition, B) gremlin blocks BMP-4 inhibition of TGF-β2 effects on ECM proteins, and C) gremlin increases ECM proteins in ONH astrocytes and LC cells.
Age matched normal and glaucomatous (N=3) human ONH tissues were utilized to immunolocalize fibronectin, TGF-β2, and gremlin. ONH astrocytes (N=3) and LC cells (N=5) were treated with a) TGF-β2 (5ng/ml) or BMP-4 (10ng/ml), b) TGF-β2 and BMP-4, c) TGF-β2, BMP-4 and gremlin (1ug/ml). ONH astrocytes were treated with recombinant mouse gremlin with or without siRNA for TGF- β2 or Smad3 (N=2). Changes in ECM components were assessed by western blot and ELISA. Effect of TGF-β2 on gremlin was assessed by QPCR and western blot analysis.
Fibronectin (FN), TGF-β2, and gremlin were significantly increased in glaucomatous human ONH tissues (P<0.05). BMP-4 inhibited TGF-β2 stimulated FN (P< 0.001), PAI-1, collagen I, collagen VI, and elastin protein levels. Gremlin significantly blocked BMP-4 inhibition of the TGF-β2 effects (P<0.001). TGF-β2 increased gremlin mRNA and protein levels. Recombinant gremlin increased FN, PAI-1, collagen I, collagen VI, and elastin protein levels. Inhibition of the TGF-β receptor via SB431542 or siRNA knockdown of Smad3 or TGF-β2 blocked the effect of gremlin on FN and PAI-1.
Elevated gremlin levels in ONH cells blocked BMP-4 antagonism of TGF-β2 induced ECM synthesis and deposition, thus leading to increased ECM deposition. ECM modulation via gremlin provides a novel therapeutic target for glaucoma.
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