Gremlin induces ocular hypertension in mice through Smad3-dependent signaling

PURPOSE. Transforming growth factor-β2 induces extracellular matrix (ECM) remodeling, which likely contributes to the defective function of the trabecular meshwork (TM) leading to glaucomatous ocular hypertension. Bone morphogenetic proteins (BMPs) inhibit these profibrotic effects of TGFβ2. The BMP antagonist gremlin is elevated in glaucomatous TM cells and increases IOP in an ex vivo perfusion culture model. The purpose of this study was to determine whether gremlin regulates ECM proteins in the TM, signals through the Smad3- dependent pathway, and induces ocular hypertension in mice. METHODS. Ad5.Gremlin or Ad5.TGFβ2 was injected intravitreally into one eye of each mouse. Intraocular pressure measurements were taken using a TonoLab tonometer. Gremlin, TGFβ2, fibronectin (FN), and collagen-1 (Col-1) expression in the TM was determined by immunofluorescence, Western immunoblot, and quantitative (q)PCR analyses. RESULTS. Ad5.Gremlin or Ad5.TGFβ2 each caused significant IOP elevation in mice. Immunofluorescence and Western blot analysis demonstrated that gremlin and TGFβ2 reciprocally increased the expression of each other, and both increased FN expression in the TM and surrounding tissues. Ad5.Gremlin elevated IOP and increased Fn and Col-1 gene expression in the TM of Smad3 wild-type (WT) mice, but had no effect in Smad3 HET or Smad3 KO mice. CONCLUSIONS. Our results demonstrate that intravitreal injections of either Ad5.Gremlin or Ad5.TGFβ2 elevate IOP and upregulate the ECM protein FN in the TM of mice. These data show that gremlin signals through the Smad3-dependent pathway in the TM to elevate IOP. We determined for the first time gremlin’s role in inducing ocular hypertension in an in vivo model system.