BMP4 Induced ID Protein Protects TM From Glaucomatous Effects of TGFβ-2

Purpose: Elevated levels of pro-fibrotic growth factor transforming growth factor b2 (TGFb2) are have been reported in the aqueous humor and trabecular meshwork (TM) of primary open angle glaucoma (POAG) patients. TGFb2 treatment results in accumulation of extracellular matrix (ECM) molecules in the TM, which are associated with increased outflow resistance. Expression of TGFb2 in rodent eyes and ex-vivo anterior segment perfusion models elevate intraocular pressure, suggesting that TGFb2 plays a role in the development and progression of glaucoma. Interestingly, bone morphogenetic protein 4 (BMP4) inhibits ECM proteins that are up-regulated in TM cells by TGFb2.The purpose of our study is to determine the mechanism by which BMP4 inhibits the TGFb2 induction of ECM proteins in the TM. Prominent downstream targets of the BMP4 pathway are inhibitor of DNA binding proteins (IDs). There are four family members of IDs (ID1-4). In this study, we determine the expression of IDs in TM cells and determine the role of BMP4 induced ID1 and ID3 in regulating TGFb2 induction of ECM proteins Methods: Time and dose dependent BMP4 induction of ID1 and ID3 were studied in cultured human TM cells by Q-PCR and western blot analysis. GTM3 cells were transfected with pCMV-ID1 and pCMV-ID3 plasmids to determine their effect on TGFb2 induced ECM proteins (Fibronectin, PAI-1) by western blot analysis. Results: BMP4 (10ng/ml) significantly induced ID1 and ID3 mRNA and protein expression, starting 30 minutes after treatment. Conclusions: BMP4 induced ID1 and ID3 expression in TM cells, and ID1/ID3 suppressed the profibrotic ECM effects of TGFb2. Therefore, the BMP4 suppression of TGFb2 effects in TM cells may be mediated by ID1 and ID3. Further this study suggests ID1 and ID3 to be potential therapeutic targets for POAG.