TRANSFORMING GROWTH FACTOR-β2 EFFECTS EXPRESSION OF PERIOSTIN AND PROCOLLAGEN C-ENDOPEPTIDASE ENHANCER 1 IN HUMAN TRABECULAR MESHWORK CELLS

Transforming growth factor-beta 2 (TGF-β2) has been implicated in the development of elevated intraocular pressure (IOP) in primary open-angle glaucoma (POAG). Glaucoma patients have increased levels of TGF-β2 in their aqueous humor and trabecular meshwork (TM), and TGF-β2 increases extracellular matrix (ECM) proteins. Thus, we are interested in growth factors that are associated with glaucoma and the ECM. Purpose (a): Transforming growth beta-2 (TGF-β2) has been associated with increased extracellular matrix (ECM) deposition, which is attributed to increased aqueous humor outflow resistance through the trabecular meshwork (TM). We have previously demonstrated that bone morphogenetic protein 1 (BMP1) (an enzyme responsible for the cleavage and maturation of ECM proteins) is expressed and regulated by TGF-β2 in the human TM and that BMP1 regulates lysyl oxidase activity. Also, other factors associated with the ECM remodeling include periostin (POSTN) and procollagen c-endopeptidase enhancer 1 (PCOLCE1). The purpose of this study was to determine whether human TM cells (a) express POSTN and PCOLCE1 (b) whether expression of POSTN and PCOLCE1 are regulated by TGF-β2. Methods (b): Primary human normal (NTM) and glaucomatous (GTM) cells were isolated and subjected to qPCR and Western immunoblotting (WB) for POSTN and PCOLCE1 expression. qPCR was used to determine POSTN and PCOLCE1 expression between control and TGF-β2 treated (5ng/ml for 24 hours) TM cells. WBs of cell lysates and conditioned medium were used to compare POSTN and PCOLCE1 protein expression between control and TGF-β2 treated NTM and GTM cells. Results (c): Human TM cells expressed POSTN and PCOLCE1 mRNA and protein. Exogenous TGF-β2 increased POSTN mRNA expression (p<0.05) and decreased PCOLCE1 expression (p<0.0005) compared to control cells. WB analysis showed increased POSTN secretion in NTM compared to GTM cells (p<0.05). TGF-β2 induced POSTN in NTM cells (p<0.05). However, no POSTN was detected in cell lysates of TM cells. WB analysis showed decreased PCOLCE1 secretion in NTM cells compared to GTM cells (p<0.05). Conclusions (d): POSTN and PCOLCE1 are expressed in the human TM. These molecules may be involved in the normal function of the TM as well as TM pathogenesis. Altered expression of POSTN and PCOLCE1 may lead to structural and functional changes in the ECM within the TM.