Transforming growth factor-β2 induces expression of biologically active bone morphogenetic protein-1 in human trabecular meshwork cells

PURPOSE. There are limited studies on the factors that regulate the processing of TGF-β2 and extracellular matrix (ECM) proteins into their mature form. Bone morphogenic protein 1 (BMP1) is an enzyme responsible for the cleavage and maturation of growth factors and ECM proteins. The purpose of our study was to determine whether cultured human trabecular meshwork (TM) cells express BMP1, BMP1 expression is regulated by TGF-β2, BMP1 is biologically active, and BMP1 regulates LOX activity. METHODS. Primary human TM cells were isolated and subjected to quantitative PCR (qPCR) and Western immunoblotting (WB) for BMP1. BMP1 immunolocalization was performed in TM tissues. qPCR was used to determine BMP1 mRNA expression and WB results were used to determine BMP1 protein expression. BMP1 activity was measured in TM cells treated with TGF-β2 or with a combination of TGF-β2/UK383367. Lysyl oxidase (LOX) enzyme activity was evaluated by WB in TM cells treated with BMP1 or with a combination of BMP1/βaminoprorionitrile (BAPN). RESULTS. Human TM cells expressed mRNA and protein for BMP1. Exogenous TGF-β2 increased mRNA expression compared to their controls (P < 0.05). An ELISA showed TGF-β2- induced BMP1 secretion compared to their controls in all cell strains (P < 0.05). Secreted BMP1 stimulated LOX enzymatic activity in TM cells. CONCLUSIONS. BMP1 is expressed in the human TM. TGF-β2 induction of BMP1 may be responsible for increased processing of growth factors and ECM proteins into their mature forms, resulting in TM stiffness and resistance to ECM degradation.