Induction of TGF-beta1 in the trabecular meshwork under cyclic mechanical stress

The pathophysiological mechanisms involved in the failure of the trabecular meshwork (TM) to maintain normal levels of aqueous outflow in glaucoma are not yet understood. Aberrant activation of the transforming growth factor beta-1 (TGF-beta1) pathway has been implicated in several degenerative diseases. We investigated the possibility that chronic cyclic mechanical stress that affects the TM might result in increased production of TGF-beta1. Primary cultures of TM cells subjected to cyclic mechanical stress (5% stretching, 1 cycle/sec) demonstrate a significant increase in total and biologically active secreted TGF-beta1 that was associated with activation of the TGF-beta1 promoter, measured using a recombinant adenovirus expressing the secreted reporter gene secreted alkaline phosphatase protein (SEAP) under the TGF-beta1 gene promoter (AdTGFbeta1-SEAP). Associated changes in the transcription of MMP-2, TIMP-2, and CTGF were assessed by semiquantitative PCR. Immunohistochemical analysis of TGF-beta1 in organ culture of human eyes revealed a generalized accumulation of this protein in the extracellular matrix (ECM) of the TM, while expression of the TGF-beta1 promoter, analyzed using the LacZ reporter gene, was localized in some specific cells within the outflow pathway. Induction of the TGF-beta1 promoter in organ culture was demonstrated using a novel model for cyclic mechanical stress in human perfused anterior segments infected with AdTGFbeta1-SEAP. Given the relevant physiological and pathophysiological roles of TGF-beta1, its induction after cyclic mechanical stress in the TM supports the hypothesis that this cytokine might play a significant role in the physiology of the TM, and contribute to the pathological changes of this tissue in certain forms of glaucoma.