EFFECTS OF TGF-BETA2 ON THE ELASTIC MODULUS OF TRABECULAR MESHWORK TISSUE

Purpose: The primary risk factor for developing glaucoma is elevated intraocular pressure (IOP.) The key outflow passage for aqueous humor (AH) in the human eye involves the trabecular meshwork (TM) and the Schlemm's canal (SC) with the main regulator of IOP being at the junction of the two. Elevated IOP has been attributed to increased resistance to flow at the TM/SC junction. Aqueous humor levels of transforming growth factor beta-2 (TGF-b2) are elevated in glaucoma patients, suggesting its contribution to the progression of the disease. Studies using cultured TM cells as well as ex vivo tissue have shown that TGF-b2 induces extracellular matrix (ECM) remodeling. A separate study used atomic force microscopy (AFM) to measure the elastic modulus (e.g. stiffness) of TM tissue obtained from glaucoma patients compared to age-matched controls. A marked increase in stiffness in the glaucoma tissue was observed compared to non-glaucomatous controls. Taken together, these findings imply that an elevated level of TGF-b2 may lead to ECM remodeling and increased stiffness thus reducing AH outflow and elevating IOP. The hypothesis of this study was that increased expression of TGF-b2 will cause increased stiffness (e.g. increased elastic modulus) of the TM. The goal of our study was to compare the stiffness of the TM cultured overnight with or without TGF-b2. Methods: Bovine eyes were obtained from an abattoir and the TM dissected from the anterior segment. The dissected TM was then cut into halves. One half was cultured in control media and the other half cultured in media containing TGF-b2 (5 ng/ml). Both TM halves were incubated at 37oC for a period of 72 hours. The TM was then loaded onto a force transducer and contraction induced with carbachol to measure stiffness. Results: The raw data obtained indicated that the TM exposed to TGF-b2 contracted with greater force than control indicating that TGF-b2 reduced the stiffness of the TM. However, using a Students T test at a p of 0.05 the results showed no statistical significance. Conclusions: The results obtained are from one experiment with an N =8 and since no statistical significance was observed, the data has to be considered inconclusive. The force transducer used was actually that designed for skeletal muscles which may not be the best system to test trabecular meshwork which has some smooth muscle components. The future goal of the study is to actually use force microscopy, the current standard for such experiments.