Purpose: TGF-beta2 is known to be present at elevated levels in the aqueous humor of patients with primary open-angle glaucoma (POAG). Studies have shown that TGF-beta2 influences cultured trabecular meshwork (TM) cells, but the effects of this cytokine on intact TM and outflow facility have not been studied. The purpose of this study was to investigate whether TGF-beta2 treatment induces changes in outflow facility and morphologic changes in the TM tissue and whether these changes are comparable to those previously recorded in glaucomatous eyes.
Methods: Baseline facility was measured in paired human eyes (n = 8 pairs), with a constant-flow anterior segment culture system. Medium perfusing experimental eyes was then supplemented with activated human recombinant TGF-beta2 (3.0 ng/mL, comparable to or slightly greater than measured aqueous humor levels in patients with POAG), and facility was measured for at least 8 days. At the conclusion of the perfusion, eyes were fixed and processed for light microscopy, transmission electron microscopy, and immunolabeling studies.
Results: TGF-beta2 perfusion reduced outflow facility by 27% (P = 0.03) and promoted focal accumulation of fine fibrillar extracellular material in multilayered structures under the inner wall of Schlemm's canal. In treated eyes, Schlemm's canal was 27% shorter (P = 0.02), and the length of the inner wall apparently available for fluid flow was 33% less (P = 0.001), both compared with paired control eyes.
Conclusions: TGF-beta2 reduces outflow facility when perfused into cultured human anterior segments. Furthermore, TGF-beta2 affects the extracellular matrix of the trabecular meshwork in a manner that is consistent with the observed reduction in outflow facility. Although the distribution of accumulated fibrillar material was different in these perfused eyes than that in POAG, the difference could be due to variation in biomechanical environment for TM cells in cultured anterior segments compared with the living eye. Overall, these results support the hypothesis that elevated TGF-beta2 levels in the aqueous humor play a role in the pathogenesis of the ocular hypertension in POAG.