Role of transforming growth factor-β1 and its latent form binding protein in pseudoexfoliation syndrome

Pseudoexfoliation (PEX) syndrome is a common and clinically important systemic condition characterized by the pathologic production and accumulation of an abnormal fibrillar extracellular material in many intra- and extraocular tissues. Recent evidence suggests that it is a type of elastosis associated with the excess synthesis of elastic microfibrillar components such as fibrillin-1. Since transforming growth factor (TGF)-β is a major modulator of extracellular matrix formation, the potential involvement of TGF-β and its latent form binding protein (LTBP) in this aberrant matrix process was investigated. The expression of various isoforms of TGF-β and LTBP was investigated in the anterior segment tissues of PEX and control eyes on the protein and mRNA level by light and electron microscopic immunohistochemistry, in situ hybridization, and semiquantitative RT-PCR, TGF-β1 and TGF-β2 levels were measured in aqueous humor and serum of PEX and control patients by ELISA. Cultures of Tenon's capsule fibroblasts were established to study the effect of TGF-β1 on fibrillin-1 mRNA expression by Northern blot analysis. Significantly increased concentrations of both total and active TGF-β1 were measured in the aqueous humor of PEX eyes without and with glaucoma as compared to control eyes, whereas levels of TGF-β2 were not significantly different. The expression of TGF-β1, LTBP-1, and LTBP-2, but not TGF-β2, was markedly increased in anterior segment tissues of PEX eyes, particularly in the non-pigmented epithelium of the ciliary body, on both the mRNA and the protein level. Latent TGF-β1 staining was consistently associated with PEX material deposits and could be released by proteolytic processing. Double immunolabeling revealed clear co-localization of LTBP-1 and -2 with latent TGF-β1 and with fibrillin-1 on PEX fibrils. The expression of mRNA coding for fibrillin-1 was up-regulated in vitro by TGF-β1. This study provides evidence for a significant role of TGF-β1 and the LTBPs 1 and 2 in PEX syndrome. The results suggest that increased levels of latent and active TGF-β1 in the aqueous humor of PEX patients, derived from enhanced local synthesis and activation, promote the buildup of the abnormal extracellular elastic material characteristic of PEX syndrome. They further support a dual role for LTBPs, both as integral structural components of PEX fibers and as a means of matrix anchorage of latent TGF-β1, representing one possible mechanism for the regulation of TGF-β1 activity in PEX eyes. Future therapeutic strategies might focus on TGF-β1 antagonistic approaches.