SPARC is expressed in scars of the Tenon's capsule and mediates scarring properties of human Tenon's fibroblasts in vitro

Purpose: To investigate the expression of the matricellular protein SPARC (secreted acidic cysteine-rich glycoprotein) in scarred human Tenon's capsule and in cultured human Tenon's fibroblasts (HTF), and to analyze the influence of SPARC on cell proliferation and collagen matrix contraction in vitro. Methods: Human Tenon's capsule scars obtained from surgical revisions after filtration surgery were analyzed for SPARC expression by immunohistochemistry. In cultured HTF cells, SPARC expression was assessed by northern and western blot analyses after incubation with transforming growth factor (TGF)-beta 1 and TGF-beta 2. Cell proliferation was determined by bromodeoxyuridine (BrdU)-labeling and HTF cells-mediated collagen matrix contraction by morphometric measurements of three-dimensional collagen lattices after treatment with SPARC and/or TGF-beta 1. Results: In scarred human Tenon's capsule specimens, an increased expression of SPARC was mainly localized to the extracellular matrix and to blood vessel walls as compared to healthy control Tenon's capsule. In cultured HTF cells, treatment with TGF-beta 1 more than TGF-beta 2 induced the expression of SPARC both on the mRNA and protein level. Incubation of HTF cells with SPARC resulted in an increase in collagen matrix contraction and cell proliferation. Moreover, a combined incubation of SPARC and TGF-beta 1 stimulated HTF cell proliferation significantly over the levels that were observed after single treatment. Conclusions: Our data provide evidence that SPARC contributes to excessive wound healing and scar formation in human Tenon's capsules after filtration surgery and may thus represent a novel target for anti-fibrotic strategies.