Transforming Growth Factor-β2 Modulated Extracellular Matrix Component Expression in Cultured Human Optic Nerve Head Astrocytes

Abstract

To study whether glaucomatous extracellular matrix (ECM) modifications in the lamina cribrosa might be induced by TGF-beta 2, the effect of TGF-beta 2 on the expression of collagen types I (Col1 alpha 1), III (Col3 alpha 1), and IV (Col4 alpha 2); fibronectin (FN); tissue transglutaminase (TGM2); connective tissue growth factor (CTGF); and thrombospondin (TSP-1) in cultured human optic nerve head (ONH) astrocytes was investigated. Astrocytes were isolated from eyes of five human donors, and cultured monolayers were treated with 1.0 ng/mL TGF-beta 2 for 24 and 48 hours. Expression of Col1 alpha 1, Col3 alpha 1, Col4 alpha 2, FN, TGM2, CTGF, and TSP-1 was examined by semiquantitative RT-PCR and Northern and Western blot analyses. The effect of CTGF silencing on the TGF-beta 2-modulated expression of these genes was investigated by transfection of CTGF small interfering (si)RNA before TGF-beta 2 treatment. TGF-beta 2 treatment upregulated the expression of Col1 alpha 1, Col4 alpha 2, FN, CTGF, TGM2, and TSP-1 mRNA and protein in cultured astrocytes. Inductions ranged between 1.5- and 4-fold. Expression of Col3 alpha 1 remained unaffected. Transfection of 10 nM CTGF siRNA inhibited the TGF-beta 2-induced upregulation of CTGF, Col4 alpha 2, Col1 alpha 1, TGM2, and FN, whereas TSP-1 expression was not reduced. TGF-beta 2 is capable of inducing the expression of ECM and basement membrane components in cultured ONH astrocytes via CTGF and upregulated TSP-1, a protein naturally involved in the activation of latent TGF-beta. Therefore, TGF-beta 2 could be a factor in the initiation of the modification of ECM in the glaucomatous ONH. In addition, TSP-1 induction may be a mechanism by which TGF-beta 2 amplifies its own activation.