Transforming growth factor-β2 modulated extracellular matrix component expression in cultured human optic nerve head astrocytes

PURPOSE. To study whether glaucomatous extracellular matrix (ECM) modifications in the lamina cribrosa might be induced by TGF-beta2, the effect of TGF-beta2 on the expression of collagen types I (Col1alpha1), III (Col3alpha1), and IV (Col4alpha2); fibronectin (FN); tissue transglutaminase (TGM2); connective tissue growth factor (CTGF); and thrombospondin (TSP-1) in cultured human optic nerve head (ONH) astrocytes was investigated. METHODS. Astrocytes were isolated from eyes of five human donors, and cultured monolayers were treated with 1.0 ng/mL TGF-beta2 for 24 and 48 hours. Expression of Col1alpha1, Col3alpha1, Col4alpha2, 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-beta2-modulated expression of these genes was investigated by transfection of CTGF small interfering (si) RNA before TGF-beta2 treatment. RESULTS. TGF-beta2 treatment upregulated the expression of Col1alpha1, Col4alpha2, FN, CTGF, TGM2, and TSP-1 mRNA and protein in cultured astrocytes. Inductions ranged between 1.5- and 4-fold. Expression of Col3alpha1 remained unaffected. Transfection of 10 nM CTGF siRNA inhibited the TGF-beta2-induced upregulation of CTGF, Col4alpha2, Col1alpha1, TGM2, and FN, whereas TSP-1 expression was not reduced. CONCLUSIONS. TGF-beta2 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-beta2 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-beta2 amplifies its own activation.