Interferon-γ differentially regulates TGF-β1 and TGF-β2 expression in human retinal pigment epithelial cells through JAK-STAT pathway

Retinal pigment epithelium (RPE) and transforming growth factor-β (TGF-β) have been shown to be involved in various retinal diseases. We have studied the role of inflammatory cytokines on the expression and secretion of TGF-β in human RPE cells (HRPE). Confluent cultures of HRPE derived from donor eyes were used. RT-PCR analyses showed that TNF-α and IL-1β increased the mRNA levels of both TGF-β1 and TGF-β2. IFN-γ enhanced constitutively expressed, as well as, TNF-α-and IL-β-induced TGF-β1 mRNA levels but decreased TGF-β2 mRNA. The effects of these cytokines on TGF-β1 and TGF-β2 secretion correlated with the mRNA levels. TGF-β1 was always produced as the latent form while 21-31% of TGF-β2 was in the active form. IFN-γ reduced the production of active form of TGF-β2 to 4-9%. TGF-β3 secretion was not detectable under any of the conditions. The Real-Time PCR analysis of TGF-β mRNAs confirmed the observed results. The TGF-β1 and TGF-β2 secretion was induced by TGF-β2 and TGF-β1, respectively. Under these conditions, the contrasting effects of IFN-γ on TGF-β1 and TGF-β2 secretion were also observed. JAK inhibitor selectively inhibited IFN-γ induced TGF-β1 secretion and mRNA levels while reversing the inhibitory effects of IFN-γ on TGF-β2. Analyses of transcription factor activity strongly indicated the role of STAT-1 but not NFκB, C-Myc, C-Jun, SP-1, MEF-2. Our data demonstrate that IFN-γ differentially regulates constitutively expressed, as well as, cytokine-induced TGF-β1 and TGF-β2 mRNA levels and secretion of TGF-βs by HRPE.