p38 MAPK mediates the expression of type I collagen induced by TGF-beta 2 in human retinal pigment epithelial cells ARPE-19.

Purpose: Transforming growth factor (TGF)-beta has been implicated as the key mediator of proliferative vitreoretinopathy, but the cellular mechanisms by which TGF-beta induces extracellular matrix protein (ECM) synthesis are not fully understood. The current study was conducted to examine whether the mitogen-activated protein kinase (MAPK) pathway is involved in TGF-beta 2-induced collagen expression in retinal pigment epithelial cells.
Methods: Human retinal pigment epithelial cells ARPE-19 were cultured and stimulated with various concentrations of TGF-beta 2. The type I collagen gene (COL1A1, COL1A2) expression induced by TGF-beta 2 was evaluated by real-time RT-PCR. Synthesis of type I collagen was evaluated by the concentration of the C-terminal propeptide of type I (PICP) in the medium. The activation of MAPK pathways by TGF-beta 2 was assessed by immunoblot with anti-phospho-p38 and anti-phospho-extracellular signal-regulated kinase (ERK)1/2 antibodies. The role of MAPK was assessed using biochemical inhibitors. To examine the transcriptional activities of COL1A1 and COL1A2, luciferase reporter assays were also performed.
Results: mRNA expression of COL1A1 and COL1A2 and type I collagen synthesis were activated by TGF-beta 2. Both ERK and p38 MAPK pathways were also activated by TGF-beta 2. The biochemical blockade of p38 MAPK activation, but not ERK activation, inhibited TGF-beta 2-induced type I collagen mRNA expression and type I collagen synthesis. Moreover, blockade of the p38 MAPK pathway inhibited the increase in both COL1A1 and COL1A2 promoter activities when induced by TGF-beta 2.
Conclusions: TGF-beta 2 activates p38 MAPK and p38 MAPK plays a role in relaying the TGF-beta 2 signal to type I collagen production in the retinal pigment epithelium.