Extracellular matrix production regulation by TGF-beta in corneal endothelial cells

Production of extracellular matrix (ECM) by corneal endothelial cells is related to physiologic functions and pathologic conditions and is regulated by many cytokines, including transforming growth factor-beta (TGF-beta). In this study, the molecular mechanism of ECM production regulation by TGF-beta was investigated in cultured corneal endothelial cells. The production of ECM components (laminin and fibronectin) was detected in cultured corneal endothelial cells by western blot analysis. To determine the signal transduction pathways, mutant TGF-beta type I receptor (TbetaR-I) and/or Smad protein family members (intracellular signal transducers in TGF-beta signaling) were overexpressed by transfecting their cDNA into the cultured cells, and the effects on ECM production were observed. The production of laminin and fibronectin was stimulated by treatment with TGF-beta1 or TGF-beta2. After transient transfection of cDNA of the constitutively active (CA) mutant of TbetaR-I, the production of laminin and fibronectin was stimulated even in the absence of TGF-beta. The transfection of the dominant negative mutant of TbetaR-I counteracted the effects of TGF-beta. These results confirm that TGF-beta directly stimulates ECM production from corneal endothelial cells through TbetaR-I. The ECM production stimulation by TGF-beta or CA TbetaR-I was accelerated by the overexpression of Smad2, Smad3, and/or Smad4 and inhibited by that of Smad7. These results show that TGF-beta signals connected to ECM production are regulated by Smad family members, located downstream of TbetaR-I. The results of this study show that TGF-beta stimulates ECM production from corneal endothelial cells through TbetaR-I and Smad family transducers.