HMGA2 Modulates the TGF beta/Smad, TGF beta/ERK and Notch Signaling Pathways in Human Lens Epithelial-Mesenchymal Transition

Background and Objective: Multiple signaling pathways coordinately promote epithelial-mesenchymal transition (EMT) in lens epithelial cells (LECs), where transforming growth factor beta (TGF beta)-mediated signaling plays a central role. But the mechanism of crosstalk among these pathways remains obscure. The objective of this study is to investigate the regulatory effect of the high mobility group protein A2 (HMGA2) on the signaling pathways in lens fibrosis. Methods: The human anterior capsulorhexis specimens were collected. The human SRA01/04 LEC line was cultured and treated with recombinant human TGF beta 2 (5ng/ml). For inhibition of signaling pathways, a selective inhibitor SB431542, U0126 or DAPT was added to LECs respectively. The specific small interfering RNA (siRNA) were transfected to LECs for gene silence. The mRNAs expressions were measured by realtime PCR and the proteins expressions were determined by western blot and immunofluorescent staining. Results: HMGA2 and EMT markers a-smooth muscle actin (SMA), fibronectin (FN) and collagen type I (Col I) were overexpressed in human ASC specimens and TGF beta 2 stimulated EMT in LECs. While blockage of EMT by a selective inhibitor of TGF beta/Smad, TGF beta/extracellular signal-regulated kinase (ERK) or Notch signaling pathway could significantly inhibited HMGA2 protein expression. And silence of HMGA2 by siRNA could significantly inhibit TGF beta 2 induced expression of EMT markers including FN, Col I, collagen type IV (Col IV), key transcription factors Snail and Slug, and remarkably upregulate the epithelial markers E-cadherin and tight junction protein (ZO-1). In addition, silence of HMGA2 gene could abrogate TGF beta 2 induced phosphorylation of Smad2, Smad3 as well as ERK1/2. Blockage of HMGA2 could also inhibit the upregulation of Jaggedl, Notch2, and Notch3 induced by TGF beta 2. Conclusion: This study indicated that HMGA2 functions as a shared effector in TGF beta 2-induced lens fibrosis, modulating the signaling network necessary for EMT in a positive feedback loop.