EGF exacerbates TGF-β-induced epithelial-mesenchymal transition in the ocular lens: a novel mechanism in cataract formation

Shu DY1,2 and Lovicu FJ1,2

  1. Discipline of Anatomy and Histology, Bosch Institute, University of Sydney, Camperdown, NSW, Australia.
  2. Save Sight Institute, Sydney Medical School, Sydney, NSW, Australia.

The ocular lens is surrounded by a cocktail of growth factors that differentially influence cellular behaviour. While many of these promote normal physiological processes, such as EGF, TGFβ induces lens pathology, namely, epithelial-mesenchymal transition (EMT) leading to cataract and subsequent visual impairment. This study seeks to decipher how EGF impacts on TGFβ-induced EMT in the lens. Lens epithelial cells (LECs) in explants prepared from 21-day-old Wistar rats were treated with either 200 pg/ml TGFβ2, 5 ng/ml EGF, or a combination of these, with or without pre-treatment with PD153035 (EGFR inhibitor), U0126 (MEK inhibitor) or SIS3 (Smad3 inhibitor). Co-treatment with TGFβ2 and EGF not only resulted in a more pronounced morphological elongation and transdifferentiation of LECs into myofibroblastic cells, compared to TGFβ2 alone, but had higher protein expression levels of mesenchymal markers (α-SMA and tropomyosin). Adding EGF to a less potent dose of TGFβ2 (50 pg/ml) induced LECs to undergo EMT similar to treatment with a standard dose of TGFβ2 at 200 pg/ml over 5 days culture. EGF alone did not induce EMT in LECs. Co-treatment with EGF and TGFβ2 activated a complex and integrated network of Smad2/3-, ERK1/2- and EGFR-signalling pathways. Inhibition of EGFR-signalling using PD153035 blocked the EMT response induced by co-treatment with EGF and TGFβ2. Taken together, our data show that EGF can exacerbate the TGFβ2-induced EMT in LECs, highlighting the importance of EGFR-signalling in cataract formation. By directly blocking EGFR signalling, the activity of both EGF and TGFβ2 can be simultaneously suppressed, thus serving as a potential drug target for treating cataract.