EGF exacerbates TGF-β-induced epithelial-mesenchymal transition in the ocular lens: a novel mechanism in cataract formation
- Discipline of Anatomy and Histology, Bosch Institute, University of Sydney, Camperdown, NSW, Australia.
- 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.