Abstract
Transforming growth factor (TGF)-β-induced epithelial-mesenchymal transition (EMT) leads to the formation of ocular fibrotic pathologies, such as anterior subcapsular cataract and posterior capsule opacification. Remodeling of the actin cytoskeleton, mediated by the Rho family of GTPases, plays a key role in EMT, however, how actin dynamics affect downstream markers of EMT has not been fully determined. Our previous work suggests that myocardin related transcription factor A (MRTF-A), an actin-binding protein, might be an important mediator of TGFβ-induced EMT in lens epithelial cells. The aim of the current study was to determine the requirement of RhoA/ROCK signaling in mediating TGFβ-induced nuclear accumulation of MRTF-A, and ultimate expression of α-smooth muscle actin (αSMA), a marker of a contractile, myofibroblast phenotype. Using rat lens epithelial explants, we demonstrate that ROCK inhibition using Y-27632 prevents TGFβ-induced nuclear accumulation of MRTF-A, E-cadherin/β-catenin complex disassembly, and αSMA expression. Using a novel inhibitor specifically targeting MRTF-A signaling, CCG-203971, we further demonstrate the requirement of MRTF-A nuclear localization and activity in the induction of αSMA expression. Overall, our findings suggest that TGFβ-induced cytoskeletal reorganization through RhoA/ROCK/MRTF-A signaling is critical to EMT of lens epithelial cells.
Highlights
Cataract is an opacification of the ocular lens that results in obstruction of light and gradual loss of vision, and it continues to be the leading cause of blindness worldwide, affecting nearly 20 million people [1,2]
Explants were immunostained for rhodamine-phalloidin, which revealed that TGFβ treatment triggered polymerization of actin into filamentous actin (F-actin)–containing stress fibers positive for α-smooth muscle actin (αSMA) (Figure 2A; n ≥ 5 per treatment)
Actin cytoskeletal reorganization is a phenotypic change widely associated with TGFβ-induced epithelial-mesenchymal transition (EMT)
Summary
Cataract is an opacification of the ocular lens that results in obstruction of light and gradual loss of vision, and it continues to be the leading cause of blindness worldwide, affecting nearly 20 million people [1,2]. Cataract surgery in developed countries is the most common operative procedure performed, while effective treatment is not readily available in economically developing countries. In reaching the target of reducing avoidable visual impairment by 25% by the year 2019, the World Health Organization has outlined a global eye health action plan that prioritizes offering cataract surgery to those in need, further increasing the number of cataract surgeries performed. Cataract surgery is not without its problems and can lead to secondary loss of vision, known as posterior capsule opacification (PCO) (for review; 3,4). Ocular trauma [5,6], implantable contact lenses [7,8], and diseases such as atopic dermatitis [9,10] and retinitis pigmentosa [11] can trigger
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