Investigation into the Unique Roles of MMP-2 and MMP-9 in TGFβ-Induced Epithelial-Mesenchymal Transition in Lens Epithelial Cells

Abstract

<p>Epithelial-mesenchymal transition (EMT) is a pathological process leading to the formation of anterior subcapsular cataract (ASC). Mediated by transforming growth factor beta (TGFβ), EMT involves the transformation of the monolayer of lens epithelial cells (LECs) into spindle-shaped myofibroblasts, which manifest as plaques directly beneath the lens capsule. TGFβ-induced EMT leading to ASC has been associated with the upregulation of two specific matrix metalloproteinases (MMPs), MMP-2 and MMP-9. Having identified MMP-2 and MMP-9 as participants in the formation of cataracts, the specific roles of either of these MMPs have yet to be determined.</p> <p>The current study utilized MMP-2 and -9 knockout (KO) mice to determine their unique roles in TGFβ-induced EMT. First, adenoviral injection of active TGFβ1 into the anterior chamber of MMP-2 KO mice led to the formation of distinct αSMA-positive anterior subcapsular plaques, in contrast to treated MMP-9 KO eyes, which were resistant. Additionally, an <em>ex vivo </em>mouse LEC explant system was established in these KO lines. In the isolated lens epithelial explants, TGFβ triggered a transformation of LECs from a tightly packed cuboidal monolayer to an elongated mesenchymal phenotype. This process involved a disruption in epithelial cell contacts indicated by a loss of E-cadherin, and an acquisition of myofibroblast marker, αSMA. In the absence of MMP-2, TGFβ was still able to induce EMT with E-cadherin loss and concurrent αSMA expression. In contrast, LEC explants from MMP-9 KO mice treated with TGFβ did not acquire a characteristic spindle-like phenotype and showed substantially less αSMA expression. Results from both of these approaches were consistent; MMP-2, but not MMP-9, KO mice stimulated with TGFβ exhibited phenotypic changes typical of those described in ASC formation, namely a loss in cell attachments, multilayering of previously epithelial-like cells, and αSMA reactivity. Therefore, while MMP-2 is not necessary, MMP-9 is critical to TGFβ-induced EMT in LECs.</p>