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Mahbubul Shihan, Mallika Pathania, Yan Wang, Melinda K Duncan; Regulation of TGF-β bioavailability in lens. Invest. Ophthalmol. Vis. Sci. 2017;58(8):3786.
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© ARVO (1962-2015); The Authors (2016-present)
Posterior capsular opacification (PCO) is the major complication of cataract surgery and compromises its outcome. Transforming growth factor beta (TGF-β) signaling mediates PCO, although how TGF-β is activated following cataract surgery is unknown. Fibronectin, an extracellular matrix (ECM) protein, concentrates latent TGF-β into the ECM. In a mouse cataract surgery model, fibronectin mRNA levels upregulate by 24 hours post cataract surgery (PCS), and fibronectin protein is deposited around fibrotic lens epithelial cells (LECs) by 48 PCS, which led us to hypothesize that fibronectin is critical for PCO pathogenesis.
Mice were created lacking fibronectin from the lens (FNcKO) using the Cre-lox system mediated by MLR10-Cre. FNcKO lens morphology was analyzed by conventional histology and scanning electron microscopy. Lens fiber cells were removed from adult mice to model cataract surgery and the capsular bags monitored for PCO development. The dynamic localization of epithelial mesenchymal transition (EMT) and fiber cell markers, latent TGF-β binding proteins (LTBPs), TGF-βs and pSMAD3 activation (downstream mediator of TGF-β signaling) were determined by immunolocalization.
FNcKO mouse lenses are morphologically indistinguishable from wild type (WT). Fibronectin protein deposition around remnant LECs was first observed at 48 hours PCS, while this was greatly increased by 5 days PCS. While both WT and FNcKO mice developed an early fibrotic response at 48 hours PCS as measured by α- smooth muscle actin (αSMA) upregulation, FNcKO mice did not maintain the long term fibrotic response at 5 days PCS. Further, pSMAD3 levels were much lower in FNcKO LECs compared to WT by 5 days PCS. Higher levels of intracellular LTBP1 and TGF-β2 (the most abundant LTBP and TGF-β expressed in the mouse lens) was seen in unoperated LECs of FNcKO mice compared to WT mice, whereas extracellular deposition of LTBP1 is lost after surgery in FNcKO mice compared to WT mice.
Loss of fibronectin after lens vesicle closure does not affect lens morphology, likely due to its low basal expression. However, fibronectin levels increase during PCO and this is crucial for the long term fibrotic response PCS. Mechanistically, in LECs, fibronectin may regulate the secretion and extracellular deposition of latent TGF-β complexes. Overall these data suggest that fibronectin is an essential regulator of TGF-β bioavailability during PCO.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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