Lens Specific Expression of TGF–ß Induces Anterior Subcapsular Cataract Formation in the Absence of Smad3 Signaling

Abstract

Abstract: : Purpose: Lens specific–expression of active TGF–ß in transgenic mice induces epithelial–to–mesenchymal transition (EMT) of lens epithelial cells and the formation of fibrotic plaques similar to that observed in anterior subcapsular cataracts (ASC) in humans. It has been shown that Smad3, a mediator of TGF–ß signaling, is required for the EMT of lens epithelial cells and plaque formation in a lens injury model. Here we investigate the requirement for Smad3 in ASC using a transgenic TGF–ß/Smad3 knockout mouse model. Methods: TGFß1 transgenic mice (containing a human TGFß1 human cDNA construct expressed under the αA–crystallin promoter) were bred with Smad3 null and heterozygote mice to generate mice with the following genotypes: TGFß1/Smad3^–/– (null), TGFß1/Smad3^+/–, TGFß1/Smad3^+/+ and non–transgenic/Smad^+/+ (controls). Lenses from 3 month old mice of each genotype were dissected and either prepared for histology and immunofluorescence or for optical analysis. Results:Lenses from TGFß1/Smad^+/+ and TGFß1/Smad3^+/– mice exhibited distinct fibrotic plaques that were immunoreactive to α–smooth muscle actin (αSMA), demonstrative of EMT. Importantly, lenses from TGFß1/Smad3^–/– mice also exhibited subcapsular plaques that were αSMA positive, albeit the plaques were reduced in size and number compared to mice with Smad3 wild–type or heterozygous backgrounds. Optical analyses revealed that the greatest increase in BVD variability (decreased sharpness of focus) was noted for TGFß1/Smad^+/+ (0.420±0.055 mm) lenses when compared to lenses from control mice (0.061±0.003 mm). TGFß1/Smad3^+/– (0.225±0.400 mm) lenses exhibited the next greatest increase over control lenses, whereas, lenses from TGFß1/Smad3^–/– (0.102±0.007 mm) mice showed the least increase in BVD variability, yet this was still significantly greater than that of controls lenses. Conclusions:These findings demonstrate that lens specific expression of TGFß1 induces anterior subcapsular plaque formation. However, in the absence of the Smad3 signaling mediator, the plaque formation occurs at a much lesser extent. This suggests that alternative TGF–ß signaling molecules and pathways participate in this model of ASC.

Keywords: cataract • optical properties • transgenics/knock-outs