Abstract
Purpose: :
Our goal was to investigate cataract incidence and gene expression in rat lenses 9 months after particle radiation.
Methods: :
With IACUC approval, Sprague-Dawley rats were irradiated with either 10 or 100 cGy of 600 MeV/u iron ions (LET~180 keV/micrometer) at the NASA Space Radiation Lab (NSRL) at Brookhaven National Lab (BNL). Lenses were examined with fully-dilated pupils using a slit-lamp monthly for 9 months. At necropsy, images of the lenses were obtained ex vivo. Lenses were either frozen without fixation for mRNA & protein analyses, or fixed for immunohistochemical analyses with specific molecular probes. mRNA was isolated from whole irradiated lenses and analyzed for quantitative changes in gene expression with a Rat ECM RT2 Profiler Array (SABiosciences, Inc). Fold changes in gene expression between the treated and unirradiated control lenses were considered significant at the p<0.09 level.
Results: :
Quantitative gene expression analyses of lenses show high reproducibility within control and treatment groups. Cataractous lesions in iron-irradiated animals are multifocal and polymorphic, with anterior cortical opacifications. Opacities appear to aggregate in the equatorial periphery suggesting likely transition at the lens bow region. Posterior subcapsular cataractous dots are clearly visible in 50% of the lenses. 10 cGy-Iron-ion-irradiated rat lenses with early cataractous changes show significant 3- to 4-fold increases in CAM & ECM functional gene groups, including > 3-fold changes in the CD44 antigen reported in cataractous human lenses. 100 cGy-Iron-ion-irradiated cataractous rat lenses show a completely different gene response with only 2 ECM & CAM genes increased 2- to 3-fold, and two CAM genes significantly down-regulated 2- to 3-fold.
Conclusions: :
We show high responsiveness of ECM gene families particularly in CD44 after a low radiation dose to the lens, and decreased expression after a 10-fold higher radiation dose. Low-dose iron ions are associated with early cataractous changes contributing to significant and persistent ECM remodeling responses in vivo, consistent with published CD44 expression in cataractous human lenses. High-dose iron ions resulted in a different ECM genetic fingerprint with dampened ECM & CAM gene expression profiles.
Keywords: cataract • gene/expression • differentiation