Reduction of corneal scarring in rabbits by targeting the TGFB1 pathway with a triple siRNA combination

Purpose: The transforming growth factor beta1 (TGFB1) pathway has been linked to fibrosis in several tissues including skin, liver, kidney and the cornea. In this study, a RNA interference-based approach using siRNAs targeting three critical scarring genes, TGFB1, TGFB receptor 2 (TGFBR2) and connective tissue growth factor (CTGF), was tested for effects on reducing alpha smooth muscle actin (SMA) and corneal scarring (haze) in excimer laser ablated rabbit corneas. Methods: Levels of TGFB1 and CTGF mRNAs were measured using qRT-PCR in the epithelial and endothelial cell layers of normal and excimer ablated rabbit corneas at 30 minutes, 1 day and 2 days after ablation. Two different scarring models were utilized to assess the effects of the triple siRNA combination on corneal scarring. In the first model, rabbit corneas were unevenly ablated creating a mesh pattern then treated immediately with the triple siRNA combination. After 1 day the ablated areas of corneas were collected and levels of mRNAs for TGFB1, TGFBR2 and CTGF were measured. After 14 days, levels of mRNA for SMA were measured and SMA protein immunolocalized in frozen sections. In the second model, rabbit corneas were uniformly ablated to a depth of 155 microns followed by three daily doses of the triple combination of siRNA. After 14 days, corneas were photographed and images were analyzed using Image J software to assess corneal scarring. Corneas were also analyzed for levels of SMA mRNA. Results: In both unwounded and wounded corneas, levels of TGFB1 and CTGF mRNA were always significantly higher in endothelial cells than in epithelial cells (10 to 30 fold). Thirty minutes after injury, levels of both TGFB1 and CTGF mRNAs increased approximately 20-fold in both epithelial and endothelial cells, and further increased approximately 60-fold in 2 days. In the first therapeutic experiment with a single siRNA dose, two of three rabbits showed substantial reductions of all three target genes after 1 day with a maximum knock down of 80% of TGFb 1, 50% reduction of TGFBR2 and 40% reduction of CTGF mRNA levels and reduced SMA mRNA at day 14. In the second therapeutic experiment with multiple doses of siRNA treatment, both rabbits showed a ~22% reduction in scar formation at day 14 as calculated by image analysis. There was also a corresponding 70% and 60% reduction of SMA RNA expression. Conclusion: These results demonstrate that both TGFB1 and CTGF dramatically increase in rabbit corneal epithelial and endothelial cells after injury. Treatment of excimer ablated rabbit corneas with a triple combination of siRNAs effectively reduced levels of the target genes and SMA, leading to reduced corneal scarring at 14 days, suggesting that this triple siRNA combination may be an effective new approach to reducing scarring in cornea and other tissues.