Abstract
Purpose: :
Chick sclera consists of fibrous and cartilaginous layers. Lens-wear causes nearly symmetric but opposite changes in the two layers: Negative lenses cause glycosaminoglycan (GAG) synthesis to increase in the cartilaginous layer and decrease in the fibrous layer; positive lenses cause the opposite changes (Marzani et al., 1997). Because Fibroblast Growth Factor (FGF) causes opposite changes in fibroblasts and chondrocytes in tissue culture (Dailey et al., 2005) and causes opposite changes in chondrocytes and osteoblasts (Dailey et al., 2003; Mansukhani et al., 2005), we tested the effect of FGF on GAG synthesis in the fibrous and cartilaginous sclera in chicks.
Methods: :
The fibrous and cartilaginous layers of the sclera (7-mm punches) from normal 3-day-old chicks were separated by dissection, cultured separately with acidic FGF (at 1, 5, 25, or 100 ng/ml) for 20 hr, pulsed with radioactive sulfate and digested with proteinase K overnight. After precipitation with cetylpyridinium chloride and filtration, the net GAG synthesis was estimated by measuring the incorporation of sulfate into GAGs.
Results: :
FGF increased GAG synthesis in the fibrous layer and decreased it in the cartilaginous layer (difference significant by ANOVA, p < 0.001). Across doses, the average increase in the fibrous layer was 32% (65% at 100 ng/ml, p < 0.01, one-sample t-test), and the average decrease in the cartilaginous layer was 42% (62% at 5 ng/ml; 55% at 100 ng/ml, p < 0.001). The dose-response differed significantly in the fibrous and cartilaginous layers (p < 0.05, 2-way ANOVA).
Conclusions: :
FGF has opposite effects on GAG synthesis in the fibrous and cartilaginous layers, which are similar in direction and magnitude to those produced by wearing positive lenses. Thus, visual modulation of FGF levels may be responsible for the coupled, but opposite, directions of growth of these tissue layers in vivo.
Keywords: myopia • sclera