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A. Luebke, J.A. Rada; Growth Factor Regulation of Scleral Proteoglycan Synthesis . Invest. Ophthalmol. Vis. Sci. 2003;44(13):414.
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Purpose: Recent studies have shown that the rate of scleral proteoglycan synthesis changes significantly during growth, aging and the development of myopia. Of much interest therefore, are the mechanisms by which scleral proteoglycan synthesis and accumulation are regulated in vivo, in order to better understand the mechanisms responsible for scleral growth and development. Consequently the current study was designed to characterize the effect of growth factor regulation on proteoglycan synthesis in the porcine eye as well in human scleral fibroblasts. Methods: Punches (5mm) of sclera were obtained from the equatorial region of fresh porcine eyes and immediately placed in organ culture in Dulbecco's Modified Medium (DMEM) containing 100 uCi/ml of 35SO4 and ßFGF (10 ng/ml), IGF-1 (0.01-1 ug/ml), TGF-ß1 (5 ng/ml), TGF-ß2 (5 ng/ml), or all-trans retinoic acid (10-5-10-7 M). Scleral punches were incubated at 37°C for 48 hrs. Sclera were then weighed, digested with proteinase K (0.5 ug/ml) and the rate of proteoglycan synthesis was estimated by measuring the rate of 35SO4 incorporation into CPC-precipitable glycosaminoglycans. Additionally, the rate of proteoglycan synthesis was evaluated in cultures of human scleral fibroblasts isolated by explant culture from donors aged 2, 24, 33, 37 and 67 years with and without IGF-1 treatment [0.1 ug/ml in platelet poor horse serum – (PPHS)]. Results: IGF-1 increased the rate of proteoglycan synthesis in organ cultures of porcine sclera as compared with sclera treated with DMEM alone (+ 289%, p < 0.05). TGF-ß1, TGF-ß2, and ßFGF had no significant effect on the rate of scleral proteoglycan synthesis. Similarly, retinoic acid had no effect on sclera proteoglycan synthesis at concentrations of 10-5-10-7 M. Additionally, IGF-1 increased the rate of proteoglycan synthesis in cultures of human scleral fibroblasts as compared with fibroblasts treated with PPHS alone only in the 24 and 33 year old fibroblast cultures (+ 275% p < 0.001 and + 177% p < 0.001, respectively). No significant increases in proteoglycan synthesis were seen in the 2, 37 or 67 year old human scleral fibroblast cultures. Conclusions: These results suggest that IGF-1 may act as a trophic agent for scleral growth and may be useful in strategies to reverse or prevent scleral proteoglycan loss associated with myopia development. We speculate that levels of IGF-binding proteins (IGF-BP) may be modulating the level of IGF-1 stimulation of scleral proteoglycan synthesis in different aged donors.
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