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Lindsey R. Hollaway, Wengtse Lam, Jody Summers Rada; Visually Induced Changes in Aggrecan Gene Expression within the Chick Sclera. Invest. Ophthalmol. Vis. Sci. 2011;52(14):6294.
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In chicks, the rate of synthesis of sulfated glycosaminoglycans (GAGs) in the posterior sclera is directly correlated with the rate of vitreous chamber elongation in response to visually induced changes in ocular growth. Previous studies indicate that significant changes in scleral GAG synthesis occur rapidly (within hours) in response to imposed defocus. In order to gain clues as to the mechanisms that control ocular size and refraction, the present study tests the hypothesis that rapid changes in mRNA pools for aggrecan play a role in regulating changes in sulfated GAG synthesis within the chick sclera.
Chicks were form vision deprived (FD) for 10 days followed by recovery period of 0 - 96 hours. The rate of proteoglycan synthesis by isolated sclera punches (5mm) of control and treated eyes was estimated in vitro by the incorporation of 35SO4 in CPC-precipitable GAGs. Total RNA was isolated from additional scleral punches from control and treated eyes and aggrecan mRNA pools were measured using RT-qPCR. GAPDH was used as a reference gene for all RT-qPCR samples.
Following 10 days of FD (0 hrs recovery) the rate of sulfated GAG synthesis was significantly increased in FD eyes as compared to controls (+63.59 ±16.22%, p <0.0001). Following 12 hrs of recovery, sulfated GAG synthesis decreased to levels significantly below controls (-22.62± 7.28%, p <0.001). Following 10 days of FD, aggrecan mRNA was increased in treated eyes as compared with controls (+124%, p<0.01). Within 3 hrs of recovery, aggrecan mRNA pools were decreased to 17% of that in FD eyes (p <0.01) and were not significantly different from paired controls. Aggrecan increased in treated eyes over the next 24 hrs to levels significantly higher than controls (+129%, p <0.05) and returned to control levels by 4 days of recovery.
These results suggest that visually induced changes in sclera GAG synthesis are initiated by rapid changes in aggrecan mRNA pools. An understanding of the regulation of aggrecan mRNA turnover may elucidate elements of the final pathway in the retina-to-sclera signaling cascade.
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