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J.T. Siegwart, T.T. Norton; Proteoglycan mRNA Levels in Tree Shrew Sclera During Minus Lens Treatment and During Recovery . Invest. Ophthalmol. Vis. Sci. 2005;46(13):3335.
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Purpose: To examine changes in proteoglycan mRNA levels in tree shrew sclera during the development of experimentally induced myopia and during recovery. Methods: Competitive RT–PCR was used to measure the levels of decorin, biglycan, lumican, and aggrecan mRNA in the scleras of normal tree shrews (28 days of visual experience [VE], days after natural eyelid opening), tree shrews that received 4 days of monocular –5D lens treatment starting at 24 days of VE, and tree shrews that received 2 days of recovery after 11 days of –5D lens wear (n=5/group). Awake, non–cycloplegic refractive measures (Nidek autorefractor) and A–scan ultrasonography under anesthesia were performed before and after treatment. Results: Decorin mRNA levels in the treated and control eyes were not significantly different from each other or from the normal eyes during lens treatment or recovery. Differential regulation: Surprisingly, aggrecan showed the strongest regulation. The aggrecan mRNA level was 30% lower (P=0.004) in the treated eyes compared to the control eyes after 4 days of lens wear and 51% higher (P=0.004) after two days of recovery. Co–regulation: Biglycan, lumican, and aggrecan mRNA levels were significantly lower by 45% to 65% (P<0.01) in both the treated and control eyes compared to normal eyes after 4 days of lens wear. All were near normal levels after 2 days of recovery except aggrecan in the recovering eye, which was 15% higher. Conclusions: These data suggest that it is primarily the expression of the core protein of the large proteoglycan aggrecan that is differentially regulated in fibrous tree shrew sclera during lens compensation. This is somewhat surprising given that aggrecan is generally considered to be a cartilage proteoglycan. In contrast, regulation of decorin, arguably the most likely candidate proteoglycan given its abundance in fibrous sclera, does not appear to be a significant factor. Modulation of the amount of aggrecan between the collagen lamellae may play an important role in the regulation of scleral extensibility.
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