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M. R. Frost, H. Gao, C. Montgomery, J. T. Siegwart, Jr., T. T. Norton; Expression of Focal Adhesion-associated mRNA Transcripts in Tree Shrew Sclera During Minus-lens Induced Myopia and Recovery. Invest. Ophthalmol. Vis. Sci. 2009;50(13):3833.
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During the juvenile period of ocular development, visual stimuli control remodeling of the scleral extra-cellular matrix (ECM) and control the viscoelasticity of the fibrous sclera (measured by the creep rate) to produce and maintain emmetropia. During the development of lens-induced myopia (LIM) with a -5 D lens, scleral creep rate rises and peaks at around 4 days. During recovery from LIM, creep rate rapidly returns to normal after 1 day. Recently, it has been suggested that myofibroblasts, contractile cells in the sclera and other tissues, play a role in resisting intraocular pressure to maintain eye size (Phillips & McBrien, IOVS 45:758, 2004). During myopia development in tree shrews, mRNA levels are reduced for integrin receptors 1, 2 and β1, components of focal adhesions that connect the myofibroblasts to collagen (McBrien et al, IOVS 47:4674, 2006), perhaps allowing the collagen layers to slide across each other more easily. To better understand this process, we examined the mRNA expression patterns for additional focal adhesion proteins during the development of LIM and during recovery from LIM.
Two groups (n=8 each) of tree shrews began to wear a monocular -5 D lens 24 days after normal eye opening. The untreated fellow eye served as a control. The LIM group wore the lens for 4 days. The recovery group wore the lens for 11 days and then lens wear was discontinued for 4 days. Real-time PCR was used to assess mRNA levels for vinculin (VCL), paxillin (PXN), focal adhesion kinase (FAK), vimentin (VIM) and syndecan-4 (SDC4).
mRNA levels in the treated eyes, relative to the control eyes (fold differences ± SEM) were: VCL, 1.16 ± 0.19; PXN, -1.07 ± 0.10; FAK, -1.10 ± 0.20; VIM, -1.48 ± 0.23; SDC4, 1.08 ± 0.08. In the recovering eyes, relative to control eyes, the mRNA levels were: VCL, 1.10 ± 0.12; PXN, -1.01 ± 0.09; FAK, 1.09 ± 0.18; VIM, 1.08 ± 0.17; SDC4, -1.04 ± 0.14. None of these differences were statistically significant (paired t-test, two-tailed, alpha = 0.05).
The mRNA levels for these additional proteins involved in focal adhesions do not change during the development of LIM or during recovery from LIM, suggesting that levels of these proteins may not change, despite a reduction in integrin mRNA levels. It may be that there are fewer direct connections between the myofibroblasts and collagen (via integrins), allowing an increased creep rate, while the internal focal adhesion machinery may remain relatively intact, perhaps allowing rapid reformation of focal adhesions during recovery. Alternatively, measurement at the mRNA level may not reflect protein levels during LIM and recovery.
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