Abstract
Purpose :
ApolipoproteinD (ApoD), an atypical lipoprotein, is a carrier protein for lipids (fats) and important for lipid metabolism. It is associated with retinol-binding protein levels, and retinoic acid is involved in signalling the direction of ocular growth (McFadden et al 2004). ApoD also interacts with other factors implicated in myopia development, including insulin, collagen, proteoglycans and ApoA; the latter proposed as a “STOP” growth signal in chick eyes (Bertrand et al 2006). We studied the expression of ApoD during the development and recovery from myopia in a mammalian retina.
Methods :
Myopia was induced in one eye in 21 guinea pigs with a -5D spectacle lens worn from 4-15 days of age. Whole retinas were extracted at 15 days of age from three randomly assigned groups: myopia (n=8); short recovery (n=7); or long recovery (n=6). Animals in the two recovery groups had the lenses removed for 48 h (short) or 96 h (long) prior to retinal extraction. Controls were matched fellow eyes and a normal untreated group of the same age (n=6). Refractive error was measured in cyclopleged eyes on day 14 (myopia, recovery short), and on day 11 and 14 (recovery long) in both eyes to confirm the degree of induced myopia. Semi-quantitative real-time PCR was used to quantify mRNA levels of ApoD in whole retina, using beta-Actin as a reference gene.
Results :
The mean difference in refractive error between the -5D lens-treated and fellow eyes was -6.2±0.6 (p<0.001). There was no difference in mean normalised expression of ApoD between the myopic and fellow eyes after 11 days of spectacle lens wear (0.112 vs. 0.111 respectively, p=0.95); or between fellow eyes and eyes from untreated animals. However, the expression of ApoD was reduced during the recovery from myopia, being significantly lower relative to fellow eyes after recovery from myopia for 48 h (recovery short eyes: 0.093, fellow eyes: 0.124, p<0.05), and both the refractive error and ApoD expression started to return to normal levels after 96 h of recovery (recovery long eyes: 0.121; fellow eyes: 0.141, p=0.21).
Conclusions :
A significant downregulation occurred in retinal ApoD mRNA within 2 days of recovery from myopia, a period in which inhibitory eye growth is initiated in the mammalian eye. This indicates that apolipoprotein pathway(s) are involved in the early retinal signalling of inhibitory eye growth.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.