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R.N. Frank, A. Kennedy, B. Yao, A. Walker; Decreased Crystallin Expression in Diabetic and Galactosemic Rat Retinas . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1737.
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A possible cause of diabetic retinopathy is the up– or down–regulation of specific genes because of chronic hyperglycemia. We therefore investigated changes in gene and corresponding protein expression in the retinas of chronically diabetic or galactosemic rats.
Sprague–Dawley rats were divided into 3 groups: control; 30% galactose diet for 4 mo.; and 30% galactose diet for 2 mo., then standard diet for 2 mo. BB/Wor spontaneously diabetic rats (a model for type 1 diabetes) were assigned to 4 groups: control (a genetically related, non–diabetic strain); poor blood glucose control; well controlled; and poorly controlled for 2 mo., then good control for 2 mo. Rats were euthanized after 4 mo., retinas were removed and extracted for mRNA, reverse transcribed to cDNA which was analyzed on Affymetrix rat CNS chips. Protein extracts of the retinas were subjected to proteomic analysis using ITRAQ techniques.
In 4 mo. galactose–fed rats, retinal α, ß, and γ crystallin proteins all decreased to an average of 32 + 9 (S.D.)% of control. When galactose was withdrawn after 2 mo., crystalline protein levels at 4 mo. were 45 + 11% of control. Mean crystallin mRNA levels in these groups were 37% (galactose alone) and 75% (galactose followed by normal diet) of control (p < 0.05). In the poorly controlled diabetic rats, the crystallin proteins declined to 78 + 15% of the non–diabetic controls. Poorly controlled diabetes followed after 2 mo. by well–controlled diabetes, and well–controlled diabetes for 4 mo. had crystallin protein levels averaging 103 + 18% and 136 + 28%, respectively, of the non–diabetic controls. Crystallin genes in the diabetic groups did not change significantly from controls.
The role of crystallins in the retina is unknown, but their decrease in diabetic or galactosemic rats, and slow recovery with restoration of normoglycemia suggests the loss of a protective effect, perhaps against oxidative stress. The changes in short term diabetic rats are not large, but may produce damage long term in a chronic disease state.
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