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T. Fox, X. Wu, T.W. Gardner, M. Kester; Diabetes Alters Integral Lipid Raft Proteins in the Retina . Invest. Ophthalmol. Vis. Sci. 2003;44(13):3908.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: We have previously shown that insulin receptor-coupled PI3-K activity is decreased in the retinas of rats with diabetes. The present study investigates the potential roles of lipid rafts to influence insulin signaling in the diabetic state. It is hypothesized that diabetes affects lipid raft domains by altering expression and/or phosphorylation of integral lipid raft proteins, including caveolin and flotillin. Methods: Diabetes was induced in Sprague Dawley rats by streptozotocin injection. After four weeks, diabetic rats and age-matched controls were sacrificed and the retinas enucleated and frozen in liquid nitrogen. Retina homogenates were subjected to western blotting for the lipid raft markers flotillin-1 and caveolin-1. Retinas were subjected to a detergent-free discontinuous sucrose gradient to determine the association of the insulin receptor, AKT and PKC isoforms in lipid-raft enriched fractions. Results: Four weeks of diabetes resulted in a ~43% decrease (n=6, p = 0.0004) in caveolin-1 expression compared to their age-matched controls. However, while flotillin-1 expression remained unchanged in these diabetic animals compared with controls, flotillin-1 exhibited a mobility shift on the blot suggesting a change in its phosphorylation state. The insulin receptor ß subunit and AKT were found to be associated with lipid raft domains. Furthermore, five different isoforms of PKC (α, ßI ßII, ε, ζ) were also found to be associated with these lipid raft domains. When sectioned eyes were stained for caveolin-1, expression was predominantly localized to blood vessels as determined by counterstaining with occludin which has been shown previously to be localized at the tight junctions of blood vessels in the retina. Conclusions: A decrease in caveolin-1 expression, presumably in blood vessels, could have important ramifications for signaling events in endothelial cells, as evidenced by the co-localization of several kinases to these domains. These studies begin to elucidate the mechanism by which diabetes alters signaling by inducing changes in lipid raft structure and function, which could consequently influence the development of diabetic retinopathy.
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