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J. Comander, G. Trichonas, A. Thanos, X. Koufomichali, Y. Morizane, S. R. Montezuma, D. Vavvas; The Role of AMP-Dependent Kinase (AMPK) in Diabetic Retinopathy. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5909.
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Diabetic retinopathy results in a hypoxic, metabolically stressed retina which secretes mediators that promote neovascularization. This ischemic state of increased energy expenditure and decreased energy supply depletes ATP and increases AMP levels, leading to activation of the energy sensor protein AMP-dependent kinase (AMPK). Previously it has been shown that AMPK activation leads to increased levels of HIF1, VEGF and eNOS, molecules important in diabetic retinopathy and neovascularization. We studied the role of the AMPK pathway in the pathogenesis of diabetic retinopathy, using the streptozocin-induced diabetic rat model.
Sprague Dawley rats were injected with 60 mg/kg intraperitoneal streptozocin to induce hyperglycemia (>550 mg/dL) and diabetic retinopathy. At two weeks and six weeks after induction, retinas were dissected in chilled PBS under a dissecting microscope. Standard lysis buffer was used to lyse and homogenize the retina followed by SDS-PAGE gels and Western blotting. We quantified expression levels of total AMPK, phospho-AMPK, and the 1 and 2 catalytic subunits. We also measured levels of phospho-Activated Acetyl-CoA Carboxylase (pACC), a downstream target and effector of AMPK.
Two weeks after induction of diabetic retinopathy (N=12 total eyes), protein levels of pACC increased 29% (p=0.003), while levels of pAMPK and AMPK1 remained stable. Six weeks after induction of diabetic retinopathy (N=14 total eyes), protein levels of AMPK increased 48% (p=0.03), with a trend toward increased levels of p-AMPK (40%, p>0.05) and pACC (12%, p>0.05).
Expression levels of both AMP-dependent kinase and the phosphorylated form of a target protein are significantly elevated in the retinas of a rat model of diabetic retinopathy. As AMPK activity is necessary for angiogenesis in other models, more experiments are needed to determine if AMPK activity is necessary in the progression of diabetic retinopathy, and to address its potential as a novel therapeutic target. The severity of diabetic retinopathy of wild type versus knockout mice for the two catalytic isoforms of AMPK, 1 and 2, is under investigation.
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