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Todd A. Lydic, Peter N. Jajou, Madalina Opreanu, Louis Glazer, Julia V. Busik, Susanne Mohr; Il-1β And Acid Sphingomyelinase Mediate High Glucose Induced VEGF Production In Human Müller Cells. Invest. Ophthalmol. Vis. Sci. 2011;52(14):3546.
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Increased levels of VEGF and cytokines including IL-1β have been observed in the vitreous of diabetic patients, and the pathology of elevated VEGF in diabetic retinopathy has been the focus of much research. However, the mechanism of retinal VEGF production in response to high glucose is poorly understood. Recent studies suggest inhibition of the caspase-1/IL-1β pathway by the anti-inflammatory compound minocyline may prevent early retinal lesions in diabetic animal models. Cytokine activation of acid sphingomyelinase (ASM), which hydrolyzes cell membrane sphingomyelin to produce ceramide, has also recently been identified as a central pathway in diabetic retinal vascular pathology. However, potential interaction of the caspase-1/IL-1β and ASM pathways has not been explored in VEGF-producing cells. This study tested the hypothesis that pro-inflammatory cytokines and ASM are required for high glucose induced VEGF production in retinal Müller cells.
Vitreous was obtained by vitreorectomy from non-diabetic patients with macular hole and diabetic patients with proliferative retinopathy. Primary cultures of human Müller cells were treated for 12 hours with IL-1β +/- the ASM inhibitor desipramine, or grown in 5mM or 25 mM glucose +/- minocycline (100 µM) for 96 hours. VEGF was measured by ELISA, and lipids were analyzed by tandem mass spectrometry.
Increased VEGF in vitreous of diabetic patients relative to control was positively correlated with a trend toward increased ceramide levels. Exogenous IL-1β induced VEGF production in human Müller cells, suggesting IL-1β drives VEGF production. Inhibition of ASM with desipramine abrogated IL-1β induced Müller cell activation, indicating ASM is an important responder in IL-1β signaling. Müller cells grown in high glucose for 96 hours exhibited increased VEGF production compared to controls. Lipid analysis revealed increased levels of ceramide and decreased levels of sphingomyelin, with an overall increase in the ceramide/sphingomyelin ratio, indicating activation of sphingomyelinases in high glucose. Blockade of IL-1β production with minocycline prevented the increased ceramide/sphingomyelin ratio and Müller cell VEGF secretion in high glucose.
High glucose-induced IL-1β production in human Müller cells increases ceramide via ASM, with subsequent release of VEGF. This novel pathway in the production of VEGF by retinal cells may provide an important target for anti-VEGF therapies to prevent diabetic complications in the retina.
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