Abstract
Purpose: :
To demonstrate that TNFα actions in the diabetic retina regulate insulin receptor signaling and apoptosis
Methods: :
Work was completed in human retinal endothelial cells grown in normal glucose (5mM) or high glucose (25mM) and treated with TNFα, TNFα siRNA, and SOCS3 siRNA. Analyses included Western blotting and ELISAs for apoptotic factors, TNFα, and cell death assays. For animal work, both type I (streptozotocin-treated) and type II (BBZ/Wor) diabetic rats were used. Whole retinal lysates from the diabetic animals were assessed for levels of insulin activity, IRS-1 activity, TNFα, SOCS3, and apoptotic proteins.
Results: :
Hyperglycemia increases TNFα, which increases IRS-1Ser307 phosphorylation and retinal endothelial cell death. Hyperglycemia also increases levels of suppressor of cytokine signaling 3 (SOCS3). Knockdown of TNFα decreases cell death, while increasing insulin signaling proteins. Knockdown of SOCS3 produced the same responses as TNFα knockdown.
Conclusions: :
Results suggest that increased TNFα levels observed in hyperglycemia leads to increased apoptosis through inhibition of insulin receptor signaling in the retina. TNFα activates a number of independent pathways in retinal endothelial cells; all resulting in increased cell death. Inhibition of TNFα actions during hyperglycemia may prevent insulin resistance in the retina
Keywords: diabetic retinopathy • apoptosis/cell death • inflammation