Abstract 12278: ROS Signaling Facilitates FOXO-3a/FBXO-Dependent Increase in Vascular BK-β1 Degradation in Diabetes Mellitus
Background: We have reported that the forkhead box O subfamily transcription factor-3a (FOXO-3a)/the F-box only (FBXO) protein axis plays a pivotal role in the regulation of BK-β1 expression in diabetic vessels. However, the underlying upstream signaling is unclear. ROS overproduction is a common feature of vascular pathology in diabetes. We hypothesize that ROS-associated signaling is involved in the FOXO-3a/FBXO-mediated downregulation of BK-β1 expression in diabetes.
Methods and Results: To test this hypothesis, we employed a combination of cellular biology, patch clamp and videomicroscopy techniques. We found that BK-β1 expression in streptozotocin (STZ)-induced diabetic mouse aortas was reduced by 2.4 folds, accompanied by significant augmentation in atrogin-1 expression and decrease of p-Akt(S473) expression but no change in the total Akt level. Similar results were observed in human coronary smooth muscle cells (SMCs) cultured with high glucose (HG 22 mM). The effects of HG on atrogin-1 and BK-β1 expression were mimicked by a 12-h incubation with 50 μ M H2O2. PKCβ activation promotes ROS generation in vascular SMCs. We found that there was a 3- to 4-fold increase in PKCβ expression in diabetic mouse aortas and in human coronary SMC cultured with HG. A 24-h incubation with 1 μ M Go-6976 (a PKCβ activator) markedly attenuated p-Akt(S473) and p-FOXO(T32) expression in human coronary SMCs, leading to accelerated BK-β1 degradation. Coronary dilation to NS1619 (a BK channel activator) and coronary BK channel activation in response to DHS-1 (a BK-β1 specific activator) were preserved in diabetic mice after a 2-wk administration of LY333531 (10 mg/kg/day), a PKCβ inhibitor. In addition, diabetic mouse coronaries overexpressing BK-β1 by adenoviral (Ad-BK-β1) infection restored normal dilation to NS-1619, while Ad-LacZ infection had no effect.
Conclusions: Oxidative stress facilitates the FOXO-3a/FBXO-dependent increase in vascular BK-β1 degradation in diabetic vessels. Enhanced ROS signaling involves activation of PKCβ and inhibition of Akt phosphorylation. Overexpression of BK-β1 protected BK channel-mediated coronary function in diabetes. Hence, BK-β1 is a potential molecular target for the treatment of diabetic vascular complications.
- © 2011 by American Heart Association, Inc.