Role of Arginase I in Diabetes-Induced Endothelial Cell Senescence

Premature senescence of vascular endothelial cells (EC), leading to hypofunction and cessation of cell replication, has been identified as a contributor to vascular endothelial dysfunction (VED) in diabetes. Hyperglycemia is considered a primary cause of diabetic VED. We have shown that excessive arginase (ARG) activity is critically involved in diabetes-induced VED by a mechanism involving decreased availability of the L-arginine substrate for nitric oxide (NO) synthase (NOS) which decreases endothelial NO formation and increases oxidant production. Our data indicate diabetes or high glucose (HG) induced elevation of ARG activity is mediated by increases in ROS and activation of p38 mitogen-activated protein kinase (MAPK). Our data indicate ARG activation and VED during diabetes are associated with reduced NO formation, increased reactive oxygen species and premature EC senescence. Furthermore, knockout of ARG 1, but not ARG 2, in diabetic mice largely prevents premature EC senescence and VED. Thus, we hypothesize that diabetes-induced EC senescence and dysfunction are mediated by increases in ARG1 expression activity. Sirtuin 1 (SIRT1) is a histone decarboxylase, essential for self-renewal of EC and their resistance to stressors. Diabetes and oxidative stress induced decreases in SIRT1 levels are linked to premature EC senescence. We propose to identify cellular sources of ARG involved in diabetes/HG-induced premature EC senescence and VED and test whether overactive ARG induces cellular senescence via a mechanism involving depletion of SIRT1. Aim 1: To identify the cellular source(s) of arginase in diabetes/high glucose (HG)-induced premature EC senescence and VED. Our hypothesis predicts inhibition or absence of ARG1 in EC and/or bone marrow cells in diabetic mice will increase NO production and prevent premature EC senescence and VED in diabetic mice. Exposure of aortas of WT mice to HG or overexpression of ARG1 will accelerate EC senescence and enhance VED. Aim 2: To test whether overactive arginase causes premature EC senescence and VED via decreasing SIRT1. Our hypothesis predicts silencing ARG1 expression will preserve SIRT1 and prevent premature EC senescence and VED in response to HG and that overexpressing ARG1 or 2 will enhance senescence, reduce SIRT1 and increase VED w/wo HG exposure. Conversely, silencing SIRT1 will enhance premature senescence and VED and SIRT1 overexpression will reduce premature senescence and VED w/wo HG exposure. (AHA Program: Scientist Development Grant)