Abstract 003: Direct and Indirect Effects of Prostaglandin E 2 and Its EP1/EP3 Receptors on Dendritic Cell Activation in Mice with L-NAME/High Salt-induced Hypertension

Abstract

We recently identified a pathway underlying immune activation in hypertension. Proteins oxidatively modified by reactive γ-ketoaldehydes (isoketals) accumulate in dendritic cells (DCs). These are immunogenic and lead to subsequent T lymphocytes activation. The local signals that stimulate DCs to accumulate isoketal adducts remain undefined. Prostaglandin E 2 (PGE 2 ) has been implicated in the inflammation associated with hypertension. We hypothesized that PGE 2 via its EP3 receptor contributes to DC activation in hypertension. EP3 -/- mice and wild type (WT) littermates were exposed to sequential hypertensive stimuli involving an initial 2-week exposure to the NOS inhibitor L-NAME (LN) in drinking water, a 2 week washout period, and a subsequent 4% high salt diet (HS) for 3 weeks. In WT mice, this protocol increased systolic pressure from 123±2 to 148±8 mmHg (p<0.05), and renal CD4 + and CD8 + effector memory T cells by 2 to 3 fold. This was associated with a striking accumulation of isoketal protein adducts in splenic DCs. However, the increases in blood pressure, renal T cell infiltration and DC isoketal formation were completely prevented in EP3 -/- mice. We further hypothesized that EP3 receptors contribute to oxidative stress production in the kidney. As measured by dihydroethidium with confocal microscopy, the LNHS protocol induced marked increases in superoxide production in WT mice, but not in EP3 -/- mice. To examine the direct effects of PGE 2 , splenic DCs were incubated with PGE 2 in vitro for 24 hours. PGE 2 dose-dependently increased isoketal-adduct formation in DCs (vehicle: 8.8±5.1% vs. 50 nM PGE 2 : 41.4±11.7%, p<0.05). Interestingly, this effect was not blocked by the EP3 receptor antagonist DG-041 (30 nM), but was completely prevented by the EP1 receptor blocker SC-51322 (20 μM). These data indicate both direct and indirect roles of PGE 2 in DC activation in hypertension. In vivo, PGE 2 has a predominant effect on EP3 receptors to enhance renal vascular ROS production, which likely leads to isoketal-adduct formation and accumulation in DCs. PGE 2 also acts directly on DCs via its EP1 receptors to stimulate intracellular isoketal formation. Together, these findings provide additional information as to how PGE 2 modulates inflammation in hypertension.