Prostaglandin E2 and Its EP3 Receptors Contribute to Dendritic Cell and Memory T Cell Activation in Mice with L‐NAME/High Salt‐induced Hypertension
Authors: Xiao Liang , Itani Hana A , Kraemer Maria P , Breyer Richard M , Harrison David G 
Published: November 2023

We recently identified a pathway that underlies immune activation in hypertension. Proteins that are oxidatively modified by highly reactive γ‐ketoaldehydes (isoketals) accumulate in dendritic cells (DCs), and these isoketal‐adducted proteins are immunogenic and lead to subsequent activation of T lymphocytes. The local signals that stimulate DCs to accumulate isoketal adducted proteins remains undefined. Mediators such as angiotensin II, norepinephrine and prostaglandin E2 (PGE2) have been implicated in the inflammation associated with hypertension and could play a role in DC activation. To examine potential roles of these mediators, splenic dendritic cells were isolated from naïve wild type (WT) C57Bl/6 mice with CD11c magnetic beads, and plated in RPMI medium. These cells were then treated with angiotensin II, norepinephrine or PGE2 for 24 hours and flow cytometry was used to detect intracellular isoketal‐adducted proteins. Angiotensin II had no effect on the presence of isoketal‐adducts in DCs. Likewise 24 hours exposure of DCs to norepinephrine (3 mmol/L) did not stimulate isoketal formation in DCs, however treatment with norepinephrine for 48 hours caused a moderate increase of isoketal adducts in DCs (baseline: 21.1±2.6% vs. 3 μmol/L NE: 37.1±5.3%, p<0.05). In striking contrast, 24 hours exposure to PGE2 dose‐dependently increased isoketal‐adduct formation in DCs (vehicle: 8.8±5.1% vs. 50 nmol/L PGE2: 41.4±11.7%, p<0.05). To study the in vivo role of PGE2 and its EP3 receptor in the immune activation in hypertension, both EP3−/− mice and their WT littermates were exposed to sequential hypertensive stimuli involving an initial exposure to the NOS inhibitor L‐NAME in drinking water, a 2 week washout period and then a 4% high salt diet. This protocol increased systolic pressure in WT animals (148±8 mmHg vs. baseline: 123±2 mmHg, p<0.05), while not changing blood pressure in the EP3−/− mice (128±6 mmHg vs. baseline: 118±8 mmHg). Importantly, the L‐NAME/high salt protocol led to a 2 to 3‐fold increase in renal CD4+ and CD8+ effector memory T cells in WT mice, but no increase in the EP3−/− mice. Flow cytometry indicated that during the L‐NAME/high salt protocol splenic DCs develop a striking accumulation of isoketal adducts in WT mice but not in the EP3−/− mice (WT: 1.68×103 vs. EP3−/−:0.62×103, per 106 splenocytes, p<0.05). These data define a novel proinflammatory role of PGE2‐EP3 receptor signaling in the formation of isoketal‐adducted proteins in DCs. Thus, PGE2 signaling through the EP3 receptor likely contributes to activation of adaptive immunity and the development of hypertension.Support or Funding InformationThis work is supported by National Institutes of Health grants R01HL039006, P01HL058000, P01HL095070, P01GM015431, R01HL108701, R01HL105294, VITA award HHSN268201400010C (to D.G.H.) and DK37097 (to D.M.B.), the Strategically Focused Research Network Award from the American Heart Association to D.G.H., and Merit Awards from the Department of Veterans Affairs to R.M.B. (1BX000616).