Peroxisome proliferator-activated receptor γ (PPARγ) agonists reduce blood pressure (BP) and vascular injury in hypertensive rodents. Pparγ inactivation in vascular smooth muscle cells (VSMC) using a tamoxifen inducible Cre-Lox system enhanced angiotensin II-induced vascular damage. Transgenic mice overexpressing endothelin (ET)-1 in the endothelium (eET-1) exhibit endothelial dysfunction, increased oxidative stress and inflammation. We hypothesized that inactivation of the Ppar gene in VSMC (smPparγ−/−) will exaggerate ET-1-induced vascular damage.
Design and Method:
Eleven week-old male control, eET-1, smPparγ−/− and eET-1/smPparγ−/− mice were treated with tamoxifen (1 mg/kg/day, s.c.) for 5 days and sacrificed 4 weeks later. BP was measured by telemetry. Endothelial function and vascular remodeling using pressurized myography, reactive oxygen species (ROS) production by dihydroethidium staining, monocyte/macrophage infiltration by immunofluorescence and mRNA expression by reverse transcription-quantitative PCR were assessed in mesenteric arteries (MA) or perivascular fat (PVAT). Spleen T cell and monocyte profiles were assessed by flow cytometry.
Systolic BP was 20 mmHg higher in eET-1 and unaffected by Pparγ inactivation. MA vasorelaxation to acetylcholine was impaired 37% only in smPparγ−/−. Likewise, ET-1-induced contractions were enhanced only in smPparγ−/−. ROS levels were increased 1.7-fold in smPparγ−/− and 2.5-fold in eET-1/smPparγ−/−. Monocyte/macrophage infiltration in PVAT was 2-fold higher in eET-1 and smPparγ−/−, which was further increased 2-fold in eET-1/smPparγ−/−. The percentage of CD11b+ cells was increased 2.3-fold in smPparγ−/− and further increased 1.5-fold in eET-1/smPparγ−/−. The percentage of Ly-6Chi monocytes was increased ∼1.8-fold in eET-1 and smPparγ−/− but not eET-1/smPparγ−/−. The percentage of T regulatory cells was increased 1.5-fold in smPparγ−/− and decreased by 26% in eET-1, which was further decreased by 38% in eET-1/smPparγ−/−.
These results suggest that increased ET-1 paradoxically preserves endothelial function in mice with inactivated VSMC Pparγ despite enhanced oxidative stress. Flow cytometry data indicate that infiltrating monocyte/macrophages in these mice might be anti-inflammatory.