Nitro-oleic acid activation of endothelial PPARγ signaling pathway alleviates neurovascular injury and improves functional outcomes in ischemic stroke.

Nitro-oleic acid (OA-NO2) is an endogenous peroxisome proliferator-activated receptor-γ (PPARγ) ligand and can activate this receptor under both physiological and pathological conditions. In this study, we explore the role and molecular mechanisms of OA-NO2 in maintaining blood-brain barrier (BBB) integrity and enhancing neurovascular function during ischemic stroke, with a particular emphasis on the activation of endothelial PPARγ signaling pathways. Endothelial cell-selective PPARγ conditional knockout (EC-PPARγ cKO) and wild-type (WT) mice underwent 1 h middle cerebral artery occlusion (MCAO) with 1-7 days of reperfusion. Mice were treated with oleic acid (OA) or OA-NO2 (5 mg/kg) via tail vein 2 h after MCAO. Neurobehavioral deficits were assessed on days 3, 5, and 7 after MCAO. Neuroinflammation and BBB function were assessed on days 1 or 2 after MCAO by immunohistochemistry, RT-qPCR, or Western blot analysis. Compared to OA controls, intravenous administration of OA-NO2 led to reduced BBB leakage in ischemic brains, as indicated by a significant decrease in the extravasation of BBB tracers. This reduction in BBB leakage was also almost abolished in the EC-PPARγ cKO mice. Furthermore, OA-NO2 treatment reduced brain infarction in stroke mice, but this protective effect was completely reversed in the EC-PPARγ cKO mice. Interestingly, OA-NO2 treatment promoted a shift towards an anti-inflammatory microglial phenotype (M2) in the peri-infarct regions of WT mice, but not in EC-PPARγ cKO mice. Mechanistically, OA-NO2 increased levels of major endothelial tight junction proteins in WT mice but not in EC-PPARγ cKO mice following ischemic stroke. These findings suggest that OA-NO2 activation of endothelial PPARγ signaling cascade attenuates neurovascular injury after ischemic stroke.