Abstract A057: Endothelial protease-activated receptor 1 deletion preserves the blood-brain barrier and enhances functional recovery after ischemic stroke

Introduction: Ischemic stroke remains a leading cause of adult disability worldwide, with limited treatment options. Blood-brain barrier (BBB) breakdown is a key pathological event after stroke, as it promotes vasogenic edema and hemorrhagic transformation, leading to worse neurological outcomes. Understanding how different components of the neurovascular unit contribute to BBB breakdown is essential for developing new treatments. Hypothesis: We hypothesized that the activation of protease-activated receptor 1 (PAR1) in endothelial cells exacerbates BBB breakdown after ischemic stroke, and targeted endothelial PAR1 deletion would improve outcomes. Methods: We used a novel endothelial cell-specific, tamoxifen-inducible PAR1 knockout (KO) mouse line (TIE2Cre ERT2 PAR1 f/f ) in the current study. Age matched male and female mice (n = 11/sex/group) were randomized to receive daily intraperitoneal injections of vehicle or tamoxifen (150 mg/kg) for 3 days. Ten days after the final vehicle/tamoxifen injection, transient left middle cerebral artery occlusion (MCAo) was performed for 60 min followed by reperfusion. BBB permeability was assessed 2 days after stroke using dynamic contrast-enhanced (DCE) MRI to calculate the plasma-to-tissue transfer constant (K trans ) of gadolinium. Lesion volume was measured 2- and 30-days poststroke with T2-weighted MRI. Neurological recovery was evaluated using neurological deficit scoring (NDS), corner test and Barnes maze. Results: Endothelial PAR1 deletion significantly reduced BBB disruption 2 days after stroke (relative K trans 2.95 vs 1.76, P < 0.05). Lesion volume was also decreased in the endothelial PAR1 KO group at both days 2 (29.88 ± 16.49 mm 3 vs 19.69 ± 7.304 mm 3 , P < 0.05) and 30 poststroke (10.51 ± 4.464 mm 3 vs 6.725 ± 3.708 mm 3 , P < 0.01). In addition, endothelial PAR1 deletion significantly improved functional outcome in NDS on day 2 (P < 0.05) and mean reversal test in Barnes maze on day 30 (P < 0.01). However, no significant difference was observed in the corner index on day 7 after stroke. Conclusion: In conclusion, our results demonstrate a critical role of endothelial PAR1 in mediating BBB disruption after ischemic stroke. Specific deletion of endothelial PAR1 using TIE2 Cre preserves BBB integrity, reduces lesion volume and promotes functional recovery. Further studies are required to investigate the role of endothelial PAR1 on the regulation of tight junction integrity and neuroinflammation after stroke.