The Neuroprotective Effect And Manchanism Of Peroxisome Proliferator Activated Receptor β/δ After Intracerebral Hemorrhage

Background and purposeStroke is the major cause of death and disability worldwide. Intracerebral hemorrhage (ICH), referring to a lethal subtype of stroke, accounts for 15% to 20% of all strokes that occur every year. Currently, there is no specific therapy that can effectively improve the outcome, mainly because of the limited understanding for the pathophysiology after ICH. The disruption of the blood brain barrier, is known as one of the mechanisms contributing to the brain damage following ICH. In addition to large volume of hematoma itself, the brain edema in the perihematoma region caused by blood brain barrier disruption after ICH contributes to its devastating nature. Peroxisome proliferator activated receptor β/δ (PPAR (3/8) refers to a subtype of PPAR nuclear hormone receptor family. Compared to the other subtypes of PPARs, PPAR β/δ has the highest expression in the brain. However, unlike PPAR y, there is limited information regarding to its role in cerebral stroke. It has been demonstrated that PPAR β/δ confers a neuroprotective by triggering different mechanisms in rat ischemic stroke model. However, it remains unclear regarding the role of PPAR β/δ in intracerebral hemorrhage.Angiopoietin-like 4 (ANGPTL4), belongs to the family of angiopoietins and angiopoietin-like proteins. Though initially classified as an adipokine that is associated with lipid metabolism. it is further explored that ANGPTL4 is involved in the regulation of vascular permeability, angiogenesis and inflammatory responses. Moreover, it was confirmed to attenuate blood brain barrier disruption in ischemic stroke model through inhibition of Src phosphorylation, possibly via PI3k/Akt pathway. Notably, the transcription of ANGPTL4 can be enhanced by PPAR β/δ activation and suppressed by PPAR β/δ antagonist. Yet, the effect of ANGPTL4 in hemorrhagic stroke is still beyond comprehension.Based on the above considerations, we thus hypothesize that PPAR β/δ activation is able to confer blood brain barrier protection via ANGPTL4/Src signaling following intracerebral hemorrhage. Present study was designed to confirm the hypothesis by using both autologous arterial blood injection and collagenase induced mouse intracerebral hemorrhage models.Material and methodsTwo hundred and twelve CD-1 mice were used. Both collagenase and autologous arterial blood injection ICH models were established, for short-and long-term study respectively. GW0742, a high selective PPAR β/δ agonist, were administrated 30 minutes following ICH. ANGPTL4 small interfering RNA (siRNA) or scramble siRNA was injected intracerebroventricularly (icv.) 24 hours before ICH was induced. For the mechanism study, GSK0660 and r-ANGPTL4 were administrated intraperitonealy and intracerebroventricularly. The co-localization of PPAR β/δ and different cell types in the brain following ICH was observed by double immunofluorescence staining. Brain water content and neurologic scores were evaluated for the outcome study. For the mechanism study, the protein level of Src, phosphorylated Src (p-Src), ZO-1, VE-Cadherin, Claudin 5 and MMP-9 were detected by Western blots using peri-hematoma samples. MMP-9 activity was evaluated by zomography. For long-term study, mice were administrated by daily dose of 1.0mg/kg after modeling. Neurobehavior was tested by Garcia Score, T-maze, Rotrod and Water Maze. Ventricular enlargement of the animals was observed using HE staining and brain-to-body weight ratio was calculated.Results:1. PPAR β/δ selective agonist, GW0742 (0.5mg/kg and 1.0mg/kg), could significantly reduce brain water content and improve neurobehavior at both 24 and 72 hours after bICH.2. Silencing ANGPTL4 was able to reverse the protective effect of PPAR β/δ agonist on neurobehavior and brain waiter content.3. In bICH model, the administration of GW0742 (1.Omg/kg) selectively activated PPAR β/δ, consequently preserved ZO-1, Claudin 5 and VE-Cadherin, reduced MMP-9 expression and activity through ANGPTL4/Src pathway.4. GW0742 (1.0 mg/kg) could improve neurobehavior and reduce cognitive function impairment of cICH model in the long term after ICH onset, by attenuating brain atrophy and lateral ventricular enlargement.ConclusionPPAR β/δ activation by GW0742 (1.Omg/kg) was able to attenuate brain edema and neurological deficits in both short and long term after ICH. This effect was conducted by blood brain barrier preservation through ANGPTL4/Src pathway. Based on the discovery of our study, PPAR β/δ may play a promising role for further treatment for ICH.