Cerebral Ischemic Reperfusion Increases Autotaxin Expression Elevating Brain Endothelial Permeability.

INTRODUCTION: Ischemic reperfusion during stroke treatment increases the pathological progression of stroke. Reperfusion with r-TPA and mechanical thrombectomy applied to stroke patients increases the risk of intracerebral hemorrhage. In addition, various molecular signals initiated during ischemic reperfusion exacerbate the disease due to increased endothelial permeability. However, a detailed molecular therapeutic regimen with r-TPA and mechanical thrombectomy could limit the detrimental effects and increase the survival rate. Lysophosphatidic acid (LPA) is a bioactive phospholipid regulated in physiological and pathological conditions. LPA is produced by the enzyme autotaxin (ATX). ATX and LPA have been observed to deteriorate physiological status in various diseases such as myocardial infarction, Alzheimer's disease, liver fibrosis, neuropathic pain etc. In cerebral ischemic-reperfusion, the ATX-LPA axis could initiate the endothelium disruption.

HYPOTHESIS: Increased ATX expression in endothelium disrupts the endothelial barrier by increasing LPA during ischemic-reperfusion.

METHODS: Transient middle cerebral artery occlusion with 90 minutes of ischemia and 24 hours of reperfusion (I/R) was used as a stroke model in mice. LPA was analyzed with mass spectrometry and immunohistochemistry. AR-2 probe fluorescence assay was used to measure ATX activity. Evans Blue Permeability in vivo was measured with an infrared imager. For the in-vitro study, oxygen and glucose deprivation and reperfusion (OGDR) were carried out in mouse brain microvascular endothelial cells (MBMEC).

RESULTS: ATX enzymatic activity is prominently raised (P<0.01) in I/R mice compared to sham mice. Increased ATX activity coheres with the Evans Blue permeability in the mice brain. Simultaneously LPA levels are elevated (P<0.01) in I/R mice. LPA was increased in brain tissue along the vasculature, indicating an unfavorable role of ATX in maintaining endothelial integrity. LPA receptors expression was regulated following stroke with upregulation of LPAR1, LPAR2, LPAR5, and LPAR6 following I/R. Permeability measured in MBMEC showed that LPA treatment increased the permeability in a time and concentration-dependent manner. ATX expression was increased (P<0.05) in MBMEC with OGDR suggesting ATX regulation in endothelial cells following ischemic-reperfusion. LPA produced during the process can disrupt the blood-brain barrier, increasing cerebral permeability.

CONCLUSION: After a stroke, enhanced LPA production by ATX can disrupt the blood-brain barrier, leading to brain edema and neural cell damage followed by irreversible brain injury. Inhibition of the ATX-LPA axis prospects to be a better therapeutic avenue for cerebral ischemic reperfusion.