Elevated Permeability with Reduced Mitochondrial Function in Ischemic Stroke by ATX‐LPA axis

Abstract

Introduction Stroke is a leading cause of death and a severe cause of long-term disability in the US. r-TPA is the only treatment available for stroke, and only 5% of patients receive it, as others have the risk of intracerebral hemorrhage. Ischemic reperfusion (I/R) following stroke exacerbates the condition and initiates various molecular signals, ultimately interrupting the blood-brain barrier so, better therapy is in need. Lysophosphatidic acid (LPA) is a bioactive lipid regulating various essential cellular functions. Autotaxin (ATX) produces LPA, which then regulates through its six G-protein coupled receptors. We hypothesize that the altered ATX-LPA axis could cause unfavorable signaling following ischemic stroke. Methods Transient middle cerebral artery occlusion (MCAO) with 90 minutes of ischemia and 24 hours of reperfusion was used as a stroke model in mice. LPA was analyzed in plasma with mass spectrometry and in tissue with immunohistochemistry. AR-2 probe fluorescence measured ATX activity. Seahorse analyzer measured the mitochondrial bioenergetics in brain and mouse brain microvascular endothelial cells (MBMEC). Permeability was studied with Electric Cell Substrate Impedance System. Results ATX was elevated 1.7 fold in mRNA level with increased activity following I/R in mice brain. LPA showed a significant (P<0.01) increase in the plasma of MCAO mice. LPA in the brain tissue of MCAO mice revealed an increased LPA following I/R injury. ATX produced LPA could be the cause for detrimental effects. Brain mitochondria isolated following I/R injury had significantly (P<0.01) reduced the mitochondrial oxygen consumption rate (OCR). Permeability measured in MBMECs showed that LPA treatment increases the permeability. The protein levels of junctional proteins such as βcatenin, Claudin5, VEcadherin, and Zo1 were significantly (P<0.05) decreased with LPA exposure. LPA, as a negative regulator of the BBB, caused permeability through LPA-LPAR1-ROCK dependent pathway. MBMECs show impaired mitochondrial function with decreased OCR and elevated glycolysis towards LPA treatment (P<0.01). Conclusion We have shownthat LPA and its regulator enzyme ATX play a significant role in ischemic stroke, increasing BBB permeability and reducing mitochondrial function. ATX inhibitors as therapy could improve the condition of stroke patients.