Abstract 17340: High Fat Diet Exacerbates Uridine Adenosine Tetraphosphate (Up4A)-Mediated Decrease in Coronary Flow in Atherosclerotic ApoE Knockout Mice: Role of Purinergic P2X1 Receptors

Introduction: Up4A, a novel endothelium-derived vasoactive agent, is proposed to play a role in cardiovascular disorder via activation of P2 receptors (P2R). Here, we evaluated the vasoactive effect of Up4A on coronary flow (CF) in ApoE knockout mice (KO) with and without high fat diet (HFD). Methods: Functional studies were conducted in isolated mouse hearts using Langendorff and isolated coronary arteries (diameter≈100 μm) using wire Myograph. Immunofluorescence was performed for P2X1R expression in isolated coronary arteries. Results: There was no significant difference in baseline CF (ml/min/g) among wild type (WT, 18.4±0.5), ApoE KO (17.6±1.1) and ApoE KO+HFD (15.9±1.0). Infusion of Up4A (10-9-10-5 M) resulted in a dose-dependent reduction in CF in WT (by ~38%), which was similar to ApoE KO (by ~40%). In isolated coronary arteries of WT, Up4A produced a mild contraction up to ~20%, indicating a vasoconstrictor effect of Up4A. Notably, Up4A further decreased CF in ApoE+HFD as compared to ApoE. Moreover, selective P2X1R antagonist MRS2159 (10 μM) restored Up4A-mediated decrease in CF more in ApoE+HFD than ApoE (Figure). Finally, the percentage expression of vasoconstrictor P2X1R on smooth muscle cells (SMC) of coronary arteries was higher in ApoE+HFD than ApoE, which was due to a markedly reduced vasodilator P2X1R expression on EC in ApoE+HFD (8.7±0.6 fluorescence intensity in A.U.) than ApoE (22.1±0.5), while P2X1R expression on SMC was similar between ApoE+HFD (6.3±0.4) and ApoE (8.4±0.3). Conclusion: Up4A exerts a vasoconstrictor influence in mouse coronary microcirculation. Up4A decreases CF in WT to a similar extent in ApoE, whereas HFD exacerbates Up4A-decreased CF in ApoE possibly through downregulation of vasodilator P2X1R on EC. These findings indicate that Up4A alters CF in atherosclerosis and P2X1R may represent a potential therapeutic target.