Microglial P2X₇ receptor in the hypothalamic paraventricular nuclei contributes to sympathoexcitatory responses in acute myocardial infarction rat

Abstract

Several pieces of evidence indicate that the microglial P2X7 receptor (P2X7R) regulate cardiovascular activities. We explored the possible roles of microglial P2X7R in the PVN mediated sympathoexcitatory responses in acute myocardial infarction (AMI) rat. Sprague-Dawley rats underwent coronary artery ligation to induce AMI. The rats received intraperitoneal administration of the P2X7R antagonist Brilliant Blue-G (BBG, 25 or 50 mg kg(-1), once a day for 5 days) prior to myocardial ischemia. Other rats received bilateral microinjection of P2X7R-siRNA (0.015 or 0.03 nmol 0.1μl per side, once a day for 2 days) targeting P2X7R mRNA into the PVN prior to myocardial ischemia. First, we examined the ATP levels and protein expression P2X7R in the PVN in different ischemia time groups, and we found that the change of P2X7R was positive correlated with the ATP levels in a time-dependent manner. The double-immunofluorescence evidence showed that P2X7R was mainly co-localizated with the microglial marker Iba-1 in the PVN. Second, gene knockdown of P2X7R with P2X7-siRNA or inhibition of P2X7R with BBG reduce the mRNA and protein expression of IL-1β and TNF-α in the PVN of AMI rat. Third, microinjected P2X7-siRNA also suppressed the up-regulation of P2X7R, oxytocin and vasopressin in the PVN of AMI rats. Fourth, P2X7-siRNA and BBG also attenuated the renal sympathetic nerve activity (RSNA) in the AMI rats. Our results indicate that microglial P2X7R activation in PVN mediating the production of proinflammatory cytokines that activate oxytocinergic and vasopressinergic neuron, which augmented the RSNA in the AMI rat.

Keywords: Acute myocardial infarction; Hypothalamic paraventricular nucleus; Microglia; Oxytocinergic and vasopressinergic neuron; P2X(7) receptor; Proinflammatory cytokines.