Preconditioning-induced facilitation of lactate release from astrocytes is essential for brain ischemic tolerance.

A sub-lethal ischemic episode (termed preconditioning [PC]) protects neurons in the brain against a subsequent severe ischemic injury. This phenomenon is known as brain ischemic tolerance, and has received much attention from researchers because of its robust neuroprotective effects. We have previously reported that PC activates astrocytes and subsequently upregulates P2X7 receptors, thereby leading to ischemic tolerance. However, the downstream signals of P2X7 receptors that are responsible for PC-induced ischemic tolerance remain unknown. Here, we show that PC-induced P2X7 receptor-mediated lactate release from astrocytes has an indispensable role in this event. Using a transient focal cerebral ischemia model caused by middle cerebral artery occlusion, extracellular lactate levels during severe ischemia were significantly increased in mice who experienced PC; this increase was dependent on P2X7 receptors. In addition, the intracerebroventricular injection of lactate protected against cerebral ischemic injury. In in vitro experiments, although stimulation of astrocytes with the P2X7 receptor agonist BzATP had no effect on the protein levels of monocarboxylate transporter (MCT) 1 and MCT4 (which are responsible for lactate release from astrocytes), BzATP induced the plasma membrane translocation of these MCTs via their chaperone CD147. Importantly, CD147 was increased in activated astrocytes after PC, and CD147-blocking antibody abolished the PC-induced facilitation of astrocytic lactate release and ischemic tolerance. Taken together, our findings suggest that astrocytes induce ischemic tolerance via P2X7 receptor-mediated lactate release.Significance Statement Brain ischemic tolerance refers to an endogenous neuroprotective phenomenon whereby a non-lethal ischemic episode, termed preconditioning (PC), induces resistance to a subsequent severe ischemic injury. This phenomenon has received much attention because of its robust neuroprotective effects. We have previously reported that the PC-evoked activation of astrocytes leads to ischemic tolerance; however, the underlying molecular mechanisms remain unknown. Here, we have demonstrated that PC induces the membrane translocation of lactate transporters in activated astrocytes, thereby promoting lactate release from astrocytes during severe ischemia; this effect likely plays a role in ischemic tolerance. These findings may facilitate the development of new therapeutic strategies for cerebral ischemia.