Ginsenoside Rb1 inhibits astrocyte activation and promotes transfer of astrocytic mitochondria to neurons against ischemic stroke

Astrocytes activation in response to stroke results in altered mitochondrial exchange with neurons. Ginsenoside Rb1is a major ginsenoside of Panax ginseng particularly known for its neuroprotective potential. This work aimed to investigate if Rb1 could rescue neurons from ischemic insult via astrocyte inactivation and mitochondrial transfer. We prepared conditioned astrocytes-derived medium for co-culture with neurons and examined the role of Rb1 in mitochondrial transfer from astrocytes to neurons. The neuroprotective potential of Rb1 was further confirmed in vivo using a mouse model of brain ischemia. In response to oxygen-glucose deprivation and reperfusion (OGD/R), astrocytes were reactivated and produced reactive oxygen species (ROS), an action that was blocked by Rb1. Mechanistically, Rb1 inhibited NADH dehydrogenase in mitochondrial complex I to block reverse electron transport-derived ROS production from complex I, and thus inactivated astrocytes to protect the mitochondria. Mitochondrial signal, mitochondrial membrane potential and ATP production detected in conditioned astrocyte-derived medium indicated that Rb1 protected functional mitochondria and facilitated their transfer. When neurons were injured by OGD/R insult, co-culturing with conditioned medium increased mitochondrial membrane potential and oxygen consumption rate within the neurons, indicating the protection conferred on them by Rb1 via mitochondrial transfer from astrocytes. Using the ischemic mouse brain model, CD38 knockdown in the cerebral ventricles diminished the neuroprotective effects of Rb1, providing evidence in support of the role of astrocyte mitochondrial transfer. Transient inhibition of mitochondrial complex I by Rb1 reduced mitochondrial ROS production and consequently avoided astrocyte activation. Astrocyte mitochondrial transfer therefore seemed a means by which Rb1 could promote neuronal survival and function. Different from the neurocentric view, these findings suggest the astrocytes may be a promising target for pharmacological interventions in ischemic brain injury.