The Cholinergic Pathway and MitoKATP Induce UCP4 Expression Involved in Neuroprotection of FN Stimulation in Rats

Abstract

Background Electrical stimulation of the cerebellar fastigial nucleus (FN) reduces the infarct size induced by middle cerebral artery occlusion in rats. FN stimulation confers long‐lasting protection from brain injury; however, its underlying mechanism is not yet understood. We aimed to elucidate the mechanism by which FN stimulation exerts neuroprotection. We hypothesized that the neuroprotective effect of FN stimulation involves activation of cholinergic pathways, which increases reactive oxygen species (ROS) production by opening mitochondrial K+ATP channels, thus leading to an increase in UCP4 (uncoupling protein 4) expression and subsequent neuroprotection. Methods FN stimulation was performed for 1 hour in rats. The UCP4 protein and mRNA levels were measured by western blot, dot blot, and in situ hybridization. Carbachol was applied following UCP4‐promoter tdTomato reporter vector transfection of the rat primary cortical cell culture (in vitro) and rat brain (in vivo). We observed cellular UCP4 expression using fluorescence microscopy. UCP4 expression in the cell culture in response to diazoxide application was determined by a reverse transcription‐polymerase chain reaction and western blotting. Results Whereas FN stimulation increased UCP4 protein and mRNA levels, carbachol administration induced UCP4 expression in vitro and in vivo. The attenuation of this effect by atropine suggests that FN‐induced UCP4 expression involves the cholinergic pathway. The opening of mitochondrial K+ATP channels with diazoxide increased the production of ROS and led to increased UCP4 expression. In contrast, quenching ROS with superoxide dismutase reversed the effect of diazoxide on UCP4 expression. Therefore, the opening of mitochondrial K+ATP channels increased ROS production, which subsequently enhanced UCP4 expression and attenuated ROS generation. Conclusion Neuroprotective effect of FN stimulation involves activation of the cholinergic pathways, which increases ROS production by opening mitochondrial K+ATP channels, leading to increased expression of neuroprotective UCP4.

Keywords

• brain injury
• ischemic tolerance
• middle cerebral artery occlusion
• reactive oxygen species
• uncoupling protein