Pre-B-cell colony-enhancing factor exerts a neuronal protection through its enzymatic activity and the reduction of mitochondrial dysfunction in in vitro ischemic models

Pre-B-cell colony-enhancing factor (PBEF) is known as a rate-limiting enzyme that converts nicotinamide (NAM) to NMN in the salvage pathway of mammalian NAD+ biosynthesis. Previously we found PBEF is exclusively expressed in neurons in the mouse brain; heterozygous PBEF knockout (Pbef+/-) mice have larger ischemic lesion than wild type mice in photothrombosis-induced ischemia. For the mechanistic study of neuronal protective role of PBEF, we used in vitro oxygen-glucose deprivation (OGD) and glutamate excitotoxicity models of primary cultured neurons in current study. Our results showed that the treatments of neurons with NAM and NAD+, the substrate and downstream product of PBEF, respectively, significantly reduced neuronal death after OGD and glutamate excitotoxicity, while treatment of neurons treated with FK866, a PBEF inhibitor, increased neuronal death after OGD. Furthermore, over-expression of human PBEF reduced glutamate excitotoxicity, while over-expression of human PBEF mutants (i.e. H247A and H247E) without enzymatic activity had no effect on neuronal death. We further tested the effect of PBEF on mitochondrial function and biogenesis. Our results show that addition of NAD+ and NAM increased mitochondrial biogenesis in neurons after OGD. Over-expression of PBEF in neurons reduced mitochondrial membrane potential depolarization following glutamate stimulation, while over-expression of H247A and H247E did not affect mitochondrial membrane potential depolarization. We conclude that PBEF has a neuroprotective effect in ischemia through its enzymatic activity for NAD+ production that can ameliorate mitochondrial dysfunction.