Protein Kinase C Epsilon Regulates Mitochondrial Pools of Nampt and NAD Following Resveratrol and Ischemic Preconditioning in the Rat Cortex

Preserving mitochondrial pools of nicotinamide adenine dinucleotide (NAD) or nicotinamide phosphoribosyltransferase (Nampt), an enzyme involved in NAD production, maintains mitochondrial function and confers neuroprotection after ischemic stress. However, the mechanisms involved in regulating mitochondrial-localized Nampt or NAD have not been defined. In this study, we investigated the roles of protein kinase C epsilon (PKCε) and AMP-activated protein kinase (AMPK) in regulating mitochondrial pools of Nampt and NAD after resveratrol or ischemic preconditioning (IPC) in the cortex and in primary neuronal-glial cortical cultures. Using the specific PKCε agonist ψεRACK, we found that PKCε induced robust activation of AMPK in vitro and in vivo and that AMPK was required for PKCε-mediated ischemic neuroprotection. In purified mitochondrial fractions, PKCε enhanced Nampt levels in an AMPK-dependent manner and was required for increased mitochondrial Nampt after IPC or resveratrol treatment. Analysis of intrinsic NAD autofluorescence using two-photon microscopy revealed that PKCε modulated NAD in the mitochondrial fraction. Further assessments of mitochondrial NAD concentrations showed that PKCε has a key role in regulating the mitochondrial NAD+/nicotinamide adenine dinucleotide reduced (NADH) ratio after IPC and resveratrol treatment in an AMPK- and Nampt-dependent manner. These findings indicate that PKCε is critical to increase or maintain mitochondrial Nampt and NAD after pathways of ischemic neuroprotection in the brain.