The role of nicotinamide riboside in the preservation of retinal ganglion cells using an in vitro glutamate-induced excitotoxicity model

Delaying or preventing the loss of retinal ganglion cells (RGCs) in glaucoma is needed for vision preservation. Glutamate-mediated neurotoxicity arises from the excessive stimulation of N-methyl-D-aspartate membrane receptors by glutamate. This overstimulation, occurring specifically in RGCs, triggers a progressive deterioration of the optic nerve that ultimately leads to the vision loss in glaucoma. Our previous investigation demonstrated that nicotinamide riboside (NR) effectively preserved RGCs in multiple mouse models of glaucoma. To investigate the precise role of NR concerning RGCs which remains uncertain, a glutamate-induced excitotoxicity RGCs damage model was established using R28 cells in this study. Results showed that NR treatment could not only prevent the decrease in cell viability but also effectively inhibit the apoptosis of R28 cells induced by glutamate, as proven by flow cytometry and expression of key pro-apoptotic proteins. Additionally, it significantly attenuated oxidative stress induced by glutamate, as evaluated by the production of inflammatory factors, reactive oxygen species (ROS) and mitochondrial ROS (mtROS). Furthermore, NR elevated the intracellular nicotinamide adenine dinucleotide (NAD+) levels in R28 cells. Lastly, we used RNA-seq to reveal the underlying mechanism of NR protection. Combining the results of RNA-seq and Western blot, we found that NR also restored the decreased protein expression of sirtuin 1 (SIRT1) and peroxisome proliferator-activated receptor-gamma coactivator (PGC1α) induced by glutamate. These findings strongly indicated that NR exhibits a protective effect against R28 cell apoptosis in a glutamate-induced excitotoxicity RGCs damage model. This protective effect is likely mediated through the activation of the SIRT1/PGC1α pathway, achieved by increasing intracellular NAD + levels.