The question for Wencui Wan and colleagues then became centered around how GSPE was exerting its anti-aging effects in the eye. On the one hand, they found that these effects correlated with significant decreases in NAD+ and NAMPT contents in aging mouse RPE cells. On the other hand, GSPE treatment increased the levels of both NAD+ and NAMPT.
To go one step further and show that this relationship was not just a correlation, Wencui Wan and colleagues looked at how aged mouse RPE cells treated with GSPE behaved when NAMPT activity was blocked. When they used an inhibitor of NAMPT activity, the protective effects of GSPE on cellular senescence in aging RPE cells were blocked. However, when they jumped over this step by directly supplementing the cells with NMN, the product of NAMPT, the protective effect was reinstated.