MAPT and Alzheimer disease: The study of Li et al. (2021) found that, Yuan Zhi San could up-regulate the expression levels of ubiquitin-related molecules and the 26S proteasome in the brains of the AD model animals, and restored the impaired UPS enzyme cascade reaction, which in turn, through the restoration of the UPS activity, promoted the degradation of hyperphosphorylated Tau protein in the brain of AD rats, which in turn improved the learning and memory ability of AD model animals and inhibited the further development of AD.