FNDC5 and Alzheimer disease: Furthermore, irisin, the cleaved and circulating form of the exercise-induced fibronectin type III domain-containing membrane protein (FNDC5), stimulates BDNF production (Rabiee et al., 2020; Islam et al., 2021); its genetic deletion was shown to impair cognitive function in exercise, aging and AD; and its peripheral application was observed to be sufficient to rescue the learning behavior decline in mouse models of AD (Islam et al., 2021).