Irisin as an Exerkine of Neuroprotection in Aging and Alzheimer's Disease.

Alzheimer's disease (AD) is a neurodegenerative disease impacting over 6 million Americans, with cases projected to increase to over 14 million by 2060. The AD pathology leads to difficulty completing everyday tasks or conversations, and ultimately, progresses to disrupt the most basic bodily functions and require full-time caretaking. While disease-modifying therapy remains elusive, reducing the incidence of AD is crucial to mitigate the projected increase in cases. Exercise has emerged as an effective strategy to promote brain health in late adulthood and to protect against the onset of AD. Exercise opposes several disease processes, including cognitive dysfunction, amyloid beta aggregation, tau phosphorylation, and deficits in hippocampal volume, mitochondrial function, cerebral blood flow, and neurogenesis, through various pathways, including the systemic release of exerkines. The exerkine irisin is an important mediator of the beneficial relationship between exercise and the brain. Previous work administering irisin therapeutically to healthy and preclinical AD mice has demonstrated irisin use to replicate multiple exercise-induced effects in the brain and protect against AD-induced deficits. Although irisin is suggested as a promising strategy for promoting brain health in late adulthood, our understanding of irisin signaling and its protective effects against AD remains incomplete. This review will investigate irisin as an important, physiologically relevant promoter of brain health in aging and AD.