FNDC5 and Alzheimer disease: Prominent examples include irisin (173), IL-6 (174), CTSB (175), and glycosylphosphatidylinositol-specific phospholipase D1 (GPLD1) (176), which have been shown to enhance BDNF expression, promote synaptic plasticity, and facilitate Aβ clearance, thereby attenuating AD pathology.