SIRT6 and Alzheimer disease: 1. NR improves learning and memory in AD/Polβ mice and restores hippocampal synaptic plasticity in AD/Polβ mice2. NR increases neurogenesis and decreases neuroinflammation and tau phosphorylation but not Aβ accumulation in AD and AD/Polβ mice3. NR normalizes mitochondrial stress in human AD fibroblasts and decreases DNA damage and apoptosis through SIRT3 and SIRT6