Dietary Vitamin B12 reduces amyloid-β proteotoxicity by alleviating oxidative stress and mitochondrial dysfunction

SUMMARYAlzheimer’s disease (AD) is a devastating neurodegenerative disorder with no effective treatment. Diet, as a modifiable risk factor for AD, could potentially be targeted to slow disease onset and progression. However, complexity of the human diet and indirect effects of the microbiome make it challenging to identify protective nutrients. Multiple factors contribute to AD pathogenesis including amyloid beta (Aβ) deposition, mitochondrial dysfunction, and oxidative stress. Here we used Caenorhabditis elegans to define the impact of diet on Aβ proteotoxicity. We discovered that dietary vitamin B12 alleviated mitochondrial fragmentation, bioenergetic defects, and oxidative stress, delaying Aβ-induced paralysis without affecting Aβ accumulation. Vitamin B12 had this protective effect by acting as a cofactor for methionine synthase rather than as an antioxidant. Vitamin supplementation of B12 deficient adult Aβ animals was beneficial, demonstrating potential for vitamin B12 as a therapy to target pathogenic features of AD triggered by both aging and proteotoxic stress.