Dietary sulfur amino acid restriction to prevent Alzheimer’s Disease

Abstract Background High serum homocysteine is a risk factor for Alzheimer’s Disease (AD). It has been reported to influence the accumulation of its characteristic lesions ‐ senile plaques (SP) and neurofibrillary tangles (NFT) ‐ containing amyloid β protein (Abeta) and microtubule‐associated protein Tau (MAPT), respectively. Reduced food or calorie intake or branched‐chain amino acids are reported to benefit AD model mice. Restriction of Methionine (Met), an essential amino acid, contributes to increased longevity without calorie restriction. Method We treated APP/PS1 transgenic mice with a 75% Met restricted (MR) diet and compared it to an isocaloric isonitrogenous complete diet (CD) for up to 12 months. We subsequently evaluated amyloid loads by ELISA and other APP metabolites by western blotting as described previously (Barnwell et al., 2014, Teich et al., 2018). We collected fecal matter from the colon, extracted DNA, and evaluated the gut microbiome. Result Our data show that MR treatment substantially lowered brain soluble Abeta at 3 and 6 months. Abeta levels are excessively and presumably saturated in older mice, accounting for the lack of statistically significant differences between the different diets evaluated after twelve months. Nevertheless, older mice showed substantial improvement in behavior in a novel object recognition task after MR treatment. MR treatment is known to be senolytic, and therefore, we are currently examining related processes, such as preservation of lysosomal capacity changes in metabolome, mRNA, and miRNA profiles. Future work involves evaluating methionine and branch‐chain amino acid restriction in AD animal models, such as in human tau‐overexpressing Tg mice, and evaluating miRNAs. MR diets significantly alter gut microbiota. As expected, the bacteria that metabolize Met and Cys were decreased. Specifically, several major species of bacteria were reduced, and the overall diversity of microbiota was increased. Senolysis and improvements in AD pathology may also be mediated by reduced inflammation due to the increased diversification of the microbiome. Thus, such diets may play an important role in strategies to prevent AD, retinal degeneration, and other age‐associated disorders. Conclusion Sulfur amino acid restriction reduces amyloid production and preserves cognitive function in mice. Reduced protein diets may be useful in preventing proteinopathies that lead to neurodegeneration.