Skeletal Muscle Mitochondrial Response to Diet Differs by Genotype and Sex in an Alzheimer’s Disease Mouse Model

Abstract

Introduction: Skeletal muscle mass is reduced in the early stages of cognitive decline. Apolipoprotein ε4 ( APOE4) is the most prevalent genetic risk factor for Alzheimer’s disease (AD) and is associated with faster motor decline in cognitively healthy individuals. APOE4 also increases the risk of insulin resistance and cardiovascular disease, conditions associated with altered bioenergetic function in muscle. However, no studies have examined the role of APOE4 in modulating muscle physiology and the impact this would have on cognitive function. We sought to determine if APOE4 affects skeletal muscle mitochondrial metabolism in response to a high-fat diet (HFD) and if this is reflected in whole-body metabolism. We also examined the role of sex since APOE4 carriers who are female are more likely to develop AD. Methods: Male and female APOE3 (n=32) and APOE4 (n= 29) targeted-replacement mice on a C57BL/6 background purchased from Taconic were fed a standard chow diet until 4 months old. Mice were then switched to a low-fat diet (LFD, 10% kcal fat) or HFD (45% kcal fat) until sacrifice. Glucose tolerance was tested at 7 months by administering an intraperitoneal glucose injection of 1g/kg lean mass. Blood glucose was measured before and 15, 30, 45, 60, 90 and 120 minutes after glucose injection. Resting respiratory exchange ratio (RER) was determined using the Promethion Indirect Calorimetry system at 8 months to determine the relative contribution of carbohydrates versus lipids to whole body metabolism. Mice were sacrificed at 9 months and carbohydrate-driven oxygen consumption was measured at basal, state 3 (ADP), state 3 + glutamate, state 3S (succinate) and uncoupled respiratory states in mitochondria isolated from quadriceps tissue on the Oroboros Oxygraph-2k system. Results: Mice fed a HFD had greater glucose area under the curve (p<0.0001) and reduced RER (p= <0.001) compared to mice fed a LFD, regardless of sex or genotype. At the level of skeletal muscle, APOE4 female mice had increased state 3 (p=0.027) and state 3 + glutamate oxygen consumption (p=0.037) on a HFD compared to a LFD while no diet effect was observed in APOE4 males or any APOE3 mice. Conclusion: We provide evidence that female APOE4 mice are susceptible to diet-induced increases in carbohydrate-driven mitochondrial oxygen consumption in muscle. Future studies are needed to determine the underlying mechanism and consequences of increased muscle mitochondrial activity, which could help identify treatment targets in female APOE4 carriers. BHTP T32 AG078114, P30 AG072973 (Chelsea Johnson). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.