Early Decline in Glucose Transport and Metabolism
Precedes Shift to Ketogenic System in Female Aging and
Alzheimer’s Mouse Brain: Implication for Bioenergetic
Intervention
We previously demonstrated that mitochondrial bioenergetic deficits in the female brain accompanied reproductive
senescence and was accompanied by a shift from an aerobic glycolytic to a ketogenic phenotype. Herein, we investigated
the relationship between systems of fuel supply, transport and mitochondrial metabolic enzyme expression/activity during
aging (3–15 months) in the hippocampus of nontransgenic (nonTg) background and 3xTgAD female mice. Results indicate
that during female brain aging, both nonTg and 3xTgAD brains undergo significant decline in glucose transport, as
detected by FDG-microPET, between 6–9 months of age just prior to the transition into reproductive senescence. The deficit
in brain metabolism was sustained thereafter. Decline in glucose transport coincided with significant decline in neuronal
glucose transporter expression and hexokinase activity with a concomitant rise in phosphorylated/inactivated pyruvate
dehydrogenase. Lactate utilization declined in parallel to the decline in glucose transport suggesting lactate did not serve as
an alternative fuel. An adaptive response in the nonTg hippocampus was a shift to transport and utilization of ketone
bodies as an alternative fuel. In the 3xTgAD brain, utilization of ketone bodies as an alternative fuel was evident at the
earliest age investigated and declined thereafter. The 3xTgAD adaptive response was to substantially increase
monocarboxylate transporters in neurons while decreasing their expression at the BBB and in astrocytes. Collectively,
these data indicate that the earliest change in the metabolic system of the aging female brain is the decline in neuronal
glucose transport and metabolism followed by decline in mitochondrial function. The adaptive shift to the ketogenic system
as an alternative fuel coincided with decline in mitochondrial function. Translationally, these data provide insights into the
earliest events in bioenergetic aging of the female brain and provide potential targets for preventing shifts to less efficient
bioenergetic fuels and transition to the ketogenic phenotype of the Alzheimer’s brain.