The role of ketogenic diet metabolites in molecular signaling within distinct brain cell populations.

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Project Summary The brain exhibits considerable energy demand and consumes as much as 20% of total caloric intake. Primarily, the adult brain acquires the vast majority of its energy through the breakdown of carbohydrates. The capacity to utilize carbohydrates as an energy source is reduced during brain aging and in the Alzheimer's disease (AD) afflicted brain as evidenced by FDG-PET studies. This decline in carbohydrate utilization is an early preclinical change in AD and may be a viable therapeutic target to slow or prevent disease progression. This shortfall may be corrected by substituting an alternative energy source for the brain. The brain will readily catabolize ketone bodies for energy production in certain circumstances. Typically, ketone bodies are only produced in the adult human during periods of sustained caloric restriction or when maintained on a diet high in fat and low in carbohydrate content. These so-called ketogenic diets have been in use for nearly a century in the clinic for the treatment of intractable epilepsy. Additionally, a randomized control trial has demonstrated some efficacy for the ketogenic diet in improving cognitive performance in patients with AD. While the ketogenic diet has neurologic benefit in humans, its mechanism of action remains poorly understood. The present proposal seeks to explain how the ketogenic diet and its primary metabolites, fats and ketone bodies, influence molecular signaling pathways in the central nervous system in distinct brain cell populations. We hypothesize that neurons preferentially utilize ketone bodies as an energy source and spare fats with the reverse being true of astrocytes. We further hypothesize that these metabolites further influence intracellular signaling pathways by altering bioenergetic flux and gene transcription. For our first aim, we plan to assess how primary nervous system cell lines respond bioenergetically to the presence of fatty acids and ketone bodies. This aim will be tested in vitro through primary cultures of neurons and astrocytes generated from embryonic rat forebrain and in vivo through the isolation of distinct cell types from adult mouse brain using FACS technology. Our second aim will make use of a transgenic mouse line exhibiting constitutive ketogenesis in the absence of dietary manipulation to examine the effects of sustained brain ketone delivery. This approach will allow us to examine the in vivo effects of ketone bodies on the brain without creating confounding variables introduced by the use of the ketogenic diet. The broad, long-term objective of this research is to further elucidate how the brain utilizes bioenergetics substrates in specific brain cell populations. This includes defining the mechanism of benefit of ketogenic therapies in AD and epilepsy to better target novel molecular pathways in the treatment of these pathologies and improve patient lives.