Metabolic control of neuronal activity by fuel substrate switching. Fuel metabolism is important not only for cellular life-and-death decisions of neurons and astrocytes in the brain, but also as a key regulator of neuronal activity. A remarkable example of how metabolism can alter brain activity is the strong resistance to epileptic seizures exhibited by mice with deletion or alteration of BAD, a BCL-2 family protein that imparts reciprocal effects on glucose and ketone body consumption independent of its ability to regulate apoptosis. We have found that alterations in BAD's metabolic function can lead to reduced mitochondrial oxidation of glucose and enhanced oxidation of ketone bodies, in both neurons and astrocytes. Similar to animals treated with ketogenic diet, BAD mutant mice with these metabolic changes show a striking resistance to behavioral and electrographic seizures induced by chemical proconvulsants. Genetic and electrophysiologic studies also show that these same mutations in BAD increase the open probability of the ATP-sensitive potassium (KATP) channels and that activation of these channels is a necessary intermediate in this metabolically induced seizure resistance. Our proposed studies address two key questions about the mechanism by which BAD alters metabolism and neuronal excitability. The first question is at the level of the metabolic pathways for fuel utilization: What are the precise steps at which the metabolism of glucose and ketone bodies is changed when BAD is modified? Targeted metabolomics and 13C tracing will be used in conjunction with genetic manipulation of BAD to learn specifically how glucose and ketone bodies are routed through different metabolic pathways, and how this routing is affected by BAD, in cultured neurons and astrocytes as well as in brain slices. Second, what are the possible causes and consequences of KATP channel activation in BAD mutant neurons? We will employ fluorescent biosensors to assess the levels of key metabolic signals - ATP, ROS/glutathione redox, and NADH redox - in individual neurons and astrocytes in culture or slices, to learn the causes of KATP channel activation. Complementary electrophysiological studies will address how excitability and signaling in dentate granule neurons are altered in BAD mutant brain slices. The answer to these questions should give an integrated picture of the pathway connecting BAD and fuel metabolism with altered neuronal excitability. Understanding this pathway should yield valuable clues for translating this potent anticonvulsant effect of metabolism into improved therapies for the many individuals with intractable epilepsy.
Epilepsy affects 1-2% of the US population, and about one-third of people with epilepsy are not well-treated by existing medications. Changing the brain's use of fuel molecules - glucose versus other fuels like fatty acids - can produce substantial changes in brain excitability, including resistance to epileptic seizures. This research examines the mechanism by which alteration of a protein called BAD produces metabolic changes that lead to seizure resistance, with the ultimate goal of translating this understanding into new effective therapies for epilepsy.
|Giménez-Cassina, Alfredo; Danial, Nika N (2015) Regulation of mitochondrial nutrient and energy metabolism by BCL-2 family proteins. Trends Endocrinol Metab 26:165-75|