, 2011). These pathways are often intertwined with the control of metabolism, as exemplified by the function of BAD (BCL-2 associated agonist of cell death), a proapoptotic member of the family of Bcl-2 death regulators, in glucose metabolism and utilization (Danial et al., 2003 and Danial et al., 2008). Whether the regulation of neuronal excitability depends on how mitochondria shape intermediate metabolism is however unclear. With this question in mind, Giménez-Cassina et al. (2012) investigated ATM inhibitor the potential role of BAD in seizures, unraveling in this issue of Neuron the existence of a phosphodependent regulatory switch in BAD that reduces neuronal excitability

upon kainic acid-induced seizures. BAD exists in a phosphorylated and dephosphorylated state, which have opposite effects on cell death. Dephosphorylated BAD goes to mitochondria, where it interacts with prosurvival proteins BCL-2 and much more strongly with BCL-XL, sensitizing mitochondria to the action of other BH3-only proapoptotic proteins that can initiate BAX/BAK-dependent apoptosis (Yang et al., 1995). BAD can be specifically phosphorylated on one or multiple specific residues by different protein kinases, including Rsk, PKC, PKB, PKA, and phosphatidylinositol-3-kinase (PI3K). BAD dephosphorylation C646 is also finely

tuned by different phosphatases, including PP1, PP2A, and Calcineurin (CnA, Methisazone also known as PP2B) (Klumpp and Krieglstein, 2002). Phosphorylation

of different residues has different effects: for example, phosphorylation of Serine 155 impairs BAD interaction with BCL2/BCL-XL, whereas upon phosphorylation of Serine 112 and Serine 136, binding sites are exposed for its interaction with the cytosolic 14-3-3 proteins. In parallel to and separate from its role in apoptosis, BAD also controls glucose metabolism (Danial et al., 2003). In this respect, BAD phosphorylation does not only prevent initiation of cell death, but it is also required for efficient mitochondrial utilization of glucose in liver, via the scaffolding of a complex containing glucokinase on the surface of the organelle (Danial et al., 2003). Similarly to what occurs in liver, Giménez-Cassina et al. (2012) show that also cortical neurons and astrocytes from Bad−/− mice display lower glucose utilization for mitochondrial respiration. Intriguingly, cortical neurons and astrocytes from mice bearing a phosphodeficient knockin allele of Bad at serine 155 (BadS155A) harbor the same defect. Conversely, mitochondrial consumption of the non glucose carbon source β-D-hydroxybutyrate (a ketone body) is increased. Therefore, mitochondria lacking Bad selectively switch from glucose to ketone body utilization, whereas BAD phosphorylation on serine 155 favors the opposite switch, from ketone body to glucose.