Stroke is a leading cause of morbidity and mortality in the US despite the availability of therapies such thrombolysis and thrombectomy. Focal ischemic stroke occurs when the blood supply to a portion of the brain is interrupted. The affected brain tissue experiences energy failure that can cause cell death. When the interruption is temporary, the ischemia reperfusion sequence initiates a cascade of events causing necrotic and apoptotic cell death. The metabolic response of the brain to energy failure is not completely understood, though one component of this response is a massive release of free fatty acids from plasma membrane phospholipids. Oxidation of these free fatty acids could produce ketone bodies. This project tests the hypothesis that locally produced ketone bodies within the brain are neuroprotective. This hypothesis extends the observation that ketone bodies administered exogenously or synthesized by the liver while on a ketogenic diet protect the brain from ischemic damage in animal models. Regardless of their source, whether neuroprotection from ischemia depends on ketone body oxidation is unknown. Ketone body oxidation requires the ketolytic enzyme (SCOT), which participates in the conversion of ketone bodies into acetyl CoA for entry into the tricarboxylic acid cycle. SCOT is present in neurons and astrocytes. Notably, astrocytes but not neurons oxidize fatty acids, and the synthesis of ketone bodies by astrocytes likely depends on SCOT. A role for SCOT in ketone body oxidation and synthesis is possible because the reaction it catalyzes is near equilibrium. The hypothesis that locally synthesized ketone bodies are neuroprotective during focal ischemia requires an astrocyte-neuron ketone body shuttle. Accordingly, astrocytes would oxidize fatty acids and need SCOT to synthesize ketone bodies. The astrocytes would then send the ketone bodies to neurons, which then oxidize them in a SCOT dependent manner. This model provides a framework to test the hypothesis that ketone bodies protect the brain from ischemia / reperfusion damage via a mechanism requiring their oxidation. This project will test this hypothesis by examining the effects of transient proximal middle cerebral artery occlusion (tMCAO) in neuron-specific and astrocyte-specific SCOT knockout mice using histological, biochemical, and behavioral assays.
Ketosis is a unique metabolic state achieved when carbohydrates are limited and fats are metabolized to small molecules called ketone bodies. Ketosis and ketone bodies reduce brain injury in animal models of stroke. This proposal will determine whether ketone body metabolism contributes to the beneficial effects of ketosis in stroke. The results could lead to new therapies and strategies for treating stroke and for identifying those at highest risk for severe brain injury from stroke.