Abstract TP104: Thyroid Hormone Neuroprotection After Stroke and Fatty Acid Oxidation

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Thyroid hormone (TH) has long been known to decrease lesion volume in mammals after stroke, yet its mechanism of action remains elusive. Our lab previously reported that TH stimulates fatty acid oxidation (FAO), a mitochondrial process that provides substrates for cellular ATP production. During ischemic stroke, glucose is unable to support the normal mechanisms of cellular metabolism, making FAO a critical source of energy. In this study, we assess the role of brain FAO in TH neuroprotection and we investigate the upstream mechanisms of astrocyte FAO regulation. Using an in vivo model of stroke, we observe that by reducing FAO in the adult brain we block the protective effect of TH. In addition, we find that pre-treatment with L-NAME, an inhibitor of nitric oxide synthases, blocks the TH-stimulated increase in FAO, suggesting a possible upstream mechanism involving nitric oxide signaling. Lastly, our experiments showed that TH increases expression of GLAST, a glutamate transporter, and that this response is not seen in astrocytes lacking FAO. Altogether, our data indicate that the oxidation of fatty acids is an essential step in TH-mediated neuroprotection from stroke, and that this metabolic stimulation is regulated by nitric oxide synthase activity. During ischemia, this pathway may lead to an increased transport of excess glutamate from the extracellular space, accounting for increased neuron survival.

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