P450 Eicosannoids: Novel Nerve-Deerived Relaxing Factors in the Brain

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DESCRIPTION (provided by applicant): Blood flow to the brain is tightly coupled to local metabolic demand through signaling mechanisms collectively termed neurovascular coupling (NVC). A number of endogenous regulators of NVC have been identified including astrocyte-derived P450 vasodilator eicosanoids referred to as epoxyeicosatrienoic acids (EETs). At the regional level, cerebral blood flow (CBF) is regulated in part by extrinsic perivascular vasodilator and vasoconstrictor nerves that innervate conduit arteries such as the middle cerebral (MCA) and basilar arteries (BAS). We provide herein preliminary data demonstrating the expression of EETs synthetic and metabolizing enzymes within parasympathetic vasodilator perivascular nerves. Based on these findings, we propose to test the hypothesis that EETs are novel parasympathetic nerve-derived relaxing factors involved in the neurogenic regulation of CBF. We will first utilize immunofluorescent double-labeling, Western blot, real-time quantitative RT-PCR (rtqRT-PCR) and anterograde nerve tracing to characterize the expression of EETs-synthetic enzyme cytochrome P450 2C11 epoxygenase and EETs-inactivating enzyme soluble epoxide hydrolase (sEH) within the cerebral vascular nerves and their ganglia of origin. We will then utilize an in vivo cranial window preparation to determine the functional role of EETs in the neurogenic vasodilator response of the MCA to parasympathetic ganglia stimulation. Lastly, we will employ compartmented co-culture model of parasympathetic neurons (PSN) and vascular smooth muscle cells (VSMC) to determine the mechanism of EETs release by parasympathetic neurons and their hyperpolarizing action upon VSMC. The proposed studies will explore a novel mechanism of CBF regulation, which will further our understanding of CBF regulation under physiological conditions, and may have important clinical implications relevant to neurovascular dysfunction in such disease states as vasospasm after subarachnoid hemorrhage, vascular dementia, migraine, stroke and traumatic brain injury.