Regulation of Cerebral Blood Flow by Acid-Sensing Ion Channels (ASICs)

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DESCRIPTION (provided by applicant): Adequate perfusion is essential for normal brain function and impaired regulation of cerebral blood flow (CBF) may contribute to neurological dysfunction and disease. Despite recent progress, our knowledge of mechanisms that regulate CBF remains inadequate. Two of the most powerful stimuli that affect CBF are hypercapnia and increased cellular activity (cellular metabolism and synaptic activity). Both of these stimuli increase local concentrations of hydrogen ion (reduce extracellular pH). The overall goal of this application is to examine the role of acid-sensing ion channels (ASICs) in control of CBF. We found recently that ASICs are required for acid-evoked effects on synaptic plasticity. Moreover, the ASIC1a subtype functions as a chemosensor in neurons mediating hypercapnia- and acid-evoked behaviors. These findings led to preliminary experiments testing whether ASICs also play a role in regulation of CBF. Although effects of hypercapnia and acidosis have been known for decades, mechanisms that initiate vascular responses to these stimuli remain undefined. Based on this background, we propose two Aims. Aim 1 will examine the hypothesis that ASICs mediate vascular responses to hypercapnia. We will examine vascular effects of hypercapnia and acidosis following manipulation of ASICs using genetic and pharmacological approaches. To define the importance of neuronal ASIC, we will take advantage of mice lacking or overexpressing ASIC1a specifically in neurons. We will also use ASIC inhibitors to pharmacologically probe ASIC function. Aim 2 will use similar approaches to examine the hypothesis that neuronal ASICs contribute to vascular responses in models of neurovascular coupling. In pilot studies, we found that disrupting ASIC1a nearly eliminated hypercapnia-induced vasodilation but also significantly attenuated vasodilator responses in a model of neurovascular coupling. Together these studies will unambiguously determine the importance and site of ASIC action in hypercapnia- and proton-dependent regulation of cerebrovascular responses. The studies may provide new and unprecedented insight into the complex interaction between brain and its vascular supply. Such insight may ultimately lead to improved therapeutic approaches for cerebrovascular disease and brain injury. This project was conceived and will be carried out by an innovative collaboration between investigators with diverse expertise in CBF, neurovascular coupling, pH regulation, and ASICs.