Stroke is a significant health problem with limited treatment options. In this application, we present a new model in which activation of transient receptor potential vanilloid 1 (TRPV1) channels provides neuroprotection following ischemia/reperfusion (I/R) through two independent yet additive mechanisms. First, we provide evidence that pharmacological activation of vascular TRPV1 channels during the reperfusion phase selectively restores cerebral perfusion to the damaged brain regions. The hypoperfusion which occurs in damaged brain during early reperfusion can be dramatically and quickly restored without affecting the flow in non-injured brain regions. We propose that reactive oxygen species (ROS) produced following stroke lead to increased TRPV1 channel sensitivity to agonists. Second, activation of TRPV1 channels in the thermoregulatory system produces a rapid and sustainable decrease in body temperature (mild hypothermia) that is neuroprotective. In this context, TRPV1 activation effectively lowers the body's temperature set point, allowing for a more rapid and controlled level of therapeutic hypothermia to be achieved. We have already established that pharmacological activation of TRPV1 channels (TRPV1 agonism) is neuroprotective. While part of the neuroprotective effect is through induction of mild hypothermia, our new studies indicate that an additional protective effect may be through restoration of flow to hypoperfused brain regions. We now propose the overall hypothesis that TRPV1 agonism provides two arms of protection following stroke by 1) improving reperfusion in injured brain regions and 2) promoting protective hypothermia. We will study these mechanisms separately and then in combination to determine the additive benefit following stroke in adult and aged mice.
In aim 1, we will demonstrate selective increase in cerebral blood flow within the ischemia/reperfusion territory with TRPV1 agonism. These studies include cerebral blood flow measurements in adult and aged mice following stroke. The effect of TRPV1 agonist on cerebral perfusion will be determined in normothermic and hypothermic conditions.
In aim 2, we will determine the role of ROS in potentiating endothelial TRPV1-mediated vasodilation. We will examine the mechanism by which ROS promote potentiated TRPV1-mediated vasodilation and increased cerebral blood flow. These studies will utilize isolated cerebral arteries and laser Doppler assessment of the intact cerebral microvasculature.
In aim 3, we will demonstrate the neuroprotective benefit of hypothermia- independent and hypothermia-dependent mechanisms of TRPV1 agonism following stroke. We will determine the roles of improved cerebral perfusion and hypothermia in the mechanism of TRPV1-mediated neuroprotection. Aged mice will be evaluated by behavioral testing, histology, and blood brain barrier function during the course of one month of reperfusion. All together, these studies should establish TRPV1 agonism as a multi-faceted approach to neuroprotection following stroke.
This project explores new methods in the treatment of stroke. In particular, these studies define the way capsaicin-like compounds can be used to produce protective whole body cooling (induced hypothermia) as well as increased blood flow in the injured region of the brain.
|Fasipe, Titilope A; Hong, Sung-Ha; Da, Qi et al. (2018) Extracellular Vimentin/VWF (von Willebrand Factor) Interaction Contributes to VWF String Formation and Stroke Pathology. Stroke 49:2536-2540|