The long term goal of this project is to identify blood-brain barrier (BBB) ion transporters that mediate ischemia-induced brain edema. During the early hours of ischemic stroke, edema forms in the presence of an intact BBB by a process involving BBB transport of Na and Cl from blood into brain. Our studies have shown that Na-K-CI cotransport, present in the luminal BBB membrane, is stimulated by ischemic factors, including hypoxia, aglycemia, vasopressin (AVP) and that inhibiting the cotransporter reduces edema in a rat model of stroke. Thus, the BBB Na-K-CI cotransporter appears to be a major contributor to ischemia-induced edema. We have now found in preliminary studies that a BBB Na/H exchanger also appears to participate in ischemia-induced edema formation which suggests the exciting possibility of an additional BBB target for reduction of edema during the early hours of stroke. Our hypothesis is that, in addition to the cotransporter, a luminal BBB Na/H exchanger is stimulated during ischemia to increase transport of Na from blood into brain.
The first aim i s to determine whether Na/H exchange is present at the luminal BBB membrane and is stimulated by ischemic factors. We will use immunoelectron microscopy to evaluate BBB Na/H exchange protein in situ and microspectrofluorometry to assess ischemic factor effects on CMEC Na/H exchange activity.
The second aim i s to determine whether inhibition of the BBB Na/H exchanger attenuates ischemiainduced edema. Here, we will examine the effect of BBB Na/H exchange inhibition on ischemia-induced changes in rat brain Na and water, using nuclear magnetic resonance methods. We will also assess the efficacy of Na/H exchange and Na-K-CI cotransport inhibitors for reduction of cerebral edema when administered after the onset of ischemia.
The third aim of this project is to evaluate the signaling pathways by which ischemia stimulates BBB Na-K-CI cotransporter and Na/H exchanger activities. We will start by evaluating the roles of AMP kinase, p38 MAP kinase and intracellular [Ca] in hypoxia, aglycemia and AVPinduced stimulation of the cotransporter and exchanger for reasons detailed in the proposal. However, our studies will also include an initial assessment of protein kinase C, ERK1/2 MAP kinase and JNK MAP kinase. For these studies we will use cerebral microvascular endothelial cells to evaluate ischemia-induced activation of the kinases (by Western blot) and the effects of kinase inhibitors on ischemia (hypoxia, aglycemia and AVP) stimulated cotransporter activity (radioisotope flux) and Na/H exchanger activity (spectrofluorometry and radioisotope flux). Ischemia-induced edema is a major cause of brain damage in stroke, a leading cause of death in the U.S. The proposed studies will reveal whether therapeutic approaches aimed at preventing ischemia stimulation of Na-K-CI cotransporter and/or Na/H exchange activity may be of value for attenuating stroke-induced brain edema.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
High Priority, Short Term Project Award (R56)
Project #
2R56NS039953-05A1
Application #
7441319
Study Section
Brain Injury and Neurovascular Pathologies Study Section (BINP)
Program Officer
Jacobs, Tom P
Project Start
2000-04-01
Project End
2008-06-30
Budget Start
2007-07-01
Budget End
2008-06-30
Support Year
5
Fiscal Year
2007
Total Cost
$380,000
Indirect Cost
Name
University of California Davis
Department
Physiology
Type
Schools of Medicine
DUNS #
047120084
City
Davis
State
CA
Country
United States
Zip Code
95618
Chen, Yi-Je; Wallace, Breanna K; Yuen, Natalie et al. (2015) Blood-brain barrier KCa3.1 channels: evidence for a role in brain Na uptake and edema in ischemic stroke. Stroke 46:237-44
Yuen, Natalie; Lam, Tina I; Wallace, Breanna K et al. (2014) Ischemic factor-induced increases in cerebral microvascular endothelial cell Na/H exchange activity and abundance: evidence for involvement of ERK1/2 MAP kinase. Am J Physiol Cell Physiol 306:C931-42
Wallace, Breanna K; Jelks, Karen A; O'Donnell, Martha E (2012) Ischemia-induced stimulation of cerebral microvascular endothelial cell Na-K-Cl cotransport involves p38 and JNK MAP kinases. Am J Physiol Cell Physiol 302:C505-17
Wallace, Breanna K; Foroutan, Shahin; O'Donnell, Martha E (2011) Ischemia-induced stimulation of Na-K-Cl cotransport in cerebral microvascular endothelial cells involves AMP kinase. Am J Physiol Cell Physiol 301:C316-26
Rutkowsky, Jennifer M; Wallace, Breanna K; Wise, Phyllis M et al. (2011) Effects of estradiol on ischemic factor-induced astrocyte swelling and AQP4 protein abundance. Am J Physiol Cell Physiol 301:C204-12
Lam, Tina I; Wise, Phyllis M; O'Donnell, Martha E (2009) Cerebral microvascular endothelial cell Na/H exchange: evidence for the presence of NHE1 and NHE2 isoforms and regulation by arginine vasopressin. Am J Physiol Cell Physiol 297:C278-89