This is a revised competitive renewal grant application (R01NS48216-A1) to study the role of Na+/H+ exchanger isoform 1 (NHE1) in focal ischemic damage. Limited information is known about the role of NHE-1 in cerebral ischemia and whether inhibition of NHE-1 is neuroprotective against ischemic brain damage. In the initial funding period, we found that NHE-1 was essential in regulation of somata pHi in cortical astrocytes and neurons. NHE-1 activity in astrocytes and neurons was stimulated during reoxygenation (REOX) following oxygen and glucose deprivation (OGD). Either pharmacological inhibition or genetic ablation of NHE-1 activity protected cells from ischemic damage in in vitro and in vivo ischemic models. Excessive stimulation of NHE-1 activity led to dysregulation of intracellular Na+ and Ca2+ homeostasis in conjunction of reversal of Na+/Ca2+ exchange (NCXrev). Many important issues remain unresolved. First, the postsynaptic neuronal dendrite is selectively vulnerable to hypoxic-ischemic brain injury. Dendritic beading and injury are an early hallmark of neuronal injury in the absence of neuronal death. Na+ influx and mitochondrial dysfunction are important in the acute dendritic injury. However, it is unknown whether NHE-1 and NCXrev contribute to the selective vulnerability of postsynaptic neuronal dendrites. Secondly, activated microglia produce a "respiratory burst" via NADPH oxidase. Therefore, activation of microglia is associated with a large amount of intracellular H+ generation. But, the role of NHE-1 in regulation of microglial pHi and inflammatory responses following ischemia remains unexplored. In the next stage of our study, we will propose two hypotheses: 1) the robust activity of Na+- dependent H+ extrusion mechanism (NHE) in conjunction with activation of NCXrev contributes to ischemic dendritic injury by excessive accumulation of Na+, Ca2+, and mitochondrial dysfunction;2) NHE-1 activity is stimulated upon microglia activation to meet the demand of maintaining the optimal pHi for NADPH oxidase function following ischemia. Moreover, NHE1-mediated [Na+]i overload and subsequent activation of NCXrev may elevate [Ca2+]i and enhance the p38 MAPK- and/or NF-?B-mediated inflammatory responses. Therefore, inhibition of NHE-1 activity pharmacologically or via genetic ablation may offer neuroprotection against the acute cerebral ischemic injury via blocking these cellular events. The hypotheses will be tested in three Aims. The results of the proposed studies will enhance our understanding of the appeared paradoxical role of NHE1 in the CNS following ischemia. This knowledge will be beneficial for developing a more effective approach to stroke treatment.

Public Health Relevance

This proposal is to study the role of Na+/H+ exchanger isoform 1 (NHE1) in cerebral ischemic damage. The long-term goal of the research is to understand the role of ion transport proteins in disruption of ion homeostasis following ischemia and to determine whether these ion transport proteins are potential targets for developing more effective stroke treatments.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Research Project (R01)
Project #
5R01NS048216-09
Application #
8256768
Study Section
Brain Injury and Neurovascular Pathologies Study Section (BINP)
Program Officer
Silberberg, Shai D
Project Start
2003-12-01
Project End
2014-04-30
Budget Start
2012-05-01
Budget End
2013-04-30
Support Year
9
Fiscal Year
2012
Total Cost
$341,507
Indirect Cost
$116,090
Name
University of Pittsburgh
Department
Neurology
Type
Schools of Medicine
DUNS #
004514360
City
Pittsburgh
State
PA
Country
United States
Zip Code
15213
Leng, Tiandong; Shi, Yejie; Xiong, Zhi-Gang et al. (2014) Proton-sensitive cation channels and ion exchangers in ischemic brain injury: new therapeutic targets for stroke? Prog Neurobiol 115:189-209
Cong, Damin; Zhu, Wen; Shi, Yejie et al. (2014) Upregulation of NHE1 protein expression enables glioblastoma cells to escape TMZ-mediated toxicity via increased H? extrusion, cell migration and survival. Carcinogenesis 35:2014-24
Cengiz, Pelin; Kintner, Douglas B; Chanana, Vishal et al. (2014) Sustained Na+/H+ exchanger activation promotes gliotransmitter release from reactive hippocampal astrocytes following oxygen-glucose deprivation. PLoS One 9:e84294
Lam, Tina I; Brennan-Minnella, Angela M; Won, Seok Joon et al. (2013) Intracellular pH reduction prevents excitotoxic and ischemic neuronal death by inhibiting NADPH oxidase. Proc Natl Acad Sci U S A 110:E4362-8
Shi, Yejie; Yuan, Hui; Kim, Dong et al. (2013) Stimulation of Na(+)/H(+) exchanger isoform 1 promotes microglial migration. PLoS One 8:e74201
Uluc, Kutluay; Kendigelen, Pýýnar; Fidan, Emin et al. (2013) TrkB receptor agonist 7, 8 dihydroxyflavone triggers profound gender- dependent neuroprotection in mice after perinatal hypoxia and ischemia. CNS Neurol Disord Drug Targets 12:360-70
Shi, Yejie; Kim, Dong; Caldwell, Marie et al. (2013) The role of Na(+)/h (+) exchanger isoform 1 in inflammatory responses: maintaining H(+) homeostasis of immune cells. Adv Exp Med Biol 961:411-8
Ferrazzano, Peter; Chanana, Vishal; Uluc, Kutluay et al. (2013) Age-dependent microglial activation in immature brains after hypoxia- ischemia. CNS Neurol Disord Drug Targets 12:338-49
Begum, Gulnaz; Kintner, Douglas; Liu, Yan et al. (2012) DHA inhibits ER Ca2+ release and ER stress in astrocytes following in vitro ischemia. J Neurochem 120:622-30
Cengiz, Pelin; Kleman, Neil; Uluc, Kutluay et al. (2011) Inhibition of Na+/H+ exchanger isoform 1 is neuroprotective in neonatal hypoxic ischemic brain injury. Antioxid Redox Signal 14:1803-13

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