Intracellular pH in the Brain following Transient Ischemia

Mabe, Hideo; Blomqvist, Photjanee; Siesjö, Bo K.

doi:10.1038/jcbfm.1983.13

Cited by 132 publications

(58 citation statements)

References 26 publications

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“…Moreover, this elevated NHE1 activity increased pH i to 7.38 after 60 min REOX from a basal level of 7.05. It has been reported that pH i is reduced in brain during transient ischemia and shifts in the alkaline direction during 60 min recovery and returns to normal levels at 3 h recovery (27). Activation of NHEs is thought to be one of the main mechanisms of alkalinization during reperfusion, which is consistent with our findings.…”

Section: Nhe1 Activity Is Stimulated In Cortical Neurons Aftersupporting

confidence: 82%

ERK1/2-p90RSK-mediated Phosphorylation of Na+/H+ Exchanger Isoform 1

Luo

Kintner

Shull

et al. 2007

Journal of Biological Chemistry

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The function and regulation of Na ؉ /H ؉ exchanger isoform 1 (NHE1) following cerebral ischemia are not well understood. In this study, we demonstrate that extracellular signal-related kinases (ERK1/2) play a role in stimulation of neuronal NHE1 following in vitro ischemia. NHE1 activity was significantly increased during 10 -60 min reoxygenation (REOX) after 2-h oxygen and glucose deprivation (OGD). OGD/REOX not only increased the V max for NHE1 but also shifted the K m toward decreased [H ؉ ] i . These changes in NHE1 kinetics were absent when MAPK/ERK kinase (MEK) was inhibited by the MEK inhibitor U0126. There were no changes in the levels of phosphorylated ERK1/2 (p-ERK1/2) after 2 h OGD. The p-ERK1/2 level was significantly increased during 10 -60 min REOX, which was accompanied by nuclear translocation. U0126 abolished REOX-induced elevation and translocation of p-ERK1/2. We further examined the ERK/90-kDa ribosomal S6 kinase (p90 RSK ) signaling pathways. At 10 min REOX, phosphorylated NHE1 was increased with a concurrent elevation of phosphorylation of p90 RSK , a known NHE1 kinase. Inhibition of MEK activity with U0126 abolished phosphorylation of both NHE1 and p90 RSK . Moreover, neuroprotection was observed with U0126 or genetic ablation or pharmacological inhibition of NHE1 following OGD/REOX. Taken together, these results suggest that activation of ERK1/2-p90 RSK pathways following in vitro ischemia phosphorylates NHE1 and increases its activity, which subsequently contributes to neuronal damage. The Naϩ /H ϩ exchanger (NHE) 2 family is a group of membrane transport proteins that catalyzes the secondary active electroneurtral exchange of one Na ϩ for one H ϩ . To date, nine NHE isoforms (NHE1-9) have been cloned in mammalian tissues (1). Na ϩ /H ϩ exchanger isoform 1 (NHE1) is the most abundant NHE isoform in the rat central nervous system (2) and crucial in regulation of neuronal pH i (3, 4). We have recently reported that NHE1 activity plays an important role in neuronal damage in both in vitro and in vivo ischemic models (4). Inhibition of NHE1 activity during OGD/REOX prevents intracellular Na ϩ and Ca 2ϩ overload and thus reduces the Ca 2ϩ -mediated cascade of deleterious events (4). In acutely isolated CA1 neurons, an anoxia-triggered intracellular alkalization depends on activation of NHE1 (5). We also found that NHE1 activity is stimulated in cortical astrocytes following in vitro ischemia (6). However, whether NHE1 activity is overstimulated in cortical neurons following in vitro ischemia remains unknown.NHE1 has two large functional domains. The N-terminal transmembrane domain (ϳ500 amino acids) is responsible for cation translocation, and the cytoplasmic C-terminal domain (ϳ315 amino acids) is the main regulatory site for the NHE1 activity (7). The distal C-terminal tail of NHE1 contains a number of serine and threonine residues that are phosphorylated by several protein kinases, including extracellular signal-related kinases (ERK1/2) and 90-kDa ribosomal S6 kinase (p90 RSK ) (8). Activa...

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Section: Nhe1 Activity Is Stimulated In Cortical Neurons Aftersupporting

confidence: 82%

ERK1/2-p90RSK-mediated Phosphorylation of Na+/H+ Exchanger Isoform 1

Luo

Kintner

Shull

et al. 2007

Journal of Biological Chemistry

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“…Since the values agreed well with the results obtained in four control animals in a concur rent study (Mabe et al, 1983), the values were pooled with these to give a group of six animals.…”

Section: Experimental Groupssupporting

confidence: 61%

Recirculation in the Rat Brain following Incomplete Ischemia

Kågström

Smith

Siesjö

1983

J Cereb Blood Flow Metab

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154

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Summary: The objective of this study was to charac terize local cerebral blood flow (CBF) in the recirculation period following incomplete forebrain ischemia. Specifi cally, we wished to determine whether perfusion defects developed in the immediate recirculation period, to study how initial hyperemia and delayed hypoperfusion at the local level were related to the severity of the preceding ischemia, and to find out whether reflow was influenced by the nutritional state of the animals. To that end, fore brain ischemia of 15 min duration was induced in fed and fasted ventilated rats under 70% N20. Local CBF was measured with an autoradiographic technique at the end of ischemia, as well as at 5 and 60 min following the start of recirculation. Control experiments were performed to examine the influence of ischemia on cerebral metabolic state in fed and fasted animals. The ischemia reduced CBF to excessively low values «5% of control) in manyIn the accompanying article (Kl:1gstrom et aI., 1983) we reviewed previous results demonstrating that transient ischemia is usually followed by an initial hyperemia, later to be succeeded by a sec ondary decrease in cerebral blood flow (CBF) ("delayed hypoperfusion" ). In that article we re ported on experiments designed to characterize local cerebral blood flow (lCBF) in the recovery period following complete brain ischemia of 5 -30 min duration, as induced in lightly anaesthetized, artificially ventilated rats. The results obtained with 15 min of ischemia confirmed that a delayed hypoperfusion occurs. However, the autoradio graphic techniques used made it possible to reveal the appearance of a true "no-reflow" phenomenon, i.e., an initial hindrance to recirculation in centrally located brain structures. Thus, circulatory events following complete ischemia do not conform to the Address correspondence and reprint requests to Dr. Kiigstrom at Department of Neurosurgery, University Hospital, S-22185 Lund, Sweden .Abbreviations used: PCr, Phosphocreatine; EC, energy charge. 183forebrain structures, including the cerebral cortices, caudoputamen, and hippocampus. In spite of this, perfu sion defects failed to appear after 5 min of recirculation. Instead, moderate to marked hyperemia was present in all previously ischemic structures. After 60 min of recircula tion, pronounced hypoperfusion developed. The mag nitude of the initial hyperemia was poorly related to the severity of the preceding ischemia, but the latter partly determined the degree of delayed hypoperfusion. Thus, little or no hypoperfusion developed in structures whose flow rates exceeded 30-40% of control during ischemia. Fasted animals had a better preserved flow to many structures than did fed animals, indicating that the detri mental effect of feeding (or glucose infusion) is also re flected in lower perfusion rates. Key Words: Acidosis Cerebral blood flow-Delayed hypoperfusion-Incom plete forebrain ischemia-Rat-Reflow patterns.simple sequence, ischemia-initial hyperemia delayed hypoperfusion.

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“…Thus, phosphorylated polyUb can be either recruited or generated onsite. Upon oxidative stress, neurodegeneration, and aging, Ub phosphorylation level drastically increases (4,8,31), whereas mitophagy, apoptosis, ischemia, inflammation, aging, and many pathophysiological conditions are all associated with changes in cellular pH (32)(33)(34)(35). Altogether, it is likely that certain functions of pUb are only turned on in response to changes in both Ub phosphorylation level and environmental pH.…”

Section: Discussionmentioning

confidence: 99%

Ubiquitin S65 phosphorylation engenders a pH-sensitive conformational switch

Gong

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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Ubiquitin (Ub) is an important signaling protein. Recent studies have shown that Ub can be enzymatically phosphorylated at S65, and that the resulting pUb exhibits two conformational states-a relaxed state and a retracted state. However, crystallization efforts have yielded only the structure for the relaxed state, which was found similar to that of unmodified Ub. Here we present the solution structures of pUb in both states obtained through refinement against state-specific NMR restraints. We show that the retracted state differs from the relaxed state by the retraction of the last β-strand and by the extension of the second α-helix. Further, we show that at 7.2, the pK a value for the phosphoryl group in the relaxed state is higher by 1.4 units than that in the retracted state. Consequently, pUb exists in equilibrium between protonated and deprotonated forms and between retracted and relaxed states, with protonated/relaxed species enriched at slightly acidic pH and deprotonated/retracted species enriched at slightly basic pH. The heterogeneity of pUb explains the inability of phosphomimetic mutants to fully mimic pUb. The pHsensitive conformational switch is likely preserved for polyubiquitin, as single-molecule FRET data indicate that pH change leads to quaternary rearrangement of a phosphorylated K63-linked diubiquitin. Because cellular pH varies among compartments and changes upon pathophysiological insults, our finding suggests that pH and Ub phosphorylation confer additional target specificities and enable an additional layer of modulation for Ub signals., a 76-residue signaling protein, is found ubiquitously in cells. Two or more Ub molecules can be covalently linked to form a diubiquitin (diUb) and then a polyubiquitin (polyUb), as an isopeptide bond is formed between the carboxylate group of one Ub (called the distal Ub) and the amine group of another Ub (called the proximal Ub). Owing to the characteristic quaternary structures of polyUb and specific interactions between polyUb and its target proteins (1, 2), a polyUb with a specific linkage can be involved in a distinctive set of cellular functions (3).The heterogeneity of Ub also arises from other types of covalent modifications. Proteomics studies have indicated that Ub is phosphorylated at multiple sites (4, 5). However, PINK1 is the only Ub kinase known to date, which specifically phosphorylates Ub at S65 (6, 7). Under normal conditions, only a fraction of Ub is S65-phosphorylated. However, upon oxidative stress, neurodegeneration, or aging, the level of S65 phosphorylation increases significantly (4, 8). S65-phosphorylated Ub (pUb) in turn can activate PARKIN, a ubiquitin ligase, and induce mitophagy (9-12). However, no other pUb-specific targets have been clearly identified, and how phosphorylation affects Ub signaling in general remains unclear.Previously, Komander and coworkers showed that pUb gives two distinct sets of NMR peaks, which correspond to the two conformational states of pUb exchanging at a slow timescale (13). Based on NMR long-r...

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Intracellular pH in the Brain following Transient Ischemia

Cited by 132 publications

References 26 publications

ERK1/2-p90RSK-mediated Phosphorylation of Na+/H+ Exchanger Isoform 1

ERK1/2-p90RSK-mediated Phosphorylation of Na+/H+ Exchanger Isoform 1

Recirculation in the Rat Brain following Incomplete Ischemia

Ubiquitin S65 phosphorylation engenders a pH-sensitive conformational switch

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