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Erythropoietin modulation of astrocyte water permeability as a component of neuroprotection.

ABSTRACT: Disturbed brain water homeostasis with swelling of astroglial cells is a common complication in stroke, trauma, and meningitis and is considered to be a major cause of permanent brain damage. Astroglial cells possess the water channel aquaporin 4 (AQP4). Recent studies from our laboratory have shown that glutamate, acting on group I metabotropic glutamate receptors (mGluRs), increases the permeability of astrocyte AQP4, which, in situations of hypoxia-ischemia, will increase astrocyte water uptake. Here we report that erythropoietin (EPO), which in recent years has emerged as a potent neuro-protective agent, antagonizes the effect of a group I mGluR agonist on astrocyte water permeability. Activation of group I mGluRs triggers fast and highly regular intracellular calcium oscillations and we show that EPO interferes with this signaling event by altering the frequency of the oscillations. These effects of EPO are immediate, in contrast to the neuroprotective effects of EPO that are known to depend upon gene activation. Our findings indicate that EPO may directly reduce the risk of astrocyte swelling in stroke and other brain insults. In support of this conclusion we found that EPO reduced the neurological symptoms in a mouse model of primary brain edema known to depend upon AQP4 water transport.

SUBMITTER: Gunnarson E

PROVIDER: S-EPMC2629445 | biostudies-literature | 2009 Feb

REPOSITORIES: biostudies-literature

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Erythropoietin modulation of astrocyte water permeability as a component of neuroprotection.

Gunnarson Eli E Song Yutong Y Kowalewski Jacob M JM Brismar Hjalmar H Brines Michael M Cerami Anthony A Andersson Ulf U Zelenina Marina M Aperia Anita A

Proceedings of the National Academy of Sciences of the United States of America 20090121 5

Disturbed brain water homeostasis with swelling of astroglial cells is a common complication in stroke, trauma, and meningitis and is considered to be a major cause of permanent brain damage. Astroglial cells possess the water channel aquaporin 4 (AQP4). Recent studies from our laboratory have shown that glutamate, acting on group I metabotropic glutamate receptors (mGluRs), increases the permeability of astrocyte AQP4, which, in situations of hypoxia-ischemia, will increase astrocyte water upta ...[more]

PMID: 19164545

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Project description:Despite of the major role of aquaporin (AQP) water channels in controlling transmembrane water fluxes, alternative ways for modulating water permeation have been proposed. In the Central Nervous System (CNS), Aquaporin-4 (AQP4) is reported to be functionally coupled with the calcium-channel Transient-Receptor Potential Vanilloid member-4 (TRPV4), which is controversially involved in cell volume regulation mechanisms and water transport dynamics. The present work aims to investigate the selective role of TRPV4 in regulating plasma membrane water permeability in an AQP4-independent way. Fluorescence-quenching water transport experiments in Aqp4-/- astrocytes revealed that cell swelling rate is significantly increased upon TRPV4 activation and in the absence of AQP4. The biophysical properties of TRPV4-dependent water transport were therefore assessed using the HEK-293 cell model. Calcein quenching experiments showed that chemical and thermal activation of TRPV4 overexpressed in HEK-293 cells leads to faster swelling kinetics. Stopped-flow light scattering water transport assay was used to measure the osmotic permeability coefficient (Pf, cm/s) and activation energy (Ea, kcal/mol) conferred by TRPV4. Results provided evidence that although the Pf measured upon TRPV4 activation is lower than the one obtained in AQP4-overexpressing cells (Pf of AQP4 = 0.01667 ± 0.0007; Pf of TRPV4 = 0.002261 ± 0.0004; Pf of TRPV4 + 4αPDD = 0.007985 ± 0.0006; Pf of WT = 0.002249 ± 0.0002), along with activation energy values (Ea of AQP4 = 0.86 ± 0.0006; Ea of TRPV4 + 4αPDD = 2.73 ± 1.9; Ea of WT = 8.532 ± 0.4), these parameters were compatible with a facilitated pathway for water movement rather than simple diffusion. The possibility to tune plasma membrane water permeability more finely through TRPV4 might represent a protective mechanism in cells constantly facing severe osmotic challenges to avoid the potential deleterious effects of the rapid cell swelling occurring via AQP channels.

Project description:BackgroundHigh-dose erythropoietin has been shown to have a neuroprotective effect in preclinical models of neonatal brain injury, and phase 2 trials have suggested possible efficacy; however, the benefits and safety of this therapy in extremely preterm infants have not been established.MethodsIn this multicenter, randomized, double-blind trial of high-dose erythropoietin, we assigned 941 infants who were born at 24 weeks 0 days to 27 weeks 6 days of gestation to receive erythropoietin or placebo within 24 hours after birth. Erythropoietin was administered intravenously at a dose of 1000 U per kilogram of body weight every 48 hours for a total of six doses, followed by a maintenance dose of 400 U per kilogram three times per week by subcutaneous injection through 32 completed weeks of postmenstrual age. Placebo was administered as intravenous saline followed by sham injections. The primary outcome was death or severe neurodevelopmental impairment at 22 to 26 months of postmenstrual age. Severe neurodevelopmental impairment was defined as severe cerebral palsy or a composite motor or composite cognitive score of less than 70 (which corresponds to 2 SD below the mean, with higher scores indicating better performance) on the Bayley Scales of Infant and Toddler Development, third edition.ResultsA total of 741 infants were included in the per-protocol efficacy analysis: 376 received erythropoietin and 365 received placebo. There was no significant difference between the erythropoietin group and the placebo group in the incidence of death or severe neurodevelopmental impairment at 2 years of age (97 children [26%] vs. 94 children [26%]; relative risk, 1.03; 95% confidence interval, 0.81 to 1.32; P = 0.80). There were no significant differences between the groups in the rates of retinopathy of prematurity, intracranial hemorrhage, sepsis, necrotizing enterocolitis, bronchopulmonary dysplasia, or death or in the frequency of serious adverse events.ConclusionsHigh-dose erythropoietin treatment administered to extremely preterm infants from 24 hours after birth through 32 weeks of postmenstrual age did not result in a lower risk of severe neurodevelopmental impairment or death at 2 years of age. (Funded by the National Institute of Neurological Disorders and Stroke; PENUT ClinicalTrials.gov number, NCT01378273.).

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Erythropoietin modulation of astrocyte water permeability as a component of neuroprotection.

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Erythropoietin modulation of astrocyte water permeability as a component of neuroprotection.

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