Aquaporin-4 deletion in mice reduces brain edema after acute water intoxication and ischemic stroke

Cerebral edema contributes significantly to morbidity and death associated with many common neurological disorders. However, current treatment options are limited to hyperosmolar agents and surgical decompression, therapies introduced more than 70 years ago. Here we show that mice deficient in aquaporin-4 (AQP4), a glial membrane water channel, have much better survival than wild-type mice in a model of brain edema caused by acute water intoxication. Brain tissue water content and swelling of pericapillary astrocytic foot processes in AQP4-deficient mice were significantly reduced. In another model of brain edema, focal ischemic stroke produced by middle cerebral artery occlusion, AQP4-deficient mice had improved neurological outcome. Cerebral edema, as measured by percentage of hemispheric enlargement at 24 h, was decreased by 35% in AQP4-deficient mice. These results implicate a key role for AQP4 in modulating brain water transport, and suggest that AQP4 inhibition may provide a new therapeutic option for reducing brain edema in a wide variety of cerebral disorders.

Brain tissue oxygenation during hemorrhagic shock, resuscitation, and alterations in ventilation

OBJECTIVES

Recently developed polarographic microelectrodes permit continuous, reliable monitoring of oxygen tension in brain tissue (PbrO2). The aim of this study was to investigate the feasibility and utility of directly monitoring PbrO2 in cerebral tissue during changes in oxygenation or ventilation and during hemorrhagic shock and resuscitation. We also sought to develop a model in which treatment protocols could be evaluated using PbrO2 as an end point.

METHODS

Licox Clark-type polarographic probes were inserted in the brain tissue of 16 swine to monitor PbrO2. In eight swine, changes in PbrO2 were observed over a range of fractional concentrations of inspired O2 (FiO2) as well as during periods of hyperventilation and hypoventilation. In eight other swine, PbrO2 was monitored during a graded hemorrhage of up to 70% estimated blood volume and during the resuscitation period.

RESULTS

When FiO2 was elevated to 100%, PbrO2 increased from a baseline of 15+/-2 mm Hg to 36+/-11 mm Hg. Hyperventilation while breathing 100% oxygen resulted in a 40% decrease in PbrO2 (p < 0.05), whereas hypoventilation increased PbrO2 to 88 mm Hg (p < 0.01). A graded hemorrhage to 50% estimated blood volume significantly reduced PbrO2, mean arterial pressure, and intracranial pressure (p < 0.01). Continued hemorrhage to 70% estimated blood volume resulted in a PbrO2 of 2.9+/-1.5 mm Hg. After resuscitation, PbrO2 was significantly elevated, reaching 65+/-13 mm Hg (p < 0.01), whereas mean arterial pressure and cerebral perfusion pressure simply returned to baseline.

CONCLUSION

Directly measured PbrO2 was highly responsive to changes in FiO2, ventilatory rate, and blood volume in this experimental model. In particular, hypoventilation significantly increased PbrO2, whereas hyperventilation had the opposite effect. The postresuscitation increase in PbrO2 may reflect changes in both O2 delivery and O2 metabolism. These experiments set the stage for future investigations of a variety of resuscitation protocols in both normal and injured brain.

HuD, a neuronal-specific RNA-binding protein, is a potential regulator of MYCN expression in human neuroblastoma cells

HuD is one of a family of neural antigens recognised by the sera of patients with antibody-associated paraneoplastic encephalomyelitis. Localised exclusively to neurons, these proteins are among the earliest markers of the developing nervous system. Sequence analysis suggests that HuD is an RNA-binding protein. Hu protein levels were determined for the three cell types characterising human neuroblastoma cell lines: sympathoadrenal neuroblasts (N), substrate-adherent Schwann/glial/melanoblastic precursors (S) and stem cells (I) which can give rise to both N and S cells. Western blot analysis showed similar levels of protein in three N-type cell lines; S cells have no detectable Hu protein. Northern blot analysis indicated that N cells express all three Hu genes, HuD, HuC and Hel-N1. N cells, mostly from MYCN-amplified cell lines, have consistently higher steady-state levels of MYCN mRNA than S cell counterparts. Nuclear run-on and mRNA half-life experiments revealed no differences in transcription rate or mRNA stability between N and S cells from the LA-N-1 cell line, implicating differences in post-transcriptional regulation. HuD is postulated to be instrumental in splicing/processing and/or stabilisation of mRNAs involved in cell growth and neuronal differentiation. As determined by gel-mobility shift assays, HuD fusion protein binds to the 3'UTR of human MYCN mRNA. Analysis of HuD deletion mutants has demonstrated that the first and second RNA-recognition motifs (RRMs) are required for binding. Whether HuD regulates MYCN expression and thereby influences tumour aggressiveness is of major interest.

Immunization with the paraneoplastic encephalomyelitis antigen HuD does not cause neurologic disease in mice

Paraneoplastic encephalomyelitis/paraneoplastic sensory neuronopathy (PEM/PSN) associated with small cell lung cancer is characterized by high serum and CSF titers of anti-neuronal (anti-Hu) antibodies and by intrathecal synthesis of anti-Hu IgG. A pathologic role for the anti-Hu antibodies in PEM/PSN is further suggested by reported intraneuronal accumulation of the antibodies in the nervous system of PEM/PSN patients at autopsy. We immunized SJL/J mice, Lewis rats, and Hartley guinea pigs with purified recombinant HuD fusion protein. In spite of high-titer anti-HuD antibodies, neurologic and pathologic examination of the animals was normal. Apparent uptake of purified IgG by neurons in the brain proved to be artifactual.

Inhibition of proliferation and induction of differentiation in medulloblastoma- and astrocytoma-derived cell lines with phenylacetate

The authors investigated the effects of a nontoxic differentiation inducer, phenylacetate (PA), on neuroectodermal tumor-derived cell lines. Treatment of medulloblastoma (Daoy and D283 MED) and glioma (U-251MG, C6, and RG2) cell lines resulted in a dose-dependent decline in DNA synthesis and cell proliferation, associated with accumulation in the G0/G1 phase of the cell cycle. Phenylacetate decreased transforming growth factor (TGF)-beta 2 production by medulloblastoma Daoy cells. Neutralizing antibodies against either TGF beta 2 or TGF beta 1 failed to block the growth arrest observed. This suggests that, unlike other differentiation agents, such as retinoic acid, the effect of PA on medulloblastoma proliferation is not mediated by a TGF beta pathway. In addition to cytostasis, PA induced marked morphological changes in U-251MG and C6 glioma cells associated with increased abundance of glial fibrillary acidic protein-positive processes. Although the morphology of PA-treated medulloblastoma cells was not significantly altered, the D283 MED cells exhibited increased expression of neurofilament proteins and Hu antigen, indicative of differentiation along a neuronal pathway. The effects of PA on the medulloblastoma cell lines were compared to its effects on the human neuroblastoma cell line BE(2)C, which is capable of a bidirectional differentiation toward a neuronal or a glial/schwann cell pathway. In BE(2)C cells, PA induced differentiation toward a schwann/glial cell-like phenotype, suggesting that the choice of differentiation pathway is cell type and agent specific. These in vitro antiproliferative and differentiation inducing effects of PA suggest that this agent warrants further evaluation as a potential therapeutic modality for the treatment of medulloblastoma and malignant glioma in humans.

Hu antigens: reactivity with Hu antibodies, tumor expression, and major immunogenic sites

HuD, a human neuronal RNA-binding protein, was the first identified member of a family of antigens that also includes HuC and Hel-N1 (Hu antigens). The serum of all patients with anti-Hu-associated paraneoplastic encephalomyelitis and sensory neuronopathy react with HuD and Hel-N1, but the reactivity with HuC is unknown. In the current study we examined (1) the reactivity of anti-Hu sera with HuD, HuC, and Hel-N1; (2) the expression of HuD, HuC, and Hel-N1 messenger RNA in small-cell lung cancer of patients with and those without paraneoplastic encephalomyelitis/sensory neuronopathy; (3) the correlation between anti-Hu serum reactivity with these three Hu antigens and the type of neurological symptoms; and (4) the major immunogenic sites of HuD. Our findings indicate that all anti-Hu sera react with HuD, HuC, and Hel-N1. However, only HuD is expressed in the small-cell lung cancer tumors, indicating that among the three Hu antigens, HuD appears to play a central role in triggering the anti-Hu immune response. No differences were identified regarding the reactivity of the anti-Hu antibodies with HuD, HuC, and Hel-N1 and the spectrum of neurological symptoms presented by the patients. Study of the major immunogenic sites of HuD resulted in the identification of two major immunodominant regions with at least two distinct epitopes recognized by the serum of all patients with anti-Hu-associated paraneoplastic encephalomyelitis/sensory neuronopathy.