Loss of merlin expression in sporadic meningiomas, ependymomas and schwannomas.

Neurofibromatosis 2 (NF2) is an inherited disorder in which affected individuals develop schwannomas and meningiomas. NF2 is mapped to chromosome 22q in a region where frequent loss of heterozygosity also occurs in sporadic meningiomas, ependymomas, and schwannomas. Using NF2 protein (merlin or schwannomin)-specific antibodies, 11 of 14 sporadic schwannomas, three of eight sporadic ependymomas, and 16 of 19 sporadic meningiomas demonstrated significantly reduced or absent merlin expression, suggesting that NF2 may be involved in the pathogenesis of these sporadic tumors.

Up-regulation of specific NF 1 gene transcripts in sporadic pilocytic astrocytomas.

Pilocytic astrocytomas of the optic nerve (optic nerve gliomas) are closely associated with neurofibromatosis 1 (NF1), and allelic losses of the NF1 gene region on chromosome 17q occur in sporadic pilocytic astrocytomas. We therefore hypothesized that the NF1 gene acts as a tumor suppressor gene in pilocytic astrocytomas, and that NF1 gene expression would be reduced or absent in these tumors. To evaluate this possibility, we examined quantitative and qualitative aspects of NF1 gene expression in six sporadic pilocytic astrocytomas. Surprisingly, the NF1 gene was overexpressed up to fourfold in these tumors when compared with normal brain. This up-regulation was accompanied by immunohistochemical positivity using a carboxyl-terminal antibody and by the absence of mutations in one kilobase of the NF1 coding sequence, consistent with the expressed transcript and protein being full length and probably wild type. Pilocytic astrocytomas showed a marked predominance of transcripts containing exon 23a and lacking exon 9br, the same isoforms that are expressed by normal and reactive astrocytes and malignant astrocytomas. These data illustrate that pilocytic astrocytomas overexpress specific NF1 gene transcripts, perhaps as a regulatory response to growth stimuli. The role of the NF1 gene as a tumor suppressor in pilocytic astrocytomas, however, remains to be proven.

Increased neurofibromatosis 1 gene expression in astrocytic tumors: positive regulation by p21-ras.

The neurofibromatosis 1 (NF1) gene has been implicated in astrocyte growth regulation in several studies. To determine whether loss of NF1 expression is associated with progression towards malignancy in sporadic astrocytomas from individuals without NF1, twenty-eight fresh astrocytoma operative specimens (low and high grade tumors) and seven primary human astrocytoma cell lines were examined for NF1 mRNA and protein expression. In all astrocytomas examined, increased NF1 expression was observed in the tumors relative to normal resting astrocytes. This increased neurofibromin expression correlated with elevated levels of activated p21-ras measured in both the fresh tumor specimens and the primary cell lines. Furthermore, when levels of activated p21 ras were decreased in astrocytoma cells expressing the ras inhibitory Asn-17 dominant-negative mutant, levels of neurofibromin expression decreased. In addition, fibroblasts induced to express oncogenic activated p21-ras(val12) had increased expression of NF1. These results suggested that neurofibromin expression is increased in human astrocytic tumors as a result of positive feedback regulation by increased levels of activated p21-ras.

Increased expression of the neurofibromatosis 1 (NF1) gene product, neurofibromin, in astrocytes in response to cerebral ischemia.

Tumor suppressor genes encode proteins involved in growth regulation in differentiating and proliferating cells. Previous work from our laboratory has demonstrated that the neurofibromatosis 1 (NF1) tumor suppressor gene is dramatically upregulated in astrocytes stimulated with dibutyryl cyclic AMP and proinflammatory cytokines. To explore the possibility that the NF1 gene product, neurofibromin, plays a role in the reactive gliosis seen in response to cerebral ischemia, expression of NF1 was examined in both focal and global models of rat cerebral ischemia. In this report, we demonstrate the increased expression of both neurofibromin and glial fibrillary acidic protein (GFAP) in astrocytes surrounding areas of focal ischemia. Similar increases in neurofibromin and GFAP immunoreactivity were also observed in reactive astrocytes in the hippocampal region in a global model of ischemia. These results suggest a novel role for the NF1 tumor suppressor gene in growth regulatory pathways involved in cellular remodeling and in response to injury.

Sjogren's cerebritis complicated by subarachnoid hemorrhage and bilateral superior cerebellar artery occlusion: case report.

We report a case of chronic Sjogren's cerebritis complicated by bilateral superior cerebellar artery occlusion and diffuse subarachnoid hemorrhage. Although primary Sjogren's syndrome with chronic leptomeningeal involvement has been well documented and a spectrum of central nervous system disease previously outlined, no case of intracranial subarachnoid hemorrhage with major intracranial vessel occlusion has been reported.

Differential metabolism of hydroxyeicosatetraenoic acid isomers by mouse cerebromicrovascular endothelium.

Hydroxyeicosatetraenoic acid (HETE) derivatives of arachidonic acid are produced in the brain and have been implicated as pathologic mediators in various types of brain injury. To understand better their fate in the brain, particularly in cerebral microvessels, several HETEs were incubated with cultured mouse cerebromicrovascular endothelium for 1, 2, and 4 h, followed by HPLC analysis of medium and cellular lipids. 5(S)-, 8(RS)-, and 9(RS)-HETE were not metabolized by the cells, but were extensively incorporated, unmodified, into cell lipids. On the other hand, 11(RS)-, 12(S)-, and 15(S)-HETE were extensively metabolized and only minimally incorporated into cell lipids. Previously, the major 12-HETE metabolite was identified as 8-hydroxyhexadecatrienoic acid. In the present study, we identified the major 11-HETE metabolite as 7-hydroxyhexadecatrienoic acid and the major 15-HETE metabolite as 11-hydroxyhexadecatrienoic acid. omega-3 compounds, 15(S)- and 12(S)-hydroxyeicosapentaenoic acids (HEPE), were also metabolized to more polar compounds, but to a lesser extent than their tetraenoic acid, omega-6 counterparts. Comparison of 5-, 12-, and 15-HETE enantiomers revealed no differences in metabolism or incorporation between the R and S stereoisomers. These data suggest that many isomers of HETE and HEPE can be incorporated into cell lipids or metabolized by pathways that do not distinguish between enantiomers. These pathways, however, are sensitive to the position or number of double bonds and are selective based on the position of the hydroxyl group.

Brain microvessel 12-hydroxyeicosatetraenoic acid is the (S) enantiomer and is lipoxygenase derived.

12-Hydroxyeicosatetraenoic acid (12-HETE) production from arachidonic acid by cerebral microvessels isolated from perfused adult murine brain was reduced by the lipoxygenase inhibitors baicalein, esculetin, gossypol, nordihydroguaiaretic acid, and quercetin. Except for quercetin and gossypol, the IC50 did not exceed 10 microM. Each inhibitor, except baicalein, also decreased microvessel prostaglandin production when present in concentrations above their IC50 value for 12-HETE. In contrast, inhibitors of the cytochrome P450 monooxygenase system, clotrimazole, metyrapone, and proadifen (SKF-525A), had little effect on microvessel 12-HETE production. Chiral phase HPLC analysis revealed that only the (S) enantiomer of 12-HETE was formed. The major microvessel metabolite of eicosapentaenoic acid co-eluted with 12-hydroxyeicosapentaenoic acid (12-HEPE) on reverse-phase HPLC and the (S) enantiomer of 12-HEPE on chiral phase HPLC. Furthermore, like 12-HETE, 12-HEPE production was blocked by lipoxygenase inhibitors. These studies demonstrate that brain microvessels produce only the (S) enantiomeric 12-hydroxy derivatives of both arachidonic acid and eicosapentaenoic acid by the action of a lipoxygenase that can be selectively inhibited by baicalein. Since arachidonic acid and eicosapentaenoic acid are available to cerebral blood vessels in certain pathological settings, these 12-hydroxy acid lipoxygenase products may mediate some of the cerebrovascular dysfunction that occurs following stroke, brain trauma, or seizures.