Increased Mdm2 expression in rat brain after transient middle cerebral artery occlusion.

The negative regulator of p53 transactivation, Mdm2, increased in the ischemic territory after 90 minutes of transient middle cerebral artery occlusion in spontaneously hypertensive rats compared to sham controls. Increased mdm2 mRNA was detected by semiquantitative reverse transcriptase polymerase chain reaction by 6 hours of reperfusion in the ipsilateral hemisphere. In situ hybridization histochemistry was used to localize increases in mdm2 mRNA which occurred in neurons of ischemic cortex and dorsolateral striatum. The number of labeled neurons increased by approximately 20-fold and the cells displayed five-fold increases of mdm2 mRNA in the cortex. Immunohistochemical staining for Mdm2 revealed that its mRNA was efficiently translated in the ischemic cortex, but not striatum, by 8 to 24 hours of reperfusion. Western blotting confirmed 30- to 40-fold increases in the full-length protein of 90 kd at these time points without evidence of alternative splicing. Because Mdm2 is a negative regulator of the apoptosis promoting activity of p53, increased expression of Mdm2 may be a component of a repair response in injured neurons, and supports Mdm2 being an indicator of DNA damage in the brain early after an ischemic insult in a similar way to Gadd45.

Ribotyping and random amplification of polymorphic DNA for nosocomial Enterobacter cloacae isolates in a pediatric intensive-care unit.

Between 1987 and 1989, two sequential outbreaks of nosocomial infection caused by Enterobacter cloacae occur-red in the pediatric intensive-care unit of a tertiary-care teaching hospital. Seventeen strains retrieved from the outbreaks and two control strains identified in other wards were typed by ribotyping and random amplification of polymorphic DNA (RAPD). The results indicated that the genomic pattern of strains identified between the first and second outbreaks was different. We conclude that both ribotyping and RAPD are highly discriminatory and reproducible methods for typing E cloacae. RAPD seems to be more efficacious and cost-effective.

Increased expression of the transcription factor E2F1 during dopamine-evoked, caspase-3-mediated apoptosis in rat cortical neurons.

The transcription factor E2F1 mRNA and protein levels increased in rat cortical neurons in response to dopamine (DA)- or 6-hydroxydopamine (OHDA)-evoked apoptosis. Increased E2F1 protein was detected in the nucleus of neurons by double fluorescent immunocytochemistry using antibodies to E2F1 and NeuN. DA and 6-OHDA induced caspase-3-mediated apoptosis of cortical neurons which was attenuated by the addition of antioxidants or caspase-3 inhibitors to the cultures. Antioxidants prevented DA-evoked neuronal apoptosis, and also attenuated the increase in E2F1 expression. These findings suggest that increased expression of the transcription factor E2F1 may serve as a death signal during DA-evoked neuronal apoptosis.

Early-life exposure to lipopolysaccharide reduces the severity of experimental autoimmune encephalomyelitis in adulthood and correlated with increased urine corticosterone and apoptotic CD4+ T cells.

Early-life exposure to bacterial endotoxins, such as lipopolysaccharides (LPS), can provide neuroprotection against experimental autoimmune encephalomyelitis (EAE) during adulthood, possibly through altering the responsiveness of the immune system. Here, we show that exposure of LPS to neonatal rats resulted in a sustained elevation of corticosterone level in urine when compared with saline-treated rats, and that the high level of urine corticosterone was maintained during the progression of EAE (P<0.05). This high level of production of corticosterone plays an important role in altering the predisposition to EAE-induced neuroinflammation, as a positive correlation occurred between the concentration of urine corticosterone and the increased apoptotic CD4(+) T cells from the peripheral blood. LPS-treated rats also showed a reduced number of CD3(+) T cells in the spinal cord. The splenic antigen-presenting cells showed a reduced expression of MHC II during EAE development in LPS-exposed rats when compared with rats exposed to the saline-treated control. Together, these findings suggest that treating neonatal rats with LPS evokes a sustained elevation of glucocorticoid, which may suppress immune response during EAE by increasing apoptosis of CD4(+) T cells and reducing the expression of MHC II on antigen-presenting cells. Therefore, exposing neonates to bacterial endotoxin may further be developed as an immunization strategy to prevent human multiple sclerosis and other inflammatory brain diseases.

A novel adenoviral vector which mediates hypoxia-inducible gene expression selectively in neurons.

Selective gene expression in neurons is still a challenge. We have developed several expression vectors using a combination of neuron restrictive silencer elements (NRSEs), hypoxia responsive elements (HREs) and CMV minimal promoter (CMVmp). These elements were packaged into replication defective adenovirus to target gene expression selectively in neurons in a hypoxia-regulated manner. Neuronal selectivity and responsiveness to hypoxia of these novel constructs were determined empirically in both neural cell lines and primary cerebellar granule neurons (CGNs). The construct p5HRE-3NRSE exhibited not only the highest level of reporter gene expression in neuronal cells but also in an oxygen concentration-dependent manner when compared with all other constructs. As expected, this construct did not elicit reporter gene expression in non-neuronal cells including human HEK293A and HT29 cells, rat NRK cells, mouse 3T6 cells and 3T3 L1 cells. This construct was packaged into a replication defective adenoviral vector (Ad/5HRE-3NRSE) to determine neuron-selective and hypoxia-inducible gene expression in cultured mouse postmitotic primary CGNs and differentiated human NT2 neurons (NT2/Ns). Remarkably, in response to hypoxia, Ad/5HRE-3NRSE showed strong hypoxia-inducible gene expression selectively in neurons (12-fold induction in CGNs and 22-fold in NT2/Ns), but not in glial cells. Taken together, this vector with restricted gene expression to neurons under the regulation of hypoxia will be a useful tool for investigations of mechanisms of neuronal damage caused by ischemic insult.

Molecular cloning and characterization of rat sperm surface antigen 2B1, a glycoprotein implicated in sperm-zona binding.

The rat sperm surface antigen, 2B1, that has been proposed to play a key role in sperm adhesion to the zona pellucida, has been cloned and its entire cDNA sequenced. Northern blot analysis indicates that 2B1 is encoded by a 2.2-kb RNA transcript that is abundantly expressed in the testis. The deduced protein sequence contains 512 amino-acid residues with a strong candidate signal sequence and C-terminal transmembrane domain. Data base searches reveal a high degree of sequence similarity to guinea pig, rabbit, monkey, and human PH20 sperm surface antigens, and a lower degree of similarity to honey bee and whiteface hornet venom hyaluronidases. Rat 2B1 antigen also possesses hyaluronidase activity, suggesting that it is a bifunctional protein with putative roles in the dispersion of cumulus oophorus cells as well as zona adhesion. However, while it would appear that 2B1 is the rat homologue of the guinea pig PH20 antigen, they differ in a number of important biochemical respects (including their mode of attachment to the sperm membrane and distribution between soluble and membrane-bound fractions), as well as in their localization on the sperm membrane. Expression of regions of the 2B1 protein in recombinant bacterial cells has allowed a preliminary mapping of the 2B1 epitope, and has provided more definitive information on the endoproteolytic processing of 2B1 during epididymal transit.

Testicular biosynthesis and epididymal endoproteolytic processing of rat sperm surface antigen 2B1.

Binding of mammalian spermatozoa to the zona pellucida of homologous eggs is mediated by specific molecules on their surface membranes. In the present investigation we describe the biogenesis, epididymal processing and cellular distribution of a plasma membrane antigen (2B1) on rat spermatozoa that has a potential role in mediating zona binding. 2B1 is expressed postmeiotically in the testis as a precursor glycoprotein (approximately 60 kDa) that first appears on the plasma membrane of stage 6 to 8 round spermatids. Northern and western blot analyses show that there is a close correlation between the timing of transcription and expression of the glycoprotein on the cell surface. During spermatid elongation 2B1 is excluded from the head domain and is sequestered onto the sperm tail. As spermatozoa pass through the caput epididymidis 2B1 is endoproteolytically cleaved at a specific arginine residue (Arg 312) to produce a heterodimeric glycoprotein (approximately 40 kDa and approximately 19 kDa) containing intramolecular disulphide bridges. Endoproteolysis at Arg 312 also takes place during culture of washed testicular or caput spermatozoa in vitro and can be prevented by serine proteinase inhibitors or enhanced by trypsinisation. However, neither processing in vivo or in vitro has any effect on the domain organisation of 2B1 antigen i.e. it remains localised to the tail. These results support the hypothesis that sperm antigens that are important for fertilization are synthesized as precursor molecules in the testis and are then "activated' during epididymal maturation and capacitation, thereby ensuring that they only become fully functional at the site of fertilization.

The transcription factor E2F1 promotes dopamine-evoked neuronal apoptosis by a mechanism independent of transcriptional activation.

The E2F1 transcription factor plays an important role in promoting neuronal apoptosis; however, it is not clear how E2F1 does this. Here we show that E2F1 is involved in dopamine (DA)-evoked apoptosis in cerebellar granule neurons (CGNs). E2F1 -/- CGNs and CGNs expressing an antisense E2F1 cDNA were significantly protected from DA-toxicity relative to controls. The neuronal protection was accompanied by significantly reduced caspase 3 activity. E2F1-mediated neuronal apoptosis did not require activation of gene transcription because: (1) ectopic expression of E2F1 or its mutants lacking the transactivation domain induced neuronal apoptosis, whereas an E2F1 mutant lacking the DNA-binding domain did not; (2) under all of these conditions, known E2F1 target genes including cyclin A, cdc2 and p19(ARF) were not induced; and (3) DA-evoked neuronal apoptosis was associated with up-regulated E2F1, but not transcription of its target genes. Finally, E2F1-mediated neuronal apoptosis was associated with reduced nuclear factor (NF)-kappaB DNA-binding activity. Taken together, these data suggest that E2F1 promotes DA-evoked caspase 3-dependent neuronal apoptosis by a mechanism independent of gene transactivation, and this may possibly occur through inhibition of anti-apoptotic genes including NF-kappaB.

E2F1 mediates death of B-amyloid-treated cortical neurons in a manner independent of p53 and dependent on Bax and caspase 3.

Although B-amyloid (AB) is suggested to play an important role in Alzheimer's disease, the mechanisms that control AB-evoked toxicity are unclear. We demonstrated previously that the cell cycle-related cyclin-dependent kinase 4/6/retinoblastoma protein pathway is required for AB-mediated death. However, the downstream target(s) of this pathway are unknown. We show here that neurons lacking E2F1, a transcription factor regulated by the retinoblastoma protein, are significantly protected from death evoked by AB. Moreover, p53 deficiency does not protect neurons from death, indicating that E2F1-mediated death occurs independently of p53. Neurons protected by E2F1 deficiency have reduced Bax-dependent caspase 3-like activity. However, protection afforded by E2F1, Bax, or caspase 3 deficiency is transient. In the case of E2F1, but not with Bax or caspase 3 deficiency, delayed death is accompanied by DEVD-AFC cleavage activity. Taken together, these results demonstrate the required role of E2F1, Bax, and caspase 3 in AB evoked death, but also suggest the participation of elements independent of these apoptosis regulators.

Induction and modulation of cerebellar granule neuron death by E2F-1.

Growing evidence suggests that certain cell cycle regulators also mediate neuronal death. Of relevance, cyclin D1-associated kinase activity is increased and the retinoblastoma protein (Rb), a substrate of the cyclin D1-Cdk4/6 complex, is phosphorylated during K(+) deprivation-evoked death of cerebellar granule neurons (CGNs). Cyclin-dependent kinase (CDK) inhibitors block this death, suggesting a requirement for the cyclin D1/Cdk4/6-Rb pathway. However, the downstream target(s) of this pathway are not well defined. The transcription factor E2F-1 is regulated by Rb and is reported to evoke death in proliferating cells when overexpressed. Accordingly, we examined whether E2F-1 was sufficient to evoke death of CGNs and whether it was required for death evoked by low K(+). We show that adenovirus-mediated expression of E2F-1 in CGNs results in apoptotic death, which is independent of p53, dependent upon Bax, and associated with caspase 3-like activity. In addition, we demonstrate that levels of E2F-1 mRNA and protein increase during K(+) deprivation-evoked death. The increase in E2F-1 protein is blocked by the CDK inhibitor flavopiridol. Finally, E2F-1-deficient neurons are modestly resistant to death induced by low K(+). These results indicate that E2F-1 expression is sufficient to promote neuronal apoptosis and that endogenous E2F-1 modulates the death of CGNs evoked by low K(+).

Increases in DNA lesions and the DNA damage indicator Gadd45 following transient cerebral ischemia.

Transient global or focal ischemia leads to the production of several types of lesions in the DNA backbone including alkali-labile sites, and both single-stranded (ss) and double-stranded (ds) breaks. The ds breaks result in high molecular weight fragments of 10-50 kbp that contain both 3'- and 5'-OH end-groups, suggesting that more than one endonuclease is involved. This lesioning of DNA is followed by the appearance of the damage-response indicator Gadd45 in the ischemic hemisphere following middle cerebral artery occlusion. By 6 h, gadd45 mRNA was shown to increase by semi-quantitative reverse transcriptase - polymerase chain reaction. In situ hybridization histochemistry indicated that these increases in gadd45 mRNA occurred in pyramidal neurons located on the edge of the infarcted cortex. Gadd45 immunostaining yielded similar findings with maximal protein staining detected at 18 h after occlusion. In neurons, in the infarct core with frank DNA fragmentation shown by in situ TdT-mediated dUTP-biotin nick end labeling (TUNEL) at 24 h, the Gadd45 immunostaining was not visible. Taken together, these findings suggest that Gadd45 responds to DNA damage following ischemia as part of a repair response mounted by brain cells attempting to survive the insult.

Attenuation of neurotoxicity in cortical cultures and hippocampal slices from E2F1 knockout mice.

The E2F1 transcription factor modulates neuronal apoptosis induced by staurosporine, DNA damage and beta-amyloid. We demonstrate E2F1 involvement in neuronal death induced by the more physiological oxygen-glucose deprivation (OGD) in mouse cortical cultures and by anoxia in mouse hippocampal slices. E2F1(+/+) and (-/-) cultures were comparable, in that they contained similar neuronal densities, responded with similar increases in intracellular calcium concentration ([Ca(2+)]i) to glutamate receptor agonists, and showed similar NMDA receptor subunit mRNA expression levels for NR1, NR2A and NR2B. Despite these similarities, E2F1(-/-) cultures were significantly less susceptible to neuronal death than E2F1(+/+) cultures 24 and 48 h following 120-180 min of OGD. Furthermore, the absence of E2F1 significantly improved the ability of CA1 neurons in hippocampal slices to recover synaptic transmission following a transient anoxic insult in vitro. These results, along with our finding that E2F1 mRNA levels are significantly increased following OGD, support a role for E2F1 in the modulation of OGD- and anoxia-induced neuronal death. These findings are consistent with studies showing that overexpression of E2F1 in postmitotic neurons causes neuronal degeneration and the absence of E2F1 decreases infarct volume following cerebral ischemia.

The transcription factor E2F1 modulates apoptosis of neurons.

The transcription factor E2F1 is known to mediate apoptosis in isolated quiescent and postmitotic cardiac myocytes, and its absence decreases the size of brain infarction following cerebral ischemia. To demonstrate directly that E2F1 modulates neuronal apoptosis, we used cultured cortical neurons to show a temporal association of the transcription and expression of E2F1 in neurons with increased neuronal apoptosis. Cortical neurons lacking E2F1 expression (derived from E2F1 -/- mice) were resistant to staurosporine-induced apoptosis as evidenced by the significantly lower caspase 3-like activity and a lesser number of cells with apoptotic morphology in comparison with cortical cultures derived from wild-type mice. Furthermore, overexpressing E2F1 alone using replication-deficient recombinant adenovirus was sufficient to cause neuronal cell death by apoptosis, as evidenced by the appearance of hallmarks of apoptosis, such as the threefold increase in caspase 3-like activity and increased laddered DNA fragmentation, in situ endlabeled DNA fragmentation, and numbers of neuronal cells with punctate nuclei. Taken together, we conclude that E2F1 plays a key role in modulating neuronal apoptosis.

Different patterns of neuropathological disease in rhesus monkeys infected by simian immunodeficiency virus, and their relation to the humoral immune response.

The brains of 21 rhesus monkeys inoculated with SIVMAC251 were examined after intervals ranging from 3 to 27 months and compared with five uninoculated controls. Eighteen animals became infected and individually exhibited several distinct patterns of disease. Nine (50%) had largely intramural leptomeningeal venous infiltrates (LMVI) without multinucleate giant cells (MGC) or foamy macrophages. Three (17%) had only MGC lesions, involving the cerebral parenchyma. One had both patterns and five (33%) neither. The controls had sparse and tiny LMVI only, similar to three inoculated animals that did not become infected. Immunohistochemistry showed the predominance of T and B lymphocytes in LMVI and choroid plexus mononuclear lesions but a predominance of macrophages over lymphocytes in the MGC lesions. Specific disease patterns differed in their association with the humoral immune response. Animals with LMVI were all hypergammaglobulinaemic when killed compared to pre-inoculation levels, and the size of the change in serum immunoglobulin concentration was positively correlated with a quantitative index of LMVI density. Furthermore, their post-mortem lymph node histology was hyperplastic. In contrast, animals found at autopsy to have MGC brain lesions were hypogammaglobulinaemic compared to preinoculation. The results are consistent with two phases in SIV-associated disease: one characterized by LMVI and hypergammaglobulinaemia and another featuring MGC and hypogammaglobulinaemia.