Neuron-specific enolase (NSE) and non-neuronal enolase (NNE) mRNAs are co-expressed in neurons of the rat cerebellum: in situ hybridization histochemistry

Cannabinoid CB2 receptor agonists protect the striatum against malonate toxicity: relevance for Huntington's disease

Cannabinoid agonists might serve as neuroprotective agents in neurodegenerative disorders. Here, we examined this hypothesis in a rat model of Huntington's disease (HD) generated by intrastriatal injection of the mitochondrial complex II inhibitor malonate. Our results showed that only compounds able to activate CB2 receptors were capable of protecting striatal projection neurons from malonate-induced death. That CB2 receptor agonists are neuroprotective was confirmed by using the selective CB2 receptor antagonist, SR144528, and by the observation that mice deficient in CB2 receptor were more sensitive to malonate than wild-type animals. CB2 receptors are scarce in the striatum in healthy conditions, but they are markedly upregulated after the lesion with malonate. Studies of double immunostaining revealed a significant presence of CB2 receptors in cells labeled with the marker of reactive microglia OX-42, and also in cells labeled with GFAP (a marker of astrocytes). We further showed that the activation of CB2 receptors significantly reduced the levels of tumor necrosis factor-alpha (TNF-alpha) that had been increased by the lesion with malonate. In summary, our results demonstrate that stimulation of CB2 receptors protect the striatum against malonate toxicity, likely through a mechanism involving glial cells, in particular reactive microglial cells in which CB2 receptors would be upregulated in response to the lesion. Activation of these receptors would reduce the generation of proinflammatory molecules like TNF-alpha. Altogether, our results support the hypothesis that CB2 receptors could constitute a therapeutic target to slowdown neurodegeneration in HD.

Cannabidiol reduced the striatal atrophy caused 3-nitropropionic acid in vivo by mechanisms independent of the activation of cannabinoid, vanilloid TRPV1 and adenosine A2A receptors

The neuroprotective potential of cannabinoids has been examined in rats with striatal lesions caused by 3-nitropropionic acic (3NP), an inhibitor of mitochondrial complex II. We used the CB1 agonist arachidonyl-2-chloroethylamide (ACEA), the CB2 agonist HU-308, and cannabidiol (CBD), an antioxidant phytocannabinoid with negligible affinity for cannabinoid receptors. The administration of 3NP reduced GABA contents and also mRNA levels for several markers of striatal GABAergic projection neurons, including proenkephalin (PENK), substance P (SP) and neuronal-specific enolase (NSE). We also found reductions in mRNA levels for superoxide dismutase-1 (SOD-1) and -2 (SOD-2), which indicated that 3NP reduced the endogenous antioxidant defences. The administration of CBD, but not ACEA or HU-308, completely reversed 3NP-induced reductions in GABA contents and mRNA levels for SP, NSE and SOD-2, and partially attenuated those found in SOD-1 and PENK. This indicates that CBD is neuroprotective but acted preferentially on striatal neurons that project to the substantia nigra. The effects of CBD were not reversed by the CB1 receptor antagonist SR141716. The same happened with the TRPV1 receptor antagonist capsazepine, in concordance with the observation that capsaicin, a TRPV1 receptor agonist, failed to reproduce the CBD effects. The effects of CBD were also independent of adenosine signalling as they were not attenuated by the adenosine A2A receptor antagonist MSX-3. In summary, this study demonstrates that CBD provides neuroprotection against 3NP-induced striatal damage, which may be relevant for Huntington's disease, a disorder characterized by the preferential loss of striatal projection neurons. This capability seems to be based exclusively on the antioxidant properties of CBD.

Induction of Reversible Cysteine-Targeted Protein Oxidation by an Endogenous Electrophile 15-Deoxy-Δ12,14-prostaglandin J2

We have previously shown that a prostaglandin D(2) metabolite, 15-deoxy-delta(12,14)-prostaglandin J(2) (15d-PGJ(2)), is the potent inducer of intracellular oxidative stress on human neuroblastoma SH-SY5Y cells [Kondo, M., Oya-Ito, T., Kumagai, T., Osawa, T., and Uchida, K. (2001) Cyclopentenone prostaglandins as potential inducers of intracellular oxidative stress. J. Biol. Chem. 276, 12076-12083.]. In the present study, to investigate the correlation between the redox regulation and the 15d-PGJ(2)-induced oxidative stress and to establish the cellular mechanism for protection against the endogenous electrophile, we analyzed S-oxidized proteins using biotinylated cysteine as a molecular probe. In addition, the reversible regulation of protein function by S-oxidation/thiolation was characterized in vitro. When human neuroblastoma SH-SY5Y cells were exposed to 15d-PGJ(2), followed by treatment with biotinylated cysteine, 26 proteins, including glycolytic enzymes, cytoskeletal proteins, redox enzymes, and stress proteins, were identified as substrates for reversible cysteine-targeted oxidation. To investigate the regulatory mechanism of protein function by S-oxidation/thiolation, the binding of a low molecular weight thiol (glutathione) to a glycolytic enzyme alpha-enolase was characterized. Treatment of alpha-enolase with the thiol oxidant diamide in the presence of glutathione in vitro resulted in the binding of glutathione to the protein and concomitant loss of the enzymatic activity, whereas the glutathiolation and inactivation of alpha-enolase were fully reversed by dithiothreitol. Mass spectrometric analysis of the tryptic fragments from native and oxidized alpha-enolase identified two cysteine residues, Cys-118 and Cys-388, as the S-oxidation sites, which may play a role in the regulation of the biological activities of the protein and may be regulated by a reversible S-oxidation/thiolation reaction. These results suggest that cysteine-targeted oxidation/thiolation plays a critical role in the regulation of protein function under conditions of electrophile-induced oxidative stress.

A palmitoylated RING finger ubiquitin ligase and its homologue in the brain membranes

Ubiquitin (Ub) ligation is implicated in active protein metabolism and subcellular trafficking and its impairment is involved in various neurologic diseases. In rat brain, we identified two novel Ub ligases, Momo and Sakura, carrying double zinc finger motif and RING finger domain. Momo expression is enriched in the brain gray matter and testis, and Sakura expression is more widely detected in the brain white matter as well as in many peripheral organs. Both proteins associate with the cell membranes of neuronal and/or glial cells. We examined their Ub ligase activity in vivo and in vitro using viral expression vectors carrying myc-tagged Momo and Sakura. Overexpression of either Momo or Sakura in mixed cortical cultures increased total polyubiquitination levels. In vitro ubiquitination assay revealed that the combination of Momo and UbcH4 and H5c, or of Sakura and UbcH4, H5c and H6 is required for the reaction. Deletion mutagenesis suggested that the E3 Ub ligase activity of Momo and Sakura depended on their C-terminal domains containing RING finger structure, while their N-terminal domains influenced their membrane association. In agreement, Sakura associating with the membrane was specifically palmitoylated. Although the molecular targets of their Ub ligation remain to be identified, these findings imply a novel function of the palmitoylated E3 Ub ligase(s).

Primary malignant lymphoma of the brain: mutation pattern of rearranged immunoglobulin heavy chain gene

Using reverse transcription-polymerase chain reaction (RT-PCR), six primary brain lymphomas, pathologically diagnosed as diffuse large B-cell lymphoma, were examined for rearranged VH-D-JH sequences of the immunoglobulin heavy chain gene, focusing on somatic mutations and intraclonal heterogeneity. The reliability of the isolated PCR clones was confirmed by in situ hybridization (ISH) with complementarity-determining region (CDR) 3 oligonucleotide probes. Sequence analysis of the PCR clones revealed a high frequency of somatic mutation, ranging from 8.8 to 27.3% (mean 18.2%) in the VH gene segments in all the lymphomas. A significantly lower frequency of replacement (R) mutations than expected was also seen in their frameworks (FRs) in all cases. These findings suggested that the precursor cells were germinal center (GC)-related cells in these lymphomas. However, despite extensive cloning experiments, intraclonal heterogeneity was not detected in any case except for one in which it could not be ruled out. Thus, it seemed likely that all of our brain lymphomas were derived from GC-related cells and that at least most of them were from post-GC cells.

Loss of cannabinoid CB(1) receptors in the basal ganglia in the late akinetic phase of rats with experimental Huntington's disease

We have recently examined the status of the endocannabinoid transmission in the basal ganglia in Huntington's disease (HD) using a rat model generated by bilateral intrastriatal injections of 3-nitropropionic acid (3-NP). In these previous studies, we focused on the early phase of hyperactivity that occurs 1-2 weeks after the lesion, comparable to early grades of the human disease, while in the present study, we wanted to explore the late akinetic phase observed 3-4 weeks after the lesion (similar to advanced grades). First, we confirmed that 3-NP-lesioned rats exhibited a marked akinesia tested at 4 weeks post-lesion. We observed a marked reduction in ambulatory and exploratory activities and a trend towards a decrease in stereotypies, paralleled by a strong increase in the time spent in inactivity. There was also a profound reduction in GABA contents and glutamic acid decarboxylase activity, particularly in the caudate-putamen and the globus pallidus. Dopamine and DOPAC contents, as well as the activity of tyrosine hydroxylase, were also reduced, particularly in the caudate-putamen. mRNA levels for neuronal-specific enolase, proenkephalin and substance P were also dramatically reduced in the caudate-putamen, thus indicating a death of both the direct (striatonigral) and the indirect (striatopallidal) GABAergic projection pathways, which corresponded with a marked loss of CB(1) receptor-mRNA levels observed in both parts, lateral and medial, of the caudate-putamen. However, losses of CB(1) receptor binding were confined to the globus pallidus and the caudate-putamen, whereas there were no changes in the substantia nigra and the entopeduncular nucleus. Finally, we failed to reduce the marked akinesia found in these animals by administering SR141716A, a selective antagonist of CB(1) receptors, which had exhibited hyperlocomotor effects in previous studies with naive animals. In summary, behavioral and biochemical changes observed in rats intrastriatally lesioned with 3- NP were compatible with a profound degeneration of striatal efferent GABAergic neurons, similar to those occurring in advances stages of the human disease. As expected, a loss of CB(1) receptors was evident in the basal ganglia of these rats during the late akinetic stage of the disease. Further studies should demonstrate whether these receptors might be a target for a new therapy in HD, a disease with a poor pharmacological outcome.

Decreased calretinin expression in cerebellar granule cells in the leaner mouse

We investigated calretinin expression in cerebellar granule cells of 30-day-old leaner mice to understand possible changes in calcium homeostasis due to the calcium channel mutation that these mice carry. Quantitative in situ hybridization histochemistry showed decreased calretinin mRNA expression in the leaner cerebellum. Immunohistochemical staining also revealed decreased calretinin immunoreactivity in the leaner cerebellum. To exclude the effect of granule cell loss that occurs in the leaner mouse when comparing cerebellar calretinin expression, the number of granule cells per unit area in the cerebellum was compared to the wild-type cerebellum. Granule cell counts per unit area of cerebellum revealed similar numbers of granule cells present in wild-type and leaner mice. Laser capture microdissection (LCM) was employed to obtain an equal number of granule cells from wild-type and leaner mice. Western blot analysis with LCM-procured cerebellar granule cells showed decreased calretinin expression in leaner granule cells. These results indicate that there is an absolute decrease in calretinin expression in leaner granule cells even when granule cell loss is taken into account. Decreased calretinin expression in leaner granule cells may contribute to altered calcium buffering capacity. This alteration could be an adaptive change due to the calcium channel dysfunction, and may result in abnormal neuronal excitability and gene expression.

Isolation and structure of the mouse 14-3-3 eta chain gene and the distribution of 14-3-3 eta mRNA in the mouse brain

14-3-3 protein is a brain-specific protein discovered by Moore and Perez, but at present is thought to be a multifunctional protein. To clarify the brain-specific function of the protein, we intend constructing a 14-3-3 eta gene knock-out mouse. As the first step of this process, we isolated the mouse 14-3-3 eta chain gene and determined its structure. The mouse gene is about 10 kb long and composed of two exons separated by a long intron. The transcription start site was identified and the polyadenylation signals (AATAAA) were found in exon 2 of the mouse gene. In the 5'-upstream sequence, we found several cis elements including a CRE sequence, a TATA box-like sequence, and a C/EBP element. Furthermore, the distribution of 14-3-3 eta mRNA in the mouse brain was examined by in situ hybridization histochemistry. The highest signals were found in the Purkinje cells of the cerebellum, the pyramidal cells of the hippocampus and the olfactory bulb neurons of the adult mouse. Neuronal expression of 14-3-3 eta in these regions mRNA may generally increase during postnatal brain development. The distribution of protein kinase C gamma in the mouse brain was also examined by immunohistochemistry. From the distribution of 14-3-3 eta mRNA and protein kinase C gamma in the mouse brain, the involvement of these compounds in the induction and maintenance of LTP was discussed.

Alleviation of motor hyperactivity and neurochemical deficits by endocannabinoid uptake inhibition in a rat model of Huntington's disease

Recent studies have demonstrated a loss of cannabinoid CB1 receptors in the postmortem basal ganglia of patients affected by Huntington's disease (HD) and in transgenic mouse models for this disease. These studies have led to the notion that substances that increase the endocannabinoid activity, such as receptor agonists or inhibitors of endocannabinoid uptake and/or metabolism, might be useful in the treatment of hyperkinetic symptoms of this disease. In the present study, we employed a rat model of HD generated by bilateral intrastriatal injections of 3-nitropropionic acid (3-NP), a toxin that selectively damages striatal GABAergic efferent neurons. These rats exhibited biphasic motor disturbances, with an early (1-2 weeks) hyperactivity followed by a late (3-4 weeks) motor depression. Analysis of GABA, dopamine, and their related enzymes, glutamic acid decarboxylase and tyrosine hydroxylase, in the basal ganglia proved marked decreases compatible with the motor hyperkinesia. In addition, mRNA levels for CB1 receptor, neuronal-specific enolase, proenkephalin, and substance P decreased in the caudate-putamen of 3-NP-injected rats. There were also reductions in CB1 receptor binding in the caudate putamen, the globus pallidus, and, to a lesser extent, the substantia nigra. By contrast, mRNA levels for tyrosine hydroxylase in the substantia nigra remained unaffected. Interestingly, the administration of AM404, an inhibitor of endocannabinoid uptake, to 3-NP-injected rats attenuated motor disturbances observed in the early phase of hyperactivity. Administration of AM404 also tended to induce recovery from the neurochemical deficits caused by the toxin in GABA and dopamine indices in the basal ganglia. In summary, morphological, behavioral, and biochemical changes observed in rats intrastriatally lesioned with 3-NP acid were compatible with a profound degeneration of striatal efferent GABAergic neurons, similar to that occurring in the brain of HD patients. As expected, a loss of CB1 receptors was evident in the basal ganglia of these rats. However, the administration of substances that increase endocannabinoid activity, by inhibiting the uptake process, allowed an activation of the remaining population of CB1 receptors, resulting in a significant improvement of motor disturbances and neurochemical deficits. These observations might be relevant to the treatment of hyperkinetic symptoms in HD, a human disorder with unsatisfactory symptomatic treatment for most patients.

Loss of mRNA levels, binding and activation of GTP-binding proteins for cannabinoid CB1 receptors in the basal ganglia of a transgenic model of Huntington's disease

Data obtained from the basal ganglia of postmortem Huntington's disease (HD) brains have revealed that the level of cannabinoid CB1 receptors in striatal efferent neurons decreases in parallel to the dysfunction and subsequent degeneration of these neurons. These findings, and others from rat models of HD generated by lesions with mitochondrial toxins, suggest that the loss of CB1 receptors may be involved in the pathogenesis of the disease. To explore further the changes in the endocannabinoid system, as well as the potential of endocannabinoid-related compounds, we examined the status of CB1 receptors in the HD94 transgenic mouse model of HD. These mice express huntingtin exon 1 with a polyglutamine tract of 94 repeats in a tissue-specific and conditional manner using the tet regulatable system. They develop many features of HD, such as striatal atrophy, intraneuronal aggregates and progressive dystonia. In these animals, we analyzed mRNA levels for the CB1 receptor, in addition to the number of specific binding sites and the activation of GTP-binding proteins by CB1 receptor agonists. mRNA transcripts of the CB1 receptor were significantly decreased in the caudate-putamen of HD transgenic mice compared to age-matched littermate controls. The decrease concurred with a marked reduction in receptor density in both the caudate-putamen and its projection areas such as the globus pallidus, entopeduncular nucleus and substantia nigra pars reticulata. Furthermore, the efficacy of CB1 receptor activation was reduced in the globus pallidus, as determined by agonist-induced [35S]GTPgammaS binding, and tended towards a decrease in the substantia nigra. None of these changes was seen in the cerebral cortex and hippocampus, despite high levels of expression of the mutant protein in these regions. The decrease in CB1 receptor levels was accompanied by a decrease in the proenkephalin-mRNA levels but not in substance P-mRNA levels. Taken together, these results suggest that the loss of CB1 receptor might be preferential to the enkephalinergic CB1 receptor-containing striatopallidal neurons, and further implicate the CB1 receptor to the subsequent HD symptomatology and neuropathology.

Anandamide, but not 2-arachidonoylglycerol, accumulates during in vivo neurodegeneration

Endogenous cannabinoid receptor ligands (endocannabinoids) may rescue neurons from glutamate excitotoxicity. As these substances also accumulate in cultured immature neurons following neuronal damage, elevated endocannabinoid concentrations may be interpreted as a putative neuroprotective response. However, it is not known how glutamatergic insults affect in vivo endocannabinoid homeostasis, i.e. N-arachidonoylethanolamine (anandamide) and 2-arachidonoylglycerol (2-AG), as well as other constituents of their lipid families, N-acylethanolamines (NAEs) and 2-monoacylglycerols (2-MAGs), respectively. Here we employed three in vivo neonatal rat models characterized by widespread neurodegeneration as a consequence of altered glutamatergic neurotransmission and assessed changes in endocannabinoid homeostasis. A 46-fold increase of cortical NAE concentrations (anandamide, 13-fold) was noted 24 h after intracerebral NMDA injection, while less severe insults triggered by mild concussive head trauma or NMDA receptor blockade produced a less pronounced NAE accumulation. By contrast, levels of 2-AG and other 2-MAGs were virtually unaffected by the insults employed, rendering it likely that key enzymes in biosynthetic pathways of the two different endocannabinoid structures are not equally associated to intracellular events that cause neuronal damage in vivo. Analysis of cannabinoid CB(1) receptor mRNA expression and binding capacity revealed that cortical subfields exhibited an up-regulation of these parameters following mild concussive head trauma and exposure to NMDA receptor blockade. This may suggest that mild to moderate brain injury may trigger elevated endocannabinoid activity via concomitant increase of anandamide levels, but not 2-AG, and CB(1) receptor density.

Olivocerebellar projections modify hereditary Purkinje cell degeneration

Brainstem inferior olivary neurons, through their olivocerebellar efferent projections, dynamically regulate the structure and function of Purkinje neurons. To test the hypothesis that the inferior olive can epigenetically modify adult-onset hereditary Purkinje cell death, olivocerebellar projections were destroyed by 3-acetylpyridine chemoablation of the inferior olive in Shaker mutant rats. Starting around seven weeks of age, mutant Purkinje cells degenerate in a highly predictable spatial and temporal pattern. Chemoablation of the inferior olive at the onset of hereditary Purkinje cell degeneration accelerated the temporal pattern of Purkinje cell death from a natural phenotypic course of six to eight weeks to one and two weeks. When chemoablation of the inferior olive was performed three and a half weeks earlier, the onset of Purkinje cell death was accelerated by seven to 10days, but the spatial pattern and natural rate of temporal degeneration was maintained. Chemoablation of the inferior olive in normal rats did not result in any apparent death of Purkinje cells. These findings indicate that the olivocerebellar system can markedly modify hereditary Purkinje cell death. The accelerated death of Purkinje cells following chemoablation of the inferior olive can result from either the interruption of a trophic signal by climbing fiber deafferentation or parallel fiber excitotoxicity due to cortical disinhibition, but not due to olivocerebellar excitotoxicity.

Postnatal developmental changes in NSE and NNE mRNA expression in the rat pineal gland: in situ hybridization histochemistry

By in situ hybridization, neuron-specific enolase (NSE) and non-neuronal enolase (NNE) mRNAs were examined in the rat pineal gland at the postnatal developmental and adult stages. The distributions of hybridized signals were analyzed in comparison with immunohistochemical staining of synaptophysin (SYN), which is a marker for pinealocytes. In SYN-positive areas that were observed throughout postnatal developmental and adult stages, we detected both NSE and NNE signals, which increased simultaneously during early postnatal development and thereafter became stationary. Quantitative analysis revealed that NNE signals were 2- to 3-fold greater in number than NSE signals at any given stage. This predominant expression pattern of NNE differed from that in neurons, which usually showed both signals at similar levels and seemed to reflect the difference in physiological function from neurons. During the early postnatal stages, a cord-like arrangement of cells without distinct SYN staining was observed. This arrangement was the thickest at postnatal day 0 and became dispersed and thinner with development, showing a relationship with formation of vascularized connective tissue stroma. By in situ hybridization, many of the constituent cells showed weak NNE signals but no distinct NSE signals. However, some cells also showed weak NSE signals, suggesting heterogeneity of these cells. The characteristic NSE and NNE expression patterns in the pineal gland cells clarified in this study might provide a basis for further studies of the differentiation and function of the pineal gland.

A comparative study of the distribution of alpha- and gamma-enolase subunits in cultured rat neural cells and fibroblasts

We report the presence and distribution of alpha (ubiquitous) and gamma (neuron-specific) subunits of the dimeric glycolytic enzyme enolase (2-phospho-D-glycerate hydrolase) in cultured neural cells. The gamma gamma enolase is found in vivo at high levels only in neurons and neuroendocrine cells. Neuronal cells in culture also contain relatively high levels of alpha gamma and gamma gamma enolase. Here we show, by enzymatic and immunological techniques, that the gamma subunit also is expressed in cultured rat astrocytes and meningeal fibroblasts and, as we previously reported, in oligodendrocytes. Both neuron-specific isoforms alpha gamma and gamma gamma are expressed in all these cells, but the alpha alpha isoform accounts for the major part of total enolase activity. The sum of alpha gamma and gamma gamma enolase activities increases with time in culture. i.e. maturation processes, reaching the highest level in oligodendrocytes (40% of total enolase activity) and 15 and 10% of total enzymatic activity in astrocytes and fibroblasts, respectively. The gamma enolase transcripts were found not only in cultured neuronal cells but also in cultured oligodendrocytes astrocytes, and meningeal fibroblasts. Our data indicate that neuron-specific enolase should be used with caution as a specific marker for neuronal cell differentiation.

Non-neuronal enolase is an endothelial hypoxic stress protein

The hypoxia-associated proteins (HAPs) are five cell-associated stress proteins (M(r) 34, 36, 39, 47, and 57) up-regulated in cultured vascular endothelial cells (EC) exposed to hypoxia. While hypoxic exposure of other cell types induces heat shock and glucose-regulated proteins, EC preferentially up-regulate HAPs. In order to identify the 47-kDa HAP, protein from hypoxic bovine EC lysates was isolated, digested with trypsin, and sequenced. Significant identity was found with enolase, a glycolytic enzyme. Western analyses confirmed that non-neuronal enolase (NNE) is up-regulated in hypoxic EC. Western analysis of subcellular fractions localized NNE primarily to the cytoplasm and confirmed that it was up-regulated 2.3-fold by hypoxia. Interestingly, NNE also appeared in the nuclear fraction of EC but was unchanged by hypoxia. Northern analyses revealed that NNE mRNA hypoxic up-regulation began at 1-2 h, peaked at 18 h, persisted for 48 h, and returned to base line after return to 21% O2 for 24 h. Hypoxia maximally up-regulated NNE mRNA levels 3.4-fold. While hypoxic up-regulation of NNE may have a protective effect by augmenting anaerobic metabolism, we speculate that enolase may contribute to EC hypoxia tolerance through one or more of its nonglycolytic functions.

Characterization of squid enolase mRNA: sequence analysis, tissue distribution, and axonal localization

Enolase is a glycolytic enzyme whose amino acid sequence is highly conserved across a wide range of animal species. In mammals, enolase is known to be a dimeric protein composed of distinct but closely related subunits: alpha (non-neuronal), beta (muscle-specific), and gamma (neuron-specific). However, little information is available on the primary sequence of enolase in invertebrates. Here we report the isolation of two overlapping cDNA clones and the putative primary structure of the enzyme from the squid (Loligo pealii) nervous system. The composite sequence of those cDNA clones is 1575 bp and contains the entire coding region (1302 bp), as well as 66 and 207 bp of 5' and 3' untranslated sequence, respectively. Cross-species comparison of enolase primary structure reveals that squid enolase shares over 70% sequence identity to vertebrate forms of the enzyme. The greatest degree of sequence similarity was manifest to the alpha isoform of the human homologue. Results of Northern analysis revealed a single 1.6 kb mRNA species, the relative abundance of which differs approximately 10-fold between various tissues. Interestingly, evidence derived from in situ hybridization and polymerase chain reaction experiments indicate that the mRNA encoding enolase is present in the squid giant axon.

Upstream and intron regulatory regions for expression of the rat neuron-specific enolase gene

Neuron-specific enolase (NSE) occurs in mature neurons and paraneurons. We have isolated the genomic clone coding for rat NSE and clarified its gene structure. In order to analyze the regulatory sequence in the 5'-upstream region and introns, we carried out transient expression experiments of NSE genomic DNA fragments fused to chloramphenicol acetyltransferase (CAT) gene which were transfected into several cultured cells. The used cells were primary cultured rat neurons, PC12, neuroblastoma 35, neuroblastoma 103, C6, primary cultured rat glial cells and HeLa cells. The promoter sequence (190 bp) upstream to the transcription initiation site was important in the expression of CAT gene in these cells. From the experiments with external and internal deletion mutants of the fusion gene, the cis-acting regulatory region responsible for the enhanced expression of the CAT activity in the primary cultured neuron and PC12 cells was found to be localized at upstream 500 bp sequence of the intron 1 and 1.5 kbp upstream sequence of the transcription initiation site. In the upstream important sequences, there were the nearest sequences for AP-1 binding motif, AP-2 binding element, SP-1 binding sequence, cAMP response element, half site of glucocorticoid receptor (GRE) binding sequence, half site of thyroid hormor receptor (TR) or retinoic acid receptor (RAR) binding sequence and MTF-1 binding sequence. Furthermore, Octamer-6 binding motifs also were found. In the intron 1, 5' end upstream 50 bp and downstream 100 bp were the most important sequences. We found the nearest sequences for cAMP response element, E2F binding sequence, early growth response (EGR)-1 binding motif, half site of TCF-1 binding sequence and a neuron-specific element-like sequence in the intron 1.

Repeated electroconvulsive shock selectively increases the expression of the neuron specific enolase in piriform cortex

The effect of repeated electroconvulsive shock (ECS) on the activities of the three enolase isoenzymes present in rat brain: neuron specific enolase (NSE), non-neuronal enolase (NNE) and the hybrid enolase was investigated in piriform cortex. The activities were estimated on isoenzymes separated by agarose gel electrophoresis. Whereas the specific activities of NNE and hybrid enolase were unchanged in piriform cortex or ECS-treated rats the specific activity of NSE was increased by 16.3 percent (P < 0.02). The brain enolase isoenzymes are dimers of alpha- and gamma-enolase subunits. The calculated ratio between the gamma-subunit present in both NSE and hybrid enolase and the alpha-subunits present in both NNE and hybrid enolase was increased by 11.7 percent in piriform cortex of ECS-treated rats (P < 0.05). Previously, it has been shown that the gamma-subunit is only expressed in neurons whereas the alpha-subunit is expressed in both neurons and glial cells. The selectively increased expression of the enolase gamma-subunit in ECS-treated rats might either reflect an increased transcription of a whole group of neuronal genes or rather the trophic role of NSE in ECS-enhanced synaptic remodelling of the rat brain.

Coexpression of alpha and gamma enolase genes in neurons of adult rat brain

Enolase (EC 4.2.1.11) is a glycolytic enzyme active as a dimer. In adult brain extracts, three forms, alpha alpha, alpha gamma and gamma gamma, have been described, with the alpha gamma hybrid accounting for 30% of total enolase activity (Fletcher et al., Dev Biol 65:462-475, 1978; Lucas et al., Dev Neurosci 10:91-98, 1988). Previous biochemical studies strongly suggest that this hybrid is not generated artefactually during the extraction procedures (Keller et al., J Neurochem 36:1389-1397, 1981; Shimizu et al., BBA 748:278-284, 1983). Immunocytological observations have demonstrated the cell specific localization of the alpha subunit in astrocytes and of the gamma subunit in neurons at the adult stage, but failed to identify a cell type containing both the alpha and gamma subunits necessary for the formation of the alpha gamma hybrid isoform (Ghandour et al., Exp Brain Res 41:271-279, 1981; Vinores et al., J Histochem Cytochem 32:1295-1302, 1984; Iwanaga et al., Arch Histol Cytol [Suppl] 52:13-24, 1989). We sought to approach this question by performing in situ hybridization studies in order to visualize the alpha and gamma mRNAs. In agreement with the immunocytological reports, we observe a specific accumulation of the gamma enolase transcripts in neurons and a high accumulation of alpha enolase transcripts in some glial cells such as the ependymocytes lining the ventricles. Our observations, following hybridization with 35S labeled oligonucleotide specific probes on adjacent thin sections, demonstrate for the first time that transcription of both alpha and gamma enolase genes occurs in many neurons of different brain regions. These results render highly probable the formation of the alpha gamma hybrid in mature neurons. Furthermore, we observe a differential expression of the genes encoding the alpha and gamma enolase subunits in various neuronal populations of the brain. The implications of these observations are discussed.