Determination of RNA content in postischemic gerbil brain by in situ hybridization

Validation of the Reference Genes for Expression Analysis in the Hippocampus after Transient Ischemia/Reperfusion Injury in Gerbil Brain

Transient brain ischemia in gerbils is a common model to study the mechanisms of neuronal changes in the hippocampus. In cornu ammonnis 2-3, dentate gyrus (CA2-3,DG) regions of the hippocampus, neurons are resistant to 5-min ischemia/reperfusion (I/R) insult, while cornu ammonnis 1 (CA1) is found to be I/R-vulnerable. The quantitative polymerase chain reaction (qRT-PCR) is widely used to study the expression of genes involved in these phenomena. It requires stable and reliable genes for normalization, which is crucial for comparable and reproducible analyses of expression changes of the genes of interest. The aim of this study was to determine the best housekeeping gene for the I/R gerbil model in two parts of the hippocampus in controls and at 3, 48, and 72 h after recanalization. We selected and tested six reference genes frequently used in central nervous system studies: Gapdh, Actb, 18S rRNA, Hprt1, Hmbs, Ywhaz, and additionally Bud23, using RefFinder, a comprehensive tool based on four commonly used algorithms: delta cycle threshold (Ct), BestKeeper, NormFinder, and geNorm, while Hprt1 and Hmbs were the most stable ones in CA2-3,DG. Hmbs was the most stable in the whole hippocampal formation. This indicates that the general use of Hmbs, especially in combination with Gapdh, a highly expressed reference gene, seems to be suitable for qRT-PCR normalization in all hippocampal regions in this model.

Comparative aspects of laboratory testing for the detection of Toxoplasma gondii and its differentiation from Neospora caninum as the etiologic agent of ovine abortion

Histologic examination of aborted material is an essential component in the diagnosis of ovine toxoplasmosis. However, the detection of Toxoplasma gondii in histologic sections, and its differentiation from the closely related protozoan Neospora caninum, is challenging. We developed a chromogenic in situ hybridization (ISH) assay for the identification of T. gondii in paraffin-embedded tissue samples. We examined retrospectively the archived placental tissue of 200 sheep abortion submissions for the presence of T. gondii by immunohistochemistry (IHC), ISH, and real-time PCR (rtPCR). All placental samples that tested positive for T. gondii by rtPCR (9 of 200) were also positive by IHC, with inconclusive IHC staining in an additional 7 rtPCR-negative cases. Further testing for N. caninum of all 200 placentas by rtPCR revealed 7 Neospora-positive cases. T. gondii ISH was positive in 4 of 9 IHC-positive samples and 1 of the 7 N. caninum rtPCR-positive samples. Real-time PCR was used as the reference standard for specificity and sensitivity calculations regarding placenta samples. Specificity of ISH and IHC was 99% and 96-100%, respectively. The sensitivity of ISH (44%) was quite low compared to IHC (100%). The exclusive use of ISH for the detection of T. gondii, and thus for the diagnosis of ovine toxoplasmosis, was not acceptable. However, combined with rtPCR, both ISH and IHC can be useful detection methods to improve histologic evaluation by visualizing the parasite within tissue sections.

The quantification of ADAMTS expression in an animal model of cerebral ischemia using real-time PCR

BACKGROUND

ADAMTS1 and ADAMTS8 are proteases involved in extracellular matrix proteolysis and antiangiogenesis, but little is known about their expression and function in cerebral ischemia. We investigated the changes in ADAMTS1 and ADAMTS8 in a rat model of permanent middle cerebral artery occlusion (pMCAO). The expressions of glyseraldehyde-3-phosphate dehydrogenase (GAPDH), beta-actin, cyclophilin, and RPL13A were examined in order to validate the appropriate housekeeping genes for a long duration after inducing cerebral ischemia.

METHODS

Male Sprague-Dawley rats were subjected to pMCAO, and ischemic penumbra was collected at 2, 24 h, 3, 7, and 21 days after inducing ischemia, ADAMTS1, ADAMTS8, and the four housekeeping genes were quantified using real-time polymerase chain reaction (PCR).

RESULTS

The expression of beta-actin increased up to 21 days, and that of GAPDH decreased at 24 h after pMCAO, with no statistically significant changes in RPL13A and cyclophilin being detected. ADAMTS1 mRNA increased at 2 h after pMCAO, peaked at 24 h, and remained at a high level until 21 days. The expression of ADAMTS8 mRNA decreased at 2 and 24 h after pMCAO, followed by a slight increase at 3 days, and then decreased again at 7 days.

CONCLUSION

The results suggest that RPL13A and cyclophilin are two appropriate housekeeping genes for the rat pMCAO model up to 21 days. ADAMTS1 mRNA levels increased, but ADAMTS8 decreased after pMCAO. Our data provide new insight into the mechanism of brain ischemia and self-repair after injury.

Decreased β-actin mRNA expression in hyperglycemic focal cerebral ischemia in the rat

beta-Actin is often used as a housekeeping gene when performing reverse transcription-polymerase chain reaction (RT-PCR) analysis for cerebral ischemia models. In the present study, we tested two different control genes used for RT-PCR experiments, beta-actin and porphobilinogen deaminase (PBG-D), in a rat model of focal cerebral ischemia under normo- or hyperglycemic conditions. A three-vessel occlusion model with permanent middle cerebral artery occlusion was used in the rat. beta-Actin mRNA expression was decreased in hyperglycemic ischemic rats compared to normoglycemic ischemic animals 3 h post-ischemia. beta-Actin protein content was unchanged. As for PBG-D, its mRNA expression remained constant throughout the groups. Our data thus show that, following focal cerebral ischemia in hyperglycemic conditions, beta-actin is an unsuitable housekeeping gene whereas PBG-D is more appropriate. This study clearly demonstrates the importance of selecting a stable housekeeping gene when performing RT-PCR experiments.

Brain ischemia and reperfusion: molecular mechanisms of neuronal injury

Brain ischemia and reperfusion engage multiple independently-fatal terminal pathways involving loss of membrane integrity in partitioning ions, progressive proteolysis, and inability to check these processes because of loss of general translation competence and reduced survival signal-transduction. Ischemia results in rapid loss of high-energy phosphate compounds and generalized depolarization, which induces release of glutamate and, in selectively vulnerable neurons (SVNs), opening of both voltage-dependent and glutamate-regulated calcium channels. This allows a large increase in cytosolic Ca(2+) associated with activation of mu-calpain, calcineurin, and phospholipases with consequent proteolysis of calpain substrates (including spectrin and eIF4G), activation of NOS and potentially of Bad, and accumulation of free arachidonic acid, which can induce depletion of Ca(2+) from the ER lumen. A kinase that shuts off translation initiation by phosphorylating the alpha-subunit of eukaryotic initiation factor-2 (eIF2alpha) is activated either by adenosine degradation products or depletion of ER lumenal Ca(2+). Early during reperfusion, oxidative metabolism of arachidonate causes a burst of excess oxygen radicals, iron is released from storage proteins by superoxide-mediated reduction, and NO is generated. These events result in peroxynitrite generation, inappropriate protein nitrosylation, and lipid peroxidation, which ultrastructurally appears to principally damage the plasmalemma of SVNs. The initial recovery of ATP supports very rapid eIF2alpha phosphorylation that in SVNs is prolonged and associated with a major reduction in protein synthesis. High catecholamine levels induced by the ischemic episode itself and/or drug administration down-regulate insulin secretion and induce inhibition of growth-factor receptor tyrosine kinase activity, effects associated with down-regulation of survival signal-transduction through the Ras pathway. Caspase activation occurs during the early hours of reperfusion following mitochondrial release of caspase 9 and cytochrome c. The SVNs find themselves with substantial membrane damage, calpain-mediated proteolytic degradation of eIF4G and cytoskeletal proteins, altered translation initiation mechanisms that substantially reduce total protein synthesis and impose major alterations in message selection, down-regulated survival signal-transduction, and caspase activation. This picture argues powerfully that, for therapy of brain ischemia and reperfusion, the concept of single drug intervention (which has characterized the approaches of basic research, the pharmaceutical industry, and clinical trials) cannot be effective. Although rigorous study of multi-drug protocols is very demanding, effective therapy is likely to require (1) peptide growth factors for early activation of survival-signaling pathways and recovery of translation competence, (2) inhibition of lipid peroxidation, (3) inhibition of calpain, and (4) caspase inhibition. Examination of such protocols will require not only characterization of functional and histopathologic outcome, but also study of biochemical markers of the injury processes to establish the role of each drug.

Differential expressions of glycine transporter 1 and three glutamate transporter mRNA in the hippocampus of gerbils with transient forebrain ischemia

The extracellular concentrations of glutamate and its co-agonist for the N-methyl-d-aspartate (NMDA) receptor, glycine, may be under the control of amino acid transporters in the ischemic brain. However, there is little information on changes in glycine and glutamate transporters in the hippocampal CA1 field of gerbils with transient forebrain ischemia. This study investigated the spatial and temporal expressions of glycine transporter 1 (GLYT1) and three glutamate transporter (excitatory amino acid carrier 1, EAAC1; glutamate/aspartate transporter, GLAST; glutamate transporter 1, GLT1) mRNA in the gerbil hippocampus after 3 minutes of ischemia. The GLYT1 mRNA was transiently upregulated by the second day after ischemia in astrocytelike cells in close vicinity to hippocampal CA1 pyramidal neurons, possibly to reduce glycine concentration in the local extracellular spaces. The EAAC1 mRNA was abundantly expressed in almost all pyramidal neurons and dentate granule cells in the control gerbil hippocampus, whereas the expression level in CA1 pyramidal neurons started to decrease by the fourth day after ischemia in synchrony with degeneration of the CA1 neurons. The GLAST and GLT1 mRNA were rather intensely expressed in the dentate gyrus and CA3 field of the control hippocampus, respectively, but they were weakly expressed in the CA1 field before and after ischemia. As GLAST and GLT1 play a major role in the control of extracellular glutamate concentration, the paucity of these transporters in the CA1 field may account for the vulnerability of CA1 neurons to ischemia, provided that the functional GLAST and GLT1 proteins are also less in the CA1 field than in the CA3 field. This study suggests that the amino acid transporters play pivotal roles in the process of delayed neuronal death in the hippocampal CA1 field.

Neuroprotective effect of YM-39558 in focal cerebral ischemia in cats

We studied the effect of YM-39558, orotic acid ethylester, in a focal cerebral ischemia model in anesthetized cats. YM-39558 has good permeability across the blood brain barrier, and in the brain is hydrolyzed to orotic acid, the main active substance. Cats were subjected to permanent occlusion of the middle cerebral artery (MCA) for 6 h, then killed and examined histologically. Treatment with YM-39558 (intravenous infusion of 11.8 mg (10 mg as orotic acid)/6 ml per kg per h) starting 15 min after MCA occlusion markedly reduced the volume of ischemic damage (from 2450 +/- 82 mm3 of the cerebral hemisphere in the saline-treated cats to 1644 +/- 123 mm3 in the YM-39558-treated cats, P < 0.01). In contrast, YM-39558 (2.26 and 1.18 mg/0.8 ml per kg per h) showed no significant protective effect on ischemic damage. No significant differences were observed between saline- and YM-39558-treated cats concerning physiological variables including brain temperature. This evidence for the neuroprotective efficacy of YM-39558 in gyrencephalic species suggests its therapeutic potential in the treatment of stroke in humans.

Effects of ischemic tolerance on mRNA levels of IP3R1, beta-actin, and neuron-specific enolase in hippocampal CA1 area of the gerbil brain

Global cerebral ischemia induced to Mongolian gerbils by ligation of common carotid arteries (CCAs) is known to result in injury to the hippocampal CA1 region. In this study, we examined whether neuronal injury can be depicted by measuring levels of mRNA encoding inositol 1,4,5-trisphosphate receptor type 1 (IP3R1), neuron specific enolase (NSE) and beta-actin and whether these measurements can be use to assess ischemic tolerance. Gerbils were subjected either to cerebral ischemia induced by ligation of both CCAs for 5 min, or to an ischemic tolerance paradigm in which a 2 min ischemic preconditioning was performed 24 hr prior to the 5 min ischemia. At 48 hr after the 5 min ischemic insult, significant decreases in mRNA levels for IP3R1 (26%), NSE (38%) and beta-actin (50%) could be observed in the hippocampal CA1 region. Although levels of mRNA in the preconditioning group were decreased as compared to the sham control, the levels were significantly higher than those in the ischemic group. These results indicate the feasibility of using mRNA measurement as a parameter to assess cerebral ischemic damage. In addition, based on the differences in the decline in mRNA levels between the ischemia group and the preconditioned ischemia group, it can be concluded that this ischemic tolerance paradigm could offer partial protection (around 45%) against the injury due to the 5 min cerebral ischemic insult.

PRL-1, a protein tyrosine phosphatase, is expressed in neurons and oligodendrocytes in the brain and induced in the cerebral cortex following transient forebrain ischemia

Protein tyrosine phosphorylation is thought to play an important role in the regulation of neural function. We reported previously that CL100, a cytoplasmic type protein tyrosine phosphatase (PTP), was induced after transient forebrain ischemia. In the present study, changes in the mRNA levels after ischemia of PRL-1, a cytoplasmic type PTP and immediate-early gene similar to CL100, was examined. In situ hybridization histochemistry showed that PRL-1 mRNA was expressed in normal adult rats in neurons and oligodendrocytes in widespread regions including the cerebral cortex, hippocampus and cerebellum. PRL-1 mRNA was expressed in the developing brains on embryonic days 15 and 19 and postnatal day 1. Northern blot analysis showed that PRL-1 mRNA was induced from 6 h to 9 h after reperfusion in the cerebral cortex of postischemic rats. These findings suggest that PRL-1 plays a role in neurons and oliogodendrocytes, and that expression of PRL-1 mRNA is regulated by a mechanism different from those of other immediate-early genes such as c-fos and c-jun.

Canine brain glucose transporter 3: gene sequence, phylogenetic comparisons and analysis of functional sites

There has been a sparsity of various mammalian neuronal glucose transporter 3-encoding sequences(Glut3) available for the purposes of alignment studies. We report here a 2355-bp sequence of canine Glut3 that encodes a deduced protein of 496 amino acids (aa). The full-length canine aa sequence was compared to those of the human, mouse and rat glucose transporter 3 (Glut3), and found to be 88.3, 84.9 and 84.3% identical, respectively. However, while mouse and rat identical C-termini, the canine nd human C-termini share markedly little identity or similarity to one another, or to that of rat/mouse. The canine Glut3 sequence also exhibits 74.5% aa identity with a non-mammalian chicken Glut3 sequence. These differences in the C-termini of Glut3 among the species may result in kinetic or mechanistic differences in transport of glucose. Computer searches were made for conserved functional motifs, and a brief review of ten sites is provided. This review includes the determination of their locations in two transmembrane (TM) motifs that have been proposed for glucose transporters. The nucleotide (nt) sequence of the 5'-untranslated region (UTR) of canine Glut3 was aligned with the comparable human glut3 region and was shown to be 70% identical over a region of 129 nt just prior to the ATG start codons. A similar comparison of the 3'-UTR shows 74% identity over 350 nt immediately following the stop codons. An adenosine-uridine-binding factor (AUBF) region, which has been identified as a region of importance in mRNA stabilization, is conserved in the 3'-UTR of both canine and human Glut3. The conservation in the UTR suggests that Glut3 may be post-transcriptionally regulated.

Reactive microglia in cerebral ischaemia: an early mediator of tissue damage?

Microglial cell activation is a rapidly occurring cellular response to cerebral ischaemia. Microglia proliferate, are recruited to the site of lesion, upregulate the expression of several surface molecules including major histocompatibility complex class I and II antigens, complement receptor and the amyloid precursor protein (APP) as well as newly expressed cytokines, e.g. interleukin-1 and transforming growth factor beta 1. The ischaemia-induced production of APP may contribute to amyloid deposition in the aged brain under conditions of hypofusion. Ultrastructurally, microglia transform into phagocytes removing necrotic neurons but still respecting the integrity of eventually surviving neurons even in the close vicinity of necrotic neurons. Microglial activation starts within a few minutes after ischaemia and thus precedes the morphologically detectable neuronal damage. It additionally involves a transient generalized response within the first 24 hours post-ischaemia even at sites without eventual neuronal cell death. In functional terms, the microglial reaction appears to be a double-edged sword in ischaemia. Activated microglia may exert a cytotoxic effector function by releasing reactive oxygen species, nitric oxide, proteinases or inflammatory cytokines. All of these cytotoxic compounds may cause bystander damage following ischaemia. Pharmacological suppression of microglial activation after ischaemia has accordingly attenuated the extent of cell death and tissue damage. However, activated microglia support tissue repair by secreting factors such as transforming growth factor beta 1 which may limit tissue damage as well as suppress astroglial scar formation. In line with ultrastructural observations microglial activation in ischaemia is a strictly controlled event. By secreting cytokines and growth factors activated microglia most likely serve seemingly opposed functions in ischaemia, i.e. maintenance as well as removal of injured neurons. Post-ischaemic pharmacological modulation of microglial intervention in the cascade of events that lead to neuronal necrosis may help to improve the structural and functional outcome following CNS ischaemia.

Ischemic delayed neuronal death. A mitochondrial hypothesis

BACKGROUND

A brief period of global brain ischemia causes cell death in hippocampal CA1 pyramidal neurons days after reperfusion in rodents and humans. Other neurons are much less vulnerable. This phenomenon is commonly referred to as delayed neuronal death, but the cause has not been fully understood although many mechanisms have been proposed.

SUMMARY OF REVIEW

Hippocampal CA1 neuronal death usually occurs 3 to 4 days after an initial ischemic insult. Such a delay is essential for the mechanism of this type of cell death. Previous hypotheses have not well explained the reason for the delay and the exact mechanism of the cell death, but a disturbance of mitochondrial gene expression could be a possibility. Reductions of mitochondrial RNA level and the activity of a mitochondrial protein, encoded partly by mitochondrial DNA, occurred exclusively in CA1 neurons at the early stage of reperfusion and were aggravated over time. In contrast, the activity of a nuclear DNA-encoded mitochondrial enzyme and the level of mitochondrial DNA remained intact in CA1 cells until death. Immunohistochemical staining for cytoplasmic dynein and kinesin, which are involved in the shuttle movement of mitochondria between cell body and the periphery, also showed early and progressive decreases after ischemia, and the decreases were found exclusively in the vulnerable CA1 subfield.

CONCLUSIONS

A disturbance of mitochondrial DNA expression may be caused by dysfunction of the mitochondrial shuttle system and could cause progressive failure of energy production of CA1 neurons that eventually results in cell death. Thus, the mitochondrial hypothesis could provide a new and exciting potential for elucidating the mechanism of the delayed neuronal death of hippocampal CA1 neurons.

Glial expression of the beta-amyloid precursor protein (APP) in global ischemia

The beta-amyloid precursor protein (APP) bears characteristics of an acute-phase protein and therefore is likely to be involved in the glial response to brain injury. In the brain, APP is rapidly synthesized by activated glial cells in response to comparatively mild neuronal lesions, e.g., a remote peripheral nerve injury. Perfusion deficits in the brain result largely in neuronal necrosis and are a common condition in elderly patients. This neuronal necrosis is accompanied by a pronounced reaction of astrocytes and microglia, which can also be observed in animal models. We have therefore studied in the rat, immunocytochemically, the induction of APP after 30 min of global ischemia caused by four-vessel occlusion. The postischemic brain injuries were examined at survival times from 12 h to 7 days. From day 3 onward, APP immunoreactivity was strongly induced in the CA1 and CA4 regions of the rat dorsal hippocampus as well as in the dorsolateral striatum. In these areas, the majority of APP-immunoreactive cells were reactive glial fibrillary acidic protein (GFAP)-positive astrocytes, as shown by double-immunofluorescence labeling for GFAP and APP. Additionally, small ramified cells, most likely activated microglia, expressed APP immunoreactivity. In contrast, in the parietal cortex, APP immunoreactivity occurred focally in clusters of activated microglia rather than in astrocytes, as demonstrated by double-immunofluorescence labeling for APP and the microglia-binding lectin Griffonia simplicifolia isolectin B4. In conclusion, following global ischemia, APP is induced in reactive glial cells with spatial differences in the distribution pattern of APP induction in astrocytes and microglia.

Expression of beta-actin and alpha-tubulin mRNA in gerbil brain following transient ischemia and reperfusion up to 1 month

The time course of mRNA expressions of two cytoskeletal proteins, beta-actin and alpha-tubulin, was studied by Northern blot analysis and in situ hybridization in the same gerbil brains at various periods of recirculation following 10 min of forebrain ischemia. On Northern blot analysis, beta-actin mRNA in the forebrain showed increase after 6 h and 24 h recirculation. There was wide variation in its expression 3 days postischemia (PI), and by 7 days PI it had returned to control. The alpha-tubulin mRNA in the forebrain was shown to be reduced 6 h PI in our previous study. In the present analysis of Northern blots of delayed postischemic periods, there was no significant change in its expression even though there were variations. In situ hybridization revealed a decline in the mRNA expressions of both alpha-tubulin and beta-actin in the CA1 region as early as 6-24 h PI with the reductions being prominent at 3 days PI. By 7 days PI, beta-actin was only faintly visible while alpha-tubulin was completely absent in the CA1 region. Neither RNA was detectable in CA1 1 month PI. The heat shock-70 protein was expressed by 1 h PI, and it continued to be expressed up to 24 h, returning to control by 3 days PI. These results indicate that ischemia inhibits mRNA expressions of cytoskeletal protein in the selectively vulnerable region of the brain, i.e. CA1. The time course of the reduction of the two mRNAs coincides with delayed neuronal death suggesting that the cytoskeletal proteins may play important roles in selective postischemic neuronal injury.

Amino acid transport after transient global ischemia in rats: quantitative autoradiographic study using 3-[125I]iodo-alpha-methyl-L-tyrosine

We studied the influence of reperfusion on amino acid transport of the brain after transient global ischemia in rats. The animals were subjected to 30-min four-vessel occlusion according to the procedures developed by Pulsinelli prior to recirculation for 3, 6, 24, 48 and 72 h. We used 3-[125I]iodo-alpha-methyl-L-tyrosine as an autoradiographic tracer for selective cerebral amino acid transport maker. Following 30-min global ischemia, uptakes of 3-[125I]iodo-alpha-methyl-L-tyrosine were significantly (P < 0.05) lower in substantia nigra, striatum and ventral tegmental area (6, 24, 48 and 72 h post-reperfusion), but significantly (P < 0.05) higher in cortex and thalamus (3 and 6 h post-reperfusion). The influence of transient global ischemia on cerebral amino acid transport manifested region-specific three different patterns; namely, suppression, acceleration and no change in amino acid transport. The influence of transient ischemia on catecholamine-synthesizing brain sites is most remarkable.

Induction of CL100 protein tyrosine phosphatase following transient forebrain ischemia in the rat brain

Protein tyrosine phosphorylation is thought to play an important role in the regulation of neural function. To elucidate the role that protein tyrosine phosphatases (PTPs) may play in the postischemic brain, PTPs expressed in regions of the rat brain vulnerable to transient forebrain ischemia were examined. With the reverse-transcriptase polymerase chain reaction using degenerate primers, three PTPs, STEP, PTP delta, and SH-PTP2, were identified. They were expressed in the hippocampus 12 h after transient ischemia for 20 min. During the reperfusion period, the mRNA levels of these PTPs were not different from those in sham-operated rats. In contrast, a fourfold increase in the mRNA level of CL100 (3CH134), a PTP that is inducible by oxidative stress, was detected by Northern blotting in the hippocampus and cerebral cortex 1 h after the onset of reperfusion. In situ hybridization histochemistry showed a slight increase in the level of CL100 mRNA in neuronal cells in the hippocampus and cortex of postischemic rats compared to control rats. These findings suggest that PTPs play a role in the normal function of the hippocampus and cerebral cortex and demonstrate that ischemia induced CL100 expression.

Gene expression in astrocytes during and after ischemia

Involvement of the IEGs in brain injury and ischemia is under intensive investigation (Gubits et al., 1993). There are several families of the IEGs. They include the fos, jun, and zinc finger genes that encode transcription factors. Products of the fos family (c-fos, fra-1, fra-2, and fos B) bind to members of the jun family (c-jun, jun B, jun D) via leucine zippers, and this dimer then binds to the AP-1 site (consensus sequence -TGACTCA-) in the promoter of target genes, which in turn regulate the expression of late response genes that produce long-term changes in cells. For example, c-fos may regulate the long-term expression of preproenkephalin, nerve growth factor, dynorphin, vasoactive intestinal polypeptide, tyrosine hydroxylase and other genes with AP-1 sites in their promoters (Curran and Morgan, 1987; Sheng and Greenberg, 1990). It is likely that the c-fos gene up-regulation observed in ischemic astrocytes leads to the changes observed in the expressions of hsp and cytoskeleton protein genes in this experimental model. This is supported by the findings of Sarid (1991) and Pennypacker et al. (1994) who have shown that AP-1 DNA binding activity in hippocampus recognized an AP-1 sequence from the promoter region of the GFAP which is a potential target gene. van de Klundert et al. (1992) also suggested the involvement of AP-1 in transcriptional regulation of vimentin. IEGs can be induced within minutes by extracellular stimuli including transmitters, peptides, and growth factors. In this study, we have shown that c-fos induction by ischemia was rapid and transient.(ABSTRACT TRUNCATED AT 250 WORDS)

GLUT1 and GLUT3 gene expression in gerbil brain following brief ischemia: an in situ hybridization study

GLUT1 and GLUT3 mRNAs in normal and post-ischemic gerbil brains were examined qualitatively and semi-quantitatively using in situ hybridization in conjunction with image analysis. Coronal brain sections at the level of the anterior hippocampus were prepared three hours, one day, and three days after animals were subjected to six min of ischemia. The sections were hybridized with vector- and PCR-generated RNA probes labeled with 35S. Microscopic evaluation of hybridized brain sections coated with autoradiographic emulsion indicated that GLUT1 mRNA was associated with brain microvessels, choroid plexus, and some ependymal cells. GLUT1 mRNA was not observed in neurons, except that one day following ischemia, this mRNA was induced in neurons of the dentate gyrus. GLUT3 mRNA was detected only in neurons. Image analysis of film autoradiograms revealed that both the GLUT1 and GLUT3 messages increased following ischemia but returned nearly to control levels by day three. In the CA1 region of the hippocampus the increase in GLUT3 mRNA was not statistically significant, and by day three the level had fallen significantly below the control, coinciding with the degeneration of the CA1 neurons. Our results suggest that the brain possesses mechanisms for induction and up-regulation of glucose transporter gene expression.

Rapid decline of GABAA receptor subunit mRNA expression in hippocampus following transient cerebral ischemia in the gerbil

Inhibitory neurotransmission may play an important role in neuronal degeneration following transient cerebral ischemia. We studied the effect of transient forebrain ischemia on the GABAA receptor system in the gerbil hippocampus. Gerbils were subjected to 5 minutes of bilateral carotid occlusion and were sacrificed at various times over 4 days following reperfusion. There was a substantial loss of pyramidal cells in the CA1 area of the hippocampus 4 days following ischemia. No cell loss was detected in CA3 pyramidal cells of the hippocampus, granule cell layer of the dentate gyrus, and ventroposterior medial and ventroposterior lateral nuclei of the thalamus at any time following ischemia. Examination of brain slices by in situ hybridization histochemistry revealed that a change in expression of the GABAA receptor alpha 1 and beta 2 subunit mRNAs occurred in two phases following onset of reperfusion. The early phase (rapid) occurred within the first 4 hours following reperfusion. The expression of mRNAs significantly decreased (up to 25%) within 1 hour after occlusion in CA1 and CA3 pyramidal cell layers of the hippocampus and in the granule cell layer of the dentate gyrus. The expression of the mRNAs in these regions continued to decrease for 4 hours (up to 43%). In the second phase, which began between 4 and 12 hours following reperfusion, mRNA expression started to return to control levels in CA3 hippocampus and in the dentate. However, expression of both mRNAs continued to decline slowly in the CA1 pyramidal cell layer (up to 85%) over the next 3 days, concomitantly with degeneration of the CA1 pyramidal cells. Expression of mRNAs in the ventroposterior medial or ventroposterior lateral nuclei of the thalamus was similar to control values. To determine if a change in GABAA receptor distribution paralleled changes in receptor subunit mRNA expression, we also measured the binding of [35S]t-butylbicyclophosphorothionate to GABAA receptor chloride channels. The t-butylbicyclophosphorothionate [35S] binding decreased between 1 and 4 days after reperfusion in the dendritic fields of CA1 pyramidal cells (strata oriens, radiatum, and lacunosum-moleculare) but not in the pyramidal cell body layer. These results indicate that expression of GABAA receptor subunit mRNAs decrease well before CA1 pyramidal cell degeneration and loss of GABAA receptors. At present, it is not clear if an early loss of mRNA expression after an ischemic insult leads to a functional defect in GABAA receptors. If so, a loss of GABA neurotransmission may contribute to the development of neuronal degeneration following cerebral ischemia.(ABSTRACT TRUNCATED AT 400 WORDS)

Recovery of protein synthesis in tolerance-induced hippocampal CA1 neurons after transient forebrain ischemia

Protein synthesis at various recirculation times after 5-min transient forebrain ischemia was evaluated in gerbil hippocampal CA1 pyramidal neurons that had acquired tolerance to delayed-type ischemic injury. Evaluation was performed by observing polyribosomes under electron microscopy, and by [14C]leucine autoradiography. Hippocampal CA1 pyramidal neurons in the gerbils acquired stable and reproducible tolerance to delayed-type ischemic injury subsequent to a 5-min ischemia by pretreatment that consisted of loading two 2-min ischemic periods at a 1-day interval, followed by 48 h of recirculation. During the early phase following the 5-min ischemia, polyribosomal disaggregation, loss of dendritic microtubules, and significant suppression of radiolabeled leucine incorporation were observed in the tolerance-induced CA1 neurons as well as in the non-tolerance-induced neurons. While these findings persisted in the non-tolerance-induced neurons throughout the duration of the experiment, most of the tolerance-induced neurons demonstrated reaggregation of cytosomal ribosomes, increase in the number of dendritic microtubules, and restoration of impaired amino acid incorporation 24 h after the ischemia. These findings suggest that recovery of protein synthesis during the early post ischemic phase is essential for CA1 neuron survival after ischemic injury.

Suppression of protein synthesis in the reperfused brain

BACKGROUND

Brain ischemia and reperfusion produce profound protein synthesis alterations, the extent and persistence of which are dependent on the nature of the ischemia, the brain region, the cell layer within a region, and the particular proteins studied. After transient ischemia, most brain regions recover their protein synthesis capability; however, recovery in the selectively vulnerable areas is poor. It is unknown whether this phenomenon itself provokes or is a consequence of the process of neuronal death.

SUMMARY OF REVIEW

Protein synthesis suppression during ischemia is due to energy depletion, but this is quickly reversed upon recirculation. Reperfusion does not appear to damage DNA or transcription mechanisms, although there are changes in the profile of transcripts being made. Similarly, purified ribosomes isolated from reperfused brains can make the normal repertoire of proteins and heat-shock proteins. However, during early reperfusion, newly synthesized messenger RNAs appear to accumulate in the nucleus; this alteration in RNA handling could reflect disruption at any of several steps, including posttranscriptional processing, nuclear pore transport, cytoskeletal binding, or formation of the translation initiation complex. Another mechanism that may be responsible for protein synthesis suppression during late reperfusion is progressive membrane destruction, with consequent shifts in the concentration of ions crucial for ribosomal function.

CONCLUSIONS

Protein synthesis suppression after ischemia likely involves a progression of multiple mechanisms during reperfusion. Although the recent work reviewed here offers new insight into the potential mechanisms disrupting protein synthesis, detailed understanding will require further investigation.

Studies of the protein synthesis system in the brain cortex during global ischemia and reperfusion

Previous studies have demonstrated that brain protein synthesis declines after global ischemia and reperfusion. To investigate the role of the translation system in this phenomenon, we examined the ability of partially purified ribosomes, ribosome-bound mRNA and translation cofactors derived from the transiently ischemic cerebral cortex to synthesize protein in vitro. Samples were prepared from canines subjected to 20-min cardiac arrest and after 2 or 8 h of post-resuscitation intensive care. There was no significant decrease in the rate of in vitro protein synthesis as a consequence of either ischemia or reperfusion. Northern hybridization of ribosome-bound RNA revealed a discrete band of mRNA for brain-specific creatine kinase (ck-bb) that was consistent in presence and intensity in all groups. However, mRNA for heat shock 70 protein (hsp-70) was observed only during reperfusion and markedly increased between 2 and 8 h reperfusion. Thus, we conclude that (1) the transcription system is intact during reperfusion and hsp-70 mRNA is made and translocated to the ribosomes during reperfusion, (2) mRNA for ck-bb is not displaced from ribosomes by the appearance of hsp-70 during reperfusion and (3) isolated ribosomes maintain their ability to translate in vitro during the first 8 h of reperfusion after global brain ischemia. Therefore, the early reduction in protein synthesis observed in vivo during post-ischemic brain reperfusion is not due to an intrinsic dysfunction of the ribosomes.

Cytoplasmic beta-actin promoter produces germ cell and preimplantation embryonic transgene expression

The cytoplasmic beta-actin promoter, commonly used as strong promoter in many gene regulation studies, produces a pattern of male germ cell and preimplantation, embryonic gene expression in transgenic mice. In seven of ten expressing transgenic lines, a chicken beta-actin-lacZ fusion gene was expressed in adult testes. In addition, five of the ten lines demonstrated transgene expression in the preimplantation mouse embryo. This is the first example of transgene expression at the stages of both gamete and early embryo. Overall, the site or transgene integration appeared to influence transgene expression in adult tissues.

[14C]leucine incorporation into brain proteins in gerbils after transient ischemia: relationship to selective vulnerability of hippocampus

Regional [14C]leucine incorporation into brain proteins was studied in gerbils after global ischemia for 5 min and recirculation times of 45 min to 7 days, using a combination of quantitative autoradiography and biochemical analysis. After recirculation for 45 min, incorporated radioactivity was reduced to approximately 20-40% of control values in all ischemic brain regions. Specific activity of the tracer, in contrast, was increased, a finding indicating that the reduced incorporation of radioactivity was not due to reduced tracer influx from plasma or a dilution of the tracer by increased proteolysis. After recirculation for 6 h, [14C]leucine incorporation returned to control levels in all regions except the CA1 sector of the hippocampus, where it amounted to less than 50%. After 1 day, protein synthesis in the CA1 sector returned to approximately 70% of control values, followed by a secondary decline to less than 50% after 3 days and returned to near control values after 7 days. Histological evaluations revealed selective neuronal death in the CA1 sector of the hippocampus after 3 days of recirculation. The complex time course of protein synthesis in the CA1 sector suggests a biphasic mode of injury, which may be related to similar changes of calcium homeostasis. The final return to near normal after CA1 neurons have disappeared is explained by astroglial proliferation and demonstrates that at this time protein synthesis is not a marker of neuronal viability.