(Stroke. 1997;28:412-418.)
© 1997 American Heart Association, Inc.
Articles |
Prolongation and Enhancement of Postischemic c-fos Expression After Fasting
the Institute of Biomedical Sciences, Academia Sinica, Taipei (T.N.L., J.T., H.C.H.), and the Department of Physiology, Tzu-Chi College of Medicine, Hualien (S.I.C.), Taiwan, Republic of China; and the Department of Neurology, Washington University School of Medicine, St Louis, Mo (C.Y.H.).
Correspondence to Teng-nan Lin, PhD, Neuroscience Division, Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan. E-mail bmltn@ibms.sinica.edu.tw.
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Abstract |
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Background and Purpose A rapid but transient expression of c-fos after cerebral ischemia has been extensively documented. However, the mechanism of this induction and whether induction of c-fos is neuroprotective or detrimental to the brain after ischemia is presently not clear. Fasting before transient cerebral ischemia has been shown to reduce delayed neuronal necrosis and infarct volume. The purpose of the present study was to examine the effect of preischemic fasting for 24 hours on the expression of c-fos after transient focal cerebral ischemia.
Methods Focal cerebral ischemia was induced by temporary occlusion of the right middle cerebral artery and both common carotid arteries for 60 minutes. Male Long-Evans rats weighing 250 to 300 g were randomly divided into two groups: fed (control group) and food deprived for 24 hours (fasted group) before ischemic surgery. Infarct volumes were measured on the basis of triphenyltetrazolium chloride–delineated infarct areas, and plasma glucose levels were determined by the glucose oxidase method. Temporal and spatial expression of c-fos was assessed by Northern blot analysis, in situ hybridization, and immunohistochemistry.
Results Fasting for 24 hours before 60 minutes of ischemia resulted in a 26.6% decrease in preischemic plasma glucose levels and a 74.5% reduction in infarct volumes in the fasted group compared with the control group. A rapid but transient induction of c-fos mRNA was observed in the ischemic cortex in control animals after 60 minutes of ischemia. Fasting not only prolonged but also enhanced the intensity of c-fos expression in the ischemic cortex. Regional c-fos expression was also different between these two groups.
Conclusions The results support the contention that c-fos expression may be compatible with its purported neuroprotective role in selected experimental paradigms. The signaling mechanisms underlying the effect of fasting and subsequent lowering of plasma glucose levels on postischemic c-fos expression remain to be explored.
Key Words: cerebral ischemia • gene expression • glucose • hypoglycemia • rats
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Introduction |
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Cerebral ischemia is known to decrease the synthesis of most proteins in cells. In contrast, a small number of genes, including immediate early genes, heat shock and other stress genes, and growth factor/receptor genes, are induced after cerebral ischemia.1 2 The c-fos gene is a member of the immediate early gene family. Fos is a transcriptional factor that binds to the promoter region, the AP-1 site, of many target genes and regulates their expression.3 4 Genes with AP-1 sites in their promoters include preproenkephalin, tyrosine hydroxylase, neuropeptide Y, vasoactive intestinal polypeptide, cholecystokinin, NGF, GFAP, vimentin, the heme-oxygenase stress gene, and many others.3 5 A rapid but transient induction of c-fos mRNA after focal and global cerebral ischemia has been shown.1 2 Cerebral ischemia has also been shown to result in an increased induction of NGF, GFAP, and vimentin mRNAs and many others.1 2 However, it is not known whether changes in the expression of these AP-1–containing genes after neural injury are mediated by Fos protein or by some other mechanisms. Furthermore, it is not known whether the induction of c-fos gene is neuroprotective or detrimental to the brain.2
Recent data have shown that hyperglycemia increases brain damage6 7 and fasting with subsequent hypoglycemia reduces tissue necrosis8 9 10 11 after transient cerebral ischemia. The molecular mechanisms underlying glycemic effects in ischemic brain are not fully understood. It has been proposed that the c-fos gene is a marker of metabolic activity of individual neurons.12 The purpose of this study was to examine the temporal and spatial profiles of c-fos expression in the brain of control and fasted animals after focal cerebral ischemia.
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Materials and Methods |
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Stroke Model
Rats were randomly divided into two groups. One group had free access to water and lab chow until ischemic surgery and was designated the control group. Others, which had free access to water but were deprived of lab chow for 24 hours before ischemic surgery, were designated the fasted group. The focal cerebral ischemia/reperfusion model in the rat has been described previously.13 14 Briefly, male Long-Evans rats weighing 250 to 300 g were anesthetized with 100 mg/kg ketamine IP and 6 mg/kg xylazine IM. The trunk of the right MCA above the rhinal fissure was identified under a stereomicroscope and ligated with a 10-0 suture. Complete interruption of blood was confirmed under the microscope. Both common carotid arteries were then occluded with nontraumatic aneurysm clips. After a predetermined duration of ischemia (60 minutes), the aneurysm clips and the suture were removed, and restoration of blood flow in all three arteries was verified. During the operation, rectal temperature was monitored and maintained at 37.0±0.5°C using a homeothermic blanket (Harvard). The left femoral artery was cannulated for measurement of pH, PCO2, PO2, and mean arterial pressure, and the results were similar to those in the previous report by Yip et al.10 After ischemic insult, rats were maintained in an air-ventilated incubator at 24.0±0.5°C for various reperfusion periods (-30, 0, 30, 60, and 90 minutes and 2 and 4 hours) and were provided with water and lab chow ad libitum. At the end of the experiments, rats were killed either by transcardial perfusion with normal saline (50 mL) followed by cold 4% paraformaldehyde (pH 6.5, 200 mL, followed by pH 9.5, 300 mL), and brains removed and cryoprotected in 30% sucrose at 4°C overnight, or by decapitation where the cerebral cortices were rapidly dissected out and frozen in liquid nitrogen. Samples were stored at -70°C until further processing. Rats were housed in animal facilities of the Institute of Biomedical Sciences according to the guidelines established in the Guide for the Care and Use of Laboratory Animals prepared by the Committee on Care and Use of Laboratory Animals of the Institute of Laboratory Animal Resources Commission on Life Sciences, National Research Council (1985).
Morphometric Measurement of Infarct Volume
The infarct volume in the right MCA territory was measured indirectly14 as proposed by Swanson et al.15 Twenty-four hours after ischemic insult, animals were killed under ketamine anesthesia and intracardiac perfusion with 200 mL of 0.9% NaCl. Brains were carefully removed, cooled in ice-cold saline for 5 minutes, and then dissected into coronal 2-mm sections using a Jacobowitz brain slicer (Zivic-Miller). For morphometric measurement of the total infarct volume, the brain slices were incubated in PBS (pH 7.4) containing 2% TTC at 37°C for 30 minutes and then stored in 10% neutral-buffered formalin. The cross-sectional area of infarction in the right MCA territory for each brain slice was measured with a Zeiss IBAS image analyzer.14
Measurement of Plasma Glucose
Blood samples were collected from tail snips of each animal after anesthesia and before surgery. Blood samples were collected in heparinized tubes and centrifuged to obtain plasma fraction. Plasma glucose was measured by the glucose oxidase method using a glucose analyzer (2300 STAT, YSI).
RNA Isolation and Northern Blot Analysis
Northern blot analysis to detect c-fos mRNA has been previously described.16 Total RNA was isolated from the frozen brain tissue using the single-step acid guanidinium thiocyanate-phenol-chloroform extraction method.17 For Northern blot analysis, RNA samples (15 µg per lane) were applied on 1.2% agarose gel in the presence of 2.2 mol/L formaldehyde. After electrophoresis, the gel was transblotted onto Nytran membranes (Gene Screen Plus, DuPont).18 Membranes were prehybridized at 60°C in a solution containing 1% SDS, 1 mol/L NaCl, 10% dextran sulfate, and 100 µg/mL ssDNA. 32P-labeled c-fos probe,16 19 1x106 cpm/mL, was added directly to the prehybridization solution. Radioactive probes were prepared by random-primer labeling method (Amersham). After hybridization ranging from 24 to 48 hours at 60°C, membranes were washed twice in 2x SSC at room temperature for 5 minutes each, followed by two 30-minute washes at 60°C in 2x SSC/1% SDS and two 30-minute washes at 60°C in 0.1x SSC. Membranes were then exposed to Hyperfilm-MP (Amersham). The radioactive bands in the film were quantified by a 300S Computing Densitometer (Molecular Dynamics).
In Situ Hybridization
In situ hybridization to detect the regional distribution of c-fos mRNA signals has been previously described.16 Briefly, brain slices were frozen-sectioned at 25 µm and mounted on poly-L-lysine–coated slides. Brain sections were subjected to 0.001% proteinase K digestion at 37°C for 30 minutes, then immersed in 0.1 mol/L triethanolamine with 0.25% acetic acid anhydride at room temperature for 10 minutes, and subsequently dehydrated in 50%, 70%, 95%, and 100% ethanol (3 minutes each). Hybridization was carried out in a solution containing 12.5 mol/L formamide, 10% dextran sulfate, 0.3 mol/L NaCl, 1x Denhardt's solution, 10 mmol/L Tris-Cl 8.0, 500 µg/mL ssDNA, 100 µg/mL tRNA, 20 mmol/L DTT, and 107 cpm/mL of probes at 48°C overnight. cDNA probes were labeled with 35S-dCTP using the random-primer labeling method (Amersham). Slides were then washed sequentially in 2x, 1x, 0.2x, and 0.1x SSC containing 1 mmol/L DTT at 48°C for 30 minutes each, followed by dehydration in 50%, 70%, 95%, and 100% ethanol (3 minutes each). Brain sections were exposed to BioMax film (BMR1, Kodak), and autoradiographs were analyzed with a Bio-imaging analyzer system (BAS 1500/Pictrography 3000, Fuji). In control experiments, sections were (1) incubated with a 100-fold excess of unlabeled probe or (2) pretreated with RNase A (100 µg/mL, 37°C, 30 minutes). These experiments resulted in no or negligible signal.
Immunohistochemical Staining
Immunohistochemical staining to localize the Fos protein in the ischemic brain has been previously reported.20 Briefly, brain slices of 25 µm were frozen-sectioned and incubated in a free-floating manner. The endogenous peroxidase was blocked with 0.3% hydrogen peroxide for 30 minutes at room temperature. Preincubation with 3% normal goat serum containing 0.2% Triton X-100 was carried out at room temperature for 60 minutes to block nonspecific binding of immunoglobin G. An affinity-purified rabbit polyclonal anti-Fos antibody (0.2 µg/mL; Oncogene Science), which was raised against a peptide corresponding to the amino acid residue 4 to 17 of human Fos, was used in the present study.21 22 Sections were incubated with anti-Fos antibody diluted in 1% normal goat serum at 4°C for 48 hours, then rinsed with PBS for 30 minutes, and incubated in biotinylated goat anti-rabbit immunoglobin G for 1 hour. After several rinses with PBS, sections were incubated in avidin-horseradish-peroxidase complex for 1 hour, then incubated in 3,3'-diaminobenzidine (0.5 mg/mL) in the presence of 0.009% H2O2, and subsequently mounted on gelatinized slides. The specificity of each antiserum was demonstrated by the absence of stain when the diluted primary antiserum was preabsorbed with the respective antigen or was replaced by normal serum. For the negative control, sections were incubated with primary antibody denatured by heat. The results of these immunohistochemical controls were consistently negative.
Chemicals
All chemicals were of reagent quality and purchased either from E. Merck or Sigma Chemical Co unless otherwise indicated.
Statistics
Two-way ANOVA was used to compare the temporal expression of c-fos mRNA. The level of significance for differences between two groups was further analyzed with post-hoc Tukey's protected t tests using statistical software (GB-STAT 2.1, Dynamic Microsystem Inc). A value of P<.05 was considered significant.
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Coronal sections of the ischemic brain depicting representative TTC-delineated infarcts from both control and fasted groups are shown in Fig 1
. Under this condition, as shown in the Table, the infarct volumes were 182.9±41.4 mm3 (n=9) and the preischemia plasma glucose levels were 151.3±25.2 mg/dL (n=7). In rats fasted for 24 hours before ischemic surgery, the preischemia plasma glucose levels were decreased to 111.0±16.0 mg/dL (n=6), and the infarct volumes were reduced to 46.7±69.7 mm3 (n=8); both were significantly lower compared with control animals.
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The temporal expression of c-fos mRNA was examined by Northern blot analysis (Fig 2). Ischemia for 60 minutes resulted in a rapid but transient induction of c-fos mRNA in the ipsilateral cerebral cortex in control rats (Fig 2A). A peak level was observed at 30 minutes after reperfusion. A quantitative analysis of the blots showed an eightfold increase at the peak level compared with the sham-operated controls (Fig 2G). This finding is in line with that of a previous report by An et al.23 In rats fasted for 24 hours before ischemic surgery, they showed that induction of c-fos mRNA in the ischemic cortex was sustained longer (Fig 2C and 2G) and to a greater extent compared with the control animals (Fig 2E and 2G). After 30 minutes of reperfusion, c-fos mRNA reached a plateau and remained elevated for up to 1 hour of reperfusion in the control group. A decline in c-fos mRNA signal was noted as early as 1.5 hours during reperfusion (Fig 2G). In the fasted group, the peak of c-fos mRNA signal was sustained for up to 2 hours and declined at 4 hours during reperfusion (Fig 2G). Two-way ANOVA showed an independent effect of both control (P<.0001) and fasted (P<.0001) groups, as well as an interactive effect of control and fasted (P=.0012) group.
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In situ hybridization was used to further investigate the regional expression of c-fos mRNA (Fig 3). In this study, coronal brain slices (25 µm, rostral to caudal) were obtained from both control and fasted rats subjected to 60 minutes of ischemia followed by 30 (60/30), 60 (60/60), and 90 (60/90) minutes of reperfusion. In control animals, 60 minutes of ischemia followed by 30 minutes of reperfusion led to a marked induction of c-fos mRNA over the entire ipsilateral cerebral cortex, with relatively higher induction in the peri-infarct regions (in particular, the cingulate, frontal, insular, and piriform cortex) than in the MCA cortex. No signal was detected in the contralateral cortex. An increase in c-fos mRNA signal was also noted in both ipsilateral and contralateral hippocampus. A slight induction of c-fos mRNA was also observed in the ipsilateral caudate putamen, striatum, and amygdala areas. At 60 minutes of reperfusion in the control group, c-fos mRNA was expressed in the same regions of the ipsilateral cortex. However, the intensity of c-fos mRNA was reduced compared with intensities at 30 minutes of reperfusion. After 90 minutes of reperfusion, the c-fos mRNA virtually returned to the basal level, with only sporadic signals detected in and around the infarct. Rats fasted for 24 hours before ischemia showed a marked induction of c-fos mRNA at 30 minutes of reperfusion; however, the message was mainly localized within the ipsilateral MCA cortex, which is destined for infarction after severe ischemia in control animals. A slight increase in c-fos mRNA intensity was noted in the cingulate and piriform cortex. In addition, a marked induction of c-fos mRNA was noted within the dentate gyrus of both ipsilateral and contralateral hippocampus. No signals were detected in the caudate putamen, striatum, or amygdala regions. At 60 minutes of reperfusion, levels of c-fos mRNA remained elevated over the same areas of the ipsilateral cerebral cortex. However, c-fos mRNA expression declined in the dentate gyrus area but was increased in the CA1 to CA3 regions. A slight induction of c-fos mRNA was also noted in the ipsilateral caudate putamen. After 90 minutes of reperfusion, levels of c-fos mRNA remained elevated within the MCA irrigated region of the ipsilateral cerebral cortex. Little c-fos mRNA was detected in the ipsilateral CA1 to CA3 regions. Moreover, a marked increase in levels of c-fos mRNA was observed in the ipsilateral striatum region at this time point.
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We further examined whether increased expression of c-fos mRNA resulted in an increase in the protein levels. Fos immunoreactivity was studied in brain sections of control and fasted rats subjected to 60 minutes of ischemia followed by reperfusion for 30 (60/30), 60 (60/60), and 90 (60/90) minutes and 2 (60/120) and 4 (60/240) hours. In the ipsilateral dentate gyrus, Fos immunoreactivity was noted after 30 minutes of reperfusion, reaching a peak level at 90 minutes of reperfusion but no longer detected after 4 hours of reperfusion in control animals (Fig 4). Fos immunoreactivity was also observed in the ipsilateral dentate gyrus of fasted animals. However, the peak level was reached at 2 hours of reperfusion, and residual Fos immunoreactivity was still detected as late as 4 hours of reperfusion (Fig 4).
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In the ipsilateral piriform cortex, Fos immunoreactivity was noted after 30 minutes of reperfusion, reaching a peak level at 90 minutes of reperfusion, and then gradually decreased. Fos immunoreactivity was still evident after 4 hours of reperfusion in control animals (Fig 5). Relatively lower levels of Fos immunoreactivity were expressed for a shorter period in the ipsilateral piriform cortex of fasted animals (Fig 5).
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In the MCA cortex, expression of Fos was inconsistently noted in the infarcted region in nonfasted rats in a previous report.20 In the present study, only sporadic Fos immunoreactivity was detected in the infarct regions in control animals (Fig 6A) up to 4 hours of reperfusion. However, a marked increased in Fos immunoreactivity was detected at 4 hours of reperfusion in fasted animals (Fig 6B). In addition, Fos immunoreactivity was detected in the ipsilateral CA1 regions of fasted animals (Fig 6D). However, only sporadic signals were detected in the same regions of control animals (Fig 6C).
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The c-fos gene has been implicated in a wide variety of fundamental cellular processes, including mitosis, differentiation, senescence, carcinogenesis, and neuronal activity.3 In addition, c-fos has served as a marker of metabolic activity in individual neurons.12 Expression of c-fos after focal cerebral ischemia has been extensively studied (for review, see Akins et al2 ). The exact roles of this immediate early gene in ischemic brain injury remain to be defined. Hengerer et al24 have shown that a lesion-induced increase in NGF mRNA is mediated by c-fos and NGF ameliorated delayed neuronal death after ischemia.25 It is thus possible that induction of c-fos mRNA may be associated with cellular mechanisms that promote survival subsequent to ischemic insult.2 In the present study, fasting for 24 hours before ischemia not only prolonged but also enhanced the induction of c-fos mRNA in the ipsilateral cortex compared with the control animals (Figs 2 and 3
). In control animals, c-fos mRNA was observed predominantly in the peri-infarct regions. In the fasted group, c-fos mRNA expression was largely confined to the MCA cortex (destined for infarction in the control group). The mechanism and physiological significance of this differential temporal and spatial induction profile of c-fos mRNA between control and fasted rats are not clear. Because fasting resulted in a 74.5% decrease in infarct volumes (Table), it is possible that the MCA cortex in the fasted animals is somewhat similar to the peri-infarct region of control animals, which sustained less severe ischemia. In a previous study,23 we showed that after 30 minutes of ischemic insult, when no evident structural damage or only a small infarct was noted in the right ischemic cortex, the c-fos mRNA was expressed mainly within the MCA cortex. However, after 90 minutes of ischemia, when a consistently large infarct was noted in the ischemic MCA cortex, the c-fos mRNA was expressed mainly in the peri-infarct area. If c-fos expression is neuroprotective,2 then severe ischemia (60 to 90 minutes) may have rendered the MCA cortex incapable of mounting a c-fos–mediated stress response. Recently, Kobayashi et al26 reported that KCl-induced spreading depression resulted in a widespread expression of c-fos mRNA in the ipsilateral cortex and subsequently reduced the neuronal cell death after ischemic challenge. In addition, intraischemic hypothermia, which protects the brain against ischemic brain injury,27 has been shown to increase the induction of c-fos mRNA after transient forebrain ischemia.28 Moreover, a mild focal ischemia, which leads to a prolonged induction of c-fos and hsp70 mRNA in CuZn–superoxide dismutase transgenic mice,29 causes ischemic neuronal injury to a lesser degree compared with that in normal nontransgenic mice.30 Hyperglycemia, which increased brain damage caused by transient cerebral ischemia,10 has been shown to suppress c-fos mRNA expression after transient cerebral ischemia.31 Together, these data support the contention that, under selected experimental conditions, c-fos expression maybe neuroprotective and is induced promptly and vigorously in ischemic areas that ultimately do not sustain irreversible damage. The diffuse induction of c-fos mRNA beyond ischemic regions may likely be due to spreading depression (repeated cortical depolarizations)26 32 and/or diaschisis (effects expressed in brain regions remote from the initiation site)4 33 in response to the ischemic insult. However, the underlying signaling processes leading to this type of ischemic response have not been established.
A marked increase in c-fos mRNA was also observed in the hippocampus where no structural damage was found. In control animals, the expression was rapid but transient with marked induction noted in the dentate gyrus and CA1 to CA3 regions at 30 minutes but only sporadic signals detected at 60 and 90 minutes of reperfusion. In fasted animals, the expression of c-fos mRNA was most intense in the granule cells of the dentate gyrus after 30 minutes of reperfusion. The expression subsequently and gradually decreased. In the pyramidal cells of the CA1 to CA3 regions, the expression of c-fos mRNA was delayed to 60 minutes of reperfusion. Similar transsynaptic induction of c-fos mRNA (dentate gyrus
CA3CA1) has been reported in seizure by Morgan et al34 and in forebrain ischemia by Wessel et al.35 The mechanism leading to this induction remains to be determined. A similarly delayed induction of c-fos mRNA has also been observed in the ipsilateral caudate putamen and striatum areas of fasted animals at 60 and 90 minutes of reperfusion, respectively (Fig 3).
Previously, we have shown that increased expression of c-fos mRNA after cerebral ischemia/reperfusion is due to an increase in the transcription rate. An increase in Fos expression was demonstrated by mobility shift assay23 and immunohistochemistry.20 In the present study, we further demonstrate that Fos immunoreactivity is detectable in the area where marked induction of c-fos mRNA is also found. In line with the results from in situ hybridization, a prolonged induction of Fos immunoreactivity was observed in the dentate gyrus of fasted animals, but higher intensity of Fos immunoreactivity was observed in the piriform cortex of control animals. Furthermore, a marked expression of Fos immunoreactivity was observed in the MCA cortex of fasted animals at 4 hours of reperfusion in contrast to little expression in the same regions in control animals. Double labeling with anti-GFAP antibody indicates that these Fos-positive cells do not originate as astrocytes (data not shown). Intense Fos immunoreactivity was detected in the ipsilateral CA1 region of fasted animals. However, only sporadic Fos immunoreactivity was detected in the CA1 region of control animals. Takemoto et al22 reported that Fos protein is rapidly induced in the CA1 region after brief ischemia. However, Fos protein is absent or negligible in CA1 after prolonged ischemia. These results again suggest that no or minimal Fos protein is observed in areas destined for irreversible ischemic damage. Why Fos is expressed in regions, including the hippocampus, that are remote from the ischemic cortex is not well understood but has been shown by a number of investigators using the same MCA occlusion described in the present study.20 36 37 Regional intensity of c-fos expression serves as an indicator of metabolic activity in particular regions of the brain.12 It is likely that expression of c-fos and Fos in areas outside the ischemic zone represents ischemia-induced activation of selected neuronal pathways.23 The exact mechanism, however, needs to be further explored.
In summary, the present studies show that 24 hours of preischemic fasting, which reduces ischemic brain injury, not only prolongs but also enhances the expression of c-fos gene products. Although the areas with c-fos induction and Fos expression are different between control and fasted animals, c-fos appears to express only in areas that sustain ischemia but do not develop irreversible ischemic damage. This finding is similar to the regional expression of c-fos and hsp70 in another focal ischemia model.29 Since Fos and Jun form heterodimers, which bind an AP-1 sequence upstream of genes such as NGF and HSP 70, it is possible that induction of c-fos gene products may promote cell survival after ischemic insult. Thus, prolonged and enhanced induction of c-fos gene product after recirculation may be compatible with the beneficial effect of fasting in reducing infarct volume after ischemic insult. Why fasting with consequent lowering of plasma glucose levels affects the extent and duration of c-fos expression after cerebral ischemia warrants further investigation. Currently, the regulation of postischemic c-fos expression is still not clear. Fasting and subsequent lowering of plasma glucose have been shown to cause a multitude of pathophysiological and biochemical changes in the ischemic brain. These include alteration of blood flow, lactic acidosis, and enhanced free radical generation.10 It remains to be determined whether any of these changes is causally linked to the modulation of c-fos expression.
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Acknowledgments |
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This work was supported by grants from the National Science Council (NSC-84-2331-B001-001) and Academia Sinica, Taipei, Taiwan, Republic of China.
Received September 9, 1996; revision received October 16, 1996; accepted October 16, 1996.
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Editorial Comment
Department of Neurological Surgery and Neurology University of California San Francisco, Calif
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferencesIntroduction References |
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It is well known that immediate early genes, including c-fos, are induced rapidly and transiently in brain cells after cerebral ischemia. However, the role that the c-fos gene plays either as protective of or detrimental to brain cells after its expression is not clear at present.1R
In this article, Lin and his colleagues have correlated the postischemic c-fos gene expression after fasting with reduced neuronal injury. They have demonstrated that both the mRNA and Fos protein of c-fos are expressed postischemically at a higher level and in a more prolonged fashion in the fasting animals than in the normally fed counterparts. The mechanisms underlying such change in gene expression after fasting are not clear at present. For example, what are the signaling mechanisms that trigger the prolonged c-fos expression, especially in the dentate gyrus, an area that is remote from the MCA territory? Another unanswered question is whether such prolonged and region-specific c-fos gene expression can be extended to other immediate early genes or other genes. An additional question that could be asked is whether there is a cause and effect relationship between the increased c-fos expression and the reduced infarct volume in the fasting animals. However, this study points to the unique and provocative observation that it may be feasible to extend this finding to reduce ischemic brain damage at a nutritional level by manipulating gene expression in the brain with limited food intake.
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Values are mean±SD. n indicates number of rats in each group.
*P<.01 compared with the value in control group.
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1R. Akins PT, Liu PK, Hsu CY. Immediate early gene expression in response to cerebral ischemia: friend or foe? Stroke. 1996;27:1682-1687.
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