Induction of c-fos, junB, c-jun, and hsp70 mRNA in cortex, thalamus, basal ganglia, and hippocampus following middle cerebral artery occlusion

Induction of brain-derived neurotrophic factor (BDNF) and the receptor trk B mRNA following middle cerebral artery occlusion in rat

Middle cerebral artery (MCA) occlusion in halothane-anesthetized rats induced brain-derived neurotrophic factor (BDNF) and the receptor, trk B mRNA, in brain. In situ hybridization studies showed that BDNF and trk B mRNAs were induced in a widespread region of the ipsilateral cortex outside the infarct at 4 h following MCA occlusion. They were also induced in the bilateral hippocampi which are remote from the ischemic MCA region. These data show that changes in neurotrophic factor and receptor gene expressions can occur in the areas outside the infarct which could survive.

Astrocyte survival and HSP70 heat shock protein induction following heat shock and acidosis

Although severe acidosis is an important mediator of brain infarction, recent evidence suggests that mild acidosis may protect ischemic cells. The HSP70 heat shock protein is induced by acidosis in cultured cells and in ischemic brain and protects cells against many types of injury. Therefore, this study determined whether induction of heat shock proteins protects cultured astrocytes against acidosis. Brief exposure of cultured cortical astrocytes to acid (pH 5.2 for 40 min) or heat shock (45 degrees C for 40 min) markedly induced hsp70 mRNA and HSP70 protein. HSP70 protein was detected with the C92 monoclonal antibody (Welch and Suhan: J Cell Biol 103:2035, 1986), which has been shown to recognize the protein product of the full-length rat hsp70 cDNA (Longo et al: J Neurosci Res 36:325, 1993). Heat shock of the cultured cortical astrocytes completely protected the astrocytes from an otherwise lethal heat exposure 24 h later (45 degrees C for 4 h). In contrast, heat pretreatment sensitized the astrocytes to injury from acidosis 24 h later. Acid pretreatment, which markedly induced the HSP70 protein without producing astrocytic cell death, similarly sensitized the cells to injury from acidosis 24 h later (60% survival following pH 5.2 for 3 h versus 90% survival in controls; P < 0.0001). Surprisingly, heat shock pretreatment protected astrocytes against exposure to acid 48 h later (P < 0.05, 1.5-3 h), whereas acid pretreatment had no effect on astrocyte survival 48 h later. Since heat shock did not protect against acidosis at 24 h when HSP70 induction was maximal but did protect at 48 h when HSP70 was markedly diminished, the protective effect of heat shock at 48 h may be related to stress proteins present at 48 h. It is concluded that induction of HSP70 and other heat shock proteins by heat shock protects astrocytes against subsequent lethal heat shock. However, heat shock and acid treatment increase the vulnerability of astrocytes to acidosis 24 h later in spite of the induction of HSP70 heat shock proteins. The finding that heat shock protected astrocytes against acidosis 2 days later may suggest that delayed induction of stress proteins partially protects the astrocytes against damage produced by high concentrations of hydrogen ions.

Developmental expression of Fos-lacZ in the brains of postnatal transgenic rats

Previously, we reported the production and characterization of fos-lacZ transgenic mice [41] and rats [19] that can be used to monitor both constitutive and evoked expression of c-fos in vivo. When we compared the sites of spontaneous fos-lacZ expression in the brains of developing transgenic fos-lacZ mice and rats, the patterns were almost identical. However, throughout the first postnatal month, the rat striatum contained a large number of Fos-lacZ-positive cells whereas only a few positive cells were seen in the mouse. By adulthood, the number of Fos-lacZ-positive cells in the rat striatum had declined dramatically to the low basal values seen in mice. To establish whether this species difference was evident in the adult striatum, rats and mice were treated with metamphetamine. This indirect D1 agonist, triggered a pronounced induction of fos-lacZ in the rat striatum while only a modest response was observed in the mouse. These data imply: (1) there are differences in dopamine-dependent stimulus-transcription coupling between the two species. (2) Maturation of dopaminergic signalling pathways may underlie the spontaneous immediate-early gene response in the developing rat striatum.

Selective c-Jun overexpression is associated with ionizing radiation-induced apoptosis in the developing cerebellum of the rat

Immunohistochemistry to Bcl-2, Bax, c-Myc, c-Fos, Fos-related, c-Jun, Jun B and Jun D was used to study the involvement of these factors in ionizing radiation-induced apoptosis in the cerebellum of the developing rat. Selective c-Jun overexpression was observed during the whole process of radiation-induced cell death. Furthermore, c-Jun overexpression was restricted to apoptotic cells, as shown by double labeling with the method of in situ labeling of nuclear DNA fragmentation and c-Jun immunohistochemistry. This is the first in vivo evidence that selective c-Jun overexpression is associated with apoptotic cell death in the developing nervous system following ionizing radiation.

Proteolytic cascade enzymes increase in focal cerebral ischemia in rat

Cerebral infarction initiates a cascade of molecular events, leading to proteolytic cell death. Matrix-degrading metalloproteinases (MMPs) are neutral proteases involved in extracellular matrix damage. Type IV collagenase is an MMP that increases cerebral capillary permeability after intracerebral injection and may be important along with plasminogen activators (PA) in secondary brain edema in stroke. Therefore, we measured MMPs and PAs in spontaneously hypertensive (SHR) or Wistar-Kyoto (WKY) rats with permanent middle cerebral artery occlusion (MCAO). Brain tissue was assayed for MMPs and PAs at 1, 3, 12, and 24 h and 5 days after occlusion, using substrate gel polyacrylamide electrophoresis (zymography). SHR showed an increase in 92-kDa type IV collagenase (gelatinase B) in the infarcted hemisphere compared with the opposite side at 12 and 24 h (p < 0.05). Gelatinase A remained the same in both infarcted and normal tissue until 5 days after injury, when it increased significantly (p < 0.05). Urokinase-type PA was increased significantly at 12 and 24 h and 5 days, while tissue-type PA was decreased significantly at 1, 12, and 24 h in the ischemic compared with the nonischemic hemisphere. Gelatinase B was markedly increased in SHR at 12 and 24 h compared with WKY (p < 0.05). Secondary vasogenic edema is maximal 1-2 days after a stroke, which is the time that gelatinase B was elevated. The time of appearance of gelatinase B suggests a role in secondary tissue damage and vasogenic edema, while gelatinase A may be involved in tissue repair.

Heme oxygenase-1 (HO-1) protein induction in rat brain following focal ischemia

The induction of the heme oxygenase-1 (HO-1) protein, also called HSP32, was compared to HSP70 heat shock protein induction following focal ischemia. Adult Sprague-Dawley male rats (n = 14) were subjected to either 30 min or 2 h of focal cerebral ischemia using the suture, middle-cerebral-artery (MCA) occlusion model. Controls (n = 4) had sham surgery. Following 24 h of reperfusion, subjects were killed and their brains stained immunocytochemically for HO-1 and the HSP70 heat shock proteins. One day following 30 min of ischemia, HO-1 and HSP70 staining in striatum occurred mainly in endothelial cells in infarcts and in glial cells surrounding the areas of infarction. Following the 30 min ischemia HO-1 was not induced in cortex whereas HSP70 was induced in cortical neurons in the MCA distribution. One day following 2 h of MCA ischemia, both HO-1 and HSP70 were induced in neurons in cortex in the MCA distribution. HO-1, however, was induced in glial cells throughout ipsilateral cortex, inside as well as outside the MCA distribution. This suggests that translation and/or transcription of the HO-1 and HSP70 genes are blocked in neurons and glia destined to die within infarcts, whereas translation of these stress genes continues in the endothelial cells. The duration of ischemia required to induce HSP70 in cortical neurons appears to be less than that required to induce HO-1 in cortical glia. Prolonged spreading depression and/or diffuse hemispheric ischemia may induce HO-1 in glia throughout the ipsilateral cortex via immediate early gene activation of the AP-1 site in the HO-1 promoter. Since HO-1 degrades heme, a pro-oxidant, to antioxidant molecules, the induction of HO-1 may augment oxidative defense mechanisms compromised by cerebral ischemia.

Regionally and temporally distinct patterns of induction of c-fos, c-jun and junB mRNAs following experimental brain injury in the rat

Lateral (parasagittal) fluid-percussion brain injury of mild (1.0-1.5 atm) and moderate (2.1-2.4 atm) severity induced expression of mRNAs for the immediate early genes (IEGs) c-fos, c-jun and junB. At 5 min following mild brain injury, c-fos and junB mRNA were co-induced in the cortex ipsilateral to the impact site. Expression remained elevated up to 2 h after injury and returned to control levels by 6 h. Levels of c-fos mRNA increased in the cells of the hippocampal dentate gyrus as early as 5 min after mild brain injury and additionally in the areas CA1-3 by 30 min. By 2 h, no hippocampal c-fos mRNA was detectable. Induction of junB mRNA in the hippocampus was delayed, occurring at 30 min after injury, and remained elevated up to 2 h post injury. Increased levels of junB mRNA were also observed in the striatum ipsilateral to the injury. Increased expression of c-jun mRNA was restricted to the ipsilateral dentate gyrus and was observed at 5 min after injury and remained elevated up to 6 h. Although the temporal pattern of induction of individual IEGs after brain injury of moderate severity was similar to that observed after mild severity, moderate injury induced IEG mRNA in both injured and contralateral hemispheres. These data suggest that traumatic brain injury invokes a complex acute regional and cellular response which may involve the activation of multiple signal transduction pathways.

Evidence for apoptotic cell death in the choroid plexus following focal cerebral ischemia

Focal cerebral ischemia in rats subjected to middle cerebral artery (MCA) occlusion results in apoptotic DNA fragmentation and activation of putative cell death effector genes in neurons and functional impairment of the plexus choroideus. In the present study we investigated whether cerebral ischemia may induce apoptotic cell death in the choroid plexus. Using in situ end-labeling by terminal transferase and fluorescein-dUTP, nuclear DNA breaks were detected in the choroid plexus of the lateral ventricle of the ischemic hemisphere after 6 h but not after 1.5 h of MCA occlusion. Intense cytoplasmic immunostaining for pro-apoptotic Bax protein and moderate immunolabeling for Bcl-X was observed in the epithelium of the choroid plexus of the lateral and third ventricles. However, constitutive expression of Bax and Bcl-X proteins in the plexus choroideus did not change significantly following focal ischemia. Thus, cells of the choroid plexus may die by apoptosis after several hours of cerebral ischemia. Modulation of cell death effector genes of the bcl-2 family however, may not be required for apoptotic cell death to occur.

Temporal correlation analysis of penumbral dynamics in focal cerebral ischemia

A novel temporal correlation technique was used to map the first-pass transit of iodinated contrast agents through the brain. Transit profiles after bolus injections were measured with dynamic computed tomography (CT) scanning (1 image/s over 50 s). A rabbit model of focal cerebral ischemia (n = 6) was used, and dynamic CT scans were performed at 30, 60, 90, and 120 min postocclusion. Within the ischemic core, no bolus transit was detectable, demonstrating that complete ischemia was present after arterial occlusion. In the periphery of the ischemic distribution, transit dynamics showed smaller peaks, broadened profiles, and overall delay in bolus transit. A cross-correlation method was used to generate maps of delays in ischemic transit profiles compared with normal transit profiles from the contralateral hemisphere. These maps showed that penumbral regions surrounding the ischemic core had significantly delayed bolus transit profiles. Enlargement of the ischemic core over time (from 30 to 120 min postocclusion) was primarily accomplished by the progressive deterioration of the penumbral regions. These results suggest that (a) temporal correlation methods can define regions of abnormal perfusion in focal cerebral ischemia, (b) peripheral regions of focal cerebral ischemia are characterized by delays in bolus transit profiles, and (c) these regions of bolus transit delay deteriorate over time and thus represent a hemodynamic penumbra.

Induction of cyclooxygenase-2 mRNA and protein following transient focal ischemia in the rat brain

Expression of cyclooxygenase-2 (cox-2) mRNA and inducible heat-shock protein-70 (hsp-70) mRNA was studied with in situ hybridization techniques at 30 min and 4 h following 1 h transient middle cerebral artery (MCA) occlusion in the rat brain. In addition, immunoreactivity for cox-2 was studied after 8 h of reperfusion. Induction of hsp-70 and cox-2 mRNA was found in the brain side ipsilateral to MCA occlusion. Hsp-70 mRNA was induced in the parietal cortex and striatum within the territory of the occluded MCA. Induction of cox-2 mRNA was particularly seen in cortical layer II in the brain side ipsilateral to MCA occlusion. At 30 min of reperfusion, areas showing cox-2 mRNA induction included the cingulate and frontal cortices located perifocally to the areas showing hsp-70 mRNA induction, and the piriform cortex. At 4 h of reperfusion, induction of cox-2 mRNA was seen within the parietal cortex. At 8 h of reperfusion, immunoreactivity for cox-2 was mainly seen in the ipsilateral cortex. These results demonstrate that transient focal ischemia induces the expression of cox-2 mRNA and protein in discrete areas of the rat brain during reperfusion, which might lead to local increases of arachidonic acid metabolism.

Amino acid uptake in ischemically compromised brain tissue

BACKGROUND AND PURPOSE

Multitracer positron emission tomography (PET) was used to investigate local amino acid accumulation in brain tissue surrounding focal ischemia.

METHODS

PET using 15O-labeled oxygen and water for measuring cerebral metabolic rate of oxygen (CMRO2) and cerebral blood flow (CBF), C15O for determination of blood volume (CBV) and calculation of oxygen extraction fraction, and L-[11C]methylmethionine (11C-MET) for the assessment of amino acid accumulation was applied in 14 patients (mean age, 52 +/- 9.1 years) with acute ischemic hemispheric stroke. Two multitracer PET studies were completed, the first 8 to 24 hours after onset of neurological symptoms and the follow-up study 14 +/- 1 days after the ischemic attack. Functional changes were compared with morphological damage on cranial CT or MRI. Three-dimensional matching and volume of interest evaluation procedures were used to study 11C-MET accumulation in relation to various physiological variables in infarcted and noninfarcted tissue.

RESULTS

Compared with contralateral mirror regions, initially increased regional 11C-MET uptake (21.2 +/- 10.9%, P < .001) was found in patchy areas in the immediate vicinity of infarction as well as in distant areas within the same hemisphere. In those areas, regional CBF (-11.4 +/- 21.2%, P < .01) and oxygen extraction fraction (2.8 +/- 29.1%, P = NS) were highly variable, and regional CMRO2 was preserved or slightly reduced (-12.4 +/- 16.0%, P < .001). CBF data comprised severely ischemic as well as high values (14.6 to 64.2 mL/100 g per minute). Cranial CT and coregistered MRI in five patients demonstrated preserved morphology. In all peri-infarct areas (n = 62), the 11C-MET uptake showed a positive correlation with delta CMRO2 as the relative improvement of ipsilateral CMRO2 between the two PET studies (r = .378, P < .01). Particularly in areas with increased oxygen extraction fraction (n = 42), the 11C-MET uptake showed a mild correlation with CMRO2 at follow-up measurement (r = .31, P < .05). In all peri-infarct areas, 11C-MET uptake showed a negative correlation with oxygen extraction fraction (r = -.672, P < .001) and a positive correlation with CBF (r = .4, P = .001). In all infarcted and peri-infarct areas, normalized initial 11C-MET uptake was positively correlated with CMRO2 at follow-up (r = .603, P < .001).

CONCLUSIONS

Focal increases of 11C-MET uptake seen in this study were generally mild. They might be seen in the core of ischemia, indicating breakdown of the blood-brain barrier with poor tissue prognosis, but they also frequently occurred during or after ischemic compromise in surviving brain tissue surrounding focal cerebral infarction, perhaps representing alterations of amino acid transport or protein synthesis in brain tissue with a favorable prognosis.

Cellular responses to experimental brain injury

Little is known regarding the molecular (genomic) events associated with the pathophysiology of traumatic brain injury (TBI). This review focusses on the experimental efforts to date elucidating the acute alterations in expression of immediate early genes (IEGs), heat shock proteins (HSPs) and cytokines following experimental brain injury. The immediate early genes, c-fos, c-jun and junB were observed to be bilaterally induced in the cortex and hippocampus as early as 5 min following lateral fluid-percussion (FP) brain injury in the rat. While levels of c-fos and junB mRNA returned to control levels by 2h, c-jun mRNA remained elevated up to 6h post-injury. Increased levels of mRNA for the inducible heat-shock protein (hsp72) were observed up to 12h following injury and were restricted to the cortex ipsilateral to the impact site. Mild induction of the glucose-regulated proteins (grp78 and grp94), which share sequence homology with hsp72, was apparent in the ipsilateral cortex. The cytokines IL-1 beta and TNF alpha were induced at 1h following FP brain injury and remained elevated up to 6h post-injury. These data, while indicative of the complex genomic response to TBI, are also suggestive of the trauma-induced activation of multiple signal transduction pathways.

Expression of c-fos and inducible hsp-70 mRNA following a transient episode of focal ischemia that had non-lethal effects on the rat brain

Expression of c-fos and inducible hsp-70 mRNA was studied with in situ hybridization techniques at different times following an episode of middle cerebral artery (MCA) occlusion not resulting in any apparent lethal effect on the rat brain. hsp-70 and c-fos mRNA were found in the ipsilateral striatum and adjacent cortex. In the striatum, levels of hsp-70 mRNA increased from 1 to 2 and 4 h of reperfusion, whereas levels of c-fos mRNA decreased from 1 to 4 h of reperfusion. These results demonstrate that following non-lethal focal ischemia the brain areas within the MCA territory show high c-fos and hsp-70 mRNA expression response, illustrating the concomitant induction of these mRNAs in cells that survive the ischemic insult.

Induction of NGFI-A mRNA following middle cerebral artery occlusion in rats: in situ hybridization study

Middle cerebral artery (MCA) occlusion in halothane-anesthetized rats induced the zinc finger gene, NGFI-A, in brain. In situ hybridization studies showed that NGFI-A was induced throughout all of the cortex following MCA occlusion. By 24 h after MCA occlusion there was little expression of NGFI-A mRNA in the core of the MCA infarct, but the mRNA was still induced in all of cortex outside the infarct. MCA occlusion also induced this gene in subcortical structures: ipsilateral medial striatum; most of thalamus including medial and lateral geniculate nuclei; substantia nigra; and hippocampus at 4 h of MCA occlusion which generally disappeared by 24 h of MCA occlusion. Most of these structures, except for the striatum, are not supplied by the MCA. These data show that changes in brain gene expression can occur in many regions remote from an infarction.