Homogeneous repair of nuclear genes after experimental stroke

The repair of oxidative DNA lesions (ODLs) in the nucleus of ischemic cortical brain cells was examined following experimentally induced stroke by occluding the right middle cerebral artery and both common carotid arteries for 60-90 min followed by reperfusion in male long-Evans hooded rats. The control group consisted of sham-operated animals undergoing the same surgery without vessel occlusion. Using a gene-specific assay based upon the presence of Escherichia coli Fpg protein-sensitive sites, we noted that animals with stroke exhibited six and four ODLs per gene in the actin and DNA polymerase-beta genes, respectively. This was increased from one per four copies of each gene in the sham-operated control (p < 0.01). One half of the initial ODLs was repaired within 30 min, and 83% of them were repaired as early as 45 min of reperfusion. There was no further increase when gene repair was measured again at 2 h of reperfusion. The rates of active repair within 45 min of reperfusion were the same in these two genes (p = 0.103, ANOVA). BrdU (10 mg/kg) was administered via intraperitoneal injection at least one day before surgery. We observed that there was no significant incorporation of BrdU triphosphates into genomic DNA during active repair, but there were significant amounts of BrdU triphosphate in nuclear DNA after active repair. The result indicates that genomic repair of ODLs in the brain did not significantly incorporate BrdU, and the initiation of neurogenesis probably starts after the completion of repair in the brain.

Suppression of post-ischemic-induced fos protein expression by an antisense oligonucleotide to c-fos mRNA leads to increased tissue damage

Activation of c-fos, an immediate early gene, and the subsequent upregulation of Fos protein expression occur following neural injury, including focal cerebral ischemia (fci). Fos and Jun form a heterodimer known as activator protein 1, which regulates the expression of many late effector genes. To study the downstream effects of c-fos expression following ischemia, we suppressed the translation of c-fos by administering an antisense oligonucleotide (AO) to c-fos mRNA. Eighteen hours prior to fci, male, Long Evans (LE) rats received intraventricular injections of AO, mismatched AO (MS) or artificial cerebrospinal fluid (aCSF). Fci was induced by permanent right middle cerebral artery occlusion. At 24-h post-occlusion, neurological function was assessed, and the animals were sacrificed. The brains were removed and stained with triphenyltetrazolium chloride for infarct volume determination. Fos immunohistochemistry was performed in separate animals to determine the effects of treatment on Fos expression number of Fos positive cells. AO administration reduced the number of cells with fci-induced Fos expression by approximately 75%. No differences in neurological scores existed between any of the groups. AO-treated LE developed larger infarcts (40.1+/-1.0%, mean+/-S.D., p<0.001) than MS- or aCSF-treated controls (34.3+/-1.0%, 34.6+/-1.0%, respectively). These results suggest that c-fos activation and subsequent Fos protein expression exerts a neuroprotective effect, which is likely via upregulation of neurotrophins, following focal cerebral ischemia. This response, among others, may contribute to brain adaptation to injury that underlies functional recovery after stroke.

Suppression of postischemic hippocampal nerve growth factor expression by a c-fos antisense oligodeoxynucleotide

We examined the uptake and distribution of an antisense phosphorothioated oligodeoxynucleotide (s-ODN) to c-fos, rncfosr115, infused into the left cerebral ventricle of male Long-Evans rats and the effect of this s-ODN on subsequent Fos, NGF, neurotrophin-3 (NT-3), and actin expression. To establish the uptake and turnover of s-ODN in the brain, we studied the copurification of the immunoreactivity of biotin with biotinylated s-ODN that was recovered from different regions of the brain. A time-dependent diffusion and the localization of s-ODN were further demonstrated by labeling the 3'-OH terminus of s-ODN in situ with digoxigenin-dUTP using terminal transferase and detection using anti-digoxigenin IgG-FITC. Cellular uptake of the s-ODN was evident in both the hippocampal and cortical regions, consistent with a gradient originating at the ventricular surface. Degradation of the s-ODN was observed beginning 48 hr after delivery. The effectiveness of c-fos antisense s-ODN was demonstrated by its suppression of postischemic Fos expression, which was accompanied by an inhibition of ischemia-induced NGF mRNA expression in the dentate gyrus. Infusion of saline, the sense s-ODN, or a mismatch antisense s-ODN did not suppress Fos expression. That this effect of c-fos antisense s-ODN was specific to NGF was demonstrated by its lack of effect on the postischemic expression of the NT-3 and beta-actin genes. Our results demonstrate that c-fos antisense s-ODN blocks selected downstream events and support the contention that postischemic Fos regulates the subsequent expression of the NGF gene and that Fos expression may have a functional component in neuroregeneration after focal cerebral ischemia-reperfusion.

Gene expression and apoptosis in the spinal cord neurons after sciatic nerve injury

To demonstrate a dependence of spinal cord motoneurons on the communication with their targets, the expression of immediate early gene c-fos and neurotrophin genes in the lumbar (L3-L6) spinal cord neurons was examined in Sprague-Dawley rats (male > or = 9-weeks-old) with unilateral sciatic nerve transection. Using in situ hybridization, we detected the expression of c-fos mRNA in the motoneurons of the spinal cord segments within 45 min to 3 h of peripheral nerve transection (n = 4 in each time point). The expression of c-fos mRNA was also correlated positively with the expression of Fos antigen using immunohistochemistry, while no change in calbindin and parvalbumin antigens were noted. The expression of BDNF mRNA increased at 90 min after sciatic nerve transection. However, no detectable enhancement in the expression of NGF mRNA was observed. DNA fragmentation in neurons was observed using the incorporation of digoxigenin-dUTP by terminal transferase into 3'-OH terminals of DNA fragments in the ipsilateral section of the spinal cords 48h after nerve injury. Nuclei that exhibited DNA fragmentation were not observed in the spinal cord of the control animals. Lastly, we observed that the majority of astrocytes did not have DNA fragmentation. Because the detection of DNA fragmentation using this assay is one of early detections of apoptosis or programmed cell death, the result suggested we could detect early cell death in spinal cord, and indicated a target dependence of the neurons in the spinal cord after transection of sciatic nerve.

Damage, repair, and mutagenesis in nuclear genes after mouse forebrain ischemia-reperfusion

To determine whether oxidative stress after cerebral ischemia-reperfusion affects genetic stability in the brain, we studied mutagenesis after forebrain ischemia-reperfusion in Big Blue transgenic mice (male C57BL/6 strain) containing a reporter lacI gene, which allows detection of mutation frequency. The frequency of mutation in this reporter lacI gene increased from 1.5 to 7.7 (per 100,000) in cortical DNA after 30 min of forebrain ischemia and 8 hr of reperfusion and remained elevated at 24 hr reperfusion. Eight DNA lesions that are characteristic of DNA damage mediated by free radicals were detected. Four mutagenic lesions (2,6-diamino-4-hydroxy-5-formamidopyrimidine, 8-hydroxyadenine, 5-hydroxycytosine, and 8-hydroxyguanine) examined by gas chromatography/mass spectrometry and one corresponding 8-hydroxy-2'-deoxyguanosine by a method of HPLC with electrochemical detection increased in cortical DNA two- to fourfold (p < 0.05) during 10-20 min of reperfusion. The damage to gamma-actin and DNA polymerase-beta genes was detected within 20 min of reperfusion based on the presence of formamidopyrimidine DNA N-glycosylase-sensitive sites. These genes became resistant to the glycosylase within 4-6 hr of reperfusion, suggesting a reduction in DNA damage and presence of DNA repair in nuclear genes. These results suggest that nuclear genes could be targets of free radicals.