Heat shock proteins in brain ischemia: role undefined as yet

Marked, sustained expression of a novel 150-kDa oxygen-regulated stress protein, in severely ischemic mouse neurons

The 150-kDa oxygen-regulated protein (ORP150) first was described with reference to the central nervous system in cultured astrocytes subjected to dense hypoxia. Subsequently its transcript was found in macrophages within human aortic atherosclerotic plaques, suggesting a role in protecting cells under hypoxic stress. In a mouse model of permanent focal brain ischemia, we aimed to elucidate the constitutive cellular localization in vivo of ORP150 in the central nervous system as well as the sequential alteration in its mRNA and protein expression during this severe ischemic insult. Immunohistochemical study demonstrated that ORP150 protein normally is present predominantly in neurons. The 78-kDa glucose-regulated protein, which is another well-known stress protein retained in the endoplasmic reticulum, also was stained in neurons. During the first 3 h after ischemia, ORP150 antigenicity was markedly enhanced in severely damaged neurons, while the amount of the glucose-regulated protein was decreased. Preceding this change, orp150 mRNA was selectively induced in neurons undergoing postischemic cytoskeletal proteolysis, as early as 1 h after middle cerebral artery occlusion. These results indicated that ORP150 might be regulated by transcriptional level as for many stress proteins, but unlike previously described other stress proteins it was translated in the center of ischemic lesions despite nearly complete energy depletion. In this paper, the biological potentials of ORP150 protein in the setting of brain ischemia in vivo will also be discussed.

The effect of hypothermia on induction of heat shock protein (HSP)-72 in ischemic brain

Intra-ischemic hypothermia has been demonstrated to be protective against ischemic neuronal injury. The present study examined the effect of moderate hypothermia on the expression of heat shock protein (HSP)-72 following transient forebrain ischemia in gerbils by immunohistochemistry. Global forebrain ischemia with concurrent moderate hypothermia (30 degrees C) was induced in gerbils by 10-minute bilateral carotid artery occlusion followed by recirculation periods of 1 hour (h), 6h, 24h, and 48h. Normothermic forebrain ischemic animals with similar recirculation periods were utilized for comparison of the HSP expression. Sham-operated normothermic and hypothermic animals were also included. 72-kDa heat shock protein immunoreactivity was demonstrated in the hippocampus and neocortex of the normothermic ischemic animals following 24h and 48h recirculation similar to that reported previously. However, the immunoreactivity was absent in the brains of the animals subjected to hypothermic ischemia or sham-operation. Only the ependymal cells were immunopositive in all hypothermic brains as was the case with all normothermic brains. The hypothermic ischemic brains showed no significant necrosis in the hippocampus. These findings suggest that the protection of ischemic neuronal necrosis conferred by intra-ischemic hypothermia is not associated with induction of HSP-72 protein and that mechanisms other then HSP-72 protein induction are likely to be responsible for this neuroprotective effect.

A serotonin synthesis inhibitor, p-chlorophenylalanine reduces the heat shock protein response following trauma to the spinal cord: an immunohistochemical and ultrastructural study in the rat

The influence of the serotonin synthesis inhibitor, p-CPA on the expression of the heat shock protein (70 kDa), which occurs around an injury to the rat spinal cord, was examined by immunohistochemistry. A longitudinal incision was made into the right dorsal horn at the T10-11 level. Five hours later samples were removed from the T9 and T12 segments. Samples from untreated traumatised animals showed signs of edema and many distorted neurons, particularly in the ipsilateral grey matter. Neurons of the same regions showed a profound increase in HSP-70 immunostaining compared with intact controls. At ultrastructural level, the immunoreactivity was detected in neuronal cytoplasm attached to the surface of organelles including endoplasmic reticulum, in the nucleus and in dendrites. Other groups of rats were given p-CPA before injury to reduce the synthesis of serotonin and to minimise its stores in the cord. The HSP-immunostaining in neurons of the T9 and T12 segments of the spinal cord was virtually lacking in the drug treated animals. The signs of edema and the structural changes of these segments were markedly reduced. The results show that inhibition of serotonin synthesis prior to the traumatic insult has an inhibitory influence on HSP response occurring in neurons around the site of injury to the spinal cord, not reported earlier.

Comparison of alpha-tubulin mRNA and heat shock protein-70 mRNA in gerbil brain following 10 min of ischemia

In situ hybridization and Northern blot analysis were used to characterize the mRNA expression of alpha-tubulin, a neuroprotein crucial for neuronal structural and functional restoration, in comparison to that of the stress inducible heat shock protein-70 (HSP-70), in the same gerbil brain following 10 min of forebrain ischemia. The HSP-70 expression was noted in the dentate granule layer 1 h postischemia (PI) and became prominent in all pyramidal cell fields of the hippocampus in addition to the dentate layer at 6 h PI. The induction of HSP-70 persisted in CA1 and CA2 regions and partly in dentate gyrus for up to the 1 day PI period examined. There was no significant HSP-70 expression in any of the regions of the nonischemic or 15 min PI brain. alpha-Tubulin, on the other hand, was expressed in all pyramidal fields of the hippocampus as well as dentate gyrus in nonischemic controls. A decline was noted in the CA1 region 1 h PI onward and was maximal at 6 h PI. Its expression, however, increased at 24 h PI (significant only in comparison to 15 min and 6 h PI but not to control) when it became rather strong in the dentate gyrus. Thus, the temporal pattern of expression of alpha-tubulin sharply contrasted with that of HSP-70 in the PI brain as it declined in the vulnerable CA1 region during the 1st 24 h PI, i.e., the period when HSP-70 was induced and its expression was lowest in the 6 h group when HSP-70 peaked. It was maximum in the dentate gyrus at 24 h PI when HSP-70 was marginally detectable in that region. These studies indicate that in early recirculation period following prolonged ischemia, HSP-70 mRNA is expressed in both vulnerable regions as well as in regions of the brain that are destined to survive while alpha-tubulin is diminished in vulnerable regions. These data suggest a positive correlation between the loss of alpha-tubulin mRNA and delayed neuronal necrosis that follows in the vulnerable CA1 region.