Heat-Shock 70 Messenger RNA Levels in Human Brain: Correlation with Agonal Fever

Abstract: Systematic review of antemortem clinical information on randomly selected Alzheimer disease (AD) patients revealed that ∼40% of the patients had a recorded fever of ≥39.2°C at or near death. Using isolation and quantitation techniques appropriate for analysis of human brain mRNAs, we found that low levels of inducible heat-shock protein 70 (hsp70) mRNAs were present in cerebellum of afebrile AD patients and that mRNA levels were usually lower in two brain regions affected in AD, i.e., hippocampus and temporal cortex. Levels of hsp70 mRNAs were increased three- to 33-fold in cerebellum of febrile patients compared with levels in patients whose recorded temperatures were ≤37.5°C. Levels of hsp70 mRNAs were also increased in hippocampus and cortex of these febrile patients, but to a lesser extent than cerebellum. Heat-shock cognate 70 (hsc70) mRNAs were present at highest levels in afebrile cerebellum and were also present in the other brain regions. In cerebellum of patients with the highest temperatures, hsc70 mRNAs were induced severalfold over basal levels. Although there was a low and variable induction of hsc70 mRNAs in temporal cortex of these patients, there was no evidence for any induction in hippocampus. Increased heat-shock 70 mRNA levels did not correlate with hypoxia, coma, hypertension, hypoglycemia, seizures, or medication. These results indicate that a specific agonal stress, namely fever, can increase the levels of heat shock 70 mRNAs in AD brain; however, there is no evidence to suggest that affected regions of AD brain have higher overall levels of these mRNAs. Failure to obtain adequate agonal state information could result in inaccurately identifying short-term stress-related changes in postmortem brain as neuropathology characteristic of a chronic disease state.     

hsp47 and hsp70 gene expression is differentially regulated in a stress- and tissue-specific manner in zebrafish embryos

We have examined differences in the spatial and temporal regulation of stress-induced hsp47 and hsp70 gene expression following exposure of zebrafish embryos to heat shock or ethanol. Using Northern blot analysis, we found that levels of hsp47 and hsp70 mRNA were dramatically elevated during heat shock in 2-day-old embryos. In contrast, ethanol exposure resulted in strong upregulation of the hsp47 gene whereas hsp70 mRNA levels increased only slightly following the same treatment. Whole-mount in situ hybridization analysis revealed that hsp47 mRNA was expressed predominantly in precartilagenous cells, as well as several other connective tissue cell populations within the embryo following exposure to either stress. hsp70 mRNA displayed a very different cell-specific distribution. For example, neither stress induced hsp70 mRNA accumulation in precartilagenous cells. However, high levels of hsp70 mRNA were detectable in epithelial cells of the developing epidermis following exposure to heat shock, but not to ethanol. These cells did not express the hsp47 gene following exposure to either of these stresses. The results suggest the presence of different inducible regulatory mechanisms for these genes which operate in a cell- and stress-specific manner in zebrafish embryos. Dev. Genet. 21:123–133, 1997. © 1997 Wiley-Liss, Inc.     

Induction of a heat shock gene (hsp 70) in rabbit retinal ganglion cells detected by in situ hybridization with plastic-embedded tissue

Elevation of body temperature by 2–3°C induces a 2.7 kilobase hsp70 mRNA species in the rabbit retina within 1 hr. In situ hybridization with thin sections derived from plastic-embedded tissue permitted a higher level of resolution of retinal cell types compared to procedures which involved the use of frozen tissue sections. A prominent induction of hsp70 mRNA in retinal ganglion cells was observed when an hsp70 riboprobe was utilized for in situ hybridization. These results indicate that this neuronal cell type responds rapidly to fever-like body temperatures by inducing one of the major heat shock genes.     

Involvement of differential gene expression and mRNA stability in the developmental regulation of the hsp 30 gene family in heat-shocked Xenopus laevis embryos

Four complete hsp 30 genes have been isolated from Xenopus laevis: hsp 30A, hsp 30B (a pseudogene), hsp 30C, and hsp 30D. The hsp 30A and hsp 30C genes are first heat inducible at the early tailbud stage, as determined by RNase protection and RT-PCR assays. In this study, we determined by RT-PCR that the hsp 30D gene was first heat inducible (33^oC for 1 h) at the mid-tailbud stage, approximately 1 day later in development than hsp 30A and hsp 30C. Furthermore, using Northern blot analysis, we detected the presence of very low levels of hsp 30 mRNA at the heat-shocked late blastula stage. The relative levels of these pre-tailbud (PTB) hsp 30 mRNAs increased at the gastrula and neurula stage followed by a dramatic enhancement in heat shocked tail-bud and tadpole stage embryos (50- to 100- fold relative to late blastula). Interestingly, treatment of blastula or gastrula embryos at high temperatures (37^oC for 1 h) or with the protein synthesis inhibitor, cycloheximide, followed by heat shock, led to enhanced accumulation of the pre-tailbud (PTB) hsp 30 mRNAs. hsp 70, hsp 87, and actin messages were not stabilized at high temperatures or by cycloheximide treatment. Finally, hsp 30D mRNA was not detected by RT-PCR analysis of cycloheximidetreated, heat-shocked blastula stage embryos, confirming that it is not a member of the PTB hsp 30 mRNAs. This study indicates that differential gene expression and mRNA stability are involved in the regulation of hsp 30 gene expression during early Xenopus laevis development. © 1995 Wiley-Liss, Inc.     

Cryptic Expression of the 70-kDa Heat Shock Protein,hsp72, in Gerbil Hippocampus after Transient Ischemia

The 70 kDa heat shock protein, hsp72, is known to be induced following transient global ischemia in brain, as detected by immunocytochemistry and in situ hybridization techniques. However, while hsp72 mRNA is expressed rapidly following postischemic recirculation, immunocytochemistry fails to detect hsp72 protein for many hours after such insults, even in cell populations that readily express Fos and other proteins encoded by ischemia-induced mRNAs. In the present study, hsp72 expression in gerbil hippocampus was compared by immunocytochemistry and immunoblot methods at several intervals following 10 min ischemia. As established in previous studies, hsp72 immunoreactivity remained undetectable in postischemic neurons at 6 h following such insults. In contrast, immunoblots of dissected gerbil hippocampus demonstrated nearly maximal accumulation of hsp72 at this time point. These results indicate that the protein is present, but cryptic to detection in perfusion-fixed sections, during early recirculation. The constitutively expressed heat shock cognate protein, hsc70, did not show significant changes in level or distribution by either method, except for a decrease in CA1 staining at 48 h. These results confirm that hsp72 rapidly accumulates to high levels in postischemic hippocampus, and suggest that further studies of its subcellular localization during this interval may offer insight into its functional role as a component of the stress response in neurons after such insults.     

The effects of heat shock and acclimation temperature on hsp70 and hsp30 mRNA expression in rainbow trout: in vivo and in vitro comparisons

Heat shock (25° C) of 10° C-acclimated rainbow trout Oncorhynchus mykiss led to increases in heat shock protein 70 (hsp70) mRNA in blood, brain, heart, liver, red and white muscle, with levels in blood being amongst the highest. Hsp30 mRNA also increased with heat shock in all tissues with the exception of blood. When rainbow trout blood was heat shocked in vitro , both hsp70 and hsp30 mRNA increased significantly. In addition, these in vitro experiments demonstrated that blood from fish acclimated to 17° C water had a lower hsp70 mRNA heat shock induction temperature than did 5° C acclimated fish (20 v. 25° C). The hsp30 mRNA induction temperature (25° C), however, was unaffected by thermal acclimation. While increases in hsp70 mRNA levels in blood may serve as an early indicator of temperature stress in fish, tissue type, thermal history and the particular family of hsp must be considered when evaluating stress by these molecular means.     

Time course of induction of a heat shock gene (hsp70) in the rabbit cerebellum after LSD in vivo: Involvement of drug-induced hyperthermia

In situ hybridization studies were carried out to determine whether induction of hsp70 mRNA in various cellular layers of the rabbit cerebellum was due to hyperthermic effects of the psychotropic drug LSD. Results indicated that induction was not present when LSD-induced hyperthermia was blocked. The pattern of induction of hsp70 mRNA in various cell types of the cerebellum was similar when hyperthermia was induced by either drug (LSD) or nondrug means (placement of animals in a warm incubator). A time course analysis of the induction of hsp70 mRNA following LSD-induced hyperthermia revealed maximal levels of mRNA at 1 hr in all cerebellar cell layers except the Purkinje layer where highest levels were attained at 5 hr. By 10 hr hsp70 mRNA had returned to constitutive levels in all cellular layers of the cerebellum.     

Cellular localization of heat shock gene expression in rabbit cerebellum by in situ hybridization with plastic-embedded tissue

The major cell types in rabbit cerebellum which engage in the expression of a heat shock gene (hsp 70) after hyperthermia were identified. This required in situ hybridization on thin sections derived from plastic-embedded tissue. All classes of cerebellar neurons which were examined (Purkinje, granule, and stellate cells) responded by induction of hsp 70 mRNA within 1 hr after hyperthermia. Prominent induction of hsp 70 mRNA was also observed in oligodendroglia in the deep white matter.     

Cell Size and the Heat-Shock Response in Rat Brain

Abstract: The expression of mRNAs encoding two members of the heat-shock protein 70 family, the constitutively-expressed heat-shock cognate (hsc70) mRNA and the strictly heat-inducible (hsp70) mRNA, was quantitated in cerebellar and hippocampal cells of rats 3 h after amphetamine-induced or heat-induced hyperthermia. Intracellular heat-shock mRNA levels in specific cell types were compared with those of total polyadenylic acid [poly(A)] mRNA or 18S rRNA in the same cell type. Levels of poly(A) mRNAs, 18S rRNAs, and hsc70 mRNAs were highest in large neurons and lowest in glia. hsp70 mRNAs were also present at highest levels in large neurons, suggesting that hsp70 mRNAs accumulated as rapidly in these cell types as they did in small neurons and glia. However, compared with levels of intracellular poly(A) mRNAs or levels of rRNAs, large neurons contained two- to 12-fold lower levels of hsp70 mRNAs than neurons of intermediate size and five- to 30-fold lower levels than glia. These results suggest that hsp70 mRNAs accumulated as rapidly in large neurons as in small neurons and glia, but that the large size of these neurons precluded intracellular hsp70 mRNA concentrations increasing as quickly. The susceptibility of large neurons to stress-induced cell death could be due, in part, to their inability to synthesize rapidly hsp70 in sufficient amounts to protect these cells from the initial molecular consequences of stress.     

Stress-induced, tissue-specific enrichment of hsp70 mRNA accumulation in Xenopus laevis embryos

In this study, we have employed whole-mount, in situ hybridization to study the spatial pattern of hsc70 and hsp70 mRNA accumulation in normal and heat shocked embryos during Xenopus laevis development. Our findings revealed that hsc70 mRNA was constitutively present in a global fashion throughout the embryo and was not heat inducible. Accumulation of hsp70 mRNA, however, was detected only in heat shocked embryos. Furthermore, hsp70 mRNA accumulation was enriched in a tissue-specific manner in X. laevis tailbud embryos within 15 minutes of a 33 degrees C heat shock. Abundant levels of heat shock-induced hsp70 mRNA were detected in the head region, including the lens placode, the cement gland, and in the somitic region and proctodeum. Preferential heat-induced accumulation of hsp70 mRNA was first detected at a heat shock temperature of 30 degrees C. Placement of embryos at 22 degrees C after a 1-hour, 33 degrees C heat shock resulted in decreased hsp70 mRNA with time, but the message persisted in selected tissues, including the lens placode and somites. Treatment of tailbud embryos with either sodium arsenite or zinc chloride induced a tissue-specific enrichment of hsp70 mRNA in the lens placode and somitic region. These studies reveal the complex nature of the heat shock response in different embryonic tissues and suggest the presence of regulatory mechanisms that lead to a stressor-induced, tissue-specific enrichment of hsp70 mRNA.     

Extreme thermotolerance and behavioral induction of 70-kDa heat shock proteins and their encoding genes in honey bees

Foraging honey bees frequently leave the hive to gather pollen and nectar for the colony. This period of their lives is marked by periodic extremes of body temperature, metabolic expenditure, and flight muscle activity. Following ecologically relevant episodes of hyperthermia between 33°C and 50°C, heat shock protein 70 (Hsp70) expression and hsp70/hsc70-4 activity in brains of nonflying laboratory-held bees increased by only two to three times baseline at temperatures 46–50°C. Induction was undetectable in thoracic–flight muscles. Yet, thorax hsp70 mRNA (but not hsc70-4 mRNA) levels were up to ten times higher in flight-capable hive bees and foraging bees compared to 1-day-old, flight-incapable bees, while brain hsp70/hsc70-4 mRNA levels were low and varied little among behavioral groups. These data suggest honey bee tissues, especially flight muscles, are extremely thermotolerant. Furthermore, Hsp70 expression in the thoraces of flight-capable bees is probably flight-induced by oxidative and mechanical damage to flight muscle proteins rather than temperature.     

Heat Shock RNA Levels in Brain and Other Tissues After Hyperthermia and Transient Ischemia

A number of studies have demonstrated increased synthesis of heat shock proteins in brain following hyperthermia or transient ischemia. In the present experiments we have characterized the time course of heat shock RNA induction in gerbil brain after ischemia, and in several mouse tissues after hyperthermia, using probes for RNAs of the 70-kilodalton heat shock protein (hsp70) family, as well as ubiquitin. A synthetic oligonucleotide selective for inducible hsp70 sequences proved to be the most sensitive indicator of the stress response whereas a related rat cDNA detected both induced RNAs and constitutively expressed sequences that were not strongly inducible in brain. Considerable polymorphism of ubiquitin sequences was evident in the outbred mouse and gerbil strains used in these studies when probed with a chicken ubiquitin cDNA. Brief hyperthermic exposure resulted in striking induction of hsp70 and several-fold increases in ubiquitin RNAs in mouse liver and kidney peaking 3 h after return to room temperature. The oligonucleotide selective for hsp70 showed equivalent induction in brain that was more rapid and transient than observed in liver, whereas minimal induction was seen with the ubiquitin and hsp70-related cDNA probes. Transient ischemia resulted in 5- to 10-fold increases in hsp70 sequences in gerbil brain which peaked at 6 h recirculation and remained above control levels at 24 h, whereas a modest 70% increase in ubiquitin sequences was noted at 6 h. These results demonstrate significant temporal and quantitative differences in heat shock RNA expression between brain and other tissues following hyperthermia in vivo, and indicate that hsp70 provides a more sensitive index of the stress response in brain than does ubiquitin after both hyperthermia and ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)