Response of mice to continuous 5-day passive hyperthermia resembles human heat acclimation

Adjustments in energy metabolism of brown adipose tissue in heat-acclimated Kunming mice

The thermogenic capacity of brown adipose tissue (BAT) in rodents decreases with prolonged heat exposure. However, the underlying mechanisms are not well understood. In this study, Kunming mice were acclimated at 23 ± 1 °C and 33 ± 1 °C for four weeks each to examine the body heat balance and BAT alterations. Results showed that heat-acclimated Kunming mice exhibited reduced body mass and elevated body temperature. Additionally, they displayed lower resting metabolic rates, diminished non-shivering thermogenesis, and reduced BAT thermogenic function. Metabolically, there was a significant reduction in several key metabolites involved in energy metabolism in BAT, including thiamine pyrophosphate, citric acid, cis-Aconitate, isocitric acid, oxoglutaric acid, succinate, fumarate, L-Malic acid, oxaloacetate, flavin mononucleotide, nicotinamide adenine dinucleotide, and adenosine 5'-triphosphate. These findings suggest that BAT adapts to heat acclimation by regulating pathways related to pyruvate oxidation, tricarboxylic acid cycle, and oxidative phosphorylation, which may help maintain thermal homeostasis in Kunming mice.

A Review of the Effects of Some Extrinsic Factors on Mice Used in Research

Animals have been used in research for over 2,000 y. From very crude experiments conducted by ancient scholars, animal research, as a science, was refined over hundreds of years to what we know it as today. However, the housing conditions of animals used for research did not improve significantly until less than 100 years ago when guidelines for housing research animals were first published. In addition, it was not until relatively recently that some extrinsic factors were recognized as a research variable, even when animals were housed under recommended guidelines. For example, temperature, humidity, light, noise, vibration, diet, water, caging, bedding, etc., can all potentially affect research using mice, contributing the inability of others to reproduce published findings. Consequently, these external factors should be carefully considered in the design, planning, and execution of animal experiments. In addition, as recommended by others, the housing and husbandry conditions of the animals should be described in detail in publications resulting from animal research to improve study reproducibility. Here, we briefly review some common, and less common, external factors that affect research in one of the most popular animal models, the mouse.

Rodents Inhabiting the Southeastern Mu Us Desert May Not Have Experienced Prolonged Heat Stress in Summer 2022

Climate change combined with human activities has altered the spatial and temporal patterns of summer extreme heat in the Mu Us Desert. To determine how those rodents living in the desert respond to increased extreme heat in summer, in July 2022, during the hottest month, we examined the rodent species, vegetation coverage, and small-scale heterogeneity in ambient temperature in the southeastern Mu Us Desert. The results showed that Meriones meridianus, Meriones unguiculatus, and Cricetulus longicaudatus were found in the study area, where the vegetation coverage is 33.5-40.8%. Moreover, the maximum temperature of the desert surface was 61.8 °C. The maximum air temperature at 5 cm above the desert surface was 41.3 °C. The maximum temperature in the burrow at a depth of 15 cm was 31 °C. M. unguiculatus might experience 4-9.3 h of heat stress in a day when exposed outside the burrow, whereas M. meridianus would experience 8.5-10.8 h of heat stress. Yet, inside the burrow, both species were barely exposed to heat stress. In conclusion, adjustments in behavioral patterns can be the main way that rodents in the Mu Us Desert adapt to the extreme heat in the summer.

Acquired heat acclimation in rats subjected to physical exercise under environmental heat stress alleviates brain injury caused by exertional heat stroke

BACKGROUND

Exertional heatstroke (EHS) is an emergency with a high mortality rate, characterized by central nervous system dysfunctions. This study aims to establish a Heat acclimation/acclimatization (HA) rat model in locomotion to recapitulate the physical state of human in severe environment of high temperature and humidity, and investigate the mechanism of organism protection in HA. (2) Methods: Wistar rats were exposed to 36°C and ran 2 h/d for 21 days, acquired thermal tolerance test was conducted to assess the thermotolerance and exercise ability. Core temperature and consumption of water and food were observed. Expression of HSP70 and HSP90 of different tissues were determined by WB. Pathological structure of brain tissue was detected with HE staining. Proteomics was used to identify the differently expressed proteins in cerebral cortex of different groups. And key molecules were identified by RT-PCR and WB. (3) Results: HA rats displayed stronger thermotolerance and exercised ability on acquired thermal tolerance test. Brain water content of HA+EHS group reduced compared with EHS group. HE staining revealed slighter brain injuries of HA+EHS group than that of EHS. Proteomics focused on cell death-related pathways and key molecules Aquaporin 4 (AQP4) related to cell edema. Identification results showed HA increased AQP4, Bcl-xl, ratio of p-Akt/AKT and Bcl-xl/Bax, down-regulated Cleaved Caspase-3. (4) Conclusions: This HA model can ameliorate brain injury of EHS by reducing cerebral edema and cell apoptosis, offering experimental evidence for EHS prophylaxis.

Thermoregulatory trade-offs underlie the effects of warming summer temperatures on deer mice

Climate warming could challenge the ability of endotherms to thermoregulate and maintain normal body temperature (Tb), but the effects of warming summer temperatures on activity and thermoregulatory physiology in many small mammals remain poorly understood. We examined this issue in deer mice (Peromyscus maniculatus), an active nocturnal species. Mice were exposed in the lab to simulated seasonal warming, in which an environmentally realistic diel cycle of ambient temperature (Ta) was gradually warmed from spring conditions to summer conditions (controls were maintained in spring conditions). Activity (voluntary wheel running) and Tb (implanted bio-loggers) were measured throughout, and indices of thermoregulatory physiology (thermoneutral zone, thermogenic capacity) were assessed after exposure. In control mice, activity was almost entirely restricted to the night-time, and Tb fluctuated ∼1.7°C between daytime lows and night-time highs. Activity, body mass and food consumption were reduced and water consumption was increased in later stages of summer warming. This was accompanied by strong Tb dysregulation that culminated in a complete reversal of the diel pattern of Tb variation, with Tb reaching extreme highs (∼40°C) during daytime heat but extreme lows (∼34°C) at cooler night-time temperatures. Summer warming was also associated with reduced ability to generate body heat, as reflected by decreased thermogenic capacity and decreased mass and uncoupling protein (UCP1) content of brown adipose tissue. Our findings suggest that thermoregulatory trade-offs associated with daytime heat exposure can affect Tb and activity at cooler night-time temperatures, impacting the ability of nocturnal mammals to perform behaviours important for fitness in the wild.

Effect of Different Ambient Temperatures on Reproductive Outcome and Stress Level of Lactating Females in Two Mouse Strains

Simple Summary

The optimal temperature for laboratory mice has been under discussion for some time. Current standard temperature is 20 °C–24 °C but it has been suggested to elevate the standard to 30 °C, which is the thermoneutral zone for mice. In this study, the effect of different cage temperatures (20 °C, 25 °C, 30 °C) on reproduction and stress hormone metabolite excretion was evaluated in lactating females of two commonly used mouse strains. Pup loss was higher, and weights of mothers and pups were reduced at 30 °C compared to the lower temperatures. In addition, pups showed increased tail length at weaning under the high temperature (30 °C). There was no difference in stress hormone metabolite excretion in mice between temperature groups. We could not show any detrimental effects of the lower or higher cage temperature on stress hormone metabolite excretion, but found decreased reproductive outcome under the higher temperature.

Abstract

Ambient temperature is an important non-biotic environmental factor influencing immunological and oncological parameters in laboratory mice. It is under discussion which temperature is more appropriate and whether the commonly used room temperature in rodent facilities of about 21 °C represents a chronic cold stress or the 30 °C of the thermoneutral zone constitutes heat stress for the animals. In this study, we selected the physiological challenging period of lactation to investigate the influence of a cage temperature of 20 °C, 25 °C, and 30 °C, respectively, on reproductive performance and stress hormone levels in two frequently used mouse strains. We found that B6D2F1 hybrid mothers weaned more pups compared to C57BL/6N mothers, and that the number of weaned pups was reduced when mothers of both strains were kept at 30 °C. Furthermore, at 30 °C, mothers and pups showed reduced body weight at weaning and offspring had longer tails. Despite pronounced temperature effects on reproductive parameters, we did not find any temperature effects on adrenocortical activity in breeding and control mice. Independent of the ambient temperature, however, we found that females raising pups showed elevated levels of faecal corticosterone metabolites (FCMs) compared to controls. Peak levels of stress hormone metabolites were measured around birth and during the third week of lactation. Our results provide no evidence of an advantage for keeping lactating mice in ambient temperatures near the thermoneutral zone. In contrast, we found that a 30 °C cage temperature during lactation reduced body mass in females and their offspring and declined female reproductive performance.

Heat acclimation ameliorated heat stress-induced acute kidney injury and prevented changes in kidney macrophages and fibrosis

Heatstroke can cause acute kidney injury (AKI), which reportedly progresses to chronic kidney disease. Kidney macrophages may be involved in such injury. Although heat acclimation (HA) provides thermal resilience, its renoprotective effect and mechanism remain unclear. To investigate heat stress-induced kidney injuries in mice and the mitigating effect of HA on them, male C57/BL6J mice were exposed to heat stress (40℃, 1 h), with or without 5-day HA (38℃, 3 h/day) prior to heat stress. Heat stress damaged kidney proximal tubules with elevation of urinary kidney injury molecule-1 (KIM-1). Kidney fibrosis was observed on day 7 and correlated with the urinary KIM-1 levels on day 3. Kidney resident macrophages decreased on day 1, whereas the number of infiltrating macrophages in the kidney did not change. Both subsets of macrophages polarized to the pro-inflammatory M1 phenotype on day 1; however, they polarized to the anti-inflammatory M2 phenotype on day 7. HA significantly ameliorated heat stress-induced proximal tubular damage and kidney fibrosis. HA substantially increased heat shock protein 70 (Hsp70) expression in the tubules before heat stress and reduced an elevation of cleaved caspase-3 expression after heat stress. HA also induced the Hsp70 expression of resident macrophages and prevented heat stress-induced changes in both subsets of kidney macrophages. These results provide pathophysiological data supporting the renoprotective effect of HA. Further studies are needed to confirm that HA can prevent kidney damage due to heat stress in humans.

Genetically Encoded Protein Thermometer Enables Precise Electrothermal Control of Transgene Expression

Body temperature is maintained at around 37 °C in humans, but may rise to 40 °C or more during high-grade fever, which occurs in most adults who are seriously ill. However, endogenous temperature sensors, such as ion channels and heat-shock promoters, are fully activated only at noxious temperatures above this range, making them unsuitable for medical applications. Here, a genetically encoded protein thermometer (human enhanced gene activation thermometer; HEAT) is designed that can trigger transgene expression in the range of 37-40 °C by linking a mutant coiled-coil temperature-responsive protein sensor to a synthetic transcription factor. To validate the construct, a HEAT-transgenic monoclonal human cell line, FeverSense, is generated and it is confirmed that it works as a fever sensor that can temperature- and exposure-time-dependently trigger reporter gene expression in vitro and in vivo. For translational proof of concept, microencapsulated designer cells stably expressing a HEAT-controlled insulin production cassette in a mouse model of type-1 diabetes are subcutaneously implanted and topical heating patches are used to apply heat corresponding to a warm sensation in humans. Insulin release is induced, restoring normoglycemia. Thus, HEAT appears to be suitable for practical electrothermal control of cell-based therapy, and may also have potential for next-generation treatment of fever-associated medical conditions.

Housing of A350V IQSEC2 pups at 37 °C ambient temperature prevents seizures and permits the development of social vocalizations in adulthood

OBJECTIVES

Mutations in the human IQSEC2 gene are associated with drug-resistant epilepsy and severe behavioral dysfunction. We have focused on understanding one human IQSEC2 missense mutation (A350V) for which we have created a corresponding A350V IQSEC2 mouse model by CRISPR which demonstrates seizures when the mice are 15-20 days old and impaired social vocalizations in adulthood. We observed that a child with the A350V mutation stops having seizures when experiencing a fever of greater than 38 °C. In this study, we first sought to determine if we could recapitulate this phenomenon in A350V 15-20 day old mice using a previously established protocol to raise body temperature to 39 °C achieved by housing the mice at 37 °C. We then sought to determine if mice in whom seizure activity had been prevented as pups would develop social vocalization activity in adulthood.

METHODS

15-20 day old A350V male mice were housed either at 37 °C or 22 °C. Ultrasonic vocalizations of these mice were assessed at 8-10 weeks in response to a female stimulus.

RESULTS

Housing of 15-20 day old A350V mice at 37 °C resulted in a reduction in lethal seizures to 2% (1/41) compared to 45% (48/108) in mice housed at 22 °C, p = 0.0001. Adult A350V mice who had been housed at 37 °C as pups displayed a significant improvement in the production of social vocalizations.

CONCLUSION

Raising the body temperature by raising the ambient temperature might provide a means to reduce seizures associated with the A350V IQSEC2 mutation and thereby allow for an improved neurodevelopmental trajectory.

Role of transient receptor potential vanilloid-1 in behavioral thermoregulation of the Mongolian gerbil Meriones unguiculatus

Ambient temperature considerably affects the physiology and behavior of mammals. Thermosensory and thermoregulatory abilities play an important role in the response to changing ambient temperature in endotherms. However, the molecular mechanisms of behavioral thermoregulation remain poorly understood. Transient receptor potential vanilloid-1 (TRPV1) is activated by changes in ambient temperature and is involved in acute thermoregulation. Here, we aimed to determine whether TRPV1 is involved in behavioral thermoregulation in wild rodents by conducting 2 experiments. In the first, 42 adult Mongolian gerbils (Meriones unguiculatus; 14 per treatment) were randomly assigned to 3 housing temperatures (4, 23, and 36°C) for 4 weeks. In the second, 20 gerbils (10 per treatment) were randomly injected with capsaicin (TRPV1 agonist) or AMG517 (TRPV1 antagonist). The results showed a significant decrease in food intake and non-shivering thermogenesis in the gerbils housed at 36°C. Additionally, there was a significant increase in the preference of gerbils housed at 4°C to low temperatures. The expression of TRPV1 protein in the brown adipose tissue (BAT) and liver was significantly positively correlated with that of protein kinase A (PKA). The expression of TRPV1 and PKA proteins in the BAT was positively correlated with the temperature preference of the gerbils. The gerbils injected with capsaicin preferred significantly lower temperatures than the control group gerbils. These findings suggest that TRPV1 and PKA are involved in behavioral thermoregulation in Mongolian gerbils.

Ursolic acid alleviates heat stress-induced lung injury by regulating endoplasmic reticulum stress signaling in mice

Acute lung injury has been reported to be associated with heat stress in various animals. Ursolic acid is a natural pentacyclic triterpenoid compound with multiple bioactivities. However, it remains unknown whether ursolic acid supplementation alleviates heat stress-induced lung injury. In the present study, male Institute of Cancer Research mice were left untreated under a normal temperature condition (23±1°C), receiving orally administrated with vehicle (phosphate buffered saline) or ursolic acid (40 mg/kg BW-1·d-1 for 2 d), and then were subjected to high temperature (41±1°C) for 2 h. Histological alterations, activities of antioxidative enzymes, apoptosis, generation of reactive oxygen species, abundance of inflammatory cytokines, and endoplasmic reticulum stress-related proteins were analyzed. Compared with the controls, heat stress treatment led to enhanced apoptosis, increased H2O2 production, and upregulated protein levels of inflammatory cytokines in the serum, including tumor necrosis factor alpha, interleukin-6, and interleukin-1 beta. Activities of malondialdehyde, lactate dehydrogenase, and myeloperoxidase were increased, while the activities for superoxide dismutase and catalase were reduced in lung tissues of mice. All these alterations were significantly prevented by ursolic acid administration. Further study showed that heat stress led to activation of protein kinase-like ER kinase eukaryotic initiation factor 2 alpha -the transcription factor CCAAT-enhancer-binding protein homologous protein (CHOP) signaling, which was attenuated by ursolic acid supplementation. These findings indicated that ursolic acid pretreatment protected lung tissues against heat stress-induced injury by regulating inflammatory cytokines and unfolded protein response in mice. Ursolic acid supplementation might be a therapeutic strategy to alleviate high temperature-induced lung injury in humans and animals.

Alterations in the gut microbiome and metabolic profile in rats acclimated to high environmental temperature

Heat acclimation (HA) is the best strategy to improve heat stress tolerance by inducing positive physiological adaptations. Evidence indicates that the gut microbiome plays a fundamental role in the development of HA, and modulation of gut microbiota can improve tolerance to heat exposure and decrease the risks of heat illness. In this study, for the first time, we applied 16S rRNA gene sequencing and untargeted liquid chromatography–mass spectrometry (LC‐MS) metabolomics to explore variations in the gut microbiome and faecal metabolic profiles in rats after HA. The gut microbiota of HA subjects exhibited higher diversity and richer microbes. HA altered the gut microbiota composition with significant increases in the genera Lactobacillus (a major probiotic) and Oscillospira alongside significant decreases in the genera Blautia and Allobaculum. The faecal metabolome was also significantly changed after HA, and among the 13 perturbed metabolites, (S)‐AL 8810 and celastrol were increased. Moreover, the two increased genera were positively correlated with the two upregulated metabolites and negatively correlated with the other 11 downregulated metabolites, while the correlations between the two decreased genera and the upregulated/downregulated metabolites were completely contrary. In summary, both the structure of the gut microbiome community and the faecal metabolome were improved after 28 days of HA. These findings provide novel insights regarding the improvement of the gut microbiome and its functions as a potential mechanism by which HA confers protection against heat stress.

Impact of single or repeated short-term heat challenges mimicking summer heat waves on thermoregulatory responses and performances in finishing pigs

The objectives of this study were to determine the effects of single or repeated short heat stress (HS) challenges that mimicked summer heat waves on performance and thermoregulatory responses in finishing pigs. A total of 45 crossbred castrated males were tested in three consecutive replicates of 15 pigs. Within each replicate, pigs were assigned to one of five treatments. Pigs in treatment group TTT were maintained in thermoneutral conditions (22 °C) for the entire experiment (45 d). Pigs in treatment group HHH were subjected to an HS challenge (32 °C for 5 d) at 113, 127, and 141 d of age (in experimental periods P1, P2, and P3, respectively). Pigs in treatment groups HTT, THT, and TTH were subjected to the HS challenge at 113, 127, or 141 d of age, respectively. Each 5-d challenge was preceded by a 3-d prechallenge period and followed by a 7-d recovery period. Pigs were housed in individual pens and fed ad libitum. HS significantly reduced average daily feed intake (ADFI) and the average daily gain (ADG). Expressed as a percentage of the performance observed during the prechallenge period, ADFI decreased by 12%, 22%, and 26% and ADG decreased by 12%, 43%, and 72% in the HTT, THT, and TTH groups, respectively. Regardless of the experimental group, no compensatory performance was observed during the recovery period, suggesting that HS has a long-lasting effect on animal performance. Pigs subjected to HS had an immediate increase in core body temperature (T_core), skin temperature, and respiratory rate, all of which gradually decreased during the HS challenge. Based on T_core measurements, hypothermia was observed during the recovery period in each of the three experimental periods, especially for pigs in the HHH and the HTT groups but only during the first HS cycle. Repeated exposure to HS for the HHH group resulted in heat acclimation responses characterized by a lower increase in T_core and lower decrease in ADFI during P2 and P3 than during P1.

Aquaporins, evaporative water loss and thermoregulation in heat-acclimated Mongolian gerbils (Meriones unguiculatus)

Evaporative water loss is an essential strategy to maintain stable body temperature in heat-exposed rodents. However, the thermoregulatory role and adjustment of evaporative heat loss capacity is unclear during prolonged heat exposure. Here, we studied the role of evaporative water loss in thermoregulation in Mongolian gerbils during heat acclimation. After 3 weeks of heat acclimation, gerbils exhibited a lower body temperature than the controls, and no difference in evaporative losses of water from the lung or saliva spreading compared with the controls. Heat acclimation did not alter the expression of aquaporin-1 and aquaporin-5 in the lungs and the expression of aquaporin-5 in the salivary glands. The expression of aquaporin-2 in the kidneys was kept stable, while the expression of aquaporin-1 in the kidneys was down-regulated. In addition, resting metabolic rate and non-shivering thermogenesis of heat-acclimated gerbils were reduced to 51% and 55% of the control group, respectively. Taken together, heat-acclimated Mongolian gerbils can reduce the metabolic thermogenesis without enhancing the evaporative water loss capacity for thermoregulation.

Comparative effects of two heat acclimation protocols consisting of high-intensity interval training in the heat on aerobic performance and thermoregulatory responses in exercising rats

Acclimation resulting from low- to moderate-intensity physical exertion in the heat induces several thermoregulatory adaptations, including slower exercise-induced increases in core body temperature. However, few studies have investigated the thermoregulatory adaptations induced by high-intensity interval training (HIIT) protocols. Thus, the present study aimed to compare the adaptations in rats’ thermoregulatory parameters and aerobic performance observed after two different heat acclimation regimens consisting of HIIT protocols performed in a hot environment. Twenty-three adult male Wistar rats were initially subjected to an incremental-speed exercise at 32°C until they were fatigued and then randomly assigned to one of the following three heat acclimation strategies: passive heat exposure without any exercise (untrained controls–UN; n = 7), HIIT performed at the maximal aerobic speed (HIIT_100%; n = 8) and HIIT performed at a high but submaximal speed (HIIT_85%; n = 8). Following the two weeks of interventions, the rats were again subjected to a fatiguing incremental exercise at 32°C, while their colonic temperature (T_COL) was recorded. The workload performed by the rats and their thermoregulatory efficiency were calculated. After the intervention period, rats subjected to both HIIT protocols attained greater workloads (HIIT_100%: 313.7 ± 21.9 J vs. HIIT_85%: 318.1 ± 32.6 J vs. UN: 250.8 ± 32.4 J; p < 0.01) and presented a lower ratio between the change in T_COL and the distance travelled (HIIT_100%: 4.95 ± 0.42°C/km vs. HIIT_85%: 4.33 ± 0.59°C/km vs. UN: 6.14 ± 1.03°C/km; p < 0.001) when compared to UN rats. The latter finding indicates better thermoregulatory efficiency in trained animals. No differences were observed between rats subjected to the two HIIT regimens. In conclusion, the two HIIT protocols induce greater thermoregulatory adaptations and performance improvements than passive heat exposure. These adaptations do not differ between the two training protocols investigated in the present study.

Heat acclimation-induced intracellular HSP70 in humans: a meta-analysis

Heat acclimation (HA) in humans promotes thermoregulatory adaptations that support management of core temperature in hot environments and reduces the likelihood of heat related illness. Another adaptation to HA is thermotolerance through induction of the heat shock protein (HSP) stress system, which provides protection against thermal insult. However, whether or not HA leads to upregulation of the intracellular HSP system, namely intracellular HSP70 (HSP70), is unclear in humans. Therefore, the purposes of this meta-analysis were to determine if HA leads to HSP70 induction among humans and to evaluate how methodological differences among HA studies influence findings regarding HA-induced HSP70 accumulation. Several databases were searched to identify studies that measured HSP70 (protein and mRNA) changes in response to HA among humans. The effect of HA on HSP70 was analyzed. Differences in the effect of HA were assessed between protein and mRNA. The moderating effect of several independent variables (HA frequency, HA duration, core temperature, exercise intensity) on HSP70 was also evaluated. Data were extracted from 12 studies including 118 participants (mean age 24 years, 98% male). There was a significant effect of HA on HSP70 expression, g = 0.97 (95% CI, 0.08-1.89). The effect of HA was different between subgroups (protein vs. mRNA), g = 1.51 (95% CI, 0.71-2.31), and g = - 0.39 (95% CI, - 1.36), respectively. The frequency of HA (in days) moderated HSP70 protein expression. There was a significant effect of heat acclimation on HSP70 induction in humans. The only factor among identified studies that may moderate this response was the frequency (number of days) of heat exposure.

HSP70 plays a role in the defense of acute and chronic heat stress in Mongolian gerbils (Meriones unguiculatus)

Mongolian gerbils (Meriones unguiculatus) show a wide thermal neutral zone (TNZ, 26.5-38.9 °C). Whether heat shock proteins (HSPs) are involved in thermal tolerance for gerbils has still been unknown. We investigated the effects of acute and chronic high temperature within and above TNZ on the expressions of HSP70 and HSP90 and oxidative status in Mongolian gerbils, to test the hypothesis that the gerbils need increase the expression in HSPs to defense the acute and chronic heat stress. In experiment I, 50 Mongolian gerbils were exposed to 23 °C, 27 °C, 37 °C, 40 °C and 43.5 °C for 80 min respectively, and then sacrificed 12 h after treatment. HSP70 expression in the liver increased at 40 °C compared to that at 23 °C, but did not change after 27 °C, 37 °C or 43.5 °C exposure. There were no differences in HSP90 expression, oxidative stress parameters such as malonaldehyde (MDA) and hydrogen peroxide (H₂O₂), or antioxidant parameters such as superoxide dismutase (SOD) and total antioxidant capacity (T-AOC) in the liver. HSP70 and HSP90 expression both in the heart and brain showed no differences among groups. In experiment II, another set of 30 gerbils were acclimated to 23 °C, 27 °C and 37 °C for 21 days, respectively. During chronic acclimation, HSP70 expression increased and H₂O₂ level decreased in the liver in 37 °C group compared to other two groups. Both H₂O₂ and SOD in the brain decreased in 37 °C group, but there were no differences in HSP70, MDA or T-AOC in the brain. These data indicate that Mongolian gerbils can maintain basal levels of HSPs after acute exposure to temperatures within the wide TNZ, but rely on increased HSP70 in the liver to protect from heat damage at temperatures above TNZ and during chronic heat acclimation. The increased HSP70 expression in the liver may contribute to keeping from heat damage in desert rodents.

Brown adipose tissue plays thermoregulatory role within the thermoneutral zone in Mongolian gerbils (Meriones unguiculatus)

Brown adipose tissue (BAT) plays an important role in thermoregulation and many metabolic processes in small mammals, especially in cold adaptation. However, in warm adaptation, ambient temperature cannot directly activate BAT by sympathetic nervous system. Mongolian gerbils exhibit a wider thermoneutral zone (26.5-38.9 °C). We hypothesized that BAT atrophied near the lower critical temperature and further atrophied near the upper critical temperature. Male gerbils were acclimated to 23 °C, 27 °C or 37 °C, respectively, for 3 weeks. Results showed that regulatory non-shivering thermogenesis did not change in gerbils acclimated to 27 °C compared with 23 °C group, whereas it was reduced by 43.5% in gerbils acclimated to 37 °C. Bigger lipid droplet in BAT was observed in gerbils acclimated to 27 °C and 37 °C compared with 23 °C group, while the expression of uncoupling protein 1 and tyrosine hydroxylase was only reduced in gerbils acclimated to 37 °C. Further, thermoneutral acclimation did not change BAT thermogenesis by down-regulation of peroxisome proliferator-activated receptor gamma coactivator-1α, PR domain containing 16, peroxisome proliferator-activated receptor-α or peroxisome proliferator activated receptor-γ gene expression in BAT. In addition, body temperature was reduced in gerbils acclimated to 37 °C compared with 23 °C group, which was associated with a decreased resting metabolic rate and regulatory non-shivering thermogenesis. In conclusion, BAT does not atrophy near the lower critical temperature, whereas it atrophies near the upper critical temperature, suggesting that BAT may play thermoregulatory role within the TNZ in Mongolian gerbils.

Glucocorticoid receptor activation is associated with increased resistance to heat-induced hyperthermia and injury

AIM

Anti-inflammatory mediators likely play a key role in maintaining thermal homeostasis and providing protection against heat stress. The aim of this study was to investigate the association between activation of the glucocorticoid receptor (GR) and resistance to heat-induced hyperthermia and injury.

METHODS

Effects of heat exposure on core body temperature, muscle GR phosphorylation status and subcellular expression were examined in control mice and thermal acclimation (TA)-exposed mice. In addition, effects of TA and corticosterone on C2C12 mouse myoblast viability and subcellular GR were assessed during heat exposure.

RESULTS

Phosphorylated, nuclear and mitochondrial GR levels were significantly higher in the gastrocnemius muscles of mice with mild hyperthermia (tolerant), compared to mice with severe hyperthermia (intolerant) during a heat exposure test. Similar changes were found in mice after TA, compared to non-TA-exposed controls. Additional groups of TA and non-TA-exposed mice underwent a heat exposure test. TA mice presented a significantly lower hyperthermic response during heat exposure than non-TA-exposed control. C2C12 cells exposed to TA incubation had higher viability against heat shock and showed higher GR levels in their mitochondria and nuclei detected by Western blot analysis and fluorescence microscopy, compared to cells exposed to normal incubation. Furthermore, pre-incubation with 0.1 μM corticosterone increased C2C12 cell viability during heat exposure and mitochondrial and nuclear GR expression.

CONCLUSION

The results of these in vivo and in vitro studies suggest that GR activation is associated with increased resistance against heat-induced hyperthermia and injury.

Thermophysiological adaptations to passive mild heat acclimation

Passive mild heat acclimation (PMHA) reflects realistic temperature challenges encountered in everyday life. Active heat acclimation, combining heat exposure and exercise, influences several important thermophysiological parameters; for example, it decreases core temperature and enhances heat exchange via the skin. However, it is unclear whether PMHA elicits comparable adaptations. Therefore, this study investigated the effect of PMHA on thermophysiological parameters. Participants were exposed to slightly increased temperatures (∼33°C/22% RH) for 6 h/d over 7 consecutive days. To study physiologic responses before and after PMHA, participants underwent a temperature ramp (UP), where ambient temperature increased from a thermoneutral value (28.8 ± 0.3°C) to 37.5 ± 0.6°C. During UP, core and skin temperature, water loss, cardiovascular parameters, skin blood flow and energy expenditure were measured. Three intervals were selected to compare data before and after PMHA: baseline (minutes 30–55: 28.44 ± 0.21°C), T1 (minutes 105–115: 33.29 ± 0.4°C) and T2 (minutes 130–140: 35.68 ± 0.61°C). After 7 d of PMHA, core (T1: −0.13 ± 0.13°C, P = 0.011; T2: −0.14 ± 0.15°C, P = 0.026) and proximal skin temperature (T1: −0.22 ± 0.29°C, P = 0.029) were lower during UP, whereas distal skin temperature was higher in a thermoneutral state (baseline: +0.74 ± 0.77°C, P = 0.009) and during UP (T1: +0.49 ± 0.76°C, P = .057 (not significant), T2:+0.51 ± 0.63°C, P = .022). Moreover, water loss was reduced (−30.5 ± 33.3 ml, P = 0.012) and both systolic (−7.7 ± 7.7 mmHg, P = 0.015) and diastolic (−4.4 ± 4.8 mmHg, P = 0.001) blood pressures were lowered in a thermoneutral state. During UP, only systolic blood pressure was decreased (T2: −6.1 ± 4.4 mmHg, P = 0.003). Skin blood flow was significantly decreased at T1 (−28.35 ± 38.96%, P = 0.037), yet energy expenditure remained unchanged. In conclusion, despite the mild heat stimulus, we show that PMHA induces distinct thermophysiological adaptations leading to increased resilience to heat.

Proteomic profiling of heat acclimation in cerebrospinal fluid of rabbit

Heat acclimation (AC) is a phenotypic adaptation to the high ambient temperatures. So far, the physiological effects of AC have been well studied, but the molecular mechanisms underlying it, especially the proteomic studies have been rarely reported. Conducting a protein profile of cerebrospinal fluid (CSF) can facilitate the understanding of molecular pathways involved in AC and identifying stress-specific proteins as a laboratory biomarker. In this study we carried out proteomic profiling of the AC in CSF of rabbit, which would allow a deep insight into molecular signals underlying the AC. For this purpose, rabbits were subjected to AC (dry bulb temperature of (36±1)°C, wet bulb temperature of (29±0.5)°C, black-bulb temperature of (40±1.0)°C, 100min per day for 21days, untreated rabbits were used as controls. We adopted a gel-free proteomic approach (iTRAQ) method to identify protein composition in CSF of rabbits with AC. In total, 1310 proteins were identified. Among which 127 were significant up-regulated and 77 were down-regulated. According to the functions, all AC-induced proteins were classified into 8 categories, including plasma protein factors, metabolism-related proteins, energy metabolism-related proteins, cell surface/intercellular matrix proteins, stress related proteins, tumor-related proteins, as well as housekeeping proteins and putative proteins. Meanwhile, a total of 21 pathways were found involved in the developing of AC. Further analysis indicated that proteins mostly close to AC were grouped into two signal pathways, the immune-related signal pathways and the carbohydrate/lipoprotein metabolism-related signal pathways. Our study was first to carry out the whole proteomic picture of AC, and screen out the critical signaling pathways involved in this physical procedure.

BIOLOGICAL SIGNIFICANCE

This study reported the comparative proteomic analysis of cerebrospinal fluid of rabbits between heat acclimation and normal conditions using the gel-free proteomic mass-spectrometry approach with isotope-labeled samples (iTRAQ) techniques. Mass spectrometry analysis of the proteins from heat acclimated rabbits resulted in the identification of a total of 1310 proteins, among these, 204 proteins were related to the formation of heat acclimation. These proteins were assigned to 8 categories according to their functions. Additionally, 21 pathways involved in infectious diseases, metabolism, immunology, blood circulation, transcriptional regulation and renin-angiotensin were identified by pathway analysis in heat acclimation. This study was the first to use rabbits as a model for unraveling the molecular pathways underlying the establishment of integrative heat acclimation.

Differentially expressed genes associated with adaptation to different thermal environments in three sympatric Cuban Anolis lizards

How animals achieve evolutionary adaptation to different thermal environments is an important issue for evolutionary biology as well as for biodiversity conservation in the context of recent global warming. In Cuba, three sympatric species of Anolis lizards (Anolis allogus, A. homolechis and A. sagrei) inhabit different thermal microhabitats, thereby providing an excellent opportunity to examine how they have adapted to different environmental temperatures. Here, we performed RNA-seq on the brain, liver and skin tissues from these three species to analyse their transcriptional responses at two different temperatures. In total, we identified 400, 816 and 781 differentially expressed genes (DEGs) between the two temperatures in A. allogus, A. homolechis and A. sagrei, respectively. Only 62 of these DEGs were shared across the three species, indicating that global transcriptional responses have diverged among these species. Gene ontology (GO) analysis showed that large numbers of ribosomal protein genes were DEGs in the warm-adapted A. homolechis, suggesting that the upregulation of protein synthesis is an important physiological mechanism in the adaptation of this species to hotter environments. GO analysis also showed that GO terms associated with circadian regulation were enriched in all three species. A gene associated with circadian regulation, Nr1d1, was detected as a DEG with opposite expression patterns between the cool-adapted A. allogus and the hot-adapted A. sagrei. Because the environmental temperature fluctuates more widely in open habitats than in forests throughout the day, the circadian thermoregulation could also be important for adaptation to distinct thermal habitats.

A lotus root inspired implant system with fever responsive characteristics and 3D printing defined nano-antibiotic release patterns

Lotus root imitated scaffolds were fabricated with several critical releasing parameters could be prearranged. Furthermore, when postoperative infection caused hyperthermia occurred, the inner drugs, could be spontaneously released.

Long-term heat exposure prevents hypoxia-induced apoptosis in mouse fibroblast cells

Long-term continuous exposure to high ambient temperatures induces complete heat acclimation in humans and animals. However, to date, the effects of long-term exposure to heat stress on cells have not been fully evaluated. In this study, we investigated an adaptive physiological process induced in culture cells by continuous exposure to mild heat stress for 60 days. The results of this investigation provide evidence that after long-term heat acclimation in cells, (1) heat shock protein levels are increased, (2) hypoxia inducible factor-1α (HIF-1α) expression is upregulated, and (3) heat shock-induced and hypoxia-induced apoptoses are attenuated. These results suggest that the hypoxia response pathway is an intrinsic part of the heat acclimation repertoire and that the HIF-1 pathway following long-term heat acclimation induces cells with cross tolerance against hypoxia.

Housing temperature influences the pattern of heat shock protein induction in mice following mild whole body hyperthermia

PURPOSE

Researchers studying the murine response to stress generally use mice housed under standard, nationally mandated conditions as controls. Few investigators are concerned whether basic physical aspects of mouse housing could be an additional source of stress, capable of influencing the subsequent impact of an experimentally applied stressor. We have recently become aware of the potential for housing conditions to impact important physiological and immunological properties in mice.

MATERIALS AND METHODS

Here we sought to determine whether housing mice at standard temperature (ST; 22 °C) vs. thermoneutral temperature (TT; 30 °C) influences baseline expression of heat shock proteins (HSPs) and their typical induction following a whole body heating.

RESULTS

There were no significant differences in baseline expression of HSPs at ST and TT. However, in several cases, the induction of Hsp70, Hsp110 and Hsp90 in tissues of mice maintained at ST was greater than at TT following 6 h of heating (which elevated core body temperature to 39.5 °C). This loss of HSP induction was also seen when mice housed at ST were treated with propranolol, a β-adrenergic receptor antagonist, used clinically to treat hypertension and stress.

CONCLUSIONS

Taken together, these data show that housing temperature significantly influences the expression of HSPs in mice after whole body heating and thus should be considered when stress responses are studied in mice.

Genetic polymorphisms within exon 3 of heat shock protein 90AA1 gene and its association with heat tolerance traits in Sahiwal cows

AIM

The present study was undertaken to identify novel single nucleotide polymorphism (SNP) in Exon 3 of HSP90AA1 gene and to analyze their association with respiration rate (RR) and rectal temperature (RT) in Sahiwal cows.

MATERIALS AND METHODS

The present study was carried out in Sahiwal cows (n=100) with the objectives to identify novel SNP in exon 3 of HSP90AA1 gene and to explore the association with heat tolerance traits. CLUSTAL-W multiple sequence analysis was used to identify novel SNPs in exon 3 of HSP90AA1 gene in Sahiwal cows. Gene and genotype frequencies of different genotypes were estimated by standard procedure POPGENE version 1.32 (University of Alberta, Canada). The significant effect of SNP variants on physiological parameters, e.g. RR and RT were analyzed using the General Linear model procedure of SAS Version 9.2.

RESULTS

The polymerase chain reaction product with the amplicon size of 450 bp was successfully amplified, covering exon 3 region of HSP90AA1 gene in Sahiwal cows. On the basis of comparative sequence analysis of Sahiwal samples (n=100), transitional mutations were detected at locus A1209G as compared to Bos taurus (NCBI GenBank AC_000178.1). After chromatogram analysis, three genotypes AA, AG, and GG with respective frequencies of 0.23, 0.50, and 0.27 ascertained. RR and RT were recorded once during probable extreme hours in winter, spring, and summer seasons. It was revealed that significant difference (p<0.01) among genetic variants of HSP90AA1 gene with heat tolerance trait was found in Sahiwal cattle. The homozygotic animals with AA genotype had lower heat tolerance coefficient (HTC) (1.78±0.04(a)), as compared to both AG and GG genotypes (1.85±0.03(b) and 1.91±0.02(c)), respectively. The gene and genotype frequencies for the locus A1209G were ascertained.

CONCLUSIONS

Novel SNP was found at the A1209G position showed all possible three genotypes (homozygous and heterozygous). Temperature humidity index has a highly significant association with RR, RT, and HTC in all the seasons. Perusal of results across different seasons showed the significant (p<0.01) difference in RR, RT, and HTC among winter, spring, and summer seasons. Genetic association with heat tolerance traits reveals their importance as a potential genetic marker for heat tolerance traits in Sahiwal cows.

A comparative study on the expression profile of MCTs and HSPs in Ghungroo and Large White Yorkshire breeds of pigs during different seasons

Thermal stress has a significant adverse effect on commercial swine production but it is not easy to measure. Animals may adapt to stress conditions by an alteration in the expression of stress-related genes such as heat shock proteins (HSPs) and monocarboxylate transporters (MCTs). The present study presents a comparative analysis of seasonally varied effects on the expression profiles of HSPs (27, 70, and 90) and MCTs (1, 2, and 4) transcripts in thigh muscle and colon tissue of Ghungroo and Large White Yorkshire (LWY) breeds of pig. By real-time polymerase chain reaction, the mRNA expression of HSP27 and HSP90 genes was found to be higher in both thigh muscle and colon tissue in Ghungroo compared to Large White Yorkshire pigs during the summer. However, the relative expression of HSP70 was significantly higher (P < 0.01) in Ghungroo compared to Large White Yorkshire pigs during both seasons in both thigh muscle and colon tissue. The expression of HSP90 was higher in Ghungroo when compared to LWY though the variation was non-significant (P > 0.05) in the colon during different seasons. However, in Ghungroo, the mRNA expression of MCT1 was found to be significantly (P < 0.05) higher in thigh muscle and colon regions during the summer compared to LWY, whereas MCT2 was expressed more in the colon in LWY compared to Ghungroo during the summer. The relative expression of mRNA of MCT4 was found to be significantly (P < 0.05) higher in thigh region in both summer and winter in Ghungroo compared with LWY. Thus, the study demonstrated that both HSPs and MCTs gene expression during thermal stress suggests the possible involvement of these genes in reducing the deleterious effect of thermal stress, thus maintaining cellular integrity and homeostasis in pigs. These genes could be used as suitable markers for the assessment of stress in pigs.

Fever, immunity, and molecular adaptations

The heat shock response (HSR) is an ancient and highly conserved process that is essential for coping with environmental stresses, including extremes of temperature. Fever is a more recently evolved response, during which organisms temporarily subject themselves to thermal stress in the face of infections. We review the phylogenetically conserved mechanisms that regulate fever and discuss the effects that febrile-range temperatures have on multiple biological processes involved in host defense and cell death and survival, including the HSR and its implications for patients with severe sepsis, trauma, and other acute systemic inflammatory states. Heat shock factor-1, a heat-induced transcriptional enhancer is not only the central regulator of the HSR but also regulates expression of pivotal cytokines and early response genes. Febrile-range temperatures exert additional immunomodulatory effects by activating mitogen-activated protein kinase cascades and accelerating apoptosis in some cell types. This results in accelerated pathogen clearance, but increased collateral tissue injury, thus the net effect of exposure to febrile range temperature depends in part on the site and nature of the pathologic process and the specific treatment provided.

A Novel Mechanism for Cross-Adaptation between Heat and Altitude Acclimation: The Role of Heat Shock Protein 90

Heat shock protein 90 (HSP90) is a member of a family of molecular chaperone proteins which can be upregulated by various stressors including heat stress leading to increases in HSP90 protein expression. Its primary functions include (1) renaturing and denaturing of damaged proteins caused by heat stress and (2) interacting with client proteins to induce cell signaling for gene expression. The latter function is of interest because, in cancer cells, HSP90 has been reported to interact with the transcription hypoxic-inducible factor 1α (HIF1α). In a normoxic environment, HIF1α is degraded and therefore has limited physiological function. In contrast, in a hypoxic environment, stabilized HIF1α acts to promote erythropoiesis and angiogenesis. Since HSP90 interacts with HIF1α, and HSP90 can be upregulated from heat acclimation in humans, we present a proposal that heat acclimation can mimic molecular adaptations to those of altitude exposure. Specifically, we propose that heat acclimation increases HSP90 which then stabilizes HIF1α in a normoxic environment. This has many implications since HIF1α regulates red blood cell and vasculature formation. In this paper we will discuss (1) the functional roles of HSP90 and HIF1α, (2) the interaction between HSP90 and other client proteins including HIF1α, and (3) results from in vitro studies that may suggest how the relationship between HSP90 and HIF1α might be applied to individuals preparing to make altitude sojourns.

Upregulation of aquaporin expression in the salivary glands of heat-acclimated rats

It is known that aquaporin (AQP) 5 expression in the apical membrane of acinar cells in salivary glands is important for the secretion of saliva in rodents and humans. Although heat acclimation enhances saliva secretion in rodents, the molecular mechanism of how heat induces saliva secretion has not been determined. Here, we found that heat acclimation enhanced the expression of AQP5 and AQP1 in rat submandibular glands concomitant with the promotion of the HIF-1α pathway, leading to VEGF induction and CD31-positive angiogenesis. The apical membrane distribution of AQP5 in serous acinar cells enhanced after heat acclimation, while AQP1 expression was restricted to the endothelial cells in the submandibular glands. A network of AQPs may be involved in heat-acclimated regulation in saliva secretion. Because AQPs probably plays a crucial role in saliva secretion in humans, these findings may lead to a novel strategy for treating saliva hyposecretion.

Continuous fever-range heat stress induces thermotolerance in odontoblast-lineage cells

OBJECTIVE

Heat shock during restorative procedures can trigger damage to the pulpodentin complex. While severe heat shock has toxic effects, fever-range heat stress exerts beneficial effects on several cells and tissues. In this study, we examined whether continuous fever-range heat stress (CFHS) has beneficial effects on thermotolerance in the rat clonal dental pulp cell line with odontoblastic properties, KN-3.

METHODS

KN-3 cells were cultured at 41°C for various periods, and the expression level of several proteins was assessed by Western blot analysis. After pre-heat-treatment at 41°C for various periods, KN-3 cells were exposed to lethal severe heat shock (LSHS) at 49°C for 10min, and cell viability was examined using the MTS assay. Additionally, the expression level of odontoblast differentiation makers in surviving cells was examined by Western blot analysis.

RESULTS

CFHS increased the expression levels of several heat shock proteins (HSPs) in KN-3 cells, and induced transient cell cycle arrest. KN-3 cells, not pre-heated or exposed to CFHS for 1 or 3h, died after exposure to LSHS. In contrast, KN-3 cells exposed to CFHS for 12h were transiently lower on day 1, but increased on day 3 after LSHS. The surviving cells expressed odontoblast differentiation markers, dentine sialoprotein and dentine matrix protein-1. These results suggest that CFHS for 12h improves tolerance to LSHS by inducing HSPs expression and cell cycle arrest in KN-3 cells.

CONCLUSIONS

The appropriate pretreatment with continuous fever-range heat stress can provide protection against lethal heat shock in KN-3 cells.

Effect of heat stress on the expression profile of Hsp90 among Sahiwal (Bos indicus) and Frieswal (Bos indicus × Bos taurus) breed of cattle: a comparative study

We evaluated the effect of thermal challenge on the expression profile of heat shock protein 90 (Hsp90) among Sahiwal (Bos indicus) and Frieswal (Bos indicus × Bos taurus) breeds of cattle. The present investigation was focused on the comparative studies on Hsp90 expression among Frieswal and Sahiwal under in vitro and environmental heat stress. Measured immediately after the in vitro heat shock to the peripheral blood mononuclear cells (PBMCs), the relative expression of Hsp90 mRNA was significantly (P<0.05) higher in Sahiwal compared to those in Frieswal. In later intervals of time, the differences in the expression levels between the two breeds become negligible coming down towards the basal level. A similar pattern was observed in the protein concentration showing significantly (P<0.05) higher levels in Sahiwal compared to those in Frieswal. The second sets of experiments were undertaken during summer months (March to May) when temperature peaked from 37 to 45 °C. During these months, Frieswal cows consistently recorded higher rectal temperatures than the Sahiwal breed. Further during this peak summer stress, Sahiwal showed significantly higher levels of mRNA transcripts as well as protein concentration compared to the Frieswal breed. Our findings also interestingly showed that, the cell viability of PBMC are significantly higher among the Sahiwal than Frieswal. Taken together, the experiments of both induced in vitro and environmental stress conditions indicate that, Sahiwal may express higher levels of Hsp90 then Frieswal to regulate their body temperature and increase cell survivality under heat stressed conditions.

Fever, hyperthermia and the heat shock response

The heat shock response is a highly conserved primitive response that is essential for survival against a wide range of stresses, including extremes of temperature. Fever is a more recently evolved response, during which organisms raise their core body temperature and temporarily subject themselves to thermal stress in the face of infections. The present review documents studies showing the potential overlap between the febrile response and the heat shock response and how both activate the same common transcriptional programme (although with different magnitudes) including the stress-activated transcription factor, heat shock factor-1, to modify host defences in the context of infection, inflammation and injury. The review focuses primarily on how hyperthermia within the febrile range that often accompanies infections and inflammation acts as a biological response modifier and modifies innate immune responses. The characteristic 2-3 °C increase in core body temperature during fever activates and utilises elements of the heat shock response pathway to modify cytokine and chemokine gene expression, cellular signalling and immune cell mobilisation to sites of inflammation, infection and injury. Interestingly, typical proinflammatory agonists such as Toll-like receptor agonists modify the heat shock-induced transcriptional programme and expression of HSP genes following co-exposure to febrile range hyperthermia or heat shock, suggesting a complex reciprocal regulation between the inflammatory pathway and the heat shock response pathway.

Tolerance for chronic heat exposure is greater in female than male mice

PURPOSE

Chronic heat exposure in mice has cellular and physiological effects that improve thermal tolerance [1], but also modifies innate immune responses with potential adverse consequences [2]. While male and female mice are known to respond differently to acute exposure to severe hyperthermia, sex-based differences in responses to chronic moderate heat exposure have not been reported. The major objective of this study was to compare the tolerance of male and female mice for chronic heat exposure.

MATERIALS AND METHODS

We used a mouse model of 5-day moderate heat exposure (ambient temperature ∼37°C) to compare the physiological and cellular heat shock response in male and female mice. Core temperature, heart rate, and activity were monitored telemetrically and heat shock protein levels were measured in brain and lung by western blotting.

RESULTS

Adult CD-1 female mice maintained a 1.2°C lower core temperature (38.31 ± 0.64 versus 39.51 ± 0.72°C; p = 0.002), experienced less weight loss (1.54 ± 0.45 versus 4.54 ± 1.97 g; p = 0.0007), and had improved survival (16/16 survived versus 13/21, p < 0.006) than male mice of the same age. After 5 days of moderate heat exposure Hsp72 levels in brain and lung increased 2.1-fold (p = 0.007) and 5-fold (p = 0.048) in male mice compared with 1.3- (p = 0.054) and 1.5-fold (p = 0.134) in female mice.

CONCLUSIONS

This study reveals previously unknown and potentially important differences between male and female mice in physiological and cellular responses to chronic heat exposure, which had consequences for survival. Future studies may identify biomarkers of differential heat tolerance and treatments to improve heat tolerance in humans.

Heat acclimation affects circulating levels of prostaglandin E2, COX-2 and orexin in humans

We examined serum levels of prostaglandin E2 (PGE2), cyclooxygenase (COX)-2 and orexin before and after heat acclimation (HA) to test the hypothesis that decreased basal body temperature due to HA correlate with circulating levels of these key thermoregulatory molecules. Nine healthy human male volunteers were recruited (age, 21.9±2.7 years). The subjects were exposed to half-body immersion in hot water (42±0.5°C) at the same time of day (2-5p.m.) on alternate days for 3 weeks. The HA protocol included 10 bouts of 30min immersion. All experiments were performed in an automated climate chamber (temperature, 26.0±0.5°C; relative humidity, 60±3.0%; air velocity, <1m/s). Tympanic and skin temperatures were measured, and mean body temperature was calculated. The difference in body weight was used to estimate total sweat loss. Serum levels of PGE2, COX-2 and orexin were analyzed before and after HA. Body temperature decreased significantly (P<0.05) after HA, whereas sweat volume increased significantly (P<0.01). Serum PGE2, COX-2 and orexin concentrations decreased significantly compared to those at pre-acclimation (P<0.001, P<0.01, P<0.01, respectively). Our data suggest that decreased basal body temperature after HA is associated with decreases in thermoregulatory molecules, such as PGE2, COX-2 and orexin.

Toll-like receptor agonists and febrile range hyperthermia synergize to induce heat shock protein 70 expression and extracellular release

Heat shock protein (Hsp) 70 expression can be stimulated by febrile range temperature (FRT). Hsp70 has been shown to be elevated in serum of patients with sepsis, and when released from cells, extracellular Hsp70 exerts endotoxin-like effects through Toll-like receptor 4 (TLR4) receptors. Circulating TLR agonists and fever both persist for the first several days of sepsis, and each can activate Hsp70 expression; however, the effect of combined exposure to FRT and TLR agonists on Hsp70 expression is unknown. We found that concurrent exposure to FRT (39.5 °C) and agonists for TLR4 (LPS), TLR2 (Pam3Cys), or TLR3 (poly(IC)) synergized to increase Hsp70 expression and extracellular release in RAW264.7 macrophages. The increase in Hsp70 expression was associated with activation of p38 and ERK MAP kinases, phosphorylation of histone H3, and increased recruitment of HSF1 to the Hsp70 promoter. Pretreatment with the p38 MAPK inhibitor SB283580 but not the ERK pathway inhibitor UO126 significantly reduced Hsp70 gene modification and Hsp70 expression in RAW cells co-exposed to LPS and FRT. In mice challenged with intratracheal LPS and then exposed to febrile range hyperthermia (core temperature, ∼39.5 °C), Hsp70 levels in lung tissue and in cell-free lung lavage were increased compared with mice exposed to either hyperthermia or LPS alone. We propose a model of how enhanced Hsp70 expression and extracellular release in patients concurrently exposed to fever and TLR agonists may contribute to the pathogenesis of sepsis.

Expression profile of HSP genes during different seasons in goats (Capra hircus)

The present study has demonstrated the expression of HSP60, HSP70, HSP90, and UBQ in peripheral blood mononuclear cells (PBMCs) during different seasons in three different age groups (Groups I, II, and III with age of 0-2, 2-5, and >5 years, respectively) of goats of tropical and temperate regions. Real-time polymerase chain reaction was applied to investigate mRNA expression of examined factors. Specificity of the desired products was documented using analysis of the melting temperature and high-resolution gel electrophoresis to verify that the transcripts are of the exact molecular size predicted. The mRNA expression of HSP60, HSP90, and UBQ was significantly higher (P < 0.05) in all age groups during peak summer season as compared with peak winter season in both tropical and temperate region goats. HSP70 mRNA expression was significantly higher (P < 0.05) during summer season as compared with winter season in tropical region goats. However, in the temperate region, in goats from all the three age groups studied, a non-significant difference of HSP70 expression between summer and winter seasons was noticed. In conclusion, results demonstrate that (1) HSP genes are expressed in caprine PBMCs and (2) higher expression of HSPs during thermal stress suggest possible involvement of them to ameliorate deleterious effect of thermal stress so as to maintain cellular integrity and homeostasis in goats.

Febrile-range hyperthermia modifies endothelial and neutrophilic functions to promote extravasation

Acute respiratory distress syndrome (ARDS) is a neutrophil (polymorphonuclear leukocyte; PMN)-driven lung injury that is associated with fever and heat-stroke, and involves approximately 40% mortality. In murine models of acute lung injury (ALI), febrile-range hyperthermia (FRH) enhanced PMN accumulation, vascular permeability, and epithelial injury, in part by augmenting pulmonary cysteine-x-cysteine (CXC) chemokine expression. To determine whether FRH increases chemokine responsiveness within the lung, we used in vivo and in vitro models that bypass the endogenous generation of chemokines. We measured PMN transalveolar migration (TAM) in mice after intratracheal instillations of the human CXC chemokine IL-8 in vivo, and of IL-8-directed PMN transendothelial migration (TEM) through human lung microvascular endothelial cell (HMVEC-L) monolayers in vitro. Pre-exposure to FRH increased in vivo IL-8-directed PMN TAM by 23.5-fold and in vitro TEM by 7-fold. Adoptive PMN transfer demonstrated that enhanced PMN TAM required both PMN donors and recipients to be exposed to FRH, suggesting interdependent effects on PMNs and endothelium. FRH exposure caused the activation of extracellular signal-regulated kinase (ERK) and p38 mitogen-activated protein kinase in lung homogenates and circulating PMNs, with an associated increase in HSP27 phosphorylation and stress-fiber formation. The inhibition of these signaling pathways with U0126 and SB203580 blocked the effects of FRH on PMN extravasation in vivo and in vitro. Collectively, these results (1) demonstrate that FRH augments chemokine-directed PMN extravasation through direct effects on endothelium and PMNs, (2) identify ERK and p38 signaling pathways in the effect, and (3) underscore the complex effects of physiologic temperature change on innate immune function and its potential consequences for lung injury.

Fever, hyperthermia, and the lung: it's all about context and timing

Although body temperature is tightly regulated in humans, elevated temperatures are frequently encountered during febrile illnesses and exertional and environmental hyperthermia. Such temperature increases exert profound effects on cell signaling and gene expression patterns, which have important consequences for innate immune function and cell injury, apoptosis, and recovery. The lung offers a framework for understanding how these effects can either benefit or harm the host. We present data demonstrating that exposure to febrile-range hyperthermia (∼39.5 °C) exerts multiple biologic effects that converge on enhanced neutrophil recruitment to the lung, and describe the consequences of these effects for pathogen clearance and collateral tissue injury. We also discuss the influence of temperature on apoptosis in lung epithelium. Collectively, the data presented identify body temperature as a modifiable factor that exerts profound influence on the outcome of infection and injury.