Posttranslational modifications in histones underlie heat acclimation-mediated cytoprotective memory

Nickel-induced transcriptional memory in lung epithelial cells promotes interferon signaling upon nicotine exposure

Exposure to nickel, an environmental respiratory toxicant, is associated with lung diseases including asthma, pulmonary fibrosis, bronchitis and cancers. Our previous studies have shown that a majority of the nickel-induced transcriptional changes are persistent and do not reverse even after the termination of exposure. This suggested transcriptional memory, wherein the cell 'remembers' past nickel exposure. Transcriptional memory, due to which the cells respond more robustly to a previously encountered stimulus has been identified in a number of organisms. Therefore, transcriptional memory has been described as an adaptive mechanism. However, transcriptional memory caused by environmental toxicant exposures has not been well investigated. Moreover, how the transcriptional memory caused by an environmental toxicant might influence the outcome of exposure to a second toxicant has not been explored. In this study, we investigated whether nickel-induced transcriptional memory influences the outcome of the cell's response to a second respiratory toxicant, nicotine. Nicotine, an addictive compound in tobacco, is associated with the development of chronic lung diseases including chronic obstructive pulmonary disease (COPD) and pulmonary fibrosis. Our results show that nicotine exposure upregulated a subset of genes only in the cells previously exposed to nickel. Furthermore, our analyses indicate robust activation of interferon (IFN) signaling in these cells. IFN signaling is a driver of inflammation, which is associated with many chronic lung diseases. Therefore, our results suggest that nicotine exposure of lung cells that retain the transcriptional memory of previous nickel exposure could result in increased susceptibility to developing chronic inflammatory lung diseases.

Climate change and pregnancy complications: From hormones to the immune response

Pregnant women are highly vulnerable to adverse environments. Accumulating evidence highlights that increasing temperatures associated with the ongoing climate change pose a threat to successful reproduction. Heat stress caused by an increased ambient temperature can result in adverse pregnancy outcomes, e.g., preterm birth, stillbirth and low fetal weight. The pathomechanisms through which heat stress interferes with pregnancy maintenance still remain vague, but emerging evidence underscores that the endocrine system is severely affected. It is well known that the endocrine system pivotally contributes to the physiological progression of pregnancy. We review – sometimes speculate - how heat stress can offset hormonal dysregulations and subsequently derail other systems which interact with hormones, such as the immune response. This may account for the heat-stress related threat to successful pregnancy progression, fetal development and long-term children’s health.

Vascular compliance and left ventricular compliance cross talk: Implications for using long-term heat acclimation in cardiac care

1) The first evidence of the beneficial impact of Long-Term-Heat-Acclimation (LTHA) on cardio-vascular compliance was the positive inotropic response and improved left ventricular (LV) compliance noted when isolated hearts from LTHA rats were studied. Human echo study demonstrates that passive HA affects the right ventricle and the atria as well. 2) There is a cross-talk between vascular and cardiac compliance. Vascular compliance per se is defined by central venous pressure-Blood volume relationship-Global Vascular Compliance (GVC). It is determined by the sum of the vascular compliance of the vessels in every organ in any physiological state, varies with LTHA and thus influences cardiac performance. LTHA improves endothelial function, increases NO (nitric oxide) production, in-turn stimulating alterations in ECM (extracellular matrix) via the TGF β1-SMAD pathway. 3) LTHA is associated with transformation from fast to slow myosin, heat acclimation ischemic/hypoxic cross-tolerance and alterations in the extracellular matrix. 4) A human translational study demonstrated improved LV compliance following bypass surgery in LTHA subjects compared to controls. 5) Diastolic dysfunction and the impact of comorbidities with vascular and non- vascular origins are major contributors to the syndrome of heart failure with preserved ejection function (HFPEF). Unfortunately, there is a paucity of treatment modalities that improve diastolic dysfunction. 6) In the current mini-review we suggest that LTHA may be beneficial to HFPEF patients by remodeling cardiac compliance and vascular response.

Long-term epigenetic and metabolomic changes in the mouse ventricular myocardium after exertional heat stroke

Evidence from human epidemiological studies suggests that exertional heat stroke (EHS) results in an elevated risk of long-term cardiovascular and systemic disease. Previous results using a preclinical mouse model of EHS demonstrated severe metabolic imbalances in ventricular myocardium developing at 9-14 days of recovery. Whether this resolves over time is unknown. We hypothesized that the long-term effects of EHS on the heart reflect retained maladaptive epigenetic responses. In this study, we evaluated genome-wide DNA methylation, RNA-Seq, and metabolomic profiles of the left ventricular myocardium in female C57BL/6 mice, 30 days after EHS (exercise in 37.5°C; n = 7-8), compared with exercise controls. EHS mice ran to loss of consciousness, reaching core temperatures of 42.4 ± 0.2°C. All mice recovered quickly. After 30 days, the left ventricles were rapidly frozen for DNA methyl sequencing, RNA-Seq, and untargeted metabolomics. Ventricular DNA from EHS mice revealed >13,000 differentially methylated cytosines (DMCs) and >900 differentially methylated regions (DMRs; ≥5 DMCs with ≤300 bp between each CpG). Pathway analysis using DMRs revealed alterations in genes regulating basic cell functions, DNA binding, transcription, and metabolism. Metabolomics and mRNA expression revealed modest changes that are consistent with a return to homeostasis. Methylation status did not predict RNA expression or metabolic state at 30 days. We conclude that EHS induces a sustained DNA methylation memory lasting over 30 days of recovery, but ventricular gene expression and metabolism return to a relative homeostasis at rest. Such long-lasting alterations to the DNA methylation landscape could alter responsiveness to environmental or clinical challenges later in life.

Epigenetic responses to heat: From adaptation to maladaptation

NEW FINDINGS

What is the topic of this review? This review outlines the history of research on epigenetic adaptations to heat exposure. The perspective taken is that adaptations reflect properties of hormesis, whereby low, repeated doses of heat induce adaptation (acclimation/acclimatization); whereas brief, life-threatening exposures can induce maladaptive responses. What advances does it highlight? The epigenetic mechanisms underlying acclimation/acclimatization comprise specific molecular programmes on histones that regulate heat shock proteins transcriptionally and protect the organism from subsequent heat exposures, even after long delays. The epigenetic signalling underlying maladaptive responses might rely, in part, on extensive changes in DNA methylation that are sustained over time and might contribute to later health challenges.

ABSTRACT

Epigenetics plays a strong role in molecular adaptations to heat by producing a molecular memory of past environmental exposures. Moderate heat, over long periods of time, induces an 'adaptive' epigenetic memory, resulting in a condition of 'resilience' to future heat exposures or cross-tolerance to other forms of toxic stress. In contrast, intense, life-threatening heat exposures, such as severe heat stroke, can result in a 'maladaptive' epigenetic memory that can place an organism at risk of later health complications. These cellular memories are coded by post-translational modifications of histones on the nucleosomes and/or by changes in DNA methylation. They operate by inducing changes in the level of gene transcription and therefore phenotype. The adaptive response to heat acclimation functions, in part, by facilitating transcription of essential heat shock proteins and exhibits a biphasic short programme (maintaining DNA integrity, followed by a long-term consolidation). The latter accelerates acclimation responses after de-acclimation. Although less studied, the maladaptive responses to heat stroke appear to be coded in long-lasting changes in DNA methylation near the promoter region of genes involved with basic cell function. Whether these memories are also encoded in histone modifications is not yet known. There is considerable evidence that both adaptive and maladaptive epigenetic responses to heat can be inherited, although most evidence comes from lower organisms. Future challenges include understanding the signalling mechanisms responsible and discovering new ways to promote adaptive responses while suppressing maladaptive responses to heat, as all life forms adapt to life on a warming planet.

Human temperature regulation under heat stress in health, disease, and injury

The human body constantly exchanges heat with the environment. Temperature regulation is a homeostatic feedback control system that ensures deep body temperature is maintained within narrow limits despite wide variations in environmental conditions and activity-related elevations in metabolic heat production. Extensive research has been performed to study the physiological regulation of deep body temperature. This review focuses on healthy and disordered human temperature regulation during heat stress. Central to this discussion is the notion that various morphological features, intrinsic factors, diseases, and injuries independently and interactively influence deep body temperature during exercise and/or exposure to hot ambient temperatures. The first sections review fundamental aspects of the human heat stress response, including the biophysical principles governing heat balance and the autonomic control of heat loss thermoeffectors. Next, we discuss the effects of different intrinsic factors (morphology, heat adaptation, biological sex, and age), diseases (neurological, cardiovascular, metabolic, and genetic), and injuries (spinal cord injury, deep burns, and heat stroke), with emphasis on the mechanisms by which these factors enhance or disturb the regulation of deep body temperature during heat stress. We conclude with key unanswered questions in this field of research.

Effect of in utero exposure to hyperthermia on postnatal hair length, skin morphology, and thermoregulatory responses

Skin and hair coat play important functions in maintaining homeostasis and thermoregulation for cattle, which can affect all modes of heat loss. Our objective was to investigate the effect of hyperthermia experienced in utero during late gestation on postnatal hair length, skin properties, and thermoregulation. Pregnant dams were heat stressed (n = 41) or actively cooled (n = 41) for the last ∼56 d of gestation and gave birth to heifers that were in utero heat stressed (IUHT) or in utero cooled (IUCL), respectively. Hair samples and skin tissue biopsies were collected from neck and rump locations at birth (d 0), 1 wk after weaning (d 63), and at 12 mo. Hair samples were also obtained at 4 and 8 mo. Skin tissue was stained with hematoxylin and eosin to visualize morphology. Hair length (short and long hairs, undercoat and topcoat, respectively), stratum corneum (SC) area, SC thickness, epidermis thickness, sweat gland (SWT) number, SWT cross-sectional area, SWT average size, sebaceous gland (SEB) number, SEB cross-sectional area, SEB average size, and sweat gland depth were assessed. Respiration rate, skin temperature, sweating rate, and rectal temperature was measured weekly from d 7 to 63. Additionally, thermoregulatory patterns were measured every 4 h over a 36-h interval beginning 4 d after weaning. Data were analyzed using PROC MIXED in SAS with a main effect of in utero treatment with location and time points analyzed separately. No difference in hair parameters were detected at d 0 or 12 mo. At d 63, IUHT heifers had longer average hair length (14.8 vs. 13.8 ± 0.2 mm, standard error), shorter undercoats (9.3 vs. 10.4 ± 0.3 mm), longer topcoats (19.6 vs. 17.1 ± 0.3 mm), and a greater difference between topcoat and undercoat (10.1 vs. 7.0 ± 0.4 mm). At 4 mo, IUHT heifers had longer average hair lengths (26.1 vs. 22.2 ± 1.0 mm) and longer topcoats (36.9 vs. 33.9 ± 1.1 mm), and at 8 mo, IUHT had longer average hair lengths (17.9 vs. 16.2 ± 0.6 mm), relative to IUCL. At d 0, IUHT heifers had more (13 vs. 9 ± 2 glands) but smaller average sized SEB (neck: 1,636 vs. 2,238 ± 243 µm²; rump: 2,100 vs. 3,352 ± 379 µm²) and reduced SC area (79,243 vs. 169,419 ± 13,071 µm²). At d 63, IUHT had fewer SEB (11 vs. 15 ± 2 glands), smaller SWT (0.16 vs. 0.23 ± 0.02 mm²), fewer SWT (16 vs. 23 ± 4 glands), and deeper SWT (0.5 vs. 0.4 ± 0.03 mm). At 12 mo, IUHT had greater distance from the skin surface to the most superficial SWT (0.016 vs. 0.015 ± 0.0004 mm), shorter distance to the deepest SWT (0.031 vs. 0.033 ± 0.001 mm), and smaller SWT (81.1 vs. 108.9 ± 10.8 µm²), relative to IUCL. When measured both weekly and hourly, IUHT heifers had higher rectal temperature and sweating rate. Overall, in utero hyperthermia triggers long-lasting hair and skin adaptations, possibly leading to differences in postnatal thermoregulation.

Classic and exertional heatstroke

In the past two decades, record-breaking heatwaves have caused an increasing number of heat-related deaths, including heatstroke, globally. Heatstroke is a heat illness characterized by the rapid rise of core body temperature above 40 °C and central nervous system dysfunction. It is categorized as classic when it results from passive exposure to extreme environmental heat and as exertional when it develops during strenuous exercise. Classic heatstroke occurs in epidemic form and contributes to 9-37% of heat-related fatalities during heatwaves. Exertional heatstroke sporadically affects predominantly young and healthy individuals. Under intensive care, mortality reaches 26.5% and 63.2% in exertional and classic heatstroke, respectively. Pathological studies disclose endothelial cell injury, inflammation, widespread thrombosis and bleeding in most organs. Survivors of heatstroke may experience long-term neurological and cardiovascular complications with a persistent risk of death. No specific therapy other than rapid cooling is available. Physiological and morphological factors contribute to the susceptibility to heatstroke. Future research should identify genetic factors that further describe individual heat illness risk and form the basis of precision-based public health response. Prioritizing research towards fundamental mechanism and diagnostic biomarker discovery is crucial for the design of specific management approaches.

The roles of inducible chromatin and transcriptional memory in cellular defense system responses to redox-active pollutants

People are exposed to wide range of redox-active environmental pollutants. Air pollution, heavy metals, pesticides, and endocrine disrupting chemicals can disrupt cellular redox status. Redox-active pollutants in our environment all trigger their own sets of specific cellular responses, but they also activate a common set of general stress responses that buffer the cell against homeostatic insults. These cellular defense system (CDS) pathways include the heat shock response, the oxidative stress response, the hypoxia response, the unfolded protein response, the DNA damage response, and the general stress response mediated by the stress-activated p38 mitogen-activated protein kinase. Over the past two decades, the field of environmental epigenetics has investigated epigenetic responses to environmental pollutants, including redox-active pollutants. Studies of these responses highlight the role of chromatin modifications in controlling the transcriptional response to pollutants and the role of transcriptional memory, often referred to as "epigenetic reprogramming", in predisposing previously exposed individuals to more potent transcriptional responses on secondary challenge. My central thesis in this review is that high dose or chronic exposure to redox-active pollutants leads to transcriptional memories at CDS target genes that influence the cell's ability to mount protective responses. To support this thesis, I will: (1) summarize the known chromatin features required for inducible gene activation; (2) review the known forms of transcriptional memory; (3) discuss the roles of inducible chromatin and transcriptional memory in CDS responses that are activated by redox-active environmental pollutants; and (4) propose a conceptual framework for CDS pathway responsiveness as a readout of total cellular exposure to redox-active pollutants.

Stress-induced transcriptional memory accelerates promoter-proximal pause release and decelerates termination over mitotic divisions

Heat shock instantly reprograms transcription. Whether gene and enhancer transcription fully recover from stress and whether stress establishes a memory by provoking transcription regulation that persists through mitosis remained unknown. Here, we measured nascent transcription and chromatin accessibility in unconditioned cells and in the daughters of stress-exposed cells. Tracking transcription genome-wide at nucleotide-resolution revealed that cells precisely restored RNA polymerase II (Pol II) distribution at gene bodies and enhancers upon recovery from stress. However, a single heat exposure in embryonic fibroblasts primed a faster gene induction in their daughter cells by increasing promoter-proximal Pol II pausing and by accelerating the pause release. In K562 erythroleukemia cells, repeated stress refined basal and heat-induced transcription over mitotic division and decelerated termination-coupled pre-mRNA processing. The slower termination retained transcripts on the chromatin and reduced recycling of Pol II. These results demonstrate that heat-induced transcriptional memory acts through promoter-proximal pause release and pre-mRNA processing at transcription termination.

Early life thermal stress: impacts on future temperature preference in weaned pigs (3 to 15 kg)

Thermal stress can result in productivity losses, morbidity, and mortality if proper management practices are not employed. A basic understanding of the relationship between animals and the thermal environment is crucial to assess the environment’s impact on livestock performance. Therefore, the study objective was to evaluate whether different early life thermal stressors (ELTS) altered the temperature preference of pigs later in life. Twelve sows and their litters were randomly exposed to 1 of 3 ELTS treatments from 7 to 9 d of age: early life heat stress (ELHS; cycling 32 to 38 °C; n = 4), early life cold stress (ELCS; 25.4±1.1 °C without heating lamp; n = 4), or early life thermoneutral (ELTN; 25.4±1.1 °C with a heating lamp; n = 4) conditions. From 10 to 20 d, (weaning) all piglets were exposed to ELTN conditions. At weaning, pigs were randomly assigned to groups of 4 of the same sex and ELTS treatment. Temperature preference, where pigs freely choose a temperature, was assessed in 21 groups (n = 7 groups per ELTS treatment) using 1 of 3 thermal gradient apparatuses (22 to 40 °C). Testing began at 26 ± 1.3 d of age to give pigs time to acclimate to solid food after weaning and 1 group per ELTS treatment were tested simultaneously in each apparatus. Pigs were given 24 h to acclimate followed by a 24-h testing period. Behavior (active and inactive), posture (upright, sternal, and lateral lying), and location were documented every 20 min using instantaneous scan samples. Preferred feeding temperature was determined by the latency to empty a feeder in each location. Data were analyzed using PROC MIXED in SAS 9.4. A cubic regression model was used to calculate the peak temperature preference of pigs based on the temperature pigs spent most of their time. The preference range was calculated using peak temperature preference ±SE for each ELTS treatment group. Early life thermal stress altered where pigs spent most of their time within the thermal gradient (P = 0.03) with ELTN pigs preferring cooler temperatures (peak preference of 23.8 °C) compared with their ELCS exposed counterparts (peak preference of 26.0 °C; P < 0.01). However, ELHS exposed pigs (peak preference of 25.6 °C) did not differ in their temperature preference compared with ELTN or ELCS exposed counterparts (P > 0.05). In summary, ELCS exposure altered pig temperature preference later in life indicating that ELTS can alter temperature preference in pigs.

Four-month operational heat acclimatization positively affects the level of heat tolerance 6 months later

Benefits obtained after heat acclimation/acclimatization should be completely lost after an estimated period of 6 weeks. However, this estimate is still hypothetical. We evaluate the long-term effects of heat acclimatization on the level of heat tolerance. Physiological and subjective markers of heat tolerance were assessed during a heat stress test (HST: 3 × 8-min runs outdoors [~ 40 °C and 20% RH] at 50% of their estimated speed at VO_2max) performed on the 2nd day upon arrival to the desert military base in the United Arab Emirates after a first day of mostly passive exposure to heat. Among the 50 male French soldiers, 25 partook in a 4-month military mission in countries characterized by a hot environment ~ 6 months prior to the study (HA). The other 25 participants were never heat acclimatized (CT). Rectal temperature (p = 0.023), heart rate (p = 0.033), and perceived exertion (p = 0.043) were lower in the HA than CT group at the end of HST. Soldiers who experienced a former 4-month period of natural heat acclimatization very likely had a higher level of heat tolerance during exercise in the heat, even 6 months after returning from the previous desert mission, than that of their non-acclimatized counterparts.

Exertional heat stroke leads to concurrent long-term epigenetic memory, immunosuppression and altered heat shock response in female mice

KEY POINTS

Exposure to exertional heat stroke (EHS) has been linked to increased long-term decrements of health. Epigenetic reprogramming is involved in the response to heat acclimation; however, whether the long-term effects of EHS are mediated by epigenetic reprogramming is unknown. In female mice, we observed DNA methylation reprogramming in bone marrow-derived (BMD) monocytes as early as 4 days of recovery from EHS and as late as 30 days compared with sham exercise controls. Whole blood, collected after 30 days of recovery from EHS, exhibited an immunosuppressive phenotype when challenged in vitro by lipopolysaccharide. After 30 days of recovery from EHS, BMD monocytes exhibited an altered in vitro heat shock response. The location of differentially methylated CpGs are predictive of both the immunosuppressive phenotype and altered heat shock responses.

ABSTRACT

Exposure to exertional heat stroke (EHS) has been linked to increased susceptibility to a second heat stroke, infection and cardiovascular disease. Whether these clinical outcomes are mediated by an epigenetic memory is unknown. Using a preclinical mouse model of EHS, we investigated whether EHS exposure produces a lasting epigenetic memory in monocytes and whether there are phenotypic alterations that may be consistent with these epigenetic changes. Female mice underwent forced wheel running at 37.5°C/40% relative humidity until symptom limitation, characterized by CNS dysfunction. Results were compared with matched exercise controls at 22.5°C. Monocytes were isolated from bone marrow after 4 or 30 days of recovery to extract DNA and analyse methylation. Broad-ranging alterations to the DNA methylome were observed at both time points. At 30 days, very specific alterations were observed to the promoter regions of genes involved with immune responsiveness. To test whether these changes might be related to phenotype, whole blood at 30 days was challenged with lipopolysaccharide (LPS) to measure cytokine secretion; monocytes were also challenged with heat shock to quantify mRNA expression. Whole blood collected from EHS mice showed markedly attenuated inflammatory responses to LPS challenge. Furthermore, monocyte mRNA from EHS mice showed significantly altered responses to heat shock challenge. These results demonstrate that EHS leads to a unique DNA methylation pattern in monocytes and altered immune and heat shock responsiveness after 30 days. These data support the hypothesis that EHS exposure can induce long-term physiological changes that may be linked to altered epigenetic profiles.

Recent Advances in Genetic and Epigenetic Modulation of Animal Exposure to High Temperature

Animals have evolved multiple systems, including genetic and epigenetic systems, to respond accordingly to heat exposure and heat acclimation. Heat exposure greatly affects immunity, changes metabolic processes, and poses a serious threat to animals. Heat acclimation is induced by repeated organism exposure to heat stress to dissipate heat. This review focuses on genetic modulation via heat shock transcription factors and calcium as two important factors and compares the changes in HSPs under heat stress and heat acclimation. Epigenetic regulation summarizes the role of HSPs in DNA methylation and histone modifications under heat stress and heat acclimation. These genetic and epigenetic modifications protect cells from thermal damage by mediating the transcriptional levels of heat-responsive genes. This review highlights recent advances in the genetic and epigenetic control of animal thermal responses and their interactions.

Differentiating between the effects of heat stress and lipopolysaccharide on the porcine ovarian heat shock protein response1

Heat stress (HS) negatively affects both human and farm-animal health and undermines efficiency in a variety of economically important agricultural variables, including reproduction. HS impairs the intestinal barrier, allowing for translocation of the resident microflora and endotoxins, such as lipopolysaccharide (LPS), from the gastrointestinal lumen into systemic circulation. While much is known about the cellular function of heat shock proteins (HSPs) in most tissues, the in vivo ovarian HSP response to stressful stimuli remains ill-defined. The purpose of this study was to compare the effects of HS or LPS on ovarian HSP expression in pigs. We hypothesized that ovarian HSPs are responsive to both HS and LPS. Altrenogest (15 mg/d) was administered per os for estrus synchronization (14 d) prior to treatment and three animal paradigms were used: (i) gilts were exposed to cyclical HS (31 ± 1.4 °C) or thermoneutral (TN; 20 ± 0.5 °C) conditions immediately following altrenogest withdrawal for 5 d during follicular development; (ii) gilts were subjected to repeated (4×/d) saline (CON) or LPS (0.1 μg/kg BW) i.v. infusion immediately following altrenogest withdrawal for 5 d; and (iii) gilts were subjected to TN (20 ± 1 °C) or cyclical HS (31 to 35 °C) conditions 2 d post estrus (dpe) until 12 dpe during the luteal phase. While no differences were detected for transcript abundances of the assessed ovarian HSP, the protein abundance of specific HSP was influenced by stressors during the follicular and luteal phases. HS during the follicular phase tended (P < 0.1) to increase ovarian protein abundance of HSP90AA1 and HSPA1A, and increased (P ≤ 0.05) HSF1, HSPD1, and HSPB1 compared with TN controls, while HS decreased HSP90AB1 (P = 0.01). Exposure to LPS increased (P < 0.05) HSP90AA1 and HSPA1A and tended (P < 0.1) to increase HSF1 and HSPB1 compared with CON gilts, while HSP90AB1 and HSPD1 were not affected by LPS. HS during the luteal phase increased (P < 0.05) abundance of HSPB1 in corpora lutea (CL), decreased (P < 0.05) CL HSP90AB1, but did not impact HSF1, HSPD1, HSP90AA1, or HSPA1A abundance. Thus, these data support that HS and LPS similarly regulate expression of specific ovarian HSP, which suggest that HS effects on the ovary are in part mediated by LPS.

Cross-talk between energy metabolism and epigenetics during temperature stress response in C2C12 myoblasts

Objective: Environmental stress induces disturbances in cell energy metabolism and may cause epigenetic modifications. This study aimed to understand the possible impact of temperature stress (35 °C, 39 °C and 41 °C, compared to control 37 °C) on energy metabolism and epigenetic modifications, such as DNA methylation and histone H4 acetylation, as well as its effects on the expression of genes responsible for epigenetic changes, in mouse skeletal myoblasts (C2C12 cells). Methods: The results showed significantly reduced maximal respiration and spare respiratory capacity under heat stress (39 °C and 41 °C), suggesting that mitochondrial functions were compromised under these conditions. The glycolytic capacity and glycolysis markedly increased following low-temperature stress (35 °C). The results suggested that, under cold stress, cells prefer glycolysis as a rapid compensatory mechanism to meet energy requirements for adaptive thermogenic response. Results: Epigenetic changes (histone H4 acetylation and global DNA methylation) were observed under both heat and cold stress. Among the genes coding for DNA methyltransferases, the Dnmt3a was significantly increased under high-temperature conditions (39 °C and 41 °C), while Dnmt1 expression was significantly increased at low temperature (35 °C), indicating that under these conditions the cells preferred maintenance of methylation to de novo methylation activity. An expression pattern similar to Dnmt3a was observed for Gcn5, encoding for a histone acetyltransferase. The study revealed that temperature stress induced changes in the metabolic profiles, as well as epigenetic modifications, including the dynamics of the key enzymes. Conclusion: The results indicated the existence of crosstalk mechanisms between energy metabolism and epigenetics during cell stress response.

Early life thermal stress: Impact on future thermotolerance, stress response, behavior, and intestinal morphology in piglets exposed to a heat stress challenge during simulated transport

Study objectives were to evaluate the impact of early life thermal stress (ELTS) on thermoregulation, stress response, and intestinal health of piglets subjected to a future heat stress (HS) challenge during simulated transport. From d 7 to 9 post-farrowing, 12 first-parity sows and their litters were exposed to thermoneutral (ELTN; 25.4 ± 1.1 °C w/heat lamp; n = 4), HS (ELHS; cycling 32-38 °C w/heat lamp; n = 4), or cold stress (ELCS; 25.4 ± 1.1 °C w/no heat lamp; n = 4) conditions, and then from d 10 until weaning all piglets were exposed to thermoneutral (TN) conditions (25.3 ± 1.9 °C w/heat lamp). During the ELTS period, respiration rate, rectal temperature (TR), and skin temperature (TS) of three mixed-sex piglets per dam were monitored daily (0800, 1200, 1600, 2000 h). At 13 ± 1.3 d of age, temperature recorders were implanted intra-abdominally into all piglets. At weaning (20.0 ± 1.3 d of age), piglets were bled and then herded up a ramp into a simulated transport trailer and exposed to HS conditions (cycling 32-38 °C) for 8 h. During the 8 h simulated transport, core body temperature (TC) and TS were assessed every 15 min. After the simulated transport, piglets were unloaded from the trailer, bled, weighed, and then housed individually in TN conditions (28.5 ± 0.7 °C) for 7 d. During this time, ADFI and ADG were monitored, blood samples were taken on d 1, 4, and 7, and piglets were video-recorded to assess behavior. Piglets were sacrificed on d 8 post-simulated transport and intestinal morphology was assessed. Data were analyzed using PROC MIXED in SAS 9.4. In the ELTS period, piglet TR was increased overall (P = 0.01) in ELHS (39.77 ± 0.05 °C) compared to ELTN (39.34 ± 0.05 °C) and ELCS (39.40 ± 0.05 °C) litters. During simulated transport, TC was greater (P = 0.02) in ELHS (40.84 ± 0.12 °C) compared to ELTN (40.49 ± 0.12 °C) and ELCS (40.39 ± 0.12 °C) pigs. Following simulated transport, BW loss was greater (P = 0.01; 40%) for ELHS compared to ELTN and ELCS pigs and ADFI was reduced (P = 0.05; 28.6%) in ELHS compared to ELTN pigs. Sitting behavior tended to be increased (P = 0.06; 47.4%) in ELHS vs. ELCS or ELTN pigs. Overall, circulating cortisol was greater for ELHS (P ≤ 0.01; 38.8%) compared to ELCS and ELTN pigs. Goblet cells per villi were reduced (P = 0.02; 20%) in the jejunum of ELHS vs. ELCS and ELTN pigs. In summary, ELHS reduced thermotolerance and increased the future stress response of piglets compared to ELCS and ELTN.

Maximizing Cellular Adaptation to Endurance Exercise in Skeletal Muscle

The application of molecular techniques to exercise biology has provided novel insight into the complexity and breadth of intracellular signaling networks involved in response to endurance-based exercise. Here we discuss several strategies that have high uptake by athletes and, on mechanistic grounds, have the potential to promote cellular adaptation to endurance training in skeletal muscle. Such approaches are based on the underlying premise that imposing a greater metabolic load and provoking extreme perturbations in cellular homeostasis will augment acute exercise responses that, when repeated over months and years, will amplify training adaptation.

Heat Acclimatization Protects the Left Ventricle from Increased Diastolic Chamber Stiffness Immediately after Coronary Artery Bypass Surgery: A Lesson from 30 Years of Studies on Heat Acclimation Mediated Cross Tolerance

During the period of 1986–1997 the first 4 publications on the mechanical and metabolic properties of heat acclimated rat's heart were published. The outcome of these studies implied that heat acclimation, sedentary as well as combined with exercise training, confers long lasting protection against ischemic/reperfusion insult. These results promoted a clinical study on patients with coronary artery disease scheduled for elective coronary artery bypass operations aiming to elucidate whether exploitation of environmental stress can be translated into human benefits by improving physiological recovery. During the 1998 study, immediate-post operative chamber stiffness was assessed in patients acclimatized to heat and low intensity training in the desert (spring in the Dead Sea, 17–33°C) vs. patients in colder weather (spring in non-desert areas, 6–19°C) via echocardiogram acquisition simultaneous with left atrial pressure measurement during fast intravascular fluid bolus administration. We showed that patients undergoing “heat acclimatization combined with exercise training” were less susceptible to ischemic injury, therefore expressing less diastolic dysfunction after cardiopulmonary bypass compared to non-acclimatized patients. This was the first clinical translational study on cardiac patients, while exploiting environmental harsh conditions for human benefits. The original experimental data are described and discussed in view of the past as well as the present knowledge of the protective mechanisms induced by Heat Acclimation Mediated Cross-tolerance.

Heat Acclimation-Mediated Cross-Tolerance: Origins in within-Life Epigenetics?

The primary outcome of heat acclimation is increased thermotolerance, which stems from enhancement of innate cytoprotective pathways. These pathways produce “ON CALL” molecules that can combat stressors to which the body has never been exposed, via cross-tolerance mechanisms (heat acclimation-mediated cross-tolerance—HACT). The foundation of HACT lies in the sharing of generic stress signaling, combined with tissue/organ- specific protective responses. HACT becomes apparent when acclimatory homeostasis is achieved, lasts for several weeks, and has a memory. HACT differs from other forms of temporal protective mechanisms activated by exposure to lower “doses” of the stressor, which induce adaptation to higher “doses” of the same/different stressor; e.g., preconditioning, hormesis. These terms have been adopted by biochemists, toxicologists, and physiologists to describe the rapid cellular strategies ensuring homeostasis. HACT employs two major protective avenues: constitutive injury attenuation and abrupt post-insult release of help signals enhanced by acclimation. To date, the injury-attenuating features seen in all organs studied include fast-responding, enlarged cytoprotective reserves with HSPs, anti-oxidative, anti-apoptotic molecules, and HIF-1α nuclear and mitochondrial target gene products. Using cardiac ischemia and brain hypoxia models as a guide to the broader framework of phenotypic plasticity, HACT is enabled by a metabolic shift induced by HIF-1α and there are less injuries caused by Ca⁺² overload, via channel or complex-protein remodeling, or decreased channel abundance. Epigenetic markers such as post-translational histone modification and altered levels of chromatin modifiers during acclimation and its decline suggest that dynamic epigenetic mechanisms controlling gene expression induce HACT and acclimation memory, to enable the rapid return of the protected phenotype. In this review the link between in vivo physiological evidence and the associated cellular and molecular mechanisms leading to HACT and its difference from short-acting cross-tolerance strategies will be discussed.

In utero heat stress increases postnatal core body temperature in pigs

In utero heat stress (IUHS) negatively impacts postnatal development, but how it alters future body temperature parameters and energetic metabolism is not well understood. Future body temperature indices and bioenergetic markers were characterized in pigs from differing in utero thermal environments during postnatal thermoneutral (TN) and cyclical heat stress (HS) exposure. First-parity pregnant gilts ( = 13) were exposed to 1 of 4 ambient temperature (T) treatments (HS [cyclic 28°C to 34°C] or TN [cyclic 18°C to 22°C]) applied for the entire gestation (HSHS, TNTN), HS for the first half of gestation (HSTN), or HS for the second half of gestation (TNHS). Twenty-four offspring (23.1 ± 1.2 kg BW; = 6 HSHS, = 6 TNTN, = 6 HSTN, = 6 TNHS) were housed in TN (21.7°C ± 0.7°C) conditions and then exposed to 2 separate but similar HS periods (HS1 = 6 d; HS2 = 6 d; cycling 28°C to 36°C). Core body temperature (T) was assessed every 15 min with implanted temperature recorders. Regardless of in utero treatment, T increased during both HS periods ( = 0.01; 0.58°C). During TN, HS1, and HS2, all IUHS pigs combined had increased T ( = 0.01; 0.36°C, 0.20°C, and 0.16°C, respectively) compared to TNTN controls. Although unaffected by in utero environment, the total plasma thyroxine to triiodothyronine ratio was reduced ( = 0.01) during HS1 and HS2 (39% and 29%, respectively) compared with TN. In summary, pigs from IUHS maintained an increased T compared with TNTN controls regardless of external T, and this thermal differential may have practical implications to developmental biology and animal bioenergetics.

Genomic analysis of Ugandan and Rwandan chicken ecotypes using a 600 k genotyping array

Background

Indigenous populations of animals have developed unique adaptations to their local environments, which may include factors such as response to thermal stress, drought, pathogens and suboptimal nutrition. The survival and subsequent evolution within these local environments can be the result of both natural and artificial selection driving the acquisition of favorable traits, which over time leave genomic signatures in a population. This study’s goals are to characterize genomic diversity and identify selection signatures in chickens from equatorial Africa to identify genomic regions that may confer adaptive advantages of these ecotypes to their environments.

Results

Indigenous chickens from Uganda (n = 72) and Rwanda (n = 100), plus Kuroilers (n = 24, an Indian breed imported to Africa), were genotyped using the Axiom® 600 k Chicken Genotyping Array. Indigenous ecotypes were defined based upon location of sampling within Africa. The results revealed the presence of admixture among the Ugandan, Rwandan, and Kuroiler populations. Genes within runs of homozygosity consensus regions are linked to gene ontology (GO) terms related to lipid metabolism, immune functions and stress-mediated responses (FDR < 0.15). The genes within regions of signatures of selection are enriched for GO terms related to health and oxidative stress processes. Key genes in these regions had anti-oxidant, apoptosis, and inflammation functions.

Conclusions

The study suggests that these populations have alleles under selective pressure from their environment, which may aid in adaptation to harsh environments. The correspondence in gene ontology terms connected to stress-mediated processes across the populations could be related to the similarity of environments or an artifact of the detected admixture.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2711-5) contains supplementary material, which is available to authorized users.

Epigenetics and cytoprotection with heat acclimation

Studying “phenotypic plasticity” involves comparison of traits expressed in response to environmental fluctuations and aims to understand tolerance and survival in new settings. Reversible phenotypic changes that enable individuals to match their phenotype to environmental demands throughout life can be artificially induced, i.e., acclimation or occur naturally, i.e., acclimatization. The onset and achievement of acclimatory homeostasis are determined by molecular programs that induce the acclimated transcriptome. In heat acclimation, much evidence suggests that epigenetic mechanisms are powerful players in these processes. Epigenetic mechanisms affect the accessibility of the DNA to transcription factors, thereby regulating gene expression and controlling the phenotype. The heat-acclimated phenotype confers cytoprotection against novel stressors via cross-tolerance mechanisms, by attenuation of the initial damage and/or by accelerating spontaneous recovery through the release of help signals. This indispensable acclimatory feature has a memory and can be rapidly reestablished after the loss of acclimation and the return to the physiological preacclimated phenotype. The transcriptional landscape of the deacclimated phenotype includes constitutive transcriptional activation of epigenetic bookmarks. Heat shock protein (HSP) 70/HSP90/heat shock factor 1 memory protocol demonstrated constitutive histone H4 acetylation on hsp70 and hsp90 promotors. Novel players in the heat acclimation setup are poly(ADP-ribose)ribose polymerase 1 affecting chromatin condensation, DNA linker histones from the histone H1 cluster, and transcription factors associated with the P38 pathway. We suggest that these orchestrated responses maintain euchromatin and proteostasis during deacclimation and predispose to rapid reacclimation and cytoprotection. These mechanisms represent within-life epigenetic adaptations and cytoprotective memory.

Heat shock protein 70 induction by glutamine increases the α-synuclein degradation in SH-SY5Y neuroblastoma cells

Functional defects in heat shock proteins (HSPs), e.g. Hsp70, have been reported to have a key role in Parkinson's disease (PD). Overexpressed Hsp70 re‑folds aggregated α‑synuclein to generate the non‑toxic and non‑aggregated form. Thus, Hsp70 is a well‑defined therapeutic target, and Hsp70 promotion is an efficient strategy to prevent or even reverse the α‑synuclein‑induced toxicity in PD. The present study investigated the promotion of Hsp70 expression in SH‑SY5Y neuroblastoma cells by glutamine (Gln), which has recently been recognized to induce Hsp70 expression. Furthermore, the role of heat shock factor (HSF)‑1 in the Gln‑mediated upregulation of Hsp70 expression was investigated. In addition, the regulatory role of Gln in α‑synuclein degradation in α‑synuclein‑overexpressing SH‑SY5Y cells was determined. The results of the present study demonstrated that Gln treatment significantly upregulated Hsp70 expression at the mRNA as well as the protein level in a dose‑dependent and time‑dependent manner. Gln‑induced Hsp70 upregulation was found to be HSF‑1‑dependent, as HSF‑1 knockdown abrogated the Hsp70 upregulation by Gln in α‑synuclein‑overexpressing SH‑SY5Y cells. In conclusion, present study confirmed that Gln upregulates Hsp70 expression in SH‑SY5Y neuroblastoma cells in an HSF‑1‑dependent manner. The upregulation of Hsp70 by Gln increases the α‑synuclein degradation. Therefore, Gln may be a potential therapeutic agent to prevent α‑synuclein aggregation in PD.

Physiological consequences of heat stress in pigs

Heat stress negatively influences the global pork industry and undermines genetic, nutritional, management and pharmaceutical advances in management, feed and reproductive efficiency. Specifically, heat stress-induced economic losses result from poor sow performance, reduced and inconsistent growth, decreased carcass quality, mortality, morbidity, and processing issues caused by less rigid adipose tissue (also known as flimsy fat). When environmental conditions exceed the pig’s thermal neutral zone, nutrients are diverted from product synthesis (meat, fetus, milk) to body temperature maintenance thereby compromising efficiency. Unfortunately, genetic selection for both increased litter size and leaner phenotypes decreases pigs’ tolerance to heat, as enhanced fetal development and protein accretion results in increased basal heat production. Additionally, research has demonstrated that in utero heat stress negatively and permanently alters post-natal body temperature and body composition and both variables represent an underappreciated consequence of heat stress. Advances in management (i.e. cooling systems) have partially alleviated the negative impacts of heat stress, but productivity continues to decline during the warm summer months. The detrimental effects of heat stress on animal welfare and production will likely become more of an issue in regions most affected by continued predictions for climate change, with some models forecasting extreme summer conditions in key animal-producing areas of the globe. Therefore, heat stress is likely one of the primary factors limiting profitable animal protein production and will certainly continue to compromise food security (especially in emerging countries) and regionalise pork production in developed countries. Thus, there is an urgent need to have a better understanding of how heat stress reduces animal productivity. Defining the biology of how heat stress jeopardises animal performance is critical in developing approaches (genetic, managerial, nutritional and pharmaceutical) to ameliorate current production issues and improve animal wellbeing and performance.

Gestational heat stress alters postnatal offspring body composition indices and metabolic parameters in pigs

The study objectives were to test the hypothesis that heat stress (HS) during gestational development alters postnatal growth, body composition, and biological response to HS conditions in pigs. To investigate this, 14 first parity crossbred gilts were exposed to one of four environmental treatments (TNTN, TNHS, HSTN, or HSHS) during gestation. TNTN and HSHS dams were exposed to thermal neutral (TN, cyclical 18-22°C) or HS conditions (cyclical 28-34°C) during the entire gestation, respectively. Dams assigned to HSTN and TNHS treatments were heat-stressed for the first or second half of gestation, respectively. Postnatal offspring were exposed to one of two thermal environments for an acute (24 h) or chronic (five weeks) duration in either constant TN (21°C) or HS (35°C) environment. Exposure to chronic HS during their growth phase resulted in decreased longissimus dorsi cross-sectional area (LDA) in offspring from HSHS and HSTN treated dams whereas LDA was larger in offspring from dams in TNTN and TNHS conditions. Irrespective of HS during prepubertal postnatal growth, pigs from dams that experienced HS during the first half of gestation (HSHS and HSTN) had increased (13.9%) subcutaneous fat thickness compared to pigs from dams exposed to TN conditions during the first half of gestation. This metabolic repartitioning towards increased fat deposition in pigs from dams heat-stressed during the first half of gestation was accompanied by elevated blood insulin concentrations (33%; P = 0.01). Together, these results demonstrate HS during the first half of gestation altered metabolic and body composition parameters during future development and in biological responses to a subsequent HS challenge.

Heat acclimation memory: do the kinetics of the deacclimated transcriptome predispose to rapid reacclimation and cytoprotection?

Faster reinduction of heat acclimation (AC) after its decline indicates "AC memory." Our previous results revealed involvement of epigenetic mechanisms of transcriptional regulation. We hypothesized that the decline of AC (DeAC) is a period of "dormant memory" during which many processes are alerted to enable rapid reacclimation (ReAC). Using a genomewide approach we studied the AC, DeAC, and ReAC transcriptomes, to uncover hallmark pathways linked to "molecular memory" in the cardioacclimatome. Fifty rats subjected to heat acclimation [34°C for 2d (AC2d) or 30d (AC30)], DeAC (24°C, 30 days), ReAC (34°C, 2 days), and untreated controls were used. The GeneChip Rat Gene 1.0 ST Array was employed for left ventricular (cardiac) mRNA hybridization. Three independent bioinformatic analyses showed that 1) during AC2d enrichment of DNA impair/repair-linked genes is seen, and this is the molecular on-switch of acclimation; 2) genes activated in AC30 underlie the qualitative physiological adaptations of cardiac performance; 3) particular molecular programs encompassing constitutive upregulation of p38 MAPK, Jak/Stat, and Akt pathways and targets are specifically activated during DeAC and ReAC; and 4) epigenetic markers such as linker histones (histones H1 cluster), associated with nucleosome spacing, transcriptional chromatin modifiers, poly-(ADP-ribose) polymerase-1 (PARP1) linked to chromatin compaction, and microRNAs are only altered during DeAC/ReAC. The latter are newcomers to the AC/DeAC puzzle. We suggest that these transcriptional responses maintain euchromatin and proteostasis and enable faster physiological recovery upon ReAC by rapidly reestablishing the protected acclimated cardiophenotype. We propose that the cardiac AC model can be applied to acclimation processes in general.

Two years of combined high-intensity physical training and heat acclimatization affect lymphocyte and serum HSP70 in purebred military working dogs

Military working dogs in hot countries undergo exercise training at high ambient temperatures for at least 9 mo annually. Physiological adaptations to these harsh conditions have been extensively studied; however, studies focusing on the underlying molecular adaptations are limited. In the current study, military working dogs were chosen as a model to examine the effects of superimposing endurance exercise on seasonal acclimatization to environmental heat stress. The lymphocyte HSP70 profile and extracellular HSP70 were studied in tandem with physiological performance in the dogs from their recruitment for the following 2 yr. Aerobic power and heat shock proteins were measured at the end of each summer, with physical performance tests (PPTs) in an acclimatized room (22°C). The study shows that together with a profound enhancement of aerobic power and physical performance, hsp72 mRNA induction immediately post-PPT and 45 min later, progressively increased throughout the study period (relative change in median lymphocyte hsp72 mRNA first PPT, 4.22 and 12.82; second PPT, 17.19 and 109.05, respectively), whereas induction of HSP72 protein was stable. These responses suggest that cellular/molecular adaptive tools for maintaining HSP72 homeostasis exist. There was also a significant rise in basal and peak median optical density extracellular HSP at the end of each exercise test (first PPT, 0.13 and 0.15; second PPT, 1.04 and 1.52, respectively). The relationship between these enhancements and improved aerobic power capacity is not yet fully understood.

Effects of mammalian in utero heat stress on adolescent body temperature

In utero hyperthermia can cause a variety of developmental issues, but how it alters mammalian body temperature during adolescence is not well-understood. Study objectives were to determine the extent to which in utero hyperthermia affects future phenotypic responses to a heat load. Pregnant first parity pigs were exposed to thermal neutral (TN) or heat stress (HS) conditions during the entire gestation. Of the resultant offspring, 12 were housed in TN conditions, and 12 were maintained in HS conditions for 15 days. Adolescent pigs in HS conditions had increased rectal temperature and respiration rate (RR) compared to TN pigs, regardless of gestational treatment. Within the HS environment, no gestational difference in RR was detected; however, GHS pigs had increased rectal temperature compared to GTN pigs. As rectal temperature increased, GTN pigs had a more rapid increase in RR compared to the GHS pigs. Adolescent HS decreased nutrient intake, and body weight gain, but neither variable was statistically influenced by gestational treatments. In summary, in utero HS compromises the future thermoregulatory response to a thermal insult.

Proteomic profiling of thermal acclimation in Drosophila melanogaster

Thermal acclimation drastically alters thermotolerance of ectotherms, but the mechanisms determining this plastic response are not fully understood. The present study investigates the proteomic response (2D-DIGE) of adult Drosophila melanogaster acclimated at 11, 25 or 31 °C. As expected 11 °C-acclimation improved cold tolerance and 31 °C-acclimation improved heat tolerance. We hypothesized that the marked organismal responses to acclimation could be detected at the proteomic level assuming that changes in the abundance of specific proteins are linked to the physiological changes underlying the phenotypic response. The 31 °C-acclimated flies displayed a particular divergent proteomic profile where molecular chaperones made up a large number of the proteins that were modulated during heat acclimation. Many other proteins showed significant modulation during acclimation including proteins involved in iron ion and cell redox homeostasis, carbohydrate and energy metabolism, chromatin remodeling and translation, and contractile machinery. Interestingly the changes in protein abundance were often unrelated to transcriptional activity of the genes coding for the proteins, except for the most strongly expressed proteins (e.g. Hsp70). The 11 °C-acclimation evoked weak proteomic response despite the marked effect on the organismal phenotype. Thus the acquired cold tolerance observed here may involve regulatory process such as posttranslational regulation rather than de novo protein synthesis.

Is the interplay between epigenetic markers related to the acclimation of cork oak plants to high temperatures?

Trees necessarily experience changes in temperature, requiring efficient short-term strategies that become crucial in environmental change adaptability. DNA methylation and histone posttranslational modifications have been shown to play a key role in both epigenetic control and plant functional status under stress by controlling the functional state of chromatin and gene expression. Cork oak (Quercus suber L.) is a key stone of the Mediterranean region, growing at temperatures of 45°C. This species was subjected to a cumulative temperature increase from 25°C to 55°C under laboratory conditions in order to test the hypothesis that epigenetic code is related to heat stress tolerance. Electrolyte leakage increased after 35°C, but all plants survived to 55°C. DNA methylation and acetylated histone H3 (AcH3) levels were monitored by HPCE (high performance capillary electrophoresis), MS-RAPD (methylation-sensitive random-amplified polymorphic DNA) and Protein Gel Blot analysis and the spatial distribution of the modifications was assessed using a confocal microscope. DNA methylation analysed by HPCE revealed an increase at 55°C, while MS-RAPD results pointed to dynamic methylation-demethylation patterns over stress. Protein Gel Blot showed the abundance index of AcH3 decreasing from 25°C to 45°C. The immunohistochemical detection of 5-mC (5-methyl-2′-deoxycytidine) and AcH3 came upon the previous results. These results indicate that epigenetic mechanisms such as DNA methylation and histone H3 acetylation have opposite and particular dynamics that can be crucial for the stepwise establishment of this species into such high stress (55°C), allowing its acclimation and survival. This is the first report that assesses epigenetic regulation in order to investigate heat tolerance in forest trees.

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.

Conformational temperature-dependent behavior of a histone H2AX: a coarse-grained Monte Carlo approach via knowledge-based interaction potentials

Histone proteins are not only important due to their vital role in cellular processes such as DNA compaction, replication and repair but also show intriguing structural properties that might be exploited for bioengineering purposes such as the development of nano-materials. Based on their biological and technological implications, it is interesting to investigate the structural properties of proteins as a function of temperature. In this work, we study the spatial response dynamics of the histone H2AX, consisting of 143 residues, by a coarse-grained bond fluctuating model for a broad range of normalized temperatures. A knowledge-based interaction matrix is used as input for the residue-residue Lennard-Jones potential.We find a variety of equilibrium structures including global globular configurations at low normalized temperature (T* = 0.014), combination of segmental globules and elongated chains (T* = 0.016,0.017), predominantly elongated chains (T* = 0.019,0.020), as well as universal SAW conformations at high normalized temperature (T* ≥ 0.023). The radius of gyration of the protein exhibits a non-monotonic temperature dependence with a maximum at a characteristic temperature (T(c)* = 0.019) where a crossover occurs from a positive (stretching at T* ≤ T(c)*) to negative (contraction at T* ≥ T(c)*) thermal response on increasing T*.

Regulation of survival gene hsp70

Rapid expression of the survival gene, inducible heat shock protein 70 (hsp70), is critical for mounting cytoprotection against severe cellular stress, like elevated temperature. Hsp70 protein chaperones the refolding of heat-denatured peptides to minimize proteolytic degradation as a part of an eukaryotically conserved phenomenon referred to as the heat shock response. The physiologic stress associated with exercise, which can include elevated temperature, mechanical damage, hypoxia, lowered pH, and reactive oxygen species generation, may promote protein unfolding, leading to hsp70 gene expression in skeletal myofibers. Although the pre-transcriptional activation of hsp70 gene expression has been thoroughly reviewed, discussion of downstream hsp70 gene regulation is less extensive. The purpose of this brief review was to examine all levels of hsp70 gene regulation in response to heat stress and exercise with a special focus on skeletal myofibers where data are available. In general, while heat stress represses bulk gene expression, hsp70 mRNA expression is enhanced. Post-transcriptionally, intronless hsp70 mRNA circumvents a host of decay pathways, as well as heat stress-repressed pre-mRNA splicing and nuclear export. Pre-translationally, hsp70 mRNA is excluded from stress granules and preferentially translated during heat stress-repressed global cap-dependent translation. Post-translationally, nascent Hsp70 protein is thermodynamically stable at elevated temperatures, allowing for the commencement of chaperoning activity early after synthesis to attenuate the heat shock response and protect against subsequent injury. This review demonstrates that hsp70 mRNA expression is closely coupled with functional protein translation.

Heat acclimation and exercise training interact when combined in an overriding and trade-off manner: physiologic-genomic linkage

Combined heat acclimation (AC) and exercise training (EX) enhance exercise performance in the heat while meeting thermoregulatory demands. We tested the hypothesis that different stress-specific adaptations evoked by each stressor individually trigger similar cardiac alterations, but when combined, overriding/trade-off interactions take place. We used echocardiography, isolated cardiomyocyte imaging and cDNA microarray techniques to assay in situ cardiac performance, excitation-contraction (EC) coupling features, and transcriptional programs associated with cardiac contractility. Rat groups studied were controls (sedentary 24°C); AC (sedentary, 34°C, 1 mo); normothermic EX (treadmill at 24°C, 1 mo); and heat-acclimated, exercise-trained (EXAC; treadmill at 34°C, 1 mo). Prolonged heat exposure decreased heart rate and contractile velocity and increased end ventricular diastolic diameter. Compared with controls, AC/EXAC cardiomyocytes demonstrated lower l-type Ca(2+) current (I(CaL)) amplitude, higher Ca(2+) transient (Ca(2+)T), and a greater Ca(2+)T-to-I(CaL) ratio; EX alone enhanced I(CaL) and Ca(2+)T, whereas aerobic training in general induced cardiac hypertrophy and action potential elongation in EX/EXAC animals. At the genomic level, the transcriptome profile indicated that the interaction between AC and EX yields an EXAC-specific molecular program. Genes affected by chronic heat were linked with the EC coupling cascade, whereas aerobic training upregulated genes involved with Ca(2+) turnover via an adrenergic/metabolic-driven positive inotropic response. In the EXAC cardiac phenotype, the impact of chronic heat overrides that of EX on EC coupling components and heart rate, whereas EX regulates cardiac morphometry. We suggest that concerted adjustments induced by AC and EX lead to enhanced metabolic and mechanical performance of the EXAC heart.