Heat Tolerance Research Articles

A Look at Genomic Selection Techniques for Climate Change Adaptation and Production in Livestock

Livestock production profoundly intersects with global climate dynamics, contributing to greenhouse gas emissions and confronting vulnerability to climate impacts. In addressing these challenges, imperative adjustments are requisite to fortify the climate robustness of livestock systems. Notably, the prevalent reliance on commercial breeds with limited genetic diversity exposes production strategies to disruption, especially if these breeds are confined to environments that may lose economic viability under future climate scenarios. Consequently, understanding the adaptability of animal populations to forthcoming environmental conditions is paramount for sustaining livestock production. Assessing the genetic underpinnings of climate adaptation necessitates the exploration of tailored genomic selection techniques encompassing both production traits, presumed to have moderate heritability, and adaptation traits, presumed to have low heritability. Through a nuanced examination of genomic selection dynamics, insights into the genetic mechanisms fostering resilience in livestock populations amidst shifting environmental contexts are garnered. Employ genomic analysis to pinpoint genetic markers associated with traits like heat tolerance, disease resistance, and feed efficiency in livestock. Collaborate across disciplines to develop tailored breeding programs integrating these markers, and validate their effectiveness through rigorous field trials and ongoing monitoring to enhance livestock resilience and productivity in varied climatic conditions. Elucidating these mechanisms and their application in breeding programs offers a comprehensive understanding of how genetic advancements can enhance both production efficiency and climate resilience in livestock. This discourse aims to bridge the chasm between scientific inquiry and pragmatic implementation, thereby facilitating informed decision-making in livestock breeding strategies tailored to mitigate the ramifications of climate change.

Pollution offsets the rapid evolution of increased heat tolerance in a natural population

Despite the increasing evidence for rapid thermal evolution in natural populations, evolutionary rescue under global warming may be constrained by the presence of other stressors. Highly relevant in our polluted planet, is the largely ignored evolutionary trade-off between heat tolerance and tolerance to pollutants. By using two subpopulations (separated 40 years in time) from a resurrected natural population of the water flea Daphnia magna that experienced a threefold increase in heat wave frequency during this period, we tested whether rapid evolution of heat tolerance resulted in reduced tolerance to the widespread metal zinc and whether this would affect heat tolerance upon exposure to the pollutant. Our results revealed rapid evolution of increased heat tolerance in the recent subpopulation. Notably, the sensitivity to the metal tended to be stronger (reduction in net energy budget) or was only present (reductions in heat tolerance and in sugar content) in the recent subpopulation. As a result, the rapidly evolved higher heat tolerance of the recent subpopulation was fully offset when exposed to zinc. Our results highlight that the many reports of evolutionary rescue to global change stressors may give a too optimistic view as our warming planet is polluted by metals and other pollutants.

Selective sweep analysis of the adaptability of the Yarkand hare (Lepus yarkandensis) to hot arid environments using SLAF-seq.

The Yarkand hare (Lepus yarkandensis) inhabits arid desert areas and is endemic to China. It has evolved various adaptations to survive in hot arid environments, including stress responses, the ability to maintain water homeostasis and heat tolerance. Here, we performed a selective sweep analysis to identify the candidate genes for adaptation to hot arid environments in the Yarkand hare. A total of 397 237 single-nucleotide polymorphisms were obtained from 80 Yarkand hares, which inhabit hot arid environments, and 36 Tolai hares (Lepus tolai), which inhabit environments with a mild climate, via specific-locus amplified fragment sequencing. We identified several candidate genes that were associated with the heat stress response (HSPE1), oxidative stress response (SLC23A and GLRX2), immune response (IL1R1 and IRG1), central nervous system development (FGF13, THOC2, FMR1 and MECP2) and regulation of water homeostasis (CDK1) according to fixation index values and θπ ratios in the selective sweep analysis, and six of these genes (GLRX2, IRG1, FGF13, FMR1, MECP2 and CDK1) are newly discovered genes. To the best of our knowledge, this is the first study to identify candidate genes for adaptation to hot arid environments in the Yarkand hare. The results of this study enhance our understanding of the adaptation of the Yarkand hare to hot arid environments and will aid future studies aiming to functionally verify these candidate genes.

Exploring the genetic control of sweat gland characteristics in beef cattle for enhanced heat tolerance

BackgroundThermal stress in subtropical regions is a major limiting factor in beef cattle production systems with around $369 million being lost annually due to reduced performance. Heat stress causes numerous physiological and behavioral disturbances including reduced feed intake and decreased production levels. Cattle utilize various physiological mechanisms such as sweating to regulate internal heat. Variation in these traits can help identify genetic variants that control sweat gland properties and subsequently allow for genetic selection of cattle with greater thermotolerance.MethodsThis study used 2,401 Brangus cattle from two commercial ranches in Florida. Precise phenotypes that contribute to an animal’s ability to manage heat stress were calculated from skin biopsies and included sweat gland area, sweat gland depth, and sweat gland length. All animals were genotyped with the Bovine GGP F250K, and BLUPF90 software was used to estimate genetic parameters and for Genome Wide Association Study.ResultsSweat gland phenotypes heritability ranged from 0.17 to 0.42 indicating a moderate amount of the phenotypic variation is due to genetics, allowing producers the ability to select for favorable sweat gland properties. A weighted single-step GWAS using sliding 10 kb windows identified multiple quantitative trait loci (QTLs) explaining a significant amount of genetic variation. QTLs located on BTA7 and BTA12 explained over 1.0% of genetic variance and overlap the ADGRV1 and CCDC168 genes, respectively. The variants identified in this study are implicated in processes related to immune function and cellular proliferation which could be relevant to heat management. Breed of Origin Alleles (BOA) were predicted using local ancestry in admixed populations (LAMP-LD), allowing for identification of markers’ origin from either Brahman or Angus ancestry. A BOA GWAS was performed to identify regions inherited from particular ancestral breeds that might have a significant impact on sweat gland phenotypes.ConclusionsThe results of the BOA GWAS indicate that both Brahman and Angus alleles contribute positively to sweat gland traits, as evidenced by favorable marker effects observed from both genetic backgrounds. Understanding and utilizing genetic traits that confer better heat tolerance is a proactive approach to managing the impacts of climate change on livestock farming.

Functional transcriptome analysis revealed upregulation of MAPK-SMAD signalling pathways in chronic heat stress in crossbred cattle.

Animal geneticists and breeders have the impending challenge of enhancing the resilience of Indian livestock to heat stress through better selection strategies. Climate change's impact on livestock is more intense in tropical countries like India where dairy cattle crossbreeds are more sensitive to heat stress. The main reason for this study was to find the missing relative changes in transcript levels in thermo-neutral and heat stress conditions in crossbred cattle through whole-transcriptome analysis of RNA-Seq data. Differentially expressed genes (DEGs) identified based on the minimum log twofold change value and false discovery rate 0.05 revealed 468 up-regulated genes and 2273 down-regulated significant genes. Functional annotation and pathway analysis of these significant DEGs were compared based on Gene Ontology (Biological process), Kyoto Encyclopedia of Genes and Genome (KEGG), and Reactome pathways using g: Profiler, ShinyGO v0.76, and iDEP.951 web tools. On finding network visualization, the most over-represented and correlated pathways were neuronal and sensory organ development, calcium signalling pathway, Mitogen-activated protein kinase (MAPK) and Smad signalling pathway, Ras-proximate-1, or Ras-related protein 1 (Rap 1) signalling pathway, apoptosis, and oxidative stress. Similarly, down-regulated genes were most expressed in mRNA processing, immune system, B-cell receptor signalling pathway, Nucleotide oligomerization domain(NOD)-like receptors (NLRs) signalling pathway and nonsense-mediated decay (NMD) pathway. The heat stress-responsive genes identified in this study will facilitate our understanding of the molecular basis for climate resilience and heat tolerance in Indian dairy crossbreeds.

Egg yolk peptide‐iron chelate: preparation, conformational structure, chelating mechanism and stability in vitro

SummaryIn this study, a method to produce iron‐chelating peptides derived from egg yolk proteins was developed and optimised. The egg yolk proteins were enzymolysed and ultrafiltered to prepare egg yolk peptide (EYP), and then the EYP was chelated with Fe to produce egg yolk peptide‐Fe (EYP‐Fe). The optimised mass ratio of peptide to iron, pH, temperature and reaction time were found at 8:1, pH 8.0, 40 °C and 30 min, respectively. The mean particle size of EYP‐Fe was 389.2 ± 2.61 nm, and the chelating ratio was 95.38 ± 1.93%. The measurements of FTIR, X‐ray photoelectron spectroscopy (XPS) and NMR showed that ferrous ions mainly combined with the amino and carboxyl of EYP to form EYP‐Fe. In vitro stability studies have shown that the iron release rate of the EYP‐Fe is maintained at around 5% under alkaline conditions, and there is no significant difference in iron release rate under conditions of 30 °C–80 °C; besides, it has a lower iron release rate (18%) in gastrointestinal digestion compared to FeSO4 (97.93%), indicating that the EYP‐Fe has good heat tolerance, alkalinity and digestion tolerance. The above results provide a scientific basis for the use of EYP‐Fe derived from egg yolk protein as a potential alternative to iron supplements.

Proposing a strategy based on body-thermal status to improve the welfare of heat-stressed and water-deprived goats (Capra hircus).

Despite the considerable body of research on the effects of heat stress coupled with water scarcity (either through restriction or deprivation) on goats, aimed at enhancing their welfare, there remains a notable gap in the literature regarding the subsequent period following water restoration, during which the cumulative impact is fully alleviated. In response to this gap, we propose a strategy grounded in the assessment of body-thermal status to improve the welfare of heat-stressed and water-deprived goats. Specifically, our strategy seeks to determine the minimally required recovery interval necessary to completely mitigate the residual effects of water deprivation endured for a duration of 72 hours. Eight healthy Aardi bucks, aged 10 months and weighing 30 kg, were subjected to three distinct stages: euhydration, dehydration, and rehydration. Each stage spanned for 72 hours except for the rehydration stage, which was left unrestricted. Various meteorological, biophysiological, and thermophysiological measurements were subsequently recorded. Exposure of heat-stressed goats, as indicated by the temperature-humidity index values, to a 72 hours deprivation period resulted in noticeable (p<0.05) alterations in their biophysiological (daily feed intake, body weight, and feces water content) and thermophysiological responses (core, rectal, skin, and surface temperatures, respiratory and heart rates, internal, external, and total body-thermal gradients, heat tolerance and adaptability coefficients, heterothermial total body-heat storage, and total water conservation). Remarkably, our findings demonstrate that all assessed variables, whether measured or estimated, returned to their baseline euhydration levels within 10 days of commencing the rehydration phase. In order to improve the welfare of heat-stressed and 72 hours water-deprived goats, it is imperative to allow a recovery period of no less than 10 days following the restoration of water access prior to initiating any subsequent experiments involving these animals. Such experiments, addressing these critical aspects, serve to advance our understanding of goat welfare and obviously hold promise for contributing to future food security and economic viability.

Physiology Evolves Convergently but Lags Behind Warming inCities.

Cities, through the generation of urban heat islands, provide a venue for exploring contemporary convergent evolution to climatic warming. We quantified how repeatable the evolution of heat tolerance, cold tolerance, and body size was among diverse lineages in response to urban heat islands. Our study revealed significant shifts toward higher heat tolerance and diminished cold tolerance among urban populations. We further found that the magnitude of trait divergence was significantly and positively associated with the magnitude of the urban heat island, suggesting that temperature played a major role in the observed divergence in thermal tolerance. Despite these trends, the magnitude of trait responses lagged behind environmental warming. Heat tolerance responses exhibited a deficit of 0.84°C for every 1°C increase in warming, suggesting limits on adaptive evolution and consequent adaptational lags. Other moderators were predictive of greater divergence in heat tolerance, including lower baseline tolerance and greater divergence in body size. Although terrestrial species did not exhibit systematic shifts toward larger or smaller body size, aquatic species exhibited significant shifts toward smaller body size in urban habitats. Our study demonstrates how cities can be used to address long-standing questions in evolutionary biology regarding the repeatability of evolution. Importantly, this work also shows how cities can be used as forecasting tools by quantifying adaptational lags and by developing trait-based associations with responses to contemporary warming.

Comparison of Hydric and Thermal Physiology in an Environmentally Diverse Clade of Caribbean Anoles.

As the world becomes warmer and precipitation patterns less predictable, organisms will experience greater heat and water stress. It is crucial to understand the factors that predict variation in thermal and hydric physiology among species. This study focuses on investigating the relationships between thermal and hydric diversity and their environmental predictors in a clade of Hispaniolan anole lizards, which are part of a broader Caribbean adaptive radiation. This clade, the "cybotoid" anoles, occupies a wide range of thermal habitats (from sea level to several kilometers above it) and hydric habitats (such as xeric scrub, broadleaf forest, and pine forest), setting up the possibility for ecophysiological specialization among species. Among the thermal traits, only cold tolerance is correlated with environmental temperature, and none of our climate variables are correlated with hydric physiology. Nevertheless, we found a negative relationship between heat tolerance (critical thermal maximum) and evaporative water loss at higher temperatures, such that more heat-tolerant lizards are also more desiccation-tolerant at higher temperatures. This finding hints at shared thermal and hydric specialization at higher temperatures, underscoring the importance of considering the interactive effects of temperature and water balance in ecophysiological studies. While ecophysiological differentiation is a core feature of the anole adaptive radiation, our results suggest that close relatives in this lineage do not diverge in hydric physiology and only diverge partially in thermal physiology.

Wheat TaAP2/ERF Genes Regulate Heat Tolerance Through Ethylene Signaling at Grain-Filling Stage

AbstractWheat is a globally important crop, and its production is critically challenged by heat stress. To understand the heat tolerance mechanism at grain-filling stage in wheat, two genotypes, W156 (tolerant) and Brazil 32 (susceptible) were evaluated for their morphological responses and expressions of TaAP2/ERF super-family transcription factor genes under heat stress (at 37/27 °C) at 11 days and 13 days post-anthesis. The W156 showed significantly higher thousand kernel weight (TKW), chlorophyll fluorescence (Fv/Fm) and delayed senescence of flag leaf and exposed peduncle. Twenty-two differentially expressed genes (DEGs) were selected from in silico expression analysis of 630 TaAP2/ERF genes under abiotic stress and their RT-qPCR expression validation identified twenty major DEGs responsive to heat stress. Co-expression network analysis of these DEGs identified hub TF genes including TraesCS1A02G221900, TraesCS6D02G324200, TraesCS6B02G331000, TraesCS4D02G298600, TraesCS5B02G193200, and TraesCS1A02G058400. Gene Ontology analysis and Gene Set Enrichment Analysis further revealed that 16 (80%) out of the 20 DEGs were involved in the ethylene-activated signaling pathway. Those DEGs involved in ethylene signaling pathway were further validated in an additional pair of contrasting genotypes (Perenjori and Yitpi). Therefore, heat tolerance regulated by TaAP2/ERF genes at grain filling stage of wheat may be mainly through ethylene signaling pathway while maintaining seed development under heat stress.

Meta QTL analysis for dissecting abiotic stress tolerance in chickpea

BackgroundChickpea is prone to many abiotic stresses such as heat, drought, salinity, etc. which cause severe loss in yield. Tolerance towards these stresses is quantitative in nature and many studies have been done to map the loci influencing these traits in different populations using different markers. This study is an attempt to meta-analyse those reported loci projected over a high-density consensus map to provide a more accurate information on the regions influencing heat, drought, cold and salinity tolerance in chickpea.ResultsA meta-analysis of QTL reported to be responsible for tolerance to drought, heat, cold and salinity stress tolerance in chickpeas was done. A total of 1512 QTL responsible for the concerned abiotic stress tolerance were collected from literature, of which 1189 were projected on a chickpea consensus genetic map. The QTL meta-analysis predicted 59 MQTL spread over all 8 chromosomes, responsible for these 4 kinds of abiotic stress tolerance in chickpea. The physical locations of 23 MQTL were validated by various marker-trait associations and genome-wide association studies. Out of these reported MQTL, CaMQAST1.1, CaMQAST4.1, CaMQAST4.4, CaMQAST7.8, and CaMQAST8.2 were suggested to be useful for different breeding approaches as they were responsible for high per cent variance explained (PVE), had small intervals and encompassed a large number of originally reported QTL. Many putative candidate genes that might be responsible for directly or indirectly conferring abiotic stress tolerance were identified in the region covered by 4 major MQTL- CaMQAST1.1, CaMQAST4.4, CaMQAST7.7, and CaMQAST6.4, such as heat shock proteins, auxin and gibberellin response factors, etc.ConclusionThe results of this study should be useful for the breeders and researchers to develop new chickpea varieties which are tolerant to drought, heat, cold, and salinity stresses.

Biological Sex Differences in Heat Acclimation and Gut Microbiome Responses

Purpose: Our broad aim was to elucidate the relationship between gut microbiome (gMB) and heat tolerance/acclimation. In this study, we hypothesized that the gMB is affected by acute exercise-heat stress/acclimation and is biologically sex-specific. Methods: Physically active men (M: n=10, 21±2yo, VO2max 51.8±6.6mL−1·kg−1·min−1) and women (W: n=6, 26±5yo, VO2max 45.5±8.0mL−1·kg−1·min−1) completed a modified heat tolerance test (HTT; 65% vVO2max, 2% grade treadmill run, 40°C, 40% relative humidity) until rectal temperature reached 39.5°C (TT39.5) or failure before (preHA) and after (postHA) a 5-day heat acclimation (HA). DNA from stool samples was sequenced via 16S rRNA (V4). a-diversity (Shannon Index) and rarified abundances of phyla, family, and genus were calculated by subsampling to 10,000 reads per sample. Blood inflammation markers were measured with commercially available kits. Significant differences (p≤0.05) were determined by nonparametric analyses for gMB indices and parametric analyses for all other variables were reported as mean ± standard deviation and Z scores for compared groups. Results: All subjects acclimated, but W were more resilient to HTT pre and postHA (preHA TT39.5: 29.14±7.14min (M), 35.02±3.67min (W), p=0.042; postHA TT39.5: 31.11±5.61min (M), 38.13±3.14min (W), p&lt;0.01). gMB changes were observed among all subjects with reductions in Peptostreptococcaceae and Proteobacteria at postHA (vs. preHA, p&lt;0.05). Comparison of W and M revealed marked differences. M had lower (vs. W) Christensenella (Z=-2.119, p=0.034), Erysipelotrichaceae (Z=-2.495, p=0.013) and higher Lactococcus (Z=-2.254, p=0.024), Peptostreptococcaceae (Z=-2.386, p=0.017), Pasteurellaceae(Z=-2.210, p=0.027), and Haemophilus (Z=-2.210, p=0.027) preHA. PostHA, M had lower (v. W) Eggerthella (Z=-2.022, p=0.043), Family XIII (Z=-2.025, p=0.043), Erysipelotrichaceae (Z=-2.061, p=0.039), Oxalobacteraceae (Z=-2.445, p=0.014), and higher Peptostreptococcaceae (Z=-2.173, p=0.030) with no differences in Shannon Index. Biomarkers IL-1β and IFN-γ were increased postHA (v. preHA, p&lt;0.05), but W had distinct I-FABP (decreased v. M, p&lt;0.05) and IFN-γ (increased v. M, p&lt;0.05) responses. Conclusion: gMB changes during heat acclimation include bacteria associated with heat stress responses in previous literature. W and M differ in gMB, acute heat tolerance, and acclimation responses with concomitant sex differences in inflammatory and metabolite markers potentially related to gMB. Ongoing research investigates associations of targets such as Proteobacteria with previous findings related to heat tolerance and acclimation and metabolite patterns in systemic circulation associated with bacterial species significantly affected by HA. DoD BA200299. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Enhancing interfacial bond strength between PEEK and inkjet-printed silver film through laser surface modification for additive manufacturing of electronics

Electronic 3D printing is a very promising technology, which is widely used in the manufacturing of conformal antennas, flexible electronics and sensors. Polyether ether ketone (PEEK) is one of the most popular substrate materials for electronic 3D printing due to its superior fatigue resistance, heat tolerance, chemical resistance, and mechanical properties. However, the deficient bond between the PEEK substrate and the conductive ink leads to the peeling and shedding of the conductive pattern. This paper investigated the enhancement of the bond strength between the PEEK substrate and the conductive layer through PEEK surface modification. A 355 nm ns solid-state laser was used to treat the PEEK surface with different values of laser scanning spacing (S) and spot overlap rate (R). The surface microstructure, surface roughness, wettability, and functional groups of the treated substrates have been measured. Then the nanoparticle silver ink was printed and cured on the treated substrate. After that, the bonding strength was measured using a pull-off adhesion tester. Results showed that regular grooves were generated and the content of active oxygen atoms was increased on the PEEK surface through laser modification. The mechanical interlocking between the grooves and silver particles and hydrogen bonds induced by the active oxygen atoms and the hydroxyl groups contribute to the enhancement of bond strength between PEEK and silver film. The bond strength for the laser treated PEEK reached the maximum of 1.9 MPa, which was 413.51% higher than that of the untreated PEEK. The laser modification can effectively enhance the interfacial bond strength for additive manufacturing of reliable electronics.

Sex Differences In Energy Expenditure, Metabolic Heat, And Substrate Utilization During Exercise-Heat Stress

Purpose: To understand the influence of repeated heat exposures and biological sex on metabolic outcomes surrounding heat acclimation (HA). Based on previous data, we hypothesized that repeated heat exposures would result in higher resting caloric expenditure and exercising metabolic heat production in men (vs. women). Methods: Twenty participants (65% men, 22±3 yrs, 70.1±13.7 kg, VO2max 49.9±6.8 mL·kg −1·min −1) had 8 daily exercise-heat sessions (40°C, 40%rh, at least 60min) including heat tolerance tests (HTT; 120 min, 3.1 mph, 2% grade) on days 1 and 8. Resting energy expenditure (REE) and respiratory exchange ratio (RER) were assessed pre- and post-HTT on days 1 and 8. Metabolic heat production (MHP) and RER were collected during the HTT. Data are presented as mean difference (MD) (95% confidence intervals). For REE and RER, a 2x2 ANOVA compared metrics before HTT vs. after HTT session, pre-HA vs. post HA with sex as a between-subjects factor. For MHP and RER during exercise, a dependent samples t-test compared pre-HA vs. post-HA and independent samples t-test compared sexes pre-HA vs. post-HA. Results: Pre-HA: RER was higher before vs. after the HTT (MD:0.07 (0.05,0.09) A.U., p&lt;0.001) overall with no difference between sexes. REE was not different before vs. after the HTT (p&gt;0.05) overall, but males had higher REE before HTT (MD:564 (291,836) kcal·day −1, p&lt;0.001) and after HTT (MD:666 (395,938) kcal·day −1, p&lt;0.001) than women. Post-HA: RER was higher before vs. after the HTT (MD:0.08 (0.06,0.10) A.U., p&lt;0.001) overall with no difference between sexes. REE was not different before vs. after the HTT (p&gt;0.05), but males had higher REE before (MD:581 (328,834) kcal·day −1, p&lt;0.001) and after HTT (MD:617 (411,823) kcal·day −1, p&lt;0.001) compared to women. Comparing HA Status: RER was not different between HA status before or after the HTT (p&gt;0.05). REE was not different between HA status before the HTT (p&gt;0.05). After HTT, REE was greater pre-HA compared to post-HA (MD:142 (26,259) kcal·day −1, p=0.019). During activity, MHP was greater pre-HA compared to post-HA (MD:14 (-2,31) W/m2, p=0.042); RER was not different (p&gt;0.05). Pre-HA there were no differences in MHP or RER between sexes (p&gt;0.05); post-HA, men had greater MHP than women (MD:36 (3,67) W/m2, p=0.016); there were no sex differences in RER. Conclusion: Men exhibited greater REE than women at each time point under both conditions and men produced more metabolic heat following HA. In response to completing 8 heat exposures as part of a HA protocol, men and women differed in caloric expenditure and MHP, but not in substrate utilization. Thus, our findings provide supporting evidence for sex-specific nutritional recommendations surrounding exercise-heat stress. Funding Source: DoD BA200299. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Skeletal muscle proteomics responses in men and women during acute exercise-heat stress and acclimation

Purpose: Our broad aim was to identify targetable mechanisms of improving skeletal muscle function and recovery during exercise-heat stress. In this study, we used proteomics to test the hypothesis that skeletal muscle proteomic changes would correspond to acclimation state. Methods: Healthy men (M: n = 7, 22 ± 2 yo, VO2max 52.86 ± 2.35 ml·kg−1·min−1) and women (F: n = 7, 24 ± 1 yo, VO2max 45.97 ± 2.57 ml·kg−1·min−1) completed a 5-day heat acclimation (HA) (40 °C, 40% rH). Before and after HA, participants completed a heat tolerance test measuring time to reach rectal temperature 39.5°C (HTT39.5) or failure (stoppage). Musculoskeletal biopsies from the vastus lateralis were harvested for protein extraction, quantification, and digestion prior to untargeted UPLC-MS/MS (Q Exactive HF). Peptide identification and label-free quantitation was achieved using Andromeda search engine and MaxQuant (v1.6.10.43), using UniProt reference proteome UP0000005640. All search results were filtered to FDR (false discovery rate) 1% and uploaded to Scaffold v5.1.0 for data visualization and t-test analyses for difference between conditions (p &lt; 0.05). Functional annotation and pathway analysis were conducted (DAVID, Reactome, String). Physiological, perceptual, and performance metrics were statistically analyzed using t-tests (p ≤ 0.05). Results: No significant differences (p = 0.931) were observed between males (mean = 27.21 ± 1.37 minutes) and females (26.91 ± 3.20 minutes) for PREHA HTT39.5. HTT39.5 for F was significantly higher than for men at PREHA (p = 0.001) and POSTHA (p = 0.014). 2741 proteins from 960,731 spectra were detected among our skeletal muscle biopsy samples with 22 and 33 proteins expressed more highly in M and F at PREHA, respectively. 149 and 81 proteins were more highly expressed in M and F, respectively, at POSTHA. Differences between M and F included more highly connected nodes in M at PREHA (average node degree: 3.7, avg. local clustering coeffcient: 0.529, PPI enrichment p-value &lt; 1.11e-16, HIST1H3 (isoforms D, H, and J), HIST1H4F, HIST2H2A (isoforms C, B, and E), HIST2HAC, H2AFX) and at POSTHA (average node degree: 4.26, avg. local clustering coeffcient: 0.455, expected number of edges 110, PPI enrichment p-value &lt; 1.0e-16, GAPDH, RPS13, TPI1, PKM, RPS21). Differences in F and M (more highly expressed) also included GO terms related to DNA, RNA, and protein quality regulation and immune function and metabolism (p &lt; 0.05). Conclusions: Acclimation is associated with different skeletal muscle responses in M and F related to protein synthesis and immune function pathways that are regulated after a bout of exercise-heat stress. Ongoing analysis examines relationships between naïve or acclimated state and individual skeletal muscle proteomic profiles. DoD BA200299. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Skeletal Muscle Mitochondrial Function and Mitochondria-related Protein Expression in Men and Women During Acute Exercise-Heat Stress and Acclimation

INTRODUCTION: Military personnel can exhibit improved performance and reduced physiological strain in hot environments with the induction of heat adaptations. Mild heat exposure at 40°C heat serves therapeutic purposes, enhancing metabolic flexibility, and promoting positive muscle adaptations. Research indicates that heat acclimation (HA) leads to increased mitochondrial biogenesis and reduced reactive oxygen species in skeletal muscle, improving thermal tolerance. However, understanding sex differences in mitochondrial function and related protein expression affected by heat acclimation remain limited. Therefore, this study aimed to explore mitochondrial respiration and the expression of mitochondria-related proteins to better understand the impact of heat stress on mitochondrial adaptations in skeletal muscle in both males and females. METHODS: Healthy men (M:n = 7, 22±2yo, VO2max 52.86±2.35ml·kg−1·min−1) and women (F:n = 7, 24±1yo, VO2max 45.97±2.57 ml·kg−1·min−1) participated in a 5-day heat acclimation (HA) at 40°C and 40% relative humidity. Before and after HA, participants completed a heat tolerance test (HTT) measuring time to reach a rectal temperature of 39.5°C or volitional failure. Biopsies from the vastus lateralis were taken immediately post-HTT for musculoskeletal analysis. Mitochondrial respiratory function was assessed using Oroboros O2K, employing high-resolution respirometry. Paired sample t-tests were used to determine statistical significance between groups (p&lt;0.05). Proteomics data were mined for Gene Ontology (GO) terms related to mitochondrial function (STRING V.12.0) (adjusted p&lt;0.05). RESULTS: Both men and women exhibited significant enhancements in complex I-mediated respiration and complex I+II maximal coupled respiration after HA (PRE-HA: M:P=0.009, P=0.026; F:P=0.016, P=0.011). No sex differences in mitochondria respiration were observed before or after HA. Before HA, skeletal muscle from women showed higher expression in 4 proteins (ND61, NDUFB1, COX1, ATP5MF) associated with 9 GO terms related to mitochondrial function compared to men. However, after HA, men exhibited higher expression in 14 proteins (MTX2, APOOL, DNAJC11, TIMM13, NDUFAB1, DNAJC11, MAVS, CHCHD4, NDUFAF4, ATP5PF, NDUFAS, UQCRH, SSBP1, ND3) associated with 21 mitochondria-related GO terms compared to women. CONCLUSION: Acclimation to heat stress is associated with positive mitochondrial adaptation in both men and women. Although enhancements in mitochondrial respiratory function in both men and women after HA, there were different skeletal muscle responses between men and women regarding the regulation of mitochondria-related proteins after a bout of exercise-heat stress. Funding: DoD BA200299. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Sex-Specific Transcriptome Responses in Circulating Immune Cells During Exercise-Heat Stress and Acclimation

Objective: To examine the sex-based differences in heat stress and acclimation we used transcriptomic analysis to test the hypotheses that 1) gene expression varies by biological sex before and after acute heat exposure and 2) circulating immune cell transcriptome responses differ between naïve and acclimated state. Methods: Participants (3F/3M, VO2max &gt;40/45 ml×kg×min−1) completed two heat tolerance tests (HTT), termed HTT1 (120min walking at 1.39 m/s at 2% grade) and HTT2 (~70% vVO2max until rectal temperature (Trec) reached 39.5°C) before and after a 5-day heat acclimation (HA1-5, daily 60min run/jog at Trec 38.5-39.5°C), in a hot environment (40°C, 40%RH). Blood was collected in PAXgene blood RNA tubes PRE and POST HTT1, HTT2, HA1, and HA5 with a recovery (REC) timepoint ~30min after HTT2. Paired end sequencing of ribodepleted total RNA from 84 samples (14 timepoints) was performed on a NovaSeq 6000 (Illumina, Inc., San Diego, CA). All samples passed quality checks with Fastp read trimming retaining 98.2% of reads with a GC content of 49.1%. HISAT2 indexed and mapped an average of 75.9M reads to GrCh38.105. Expression was quantified with htseq-counts, excluding genes with &lt;3 mapped fragments per sample resulting in 26,671 genes. Principal component analysis indicated 36% of variation could be attributed to sex. Differential expression was assessed using DESeq2's generalized linear model, applying a Benjamini-Hochberg correction with an FDR of 0.1 and an adjusted p-value threshold of 0.1. DE genes were analyzed for functional annotation and pathways. Results: In total, we detected 8611 unique DE genes composed of protein coding (6241), lncRNA (1498), and 636 pseudogenes. Males and Females exhibited significant differences in gene expression at baseline, in naïve state (PREHA) with &gt;1555 genes showing sex differences (FDR&lt;0.1). Reactome pathways differing between M and F included cytokine signaling, response, and regulation, cell senescence, cell growth and death, cell cytoskeleton and extracellular structure and innate immunity processes (p&lt;0.05). Interestingly, heat acclimation increased the responsiveness of the transcriptome while reducing the overall magnitude of the response. PREHA HTT2 had 86 DE genes at POST rising to 3170 at REC (vs. PRE, FDR&lt;0.1). While POSTHA HTT2 had 602 DE genes at POST rising to 1236 at REC (vs. PRE, FDR&lt;0.1). GO terms protein serine kinase activity, GTPase binding, and GDP binding were present at PREHA, but absent POSTHA. Conclusion: Acute exercise-heat stress induces marked changes in circulating immune cell transcriptional landscape, while acclimation reduces this response to the same challenge in an adapted state. Sex differences exist and are the subject of ongoing analyses. Funding: DoD BA200299. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

High night temperature stress on rice (Oryza sativa) - insights from phenomics to physiology. A review.

Rice (Oryza sativa ) faces challenges to yield and quality due to urbanisation, deforestation and climate change, which has exacerbated high night temperature (HNT). This review explores the impacts of HNT on the physiological, molecular and agronomic aspects of rice growth. Rise in minimum temperature threatens a potential 41% reduction in rice yield by 2100. HNT disrupts rice growth stages, causing reduced seed germination, biomass, spikelet sterility and poor grain development. Recent findings indicate a 4.4% yield decline for every 1°C increase beyond 27°C, with japonica ecotypes exhibiting higher sensitivity than indica. We examine the relationships between elevated CO2 , nitrogen regimes and HNT, showing that the complexity of balancing positive CO2 effects on biomass with HNT challenges. Nitrogen enrichment proves crucial during the vegetative stage but causes disruption to reproductive stages, affecting grain yield and starch synthesis. Additionally, we elucidate the impact of HNT on plant respiration, emphasising mitochondrial respiration, photorespiration and antioxidant responses. Genomic techniques, including CRISPR-Cas9, offer potential for manipulating genes for HNT tolerance. Plant hormones and carbohydrate enzymatic activities are explored, revealing their intricate roles in spikelet fertility, grain size and starch metabolism under HNT. Gaps in understanding genetic factors influencing heat tolerance and potential trade-offs associated with hormone applications remain. The importance of interdisciplinary collaboration is needed to provide a holistic approach. Research priorities include the study of regulatory mechanisms, post-anthesis effects, cumulative HNT exposure and the interaction between climate variability and HNT impact to provide a research direction to enhance rice resilience in a changing climate.

Sexual Dimorphism in the Slope of Rectal Temperature Rise Before Heat Acclimation, but Not After Heat Acclimation

Purpose: Our study aimed to identify if sexual dimorphism exists surrounding the slope of rectal temperature rise during a steady state exercise in the heat before and after heat acclimation (HA). In this study, we hypothesized that women would have a greater tolerance to heat stress resulting from a lesser slope of rectal temperature rise when compared to men. Methods: Physically active men (M) (n=12, VO2max: 51.3 ± 6.1 mL·kg−1·min−1, Age: 21±2 yo) and women (W) (n=12, VO2max: 44.2±5.8±6.1 mL·kg−1·min−1, Age: 24±4 yo) completed a steady state treadmill based heat tolerance test (HTT) (3 mph 2% grade for 120 minutes (min) in 40°C, 40% relative humidity). Rectal temperature (Trec) was collected during the first 10-min (PreHAF) and the last 10-min (PreHAL) of the HTT before HA, as well as the first 10-min (PostHAF) and last 10-min (PostHAL) after HA. The slope of rectal temperature rise for the first 10min was calculated by taking the difference of Trec at 10min and 0min, with the slope for the last 10min calculated using Trec at 120min and 110min. Both Trec differences were divided by 10min to obtain the slope in °C/min. One tailed independent T-tests were used to determine sex differences and dependent T-tests to determine differences within sex, both with significance at p≤0.05. All data are presented as mean ± SD. Results: Before acclimation, W demonstrated a greater slope of Trec rise PreHAF when compared to M (M: 0.01 ± 0.02°C/min, W: 0.03 ± 0.01°C/min, p=0.006) with opposite findings PreHAL (M: 0.01 ± 0.01°C/min, W: 0.00 ± 0.00°C/min, p=0.046). Following HA, there were no differences between the slope of Trec rise in M vs. W at both PostHAF (M: 0.02 ± 0.01°C/min, W: 0.02 ± 0.01°C/min, p&gt;0.05) and PostHAL (M: 0.00 ± 0.01°C/min, W: 0.00 ± 0.00°C/min, p&gt;0.05). In M, the PreHAL slope of Trec rise was greater than PostHAL (PreHAL: 0.01 ± 0.01°C/min, PostHAL: 0.00 ± 0.01°C/min, p=0.019), with no differences found within the first 10min (PreHAF: 0.01 ± 0.01°C/min, PostHAF: 0.02 ± 0.01°C/min, p=0.060). No differences in the slope of Trec rise between HA statuses were found in W (PreHAF: 0.03 ± 0.01°C/min, PostHAF: 0.02 ± 0.01°C/min, p&gt;0.05; PreHAL: 0.00 ± 0.01°C/min, PostHAL: 0.00 ± 0.01°C/min, p&gt;0.05). Conclusion: Consistent with previous literature, men exhibit better adaptations displayed by greater reductions in rectal temperature after HA, while women demonstrated consistent responses in both the first and last 10-min. These findings contribute to our understanding of sex-specific physiological adaptations to heat acclimation and underscore the importance of considering sex-based differences in heat-related research and interventions. Funding: DoD BA200299. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Biocomposite thermoplastic polyurethanes containing evolved bacterial spores as living fillers to facilitate polymer disintegration

The field of hybrid engineered living materials seeks to pair living organisms with synthetic materials to generate biocomposite materials with augmented function since living systems can provide highly-programmable and complex behavior. Engineered living materials have typically been fabricated using techniques in benign aqueous environments, limiting their application. In this work, biocomposite fabrication is demonstrated in which spores from polymer-degrading bacteria are incorporated into a thermoplastic polyurethane using high-temperature melt extrusion. Bacteria are engineered using adaptive laboratory evolution to improve their heat tolerance to ensure nearly complete cell survivability during manufacturing at 135 °C. Furthermore, the overall tensile properties of spore-filled thermoplastic polyurethanes are substantially improved, resulting in a significant improvement in toughness. The biocomposites facilitate disintegration in compost in the absence of a microbe-rich environment. Finally, embedded spores demonstrate a rationally programmed function, expressing green fluorescent protein. This research provides a scalable method to fabricate advanced biocomposite materials in industrially-compatible processes.