Proteomic changes of the porcine small intestine in response to chronic heat stress

Heat Stress Induces Alterations in Gene Expression of Actin Cytoskeleton and Filament of Cellular Components Causing Gut Disruption in Growing-Finishing Pigs

We aimed to investigate the impact of heat stress (HS) on the expression of tight junction (TJ) proteins and the interaction between genes affecting intestinal barrier function using transcriptomics in the porcine jejunum. Twenty-four barrows (crossbred Yorkshire × Landrace × Duroc; average initial body weight, 56.71 ± 1.74 kg) were placed in different temperatures (normal temperature [NT]; HS) and reared for 56 days. At the end of the experiment, jejunal samples were collected from three pigs per treatment for transcriptome and reverse-transcription quantitative polymerase chain reaction (RT-qPCR) analyses. We identified 43 differentially expressed genes, involving five Kyoto Encyclopedia of Genes and Genomes pathways, eight molecular functions, seven cellular components (CCs), and nine biological processes, using gene ontology enrichment analysis. Genes associated with the actin cytoskeleton, filament-binding pathways, and TJ proteins were selected and analyzed by RT-qPCR. Significant differences in relative mRNA expression showed that downregulated genes in the HS group included ZO1, CLDN1, OCLN, PCK1, and PCK2, whereas ACTG2, DES, MYL9, MYLK, TPM1, TPM2, CNN1, PDLIM3, and PCP4 were upregulated by HS (p < 0.05). These findings indicate that HS in growing-finishing pigs induces depression in gut integrity, which may be related to genes involved in the actin cytoskeleton and filaments of CC.

In-depth transcriptome profiling of Cherry Valley duck lungs exposed to chronic heat stress

Amidst rising global temperatures, chronic heat stress (CHS) is increasingly problematic for the poultry industry. While mammalian CHS responses are well-studied, avian-specific research is lacking. This study uses in-depth transcriptome sequencing to evaluate the pulmonary response of Cherry Valley ducks to CHS at ambient temperatures of 20°C and a heat-stressed 29°C. We detailed the CHS-induced gene expression changes, encompassing mRNAs, lncRNAs, and miRNAs. Through protein-protein interaction network analysis, we identified central genes involved in the heat stress response-TLR7, IGF1, MAP3K1, CIITA, LCP2, PRKCB, and PLCB2. Subsequent functional enrichment analysis of the differentially expressed genes and RNA targets revealed significant engagement in immune responses and regulatory processes. KEGG pathway analysis underscored crucial immune pathways, specifically those related to intestinal IgA production and Toll-like receptor signaling, as well as Salmonella infection and calcium signaling pathways. Importantly, we determined six miRNAs-miR-146, miR-217, miR-29a-3p, miR-10926, miR-146b-5p, and miR-17-1-3p-as potential key regulators within the ceRNA network. These findings enhance our comprehension of the physiological adaptation of ducks to CHS and may provide a foundation for developing strategies to improve duck production under thermal stress.

Hypoxia-inducible factor 1α inhibits heat stress-induced pig intestinal epithelial cell apoptosis through eif2α/ATF4/CHOP signaling

Unstoppable global warming and increased frequency of extreme heat leads to human and animals easier to suffer from heat stress (HS), with gastrointestinal abnormalities as one of the initial clinical symptoms. HS induces intestinal mucosal damage owing to intestinal hypoxia and hyperthermia. Hypoxia-inducible factor 1α (HIF-1α) activates numerous genes to mediate cell hypoxic responses; however, its role in HS-treated intestinal mucosa is unknown. This work aimed to explore HIF-1α function and regulatory mechanisms in HS-treated pig intestines. We assigned 10 pigs to control and moderate HS groups. Physical signs, stress, and antioxidant levels were detected, and the intestines were harvested after 72 h of HS treatment to study histological changes and HIF-1α, heat shock protein 90 (HSP90), and prolyl-4-hydroxylase 2 (PHD-2) expression. In addition, porcine intestinal columnar epithelial cells (IPEC-J2) underwent HS treatment (42 °C, 5 % O2) to further explore the functions and regulatory mechanism of HIF-1α. The results of histological examination revealed HS caused intestinal villi damage and increased apoptotic epithelial cell; the expression of HIF-1α and HSP90 increased while PHD-2 showed and opposite trend. Transcriptome sequencing analysis revealed that HS activated HIF-1 signaling. To further explore the role of HIF-1α on HS induced IPEC-J2 apoptosis, the HIF-1α was interfered and overexpression respectively, and the result confirmed that HIF-1α could inhibited cell apoptosis under HS. Furthermore, HS-induced apoptosis depends on eukaryotic initiation factor 2 alpha (eif2α)/activating transcription factor 4 (ATF4)/CCAAT-enhancer-binding protein homologous protein (CHOP) pathway, and HIF-1α can inhibit this pathway to alleviate IPEC-J2 cell apoptosis. In conclusion, this study suggests that HS can promote intestinal epithelial cell apoptosis and cause pig intestinal mucosal barrier damage; the HIF-1α can alleviate cell apoptosis by inhibiting eif2α/ATF4/CHOP signaling. These results indicate that HIF-1α plays a protective role in HS, and offers a potential target for HS prevention and mitigation.

Cellular and mitochondrial adaptation mechanisms in the colon of lactating dairy cows during hyperthermia

Heat stress causes barrier dysfunction and inflammation of the small intestine of several species. However, less is known about the molecular and cellular mechanisms underlying the response of the bovine large intestine to hyperthermia. We aimed to identify changes in the colon of dairy cows in response to constant heat stress using a proteomic approach. Eighteen lactating Holstein dairy cows were kept under constant thermoneutral conditions (16°C and 68% relative humidity [RH]; temperature-humidity index [THI] = 60) for 6 d (period 1) with free access to feed and water. Thereafter, 6 cows were equally allocated to (1) thermoneutral condition with ad libitum feeding (TNAL; 16°C, RH = 68%, THI = 60), (2) heat stress condition (HS; 28°C, RH = 50%, THI = 76) with ad libitum feeding, or (3) pair-feeding at thermoneutrality (TNPF; 16°C, RH = 68%, THI = 60) for another 7 d (period 2). Rectal temperature, milk yield, dry matter and water intake were monitored daily. Then, cows were slaughtered and colon mucosa samples were taken for proteomic analysis. Physiological data were analyzed by ANOVA and colon proteome data were processed using DESeq2 package in R. Rectal temperature was significantly higher in HS than in TNPF and TNAL cows in period 2. Proteomic analysis revealed an enrichment of activated pathways related to colonic barrier function and inflammation, heat shock proteins, AA metabolism, reduced overall protein synthesis rate, and post-transcriptional regulation induced by heat stress. Further regulations were found for enzymes of the tricarboxylic acid cycle and components of the mitochondrial electron transport chain, presumably to reduce the generation of reactive oxygen species, maintain cellular ATP levels, and prevent apoptosis in the colon of HS cows. These results highlight the cellular, extracellular, and mitochondrial adaptations of the colon during heat stress and suggest a dysfunction of the hindgut barrier integrity potentially resulting in a "leaky" colon.

Heat stress alters hematological parameters in barrows and gilts

The purpose of this investigation was to establish the role biological sex plays in circulating factors following heat stress (HS). Barrows and gilts (36.8 ± 3.7 kg body weight) were kept in either thermoneutral (TN; 20.8 ± 1.6 °C; 62.0% ± 4.7% relative humidity; n = 8/sex) conditions or exposed to HS (39.4 ± 0.6 °C; 33.7% ± 6.3% relative humidity) for either 1 (HS1; n = 8/sex) or 7 (HS7; n = 8/sex) d. Circulating glucose decreased as a main effect of the environment (P = 0.03). Circulating non-esterified fatty acid (NEFA) had an environment × sex interaction (P < 0.01) as HS1 barrows had increased NEFA compared to HS1 gilts (P = 0.01) and NEFA from HS7 gilts increased compared to HS1 gilts (P = 0.02) and HS7 barrows (P = 0.04). Cortisol, insulin, glucagon, T3, and T4 were reduced as a main effect of environment (P ≤ 0.01). Creatinine was increased in HS1 and HS7 animals compared to TN (P ≤ 0.01), indicative of decreased glomerular filtration rate. White blood cell populations exhibited differential patterns based on sex and time. Neutrophils and lymphocytes had an environment × sex interaction (P ≤ 0.05) as circulating neutrophils were increased in HS1 barrows compared to TN and HS7 barrows, and HS1 gilts (P ≤ 0.01) and HS7 barrows had less neutrophils compared to TN barrows (P = 0.01), whereas they remained similar in gilts. In contrast, barrow lymphocyte numbers were similar between groups, but in HS7 gilts they were decreased compared to TN and HS1 gilts (P ≤ 0.04). In total, these data demonstrate that HS alters a host of circulating factors and that biological sex mediates, at least in part, the physiological response to HS.

Proteomic methods for the study of porcine acute phase proteins - anything new to detect?

Acute phase proteins (APPs) reflect the health status of individuals and are important tools in diagnostics, as their altered levels are a sign of disturbed homeostasis. While, in most cases, quantitation of known serum APPs is routinely performed by immunoassays, proteomics is helpful in discovery of new biomarker candidates, especially in samples other than body fluids. Besides putting APP regulation into an overall context of differentially abundant proteins, this approach can detect further details or outright new features in protein structure or specific modifications, and help understand better their function. Thus, it can show up ways to make present diagnostic assays more sensitive and/or specific, or correlate regulations of disease-specific proteins. The APP repertoire is dependent on the species. The pig is both, an important farm animal and a model animal for human diseases, due to similarities in physiology. Besides reviewing existing literature, yet unpublished examples for two-dimensional electrophoresis in connection with pig APPs highlight some of the benefits of proteomics. Of further help would be the emerging targeted proteomics, offering the possibility to determine particular isoforms or proteoforms, without the need of specific antibodies, but this method is presently scarcely used in veterinary medicine.

Using Recombinant Superoxide Dismutase to Control Oxidative Stress in the Gastrointestinal Tract of Cyclic Heat-Stressed Pigs

Climate change is associated with an increased frequency and intensity of heat waves, posing a threat of heat stress to pig production. Heat stress compromises the efficiency of pig production partly due to causing oxidative stress, intestinal dysfunction, and inflammatory responses. Superoxide dismutase is an antioxidant enzyme reported to reduce oxidative stress and inflammation. Therefore, this experiment aimed to investigate whether recombinant superoxide dismutase (rSOD) could ameliorate oxidative stress and inflammatory responses in heat-stressed grower pigs. Sixty-four female pigs (Large White × Landrace, 27.8 ± 1.65 kg, mean ± SD) were randomly allocated to a control diet (standard grower feed, CON) or the control diet supplemented with 50 IU recombinant superoxide dismutase (rSOD) for 14 days. After acclimation to the diet, pigs were then housed under thermoneutral (TN, 20 °C, 35-50% relative humidity) or cyclic heat stress conditions (CHS, at 35 °C: 9 a.m. to 5 p.m. and 28 °C: 5 p.m. to 9 a.m., 35-50% relative humidity) for 3 days. Heat stress increased respiration rate (RR), skin and rectal temperature (RR and RT) (p < 0.001 for all), and reduced plasma thyroid hormone concentration (p < 0.001). The amount of oxidized glutathione (GSH:GSSG) was increased in the jejunum and ileum of CHS pigs. In the jejunum, rSOD also increased the amount of oxidized glutathione in both TN and CHS pigs, without any change in endogenous SOD activity. In the ileum, rSOD prevented increases in oxidized glutathione formation in the CHS pigs only. Taken together, this may reflect increased oxidative stress in both the jejunum and ileum in CHS pigs. Alternatively, rSOD increased the conversion of reduced to oxidized glutathione independently of CHS, possibly reflecting an increased overall SOD activity due to the addition of exogenous SOD. In conclusion, the use of in-feed SOD enzymes at a dose of 50 IU/kg may be a useful strategy for preventing oxidative stress in pigs.

Heat Stress-Induced Intestinal Barrier Impairment: Current Insights into the Aspects of Oxidative Stress and Endoplasmic Reticulum Stress

Heat stress (HS) occurs when the sensible temperature of animals exceeds their thermoregulatory capacity, a condition that exerts a detrimental impact on health and growth. The intestinal tract, as a highly sensitive organ, has been shown to respond to HS by exhibiting mucosal injury, intestinal leakage, and disturbances in the gut microbiota. Oxidative stress and endoplasmic reticulum stress (ERS) are both potential outcomes of long-term exposure to high temperatures and have been linked to apoptosis, autophagy, and ferroptosis. In addition, HS alters the composition of the gut microbiota accompanied by changed levels of bacterial components and metabolites, rendering the gut more vulnerable to stress-related injury. In this review, we present recent advances in mechanisms of oxidative stress-associated ERS in response to HS, which is destructive to intestinal barrier integrity. The involvement of autophagy and ferroptosis in ERS was highlighted. Further, we summarize the relevant findings regarding the engagement of gut microbiota-derived components and metabolites in modulation of intestinal mucosal injury induced by HS.

Glutamine alleviated heat stress-induced damage of porcine intestinal epithelium associated with the mitochondrial apoptosis pathway mediated by heat shock protein 70

The present study aimed to investigate the effect of glutamine (Gln) addition on the damage of porcine intestinal epithelial cells (IPEC-J2) induced by heat stress (HS). IPEC-J2 cultured in logarithmic growth period in vitro were firstly exposed to 42 °C for 0.5, 1, 2, 4, 6, 8, 10, 12, and 24 h for cell viability and cultured with 1, 2, 4, 6, 8, or 10 mmol Gln per L of culture media for heat shock protein 70 (HSP70) expression to determine the optimal disposal strategy (HS, 42 °C for 12 h and HSP70 expression, 6 mmol/L Gln treatment for 24 h). Then IPEC-J2 cells were divided into three groups: control group (Con, cultured at 37 °C), HS group (HS, cultured at 42 °C for 12 h), and glutamine group (Gln+HS, cultured at 42 °C for 12 h combined with 6 mmol/L Gln treatment for 24 h). The results showed that HS treatment for 12 h significantly decreased the cell viability of IPEC-J2 (P < 0.05) and 6 mmol/L Gln treatment for 12 h increased HSP70 expression (P < 0.05). HS treatment increased the permeability of IPEC-J2, evidenced by the increased fluorescent yellow flux rates (P < 0.05) and the decreased transepithelial electrical resistance (P < 0.05). Moreover, the downregulated protein expression of occludin, claudin-1, and zonula occludens-1 was observed in HS group (P < 0.05), but Gln addition alleviated the negative effects on permeability and the integrity of intestinal mucosal barrier induced by HS (P < 0.05). In addition, HS resulted in the elevations in HSP70 expression, cell apoptosis, cytoplasmic cytochrome c potential expression, and the protein expressions of apoptosis-related factors (apoptotic protease-activating factor-1, cysteinyl aspartate-specific proteinase-3, and cysteinyl aspartate-specific proteinase-9) (P < 0.05); however, the reductions in mitochondrial membrane potential expression and B-cell lymphoma-2 expression were induced by HS (P < 0.05). But Gln treatment attenuated HS-induced adverse effects mentioned above (P < 0.05). Taken together, Gln treatment exhibited protective effects in protecting IPEC-J2 from cell apoptosis and the damaged integrity of epithelial mucosal barrier induced by HS, which may be associated with the mitochondrial apoptosis pathway mediated by HSP70.

Upper gut heat shock proteins HSP70 and GRP78 promote insulin resistance, hyperglycemia, and non-alcoholic steatohepatitis

A high-fat diet increases the risk of insulin resistance, type-2 diabetes, and non-alcoholic steato-hepatitis. Here we identified two heat-shock proteins, Heat-Shock-Protein70 and Glucose-Regulated Protein78, which are increased in the jejunum of rats on a high-fat diet. We demonstrated a causal link between these proteins and hepatic and whole-body insulin-resistance, as well as the metabolic response to bariatric/metabolic surgery. Long-term continuous infusion of Heat-Shock-Protein70 and Glucose-Regulated Protein78 caused insulin-resistance, hyperglycemia, and non-alcoholic steato-hepatitis in rats on a chow diet, while in rats on a high-fat diet continuous infusion of monoclonal antibodies reversed these phenotypes, mimicking metabolic surgery. Infusion of these proteins or their antibodies was also associated with shifts in fecal microbiota composition. Serum levels of Heat-Shock-Protein70 and Glucose-Regulated Protein78were elevated in patients with non-alcoholic steato-hepatitis, but decreased following metabolic surgery. Understanding the intestinal regulation of metabolism may provide options to reverse metabolic diseases.

Effects of heat stress on growth performance, carcass traits, serum metabolism, and intestinal microflora of meat rabbits

To investigate the effects of heat stress on meat rabbits, we assigned 80 rabbits to the moderate temperature group (24 ± 1°C; Control group) and the continuous high-temperature group (HT group), then monitored the effects using growth performance, carcass characteristics, biochemical assays, UPLC-MS/MS-based metabolomics, and microbiome. The results showed that after continuous high-temperature exposure, the average daily gain, average daily feed intake, and thymus index were significantly decreased (p < 0.05). Contents of HSP70, ALP, and Cortisol in serum were significantly increased, while TP, GLU, T3, and T4 were significantly decreased (p < 0.05). Nine kinds of differential metabolites were screened by serum metabolomics, which can be used as biomarkers of heat stress in meat rabbits. The selected differential metabolites were analyzed by KEGG annotation and enrichment analysis. The results showed that 14 pathways affected by heat stress were identified by KEGG pathway enrichment analysis, including Sphingolipid metabolism, Pyrimidine metabolism, Citrate cycle (TCA cycle)), aminoacyl-tRNA biosynthesis, and so on. The analysis of the effect of heat stress on the cecal microflora of meat rabbits showed that the abundance of cecal Proteus in the HT group was significantly higher than that in the moderate Control group. The number of Candidatus-saccharimonas in the cecum microflora was significantly higher than that in the moderate temperature group (p < 0.05) which may be related to inflammatory diseases in the heat stress group. These findings indicated that the heat-stressed rabbits were in negative energy balance, which affected protein metabolism, and subsequently affected growth performance and carcass characteristics.

Effects of chronic heat stress on the immunophenotyping of lymphocytes in immune organs of growing pigs

This study aimed to investigate the effects of chronic heat stress on the immunophenotyping of lymphocytes in immune organs of growing pigs. A single-factor randomized block design was used, and 15 healthy growing large white barrows (5 litters, 3 pigs/litter) with similar body weight (40.8 kg) were assigned into 3 groups (5 pigs in each group). Groups were: control group (Con, in 23 °C environmental control chamber, fed ad libitum), heat stress group (HS, in 33 °C environmental control chamber, fed ad libitum), and pair-fed group (PF, in 23 °C environmental control chamber, fed diets according to the feed intake of HS group). After a 7-d adaption, the experiment lasted for 21 d. The results showed as follows: (1) activated T cells in the thymus of HS pigs were higher than those in PF pigs (P < 0.05). Monocytes and dendritic cells in the thymus of HS pigs were significantly higher than that in Con and PF pigs (P < 0.05), while the proportions of these 2 lymphocytes in the thymus of Con pigs did not differ from PF pigs (P > 0.05). Compared with Con pigs, the proportion of CD4+ (P < 0.05) and CD8+ T cells (P < 0.10) in the thymus was increased in HS pigs, while the proportion of CD4+ and CD8+ T cells in PF pigs did not differ from Con pigs (P > 0.05). (2) Compared with Con pigs, significantly decreased T cells, increased B cells and monocytes were found in the spleen of pigs exposed to heat stress (P < 0.05); the proportions of these 3 types of lymphocytes were not significantly different between Con and PF pigs (P > 0.05). The proportions of CD4+ T cells and Treg cells in the spleen of pigs exposed to heat stress tended to be lower than those in the Con pigs (P < 0.10). (3) The proportion of lymphocytes in the tonsils of pigs exposed to heat stress did not differ from Con pigs (P > 0.05); compared with PF pigs, the proportion of Treg cells was significantly decreased in HS pigs (P < 0.05). In conclusion, chronic heat stress stimulates the development and maturation of T cells in the pig thymus toward CD4+ and CD8+ T cells and increases the proportion of monocytes and dendritic cells; under the condition of chronic heat stress, the immune response process in the spleen of pigs is enhanced, but chronic heat stress impairs the survival of CD4+ T cells in the spleen.

Quantifying heat stress; the roles on metabolic status and intestinal integrity in poultry, a review

Heat stress adversely affects intestinal barrier integrity ranging from minor enterocyte injury to fatal inflammatory heat shocks. The current review discusses the physiological mechanisms of the adaptive response of poultry and the nutritional interventions to improve intestinal integrity during heat stress. There are several possible metabolic mechanisms of protection including stress adaptation signaling pathways, blood flow, intestinal barrier permeability, epithelial cell proliferation, antioxidant status, microbiota composition, expression of heat shock proteins, inflammatory responses, and energy metabolism. The current review discusses the methods of intestinal permeability determination in order to estimate the extent of damage in the farm. There is a lack of knowledge about the nutritional strategies and the interaction between nutrients to reduce intestinal barrier damage and elucidate mechanisms in heat stress.

Trehalose Attenuates Oxidative Stress and Endoplasmic Reticulum Stress-Mediated Apoptosis in IPEC-J2 Cells Subjected to Heat Stress

This study was carried out to investigate the effects of trehalose (Tre) on antioxidant capacity, endoplasmic reticulum stress (ERS) response and apoptosis of heat-stressed intestinal porcine epithelial cells (IPEC-J2). IPEC-J2 cells were cultured at 37 °C until the end of the experiment (control, CON); exposed to heat stress for 2 h (43 °C, HS); or pretreated with 0.1, 1, 5, 10, and 15 mM trehalose at 37 °C for 4 h prior to heat stress exposure for 2 h. The optimum level of trehalose for protecting against HS-induced cell injuries was determined to be 10 mM, as evidenced by the highest cellular viability and lowest malondialdehyde (MDA) content and lactate dehydrogenase (LDH) activity. Based on these, IPEC-J2 cells were divided into three groups: the first group was cultured at 37 °C until the end of the experiment (control, CON); the second group was exposed to heat stress for 2 h (43 °C, HS); the third group was pretreated with 10 mM trehalose for 4 h at 37 °C prior to heat stress exposure for 2 h (Tre + HS). The reactive oxygen species (ROS) content, superoxide dismutase (SOD) activity, mitochondrial membrane potential (MMP) changes, and expressions of the manganese superoxide dismutase (SOD2), ERS and apoptosis-related proteins were determined. Compared to the CON group, HS significantly increased ROS generation (p < 0.01), decreased SOD activity (p < 0.05), and downregulated protein expression of SOD2 (p < 0.01). Compared to the HS group, Tre supplementation reduced ROS levels and increased SOD activity and SOD2 expression to the levels that were comparable to the control (p < 0.05). The HS-induced ERS response was evidenced by the increased protein expressions of glucose-regulated protein 78 (GRP78) (p < 0.01), eukaryotic translation initiation factor 2α (p-eif2α) (p < 0.01), transcription activator 4 (ATF4) (p < 0.01), and the protein expression of C/EBP homologous protein (CHOP) (p < 0.01), which were the four hallmarks of ERS. The Tre + HS group showed lower expressions of GRP78 (p < 0.01), p-eif2α (p < 0.01), ATF4 (p < 0.01), and CHOP (p < 0.01) than that of the HS group. Tre pretreatment attenuated HS-induced mitochondrial apoptosis in IPEC-J2 cells, demonstrated by the increased MMP and decreased proapoptotic proteins active caspase 3, Bax, and cytochrome c (Cyt c). Taken together, trehalose can protect against HS-induced oxidative damage and endoplasmic reticulum stress-mediated apoptosis in IPEC-J2 cells. These data may provide a nutritional strategy for alleviating heat stress in pig production.

Transcriptomic Analysis of the Porcine Gut in Response to Heat Stress and Dietary Soluble Fiber from Beet Pulp

This study aimed to investigate the impact of heat stress (HS) and the effects of dietary soluble fiber from beet pulp (BP) on gene expression (differentially expressed genes, DEGs) of the porcine jejunum. Out of the 82 DEGs, 47 genes were up-regulated, and 35 genes were downregulated between treatments. The gene ontology (GO) enrichment analysis showed that the DEGs were related mainly to the actin cytoskeleton organization and muscle structure development in biological processes, cytoplasm, stress fibers, Z disc, cytoskeleton, and the extracellular regions in cellular composition, and actin binding, calcium ion binding, actin filament binding, and pyridoxal phosphate binding in the molecular function. The KEGG pathway analysis showed that the DEGs were involved in hypertrophic cardiomyopathy, dilated cardiomyopathy, vascular smooth muscle contraction, regulation of actin cytoskeleton, mucin type O-glycan biosynthesis, and African trypanosomiasis. Several of the genes (HSPB6, HSP70, TPM1, TAGLN, CCL4) in the HS group were involved in cellular oxidative stress, immune responses, and cellular differentiation. In contrast, the DEGs in the dietary BP group were related to intestinal epithelium integrity and immune response to pathogens, including S100A2, GCNT3, LYZ, SCGB1A1, SAA3, and ST3GAL1. These findings might help understand the HS response and the effect of dietary fiber (DF) regarding HS and be a valuable reference for future studies.

The impact of Zearalenone on heat-stressed skeletal muscle in pigs

Heat stress (HS) and Zearalenone (ZEN) exposure affect growth, production efficiency, and animal welfare; and, under extreme situations, both can be lethal. Given that both HS and ZEN independently cause oxidative stress, we hypothesized that simultaneous exposure to HS and ZEN would cause greater oxidative stress in porcine skeletal muscle than either condition, alone. To address this hypothesis, crossbred, prepubertal gilts were treated with either vehicle control (cookie dough) or ZEN (40 μg/kg) and exposed to either thermoneutral (TN; 21.0 °C) or 12-h diurnal HS conditions (night: 32.2 °C; day: 35.0 °C) for 7 d. Pigs were euthanized immediately following the environmental challenge and the glycolytic (STW) and oxidative (STR) portions of the semitendinosus muscle were collected for analysis. In STR, malondialdehyde (MDA) concentration, a marker of oxidative stress, tended to increase following ZEN exposure (P = 0.08). HS increased CAT (P = 0.019) and SOD1 (P = 0.049) protein abundance, while ZEN decreased GPX1 protein abundance (P = 0.064) and activity (P = 0.036). In STR, HS did not alter protein expression of HSP27, HSP70, or HSP90. Conversely, in STW, MDA-modified proteins remained similar between all groups. Consistent with STR, ZEN decreased GPX1 (P = 0.046) protein abundance in STW. In STW, ZEN decreased protein abundance of HSP27 (P = 0.032) and pHSP27 (P = 0.0068), while HS increased protein expression of HSP70 (P = 0.04) and HSP90 (P = 0.041). These data suggest a muscle fiber type-specific response to HS or ZEN exposure, potentially rendering STR more susceptible to HS- and/or ZEN-induced oxidative stress, however, the combination of HS and ZEN did not augment oxidative stress.

The Chinese Herbal Formula Huoxiang Zhengqi Dropping Pills Prevents Acute Intestinal Injury Induced by Heatstroke by Increasing the Expression of Claudin-3 in Rats

Intestinal injury has been regarded as an important causative factor for systemic inflammation during heatstroke, and maintaining intestinal integrity has been a potential target for the prevention of HS. Huoxiang Zhengqi Dropping Pills (HZPD) is a modern preparation of Huoxiang Zhengqi and widely used to prevent HS. The present study aims to explore the protective effect of HZDP on intestinal injury during heatstroke and analyze its potential pharmacodynamic basis. Male rats in the control and HS groups were given normal saline, and those in the HZDP groups were given HZDP (0.23, 0.46, and 0.92 g/kg) before induction of HS. Serum contents of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), intestinal fatty acid-binding protein (iFABP), and diamine oxidase (DAO) were determined using ELISA. Histopathology of intestinal injury was observed following H&E staining. The expression of claudin-3 was determined using western blot, immunohistochemistry, and immunofluorescence techniques. Moreover, network pharmacological tools were used to analyze the potential pharmacodynamic basis and the mechanism of HZDP. Treatment with HZDP significantly prolonged the time to reach Tc. Compared with the control group, the contents of TNF-α, IL-6, iFABP, and DAO in HS rats increased markedly. HZDP treatments reduced these levels significantly, and the effects in the middle dose group (0.46 g/kg) were most obvious. HZDP also attenuated intestinal injury and significantly reversed the decrease in claudin-3 expression. Bioinformatics analysis suggested that 35 active ingredients and 128 target genes of HZDP were screened from TCMSP and 93 target genes intersected with heatstroke target genes, which were considered potential therapeutic targets. TNF-α and IL-6 were the main inflammatory target genes of HZDP correlated with HS. These results indicated that HZDP effectively protected intestinal barrier function and prevented acute intestinal injury by increasing the expression of claudin-3 in rats, eventually improving heat resistance.

Potential biomarkers for chronic seasonal heat stress in Kagoshima Berkshire pigs reared in the subtropical region

Introduction

Potential biomarkers for chronic seasonal heat stress in Kagoshima Berkshire pigs reared in the subtropical region were investigated by comparing the biomarker changes in the summer (a period of chronic heat stress) and winter (a thermoneutral period) seasons.

Material and Methods

Pigs were allocated to summer- and winter-finishing cohorts, 12 each. The evaluations included assessment of carcass traits and internal organs’ normality carried out at the time of slaughter, and measurement of biomarkers in whole blood: derivatives of reactive oxygen metabolites (d-ROMs) and biological antioxidant potential as markers of oxidative stress, and serum amyloid A and albumin/globulin (A/G) ratio as markers of acute and chronic inflammation, respectively.

Results

The summer-finished pigs reared under subtropical field conditions showed lower carcass quality than the winter-finished pigs, indicating a potential adverse effect of summer temperatures on the swine industry. Marginal changes were observed in d-ROMs and the A/G ratio between the summer- and winter-finishing cohorts.

Conclusions

The results demonstrate that d-ROMs and the A/G ratio could be used as sensitive markers for heat stress under field conditions.

The Effect of Heat Stress and Vitamin and Micro-Mineral Supplementation on Some Mineral Digestibility and Electrolyte Balance of Pigs

Heat stress (HS) can have detrimental effects on intestinal integrity and can jeopardize the digestibility performance in pigs. With prolonged exposure to heat, some thermoregulatory processes in pigs are potential causes for electrolyte imbalance. The adverse effects of HS on mineral digestibility and electrolyte balance are not widely studied and information on its abatement through vitamin and micro-mineral supplementation in combinations above the recommended level in pigs is limited. The aim of this study is to research this area. Thirty-six Danbred hybrid barrows (65.1 ± 2.81kg) were distributed among the four treatments (n = 9 per treatment): (1) thermo-neutral (19.5 ± 0.9 °C, RH- 85.9 ± 7.3%)+ control diet (TC) (NRC, 2012), (2) HS (28.9 ± 0.9 °C, RH- 60.4 ± 4.3%) + control diet (HC), (3) HS +diet with elevated levels of vitamins (vitamin E and C) and micro-minerals (Zn and Se) (HT1), and (4) HS + diet with further elevation of vitamins and micro-minerals (HT2). Plasma samples were collected on days 7 and 21 of the experiment to investigate electrolyte concentration. During the experimental period, feces samples were collected from pigs placed in digestibility cages (six pigs from each treatment) to investigate the digestibility of Ca, P, Na, Se, and Zn. HS did not decrease the digestibility of minerals, but elevated supplementation of the selected vitamins and trace minerals improved it significantly. HS caused a significant decrease of Cl- (p < 0.01) in plasma, indicating an imbalance. In conclusion, pigs can have some resilience against heat stress in terms of mineral digestibility. Proper vitamin and trace mineral supplementation are key factors in the ability of pigs to overcome the negative effects of HS.

Effects of Selenium as a Dietary Source on Performance, Inflammation, Cell Damage, and Reproduction of Livestock Induced by Heat Stress: A Review

Heat stress as a result of global warming has harmful consequences for livestock and is thus becoming an urgent issue for animal husbandry worldwide. Ruminants, growing pigs, and poultry are very susceptible to heat stress because of their fast growth, rapid metabolism, high production levels, and sensitivity to temperature. Heat stress compromises the efficiency of animal husbandry by affecting performance, gastrointestinal health, reproductive physiology, and causing cell damage. Selenium (Se) is an essential nutritional trace element for livestock production, which acts as a structural component in at least 25 selenoproteins (SELs); it is involved in thyroid hormone synthesis, and plays a key role in the antioxidant defense system. Dietary Se supplementation has been confirmed to support gastrointestinal health, production performance, and reproductive physiology under conditions of heat stress. The underlying mechanisms include the regulation of nutrient digestibility influenced by gastrointestinal microorganisms, antioxidant status, and immunocompetence. Moreover, heat stress damage to the gastrointestinal and mammary barrier is closely related to cell physiological functions, such as the fluidity and stability of cellular membranes, and the inhibition of receptors as well as transmembrane transport protein function. Se also plays an important role in inhibiting cell apoptosis and reducing cell inflammatory response induced by heat stress. This review highlights the progress of research regarding the dietary supplementation of Se in the mitigation of heat stress, addressing its mechanism and explaining the effect of Se on cell damage caused by heat stress, in order to provide a theoretical reference for the use of Se to mitigate heat stress in livestock.

Crosstalk between Endoplasmic Reticulum Stress and Oxidative Stress in Heat Exposure-Induced Apoptosis Is Dependent on the ATF4-CHOP-CHAC1 Signal Pathway in IPEC-J2 Cells

The intestinal epithelium is susceptible to heat stress (HS), which leads to gut leakage and inflammation. However, the mechanisms underlying HS-induced intestine dysfunction have yet to be elucidated. We established an in vitro chronic heat exposure-induced intestinal injury of intestinal porcine epithelial cells (IPEC-J2) exposed to high temperatures (43 °C) for 12 h. The results revealed that HS increased reactive oxygen species (ROS) generation and decreased superoxide dismutase 2 (SOD2) expression, leading to oxidative stress. Western blotting analysis demonstrated that HS induced apoptosis as evidenced by increased cytochrome c (Cyt c) release in the cytoplasm and caspase 3 activation. Transcriptome sequencing analysis revealed that HS activated the endoplasmic reticulum stress (ERS) response/unfolded protein response (UPR) but inhibited glutathione metabolism. Specifically, HS triggered the pro-apoptotic activating transcription factor 4 (ATF4)/CEBP-homologous protein (CHOP) branch of the UPR. Interestingly, glutathione-specific gamma-glutamylcyclotransferase1 (CHAC1) involved in glutathione degradation was upregulated due to heat exposure and was proved to be downstream of the ATF4-CHOP signal pathway. Knockdown of CHAC1 attenuated the HS-induced decrease in glutathione level and cell apoptosis. These studies suggest that crosstalk between ERS and oxidative stress in HS-induced apoptosis might be dependent on the ATF4-CHOP-CHAC1 signal pathway in IPEC-J2 cells.

Heat stress induced IPEC-J2 cells barrier dysfunction through endoplasmic reticulum stress mediated apoptosis by p-eif2α/CHOP pathway

Heat stress (HS) induced by high ambient temperatures compromises intestinal epithelial cell. However, the underlying mechanisms by which HS causes intestinal barrier dysfunction remain unclear. In this study, we established an in vitro acute-HS-induced intestinal damage using porcine small intestinal epithelial cell (IPEC-J2) that exposed to the high temperatures (43°C) for 2 h. The cell proliferation, apoptosis, tight junction (TJ) barrier integrity and transcriptomic profiles were measured. The results showed that HS decreased cell viability while increased proapoptotic signaling evidenced by Bax/bcl2 ratio, cytochrome C release to cytosol and active-caspase 3 increases (p < 0.01). HS led to decreased transepithelial electrical resistance, increased cell permeability, and downregulated TJ proteins including ZO1, occludin, and claudin 3 (p < 0.05). Transcriptome sequencing and KEGG pathway analysis revealed HS-induced cell cycle arrest and activation of endoplasmic reticulum stress (ERS) response mediated by a critical transcript eif2α and proapoptotic molecule DDIT3 (known as CHOP). Furthermore, inhibition of ERS by 4-phenylbutyrate (4-PBA) administration and knockdown of eif2α and CHOP significantly attenuated IPEC-J2 cells apoptosis (p < 0.05). Transmission electron microscopy analysis suggested that 4-PBA inhibited HS-induced increase in ER lumen diameter, indicating ultrastructural sign of ERS. In addition, HS-induced impairment of TJs was significantly attenuated by 4-PBA (p < 0.05). Collectively, HS induces ERS and activates the p-eif2α/CHOP signaling pathway to impair epithelial barrier integrity through triggering the intestinal epithelial cell apoptosis.

Heat Stress Alters the Intestinal Microbiota and Metabolomic Profiles in Mice

Background

Heat stress has negative effects on the intestinal health of humans and animals. However, the impact of heat stress on intestinal microbial and metabolic changes remains elusive. Here, we investigated the cecal microbial and metabolic profiles in mice in response to heat stress.

Methods

The mouse heat stress model was constructed by simulating a high-temperature environment. Twenty mice were randomly assigned to two groups, the control group (CON, 25°C) and the heat treatment group (HS, 40°C from 13:00 to 15:00 every day for 7 days). Serum and cecal contents were collected from the mice for serum biochemical analysis, 16S rRNA high-throughput sequencing, and non-targeted metabolomics.

Results

Both core body temperature and water intake were significantly increased in the HS group. Serum biochemical indicators were also affected, including significantly increased triglyceride and decreased low-density lipoprotein in the heat stress group. The composition and structure of intestinal microbiota were remarkably altered in the HS group. At the species level, the relative abundance of Candidatus Arthromitus sp. SFB-mouse-Japan and Lactobacillus murinus significantly reduced, while that of Lachnospiraceae bacterium 3-1 obviously increased after HS. Metabolomic analysis of the cecal contents clearly distinguished metabolite changes between the groups. The significantly different metabolites identified were mainly involved in the fatty acid synthesis, purine metabolism, fatty acid metabolism, cyanoamino acid metabolism, glyceride metabolism, and plasmalogen synthesis.

Conclusion

In summary, high temperature disrupted the homeostatic balance of the intestinal microbiota in mice and also induced significant alterations in intestinal metabolites. This study provides a basis for treating intestinal disorders caused by elevated temperature in humans and animals and can further formulate nutritional countermeasures to reduce heat stress-induced damage.

Recent advances in the use of phytochemicals to manage gastrointestinal oxidative stress in poultry and pigs

Plants are integral components of pig and poultry feed, and aside from their raw nutritive value, some phytochemicals contain bioactive compounds. The aim of the present paper is to review recent advances in the use of some phytochemicals in pig and poultry feed, focusing on the examples of isoquinoline alkaloids, polyphenol rich sugarcane extracts and superoxide dismutase-rich melon pulp extracts. As gut health is critical for efficient production, the review will focus on recent results modulating oxidative stress within the gastrointestinal tract and the potential mechanisms of action.

Jejunal mucosa proteomics unravel metabolic adaptive processes to mild chronic heat stress in dairy cows

Climate change affects the duration and intensity of heat waves during summer months and jeopardizes animal health and welfare. High ambient temperatures cause heat stress in dairy cows resulting in a reduction of milk yield, feed intake, and alterations in gut barrier function. The objectives of this study were to investigate the mucosal amino acid, glucose and lactate metabolism, as well as the proteomic response of the small intestine in heat stressed (HS) Holstein dairy cows. Cows of the HS group (n = 5) were exposed for 4 days to 28 °C (THI = 76) in a climate chamber. Percentage decrease in daily ad libitum intake of HS cows was calculated to provide isocaloric energy intake to pair-fed control cows kept at 15 °C (THI = 60) for 4 days. The metabolite, mRNA and proteomic analyses revealed that HS induced incorrect protein folding, cellular destabilization, increased proteolytic degradation and protein kinase inhibitor activity, reduced glycolysis, and activation of NF-κB signaling, uronate cycling, pentose phosphate pathway, fatty acid and amino acid catabolism, mitochondrial respiration, ATPase activity and the antioxidative defence system. Our results highlight adaptive metabolic and immune mechanisms attempting to maintain the biological function in the small intestine of heat-stressed dairy cows.

Early Heat Exposure Effects on Proteomic Changes of the Broiler Liver under Acute Heat Stress

Simple Summary

Early heat exposure have been studied in the poultry industry as a method of reducing heat stress (HS) on poultry. However, the results of each study are inconsistent, and it has not been confirmed which mechanisms reduce HS by early heat exposure. Therefore, we tried to confirm the relaxation mechanism through proteomic analysis after applying early and acute heat exposure to broilers. The broilers were divided into three treatments, followed by CC (control group), CH (acute HS at the 35th day), and HH (early heat exposure at the fifth day and acute HS at the 35th day. Liver samples were collected and analyzed for proteomics and functional analysis. Proteins related to various functions, such as carbohydrate metabolism, fatty acid metabolism, energy metabolism, and the oxidation–reduction process, which were dramatically changed by acute HS, and were alleviated similar to the control group by early heat exposure. Through these results, the mechanism by which early heat exposure induces homeostasis during acute HS, and the possibility of the early heat exposure as a method of reducing HS were confirmed.

Abstract

As environmental temperatures continue to rise, heat stress (HS) is having a negative effect on the livestock industry. In order to solve this problem, many studies have been conducted to reduce HS. Among them, early heat exposure has been suggested as a method for reducing HS in poultry. In this study, we analyzed proteomics and tried to identify the metabolic mechanisms of early heat exposure on acute HS. A total of 48 chicks were separated into three groups: CC (control groups raised at optimum temperature), CH (raised with CC but exposed acute HS at the 35th day), and HH (raised with CC but exposed early heat at the fifth day and acute HS at the 35th day). After the whole period, liver samples were collected for proteomic analysis. A total of 97 differentially expressed proteins were identified by acute HS. Of these, 62 proteins recovered their expression levels by early heat exposure. We used these 62 proteins to determine the protective effects of early heat exposure. Of the various protein-related terms, we focused on the oxidative phosphorylation, fatty acid metabolism, carbohydrate metabolism, and energy production metabolism. Our findings suggest the possibility of early heat exposure effects in acute HS that may be useful in breeding or management techniques for producing broilers with high heat resistance.

Adverse Effects of Heat Stress on the Intestinal Integrity and Function of Pigs and the Mitigation Capacity of Dietary Antioxidants: A Review

Heat stress (HS) significantly affects the performance of pigs by its induced stressors such as inflammation, hypoxia and oxidative stress (OS), which mightily strain the intestinal integrity and function of pigs. As heat stress progresses, several mechanisms in the intestinal epithelium involved in the absorption of nutrients and its protective functions are altered. Changes in these mechanisms are mainly driven by cellular oxidative stress, which promotes disruption of intestinal homeostasis, leading to intestinal permeability, emphasizing intestinal histology and morphology with little possibility of recovering even after exposure to HS. Identification and understanding of these altered mechanisms are crucial for providing appropriate intervention strategies. Therefore, it is this papers' objective to review the important components for intestinal integrity that are negatively affected by HS and its induced stressors. With due consideration to the amelioration of such effects through nutritional intervention, this work will also look into the capability of dietary antioxidants in mitigating such adverse effects and maintaining the intestine's integrity and function upon the pigs' exposure to high environmental temperature.

Heat stress on microbiota composition, barrier integrity, and nutrient transport in gut, production performance, and its amelioration in farm animals

Livestock species experience several stresses, particularly weaning, transportation, overproduction, crowding, temperature, and diseases in their life. Heat stress (HS) is one of the most stressors, which is encountered in livestock production systems throughout the world, especially in the tropical regions and is likely to be intensified due to global rise in environmental temperature. The gut has emerged as one of the major target organs affected by HS. The alpha- and beta-diversity of gut microbiota composition are altered due to heat exposure to animals with greater colonization of pathogenic microbiota groups. HS also induces several changes in the gut including damages of microstructures of the mucosal epithelia, increased oxidative insults, reduced immunity, and increased permeability of the gut to toxins and pathogens. Vulnerability of the intestinal barrier integrity leads to invasion of pathogenic microbes and translocation of antigens to the blood circulations, which ultimately may cause systematic inflammations and immune responses. Moreover, digestion of nutrients in the guts may be impaired due to reduced enzymatic activity in the digesta, reduced surface areas for absorption and injury to the mucosal structure and altered expressions of the nutrient transport proteins and genes. The systematic hormonal changes due to HS along with alterations in immune and inflammatory responses often cause reduced feed intake and production performance in livestock and poultry. The altered microbiome likely orchestrates to the hosts for various relevant biological phenomena occurring in the body, but the exact mechanisms how functional communications occur between the microbiota and HS responses are yet to be elucidated. This review aims to discuss the effects of HS on microbiota composition, mucosal structure, oxidant-antioxidant balance mechanism, immunity, and barrier integrity in the gut, and production performance of farm animals along with the dietary ameliorations of HS. Also, this review attempts to explain the mechanisms how these biological responses are affected by HS.

The effect of Mitoquinol (MitoQ) on heat stressed skeletal muscle from pigs, and a potential confounding effect of biological sex

Heat stress (HS) poses a major threat to human health and agricultural production. Oxidative stress and mitochondrial dysfunction appear to play key roles in muscle injury caused by HS. We hypothesized that mitoquinol (MitoQ), would alleviate oxidative stress and cellular dysfunction in skeletal muscle during HS. To address this, crossbred barrows (male pigs) were treated with placebo or MitoQ (40 mg/d) and were then exposed to thermoneutral (TN; 20 °C) or HS (35 °C) conditions for 24 h. Pigs were euthanized following the environmental challenge and the red portion of the semitendinosus (STR) was collected for analysis. Unexpectedly, malondialdehyde concentration, an oxidative stress marker, was similar between environmental and supplement treatments. Heat stress decreased LC3A/B-I (p < 0.05) and increased the ratio of LC3A/B-II/I (p < 0.05), while p62 was similar among groups suggesting increased degradation of autophagosomes during HS. These outcomes were in disagreement with our previous results in muscle from gilts (female pigs). To probe the impact of biological sex on HS-mediated injury in skeletal muscle, we compared STR from these barrows to archived STR from gilts subjected to a similar environmental intervention. We confirmed our previous findings of HS-mediated dysfunction in muscle from gilts but not barrows. These data also raise the possibility that muscle from gilts is more susceptible to environment-induced hyperthermia than muscle from barrows.

Preventing necroptosis by scavenging ROS production alleviates heat stress-induced intestinal injury

Background: Worldwide heat stroke incidence has increased in recent years and is associated with high morbidity and mortality. Therefore, it is critical to identify mechanisms that mediate heat stroke. Previous studies suggested that damage to the small intestine may be a major factor in heat stroke-related morbidity and mortality. However, the mechanism underlying heat stroke related small intestine injury remains unclear.Methods: To explore how heat stroke promotes intestinal damage, we applied two well established models: mouse and IEC-6 cells heat stress (HS) to mimic heat stroke both in vivo and in vitro. The percentages of viability and cell death were assessed by WST-1 and LDH release assays. Induction of HS-induced cell death was analyzed by flow cytometry with Annexin V-FITC/PI staining. Flow cytometry was used to analyze HS-induced mitochondrial superoxide with MitoSOX staining. Malondialdehyde (MDA) levels and superoxide dismutase (SOD) levels were detected by ELISA. Flow cytometry was used to analyze HS-induced mitochondrial depolarization (low ΔΨm) with JC-1 staining. Histopathology changes in the ileum were detected by H&E staining.The ileum ultrastructure was observed by transmission electron microscopy (TEM). RIPK1, RIPK3, phosphorylated MLKL, and MLKL levels were detected by Western blot. RIPK1-RIPK3 complexes were measured by immunoprecipitation assay.Results: HS increased both necrotic cell rate and RIPK1, RIPK3, and phosphorylated MLKL expression levels in IEC-6 cells. These increased expression levels promoted higher RIPK1-RIPK3 complex formation, leading to necrosome formation both in vivo and in vitro. Moreover, HS caused dyshomeostasis, an oxidative stress response, and mitochondrial damage, along with small intestinal tissue injury and cell death. However, IEC-6 cells or mice pretreated with the RIPK1 activity chemical inhibitor Nec-1 or RIPK3 activity chemical inhibitor GSK'872 significantly reversed these phenomena and promoted balance in oxidative stress response homeostasis. More importantly, the reactive oxygen species (ROS) scavenger N-acetyl-L-cysteine (NAC) pretreatment significantly inhibited HS-induced RIPK1/RIPK3-dependent necroptosis formation both in vivo and in vitro, suggesting that preventing necroptosis via scavenging ROS production might alleviate HS-induced small intestinal tissue injury and cell death.Conclusion: This study provides strong evidence that HS causes damage to both the small intestine and intestinal epithelial cells, scavenging ROS production can significantly alleviate such RIPK1/RIPK3-dependent necroptosis, mediating HS-induced intestinal damage both in vitro and in vivo. These findings provide a clear target for future mechanism-based therapeutic strategies for patients diagnosed with heat stroke.

Betaine and Isoquinoline Alkaloids Protect against Heat Stress and Colonic Permeability in Growing Pigs

Heat stress (HS) compromises productivity of pork production, in part as a result of increased oxidative stress and inflammatory responses, particularly within the gastrointestinal tract. This study aimed to investigate whether plant-derived betaine and isoquinoline alkaloids could ameliorate HS in pigs. Fifty female Large White × Landrace grower pigs, which were acclimated to control (CON), control plus betaine (BET), or control plus isoquinoline alkaloids (IQA) diets for 14 days were then exposed to heat stress or thermoneutral condition. Both BET and IQA partially ameliorated increases in respiration rate (p = 0.013) and rectal temperature (p = 0.001) associated with HS conditions. Heat stress increased salivary cortisol concentrations and reduced plasma creatinine, lactate, and thyroid hormone concentrations. Heat stress increased colon FD4 permeability, which was reduced by IQA (p = 0.030). Heat stress increased inflammation in the jejunum and ileum, as indicated by elevated interleukin-1β (p = 0.022) in the jejunum and interleukin-1β (p = 0.004) and interleukin-8 (p = 0.001) in the ileum. No differences in plasma total antioxidant capacity (TAC) were observed with HS, but betaine increased plasma TAC compared to IQA. Dietary BET increased betaine concentrations in the jejunum, ileum (p < 0.001 for both), plasma, liver, kidney (p < 0.010 for all), urine (p = 0.002) and tended to be higher in muscle (p = 0.084). Betaine concentration was not influenced by HS, but it tended to be higher in plasma and accumulated in the liver. These data suggest that betaine and isoquinoline alkaloids supplementation ameliorated consequences of heat stress in grower pigs and protected against HS induced increases in colonic permeability.

Responses of intestinal morphology and function in offspring to heat stress in primiparous sows during late gestation

Late gestation is a key period for intestinal development. Maternal heat exposure may induce intestinal dysfunction of offspring. To investigate the responses of intestinal morphology and function of offspring to the maternal heat stress (HS), twelve first-parity Landrace × Large White sows were assigned to thermoneutral (TN) (18-22 °C; n = 6) or HS (28-32 °C; n = 6) treatment groups at 85 d of gestation until natural farrowing. Twenty-four newborn piglets (two piglets at medium body weight from each litter) were randomly selected and divided into in utero thermoneutral (IUTN, n = 12) and heat-stressed (IUHS, n = 12) groups according to the sow's treatment. Blood and intestinal samples were harvested to evaluate stress hormone levels, intestinal morphology, integrity and barrier function in the newborn piglets. Our results showed that maternal HS piglets exhibited increased serum adrenocorticotropic hormone (ACTH) concentration compared with that observed in the IUTN group. IUHS piglets showed lower lactase activities in the jejunum and ileum, whereas no significant differences were found between the two groups in the length of intestine, villus length or crypt depth. Serum diamine oxidase (DAO) activity was increased in IUHS piglets. IUHS piglets also exhibited decreased ZO-1, ZO-2 and MUC2 mRNA expression in the jejunum, while the protein levels were not affected. Additionally, IUHS piglets had a lower apoptotic percentage and FAS mRNA expression in the jejunum than those in the IUTN group. Taken together, these results demonstrate that high ambient temperature during late gestation of primiparous sows causes stress response in neonatal piglets, compromising intestinal permeability and mucosal barrier function, which may be partly mediated by inducing intestinal apoptosis.

Effects of dietary supplementation with l-arginine on the intestinal barrier function in finishing pigs with heat stress

Previous studies showed heat stress reduces body weight gain and feed intake associated with damaged intestinal barrier function, and l-arginine (L-Arg) enhanced intestinal barrier function in young animals under stress. The aim of this study was to evaluate effects of L-Arg on serum hormones, intestinal morphology, nutrients absorption and epithelial barrier functions in finishing pigs with heat stress. Forty-eight finishing pigs (Landrace) were balanced for sex and then randomly assigned to six groups: TN group, thermal neutral (22°C, ~80% humidity) with a basal diet; HS group, heat stress (cyclical 35°C for 12 hr and 22°C for 12 hr, ~80% humidity) with a basal diet; PF group, thermal neutral (22°C, ~80% humidity) and pair-fed with the HS; the TNA, HSA and PFA groups were the basal diet of TN group, HS group and PF group supplemented with 1% L-Arg. Results showed that HS decreased (p < .05) the thyroxine concentrations and increased (p < .05) the insulin concentrations in serum compared with the TN group, but 1% L-Arg had no significant effects on them. Both HS and PF significantly increased (p < .05) the mRNA expression of cationic amino acid transporters (CAT1 and CAT2) and decreased the mRNA expression of solute carrier family 5 member 10 (SGLT1) in the jejunum compared with the TN group. Compared with the TN group, HS reduced the expression of tight junction (TJ) protein zonula occluden-1 (ZO-1) and occludin, but PF only decreased ZO-1 expression in the jejunum. Results exhibited that dietary supplementation with 1% L-Arg improved the intestinal villous height, the ratio of villous height to crypt depth, and the expression of occludin and porcine beta-defensin 2 (pBD2) in the jejunum of intermittent heat-treated finishing pigs. In conclusion, dietary supplementation with 1% L-Arg could partly attenuate the intermittent heat-induced damages of intestinal morphology and epithelial barrier functions in finishing pigs.

Intestinal Injury in Heat Stroke

BACKGROUND

Heat stroke is a life-threatening syndrome that is characterized by its severe clinical symptoms, rapid progression, and high rate of mortality. Recently, research has indicated that a dysfunctional intestinal epithelia barrier plays an important role in the pathophysiology of heat stroke. Protecting the intestines from heat stress had been identified as a potentially effective treatment for patients with heat stroke and may reduce the innate immune response caused by endotoxins in circulation.

OBJECTIVES

The aim of this review is to discuss this key event in heat stroke and to describe the mechanism during progression.

DISCUSSION

Direct injuries and secondary impairments of the intestine induced by heat stress are discussed; recent studies that refer to intestine-specific prevention and treatment in heat stroke and heat stress-induced injuries are also summarized.

CONCLUSIONS

A more detailed pathogenesis of heat stroke needs to be elucidated so that potentially effective means of treatment and prevention of heat stroke can be developed and studied.

L-Arginine alleviates heat stress-induced intestinal epithelial barrier damage by promoting expression of tight junction proteins via the AMPK pathway

Heat stress (HS) and secondary restricted blood flow to the intestines cause dysfunction of the intestinal epithelial barrier. Tight junctions (TJs) are essential to maintain intestinal integrity. L-Arginine has beneficial effects on gut functions. However, the underlying mechanisms remain largely unknown. This study tested the hypothesis that L-arginine regulates the TJ network by activating AMP-activated protein kinase (AMPK) signaling, which in turn improves intestinal barrier functions under HS. IEC-6 cells and rat small intestines were used as experiment models of heat stress. AICAR and dorsomorphin were used to activate and inhibit the AMPK pathway, respectively. Cell proliferation, apoptosis, differential gene expression and KEGG pathway analysis, intestinal paracellular permeability, intestinal morphology, and expression of HSP and TJ proteins, and p-AMPK were determined. L-Arginine promoted cell proliferation and reduced apoptosis after heat exposure at an optimal concentration of 5 mmol. Transcriptome sequencing analysis revealed that differentially expressed genes associated with the HSP family and TJs were elevated by L-arginine. According to KEGG pathway analysis, L-arginine activated the AMPK signaling pathway. In vivo, intestinal damage resulted in obvious morphological changes as well as apoptosis with TUNEL and caspase-3 staining under HS and dorsomorphin treatments. Furthermore, HS and dorsomorphin increased the serum D-lactate concentration, diamine oxidase activity, and mRNA expression level of MLCK (P < 0.05). In contrast, L-arginine and AICAR treatments reduced intestinal injury, maintained intestinal permeability, and increased the villus/crypt ratio under hyperthermia. L-Arginine had the same effect as AICAR both in vitro and in vivo, namely increasing p-AMPK protein expression. L-Arginine and AICAR also upregulated the mRNA expression level of HSP70 and HSP90, and downregulated mRNA expression of MLCK (P < 0.05). The protein expression levels of TJ proteins ZO-1 and claudin-1 were suppressed by heat stroke and dorsomorphin, but enhanced by L-arginine and AICAR. Our findings indicate that activation of AMPK signaling by L-arginine is associated with improved intestinal mucosal barrier functions by enhancing the expression of TJs in rat small intestines and IEC-6 cells during HS.

Chronic Heat Stress Induces Acute Phase Responses and Serum Metabolome Changes in Finishing Pigs

Simple Summary

There is limited information on the serum metabolome of heat-stressed finishing pigs. Our results indicated that heat stress led to oxidative stress and acute phase response. Pigs chronically exposed to high ambient temperature were in negative energy balance status. Three gut microbiome-derived metabolites (fluorine, lyxose 1, and D-galacturonic) were likely to be biomarkers for monitoring animal health.

Abstract

Heat stress (HS) is a main environmental challenge affecting the animal welfare and production efficiency in pig industry. In recent years, numerous reports have studied the alterations in gene expressions and protein profiles in heat-stressed pigs. However, the use of metabolome to unravel adaptive mechanisms of finishing pig in response to chronic HS have not yet been elucidated. We aimed to investigate the effects of chronic HS on serum metabolome in finishing pigs, and to identify the biomarkers of heat stress. Pigs (n = 8 per treatment) were exposed to either thermal neutral (TN; 22 °C) or heat stress (HS, 30 °C) conditions for three weeks. Serum metabonomics of TN- and HS-treated pigs were compared using the GC-MS approach. Metabonomics analysis revealed that twenty-four metabolites had significantly different levels in TN compared to HS (variable importance in the projection values >1 and p < 0.05). These metabolites are involved in carbohydrate, amino acid, fatty acid, amines metabolism, and gut microbiome-derived metabolism. Three serum monoses (glucose, mannose 2, and galactose) and 6-phosphogluconic acid were decreased, indicating insufficient source of fuel for energy supply, resulting in negative energy balance (NEB) in heat-stressed pigs. Increased levels of non-esterified fatty acid (myristic acid, palmitic acid, and linoleic acid) and short-chain fatty acids (3-hydroxybutanoic acid and maleic acid) suggested fat decomposition compensating for energy shortage, which was an adaptive response to NEB. Increased concentrations of fluorine, lyxose 1, and D-galacturonic acid were significantly correlated with the levels of acute phase proteins (HP, LBP, α2-HSG, and Lysozyme), suggesting acute phase response in HS-stressed pigs. These metabolites are expected to be novel biomarkers of chronic HS in pigs, yet the use of which awaits further validation.

Role of MAPKs in HSP70's Protection against Heat Stress-Induced Injury in Rat Small Intestine

Aim

To evaluate the role of heat shock protein 70 (HSP70) on the MAPK pathway activation with quercetin treatment and its protection against small intestine impairments of heat stressed rats.

Methods

Forty-eight male Sprague-Dawley rats aged 6 weeks were randomized to three groups (n=16/group), namely, control (CON), heat stress (HS), and heat stress + quercetin (HQ). The experiment lasted for 14 days with daily 50 min of heat stress treatment (43°C) for the HS and HQ groups. Rats of HQ group were intragastrically given 0.5 ml quercetin solution (50 mg/kg body weight) before the heat stress treatment. Half of the animals were sacrificed on day 7 and the rest on day 14 for tissue sampling. Intestinal morphology, small intestine morphology and permeability, protein expression of HSP70, phosphorylation of extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), p38 mitogen-activated protein kinase (MAPK), and caspase-3 activity were examined.

Results

Heat stress caused morphological damage to the small intestine and increased intestinal permeability. HSP70 expression and MAPK activity in the small intestine were increased by heat stress. Inhibition of HSP70 by quercetin did not change intestinal permeability compared with the HS group but aggravated intestinal injury and affected the activation of MAPKs and caspase-3.

Conclusions

HSP70 may modulate stress-activated signaling and acts in a protective manner via MAPK signaling. Affecting HSP70 protective mechanisms could be useful for protection against heat stress-induced injury in rat small intestine.

Proteomic changes of the porcine skeletal muscle in response to chronic heat stress

BACKGROUND

Heat stress (HS) has an adverse effect on meat quality; however, the underlying molecular mechanisms altering meat quality due to muscle responses to stress remain unclear. Sixteen castrated male crossbreeds between Landrace × Yorkshire sows and Duroc boars (79.00 ± 1.50 kg body weight) were exposed to either thermal neutral (22 °C, n = 8) or HS (30 °C, n = 8) conditions for 3 weeks. Subsequently, the longissimus dorsi (LD) muscle of all pigs was assayed for meat quality parameters and proteome analysis.

RESULTS

HS decreased post mortem (24 h) pH and intramuscular fat, changed ultimate L*, a* and b* values and increased drip loss and shear force. Proteome analysis of the LD was conducted by two-dimensional gel electrophoresis and mass spectrometry. A total of 23 differentially expressed proteins were identified, of which three were verified by western blotting analysis. The identified proteins were involved in six types of biological process: carbohydrate metabolism, myofibrillar and cytoskeleton structure, stress response, antioxidant and detoxification, calcium binding and cellular apoptosis. Interestingly, HS induced higher levels of heat shock protein, antioxidants and calcium binding proteins, which are involved in the mechanisms of defense and homeostasis.

CONCLUSION

The results indicate that HS-induced changes in the expression of myofibrillar proteins, glucose and energy metabolism-related proteins, heat shock protein and antioxidant enzymes might, at least partly, contribute to increase in meat tenderness. These findings will provide the foundation for developing future mitigating solutions and preventative therapies to reduce the detrimental effects of chronic HS on muscle function, metabolism and meat quality. © 2017 Society of Chemical Industry.

Chronic Heat Stress Induces Immune Response, Oxidative Stress Response, and Apoptosis of Finishing Pig Liver: A Proteomic Approach

Heat stress (HS) negatively affects human health, animal welfare, and livestock production. We analyzed the hepatic proteomes of finishing pigs subjected to chronic heat stress (HS), thermal neutral (TN), and restricted feed intake conditions, identifying differences between direct and indirect (via reduced feed intake) HS. Twenty-four castrated male pigs were randomly allocated to three treatments for three weeks: (1) thermal neutral (TN) (22 °C) with ad libitum feeding; (2) chronic HS (30 °C) with ad libitum feeding; and (3) TN, pair-fed to HS intake (PF). Hepatic proteome analysis was conducted using two-dimensional gel electrophoresis and mass spectrometry. Both HS and PF significantly reduced liver weight (p < 0.05). Forty-five hepatic proteins were differentially abundant when comparing HS with TN (37), PF with TN (29), and HS with PF (16). These proteins are involved in heat shock response and immune defense, oxidative stress response, cellular apoptosis, metabolism, signal transduction, and cytoskeleton. We also observed increased abundance of proteins and enzymes associated with heat shock response and immune defense, reduced the redox state, enhanced multiple antioxidant abilities, and increased apoptosis in HS liver. Heat-load, independent of reduced feed intake, induced an innate immune response, while food restriction caused stress and cellular apoptosis. Our results provide novel insights into the effects of chronic HS on liver.

Selenium and vitamin E together improve intestinal epithelial barrier function and alleviate oxidative stress in heat-stressed pigs

What is the central question of this study? Oxidative stress may play a role in compromising intestinal epithelial barrier integrity in pigs subjected to heat stress, but it is unknown whether an increase of dietary antioxidants (selenium and vitamin E) could alleviate gut leakiness in heat-stressed pigs. What is the main finding and its importance? Levels of dietary selenium (1.0 p.p.m.) and vitamin E (200 IU kg(-1) ) greater than those usually recommended for pigs reduced intestinal leakiness caused by heat stress. This finding suggests that oxidative stress plays a role in compromising intestinal epithelial barrier integrity in heat-stressed pigs and also provides a nutritional strategy for mitigating these effects. Heat stress compromises the intestinal epithelial barrier integrity of mammals through mechanisms that may include oxidative stress. Our objective was to test whether dietary supplementation with antioxidants, selenium (Se) and vitamin E (VE), protects intestinal epithelial barrier integrity in heat-stressed pigs. Female growing pigs (n = 48) were randomly assigned to four diets containing from 0.2 p.p.m. Se and 17 IU kg(-1) VE (control, National Research Council recommended) to 1.0 p.p.m. Se and 200 IU kg(-1) VE for 14 days. Six pigs from each dietary treatment were then exposed to either thermoneutral (20°C) or heat-stress conditions (35°C 09.00-17.00 h and 28°C overnight) for 2 days. Transepithelial electrical resistance and fluorescein isothiocyanate-dextran (4 kDa; FD4) permeability were measured in isolated jejunum and ileum using Ussing chambers. Rectal temperature, respiratory rate and intestinal HSP70 mRNA abundance increased (all P < 0.001), and respiratory alkalosis occurred, suggesting that pigs were heat stressed. Heat stress also increased FD4 permeability and decreased transepithelial electrical resistance (both P < 0.01). These changes were associated with changes indicative of oxidative stress, a decreased glutathione peroxidase (GPX) activity and an increased glutathione disulfide (GSSG)-to-glutathione (GSH) ratio (both P < 0.05). With increasing dosage of Se and VE, GPX-2 mRNA (P = 0.003) and GPX activity (P = 0.049) increased linearly, the GSSG:GSH ratio decreased linearly (P = 0.037), and the impacts of heat stress on intestinal barrier function were reduced (P < 0.05 for both transepithelial electrical resistance and FD4 permeability). In conclusion, in pigs an increase of dietary Se and VE mitigated the impacts of heat stress on intestinal barrier integrity, associated with a reduction in oxidative stress.