Days Of Cold Exposure Research Articles

Mitigation of extreme winter stress in European seabass, Dicentrarchus labrax through dietary supplementation

Climate change is driving the dangerous confluence of extreme weather events. Among others, aquatic ecosystems are the most affected one. This study sheds light on how dietary supplements affect the physiological responses of European seabass during extreme winter exposure. Fish were provided with three dietary supplements: vitamins C and E (diet-1), propolis (diet-2), and phycocyanin (diet-3) for 45 days. They were then exposed to a simulated extreme winter cold (7 °C) for 20 days. The results showed that dietary supplements do not have a significant impact on weight, growth rate, and protein efficiency ratio before cold exposure. Levels of Na + and Cl − in the fish remained stable across all diets during both control (20 °C) and 7 °C exposure. However, on the 20th day of cold exposure, fish fed diet-3 exhibited notably higher levels of K+ compared to the other two diets, whereas blood glucose was significantly lower in fish fed diet-1. On day 20, significantly higher GPT activities were observed in fish fed diet-1. No significant effects of dietary supplementation were observed in fish serum cholesterol and protein levels. Before cold stress, fish fed the control diet exhibited significantly lower triglyceride levels (p < 0.05). However, during cold exposure, triglyceride levels increased in fish fed diet-1 and the control diet. On day 20, fish fed diet-3 exhibited a comparatively higher lactate content. Conversely, cortisol levels were significantly lower (p < 0.05) in fish fed diets 2 and 3 on the same day. No dietary effects were observed on fish muscle HSP70 gene expression. On days 10 and 20, SREBP1 was significantly upregulated in fish fed all diets. On day 20 of cold exposure, FADS2 and GLUT2 genes were downregulated in the fish fed control diet compared to those fed diets 2 and 3. Before cold stress, fish on the control diet showed higher TNF-1α expression in the spleen. SREBP1 showed a significant upregulation on day 10 in fish fed diet-2. FADS2 gene expression remained unchanged during cold stress. GLUT2 expression showed no noticeable effects throughout the study. Overall, during extreme cold exposure, we observed decreased levels of blood cortisol, transaminase, dehydrogenase, and metabolites, along with a comparatively higher upregulation of growth, metabolic, and immune genes in fish fed diets supplemented with propolis, phycocyanin, and vitamins C&E. These results suggest that dietary supplements can help European seabass cope better with extreme cold, at least for short periods of up to 20 days.

Wide-characterization of high and low dry matter kiwifruit through spatiotemporal multi-omic approach

Despite the widespread use of dry matter content (DMC) as an indicator of kiwifruit quality, the physiological and molecular impact of DMC in fruit ripening remains unknown. Herein, the post-harvest physiological, metabolomic, and transcriptomic influence of DMC status on the pericarp and placenta tissue of ‘Hayward’ kiwifruit at harvest and at the onset of post-cold ripening was investigated. A segregation strategy based on DMC in commercially harvested kiwifruit was achieved with near-infrared spectroscopy for the estimation of DMC in individual fruits. Additionally, kiwifruits with distinct DMC levels were treated with 1-methylcyclopropene (1-MCP) and systematically monitored for ripening changes (20°C) at various intervals after cold storage (0°C). Following 90 and 120 days of cold exposure, high DMC kiwifruit generally exhibited superior physiological characteristics, such as increased pericarp and placenta firmness, and soluble solid and starch contents compared to low DMC kiwifruit, regardless of the 1-MCP application. Evidence is also presented for 1-MCP delaying the ripening of low-DMC fruit to the level of the untreated high-DMC kiwifruit. An accumulation of primary metabolites, particularly sugars and polyphenolic compounds, such as catechin, chlorogenic acid and procyanidin B1/B2 was evidenced in the high DMC group. At harvest, gene expression analysis revealed minor differences between DMC groups, with beta-amylase being the highest up-regulated gene in high DMC kiwifruit. Moreover, the gene expression patterns between DMC groups became more distinct after cold storage. Genes related to starch biosynthesis (i.e., glucose-1-phosphate adenyltransferase), water movement (i.e., aquaporin), polyphenolic biosynthesis (i.e., chalcone synthase) and lipid metabolism (i.e., diacylglycerol acyltransferase) showed strong variations between low and high DMC. Interestingly, the placenta tissue displayed almost 4 times more than DMC-affected differentially expressed genes compared to the pericarp, highlighting the key role of the placenta in kiwifruit ripening, notably following 1-MCP treatment. This study provides insights into the tissue-specific ripening response between kiwifruit with distinct DMC, as well as the gene expression influenced by an interaction of 1-MCP and DMC level, thereby helping develop postharvest programs aimed at improving kiwifruit quality traits.

ATF4 expression in thermogenic adipocytes is required for cold-induced thermogenesis in mice via FGF21-independent mechanisms

In brown adipose tissue (BAT), short-term cold exposure induces the activating transcription factor 4 (ATF4), and its downstream target fibroblast growth factor 21 (FGF21). Induction of ATF4 in BAT in response to mitochondrial stress is required for thermoregulation, partially by increasing FGF21 expression. In the present study, we tested the hypothesis that Atf4 and Fgf21 induction in BAT are both required for BAT thermogenesis under physiological stress by generating mice selectively lacking either Atf4 (ATF4 BKO) or Fgf21 (FGF21 BKO) in UCP1-expressing adipocytes. After 3 days of cold exposure, core body temperature was significantly reduced in ad-libitum-fed ATF4 BKO mice, which correlated with Fgf21 downregulation in brown and beige adipocytes, and impaired browning of white adipose tissue. Conversely, despite having reduced browning, FGF21 BKO mice had preserved core body temperature after cold exposure. Mechanistically, ATF4, but not FGF21, regulates amino acid import and metabolism in response to cold, likely contributing to BAT thermogenic capacity under ad libitum-fed conditions. Importantly, under fasting conditions, both ATF4 and FGF21 were required for thermogenesis in cold-exposed mice. Thus, ATF4 regulates BAT thermogenesis under fed conditions likely in a FGF21-independent manner, in part via increased amino acid uptake and metabolism.

Effect of constant and fluctuating low temperature on the survival of Tuta absoluta pupae.

Temperature is among the key factors impacting the establishment and spread of invasive pests. The tomato leafminer Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) is one of the major pests attacking Solanaceae plants and is known to possess overwintering capacities. However, the cold hardiness of T. absoluta pupae is poorly documented. In this study, we investigated the effect of constant temperature and stepwise cooling on T. absoluta pupae under laboratory conditions. For this purpose, bioassays on pupal development under constant temperature (5°C) for 30, 60 and 90 days, and stepwise changes in temperature (11, 10 and 8°C; in this order every 30 days), were assessed. We found that exposure to 5°C for 30 and 60 days did not affect the post-cooling emergence time of adults compared to the control. Pupae completed their development after 60 days of cold exposure at 5°C, but more adults emerged after 30 than 60 days. Even though alive pupae were observed after 90 days of cold exposure at 5°C, no adults emerged. External colours of pupae depended on the duration of cold periods, and green pupae obtained after 30 and 60 days were found to be positively correlated with the emergence of adults. When pupae were kept at 11°C for 30 days, 47% emerged, and when the temperature was changed to 10, only 12% of pupae emerged for the period 31-60 days. However, the decrease of the temperature to 8°C yielded no emergence for the period 61-90 days. Our study provides useful information to better understand the population dynamics of overwintering T. absoluta, and to underpin the development of monitoring and control strategies for the pest.

Epistatic interactions among multiple copies of FLC genes with naturally occurring insertions correlate with flowering time variation in radish.

Brassicaceae crops, which underwent whole-genome triplication during their evolution, have multiple copies of flowering-related genes. Interactions among multiple gene copies may be involved in flowering time regulation; however, this mechanism is poorly understood. In this study, we performed comprehensive, high-throughput RNA sequencing analysis to identify candidate genes involved in the extremely late-bolting (LB) trait in radish. Then, we examined the regulatory roles and interactions of radish FLOWERING LOCUS C (RsFLC) paralogs, the main flowering repressor candidates. Seven flowering integrator genes, five vernalization genes, nine photoperiodic/circadian clock genes and eight genes from other flowering pathways were differentially expressed in the early-bolting (EB) cultivar 'Aokubinagafuto' and LB radish cultivar 'Tokinashi' under different vernalization conditions. In the LB cultivar, RsFLC1 and RsFLC2 expression levels were maintained after 40 days of cold exposure. Bolting time was significantly correlated with the expression rates of RsFLC1 and RsFLC2. Using the EB × LB F2 population, we performed association analyses of genotypes with or without 1910- and 1627-bp insertions in the first introns of RsFLC1 and RsFLC2, respectively. The insertion alleles prevented the repression of their respective FLC genes under cold conditions. Interestingly, genotypes homozygous for RsFLC2 insertion alleles maintained high RsFLC1 and RsFLC3 expression levels under cold conditions, and two-way analysis of variance revealed that RsFLC1 and RsFLC3 expression was influenced by the RsFLC2 genotype. Our results indicate that insertions in the first introns of RsFLC1 and RsFLC2 contribute to the late-flowering trait in radish via different mechanisms. The RsFLC2 insertion allele conferred a strong delay in bolting by inhibiting the repression of all three RsFLC genes, suggesting that radish flowering time is determined by epistatic interactions among multiple FLC gene copies.

High daily energy expenditure of Tuvan nomadic pastoralists living in an extreme cold environment

Research investigating thermoregulatory energy costs in free-living humans is limited. We determined the total energy expenditure (TEE) of Tuvan pastoralists living in an extreme cold environment and explored the contribution of physical activity and cold-induced thermogenesis. Twelve semi-nomadic pastoralists (47 ± 8 years, 64 ± 8 kg) living under traditional circumstances, in Tuva, south-central Siberia, Russia, were observed during two consecutive 6-day periods in winter. TEE was measured via the doubly labelled water technique. Skin and ambient temperatures, and physical activity were continuously monitored. The outdoor temperature during the observation period was − 27.4 ± 5.4 °C. During the daytime, the participants were exposed to ambient temperatures below 0 °C for 297 ± 131 min/day. The Tuvan pastoralists were more physically active compared to western populations (609 ± 90 min/day of light, moderate, and vigorous physical activity). In addition, TEE was 13.49 ± 1.33 MJ/day (3224 ± 318 kcal/day), which was significantly larger by 17% and 31% than predicted by body mass, and fat-free mass, respectively. Our research suggests the daily cold exposure combined with high levels of physical activity contributed to the elevated TEE. Future research should reconsider the assumption that energy costs due to thermoregulation are negligible in free-living humans.

Brown Adipose Tissue Rescues Bone Loss Induced by Cold Exposure.

Cold temperature activates the sympathetic nervous system (SNS) to induce bone loss by altering bone remodeling. Brown adipose tissue (BAT) is influenced by the SNS in cold environments. Many studies have confirmed a positive relationship between BAT volume and bone mass, but the influence and mechanism of BAT on bone in vivo and in vitro is still unknown. Two-month-old C57/BL6j male mice were exposed to cold temperature (4°C) to induce BAT generation. BAT volume, bone remodeling and microstructure were assessed after 1 day, 14 days and 28 days of cold exposure. CTX-1, P1NP and IL-6 levels were detected in the serum by ELISA. To determine the effect of BAT on osteoclasts and osteoblasts in vitro, brown adipocyte conditional medium (BAT CM) was collected and added to the differentiation medium of bone marrow-derived macrophages (BMMs) and bone marrow mesenchymal stem cells (BMSCs). Micro-CT results showed that the bone volume fraction (BV/TV, %) significantly decreased after 14 days of exposure to cold temperature but recovered after 28 days. Double labeling and TRAP staining in vivo showed that bone remodeling was altered during cold exposure. BAT volume enlarged after 14 days of cold stimulation, and IL-6 increased. BAT CM promoted BMSC mineralization by increasing osteocalcin (Ocn), RUNX family transcription factor 2 (Runx2) and alkaline phosphatase (Alp) expression, while bone absorption was inhibited by BAT CM. In conclusion, restoration of bone volume after cold exposure may be attributed to enlarged BAT. BAT has a beneficial effect on bone mass by facilitating osteogenesis and suppressing osteoclastogenesis.

Cold exposure aggravates pulmonary arterial hypertension through increased miR-146a-5p, miR-155-5p and cytokines TNF-α, IL-1β, and IL-6

BackgroundCold temperatures can aggravate pulmonary diseases and promote pulmonary arterial hypertension (PAH); however, the underlying mechanism has not been fully explored. AimTo explore the effect of chronic cold exposure on the production of inflammatory cytokines and microRNAs (miRNAs) in a monocrotaline (MCT)-induced PAH model. MethodsMale Sprague Dawley rats were divided into a Control (23.5 ± 2 °C), Cold (5.0 ± 1 °C for ten days), MCT (60 mg/kg body weight i.p.), and MCT + Cold (ten days of cold exposure after 3 weeks of MCT injection). Hemodynamic parameters, right ventricle (RV) hypertrophy, and pulmonary arterial medial wall thickness were determined. IL-1β, IL-6, and TNF-α levels were determined using western blotting. miR-21-5p and -3p, miR-146a-5p and -3p, and miR-155-5p and -3p and plasma extracellular vesicles (EVs) and mRNA expression of Cd68, Cd163, Bmpr2, Smad5, Tgfbr2, and Smad3 were determined using RT-qPCR. ResultsThe MCT + Cold group had aggravated RV hypertrophy hemodynamic parameters, and pulmonary arterial medial wall thickness. In lungs of the MCT + Cold, group the protein levels of TNF-α, IL-1β, and IL-6 were higher than those in the MCT group. The mRNA expression of Cd68 and Cd163 were higher in the MCT + Cold group. miR-146a-5p and miR-155-5p levels were higher in the plasma EVs and lungs of the MCT + Cold group. Cold exposure promoted a greater decrease in miR-21-5p, Bmpr2, Smad5, Tgfbr2, and Smad3 mRNA expression in lungs of the MCT + Cold group. ConclusionCold exposure aggravates MCT-induced PAH with an increase in inflammatory marker and miRNA levels in the plasma EVs and lungs.

Increased expression level of ANGPTL8 in white adipose tissue under acute and chronic cold treatment

BackgroundAngiopoietin-like proteins (ANGPTL), primarily 3, 4, and 8, play a major role in maintaining energy homeostasis by regulating triglyceride metabolism. This study evaluated the level of ANGPTL3, 4, and 8 in the liver, brown adipose tissue (BAT), and subcutaneous white adipose tissue (SAT) of mice maintained under acute and chronic cold conditions.MethodsC57BL/6J mice were exposed to cold temperature (4 °C) for 10 days with food provided ad libitum. Animal tissues were harvested at Day 0 (Control group, n = 5) and Days 1, 3, 5, and 10 (cold treatment groups, n = 10 per group). The expression levels of various genes were measured in the liver, SAT, and BAT. ANGPTL3, 4, and 8 expressions were measured in the liver. ANGPTL4, 8, and genes involved in browning and lipid metabolism [uncoupling protein 1 (UCP1), lipoprotein lipase (LPL), and adipose triglyceride lipase (ATGL)] were measured in SAT and BAT. Western blotting (WB) analysis and immunohistochemistry (IHC) were performed to confirm ANGPTL8 expression in these tissues.ResultsThe expressions of ANGPTL3 and 8 mRNA were significantly reduced in mouse liver tissues after cold treatment (P < 0.05); however, the expression of ANGPTL4 was not significantly altered. In BAT, ANGPTL8 expression was unchanged after cold treatment, whereas ANGPTL4 expression was significantly reduced (P < 0.05). ANGPTL4 levels were also significantly reduced in SAT, whereas ANGPTL8 gene expression exhibited over a 5-fold increase. Similarly, UCP1 gene expression was also significantly increased in SAT. The mRNA levels of LPL and ATGL showed an initial increase followed by a gradual decrease with an increase in the days of cold exposure. ANGPTL8 protein overexpression was further confirmed by WB and IHC.ConclusionsThis study shows that exposure to acute and chronic cold treatment results in the differential expression of ANGPTL proteins in the liver and adipose tissues (SAT and BAT). The results show a significant reduction in ANGPTL4 in BAT, which is linked to improved thermogenesis in response to acute cold exposure. ANGPTL8 was activated under acute and chronic cold conditions in SAT, suggesting that it is involved in regulating lipolysis and enhancing SAT browning.

Effect of Cold Stress on Neurobehavioral and Physiological Parameters in Rats.

Objective: Cold stress is an important current issue and implementing control strategies to limit its sometimes harmful effects is crucial. Cold is a common stressor that can occur in our work and our occupational or leisure time activities every day. There are substantial studies on the effects of chronic stress on memory and behavior, although, the cognitive changes and anxiety disorders that can occur after exposure to chronic intermittent cold stress are not completely characterized. Therefore, the present study was undertaken with an aim to investigate the effects of chronic intermittent cold stress on body weight, food intake and working memory, and to elucidate cold stress related anxiety disorders using cognitive and behavioral test batteries.Methods: We generated a cold stress model by exposing rats to chronic intermittent cold stress for 5 consecutive days and in order to test for the potential presence of sex differences, a comparable number of male and female rats were tested in the current study. Then, we measured the body weights, food intake and the adrenal glands weight. Working memory and recognition memory were assessed using the Y maze and the Novel Object Recognition (NOR) tasks. While, sex differences in the effects of chronic stress on behavior were evaluated by the elevated plus maze (EPM), open field maze (OF), and Marble burying (MB) tests.Results: We found that 2 h exposure to cold (4°C) resulted in an increase in the relative weight of the adrenal glands in male rats. Given the same chronic stress 5 days of cold exposure (2 h per day), increased weight gain in male rats, while females showed decreased food intake and no change in body weight. Both sexes successfully performed the Y maze and object recognition (OR) tasks, indicating intact spatial working memory performance and object recognition abilities in both male and female rats. In addition, we have shown that stress caused an increase in the level of anxiety in male rats. In contrast, the behavior of the female rats was not affected by cold exposure.Conclusion: Overall, the current results provide preliminary evidence that chronic intermittent cold stress model may not be an efficient stressor to female rats. Females exhibit resilience to cold exposure that causes an increase in the level of anxiety in male rats, which demonstrates that they are affected differently by stress and the gender is an important consideration in experimental design.

Genome-wide identification and expression analysis of the CBF/DREB1 gene family in lettuce

The C-repeat binding factor (CBF)/dehydration-responsive element binding (DREB1) proteins play a prominent role in freezing tolerance and are highly conserved in higher plants. Here we performed a genome-wide search of the CBF/DREB1 gene family in lettuce (Lactuca sativa L.) and identified 14 members of the family with one member gene containing a non-sense mutation within the AP2 DNA-binding domain. A comprehensive phylogenetic analysis of the CBF/DREB1 family members in 20 plant species from the Asterid or Rosid clade provided evidence that tandem duplication played an important role in the expansion of the CBF/DREB1 family. Expression analysis showed that twelve of the lettuce CBF genes were responsive to low temperature (4 °C), and that three and six of them could also be responsive to salt and heat stresses, respectively. Unlike Arabidopsis thaliana whose members of the CBF/DREB1 family respond only to a particular stress, lettuce CBFs provide wider protection from combinations of abiotic stresses. A global transcriptome analysis revealed distinctive temporal expression patterns among the cold-regulated genes in lettuce plants exposed to low temperature. Genes induced throughout the cold treatment are enriched in functions associated with protection from UV and high-light intensity and the genes suppressed after 7 days of cold exposure are enriched in photosynthesis-associated functions. These results provide insight into the molecular evolutionary properties of the CBF/DREB1 gene family in lettuce and a reference for genetic improvement of the lettuce response to cold acclimation.

Physiological Responses and Expression Changes of Fatty Acid Metabolism–Related Genes in Wheat (Triticum aestivum) Under Cold Stress

Cold stress changes the molecular and physiological responses in wheat genotypes according to their genetic potential and duration of stress. Cold stress (6 °C) has been applied in time series of 9 days (1, 3, 6, and 9 days) and evaluated the morpho-physiological responses and genes involved in fatty acid metabolisms such as desaturases and lipid transfer protein by real-time PCR technique in two cultivars of wheat, including MV-17 (cold-tolerant) and Kuhdasht (cold-sensitive). Results indicated that cold stress had a significant effect on morpho-physiological traits in MV-17 when compared with Kuhdasht. Moreover, cold stress for a long period of time could induce more bioactive compounds like hydrogen peroxide and malondialdehyde in MV-17 cultivar than in Kuhdasht. The contents of proline and glycine betaine as osmoregulators increased during times after cold exposure in both cultivars, but ascorbic acids as an antioxidant significantly increased in MV-17 cultivar during prolonged cold treatments. Meanwhile, fatty acid desaturase and lipid transfer genes are involved in fatty acid biosynthesis and lipid changes and differently expressed in cold stress. The fatty acid desaturase 2 (FAD2) leads to lipid unsaturation and its transcript significantly increased in MV-17 cultivar, but it was non-significant in Kuhdasht cultivar. With prolonged cold exposure, fatty acid desaturase 3 (FAD3) and lipid transfer protein 1 (LTP1) gene expression increased and showed the similar trend in both cultivars, while stearoyl-acyl carrier protein desaturases (SAD1) reached to maximum level after 6 days of cold exposure. We found that MV-17 cultivar could be resistant to cold stress during prolonged exposure to 6 °C by the increase in the contents of osmolytes, antioxidant, and fatty acid desaturases especially FAD2 in comparison with Kuhdasht cultivar.

Cold exposure promotes obesity and impairs glucose homeostasis in mice subjected to a high‑fat diet

Cold exposure is considered to be a form of stress and has various adverse effects on the body. The present study aimed to investigate the effects of chronic daily cold exposure on food intake, body weight, serum glucose levels and the central energy balance regulatory pathway in mice fed with a high-fat diet (HFD). C57BL/6 mice were divided into two groups, which were fed with a standard chow or with a HFD. Half of the mice in each group were exposed to ice-cold water for 1 h/day for 7 weeks, while the controls were exposed to room temperature. Chronic daily cold exposure significantly increased energy intake, body weight and serum glucose levels in HFD-fed mice compared with the control group. In addition, 1 h after the final cold exposure, c-fos immunoreactivity was significantly increased in the central amygdala of HFD-fed mice compared with HFD-fed mice without cold exposure, indicating neuronal activation in this brain region. Notably, 61% of these c-fos neurons co-expressed the neuropeptide Y (NPY), and the orexigenic peptide levels were significantly increased in the central amygdala of cold-exposed mice compared with control mice. Notably, cold exposure significantly decreased the anorexigenic brain-derived neurotropic factor (BDNF) messenger RNA (mRNA) levels in the ventromedial hypothalamic nucleus and increased growth hormone releasing hormone (GHRH) mRNA in the paraventricular nucleus. NPY-ergic neurons in the central amygdala were activated by chronic cold exposure in mice on HFD via neuronal pathways to decrease BDNF and increase GHRH mRNA expression, possibly contributing to the development of obesity and impairment of glucose homeostasis.

Interleukin-6 is important for regulation of core body temperature during long-term cold exposure in mice.

Interleukin-6 (IL6) is a cytokine important for inducing the fever response during infection and has been reported to uphold core body temperature during acute cold exposure. Recently it has also been indicated that IL6 in serum increases in cold-exposed mice. The aim of the present study was to investigate if IL6 is important for core body temperature regulation following a long-term cold exposure in mice. Experiments were performed with global IL6 deficient (-/-) mice, mice with conditional IL6 receptor α (IL6Rα) knockdown in the central nervous system (CNS; IL6RαNesCre) and appropriate wild-type (Wt) controls. All mice were placed in a cold environment (4°C) for 6 days. Core body temperature and oxygen consumption were measured by telemetry probes and indirect calorimetry at room temperature (20°C), and during the first and last day of cold exposure. Brain stem, hypothalamus and white and brown adipose tissues from the cold-exposed mice were subjected to gene expression analysis. After 6 days in 4°C, the IL6-/- mice exhibited significantly lower body temperature and oxygen consumption compared with Wt mice (P<0.05). The IL6RαNesCre mice also exhibited lower body temperature compared with WtNesCre controls during the last day of cold exposure (P<0.05). Furthermore, an increase in the mRNA level of brain-derived neurotrophic factor (Bdnf) was detected in the brain stem of both IL6-/- and IL6RαNesCre mice compared with the Wt groups (P<0.05). The finding that body temperature was decreased in IL6-/- and IL6RαNesCre mice indicates a decrease in thermogenesis in these animals. Bdnf has previously been indicated to increase body temperature and could in the present study be a mechanistic factor involved in counteracting the low body temperature in IL6-/- and IL6RαNesCre mice. These results suggest that IL6 is not only involved in body temperature regulation during infection, but also during long-term cold exposure, probably through mechanisms in the CNS.

CATALASE AND PEROXIDASE CONTRIBUTION TO PROMOTING COLD TOLERANCE IN WHEAT

The dynamics of catalase (CaT) and guaiacol peroxidase (POD) activity in winter wheat ( Triticum aestivum L.) leaves under exposure to a low hardening temperature of 4 ° C for 7 days was studied. It was established that the freezing tolerance of the seedlings increased already after 1 hour of exposure, and then continued to grow, reaching a maximum on the 7 th day. The content of malondialdehyde increased slightly during the first 2 days of cold exposure and then declined, possibly pointing to attenuation of the oxidative stress in plant cells. It was also found that the activity of one of the key antioxi dant enzymes involved in hydrogen peroxide (h 2 O 2 ) recycling – CaT, increased after 1 hour of cold exposure. CaT activity then continued to increase, reaching a maximum on the 2 nd day, with a decline following afterwards. along with this, POD activity increased throughout the cold hardening period. In addition, a slight increase in H 2 O 2 content in leaves was detected during the first 24 hours of cold exposure, but then H 2 O 2 level in the cells decreased towards the end of chilling. Based on these data we can conclude that the increase in the activity of antioxidant enzymes plays an important role in promoting the tolerance to hypothermia in wheat. CaT and POD are involved in h 2 O 2 recycling at the initial stage of low-temperature adaptation in the plants, whereas later on POD plays the main role in this process. Thus, the activation of antioxidant enzymes in leaves prevents the development of oxidative stress and promotes the tolerance of low temperature in wheat.

Four-week cold acclimation in adult humans shifts uncoupling thermogenesis from skeletal muscles to brown adipose tissue.

Muscle-derived thermogenesis during acute cold exposure in humans consists of a combination of cold-induced increases in skeletal muscle proton leak and shivering. Daily cold exposure results in an increase in brown adipose tissue oxidative capacity coupled with a decrease in the cold-induced skeletal muscle proton leak and shivering intensity. Improved coupling between electromyography-determined muscle activity and whole-body heat production following cold acclimation suggests a maintenance of ATPase-dependent thermogenesis and decrease in skeletal muscle ATPase independent thermogenesis. Although daily cold exposure did not change the fibre composition of the vastus lateralis, the fibre composition was a strong predictor of the shivering pattern evoked during acute cold exposure. We previously showed that 4weeks of daily cold exposure in humans can increase brown adipose tissue (BAT) volume by 45% and oxidative metabolism by 182%. Surprisingly, we did not find a reciprocal reduction in shivering intensity when exposed to a mild cold (18°C). The present study aimed to determine whether changes in skeletal muscle oxidative metabolism or shivering activity could account for these unexpected findings. Nine men participated in a 4week cold acclimation intervention (10°C water circulating in liquid-conditioned suit, 2hday-1 , 5daysweek-1 ). Shivering intensity and pattern were measured continuously during controlled cold exposure (150min at 4°C) before and after the acclimation. Muscle biopsies from the m. vastus lateralis were obtained to measure oxygen consumption rate and proton leak of permeabilized muscle fibres. Cold acclimation elicited a modest 21% (P<0.05) decrease in whole-body and m. vastus lateralis shivering intensity. Furthermore, cold acclimation abolished the acute cold-induced increase in proton leak. Although daily cold exposure did not change the fibre composition of the m. vastus lateralis, fibre composition was a strong predictor of the shivering pattern evoked during acute cold. We conclude that muscle-derived thermogenesis during acute cold exposure in humans is not only limited to shivering, but also includes cold-induced increases in proton leak. The efficiency of muscle oxidative phosphorylation improves with cold acclimation, suggesting that reduced muscle thermogenesis occurs through decreased proton leak, in addition to decreased shivering intensity as BAT capacity and activity increase. These changes occur with no net difference in whole-body thermogenesis.

Cold stress affects antioxidative response and accumulation of medicinally important withanolides in Withania somnifera (L.) Dunal

Withania somnifera (L.) Dunal (Indian ginseng) is a high value medicinal plant. It synthesizes a large array of biologically active withanolides. In this study, two month old seedlings of AGB002 (wild genotype) and AGB025 (cultivated genotype) of W. somnifera were subjected to cold stress (4°C) under controlled environment. Plants were analyzed for three medicinally important secondary metabolites (withanolide A, withanone and withaferin A), lipid peroxidation (MDA), cell injury, superoxide radical (O2−) accumulation and anti-oxidative enzymes activities such as superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR). Increases in the titers of superoxide anion and MDA were observed from day 1 to day 7 in both genotypes, although the increase on the first day of exposure was significantly higher. Enzymatic activities of SOD, CAT, APX and GR also showed an increasing trend in both genotypes and reached a maximum on day 7 of the cold temperature exposure; however, this increase was higher in AGB002 than AGB025. Withanolide A (WS-1) in the roots of both genotypes significantly decreased on the first day of cold exposure and then showed a recovery until day 7. WS-1 was not detected in the leaves of either genotype. Withanone (WS-2) content in the leaves also decreased towards the end of the cold period in both genotypes. Cold stress also elicited the accumulation of WS-2 in AGB025, but was not detectable in control seedlings. At maturity, WS-2 was also detected in control plants. Furthermore, a significant increase in the leaf withaferin A (WS-3) content was recorded from day 1 to day 7 of the cold exposure in both the genotypes, suggesting the possible involvement of withanolides in cold-protection. AGB002 showed comparatively higher accumulation of antioxidant enzymes and selected marker withanolides than AGB025, indicating that AGB002 is better adapted to cold than AGB025. It could be inferred from these observations that cold stress induces bioactive withanolide accumulation in W. somnifera as a mechanism for scavenging reactive oxygen species (ROS). These studies also provide an impetus for enhancing the withanolide accumulation in W. somnifera using controlled environment technology.

Daily cold exposure – A therapy to stimulate beige fat or a recipe for diabesity in mice?

Since the discovery that cold exposure stimulates browning of human white fat, clinical trials have been investigating cold exposure as a potential treatment for obesity. However, cold exposure is a form of stress and might be expected to have some adverse consequences. We thus investigated the effects of chronic daily cold exposure (standing in iced water for 1 hour/day for 6 weeks) on food intake, body weight and serum glucose in male C57/Bl6 mice fed either normal chow or a high fat diet (HFD), and potential neuronal pathways for any effects. Chronic daily cold exposure increased energy intake, body weight and serum glucose levels compared to control values, significantly so in mice on the HFD. One hour after the final cold exposure in mice on the HFD, c-fos immunoreactivity was significantly increased in the medial amygdala compared to control mice on the HFD, indicating neuronal activation in this brain region. Notably, 60% of these c-fos-immunopositive neurons also expressed the anorexigenic peptide neuropeptide Y (NPY), and NPY mRNA and peptide levels were significantly increased in the medial amygdala of cold-exposed versus control mice. Interestingly, cold exposure also led to a significant decrease in ventromedial hypothalamic (VMH) mRNA levels of the anorexigenic brain-derived neurotrophic factor (BDNF), and an increase in mRNA for growth hormone releasing hormone (GHRH), which stimulates circulating glucose levels. Taken together, we thus hypothesize that NPYergic neurons in the amygdala are activated by chronic cold exposure combined with a high fat diet, leading via direct or indirect neuronal pathways to decreased BDNF and increased GHRH mRNA expression in the VMH, in turn contributing to positive energy balance and deregulated glucose homeostasis. Further work is required to test this hypothesis, but such potential adverse effects should be taken into consideration whenmanipulating temperature to stimulate the browning of white fat.

Type 2 iodothyronine deiodinase is upregulated in rat slow- and fast-twitch skeletal muscle during cold exposure.

During cold acclimation, shivering is progressively replaced by nonshivering thermogenesis. Brown adipose tissue (BAT) and skeletal muscle are relevant for nonshivering thermogenesis, which depends largely on thyroid hormone. Since the skeletal muscle fibers progressively adapt to cold exposure through poorly defined mechanisms, our intent was to determine whether skeletal muscle type 2 deiodinase (D2) induction could be implicated in the long-term skeletal muscle cold acclimation. We demonstrate that in the red oxidative soleus muscle, D2 activity increased 2.3-fold after 3 days at 4°C together with the brown adipose tissue D2 activity, which increased 10-fold. Soleus muscle and BAT D2 activities returned to the control levels after 10 days of cold exposure, when an increase of 2.8-fold in D2 activity was detected in white glycolytic gastrocnemius but not in red oxidative gastrocnemius fibers. Propranolol did not prevent muscle D2 induction, but it impaired the decrease of D2 in BAT and soleus after 10 days at 4°C. Cold exposure is accompanied by increased oxygen consumption, UCP3, and PGC-1α genes expression in skeletal muscles, which were partialy prevented by propranolol in soleus and gastrocnemius. Serum total and free T3 is increased during cold exposure in rats, even after 10 days, when BAT D2 is already normalized, suggesting that skeletal muscle D2 activity contributes significantly to circulating T3 under this adaptive condition. In conclusion, cold exposure is accompanied by concerted changes in the metabolism of BAT and oxidative and glycolytic skeletal muscles that are paralleled by type 2 deiodinase activation.

Increased Brown Adipose Tissue Oxidative Capacity in Cold-Acclimated Humans

Context:Recent studies examining brown adipose tissue (BAT) metabolism in adult humans have provided convincing evidence of its thermogenic potential and role in clearing circulating glucose and fatty acids under acute mild cold exposure. In contrast, early indications suggest that BAT metabolism is defective in obesity and type 2 diabetes, which may have important pathological and therapeutic implications. Although many mammalian models have demonstrated the phenotypic flexibility of this tissue through chronic cold exposure, little is known about the metabolic plasticity of BAT in humans.Objective:Our objective was to determine whether 4 weeks of daily cold exposure could increase both the volume of metabolically active BAT and its oxidative capacity.Design:Six nonacclimated men were exposed to 10°C for 2 hours daily for 4 weeks (5 d/wk), using a liquid-conditioned suit. Using electromyography combined with positron emission tomography with [11C]acetate and [18F]fluorodeoxyglucose, shivering intensity and BAT oxidative metabolism, glucose uptake, and volume before and after 4 weeks of cold acclimation were examined under controlled acute cold-exposure conditions.Results:The 4-week acclimation protocol elicited a 45% increase in BAT volume of activity (from 66 ± 30 to 95 ± 28 mL, P < .05) and a 2.2-fold increase in cold-induced total BAT oxidative metabolism (from 0.725 ± 0.300 to 1.591 ± 0.326 mL·s−1, P < .05). Shivering intensity was not significantly different before compared with after acclimation (2.1% ± 0.7% vs 2.0% ± 0.5% maximal voluntary contraction, respectively). Fractional glucose uptake in BAT increased after acclimation (from 0.035 ± 0.014 to 0.048 ± 0.012 min−1), and net glucose uptake also trended toward an increase (from 163 ± 60 to 209 ± 50 nmol·g−1·min−1).Conclusions:These findings demonstrate that daily cold exposure not only increases the volume of metabolically active BAT but also increases its oxidative capacity and thus its contribution to cold-induced thermogenesis.