Dietary fats and body lipid composition in relation to hibernation in free-ranging echidnas

Laboratory studies have shown that high levels of dietary unsaturated fatty acids prolong torpor and lower body temperatures in hibernating herbivorous rodents, which may in turn improve winter survival. The importance of nutritional ecology in relation to hibernation in insectivorous hibernators is unknown. We therefore studied fatty acid composition of dietary insects and the depot fat of echidnas Tachyglossus aculeatus (Monotremata) during the pre-hibernation season and compared depot fat fatty acid composition before and after hibernation. Echidna depot fat fatty acid composition during the pre-hibernation season was almost identical to that of the most abundant prey species, the ant Iridomyrmex sp. Oleic acid (C18:1) was by far the most common fatty acid in both Iridomyrmex sp. (60%) and echidna depot fat (62%). After about 5 months of hibernation and an 18% loss of body mass, echidna fatty acid composition had changed significantly. The percentage of the monounsaturated oleic acid (C18:1) and palmitoleic acid (C16:1) had declined, whereas that of the saturated fatty acids (C12:0, C16:0, C18:0) and the polyunsaturated linoleic acid (C18:2) had increased. Our study suggests that, unlike herbivorous rodent hibernators, echidnas rely to a large extent on monounsaturated fatty acids as fuel for hibernation, reflecting the most common fatty acid in their food. Moreover, it appears that the high concentration of monounsaturated fatty acids compensates for the moderate availability of polyunsaturates and enables them to hibernate at low body temperatures.     

The optimal depot fat composition for hibernation by golden-mantled ground squirrels (Spermophilus lateralis)

Golden-mantled ground squirrels (Spermophilus lateralis) are herbivores that hibernate during winter. Although little is known about the nutritional/physiological constraints on hibernation, numerous studies have demonstrated that increasing the amount of linoleic acid (a polyunsaturated fatty acid) in the diet enhances hibernation. This is probably because high linoleic acid diets reduce the melting points of the depot fats produced for hibernation which makes them more metabolizable at low body temperatures. This suggests that a major limitation on hibernation may be obtaining enough linoleic acid in the diet for proper hibernation. In all previous studies, however, the amount of linoleic acid in the diets of free-ranging animals was either not considered, or the range of dietary linoleic acid contents in the experiments was less than that of natural diets. It is thus not known whether the amount of linoleic acid available to hibernators under natural conditions actually limits their torpor patterns. A series of laboratory feeding and hibernation experiments were conducted with S. lateralis and artificial diets with different linoleic acid contents that were either below or above the linoleic acid content of the natural diet. The results demonstrated that when dietary linoleic acid contents are either below or above natural levels, hibernation ability is greatly reduced. Hibernation ability was reduced when the squirrels were maintained on a high linoleic acid diet probably by the production of toxic lipid peroxides in brown adipose tissues. The results indicate that there is an optimal level of dietary linoleic acid for proper hibernation, and this is equal to that of the natural diet. The amount of linoleic acid available in the diet thus does not limit hibernation under normal natural conditions.Abbreviations BAT brown adipose tissue - bm body mass - FA fatty acid - PUFA polyunsaturated fatty acid - T _a ambient temperature - T _b body temperature - WAT white adipose tissue     

Changes of peroxisomal fatty acid metabolism during cold acclimatization in hibernating jerboa (Jaculus orientalis)

Jerboa (Jaculus orientalis) is a deep hibernator originating from sub-desert highlands and represents an excellent model to help to understand the incidence of seasonal variations of food intake and of body as well as environmental temperatures on lipid metabolism. In jerboa, hibernation processes are characterized by changes in the size of mitochondria, the number of peroxisomes in liver and in the expression of enzymes linked to fatty acid metabolism. In liver and kidney, cold acclimatization shows an opposite effect on the activities of the mitochondrial acyl-CoA dehydrogenase (-50%) and the peroxisomal acyl-CoA oxidase (AOX) (+50%), while in brown and white adipose tissues, both activities are decreased down to 85%. These enzymes activities are subject to a strong induction in brown and in white adipose tissue (3.4- to 7.5-fold, respectively) during the hibernation period which is characterized by a low body temperature (around 10 degrees C) and by starvation. Expression level of AOX mRNA and protein are increased during both pre-hibernation and hibernation periods. Unexpectedly, treatment with ciprofibrate, a hypolipemic agent, deeply affects lipolysis in brown adipose tissue by increasing acyl-CoA dehydrogenase activity (3.4-fold), both AOX activity and mRNA levels (2.8- and 3.8-fold, respectively) during pre-hibernation. Therefore, during pre-hibernation acclimatization, there is a negative regulation of fatty acid degradation allowing to accumulate a lipid stock which is later degraded during the hibernation period (starvation) due to a positive regulation of enzymes providing the required energy for animal survival.     

Seasonal changes in critical enzymes of lipogenesis and triacylglycerol synthesis in the marmot (Marmota flaviventris)

Fatty acid metabolism and triacylglycerol synthesis are critical processes for the survival of hibernating mammals that undergo a prolonged fasting period. Fatty acid synthase, fatty-acid-CoA ligase, diacylglycerol acyltransferase, and monoacylglycerol acyltransferase activities were measured in liver and in white and brown adipose tissue, in order to determine whether enzymes of lipogenesis and triacylglycerol synthesis vary seasonally during hibernation in the yellow-bellied marmot (Marmota flaviventris). Compared with mid-winter hibernation, fatty acid synthase activity was higher in all three tissues during early spring when marmots emerged from hibernation and in mid-summer when they were feeding, consistent with the synthesis of fatty acids from the carbohydrate-rich summer diet. Fatty-acid-CoA ligase and diacylglycerol acyltransferase activities were highest in summer in white adipose tissue when triacylglycerol synthesis would be expected to be high; diacylglycerol acyltransferase activity was also high in brown adipose tissue during spring and summer. In liver, however, diacylglycerol acyltransferase specific activity was highest during hibernation, suggesting that triacylglycerol synthesis may be prominent in liver in winter. Monoacylglycerol acyltransferase activity, which may aid in the retention of essential fatty-acids, was 80-fold higher in liver than in white or brown adipose tissue, but did not vary seasonally. Its dependence on palmitoyl-CoA suggests that a divalent cation might play a role in enzyme activation. The high hepatic diacylglycerol acyltransferase activity during hibernation suggests that the metabolism of very low density lipoprotein may be important in the movement of adipose fatty acids to brown adipose tissue and muscle during the rewarming that occurs periodically during hibernation. These studies suggest that enzymes of lipid metabolism vary seasonally in the marmot, consistent with requirements of this hibernator for triacylglycerol synthesis and metabolism.Abbreviations BAT brown adipose tissue - DGAT diacylglycerol acyltransferase - FAS fatty acid synthase - K _m Michaelis constant - MGAT monoacylglycerol acyltransferase - RQ respiratory quotiant - VLDL very low density lipoprotein - WAT white adipose tissue     

Lipid synthesis and deposition by adult Richardson's ground squirrels in the natural environment

Summary Adult male Richardson's ground squirrels,Spermophilus richardsonii, were estimated to have emerged from hibernation in late February to early March, and adult females in mid to late March. Half of the females trapped in late March were not pregnant, as against 10% after that time. In late March males and all females had similar WAT (white adipose tissue) deposits. Between late March and early June, WAT deposits in males increased from 14 g to 64 g (a rate of 5.6 g per week). In non-parous females WAT deposits increased from 13 g to 48 g from late March to late May (4.2 g per week). Fat deposits decreased during lactation but thereafter increased from 8 g to 29 g (a rate of 6.0 g per week) between early May and early June. In males the rate of fatty acid synthesis in BAT (brown adipose tissue), liver and WAT did not change from late March to late May, and rates in the corresponding tissues of non-pregnant females were similar to those in males. Fatty acid synthesis decreased during late pregnancy and lactation. After lactation, the rate of fatty acid synthesis in all tissues increased to that in males and non-pregnant females. Males initiated fattening 5–7 weeks earlier than females. It is concluded that compared with adult males, the later immergence of adult female Richardson's ground squirrels into hibernation is due primarily to later initiation of fattening and less to differences in rate of lipid synthesis after the reproductive period. Rates of fatty acid synthesis in liver and BAT were several times greater than that in WAT. The former tissues may contribute fatty acids for prehibernatory fattening.Abbreviations BAT brown adipose tissue - WAT white adipose tissue     

Influences of the feeding ecology on body mass and possible implications for reproduction in the edible dormouse (<Emphasis Type="Italic">Glis glis</Emphasis>)

The edible dormouse (Glis glis) is a small rodent and an obligate hibernator. Dormice undergo strong fluctuations of reproductive output during years that seem to be timed to coincide with future food supply. This behaviour enables them to avoid producing young that will starve with a high probability due to food shortage, and to increase their lifetime reproductive success. Aims of this study were to elucidate the extent to which feeding ecology in the edible dormouse has an impact on body mass and the fatty acid (FA) pattern of the white adipose tissue (WAT) before and after hibernation, which in turn might influence reproductive status in spring. Dormice show strong seasonal fluctuations of the body mass, which is reduced by one third during hibernation. Body mass and its changes depend on autumnal food availability as well as on the dietary FA pattern. During the pre-hibernation fattening period, dormice eat lipid rich food with a high content of linoleic acid. During hibernation, linoleic acid content is slightly but significantly reduced and body mass loss during winter is negatively correlated with the pre-hibernation linoleic acid content in the WAT. No relation between reproductive status and body mass, body condition or the FAs pattern of the WAT could be detected. However, in a year of high reproduction, dormice commence the shift to seed eating earlier than in a year of low reproduction. These seeds could be either a predictor for future food supply in autumn, or represent a high-energy food compensating high energetic costs of sexual activity in male edible dormice.     

The influence of hibernation patterns on the critical enzymes of lipogenesis and lipolysis in prairie dogs

White-tailed prairie dogs (Cynomys leucurus) are spontaneous hibernators that enter torpor each fall, whereas black-tailed prairie dogs (C. ludovicianus) hibernate facultatively only when food- or water-stressed during the winter. The body masses of both species greatly increase during the fall feeding period, with most of this gain in the form of depot fat. Body fat is utilized during winter fasting and/or hibernation. We measured the activities of fatty acid synthase (FAS), ATP-citrate lyase (ACL), malic enzyme (ME), glucose-6-phosphate dehydrogenase (G6PDH), and hormone-sensitive lipase (HSL) in the tissues of both C.leucurus (hibernating and euthermic) and C. ludovicianus (euthermic only) under controlled conditions. The activities of FAS, ACL, and G6PDH in the liver all decreased during hibernation. The activities of ME and G6PDH in white adipose tissue (WAT) were also reduced during hibernation. Euthermic C. leucurus and euthermic C. ludovicianus differed only in brown adipose (BAT) ACL and WAT G6PDH activities. No significant differences in HSL activities were found between these two species or between euthermic and hibernating animals. These results suggest that this seasonal body fat cycle is due, at least in part, to seasonal variations in the activities of FAS, ME, ACL, and G6PDH that affect the rate of fatty acid synthesis. This study also demonstrates that spontaneous hibernators do not have a greater capacity to synthesize fatty acids during the fall than facultative hibernators, as previously suggested.     

Seasonal differences in the feeding ecology and behavior of male edible dormice (Glis glis)

Mammalian hibernators undergo dramatic seasonal changes of food intake and the use of their gastrointestinal tract. During several months of hibernation fat-storing hibernators do not use their intestinal tract for nutritional intake. However, during the rest of the year they have to increase their energy intake in order to compensate high reproductive investment and store sufficient body fat to survive the following hibernation period. Edible dormice (Glis glis) are obligate fat-storing hibernators which hibernate in Germany from September until June. Males incur high energetic costs during mating and as soon as reproduction is terminated they have to accumulate high quantities of fat to survive hibernation. In order to understand how fat-storing hibernators like edible dormice cope with these energetically demanding situations, we measured body mass changes of captured male edible dormice in the field and studied their feeding ecology. Furthermore, we measured seasonal changes in food ingestion and assimilation rates by feeding experiments carried out in captivity.Results of this study revealed that during the mating season males significantly lowered their body mass, while food ingestion and assimilation rates remained constant. The body mass reduction showed that they used their body fat reserves to pay at least part of the energetic costs of reproduction. During the pre-hibernation fattening period males increased their body mass but held their assimilation rates on a constant level. Nevertheless, they increased the amount of ingested food and subsequently the amount of energy intake. Furthermore, they changed their dietary spectrum in the field by turning to lipid-rich seeds. These behavioral adaptations enable them to restore their energy losses during reproduction and to accumulate sufficient body fat to survive hibernation.     

The Relationship Between Lipid Peroxidation, Hibernation, and Food Selection in Mammals

SYNOPSIS. A diet that has high levels of polyunsaturated fattyacids enhances mammalian torpor. Polyunsaturated fatty acidsare not synthesized by mammals, but are incorporated into bothmembrane and storage lipids when they occur in the diet. Polyunsaturatedfatty acids also undergo autoxidation more readily than otherfatty acids, thereby producing highly toxic lipid peroxides.Lipid peroxidation increases during torpor. Natural selectionin mammalian hibernators should thus have favored the evolutionof dietary preferences that maximize hibernation ability whilesimultaneously minimizing the degree of lipid peroxidation duringtorpor. This hypothesis was tested in laboratory experimentsand field studies involving golden-mantled ground squirrels(Spermophilus lateralis). We found that the intake of polyunsaturatedfatty acids isrestricted during the fall and autoxidation intissues occurs mostly during the later phases of hibernation.     

Hormonal control of lipolysis from the white adipose tissue of hibernating jerboa (Jaculus orientalis)

1. Plasma glucose, glycerol, free fatty acids and total lipid content of the white adipose tissue were measured in euthermic and hibernating jerboa. 2. During hibernation, plasma glucose and glycerol were low compared to the euthermic animals, whereas there was no obvious difference in plasma free fatty acids. The white adipose tissue lipid content was strongly reduced in the hibernating state. 3. The effect of lipolytic hormones (norepinephrine and glucagon) and antilipolytic hormone (insulin) on in vitro glycerol release by adipose tissue isolated from hibernating or euthermic jerboa has been studied. 4. The white adipose tissue from hibernating jerboa presented a higher sensitivity to norepinephrine and glucagon than that of euthermic jerboa; insulin did not modify either basal glycerol release or lipolysis induced by the two lipolytic hormones at low temperatures (7 degrees C) and during the rewarming (from 7 degrees C to 37 degrees C) of the tissue slices. 5. These results suggested that white adipose tissue constitutes an important source of substrates derived from lipolysis during hibernation.     

Nutritional factors affecting quantity and quality of carcass fat in chickens.

Nonpathological fattening of a bird occurs when the amount of energy consumed exceeds its requirements for maintenance and growth. Dietary energy and protein levels, particularly the ratio of these two, are the main dietary factors affecting fatness. Consumption of diets low in protein results in excess energy intake and an increased hepatic lipogenesis. Excess protein has the opposite effect. It also increases the energy expenditure required to dispose of excess amino acids in the body. Severe deficiency of a specific amino acid does not increase fattening. The degree of fattening, particularly of the liver, induced by corticosterone injection is greater in birds fed diets containing a wide energy-to-protein ratio in comparison to a narrow ratio. The content of dietary fat per se does not affect carcass fat concentration although it alters the rate of liver fatty acid synthesis. The dietary fatty acid composition affects the composition of tissue fatty acids. Consumption of diets containing vegetable oils or high in protein increases the degree of unsaturation of tissue fat and thereby its susceptibility to oxidation. Dietary dl-alpha-tocopheryl acetate increases the stability of the lipids of adipose and muscle tissue of chicks with relatively saturated body fat, but the dietary effectiveness of this vitamin in improving the stability of tissues of birds having relatively unsaturated fat is limited.     

Changes in diet, body mass and fatty acid composition during pre-hibernation in a subtropical bat in relation to NPY and AgRP expression

Prior to hibernation, mammals accumulate large amounts of fat in their bodies. In temperate mammalian species, hibernation is improved by increasing the levels of poly-unsaturated fatty acids (PUFA) in the body. The saturation of fatty acids (FA) in both white adipose tissue (WAT) and membrane phospholipids of mammals often reflects their diet composition. We found that the greater mouse-tailed bat (Rhinopoma microphyllum) accumulates large amounts of fat at the end of summer by gradually shifting to a fat-rich diet (queen carpenter ants, Camponotus felah). PUFA are almost absent in this diet (<1 % of total FA), which contains a high fraction of saturated (SFA) and mono-unsaturated (MUFA) fatty acids. We found similar low levels of PUFA in mouse-tailed bat WAT, but not in their heart total lipids. The expression of two appetite-stimulating (orexigenic) hypothalamic neuropeptides, AgRP and NPY, increased in parallel to the shift in diet and with fat gain in these bats. To the best of our knowledge, this is the only documented example of specific pre-hibernation diet in bats, and one which reveals the most saturated FA composition ever documented in a mammal. We suggest that the increase in expression levels of NPY and AgRP may contribute to the observed diet shift and mass gain, and that the FA composition of the bat’s specialized diet is adaptive in the relatively high temperatures we recorded in both their winter and summer roosts.     

Evaluation of the role of AMP-activated protein kinase and its downstream targets in mammalian hibernation

Mammalian hibernation requires an extensive reorganization of metabolism that typically includes a greater than 95% reduction in metabolic rate, selective inhibition of many ATP-consuming metabolic activities and a change in fuel use to a primary dependence on the oxidation of lipid reserves. We investigated whether the AMP-activated protein kinase (AMPK) could play a regulatory role in this reorganization. AMPK activity and the phosphorylation state of multiple downstream targets were assessed in five organs of thirteen-lined ground squirrels (Spermophilus tridecemlineatus) comparing euthermic animals with squirrels in deep torpor. AMPK activity was increased 3-fold in white adipose tissue from hibernating ground squirrels compared with euthermic controls, but activation was not seen in liver, skeletal muscle, brown adipose tissue or brain. Immunoblotting with phospho-specific antibodies revealed an increase in phosphorylation of eukaryotic elongation factor-2 at the inactivating Thr56 site in white adipose tissue, liver and brain of hibernators, but not in other tissues. Acetyl-CoA carboxylase phosphorylation at the inactivating Ser79 site was markedly increased in brown adipose tissue from hibernators, but no change was seen in white adipose tissue. No change was seen in the level of phosphorylation of the Ser565 AMPK site of hormone-sensitive lipase in adipose tissues of hibernating animals. In conclusion, AMPK does not appear to participate in the metabolic re-organization and/or the metabolic rate depression that occurs during ground squirrel hibernation.     

Plasma lipoprotein cholesterol concentrations in the golden-mantled ground squirrel (Spermophilus lateralis): a comparison between pre-hibernators and hibernators.

1. The concentrations of total cholesterol (free cholesterol plus cholesteryl ester) in the plasma and in two lipoprotein fractions of golden-mantled ground squirrels (Spermophilus lateralis) were measured during pre-hibernation and compared to those values measured during hibernation. 2. Hibernating ground squirrels had significantly higher (P less than 0.005) very low density lipoprotein plus low density lipoprotein cholesterol (VLDL + LDL-C) concentrations than did pre-hibernating ground squirrels. 3. Hibernating squirrels additionally exhibited significantly higher (P less than 0.005) total plasma cholesterol concentration per high density lipoprotein cholesterol concentration (TPC/HDL-C) ratios than did pre-hibernating squirrels. 4. The significant differences in the lipoprotein cholesterol concentrations observed in this study suggest that lipoprotein metabolism in pre-hibernators was significantly different from that in hibernators and was a reflection of the marked biochemical and physiological adjustments these animals must undergo during their transition from pre-hibernation to hibernation.     

Origin of hepatic triglyceride fatty acids: quantitative estimation of the relative contributions of linoleic acid by diet and adipose tissue in normal and ethanol-fed rats

The present study demonstrates that the rat liver obtains most of its triglyceride fatty acids from dietary sources. The dietary and adipose tissue contributions of linoleic acid for hepatic triglyceride esterification were shown to be 50.42 and 13.85 micro moles, respectively, during a 4-day period. When ethanol provided 40% of the caloric intake, fatty liver developed and hepatic triglyceride content increased threefold. Under these conditions, the dietary and adipose tissue contributions of linoleic acid were estimated at 192.85 and 10.73 micro moles, respectively. This increase in dietary fatty acid utilization was sufficient to account for the entire increase in esterified hepatic linoleic acid. Any explanation of these observations must include the high dietary fatty acid utilization in both control and ethanol-treated animals. One possibility is that most dietary lipids first enter a rapidly turning over pool in adipose tissue from which most hepatic triglyceride fatty acids are derived. Another is that dietary fatty acids, incorporated into chylomicrons, are stored separately and used preferentially by the liver as compared with lipids derived from adipose tissue and bound to albumin. The pros and cons of these possibilities are discussed.     

Comparison of blood leptin and vitamin E and blood and adipose fatty acid compositions in wild and captive populations of critically endangered Vancouver Island marmots (Marmota vancouverensis)

Vancouver Island marmots (Marmota vancouverensis) (VIMs) are a critically endangered species of fat-storing hibernators, endemic to Vancouver Island, British Columbia, Canada. In addition to in-situ conservation efforts, a captive breeding program has been ongoing since 1997. The captive diet is mostly pellet-based and rich in n−6 polyunsaturated fatty acids (PUFAs). In captivity, overall length of hibernation is shortened, and marmots have higher adipose tissue reserves compared to their wild-born counterparts, which may be a risk factor for cardiovascular disease, the leading cause of mortality in captive marmots. To investigate differences in lipid metabolism between wild and captive populations of VIMs, blood vitamin E, fatty acid (FA) profiles and leptin, and white adipose tissue (WAT) FA profiles were compared during the active season (May to September 2019). Gas chromatography, high-performance liquid chromatography, and multiplex kits were used to obtain FA profiles, α-tocopherol, and leptin values, respectively. In both plasma and WAT, the concentration of the sum of all FA in the total lipids was significantly increased in captive VIMs. The n−6/n−3 ratio, saturated FAs, and n−6 PUFAS were higher in captive marmots, whereas n−3 PUFAs and the HUFA score were higher in wild marmots. Serum concentrations of α-tocopherol were greater by an average of 45% in captive marmots, whereas leptin concentrations did not differ. Results from this study may be applied to improve the diet and implement weight management to possibly enhance the quality of hibernation and decrease the risk of cardiovascular and metabolic diseases of captive VIMs.