Torpor Research Articles

IGF-1 and myostatin-mediated co-regulation in skeletal muscle and bone of Daurian ground squirrels (Spermophilus dauricus) during different hibernation stages

Muscle and bone are cooperatively preserved in Daurian ground squirrels (Spermophilus dauricus) during hibernation. As such, we hypothesized that IGF-1 and myostatin may contribute to musculoskeletal maintenance during this period. Thus, we systematically assessed changes in the protein expression levels of IGF-1 and myostatin, as well as their corresponding downstream targets, in the vastus medialis (VM) muscle and femur in Daurian ground squirrels during different stages. Group differences were determined using one-way analysis of variance (ANOVA). Results indicated that the co-localization levels of IGF-1 and its receptor (IGF-1R) increased by 50% during the pre-hibernation period (PRE) and by 35% during re-entry into torpor (RET) compared to the summer active period (SA). The phosphorylation level of FOXO1 in the VM muscle increased by 50% in the torpor (TOR) group and by 82% in the inter-bout arousal (IBA) group compared to the PRE group. The phosphorylation level of SGK-1 increased by 54% in the IBA group and by 62% in the RET group compared to the SA group. In contrast, the protein expression of IGF-1 and phosphorylation levels of PI3K, Akt, mTOR, and GSK3β in the VM muscle showed no obvious differences among the different groups. β-catenin protein expression was up-regulated by 84% in the RET group compared to the SA group, while the content of IGF-1 protein, correlation coefficients of IGF-1 and IGF-1R, and phosphorylation levels of PI3K, Akt, and GSK3β in the femur showed no significant differences among groups. Regarding myostatin and its downstream targets, myostatin protein expression decreased by 70% in the RET group compared to the SA group, whereas ActRIIB protein expression and Smad2/3 phosphorylation in the VM muscle showed no obvious differences among groups. Furthermore, Smad2/3 phosphorylation decreased by 58% in the TOR group and 53% in the RET group compared to the SA group, whereas ActRIIB protein expression in the femur showed no obvious differences among groups. Overall, the observed changes in IGF-1 and myostatin expression and their downstream targets may be involved in musculoskeletal preservation during hibernation in Daurian ground squirrels.

Integrated metabolomics and proteomics analysis to understand muscle atrophy resistance in hibernating Spermophilus dauricus

Hibernating Spermophilus dauricus experiences minor muscle atrophy, which is an attractive anti-disuse muscle atrophy model. Integrated metabolomics and proteomics analysis was performed on the hibernating S. dauricus during the pre-hibernation (PRE) stage, torpor (TOR) stage, interbout arousal (IBA) stage, and post-hibernation (POST) stage. Time course stage transition-based (TOR vs. PRE, IBA vs. TOR, POST vs. IBA) differential expression analysis was performed based on the R limma package. A total of 14 co-differential metabolites were detected. Among these, l-cystathionine, l-proline, ketoleucine, serine, and 1-Hydroxy-3,6,7-Trimethoxy-2, 8-Diprenylxanthone demonstrated the highest levels in the TOR stage; Beta-Nicotinamide adenine dinucleotide, Dihydrozeatin, Pannaric acid, and Propionylcarnitine demonstrated the highest levels in the IBA stage; Adrenosterone, PS (18:0/14,15-EpETE), S-Carboxymethylcysteine, TxB2, and 3-Phenoxybenzylalcohol demonstrated the highest levels in the POST stage. Kyoto Encyclopedia of Genes and Genomes pathways annotation analysis indicated that biosynthesis of amino acids, ATP-binding cassette transporters, and cysteine and methionine metabolism were co-differential metabolism pathways during the different stages of hibernation. The stage-specific metabolism processes and integrated enzyme-centered metabolism networks in the different stages were also deciphered. Overall, our findings suggest that (1) the periodic change of proline, ketoleucine, and serine contributes to the hindlimb lean tissue preservation; and (2) key metabolites related to the biosynthesis of amino acids, ATP-binding cassette transporters, and cysteine and methionine metabolism may be associated with muscle atrophy resistance. In conclusion, our co-differential metabolites, co-differential metabolism pathways, stage-specific metabolism pathways, and integrated enzyme-centered metabolism networks are informative for biologists to generate hypotheses for functional analyses to perturb disuse-induced muscle atrophy.

Weakened Contractile Performance and Mitochondrial Respiratory Complex Activity in Skeletal Muscle Improve during Interbout Arousal in Hibernating Daurian Ground Squirrel, Spermophilus dauricus

Mammalian hibernation is composed of multiple episodes of torpor bout, separated by phases of interbout arousal. During torpor, the skeletal muscles of mammals are undoubtedly inactive, but it has been proven to mitigate disuse atrophy. While interbout arousal has been implicated in the prevention of muscle atrophy, the underlying mechanisms sustaining muscle contraction remain to be explored. In the present study, Daurian ground squirrels (Spermophilus dauricus) were divided into four groups: pre-hibernation (PRE), torpor (TOR), interbout arousal (IBA), and post-hibernation (POST). The contractile performance of slow-twitch soleus muscle (SOL) and fast-twitch extensor digitorum longus muscle (EDL) was detected both in situ and in vitro. Concurrently, mitochondrial respiratory chain complex activity in these muscles was quantified. Our findings revealed that in situ contractile properties of both muscles, including force, power output, time duration, and force development/relaxation rates of twitch contraction, and force and power output of tetanic contraction declined in the TOR group compared to the PRE group, but improved in the IBA and POST groups. Fatigue resistance of muscles, determined by the power output of repetitive tetanic contractions in situ, decreased in the TOR group but recovered in the IBA and POST groups. In vitro studies demonstrated that tetanic contraction power output in isolated muscles increased with muscle temperature in both TOR and IBA groups. However, at the same temperature, power output was consistently lower in the TOR group compared to the IBA group. Moreover, the activity of the mitochondrial respiratory chain complex, especially Complexes I and II, decreased in the TOR group but showed recovery in the IBA and POST groups. These findings suggest that both the contractile performance and fatigue resistance of mammalian skeletal muscle are compromised during torpor but can be improved during interbout arousal and post-hibernation. The rebound in body temperature and rise in mitochondrial respiratory chain complex activity in skeletal muscle are involved in enhancing contractile performance and fatigue resistance. This study suggests that interbout arousal functions as a vital temporal interval during which skeletal muscles can transition from the inactivity induced by torpor to a state of restored contractile functionality. Thus, interbout arousal serves as a behavioral safeguard against disuse-induced damage to skeletal muscles during hibernation.

A temporal study on musculoskeletal morphology and metabolism in hibernating Daurian ground squirrels (Spermophilus dauricus).

Hibernators provide a natural model to study the mechanisms underlying the prevention of disuse-induced musculoskeletal deterioration. Currently, however, these mechanisms remain poorly understood. Here, we investigated changes in morphology and metabolic indices in the hindlimb skeletal muscle and bone of Daurian ground squirrels (Spermophilus dauricus) during different periods of hibernation, and further explored the possible mechanisms involved in the musculoskeletal maintenance of hibernators after prolonged inactivity. Results showed that, compared with levels in the summer active group (SA), almost all morphological indices of skeletal muscle and bone, including muscle mass, muscle fiber cross-sectional area, bone mass, bone length, and bone mechanical properties, were unchanged in the different periods of hibernation. Only a few microstructural parameters of bone showed deterioration in the post-hibernation group (POST), including increased specific bone surface (+71%), decreased trabecular thickness (-43%), and decreased average cortical thickness (-51%) in the tibia, and increased trabecular separation (+60%) in the femur. Furthermore, most examined metabolic indices involved in muscle protein turnover and bone remodeling were unchanged, except for several indices in the inter-bout arousal group (IBA), i.e., increase in the phosphorylation of eukaryotic initiation factor 4E binding protein 1 (4E-BP1) (IBA vs. SA, +80%) in the vastus medialis muscle, increase in chymotrypsin-like activity (IBA vs. SA, +62%) in the tibialis anterior muscle, increase in osteoblast number (IBA vs. SA, +110%; IBA vs. torpor (TOR), +68%) and osteoclast number (IBA vs. TOR, +105%) per bone surface in the tibia, and increase in osteoclast surface per bone surface (IBA vs. TOR, +128%) in the femur. The above evidence demonstrates that the musculoskeletal morphology of squirrels was largely preserved, and musculoskeletal metabolism was generally maintained after prolonged hibernation inactivity. These findings suggest that the well-maintained musculoskeletal metabolism may be a vital mechanism underlying the preservation of the musculoskeletal system during hibernation. The coincident up-regulation of several metabolic indicators during IBA indicates that musculoskeletal metabolism may be relatively active during this period; however, its role in musculoskeletal maintenance during hibernation needs further clarification.

Autophagy and Akt-mTOR signaling display periodic oscillations during torpor-arousal cycles in oxidative skeletal muscle of Daurian ground squirrels (Spermophilus dauricus).

Whether hibernation accelerates or suppresses autophagy is still unknown. In the current study, we examined changes in autophagy in oxidative soleus (SOL) muscle in summer active (SA), pre-hibernation (PRE), torpor (TOR), interbout arousal (IBA), and post-hibernation groups of Daurian ground squirrels (Spermophilus dauricus). Here, the SOL muscle showed no significant atrophy during hibernation in regard to muscle wet weight, fiber cross-sectional area, or MuRF1 protein level. Autophagy-related proteins beclin1 and Atg7 increased significantly, whereas LC3-II decreased significantly in the PRE group compared with the SA group. However, neither the expression nor activity of cathepsin L showed any differences between the SA and PRE groups. In addition, beclin1, LC3-II, and the LC3-II/LC3-I ratio increased, p62 decreased, LC3 puncta increased, p62 puncta decreased, and cathepsin L activity increased in the TOR group compared with the PRE group. In contrast, beclin1, LC3-II, and the LC3-II/LC3-I ratio decreased, p62 increased, LC3 puncta decreased, p62 puncta increased, and cathepsin L activity declined in the IBA group compared with the TOR group. Moreover, the phosphorylation of Akt (Ser473) and mTOR (Ser2448) changed significantly during hibernation and showed an inverse relationship with autophagy changes. In conclusion, autophagy proteins displayed periodic oscillation in the torpor-arousal cycle, which may be advantageous in maintaining SOL muscle mass during the entire hibernation period. Furthermore, the Akt-mTOR signaling was decreased in TOR and increased in IBA group in the SOL muscle of Daurian ground squirrels during hibernation.

Wiedemann-Steiner syndrome caused by novel mutation of KMT2A gene: one case report and literature review

Objective To analyze the clinical and biochemical, as well as genetic characteristics of a patient with Wiedemann-Steiner syndrome (WDSTS). Methods The clinical data of a patient with WDSTS were collected. The patient was treated with recombinant human growth hormone (rhGH) combined with gonadotrophine-releasing hormone agonist (GnRHa). Blood samples of the patient and her parents were taken for whole-Exome Sequencing (WES). Relevant literatures about KMT2A mutations were reviewed. Results The 5-year old girl presented with growth retardation, with height 100 cm (-2.4 SD), torpid reaction, and facial anomalies including low hairline, thick eyebrow and hair, hypertelorism, a wide nasal bridge. She had small and puffy hands and feet, excessive hair around back of neck, bilateral forearm and lower limbs. Her GH peak level was 26.6 ng/ml during GH stimulation test. She was re-examined at the age of 10.4 years, with severe short stature (120 cm/-3.58 SD) and a Tanner stage 2 of breast development. Her bone age was found to be approximately 11.4 years. Height increased from 120 cm at the age of 10.4 years to 147.3 cm after rhGH treatment combined with GnRHa for 2.5 years. rhGH therapy alone continued for 1.1 years and a height of 150 cm was reached at the age of 14.9 years, with bone age 14 years. Gene sequencing revealed a de novo frameshift mutation (c.10051delA, p. Thr3351Leufs*17) of exon 27 in KMT2A gene of the patient, but without any mutation in her parents. Through a literature review, seventy-one patients with WDSTS (including present case) presented with intellectual disability(70/71), facial anomalies (70/71), short stature (50/71), and hypertrichosis(39/71). Conclusion Patients presented with short stature, typical facial dysmorphism, intellectual disability, and hypertrichosis should be considered for WDSTS. The mutation p. Thr3351Leufs*17 in the KMT2A gene detected in our patient is a novel mutation. This is so far the first report of WDSTS patient who was successfully treated with a combination of GH and GnRHa at the onset of puberty to improve her adult height. Key words: Wiedemann-Steiner syndrome; KMT2A gene; Short stature; Hypertrichosis; Therapy

Testing for torpor

Testing for torpor

Commentary: Torpor: The Rise and Fall of 3-Monoiodothyronamine from Brain to Gut-From Gut to Brain?

Commentary: Torpor: The Rise and Fall of 3-Monoiodothyronamine from Brain to Gut-From Gut to Brain?

Enhanced oxidative capacity of ground squirrel brain mitochondria during hibernation.

During hibernation, thirteen-lined ground squirrels (Ictidomys tridecemlineatus) regularly cycle between bouts of torpor and interbout arousal (IBA). Most of the brain is electrically quiescent during torpor but regains activity quickly upon arousal to IBA, resulting in extreme oscillations in energy demand during hibernation. We predicted increased functional capacity of brain mitochondria during hibernation compared with spring to accommodate the variable energy demands of hibernation. To address this hypothesis, we examined mitochondrial bioenergetics in the ground squirrel brain across three time points: spring (SP), torpor (TOR), and IBA. Respiration rates of isolated brain mitochondria through complex I of the electron transport chain were more than twofold higher in TOR and IBA than in SP (P < 0.05). We also found a 10% increase in membrane potential between hibernation and spring (P < 0.05), and that proton leak was lower in TOR and IBA than in SP. Finally, there was a 30% increase in calcium loading in SP brain mitochondria compared with TOR and IBA (P < 0.01). To analyze brain mitochondrial abundance between spring and hibernation, we measured the ratio of copy number in a mitochondrial gene (ND1) vs. a nuclear gene (B2M) in frozen cerebral cortex samples. No significant differences were observed in DNA copies between SP and IBA. These data show that brain mitochondrial bioenergetics are not static across the year and suggest that brain mitochondria function more effectively during the hibernation season, allowing for rapid production of energy to meet demand when extreme physiological changes are occurring.

Bats on a Budget: Use of Torpor by Bats to Conserve Energy during Migration

Bats on a Budget: Use of Torpor by Bats to Conserve Energy during Migration

SEASONAL CHANGES IN BODY MASS, TORPIDITY, AND REPRODUCTIVE ACTIVITY OF CAPTTVE FAT MICE, STEATOMYS PRATENSIS

ABSTRACT Captive, adult Steatomys pratensis do not exhibit seasonal changes in body mass, but they do show seasonal changes in reproductive activity and an annual cycle of torpor. The breeding season commences in December (mid-summer) and continues until June or July. All individuals demonstrated torpor, but it was more evident in subadults than adults, and in females than males. These differences are ecologically adaptive traits related to life history. Cycles of torpor and reproductive activity are a co-evolved species characteristic.

Daily energy expenditure in the pouched mouse (Saccostomus campestris Peters 1896)

ABSTRACT Previous studies of the pouched mouse (Saccostomus campestris) have revealed that during reproduction there is no increase in food consumption, although resting energy demands, measured by respirometry, increase substantially. One explanation for this anomalous situation is that these mice may routinely use torpor to compensate their energy budgets. We measured the daily energy expenditure of eleven individual pouched mice over three consecutive days using the doubly-labelled water technique. The mice were housed in cages where they had free access to food and water, at an average temperature of 26.5 °C, and exposed to a natural photoperiod (February Pretoria). There was a large day-to-day variation in energy expenditure within each individual. The coefficient of variation in daily energy demand averaged 24.5%. By comparing the correlation of estimates for consecutive and nonconsecutive days we established that this variation was not a consequence of errors in the isotopic technique. The scaling ...

Molecular mechanism underlying muscle mass retention in hibernating bats: Role of periodic arousal

Hibernators like bats show only marginal muscle atrophy during prolonged hibernation. The current study was designed to test the hypothesis that hibernators use periodic arousal to increase protein anabolism that compensates for the continuous muscle proteolysis during disuse. To test this hypothesis, we investigated the effects of 3-month hibernation (HB) and 7-day post-arousal torpor (TP) followed by re-arousal (RA) on signaling activities in the pectoral muscles of summer-active (SA) and dormant Murina leucogaster bats. The bats did not lose muscle mass relative to body mass during the HB or TP-to-RA period. For the first 30-min following arousal, the peak amplitude and frequency of electromyographic spikes increased 3.1- and 1.4-fold, respectively, indicating massive myofiber recruitment and elevated motor signaling during shivering. Immunoblot analyses of whole-tissue lysates revealed several principal outcomes: (1) for the 3-month HB, the phosphorylation levels of Akt1 (p-Akt1) and p-mTOR decreased significantly compared to SA bats, but p-FoxO1 levels remained unaltered; (2) for the TP-to-RA period, p-Akt1 and p-FoxO1 varied little, while p-mTOR showed biphasic oscillation; (3) proteolytic signals (i.e., atrogin-1, MuRF1, Skp2 and calpain-1) remained constant during the HB and TP-to-RA period. These results suggest that the resistive properties of torpid bat muscle against atrophy might be attained primarily by relatively constant proteolysis in combination with oscillatory anabolic activity (e.g., p-mTOR) corresponding to the frequency of arousals occurring throughout hibernation.

Bald Eagle Predation on Harbor Seal Pups

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Natural versus induced arousal from torpor: differences in fuel utilization and rewarming dynamics

Natural versus induced arousal from torpor: differences in fuel utilization and rewarming dynamics

The Wool Gatherer

The immense beast slumbered upon a wide stone ledge that knifed out from the hillside overlooking the vast expanse of the green Pacific. Ivoryplumed waves crashed almost soundlessly hundreds of feet below cliffs that only marginally accommodated a wagon trail that ran north to south, fifty feet below the ledge. With a massive head resting motionless upon two equally enormous paws, the creature remained so still that one could be forgiven for mistaking the shaggy, gray enormity for a huge boulder. A closer inspection, though undoubtedly lethal, would have revealed an occasional torpid movement of ancient eyes, or the intermittent widening of cavernous nostrils as itinerant aromas drifted within the creature's orbit of in-

Seasonal proteomic plasticity in the brain of a mammalian hibernator

Fine control of protein expression must be crucial for hibernators to promote energy conservation and survival during harsh winters. This study was aimed at investigating seasonal proteomic plasticity in order to evaluate physiological relevance of proteomic adjustments in the brain of the Murina leucogaster bat in three functional states: summer-active (SA), torpor (TR), and early phase of arousal (AR). Our two-dimensional electrophoresis and immunoblotting analyses revealed that 74% of identified neuronal, synaptic, metabolic, and stress proteins maintained stable levels throughout the three states. Proteins associated with axonal outgrowth and synaptic transmission (e.g., dihydropyrimidinase related protein-2 and N-ethylmaleimide sensitive fusion protein) and heme catabolism (biliverdin reductase B) were generally downregulated in TR and upregulated in AR. The levels of molecular chaperones such as heat shock protein 70 and glucose-regulated protein 78 remained unchanged over the three states. In parallel, glucose and lactate concentrations were relatively low in TR, whereas the glucose concentration was low but the lactate level was high in AR, implying metabolic stress due to arousal. These findings suggest that seasonal proteomic variability was observed mainly in proteins that functioned to regulate neural network, antioxidant activity, and neuroprotection in the hibernator brain.

Torpor and Rage: From Haute-Frêne to Hautefaye

Torpor and Rage: From Haute-Frêne to Hautefaye

Rhythmicity and the evolution of euthermy and torpidity

Rhythmicity and the evolution of euthermy and torpidity

Combating Student Torpor

Combating Student Torpor