Kenneth Storey

Daily torpor reduces mass and changes stress and power output of soleus and EDL muscles in the Djungarian hamster, Phodopus sungorus

Publisher: The Company of Biologists

Date: 09-2011

DOI: 10.1242/JEB.057877

Abstract: Djungarian hamsters (Phodopus sungorus) undergo bouts of daily torpor in response to reduced photoperiod. Metabolic rate, body temperature and energy cost are reduced during torpor. The present study exposed Djungarian hamsters to two different photoperiod regimes at a room temperature of 19–21°C: long photoperiod (control, 16 h:8 h light:dark, N=8) and short photoperiod (torpor, 8 h:16 h light:dark, N=8). After 14 weeks, muscle mechanics were analyzed in each group, examining both extensor digitorum longus (EDL) muscle and soleus muscle from each in idual. Control hamsters had significantly greater body mass (43%), EDL mass (24%), EDL length (9%) and soleus mass (48%) than the torpor hamsters. However, there were no significant differences between control and torpor groups in forearm length or soleus muscle length. There were no significant differences in either muscle between control and torpor hamsters in maximum twitch stress (force per unit area), tetanus force generation or relaxation times. Maximum soleus tetanic stress was 43% greater (P=0.039) and soleus work loop power output (P& .001) was higher in torpor than in control hamsters. Maximum EDL tetanic stress was 26% greater in control than in torpor hamsters (P=0.046), but there was no significant effect on EDL power output (P=0.38). Rate of fatigue was not affected by torpor in either soleus or EDL muscles (P& .43). Overall, extended use of daily torpor had no effect on the rate at which stress or work was produced in soleus and EDL muscles in Djungarian hamsters however, torpor did increase the stress and power produced by the soleus.

Torpor‐responsive microRNAs in the heart of the Monito del monte, Dromiciops gliroides

Publisher: Wiley

Date: 23-05-2023

DOI: 10.1002/BIOF.1976

Abstract: The marsupial Monito del monte ( Dromiciops gliroides ) utilizes both daily and seasonal bouts of torpor to preserve energy and prolong survival during periods of cold and unpredictable food availability. Torpor involves changes in cellular metabolism, including specific changes to gene expression that is coordinated in part, by the posttranscriptional gene silencing activity of microRNAs (miRNA). Previously, differential miRNA expression has been identified in D . gliroides liver and skeletal muscle however, miRNAs in the heart of Monito del monte remained unstudied. In this study, the expression of 82 miRNAs was assessed in the hearts of active and torpid D . gliroides , finding that 14 were significantly differentially expressed during torpor. These 14 miRNAs were then used in bioinformatic analyses to identify Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways that were predicted to be most affected by these differentially expressed miRNAs. Overexpressed miRNAs were predicted to primarily regulate glycosaminoglycan biosynthesis, along with various signaling pathways such as Phosphoinositide‐3‐kinase rotein kinase B and transforming growth factor‐β. Similarly, signaling pathways including phosphatidylinositol and Hippo were predicted to be regulated by the underexpression of miRNAs during torpor. Together, these results suggest potential molecular adaptations that protect against irreversible tissue damage and enable continued cardiac and vascular function despite hypothermia and limited organ perfusion during torpor.

A functional transcriptomics analysis in the relict marsupial Dromiciops gliroides reveals adaptive regulation of protective functions during hibernation

Publisher: Wiley

Date: 11-2018

DOI: 10.1111/MEC.14876

Abstract: The small South American marsupial, Dromiciops gliroides, known as the missing link between the American and the Australian marsupials, is one of the few South American mammals known to hibernate. Expressing both daily torpor and seasonal hibernation, this species may provide crucial information about the mechanisms and the evolutionary origins of marsupial hibernation. Here, we compared torpid and active in iduals, applying high-throughput sequencing technologies (RNA-seq) to profile gene expression in three D. gliroides tissues and determine whether hibernation induces tissue-specific differential gene expression. We found 566 transcripts that were significantly up-regulated during hibernation (369 in brain, 147 in liver and 50 in skeletal muscle) and 339 that were down-regulated (225 in brain, 79 in liver and 35 in muscle). The proteins encoded by these differentially expressed genes orchestrate multiple metabolic changes during hibernation, such as inhibition of angiogenesis, prevention of muscle disuse atrophy, fuel switch from carbohydrate to lipid metabolism, protection against reactive oxygen species and repair of damaged DNA. According to the global enrichment analysis, brain cells seem to differentially regulate a complex array of biological functions (e.g., cold sensitivity, circadian perception, stress response), whereas liver and muscle cells prioritize fuel switch and heat production for rewarming. Interestingly, transcripts of thioredoxin-interacting protein (TXNIP), a potent antioxidant, were significantly over-expressed during torpor in all three tissues. These results suggest that marsupial hibernation is a controlled process where selected metabolic pathways show adaptive modulation that can help to maintain homeostasis and enhance cytoprotection in the hypometabolic state.

University Of Calgary

Location: Canada

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University Of British Columbia

Location: Canada

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Carleton University

Location: Canada

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Discovery Projects - Grant ID: DP120104360

Start Date: 2012

End Date: 03-2015

Amount: $145,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP180103694

Start Date: 01-2018

End Date: 03-2021

Amount: $270,012.00

Funder: Australian Research Council