Mitochondrial proteomic adaptations to daily torpor in the Djungarian hamster (Phodopus sungorus)

Abstract

Hibernation is an adaptive strategy that conserves energy in response to environmental challenges. While mitochondrial proteomic adaptations are well-documented in deep hibernators, the proteomic changes underlying daily torpor remain less clear. We investigated mitochondrial proteomic adaptations in the liver of a daily hibernator, the Djungarian hamster (Phodopus sungorus), across different hibernation phases. Hamsters were maintained under long-day (summer) or short-day photoperiods (winter), to induce torpor. Livers from summer, torpor, and interbout euthermia phases were analyzed by liquid chromatography-mass spectrometry with labelled standards of mitochondrial energy metabolism proteins, resulting in accurate quantitative proteomics. Differential protein regulation was assessed using empirical Bayes models with false discovery rate correction. Increased abundance of fatty acid oxidation enzymes during hibernation indicates a seasonal metabolic shift toward lipid utilization, similar to deep hibernators. Additionally, torpor featured elevated complex II subunits and tricarboxylic acid cycle enzymes representing evolutionary adaptations specific to daily torpor, likely to cater higher energy demands necessary to maintain torpid body temperature above 15 °C in near-freezing ambient temperatures. This represents evolutionary adaptations specific to daily torpor. Increased levels of the mitochondrial uncoupling-related solute carrier family 25 member 5 (SLC25A5) may be responsible for both thermogenesis and limiting production of reactive oxygen species. Furthermore, the selective upregulation of SOD2 during torpor underscores its critical role in mitigating reactive oxygen species accumulation during metabolic transitions. In summary, daily torpor exhibits unique mitochondrial proteomic adaptations that distinguish it from deep torpor, which may be necessary to enable torpor at body temperatures well above the ambient temperature.

Keywords: Daily torpor; Djungarian hamster; Energy metabolism; Hibernation; Mitochondrial proteomics.

Fig. 1

Principal component analysis (PCA) of mitochondrial protein abundance across different seasons and metabolic states. PCA1, which explains 52.2% of variance in the data, is plotted against PCA2, which explains 13.3% of the variance. The animals (points) are clustered based on their protein abundance profiles. Colors indicate the phase of hibernation: LD = long-day, IBE = Interbout euthermia, T = torpor

Fig. 2

Heatmap of the mitochondrial protein abundances across different seasons and metabolic states. The animals (columns) are clustered by their protein abundance profile (rows). Colors indicate protein abundance, ranging from high (red) to low (blue). Animal sex and phase of hibernation are annotated at the top of the heatmap

Fig. 3

Changes in mitochondrial protein abundance across different seasons and metabolic states in the Djungarian hamster: torpor (T), interbout euthermia (IBE), and long-day (LD). Only proteins that exhibit significant differences between phases are displayed for each contrast (FDR < 0.05). Bar charts depict the log-fold changes (LogFC) in protein abundance, with bars color-coded according to the biological pathway associated with each protein. Symbol ‘o’ is inserted above the x-axis for proteins that are oppositely regulated between panel 1 and 2. Symbol ‘*’ is inserted above the x-axis for proteins that are oppositely regulated between panel 1 and 3

Fig. 4

Schematic representation of the mitochondrial functional regulation in daily heterotherms (Djungarian hamsters, this study) versus deep hibernators (13-lined ground squirrels, literature*) across metabolic states: long-day control (LD), torpor (T), and interbout euthermia (IBE). Green boxes denote shared regulatory patterns, while red boxes indicate species-specific differences. Abbreviations: FAO: fatty acid oxidation; TCA: tricarboxylic acid cycle. *Literature used to create this figure: (Ballinger et al. ; Green and Storey ; Hampton et al. ; Laursen et al. ; Mathers et al. ; Mathers and Staples ; Vucetic et al. ; Wijenayake et al. ; Yan et al. 2006, 2008)