Up-Regulation of Glycogen Synthesis and Degradation Enzyme Level Maintained Myocardial Glycogen in Huddling Brandt's Voles Under Cool Environments.

Jin-Hui Xu,Lai-Xiang Xu,Jun-Jie Mou,Ming Wu,Zhe Wang,Hui-Liang Xue,Wei-Mei Huang,Lei Chen,Chuan-Li Wang

doi:10.3389/fphys.2021.593129

Abstract

Small mammals exhibit limited glucose use and glycogen accumulation during hypothermia. Huddling is a highly evolved cooperative behavioral strategy in social mammals, allowing adaptation to environmental cooling. However, it is not clear whether this behavior affects the utilization of glycogen in cold environments. Here, we studied the effects of huddling on myocardial glycogen content in Brandt’s voles (Lasiopodomys brandtii) under a mild cold environment (15°C). Results showed that (1) Compared to the control (22°C) group (CON), the number of glycogenosomes more than tripled in the cool separated group (CS) in both males and females; whereas the number of glycogenosomes increased in females but was maintained in males in the cool huddling group (CH). (2) Glycogen synthase (GS) activity in the CS group remained unchanged, whereas glycogen phosphorylase (GYPL) activity decreased, which mediated the accumulation of glycogen content of the CS group. (3) Both GS and GYPL activity increased which may contribute to the stability of glycogen content in CH group. (4) The expression levels of glucose transporters GLUT1 and GLUT4 increased in the CS group, accompanied by an increase in glucose metabolism. These results indicate that the reduced glycogen degradation enzyme level and enhanced glucose transport may lead to an increase in myocardial glycogen content of the separated voles under cool environment; while the up-regulation of glycogen synthesis and degradation enzyme level maintained myocardial glycogen content in the huddling vole.

Highlights

Low temperature is a stress stimulus for mammals, especially for small mammals as their energy requirements are high due to the large surface area to volume ratio
These results indicate that the reduced glycogen degradation enzyme level and enhanced glucose transport may lead to an increase in myocardial glycogen content of the separated voles under cool environment; while the up-regulation of glycogen synthesis and degradation enzyme level maintained myocardial glycogen content in the huddling vole
Most glycogenosomes were distributed between the muscle filaments, with a small number distributed around the mitochondria (Figure 1)

Summary

Introduction

Low temperature is a stress stimulus for mammals, especially for small mammals as their energy requirements are high due to the large surface area to volume ratio. When environmental stressors persist for prolonged periods, small animal tissues and organs are more vulnerable to the impact of external environmental temperature (Gilbert et al, 2010; Wei et al, 2018). The cardiac muscle of small mammals is more susceptible to low external temperatures. Glucose is the energy supply of mitochondria, and changes in mitochondrial function may involve changes in glycogen content in tissues (Hall and Mackay, 1933; Tarnopolsky, 2016; Xu et al, 2020). Exposure to only 4 h of cold temperature (15◦C) can lead to an increase in myocardial glycogen content in rats (Steffen, 1988), suggesting that the effects of hypothermia on cardiac muscle may involve the balance between glycogen synthesis and degradation

Methods

Results

Conclusion