Carb-Loading: Freeze-Induced Activation of the Glucose-Responsive ChREBP Transcriptional Network in Wood Frogs

Physiol Biochem Zool. Jan/Feb 2020;93(1):49-61. doi: 10.1086/706463.

Abstract

The freeze-tolerant wood frog, Rana sylvatica, is one of few vertebrate organisms that can tolerate freezing, with up to 70% of its total body water being converted into extracellular ice. Physiologically, wood frogs show no signs of muscle movement, breathing, heartbeat, or brain activity for several weeks or months at a time but emerge unharmed upon thawing. Given that wood frogs rely mainly on carbohydrate metabolism during freezing, the involvement of the carbohydrate-responsive element-binding protein (ChREBP) in response to freezing is of interest. In liver tissue, protein and transcript levels of ChREBP increased by 1.4±0.09-fold and 1.9±0.26-fold, respectively, and nuclear distribution and DNA-binding activity rose by 2.0±0.08-fold and 1.5±0.08-fold, respectively. This enhanced transcriptional activity of ChREBP was corroborated by increased transcript expression of select downstream genes of fatty acid synthase, pyruvate kinase, and stearoyl-CoA desaturase in liver tissue. While liver tissue displayed ChREBP activation, in muscle tissue, ChREBP protein levels, DNA-binding activity, and downstream gene targets were generally found to decrease or to remain unchanged during freezing. Overall, our results demonstrate that ChREBP regulates metabolism in a tissue-dependent manner during freezing, when its activity is required for liver tissue but not for skeletal muscle tissue in wood frogs.

Keywords: Rana sylvatica; fatty acid synthase; freeze tolerance; metabolic rate depression; pyruvate kinase; stearoyl-CoA desaturase.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amphibian Proteins / genetics*
  • Amphibian Proteins / metabolism
  • Animals
  • Basic Helix-Loop-Helix Leucine Zipper Transcription Factors / genetics*
  • Basic Helix-Loop-Helix Leucine Zipper Transcription Factors / metabolism
  • Cold Temperature
  • Freezing
  • Gene Regulatory Networks*
  • Glucose / metabolism*
  • Liver / metabolism
  • Male
  • Muscle, Skeletal / metabolism
  • Ontario
  • RNA, Messenger / metabolism
  • Ranidae / genetics
  • Ranidae / physiology*
  • Transcription, Genetic*

Substances

  • Amphibian Proteins
  • Basic Helix-Loop-Helix Leucine Zipper Transcription Factors
  • RNA, Messenger
  • Glucose