Transcriptome Remodeling and Adaptive Preservation of Muscle Protein Content in Hibernating Black Bears

Area of Science:

• Molecular Biology
• Physiology
• Comparative Biology

Background:

• Hibernation is an adaptation for energy conservation during winter inactivity.
• Bears uniquely maintain muscle mass and protein content despite prolonged immobility and fasting.
• Understanding bear muscle preservation mechanisms can offer insights into human muscle atrophy.

Purpose of the Study:

• To identify transcriptional changes underlying muscle mass preservation in hibernating bears.
• To elucidate the molecular pathways involved in preventing muscle loss during hibernation.

Main Methods:

• Transcriptome sequencing of quadriceps femoris muscle from hibernating and active adult black bears (n=5 each).
• Large-scale gene expression profiling of 14,199 genes.
• Gene set enrichment analysis to identify differentially expressed pathways.

Main Results:

• Hibernating bears showed upregulated genes in translation, ribosome biogenesis, and mTORC1 signaling.
• Downregulation of genes involved in branched-chain amino acid (BCAA) catabolism suggests BCAA preservation.
• Key mTORC1 regulators (RRAGD, RRAGB) and downstream targets (EIF4B) were upregulated.
• Autophagy-related genes (MAP1LC3A, ULK1) were downregulated, indicating reduced protein degradation.

Conclusions:

• Hibernating bears maintain muscle protein by enhancing protein biosynthesis through mTORC1 signaling.
• mTORC1 activation is linked to BCAA availability, promoting muscle anabolism.
• Suppression of autophagy contributes to reduced protein catabolism, preserving muscle mass during hibernation.