Ulk1 phosphorylation at S555 is not required for endurance training-induced improvements in exercise and metabolic capacity in mice

• Published in: Journal of applied physiology (1985) Vol. 137; no. 2; pp. 223 - 232
• Main Authors: Guan, Yuntian, Spaulding, Hannah, Yu, Qing, Zhang, Mei, Willoughby, Orion, Drake, Joshua C, Yan, Zhen
• Format: Journal Article
• Language: English
• Published: United States American Physiological Society 01.08.2024
• Subjects: Alanine; Animals; Autophagy; Autophagy-Related Protein-1 Homolog - genetics; Autophagy-Related Protein-1 Homolog - metabolism; CRISPR; Endurance capacity; Endurance Training - methods; Energy metabolism; Energy Metabolism - physiology; Gene Knock-In Techniques; Genetic modification; Kinases; Male; Metabolic flux; Metabolism; Mice; Mice, Inbred C57BL; Mitophagy; Mitophagy - physiology; Muscle, Skeletal - metabolism; Muscle, Skeletal - physiology; Muscles; Musculoskeletal system; Phosphorylation; Physical Conditioning, Animal - physiology; Physical training; Quality of life; Respiration; Skeletal muscle; exercise; mitophagy; endurance capacity; metabolism; autophagy
• ISSN: 8750-7587; 1522-1601; 1522-1601
• DOI: 10.1152/japplphysiol.00742.2023

Endurance exercise training improves exercise capacity as well as skeletal muscle and whole body metabolism, which are hallmarks of high quality-of-life and healthy aging. However, its mechanisms are not yet fully understood. Exercise-induced mitophagy has emerged as an important step in mitochondrial remodeling. Unc-51-like autophagy-activating kinase 1, ULK1, specifically its activation by phosphorylation at serine 555, was discovered as an autophagy driver and to be important for energetic stress-induced mitophagy in skeletal muscle, making it a potential mediator of the beneficial effects of exercise on mitochondrial remodeling. Here, we used CRISPR/Cas9-mediated gene editing and generated knock-in mice with a serine-to-alanine mutation of Ulk1 on serine 555. We now report that these mice displayed normal endurance capacity and cardiac function at baseline with a mild impairment in energy metabolism as indicated by an accelerated increase of respiratory exchange ratio (RER) during acute exercise stress; however, this was completely corrected by 8 wk of voluntary running. Ulk1-S555A mice also retained the exercise-mediated improvements in exercise capacity and metabolic flux. We conclude that Ulk1 phosphorylation at S555 is not required for exercise-mediated improvements of exercise and metabolic capacity in healthy mice. We have used CRISPR/Cas9-mediated gene editing to generate Ulk1-S555A knock-in mice to show that loss of phosphorylation of Ulk1 at S555 blunted exercise-induced mitophagy and mildly impairs energy metabolism during exercise in healthy mice. However, the knock-in mice retained exercise training-mediated improvements of endurance capacity and energy metabolism during exercise. These findings suggest that exercise-induced mitophagy through Ulk1 activation is not required for the metabolic adaptation and improved exercise capacity in young, healthy mice.