Cross-tissue multi-omics analysis reveal that yak milk alleviates exercise fatigue by activating muscle AMPK-PGC-1\u03b1-NRF2 signaling pathway via the modulation of intestinal microbial and host metabolism

In recent years, with the development of society, fatigue has become an important factor affecting people's quality of life and health. The exercise fatigue (EF) is manifested in the inability of the body's physiological processes to continue their function at a specific level and/or fail to maintain a predetermined intensity of exercise. Intestinal flora plays a crucial role in the occurrence and development of EF. Yak milk (YM) is a specialty livestock milk with potential anti-fatigue effects. However, vital microbial signaling metabolites and the host targets related to the metabolic benefits of YM remain to be clarified. This study first found through behavioral tests that YM supplementation could increase muscle endurance and improve sports performance in EF mice. Subsequent physiological and pathological section analysis also confirmed that YM increased the gene expression of monocarboxylic acid transporter (MCT1) that regulates lactate shuttle and reduced the accumulation of lactate in muscle. After lactate is released into the blood, it is ingested by hepatocytes. By upregulating the expression of the glucogene-limiting enzymes phosphoenolpyruvate carboxykinase (PEPCK1) and glucose-6-phosphatase (G6Pase), it promotes liver glycogen synthesis, thereby providing energy for skeletal muscle movement. It could also relieve oxidative stress and inflammatory responses in the liver and muscles, and relieved muscle tissue damage. Intestinal flora 16S rRNA sequencing showed that YM supplementation was associated with significant shifts in gut microbiota composition, specifically an augmentation in Alistipes and Prevotellaceae_UCG-001. Alterations in gut metabolites were also recorded, including the enhancement of propionate, PC, LPC, and polypeptides. Transcriptome sequencing also confirmed that the Mups family genes and chREBP metabolic pathway that regulated gluconeogenesis pathways were significantly enriched after YM supplementation. Mechanistically, these metabolites could activate muscle AMPK-PGC-1\u03b1-NRF2 signaling pathway, promoted mitochondrial biosynthesis, and increased ATP production. At the same time, it activated the downstream Mfn1/2 signaling pathway, regulated mitochondrial fusion to form continuous mitochondrial network integrity to maintain energy metabolism homeostasis. These findings uncover the core role of the gut microbiota-metabolites-muscle axis in relieving EF. This study accentuates the potential health advantages of YM and unveils potential avenues for developing therapeutic strategies for fatigue-related disease based on the interplay between YM and the gut microbiota.