Comparative Quantitative Profiling of Protein Lactylation Reveals a Dynamic Tissues-Specific Network Associated with Metabolic Specialization in Yaks.

Protein lysine lactylation is an emerging post-translational modification with broad roles in metabolic regulation. The yak (Bos grunniens) has evolved strong metabolic adaptability on the Qinghai-Tibetan Plateau, yet its tissue-specific lactylation patterns remain poorly characterized. Here, we collected liver, muscle, and heart tissues from three adult male yaks (4.5 years; 305-355 kg) and integrated quantitative proteomics with lactylomics to map lactylation profiles across these tissues. After normalizing each lactylation site to its parent protein abundance and applying Benjamini-Hochberg correction, we identified 628, 982, and 541 differentially lactylated sites (|log2FC| ≥ 0.585, adjusted p < 0.05) in liver-muscle, liver-heart, and muscle-heart comparisons, with median fold changes of 4.11, 7.08, and 3.08, corresponding to 267, 372, and 219 proteins, respectively. Subcellular localization showed that approximately 27-30% of these sites were localized to mitochondria. Functional enrichment across these comparisons consistently highlighted pathways such as the TCA cycle (fold enrichment: 1.56-2.38) and HIF-1 signaling (up to 2.69). A total of 135 proteins were common to all three comparisons, some with both up- and downregulated sites within the same tissue pair. Our results reveal decoupling between protein abundance and lactylation levels, tissue-specific lactylation patterns on the same proteins, and expression-independent lactylation of key enzymes (e.g., LDHA, SIRT3). Functional enrichment suggests lactylation serves as a multimodal regulatory mechanism coordinating energy metabolism, protein homeostasis, and electromechanical coupling across tissues. Expression profiling of lactate-metabolizing enzymes and lactylation regulators further supports an organ-specific model of post-translational regulation. Collectively, these findings detail a complex, tissue-specific lactylation network in yaks and provide insights into the metabolic homeostasis essential for high-altitude life.