In Vivo Quantification of Histone Acetylation Turnover and Acetyl-CoA Sources Using 2H2O Metabolic Labeling and High-Resolution Mass Spectrometry.

Dysregulated histone acetylation links cellular metabolism to gene expression, but measuring its in vivo turnover remains technically challenging. Here, we introduce a 2H2O-based metabolic labeling method coupled with high-resolution Orbitrap mass spectrometry to quantify in vivo histone acetylation dynamics. The approach leverages differing deuterium incorporation rates between fast-labeling acetyl groups and slow-labeling peptide backbones. A two-tier analytical workflow uses full-scan mass spectrometry for mono-acetylated peptides, combined with parallel reaction monitoring (PRM) to resolve site-specific turnover and stoichiometry. Furthermore, monitoring acetyl-group plateau 2H enrichment enables the evaluation of specific substrate contributions to the acetyl-CoA pool supporting histone acetylation. To demonstrate biological utility, we applied this approach to mice maintained on a high-carbohydrate diet or subjected to 48-h fasting to assess nutrient-dependent histone acetylation dynamics. Acetyl-group labeling reflected the metabolic origin of acetyl-CoA, showing greater 2H enrichment in the fed state and reduced enrichment during fasting due to increased utilization of unlabeled fatty acid-derived acetyl-CoA. Fasting accelerated acetylation turnover across multiple histone sites and reduced overall acetylation stoichiometry. Quantitative tracing revealed that fatty acid oxidation becomes an important contributor to histone acetylation during fasting, whereas glucose remains the predominant source of nucleo-cytosolic acetyl-CoA (supplying > 60% of acetylation used carbon). This approach enables simultaneous in vivo assessment of histone acetylation turnover, site occupancy, and acetyl-CoA substrate utilization, offering a robust platform to investigate metabolic-epigenetic crosstalk in health and disease.