Formaldehyde regulates S-adenosylmethionine biosynthesis and one-carbon metabolism

One-carbon metabolism is an essential branch of cellular metabolism that intersects with epigenetic regulation. Here, we show formaldehyde, a one-carbon unit derived from both endogenous sources and environmental exposure, regulates one-carbon metabolism by inhibiting the biosynthesis of S-adenosylmethionine (SAM), the major methyl donor in cells. Formaldehyde reacts with privileged, hyperreactive cysteine sites in the proteome, including Cys120 in S-adenosylmethionine synthase isoform type-1 (MAT1A). Formaldehyde exposure inhibited MAT1A activity and decreased SAM production with MAT-isoform specificity. A genetic mouse model of chronic formaldehyde overload showed a decrease in SAM and in methylation on selected histones and genes. Epigenetic and transcriptional regulation of Mat1a and related genes function as compensatory mechanisms for formaldehyde-dependent SAM depletion, revealing a biochemical feedback cycle between formaldehyde and SAM one-carbon units. We performed genome-wide CpG methylation analysis in liver samples from Adh5–/– mice compared to WT controls using the Infinium Mouse Methylation BeadChip that interrogates more than 285k methylation sites per sample at single-nucleotide resolution.