<i>NAT10</i> supports CAG repeat-associated mRNA stabilization and is associated with hepatic metabolic reprogramming during spaceflight

Summary The regulatory factors underlying posttranscriptional adaptation to spaceflight are incompletely understood. We identified NAT10 , an RNA acetyltransferase, among RNA modification enzymes significantly upregulated in spaceflight-exposed mouse liver. Transcriptome-wide correlation analysis linked NAT10 expression to an RNA-metabolism module enriched for CAG repeat density in coding sequences. Actinomycin D chase assays showed that NAT10 knockdown destabilized CAG repeat-containing transcripts, with DDX17 serving as the primary validated target; DCP1A showed a directionally consistent pattern. Wild-type NAT10 re-expression fully rescued DDX17 mRNA stability, the acetyltransferase-dead G641E mutant rescued mRNA stability to a comparable extent, and the K290A helicase-domain mutant failed to rescue, consistent with a requirement for helicase domain integrity, whereas acetyltransferase activity was not strictly required under these experimental conditions. RNA immunoprecipitation further supported preferential NAT10 association with CAG repeat-containing mRNAs, with reduced association after single-site CAGCAG deletion in DDX17 and DCP1A reporters. Gene set enrichment analysis associated NAT10 upregulation in spaceflight liver with suppressed fatty acid beta-oxidation and induced cholesterol biosynthesis; NAT10 depletion in hepatocellular carcinoma cells selectively opposed the cholesterol-associated, but not the broader metabolic, component of this signature. These findings support a model linking NAT10 to CAG repeat-associated mRNA stabilization in the context of hepatic metabolic and posttranscriptional to spaceflight.