Targeting Cytoplasmic SAM by Expressing Slc25a26 Inhibits Protein Synthesis in Cardiac Hypertrophy via SAMTOR/mTOR signaling

Excess protein synthesis is the major pathological manifestation of cardiac hypertrophy; however, the underlying mechanism remains elusive. Here we found that a SAM transporter Slc25a26 translocated to mitochondria during cardiac hypertrophy. Silencing Slc25a26 aggravated phenylephrine-induced cardiomyocyte hypertrophy in neonatal rat ventricular myocytes. Transcriptome analysis revealed a specific regulation of ribosome genes by Slc25a26. Puromycin incorporation assay showed a negative regulation of protein synthesis rate by Slc25a26. The translational regulation was independent of ribosome assembly, but abolished by mTOR inhibitor rapamycin. Administration of SAM, or silencing Samtor, reversed the inhibitory impact of Slc25a26 on protein synthesis. AAV9-mediated Slc25a26 overexpression in mouse heart increased the SAM level in mitochondria, but reduced that in nucleus and cytoplasm. Transaortic-constriction-induced hypertrophic pathologies, including pathological gene induction, cardiomyocyte enlargement, myocardial remodeling and heart dysfunction were significantly alleviated by Slc25a26 overexpression. Our data demonstrate a crucial role of subcellular SAM homeostasis in translational control during cardiac hypertrophy. NRVMs were first transfected with siSlc25a26 or siNeg, then treated with PE for 36h after 12h of transfection. NRVMs were used to extracted RNA according to the manufacturer's instructions. Transcriptome sequencing of RNA was completed by Beijing Genomics Institution (BGI). Three independent biological replicate samples were sequenced for each group.