NAP1L5 is required for translation activation during cardiomyocyte hypertrophy

Pathological growth of cardiomyocytes during hypertrophy is characterized by excess protein synthesis; however, the regulatory mechanism remains largely unknown. Using a neonatal rat ventricular myocyte (NRVMs) model, here we find that the expression of nucleosome assembly protein 1 like 5 (Nap1l5) is upregulated in phenylephrine (PE)-induced hypertrophy. Knockdown of Nap1l5 expression by siRNA significantly blocks cell size enlargement and pathological gene induction after PE treatment. In contrast, Adenovirus-mediated Nap1l5 overexpression significantly aggravates the pro-hypertrophic effects of PE on NRVMs. RNA-seq analysis reveals that Nap1l5 knockdown reverses the pro-hypertrophic transcriptome reprogramming after PE treatment. Whereas immune response is dominantly enriched in the upregulated genes, oxidative phosphorylation, cardiac muscle contraction and ribosome related pathways are remarkably enriched in the down-regulated genes. Although PRC2 and PRC1 are involved in Nap1l5-mediated gene regulation, Nap1l5 does not directly alter the levels of global histone methylations. However, puromycin incorporation assay shows that Nap1l5 is both necessary and sufficient to drive the increased protein synthesis rate in cardiomyocyte hypertrophy. This is attributable to a direct regulation of ribosome assembly by Nap1l5. Our findings demonstrate a previously unrecognized role of Nap1l5 in translation control during cardiac hypertrophy. NRVMs were first transfected with siNap1l5 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.