Abstract
Regulation, evolution and impact of repetitive elements in human genome function is largely unknown. Recent reports indicate that LINE-1 (L1) occurs in brain cells, and stem cells, contributing to neuronal plasticity and somatic diversification. Defects in their mobilization are associated with neurological disorder, as Rett syndrome or Schizophrenia. However, whether somatic L1 retro-transposition regulation could positively contribute to cellular differentiation program is still unexplored. We investigated L1epigenetic regulation and retro transposition activity during differentiation of human primary muscle cells, finding that skeletal myogenesis supports a MyoD-dependent and Dystrophyn-nNOS dependent activity of this class of repetitive elements that results in the acquisition of additional L1 copies in differentiated cells. Such mechanism is impaired during differentiation of muscle cells derived by patients affected by Duchene muscular Dystrophy, being HDAC2 aberrantly recruited at L1 promoter and their transcription repressed. Notably, functional restoration ofdystrophin-nNOS-HDAC2 signaling and fiber functionality by HDAC inhibitors or dystrophin re-expression by exon-skipping could restore normal L1 expression levels and CNV either in the mdx mice and in DMD primary muscle cells. We further prove that impairment of L1 mobilization by reverse transcriptase pharmacological inhibition reduces the differentiation ability of normal human primary muscle cells, specifically interfering with sarcolemma and muscle fibers correct formation. In this regard, L1-RC-seq (L1-retrotransposon–capturing and sequencing) revealed muscle site specific L1 insertions in the genome, recurrent in different individuals, with an enhanced CNV during control differentiation, and not in DMD patients where transcriptome program and muscle fiber formation is impaired. We propose that L1 repetitive elements are positive players in cellular differentiation and cell identity, and their epigenetic deregulation a key trait in muscular dystrophy manifestation.