Replicative Senescence-Associated LINE1 Methylation and LINE1-Alu Expression Levels in Human Endothelial Cells

Abstract

One of the main challenges of current research on aging is to identify the complex epigenetic mechanisms involved in the acquisition of the cellular senescent phenotype. Despite some evidence suggested that epigenetic changes of DNA repetitive elements, including transposable elements (TE) sequences, are associated with replicative senescence of fibroblasts, data on different types of cells are scarce. We previously analysed genome-wide DNA methylation of young and replicative senescent human endothelial cells (HUVECs), highlighting increased levels of demethylated sequences in senescent cells. Here, we aligned the most significantly demethylated single CpG sites to the reference genome and annotated their localization inside TE sequences and found a significant hypomethylation of sequences belonging to the Long-Interspersed Element-1 (LINE-1 or L1) subfamilies L1M, L1P, and L1HS. To verify the hypothesis that L1 demethylation could be associated with increased transcription/activation of L1s and/or Alu elements (non-autonomous retroelements that usually depend on L1 sequences for reverse transcription and retrotransposition), we quantified the RNA expression levels of both L1 (generic L1 elements or site-specific L1PA2 on chromosome 14) and Alu elements in young and senescent HUVECs and human dermal fibroblasts (NHDFs). The RNA expression of Alu and L1 sequences was significantly increased in both senescent HUVECs and NHDFs, whereas the RNA transcript of L1PA2 on chromosome 14 was not significantly modulated in senescent cells. Moreover, we found an increased amount of TE DNA copies in the cytoplasm of senescent HUVECs and NHDFs. Our results support the hypothesis that TE, which are significantly increased in senescent cells, could be retrotranscribed to DNA sequences.

Accelerated Hematopoietic Stem Cell Aging in Space

“…Human LINE-1 elements are seen in many cancers and the most active L1 elements have been shown to evade somatic repression 42 . APOBEC3 has been shown to repress LINEs and restrict replication 43 ; L1ME3A is differentially regulated in young versus senescent human umbilical vein endothelial cells (HUVECs) 44 and was repressed in post-flight samples. Genetic and epigenetic changes and immune responses elicited by retrotransposon reactivation have been linked to aging 35 and cancer 44 .…”

“…APOBEC3 has been shown to repress LINEs and restrict replication 43 ; L1ME3A is differentially regulated in young versus senescent human umbilical vein endothelial cells (HUVECs) 44 and was repressed in post-flight samples. Genetic and epigenetic changes and immune responses elicited by retrotransposon reactivation have been linked to aging 35 and cancer 44 . Data from the NASA Twins study showed that APOBEC3A was up-regulated in lymphocyte-depleted cells as time in space increased 26 .…”

Replicative senescence and high glucose induce the accrual of self-derived cytosolic nucleic acids in human endothelial cells

“…One mechanism leading to the accumulation of cytoplasmic dsRNA and RNA:DNA hybrids during cellular senescence is related to the relocalization of sirtuins to areas of DNA double-strand break, causing the loss of heterochromatin structure and ultimately leading to the transcription of retrotransposable elements [ 31 ]. In this regard, we previously demonstrated a higher abundance of the RNA and complementary DNA sequences of two among the major retrotransposable elements, i.e., Alu and LINE1, in senescent ECs [ 32 ]. The increased presence of cytoplasmic RNA:DNA hybrids in senescent and HG-treated ECs corroborates our previous observation of reduced expression of RNase H2, the enzyme that specifically degrades the RNA moiety of RNA:DNA hybrids [ 22 ].…”

Endothelial Senescence in Neurological Diseases

“…DNA methylation is an epigenetic mechanism that is regulated by a combination of methyltransferases and demethylases, and a central role for DNA methylation in vascular senescence-related diseases has been identified [ 60 ]. Ramini et al analyzed genome-wide DNA methylation in normal and senescent HUVECs and noted a significant increase in demethylated sequences in senescent cells [ 61 ]. Zhang et al reported that homocysteine promotes EC senescence by promoting hTERT promoter demethylation and downregulating hTERT expression in mouse aortic ECs [ 62 ].…”