Selective pericentromeric heterochromatin dismantling caused by TP53 activation during senescence.

Cellular senescence triggers various types of heterochromatin remodeling that contribute to aging. However, the age-related mechanisms that lead to these epigenetic alterations remain elusive. Here, we asked how two key aging hallmarks, telomere shortening and constitutive heterochromatin loss, are mechanistically connected during senescence. We show that, at the onset of senescence, pericentromeric heterochromatin is specifically dismantled consisting of chromatin decondensation, accumulation of DNA breakages, illegitimate recombination and loss of DNA. This process is caused by telomere shortening or genotoxic stress by a sequence of events starting from TP53-dependent downregulation of the telomere protective protein TRF2. The resulting loss of TRF2 at pericentromeres triggers DNA breaks activating ATM, which in turn leads to heterochromatin decondensation by releasing KAP1 and Lamin B1, recombination and satellite DNA excision found in the cytosol associated with cGAS. This TP53-TRF2 axis activates the interferon response and the formation of chromosome rearrangements when the cells escape the senescent growth arrest. Overall, these results reveal the role of TP53 as pericentromeric disassembler and define the basic principles of how a TP53-dependent senescence inducer hierarchically leads to selective pericentromeric dismantling through the downregulation of TRF2.

Firalink: A bioinformatics pipeline for long non-coding RNA data analysis.

Summary: The Firalink bioinformatics pipeline has been developed to analyse long non-coding RNA (lncRNA) data generated by targeted sequencing. This pipeline has been first implemented for use with the FIMICS panel containing 2906 lncRNAs useful for investigations in cardiovascular disease. It has been subsequently tested and validated using a panel of lncRNAs targeting brain disease. The pipeline can be adapted to other targeted sequencing panels or other transcriptomics data (e.g. whole transcriptome) through a change of the reference genome/panel. Therefore, Firalink can be applied to different lncRNA panels and transcriptomics data targeting multiple diseases. Availability and implementation: The Firalink pipeline works on Linux and is freely available to non-commercial users at https://gitlab.lcsb.uni.lu/covirna/covirna-ext/covirna-firalink-pipeline. Access will be granted after contacting bioinformatics@firalis.com. The pipeline is implemented with the Nextflow workflow manager using Python and R scripts. It will remain available for at least two years following publication and will be regularly updated and upgraded. Supplementary information: For an example of the application of the Firalink pipeline using the FIMICS panel, see www.covirna.eu.

Mitochondrial function in skeletal myofibers is controlled by a TRF2-SIRT3 axis over lifetime.

Telomere shortening follows a developmentally regulated process that leads to replicative senescence of dividing cells. However, whether telomere changes are involved in postmitotic cell function and aging remains elusive. In this study, we discovered that the level of the TRF2 protein, a key telomere-capping protein, declines in human skeletal muscle over lifetime. In cultured human myotubes, TRF2 downregulation did not trigger telomere dysfunction, but suppressed expression of the mitochondrial Sirtuin 3 gene (SIRT3) leading to mitochondrial respiration dysfunction and increased levels of reactive oxygen species. Importantly, restoring the Sirt3 level in TRF2-compromised myotubes fully rescued mitochondrial functions. Finally, targeted ablation of the Terf2 gene in mouse skeletal muscle leads to mitochondrial dysfunction and sirt3 downregulation similarly to those of TRF2-compromised human myotubes. Altogether, these results reveal a TRF2-SIRT3 axis controlling muscle mitochondrial function. We propose that this axis connects developmentally regulated telomere changes to muscle redox metabolism.