Multigenerational epigenetic adaptation of the hepatic wound-healing response.

We investigated whether ancestral liver damage leads to heritable reprogramming of hepatic wound healing in male rats. We found that a history of liver damage corresponds with transmission of an epigenetic suppressive adaptation of the fibrogenic component of wound healing to the male F1 and F2 generations. Underlying this adaptation was less generation of liver myofibroblasts, higher hepatic expression of the antifibrogenic factor peroxisome proliferator-activated receptor γ (PPAR-γ) and lower expression of the profibrogenic factor transforming growth factor ß1 (TGF-ß1) compared to rats without this adaptation. Remodeling of DNA methylation and histone acetylation underpinned these alterations in gene expression. Sperm from rats with liver fibrosis were enriched for the histone variant H2A.Z and trimethylation of histone H3 at Lys27 (H3K27me3) at PPAR-γ chromatin. These modifications to the sperm chromatin were transmittable by adaptive serum transfer from fibrotic rats to naive rats and similar modifications were induced in mesenchymal stem cells exposed to conditioned media from cultured rat or human myofibroblasts. Thus, it is probable that a myofibroblast-secreted soluble factor stimulates heritable epigenetic signatures in sperm so that the resulting offspring better adapt to future fibrogenic hepatic insults. Adding possible relevance to humans, we found that people with mild liver fibrosis have hypomethylation of the PPARG promoter compared to others with severe fibrosis.

Telomeres are favoured targets of a persistent DNA damage response in ageing and stress-induced senescence.

Telomeres are specialized nucleoprotein structures, which protect chromosome ends and have been implicated in the ageing process. Telomere shortening has been shown to contribute to a persistent DNA damage response (DDR) during replicative senescence, the irreversible loss of division potential of somatic cells. Similarly, persistent DDR foci can be found in stress-induced senescence, although their nature is not understood. Here we show, using immuno-fluorescent in situ hybridization and ChIP, that up to half of the DNA damage foci in stress-induced senescence are located at telomeres irrespective of telomerase activity. Moreover, live-cell imaging experiments reveal that all persistent foci are associated with telomeres. Finally, we report an age-dependent increase in frequencies of telomere-associated foci in gut and liver of mice, occurring irrespectively of telomere length. We conclude that telomeres are important targets for stress in vitro and in vivo and this has important consequences for the ageing process.