Epigenetics is the study of molecules and mechanisms that modify gene expression while the DNA sequence remains unchanged. DNA methylation is a widely studied epigenetic marker for its role in cell differentiation and as a biomarker for certain diseases such as cancer, or for exposure to environmental risk factors. While the effects of aging and smoking on the human "methylome" are now well known, the epigenetic effects of many other factors, particularly those linked to immunity, have yet to be determined.
As part of the Milieu Intérieur project, researchers from the Institut Pasteur, the CNRS, the Karolinska Institute (Sweden) and the University of British Columbia (Canada), including Prof. Lluis Quintana-Murci, Chair of Human Genomics and Evolution at the Collège de France, measured the effects of 140 lifestyle and immunity variables on the methylome of 958 healthy donors.
Their analyses, published on October 7, 2022 in Nature Communications, reveal that a very common viral infection in the general population, due to cytomegalovirus, modifies the genome methylation levels of infected individuals, by deregulating a transcription factor used by the virus to enter the latent phase. This study also shows that the effects of age on the methylome have been overestimated, as many of these effects are actually due to the effects of age on blood cell composition. Furthermore, the researchers showed that epigenetic differences between individuals increase with age, suggesting altered maintenance of methylation levels during aging. Finally, an integrative analysis of the different factors affecting the methylome suggests that genetics control a greater proportion of epigenetic variation than the environment, in contradiction with current hypotheses implying strong environmental effects on the human epigenome.
