Researchers at the University of Barcelona (UB) and the August Pi i Sunyer Biomedical Research Institute (IDIBAPS) lead a paper, published in Nature Genetics (doi:10.1038/ng.3291), which reveals an unexpected connection between epigenetic changes associated with lymphocytes’ maturation and those observed in cancer. Both processes share similar changes in large regions of the genome. To decipher how the epigenome changes when cells mature, the participation of the National Center for Genome Analysiss (CNAG), located at the Barcelona Science Park, has been essential. The study breaks new ground in the study of immune system cells, aging and cancer and offers the scientific community a new tool with implications for both basic and translational research.

The study, led by Iñaki Martín Subero, researcher in the Department of Pathology, Pharmacology and Microbiology of the UB and IDIBAPS, first analyses the epigenome during cell maturation of B lymphocytes —the immune system cells responsible of the antibodies production— and provides epigenetic maps of each step in this process.

In 2001, after completing the sequence of the human genome, scientists realized that knowing the complete DNA sequence did not allow them to understand its role and how the same gene sequence could give rise to the multiple cell types that make up the body. From there arises the importance of studying the epigenome, which is anything that alters the expression of genes without changing the DNA strand. “It is like the software that control the genome functions, which in this case would represent the hardware”, explains Professor Iñaki MartínSubero.

The article deepens in the epigenetic processes that occur during B lymphocytes maturation and demonstrates that the human epigenome is much more dynamic than it was previously thought: in the normal process of maturation of these cells the epigenome changes in a 30%, affecting several million regions of the genome. “This may be the reason why a single genome can generate the large numbers of cells with different functions that make up our organism”, remarks Martin Subero.

The study also shows, unlike what has been published to date regarding DNA methylation —the main epigenetic mechanism—, that only a small proportion of changes in the degree of methylation are related to gene expression. In this sense, Martin Subero emphasizes that “it seems that methylation is the process printing the history in cells’ DNA, from their original stage as a stem cell until they are completely differentiated. This process tells us about which parts of the genome have essential functions for the lymphocytes maturation, about how much they have proliferated during this process and also about their cellular age”.

New approach in cancer epigenetics

Furthermore, this new study has revealed that more than a half of epigenetic changes believed to be specific of tumour cells are also observed in long-life blood cells. This unexpected finding challenges the current models of cancer epigenetics. “We have found an epigenetic signature in long life lymphocytes that was previously only associated with cancer cells”, says Martín Subero. This article proposes a new integrative model in which cellular longevity, whether it occurs in the context of cancer, aging or healthy cells, is associated with similar epigenetic features.

The study has been coordinated by IDIBAPS and UB. Laboratories in Barcelona, Madrid and Pamplona, and institutions and researchers from Germany, France, Netherlands, United Kingdom, United States and South Korea have participated in it. To decipher how the epigenome changes when cells mature, the participation of the National Center for Genome Analysis (CNAG) in Barcelona has been essential. According to Ivo Gut, director of CNAG, “this study has required the application of advanced mass sequencing techniques and the development of new analysis methods”. Marta Kulis, UB researcher and first author of the study, explains that “data analysis was a real challenge: it has taken us three years to perform the experiments and extract all the information within the huge amount of generated data”.
 

The Blueprint project

The study is part of the Blueprint project, the contribution of the EU to the International Human Epigenome Consortium. With an investment of 30 million euros, it is responsible for generating at least 100 reference epigenomes of healthy people’s blood cells and of those with different associated diseases such as leukemias, lymphomas or autoimmune diseases. The team led by Martin Subero and Campo is responsible for generating the epigenome of B lymphocytes and of several types of cancers derived from this cell type.