Reply Reply All Forward Move Delete Close Previous Item Next Item Close Culture-induced recurrent epigenetic aberrations in human pluripotent stem cells (hPSCs)

After fertilization of the ovum by a sperm, the fertilized egg is called the “zygote” and progresses from one cell to two cells, to four, eight, sixteen, etc. At least through the first 16 cells, these cells are called “totipotent” (able to differentiate into anything). Then they become pluripotent stem cells (PSCs), differentiating into endoderm (to make the internal organs), ectoderm (to make the skin and brain), and mesoderm (to form muscles/bone/connective tissue). Further differentiation proceeds to form specific cell-types –– including e.g. intestinal stem cells, epithelial stem cells, and mesenchymal stem cells, respectively.

Human pluripotent stem cells (hPSCs) are being increasingly studied in the fields of developmental biology, genetic research, and regenerative medicine. The requirement to have “genetically intact, accurate” cells hPSC cultures is obviously crucial in order to ensure safe hPSC-based treatments as well as reliable analysis of their characteristics. However, as we have discussed in previous GEITP emails, prolonged culturing of ANY type of cells –– alongside their unique cell-cycle checkpoints, rapid cell cycle, and high levels of replication stress, places them under constant selection pressures (environment). Prolonged culturing might very easily lead to UNDESIRABLE culturing artifacts such as full trisomies to copy number changes and point mutations, in a process termed culture adaptation.

Whereas gene expression levels are greatly affected by copy number variations or genetic mutations, they may also be modulated by epigenetic changes. Epigenetic mechanisms such as DNA methylation have crucial roles in maintaining gene expression patterns; hence, alterations in DNA methylation patterns may lead to erroneous gene expression. This phenomenon is well-documented in cancers, where epigenetic aberrations may contribute to tumor formation, growth, and metastasis. Global DNA hypomethylation is a common feature of both benign and malignant tumors.

Authors [see attached] showed that hPSCs do acquire genetic aberrations during their growth in culture. The aberrations are non-random and positively selected, by altering multiple cellular phenotypes. Similarly to genetic mutations, epigenetic aberrations may also change gene expression levels, leading to altered cellular behaviors, as seen in tumors. Authors found that, upon silencing of differentiation genes and tumor-suppressor genes, they are down-regulated, and pluripotency- and growth promoting genes are upregulated –– which drive the positive selection. These data therefore highlight another challenge faced by scientists studying hPSC cultures, with regard to maintenance of intact gene expression program, and emphasize the role of epi-mutations (similar to those described in cancer cells) which can occur during prolonged culturing of hPSCs.

PloS Genet Aug 2o17; 13: e1006979

This entry was posted in Center for Environmental Genetics. Bookmark the permalink.