iPSC mutants
Induced stem cells accumulate mutations during reprogramming
Sofia Dubovskova, PCR.news
Human induced Pluripotent Stem Cells (hiPSC) are an attractive object for research in regenerative medicine. They can be multiplied and differentiated into many types of cells, they can be used to model diseases in vitro and, in the future, used for cell therapy. However, hiPSCs can inherit mutations of the original donor somatic cells and accumulate new mutations during reprogramming and cultivation. Scientists from the UK conducted the first systematic study of genome integrity and oncogenic potential of hiPSC. They tested whether mutations affect the behavior and functions of stem cells.
The scientists worked with hiPSCs derived from skin fibroblasts (F-hiPSC) and endothelial progenitor cells (B-hiPSC) from seven healthy men and four healthy women. Analysis of genome-wide sequencing data revealed a greater number of mutations in F-hiPSC compared to B-hiPSC. At the same time, mutations associated with UV exposure prevailed in F-hiPSC. These results were confirmed by analyzing the full-exome data of 452 F-hiPSC lines obtained from 288 donors from the HipSci bank.
In contrast, there were no signs of UV damage in the B-hiPSC genome, but evidence of oxidative damage was present. The mutational load in the F-hiPSC sister lines obtained in the same fibroblast reprogramming experiment from a single donor differed significantly. This may indicate different mutational landscapes of the original fibroblasts. The researchers concluded that mutations in F-hiPSC are associated with exposure to sunlight on skin fibroblasts, while different cells are exposed to different levels of radiation.
At the next stage, the scientists analyzed the mutations found in hiPSC using the COSMIC Cancer Gene Census database. They identified 272 mutations in 145 genes associated with cancer, but note that some of these mutations may be so-called passenger mutations, which do not give an advantage in growth rate. In both F-hiPSC and B-hiPSC, scientists found signs of positive selection of mutations in the oncogene BCOR. However, these mutations were not found in the DNA sequencing results of the original fibroblasts. This means that they originated in F-hiPSC during in vitro manipulations.
BCOR encodes a corepressor of the proto-oncogenic transcription factor BCL6. Somatic mutations in BCOR are found in malignant blood diseases and other types of cancer. The BCOR protein is part of the polycomb group, which regulates the self-renewal and differentiation of stem cells and is crucial for maintaining pluripotency. Scientists have shown that mutations in BCOR reduce the differentiation potential of B-hiPSC cells, that is, changes in the DNA of stem cells that occur when working with them can have functional consequences.
Based on the results of the study, the authors formulated recommendations for working with hiPSC. First, they should be obtained from somatic cells with a minimally damaged genome. Secondly, the duration of cultivation should be as short as possible. In addition, before using hiPSC, it is necessary to carefully analyze their genomes.
Article by Rouhani et al. Substantial somatic genomic variation and selection for BCOR mutations in human induced pluripotent stem cells is published in the journal Nature Genetics.
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