Abstract
BackgroundReprogramming somatic cells to induced pluripotent stem cells (iPSCs) has opened new therapeutic possibilities. However, karyotypic abnormalities detected in iPSCs compromised their utility, especially chromosomal aberrations found at early passages raised serious safety concerns. The mechanism underlying the chromosomal abnormality in early-passage iPSCs is not known.MethodsHuman dermal fibroblasts (HDFs) were stimulated with KMOS (KLF4, cMYC, OCT4 and SOX2) proteins to enhance their proliferative capacity and many vigorous clones were obtained. Clonal reprogramming was carried out by KMOS mRNAs transfection to confirm the ‘chromosomal mutagenicity’ of reprogramming process. Subculturing was performed to examine karyotypic stability of iPSCs after the re-establishment of stemness. And antioxidant N-acetyl-cysteine (NAC) was added to the culture medium for further confirmming the mutagenicity in the first few days of reprogramming.ResultsChromosomal aberrations were found in a small percentage of newly induced iPS clones by reprogramming transcription factors. Clonal reprogramming ruled out the aberrant chromosomes inherited from rare karyotypically abnormal parental cell subpopulation. More importantly, the antioxidant NAC effectively reduced the occurrence of chromosomal aberrations at the early stage of reprogramming. Once iPS cell lines were established, they restored karyotypic stability in subsequent subculturing.ConclusionsOur results provided the first line of evidence for the ‘chromosomal mutagenicity’ of reprogramming process.
Highlights
Reprogramming somatic cells to induced pluripotent stem cells has opened new therapeutic possibilities
Induced pluripotent stem cells have become a valuable model system for studying tissue development and related human diseases, holding great promise for autogenous cell therapy [1].Further investigation focusing on the genetic stability of induced pluripotent stem cells (iPSCs) is necessary, especially as genetic abnormalities in their therapeutic derivatives might harbor the risk of tumorigenesis [2]
It was reported that chromosomal abnormalities not found in parental cells have been detected in iPSC lines as early as passage 5 (P5) [10], suggesting that the abnormal chromosomes observed in early-passage iPSCs might be derived from the large-scale genetic abnormalities that occurred during reprogramming
Summary
Reprogramming somatic cells to induced pluripotent stem cells (iPSCs) has opened new therapeutic possibilities. It was reported that chromosomal abnormalities not found in parental cells have been detected in iPSC lines as early as passage 5 (P5) [10], suggesting that the abnormal chromosomes observed in early-passage iPSCs might be derived from the large-scale genetic abnormalities that occurred during reprogramming Since they were observed more than one month after the end of reprogramming, it is difficult to rule out the possibility that the aberrations occurred during the cell proliferation stage. It is not straightforward to determine the origin of ‘chromosomal mutagenicity’ of reprogramming process Another possibility is that the genetic aberrations may arise from rare karyotypically abnormal parental cell subpopulation, but no effective method has been established to exclude this possibility [9]. It is technically challenging or impossible to grow primary somatic cells from single cell to a clone due to their limited life span
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