Abstract
Adipose‐derived stem cells (ADSCs) have led to growing interest in cell‐based therapy because they can be easily harvested from an abundant tissue. ADSCs must be expanded in vitro before transplantation. This essential step causes concerns about the safety of adult stem cells in terms of potential transformation. Tumorigenesis is driven in its earliest step by DNA replication stress, which is characterized by the accumulation of stalled DNA replication forks and activation of the DNA damage response. Thus, to evaluate the safety of ADSCs during ex vivo expansion, we monitored DNA replication under atmospheric (21%) or physiologic (1%) oxygen concentration. Here, by combining immunofluorescence and DNA combing, we show that ADSCs cultured under 21% oxygen accumulate endogenous oxidative DNA lesions, which interfere with DNA replication by increasing fork stalling events, thereby leading to incomplete DNA replication and fork collapse. Moreover, we found by RNA sequencing (RNA‐seq) that culture of ADSCs under atmospheric oxygen concentration leads to misexpression of cell cycle and DNA replication genes, which could contribute to DNA replication stress. Finally, analysis of acquired small nucleotide polymorphism shows that expansion of ADSCs under 21% oxygen induces a mutational bias toward deleterious transversions. Overall, our results suggest that expanding ADSCs at a low oxygen concentration could reduce the risk for DNA replication stress‐associated transformation, as occurs in neoplastic tissues. Stem Cells Translational Medicine 2017;6:68–76
Highlights
Human mesenchymal stem cells are adult immature cells characterized by their self-renewal ability and multipotency
We found that the proportion of cyclin-A-negative (G1-phase) cells with large 53BP1 bodies was higher in Adipose-derived stem cells (ADSCs) expanded under 21% oxygen than in ADSCs expanded under 1% oxygen at P1 and P4 (Fig. 3C, 3D), suggesting that ADSCs cultured in normoxia accumulate under-replicated loci
Because DNA replication stress is recognized as a strong driver of tumorigenesis [11], our results suggest that ADSCs cultured under atmospheric oxygen concentration are more likely to transform than cells cultivated under hypoxia
Summary
Human mesenchymal stem cells (hMSCs) are adult immature cells characterized by their self-renewal ability and multipotency. First identified in bone marrow, MSCs found in the stromal vascular fraction of fat tissue have attracted growing interest in the past few years. These adipose-derived stem cells (ADSCs) can be isolated with minimal invasiveness by liposuction or dermolipectomy [1]. ADSCs provide tremendous advantages for regenerative medicine because they can be induced in vitro to differentiate or even transdifferentiate into several cell lineages [2]. ADSCs can home to damaged tissues and enhance tissue repair by secreting angiogenic, antiapoptotic, immunomodulatory, and hematopoietic factors [2]. ADSCs represent an attractive material for cell-based therapies [2]
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