Post-irradiation promotes susceptibility to reprogramming to pluripotent state in human fibroblasts

Abstract

Ionizing radiation causes not only targeted effects in cells that have been directly irradiated but also non-targeted effects in several cell generations after initial exposure. Recent studies suggest that radiation can enrich for a population of stem cells, derived from differentiated cells, through cellular reprogramming. Here, we elucidate the effect of irradiation on reprogramming, subjected to two different responses, using an induced pluripotent stem cell (iPSC) model. iPSCs were generated from non-irradiated cells, directly-irradiated cells, or cells subsequently generated after initial radiation exposure. We found that direct irradiation negatively affected iPSC induction in a dose-dependent manner. However, in the post-irradiated group, after five subsequent generations, cells became increasingly sensitive to the induction of reprogramming compared to that in non-irradiated cells as observed by an increased number of Tra1-81-stained colonies as well as enhanced alkaline phosphatase and Oct4 promoter activity. Comparative analysis, based on reducing the number of defined factors utilized for reprogramming, also revealed enhanced efficiency of iPSC generation in post-irradiated cells. Furthermore, the phenotypic acquisition of characteristics of pluripotent stem cells was observed in all resulting iPSC lines, as shown by morphology, the expression of pluripotent markers, DNA methylation patterns of pluripotency genes, a normal diploid karyotype, and teratoma formation. Overall, these results suggested that reprogramming capability might be differentially modulated by altered radiation-induced responses. Our findings provide that susceptibility to reprogramming in somatic cells might be improved by the delayed effects of non-targeted response, and contribute to a better understanding of the biological effects of radiation exposure.

Radiation‐induced tissue damage and response

“…LGR5 + cells in the crypt niche as well as the radiosensitive transit amplifying compartment following irradiation exposure [42,46]. It should be noted that reprogramming may be limited by p53-mediated DNA damage responses (DDR) [47] and it is dose and time dependent, senescence sensitive [32] and influenced by non-targeted effects [48]. Bone marrow, under steady-state conditions, contains primitive hematopoietic stem cells (HSC) that are functionally and molecularly heterogeneous but within which is a rare population with unique capability for self-renewal and multilineage differentiation [49].…”

“…Mindful of the pitfalls involved in the use of markers , the data suggest that a Bmi1 + radioresistant reserve stem cell pool, or at least a reprogrammable plastic population, restores LGR5 + cells in the crypt niche as well as the radiosensitive transit amplifying compartment following irradiation exposure . It should be noted that reprogramming may be limited by p53‐mediated DNA damage responses (DDR) and it is dose and time dependent, senescence sensitive and influenced by non‐targeted effects .…”

Direct cellular reprogramming and transdifferentiation of fibroblasts on wound healing—Fantasy or reality?

“…The future challenge is to tackle current drawbacks by pursuing further research on optimal reprogramming and culture microenvironment so as to prevent telomere dysfunction 60 and tumorigenic, as well as fibrosis and hypertrophic activities. Additional techniques such as 3D bioprinting, 59,61 nano biomaterials, 62,63 electrospinning, 64 and ionizing radiation 63,65 may promote direct reprogramming. The techniques for cellular direct reprogramming will improve these technologies and change the face of regenerative medicine and patient care.…”