ICRP Publication 131: Stem Cell Biology with Respect to Carcinogenesis Aspects of Radiological Protection

Abstract

This report provides a review of stem cells/progenitor cells and their responses to ionising radiation in relation to issues relevant to stochastic effects of radiation that form a major part of the International Commission on Radiological Protection's system of radiological protection. Current information on stem cell characteristics, maintenance and renewal, evolution with age, location in stem cell 'niches', and radiosensitivity to acute and protracted exposures is presented in a series of substantial reviews as annexes concerning haematopoietic tissue, mammary gland, thyroid, digestive tract, lung, skin, and bone. This foundation of knowledge of stem cells is used in the main text of the report to provide a biological insight into issues such as the linear-no-threshold (LNT) model, cancer risk among tissues, dose-rate effects, and changes in the risk of radiation carcinogenesis by age at exposure and attained age. Knowledge of the biology and associated radiation biology of stem cells and progenitor cells is more developed in tissues that renew fairly rapidly, such as haematopoietic tissue, intestinal mucosa, and epidermis, although all the tissues considered here possess stem cell populations. Important features of stem cell maintenance, renewal, and response are the microenvironmental signals operating in the niche residence, for which a well-defined spatial location has been identified in some tissues. The identity of the target cell for carcinogenesis continues to point to the more primitive stem cell population that is mostly quiescent, and hence able to accumulate the protracted sequence of mutations necessary to result in malignancy. In addition, there is some potential for daughter progenitor cells to be target cells in particular cases, such as in haematopoietic tissue and in skin. Several biological processes could contribute to protecting stem cells from mutation accumulation: (a) accurate DNA repair; (b) rapidly induced death of injured stem cells; (c) retention of the DNA parental template strand during divisions in some tissue systems, so that mutations are passed to the daughter differentiating cells and not retained in the parental cell; and (d) stem cell competition, whereby undamaged stem cells outcompete damaged stem cells for residence in the niche. DNA repair mainly occurs within a few days of irradiation, while stem cell competition requires weeks or many months depending on the tissue type. The aforementioned processes may contribute to the differences in carcinogenic radiation risk values between tissues, and may help to explain why a rapidly replicating tissue such as small intestine is less prone to such risk. The processes also provide a mechanistic insight relevant to the LNT model, and the relative and absolute risk models. The radiobiological knowledge also provides a scientific insight into discussions of the dose and dose-rate effectiveness factor currently used in radiological protection guidelines. In addition, the biological information contributes potential reasons for the ...

γH2AX, 53BP1 and Rad51 protein foci changes in mesenchymal stem cells during prolonged X-ray irradiation

“…Relatively recent realization that stem cells substantially contribute to tumorigenesis, has led to a high interest in radiation responses in stem cells [ 40 , 41 ]. Yet, a number of barriers, such as complexity of long-term biological consequences of radiation exposure and differences in the biology of stem cells of various types, exist in this rapidly developing area of radiation biology [ 42 ]. These barriers are behind substantial knowledge gaps that remain to be filled.…”

Mechanical loading causes site-specific anabolic effects on bone following exposure to ionizing radiation

“…In contrast, whether or not radiation-induced skeletal decrements persist in long duration studies appears to depend heavily on animal age at the time of irradiation, elapsed time, as well as absorbed dose [61]. Cancellous osteopenia can persist for many months in rodents, especially if animals are exposed to radiation while still growing or if exposed to high enough doses [34,60].…”

Radiotherapy targeting cancer stem cells “awakens” them to induce tumour relapse and metastasis in oral cancer

“…The inherent function of stem cells, permanently providing genetically correct cells to replenish functional tissues, suggests that stem cells have a natural advantage in resisting DNA damage; this resistance aids them in response to radiotherapy, and the radioresistance of these cells is a direct reflection of their inherent ability of DNA repair. 84 CSCs are considered to have greater radiation resistance than cancer cells, enabling them to survive radiotherapy in various ways, such as controlling the cell cycle, effective DNA repair and modified division patterns. 23,85 The radioresistance of CSCs due to their innate stemness enables them to survive after radiotherapy, eventually leading to tumour recurrence or metastasis.…”