Adult stem cells have been proposed to be quiescent and radiation resistant, repairing DNA double-strand breaks by nonhomologous end joining. However, the population of putative small intestinal stem cells (ISCs) at position +4 from the crypt base contradicts this model, in that they are highly radiosensitive. Cycling crypt base columnar cells (CBCs) at crypt positions +1-3 recently were defined as an alternative population of ISCs. Little is known about the sensitivity of this stem cell population to radiation.
Radiation-induced lethality of CBCs was quantified kinetically in Lgr5-lacZ transgenic mice. γ-H2AX, BRCA1, RAD51, and DNA-PKcs foci were used as DNA repair surrogates to investigate the inherent ability of CBCs to recognize and repair double-strand breaks. 5-ethynyl-2'-deoxyuridine and 5-bromo-2'-deoxyuridine incorporation assays were used to study patterns of CBC growth arrest and re-initiation of cell cycling. Apoptosis was evaluated by caspase-3 staining.
CBCs are relatively radioresistant, repairing DNA by homologous recombination significantly more efficiently than transit amplifying progenitors or villus cells. CBCs undergo apoptosis less than 24 hours after irradiation (32% ± 2% of total lethality) or mitotic death at 24-48 hours. Survival of CBCs at 2 days predicts crypt regeneration at 3.5 days and lethality from gastrointestinal syndrome. Crypt repopulation originates from CBCs that survive irradiation.
Adult ISCs in mice can cycle rapidly yet still be radioresistant. Importantly, homologous recombination can protect adult stem cell populations from genotoxic stress. These findings broaden and refine concepts of the phenotype of adult stem cells.
"Subpopulations of intestinal stem cells (ISCs) seem to repair high loads of DNA damage with faster kinetics as compared to their progeny (Hua et al., 2012). However, in contrast to stem cells of the hair bulge or satellite cells, they make use of HR and NHEJ (Hua et al., 2012). "
[Show abstract][Hide abstract] ABSTRACT: The mammalian organism is comprised of tissue types with varying degrees of self-renewal and regenerative capacity. In most organs self-renewing tissue-specific stem and progenitor cells contribute to organ maintenance, and it is vital to maintain a functional stem cell pool to preserve organ homeostasis. Various conditions like tissue injury, stress responses, and regeneration challenge the stem cell pool to re-establish homeostasis (Figure 1). However, with increasing age the functionality of adult stem cells declines and genomic mutations accumulate. These defects affect different cellular response pathways and lead to impairments in regeneration, stress tolerance, and organ function as well as to an increased risk for the development of ageing associated diseases and cancer. Maintenance of the genome appears to be of utmost importance to preserve stem cell function and to reduce the risk of ageing associated dysfunctions and pathologies. In this review, we discuss the causal link between stem cell dysfunction and DNA damage accrual, different strategies how stem cells maintain genome integrity, and how these processes are affected during ageing.
"We found that WT intestines specifically accumulate γH2A.X staining in the villus regions, which is an indication of unrepaired DNA breaks. However, intestinal crypt cells only showed discrete γH2A.X foci as a result of efficient DNA repair, as previously published (Hua et al., 2012). By contrast, Bmi1- deficient intestines displayed an intense homogeneous γH2A.X staining pattern arising from the base of the crypts to the top of the villi (Fig. 5F), indicating that Bmi1 protein is involved in regulating DNA damage repair in the intestinal crypt cells. "
"The accumulation of DNA damage and consequent loss of genome integrity due to double strand breaks (DSBs) is one of the major causes of apoptosis, senescence and aging, including in stem cells (Lombard et al., 2005; Nijnik et al., 2007; Rossi et al., 2007; Ruzankina et al., 2008). In the small intestine, stem cells at the bottom of the crypt are proliferating and radioresistant, whereas those around the +4 position are quiescent and radiosensitive (Hua et al., 2012; Li and Clevers, 2010; Potten et al., 2009), therefore the response of stem cells to DNA damage can be distinct depending on their origin, cell cycle status, or both. In another report, melanocyte stem cells did not undergo detectable ionizing radiation (IR)-induced apoptosis, but the stem cell niche was depleted due to their differentiation (Inomata et al., 2009). "
[Show abstract][Hide abstract] ABSTRACT: The loss of genome integrity in adult stem cells results in accelerated tissue aging and possibly cancerogenesis. Adult stem cells in different tissues appear to react robustly to DNA damage. We report that adult skeletal stem (satellite) cells do not primarily respond to radiation-induced DNA double-strand breaks (DSBs) via differentiation and exhibit less apoptosis compared to other myogenic cells. Satellite cells repair these DNA lesions more efficiently than their committed progeny. Importantly, non-proliferating satellite cells and post-mitotic nuclei in the fibre exhibit dramatically distinct repair efficiencies. Altogether, reduction of the repair capacity appears to be more a function of differentiation than of the proliferation status of the muscle cell. Notably, satellite cells retain high efficiency of DSB repair also when isolated from the natural niche. Finally, we show that repair of DSB substrates is not only very efficient but, surprisingly, also very accurate in satellite cells and that accurate repair depends on the key non-homologous end-joining factor DNA-PKcs.
Stem Cell Research 08/2014; 13(3). DOI:10.1016/j.scr.2014.08.005 · 3.69 Impact Factor
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