Article

Crypt Base Columnar Stem Cells in Small Intestines of Mice Are Radioresistant

Laboratory of Signal Transduction, Memorial Sloan-Kettering Cancer Center, New York, New York.
Gastroenterology (Impact Factor: 13.93). 07/2012; 143(5):1266-76. DOI: 10.1053/j.gastro.2012.07.106
Source: PubMed

ABSTRACT 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.

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    • "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. "
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    • "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). "
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