NOD2 Supports Crypt Survival and Epithelial Regeneration after Radiation-Induced Injury

Nucleotide-binding oligomerization domain-containing protein 2 (NOD2) affords stem cell protection and links microbes to intestinal epithelial regeneration. We investigated whether NOD2 status is associated with crypt survival and intestinal epithelial regeneration independent of microbiota-derived molecules. To assess crypt survival, a clonogenic microcolony assay was performed with 15 Gy of X-ray irradiation. The fractional crypt survival rate (46.0 ± 15.5% vs. 24.7 ± 9.2%, p < 0.01) and fractional EdU-positive crypt survival rate (29.8 ± 14.5% vs. 9.79 ± 4.37%, p = 0.015) were significantly decreased in the NOD2^-/- mice compared with the wild-type (WT) mice at 3.5 days after irradiation. To evaluate intestinal epithelial regeneration capability, organoid reconstitution assays were performed. Small bowel crypts of the WT and NOD2^-/- mice were isolated and seeded into Matrigel for 3D culture. In the organoid reconstitution assays, the number of organoids formed did not differ between the NOD2^-/- and WT mice. Organoid formation ability was also assessed after exposure to 5 Gy irradiation. Organoid formation ability was significantly decreased in the NOD2^-/- mice compared with the WT ones after exposure to 5 Gy irradiation (33.2 ± 5.9 vs. 19.7 ± 8.8/well, p < 0.01). NOD2 supports crypt survival after potentially lethal irradiation damage and is associated with intestinal epithelial regeneration.