Microbiota-Derived I3A Accelerates Intestinal Stem-Cell-Mediated Epithelial Development after Ionizing Radiation

Purpose/Objective(s)

The intestine is a highly radiosensitive tissue that is susceptible to structural and functional damage due to systemic as well as localized radiation exposure. Unfortunately, no effective prophylactic or therapeutic agents are available at present to manage radiation-induced intestinal injuries (RIII). Gut microbiome play pivotal roles in intestinal homeostasis. Several studies have demonstrated the potential of gut microbiome and metabolites as a therapeutic for RIII. Our results demonstrate that microbiota-derived Indole-3-carboxaldehyde (I3A) plays a pivotal role in promoting ISC-mediated epithelial development.

Materials/Methods

Male C57BL/6J mice were treated with 13Gy of Whole abdominal irradiation (WAI). Probiotics or I3A were gavage before (once a day for 30 days) WAI. The survival and body weight were recorded, while the severity of RIII was evaluated by HE staining, Immunohistochemistry (IHC) and TUNEL assay of gut tissues for each irradiated group. Meanwhile, stool samples were obtained 6h and 3.5d after irradiation. Gut microbiome were measured by 16S rRNA sequencing, and metabolites were detected by LC-MS analysis.

Results

Compared to the control, probiotics (Lactobacillus plantarum, Bifidobacterium longum, Lactobacillus paracasei) treatment significantly increased survival rates by 50% (P<0.05) and improved clinical scores of mice after WAI. HE staining of jejunum tissues showed that probiotics mitigated RIII, as reflected by the dramatic attenuation of crypt-villi architecture destruction. IHC results showed that probiotics treatment remarkably increased the Lgr5⁺ cells, Paneth cells, and Ki67+cells (P<0.001) per crypt, indicating that probiotics promoted proliferation and differentiation of ISC after WAI. The most highly enriched metabolites from the feces of probiotics treatment mice in the tryptophan metabolic pathway, with a threefold change seen in level of I3A. Specifically, I3A -treated groups showed survival rates of ∼20%%, with the protection persisting for >200 days after radiation. In addition, mice fed the I3A daily for 3 days before IR had significantly more Lgr5+, Paneth cells, Goblet cells, and Ki67⁺cells in the SI crypt than mice of control. Moreover, treatment with I3A resulted in enhanced numbers of Lgr5⁺ cells and Paneth cells and Wnt3 expression in SI organoids.

Conclusion

Collectively, our findings suggested that microbiota-derived I3A protects against RIII by promote the proliferation and differentiation of Lgr5+ intestinal stem cells via Wnt signaling pathway.