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Zymosan-A promotes the regeneration of intestinal stem cells by upregulating ASCL2

1st January 2023

The intestinal epithelium is characterised by intense self-renewal which is accomplished by intestinal stem cells (ISCs), located at the base of the crypts.  Beyond normal tissue homeostasis, these cells play a major role in the regeneration of the damaged intestinal epithelia following external insults such as ionizing radiation (IR).

In this paper the authors demonstrate that Zymosan-A, a TLR2 ligand extracted from S.cerevisiae, protects against radiation-induced intestinal injury with a direct effect on ISCs. The protective effect was assessed both in vivo, and in vitro by using small intestinal organoids.

Taken together, the data show that Zymosan-A is able to protect from IR-induced intestinal damage by upregulating TLR2 and WNT signalling pathways. ASCL2, which is a WNT target gene, promotes the regeneration of the ISCs and has an important role in the protective effect of Zymosan-A. Zymosan-A may be an effective radioprotective drug for the prevention and treatment of IR-induced intestinal injury.

  • Mice pre-treated with Zymosan-A showed an increased survival rate after total body or abdominal irradiation.
  • Zymosan-A pre-treatment reduced body weight loss after abdominal irradiation, as well as the degree of bleeding and oedema in the abdominal tissue.
  • The small intestinal tissue integrity was better maintained in the Zymosan-A treated group with a higher number of viable crypts, longer intestinal crypts and villi, increased number of Ki-67+ cells and reduced number of apoptotic cells.
  • RNA-FISH against Lgr5 mRNA (a marker of ISCs) showed that IR reduced the number of ISCs but pre-treatment with Zymosan-A protected from ISC loss.
  • Further confirmation was obtained by analysing the fluorescence signal coming from Lgr5-EGFP-IRES-creERT2 mouse intestine where Zymosan-A protected from the loss of fluorescent stem cells after IR.
  • Crypts were extracted from C57BL/6 mice to culture small intestinal organoids. After plating, the crypts were pre-treated with Zymosan-A prior to irradiation and the growth of the organoids was analysed after 7 days. Zymosan-A protected the organoids from IR-induced damage, increasing the size and the percent of budding organoids.
  • Ki-67 immunofluorescence showed an increase in proliferative cells and TUNEL assay showed a decrease in apoptosis.
  • RNAseq from irradiated mouse intestine showed upregulation of TLR2 and WNT signalling pathways in mice pre-treated with Zymosan-A.
  • TLR2 inhibition in organoids prior to Zymosan-A treatment blocked its protective effect on IR-induced damage.
  • RNAseq data showed strong upregulation of the ASCL2 gene. Knock-down of ASCL2 in organoids reduced the radioprotective effect of Zymosan-A.