Gut microbial-derived N-acetylmuramic acid alleviates colorectal cancer via the AKT1 pathway

Background Gut microbial metabolites are recognised as critical effector molecules that influence the development of colorectal cancer (CRC). Peptidoglycan fragments (PGFs) produced by microbiota play a crucial role in maintaining intestinal homeostasis, but their role in CRC remains unclear. Objective Here, we aimed to explore the potential contribution of PGFs in intestinal tumourigenesis. Design The relative abundance of peptidoglycan synthase and hydrolase genes was assessed by metagenomic analysis. Specific PGFs in the faeces and serum of CRC patients were quantified using targeted mass spectrometry. The effects of PGF on intestinal tumourigenesis were systematically evaluated using various murine models of CRC and organoids derived from CRC patients. Downstream molecular targets were screened and evaluated using proteome microarray, transcriptome sequencing and rescue assays. Results Metagenomic analysis across seven independent cohorts (n=1121) revealed a comprehensive reduction in peptidoglycan synthase gene relative abundance in CRC patients. Targeted mass spectrometry identified significant depletion of a specific PGF, N-acetylmuramic acid (NAM) in CRC patients, which decreased as tumours progressed (p<0.001). NAM significantly inhibits intestinal tumourigenesis in various models, including Apc Min/+, AOM/DSS-treated and MC38 tumour-bearing mice. Additionally, NAM inhibits the growth of patient-derived CRC organoids in a concentration-dependent manner. Mechanistically, NAM inhibits the activation of AKT1 by directly binding to it and blocking its phosphorylation, which is a partial mediator of NAM’s anticancer effects. Conclusion The PGF NAM protects against intestinal tumourigenesis by targeting the AKT1 signalling pathway. NAM may serve as a novel potential preventive and therapeutic biomarker against CRC. Data are available upon reasonable request. All data relevant to the study are included in the article or uploaded as supplementary information. All data relevant to the study are included in the article or uploaded as supplementary information. Data are available on reasonable request. Transcriptome data are available in the Genome Sequence Archive (GSA) database: Bioproject PRJCA025871. The metagenomic sequencing data reported in this paper has been deposited in the European Nucleotide Archive under the study accession number PRJEB81237. Raw data not included therein can be obtained with the consent of the corresponding author.