NNMT enriches for AQP5⁺cancer stem cells to drive malignant progression in early gastric cardia adenocarcinoma

Abstract

ObjectiveEarly gastric cardia adenocarcinoma (EGCA) is a highly heterogeneous cancer, and the understanding of its classification and malignant progression is limited. This study explored the cellular and molecular heterogeneity in EGCA using single-cell RNA sequencing (scRNA-seq).DesignscRNA-seq was conducted on 95 551 cells from endoscopic biopsies of low-grade intraepithelial neoplasia, well/moderately/poorly differentiated EGCA and their paired adjacent nonmalignant biopsy samples. Large-scale clinical samples and functional experiments were employed.ResultsIntegrative analysis of epithelial cells revealed that chief cells, parietal cells and enteroendocrine cells were rarely detected in the malignant epithelial subpopulation, whereas gland and pit mucous cells and AQP5+stem cells were predominant during malignant progression. Pseudotime and functional enrichment analyses showed that the WNT and NF-κB signalling pathways were activated during the transition. Cluster analysis of heterogeneous malignant cells revealed that NNMT-mediated nicotinamide metabolism was enriched in gastric mucin phenotype cell population, which was associated with tumour initiation and inflammation-induced angiogenesis. Furthermore, the expression level of NNMT was gradually increased during the malignant progression and associated with poor prognosis in cardia adenocarcinoma. Mechanistically, NNMT catalysed the conversion of nicotinamide to 1-methyl nicotinamide via depleting S-adenosyl methionine, which led to a reduction in H3K27 trimethylation (H3K27me3) and then activated the WNT signalling pathway to maintain the stemness of AQP5+stem cells during EGCA malignant progression.ConclusionOur study extends the understanding of the heterogeneity of EGCA and identifies a functional NNMT+/AQP5+population that may drive malignant progression in EGCA and could be used for early diagnosis and therapy.

Single-cell profiling of gastric cardia adenocarcinoma reveals drivers of cancer stemness and therapeutic targets

“…Functionally, NNMT is a metabolic enzyme that transfers S-adenosyl-L-methionine to nicotinamide to generate S-adenosyl homocysteine and 1-methyl nicotinamide, allowing NNMT to fine-tune the methylation status of cancer cells (figure 1). 11 Consistent with an epigenetic role for NNMT, Wang et al 10 found that NNMT overexpression reduced H3K27me3 repressive histone mark levels at the CTNNB1 (encoding β-catenin) and WNT5A promoter regions. This resulted in increased CTNNB1 expression, enhanced β-catenin binding to the AQP5 promoter, and activation of AQP5 transcription to maintain AQP5 + CSCs.…”

“…The NAPRT-mediated NAD synthesis pathway is termed the Preiss-Handler pathway. see Wang et al 10 for details. NAAD, nicotinic acid adenine dinucleotide; NAMN, nicotinic acid mononucleotide; NAMPT, nicotinamide phosphoribosyltransferase; NAPRT, nicotinate phosphoribosyltransferase; SAH, S-adenosyl homocysteine; SAM, S-adenosyl-L-methionine.…”

“…In Gut , Wang et al 10 (figure 1) report a scRNA-seq atlas (95 551 cells) of GCA comprising 1 low-grade gastric intraepithelial neoplasia, 3 well differentiated GCAs, 3 moderately differentiated GCAs and 3 poorly differentiated GCAs from 10 patients. Analysis of this single-cell atlas enabled the investigators to classify the GCA malignant epithelial cells into two distinct subpopulations, termed ‘gastric phenotype’ and ‘intestinal phenotype’.…”

“…This resulted in increased CTNNB1 expression, enhanced β-catenin binding to the AQP5 promoter, and activation of AQP5 transcription to maintain AQP5 + CSCs. From a therapeutic perspective, Wang et al 10 also tested an NNMT small molecule inhibitor (NNMTi) and found that NNMTi treatment decreased NNMT expression, upregulated H3K27me3 repression, and inhibited GCA cell proliferation, thereby implicating NNMT as a possible therapeutic target in GCA.…”

“…In conclusion, Wang et al 10 have established a valuable single-cell GCA resource for the field, leading to the identification of NNMT as a regulator of GCA stemness and a potential therapeutic target. However, this work has certain limitations.…”