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Lacking a clear understanding of the molecular mechanism determining cancer cell sensitivity to oxidative phosphorylation (OXPHOS) inhibition limits the development of OXPHOS‐targeting cancer treatment. Here, cancer cell lines sensitive or resistant to OXPHOS inhibition are identified by screening. OXPHOS inhibition‐sensitive cancer cells possess increased OXPHOS activity and silenced nicotinamide N‐methyltransferase (NNMT) expression. NNMT expression negatively correlates with OXPHOS inhibition sensitivity and functionally downregulates the intracellular levels of S‐adenosyl methionine (SAM). Expression of DNA methyltransferase 1 (DNMT1), a SAM consumer, positively correlates with OXPHOS inhibition sensitivity. NNMT overexpression and DNMT1 inhibition render OXPHOS inhibition‐sensitive cancer cells resistant. Importantly, treatments of OXPHOS inhibitors (Gboxin and Berberine) hamper the growth of mouse tumor xenografts by OXPHOS inhibition sensitive but not resistant cancer cells. What's more, the retrospective study of 62 tumor samples from a clinical trial demonstrates that administration of Berberine reduces the tumor recurrence rate of NNMTlow/DNMT1high but not NNMThigh/DNMT1low colorectal adenomas (CRAs). These results thus reveal a critical role of the NNMT‐DNMT1 axis in determining cancer cell reliance on mitochondrial OXPHOS and suggest that NNMT and DNMT1 are faithful biomarkers for OXPHOS‐targeting cancer therapies. The mitochondrial oxidative phosphorylation (OXPHOS) is a promising target for cancer treatment. NNMT‐DNMT1 axis plays an essential role in maintaining cancer cell sensitivity to OXPHOS inhibition, and the statuses of NNMT and DNMT1 genes are faithful biomarkers for OXPHOS‐targeting cancer therapies.

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.

Cell cycle dysregulation is a defining feature of breast cancer. Here, 1‐methyl‐nicotinamide (1‐MNA), metabolite of nicotinamide N‐methyltransferase(NNMT) is identified, as a novel driver of cell‐cycle progression in breast cancer. NNMT, highly expressed in breast cancer tissues, positively correlates with tumor grade, TNM stage, Ki‐67 index, and tumor size. Ablation of NNMT expression dramatically suppresses cell proliferation and causes cell‐cycle arrest in G0/G1 phase. This phenomenon predominantly stems from the targeted action of 1‐MNA, resulting in a specific down‐regulation of p27 protein expression. Mechanistically, 1‐MNA expedites the degradation of p27 proteins by enhancing cullin‐1 neddylation, crucial for the activation of Cullin‐1‐RING E3 ubiquitin ligase(CRL1)—an E3 ubiquitin ligase targeting p27 proteins.  NNMT/1‐MNA specifically up‐regulates the expression of UBC12, an E2 NEDD8‐conjugating enzyme required for cullin‐1 neddylation. 1‐MNA showes high binding affinity to UBC12, extending the half‐life of UBC12 proteins via preventing their localization to lysosome for degradation. Therefore, 1‐MNA is a bioactive metabolite that promotes breast cancer progression by reinforcing neddylation pathway‐mediated p27 degradation. The study unveils the link between NNMT enzymatic activity with cell‐cycle progression, indicating that 1‐MNA may be involved in the remodeling of tumor microenvironment. In this study, it is demonstrated that the NNMT‐specific metabolite, 1‐methyl‐nicotinamide (1‐MNA), promotes breast cancer cell‐cycle progression by enhancing CRL1‐mediated degradation of p27 proteins. This is facilitated by 1‐MNA's direct interaction with UBC12 proteins, preventing their lysosomal degradation and increasing cullin‐1 neddylation, crucial for CRL1 ligase activation. The findings suggest NNMT/1‐MNA's potential role in reshaping the tumor microenvironment.

Background Nicotinamide N -methyltransferase (NNMT) is overexpressed in various human tumors and involved in the development and progression of several carcinomas. In breast cancer, NNMT was found to be overexpressed in several cell lines. However, the clinical relevance of NNMT in breast cancer is not yet clear. Methods NNMT expression in breast carcinoma was examined by immunohistochemistry, and then, its relationship with patient clinicopathological characteristics was analyzed. The effects of NNMT on chemoresistance in breast cancer cells were assessed by cell viability, colony formation, and apoptosis assay. The NNMT, SIRT1, p53, and acetyl-p53 proteins, which are involved in NNMT-related chemoresistance, were examined by Western blotting. The SIRT1 mRNA was examined by real-time PCR, and its activity was measured by using the SIRT1 deacetylase fluorometric reagent kit. Results NNMT expression was significantly higher (53.9%) in breast carcinoma than in paracancerous tissues (10.0%) and breast hyperplasia (13.3%). A high level of NNMT expression correlated with poor survival and chemotherapy response in breast cancer patients who received chemotherapy. Ectopic overexpression of NNMT significantly inhibited the apoptotic cell death and suppression of colony formation induced by adriamycin and paclitaxel. Mechanistic studies revealed that NNMT overexpression increased SIRT1 expression and promoted its activity. Either inhibition of SIRT1 by EX527 or knockdown of SIRT1 by siRNA could reverse NNMT-mediated resistance to adriamycin and paclitaxel, which suggests that SIRT1 plays a critical role in NNMT-related chemoresistance in breast cancer. Conclusions The results of this study demonstrate a novel correlation between the NNMT expression level and patient survival, suggesting that NNMT has the potential to become a new prognostic biomarker to predict the treatment outcomes of the clinical chemotherapy in breast cancer. Moreover, targeting NNMT or downstream SIRT1 may represent a new therapeutic approach to improve the efficacy of breast cancer chemotherapy.

Hypertrophic scar (HS) is a cutaneous fibrotic disorder characterized by persistent myofibroblast activation and excessive extracellular matrix deposition. Elucidating the origin and characteristics of myofibroblasts remains a central focus in the field. This study identifies a novel subtype of scar myofibroblasts originating from macrophage‐myofibroblast transition (MMT). MMT cells constitute a significant proportion of HS myofibroblasts and drive HS progression. Multi‐omics analysis uncovered nicotinamide N‐methyltransferase (NNMT) as a metabolic orchestrator of MMT. Liquid chromatograph mass spectrometer reveals NNMT‐mediated depletion of nicotinamide adenine dinucleotide (NAD+) and S‐adenosyl methionine(SAM), triggering H3K27ac accumulation and H3K27me3 loss. This epigenetic reprogramming facilitated the expression of master transcription factor paired‐related homeobox 1 (Prrx1) and its nuclear co‐condensation with super‐enhancer (SE)  components. Inhibition of NNMT disrupted Prrx1‐SE interactions, suppressed MMT in vitro, and reduced scar volume in vivo. This study 1) identifies a new origin of scar‐associated myofibroblasts, 2) establishes metabolite‐guided epigenetic alteration as a regulator of myofibroblasts cellular plasticity, and 3) nominates NNMT as a therapeutic target for HS and related fibrotic disorders. In macrophage‐myofibroblast transition, upregulated NNMT depletes S‐Adenosylmethionine‌ (SAM) and nicotinamide adenine dinucleotide(NAD+), thereby triggering epigenetic reprogramming via Histone H3 Lysine 27 acetylation (H3K27ac) accumulation at the promoter region of master transcription factor Prrx1. This chromatin remodeling drives Prrx1 overexpression, enhancing its binding to super‐enhancers to activate a pro‐fibrotic transcriptional program that promotes myofibroblast lineage commitment and hypertrophic scar progression.

Nicotinamide adenine dinucleotide (NAD+) is a ubiquitous metabolite that takes part in many key redox reactions. NAD+ biosynthesis and NAD+-consuming enzymes have been attracting markedly increasing interest since they have been demonstrated to be involved in several crucial biological pathways, impacting genes transcription, cellular signaling, and cell cycle regulation. As a consequence, many pathological conditions are associated with an impairment of intracellular NAD+ levels, directly or indirectly, which include cardiovascular diseases, obesity, neurodegenerative diseases, cancer, and aging. In this review, we describe the general pathways involved in the NAD+ biosynthesis starting from the different precursors, analyzing the actual state-of-art of the administration of NAD+ precursors or blocking NAD+-dependent enzymes as strategies to increase the intracellular NAD+ levels or to counteract the decline in NAD+ levels associated with ageing. Subsequently, we focus on the disease-related and age-related alterations of NAD+ homeostasis and NAD+-dependent enzymes in endothelium and the consequent vascular dysfunction, which significantly contributes to a wide group of pathological disorders.

\"Stromal high expression\" of Nicotinamide N-methyltransferase (NNMT), previously reported as a poor prognostic factor of gastric cancer, was based on immunohistochemical H-score. However, this could simply indicate an increase in cancer-associated fibroblasts (CAFs) because NNMT is positive for fibroblasts. To verify this, the proportion and staining intensity of stromal NNMT-positive stellate/spindle cells were evaluated separately and examined for its association with related proteins (H3K4me3, H3K27me3, and LOXL2). Immunohistochemistry for NNMT, H3K4me3, H3K27me3, and LOXL2 was performed on 521 tissue microarrays of gastric cancer. Cancer stromal stellate/spindle cells were evaluated according to morphology, proportion, and stain intensity of NNMT, loss of H3K4me3 and H3K27me3, and stain intensity of LOXL2. Their associations with clinicopathological characteristics and overall survival were examined. Higher staining intensity of NNMT was not related to a poorer prognosis. However, higher proportion of NNMT-positive stellate/spindle cells indirectly contributed to a poor prognosis. It was associated with CAF-like morphology and a global decrease in H3K4me3/H3K27me3, which were both associated with high LOXL2 expression. These three factors were independent poor prognostic factors. In addition, in the LOXL2-high group, prognosis significantly deteriorated with the presence of a global decrease in H3K4me3/H3K27me3. The higher proportion of NNMT-positive cancer stromal cells in gastric cancer serves as an indicator for identifying unfavorable prognostic CAFs that show a global decrease in H3K4me3/H3K27me3. This facilitates research on the nature of these cells and their characteristics.

Nicotinamide adenine dinucleotide (NAD) provides an important link between metabolism and signal transduction and has emerged as central hub between bioenergetics and all major cellular events. NAD-dependent signaling (e.g., by sirtuins and poly–adenosine diphosphate [ADP] ribose polymerases [PARPs]) consumes considerable amounts of NAD. To maintain physiological functions, NAD consumption and biosynthesis need to be carefully balanced. Using extensive phylogenetic analyses, mathematical modeling of NAD metabolism, and experimental verification, we show that the diversification of NAD-dependent signaling in vertebrates depended on 3 critical evolutionary events: 1) the transition of NAD biosynthesis to exclusive usage of nicotinamide phosphoribosyltransferase (NamPT); 2) the occurrence of nicotinamide N-methyltransferase (NNMT), which diverts nicotinamide (Nam) from recycling into NAD, preventing Nam accumulation and inhibition of NAD-dependent signaling reactions; and 3) structural adaptation of NamPT, providing an unusually high affinity toward Nam, necessary to maintain NAD levels. Our results reveal an unexpected coevolution and kinetic interplay between NNMT and NamPT that enables extensive NAD signaling. This has implications for therapeutic strategies of NAD supplementation and the use of NNMT or NamPT inhibitors in disease treatment.

Human hallmarks of sarcopenia include muscle weakness and a blunted response to exercise. Nicotinamide N-methyltransferase inhibitors (NNMTis) increase strength and promote the regenerative capacity of aged muscle, thus offering a promising treatment for sarcopenia. Since human hallmarks of sarcopenia are recapitulated in aged (24-month-old) mice, we treated mice from 22 to 24 months of age with NNMTi, intensive exercise, or a combination of both, and compared skeletal muscle adaptations, including grip strength, longitudinal running capacity, plantarflexor peak torque, fatigue, and muscle mass, fiber type, cross-sectional area, and intramyocellular lipid (IMCL) content. Exhaustive proteome and metabolome analyses were completed to identify the molecular mechanisms underlying the measured changes in skeletal muscle pathophysiology. Remarkably, NNMTi-treated aged sedentary mice showed ~ 40% greater grip strength than sedentary controls, while aged exercised mice only showed a 20% increase relative to controls. Importantly, the grip strength improvements resulting from NNMTi treatment and exercise were additive, with NNMTi-treated exercised mice developing a 60% increase in grip strength relative to sedentary controls. NNMTi treatment also promoted quantifiable improvements in IMCL content and, in combination with exercise, significantly increased gastrocnemius fiber CSA. Detailed skeletal muscle proteome and metabolome analyses revealed unique molecular mechanisms associated with NNMTi treatment and distinct molecular mechanisms and cellular processes arising from a combination of NNMTi and exercise relative to those given a single intervention. These studies suggest that NNMTi-based drugs, either alone or combined with exercise, will be beneficial in treating sarcopenia and a wide range of age-related myopathies.

Background Clear cell renal cell carcinoma (ccRCC), with its hallmark phenotype of high cytosolic lipid content, is considered a metabolic cancer. Despite the implication of this lipid-rich phenotype in ccRCC tumorigenesis, the roles and regulators of de novo lipid synthesis (DNL) in ccRCC remain largely unexplained. Methods Our bioinformatic screening focused on ccRCC-lipid phenotypes identified glutathione peroxidase 8 (GPX8), as a clinically relevant upstream regulator of DNL. GPX8 genetic silencing was performed with CRISPR-Cas9 or shRNA in ccRCC cell lines to dissect its roles. Untargeted metabolomics, RNA-seq analyses, and other biochemical assays (e.g., lipid droplets staining, fatty acid uptake, cell proliferation, xenograft, etc.) were carried out to investigate the GPX8’s involvement in lipid metabolism and tumorigenesis in ccRCC. The lipid metabolic function of GPX8 and its downstream were also measured by isotope-tracing-based DNL flux measurement. Results GPX8 knockout or downregulation substantially reduced lipid droplet levels (independent of lipid uptake), fatty acid de novo synthesis, triglyceride esterification in vitro, and tumor growth in vivo. The downstream regulator was identified as nicotinamide N-methyltransferase (NNMT): its knockdown phenocopied, and its expression rescued, GPX8 silencing both in vitro and in vivo. Mechanically, GPX8 regulated NNMT via IL6-STAT3 signaling, and blocking this axis suppressed ccRCC survival by activating AMPK. Notably, neither the GPX8-NNMT axis nor the DNL flux was affected by the von Hippel Lindau (VHL) status, the conventional regulator of ccRCC high lipid content. Conclusions Taken together, our findings unravel the roles of the VHL-independent GPX8-NNMT axis in ccRCC lipid metabolism as related to the phenotypes and growth of ccRCC, which may be targeted for therapeutic purposes. Graphical abstract