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Sarcopenia is a significant geriatric syndrome that involves the loss of skeletal muscle mass and strength. Due to its substantial endocrine role, the metabolic microenvironment of skeletal muscle undergoes changes with age. Examining the pathogenesis of sarcopenia through focusing on metabolic dysregulation could offer insights for developing more effective intervention strategies. In this study, we analyzed the transcriptomics data to identify specific genes involved in the regulation of metabolism in skeletal muscle during the development of sarcopenia. Three machine learning algorithms were employed to screen key target genes exhibiting strong correlations with metabolism, which were further validated using RNA‐sequencing data and publicly accessible datasets. Among them, the metabolic enzyme nicotinamide N‐methyltransferase (NNMT) was elevated in sarcopenia, and predicted sarcopenia with an area under the curve exceeding 0.7, suggesting it as a potential therapeutic target for sarcopenia. As expected, inhibition of NNMT improved the grip strength in aging mice and alleviated age‐related decline in the mass index of the quadriceps femoris muscles and whole‐body lean mass index. Additionally, the NNMTi treatment increased the levels of nicotinamide adenine dinucleotide (NAD+) content, as well as PGC1α and p‐AMPK expression in the muscles of both the D‐galactose‐treated mouse model and naturally aging mouse model. Overall, this work demonstrates NNMT as a promising target for preventing age‐related decline in muscle mass and strength. [ABSTRACT FROM AUTHOR]

Metastatic colonization of distant organs accounts for over 90% of deaths related to solid cancers, yet the molecular determinants of metastasis remain poorly understood. Here, we unveil a mechanism of colonization in the aggressive basal‐like subtype of breast cancer that is driven by the NAD+ metabolic enzyme nicotinamide N‐methyltransferase (NNMT). We demonstrate that NNMT imprints a basal genetic program into cancer cells, enhancing their plasticity. In line, NNMT expression is associated with poor clinical outcomes in patients with breast cancer. Accordingly, ablation of NNMT dramatically suppresses metastasis formation in pre‐clinical mouse models. Mechanistically, NNMT depletion results in a methyl overflow that increases histone H3K9 trimethylation (H3K9me3) and DNA methylation at the promoters of PR/SET Domain‐5 (PRDM5) and extracellular matrix‐related genes. PRDM5 emerged in this study as a pro‐metastatic gene acting via induction of cancer‐cell intrinsic transcription of collagens. Depletion of PRDM5 in tumor cells decreases COL1A1 deposition and impairs metastatic colonization of the lungs. These findings reveal a critical activity of the NNMT‐PRDM5‐COL1A1 axis for cancer cell plasticity and metastasis in basal‐like breast cancer. Synopsis: The molecular basis for metastatic colonization of distant organs remains incompletely understood. This study uncovers a critical role for NAD+ metabolic enzyme nicotinamide N‐methyltransferase (NNMT) in driving cancer cell plasticity and extracellular matrix remodeling in basal‐like breast cancer. NNMT promotes metastatic colonization and predicts poor survival in breast cancer patients.NNMT enhances tumor initiation and stemness of breast cancer in xenografts.NNMT ablation elevates the pool of the methyl donor S‐adenosylmethionine (SAM), specifically increasing DNA and H3K9 histone methylation.NNMT ablation promotes the epigenetic silencing of collagens, collagen‐processing genes, and the transcriptional regulator PRDM5.Cancer‐cell intrinsic expression of PRDM5 and COL1A1 promotes metastatic colonization. [ABSTRACT FROM AUTHOR]

Background: The metabolic enzyme nicotinamide‐N‐methyltransferase (NNMT) is highly expressed in various cancer entities, suggesting tumour‐promoting functions. We systematically investigated NNMT expression and its metabolic interactions in clear cell renal cell carcinoma (ccRCC), a prominent RCC subtype with metabolic alterations, to elucidate its role as a drug target. Methods: NNMT expression was assessed in primary ccRCC (n = 134), non‐tumour tissue and ccRCC‐derived metastases (n = 145) by microarray analysis and/or immunohistochemistry. Findings were validated in The Cancer Genome Atlas (kidney renal clear cell carcinoma [KIRC], n = 452) and by single‐cell analysis. Expression was correlated with clinicopathological data and survival. Metabolic alterations in NNMT‐depleted cells were assessed by nontargeted/targeted metabolomics and extracellular flux analysis. The NNMT inhibitor (NNMTi) alone and in combination with the inhibitor 2‐deoxy‐D‐glucose for glycolysis and BPTES (bis‐2‐(5‐phenylacetamido‐1,3,4‐thiadiazol‐2‐yl)ethyl‐sulfide) for glutamine metabolism was investigated in RCC cell lines (786‐O, A498) and in two 2D ccRCC‐derived primary cultures and three 3D ccRCC air–liquid interface models. Results: NNMT protein was overexpressed in primary ccRCC (p = 1.32 × 10–16) and ccRCC‐derived metastases (p = 3.92 × 10–20), irrespective of metastatic location, versus non‐tumour tissue. Single‐cell data showed predominant NNMT expression in ccRCC and not in the tumour microenvironment. High NNMT expression in primary ccRCC correlated with worse survival in independent cohorts (primary RCC—hazard ratio [HR] = 4.3, 95% confidence interval [CI]: 1.5–12.4; KIRC—HR = 3.3, 95% CI: 2.0–5.4). NNMT depletion leads to intracellular glutamine accumulation, with negative effects on mitochondrial function and cell survival, while not affecting glycolysis or glutathione metabolism. At the gene level, NNMT‐depleted cells upregulate glycolysis, oxidative phosphorylation and apoptosis pathways. NNMTi alone or in combination with 2‐deoxy‐D‐glucose and BPTES resulted in inhibition of cell viability in ccRCC cell lines and primary tumour and metastasis‐derived models. In two out of three patient‐derived ccRCC air–liquid interface models, NNMTi treatment induced cytotoxicity. Conclusions: Since efficient glutamine utilisation, which is essential for ccRCC tumours, depends on NNMT, small‐molecule NNMT inhibitors provide a novel therapeutic strategy for ccRCC and act as sensitizers for combination therapies. [ABSTRACT FROM AUTHOR]

Grade 1 (G1) endometrioid carcinoma (EC) is relatively a good prognosis. However, in a minority of cases, G1 shows an aggressive histological pattern known as the microcystic, elongated, and fragmented (MELF) pattern. We previously reported that EC with high expression levels of S100A4 and serum deprivation‐response protein (SDPR) was related to MELF pattern invasion. However, the molecular features of the invasive front area of the MELF pattern have not been investigated. In this study, we searched for genes preferentially expressed in the invasive front area of EC with the MELF pattern using laser microdissection and RNA sequencing, and showed that nicotinamide N‐methyltransferase (NNMT) is related to MELF pattern invasiveness. Immunohistochemical analyses confirmed high NNMT expression in the invasive front area of the MELF pattern. Moreover, NNMT promoted migration, invasion, colony formation, epithelial–mesenchymal transition (EMT), and chemoresistance using EC cell lines. We speculate that depletion of NNMT promotes histone methylation and leads to tumor suppression because NNMT consumes S‐adenosyl methionine (SAM), which is an essential methylation cofactor. NNMT knockout cells showed enhanced expression of H3K9me2. RNA sequencing using NNMT knockout cell lines suggested that methylation of H3K9 leads to repression of the transcription of various oncogenic genes. Our findings demonstrate the possibility that NNMT inhibitors, which are expected to be used for the treatment of metabolic disorders, would be effective for the treatment of aggressive EC. This is the first report of gene analyses focusing on the morphological changes associated with MELF pattern invasion of EC. [ABSTRACT FROM AUTHOR]

Peritoneal metastasis (PM) is the major cause of recurrence in patients with gastric cancer (GC) and is associated with poor prognosis. The oncogenic role of Nicotinamide N‐methyltransferase (NNMT) in GC has been reported, but the role of secreted NNMT that is transported by exosomes remains unknown. In this study, exosomes were isolated from GC patients with or without PM and from GC cell line, including GC‐114, GC‐026, MKN45, and SNU‐16 cells. The contents of NNMT were significantly enhanced in exosomes isolated from GC patients with PM compared with those from GC patients without PM. Furthermore, the levels of NNMT were significantly enhanced in exosomes from GC cell lines relative to those from normal human gastric epithelial cell line GES‐1 cells. These data indicate that NNMT may be involved in intercellular communication for peritoneal dissemination. Moreover, colocalization of GC‐derived exosomal NNMT was found in human peritoneal mesothelial cell line HMrSV5 cells. Additionally, relative to GES‐1 exosomes, SNU‐16 exosomes significantly activated TGF‐β/smad2 signaling in HMrSV5 cells. However, when NNMT was silenced, the activation of TGF‐β/smad2 by SNU‐16 exosomes was abolished in HMrSV5 cells. We propose that NNMT‐containing exosomes derived from GC cells could promote peritoneal metastasis via TGF‐β/smad2 signaling. [ABSTRACT FROM AUTHOR]

Background: Odontogenic tumours are a group of rare heterogeneous diseases that range from hamartomatous tissue proliferations to benign and malignant neoplasms. Recurrences can occur after 10 years, so long‐term clinical and radiological follow‐up is required. The study of the molecular mechanisms involved in the development of these lesions is necessary to identify new prognostic markers. In this study, we evaluate the possible role of nicotinamide N‐methyltransferase (NNMT) in ameloblastomas (AM) and odontogenic keratocysts (OKC). Materials and methods: A total of 105 surgical specimens of primary and recurrent lesions were obtained from 55 patients (25 AM, 30 OKC). In particular, 50 AMs (25 primary, 25 recurrences) and 55 OKCs (30 primary, 25 recurrences) were retrieved. We carried out immunohistochemical analyses to evaluate the cytoplasmic expression of NNMT, measuring the percentage of positive cells and the value of NNMT expression intensity. Results: NNMT expression was significantly higher in recurrent than primary AMs (P =.0430). This result was confirmed by staining intensity, showing more cases with moderate/intense staining in recurrent AMs (P =.0470). NNMT expression was significantly lower in recurrent than primary OKC (P =.0014). Staining intensity showed more cases with moderate/intense staining in primary OKCs (P =.0276). Conclusions: This report is the first to evaluate NNMT expression in odontogenic lesions and to demonstrate a differential expression in recurrent AMs and OKCs, suggesting that there is potential for use of NNMT as prognostic marker. [ABSTRACT FROM AUTHOR]

Purpose: Nicotinamide n‐methyltransferase (NNMT) has good biochemical activity and epigenetic regulation, and has been reported as a major metabolic regulator of cancer. The goal of this study was to investigate the significance of stromal NNMT expression in colorectal cancer (CRC). Patients and methods: Stromal expression of NNMT in primary CRC, metastasis CRC, and their non‐cancerous tissues from 1088 CRC patients was examined by immunohistochemistry. The associations between stromal NNMT expression and survival outcomes in 967 patients with stage I‐III CRC were further evaluated with Kaplan‐Meier curve and Cox model analyses. Results: NNMT expression was mainly sourced from stromal compartments and also elevated in CRC. Patients with high stromal NNMT (IHC‐score ≥ 106) have a worse survival than those patients with low stromal NNMT. In multiple Cox analyses, high expression of stromal NNMT remained as an independent risk factor in CRC for disease‐free survival with a hazard ratio (HR) of 1.415 (95% confidence interval [CI], 1.015‐1.972) and disease‐specific survival with a HR of 5.004 (95% CI, 2.301‐10.883). In addition, high stromal NNMT expression in CRC also indicates the poor survival outcomes in patients with early stage CRC (stage I and II) and in patients who undergo chemotherapy. Conclusion: NNMT is mainly located in CRC stromal compartment. High stromal NNMT expression predicts an unfavorable postoperative prognosis. [ABSTRACT FROM AUTHOR]

The cross‐talk between hepatic stellate cells (HSCs) and hepatic carcinoma cells contributes to hepatocellular carcinoma (HCC) progression, but the underlying mechanism is largely unknown. We report here that activated HSCs induce upregulation of nicotinamide N‐methyltransferase (NNMT), which is known to regulate multiple metabolic pathways in hepatoma cells of the liver. High levels of NNMT in HCC tissues were positively correlated with vascular invasion, increased serum HBV‐DNA levels, and distant metastasis. In addition, functional assays showed that NNMT promoted HCC cell invasion and metastasis by altering the histone H3 methylation on 27 methylation pattern and transcriptionally activating cluster of differentiation 44 (CD44). NNMT‐mediated N6‐methyladenosine modification of CD44 mRNA resulted in the formation of a CD44v3 splice variant, while its product 1‐methyl‐nicotinamide stabilized CD44 protein by preventing ubiquitin‐mediated degradation. Finally, NNMT was also shown to be a target of statins that inhibited metastasis of hepatoma cells. Taken together, our study shows for the first time that the NNMT/CD44v3 axis regulates HCC metastasis and presents NNMT as a promising prognostic biomarker and therapeutic target for HCC. [ABSTRACT FROM AUTHOR]