Correlation of serum homocysteine and cystatin C levels with prognosis in heart failure with preserved ejection fraction patients.

OBJECTIVE: This study investigated the relationship of serum homocysteine (Hcy) and cystatin C (Cys C) levels with the prognosis of patients with heart failure with preserved ejection fraction (HFpEF). METHODS: A total of 178 patients with HFpEF who were admitted to our hospital between December 2019 and November 2020 were included. Patients were grouped based on their serum Hcy and Cys C levels: high Hcy level, normal Hcy level, high Cys C level, and normal Cys C level. Cardiac function, ventricular remodeling indices, and prognosis were compared among patients in these groups. Additionally, the predictive value of serum Hcy and Cys C levels for adverse cardiovascular events in HFpEF patients was analyzed. RESULTS: Patients' mean age in the high Hcy level, normal Hcy level, high Cys C level, and normal Cys C level groups was 69.21 ± 4.17,67.74 ± 4.28,69.95 ± 4.98, and 67.06 ± 4.13 years old, respectively. The high Hcy level group exhibited a lower proportion of class II cardiac function according to the New York Heart Association (NYHA) classification and a higher proportion of class IV cardiac function than the normal Hcy level group, with statistically significant differences. Similarly, the high Cys C level group had a lower proportion of class II cardiac function and a higher proportion of class IV cardiac function compared with the normal Cys C level group, with statistically significant differences. Left ventricular end-diastolic internal diameter (LVEDD), left ventricular end-systolic internal diameter (LVESD), and left ventricular mass index (LVMI) were significantly higher in both the high Hcy level and high Cys C level groups compared with the normal group, with statistically significant differences. The rates of all-cause mortality and class I endpoint events were significantly higher in the high Hcy level and high Cys C level groups than in the normal group. Multifactorial logistic regression analysis demonstrated that adverse cardiovascular events were significantly associated with cardiac function class, LVEDD, LVESD, LVMI, Hcy, and Cys C in patients with HFpEF. The area under the curve (AUC) values for Hcy and Cys C, determined using receiver operating characteristic (ROC) curve analysis, were 0.778 (optimal critical value, 25.38) and 0.681 (optimal critical value, 1.56), respectively, for predicting adverse cardiovascular events. Both Hcy and Cys C serum levels were positively correlated with LVEDD, LVESD, LVMI, and NYHA classification. CONCLUSION: Serum levels of Hcy and Cys C were closely associated with cardiac function, ventricular remodeling indices, and prognosis in patients with HFpEF. These levels may serve as valuable indices for assessing HFpEF patients' health status and prognosis, providing important insights into their potential role as biomarkers for HFpEF management and prognosis.

Metabolomic Profiling of Tumor Tissues Unveils Metabolic Shifts in Non-Small Cell Lung Cancer Patients with Concurrent Diabetes Mellitus.

A comprehensive understanding of the exact influence of type 2 diabetes mellitus (T2DM) on the metabolic status of non-small cell lung cancer (NSCLC) is still lacking. This study explores metabolic alterations in tumor tissues among patients with coexisting NSCLC and T2DM in comparison with NSCLC patients. A combined approach of clinical analysis and metabolomics was employed, including 20 NSCLC patients and 20 NSCLC+T2DM patients. Targeted metabolomics analysis was performed on tumor tissues using the liquid chromatography-mass spectrometry (LC-MS) approach. A clear segregation was observed between NSCLC+T2DM and matched NSCLC tissue samples in Orthogonal Partial Least Squares Discrimination Analysis (OPLS-DA). Furthermore, the levels of 7 metabolites are found to be significantly different between diabetes/nondiabetes tumor tissue samples. The related pathways included arginine biosynthesis, glutathione metabolism, arginine and proline metabolism, purine metabolism, biotin metabolism, and histidine metabolism. 3-Phenyllactic acid, carnitine-C5, carnitine-C12, and serotonin showed a positive linear correlation with fasting blood glucose levels in NSCLC patients. Uridine, pipecolic acid, cytosine, and fasting blood glucose levels were found to have a negative correlation. Our results suggest that NSCLC patients with concurrent T2DM exhibit distinct metabolic shifts in tumor tissues compared to those of solely NSCLC patients.

Small-molecule agents for cancer immunotherapy.

Cancer immunotherapy, exemplified by the remarkable clinical benefits of the immune checkpoint blockade and chimeric antigen receptor T-cell therapy, is revolutionizing cancer therapy. They induce long-term tumor regression and overall survival benefit in many types of cancer. With the advances in our knowledge about the tumor immune microenvironment, remarkable progress has been made in the development of small-molecule drugs for immunotherapy. Small molecules targeting PRR-associated pathways, immune checkpoints, oncogenic signaling, metabolic pathways, cytokine/chemokine signaling, and immune-related kinases have been extensively investigated. Monotherapy of small-molecule immunotherapeutic drugs and their combinations with other antitumor modalities are under active clinical investigations to overcome immune tolerance and circumvent immune checkpoint inhibitor resistance. Here, we review the latest development of small-molecule agents for cancer immunotherapy by targeting defined pathways and highlighting their progress in recent clinical investigations.

Piceatannol protects against myocardial ischemia/reperfusion injury by inhibiting ferroptosis via Nrf-2 signaling-mediated iron metabolism.

Myocardial tissue ischemia damages myocardial cells. Although reperfusion is an effective technique to rescue myocardial cell damage, it may also exacerbate myocardial cell damage. Ferroptosis, an iron-dependent cell death, occurs following myocardial ischemia-reperfusion (I/R). Piceatannol (PCT) is a natural stilbene compound with excellent antioxidant properties that protect against I/R injury and exerts protective effects against ferroptosis-induced cardiomyocytes following I/R injury; however, the exact mechanism remains to be elucidated. PURPOSE: This study aims to investigate the protective effect and mechanism of PCT on myocardial ischemia-reperfusion injury. METHODS: An ischemia-reperfusion model was established via ligation of the left anterior descending branch of mice's hearts and hypoxia-reoxygenation (H/R) of cardiomyocytes. RESULTS: During ischemia-reperfusion, Nuclear factor E2-related factor 2 (Nrf-2) expression was downregulated, the left ventricular function was impaired, intracellular iron and lipid peroxidation product levels were elevated, and cardiomyocytes underwent ferroptosis. Furthermore, ferroptosis was enhanced following treatment with an Nrf-2 inhibitor. After PCT treatment, Nrf-2 expression significantly increased, intracellular ferrous ions and lipid peroxidation products significantly reduced, Ferroportin1 (FPN1) expression increased, and transferrin receptor-1 (TfR-1) expression was inhibited. CONCLUSIONS: PCT regulates iron metabolism through Nrf-2 to protect against myocardial cell ferroptosis induced by myocardial I/R injury.

Metabolomic machine learning predictor for diagnosis and prognosis of gastric cancer.

Gastric cancer (GC) represents a significant burden of cancer-related mortality worldwide, underscoring an urgent need for the development of early detection strategies and precise postoperative interventions. However, the identification of non-invasive biomarkers for early diagnosis and patient risk stratification remains underexplored. Here, we conduct a targeted metabolomics analysis of 702 plasma samples from multi-center participants to elucidate the GC metabolic reprogramming. Our machine learning analysis reveals a 10-metabolite GC diagnostic model, which is validated in an external test set with a sensitivity of 0.905, outperforming conventional methods leveraging cancer protein markers (sensitivity < 0.40). Additionally, our machine learning-derived prognostic model demonstrates superior performance to traditional models utilizing clinical parameters and effectively stratifies patients into different risk groups to guide precision interventions. Collectively, our findings reveal the metabolic landscape of GC and identify two distinct biomarker panels that enable early detection and prognosis prediction respectively, thus facilitating precision medicine in GC.

Osteoclast Cancer Cell Metabolic Cross-talk Confers PARP Inhibitor Resistance in Bone Metastatic Breast Cancer.

The majority of patients with late-stage breast cancer develop distal bone metastases. The bone microenvironment can affect response to therapy, and uncovering the underlying mechanisms could help identify improved strategies for treating bone metastatic breast cancer. Here, we observed that osteoclasts reduced the sensitivity of breast cancer cells to DNA damaging agents, including cisplatin and the PARP inhibitor (PARPi) olaparib. Metabolic profiling identified elevated glutamine production by osteoclasts. Glutamine supplementation enhanced the survival of breast cancer cells treated with DNA damaging agents, while blocking glutamine uptake increased sensitivity and suppressed bone metastasis. GPX4, the critical enzyme responsible for glutathione oxidation, was upregulated in cancer cells following PARPi treatment through stress-induced ATF4-dependent transcriptional programming. Increased glutamine uptake and GPX4 upregulation concertedly enhanced glutathione metabolism in cancer cells to help neutralize oxidative stress and generate PARPi resistance. Analysis of paired patient samples of primary breast tumors and bone metastases revealed significant induction of GPX4 in bone metastases. Combination therapy utilizing PARPi and zoledronate, which blocks osteoclast activity and thereby reduces the microenvironmental glutamine supply, generated a synergistic effect in reducing bone metastasis. These results identify a role for glutamine production by bone-resident cells in supporting metastatic cancer cells to overcome oxidative stress and develop resistance to DNA-damaging therapies. SIGNIFICANCE: Metabolic interaction between osteoclasts and tumor cells contributes to resistance to DNA-damaging agents, which can be blocked by combination treatment with PARP and osteoclast inhibitors to reduce bone metastatic burden.

Induction of mouse totipotent stem cells by a defined chemical cocktail.

In mice, only the zygotes and blastomeres from 2-cell embryos are authentic totipotent stem cells (TotiSCs) capable of producing all the differentiated cells in both embryonic and extraembryonic tissues and forming an entire organism1. However, it remains unknown whether and how totipotent stem cells can be established in vitro in the absence of germline cells. Here we demonstrate the induction and long-term maintenance of TotiSCs from mouse pluripotent stem cells using a combination of three small molecules: the retinoic acid analogue TTNPB, 1-azakenpaullone and the kinase blocker WS6. The resulting chemically induced totipotent stem cells (ciTotiSCs), resembled mouse totipotent 2-cell embryo cells at the transcriptome, epigenome and metabolome levels. In addition, ciTotiSCs exhibited bidirectional developmental potentials and were able to produce both embryonic and extraembryonic cells in vitro and in teratoma. Furthermore, following injection into 8-cell embryos, ciTotiSCs contributed to both embryonic and extraembryonic lineages with high efficiency. Our chemical approach to totipotent stem cell induction and maintenance provides a defined in vitro system for manipulating and developing understanding of the totipotent state and the development of multicellular organisms from non-germline cells.

Targeting acetylcholine signaling modulates persistent drug tolerance in EGFR-mutant lung cancer and impedes tumor relapse.

Although first-line epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI) therapy is effective for treating EGFR-mutant non-small cell lung cancer (NSCLC), it is now understood that drug-tolerant persister (DTP) cells escaping from initial treatment eventually drives drug resistance. Here, through integration of metabolomics and transcriptomics, we found that the neurotransmitter acetylcholine (ACh) was specifically accumulated in DTP cells, and demonstrated that treatment with EGFR-TKI heightened the expression of the rate-limiting enzyme choline acetyltransferase (ChAT) in ACh biosynthesis via YAP mediation. Genetic and pharmacological manipulation of ACh biosynthesis or ACh signaling could predictably regulate the extent of DTP formation in vitro and in vivo. Strikingly, pharmacologically targeting ACh/M3R signaling with an FDA-approved drug, darifenacin, retarded tumor relapse in vivo. Mechanistically, upregulated ACh metabolism mediated drug tolerance in part through activating WNT signaling via ACh muscarinic receptor 3 (M3R). Importantly, we showed that aberrant ACh metabolism in patients with NSCLC played a potential role in predicting EGFR-TKI response rate and progression-free survival. Our study therefore defines a therapeutic strategy - targeting the ACh/M3R/WNT axis - for manipulating EGFR TKI drug tolerance in the treatment of NSCLC.

Cancer-associated fibroblasts employ NUFIP1-dependent autophagy to secrete nucleosides and support pancreatic tumor growth.

Cancer-associated fibroblasts (CAFs) are one of the most prominent and active components in the pancreatic tumor microenvironment. Our data show that CAFs are critical for survival from pancreatic ductal adenocarcinoma (PDAC) on glutamine deprivation. Specifically, we uncovered a role for nucleosides, which are secreted by CAFs through autophagy in a nuclear fragile X mental retardation-interacting protein 1 (NUFIP1)-dependent manner, increased glucose utilization and promoted growth of PDAC. Moreover, we demonstrate that CAF-derived nucleosides induced glucose consumption under glutamine-deprived conditions and displayed a dependence on MYC. Using an orthotopic mouse model of PDAC, we found that inhibiting nucleoside secretion by targeting NUFIP1 in the stroma reduced tumor weight. This finding highlights a previously unappreciated metabolic network within pancreatic tumors in which diverse nutrients are used to promote growth in an austere tumor microenvironment.

Neddylation inhibition induces glutamine uptake and metabolism by targeting CRL3SPOP E3 ligase in cancer cells.

Abnormal neddylation activation is frequently observed in human cancers and neddylation inhibition has been proposed as a therapy for cancer. Here, we report that MLN4924, a small-molecule inhibitor of neddylation activating enzyme, increases glutamine uptake in breast cancer cells by causing accumulation of glutamine transporter ASCT2/SLC1A5, via inactivation of CRL3-SPOP E3 ligase. We show the E3 ligase SPOP promotes ASCT2 ubiquitylation, whereas SPOP itself is auto-ubiquitylated upon glutamine deprivation. Thus, SPOP and ASCT2 inversely regulate glutamine uptake and metabolism. SPOP knockdown increases ASCT2 levels to promote growth which is rescued by ASCT2 knockdown. Adding ASCT2 inhibitor V-9302 enhances MLN4924 suppression of tumor growth. In human breast cancer specimens, SPOP and ASCT2 levels are inversely correlated, whereas lower SPOP with higher ASCT2 predicts a worse patient survival. Collectively, our study links neddylation to glutamine metabolism via the SPOP-ASCT2 axis and provides a rational drug combination for enhanced cancer therapy.

Evolutionary metabolic landscape from preneoplasia to invasive lung adenocarcinoma.

Metabolic reprogramming evolves during cancer initiation and progression. However, thorough understanding of metabolic evolution from preneoplasia to lung adenocarcinoma (LUAD) is still limited. Here, we perform large-scale targeted metabolomics on resected lesions and plasma obtained from invasive LUAD and its precursors, and decipher the metabolic trajectories from atypical adenomatous hyperplasia (AAH) to adenocarcinoma in situ (AIS), minimally invasive adenocarcinoma (MIA) and invasive adenocarcinoma (IAC), revealing that perturbed metabolic pathways emerge early in premalignant lesions. Furthermore, three panels of plasma metabolites are identified as non-invasive predictive biomarkers to distinguish IAC and its precursors with benign diseases. Strikingly, metabolomics clustering defines three metabolic subtypes of IAC patients with distinct clinical characteristics. We identify correlation between aberrant bile acid metabolism in subtype III with poor clinical features and demonstrate dysregulated bile acid metabolism promotes migration of LUAD, which could be exploited as potential targetable vulnerability and for stratifying patients. Collectively, the comprehensive landscape of the metabolic evolution along the development of LUAD will improve early detection and provide impactful therapeutic strategies.

Immune Modulating Antibody-Drug Conjugate (IM-ADC) for Cancer Immunotherapy.

Antibody-drug conjugate (ADC) and immune checkpoint blockade (ICB) offer promising approaches for cancer treatment. Here, we describe an ADC constructed by conjugating anti-PD-L1 THIOMAB with a bifunctional immunomodulator D18 via a redox-cleavable linker. The resulting ADC HE-S2 not only triggers a potent antitumor immune response by blocking the PD-1/PD-L1 interaction and activating the Toll-like receptor 7/8 (TLR7/8) signaling pathway but also upregulates its targeted PD-L1 expression via epigenetic regulation and/or IFN-γ induction, thus conferring more sensitivity to the PD-1/PD-L1 blockade. We identify that ADC HE-S2 treatment could lead to more pronounced tumor suppression than the treatment of D18 in combination with the anti-PD-L1 antibody. Accordingly, this study provides a novel ADC strategy to enhance the antitumor immune response to ICB therapy.

Simultaneous 3-Nitrophenylhydrazine Derivatization Strategy of Carbonyl, Carboxyl and Phosphoryl Submetabolome for LC-MS/MS-Based Targeted Metabolomics with Improved Sensitivity and Coverage.

Metabolomics is a powerful and essential technology for profiling metabolic phenotypes and exploring metabolic reprogramming, which enables the identification of biomarkers and provides mechanistic insights into physiology and disease. However, its applications are still limited by the technical challenges particularly in its detection sensitivity for the analysis of biological samples with limited amount, necessitating the development of highly sensitive approaches. Here, we developed a highly sensitive liquid chromatography tandem mass spectrometry method based on a 3-nitrophenylhydrazine (3-NPH) derivatization strategy that simultaneously targets carbonyl, carboxyl, and phosphoryl groups for targeted metabolomic analysis (HSDccp-TM) in biological samples. By testing 130 endogenous metabolites including organic acids, amino acids, carbohydrates, nucleotides, carnitines, and vitamins, we showed that the derivatization strategy resulted in significantly improved detection sensitivity and chromatographic separation capability. Metabolic profiling of merely 60 oocytes and 5000 hematopoietic stem cells primarily isolated from mice demonstrated that this method enabled routine metabolomic analysis in trace amounts of biospecimens. Moreover, the derivatization strategy bypassed the tediousness of inferring the MS fragmentation patterns and simplified the complexity of monitoring ion pairs of metabolites, which greatly facilitated the metabolic flux analysis (MFA) for glycolysis, the tricarboxylic acid (TCA) cycle, and pentose phosphate pathway (PPP) in cell cultures. In summary, the novel 3-NPH derivatization-based method with high sensitivity, good chromatographic separation, and broad coverage showed great potential in promoting metabolomics and MFA, especially in trace amounts of biospecimens.

Influence of YES1 Kinase and Tyrosine Phosphorylation on the Activity of OCT1.

Organic cation transporter 1 (OCT1) is a transporter that regulates the hepatic uptake and subsequent elimination of diverse cationic compounds. Although OCT1 has been involved in drug-drug interactions and causes pharmacokinetic variability of many prescription drugs, details of the molecular mechanisms that regulate the activity of OCT1 remain incompletely understood. Based on an unbiased phospho-proteomics screen, we identified OCT1 as a tyrosine-phosphorylated transporter, and functional validation studies using genetic and pharmacological approaches revealed that OCT1 is highly sensitive to small molecules that target the protein kinase YES1, such as dasatinib. In addition, we found that dasatinib can inhibit hepatic OCT1 function in mice as evidenced from its ability to modulate levels of isobutyryl L-carnitine, a hepatic OCT1 biomarker identified from a targeted metabolomics analysis. These findings provide novel insight into the post-translational regulation of OCT1 and suggest that caution is warranted with polypharmacy regimes involving the combined use of OCT1 substrates and kinase inhibitors that target YES1.

Metabolomics, metabolic flux analysis and cancer pharmacology.

Metabolic reprogramming is a hallmark of cancer and increasing evidence suggests that reprogrammed cell metabolism supports tumor initiation, progression, metastasis and drug resistance. Understanding metabolic dysregulation may provide therapeutic targets and facilitate drug research and development for cancer therapy. Metabolomics enables the high-throughput characterization of a large scale of small molecule metabolites in cells, tissues and biofluids, while metabolic flux analysis (MFA) tracks dynamic metabolic activities using stable isotope tracer methods. Recent advances in metabolomics and MFA technologies make them powerful tools for metabolic profiling and characterizing metabolic activities in health and disease, especially in cancer research. In this review, we introduce recent advances in metabolomics and MFA analytical technologies, and provide the first comprehensive summary of the most commonly used isotope tracing methods. In addition, we highlight how metabolomics and MFA are applied in cancer pharmacology studies particularly for discovering targetable metabolic vulnerabilities, understanding the mechanisms of drug action and drug resistance, exploring potential strategies with dietary intervention, identifying cancer biomarkers, as well as enabling precision treatment with pharmacometabolomics.

Gluconeogenic enzyme PCK1 deficiency promotes CHK2 O-GlcNAcylation and hepatocellular carcinoma growth upon glucose deprivation.

Although cancer cells are frequently faced with a nutrient- and oxygen-poor microenvironment, elevated hexosamine-biosynthesis pathway (HBP) activity and protein O-GlcNAcylation (a nutrient sensor) contribute to rapid growth of tumor and are emerging hallmarks of cancer. Inhibiting O-GlcNAcylation could be a promising anticancer strategy. The gluconeogenic enzyme phosphoenolpyruvate carboxykinase 1 (PCK1) is downregulated in hepatocellular carcinoma (HCC). However, little is known about the potential role of PCK1 in enhanced HBP activity and HCC carcinogenesis under glucose-limited conditions. In this study, PCK1 knockout markedly enhanced the global O-GlcNAcylation levels under low-glucose conditions. Mechanistically, metabolic reprogramming in PCK1-loss hepatoma cells led to oxaloacetate accumulation and increased de novo uridine triphosphate synthesis contributing to uridine diphosphate-N-acetylglucosamine (UDP-GlcNAc) biosynthesis. Meanwhile, deletion of PCK1 also resulted in AMPK-GFAT1 axis inactivation, promoting UDP-GlcNAc synthesis for elevated O-GlcNAcylation. Notably, lower expression of PCK1 promoted CHK2 threonine 378 O-GlcNAcylation, counteracting its stability and dimer formation, increasing CHK2-dependent Rb phosphorylation and HCC cell proliferation. Moreover, aminooxyacetic acid hemihydrochloride and 6-diazo-5-oxo-L-norleucine blocked HBP-mediated O-GlcNAcylation and suppressed tumor progression in liver-specific Pck1-knockout mice. We reveal a link between PCK1 depletion and hyper-O-GlcNAcylation that underlies HCC oncogenesis and suggest therapeutic targets for HCC that act by inhibiting O-GlcNAcylation.

Melatonin inhibits macrophage infiltration and promotes plaque stabilization by upregulating anti-inflammatory HGF/c-Met system in the atherosclerotic rabbit: USPIO-enhanced MRI assessment.

Macrophage plays critical roles in the pathogenesis of atherosclerosis (AS), and is an attractive target for detecting and treating vulnerable plaque. Our previous study showed that melatonin (MLT) ameliorated AS by suppressing the pro-inflammatory Toll-like receptor 4/nuclear factor kappa B system in high-fat-fed rabbit. However, it is unknown whether the anti-atherosclerotic properties of MLT are associated with the upregulation of anti-inflammatory hepatocyte growth factor (HGF)/mesenchymal-epithelial transition factor (c-Met) system. In present study, we examined whether MLT could inhibit macrophage infiltration and promote plaque stabilization by upregulating HGF/c-Met system with ultrasmall superparamagnetic iron oxide (USPIO)-enhanced magnetic resonance imaging (MRI) assessment in AS rabbit. Rabbits in this study were randomly divided into three groups and treated with a standard diet, high-fat diet, and high-fat diet plus 10 mg/kg/day MLT for 12 weeks, respectively. MLT treatment significantly reversed spotty signal void in 3D-TOF MRI, standard signal intensity reduction in T2WI MRI and aortic luminal area reduction in 2D-TOF MRI of the atherosclerotic abdominal aorta 72 h after USPIO injection. It also decreased serum interleukin-6 (IL-6), intima/media thickness ratio of the abdominal aorta, CD68 and iron-positive areas in the aortic intima, and increased serum IL-10, HGF and c-Met protein expression and the accumulation of vascular smooth muscle cell and collagen fiber in the aortic intima of AS rabbit. Our data demonstrated that MLT significantly decreased plaque macrophage infiltration and promoted plaque stability in AS rabbit assessed by USPIO-enhanced MRI. Remarkably, it was very first revealed that upregulation of anti-inflammatory HGF/c-Met system might contribute to the atheroprotective mechanisms of MLT.

Mettl17, a regulator of mitochondrial ribosomal RNA modifications, is required for the translation of mitochondrial coding genes.

Embryonic stem cells (ESCs) are pluripotent stem cells with the ability to self-renew and to differentiate into any cell types of the 3 germ layers. Recent studies have demonstrated that there is a strong connection between mitochondrial function and pluripotency. Here, we report that methyltransferase like (Mettl) 17, identified from the clustered regularly interspaced short palindromic repeats knockout screen, is required for proper differentiation of mouse embryonic stem cells (mESCs). Mettl17 is located in mitochondria through its N-terminal targeting sequence and specifically interacts with 12S mitochondrial ribosomal RNA (mt-rRNA) as well as small subunits of mitochondrial ribosome (MSSUs). Loss of Mettl17 affects the stability of both 12S mt-rRNA and its associated proteins of MSSUs. We further showed that Mettl17 is an S-adenosyl methionine (SAM)-binding protein and regulates mitochondrial ribosome function in a SAM-binding-dependent manner. Loss of Mettl17 leads to around 70% reduction of m4C840 and 50% reduction of m5C842 of 12S mt-rRNA, revealing the first regulator of the m4C840 and indicating a crosstalk between the 2 nearby modifications. The defects of mitochondrial ribosome caused by deletion of Mettl17 lead to the impaired translation of mitochondrial protein-coding genes, resulting in significant changes in mitochondrial oxidative phosphorylation and cellular metabolome, which are important for mESC pluripotency.-Shi, Z., Xu, S., Xing, S., Yao, K., Zhang, L., Xue, L., Zhou, P., Wang, M., Yan, G., Yang, P., Liu, J., Hu, Z., Lan, F. Mettl17, a regulator of mitochondrial ribosomal RNA modifications, is required for the translation of mitochondrial coding genes.