Serine Synthesis via PHGDH Is Essential for Heme Production in Endothelial Cells

Essentiality of SLC7A11-mediated nonessential amino acids in MASLD

Metabolic dysfunction-associated steatotic liver disease (MASLD) remains a rapidly growing global health burden. Here, we report that the nonessential amino acid (NEAA) transporter SLC7A11 plays a key role in MASLD. In patients with MASLD, we found high expression levels of SLC7A11 that were correlated directly with clinical grade. Using both loss-of-function and gain-of-function genetic models, we found that Slc7a11 deficiency accelerated MASLD progression via classic cystine/cysteine deficiency-induced ferroptosis, while serine deficiency and a resulting impairment in de novo cysteine production were attributed to ferroptosis-induced MASLD progression in mice overexpressing hepatic Slc7a11. Consistent with these findings, we found that both serine supplementation and blocking ferroptosis significantly alleviated MASLD, and the serum serine/glutamate ratio was significantly lower in these preclinical disease models, suggesting that it might serve as a prognostic biomarker for MASLD in patients. These findings indicate that defects in NEAA metabolism are involved in the progression of MASLD and that serine deficiency-triggered ferroptosis may provide a therapeutic target for its treatment.

Endothelial metabolic control of insulin sensitivity through resident macrophages

Endothelial cells (ECs) not only form passive blood conduits but actively contribute to nutrient transport and organ homeostasis. The role of ECs in glucose homeostasis is, however, poorly understood. Here, we show that, in skeletal muscle, endothelial glucose transporter 1 (Glut1/Slc2a1) controls glucose uptake via vascular metabolic control of muscle-resident macrophages without affecting transendothelial glucose transport. Lowering endothelial Glut1 via genetic depletion (Glut1ΔEC) or upon a short-term high-fat diet increased angiocrine osteopontin (OPN/Spp1) secretion. This promoted resident muscle macrophage activation and proliferation, which impaired muscle insulin sensitivity. Consequently, co-deleting Spp1 from ECs prevented macrophage accumulation and improved insulin sensitivity in Glut1ΔEC mice. Mechanistically, Glut1-dependent endothelial glucose metabolic rewiring increased OPN in a serine metabolism-dependent fashion. Our data illustrate how the glycolytic endothelium creates a microenvironment that controls resident muscle macrophage phenotype and function and directly links resident muscle macrophages to the maintenance of muscle glucose homeostasis.

Unlocking the potential: Targeting metabolic pathways in the tumor microenvironment for Cancer therapy

Cancer incidence and mortality are increasing and impacting global life expectancy. Metabolic reprogramming in the tumor microenvironment (TME) is intimately related to tumorigenesis, progression, metastasis and drug resistance. Tumor cells drive metabolic reprogramming of other cells in the TME through metabolic induction of cytokines and metabolites, and metabolic substrate competition. Consequently, this boosts tumor cell growth by providing metabolic support and facilitating immunosuppression and angiogenesis. The metabolic interplay in the TME presents potential therapeutic targets. Here, we focus on the metabolic reprogramming of four principal cell subsets in the TME: CAFs, TAMs, TILs and TECs, and their interaction with tumor cells. We also summarize medications and therapies targeting these cells' metabolic pathways, particularly in the context of immune checkpoint blockade therapy.

Animal Models of Retinopathy of Prematurity: Advances and Metabolic Regulators

Retinopathy of prematurity (ROP) is a primary cause of visual impairment and blindness in premature newborns, characterized by vascular abnormalities in the developing retina, with microvascular alteration, neovascularization, and in the most severe cases retinal detachment. To elucidate the pathophysiology and develop therapeutics for ROP, several pre-clinical experimental models of ROP were developed in different species. Among them, the oxygen-induced retinopathy (OIR) mouse model has gained the most popularity and critically contributed to our current understanding of pathological retinal angiogenesis and the discovery of potential anti-angiogenic therapies. A deeper comprehension of molecular regulators of OIR such as hypoxia-inducible growth factors including vascular endothelial growth factors as primary perpetrators and other new metabolic modulators such as lipids and amino acids influencing pathological retinal angiogenesis is also emerging, indicating possible targets for treatment strategies. This review delves into the historical progressions that gave rise to the modern OIR models with a focus on the mouse model. It also reviews the fundamental principles of OIR, recent advances in its automated assessment, and a selected summary of metabolic investigation enabled by OIR models including amino acid transport and metabolism.

Tumor Metabolism: A New Field for the Treatment of Glioma

The clinical treatment of glioma remains relatively immature. Commonly used clinical treatments for gliomas are surgery combined with chemotherapy and radiotherapy, but there is a problem of drug resistance. In addition, immunotherapy and targeted therapies also suffer from the problem of immune evasion. The advent of metabolic therapy holds immense potential for advancing more efficacious and tolerable therapies against this aggressive disease. Metabolic therapy alters the metabolic processes of tumor cells at the molecular level to inhibit tumor growth and spread, and lead to better outcomes for patients with glioma that are insensitive to conventional treatments. Moreover, compared with conventional therapy, it has less impact on normal cells, less toxicity and side effects, and higher safety. The objective of this review is to examine the changes in metabolic characteristics throughout the development of glioma, enumerate the current methodologies employed for studying tumor metabolism, and highlight the metabolic reprogramming pathways of glioma along with their potential molecular mechanisms. Importantly, it seeks to elucidate potential metabolic targets for glioblastoma (GBM) therapy and summarize effective combination treatment strategies based on various studies.

Bilirubin metabolism in early life and respiratory health during preschool age: A combined analysis of two independent birth cohorts

BACKGROUND

Bilirubin has antioxidant properties, and elevated levels within the normal range have been associated with improved lung function and decreased risk of asthma in adults, but studies of young children are scarce. Here, we investigate associations between bilirubin in early life and respiratory health endpoints during preschool age in two independent birth cohorts.

METHODS

Bilirubin metabolites were assessed at ages 0.5, 1.5, and 6 years in COPSAC2010 (Copenhagen Prospective Studies on Asthma in Childhood 2010) and ages 1, 3, and 6 years in the VDAART (The Vitamin D Antenatal Asthma Reduction Trial) cohort. Meta-analyses were done to summarize the relationship between levels of bilirubin metabolites and asthma, infections, lung function, and allergic sensitization until age 6 across the cohorts. Interaction with the glucuronosyltransferase family 1 member A1 (UGT1A) genotype encoding for an enzyme in the bilirubin metabolism was explored, and metabolomics data were integrated to study underlying mechanisms.

FINDINGS

Increasing bilirubin (Z,Z) at ages 1.5-3 years was associated with an increased risk of allergic sensitization (adjusted relative risk [aRR] = 1.85 [1.20-2.85], p = 0.005), and age 6 bilirubin (Z,Z) also showed a trend of association with allergic sensitization at age 6 (aRR = 1.31 [0.97-1.77], p = 0.08), which showed significant interaction for the age 6 bilirubin (Z,Z)xUGT1A genotype. Further, increasing bilirubin (E,E), bilirubin (Z,Z), and biliverdin at ages 1.5-3 years was associated with a lower forced expiratory volume at age 6 (aRR range = 0.81-0.91, p < 0.049) but without a significant interaction with the UGT1A genotype (p interactions > 0.05). Network analysis showed a significant correlation between bilirubin metabolism and acyl carnitines. There were no associations between bilirubin metabolites and the risk of asthma and infections.

CONCLUSIONS

Bilirubin metabolism in early life may play a role in childhood respiratory health, particularly in children with specific UGT1A genotypes.

FUNDING

The Lundbeck Foundation (Grant no R16-A1694), The Ministry of Health (Grant no 903516), Danish Council for Strategic Research (Grant no 0603-00280B), and The Capital Region Research Foundation have provided core support to the COPSAC research center. This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement No. 946228). The Vitamin D Antenatal Asthma Reduction Trial (VDDART, ClinicalTrials.gov identifier: NCT00920621) was supported by grant U01HL091528 from NHLBI, U54TR001012 from the National Centers for Advancing Translational Sciences (NCATS). Metabolomics work by VDAART was supported by the National Heart, Lung, and Blood Institute (NHLBI) grant R01HL123915 and R01HL141826. S.T.W. was supported by R01HL091528 from the NHLBI, UG3OD023268 from Office of The Director, National Institute of Health, and P01HL132825 from the NHLBI.

Mitochondrial control of hypoxia-induced pathological retinal angiogenesis

OBJECTIVE

Pathological retinal neovascularization is vision-threatening. In mouse oxygen-induced retinopathy (OIR) we sought to define mitochondrial respiration changes longitudinally during hyperoxia-induced vessel loss and hypoxia-induced neovascularization, and to test interventions addressing those changes to prevent neovascularization.

METHODS

OIR was induced in C57BL/6J mice and retinal vasculature was examined at maximum neovessel formation. We assessed total proteome changes and the ratio of mitochondrial to nuclear DNA copy numbers (mtDNA/nDNA) of OIR vs. control retinas, and mitochondrial oxygen consumption rates (OCR) in ex vivo OIR vs. control retinas (BaroFuse). Pyruvate vs. vehicle control was supplemented to OIR mice either prior to or during neovessel formation.

RESULTS

In OIR vs. control retinas, global proteomics showed decreased retinal mitochondrial respiration at peak neovascularization. OCR and mtDNA/nDNA were also decreased at peak neovascularization suggesting impaired mitochondrial respiration. In vivo pyruvate administration during but not prior to neovessel formation (in line with mitochondrial activity time course) suppressed NV.

CONCLUSIONS

Mitochondrial energetics were suppressed during retinal NV in OIR. Appropriately timed supplementation of pyruvate may be a novel approach in neovascular retinal diseases.

The significant role of amino acid metabolic reprogramming in cancer

Amino acid metabolism plays a pivotal role in tumor microenvironment, influencing various aspects of cancer progression. The metabolic reprogramming of amino acids in tumor cells is intricately linked to protein synthesis, nucleotide synthesis, modulation of signaling pathways, regulation of tumor cell metabolism, maintenance of oxidative stress homeostasis, and epigenetic modifications. Furthermore, the dysregulation of amino acid metabolism also impacts tumor microenvironment and tumor immunity. Amino acids can act as signaling molecules that modulate immune cell function and immune tolerance within the tumor microenvironment, reshaping the anti-tumor immune response and promoting immune evasion by cancer cells. Moreover, amino acid metabolism can influence the behavior of stromal cells, such as cancer-associated fibroblasts, regulate ECM remodeling and promote angiogenesis, thereby facilitating tumor growth and metastasis. Understanding the intricate interplay between amino acid metabolism and the tumor microenvironment is of crucial significance. Expanding our knowledge of the multifaceted roles of amino acid metabolism in tumor microenvironment holds significant promise for the development of more effective cancer therapies aimed at disrupting the metabolic dependencies of cancer cells and modulating the tumor microenvironment to enhance anti-tumor immune responses and inhibit tumor progression.

Central carbon metabolism exhibits unique characteristics during the handling of fungal patterns by monocyte-derived dendritic cells

Monocyte-derived dendritic cells (MDDCs) are key players in the defense against fungal infection because of their outstanding capacity for non-opsonic phagocytosis and phenotypic plasticity. Accordingly, MDDCs rewire metabolism to meet the energetic demands for microbial killing and biomass synthesis required to restore homeostasis. It has been commonplace considering the metabolic reprogramming a mimicry of the Warburg effect observed in tumor cells. However, this may be an oversimplification since the offshoots of glycolysis and the tricarboxylic acid (TCA) cycle are connected in central carbon metabolism. Zymosan, the external wall of Saccharomyces cerevisiae, contains β-glucan and α-mannan chains that engage the C-type lectin receptors dectin-1/2 and Toll-like receptors. This makes it an optimal fungal surrogate for experimental research. Using real-time bioenergetic assays and [U-13C]glucose labeling, central hubs connected to cytokine expression were identified. The pentose phosphate pathway (PPP) exhibited a more relevant capacity to yield ribose-5-phosphate than reducing equivalents of NADPH, as judged from the high levels of isotopologues showing 13C-labeling in the ribose moiety and the limited contribution of the oxidative arm of the PPP to the production of ROS by NADPH oxidases (NOX). The finding of 13C-label in the purine ring and in glutathione unveiled the contribution of serine-derived glycine to purine ring and glutathione synthesis. Serine synthesis also supported the TCA cycle. Zymosan exhausted NAD+ and ATP, consistent with intracellular consumption and/or extracellular export. Poly-ADP-ribosylated proteins detected in the nuclear fractions of MDDCs did not show major changes upon zymosan stimulation, which suggests its dependence on constitutive Fe(II)/2-oxoglutarate-dependent demethylation of 5-methylcytosine by TET translocases and/or demethylation of histone H3 lysine 27 by JMJD demethylases rather than on NOX activities. These results disclose a unique pattern of central carbon metabolism following fungal challenge, characterized by the leverage of glycolysis offshoots and an extensive recycling of NAD+ and poly(ADP-ribose).

Prognostic value and potential function of a novel heme-related LncRNAs signature in gastric cancer

Heme is a coordination complex formed by the binding of iron ions and porphyrin rings. Its metabolic processes are associated with various cancers, including gastric cancer (GC). In recent years, long non-coding RNAs (LncRNAs) have been identified as key regulatory factors in GC. However, the role of LncRNAs associated with heme metabolism in GC and their relationship with prognosis have not been reported. In this study, we constructed a novel LncRNAs signature related to heme metabolism (HMlncSig) and validated its prognostic value for predicting the survival of GC patients through training, test, and entire cohorts. Kaplan-Meier analysis demonstrated that patients in the high-risk group had shorter survival times. Univariate and multivariate Cox regression analysis showed that HMlncSig was an independent prognostic indicator for GC patients, regardless of other clinical pathological features. Gene ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analysis and gene set variation analysis pathways showed that the activation of these markers may be involved in tumor progression, influencing the survival of GC patients. The nomogram, based on HMlncSig score and clinical features, demonstrated the strong predictive ability of this signature. Additionally, significant differences were observed between the high-risk and low-risk groups in terms of immune cell subtypes, expression of immune checkpoint genes, and response to chemotherapy and immunotherapy. Through clinical validation, we found that the risk score and heme levels of GC patients were both significantly elevated and correlated with the degree of malignancy. Furthermore, we found that AP000692.1, a key gene in this signature, promoted the proliferation, migration, and invasion of GC cells. In conclusion, our HMlncSig model has significant predictive value for the prognosis of GC patients and can provide clinical guidance for personalized immunotherapy.

The gluconeogenesis enzyme PCK2 has a non-enzymatic role in proteostasis in endothelial cells

Endothelial cells (ECs) are highly glycolytic, but whether they generate glycolytic intermediates via gluconeogenesis (GNG) in glucose-deprived conditions remains unknown. Here, we report that glucose-deprived ECs upregulate the GNG enzyme PCK2 and rely on a PCK2-dependent truncated GNG, whereby lactate and glutamine are used for the synthesis of lower glycolytic intermediates that enter the serine and glycerophospholipid biosynthesis pathways, which can play key roles in redox homeostasis and phospholipid synthesis, respectively. Unexpectedly, however, even in normal glucose conditions, and independent of its enzymatic activity, PCK2 silencing perturbs proteostasis, beyond its traditional GNG role. Indeed, PCK2-silenced ECs have an impaired unfolded protein response, leading to accumulation of misfolded proteins, which due to defective proteasomes and impaired autophagy, results in the accumulation of protein aggregates in lysosomes and EC demise. Ultimately, loss of PCK2 in ECs impaired vessel sprouting. This study identifies a role for PCK2 in proteostasis beyond GNG.

Serine synthesis controls mitochondrial biogenesis in macrophages

Mitochondrial dysfunction is the pivotal driving factor of multiple inflammatory diseases, and targeting mitochondrial biogenesis represents an efficacious approach to ameliorate such dysfunction in inflammatory diseases. Here, we demonstrated that phosphoglycerate dehydrogenase (PHGDH) deficiency promotes mitochondrial biogenesis in inflammatory macrophages. Mechanistically, PHGDH deficiency boosts mitochondrial reactive oxygen species (mtROS) by suppressing cytoplasmic glutathione synthesis. mtROS provokes hypoxia-inducible factor-1α signaling to direct nuclear specificity protein 1 and nuclear respiratory factor 1 transcription. Moreover, myeloid Phgdh deficiency reverses diet-induced obesity. Collectively, this study reveals that a mechanism involving de novo serine synthesis orchestrates mitochondrial biogenesis via mitochondrial-to-nuclear communication, and provides a potential therapeutic target for tackling inflammatory diseases and mitochondria-mediated diseases.

Metabolic reprogramming and interventions in angiogenesis

BACKGROUND

Endothelial cell (EC) metabolism plays a crucial role in the process of angiogenesis. Intrinsic metabolic events such as glycolysis, fatty acid oxidation, and glutamine metabolism, support secure vascular migration and proliferation, energy and biomass production, as well as redox homeostasis maintenance during vessel formation. Nevertheless, perturbation of EC metabolism instigates vascular dysregulation-associated diseases, especially cancer.

AIM OF REVIEW

In this review, we aim to discuss the metabolic regulation of angiogenesis by EC metabolites and metabolic enzymes, as well as prospect the possible therapeutic opportunities and strategies targeting EC metabolism.

KEY SCIENTIFIC CONCEPTS OF REVIEW

In this work, we discuss various aspects of EC metabolism considering normal and diseased vasculature. Of relevance, we highlight that the implications of EC metabolism-targeted intervention (chiefly by metabolic enzymes or metabolites) could be harnessed in orchestrating a spectrum of pathological angiogenesis-associated diseases.

Targeting PHGDH reverses the immunosuppressive phenotype of tumor-associated macrophages through α-ketoglutarate and mTORC1 signaling

Phosphoglycerate dehydrogenase (PHGDH) has emerged as a crucial factor in macromolecule synthesis, neutralizing oxidative stress, and regulating methylation reactions in cancer cells, lymphocytes, and endothelial cells. However, the role of PHGDH in tumor-associated macrophages (TAMs) is poorly understood. Here, we found that the T helper 2 (Th2) cytokine interleukin-4 and tumor-conditioned media upregulate the expression of PHGDH in macrophages and promote immunosuppressive M2 macrophage activation and proliferation. Loss of PHGDH disrupts cellular metabolism and mitochondrial respiration, which are essential for immunosuppressive macrophages. Mechanistically, PHGDH-mediated serine biosynthesis promotes α-ketoglutarate production, which activates mTORC1 signaling and contributes to the maintenance of an M2-like macrophage phenotype in the tumor microenvironment. Genetic ablation of PHGDH in macrophages from tumor-bearing mice results in attenuated tumor growth, reduced TAM infiltration, a phenotypic shift of M2-like TAMs toward an M1-like phenotype, downregulated PD-L1 expression and enhanced antitumor T-cell immunity. Our study provides a strong basis for further exploration of PHGDH as a potential target to counteract TAM-mediated immunosuppression and hinder tumor progression.

Decoding Serine Metabolism: Unveiling Novel Pathways for Evolving Cancer Therapies

Serine metabolism plays a pivotal role in cancer, making it an appealing therapeutic target. Two recent studies published in Nature Metabolism and Science Translational Medicine uncovered novel players and therapeutic opportunities within this crucial metabolic pathway. Papalazarou and colleagues employed genetic tools coupled with metabolomics and high-throughput imaging to identify and characterize membrane transporters involved in serine uptake and mitochondrial import in colorectal cancer. Notably, they showed that dual inhibition of these transporters in combination with impaired serine biosynthesis reduced tumor growth in xenograft models. In a parallel study, Zhang and colleagues identified isocitrate dehydrogenase I (IDH1) as a novel regulator of serine biosynthesis in non-small cell lung cancer. Through extensive mechanistic studies, they demonstrated that IDH1 enhances the expression of the key enzymes phosphoglycerate dehydrogenase and phosphoserine aminotransferase 1 via a noncanonical function independent of its enzymatic activity. Strikingly, pharmacologic disruption of this novel function of IDH1 not only diminished tumor growth but also enhanced the anticancer efficacy of dietary serine restriction in mouse models of lung cancer. Together, these studies advance our mechanistic understanding of how cancer cells fulfill their serine requirements and reveal innovative therapeutic avenues to deprive tumors of this vital nutrient.

TIE2 expression in hypertensive ICH and its therapeutic modulation with AKB-9778: Implications for brain vascular health

Hypertensive intracerebral hemorrhage (ICH) is a devastating condition, the molecular underpinnings of which remain not fully understood. By leveraging high-throughput transcriptome sequencing and network pharmacology analysis, this study unveils the significant role of the tyrosine kinase with immunoglobulin-like and EGF-like domains 2 (TIE2) in ICH pathogenesis. Compared to controls, a conspicuous downregulation of TIE2 was observed in the cerebral blood vessels of hypertensive ICH mice. In vitro assays with human brain microvascular endothelial cells (HBMEC), HBEC-5i revealed that modulation of TIE2 expression significantly influences cellular proliferation, migration, and angiogenesis, mediated via the Rap1/MEK/ERK signaling pathway. Notably, the small molecule AKB-9778 was identified to target and activate TIE2, affecting the functional attributes of HBEC-5i. In vivo experiments further demonstrated that combining AKB-9778 with antihypertensive drugs could mitigate the incidence and volume of bleeding in hypertensive ICH mouse models, suggesting potential therapeutic implications.

Serine Metabolism Regulates the Replicative Senescence of Human Dental Pulp Cells through Histone Methylation

Tissue regeneration therapy based on human dental pulp cells (hDPCs) faces the distinct challenge of cellular senescence during massive expansion in vitro. To further explore the regulatory mechanism of cellular senescence in hDPCs, we conduct experiments on young cells (Passage 5, P5) and replicative senescent (Passage 12, P12) hDPCs. The results confirm that hDPCs undergo replicative senescence with passaging, during which their ability to proliferate and osteogenic differentiation decreases. Notably, during replicative senescence, phosphoglycerate dehydrogenase (PHGDH), the key enzyme of the serine synthesis pathway (SSP), is significantly downregulated, as well as S-adenosylmethionine (SAM) levels, resulting in reduced H3K36me3 modification on Sirtuin 1 (SIRT1)and Runt-related transcription factor 2 (RUNX2) promoters. Inhibition of PHGDH leads to the same phenotype as replicative senescence. Serine supplementation fails to rescue the senescence phenotype caused by replicative senescence and inhibitors, in which folate metabolism-related genes, including serine hydroxymethyl transferase 2 (SHMT2), methylenetetrahydrofolate dehydrogenase 1(MTHFD1), methylenetetrahydrofolate dehydrogenase 2(MTHFD2), are notably decreased. Our research raised a possibility that PHGDH may be involved in cellular senescence by affecting folate metabolism and histone methylation in addition to serine biosynthesis, providing potential targets to prevent senescence.

A comprehensive review on signaling attributes of serine and serine metabolism in health and disease

Serine is a metabolite with ever-expanding metabolic and non-metabolic signaling attributes. By providing one‑carbon units for macromolecule biosynthesis and functional modifications, serine and serine metabolism largely impinge on cellular survival and function. Cancer cells frequently have a preference for serine metabolic reprogramming to create a conducive metabolic state for survival and aggressiveness, making intervention of cancer-associated rewiring of serine metabolism a promising therapeutic strategy for cancer treatment. Beyond providing methyl donors for methylation in modulation of innate immunity, serine metabolism generates formyl donors for mitochondrial tRNA formylation which is required for mitochondrial function. Interestingly, fully developed neurons lack the machinery for serine biosynthesis and rely heavily on astrocytic l-serine for production of d-serine to shape synaptic plasticity. Here, we recapitulate recent discoveries that address the medical significance of serine and serine metabolism in malignancies, mitochondrial-associated disorders, and neurodegenerative pathologies. Metabolic control and epigenetic- and posttranslational regulation of serine metabolism are also discussed. Given the metabolic similarities between cancer cells, neurons and germ cells, we further propose the relevance of serine metabolism in testicular homeostasis. Our work provides valuable hints for future investigations that will lead to a deeper understanding of serine and serine metabolism in cellular physiology and pathology.

Multi-omics analysis reveals GAPDH posttranscriptional regulation of IFN-γ and PHGDH as a metabolic checkpoint of microglia polarization

A "switch" in the metabolic pattern of microglia is considered to be required to meet the metabolic demands of cell survival and functions. However, how metabolic switches regulate microglial function remains controversial. We found here that exposure to amyloid-β triggers microglial inflammation accompanied by increasing GAPDH levels. The increase of GAPDH, a glycolysis enzyme, leads to the reduced release of interferon-γ (IFN-γ) from inflammatory microglia. Such alternation is translational and is regulated by the binding of glycolysis enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) to IFN-γ mRNA. GAPDH, by engaging/disengaging glycolysis and through influencing IFN-γ expression, regulates microglia functions, including phagocytosis and cytokine production. Phosphoglycerate dehydrogenase (PHGDH), screened from different state microglia by metabolomics combined with METARECON analysis, is a metabolic enzyme adjacent downstream of GAPDH and synthesizes serine on the collateral pathway derived from glycolysis. Polarization of microglial with PHGDH as a metabolic checkpoint can be bidirectionally regulated by adding IL-4 or giving PHGDH inhibitors. Therefore, regulation of metabolic enzymes not only reprograms metabolic patterns, but also manipulates microglia functions. Further study should be performed to explore the mechanism of metabolic checkpoints in human microglia or more in vivo animal experiments, and may expand to the effects of various metabolic substrates or enzyme, such as lipids and amino acids, on the functions of microglia.

ZSWIM4 inhibition improves chemosensitivity in epithelial ovarian cancer cells by suppressing intracellular glycine biosynthesis

BACKGROUND

Zinc finger SWIM-type containing 4 (ZSWIM4) induces drug resistance in breast cancer cells. However, its role in epithelial ovarian cancer (EOC) remains unknown. In this study, we aimed to investigate the clinical significance of ZSWIM4 expression in EOC and develop new clinical therapeutic strategies for EOC.

METHODS

ZSWIM4 expression in control and EOC tumor tissues was examined using immunohistochemistry. Lentiviral transduction, Cell Counting Kit-8 assay, tumorsphere formation assay, flow cytometry, western blotting, and animal xenograft model were used to assess the role of ZSWIM4 in chemotherapy. Cleavage Under Targets and Tagmentation (CUT&Tag) assays, chromatin immunoprecipitation assays, and luciferase reporter assays were used to confirm FOXK1-mediated upregulation of ZSWIM4 expression. The mechanism by which ZSWIM4 inhibition improves chemosensitivity was evaluated using RNA-sequencing. A ZSWIM4-targeting inhibitor was explored by virtual screening and surface plasmon resonance analysis. Patient-derived organoid (PDO) models were constructed from EOC tumor tissues with ZSWIM4 expression.

RESULTS

ZSWIM4 was overexpressed in EOC tumor tissues and impaired patient prognoses. Its expression correlated positively with EOC recurrence. ZSWIM4 expression was upregulated following carboplatin treatment, which, in turn, contributed to chemoresistance. Silencing ZSWIM4 expression sensitized EOC cells to carboplatin treatment in vitro and in vivo. FOXK1 could bind to the GTAAACA sequence of the ZSWIM4 promoter region to upregulate ZSWIM4 transcriptional activity and FOXK1 expression increased following carboplatin treatment, leading to an increase in ZSWIM4 expression. Mechanistically, ZSWIM4 knockdown downregulated the expression of several rate-limiting enzymes involved in glycine synthesis, causing a decrease in intracellular glycine levels, thus enhancing intracellular reactive oxygen species production induced by carboplatin treatment. Compound IPN60090 directly bound to ZSWIM4 protein and exerted a significant chemosensitizing effect in both EOC cells and PDO models.

CONCLUSIONS

ZSWIM4 inhibition enhanced EOC cell chemosensitivity by ameliorating intracellular glycine metabolism reprogramming, thus providing a new potential therapeutic strategy for EOC.

FLVCR1a Controls Cellular Cholesterol Levels through the Regulation of Heme Biosynthesis and Tricarboxylic Acid Cycle Flux in Endothelial Cells

Feline leukemia virus C receptor 1a (FLVCR1a), initially identified as a retroviral receptor and localized on the plasma membrane, has emerged as a crucial regulator of heme homeostasis. Functioning as a positive regulator of δ-aminolevulinic acid synthase 1 (ALAS1), the rate-limiting enzyme in the heme biosynthetic pathway, FLVCR1a influences TCA cycle cataplerosis, thus impacting TCA flux and interconnected metabolic pathways. This study reveals an unexplored link between FLVCR1a, heme synthesis, and cholesterol production in endothelial cells. Using cellular models with manipulated FLVCR1a expression and inducible endothelial-specific Flvcr1a-null mice, we demonstrate that FLVCR1a-mediated control of heme synthesis regulates citrate availability for cholesterol synthesis, thereby influencing cellular cholesterol levels. Moreover, alterations in FLVCR1a expression affect membrane cholesterol content and fluidity, supporting a role for FLVCR1a in the intricate regulation of processes crucial for vascular development and endothelial function. Our results underscore FLVCR1a as a positive regulator of heme synthesis, emphasizing its integration with metabolic pathways involved in cellular energy metabolism. Furthermore, this study suggests that the dysregulation of heme metabolism may have implications for modulating lipid metabolism. We discuss these findings in the context of FLVCR1a's potential heme-independent function as a choline importer, introducing additional complexity to the interplay between heme and lipid metabolism.

Serine synthesis pathway enzyme PHGDH is critical for muscle cell biomass, anabolic metabolism, and mTORC1 signaling

Cells use glycolytic intermediates for anabolism, e.g., via the serine synthesis and pentose phosphate pathways. However, we still understand poorly how these metabolic pathways contribute to skeletal muscle cell biomass generation. The first aim of this study was therefore to identify enzymes that limit protein synthesis, myotube size, and proliferation in skeletal muscle cells. We inhibited key enzymes of glycolysis, the pentose phosphate pathway, and the serine synthesis pathway to evaluate their importance in C2C12 myotube protein synthesis. Based on the results of this first screen, we then focused on the serine synthesis pathway enzyme phosphoglycerate dehydrogenase (PHGDH). We used two different PHGDH inhibitors and mouse C2C12 and human primary muscle cells to study the importance and function of PHGDH. Both myoblasts and myotubes incorporated glucose-derived carbon into proteins, RNA, and lipids, and we showed that PHGDH is essential in these processes. PHGDH inhibition decreased protein synthesis, myotube size, and myoblast proliferation without cytotoxic effects. The decreased protein synthesis in response to PHGDH inhibition appears to occur mainly mechanistic target of rapamycin complex 1 (mTORC1)-dependently, as was evident from experiments with insulin-like growth factor 1 and rapamycin. Further metabolomics analyses revealed that PHGDH inhibition accelerated glycolysis and altered amino acid, nucleotide, and lipid metabolism. Finally, we found that supplementing an antioxidant and redox modulator, N-acetylcysteine, partially rescued the decreased protein synthesis and mTORC1 signaling during PHGDH inhibition. The data suggest that PHGDH activity is critical for skeletal muscle cell biomass generation from glucose and that it regulates protein synthesis and mTORC1 signaling.NEW & NOTEWORTHY The use of glycolytic intermediates for anabolism was demonstrated in both myoblasts and myotubes, which incorporate glucose-derived carbon into proteins, RNA, and lipids. We identify phosphoglycerate dehydrogenase (PHGDH) as a critical enzyme in those processes and also for muscle cell hypertrophy, proliferation, protein synthesis, and mTORC1 signaling. Our results thus suggest that PHGDH in skeletal muscle is more than just a serine-synthesizing enzyme.

Serine metabolism in macrophage polarization

OBJECTIVE

Emerging studies have revealed that macrophages possess different dependences on the uptake, synthesis, and metabolism of serine for their activation and functionalization, necessitating our insight into how serine availability and utilization impact macrophage activation and inflammatory responses.

METHODS

This article summarizes the reports published domestically and internationally about the serine uptake, synthesis, and metabolic flux by the macrophages polarizing with distinct stimuli and under different pathologic conditions, and particularly analyzes how altered serine metabolism rewires the metabolic behaviors of polarizing macrophages and their genetic and epigenetic reprogramming.

RESULTS

Macrophages dynamically change serine metabolism to orchestrate their anabolism, redox balance, mitochondrial function, epigenetics, and post-translation modification, and thus match the distinct needs for both classical and alternative activation.

CONCLUSION

Serine metabolism coordinates multiple metabolic pathways to tailor macrophage polarization and their responses to different pathogenic attacks and thus holds the potential as therapeutic target for types of acute and chronic inflammatory diseases.

Molecular and metabolic orchestration of the lymphatic vasculature in physiology and pathology

Lymphangiogenesis refers to the generation of new lymphatic vessels from pre-existing ones. During development and particular adult states, lymphatic endothelial cells (LEC) undergo reprogramming of their transcriptomic and signaling networks to support the high demands imposed by cell proliferation and migration. Although there has been substantial progress in identifying growth factors and signaling pathways controlling lymphangiogenesis in the last decades, insights into the role of metabolism in lymphatic cell functions are just emerging. Despite numerous similarities between the main metabolic pathways existing in LECs, blood ECs (BEC) and other cell types, accumulating evidence has revealed that LECs acquire a unique metabolic signature during lymphangiogenesis, and their metabolic engine is intertwined with molecular regulatory networks, resulting in a tightly regulated and interconnected process. Considering the implication of lymphatic dysfunction in cancer and lymphedema, alongside other pathologies, recent findings hold promising opportunities to develop novel therapeutic approaches. In this review, we provide an overview of the status of knowledge in the molecular and metabolic network regulating the lymphatic vasculature in health and disease.

Lycorine eliminates B-cell acute lymphoblastic leukemia cells by targeting PSAT1 through the serine/glycine metabolic pathway

B-cell acute lymphoblastic leukemia (B-ALL) has been confirmed as the most common malignant hematologic neoplasm among children. A novel antitumor mechanism of lycorine was elucidated in this study. As revealed by the result of this study, lycorine significantly inhibited the growth and proliferation of REH and NALM-6 and induced their apoptosis. The result of the RNA-seq analysis suggested that lycorine targeted PSAT1 of serine/glycine metabolism in B-ALL cells. As indicated by the result of the GSEA analysis, the genes enriched in the amino acid metabolic pathways were down-regulated by lycorine. As revealed by the results of ectopic expression, shRNA knockdown assays, and further liquid-phase tandem mass spectrometry (LC-MS) analysis, lycorine reduced serine/glycine metabolites by down-regulating PSAT1, further disrupting carbon metabolism and eliminating B-ALL cells. Furthermore, lycorine showed a synergistic effect with cytarabine in ALL treatments. Lastly, lycorine significantly down-regulated leukemia progression in the cell line-derived xenograft (CDX) model. In brief, this study has suggested for the first time that lycorine is a promising anti-ALL drug, and a novel amino acid metabolism-associated property of lycorine was identified.

Myotube growth is associated with cancer-like metabolic reprogramming and is limited by phosphoglycerate dehydrogenase

The Warburg effect links growth and glycolysis in cancer. A key purpose of the Warburg effect is to generate glycolytic intermediates for anabolic reactions, such as nucleotides → RNA/DNA and amino acids → protein synthesis. The aim of this study was to investigate whether a similar 'glycolysis-for-anabolism' metabolic reprogramming also occurs in hypertrophying skeletal muscle. To interrogate this, we first induced C2C12 myotube hypertrophy with IGF-1. We then added 14C glucose to the differentiation medium and measured radioactivity in isolated protein and RNA to establish whether 14C had entered anabolism. We found that especially protein became radioactive, suggesting a glucose → glycolytic intermediates → non-essential amino acid(s) → protein series of reactions, the rate of which was increased by IGF-1. Next, to investigate the importance of glycolytic flux and non-essential amino acid synthesis for myotube hypertrophy, we exposed C2C12 and primary mouse myotubes to the glycolysis inhibitor 2-Deoxy-d-glucose (2DG). We found that inhibiting glycolysis lowered C2C12 and primary myotube size. Similarly, siRNA silencing of PHGDH, the key enzyme of the serine biosynthesis pathway, decreased C2C12 and primary myotube size; whereas retroviral PHGDH overexpression increased C2C12 myotube size. Together these results suggest that glycolysis is important for hypertrophying myotubes, which reprogram their metabolism to facilitate anabolism, similar to cancer cells.

Dietary fat and lipid metabolism in the tumor microenvironment

Metabolic reprogramming has been considered a core hallmark of cancer, in which excessive accumulation of lipids promote cancer initiation, progression and metastasis. Lipid metabolism often includes the digestion and absorption of dietary fat, and the ways in which cancer cells utilize lipids are often influenced by the complex interactions within the tumor microenvironment. Among multiple cancer risk factors, obesity has a positive association with multiple cancer types, while diets like calorie restriction and fasting improve health and delay cancer. Impact of these diets on tumorigenesis or cancer prevention are generally studied on cancer cells, despite heterogeneity of the tumor microenvironment. Cancer cells regularly interact with these heterogeneous microenvironmental components, including immune and stromal cells, to promote cancer progression and metastasis, and there is an intricate metabolic crosstalk between these compartments. Here, we focus on discussing fat metabolism and response to dietary fat in the tumor microenvironment, focusing on both immune and stromal components and shedding light on therapeutic strategies surrounding lipid metabolic and signaling pathways.

Integrative Analysis of Transcriptomic and Lipidomic Profiles Reveals a Differential Subcutaneous Adipose Tissue Mechanism among Ningxiang Pig and Berkshires, and Their Offspring

Adipose tissue composition contributes greatly to the quality and nutritional value of meat. Transcriptomic and lipidomic techniques were used to investigate the molecular mechanisms of the differences in fat deposition in Ningxiang pigs, Berkshires and F1 offspring. Transcriptomic analysis identified 680, 592, and 380 DEGs in comparisons of Ningxiang pigs vs. Berkshires, Berkshires vs. F1 offspring, and Ningxiang pigs vs. F1 offspring. The lipidomic analysis screened 423, 252, and 50 SCLs in comparisons of Ningxiang pigs vs. Berkshires, Berkshires vs. F1 offspring, and Ningxiang pigs vs. F1 offspring. Lycine, serine, and the threonine metabolism pathway, fatty acid biosynthesis and metabolism-related pathways were significantly enriched in comparisons of Berkshires vs. Ningxiang pigs and Berkshires vs. F1 offspring. The DEGs (PHGDH, LOC110256000) and the SCLs (phosphatidylserines) may have a great impact on the glycine, serine, and the threonine metabolism pathway. Moreover, the DEGs (FASN, ACACA, CBR4, SCD, ELOV6, HACD2, CYP3A46, CYP2B22, GPX1, and GPX3) and the SCLs (palmitoleic acid, linoleic acid, arachidonic acid, and icosadienoic acid) play important roles in the fatty acid biosynthesis and metabolism of fatty acids. Thus, the difference in fat deposition among Ningxiang pig, Berkshires, and F1 offspring may be caused by differences in the expression patterns of key genes in multiple enriched KEGG pathways. This research revealed multiple lipids that are potentially available biological indicators and screened key genes that are potential targets for molecular design breeding. The research also explored the molecular mechanisms of the difference in fat deposition among Ningxiang pig, Berkshires, and F1 pigs, and provided an insight into selection for backfat thickness and the fat composition of adipose tissue for future breeding strategies.

New insights in the targets of action of dimethyl fumarate in endothelial cells: effects on energetic metabolism and serine synthesis in vitro and in vivo

Dimethyl fumarate is an ester from the Krebs cycle intermediate fumarate. This drug is approved and currently used for the treatment of psoriasis and multiple sclerosis, and its anti-angiogenic activity was reported some years ago. Due to the current clinical relevance of this compound and the recently manifested importance of endothelial cell metabolism on the angiogenic switch, we wanted to elucidate whether dimethyl fumarate has an effect on energetic metabolism of endothelial cells. Different experimental approximations were performed in endothelial cells, including proteomics, isotope tracing and metabolomics experimental approaches, in this work we studied the possible role of dimethyl fumarate in endothelial cell energetic metabolism. We demonstrate for the first time that dimethyl fumarate promotes glycolysis and diminishes cell respiration in endothelial cells, which could be a consequence of a down-regulation of serine and glycine synthesis through inhibition of PHGDH activity in these cells. Dimethyl fumarate alters the energetic metabolism of endothelial cells in vitro and in vivo through an unknown mechanism, which could be the cause or the consequence of its pharmacological activity. This new discovery on the targets of this compound could open a new field of study regarding the mechanism of action of dimethyl fumarate.

Postnatal hyperglycemia alters amino acid profile in retinas (model of Phase I ROP)

Nutritional deprivation occurring in most preterm infants postnatally can induce hyperglycemia, a significant and independent risk factor for suppressing physiological retinal vascularization (Phase I retinopathy of prematurity (ROP)), leading to compensatory but pathological neovascularization. Amino acid supplementation reduces retinal neovascularization in mice. Little is known about amino acid contribution to Phase I ROP. In mice modeling hyperglycemia-associated Phase I ROP, we found significant changes in retinal amino acids (including most decreased L-leucine, L-isoleucine, and L-valine). Parenteral L-isoleucine suppressed physiological retinal vascularization. In premature infants, severe ROP was associated with a higher mean intake of parenteral versus enteral amino acids in the first two weeks of life after adjustment for treatment group, gestational age at birth, birth weight, and sex. The number of days with parenteral amino acids support independently predicted severe ROP. Further understanding and modulating amino acids may help improve nutritional intervention and prevent Phase I ROP.

Beyond energy and growth: the role of metabolism in developmental signaling, cell behavior and diapause

Metabolism is crucial for development through supporting cell growth, energy production, establishing cell identity, developmental signaling and pattern formation. In many model systems, development occurs alongside metabolic transitions as cells differentiate and specialize in metabolism that supports new functions. Some cells exhibit metabolic flexibility to circumvent mutations or aberrant signaling, whereas other cell types require specific nutrients for developmental progress. Metabolic gradients and protein modifications enable pattern formation and cell communication. On an organism level, inadequate nutrients or stress can limit germ cell maturation, implantation and maturity through diapause, which slows metabolic activities until embryonic activation under improved environmental conditions.

Multifaceted roles of mitochondria in wound healing and chronic wound pathogenesis

Mitochondria are intracellular organelles that play a critical role in numerous cellular processes including the regulation of metabolism, cellular stress response, and cell fate. Mitochondria themselves are subject to well-orchestrated regulation in order to maintain organelle and cellular homeostasis. Wound healing is a multifactorial process that involves the stringent regulation of several cell types and cellular processes. In the event of dysregulated wound healing, hard-to-heal chronic wounds form and can place a significant burden on healthcare systems. Importantly, treatment options remain limited owing to the multifactorial nature of chronic wound pathogenesis. One area that has received more attention in recent years is the role of mitochondria in wound healing. With regards to this, current literature has demonstrated an important role for mitochondria in several areas of wound healing and chronic wound pathogenesis including metabolism, apoptosis, and redox signalling. Additionally, the influence of mitochondrial dynamics and mitophagy has also been investigated. However, few studies have utilised patient tissue when studying mitochondria in wound healing, instead using various animal models. In this review we dissect the current knowledge of the role of mitochondria in wound healing and discuss how future research can potentially aid in the progression of wound healing research.

Serine Metabolic Reprogramming in Tumorigenesis, Tumor Immunity, and Clinical Treatment

Serine has been recently identified as an essential metabolite for oncogenesis, progression, and adaptive immunity. Influenced by many physiologic or tumor environmental factors, the metabolic pathways of serine synthesis, uptake, and usage are heterogeneously reprogrammed and frequently amplified in tumor or tumor-associated cells. The hyperactivation of serine metabolism promotes abnormal cellular nucleotide/protein/lipid synthesis, mitochondrial function, and epigenetic modifications, which drive malignant transformation, unlimited proliferation, metastasis, immunosuppression, and drug resistance of tumor cells. Dietary restriction of serine or phosphoglycerate dehydrogenase depletion mitigates tumor growth and extends the survival of tumor patients. Correspondingly, these findings triggered a boom in the development of novel therapeutic agents targeting serine metabolism. In this study, recent discoveries in the underlying mechanism and cellular function of serine metabolic reprogramming are summarized. The vital role of serine metabolism in oncogenesis, tumor stemness, tumor immunity, and therapeutic resistance is outlined. Finally, some potential tumor therapeutic concepts, strategies, and limitations of targeting the serine metabolic pathway are described in detail. Taken together, this review underscores the importance of serine metabolic reprogramming in tumorigenesis and progression and highlights new opportunities for dietary restriction or selective pharmacologic intervention.

Sources and Sinks of Serine in Nutrition, Health, and Disease

Amino acid dysregulation has emerged as an important driver of disease progression in various contexts. l-Serine lies at a central node of metabolism, linking carbohydrate metabolism, transamination, glycine, and folate-mediated one-carbon metabolism to protein synthesis and various downstream bioenergetic and biosynthetic pathways. l-Serine is produced locally in the brain but is sourced predominantly from glycine and one-carbon metabolism in peripheral tissues via liver and kidney metabolism. Compromised regulation or activity of l-serine synthesis and disposal occurs in the context of genetic diseases as well as chronic disease states, leading to low circulating l-serine levels and pathogenesis in the nervous system, retina, heart, and aging muscle. Dietary interventions in preclinical models modulate sensory neuropathy, retinopathy, tumor growth, and muscle regeneration. A serine tolerance test may provide a quantitative readout of l-serine homeostasis that identifies patients who may be susceptible to neuropathy or responsive to therapy.

Endothelial cells require functional FLVCR1a during developmental and adult angiogenesis

The Feline Leukemia Virus Subgroup C Receptor 1a (FLVCR1a) is a transmembrane heme exporter essential for embryonic vascular development. However, the exact role of FLVCR1a during blood vessel development remains largely undefined. Here, we show that FLVCR1a is highly expressed in angiogenic endothelial cells (ECs) compared to quiescent ECs. Consistently, ECs lacking FLVCR1a give rise to structurally and functionally abnormal vascular networks in multiple models of developmental and pathologic angiogenesis. Firstly, zebrafish embryos without FLVCR1a displayed defective intersegmental vessels formation. Furthermore, endothelial-specific Flvcr1a targeting in mice led to a reduced radial expansion of the retinal vasculature associated to decreased EC proliferation. Moreover, Flvcr1a null retinas showed defective vascular organization and loose attachment of pericytes. Finally, adult neo-angiogenesis is severely affected in murine models of tumor angiogenesis. Tumor blood vessels lacking Flvcr1a were disorganized and dysfunctional. Collectively, our results demonstrate the critical role of FLVCR1a as a regulator of developmental and pathological angiogenesis identifying FLVCR1a as a potential therapeutic target in human diseases characterized by aberrant neovascularization.

PHGDH promotes esophageal squamous cell carcinoma progression via Wnt/β-catenin pathway

PURPOSE

Esophageal squamous carcinoma (ESCC) with a high incidence in China, lacks effective therapeutic targets. Phosphoglycerate dehydrogenase (PHGDH) is a key enzyme in serine biosynthesis. However, the biological role of PHGDH in ESCC has not been revealed.

METHODS

The expression of PHGDH in ESCC was investigated by UALCAN. The relationship between PHGDH expression and its prognostic value was analyzed by Kaplan-Meier and univariate Cox regression. Further, the potential functions of PHGDH involved in ESCC were explored through DAVID database and GSEA software. In addition, the expression of PHGDH was verified in ESCC. Then, the effects of PHGDH knockdown on ESCC were evaluated in vitro and in vivo by cell proliferation, clone formation, cell cycle, apoptosis, tube formation assays and ESCC cells derived xenograft model. In addition, western blotting and immunohistochemistry were used to detect the expression of Wnt/β-catenin pathway which was associated with PHGDH.

RESULTS

Bioinformatics analysis found that PHGDH was highly expressed in ESCC, and meaningfully, patients with high PHGDH expression had a poor prognosis. Moreover, the overexpression of PHGDH was verified in ESCC. Afterwards, PHGDH knockdown inhibited the cell proliferation, induced cell cycle arrest and apoptosis in ESCC cells, and inhibited the angiogenesis of HUVECs induced by ESCC conditioned medium, as well as inhibited the growth of xenograft tumor. Mechanistically, PHGDH knockdown inhibited Wnt/β-catenin signaling pathway in ESCC.

CONCLUSION

High expression of PHGDH predicts a poor prognosis for ESCC. PHGDH knockdown inhibits ESCC progression by suppressing Wnt/β-catenin signaling pathway, indicating that PHGDH might be a potential target for ESCC therapy.

Heme: The Lord of the Iron Ring

Heme is an iron-protoporphyrin complex with an essential physiologic function for all cells, especially for those in which heme is a key prosthetic group of proteins such as hemoglobin, myoglobin, and cytochromes of the mitochondria. However, it is also known that heme can participate in pro-oxidant and pro-inflammatory responses, leading to cytotoxicity in various tissues and organs such as the kidney, brain, heart, liver, and in immune cells. Indeed, heme, released as a result of tissue damage, can stimulate local and remote inflammatory reactions. These can initiate innate immune responses that, if left uncontrolled, can compound primary injuries and promote organ failure. In contrast, a cadre of heme receptors are arrayed on the plasma membrane that is designed either for heme import into the cell, or for the purpose of activating specific signaling pathways. Thus, free heme can serve either as a deleterious molecule, or one that can traffic and initiate highly specific cellular responses that are teleologically important for survival. Herein, we review heme metabolism and signaling pathways, including heme synthesis, degradation, and scavenging. We will focus on trauma and inflammatory diseases, including traumatic brain injury, trauma-related sepsis, cancer, and cardiovascular diseases where current work suggests that heme may be most important.

Phosphoglycerate dehydrogenase activates PKM2 to phosphorylate histone H3T11 and attenuate cellular senescence

Vascular endothelial cells (ECs) senescence correlates with the increase of cardiovascular diseases in ageing population. Although ECs rely on glycolysis for energy production, little is known about the role of glycolysis in ECs senescence. Here, we report a critical role for glycolysis-derived serine biosynthesis in preventing ECs senescence. During senescence, the expression of serine biosynthetic enzyme PHGDH is significantly reduced due to decreased transcription of the activating transcription factor ATF4, which leads to reduction of intracellular serine. PHGDH prevents premature senescence primarily by enhancing the stability and activity of pyruvate kinase M2 (PKM2). Mechanistically, PHGDH interacts with PKM2, which prevents PCAF-catalyzed PKM2 K305 acetylation and subsequent degradation by autophagy. In addition, PHGDH facilitates p300-catalyzed PKM2 K433 acetylation, which promotes PKM2 nuclear translocation and stimulates its activity to phosphorylate H3T11 and regulate the transcription of senescence-associated genes. Vascular endothelium-targeted expression of PHGDH and PKM2 ameliorates ageing in mice. Our findings reveal that enhancing serine biosynthesis could become a therapy to promote healthy ageing.

PHGDH-mediated endothelial metabolism drives glioblastoma resistance to chimeric antigen receptor T cell immunotherapy

The efficacy of immunotherapy is limited by the paucity of T cells delivered and infiltrated into the tumors through aberrant tumor vasculature. Here, we report that phosphoglycerate dehydrogenase (PHGDH)-mediated endothelial cell (EC) metabolism fuels the formation of a hypoxic and immune-hostile vascular microenvironment, driving glioblastoma (GBM) resistance to chimeric antigen receptor (CAR)-T cell immunotherapy. Our metabolome and transcriptome analyses of human and mouse GBM tumors identify that PHGDH expression and serine metabolism are preferentially altered in tumor ECs. Tumor microenvironmental cues induce ATF4-mediated PHGDH expression in ECs, triggering a redox-dependent mechanism that regulates endothelial glycolysis and leads to EC overgrowth. Genetic PHGDH ablation in ECs prunes over-sprouting vasculature, abrogates intratumoral hypoxia, and improves T cell infiltration into the tumors. PHGDH inhibition activates anti-tumor T cell immunity and sensitizes GBM to CAR T therapy. Thus, reprogramming endothelial metabolism by targeting PHGDH may offer a unique opportunity to improve T cell-based immunotherapy.

[Blood metabolites in preterm infants with retinopathy of prematurity based on tandem mass spectrometry: a preliminary study]

OBJECTIVES

To study new biomarkers for the early diagnosis of retinopathy of prematurity (ROP) by analyzing the differences in blood metabolites based on liquid chromatography-tandem mass spectrometry (LC-MS/MS) and metabolomics.

METHODS

Dried blood spots were collected from 21 infants with ROP (ROP group) and 21 infants without ROP (non-ROP group) who were hospitalized in the Sixth Affiliated Hospital of Sun Yat-sen University from January 2013 to December 2016. LC-MS/MS was used to measure the metabolites, and orthogonal partial least squares-discriminant analysis was used to search for differentially expressed metabolites and biomarkers.

RESULTS

There was a significant difference in blood metabolic profiles between the ROP and non-ROP groups. The pattern recognition analysis, Score-plot, and weight analysis obtained 10 amino acids with a relatively large difference. Further statistical analysis showed that the ROP group had significant increases in blood levels of glutamic acid, leucine, aspartic acid, ornithine, and glycine compared with the non-ROP group (P<0.05). The receiver operating characteristic curve analysis showed that glutamic acid and ornithine had the highest value in diagnosing ROP.

CONCLUSIONS

Blood metabolites in preterm infants with ROP are different from those without ROP. Glutamic acid and ornithine are the metabolic markers for diagnosing ROP. LC-MS/MS combined with metabolomics analysis has a potential application value in the early identification and diagnosis of ROP.

CSN6 Mediates Nucleotide Metabolism to Promote Tumor Development and Chemoresistance in Colorectal Cancer

Metabolic reprogramming can contribute to colorectal cancer progression and therapy resistance. Identification of key regulators of colorectal cancer metabolism could provide new approaches to improve treatment and reduce recurrence. Here, we demonstrate a critical role for the COP9 signalosome subunit CSN6 in rewiring nucleotide metabolism in colorectal cancer. Transcriptomic analysis of colorectal cancer patient samples revealed a correlation between CSN6 expression and purine and pyrimidine metabolism. A colitis-associated colorectal cancer model established that Csn6 intestinal conditional deletion decreased tumor development and altered nucleotide metabolism. CSN6 knockdown increased the chemosensitivity of colorectal cancer cells in vitro and in vivo, which could be partially reversed with nucleoside supplementation. Isotope metabolite tracing showed that CSN6 loss reduced de novo nucleotide synthesis. Mechanistically, CSN6 upregulated purine and pyrimidine biosynthesis by increasing expression of PHGDH, a key enzyme in the serine synthesis pathway. CSN6 inhibited β-Trcp-mediated DDX5 polyubiquitination and degradation, which in turn promoted DDX5-mediated PHGDH mRNA stabilization, leading to metabolic reprogramming and colorectal cancer progression. Butyrate treatment decreased CSN6 expression and improved chemotherapy efficacy. These findings unravel the oncogenic role of CSN6 in regulating nucleotide metabolism and chemosensitivity in colorectal cancer.

SIGNIFICANCE

CSN6 deficiency inhibits colorectal cancer development and chemoresistance by downregulating PHGDH to block nucleotide biosynthesis, providing potential therapeutic targets to improve colorectal cancer treatment.

Serum Starvation Accelerates Intracellular Metabolism in Endothelial Cells

Periods of low energy supply are challenging conditions for organisms and cells during fasting or famine. Although changes in nutrient levels in the blood are first sensed by endothelial cells, studies on their metabolic adaptations to diminished energy supply are lacking. We analyzed the dynamic metabolic activity of human umbilical vein endothelial cells (HUVECs) in basal conditions and after serum starvation. Metabolites of glycolysis, the tricarboxylic acid (TCA) cycle, and the glycerol pathway showed lower levels after serum starvation, whereas amino acids had increased levels. A metabolic flux analysis with ¹³C-glucose or ¹³C-glutamine labeling for different time points reached a plateau phase of incorporation after 30 h for ¹³C-glucose and after 8 h for ¹³C-glutamine under both experimental conditions. Notably, we observed a faster label incorporation for both ¹³C-glucose and ¹³C-glutamine after serum starvation. In the linear range of label incorporation after 3 h, we found a significantly faster incorporation of central carbon metabolites after serum starvation compared to the basal state. These findings may indicate that endothelial cells develop increased metabolic activity to cope with energy deficiency. Physiologically, it can be a prerequisite for endothelial cells to form new blood vessels under unfavorable conditions during the process of angiogenesis in vivo.

Endothelial senescence in vascular diseases: current understanding and future opportunities in senotherapeutics

Senescence compromises the essential role that the endothelium plays in maintaining vascular homeostasis, so promoting endothelial dysfunction and the development of age-related vascular diseases. Their biological and clinical significance calls for strategies for identifying and therapeutically targeting senescent endothelial cells. While senescence and endothelial dysfunction have been studied extensively, distinguishing what is distinctly endothelial senescence remains a barrier to overcome for an effective approach to addressing it. Here, we review the mechanisms underlying endothelial senescence and the evidence for its clinical importance. Furthermore, we discuss the current state and the limitations in the approaches for the detection and therapeutic intervention of target cells, suggesting potential directions for future research.

The new landscape of differentially expression proteins in placenta tissues of gestational diabetes based on iTRAQ proteomics

INTRODUCTION

Gestational diabetes mellitus (GDM) refers to abnormal glucose tolerance that occurs or is firstly diagnosed during pregnancy. GDM is related to various adverse pregnancy outcomes, but GDM pathogeny has not been fully elucidated. Nevertheless, previous studies have observed that many proteins in the placentas of patients with GDM are dysregulated. The present study aimed to establish a novel differentially expressed protein (DEP) landscape of GDM and normal maternal placentas and to explore the possible connection between DEPs and GDM pathogenesis. This study provides new insights into the mechanism of GDM and should make an important contribution to the development of biomarkers.

METHODS

The morphological characteristics of the placenta were observed on 30 GDM and normal maternal placental tissues stained with haematoxylin and eosin. Isobaric tags for relative and absolute quantitation (iTRAQ) was used in the proteomics screening of the DEPs of the normal and GDM maternal placentas. Bioinformatics analysis was performed on the DEPs, and parallel reaction monitoring (PRM) was performed to verify the DEPs. Finally, the quantitative analysis of iTRAQ and PRM was verified by immunohistochemical assay.

RESULTS

A total of 68 DEPs in the GDM placenta were identified with iTRAQ proteomics experiment, comprising 21 up-regulated and 47 down-regulated DEPs. Bioinformatics analysis showed that the regulation of transport, catabolic process of non-coding RNA, cytoskeleton and cell binding were the most abundant Gene Ontology terms, and RNA degradation was an important pathway for significant enrichment. Protein-protein interaction network analysis showed that heterogeneous nuclear ribonucleoproteins A2/B1 (HNRNPA2B1), heterogeneous nuclear ribonucleoprotein A/B (HNRNPAB), heterogeneous nuclear ribonucleoprotein L (HNRNPL) and heterogeneous nuclear ribonucleoprotein A3 (HNRNPA3) were the cores of the up-regulated proteins. Band 3 anion transport protein (SLC4A1), spectrin beta chain erythrocytic (SPTB), ankyrin-1 (ANK1), spectrin beta chain non-erythrocytic 2 (SPTBN2), D-3-phosphoglycerate dehydrogenase (PHGDH) and exosome complex component RRP42 (EXOSC7) were the cores of the down-regulated proteins. These proteins are involved in the binding, splicing, processing, transport and degradation of RNA and in the formation and maintenance of the cytoskeleton. PRM verification results showed that seven proteins, namely, epiplakin (EPPK1), cold-inducible RNA-binding protein (CIRBP), HNRNPA2B1, HNRNPAB, HNRNPL, Ras-related protein Rab-21 (RAB21) and Ras-related protein Rab-3B (RAB3B), were up-regulated, whereas SPTB and SLC4A1 were down-regulated. The results of immunohistochemical assay also showed that the expression of five proteins, namely EPPK1, HNRNPA2B1, HNRNPAB, CIRBP and RAB21, were significantly higher in GDM placental tissues (P < 0.01). The GDM placentas showed changes in the morphological evaluation, including poor villous maturation, obvious increase in the number of syncytiotrophoblast nodules, thickening of the wall of dry villous arterioles with lumen stenosis, increased fibrinous exudation and excessive filling of villous interstitial vessels.

DISCUSSION

Differentially expressed proteins related to a variety of biological processes in the GDM placenta were found. Fourteen proteins, namely, HNRNPA2B1, HNRNPAB, HNRNPL, HNRNPA3, EPPK1, CIRBP, RAB21, RAB3B, SLC4A1, SPTB, ANK1, SPTBN2, PHGDH and EXOSC7, which were differentially expressed in the placenta, may play an important role in regulating the occurrence and development of gestational diabetes through multi-channel and multi-link regulation.

Human Placental Endothelial Cell and Trophoblast Heterogeneity and Differentiation Revealed by Single-Cell RNA Sequencing

BACKGROUND

The placenta is an important organ for fetal and maternal health during pregnancy and impacts offspring health late in life. Defects in placental vasculature and trophoblast have been identified in several pregnancy complications. Thus, the detailed molecular profile and heterogeneity of endothelial cells and trophoblasts in placentas will aid us in better understanding placental behaviors and improving pregnancy outcomes.

METHODS

Single-cell RNA sequencing (scRNA-seq) was performed to profile the transcriptomics of human placental villous tissues from eleven patients with normal pregnancies in the first and second trimesters (6-16 weeks of gestation).

RESULTS

The transcriptomic landscape of 52,179 single cells was obtained, and the cells were classified as trophoblasts, fibroblasts, endothelial cells, erythroid cells, Hofbauer cells, and macrophages. Our analysis further revealed the three subtypes of placental endothelial cells, with distinct metabolic signatures and transcription factor regulatory networks. We also determined the transcriptomic features of the trophoblast subpopulations and characterized two distinct populations of progenitor cells in cytotrophoblasts, which were capable of differentiating to extravillous trophoblasts and syncytiotrophoblasts, respectively.

CONCLUSIONS

Our study provided a high-resolution molecular profile of the human placenta between 6 and 16 weeks of gestation. Our data revealed the placental cell complexity and demonstrated the transcriptional networks and signaling involved in placental endothelial and trophoblast differentiation during early pregnancy, which will be a resource for future studies of the human placental development.

The chromatin remodeler CHD6 promotes colorectal cancer development by regulating TMEM65-mediated mitochondrial dynamics via EGF and Wnt signaling

Chromodomain helicase DNA binding protein (CHD) family plays critical roles in regulating gene transcription. The family is linked to cancer disease, but the family member's role in tumorigenesis remains largely unknown. Here, we report that CHD6 is highly expressed in colorectal cancer (CRC). CHD6 knockdown inhibited cancer cell proliferation, migration, invasion, and tumorigenesis. Consistently, Villin-specific Chd6 knockout in mice attenuates cancer formation in AOM/DSS model. We found that aberrant EGF signals promoted the stability of CHD6 by diminishing ubiquitin-mediated degradation. EGF signal inhibits GSK3β activity, which in turn prevents phosphodegron formation of CHD6, thereby hindering E3 ligase FBXW7-mediated CHD6 ubiquitination and degradation. CHD6's chromatin remodeler activity engages in binding Wnt signaling transcription factor TCF4 to facilitate the transcriptional expression of TMEM65, a mitochondrial inner membrane protein involved in ATP production and mitochondrial dynamics. In addition, Wnt signaling is also an upstream regulator of CHD6. CHD6 promoter contains TCF4 and β-catenin binding site, and CHD6 can be transcriptionally activated by Wnt ligand to facilitate TMEM65 transcription. Thus CHD6-TMEM65 axis can be regulated by both EGF and Wnt signaling pathways through two different mechanisms. We further illustrate that CHD6-TMEM65 axis is deregulated in cancer and that co-administration of Wnt inhibitor LGK974 and the anti-EGFR monoclonal antibody cetuximab largely restricted the growth of patient-derived xenografts of CRC. Targeting CHD6-TMEM65 axis may be effective for cancer intervention.

Amino acid transporter SLC38A5 regulates developmental and pathological retinal angiogenesis

Amino acid (AA) metabolism in vascular endothelium is important for sprouting angiogenesis. SLC38A5 (solute carrier family 38 member 5), an AA transporter, shuttles neutral AAs across cell membrane, including glutamine, which may serve as metabolic fuel for proliferating endothelial cells (ECs) to promote angiogenesis. Here, we found that Slc38a5 is highly enriched in normal retinal vascular endothelium, and more specifically, in pathological sprouting neovessels. Slc38a5 is suppressed in retinal blood vessels from Lrp5-/- and Ndpy/- mice, both genetic models of defective retinal vascular development with Wnt signaling mutations. Additionally, Slc38a5 transcription is regulated by Wnt/β-catenin signaling. Genetic deficiency of Slc38a5 in mice substantially delays retinal vascular development and suppresses pathological neovascularization in oxygen-induced retinopathy modeling ischemic proliferative retinopathies. Inhibition of SLC38A5 in human retinal vascular ECs impairs EC proliferation and angiogenic function, suppresses glutamine uptake, and dampens vascular endothelial growth factor receptor 2. Together these findings suggest that SLC38A5 is a new metabolic regulator of retinal angiogenesis by controlling AA nutrient uptake and homeostasis in ECs.

Non-canonical phosphoglycerate dehydrogenase activity promotes liver cancer growth via mitochondrial translation and respiratory metabolism

Phosphoglycerate dehydrogenase (PHGDH) is a key serine biosynthesis enzyme whose aberrant expression promotes various types of tumors. Recently, PHGDH has been found to have some non-canonical functions beyond serine biosynthesis, but its specific mechanisms in tumorigenesis remain unclear. Here, we show that PHGDH localizes to the inner mitochondrial membrane and promotes the translation of mitochondrial DNA (mtDNA)-encoded proteins in liver cancer cells. Mechanistically, we demonstrate that mitochondrial PHGDH directly interacts with adenine nucleotide translocase 2 (ANT2) and then recruits mitochondrial elongation factor G2 (mtEFG2) to promote mitochondrial ribosome recycling efficiency, thereby promoting mtDNA-encoded protein expression and subsequent mitochondrial respiration. Moreover, we show that treatment with a mitochondrial translation inhibitor or depletion of mtEFG2 diminishes PHGDH-mediated tumor growth. Collectively, our findings uncover a previously unappreciated function of PHGDH in tumorigenesis acting via promotion of mitochondrial translation and bioenergetics.

Retinopathy of prematurity: Metabolic risk factors

At preterm birth, the retina is incompletely vascularized. Retinopathy of prematurity (ROP) is initiated by the postnatal suppression of physiological retinal vascular development that would normally occur in utero. As the neural retina slowly matures, increasing metabolic demand including in the peripheral avascular retina, leads to signals for compensatory but pathological neovascularization. Currently, only late neovascular ROP is treated. ROP could be prevented by promoting normal vascular growth. Early perinatal metabolic dysregulation is a strong but understudied risk factor for ROP and other long-term sequelae of preterm birth. We will discuss the metabolic and oxygen needs of retina, current treatments, and potential interventions to promote normal vessel growth including control of postnatal hyperglycemia, dyslipidemia and hyperoxia-induced retinal metabolic alterations. Early supplementation of missing nutrients and growth factors and control of supplemental oxygen promotes physiological retinal development. We will discuss the current knowledge gap in retinal metabolism after preterm birth.