Potassium Channels, Glucose Metabolism and Glycosylation in Cancer Cells

Potassium channels emerge as one of the crucial groups of proteins that shape the biology of cancer cells. Their involvement in processes like cell growth, migration, or electric signaling, seems obvious. However, the relationship between the function of K+ channels, glucose metabolism, and cancer glycome appears much more intriguing. Among the typical hallmarks of cancer, one can mention the switch to aerobic glycolysis as the most favorable mechanism for glucose metabolism and glycome alterations. This review outlines the interconnections between the expression and activity of potassium channels, carbohydrate metabolism, and altered glycosylation in cancer cells, which have not been broadly discussed in the literature hitherto. Moreover, we propose the potential mediators for the described relations (e.g., enzymes, microRNAs) and the novel promising directions (e.g., glycans-orinented drugs) for further research.

Deletion of the tyrosine phosphatase Shp2 in cervical cancer cells promotes reprogramming of glutamine metabolism

Shp2 is a nonreceptor protein tyrosine phosphatase that is overexpressed in cervical cancer. However, the role of Shp2 in the regulation of cervical cancer metabolism and tumorigenesis is unclear. EGFR signaling pathways are commonly dysregulated in cervical cancer. We showed that Shp2 knockout in cervical cancer cells decreased EGFR expression and downregulated downstream RAS-ERK activation. Although AKT was activated in Shp2 knockout cells, inhibition of AKT activation could not make cells more sensitive to death. Shp2 depletion inhibited cervical cancer cell proliferation and reduced tumor growth in a xenograft mouse model. ¹ H NMR spectroscopic analysis showed that glutamine, glutamate, succinate, creatine, glutathione, and UDP-GlcNAc were significantly changed in Shp2 knockout cells. The intracellular glutamine level was higher in Shp2 knockout cells than in control cells. Further analysis demonstrated that Shp2 knockout promoted glutaminolysis and glutathione production by up-regulating the glutamine metabolism-related genes such as glutaminase (GLS). However, inhibition of GLS did not always make cells sensitive to death, which was dependent on glucose concentration. The level of oxidative phosphorylation was significantly increased, accompanied by an increased generation of reactive oxygen species in Shp2 knockout cells. Shp2 deficiency increased c-Myc and c-Jun expression, which may be related to the upregulation of glutamine metabolism. These findings suggested that Shp2 regulates cervical cancer proliferation, glutamine metabolism, and tumorigenicity.

New insights into the metabolism of Th17 cells

T helper 17 (Th17) cells are IL-17-producing CD4 T cells that play a crucial role in autoimmune diseases. IL-17 is a key cytokine for host protection against mucosal and skin infection but is also one of the major pathogenic cytokines. IL-1 and IL-23 are requisite for stimulating pathogenic Th17 cell differentiation and proliferation. Therapeutics targeting the IL-17/IL-23 pathway are widely used clinically for the treatment of autoimmune diseases. Besides IL-17, pathogenic Th17 cells produce granulocyte-macrophage colony-stimulating factor, tumor necrosis factor α, interferon γ, IL-21 and IL-22. However, Th17-targeted therapy has not yet been established. T cell metabolism orchestrates T cell survival, cell differentiation, epigenetic change and function and each T cell subset favors a particular metabolic pathway. Recent studies have provided novel insights into the role of T cell metabolism in the pathogenesis of autoimmune diseases. The current review focuses on the role of Th17 cell metabolism in autoimmune diseases, particularly glycolysis, amino acid metabolism, lipid metabolism, as well as the regulators of these processes, including mTORC1. Therapeutics targeting T cell metabolism in autoimmune diseases could serve as a possible treatment option for patients who are refractory to or unresponsive to conventional therapy.

Metabolic rewiring in keratinocytes by miR-31-5p identifies therapeutic intervention for psoriasis

Besides genetic alterations, the cellular environment also determines disease onset and progression. When different cell types contribute to disease outcome, this imposes environmental challenges as different cell types likely differ in their extracellular dependencies. Hsa-microRNA-31-5p (miR-31) is highly expressed in keratinocytes of psoriatic skin, and we show that expression in keratinocytes is induced by limited glucose availability and enables increased survival under limiting glucose conditions by increasing glutamine metabolism. In addition, miR-31 expression results in not only secretion of specific metabolites (aspartate and glutamate) but also secretion of immunomodulatory factors. We show that this miR-31-induced secretory phenotype is sufficient to induce Th17 cell differentiation, a hallmark of psoriasis. Inhibitors of miR31-induced metabolic rewiring and metabolic crosstalk with immune cells alleviate psoriasis pathology in a mouse model of psoriasis. Together our data illustrate an emerging concept of metabolic interaction across cell compartments that characterizes disease development, which can be employed to design effective treatment options for disease, as shown here for psoriasis.

Feasibility of [18F]FSPG PET for Early Response Assessment to Combined Blockade of EGFR and Glutamine Metabolism in Wild-Type KRAS Colorectal Cancer

Early response assessment is critical for personalizing cancer therapy. Emerging therapeutic regimens with encouraging results in the wild-type (WT) KRAS colorectal cancer (CRC) setting include inhibitors of epidermal growth factor receptor (EGFR) and glutaminolysis. Towards predicting clinical outcome, this preclinical study evaluated non-invasive positron emission tomography (PET) with (4S)-4-(3-[18F]fluoropropyl)-L-glutamic acid ([18F]FSPG) in treatment-sensitive and treatment-resistant WT KRAS CRC patient-derived xenografts (PDXs). Tumor-bearing mice were imaged with [18F]FSPG PET before and one week following the initiation of treatment with either EGFR-targeted monoclonal antibody (mAb) therapy, glutaminase inhibitor therapy, or the combination. Imaging was correlated with tumor volume and histology. In PDX that responded to therapy, [18F]FSPG PET was significantly decreased from baseline at 1-week post-therapy, prior to changes in tumor volume. In contrast, [18F]FSPG PET was not decreased in non-responding PDX. These data suggest that [18F]FSPG PET may serve as an early metric of response to EGFR and glutaminase inhibition in the WT KRAS CRC setting.

Liver X Receptor Inverse Agonist GAC0001E5 Impedes Glutaminolysis and Disrupts Redox Homeostasis in Breast Cancer Cells

Liver X receptors (LXRs) are members of the nuclear receptor family of ligand-dependent transcription factors which regulate the expression of lipid and cholesterol metabolism genes. Moreover, LXRs and their ligands have been shown to inhibit tumor growth in a variety of cancers. We have previously identified the small molecule compound GAC0001E5 (1E5) as an LXR inverse agonist and a potent inhibitor of pancreatic cancer cells. Transcriptomic and metabolomic studies showed that 1E5 disrupts glutamine metabolism, an essential metabolic pathway commonly reprogrammed during malignant transformation, including in breast cancers. To determine the role of LXRs and potential application of 1E5 in breast cancer, we examined LXR expression in publicly available clinical samples, and found that LXR expression is elevated in breast tumors as compared to normal tissues. In luminal A, endocrine therapy-resistant, and triple-negative breast cancer cells, 1E5 exhibited LXR inverse agonist and "degrader" activity and strongly inhibited cell proliferation and colony formation. Treatments with 1E5 downregulated the transcription of key glutaminolysis genes, and, correspondingly, biochemical assays indicated that 1E5 lowered intracellular glutamate and glutathione levels and increased reactive oxygen species. These results indicate that novel LXR ligand 1E5 is an inhibitor of glutamine metabolism and redox homeostasis in breast cancers and suggest that modulating LXR activity and expression in tumor cells is a promising strategy for targeting metabolic reprogramming in breast cancer therapeutics.

The Interleukin-11/IL-11 Receptor Promotes Glioblastoma Survival and Invasion under Glucose-Starved Conditions through Enhanced Glutaminolysis

Glioblastoma cells adapt to changes in glucose availability through metabolic plasticity allowing for cell survival and continued progression in low-glucose concentrations. However, the regulatory cytokine networks that govern the ability to survive in glucose-starved conditions are not fully defined. In the present study, we define a critical role for the IL-11/IL-11Rα signalling axis in glioblastoma survival, proliferation and invasion when cells are starved of glucose. We identified enhanced IL-11/IL-11Rα expression correlated with reduced overall survival in glioblastoma patients. Glioblastoma cell lines over-expressing IL-11Rα displayed greater survival, proliferation, migration and invasion in glucose-free conditions compared to their low-IL-11Rα-expressing counterparts, while knockdown of IL-11Rα reversed these pro-tumorigenic characteristics. In addition, these IL-11Rα-over-expressing cells displayed enhanced glutamine oxidation and glutamate production compared to their low-IL-11Rα-expressing counterparts, while knockdown of IL-11Rα or the pharmacological inhibition of several members of the glutaminolysis pathway resulted in reduced survival (enhanced apoptosis) and reduced migration and invasion. Furthermore, IL-11Rα expression in glioblastoma patient samples correlated with enhanced gene expression of the glutaminolysis pathway genes GLUD1, GSS and c-Myc. Overall, our study identified that the IL-11/IL-11Rα pathway promotes glioblastoma cell survival and enhances cell migration and invasion in environments of glucose starvation via glutaminolysis.

Targeting Glutaminolysis Shows Efficacy in Both Prednisolone-Sensitive and in Metabolically Rewired Prednisolone-Resistant B-Cell Childhood Acute Lymphoblastic Leukaemia Cells

The prognosis for patients with relapsed childhood acute lymphoblastic leukaemia (cALL) remains poor. The main reason for treatment failure is drug resistance, most commonly to glucocorticoids (GCs). The molecular differences between prednisolone-sensitive and -resistant lymphoblasts are not well-studied, thereby precluding the development of novel and targeted therapies. Therefore, the aim of this work was to elucidate at least some aspects of the molecular differences between matched pairs of GC-sensitive and -resistant cell lines. To address this, we carried out an integrated transcriptomic and metabolomic analysis, which revealed that lack of response to prednisolone may be underpinned by alterations in oxidative phosphorylation, glycolysis, amino acid, pyruvate and nucleotide biosynthesis, as well as activation of mTORC1 and MYC signalling, which are also known to control cell metabolism. In an attempt to explore the potential therapeutic effect of inhibiting one of the hits from our analysis, we targeted the glutamine-glutamate-α-ketoglutarate axis by three different strategies, all of which impaired mitochondrial respiration and ATP production and induced apoptosis. Thereby, we report that prednisolone resistance may be accompanied by considerable rewiring of transcriptional and biosynthesis programs. Among other druggable targets that were identified in this study, inhibition of glutamine metabolism presents a potential therapeutic approach in GC-sensitive, but more importantly, in GC-resistant cALL cells. Lastly, these findings may be clinically relevant in the context of relapse-in publicly available datasets, we found gene expression patterns suggesting that in vivo drug resistance is characterised by similar metabolic dysregulation to what we found in our in vitro model.

The helminth derived peptide FhHDM-1 redirects macrophage metabolism towards glutaminolysis to regulate the pro-inflammatory response

We have previously identified an immune modulating peptide, termed FhHDM-1, within the secretions of the liver fluke, Fasciola hepatica, which is sufficiently potent to prevent the progression of type 1 diabetes and multiple sclerosis in murine models of disease. Here, we have determined that the FhHDM-1 peptide regulates inflammation by reprogramming macrophage metabolism. Specifically, FhHDM-1 switched macrophage metabolism to a dependence on oxidative phosphorylation fuelled by fatty acids and supported by the induction of glutaminolysis. The catabolism of glutamine also resulted in an accumulation of alpha ketoglutarate (α-KG). These changes in metabolic activity were associated with a concomitant reduction in glycolytic flux, and the subsequent decrease in TNF and IL-6 production at the protein level. Interestingly, FhHDM-1 treated macrophages did not express the characteristic genes of an M2 phenotype, thereby indicating the specific regulation of inflammation, as opposed to the induction of an anti-inflammatory phenotype per se. Use of an inactive derivative of FhHDM-1, which did not modulate macrophage responses, revealed that the regulation of immune responses was dependent on the ability of FhHDM-1 to modulate lysosomal pH. These results identify a novel functional association between the lysosome and mitochondrial metabolism in macrophages, and further highlight the significant therapeutic potential of FhHDM-1 to prevent inflammation.

HPV16 E6 and E7 Oncoproteins Stimulate the Glutamine Pathway Maintaining Cell Proliferation in a SNAT1-Dependent Fashion

Persistent high-risk human papillomavirus infection is the main risk factor for cervical cancer establishment, where the viral oncogenes E6 and E7 promote a cancerous phenotype. Metabolic reprogramming in cancer involves alterations in glutamine metabolism, also named glutaminolysis, to provide energy for supporting cancer processes including migration, proliferation, and production of reactive oxygen species, among others. The aim of this work was to analyze the effect of HPV16 E6 and E7 oncoproteins on the regulation of glutaminolysis and its contribution to cell proliferation. We found that the E6 and E7 oncoproteins exacerbate cell proliferation in a glutamine-dependent manner. Both oncoproteins increased the levels of transporter SNAT1, as well as GLS2 and GS enzymes; E6 also increased LAT1 transporter protein levels, while E7 increased ASCT2 and xCT. Some of these alterations are also regulated at a transcriptional level. Consistently, the amount of SNAT1 protein decreased in Ca Ski cells when E6 and E7 expression was knocked down. In addition, we demonstrated that cell proliferation was partially dependent on SNAT1 in the presence of glutamine. Interestingly, SNAT1 expression was higher in cervical cancer compared with normal cervical cells. The high expression of SNAT1 was associated with poor overall survival of cervical cancer patients. Our results indicate that HPV oncoproteins exacerbate glutaminolysis supporting the malignant phenotype.

Fungal dysbiosis facilitates inflammatory bowel disease by enhancing CD4+ T cell glutaminolysis

The fungal microbiota is an important component of the complex multikingdom microbial community colonizing the mammalian gastrointestinal tract and has an important role in immune regulation. However, how fungi regulate inflammatory bowel disease (IBD) is poorly understood. This study found that intestinal fungi regulate immune responses in IBD. Antibiotic-mediated depletion of fungi facilitated the development of IBD. Fungi greatly enhanced oxidative phosphorylation (OXPHOS) by enhancing glutaminolysis. Mechanistically, we found that fungi could activate the dectin-1-Syk- NF-κB signaling pathway to promote the expression of key enzymes and transporters involved in glutaminolysis. In summary, our findings reveal that fungal interactions in the human gut could be a promising therapeutic target for IBD.

Amino acids in hematologic malignancies: Current status and future perspective

In recent years, growing emphasis has been placed on amino acids and their role in hematologic malignancies. Cancer cell metabolism is altered during tumorigenesis and development to meet expanding energetic and biosynthetic demands. Amino acids not only act as energy-supplying substances, but also play a vital role via regulating key signaling pathways, modulating epigenetic factors and remodeling tumor microenvironment. Targeting amino acids may be an effective therapeutic approach to address the current therapeutic challenges. Here, we provide an updated overview of mechanisms by which amino acids facilitate tumor development and therapy resistance. We also summarize novel therapies targeting amino acids, focusing on recent advances in basic research and their potential clinical implications.

Therapeutic Targeting of Glutaminolysis as a Novel Strategy to Combat Cancer Stem Cells

Rare subpopulations of cancer stem cells (CSCs) have the ability to self-renew and are the primary driving force behind cancer metastatic dissemination and the preeminent hurdle to cancer treatment. As opposed to differentiated, non-malignant tumor offspring, CSCs have sophisticated metabolic patterns that, depending on the kind of cancer, rely mostly on the oxidation of major fuel substrates such as glucose, glutamine, and fatty acids for survival. Glutaminolysis is a series of metabolic reactions that convert glutamine to glutamate and, eventually, α-ketoglutarate, an intermediate in the tricarboxylic acid (TCA) cycle that provides biosynthetic building blocks. These building blocks are mostly utilized in the synthesis of macromolecules and antioxidants for redox homeostasis. A recent study revealed the cellular and molecular interconnections between glutamine and cancer stemness in the cell. Researchers have increasingly focused on glutamine catabolism in their attempt to discover an effective therapy for cancer stem cells. Targeting catalytic enzymes in glutaminolysis, such as glutaminase (GLS), is achievable with small molecule inhibitors, some of which are in early-phase clinical trials and have promising safety profiles. This review summarizes the current findings in glutaminolysis of CSCs and focuses on novel cancer therapies that target glutaminolysis in CSCs.

Reprogramming of Cellular Metabolism and Its Therapeutic Applications in Thyroid Cancer

Metabolism is a series of life-sustaining chemical reactions in organisms, providing energy required for cellular processes and building blocks for cellular constituents of proteins, lipids, carbohydrates and nucleic acids. Cancer cells frequently reprogram their metabolic behaviors to adapt their rapid proliferation and altered tumor microenvironments. Not only aerobic glycolysis (also termed the Warburg effect) but also altered mitochondrial metabolism, amino acid metabolism and lipid metabolism play important roles for cancer growth and aggressiveness. Thus, the mechanistic elucidation of these metabolic changes is invaluable for understanding the pathogenesis of cancers and developing novel metabolism-targeted therapies. In this review article, we first provide an overview of essential metabolic mechanisms, and then summarize the recent findings of metabolic reprogramming and the recent reports of metabolism-targeted therapies for thyroid cancer.

SLC1A3 facilitates Newcastle disease virus replication by regulating glutamine catabolism

As obligate intracellular parasites, viruses rely completely on host metabolic machinery and hijack host nutrients for viral replication. Newcastle disease virus (NDV) causes acute, highly contagious avian disease and functions as an oncolytic agent. NDV efficiently replicates in both chicken and tumour cells. However, how NDV reprograms host cellular metabolism for its efficient replication is still ill-defined. We previously identified a significantly upregulated glutamate transporter gene, solute carrier family 1 member 3 (SLC1A3), during NDV infection via transcriptome analysis. To investigate the potential role of SLC1A3 during NDV infection, we first confirmed the marked upregulation of SLC1A3 in NDV-infected DF-1 or A549 cells through p53 and NF-κB pathways. Knockdown of SLC1A3 inhibited NDV infection. Western blot analysis further confirmed that glutamine, but not glutamate, asparagine, or aspartate, was required for NDV replication. Metabolic flux data showed that NDV promotes the decomposition of glutamine into the tricarboxylic acid cycle. Importantly, the level of glutamate and glutaminolysis were reduced by SLC1A3 knockdown, indicating that SLC1A3 propelled glutaminolysis for glutamate utilization and NDV replication in host cells. Taken together, our data identify that SLC1A3 serves as an important regulator for glutamine metabolism and is hijacked by NDV for its efficient replication during NDV infection. These results improve our understanding of the interaction between NDV and host cellular metabolism and lay the foundation for further investigation of efficient vaccines.

Moving towards a novel therapeutic strategy for hyperammonemia that targets glutamine metabolism

Patients with urea cycle disorders intermittently develop episodes of decompensation with hyperammonemia. Although such an episode is often associated with starvation and catabolism, its molecular basis is not fully understood. First, we attempted to elucidate the mechanism of such starvation-associated hyperammonemia. Using a mouse embryonic fibroblast (MEF) culture system, we found that glucose starvation increases ammonia production, and that this increase is associated with enhanced glutaminolysis. These results led us to focus on α-ketoglutarate (AKG), a glutamate dehydrogenase inhibitor, and a major anaplerotic metabolite. Hence, we sought to determine the effect of dimethyl α-ketoglutarate (DKG), a cell-permeable AKG analog, on MEFs and found that DKG mitigates ammonia production primarily by reducing flux through glutamate dehydrogenase. We also verified that DKG reduces ammonia in an NH₄ Cl-challenged hyperammonemia mouse model and observed that DKG administration reduces plasma ammonia concentration to 22.8% of the mean value for control mice that received only NH₄ Cl. In addition, we detected increases in ornithine concentration and in the ratio of ornithine to arginine following DKG treatment. We subsequently administered DKG intravenously to a newborn pig with hyperammonemia due to ornithine transcarbamylase deficiency and found that blood ammonia concentration declined significantly over time. We determined that this effect is associated with facilitated reductive amination and glutamine synthesis. Our present data indicate that energy starvation triggers hyperammonemia through enhanced glutaminolysis and that DKG reduces ammonia accumulation via pleiotropic mechanisms both in vitro and in vivo. Thus, cell-permeable forms of AKG are feasible candidates for a novel hyperammonemia treatment.

Interplay between cellular metabolism and DNA viruses

Viruses as intracellular pathogens take over the host metabolism and reprogram to facilitate optimal virus production. DNA viruses can cause alterations in several metabolic pathways, including aerobic glycolysis also known as the Warburg effect, pentose phosphate pathway activation, and amino acid catabolism such as glutaminolysis, nucleotide biosynthesis, lipid metabolism, and amino acid biosynthesis. The available energy for productive infection can be increased in infected cells via modification of different carbon source utilization. This review discusses the metabolic alterations of the DNA viruses that will be the basis for future novel therapeutic approaches.

Evaluation of Glutaminolysis in T Cells

The activity of living cells is necessarily dependent on the amount of available bioenergy. In T cells, the latter is mainly derived from ATP, a molecular energy "coin" generated by one of several metabolic processes that differ in their ability to satisfy energy demand. Thus, whereas naïve or quiescent T cells efficiently utilize oxidative phosphorylation to generate ATP, T cells subjected to antigenic stimulation followed by clonal expansion and cytokine production meet their increased need for energy by supplementing ATP generation by oxidative phosphorylation with ATP generation by glycolysis. Yet additional need for ATP can be met by other basic biologic sources of energy such as glutamine, an amino acid that is metabolized through a process called glutaminolysis to result in end products that flows into the TCA cycle and augment ATP generation by oxidative phosphorylation. It is now possible to track the dominant energy supplying processes (i.e., the ATP generation process) in differentiating or activated T cells in a real-time manner. Here, we provide one element of such tracking by describing protocols for the assessment of the contribution of glutaminolysis to overall ATP production within different T cell subsets. © 2022 Wiley Periodicals LLC. This article has been contributed to by US Government employees and their work is in the public domain in the USA. Basic Protocol 1: Evaluation of the role of glutaminolysis during T cell activation/differentiation Basic Protocol 2: Evaluation of the role of glutaminolysis in T cell responses utilizing glutaminolysis inhibitors Basic Protocol 3: Evaluation of the effect of glutaminolysis on cellular oxidative phosphorylation/glycolysis.

Laparoscopic Sleeve Gastrectomy in Patients with Severe Obesity Restores Adaptive Responses Leading to Nonalcoholic Steatohepatitis

The surgically induced remission of liver disease represents a model to investigate the signalling processes that trigger the development of nonalcoholic steatohepatitis with the aim of identifying novel therapeutic targets. We recruited patients with severe obesity with or without nonalcoholic steatohepatitis and obtained liver and plasma samples before and after laparoscopic sleeve gastrectomy for immunoblotting, immunocytochemical, metabolomic, transcriptomic and epigenetic analyses. Functional studies were performed in HepG2 cells and primary hepatocytes. Surgery was associated with a decrease in the inflammatory response and revealed the role of mitogen-activated protein kinases. Nonalcoholic steatohepatitis was associated with an increased glutaminolysis-induced production of α-ketoglutarate and the hyperactivation of mammalian target of rapamycin complex 1. These changes were crucial for adenosine monophosphate-activated protein kinase/mammalian target of rapamycin-driven pathways that modulated hepatocyte survival by coordinating apoptosis and autophagy and affected methylation-related epigenomic remodelling enzymes. Hepatic transcriptome signatures and differentially methylated genomic regions distinguished patients with and without steatohepatitis. Our results suggest that the increased glutaminolysis-induced α-ketoglutarate production and the mammalian target of rapamycin complex 1 dysregulation play a crucial role in the inefficient adaptive responses leading to steatohepatitis in obesity.

Glutamine Is Required for M1-like Polarization of Macrophages in Response to Mycobacterium tuberculosis Infection

In response to Mycobacterium tuberculosis infection, macrophages mount proinflammatory and antimicrobial responses similar to those observed in M1 macrophages activated by lipopolysaccharide (LPS) and interferon gamma (IFN-γ). A metabolic reprogramming to hypoxia-inducible-factor 1 (HIF-1)-mediated uptake of glucose and its metabolism by glycolysis is required for M1-like polarization, but little is known about other metabolic programs driving the M1-like polarization during infection. We report that glutamine serves as a carbon and nitrogen source for the metabolic reprogramming to M1-like macrophages. Widely targeted metabolite screening identified an association of glutamine and/or glutamate with highly affected metabolic pathways of M1-like macrophages. Moreover, stable isotope-assisted metabolomics of U¹³C glutamine and U¹³C glucose revealed that glutamine, rather than glucose, is catabolized in both the oxidative and reductive tricarboxylic acid (TCA) cycles of M1-like macrophages, thereby generating signaling molecules that include succinate, biosynthetic precursors such as aspartate, and itaconate. U¹⁵N glutamine-tracing metabolomics further revealed participation of glutamine nitrogen in synthesis of intermediates of purine and pyrimidine metabolism plus amino acids, including aspartate. These findings were corroborated by diminished M1 polarization from chemical inhibition of glutaminase (GLS), the key enzyme in the glutaminolysis pathway, and by genetic deletion of GLS in infected macrophages. Thus, the catabolism of glutamine is an integral component of metabolic reprogramming in activating macrophages and it coordinates with elevated cytosolic glycolysis to satisfy the cellular demand for bioenergetic and biosynthetic precursors of M1-like macrophages. Knowledge of these new immunometabolic features of M1-like macrophages should advance the development of host-directed therapies for tuberculosis.

Dealing with Macrophage Plasticity to Address Therapeutic Challenges in Head and Neck Cancers

The head and neck tumor microenvironment (TME) is highly infiltrated with macrophages. More specifically, tumor-associated macrophages (TAM/M2-like) are one of the most critical components associated with poor overall survival in head and neck cancers (HNC). Two extreme states of macrophage phenotypes are described as conducting pro-inflammatory/anti-tumoral (M1) or anti-inflammatory/pro-tumoral (M2) activities. Moreover, specific metabolic pathways as well as oxidative stress responses are tightly associated with their phenotypes and functions. Hence, due to their plasticity, targeting M2 macrophages to repolarize in the M1 phenotype would be a promising cancer treatment. In this context, we evaluated macrophage infiltration in 60 HNC patients and demonstrated the high infiltration of CD68+ cells that were mainly related to CD163+ M2 macrophages. We then optimized a polarization protocol from THP1 monocytes, validated by specific gene and protein expression levels. In addition, specific actors of glutamine pathway and oxidative stress were quantified to indicate the use of glutaminolysis by M2 and the production of reactive oxygen species by M1. Finally, we evaluated and confirmed the plasticity of our model using M1 activators to repolarize M2 in M1. Overall, our study provides a complete reversible polarization protocol allowing us to further evaluate various reprogramming effectors targeting glutaminolysis and/or oxidative stress in macrophages.

Regulation of Cardiac Fibroblast GLS1 Expression by Scleraxis

Fibrosis is an energy-intensive process requiring the activation of fibroblasts to myofibroblasts, resulting in the increased synthesis of extracellular matrix proteins. Little is known about the transcriptional control of energy metabolism in cardiac fibroblast activation, but glutaminolysis has been implicated in liver and lung fibrosis. Here we explored how pro-fibrotic TGFβ and its effector scleraxis, which drive cardiac fibroblast activation, regulate genes involved in glutaminolysis, particularly the rate-limiting enzyme glutaminase (GLS1). The GLS1 inhibitor CB-839 attenuated TGFβ-induced fibroblast activation. Cardiac fibroblast activation to myofibroblasts by scleraxis overexpression increased glutaminolysis gene expression, including GLS1, while cardiac fibroblasts from scleraxis-null mice showed reduced expression. TGFβ induced GLS1 expression and increased intracellular glutamine and glutamate levels, indicative of increased glutaminolysis, but in scleraxis knockout cells, these measures were attenuated, and the response to TGFβ was lost. The knockdown of scleraxis in activated cardiac fibroblasts reduced GLS1 expression by 75%. Scleraxis transactivated the human GLS1 promoter in luciferase reporter assays, and this effect was dependent on a key scleraxis-binding E-box motif. These results implicate scleraxis-mediated GLS1 expression as a key regulator of glutaminolysis in cardiac fibroblast activation, and blocking scleraxis in this process may provide a means of starving fibroblasts of the energy required for fibrosis.

Bergenin, a PPARγ agonist, inhibits Th17 differentiation and subsequent neutrophilic asthma by preventing GLS1-dependent glutaminolysis

Bergenin is a natural PPARγ agonist that can prevent neutrophil aggregation, and often be used in clinics for treating respiratory diseases. Recent data show that Th17 cells are important for neutrophil aggregation and asthma through secreting IL-17A. In this study, we investigated the effects of bergenin on Th17 differentiation in vitro and subsequent neutrophilic asthma in mice. Naïve T cells isolated from mouse mesenteric lymph nodes were treated with IL-23, TGF-β, and IL-6 to induce Th17 differentiation. We showed that in naïve T cells under Th17-polarizing condition, the addition of bergenin (3, 10, 30 μM) concentration-dependently decreased the percentage of CD4⁺ IL-17A⁺ T cells and mRNA expression of specific transcription factor RORγt, and function-related factors IL-17A/F, IL-21, and IL-22, but did not affect the cell vitality and apoptosis. Furthermore, bergenin treatment prevented GLS1-dependent glutaminolysis in the progress of Th17 differentiation, slightly affected the levels of SLC1A5, SLC38A1, GLUD1, GOT1, and GPT2. Glutamine deprivation, the addition of glutamate (1 mM), α-ketoglutarate (1 mM), or GLS1 plasmid all significantly attenuated the above-mentioned actions of bergenin. Besides, we demonstrated that bergenin (3, 10, and 30 μM) concentration-dependently activated PPARγ in naïve T cells, whereas PPARγ antagonist GW9662 and siPPARγ abolished bergenin-caused inhibition on glutaminolysis and Th17 differentiation. Furthermore, we revealed that bergenin inhibited glutaminolysis by regulating the level of CDK1, phosphorylation and degradation of Cdh1, and APC/C-Cdh1-mediated ubiquitin-proteasomal degradation of GLS1 after activating PPARγ. We demonstrated a correlation existing among bergenin-affected GLS1-dependent glutaminolysis, PPARγ, "CDK1-APC/C-Cdh1" signaling, and Th17 differentiation. Finally, the therapeutic effect and mechanisms for bergenin-inhibited Th17 responses and neutrophilic asthma were confirmed in a mouse model of neutrophilic asthma by administration of GW9662 or GLS1 overexpression plasmid in vivo. In conclusion, bergenin repressed Th17 differentiation and then alleviated neutrophilic asthma in mice by inhibiting GLS1-dependent glutaminolysis via regulating the "CDK1-APC/C-Cdh1" signaling after activating PPARγ.

Inhibition of glutaminase 1-mediated glutaminolysis improves pathological cardiac remodeling

Alterations in cardiac metabolism are strongly associated with the pathogenesis of heart failure (HF). We recently reported that glutamine-dependent anaplerosis, termed glutaminolysis, was activated by H₂O₂ stimulation in rat cardiomyocytes, which seemed to be an adaptive response by which cardiomyocytes survive acute stress. However, the molecular mechanisms and fundamental roles of glutaminolysis in the pathophysiology of the failing heart are still unknown. Here, we treated wild-type mice (C57BL/6J) and rat neonatal cardiomyocytes (RNCMs) and fibroblasts (RNCFs) with angiotensin II (Ang II) to induce pathological cardiac remodeling. Glutaminase 1 (GLS1), a rate-limiting glutaminolysis enzyme, was significantly increased in Ang II-induced mouse hearts, RNCMs and RNCFs. Unexpectedly, a GLS1 inhibitor attenuated Ang II-induced left ventricular hypertrophy and fibrosis in the mice, and gene knockdown and pharmacological perturbation of GLS1 suppressed hypertrophy and the proliferation of RNCMs and RNCFs, respectively. Using mass spectrometry (MS)-based stable isotope tracing with ¹³C-labeled glutamine, we observed glutamine metabolic flux in Ang II-treated RNCMs and RNCFs. The incorporation of ¹³C atoms into tricarboxylic acid (TCA) cycle intermediates and their derivatives was markedly enhanced in both cell types, indicating the activation of glutaminolysis in hypertrophied heart. Notably, GLS1 inhibition reduced the production of glutamine-derived aspartate and citrate, which are required for the biosynthesis of nucleic acids and lipids, possibly contributing to the suppression of cardiac hypertrophy and fibrosis. The findings of the present study reveal that GLS1-mediated upregulation of glutaminolysis leads to maladaptive cardiac remodeling. Inhibition of this anaplerotic pathway could be a novel therapeutic approach for HF.

Loss of glucose 6-phosphate dehydrogenase function increases oxidative stress and glutaminolysis in metastasizing melanoma cells

Melanoma metastasis is limited by oxidative stress. Cells that enter the blood experience high levels of reactive oxygen species and usually die of ferroptosis. We found that melanoma cells become more dependent upon the oxidative pentose phosphate pathway to manage oxidative stress during metastasis. When pentose phosphate pathway function was impaired by reduced glucose 6-phosphate dehydrogenase (G6PD) function, melanoma cells increased malic enzyme activity and glutamine consumption. Melanoma cells thus have redundant and layered protection against oxidative stress.

The pentose phosphate pathway is a major source of NADPH for oxidative stress resistance in cancer cells but there is limited insight into its role in metastasis, when some cancer cells experience high levels of oxidative stress. To address this, we mutated the substrate binding site of glucose 6-phosphate dehydrogenase (G6PD), which catalyzes the first step of the pentose phosphate pathway, in patient-derived melanomas. G6PD mutant melanomas had significantly decreased G6PD enzymatic activity and depletion of intermediates in the oxidative pentose phosphate pathway. Reduced G6PD function had little effect on the formation of primary subcutaneous tumors, but when these tumors spontaneously metastasized, the frequency of circulating melanoma cells in the blood and metastatic disease burden were significantly reduced. G6PD mutant melanomas exhibited increased levels of reactive oxygen species, decreased NADPH levels, and depleted glutathione as compared to control melanomas. G6PD mutant melanomas compensated for this increase in oxidative stress by increasing malic enzyme activity and glutamine consumption. This generated a new metabolic vulnerability as G6PD mutant melanomas were more dependent upon glutaminase than control melanomas, both for oxidative stress management and anaplerosis. The oxidative pentose phosphate pathway, malic enzyme, and glutaminolysis thus confer layered protection against oxidative stress during metastasis.