Replenishment of TCA cycle intermediates and long-noncoding RNAs regulation in breast cancer.

The tricarboxylic acid (TCA) cycle is an essential interface that coordinates cellular metabolism and is as a primary route determining the fate of a variety of fuel sources, including glucose, fatty acid and glutamate. The crosstalk of nutrients replenished TCA cycle regulates breast cancer (BC) progression by changing substrate levels-induced epigenetic alterations, especially the methylation, acetylation, succinylation and lactylation. Long non-coding RNAs (lncRNA) have dual roles in inhibiting or promoting energy reprogramming, and so altering the metabolic flux of fuel sources to the TCA cycle, which may regulate epigenetic modifications at the cellular level of BC. This narrative review discussed the central role of the TCA cycle in interconnecting numerous fuels and the induced epigenetic modifications, and the underlying regulatory mechanisms of lncRNAs in BC.

Non-Mitochondrial Aconitase-2 Mediates the Transcription of Nuclear-Encoded Electron Transport Chain Genes in Fission Yeast.

Aconitase-2 (Aco2) is present in the mitochondria, cytosol, and nucleus of fission yeast. To explore its function beyond the well-known role in the mitochondrial tricarboxylic acid (TCA) cycle, we conducted genome-wide profiling using the aco2ΔNLS mutant, which lacks a nuclear localization signal (NLS). The RNA sequencing (RNA-seq) data showed a general downregulation of electron transport chain (ETC) genes in the aco2ΔNLS mutant, except for those in the complex II, leading to a growth defect in respiratory-prone media. Complementation analysis with non-catalytic Aco2 [aco2ΔNLS + aco2(3CS)], where three cysteines were substituted with serine, restored normal growth and typical ETC gene expression. This suggests that Aco2's catalytic activity is not essential for its role in ETC gene regulation. Our mRNA decay assay indicated that the decrease in ETC gene expression was due to transcriptional regulation rather than changes in mRNA stability. Additionally, we investigated the Php complex's role in ETC gene regulation and found that ETC genes, except those within complex II, were downregulated in php3Δ and php5Δ strains, similar to the aco2ΔNLS mutant. These findings highlight a novel role for nuclear aconitase in ETC gene regulation and suggest a potential connection between the Php complex and Aco2.

Metabolic rewiring promotes anti-inflammatory effects of glucocorticoids.

Glucocorticoids represent the mainstay of therapy for a broad spectrum of immune-mediated inflammatory diseases. However, the molecular mechanisms underlying their anti-inflammatory mode of action have remained incompletely understood1. Here we show that the anti-inflammatory properties of glucocorticoids involve reprogramming of the mitochondrial metabolism of macrophages, resulting in increased and sustained production of the anti-inflammatory metabolite itaconate and consequent inhibition of the inflammatory response. The glucocorticoid receptor interacts with parts of the pyruvate dehydrogenase complex whereby glucocorticoids provoke an increase in activity and enable an accelerated and paradoxical flux of the tricarboxylic acid (TCA) cycle in otherwise pro-inflammatory macrophages. This glucocorticoid-mediated rewiring of mitochondrial metabolism potentiates TCA-cycle-dependent production of itaconate throughout the inflammatory response, thereby interfering with the production of pro-inflammatory cytokines. By contrast, artificial blocking of the TCA cycle or genetic deficiency in aconitate decarboxylase 1, the rate-limiting enzyme of itaconate synthesis, interferes with the anti-inflammatory effects of glucocorticoids and, accordingly, abrogates their beneficial effects during a diverse range of preclinical models of immune-mediated inflammatory diseases. Our findings provide important insights into the anti-inflammatory properties of glucocorticoids and have substantial implications for the design of new classes of anti-inflammatory drugs.

Prognostic and immune predictive roles of a novel tricarboxylic acid cycle-based model in hepatocellular carcinoma.

Hepatocellular carcinoma (HCC) is the most prevalent type of liver cancer. Since the tricarboxylic acid cycle is widely involved in tumor metabolic reprogramming and cuproptosis, investigating related genes may help to identify prognostic signature of patients with HCC. Data on patients with HCC were sourced from public datasets, and were divided into train, test, and single-cell cohorts. A variety of machine learning algorithms were used to identify different molecular subtypes and determine the prognostic risk model. Our findings revealed that the risk score (TRscore), based on the genes OGDHL, CFHR4, and SPP1, showed excellent predictive performance in different datasets. Pathways related to cell cycle and immune inflammation were enriched in the high-risk group, whereas metabolism-related pathways were significantly enriched in the low-risk group. The high-risk group was associated with a greater number of mutations of detrimental biological behavior and higher levels of immune infiltration, immune checkpoint expression, and anti-cancer immunotherapy response. Low-risk patients demonstrated greater sensitivity to erlotinib and phenformin. SPP1 was mainly involved in the interaction among tumor-associated macrophages, T cells, and malignant cells via SPP1-CD44 and SPP1-(ITGA5 + ITGB1) ligand-receptor pairs. In summary, our study established a prognostic model, which may contribute to individualized treatment and clinical management of patients with HCC.

Metabolic reprogramming driven by EZH2 inhibition depends on cell-matrix interactions.

EZH2 (Enhancer of Zeste Homolog 2), a subunit of Polycomb Repressive Complex 2 (PRC2), catalyzes the trimethylation of histone H3 at lysine 27 (H3K27me3), which represses expression of genes. It also has PRC2-independent functions, including transcriptional coactivation of oncogenes, and is frequently overexpressed in lung cancers. Clinically, EZH2 inhibition can be achieved with the FDA-approved drug EPZ-6438 (tazemetostat). To realize the full potential of EZH2 blockade, it is critical to understand how cell-cell/cell-matrix interactions present in 3D tissue and cell culture systems influences this blockade in terms of growth-related metabolic functions. Here, we show that EZH2 suppression reduced growth of human lung adenocarcinoma A549 cells in 2D cultures but stimulated growth in 3D cultures. To understand the metabolic underpinnings, we employed [13C6]-glucose stable isotope-resolved metabolomics to determine the effect of EZH2 suppression on metabolic networks in 2D versus 3D A549 cultures. The Krebs cycle, neoribogenesis, γ-aminobutyrate metabolism, and salvage synthesis of purine nucleotides were activated by EZH2 suppression in 3D spheroids but not in 2D cells, consistent with the growth effect. Using simultaneous 2H7-glucose + 13C5,15N2-Gln tracers and EPZ-6438 inhibition of H3 trimethylation, we delineated the effects on the Krebs cycle, γ-aminobutyrate metabolism, gluconeogenesis, and purine salvage to be PRC2-dependent. Furthermore, the growth/metabolic effects differed for mouse Matrigel versus self-produced A549 extracellular matrix. Thus, our findings highlight the importance of the presence and nature of extracellular matrix in studying the function of EZH2 and its inhibitors in cancer cells for modeling the in vivo outcomes.

The connection between tricarboxylic acid cycle enzyme mutations and pseudohypoxic signaling in pheochromocytoma and paraganglioma.

Pheochromocytomas and paragangliomas (PPGLs) are rare neuroendocrine tumors originating from chromaffin cells, holding significant clinical importance due to their capacity for excessive catecholamine secretion and associated cardiovascular complications. Roughly 80% of cases are associated with genetic mutations. Based on the functionality of these mutated genes, PPGLs can be categorized into distinct molecular clusters: the pseudohypoxia signaling cluster (Cluster-1), the kinase signaling cluster (Cluster-2), and the WNT signaling cluster (Cluster-3). A pivotal factor in the pathogenesis of PPGLs is hypoxia-inducible factor-2α (HIF2α), which becomes upregulated even under normoxic conditions, activating downstream transcriptional processes associated with pseudohypoxia. This adaptation provides tumor cells with a growth advantage and enhances their ability to thrive in adverse microenvironments. Moreover, pseudohypoxia disrupts immune cell communication, leading to the development of an immunosuppressive tumor microenvironment. Within Cluster-1a, metabolic perturbations are particularly pronounced. Mutations in enzymes associated with the tricarboxylic acid (TCA) cycle, such as succinate dehydrogenase (SDHx), fumarate hydratase (FH), isocitrate dehydrogenase (IDH), and malate dehydrogenase type 2 (MDH2), result in the accumulation of critical oncogenic metabolic intermediates. Notable among these intermediates are succinate, fumarate, and 2-hydroxyglutarate (2-HG), which promote activation of the HIFs signaling pathway through various mechanisms, thus inducing pseudohypoxia and facilitating tumorigenesis. SDHx mutations are prevalent in PPGLs, disrupting mitochondrial function and causing succinate accumulation, which competitively inhibits α-ketoglutarate-dependent dioxygenases. Consequently, this leads to global hypermethylation, epigenetic changes, and activation of HIFs. In FH-deficient cells, fumarate accumulation leads to protein succination, impacting cell function. FH mutations also trigger metabolic reprogramming towards glycolysis and lactate synthesis. IDH1/2 mutations generate D-2HG, inhibiting α-ketoglutarate-dependent dioxygenases and stabilizing HIFs. Similarly, MDH2 mutations are associated with HIF stability and pseudohypoxic response. Understanding the intricate relationship between metabolic enzyme mutations in the TCA cycle and pseudohypoxic signaling is crucial for unraveling the pathogenesis of PPGLs and developing targeted therapies. This knowledge enhances our comprehension of the pivotal role of cellular metabolism in PPGLs and holds implications for potential therapeutic advancements.

An Overview: The Diversified Role of Mitochondria in Cancer Metabolism.

Mitochondria are intracellular organelles involved in energy production, cell metabolism and cell signaling. They are essential not only in the process of ATP synthesis, lipid metabolism and nucleic acid metabolism, but also in tumor development and metastasis. Mutations in mtDNA are commonly found in cancer cells to promote the rewiring of bioenergetics and biosynthesis, various metabolites especially oncometabolites in mitochondria regulate tumor metabolism and progression. And mutation of enzymes in the TCA cycle leads to the unusual accumulation of certain metabolites and oncometabolites. Mitochondria have been demonstrated as the target for cancer treatment. Cancer cells rely on two main energy resources: oxidative phosphorylation (OXPHOS) and glycolysis. By manipulating OXPHOS genes or adjusting the metabolites production in mitochondria, tumor growth can be restrained. For example, enhanced complex I activity increases NAD+/NADH to prevent metastasis and progression of cancers. In this review, we discussed mitochondrial function in cancer cell metabolism and specially explored the unique role of mitochondria in cancer stem cells and the tumor microenvironment. Targeting the OXPHOS pathway and mitochondria-related metabolism emerging as a potential therapeutic strategy for various cancers.

Long Noncoding RNA LOC554202 Predicts a Poor Prognosis and Correlates with Immune Infiltration in Thyroid Cancer.

Thyroid cancer (TC) is one of the widely diagnosed carcinomas in women before the age of 30. Nevertheless, there is currently a lack of specific biomarkers for predicting the prognosis of TC. Long noncoding RNAs (lncRNAs) were important regulators in human cancer progression as previously described. Unfortunately, there is little known on these lncRNAs' functions and molecular mechanisms in TC. In our literature, we found that LOC554202 (MIR31HG) was upregulated in TC samples and correlated with clinicopathological features, including M stage, N stage, and lymph nodes examined status in TC. In addition, we found that LOC554202 overexpression was evidently correlated with high immune infiltrate levels of CD8+ T cells, macrophage, neutrophil, myeloid dendritic cells, and B cells in TC. Knockdown of LOC554202 impeded TC cell proliferation and cycle progression. We found that LOC554202 had an association with metabolic pathways, vesicle-mediated transport, tricarboxylic acid cycle, Hedgehog signaling pathway, and Hippo signaling pathway in TC. Reducing LOC554202 hindered TC cell proliferation and cycle progression. Finally, we found that LOC554202 participated in modulating the expression of the regulators of Hippo signaling and TCA pathway, such as CCND2, CCND3, SDHC, SDHD, SUCLA2, and SUCLG1. We thought that this study would largely enhance our understanding of LOC554202's functional roles in human TC progression and immune response.

Identification of an important function of CYP123: Role in the monooxygenase activity in a novel estradiol degradation pathway in bacteria.

Nowadays, 17ß-estradiol (E2) biodegradation pathway has still not been identified in bacteria. To bridge this gap, we have described a novel E2 degradation pathway in Rhodococcus sp. P14 in this study, which showed that estradiol could be first transferred to estrone (E1) and thereby further converted into 16-hydroxyestrone, and then transformed into opened estrogen D ring. In order to identify the genes, which may be responsible for the pathway, transcriptome analysis was performed during E2 degradation in strain P14. The results showed that the expression of a short-chain dehydrogenase (SDR) gene and a CYP123 gene in the same gene cluster could be induced significantly by E2. Based on gene analysis, this gene cluster was found to play an important role in transforming E2 to 16-hydroxyestrone. The function of CYP123 was unknown before this study, and was found to harbor the activity of 16-estrone hydratase. Moreover, the global response to E2 in strain P14 was also analyzed by transcriptome analysis. It was observed that various genes involved in the metabolism processes, like the TCA cycle, lipid and amino acid metabolism, as well as glycolysis showed a significant increase in mRNA levels in response to strain P14 that can use E2 as the single carbon source. Overall, this study provides us an in depth understanding of the E2 degradation mechanisms in bacteria and also sheds light about the ability of strain P14 to effectively use E2 as the major carbon source for promoting its growth.

Targeting Mitochondrial OXPHOS and Their Regulatory Signals in Prostate Cancers.

Increasing evidence suggests that tumor development requires not only oncogene/tumor suppressor mutations to drive the growth, survival, and metastasis but also metabolic adaptations to meet the increasing energy demand for rapid cellular expansion and to cope with the often nutritional and oxygen-deprived microenvironment. One well-recognized strategy is to shift the metabolic flow from oxidative phosphorylation (OXPHOS) or respiration in mitochondria to glycolysis or fermentation in cytosol, known as Warburg effects. However, not all cancer cells follow this paradigm. In the development of prostate cancer, OXPHOS actually increases as compared to normal prostate tissue. This is because normal prostate epithelial cells divert citrate in mitochondria for the TCA cycle to the cytosol for secretion into seminal fluid. The sustained level of OXPHOS in primary tumors persists in progression to an advanced stage. As such, targeting OXPHOS and mitochondrial activities in general present therapeutic opportunities. In this review, we summarize the recent findings of the key regulators of the OXPHOS pathway in prostate cancer, ranging from transcriptional regulation, metabolic regulation to genetic regulation. Moreover, we provided a comprehensive update of the current status of OXPHOS inhibitors for prostate cancer therapy. A challenge of developing OXPHOS inhibitors is to selectively target cancer mitochondria and spare normal counterparts, which is also discussed.

Proteomic Analysis of Marinesco-Sjogren Syndrome Fibroblasts Indicates Pro-Survival Metabolic Adaptation to SIL1 Loss.

Marinesco-Sjogren syndrome (MSS) is a rare multisystem pediatric disorder, caused by loss-of-function mutations in the gene encoding the endoplasmic reticulum cochaperone SIL1. SIL1 acts as a nucleotide exchange factor for BiP, which plays a central role in secretory protein folding. SIL1 mutant cells have reduced BiP-assisted protein folding, cannot fulfil their protein needs, and experience chronic activation of the unfolded protein response (UPR). Maladaptive UPR may explain the cerebellar and skeletal muscle degeneration responsible for the ataxia and muscle weakness typical of MSS. However, the cause of other more variable, clinical manifestations, such as mild to severe mental retardation, hypogonadism, short stature, and skeletal deformities, is less clear. To gain insights into the pathogenic mechanisms and/or adaptive responses to SIL1 loss, we carried out cell biological and proteomic investigations in skin fibroblasts derived from a young patient carrying the SIL1 R111X mutation. Despite fibroblasts not being overtly affected in MSS, we found morphological and biochemical changes indicative of UPR activation and altered cell metabolism. All the cell machineries involved in RNA splicing and translation were strongly downregulated, while protein degradation via lysosome-based structures was boosted, consistent with an attempt of the cell to reduce the workload of the endoplasmic reticulum and dispose of misfolded proteins. Cell metabolism was extensively affected as we observed a reduction in lipid synthesis, an increase in beta oxidation, and an enhancement of the tricarboxylic acid cycle, with upregulation of eight of its enzymes. Finally, the catabolic pathways of various amino acids, including valine, leucine, isoleucine, tryptophan, lysine, aspartate, and phenylalanine, were enhanced, while the biosynthetic pathways of arginine, serine, glycine, and cysteine were reduced. These results indicate that, in addition to UPR activation and increased protein degradation, MSS fibroblasts have profound metabolic alterations, which may help them cope with the absence of SIL1.

A genome-wide association study reveals that the 2-oxoglutarate/malate translocator mediates seed vigor in rice.

Seed vigor is an important trait for the direct seeding of rice (Oryza sativa L.). In this study, we examined the genetic architecture of variation in the germination rate using a diverse panel of rice accessions. Four quantitative trait loci for germination rate were identified using a genome-wide association study during early germination. One candidate gene, encoding the 2-oxoglutarate/malate translocator (OsOMT), was validated for qGR11. Disruption of this gene (Osomt mutants) reduced seed vigor, including seed germination and seedling growth, in rice. Functional analysis revealed that OsOMT influences seed vigor mainly by modulating amino acid levels and glycolysis and tricarboxylic acid cycle processes. The levels of most amino acids, including the Glu family (Glu, Pro, Arg, and GABA), Asp family (Asp, Thr, Lys, Ile, and Met), Ser family (Ser, Gly, and Cys), and others (His, Ala, Leu, and Val), were significantly reduced in the mature grains and the early germinating seeds of Osomt mutants compared to wild type (WT). The glucose and soluble sugar contents, as well as adenosine triphosphate levels, were significantly decreased in germinating seeds of Osomt mutants compared to WT. These results provide important insights into the role of OsOMT in seed vigor in rice.

The impact of mitochondria on cancer treatment resistance.

BACKGROUND: The ability of cancer cells to develop treatment resistance is one of the primary factors that prevent successful treatment. Although initially thought to be dysfunctional in cancer, mitochondria are significant players that mediate treatment resistance. Literature indicates that cancer cells reutilize their mitochondria to facilitate cancer progression and treatment resistance. However, the mechanisms by which the mitochondria promote treatment resistance have not yet been fully elucidated. CONCLUSIONS AND PERSPECTIVES: Here, we describe various means by which mitochondria can promote treatment resistance. For example, mutations in tricarboxylic acid (TCA) cycle enzymes, i.e., fumarate hydratase and isocitrate dehydrogenase, result in the accumulation of the oncometabolites fumarate and 2-hydroxyglutarate, respectively. These oncometabolites may promote treatment resistance by upregulating the nuclear factor erythroid 2-related factor 2 (Nrf2) pathway, inhibiting the anti-tumor immune response, or promoting angiogenesis. Furthermore, stromal cells can donate intact mitochondria to cancer cells after therapy to restore mitochondrial functionality and facilitate treatment resistance. Targeting mitochondria is, therefore, a feasible strategy that may dampen treatment resistance. Analysis of tumoral DNA may also be used to guide treatment choices. It will indicate whether enzymatic mutations are present in the TCA cycle and, if so, whether the mutations or their downstream signaling pathways can be targeted. This may improve treatment outcomes by inhibiting treatment resistance or promoting the effectiveness of anti-angiogenic agents or immunotherapy.

Mitochondrial Mistranslation in Brain Provokes a Metabolic Response Which Mitigates the Age-Associated Decline in Mitochondrial Gene Expression.

Mitochondrial misreading, conferred by mutation V338Y in mitoribosomal protein Mrps5, in-vivo is associated with a subtle neurological phenotype. Brain mitochondria of homozygous knock-in mutant Mrps5V338Y/V338Y mice show decreased oxygen consumption and reduced ATP levels. Using a combination of unbiased RNA-Seq with untargeted metabolomics, we here demonstrate a concerted response, which alleviates the impaired functionality of OXPHOS complexes in Mrps5 mutant mice. This concerted response mitigates the age-associated decline in mitochondrial gene expression and compensates for impaired respiration by transcriptional upregulation of OXPHOS components together with anaplerotic replenishment of the TCA cycle (pyruvate, 2-ketoglutarate).

Implication of EZH2 in the Pro-Proliferative and Apoptosis-Resistant Phenotype of Pulmonary Artery Smooth Muscle Cells in PAH: A Transcriptomic and Proteomic Approach.

Pulmonary arterial hypertension (PAH) is a progressive disorder characterized by a sustained elevation of pulmonary artery (PA) pressure, right ventricular failure, and premature death. Enhanced proliferation and resistance to apoptosis (as seen in cancer cells) of PA smooth muscle cells (PASMCs) is a major pathological hallmark contributing to pulmonary vascular remodeling in PAH, for which current therapies have only limited effects. Emerging evidence points toward a critical role for Enhancer of Zeste Homolog 2 (EZH2) in cancer cell proliferation and survival. However, its role in PAH remains largely unknown. The aim of this study was to determine whether EZH2 represents a new factor critically involved in the abnormal phenotype of PAH-PASMCs. We found that EZH2 is overexpressed in human lung tissues and isolated PASMCs from PAH patients compared to controls as well as in two animal models mimicking the disease. Through loss- and gain-of-function approaches, we showed that EZH2 promotes PAH-PASMC proliferation and survival. By combining quantitative transcriptomic and proteomic approaches in PAH-PASMCs subjected or not to EZH2 knockdown, we found that inhibition of EZH2 downregulates many factors involved in cell-cycle progression, including E2F targets, and contributes to maintain energy production. Notably, we found that EZH2 promotes expression of several nuclear-encoded components of the mitochondrial translation machinery and tricarboxylic acid cycle genes. Overall, this study provides evidence that, by overexpressing EZH2, PAH-PASMCs remove the physiological breaks that normally restrain their proliferation and susceptibility to apoptosis and suggests that EZH2 or downstream factors may serve as therapeutic targets to combat pulmonary vascular remodeling.

TCA cycle metabolic compromise due to an aberrant S-nitrosoproteome in HIV-associated neurocognitive disorder with methamphetamine use.

In the brain, both HIV-1 and methamphetamine (meth) use result in increases in oxidative and nitrosative stress. This redox stress is thought to contribute to the pathogenesis of HIV-associated neurocognitive disorder (HAND) and further worsening cognitive activity in the setting of drug abuse. One consequence of such redox stress is aberrant protein S-nitrosylation, derived from nitric oxide, which may disrupt normal protein activity. Here, we report an improved, mass spectrometry-based technique to assess S-nitrosylated protein in human postmortem brains using selective enrichment of S-nitrosocysteine residues with an organomercury resin. The data show increasing S-nitrosylation of tricarboxylic acid (TCA) enzymes in the setting of HAND and HAND/meth use compared with HIV+ control brains without CNS pathology. The consequence is systematic inhibition of multiple TCA cycle enzymes, resulting in energy collapse that can contribute to the neuronal and synaptic damage observed in HAND and meth use.

Long non­coding RNAs: Key regulators involved in metabolic reprogramming in cancer (Review).

Metabolism is defined as the biochemical processes that produce or consume energy in living organisms. Otto Warburg suggested that cancer is a metabolic disease, thus metabolic reprogramming is widely considered as an emerging hallmark of cancer cells. Long non­coding RNAs (lncRNAs), which are defined as transcripts >200 nucleotides with limited protein coding potential, are involved in cancer metabolism. lncRNAs can control pathophysiological processes of cancer by regulating gene expression at epigenetic, transcriptional and post­transcriptional levels. The process of tumorigenesis is usually accompanied by alterations in metabolic patterns, involving glycolysis, the tricarboxylic acid cycle, mitochondrial oxidative phosphorylation, the pentose phosphate signaling pathway, glutamine metabolism and lipid metabolism, which is also known as metabolic reprogramming. The present review summarized the functions of lncRNAs in cancer metabolism and discussed how the dysregulation of lncRNAs contributed to metabolic reprogramming and tumorigenesis, which may provide novel therapeutic targets for cancer.

SIRT2 ablation inhibits glucose-stimulated insulin secretion through decreasing glycolytic flux.

Rationale: Sirtuins are NAD+-dependent protein deacylases known to have protective effects against age-related diseases such as diabetes, cancer, and neurodegenerative disease. SIRT2 is the only primarily cytoplasmic isoform and its overall role in glucose homeostasis remains uncertain. Methods: SIRT2-knockout (KO) rats were constructed to evaluate the role of SIRT2 in glucose homeostasis. The effect of SIRT2 on ß-cell function was detected by investigating the morphology, insulin secretion, and metabolomic state of islets. The deacetylation and stabilization of GKRP in ß-cells by SIRT2 were determined by western blot, adenoviral infection, and immunoprecipitation. Results: SIRT2-KO rats exhibited impaired glucose tolerance and glucose-stimulated insulin secretion (GSIS), without change in insulin sensitivity. SIRT2 deficiency or inhibition by AGK2 decreased GSIS in isolated rat islets, with lowered oxygen consumption rate. Adenovirus-mediated overexpression of SIRT2 enhanced insulin secretion from rat islets. Metabolomics analysis revealed a decrease in metabolites of glycolysis and tricarboxylic acid cycle in SIRT2-KO islets compared with control islets. Our study further demonstrated that glucokinase regulatory protein (GKRP), an endogenous inhibitor of glucokinase (GCK), was expressed in rat islets. SIRT2 overexpression deacetylated GKRP in INS-1 ß-cells. SIRT2 knockout or inhibition elevated GKRP protein stability in islet ß-cells, leading to an increase in the interaction of GKRP and GCK. On the contrary, SIRT2 inhibition promoted the protein degradation of ALDOA, a glycolytic enzyme. Conclusions: SIRT2 ablation inhibits GSIS through blocking GKRP protein degradation and promoting ALDOA protein degradation, resulting in a decrease in glycolytic flux.

Loss of mitochondrial aconitase promotes colorectal cancer progression via SCD1-mediated lipid remodeling.

OBJECTIVE: Mitochondrial aconitase (ACO2) is an essential enzyme that bridges the TCA cycle and lipid metabolism. However, its role in cancer development remains to be elucidated. The metabolic subtype of colorectal cancer (CRC) was recently established. We investigated ACO2's potential role in CRC progression through mediating metabolic alterations. METHODS: We compared the mRNA and protein expression of ACO2 between paired CRC and non-tumor tissues from 353 patients. Correlations between ACO2 levels and clinicopathological features were examined. CRC cell lines with knockdown or overexpression of ACO2 were analyzed for cell proliferation and tumor growth. Metabolomics and stable isotope tracing analyses were used to study the metabolic alterations induced by loss of ACO2. RESULTS: ACO2 decreased in >50% of CRC samples compared with matched non-tumor tissues. Decreased ACO2 levels correlated with advanced disease stage (P < 0.001) and shorter patient survival (P < 0.001). Knockdown of ACO2 in CRC cells promoted cell proliferation and tumor formation, while ectopic expression of ACO2 restrained tumor growth. Specifically, blockade of ACO2 caused a reduction in TCA cycle intermediates and suppression of mitochondrial oxidative phosphorylation, resulting in an increase in glycolysis and elevated citrate flux for fatty acid and lipid synthesis. Increased citrate flux induced upregulation of stearoyl-CoA desaturase (SCD1), which enhanced lipid desaturation in ACO2-deficent cells to favor colorectal cancer growth. Pharmacological inhibition of SCD selectively reduced tumor formation of CRC with ACO2 deficiency. CONCLUSIONS: Our study demonstrated that the rewiring metabolic pathway maintains CRC survival during compromised TCA cycles and characterized the therapeutic vulnerability of lipid desaturation in a meaningful subset of CRC with mitochondrial dysfunction.

Anaerobic endosymbiont generates energy for ciliate host by denitrification.

Mitochondria are specialized eukaryotic organelles that have a dedicated function in oxygen respiration and energy production. They evolved about 2 billion years ago from a free-living bacterial ancestor (probably an alphaproteobacterium), in a process known as endosymbiosis1,2. Many unicellular eukaryotes have since adapted to life in anoxic habitats and their mitochondria have undergone further reductive evolution3. As a result, obligate anaerobic eukaryotes with mitochondrial remnants derive their energy mostly from fermentation4. Here we describe 'Candidatus Azoamicus ciliaticola', which is an obligate endosymbiont of an anaerobic ciliate and has a dedicated role in respiration and providing energy for its eukaryotic host. 'Candidatus A. ciliaticola' contains a highly reduced 0.29-Mb genome that encodes core genes for central information processing, the electron transport chain, a truncated tricarboxylic acid cycle, ATP generation and iron-sulfur cluster biosynthesis. The genome encodes a respiratory denitrification pathway instead of aerobic terminal oxidases, which enables its host to breathe nitrate instead of oxygen. 'Candidatus A. ciliaticola' and its ciliate host represent an example of a symbiosis that is based on the transfer of energy in the form of ATP, rather than nutrition. This discovery raises the possibility that eukaryotes with mitochondrial remnants may secondarily acquire energy-providing endosymbionts to complement or replace functions of their mitochondria.