The mitochondrion is susceptible to neurodegenerative disorders such as Parkinson's disease (PD). Mitochondrial dysfunction has been considered to play an important role in the dopaminergic degeneration in PD. However, there are no effective drugs to protect mitochondria from dysfunction during the disease development. In the present study, fucoidan, a sulfated polysaccharide derived from Laminaria japonica, was investigated and characterized for its protective effect on the dopamine system and mitochondrial function of dopaminergic neurons in a rotenone-induced rat model of PD. We found that chronic treatment with fucoidan significantly reversed the loss of nigral dopaminergic neurons and striatal dopaminergic fibers and the reduction of striatal dopamine levels in PD rats. Fucoidan also alleviated rotenone-induced behavioral deficits. Moreover, the mitochondrial respiratory function as detected by the mitochondrial oxygen consumption and the expression of peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) and nuclear transcription factor 2 (NRF2) were reduced in the substantia nigra of PD rats, which were markedly reversed by fucoidan. Oxidative products induced by rotenone were significantly reduced by fucoidan. Taken together, these results demonstrate that fucoidan possesses the ability to protect the dopamine system in PD rats. The neuroprotective effect of fucoidan may be mediated via reserving mitochondrial function involving the PGC-1α/NRF2 pathway. This study provides new evidence that fucoidan can be explored in PD therapy.

Hyper-phosphorylation of RB controls its interaction with E2F and inhibits its tumor suppressor properties. However, during G1 active RB can be mono-phosphorylated on any one of 14 CDK phosphorylation sites. Here, we used quantitative proteomics to profile protein complexes formed by each mono-phosphorylated RB isoform (mP-RB) and identified the associated transcriptional outputs. The results show that the 14 sites of mono-phosphorylation co-ordinate RB's interactions and confer functional specificity. All 14 mP-RBs interact with E2F/DP proteins, but they provide different shades of E2F regulation. RB mono-phosphorylation at S811, for example, alters RB transcriptional activity by promoting its association with NuRD complexes. The greatest functional differences between mP-RBs are evident beyond the cell cycle machinery. RB mono-phosphorylation at S811 or T826 stimulates the expression of oxidative phosphorylation genes, increasing cellular oxygen consumption. These results indicate that RB activation signals are integrated in a phosphorylation code that determines the diversity of RB activity.

Iron deficiency is the most prevalent micronutrient disorder globally. When severe, iron deficiency leads to anemia, which can be deleterious to cardiac function. Given the central role of iron and oxygen in cardiac biology, multiple pathways are expected to be altered in iron-deficiency anemia, and identifying these requires an unbiased approach. To investigate these changes, gene expression and metabolism were studied in mice weaned onto an iron-deficient diet for 6 weeks. Whole-exome transcriptomics (RNAseq) identified over 1,500 differentially expressed genes (DEGs), of which 22% were upregulated and 78% were downregulated in the iron-deficient group, relative to control animals on an iron-adjusted diet. The major biological pathways affected were oxidative phosphorylation and pyruvate metabolism, as well as cardiac contraction and responses related to environmental stress. Cardiac metabolism was studied functionally using in vitro and in vivo methodologies. Spectrometric measurement of the activity of the four electron transport chain complexes in total cardiac lysates showed that the activities of Complexes I and IV were reduced in the hearts of iron-deficient animals. Pyruvate metabolism was assessed in vivo using hyperpolarized 13C magnetic resonance spectroscopy (MRS) of hyperpolarized pyruvate. Hearts from iron-deficient and anemic animals showed significantly decreased flux through pyruvate dehydrogenase and increased lactic acid production, consistent with tissue hypoxia and induction of genes coding for glycolytic enzymes and H+-monocarboxylate transport-4. Our results show that iron-deficiency anemia results in a metabolic remodeling toward a glycolytic, lactic acid-producing phenotype, a hallmark of hypoxia.

Monoamine neurotransmitters were detected in gastric cancer tissue and paired normal tissue, and The Cancer Genome Atlas was used to identify differentially expressed norepinephrine-degrading and synthetic enzymes. Quantitative real-time PCR and the Seahorse assay were used to determine the effect of norepinephrine on gastric cancer cell glycolysis. MAOA expression in cancer tissues was analyzed by immunohistochemistry and was compared with the patient SUVmax value of PET-CT and other clinicopathological characteristics.

Astaxanthin (AX) is a carotenoid that exerts potent antioxidant activity and acts in the lipid bilayer. This study aimed to investigate the effects of AX on muscle-atrophy-mediated disturbance of mitochondria, which have a lipid bilayer. Tail suspension was used to establish a muscle-atrophied mouse model. AX diet fed to tail-suspension mice prevented loss of muscle weight, inhibited the decrease of myofiber size, and restrained the increase of hydrogen peroxide (H2O2) production in the soleus muscle. Additionally, AX improved downregulation of mitochondrial respiratory chain complexes I and III in the soleus muscle after tail suspension. Meanwhile, AX promoted mitochondrial biogenesis by upregulating the expressions of adenosine 5'-monophosphate-activated protein kinase (AMPK) α-1, peroxisome proliferator-activated receptor (PPAR)-γ, and creatine kinase in mitochondrial (Ckmt) 2 in the soleus muscle of tail-suspension mice. To confirm the AX phenotype in the soleus muscle, we examined its effects on mitochondria using Sol8 myotubes derived from the soleus muscle. We found that AX was preferentially detected in the mitochondrial fraction; it significantly suppressed mitochondrial reactive oxygen species (ROS) production in Sol8 myotubes. Moreover, AX inhibited the activation of caspase 3 via inhibiting the release of cytochrome c into the cytosol in antimycin A-treated Sol8 myotubes. These results suggested that AX protected the functional stability of mitochondria, alleviated mitochondrial oxidative stress and mitochondria-mediated apoptosis, and thus, prevented muscle atrophy.

Low body temperature predicts a poor outcome in patients with heart failure, but the underlying pathological mechanisms and implications are largely unknown. Brown adipose tissue (BAT) was initially characterised as a thermogenic organ, and recent studies have suggested it plays a crucial role in maintaining systemic metabolic health. While these reports suggest a potential link between BAT and heart failure, the potential role of BAT dysfunction in heart failure has not been investigated. Here, we demonstrate that alteration of BAT function contributes to development of heart failure through disorientation in choline metabolism. Thoracic aortic constriction (TAC) or myocardial infarction (MI) reduced the thermogenic capacity of BAT in mice, leading to significant reduction of body temperature with cold exposure. BAT became hypoxic with TAC or MI, and hypoxic stress induced apoptosis of brown adipocytes. Enhancement of BAT function improved thermogenesis and cardiac function in TAC mice. Conversely, systolic function was impaired in a mouse model of genetic BAT dysfunction, in association with a low survival rate after TAC. Metabolomic analysis showed that reduced BAT thermogenesis was associated with elevation of plasma trimethylamine N-oxide (TMAO) levels. Administration of TMAO to mice led to significant reduction of phosphocreatine and ATP levels in cardiac tissue via suppression of mitochondrial complex IV activity. Genetic or pharmacological inhibition of flavin-containing monooxygenase reduced the plasma TMAO level in mice, and improved cardiac dysfunction in animals with left ventricular pressure overload. In patients with dilated cardiomyopathy, body temperature was low along with elevation of plasma choline and TMAO levels. These results suggest that maintenance of BAT homeostasis and reducing TMAO production could be potential next-generation therapies for heart failure.

Evidence is mounting for the central role of mitochondrial dysfunction in several pathologies including metabolic diseases, accelerated ageing, neurodegenerative diseases and in certain xenobiotic-induced organ toxicity. Assessing mitochondrial perturbations is not trivial and the outcomes of such investigations are dependent on the cell types used and assays employed. Here we systematically investigated the effect of electron transport chain (ETC) inhibitors on multiple mitochondrial-related parameters in two human cell types, HepG2 and RPTEC/TERT1. Cells were exposed to a broad range of concentrations of 20 ETC-inhibiting agrochemicals and capsaicin, consisting of inhibitors of NADH dehydrogenase (Complex I, CI), succinate dehydrogenase (Complex II, CII) and cytochrome bc1 complex (Complex III, CIII). A battery of tests was utilised, including viability assays, lactate production, mitochondrial membrane potential (MMP) and the Seahorse bioanalyser, which simultaneously measures extracellular acidification rate [ECAR] and oxygen consumption rate [OCR]. CI inhibitors caused a potent decrease in OCR, decreased mitochondrial membrane potential, increased ECAR and increased lactate production in both cell types. Twenty-fourhour exposure to CI inhibitors decreased viability of RPTEC/TERT1 cells and 3D spheroid-cultured HepG2 cells in the presence of glucose. CI inhibitors decreased 2D HepG2 viability only in the absence of glucose. CII inhibitors had no notable effects in intact cells up to 10 µM. CIII inhibitors had similar effects to the CI inhibitors. Antimycin A was the most potent CIII inhibitor, with activity in the nanomolar range. The proposed CIII inhibitor cyazofamid demonstrated a mitochondrial uncoupling signal in both cell types. The study presents a comprehensive example of a mitochondrial assessment workflow and establishes measurable key events of ETC inhibition.

Many types of tumors feature aerobic glycolysis for meeting their increased energetic and biosynthetic demands. However, it remains still unclear how this glycolytic phenomenon is achieved and coordinated with other metabolic pathways in tumor cells in response to growth stimuli. Here we report that activation of AKT1 induces a metabolic switch to glycolysis from the mitochondrial metabolism via phosphorylation of cytoplasmic malic enzyme 2 (ME2), named ME2fl (fl means full length), favoring an enhanced glycolytic phenotype. Mechanistically, in the cytoplasm, AKT1 phosphorylates ME2fl at serine 9 in the mitochondrial localization signal peptide at the N-terminus, preventing its mitochondrial translocation. Unlike mitochondrial ME2, which accounts for adjusting the tricarboxylic acid (TCA) cycle, ME2fl functions as a scaffold that brings together the key glycolytic enzymes phosphofructokinase (PFKL), glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and pyruvate kinase M2 (PKM2), as well as Lactate dehydrogenase A (LDHA), to promote glycolysis in the cytosol. Thus, through phosphorylation of ME2fl, AKT1 enhances the glycolytic capacity of tumor cells in vitro and in vivo, revealing an unexpected role for subcellular translocation switching of ME2 mediated by AKT1 in the metabolic adaptation of tumor cells to growth stimuli.

Regulatory T cells (Tregs) subdue immune responses. Central to Treg activation are changes in lipid metabolism that support their survival and function. Fatty acid binding proteins (FABPs) are a family of lipid chaperones required to facilitate uptake and intracellular lipid trafficking. One family member, FABP5, is expressed in T cells, but its function remains unclear. We show that in Tregs, genetic or pharmacologic inhibition of FABP5 function causes mitochondrial changes underscored by decreased OXPHOS, impaired lipid metabolism, and loss of cristae structure. FABP5 inhibition in Tregs triggers mtDNA release and consequent cGAS-STING-dependent type I IFN signaling, which induces heightened production of the regulatory cytokine IL-10 and promotes Treg suppressive activity. We find evidence of this pathway, along with correlative mitochondrial changes in tumor infiltrating Tregs, which may underlie enhanced immunosuppression in the tumor microenvironment. Together, our data reveal that FABP5 is a gatekeeper of mitochondrial integrity that modulates Treg function.

In mammals, autophagosome formation is initiated by ULK1 via the posttranslational modification of this protein. However, the precise role of ULK1 ubiquitination in modulating autophagy is unknown. Here, we show that NEDD4L, an E3 ubiquitin ligase, binds ULK1 in pancreatic cancer cells. ULK1 expression was stabilized in NEDD4L knockdown cells compared to that in control cells, suggesting that NEDD4L is involved in ULK1 ubiquitination and its subsequent degradation. Autophagy activity was enhanced in NEDD4L knockdown cells compared to control cells. NEDD4L-depleted cells exhibited an increase in the cellular oxygen consumption rate (OCR) and mitochondrial membrane potential, and maintained mitochondrial fusion status in response to metabolic stress. Enhanced OCR and mitochondrial fusion morphology in NEDD4L knockdown cells were repressed by siRNA targeting ULK1. In addition to ULK1, ASCT2, a glutamine transporter, was accumulated in NEDD4L-depleted cells; this is important for maintaining autophagy activation and mitochondrial metabolic function. Finally, the cellular growth and survival rate increased in NEDD4L knockdown cells compared to control cells. However, the genetic or pharmacological blockade of either ULK1 or ASCT2 in NEDD4L-depleted cells sensitized pancreatic cancer cells, particularly in response to nutrient deprivation. In a mouse xenograft model of pancreatic cancer, the use of autophagy inhibitors suppressed tumor growth more in NEDD4L-depleted cells than in tumors from control cells. NEDD4L and ULK1 levels were inversely correlated in two different pancreatic cancer mouse models-xenograft mouse and KPC mouse models. These results suggest that NEDD4L suppressed autophagy and mitochondrial metabolism by reducing cellular ULK1 or ASCT2 levels, and thus could repress the growth and survival of pancreatic cancer cells. Therefore, ubiquitin ligase-mediated autophagy plays a critical role in regulating mitochondrial metabolism, thereby contributing to the growth and survival of certain cancers with low NEDD4L levels.

Mitochondrial dysfunction is associated with a spectrum of human conditions, ranging from rare, inborn errors of metabolism to the aging process. To identify pathways that modify mitochondrial dysfunction, we performed genome-wide CRISPR screens in the presence of small-molecule mitochondrial inhibitors. We report a compendium of chemical-genetic interactions involving 191 distinct genetic modifiers, including 38 that are synthetic sick/lethal and 63 that are suppressors. Genes involved in glycolysis (PFKP), pentose phosphate pathway (G6PD), and defense against lipid peroxidation (GPX4) scored high as synthetic sick/lethal. A surprisingly large fraction of suppressors are pathway intrinsic and encode mitochondrial proteins. A striking example of such "intra-organelle" buffering is the alleviation of a chemical defect in complex V by simultaneous inhibition of complex I, which benefits cells by rebalancing redox cofactors, increasing reductive carboxylation, and promoting glycolysis. Perhaps paradoxically, certain forms of mitochondrial dysfunction may best be buffered with "second site" inhibitors to the organelle.

The microvasculature plays a key role in tissue perfusion and exchange of gases and metabolites. In this study we use human blood vessel organoids (BVOs) as a model of the microvasculature. BVOs fully recapitulate key features of the human microvasculature, including the reliance of mature endothelial cells on glycolytic metabolism, as concluded from metabolic flux assays and mass spectrometry-based metabolomics using stable tracing of 13C-glucose. Pharmacological targeting of PFKFB3, an activator of glycolysis, using two chemical inhibitors results in rapid BVO restructuring, vessel regression with reduced pericyte coverage. PFKFB3 mutant BVOs also display similar structural remodelling. Proteomic analysis of the BVO secretome reveal remodelling of the extracellular matrix and differential expression of paracrine mediators such as CTGF. Treatment with recombinant CTGF recovers microvessel structure. In this work we demonstrate that BVOs rapidly undergo restructuring in response to metabolic changes and identify CTGF as a critical paracrine regulator of microvascular integrity.

Oxidative stress has been causally linked to various diseases. Electron transport chain (ETC) inhibitors such as rotenone and antimycin A are frequently used in model systems to study oxidative stress. Oxidative stress that is provoked by ETC inhibitors can be visualized using the fluorogenic probe 2',7'-dichlorodihydrofluorescein-diacetate (DCFH2-DA). Non-fluorescent DCFH2-DA crosses the plasma membrane, is deacetylated to 2',7'-dichlorodihydrofluorescein (DCFH2) by esterases, and is oxidized to its fluorescent form 2',7'-dichlorofluorescein (DCF) by intracellular ROS. DCF fluorescence can, therefore, be used as a semi-quantitative measure of general oxidative stress. However, the use of DCFH2-DA is complicated by various protocol-related factors that mediate DCFH2-to-DCF conversion independently of the degree of oxidative stress. This study therefore analyzed the influence of ancillary factors on DCF formation in the context of ETC inhibitors. It was found that ETC inhibitors trigger DCF formation in cell-free experiments when they are co-dissolved with DCFH2-DA. Moreover, the extent of DCF formation depended on the type of culture medium that was used, the pH of the assay system, the presence of fetal calf serum, and the final DCFH2-DA solvent concentration. Conclusively, experiments with DCFH2-DA should not discount the influence of protocol-related factors such as medium and mitochondrial inhibitors (and possibly other compounds) on the DCFH2-DA-DCF reaction and proper controls should always be built into the assay protocol.

Redox signaling and cardiac function are tightly linked. However, it is largely unknown which protein targets are affected by hydrogen peroxide (H2O2) in cardiomyocytes that underly impaired inotropic effects during oxidative stress. Here, we combine a chemogenetic mouse model (HyPer-DAO mice) and a redox-proteomics approach to identify redox sensitive proteins. Using the HyPer-DAO mice, we demonstrate that increased endogenous production of H2O2 in cardiomyocytes leads to a reversible impairment of cardiac contractility in vivo. Notably, we identify the γ-subunit of the TCA cycle enzyme isocitrate dehydrogenase (IDH)3 as a redox switch, linking its modification to altered mitochondrial metabolism. Using microsecond molecular dynamics simulations and experiments using cysteine-gene-edited cells reveal that IDH3γ Cys148 and 284 are critically involved in the H2O2-dependent regulation of IDH3 activity. Our findings provide an unexpected mechanism by which mitochondrial metabolism can be modulated through redox signaling processes.

We have investigated the mechanism of mitochondrial-nuclear crosstalk during cellular stress in mouse C2C12 myocytes. For this purpose, we used cells with reduced mitochondrial DNA (mtDNA) contents by ethidium bromide treatment or myocytes treated with known mitochondrial metabolic inhibitors, including carbonyl cyanide m-chlorophenylhydrazone (CCCP), antimycin, valinomycin and azide. Both genetic and metabolic stresses similarly affected mitochondrial membrane potential (Deltapsim) and electron transport-coupled ATP synthesis, which was also accompanied by an elevated steady-state cytosolic Ca2+ level ([Ca2+]i). The mitochondrial stress resulted in: (i) an enhanced expression of the sarcoplasmic reticular ryanodine receptor-1 (RyR-1), hence potentiating the Ca2+ release in response to its modulator, caffeine; (ii) enhanced levels of Ca2+-responsive factors calineurin, calcineurin-dependent NFATc (cytosolic counterpart of activated T-cell-specific nuclear factor) and c-Jun N-terminal kinase (JNK)-dependent ATF2 (activated transcription factor 2); (iii) reduced levels of transcription factor, NF-kappaB; and (iv) enhanced transcription of cytochrome oxidase Vb (COX Vb) subunit gene. These cellular changes, including the steady-state [Ca2+]i were normalized in genetically reverted cells which contain near-normal mtDNA levels. We propose that the mitochondria-to-nucleus stress signaling occurs through cytosolic [Ca2+]i changes, which are likely to be due to reduced ATP and Ca2+ efflux. Our results indicate that the mitochondrial stress signal affects a variety of cellular processes, in addition to mitochondrial membrane biogenesis.

Metabolic reprogramming is one of cancer hallmarks. Here, we focus on functional differences and individual contribution of acyl coA synthetases (ACSL) isoforms to the previously described ACSL/stearoyl-CoA desaturase (ACSL1/ACSL4/SCD) metabolic network causing invasion and poor prognosis in colorectal cancer (CRC). ACSL4 fuels proliferation and migration accompanied by a more glycolytic phenotype. Conversely, ACSL1 stimulates invasion displaying a lower basal respiratory rate. Acylcarnitines elevation, polyunsaturated fatty acids (PUFA) lower levels, and monounsaturated fatty acids (MUFA) upregulation characterize the individual overexpression of ACSL1, ACSL4 and SCD, respectively. However, the three enzymes simultaneous overexpression results in upregulated phospholipids and urea cycle derived metabolites. Thus, the metabolic effects caused by the network are far from being caused by the individual contributions of each enzyme. Furthermore, ACSL/SCD network produces more energetically efficient cells with lower basal respiration levels and upregulated creatine pathway. These features characterize other invasive CRC cells, thus, ACSL/SCD network exemplifies specific metabolic adaptations for invasive cancer cells.

Differential WNT and Notch signaling regulates differentiation of Lgr5+ crypt-based columnar cells (CBCs) into intestinal cell lineages. Recently we showed that mitochondrial activity supports CBCs, while adjacent Paneth cells (PCs) show reduced mitochondrial activity. This implies that CBC differentiation into PCs involves a metabolic transition toward downregulation of mitochondrial dependency. Here we show that Forkhead box O (FoxO) transcription factors and Notch signaling interact in determining CBC fate. In agreement with the organoid data, Foxo1/3/4 deletion in mouse intestine induces secretory cell differentiation. Importantly, we show that FOXO and Notch signaling converge on regulation of mitochondrial fission, which in turn provokes stem cell differentiation into goblet cells and PCs. Finally, scRNA-seq-based reconstruction of CBC differentiation trajectories supports the role of FOXO, Notch, and mitochondria in secretory differentiation. Together, this points at a new signaling-metabolic axis in CBC differentiation and highlights the importance of mitochondria in determining stem cell fate.

Dendritic cell (DC) maturation induced by Toll-like receptor agonists requires activation of downstream signal transduction and metabolic changes. The endogenous metabolite citrate has recently emerged as a modulator of DC activation. However, the metabolic requirements that support citrate production remain poorly defined. Here, we demonstrate that p32/C1qbp, which functions as a multifunctional chaperone protein in mitochondria, supports mitochondrial metabolism and DC maturation. Metabolic analysis revealed that the citrate increase induced by lipopolysaccharide (LPS) is impaired in p32-deficient DCs. We also found that p32 interacts with dihydrolipoamide S-acetyltransferase (E2 component of pyruvate dehydrogenase [PDH] complex) and positively regulates PDH activity in DCs. Therefore, we suggest that DC maturation is regulated by citrate production via p32-dependent PDH activity. p32-null mice administered a PDH inhibitor show decreased DC maturation and ovalbumin-specific IgG production in vivo, suggesting that p32 may serve as a therapeutic target for DC-related autoimmune diseases.

Iron is the most abundant transition metal essential for numerous cellular processes. Although most mammalian cells acquire iron through transferrin receptors, molecular players of iron utilization under iron restriction are incompletely understood. To address this, we performed metabolism-focused CRISPRa gain-of-function screens, which revealed metabolic limitations under stress conditions. Iron restriction screens identified not only expected members of iron utilization pathways but also SLCO2B1, a poorly characterized membrane carrier. SLCO2B1 expression is sufficient to increase intracellular iron, bypass the essentiality of the transferrin receptor, and enable proliferation under iron restriction. Mechanistically, SLCO2B1 mediates heme analog import in cellular assays. Heme uptake by SLCO2B1 provides sufficient iron for proliferation through heme oxygenases. Notably, SLCO2B1 is predominantly expressed in microglia in the brain, and primary Slco2b1-/- mouse microglia exhibit strong defects in heme analog import. Altogether, our work identifies SLCO2B1 as a microglia-enriched plasma membrane heme importer and provides a genetic platform to identify metabolic limitations under stress conditions.

Autophagy is a membrane-trafficking process that directs degradation of cytoplasmic material in lysosomes. The process promotes cellular fidelity, and while the core machinery of autophagy is known, the mechanisms that promote and sustain autophagy are less well defined. Here we report that the epigenetic reader BRD4 and the methyltransferase G9a repress a TFEB/TFE3/MITF-independent transcriptional program that promotes autophagy and lysosome biogenesis. We show that BRD4 knockdown induces autophagy in vitro and in vivo in response to some, but not all, situations. In the case of starvation, a signaling cascade involving AMPK and histone deacetylase SIRT1 displaces chromatin-bound BRD4, instigating autophagy gene activation and cell survival. Importantly, this program is directed independently and also reciprocally to the growth-promoting properties of BRD4 and is potently repressed by BRD4-NUT, a driver of NUT midline carcinoma. These findings therefore identify a distinct and selective mechanism of autophagy regulation.