Up-regulation of the ATPase inhibitory factor 1 (IF1) of the mitochondrial H+-ATP synthase in human tumors mediates the metabolic shift of cancer cells to a Warburg phenotype

F-ATP synthase inhibitory factor 1 and mitochondria-organelle interactions: New insight and implications

Mitochondria are metabolic hub, and act as primary sites for reactive oxygen species (ROS) and metabolites generation. Mitochondrial Ca2+ uptake contributes to Ca2+ storage. Mitochondria-organelle interactions are important for cellular metabolic adaptation, biosynthesis, redox balance, cell fate. Organelle communications are mediated by Ca2+/ROS signals, vesicle transport and membrane contact sites. The permeability transition pore (PTP) is an unselective channel that provides a release pathway for Ca2+/ROS, mtDNA and metabolites. F-ATP synthase inhibitory factor 1 (IF1) participates in regulation of PTP opening and is required for the translocation of transcriptional factors c-Myc/PGC1α to mitochondria to stimulate metabolic switch. IF1, a mitochondrial specific protein, has been suggested to regulate other organelles including nucleus, endoplasmic reticulum and lysosomes. IF1 may be able to mediate mitochondria-organelle interactions and cellular physiology through regulation of PTP activity.

Mitochondrial protein deacetylation by SIRT3 in osteoclasts promotes bone resorption with aging in female mice

OBJECTIVES

The mitochondrial deacetylase sirtuin-3 (SIRT3) is necessary for the increased bone resorption and enhanced function of mitochondria in osteoclasts that occur with advancing age; how SIRT3 drives bone resorption remains elusive.

METHODS

To determine the role of SIRT3 in osteoclast mitochondria, we used mice with conditional loss of Sirt3 in osteoclast lineage and mice with germline deletion of either Sirt3 or its known target Pink1.

RESULTS

SIRT3 stimulates mitochondrial quality in osteoclasts in a PINK1-independent manner, promoting mitochondrial activity and osteoclast maturation and function, thereby contributing to bone loss in female but not male mice. Quantitative analyses of global proteomes and acetylomes revealed that deletion of Sirt3 dramatically increased acetylation of osteoclast mitochondrial proteins, particularly ATPase inhibitory factor 1 (ATPIF1), an essential protein for mitophagy. Inhibition of mitophagy via mdivi-1 recapitulated the effect of deletion of Sirt3 or Atpif1 in osteoclast formation and mitochondrial function.

CONCLUSIONS

Decreasing mitophagic flux in osteoclasts may be a promising pharmacotherapeutic approach to treat osteoporosis in older adults.

Photosensitive AIEgens sensitize bacteria to oxidative damage and modulate the inflammatory responses of macrophages to salvage the photodynamic therapy against MRSA

The urgent need for antimicrobial agents to combat infections caused by multidrug-resistant bacteria facilitates the exploration of alternative strategies such as photosensitizer (PS)-mediated photoinactivation. However, increasing studies have discovered uncorrelated bactericidal activities among PSs possessing similar photodynamic and pathogen-targeted properties. To optimize the photodynamic therapy (PDT) against infections, we investigated three type-I PSs of D-π-A AIEgens TI, TBI, and TTI. The capacities of reactive oxygen species (ROS) generation of TI, TBI, and TTI did not align with their bactericidal activities. Despite exhibiting the lowest photodynamic efficiency, TI exhibited the highest activities against methicillin-resistant Staphylococcus aureus (MRSA) by impairing the anti-oxidative responses of bacteria. By comparison, TTI, characterized by the strongest ROS production, inactivated intracellular MRSA by potentiating the inflammatory response of macrophages. Unlike TI and TTI, TBI, despite possessing moderate photodynamic activities and inducing ROS accumulation in both MRSA and macrophages, did not exhibit any antibacterial activity. Therefore, relying on the disturbed anti-oxidative metabolism of pathogens or potentiated host immune responses, transient ROS bursts can effectively control bacterial infections. Our study reevaluates the contribution of photodynamic activities of PSs to bacterial elimination and provides new insights into discovering novel antibacterial targets and agents.

Nicotinamide riboside Induced Energy Stress and Metabolic Reprogramming in BEAS-2B Cells

Nicotinamide riboside (NR), a NAD+ precursor, has received attention due to several health benefits it has induced in experimental models. Studies in cultured cells, animals, and humans consistently show increased NAD+ availability after NR supplementation, which is considered the only mode of NR action that leads to health benefits. In the present study, we show that a persistently low NR concentration (1 μM) in the growth medium of BEAS-2B human cells, grown in a monolayer, induces energy stress, which precedes a cellular NAD+ increase after 192 h. NR concentrations greater than 1 μM under the specified conditions were cytotoxic in the 2D cell culture model, while all concentrations tested in the 3D cell culture model (BEAS-2B cell spheroids exposed to 1, 5, 10, and 50 μM NR) induced apoptosis. Shotgun proteomics revealed that NR modulated the abundance of proteins, agreeing with the observed effects on cellular energy metabolism and cell growth or survival. Energy stress may activate pathways that lead to health benefits such as cancer prevention. Accordingly, the premalignant 1198 cell line was more sensitive to NR cytotoxicity than the phenotypically normal parent BEAS-2B cell line. The role of a mild energy stress induced by low concentrations of NR in its beneficial effects deserves further investigation. On the other hand, strategies to increase the bioavailability of NR require attention to toxic effects that may arise.

The Toxoplasma gondii homolog of ATPase inhibitory factor 1 is critical for mitochondrial cristae maintenance and stress response

The production of energy in the form of ATP by the mitochondrial ATP synthase must be tightly controlled. One well-conserved form of regulation is mediated via ATPase inhibitory factor 1 (IF1), which governs ATP synthase activity and gene expression patterns through a cytoprotective process known as mitohormesis. In apicomplexans, the processes regulating ATP synthase activity are not fully elucidated. Using the model apicomplexan Toxoplasma gondii, we found that knockout and overexpression of TgIF1, the structural homolog of IF1, significantly affected gene expression. Additionally, TgIF1 overexpression resulted in the formation of a stable TgIF1 oligomer that increased the presence of higher order ATP synthase oligomers. We also show that parasites lacking TgIF1 exhibit reduced mitochondrial cristae density, and that while TgIF1 levels do not affect growth in conventional culture conditions, they are crucial for parasite survival under hypoxia. Interestingly, TgIF1 overexpression enhances recovery from oxidative stress, suggesting a mitohormetic function. In summary, while TgIF1 does not appear to play a role in metabolic regulation under conventional growth conditions, our work highlights its importance for adapting to stressors faced by T. gondii and other apicomplexans throughout their intricate life cycles.

Ablation of Atp5if1 impairs metabolic reprogramming and proliferation of T lymphocytes and compromises mouse survival

T cells experience metabolic reprogramming to an enhanced glycolysis upon activation. Herein, we have investigated whether ATPase Inhibitory Factor 1 (IF1), the physiological inhibitor of mitochondrial ATP synthase, participates in rewiring T cells to a particular metabolic phenotype. We show that the activation of naive CD4+ T lymphocytes both in vitro and in vivo is accompanied by a sharp upregulation of IF1, which is expressed only in Th1 effector cells. T lymphocytes of conditional CD4+-IF1-knockout mice display impaired glucose uptake and flux through glycolysis, reducing the biogenesis of mitochondria and cellular proliferation after activation. Consequently, mice devoid of IF1 in T lymphocytes cannot mount an effective Th1 response against bacterial infection compromising their survival. Overall, we show that the inhibition of a fraction of ATP synthase by IF1 regulates metabolic reprogramming and functionality of T cells, highlighting the essential role of IF1 in adaptive immune responses.

Benzoylaconine Protects Skeletal Muscle Against Ischemia-Reperfusion Injury Through Activation of IF1-Dependent AMPK/Nrf2 Axis

Background

Aconitum carmichaelii (Fuzi) has been conventionally used to cure a variety of ailments, such as pain, cold sensations, and numbness of limb muscles (Bi Zheng) in China. Our prior investigations identified Benzoylaconine (BAC) as a bioactive alkaloid derived from Aconitum carmichaelii, with other studies also demonstrating its significant pharmacological potential.

Purpose

This study aimed to explore the potential of BAC as a protective agent against skeletal muscle ischemia-reperfusion (I/R) injury and to elucidate the underlying mechanisms.

Methods

In vivo models involved subjecting Sprague-Dawley rats to I/R through femoral artery ligation followed by reperfusion, while in vitro models utilized C2C12 cells subjected to hypoxia/reoxygenation (H/R). CCK-8 assay was used to assess cell viability. TUNEL staining and flow cytometric analysis were used to measure cell apoptosis. Biochemical assay was used to assess skeletal muscle injury and oxidative stress. Immunofluorescence and Western blot were performed to determine protein levels.

Results

BAC effectively protected muscle tissue from I/R injury, enhancing cell viability (p<0.01), elevating SOD levels (p<0.05), and reducing CK (p<0.01), LDH (p<0.01), ROS (p<0.01), MDA (p<0.01), and apoptosis-related molecules in vivo and in vitro (p<0.05, p<0.01). Mechanistically, BAC increased the expression of IF1, phosphorylated AMPK, facilitated the translocation of nuclear Nrf2, and induced the expression of HO-1 (p<0.01). Notably, AMPK inhibitor Compound C significantly hindered the ability of BAC to ameliorate H/R-induced cell injury (p<0.05), oxidative stress(p<0.01), and apoptosis (p<0.05), as well as promote Nrf2 nuclear translocation (p<0.01). Moreover, silencing of IF1 with siRNA abolished BAC-induced activation of AMPK/Nrf2 axis (p<0.01).

Conclusion

Our study provides novel evidence supporting the potential of BAC as a myocyte-protective agent against I/R injury, and we establish a previously unknown mechanism involving the activation of the IF1-dependent AMPK/Nrf2 axis in mediating the protective effects of BAC.

Associations between physical activity levels and ATPase inhibitory factor 1 concentrations in older adults

BACKGROUND

Adenosine triphosphatase inhibitory factor 1 (IF1) is a key protein involved in energy metabolism. IF1 has been linked to various age-related diseases, although its relationship with physical activity (PA) remains unclear. Additionally, the apolipoprotein A-I (apoA-I), a PA-modulated lipoprotein, could play a role in this relationship because it shares a binding site with IF1 on the cell-surface ATP synthase. We examined here the associations between chronic PA and plasma IF1 concentrations among older adults, and we investigated whether apoA-I mediated these associations.

METHODS

In the present work, 1096 healthy adults (63.8% females) aged 70 years and over who were involved in the Multidomain Alzheimer Prevention Trial study were included. IF1 plasma concentrations (square root of ng/mL) were measured at the 1-year visit of the Multidomain Alzheimer Prevention Trial, while PA levels (square root of metabolic equivalent task min/week) were assessed using questionnaires administered each year from baseline to the 3-year visit. Multiple linear regressions were performed to investigate the associations between the first-year mean PA levels and IF1 concentrations. Mediation analyses were conducted to examine whether apoA-I mediated these associations. Mixed-effect linear regressions were carried out to investigate whether the 1-year visit IF1 concentrations predicted subsequent changes in PA.

RESULTS

Multiple linear regressions indicated that first-year mean PA levels were positively associated with IF1 concentrations (B = 0.021; SE = 0.010; p = 0.043). Mediation analyses revealed that about 37.7% of this relationship was mediated by apoA-I (Bab = 0.008; SE = 0.004; p = 0.023). Longitudinal investigations demonstrated that higher concentrations of IF1 at the 1-year visit predicted a faster decline in PA levels over the subsequent 2 years (time × IF1: B = -0.148; SE = 0.066; p = 0.025).

CONCLUSION

This study demonstrates that regular PA is associated with plasma IF1 concentrations, and it suggests that apoA-I partly mediates this association. Additionally, this study finds that baseline concentrations of IF1 can predict future changes in PA. However, further research is needed to fully understand the mechanisms underlying these observations.

Neuroreceptor Inhibition by Clozapine Triggers Mitohormesis and Metabolic Reprogramming in Human Blood Cells

The antipsychotic drug clozapine demonstrates superior efficacy in treatment-resistant schizophrenia, but its intracellular mode of action is not completely understood. Here, we analysed the effects of clozapine (2.5-20 µM) on metabolic fluxes, cell respiration, and intracellular ATP in human HL60 cells. Some results were confirmed in leukocytes of clozapine-treated patients. Neuroreceptor inhibition under clozapine reduced Akt activation with decreased glucose uptake, thereby inducing ER stress and the unfolded protein response (UPR). Metabolic profiling by liquid-chromatography/mass-spectrometry revealed downregulation of glycolysis and the pentose phosphate pathway, thereby saving glucose to keep the electron transport chain working. Mitochondrial respiration was dampened by upregulation of the F0F1-ATPase inhibitory factor 1 (IF1) leading to 30-40% lower oxygen consumption in HL60 cells. Blocking IF1 expression by cotreatment with epigallocatechin-3-gallate (EGCG) increased apoptosis of HL60 cells. Upregulation of the mitochondrial citrate carrier shifted excess citrate to the cytosol for use in lipogenesis and for storage as triacylglycerol in lipid droplets (LDs). Accordingly, clozapine-treated HL60 cells and leukocytes from clozapine-treated patients contain more LDs than untreated cells. Since mitochondrial disturbances are described in the pathophysiology of schizophrenia, clozapine-induced mitohormesis is an excellent way to escape energy deficits and improve cell survival.

Histone lactylation bridges metabolic reprogramming and epigenetic rewiring in driving carcinogenesis: Oncometabolite fuels oncogenic transcription

Heightened lactate production in cancer cells has been linked to various cellular mechanisms such as angiogenesis, hypoxia, macrophage polarisation and T-cell dysfunction. The lactate-induced lactylation of histone lysine residues is noteworthy, as it functions as an epigenetic modification that directly augments gene transcription from chromatin. This epigenetic modification originating from lactate effectively fosters a reliance on transcription, thereby expediting tumour progression and development. Herein, this review explores the correlation between histone lactylation and cancer characteristics, revealing histone lactylation as an innovative epigenetic process that enhances the vulnerability of cells to malignancy. Moreover, it is imperative to acknowledge the paramount importance of acknowledging innovative therapeutic methodologies for proficiently managing cancer by precisely targeting lactate signalling. This comprehensive review illuminates a crucial yet inadequately investigated aspect of histone lactylation, providing valuable insights into its clinical ramifications and prospective therapeutic interventions centred on lactylation.

The inhibitor protein IF1 from mammalian mitochondria inhibits ATP hydrolysis but not ATP synthesis by the ATP synthase complex

The hydrolytic activity of the ATP synthase in bovine mitochondria is inhibited by a protein called IF1, but bovine IF1 has no effect on the synthetic activity of the bovine enzyme in mitochondrial vesicles in the presence of a proton motive force. In contrast, it has been suggested based on indirect observations that human IFI inhibits both the hydrolytic and synthetic activities of the human ATP synthase and that the activity of human IF1 is regulated by the phosphorylation of Ser-14 of mature IF1. Here, we have made both human and bovine IF1 which are 81 and 84 amino acids long, respectively, and identical in 71.4% of their amino acids and have investigated their inhibitory effects on the hydrolytic and synthetic activities of ATP synthase in bovine submitochondrial particles. Over a wide range of conditions, including physiological conditions, both human and bovine IF1 are potent inhibitors of ATP hydrolysis, with no effect on ATP synthesis. Also, substitution of Ser-14 with phosphomimetic aspartic and glutamic acids had no effect on inhibitory properties, and Ser-14 is not conserved throughout mammals. Therefore, it is unlikely that the inhibitory activity of mammalian IF1 is regulated by phosphorylation of this residue.

The ATPase Inhibitory Factor 1 (IF1) Contributes to the Warburg Effect and Is Regulated by Its Phosphorylation in S39 by a Protein Kinase A-like Activity

The relevant role played by the ATPase Inhibitory Factor 1 (IF1) as a physiological in vivo inhibitor of mitochondrial ATP synthase in cancer and non-cancer cells, and in the mitochondria of different mouse tissues, as assessed in different genetic loss- and gain-of-function models of IF1 has been extensively documented. In this review we summarize our findings and those of others that favor the implication of IF1 in metabolic reprogramming to an enhanced glycolytic phenotype, which is mediated by its binding and inhibition of the ATP synthase. Moreover, we emphasize that IF1 is phosphorylated in vivo in its S39 by the c-AMP-dependent PKA activity of mitochondria to render an inactive inhibitor that is unable to interact with the enzyme, thus triggering the activation of ATP synthase. Overall, we discuss and challenge the results that argue against the role of IF1 as in vivo inhibitor of mitochondrial ATP synthase and stress that IF1 cannot be regarded solely as a pro-oncogenic protein because in some prevalent carcinomas, it prevents metastatic disease.

The pro-oncogenic protein IF1 does not contribute to the Warburg effect and is not regulated by PKA in cancer cells

The endogenous inhibitor of mitochondrial F1Fo-ATPase (ATP synthase), IF1, has been shown to exert pro-oncogenic actions, including reprogramming of cellular energy metabolism (Warburg effect). The latter action of IF1 has been reported to be hampered by its PKA-dependent phosphorylation, but both reprogramming of metabolism and PKA-dependent phosphorylation are intensely debated. To clarify these critical issues, we prepared stably IF1-silenced clones and compared their bioenergetics with that of the three parental IF1-expressing cancer cell lines. All functional parameters: respiration rate, ATP synthesis rate (OXPHOS), and mitochondrial membrane potential were similar in IF1-silenced and control cells, clearly indicating that IF1 cannot inhibit the ATP synthase in cancer cells when the enzyme works physiologically. Furthermore, all cell types exposed to PKA modulators and energized with NAD+-dependent substrates or succinate showed similar OXPHOS rate regardless of the presence or absence of IF1. Therefore, our results rule out that IF1 action is modulated by its PKA-dependent phosphorylated/dephosphorylated state. Notably, cells exposed to a negative PKA modulator and energized with NAD+-dependent substrates showed a significant decrease of the OXPHOS rate matching previously reported inactivation of complex I. Overall, this study definitively demonstrates that IF1 inhibits neither mitochondrial ATP synthase nor OXPHOS in normoxic cancer cells and does not contribute to the Warburg effect. Thus, currently the protection of cancer cells from severe hypoxia/anoxia and apoptosis remain the only unquestionable actions of IF1 as pro-oncogenic factor that may be exploited to develop therapeutic approaches.

Irisin protected hemopoietic stem cells and improved outcome of severe bone marrow failure

Acquired aplastic anemia (AA) is a bone marrow failure (BMF) disease, characterized by fatty bone marrow (BM) and BM hypocellularity resulted from auto-immune dysregulated T cells-mediated destruction of BM haemopoietic stem cells (HPSC). The objective of this study was to investigate potential therapeutic effect of irisin, a molecule involved in adipose tissue transition, on AA mouse model. Our results showed that the concentration of irisin in serum was lower in AA patients than in healthy controls, suggesting a role of irisin in the pathogenesis of AA. In the AA mice, irisin administration prolonged the survival rate, prevented or attenuated peripheral pancytopenia, and preserved HPSC in the BM. Moreover, irisin also markedly reduced BM adipogenesis. In vitro results showed that irisin increased both cell proliferation and colony numbers of HPSC. Furthermore, our results demonstrated that irisin upregulated the expression of mitochondrial ATPase Inhibitory Factor 1 (IF1) in HPSC, inhibited the activation of mitochondrial fission protein (DRP1) and enhanced aerobic glycolysis. Taken together, our findings indicate novel roles of irisin in the pathogenesis of AA, and in the protection of HPSC through stimulation of proliferation and regulation of mitochondria function, which provides a proof-of-concept for the application of irisin in AA therapy.

Mitochondrial Dynamics and Cristae Shape Changes During Metabolic Reprogramming

Significance: The architecture of the mitochondrial network and cristae critically impact cell differentiation and identity. Cells undergoing metabolic reprogramming to aerobic glycolysis (Warburg effect), such as immune cells, stem cells, and cancer cells, go through controlled modifications in mitochondrial architecture, which is critical for achieving the resulting cellular phenotype. Recent Advances: Recent studies in immunometabolism have shown that the manipulation of mitochondrial network dynamics and cristae shape directly affects T cell phenotype and macrophage polarization through altering energy metabolism. Similar manipulations also alter the specific metabolic phenotypes that accompany somatic reprogramming, stem cell differentiation, and cancer cells. The modulation of oxidative phosphorylation activity, accompanied by changes in metabolite signaling, reactive oxygen species generation, and adenosine triphosphate levels, is the shared underlying mechanism. Critical Issues: The plasticity of mitochondrial architecture is particularly vital for metabolic reprogramming. Consequently, failure to adapt the appropriate mitochondrial morphology often compromises the differentiation and identity of the cell. Immune, stem, and tumor cells exhibit striking similarities in their coordination of mitochondrial morphology with metabolic pathways. However, although many general unifying principles can be observed, their validity is not absolute, and the mechanistic links thus need to be further explored. Future Directions: Better knowledge of the molecular mechanisms involved and their relationships to both mitochondrial network and cristae morphology will not only further deepen our understanding of energy metabolism but may also contribute to improved therapeutic manipulation of cell viability, differentiation, proliferation, and identity in many different cell types. Antioxid. Redox Signal. 39, 684-707.

Lung cancer associated with combustion particles and fine particulate matter (PM2.5) - The roles of polycyclic aromatic hydrocarbons (PAHs) and the aryl hydrocarbon receptor (AhR)

Air pollution is the leading cause of lung cancer after tobacco smoking, contributing to 20% of all lung cancer deaths. Increased risk associated with living near trafficked roads, occupational exposure to diesel exhaust, indoor coal combustion and cigarette smoking, suggest that combustion components in ambient fine particulate matter (PM2.5), such as polycyclic aromatic hydrocarbons (PAHs), may be central drivers of lung cancer. Activation of the aryl hydrocarbon receptor (AhR) induces expression of xenobiotic-metabolizing enzymes (XMEs) and increase PAH metabolism, formation of reactive metabolites, oxidative stress, DNA damage and mutagenesis. Lung cancer tissues from smokers and workers exposed to high combustion PM levels contain mutagenic signatures derived from PAHs. However, recent findings suggest that ambient air PM2.5 exposure primarily induces lung cancer development through tumor promotion of cells harboring naturally acquired oncogenic mutations, thus lacking typical PAH-induced mutations. On this background, we discuss the role of AhR and PAHs in lung cancer development caused by air pollution focusing on the tumor promoting properties including metabolism, immune system, cell proliferation and survival, tumor microenvironment, cell-to-cell communication, tumor growth and metastasis. We suggest that the dichotomy in lung cancer patterns observed between smoking and outdoor air PM2.5 represent the two ends of a dose-response continuum of combustion PM exposure, where tumor promotion in the peripheral lung appears to be the driving factor at the relatively low-dose exposures from ambient air PM2.5, whereas genotoxicity in the central airways becomes increasingly more important at the higher combustion PM levels encountered through smoking and occupational exposure.

The Pro-Oncogenic Protein IF1 Promotes Proliferation of Anoxic Cancer Cells during Re-Oxygenation

Cancer cells overexpress IF1, the endogenous protein that inhibits the hydrolytic activity of ATP synthase when mitochondrial membrane potential (ΔμH+) falls, as in ischemia. Other roles have been ascribed to IF1, but the associated molecular mechanisms are still under debate. We investigated the ability of IF1 to promote survival and proliferation in osteosarcoma and colon carcinoma cells exposed to conditions mimicking ischemia and reperfusion, as occurs in vivo, particularly in solid tumors. IF1-silenced and parental cells were exposed to the FCCP uncoupler to collapse ΔμH+ and the bioenergetics of cell models were validated. All the uncoupled cells preserved mitochondrial mass, but the implemented mechanisms differed in IF1-expressing and IF1-silenced cells. Indeed, the membrane potential collapse and the energy charge preservation allowed an increase in both mitophagy and mitochondrial biogenesis in IF1-expressing cells only. Interestingly, the presence of IF1 also conferred a proliferative advantage to cells highly dependent on oxidative phosphorylation when the uncoupler was washed out, mimicking cell re-oxygenation. Overall, our results indicate that IF1, by allowing energy preservation and promoting mitochondrial renewal, can favor proliferation of anoxic cells and tumor growth. Therefore, hindering the action of IF1 may be promising for the therapy of tumors that rely on oxidative phosphorylation for energy production.

IF1 promotes oligomeric assemblies of sluggish ATP synthase and outlines the heterogeneity of the mitochondrial membrane potential

The coexistence of two pools of ATP synthase in mitochondria has been largely neglected despite in vitro indications for the existence of reversible active/inactive state transitions in the F1-domain of the enzyme. Herein, using cells and mitochondria from mouse tissues, we demonstrate the existence in vivo of two pools of ATP synthase: one active, the other IF1-bound inactive. IF1 is required for oligomerization and inactivation of ATP synthase and for proper cristae formation. Immunoelectron microscopy shows the co-distribution of IF1 and ATP synthase, placing the inactive "sluggish" ATP synthase preferentially at cristae tips. The intramitochondrial distribution of IF1 correlates with cristae microdomains of high membrane potential, partially explaining its heterogeneous distribution. These findings support that IF1 is the in vivo regulator of the active/inactive state transitions of the ATP synthase and suggest that local regulation of IF1-ATP synthase interactions is essential to activate the sluggish ATP synthase.

The Mitochondrial ATP Synthase/IF1 Axis in Cancer Progression: Targets for Therapeutic Intervention

Cancer poses a significant global health problem with profound personal and economic implications on National Health Care Systems. The reprograming of metabolism is a major trait of the cancer phenotype with a clear potential for developing effective therapeutic strategies to combat the disease. Herein, we summarize the relevant role that the mitochondrial ATP synthase and its physiological inhibitor, ATPase Inhibitory Factor 1 (IF1), play in metabolic reprogramming to an enhanced glycolytic phenotype. We stress that the interplay in the ATP synthase/IF1 axis has additional functional roles in signaling mitohormetic programs, pro-oncogenic or anti-metastatic phenotypes depending on the cell type. Moreover, the same axis also participates in cell death resistance of cancer cells by restrained mitochondrial permeability transition pore opening. We emphasize the relevance of the different post-transcriptional mechanisms that regulate the specific expression and activity of ATP synthase/IF1, to stimulate further investigations in the field because of their potential as future targets to treat cancer. In addition, we review recent findings stressing that mitochondria metabolism is the primary altered target in lung adenocarcinomas and that the ATP synthase/IF1 axis of OXPHOS is included in the most significant signature of metastatic disease. Finally, we stress that targeting mitochondrial OXPHOS in pre-clinical mouse models affords a most effective therapeutic strategy in cancer treatment.

F-ATP synthase inhibitory factor 1 regulates metabolic reprogramming involving its interaction with c-Myc and PGC1α

F-ATP synthase inhibitory factor 1 (IF1) is an intrinsic inhibitor of F-ATP synthase. It is known that IF1 mediates metabolic phenotypes and cell fate, yet the molecular mechanisms through which IF1 fulfills its physiological functions are not fully understood. Ablation of IF1 favors metabolic switch to oxidative metabolism from glycolysis. c-Myc and PGC1α are critical for metabolic reprogramming. This work identified that IF1 interacted with Thr-58 phosphorylated c-Myc, which might thus mediate the activity of c-Myc and promote glycolysis. The interaction of IF1 with PGC1α inhibited oxidative respiration. c-Myc and PGC1α were localized to mitochondria under mitochondrial stress in an IF1-dependent manner. Furthermore, IF1 was found to be required for the protective effect of hypoxia on c-Myc- and PGC1α-induced cell death. This study suggested that the interactions of IF1 with transcription factors c-Myc and PGC1α might be involved in IF1-regulatory metabolic reprogramming and cell fate.

Methionine Sources Differently Affect Production of Reactive Oxygen Species, Mitochondrial Bioenergetics, and Growth of Murine and Quail Myoblasts In Vitro

An optimal supply of L-methionine (L-Met) improves muscle growth, whereas over-supplementation exerts adverse effects. To understand the underlying mechanisms, this study aims at exploring effects on the growth, viability, ROS production, and mitochondrial bioenergetics of C2C12 (mouse) and QM7 (quail) myoblasts additionally supplemented (100 or 1000 µM) with L-Met, DL-methionine (DL-Met), or DL-2-hydroxy-4-(methylthio)butanoic acid (DL-HMTBA). In both cell lines, all the supplements stimulated cell growth. However, in contrast to DL-Met, 1000 µM of L-Met (C2C12 cells only) or DL-HMTBA started to retard growth. This negative effect was stronger with DL-HMTBA and was accompanied by significantly elevated levels of extracellular H₂O₂, an indicator for OS, in both cell types. In addition, oversupplementation with DL-HMTBA (1000 µM) induced adaptive responses in mitochondrial bioenergetics, including reductions in basal (C2C12 and QM7) and ATP-synthase-linked (C2C12) oxygen consumption, maximal respiration rate, and reserve capacity (QM7). Only QM7 cells switched to nonmitochondrial aerobic glycolysis to reduce ROS production. In conclusion, we found a general negative effect of methionine oversupplementation on cell proliferation. However, only DL-HMTBA-induced growth retardation was associated with OS and adaptive, species-specific alterations in mitochondrial functionality. OS could be better compensated by quail cells, highlighting the role of species differences in the ability to cope with methionine oversupplementation.

P2RX7 signaling drives the differentiation of Th1 cells through metabolic reprogramming for aerobic glycolysis

Introduction

This study provides evidence of how Th1 cell metabolism is modulated by the purinergic receptor P2X7 (P2RX7), a cation cannel activated by high extracellular concentrations of adenosine triphosphate (ATP).

Methods

In vivo analysis was performed in the Plasmodium chabaudi model of malaria in view of the great relevance of this infectious disease for human health, as well as the availability of data concerning Th1/Tfh differentiation.

Results

We show that P2RX7 induces T-bet expression and aerobic glycolysis in splenic CD4+ T cells that respond to malaria, at a time prior to Th1/Tfh polarization. Cell-intrinsic P2RX7 signaling sustains the glycolytic pathway and causes bioenergetic mitochondrial stress in activated CD4+ T cells. We also show in vitro the phenotypic similarities of Th1-conditioned CD4+ T cells that do not express P2RX7 and those in which the glycolytic pathway is pharmacologically inhibited. In addition, in vitro ATP synthase blockade and the consequent inhibition of oxidative phosphorylation, which drives cellular metabolism for aerobic glycolysis, is sufficient to promote rapid CD4+ T cell proliferation and polarization to the Th1 profile in the absence of P2RX7.

Conclusion

These data demonstrate that P2RX7-mediated metabolic reprograming for aerobic glycolysis is a key event for Th1 differentiation and suggest that ATP synthase inhibition is a downstream effect of P2RX7 signaling that potentiates the Th1 response.

Leukemic cells resist lysosomal inhibition through the mitochondria-dependent reduction of intracellular pH and oxidants

Acidic lysosomes are indispensable for cancer development and linked to chemotherapy resistance. Chloroquine (CQ) and functional analogues have been considered as a potential solution to overcome the cancer progression and chemoresistance by inhibiting the lysosome-mediated autophagy and multidrug exocytosis. However, their anti-cancer efficacy in most clinical trials demonstrated modest improvement. In this study, we investigated the detailed mechanisms underlying the acquired resistance of K562 leukemic cells to CQ treatment. In response to 5-80 μM CQ, the lumen pH of endosomal-lysosomal system immediately increased and gradually reached dynamic equilibrium within 24 h. Leukemic cells produced more acidic organelles to tolerate 5-10 μM CQ. CQ (20-80 μM) concentration-dependently triggered cytosolic pH (pHi) rise, G0/G1 arrest, mitochondrial depolarization/fragmentation, and necrotic/apoptotic cell death. Oxidant induction by CQ was responsible for the mitochondria-dependent cytotoxicity and partial pHi elevation. Cells that survived the CQ cytotoxicity were accompanied with increased mitochondria. Under the 80 μM CQ challenge, co-treatment with the inhibitor of F₀ part of mitochondrial H⁺-ATP synthase, oligomycin (40 nM), prevented the elevation of oxidants as well as pHi, and attenuated stresses on mitochondria, cell survival, and cell proliferation. Besides, oligomycin-treated cells obviously displayed the lysosomal peripheralization and plasma membrane blebbing, suggesting that these cells were in process of lysosomal exocytosis and microvesicle release. Enhanced motion of these secretory processes allowed the cells to exclude CQ and repair necrotic injury. Together, the oxidant production and the proton dynamic interconnection among lysosomes, mitochondria, and cytosol are crucial for leukemic susceptibility to lysosomotropic chemotherapeutics.

Multifaceted roles of mitochondrial stress responses under ETC dysfunction - repair, destruction and pathogenesis

Electron transport chain (ETC) dysfunction is a common feature of mitochondrial diseases and induces severe cellular stresses, including mitochondrial membrane potential (Δψ_m ) reduction, mitochondrial matrix acidification, metabolic derangements and proteostatic stresses. Extensive studies of ETC dysfunction in yeast, Caenorhabditis elegans, cultured cells and mouse models have revealed multiple mitochondrial stress response pathways. Here, we summarise the current understanding of the triggers, sensors, signalling mechanisms and the functional outcomes of mitochondrial stress responses in different species. We highlight Δψ_m reduction as a major trigger of stress responses in different species, but the responses are species-specific and the outcomes are context-dependent. ETC dysfunction elicits a mitochondrial unfolded protein response (UPR^mt ) to repair damaged mitochondria in C. elegans, and activates a global adaptive programme to maintain Δψ_m in yeast. Yeast and C. elegans responses are remarkably similar at the downstream responses, although they are activated by different signalling mechanisms. UPR^mt generally protects ETC-defective worms, but its constitutive activation is toxic for wildtype worms and worms carrying mutant mtDNA. In contrast to lower organisms, ETC dysfunction in mammals mainly activates a mitochondrial integrated stress response (ISR^mt ) to reprogramme metabolism and a PINK1-Parkin mitophagy pathway to degrade damaged mitochondria. Accumulating in vivo results suggest that the ATF4 branch of ISR^mt exacerbates metabolic derangements to accelerate mitochondrial disease progression. The in vivo roles of mitophagy in mitochondrial diseases are also context-dependent. These results thus reveal the common and unique aspects of mitochondrial stress responses in different species and highlight their multifaceted roles in mitochondrial diseases.

Mitochondrial remodeling and ischemic protection by G protein-coupled receptor 35 agonists

Kynurenic acid (KynA) is tissue protective in cardiac, cerebral, renal, and retinal ischemia models, but the mechanism is unknown. KynA can bind to multiple receptors, including the aryl hydrocarbon receptor, the a7 nicotinic acetylcholine receptor (a7nAChR), multiple ionotropic glutamate receptors, and the orphan G protein-coupled receptor GPR35. Here, we show that GPR35 activation was necessary and sufficient for ischemic protection by KynA. When bound by KynA, GPR35 activated G_i- and G_12/13-coupled signaling and trafficked to the outer mitochondria membrane, where it bound, apparantly indirectly, to ATP synthase inhibitory factor subunit 1 (ATPIF1). Activated GPR35, in an ATPIF1-dependent and pertussis toxin-sensitive manner, induced ATP synthase dimerization, which prevented ATP loss upon ischemia. These findings provide a rationale for the development of specific GPR35 agonists for the treatment of ischemic diseases.

The F1Fo-ATPase inhibitor protein IF1 in pathophysiology

The endogenous inhibitor of ATP synthase is a protein of about 10 kDa, known as IF1 which binds to the catalytic domain of the enzyme during ATP hydrolysis. The main role of IF1 consists of limiting ATP dissipation under condition of severe oxygen deprivation or in the presence of dysfunctions of mitochondrial respiratory complexes, causing a collapse in mitochondrial membrane potential and therefore ATP hydrolysis. New roles of IF1 are emerging in the fields of cancer and neurodegeneration. Its high expression levels in tumor tissues have been associated with different roles favouring tumor formation, progression and evasion. Since discordant mechanisms of action have been proposed for IF1 in tumors, it is of the utmost importance to clarify them in the prospective of defining novel approaches for cancer therapy. Other IF1 functions, including its involvement in mitophagy, may be protective for neurodegenerative and aging-related diseases. In the present review we aim to clarify and discuss the emerging mechanisms in which IF1 is involved, providing a critical view of the discordant findings in the literature.

The Multifaceted ATPase Inhibitory Factor 1 (IF1) in Energy Metabolism Reprogramming and Mitochondrial Dysfunction: A New Player in Age-Associated Disorders?

Significance: The mitochondrial oxidative phosphorylation (OXPHOS) system, comprising the electron transport chain and ATP synthase, generates membrane potential, drives ATP synthesis, governs energy metabolism, and maintains redox balance. OXPHOS dysfunction is associated with a plethora of diseases ranging from rare inherited disorders to common conditions, including diabetes, cancer, neurodegenerative diseases, as well as aging. There has been great interest in studying regulators of OXPHOS. Among these, ATPase inhibitory factor 1 (IF1) is an endogenous inhibitor of ATP synthase that has long been thought to avoid the consumption of cellular ATP when ATP synthase acts as an ATP hydrolysis enzyme. Recent Advances: Recent data indicate that IF1 inhibits ATP synthesis and is involved in a multitude of mitochondrial-related functions, such as mitochondrial quality control, energy metabolism, redox balance, and cell fate. IF1 also inhibits the ATPase activity of cell-surface ATP synthase, and it is used as a cardiovascular disease biomarker. Critical Issues: Although recent data have led to a paradigm shift regarding IF1 functions, these have been poorly studied in entire organisms and in different organs. The understanding of the cellular biology of IF1 is, therefore, still limited. The aim of this review was to provide an overview of the current understanding of the role of IF1 in mitochondrial functions, health, and diseases. Future Directions: Further investigations of IF1 functions at the cell, organ, and whole-organism levels and in different pathophysiological conditions will help decipher the controversies surrounding its involvement in mitochondrial function and could unveil therapeutic strategies in human pathology. Antioxid. Redox Signal. 37, 370-393.

Mitochondrial Elongation and OPA1 Play Crucial Roles during the Stemness Acquisition Process in Pancreatic Ductal Adenocarcinoma

Simple Summary

Pancreatic ductal adenocarcinoma (PDAC) is a highly lethal neoplasia and the currently used treatments are not effective in a wide range of patients. Presently, the evidence points out that cancer stem cells (CSCs) are key players during tumor development, metastasis, chemoresistance, and tumor relapse. The study of the metabolism of CSCs, specifically the mitochondrial alterations, could pave the way to the discovery of new therapeutical targets. In this study, we show that during progressive de-differentiation, pancreatic CSCs undergo changes in mitochondrial mass, dynamics, and function. Interestingly, the silencing of OPA1, a protein involved in mitochondrial fusion, significantly inhibits the formation of CSCs. These results reveal new insight into mitochondria and stemness acquisition that could be useful for the design of novel potential therapies in PDAC.

Abstract

Pancreatic ductal adenocarcinoma (PDAC) is the most common type of pancreatic cancer with an overall 5-year survival rate of less than 9%. The high aggressiveness of PDAC is linked to the presence of a subpopulation of cancer cells with a greater tumorigenic capacity, generically called cancer stem cells (CSCs). CSCs present a heterogeneous metabolic profile that might be supported by an adaptation of mitochondrial function; however, the role of this organelle in the development and maintenance of CSCs remains controversial. To determine the role of mitochondria in CSCs over longer periods, which may reflect more accurately their quiescent state, we studied the mitochondrial physiology in CSCs at short-, medium-, and long-term culture periods. We found that CSCs show a significant increase in mitochondrial mass, more mitochondrial fusion, and higher mRNA expression of genes involved in mitochondrial biogenesis than parental cells. These changes are accompanied by a regulation of the activities of OXPHOS complexes II and IV. Furthermore, the protein OPA1, which is involved in mitochondrial dynamics, is overexpressed in CSCs and modulates the tumorsphere formation. Our findings indicate that CSCs undergo mitochondrial remodeling during the stemness acquisition process, which could be exploited as a promising therapeutic target against pancreatic CSCs.

The Effect of Deoxycholic Acid on Chitosan-Enabled Matrices for Tissue Scaffolding and Injectable Nanogels

The pathophysiology of a multitude of diseases is influenced by bioenergetic dysfunction. Healthy mitochondria are presented as essential for the regulation and function of multiple cell types, including the cells of relevance for this research: pancreatic beta cells, muscle cells, and liver cells. Hence, effects of hydrogels (particularly nanogels) on bioenergetics needs to be taken into account when designing optimum delivery matrices. Several polymers have been suggested for use in hydrogels and nanogels, with focus on chitosan due to its range of beneficial properties. Bile acids have emerged as beneficial excipients, including deoxycholic acid, which can increase membrane permeability of cells. Nanogels were manufactured containing various concentrations of chitosan and deoxycholic acid in addition to the staple sodium alginate. Nanogels then underwent an array of analysis including rheological studies and in vitro cell work assessing viability, hypoxia, and the bioenergetic profiles. Overall, deoxycholic acid showed enhanced gel strength although this resulted in slightly lower cell viability and impacted bioenergetic profiles. Results from this study showed the benefits of deoxycholic acid; however, this was found to be less suitable for cell delivery matrices and is perhaps more beneficial for drug-delivery systems.

The ATPase Inhibitory Factor 1 is a Tissue-Specific Physiological Regulator of the Structure and Function of Mitochondrial ATP Synthase: A Closer Look Into Neuronal Function

The ATP synthase is an essential multifunctional enzyme complex of mitochondria that produces most of cellular ATP, shapes the structure of the inner membrane into cristae and regulates the signals that control cell fate or demise. The ATPase Inhibitory Factor 1 (IF1) functions in vivo as a physiological regulator of the ATP synthase and thereby controls mitochondrial structure and function, and the retrograde signaling pathways that reprogram nuclear gene expression. However, IF1 is not ubiquitously expressed in mammals, showing tissue-restricted expression in humans and mice and large expression differences between the two species in some tissues. Herein, we summarized key regulatory functions of IF1 for tissue homeostasis, with special emphasis on the deleterious effects that its genetic ablation in neurons has in learning. The development and characterization of tissue-specific mouse models with regulated expression of IF1 will be crucial to disentangle the contribution of the ATP synthase/IF1 axis in pathophysiology.

Analysis of the metabolic proteome of lung adenocarcinomas by reverse-phase protein arrays (RPPA) emphasizes mitochondria as targets for therapy

Lung cancer is the leading cause of cancer-related death worldwide despite the success of therapies targeting oncogenic drivers and immune-checkpoint inhibitors. Although metabolic enzymes offer additional targets for therapy, the precise metabolic proteome of lung adenocarcinomas is unknown, hampering its clinical translation. Herein, we used Reverse Phase Protein Arrays to quantify the changes in enzymes of glycolysis, oxidation of pyruvate, fatty acid metabolism, oxidative phosphorylation, antioxidant response and protein oxidative damage in 128 tumors and paired non-tumor adjacent tissue of lung adenocarcinomas to profile the proteome of metabolism. Steady-state levels of mitochondrial proteins of fatty acid oxidation, oxidative phosphorylation and of the antioxidant response are independent predictors of survival and/or of disease recurrence in lung adenocarcinoma patients. Next, we addressed the mechanisms by which the overexpression of ATPase Inhibitory Factor 1, the physiological inhibitor of oxidative phosphorylation, which is an independent predictor of disease recurrence, prevents metastatic disease. We highlight that IF1 overexpression promotes a more vulnerable and less invasive phenotype in lung adenocarcinoma cells. Finally, and as proof of concept, the therapeutic potential of targeting fatty acid assimilation or oxidation in combination with an inhibitor of oxidative phosphorylation was studied in mice bearing lung adenocarcinomas. The results revealed that this therapeutic approach significantly extended the lifespan and provided better welfare to mice than cisplatin treatments, supporting mitochondrial activities as targets of therapy in lung adenocarcinoma patients.

Mitochondrial ATP synthase inhibitory factor 1 interacts with the p53-cyclophilin D complex and promotes opening of the permeability transition pore

The mitochondrial permeability transition pore (PTP) is a Ca2+-dependent megachannel that plays an important role in mitochondrial physiology and cell fate. Cyclophilin D (CyPD) is a well-characterized PTP regulator, and its binding to the PTP favors pore opening. It has previously been shown that p53 physically interacts with CyPD and opens the PTP during necrosis. Accumulating studies also suggest that the F-ATP synthase contributes to the regulation and formation of the PTP. F-ATP synthase IF1 (mitochondrial ATP synthase inhibitory factor 1) is a natural inhibitor of F-ATP synthase activity; however, whether IF1 participates in the modulation of PTP opening is basically unknown. Here, we demonstrate using calcium retention capacity assay that IF1 overexpression promotes mitochondrial permeability transition via opening of the PTP. Intriguingly, we show that IF1 can interact with the p53-CyPD complex and facilitate cell death. We also demonstrate that the presence of IF1 is necessary for the formation of p53-CyPD complex. Therefore, we suggest that IF1 regulates the PTP via interaction with the p53-CyPD complex, and that IF1 is necessary for the inducing effect of p53-CyPD complex on PTP opening.

Divergent effects of HIV reverse transcriptase inhibitors on pancreatic beta-cell function and survival: Potential role of oxidative stress and mitochondrial dysfunction

Antiretroviral therapy (ART), a life-saving treatment strategy in HIV/AIDS, has been implicated in increasing the risk of type 2 diabetes mellitus (T2DM). Direct damaging effects on beta-cell function and survival by either non-nucleoside reverse transcriptase inhibitors (NNRTIs) or nucleoside/tide reverse transcriptase inhibitors (NRTIs) may predispose individuals to developing T2DM or if already type 2 diabetic, to insulin dependency. The aim of this study was to investigate the effects of the NNRTIs efavirenz, rilpivirine and doravirine, and the NRTIs tenofovir disoproxil fumarate and emtricitabine, on beta-cell function and survival while suggesting potential cellular and molecular mechanism(s). Our results show contrasting effects within the NNRTI class as doravirine did not cause damaging effects in the rat insulinoma INS-1E cells while efavirenz and rilpivirine reduced insulin release and cell viability, and induced apoptosis in INS-1E cells. Additionally, efavirenz and rilpivirine increased ROS generation, disrupted Δψm and upregulated the mRNA and protein expression of CHOP and GRP78, key markers of endoplasmic reticulum stress. In silico docking studies predict a possible inhibition of the mitochondrial ATP synthase by rilpivirine. On the contrary, both the NRTIs tenofovir disoproxil fumarate and emtricitabine did not affect GSIS, cell viability and apoptosis/necrosis levels in INS-1E cells. The deleterious effects observed in beta-cells exposed to efavirenz or rilpivirine may be, at least partially, mediated by oxidative stress and mitochondrial toxicity. These findings provide potential mechanism(s) by which efavirenz and rilpivirine may contribute to the pathogenesis of T2DM and the progression of T2DM to insulin dependency in HIV-infected type 2 diabetics.

ATPase inhibitory factor 1 protects the heart from acute myocardial ischemia/reperfusion injury through activating AMPK signaling pathway

Rationale: Myocardial ischemia/reperfusion (I/R) injury is a common clinic scenario that occurs in the context of reperfusion therapy for acute myocardial infarction (AMI). The mitochondrial F1Fo-ATPase inhibitory factor 1 (IF1) blocks the reversal of the F1Fo-ATP synthase to prevent detrimental consumption of cellular ATP and associated demise. In the present study, we study the role and mechanism of IF1 in myocardial I/R injury.

Methods: Mice were ligated the left anterior descending coronary artery to build the I/R model in vivo. Rat hearts were isolated and perfused with constant pressure according to Langendorff. Also, neonatal cardiomyocytes hypoxia-reoxygenation (H/R) model was also used. Myocardial infarction area, cardiac function, cellular function, and cell viability was conducted and compared.

Results: Our data revealed that IF1 is upregulated in hearts after I/R and cardiomyocytes with hypoxia/re-oxygenation (H/R). IF1 delivered with adenovirus and adeno-associated virus serotype 9 (AAV9) ameliorated cardiac dysfunction and pathological development induced by I/R ex vivo and in vivo. Mechanistically, IF1 stimulates glucose uptake and glycolysis activity and stimulates AMPK activation during in vivo basal and I/R and in vitro OGD/R conditions, and activation of AMPK by IF1 is responsible for its cardioprotective effects against H/R-induced injury.

Conclusions: These results suggest that increased IF1 in the I/R heart confer cardioprotective effects via activating AMPK signaling. Therefore, IF1 can be used as a potential therapeutic target for the treatment of pathological ischemic injury and heart failure.

ATP synthase inhibitory factor subunit 1 regulates islet β-cell function via repression of mitochondrial homeostasis

Mitochondrial homeostasis is crucial for the function of pancreatic β-cells. ATP synthase inhibitory factor subunit 1 (IF1) is a mitochondrial protein interacting with ATP synthase to inhibit its enzyme activity. IF1 may also play a role in maintaining ATP synthase oligomerization and mitochondrial inner membrane formation. A recent study confirmed IF1 expresses in β-cells. IF1 knockdown in cultured INS-1E β-cells enhances glucose-induced insulin release. However, the role of IF1 in islet β-cells remains little known. The present study investigates islets freshly isolated from mouse lines with global IF1 knockout (IF1-/-) and overexpression (OE). The glucose-stimulated insulin secretion was increased in islets from IF1-/- mice but decreased in islets from IF1 OE mice. Transmitted Electronic Microscopic assessment of isolated islets revealed that the number of matured insulin granules (with dense core) was relatively higher in IF1-/-, but fewer in IF1 OE islets than those of controlled islets. The mitochondrial ultrastructure within β-cells of IF1 overexpressed islets was comparable with those of wild-type mice, whereas those in IF1-/- β-cells showed increased mitochondrial mass. Mitochondrial network analysis in cultured INS-1 β-cells showed a similar pattern with an increased mitochondrial network in IF1 knockdown cells. IF1 overexpressed INS-1 β-cells showed a compromised rate of mitochondrial oxidative phosphorylation with attenuated cellular ATP content. In contrast, INS-1 cells with IF1 knockdown showed markedly increased cellular respiration with improved ATP production. These results support that IF1 is a negative regulator of insulin production and secretion via inhibiting mitochondrial mass and respiration in β-cells. Therefore, inhibiting IF1 to improve β-cell function in patients can be a novel therapeutic strategy to treat diabetes.

Mitochondrial F1 FO ATP synthase determines the local proton motive force at cristae rims

The classical view of oxidative phosphorylation is that a proton motive force (PMF) generated by the respiratory chain complexes fuels ATP synthesis via ATP synthase. Yet, under glycolytic conditions, ATP synthase in its reverse mode also can contribute to the PMF. Here, we dissected these two functions of ATP synthase and the role of its inhibitory factor 1 (IF1) under different metabolic conditions. pH profiles of mitochondrial sub-compartments were recorded with high spatial resolution in live mammalian cells by positioning a pH sensor directly at ATP synthase's F1 and FO subunits, complex IV and in the matrix. Our results clearly show that ATP synthase activity substantially controls the PMF and that IF1 is essential under OXPHOS conditions to prevent reverse ATP synthase activity due to an almost negligible ΔpH. In addition, we show how this changes lateral, transmembrane, and radial pH gradients in glycolytic and respiratory cells.

Kinetic analysis of the inhibition mechanism of bovine mitochondrial F1-ATPase inhibitory protein using biochemical assay

ATPase inhibitory factor 1 (IF1) is a mitochondrial regulatory protein that blocks ATP hydrolysis of F1-ATPase, by inserting its N-terminus into the rotor-stator interface of F1-ATPase. Although previous studies have proposed a two-step model for IF1-mediated inhibition, the underlying molecular mechanism remains unclear. Here, we analysed the kinetics of IF1-mediated inhibition under a wide range of [ATP]s and [IF1]s, using bovine mitochondrial IF1 and F1-ATPase. Typical hyperbolic curves of inhibition rates with [IF1]s were observed at all [ATP]s tested, suggesting a two-step mechanism: the initial association of IF1 to F1-ATPase and the locking process, where IF1 blocks rotation by inserting its N-terminus. The initial association was dependent on ATP. Considering two principal rotation dwells, binding dwell and catalytic dwell, in F1-ATPase, this result means that IF1 associates with F1-ATPase in the catalytic-waiting state. In contrast, the isomerization process to the locking state was almost independent of ATP, suggesting that it is also independent of the F1-ATPase state. Further, we investigated the role of Glu30 or Tyr33 of IF1 in the two-step mechanism. Kinetic analysis showed that Glu30 is involved in the isomerization, whereas Tyr33 contributes to the initial association. Based on these findings, we propose an IF1-mediated inhibition scheme.

In Vivo Study of the Efficacy and Safety of 5-Aminolevulinic Radiodynamic Therapy for Glioblastoma Fractionated Radiotherapy

To treat malignant glioma, standard fractionated radiotherapy (RT; 60 Gy/30 fractions over 6 weeks) was performed post-surgery in combination with temozolomide to improve overall survival. Malignant glioblastoma recurrence rate is extremely high, and most recurrent tumors originate from the excision cavity in the high-dose irradiation region. In our previous study, protoporphyrin IX physicochemically enhanced reactive oxygen species generation by ionizing radiation and combined treatment with 5-aminolevulinic acid (5-ALA) and ionizing radiation, while radiodynamic therapy (RDT) improved tumor growth suppression in vivo in a melanoma mouse model. We examined the effect of 5-ALA RDT on the standard fractionated RT protocol using U251MG- or U87MG-bearing mice. 5-ALA was orally administered at 60 or 120 mg/kg, 4 h prior to irradiation. In both models, combined treatment with 5-ALA slowed tumor progression and promoted regression compared to treatment with ionizing radiation alone. The standard fractionated RT protocol of 60 Gy in 30 fractions with oral administration of 120 and 240 mg/kg 5-ALA, the human equivalent dose of photodynamic diagnosis, revealed no significant increase in toxicity to normal skin or brain tissue compared to ionizing radiation alone. Thus, RDT is expected to enhance RT treatment of glioblastoma without severe toxicity under clinically feasible conditions.

Generation of mitochondrial reactive oxygen species is controlled by ATPase inhibitory factor 1 and regulates cognition

The mitochondrial ATP synthase emerges as key hub of cellular functions controlling the production of ATP, cellular signaling, and fate. It is regulated by the ATPase inhibitory factor 1 (IF1), which is highly abundant in neurons. Herein, we ablated or overexpressed IF1 in mouse neurons to show that IF1 dose defines the fraction of active/inactive enzyme in vivo, thereby controlling mitochondrial function and the production of mitochondrial reactive oxygen species (mtROS). Transcriptomic, proteomic, and metabolomic analyses indicate that IF1 dose regulates mitochondrial metabolism, synaptic function, and cognition. Ablation of IF1 impairs memory, whereas synaptic transmission and learning are enhanced by IF1 overexpression. Mechanistically, quenching the IF1-mediated increase in mtROS production in mice overexpressing IF1 reduces the increased synaptic transmission and obliterates the learning advantage afforded by the higher IF1 content. Overall, IF1 plays a key role in neuronal function by regulating the fraction of ATP synthase responsible for mitohormetic mtROS signaling.

The F1Fo-ATPase inhibitor, IF1, is a critical regulator of energy metabolism in cancer cells

In the last two decades, IF1, the endogenous inhibitor of the mitochondrial F1Fo-ATPase (ATP synthase) has assumed greater and ever greater interest since it has been found to be overexpressed in many cancers. At present, several findings indicate that IF1 is capable of playing a central role in cancer cells by promoting metabolic reprogramming, proliferation and resistance to cell death. However, the mechanism(s) at the basis of this pro-oncogenic action of IF1 remains elusive. Here, we recall the main features of the mechanism of the action of IF1 when the ATP synthase works in reverse, and discuss the experimental evidence that support its relevance in cancer cells. In particular, a clear pro-oncogenic action of IF1 is to avoid wasting of ATP when cancer cells are exposed to anoxia or near anoxia conditions, therefore favoring cell survival and tumor growth. However, more recently, various papers have described IF1 as an inhibitor of the ATP synthase when it is working physiologically (i.e. synthethizing ATP), and therefore reprogramming cell metabolism to aerobic glycolysis. In contrast, other studies excluded IF1 as an inhibitor of ATP synthase under normoxia, providing the basis for a hot debate. This review focuses on the role of IF1 as a modulator of the ATP synthase in normoxic cancer cells with the awareness that the knowledge of the molecular action of IF1 on the ATP synthase is crucial in unravelling the molecular mechanism(s) responsible for the pro-oncogenic role of IF1 in cancer and in developing related anticancer strategies.

Deletion of the natural inhibitory protein Inh1 in Ustilago maydis has no effect on the dimeric state of the F1FO-ATP synthase but increases the ATPase activity and reduces the stability

Transduction of electrochemical proton gradient into ATP synthesis is performed by F₁F_O-ATP synthase. The reverse reaction is prevented by the regulatory subunit Inh1. Knockout of the inh1 gene in the basidiomycete Ustilago maydis was generated in order to study the function of this protein in the mitochondrial metabolism and cristae architecture. Deletion of inh1 gen did not affect cell growth, glucose consumption, and biomass production. Ultrastructure and fluorescence analyzes showed that size, cristae shape, network, and distribution of mitochondria was similar to wild strain. Membrane potential, ATP synthesis, and oxygen consumption in wild type and mutant strains had similar values. Kinetic analysis of ATPase activity of complex V in permeabilized mitochondria showed similar values of V_max and K_M for both strains, and no effect of pH was observed. Interestingly, the dimeric state of complex V occurs in the mutant strain, indicating that this subunit is not essential for dimerization. ATPase activity of the isolated monomeric and dimeric forms of complex V indicated V_max values 4-times higher for the mutant strain than for the WT strain, suggesting that the absence of Inh1 subunit increased ATPase activity, and supporting a regulatory role for this protein; however, no effect of pH was observed. ATPase activity of WT oligomers was stimulated several times by dodecyl-maltoside (DDM), probably by removal of ADP from F₁ sector, while DDM induced an inactive form of the mutant oligomers.

Links between mitochondrial retrograde response and mitophagy in pathogenic cell signalling

Preservation of mitochondrial quality is paramount for cellular homeostasis. The integrity of mitochondria is guarded by the balanced interplay between anabolic and catabolic mechanisms. The removal of bio-energetically flawed mitochondria is mediated by the process of mitophagy; the impairment of which leads to the accumulation of defective mitochondria which signal the activation of compensatory mechanisms to the nucleus. This process is known as the mitochondrial retrograde response (MRR) and is enacted by Reactive Oxygen Species (ROS), Calcium (Ca2+), ATP, as well as imbalanced lipid and proteostasis. Central to this mitochondria-to-nucleus signalling are the transcription factors (e.g. the nuclear factor kappa-light-chain-enhancer of activated B cells, NF-κB) which drive the expression of genes to adapt the cell to the compromised homeostasis. An increased degree of cellular proliferation is among the consequences of the MRR and as such, engagement of mitochondrial-nuclear communication is frequently observed in cancer. Mitophagy and the MRR are therefore interlinked processes framed to, respectively, prevent or compensate for mitochondrial defects.In this review, we discuss the available knowledge on the interdependency of these processes and their contribution to cell signalling in cancer.

Mitochondria and the permeability transition pore in cancer metabolic reprogramming

Mitochondria are a major source of ATP provision as well as cellular suicidal weapon store. Accumulating evidences demonstrate that mitochondrial bioenergetics, biosynthesis and signaling are important mediators of tumorigenesis. Metabolic plasticity enables cancer cell reprogramming to cope with cellular and environmental alterations, a process requires mitochondria biology. Mitochondrial metabolism emerges to be a promising arena for cancer therapeutic targets. The permeability transition pore (PTP) participates in physiological Ca²⁺ and ROS homeostasis as well as cell death depending on the open state. The hypothesis that PTP forms from F-ATP synthase provides clues to the potential collaborative role of mitochondrial respiration and PTP in regulating cancer cell fate and metabolic reprogramming.

Oligomycin A promotes radioresistance in HT29 colorectal cancer cells and its mechanisms

OBJECTIVES

Radiotherapy is one of the main therapies for colorectal cancer, but radioresistance often leads to radiotherapy failure. To improve the radioresistance, we explore the effect of oligomycin A, the H+-ATP synthase inhibitor, on the sensitivity of HT29 colorectal cancer cells to irradiation and its underlying mechanisms.

METHODS

The effects of different concentrations of oligomycin A on the survival rate and glycolysis of HT29 colorectal cancer cells at different time points were investigated via MTT and glycolysis assay. siRNA-PFK1 was synthesized in vitro and transfected into HT29 cells. The effects of oligomycin A on radiosensitivity of HT29 colorectal cancer cells were measured via MTT and colony formation assay. Western blotting was used to detect the effect of oligomycin A on the expression of glycolytic enzyme PFK1. We compared difference between the effects of siRNA-PFK1 group and oligomycin A combined with siRNA-PFK1 group on cell survival and glycolysis. After 4 Gy X-ray irradiation, the effects of cell survival and glycolysis between the siRNA-PFK1 group and the oligomycin A combined with siRNA-PFK1 group were compared.

RESULTS

Compared with the 0 μmol/L oligomycin A group, the cell survival rate of HT29 cells treated with 4 μmol/L oligomycin A was significantly increased (P<0.05), and the glucose uptake, the lactic acid, and the ATP production were also significantly increased (all P<0.01). After X-ray irradiation at different doses (0, 2, 4, 6, and 8 Gy), the colony formation rate and cell survival rate of the 4 μmol/L oligomycin A treated group were significantly higher than those in the 0 μmol/L oligomycin A group (both P<0.01). The sensitization enhancement ratio of oligomycin A on HT29 colorectal cancer cells was 0.4886. The expression of PFK1 in the 4 μmol/L oligomycin A group was significantly higher than that in the 0 μmol/L oligomycin A group (P<0.001). The glycolysis level, colony formation rate, and cell survival rate of the siRNA-PFK1 HT29 cells group were significantly lower than those in the 0 μmol/L oligomycin A group (all P<0.05), while the results in the 4 μmol/L oligomycin A combined with siRNA-PFK1 group were significantly higher than those in the siRNA-PFK1 group (all P<0.001). After 4 Gy X-ray irradiation, the colony formation rate and cell survival rate in the siRNA-PFK1 group were decreased compared with those in the irradiation group (P<0.01 or P<0.001), while the results of the 4 μmol/L oligomycin A combined with siRNA-PFK1 group were significantly higher than those in the siRNA-PFK1 group (both P<0.001).

CONCLUSIONS

Oligomycin A can promote the radioresistance of HT29 colorectal cancer cells, which may be related to up-regulation of the PFK1 expression and increase of cell glycolysis.

Coenzyme Q redox signalling and longevity

Mitochondria are the powerhouses of the cell. They produce a significant amount of the energy we need to grow, survive and reproduce. The same system that generates energy in the form of ATP also produces Reactive Oxygen Species (ROS). Mitochondrial Reactive Oxygen Species (mtROS) were considered for many years toxic by-products of metabolism, responsible for ageing and many degenerative diseases. Today, we know that mtROS are essential redox messengers required to determine cell fate and maintain cellular homeostasis. Most mtROS are produced by respiratory complex I (CI) and complex III (CIII). How and when CI and CIII produce ROS is determined by the redox state of the Coenzyme Q (CoQ) pool and the proton motive force (pmf) generated during respiration. During ageing, there is an accumulation of defective mitochondria that generate high levels of mtROS. This causes oxidative stress and disrupts redox signalling. Here, we review how mtROS are generated in young and old mitochondria and how CI and CIII derived ROS control physiological and pathological processes. Finally, we discuss why damaged mitochondria amass during ageing as well as methods to preserve mitochondrial redox signalling with age.

Inhibition of the mitochondrial ATPase function by IF1 changes the spatiotemporal organization of ATP synthase

• Mitochondrial F1FO ATP synthase is the key enzyme for mitochondrial bioenergetics. Dimeric F1FO-ATP synthase, is preferentially located at the edges of the cristae and its oligomerization state determines mitochondrial ultrastructure. The ATP synthase inhibitor protein IF1 modulates not only ATP synthase activity but also regulates both the structure and function of mitochondria. In order to understand this in more detail, we have investigated the effect of IF1 on the spatiotemporal organization of the ATP synthase. Stable cell lines were generated that overexpressed IF1 and constitutively active IF1-H49K. The expression of IF1-H49K induced a change in the localization and mobility of the ATP synthase as analyzed by single molecule tracking and localization microscopy (TALM). In addition, the ultrastructure and function of mitochondria in cells with higher levels of active IF1 displayed a gradual alteration. In state III, cristae structures were significantly altered. The inhibition of the hydrolase activity of the F1FO-ATP synthase by IF1 together with altered inner mitochondrial membrane caused re-localization and altered mobility of the enzyme.

ANT2-Mediated ATP Import into Mitochondria Protects against Hypoxia Lethal Injury

Following a prolonged exposure to hypoxia–reoxygenation, a partial disruption of the ER-mitochondria tethering by mitofusin 2 (MFN2) knock-down decreases the Ca²⁺ transfer between the two organelles limits mitochondrial Ca²⁺ overload and prevents the Ca²⁺-dependent opening of the mitochondrial permeability transition pore, i.e., limits cardiomyocyte cell death. The impact of the metabolic changes resulting from the alteration of this Ca²⁺crosstalk on the tolerance to hypoxia–reoxygenation injury remains partial and fragmented between different field of expertise. >In this study, we report that MFN2 loss of function results in a metabolic switch driven by major modifications in energy production by mitochondria. During hypoxia, mitochondria maintain their ATP concentration and, concomitantly, the inner membrane potential by importing cytosolic ATP into mitochondria through an overexpressed ANT2 protein and by decreasing the expression and activity of the ATP hydrolase via IF1. This adaptation further blunts the detrimental hyperpolarisation of the inner mitochondrial membrane (IMM) upon re-oxygenation. These metabolic changes play an important role to attenuate cell death during a prolonged hypoxia–reoxygenation challenge.

Reprogramming Oxidative Phosphorylation in Cancer: A Role for RNA-Binding Proteins

Significance: Cancer is a major disease imposing high personal and economic burden draining large part of National Health Care and Research budgets worldwide. In the last decade, research in cancer has underscored the reprogramming of metabolism to an enhanced aerobic glycolysis as a major trait of the cancer phenotype with great potential for targeted therapy. Recent Advances: Mitochondria are essential organelles in metabolic reprogramming for controlling the production of biological energy through oxidative phosphorylation (OXPHOS) and the supply of metabolic precursors that sustain proliferation. In addition, mitochondria are critical hubs that integrate different signaling pathways that control cellular metabolism and cell fate. The mitochondrial ATP synthase plays a fundamental role in OXPHOS and cellular signaling. Critical Issues: This review overviews mitochondrial metabolism and OXPHOS, and the major changes reported in the expression and function of mitochondrial proteins of OXPHOS in oncogenesis and in cellular differentiation. We summarize the prominent role that RNA-binding proteins (RNABPs) play in the sorting and localized translation of nuclear-encoded mRNAs that help define the mitochondrial cell-type-specific phenotype. Moreover, we emphasize the mechanisms that contribute to restrain the activity and expression of the mitochondrial ATP synthase in carcinomas, and illustrate that the dysregulation of proteins that control energy metabolism correlates with patients' survival. Future Directions: Future research should elucidate the mechanisms and RNABPs that promote the specific alterations of the mitochondrial phenotype in carcinomas arising from different tissues with the final aim of developing new therapeutic strategies to treat cancer.

The role of mitochondrial ATP synthase in cancer

The mitochondrial ATP synthase is a multi-subunit enzyme complex located in the inner mitochondrial membrane which is essential for oxidative phosphorylation under physiological conditions. In this review, we analyse the enzyme functions involved in cancer progression by dissecting specific conditions in which ATP synthase contributes to cancer development or metastasis. Moreover, we propose the role of ATP synthase in the formation of the permeability transition pore (PTP) as an additional mechanism which controls tumour cell death. We further describe transcriptional and translational modifications of the enzyme subunits and of the inhibitor protein IF1 that may promote adaptations leading to cancer metabolism. Finally, we outline ATP synthase gene mutations and epigenetic modifications associated with cancer development or drug resistance, with the aim of highlighting this enzyme complex as a potential novel target for future anti-cancer therapy.