Mitochondrial Adenine Nucleotide Research Articles

The cytotoxic, genotoxic and mitotoxic effects of Atractylis gummifera extract in vitro.

The Mediterranean thistle Atractylis gummifera L. (Asteraceae; AG) has diterpenoid glucosides; atractyloside and carboxyatractyloside that interact with mitochondrial protein adenine nucleotide translocator (ANT) and resulted in ATP inhibition. Despite its well-known toxicity, acute poisonings still occur with this plant. Although most symptoms are attributed to ANT and diterpenoids interaction, in-depth investigation of the effects of AG extract on various cellular processes has not been performed. We tested in vitro induction of mitochondrial permeability transition pore (MPTP) opening in bovine liver mitochondria and evaluated its cytotoxicity and genotoxicity using Allium cepa test. Cell division, mitotic index (MI) and total chromosomal and mitotic aberrations (TAs), that all seem potentially affected by ATP shortage, were studied in root cells of Allium cepa exposed to Atractylis gummifera extract. With the two different doses of two purified AG fractions, stronger induction of MPTP was observed compared to the induction with the standard pure atracyloside. Aqueous AG extract exerted inhibition root growth in A. cepa at 6 different doses. The TAs was increased in a dose-dependent manner too, while mitotic index was decreased at the same doses. Evaluation of mitotic phases revealed mitodepressive effect of AG on A. cepa roots. this work highlights cellular and mitochondrial adverse effects of Atractylis gummifera extracts. A purified fraction that likely corresponds to ATR derivatives induces MPTP opening leading to swelling of mitochondria and its dysfunction. Allium cepa test provides the evidence for A. gummifera genotoxicity and cytotoxicity.

Adenine nucleotide translocase 2 (Ant2) is required for individualization of spermatogenesis of Drosophila melanogaster.

Successful completion of spermatogenesis is crucial for the perpetuation of the species. In Drosophila, spermatid individualization, a process involving changes in mitochondrial structure and function is critical to produce functional mature sperm. Ant2, encoding a mitochondrial adenine nucleotide translocase, is highly expressed in male testes and plays a role in energy metabolism in the mitochondria. However, its molecular function remains unclear. Here, we identified an important role of Ant2 in spermatid individualization. In Ant2 knockdown testes, spermatid individualization complexes composed of F-actin cones exhibited a diffuse distribution, and mature sperms were absent in the seminal vesicle, thus leading to male sterility. The most striking effects in Ant2-knockdown spermatids were decrease in tubulin polyglycylation and disruption of proper mitochondria derivatives function. Excessive apoptotic cells were also observed in Ant2-knockdown testes. To further investigate the phenotype of Ant2 knockdown in testes at the molecular level, complementary transcriptome and proteome analyses were performed. At the mRNA level, 868 differentially expressed genes were identified, of which 229 genes were upregulated and 639 were downregulated induced via Ant2 knockdown. iTRAQ-labeling proteome analysis revealed 350 differentially expressed proteins, of which 117 proteins were upregulated and 233 were downregulated. The expression of glutathione transferase (GstD5, GstE5, GstE8, and GstD3), proteins involved in reproduction were significantly regulated at both the mRNA and protein levels. These results indicate that Ant2 is crucial for spermatid maturation by affecting mitochondrial morphogenesis.

Mitochondrial temperature homeostasis resists external metabolic stresses

Based on studies with a fluorescent reporter dye, Mito Thermo Yellow (MTY), and the genetically encoded gTEMP ratiometric fluorescent temperature indicator targeted to mitochondria, the temperature of active mitochondria in four mammalian and one insect cell line was estimated to be up to 15°C above that of the external environment to which the cells were exposed. High mitochondrial temperature was maintained in the face of a variety of metabolic stresses, including substrate starvation or modification, decreased ATP demand due to inhibition of cytosolic protein synthesis, inhibition of the mitochondrial adenine nucleotide transporter and, if an auxiliary pathway for electron transfer was available via the alternative oxidase, even respiratory poisons acting downstream of oxidative phosphorylation (OXPHOS) complex I. We propose that the high temperature of active mitochondria is an inescapable consequence of the biochemistry of OXPHOS and is homeostatically maintained as a primary feature of mitochondrial metabolism.

Mitochondrial temperature homeostasis resists external metabolic stresses.

Based on studies with a fluorescent reporter dye, Mito Thermo Yellow (MTY), and the genetically encoded gTEMP ratiometric fluorescent temperature indicator targeted to mitochondria, the temperature of active mitochondria in four mammalian and one insect cell line was estimated to be up to 15°C above that of the external environment to which the cells were exposed. High mitochondrial temperature was maintained in the face of a variety of metabolic stresses, including substrate starvation or modification, decreased ATP demand due to inhibition of cytosolic protein synthesis, inhibition of the mitochondrial adenine nucleotide transporter and, if an auxiliary pathway for electron transfer was available via the alternative oxidase, even respiratory poisons acting downstream of oxidative phosphorylation (OXPHOS) complex I. We propose that the high temperature of active mitochondria is an inescapable consequence of the biochemistry of OXPHOS and is homeostatically maintained as a primary feature of mitochondrial metabolism.

FA Sliding as the Mechanism for the ANT1-Mediated Fatty Acid Anion Transport in Lipid Bilayers.

Mitochondrial adenine nucleotide translocase (ANT) exchanges ADP for ATP to maintain energy production in the cell. Its protonophoric function in the presence of long-chain fatty acids (FA) is also recognized. Our previous results imply that proton/FA transport can be best described with the FA cycling model, in which protonated FA transports the proton to the mitochondrial matrix. The mechanism by which ANT1 transports FA anions back to the intermembrane space remains unclear. Using a combined approach involving measurements of the current through the planar lipid bilayers reconstituted with ANT1, site-directed mutagenesis and molecular dynamics simulations, we show that the FA anion is first attracted by positively charged arginines or lysines on the matrix side of ANT1 before moving along the positively charged protein-lipid interface and binding to R79, where it is protonated. We show that R79 is also critical for the competitive binding of ANT1 substrates (ADP and ATP) and inhibitors (carboxyatractyloside and bongkrekic acid). The binding sites are well conserved in mitochondrial SLC25 members, suggesting a general mechanism for transporting FA anions across the inner mitochondrial membrane.

Hidden Pool of Cardiac Adenine Nucleotides That Controls Adenosine Production.

Myocardial ischemic adenosine production decreases in subsequent events that may blunt its protective functions. To test the relation between total or mitochondrial cardiac adenine nucleotide pool (TAN) on the energy status with adenosine production, Langendorff perfused rat hearts were subjected to three protocols: 1 min ischemia at 40 min, 10 min ischemia at 50 min, and 1 min ischemia at 85 min in Group I; additional infusion of adenosine (30 µM) for 15 min after 10 min ischemia in Group I-Ado, and 1 min ischemia at 40 and 85 min in the controls (Group No I). A 31P NMR and an HPLC were used for the analysis of nucleotide and catabolite concentrations in the heart and coronary effluent. Cardiac adenosine production in Group I measured after 1 min ischemia at 85 min decreased to less than 15% of that at 40 min in Group I, accompanied by a decrease in cardiac ATP and TAN to 65% of the initial results. Adenosine production at 85 min was restored to 45% of that at 40 min in Group I-Ado, accompanied by a rebound of ATP and TAN by 10% vs. Group I. Mitochondrial TAN and free AMP concentrations paralleled that of total cardiac TAN. Changes in energy equilibrium or mitochondrial function were minor. This study highlights that only a fraction of the cardiac adenine nucleotide pool is available for adenosine production, but further studies are necessary to clarify its nature.

Inhibition of mitochondrial translocase SLC25A5 and histone deacetylation is an effective combination therapy in neuroblastoma.

The mitochondrion is a gatekeeper of apoptotic processes, and mediates drug resistance to several chemotherapy agents used to treat cancer. Neuroblastoma is a common solid cancer in young children with poor clinical outcomes following conventional chemotherapy. We sought druggable mitochondrial protein targets in neuroblastoma cells. Among mitochondria-associated gene targets, we found that high expression of the mitochondrial adenine nucleotide translocase 2 (SLC25A5/ANT2), was a strong predictor of poor neuroblastoma patient prognosis and contributed to a more malignant phenotype in pre-clinical models. Inhibiting this transporter with PENAO reduced cell viability in a panel of neuroblastoma cell lines in a TP53-status-dependant manner. We identified the histone deacetylase inhibitor, suberanilohydroxamic acid (SAHA), as the most effective drug in clinical use against mutant TP53 neuroblastoma cells. SAHA and PENAO synergistically reduced cell viability, and induced apoptosis, in neuroblastoma cells independent of TP53-status. The SAHA and PENAO drug combination significantly delayed tumour progression in pre-clinical neuroblastoma mouse models, suggesting that these clinically advanced inhibitors may be effective in treating the disease.

Gene Editing and Multi-Omics Reveal Novel Metabolic Vulnerabilities in t(4;14)-Associated Multiple Myeloma

Background: Chromosomal translocation t(4;14) is a recurrent genetic lesion in multiple myeloma (MM) which drives aberrant overexpression of the histone methyltransferase NSD2 and is associated with a more guarded prognosis. Despite its oncogenic outcomes, NSD2 overexpression in MM cells could simultaneously confer cellular vulnerabilities that can be therapeutically exploited. Aim: To define potential therapeutic susceptibilities driven by NSD2 overexpression in t(4;14) MM. Methods: We performed genome-wide knockout screening in isogenic NSD2 high and low KMS11 cells using the Brunello CRISPR library, followed by validation of key target genes in several different t(4;14) MM cell lines. Results: These screens revealed increased reliance of NSD2-overexpressing cells on multiple cellular processes including mitochondrial respiration, transcriptional elongation and proteasomal degradation. One of the top preferential dependencies in NSD2-high MM cells is the mitochondrial adenine nucleotide regulator adenylate kinase 2 (AK2). AK2 catalyzes the reversible interconversion of ADP to ATP and AMP. Cancer Dependency Map (depmap) analysis indicated that AK2 loss is detrimental to most MM cell lines but it is not a dependency in most solid tumor cells. Reliance on AK2 was modest in t(4;14) MM cells engineered to express low levels of NSD2 but the detrimental effect of AK2 depletion by shRNA or CRISPR was exacerbated upon enforced overexpression of NSD2. Gene expression studies showed that AK2 suppression leads to induction of genes involved in oxidative stress response. Metabolomic profiling of NSD2 high and low isogenic MM cells demonstrated striking reduction of NAD+ and elevation of nicotinamide (NAM) levels in NSD2 overexpressing cells, which correlates with a 10-fold induction of expression of the NAD+ consuming enzyme CD38 by NSD2. NAD+ and its metabolite NADP+ are essential co-factors of multiple antioxidant enzymes and its depletion can exacerbate oxidative damage. Therefore, NAD+ depletion likely accounts for the increased susceptibility of NSD2 high MM cells to AK2 loss. In vitro cell proliferation/viability assays demonstrated increased sensitivity of NSD2 high MM cells to PI exposure suggesting that NSD2 overexpression drives a higher load of unfolded proteins, correlating with loss of NAD+ and redox system activity. AK2 suppression in MM cells also impairs activation of the adaptive unfolded protein response through the IRE1a-XBP1 axis leading to decreased protein folding capacity. The combination of high unfolded protein load and poor ATP shuttling to the endoplasmic reticulum (ER) secondary to AK2 loss may represent an additional mechanism of selective lethality. Furthermore, AK2 deficient MM cells displayed increased sensitivity to PIs. Transcriptomic analyses in NSD2 high and low MM cells revealed that NSD2 overexpression, besides driving an oncogenic transcriptional program, alters the expression of several genes involved in nucleotide metabolism. Perturbed nucleotide metabolism was further documented by untargeted metabolite profiling which showed a notable depletion of several pyrimidine metabolites when NSD2 is overexpressed. Intriguingly, induced reduction of pyrimidine synthesis by treatment with DHODH inhibitors appeared to be more detrimental in NSD2 overexpressing MM cells. Conclusions: NSD2 overexpression in MM cells alters cellular metabolism and confers higher susceptibility to oxidative stress and unfolded protein loads. By inducing the expression of NAD+ consuming enzymes, NSD2 overexpression results in NAD+ depletion which likely underlies the described vulnerabilities. Loss of the mitochondrial adenine nucleotide regulator AK2 is more detrimental to NSD2 overexpressing MM cells as it diminishes efficient ATP utilization in the ER perturbing the ability of MM cells to handle high loads of unfolded immunoglobulins and mitigate oxidative stress. Furthermore, integrated analyses of the different omics datasets highlighted other NSD2-driven liabilities, including mitochondrial respiration, transcriptional elongation and nucleotide metabolism, that can be targeted to improve prognosis of MM.

Abstract 11029: Bioenergetic Independent Stress Signaling in the Heart Due to Mitochondrial Protein Import Stress

Mitochondrial diseases are some of the most common genetically inherited disorders, yet the prognosis for affected patients has not drastically improved in recent years. Most therapies are supportive as the underlying biochemical derangements in these diseases are incompletely understood. Mitochondrial functions rely on the import of nuclear-encoded proteins, and it has recently been appreciated that defective import of mitochondrial proteins can result in the cytosolic accumulation of these preproteins. The accumulation of these preproteins results in cellular toxicity independently of any changes to the mitochondrial bioenergetic function, raising the possibility that mitochondrial protein import stress may be a yet uncharacterized pathway that links mitochondrial dysfunction with pathology. Here, we model this cytosolic mitochondrial precursor overaccumulation stress (mPOS) in mice through overexpression of the inner mitochondrial membrane protein Adenine Nucleotide Translocase 1 (ANT1). The goal of this study is to determine whether ANT1 can induce mPOS and tissue remodeling prior to the onset of cardiac bioenergetic defects. Using isolated cardiac mitochondria from these mice, we detected a moderate decrease in the levels of Complex I, II ,and IV. By measuring oxygen consumption in these mitochondria from 2-month-old animals, we found only a mild reduction in complex II based state 3 and 4 respirations. No change in complex I-based state 3 and 4 respirations was observed. Using RNAseq and western blot analysis, we find the robust activation of the integrated stress response (ISR). Transcriptomic data further demonstrates a strong upregulation of transcripts involved with 1-carbon metabolism, the amino acid starvation response, and proteolysis. Using echocardiographic evaluation of heart function on anesthetized mice at 6 months old, we find no significant alteration in systolic function. Together these data support the idea that mPOS may be a potent trigger of the ISR in a bioenergetics-independent manner. Whether activation of the ISR can alter cardiac function later in life is being evaluated.

Effects of cadmium on oxidative stress and cell apoptosis in Drosophila melanogaster larvae

With the increase of human activities, cadmium (Cd) pollution has become a global environmental problem affecting biological metabolism in ecosystem. Cd has a very long half-life in humans and is excreted slowly in organs, which poses a serious threat to human health. In order to better understand the toxicity effects of cadmium, third instar larvae of Drosophila melanogaster (Canton-S strain) were exposed to different concentrations (1.125 mg/kg, 2.25 mg/kg, 4.5 mg/kg, and 9 mg/kg) of cadmium. Trypan blue staining showed that intestinal cell damage of Drosophila larvae increased and the comet assay indicated significantly more DNA damage in larvae exposed to high Cd concentrations. The nitroblue tetrazolium (NBT) experiments proved that content of reactive oxygen species (ROS) increased, which indicated Cd exposure could induce oxidative stress. In addition, the expression of mitochondrial adenine nucleotide transferase coding gene (sesB and Ant2) and apoptosis related genes (Debcl, hid, rpr, p53, Sce and Diap1) changed, which may lead to increased apoptosis. These findings confirmed the toxicity effects on oxidative stress and cell apoptosis in Drosophila larvae after early cadmium exposure, providing insights into understanding the effects of heavy metal stress in animal development.

The mechanism of fatty acid anion transport across the inner mitochondrial membrane by the adenine nucleotide translocase

The flip-flop of phospholipids and fatty acids across cellular membranes is mediated by lipid flippases and scramblases. It is described by the credit-card model in which the lipid head is transported through a membrane-spanning hydrophilic groove, while the lipid tail remains in the membrane1. We have previously shown that the mitochondrial adenine nucleotide translocase (ANT) transports fatty acid anions (FA-) according to the fatty acid cycling model2. However, the absence of such a groove indicates a substantially different FA- transport mechanism, which was not resolved until now.

Adenylate Kinase 2 Is a Selective Multiple Myeloma Cell Dependency That Is Preferentially Essential in NSD2-Overexpressing Cells

Background: Multiple myeloma (MM) is the second most common hematologic malignancy and remains incurable. Advances in MM therapy have come about due to therapies that target vulnerabilities of the plasma cell such as high protein load (proteasome inhibitors; PIs), dependence on specific transcription factors such as IKZF1 and IKZF3 which are degraded by immunomodulatory drugs (IMiDs), the susceptibility of B cells to glucocorticoids and the presence of specific B cell markers that can serve as targets for monoclonal antibodies and CAR-T cells. Gene editing screens offer a way to identify novel MM therapeutic targets.Objectives: The molecular heterogeneity of MM imposes challenges to discovering generalized therapeutic targets. Therefore, identification of selective dependencies associated with a particular recurrent genetic lesion is a promising strategy to personalize therapy. Here, we aim to identify vulnerabilities linked to the chromosomal translocation t(4;14), a recurrent rearrangement in MM characterized by overexpression of the histone methyltransferase NSD2.Methods: Genome-wide CRISPR-based loss-of-function screens were performed in NSD2-high and low isogenic cells derived from the t(4;14) MM cell line KMS11 to define selective dependencies associated with NSD2 overexpression. High-confidence hits were corroborated by in vitro competitive growth assays where individual candidates are genetically knocked out or suppressed or chemically inhibited. Detailed investigation was performed for selected candidates using various molecular and biochemical assays to elucidate mechanisms by which these genes contribute to MM cell fitness.Results: A fitness screen in NSD2-high and low isogenic MM cells identified 1118 essential genes which are common between the cell pair. We further revealed 282 genes whose loss is more detrimental to cells overexpressing NSD2 and 139 genes that are preferentially essential when NSD2 levels are low. Pathway analysis of NSD2-high selectively essential genes indicated that these cells are more dependent on mitochondrial processes including oxidative phosphorylation. Although proteasomal degradation is essential for all MM cells, our screens indicated that NSD2-high cells are more dependent on the proteasome, which was validated by increased sensitivity to the PI bortezomib. One of the high-confidence selective NSD2-high hits was the mitochondrial adenine nucleotide regulator adenylate kinase 2 (AK2). Analyzing the dependence of hundreds of human cell lines on AK2 using the cancer dependency map portal (depmap.org/portal/), we found that AK2 is not a common essential gene. The top enriched linages with AK2 dependency included MM with notable representation of t(4;14)-positive cell lines. Analysis of the multiple myeloma research foundation (MMRF)-CoMMPass data demonstrated that MM patients with high NSD2 expression, despite poor prognosis, display enhanced overall survival when AK2 levels are low. In vitro competitive growth assays in NSD2-high and low MM cells confirmed the increased dependence of NSD2-overexpressing cells on AK2. In addition, NSD2-high MM cells displayed elevated sensitivity to AK2 inhibitors. Moreover, AK2 knockdown in t(4;14) MM cell lines increased sensitivity to the PI bortezomib. Mechanistically, we showed that AK2 disruption activates apoptotic unfolded protein response (UPR) signaling in MM cells. Metabolomic profiling in NSD2-high and low MM cells revealed accumulation of purine metabolites and reduction of pyrimidine metabolites upon NSD2 overexpression. Intriguingly, purine supplementation rescued MM cell depletion due to AK2 loss. These observations suggested that MM cells, especially those with NSD2 overexpression, are addicted to elevated purine levels and that lethality of MM cells upon AK2 loss is due to perturbed purine metabolism. How impaired purine metabolism activates UPR signaling is currently under investigation.Conclusions: Our work indicated that NSD2 overexpression resulting from chromosomal translocation t(4;14), despite its oncogenic role, generates metabolic dependencies in MM cells. Our findings further suggest that inhibition of AK2, a mitochondrial enzyme involved in purine metabolism, can induce UPR-mediated apoptosis in MM cells and could be used in combination with PI therapy to treat MM patients with t(4;14) translocations. DisclosuresLicht: Epizyme: Research Funding.

Oligodendrocytes enhance axonal energy metabolism by deacetylation of mitochondrial proteins through transcellular delivery of SIRT2

Neurons require mechanisms to maintain ATP homeostasis in axons, which are highly vulnerable to bioenergetic failure. Here, we elucidate a transcellular signaling mechanism by which oligodendrocytes support axonal energy metabolism via transcellular delivery of NAD-dependent deacetylase SIRT2. SIRT2 is undetectable in neurons but enriched in oligodendrocytes and released within exosomes. By deleting sirt2, knocking down SIRT2, or blocking exosome release, we demonstrate that transcellular delivery of SIRT2 is critical for axonal energy enhancement. Mass spectrometry and acetylation analyses indicate that neurons treated with oligodendrocyte-conditioned media from WT, but not sirt2-knockout, mice exhibit strong deacetylation of mitochondrial adenine nucleotide translocases 1 and 2 (ANT1/2). Invivo delivery of SIRT2-filled exosomes into myelinated axons rescues mitochondrial integrity in sirt2-knockout mouse spinal cords. Thus, our study reveals an oligodendrocyte-to-axon delivery of SIRT2, which enhances ATP production by deacetylating mitochondrial proteins, providing a target for boosting axonal bioenergetic metabolism in neurological disorders.

Quantitative analysis of mitochondrial ATP synthesis

We present a computational framework for analyzing and simulating mitochondrial ATP synthesis using basic thermodynamic and kinetic principles. The framework invokes detailed descriptions of the thermodynamic driving forces associated with the processes of the electron transport chain, mitochondrial ATP synthetase, and phosphate and adenine nucleotide transporters. Assembling models of these discrete processes into an integrated model of mitochondrial ATP synthesis, we illustrate how to analyze and simulate in vitro respirometry experiments and how models identified from in vitro experimental data effectively explain cardiac respiratory control in vivo. Computer codes for these analyses are embedded as Python scripts in a Jupyter Book to facilitate easy adoption and modification of the concepts developed here. This accessible framework may also prove useful in supporting educational applications. All source codes are available on at https://beards-lab.github.io/QAMAS_book/.

Loss of Mitochondrial Adenine Nucleotide Translocase (ANT1) Regulates Cellular Senescence and Protects against Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is a destructive lung disease resulting in alveolar tissue loss, airway remodeling and inflammation with cigarette smoke (CS) being a major causative factor. Mitochondrial dysfunction can lead to changes in cell fate implicated in COPD. Cellular senescence, a state of cell cycle arrest, results in abnormal responses in lung epithelial cells. An important protein in mitochondrial metabolism and cell fate is adenine nucleotide translocase (ANT), a mitochondrial ATP transporter. Our studies suggest that levels of ANT are altered in COPD. We hypothesize that loss of ANTs results in increased cellular senescence thus altering COPD pathogenesis and airway dysfunction. Methods Utilizing siRNA knockdown of SLC25A4 (ANT1) and SLC25A5 (ANT2) in human bronchial epithelial cells, Beas-2bs, we assessed cellular senescence (p53, p21, p16) via western blot, qt-PCR and B-galactocidase analysis. Cells were also exposed to CS extract. Wildtype (WT) and ant1-null mice were exposed to CS for 2 and 6mo or air control with lung histology and morphometry analysis. We performed single cell RNA sequencing on lungs from 2mo air and CS-exposed mice. Single-cell library preparation was performed using 10X Genomics 5prime v1 reagents to analyze 5000 cells/mouse (n=3 mice/group). Alignment was performed using Cell Ranger and standard workflow analysis using R package Seurat v3.2. Cell clusters were generated using unsupervised UMAP. Pathway analysis on differential gene expression lists by cell type was performed using Ingenuity Pathway Analysis. Results Knockdown of ANT1 or ANT2 in Beas-2b cells results in an increase in cell senescence proteins p16, p21, p53 and beta-galactosidase staining. Surprisingly, ant1-null mice exposed to 6months of CS exposure are protected from alveolar destruction (fig.1), airway remodeling and chronic inflammation with fewer macrophages. Single cell RNA sequencing of WT lung cells demonstrates that CS (2 mo) causes a significant increase in genes associated with senescence in alveolar type 1 epithelial cells (AT1, p-value 1.0x10-6) with dysregulation of mitochondrial-related gene pathways when compared to air controls: mitochondrial dysfunction, upregulation of Eif2 signaling and NRF2-mediated oxidative stress, and downregulation in sirtuin signaling. Alveolar type 2 cells (AT2) from WT-smoked mice show downregulation of Eif2 signaling, unfolded protein response, NRF2-mediated oxidative stress, and sirtuin signaling. Expression of slc25a4 (ant1) is upregulated in AT2 cells in WT-smoked mice (p-value 1.7x10-17). Mitochondrial and cell fate pathways were significantly altered in AT1 and AT2 cells from WT-smoked mice but not from ant1-null mice, suggesting a key role in lung epithelial responses in COPD. Conclusions ANTs alter cell senescence in alveolar epithelial cells. An In vivo mouse model shows that ant1 is upregulated in AT2 cells after CS and loss of ant1 is protective against CS lung injury. Ant1 regulates epithelial cell fate, mitochondrial function and CS-related cell injury, providing a potential therapeutic avenue for COPD.

A Walk in the Memory, from the First Functional Approach up to Its Regulatory Role of Mitochondrial Bioenergetic Flow in Health and Disease: Focus on the Adenine Nucleotide Translocator.

The mitochondrial adenine nucleotide translocator (ANT) plays the fundamental role of gatekeeper of cellular energy flow, carrying out the reversible exchange of ADP for ATP across the inner mitochondrial membrane. ADP enters the mitochondria where, through the oxidative phosphorylation process, it is the substrate of Fo-F1 ATP synthase, producing ATP that is dispatched from the mitochondrion to the cytoplasm of the host cell, where it can be used as energy currency for the metabolic needs of the cell that require energy. Long ago, we performed a method that allowed us to monitor the activity of ANT by continuously detecting the ATP gradually produced inside the mitochondria and exported in the extramitochondrial phase in exchange with externally added ADP, under conditions quite close to a physiological state, i.e., when oxidative phosphorylation takes place. More than 30 years after the development of the method, here we aim to put the spotlight on it and to emphasize its versatile applicability in the most varied pathophysiological conditions, reviewing all the studies, in which we were able to observe what really happened in the cell thanks to the use of the “ATP detecting system” allowing the functional activity of the ANT-mediated ADP/ATP exchange to be measured.

Toxicokinetics of the tumour cell mitochondrial toxin, PENAO, in rodents.

PENAO (4-(N-(S-penicillaminylacetyl)amino)phenylarsonous acid) is a second-generation peptide arsenical that inactivates mitochondria in proliferating tumour cells by covalently reacting with mitochondrial inner-membrane adenine nucleotide transferase. The toxicokinetics of PENAO has been investigated in Sprague-Dawley rats to inform route of administration and dosing for human clinical trials. PENAO was well tolerated at 3.3mg/kg daily intravenous injections but associated with significant toxicity at 10mg/kg, primarily in the males. The major target organ for toxic effects was the kidney, with changes observed in tubular dilation, presence of casts, basophilic tubules, lymphoid aggregates and interstitial fibrosis. Kidney function was impaired in males with dose-dependent increase in serum creatinine concentration. The severity of the microscopic lesions was reduced in the females, but not the males, at the completion of the four-week recovery period. The elimination phase half-life of PENAO varied between 0.4 and 1.7h and volume of distribution ranged from 0.25 to 0.88L/kg for the different dose groups and treatment days, suggesting that PENAO distributes in the extracellular fluids at the doses tested. The area under the curve and clearance values indicate that male rats had reduced elimination of PENAO compared to females, which may account for the increased toxicity in males. PENAO is significantly better tolerated in rodents than its predecessor, GSAO. As GSAO was generally well tolerated with few side effects in a phase I trial in patients with solid tumours, these findings bode well for the tolerability of intravenous dosing of PENAO in patients.

A toolset of constitutive promoters for metabolic engineering of Rhodosporidium toruloides

BackgroundRhodosporidium toruloides is a promising host for the production of bioproducts from lignocellulosic biomass. A key prerequisite for efficient pathway engineering is the availability of robust genetic tools and resources. However, there is a lack of characterized promoters to drive expression of heterologous genes for strain engineering in R. toruloides.ResultsThis data describes a set of native R. toruloides promoters, characterized over time in four different media commonly used for cultivation of this yeast. The promoter sequences were selected using transcriptional analysis and several of them were found to drive expression bidirectionally. Promoter expression strength was determined by measurement of EGFP and mRuby2 reporters by flow cytometry. A total of 20 constitutive promoters (12 monodirectional and 8 bidirectional) were found, and are expected to be of potential value for genetic engineering of R. toruloides.ConclusionsA set of robust and constitutive promoters to facilitate genetic engineering of R. toruloides is presented here, ranging from a promoter previously used for this purpose (P7, glyceraldehyde 3-phosphate dehydrogenase, GAPDH) to stronger monodirectional (e.g., P15, mitochondrial adenine nucleotide translocator, ANT) and bidirectional (e.g., P9 and P9R, histones H3 and H4, respectively) promoters. We also identified promoters that may be useful for specific applications such as late-stage expression (e.g., P3, voltage-dependent anion channel protein 2, VDAC2). This set of characterized promoters significantly expands the range of engineering tools available for this yeast and can be applied in future metabolic engineering studies.

Regulation of permeability transition pore opening in mitochondria by external NAD(H)

BackgroundThe opening of the permeability transition pore (PTP) in mitochondria plays a critical role in the pathogenesis of numerous diseases. Mitochondrial matrix pyridine nucleotides are potent regulators of the PTP, but the role of extramitochondrial nucleotides is unclear. MethodsThe PTP opening was explored in isolated mitochondria and mitochondria in permeabilized differentiated and undifferentiated cells in the presence of added NAD(P)(H) in combination with Mg2+, adenine nucleotides (AN), and the inhibitors of AN translocase (ANT), voltage-dependent anion channel (VDAC), and cyclophilin D. ResultsAdded NAD(H) and AN, but not NADP(H), inhibited the PTP opening with comparable potency. PTP suppression required neither NAD(H) oxidation nor reduction. The protective effects of NAD(H) and cyclosporin A were synergistic, and the effects of NAD(H) and millimolar AN were additive. The conformation-specific ANT inhibitors were unable to cancel the protective effect of NADH even under total ANT inhibition. Besides, NAD(H) activated the efflux of mitochondrial AN via ANT. VDAC ligand (Mg2+) and blockers (G3139 and 4,4′-diisothiocyano-2,2′-stilbenedisulfonic acid) potentiated and attenuated the protective effect of NAD(H), respectively. However, in embryonic and cancer (undifferentiated) cells, in contrast to isolated differentiated hepatocytes and cardiocytes, the suppression of PTP opening by NADH was negligible though all cells tested possessed a full set of VDAC isoforms. ConclusionsThe study revealed a novel mechanism of PTP regulation by external (cytosolic) NAD(H) through the allosteric site in the OM or the intermembrane space. General significanceThe mechanism might contribute to the resistance of differentiated cells under different pathological conditions including ischemia/reperfusion.

193 - Antioxidant activity of calcium-independent phospholipase A2γ in brain mitochondria

Mitochondrial calcium-independent phospholipase A2γ (iPLA2γ) belongs to a family of enzymes that participate in cellular signaling by simultaneously producing free fatty acids and lysophospholipids. We have shown previously that the activity of iPLA2γ is increased following the addition of oxidants, such as tert-butyl hydroperoxide (tBHP) or H2O2. We have also shown that iPLA2γ-liberated fatty acids induce H+ transport mediated by mitochondrial uncoupling proteins and mitochondrial adenine nucleotide translocase (ANT) in heart, lung and spleen mitochondria, leading to a decrease in the mitochondrial protonmotive force and subsequent decrease in mitochondrial superoxide production [1,2]. Here we tested the hypothesis that iPLA2γ serves similar antioxidant function in brain. Using brain mitochondria isolated from wild-type (WT) mice, we found that low micromolar concentrations of tBHP induced increase in respiration and a parallel decrease in mitochondrial superoxide and H2O2 production. These effects of tBHP were fully prevented by bovine serum albumin and inhibited by R-bromoenol lactone, a selective inhibitor of iPLA2γ, and were absent in brain mitochondria isolated from iPLA2γ-KO mice. Moreover, the tBHP-induced effects were fully inhibited by carboxyatractyloside, indicating the participation of ANT. In addition, we observed decrease in mRNA levels of selected antioxidant enzymes and increase in lipid peroxidation products in brain tissues homogenates of iPLA2γ-KO mice compared to the WT controls. Our results support the hypothesis of an antioxidant role of iPLA2γ in brain, consistent with iPLA2γ-dependent, ANT-mediated attenuation of mitochondrial superoxide production. Supported by LTAUSA17174