Specific VDAC inhibitors: phosphorothioate oligonucleotides

Oxysterols in Central and Peripheral Synaptic Communication

Cholesterol is a key molecule for synaptic transmission, and both central and peripheral synapses are cholesterol rich. During intense neuronal activity, a substantial portion of synaptic cholesterol can be oxidized by either enzymatic or non-enzymatic pathways to form oxysterols, which in turn modulate the activities of neurotransmitter receptors (e.g., NMDA and adrenergic receptors), signaling molecules (nitric oxide synthases, protein kinase C, liver X receptors), and synaptic vesicle cycling involved in neurotransmitters release. 24-Hydroxycholesterol, produced by neurons in the brain, could directly affect neighboring synapses and change neurotransmission. 27-Hydroxycholesterol, which can cross the blood-brain barrier, can alter both synaptogenesis and synaptic plasticity. Increased generation of 25-hydroxycholesterol by activated microglia and macrophages could link inflammatory processes to learning and neuronal regulation. Amyloids and oxidative stress can lead to an increase in the levels of ring-oxidized sterols and some of these oxysterols (4-cholesten-3-one, 5α-cholestan-3-one, 7β-hydroxycholesterol, 7-ketocholesterol) have a high potency to disturb or modulate neurotransmission at both the presynaptic and postsynaptic levels. Overall, oxysterols could be used as "molecular prototypes" for therapeutic approaches. Analogs of 24-hydroxycholesterol (SGE-301, SGE-550, SAGE718) can be used for correction of NMDA receptor hypofunction-related states, whereas inhibitors of cholesterol 24-hydroxylase, cholestane-3β,5α,6β-triol, and cholest-4-en-3-one oxime (olesoxime) can be utilized as potential anti-epileptic drugs and (or) protectors from excitotoxicity.

Pan-Cancer Analysis of Voltage-Dependent Anion Channel (VDAC1) as a Cancer Therapeutic Target or Diagnostic Biomarker

The voltage-dependent anion channel 1 (VDAC1), a pore protein located in the outer mitochondrial membrane, has been confirmed to be related to cancer in cell or animal evidence. However, there is no available pan-cancer analysis of VDAC1. Herein, we investigated the potential roles of VDAC1 in tumorigenesis and progression based on the Cancer Genome Atlas (TCGA), Gene Expression Omnibus (GEO), and Clinical Proteomic Tumor Analysis Consortium (CPTAC) datasets. The expression of VDAC1 increased in most cancers, and the upregulation of VDAC1 distinctly correlated with the poor prognosis in patients, including breast invasive carcinoma, cervical squamous cell carcinoma, pancreatic adenocarcinoma, lung adenocarcinoma, and skin cutaneous melanoma. We also found VDAC1 S104 phosphorylation raised in various cancers, such as breast cancer, colon cancer, and lung adenocarcinoma. Moreover, the expression of VDAC1 was related to the estimated infiltration value of cancer-associated fibroblasts in bladder urothelial carcinoma, colon adenocarcinoma, kidney renal papillary cell carcinoma, and testicular germ cell tumors. At last, we showed that VDAC1-related oxidative phosphorylation and metabolic regulation may partially explain its association with tumorigenesis and progression. Taken together, this pan-cancer analysis provides relatively comprehensive information on the potential value of VDAC1 as a prognostic biomarker and therapeutic target.

PHDs/CPT1B/VDAC1 axis regulates long-chain fatty acid oxidation in cardiomyocytes

Cardiac metabolism is a high-oxygen-consuming process, showing a preference for long-chain fatty acid (LCFA) as the fuel source under physiological conditions. However, a metabolic switch (favoring glucose instead of LCFA) is commonly reported in ischemic or late-stage failing hearts. The mechanism regulating this metabolic switch remains poorly understood. Here, we report that loss of PHD2/3, the cellular oxygen sensors, blocks LCFA mitochondria uptake and β-oxidation in cardiomyocytes. In high-fat-fed mice, PHD2/3 deficiency improves glucose metabolism but exacerbates the cardiac defects. Mechanistically, we find that PHD2/3 bind to CPT1B, a key enzyme of mitochondrial LCFA uptake, promoting CPT1B-P295 hydroxylation. Further, we show that CPT1B-P295 hydroxylation is indispensable for its interaction with VDAC1 and LCFA β-oxidation. Finally, we demonstrate that a CPT1B-P295A mutant constitutively binds to VDAC1 and rescues LCFA metabolism in PHD2/3-deficient cardiomyocytes. Together, our data identify an oxygen-sensitive regulatory axis involved in cardiac metabolism.

Olesoxime, a cholesterol-like neuroprotectant restrains synaptic vesicle exocytosis in the mice motor nerve terminals: Possible role of VDACs

Olesoxime is a cholesterol-like neuroprotective compound that targets to mitochondrial voltage dependent anion channels (VDACs). VDACs were also found in the plasma membrane and highly expressed in the presynaptic compartment. Here, we studied the effects of olesoxime and VDAC inhibitors on neurotransmission in the mouse neuromuscular junction. Electrophysiological analysis revealed that olesoxime suppressed selectively evoked neurotransmitter release in response to a single stimulus and 20 Hz activity. Also olesoxime decreased the rate of FM1-43 dye loss (an indicator of synaptic vesicle exocytosis) at low frequency stimulation and 20 Hz. Furthermore, an increase in extracellular Cl^- enhanced the action of olesoxime on the exocytosis and olesoxime increased intracellular Cl^- levels. The effects of olesoxime on the evoked synaptic vesicle exocytosis and [Cl^-]_i were blocked by membrane-permeable and impermeable VDAC inhibitors. Immunofluorescent labeling pointed on the presence of VDACs on the synaptic membranes. Rotenone-induced mitochondrial dysfunction perturbed the exocytotic release of FM1-43 and cell-permeable VDAC inhibitor (but not olesoxime or impermeable VDAC inhibitor) partially mitigated the rotenone-driven alterations in the FM1-43 unloading and mitochondrial superoxide production. Thus, olesoxime restrains neurotransmission by acting on plasmalemmal VDACs whose activation can limit synaptic vesicle exocytosis probably via increasing anion flux into the nerve terminals.

Targeting mitochondrial calcium pathways as a potential treatment against Parkinson's disease

Parkinson's disease (PD) is a major health problem worldwide affecting millions of people and is a result of neurodegeneration in a small part of the brain known as substantia nigra pars compacta. Aberration in mitochondrial Ca²⁺ homeostasis plays, among several other factors, an important role for the neuronal loss in PD. Mitochondria are vital for cellular physiology, e.g. for ATP generation, and mitochondrial Ca²⁺ is a key player in cell functioning and survival. Mitochondrial Ca²⁺ homeostasis is maintained by a fine balance between the activities of proteins mediating the influx and efflux of Ca²⁺ across mitochondrial membranes. Malfunctioning of these proteins leading to Ca²⁺ overload promotes ROS generation, which induces cell death by triggering the opening of mitochondrial permeability transition pore. Till now PD remains incurable and the "gold standard" drug which can only delays the disease progression is l-Dopa from the 1960s and therefore, the situation warrants the search for novel targets for the treatment of the PD patients. In this review, we summarize the current views that suggest mitochondrial Ca²⁺ regulatory pathways are good candidates for the treatment of PD.

Pharmacological modulation of mitochondrial ion channels

The field of mitochondrial ion channels has undergone a rapid development during the last three decades, due to the molecular identification of some of the channels residing in the outer and inner membranes. Relevant information about the function of these channels in physiological and pathological settings was gained thanks to genetic models for a few, mitochondria-specific channels. However, many ion channels have multiple localizations within the cell, hampering a clear-cut determination of their function by pharmacological means. The present review summarizes our current knowledge about the ins and outs of mitochondrial ion channels, with special focus on the channels that have received much attention in recent years, namely, the voltage-dependent anion channels, the permeability transition pore (also called mitochondrial megachannel), the mitochondrial calcium uniporter and some of the inner membrane-located potassium channels. In addition, possible strategies to overcome the difficulties of specifically targeting mitochondrial channels versus their counterparts active in other membranes are discussed, as well as the possibilities of modulating channel function by small peptides that compete for binding with protein interacting partners. Altogether, these promising tools along with large-scale chemical screenings set up to identify new, specific channel modulators will hopefully allow us to pinpoint the actual function of most mitochondrial ion channels in the near future and to pharmacologically affect important pathologies in which they are involved, such as neurodegeneration, ischaemic damage and cancer. LINKED ARTICLES: This article is part of a themed section on Mitochondrial Pharmacology: Featured Mechanisms and Approaches for Therapy Translation. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.22/issuetoc.

Drp1-Zip1 Interaction Regulates Mitochondrial Quality Surveillance System

Mitophagy, a mitochondrial quality control process for eliminating dysfunctional mitochondria, can be induced by a response of dynamin-related protein 1 (Drp1) to a reduction in mitochondrial membrane potential (MMP) and mitochondrial division. However, the coordination between MMP and mitochondrial division for selecting the damaged portion of the mitochondrial network is less understood. Here, we found that MMP is reduced focally at a fission site by the Drp1 recruitment, which is initiated by the interaction of Drp1 with mitochondrial zinc transporter Zip1 and Zn²⁺ entry through the Zip1-MCU complex. After division, healthy mitochondria restore MMP levels and participate in the fusion-fission cycle again, but mitochondria that fail to restore MMP undergo mitophagy. Thus, interfering with the interaction between Drp1 and Zip1 blocks the reduction of MMP and the subsequent mitophagic selection of damaged mitochondria. These results suggest that Drp1-dependent fission provides selective pressure for eliminating "bad sectors" in the mitochondrial network, serving as a mitochondrial quality surveillance system.

Granzyme B enters the mitochondria in a Sam50-, Tim22- and mtHsp70-dependent manner to induce apoptosis

We have found that granzyme B (GB)-induced apoptosis also requires reactive oxygen species resulting from the alteration of mitochondrial complex I. How GB, which does not possess a mitochondrial targeting sequence, enter this organelle is unknown. We show that GB enters the mitochondria independently of the translocase of the outer mitochondrial membrane complex, but requires instead Sam50, the central subunit of the sorting and assembly machinery that integrates outer membrane β-barrel proteins. Moreover, GB breaches the inner membrane through Tim22, the metabolite carrier translocase pore, in a mitochondrial heat-shock protein 70 (mtHsp70)-dependent manner. Granzyme A (GA) and caspase-3 use a similar route to the mitochondria. Finally, preventing GB from entering the mitochondria either by mutating lysine 243 and arginine 244 or depleting Sam50 renders cells more resistant to GB-mediated reactive oxygen species and cell death. Similarly, Sam50 depletion protects cells from GA-, GM- and caspase-3-mediated cell death. Therefore, cytotoxic molecules enter the mitochondria to induce efficiently cell death through a noncanonical Sam50-, Tim22- and mtHsp70-dependent import pathway.

Mitochondrial channels: ion fluxes and more

The field of mitochondrial ion channels has recently seen substantial progress, including the molecular identification of some of the channels. An integrative approach using genetics, electrophysiology, pharmacology, and cell biology to clarify the roles of these channels has thus become possible. It is by now clear that many of these channels are important for energy supply by the mitochondria and have a major impact on the fate of the entire cell as well. The purpose of this review is to provide an up-to-date overview of the electrophysiological properties, molecular identity, and pathophysiological functions of the mitochondrial ion channels studied so far and to highlight possible therapeutic perspectives based on current information.

Nanomedicines based on recombinant fusion proteins for targeting therapeutic siRNA oligonucleotides

The enormous promise of siRNA technology for rational and targeted therapy can only be realized if the inherent problems in terms of pharmaceutical development are overcome. Besides liposomal and polymeric nanoparticles, fusion proteins hold great potential for cell-type specific delivery of siRNA. Consisting of a protein binder and an oligonucleotide complexing domain, fusion proteins are designed for targeted delivery to a certain tissue or organ and subsequent release of the siRNA after cellular uptake. This article focuses on the possibilities and importance of targeting and complexing domains, including polymers and dendrimers. In vitro and in vivo evaluations are discussed with an in-depth view on pharmacokinetic properties. Remaining challenges concerning specificity on the tissue and molecular levels are highlighted.

Mitochondrial adenine nucleotide transport and cardioprotection

Mitochondria are highly metabolically active cell organelles that not only act as the powerhouse of the cell by supplying energy through ATP production, but also play a destructive role by initiating cell death pathways. Growing evidence recognizes that mitochondrial dysfunction is one of the major causes of cardiovascular disease. Under de-energized conditions, slowing of adenine nucleotide transport in and out of the mitochondria significantly attenuates myocardial ischemia-reperfusion injury. The purpose of this review is to elaborate on and update the mechanistic pathways which may explain how altered adenine nucleotide transport can influence cardiovascular function. This article is part of a Special Issue entitled "Local Signaling in Myocytes".

Off-target effects related to the phosphorothioate modification of nucleic acids

Phosphorothioate antisense oligonucleotides have been widely used in clinical studies for rational sequence-specific gene silencing. However, several sequence-unspecific off-target effects have been recently described for this compound class. In contrast to siRNA-mediated knockdown of the same gene, the bcl-2-targeted oblimersen (Genasense, G3139) downregulates a number of proteins involved in apoptotic resistance and several glycolytic enzymes in 607B human melanoma cells. Regardless of their target, phosphorothioate-modified antisense and siRNA compounds, but not oligonucleotides with a phosphodiester backbone, resulted in a similar impact on the proteome. Unspecifically downregulated proteins include cancer markers involved in apoptotic resistance and endoplasmatic reticulum (ER) stress such as the 78 kDa glucose regulated protein (GRP 78), protein disulfide isomerase A3 (PDIA3, GRP 58), calumenin, and galectin-1, as well as the glycolytic enzymes triose phosphate isomerase, glyceraldehyde phosphodehydrogenase, and phosphoglycerate mutase. The depletion of the glycolytic enzymes is reflected by a decrease in L-lactate production, indicating a partial reversal of the Warburg effect. Compared with other phosphorothioate oligonucleotides, oblimersen generally led to a more pronounced effect both in terms of the number of influenced proteins and the extent of downregulation, suggesting a synergistic effect of Bcl-2 downregulation.

Hypothermia-induced increase of oligodendrocyte precursor cells: Possible involvement of plasmalemmal voltage-dependent anion channel 1

Hypothermia is believed to suppress cell proliferation by inducing apoptosis/necrosis and phase-specific/nonspecific cell cycle arrest, which are, directly or indirectly, related to a reduced energy supply. Intriguingly, hypothermia is known to improve neurological recovery of animals and humans exposed to focal brain hypoxic-ischemic injury. The underlying mechanism of the neuroprotective effect of hypothermia is unclear, although the prevention of neural cell apoptosis is thought to play a role. Herein we demonstrate that in vitro cell culture of oligodendrocyte precursor cells (OPCs) under conditions of mild hypothermia (31.5°C) results in an increase in cell number relative to cells cultured under normothermic conditions (37°C). Cell cycle analysis, immunoblotting of cyclins, TUNEL assay, and immunocytochemistry of OPC differentiation markers suggest that hypothermia shifts the balance between proliferation and apoptosis/differentiation toward proliferation. A combination of transcriptome analysis, pharmacological intervention, and immunoaffinity-based assays suggests a possible involvement of the Gα13-Rho GTPase Cdc42-ERK1/2 signaling cascade and voltage-dependent anion channel 1 (VDAC1), which associate or dissociate with Gα13 protein at 37°C and 31.5°C, respectively. Immunoelectron microscopy revealed the presence of VDAC1 in the plasma membrane of OPCs. Furthermore, the exogenous addition of impermeable VDAC1 inhibitors enhanced proliferation of OPCs at 37°C. These results may contribute to the elucidation of the mechanism of hypothermic neuroprotection as well as the possible novel role of plasmalemmal VDAC1.

Mitochondrially targeted anti-cancer agents

Cancer is an ever-increasing problem that is yet to be harnessed. Frequent mutations make this pathology very variable and, consequently, a considerable challenge. Intriguingly, mitochondria have recently emerged as novel targets for cancer therapy. A group of agents with anti-cancer activity that induce apoptosis by way of mitochondrial destabilisation, termed mitocans, have been a recent focus of research. Of these compounds, many are hydrophobic agents that associate with various sub-cellular organelles. Clearly, modification of such structures with mitochondria-targeting moieties, for example tagging them with lipophilic cations, would be expected to enhance their activity. This may be accomplished by the addition of triphenylphosphonium groups that direct such compounds to mitochondria, enhancing their activity. In this paper, we will review agents that possess anti-cancer activity by way of destabilizing mitochondria and their possible targets. We propose that mitochondrial targeting, in particular where the agent associates directly with the target, results in more specific and efficient anti-cancer drugs of potential high clinical relevance.

VDAC, a multi-functional mitochondrial protein regulating cell life and death

Research over the past decade has extended the prevailing view of the mitochondrion to include functions well beyond the generation of cellular energy. It is now recognized that mitochondria play a crucial role in cell signaling events, inter-organellar communication, aging, cell proliferation, diseases and cell death. Thus, mitochondria play a central role in the regulation of apoptosis (programmed cell death) and serve as the venue for cellular decisions leading to cell life or death. One of the mitochondrial proteins controlling cell life and death is the voltage-dependent anion channel (VDAC), also known as mitochondrial porin. VDAC, located in the mitochondrial outer membrane, functions as gatekeeper for the entry and exit of mitochondrial metabolites, thereby controlling cross-talk between mitochondria and the rest of the cell. VDAC is also a key player in mitochondria-mediated apoptosis. Thus, in addition to regulating the metabolic and energetic functions of mitochondria, VDAC appears to be a convergence point for a variety of cell survival and cell death signals mediated by its association with various ligands and proteins. In this article, we review what is known about the VDAC channel in terms of its structure, relevance to ATP rationing, Ca(2+) homeostasis, protection against oxidative stress, regulation of apoptosis, involvement in several diseases and its role in the action of different drugs. In light of our recent findings and the recently solved NMR- and crystallography-based 3D structures of VDAC1, the focus of this review will be on the central role of VDAC in cell life and death, addressing VDAC function in the regulation of mitochondria-mediated apoptosis with an emphasis on structure-function relations. Understanding structure-function relationships of VDAC is critical for deciphering how this channel can perform such a variety of functions, all important for cell life and death. This review also provides insight into the potential of VDAC1 as a rational target for new therapeutics.

Regulation and pharmacology of the mitochondrial permeability transition pore

The 'mitochondrial permeability transition', characterized by a sudden induced change of the inner mitochondrial membrane permeability for water as well as for small substances ( Collapse

Key Words

• adenine nucleotide translocator
• cyclophilin d
• mitochondrial voltage-dependent anion channel
• hexokinase
• creatine kinase
• mitochondrial peripheral benzodiazepine receptor
• bcl-2
• glycogen synthase kinase-3β

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MESH Headings

• Adenine Nucleotide Translocator 1/metabolism
• Animals
• Cardiovascular Agents/pharmacology
• Creatine Kinase, Mitochondrial Form/metabolism
• Peptidyl-Prolyl Isomerase F
• Cyclophilins/metabolism
• Hexokinase/metabolism
• Humans
• Lipid Metabolism
• Membrane Potential, Mitochondrial
• Mitochondria, Heart/drug effects
• Mitochondria, Heart/metabolism
• Mitochondrial Membrane Transport Proteins/chemistry
• Mitochondrial Membrane Transport Proteins/drug effects
• Mitochondrial Membrane Transport Proteins/genetics
• Mitochondrial Membrane Transport Proteins/metabolism
• Mitochondrial Permeability Transition Pore
• Myocardium/metabolism
• Phosphates/metabolism
• Receptors, GABA-A/metabolism
• Voltage-Dependent Anion Channels/metabolism

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Grants

• Intramural NIH HHS

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Affiliation(s)

Dmitry B. Zorov
Magdalena Juhaszova
Yael Yaniv
H. Bradley Nuss
Su Wang
Steven J. Sollott Laboratory of Cardiovascular Science, Gerontology Research Center, Box 13, Intramural Research Program, National Institute on Aging, NIH, 5600 Nathan Shock Drive, Baltimore, MD 21224-6825, USA

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A proteomic study reveals unspecific apoptosis induction and reduction of glycolytic enzymes by the phosphorothioate antisense oligonucleotide oblimersen in human melanoma cells

The question of specificity and the elucidation of the exact molecular mechanism of action of post-transcriptional gene silencing agents are two major challenges for their establishment as therapeutics. A proteomic off-target effect study (2-DE with MS) in combination with DIGE comparing the phosphorothioate antisense oligonucleotide oblimersen (Genasense, G3139) to a Bcl-2-targeting siRNA-sequence on human melanoma cells showed that additional off-target effects contribute to the apoptotic effect of oblimersen. When both oligonucleotides were transfected with lipofectamine 2000, only oblimersen increased apoptosis as determined by annexin staining and caspase activity measurement. In contrast to the highly specific siRNA, the expression level of a number of proteins was found to be altered after oblimersen treatment. Several proteins linked to apoptosis and stress response, among those galectin-1, cofilin-1, GRP78, HSP60, nucleophosmin, and peroxiredoxins, were identified and found to be down-regulated after oblimersen treatment. A down-regulation of enolase-1 and three other glycolytic enzymes indicates a reversion of the cancer-related Warburg effect. The observed effects may be caused by a phosphorothioate mediated blockage of the mitochondrial voltage dependent anion channel (VDAC).