Hypoxia as a therapy for mitochondrial disease

Genetic Screen for Cell Fitness in High or Low Oxygen Highlights Mitochondrial and Lipid Metabolism

Human cells are able to sense and adapt to variations in oxygen levels. Historically, much research in this field has focused on hypoxia-inducible factor (HIF) signaling and reactive oxygen species (ROS). Here, we perform genome-wide CRISPR growth screens at 21%, 5%, and 1% oxygen to systematically identify gene knockouts with relative fitness defects in high oxygen (213 genes) or low oxygen (109 genes), most without known connection to HIF or ROS. Knockouts of many mitochondrial pathways thought to be essential, including complex I and enzymes in Fe-S biosynthesis, grow relatively well at low oxygen and thus are buffered by hypoxia. In contrast, in certain cell types, knockout of lipid biosynthetic and peroxisomal genes causes fitness defects only in low oxygen. Our resource nominates genetic diseases whose severity may be modulated by oxygen and links hundreds of genes to oxygen homeostasis.

α-ketobutyrate links alterations in cystine metabolism to glucose oxidation in mtDNA mutant cells

Pathogenic mutations in the mitochondrial genome (mtDNA) impair organellar ATP production, requiring mutant cells to activate metabolic adaptations for survival. Understanding how metabolism adapts to clinically relevant mtDNA mutations may provide insight into cellular strategies for metabolic flexibility. In this study, we use ¹³C isotope tracing and metabolic flux analysis to investigate central carbon and amino acid metabolic reprogramming in isogenic cells containing mtDNA mutations. We identify alterations in glutamine and cystine transport which indirectly regulate mitochondrial metabolism and electron transport chain function. Metabolism of cystine can promote glucose oxidation through the transsulfuration pathway and the production of α-ketobutyrate. Intriguingly, activating or inhibiting α-ketobutyrate production is sufficient to modulate both glucose oxidation and mitochondrial respiration in mtDNA mutant cells. Thus, cystine-stimulated transsulfuration serves as an adaptive mechanism linking glucose oxidation and amino acid metabolism in the setting of mtDNA mutations.

Serine Catabolism Feeds NADH when Respiration Is Impaired

NADH provides electrons for aerobic ATP production. In cells deprived of oxygen or with impaired electron transport chain activity, NADH accumulation can be toxic. To minimize such toxicity, elevated NADH inhibits the classical NADH-producing pathways: glucose, glutamine, and fat oxidation. Here, through deuterium-tracing studies in cultured cells and mice, we show that folate-dependent serine catabolism also produces substantial NADH. Strikingly, when respiration is impaired, serine catabolism through methylene tetrahydrofolate dehydrogenase (MTHFD2) becomes a major NADH source. In cells whose respiration is slowed by hypoxia, metformin, or genetic lesions, mitochondrial serine catabolism inhibition partially normalizes NADH levels and facilitates cell growth. In mice with engineered mitochondrial complex I deficiency (NDUSF4-/-), serine's contribution to NADH is elevated, and progression of spasticity is modestly slowed by pharmacological blockade of serine degradation. Thus, when respiration is impaired, serine catabolism contributes to toxic NADH accumulation.

Ubiquitin and Receptor-Dependent Mitophagy Pathways and Their Implication in Neurodegeneration

Selective autophagy of mitochondria, or mitophagy, refers to the specific removal and degradation of damaged or surplus mitochondria via targeting to the lysosome for destruction. Disruptions in this homeostatic process may contribute to disease. The identification of diverse mitophagic pathways and how selectivity for each of these pathways is conferred is just beginning to be understood. The removal of both damaged and healthy mitochondria under disease and physiological conditions is controlled by either ubiquitin-dependent or receptor-dependent mechanisms. In this review, we will discuss the known types of mitophagy observed in mammals, recent findings related to PINK1/Parkin-mediated mitophagy (which is the most well-studied form of mitophagy), the implications of defective mitophagy to neurodegenerative processes, and unanswered questions inspiring future research that would enhance our understanding of mitochondrial quality control.

Functional Consequences of Calcium-Dependent Synapse-to-Nucleus Communication: Focus on Transcription-Dependent Metabolic Plasticity

In the nervous system, calcium signals play a major role in the conversion of synaptic stimuli into transcriptional responses. Signal-regulated gene transcription is fundamental for a range of long-lasting adaptive brain functions that include learning and memory, structural plasticity of neurites and synapses, acquired neuroprotection, chronic pain, and addiction. In this review, we summarize the diverse mechanisms governing calcium-dependent transcriptional regulation associated with central nervous system plasticity. We focus on recent advances in the field of synapse-to-nucleus communication that include studies of the signal-regulated transcriptome in human neurons, identification of novel regulatory mechanisms such as activity-induced DNA double-strand breaks, and the identification of novel forms of activity- and transcription-dependent adaptations, in particular, metabolic plasticity. We summarize the reciprocal interactions between different kinds of neuroadaptations and highlight the emerging role of activity-regulated epigenetic modifiers in gating the inducibility of signal-regulated genes.

Reactive oxygen species (ROS) as pleiotropic physiological signalling agents

'Reactive oxygen species' (ROS) is an umbrella term for an array of derivatives of molecular oxygen that occur as a normal attribute of aerobic life. Elevated formation of the different ROS leads to molecular damage, denoted as 'oxidative distress'. Here we focus on ROS at physiological levels and their central role in redox signalling via different post-translational modifications, denoted as 'oxidative eustress'. Two species, hydrogen peroxide (H₂O₂) and the superoxide anion radical (O₂^·-), are key redox signalling agents generated under the control of growth factors and cytokines by more than 40 enzymes, prominently including NADPH oxidases and the mitochondrial electron transport chain. At the low physiological levels in the nanomolar range, H₂O₂ is the major agent signalling through specific protein targets, which engage in metabolic regulation and stress responses to support cellular adaptation to a changing environment and stress. In addition, several other reactive species are involved in redox signalling, for instance nitric oxide, hydrogen sulfide and oxidized lipids. Recent methodological advances permit the assessment of molecular interactions of specific ROS molecules with specific targets in redox signalling pathways. Accordingly, major advances have occurred in understanding the role of these oxidants in physiology and disease, including the nervous, cardiovascular and immune systems, skeletal muscle and metabolic regulation as well as ageing and cancer. In the past, unspecific elimination of ROS by use of low molecular mass antioxidant compounds was not successful in counteracting disease initiation and progression in clinical trials. However, controlling specific ROS-mediated signalling pathways by selective targeting offers a perspective for a future of more refined redox medicine. This includes enzymatic defence systems such as those controlled by the stress-response transcription factors NRF2 and nuclear factor-κB, the role of trace elements such as selenium, the use of redox drugs and the modulation of environmental factors collectively known as the exposome (for example, nutrition, lifestyle and irradiation).

Mitochondrial Diseases: Hope for the Future

Mitochondrial diseases are clinically heterogeneous disorders caused by a wide spectrum of mutations in genes encoded by either the nuclear or the mitochondrial genome. Treatments for mitochondrial diseases are currently focused on symptomatic management rather than improving the biochemical defect caused by a particular mutation. This review focuses on the latest advances in the development of treatments for mitochondrial disease, both small molecules and gene therapies, as well as methods to prevent transmission of mitochondrial disease through the germline.

Comprehensive transcriptomic profiling reveals SOX7 as an early regulator of angiogenesis in hypoxic human endothelial cells

Endothelial cells (ECs) lining the vasculature of vertebrates respond to low oxygen (hypoxia) by maintaining vascular homeostasis and initiating adaptive growth of new vasculature through angiogenesis. Previous studies have uncovered the molecular underpinnings of the hypoxic response in ECs; however, there is a need for comprehensive temporal analysis of the transcriptome during hypoxia. Here, we sought to investigate the early transcriptional programs of hypoxic ECs by using RNA-Seq of primary cultured human umbilical vein ECs exposed to progressively increasing severity and duration of hypoxia. We observed that hypoxia modulates the expression levels of approximately one-third of the EC transcriptome. Intriguingly, expression of the gene encoding the developmental transcription factor SOX7 (SRY-box transcription factor 7) rapidly and transiently increased during hypoxia. Transcriptomic and functional analyses of ECs following SOX7 depletion established its critical role in regulating hypoxia-induced angiogenesis. We also observed that depletion of the hypoxia-inducible factor (HIF) genes, HIF1A (encoding HIF-1α) and endothelial PAS domain protein 1 (EPAS1 encoding HIF-2α), inhibited both distinct and overlapping transcriptional programs. Our results indicated a role for HIF-1α in down-regulating mitochondrial metabolism while concomitantly up-regulating glycolytic genes, whereas HIF-2α primarily up-regulated the angiogenesis transcriptional program. These results identify the concentration and time dependence of the endothelial transcriptomic response to hypoxia and an early key role for SOX7 in mediating angiogenesis.

Passport and biological age in the choice of metabolic geroprophylactic therapy

We compared the effectiveness of geroprophylactic means of gas and metabolic therapy (hypoxytherapy, hyperbaric oxygenation, ozone therapy, dry carbonic baths, amino acid arginine, regulatory tripeptides H- Glu-Asp-Arg-OH u H-Lys-Glu-Asp-OH, interleukin-2 in medium therapeutic dosages by their ability to reduce biological age when tested on practically healthy people or patients with mild subclinical forms of polymorbid pathology at the age of 35 – 74 years. It has been established that the effectiveness of agents and effects in terms of the degree of decrease in biological age depends on the type of geroprophylactic agent, as well as in the part of research – the passport age of patients. In this case, the biological age of the subjects after treatment decreased in the range from 12.8 to 1.3 years, depending on the means used and, in some cases, on the passport age. The greatest efficiency was achieved after the use of a combination of peptide bioregulators in the age group with a passport age of 35 – 59 years. When prescribing metabolic geroprophylaxis, it is necessary to take into account, in addition to the indications and contraindications of the means used or the correction method, the state of the body, also the calendar age and the degree of decrease in biological age.

Advances in drug therapy for mitochondrial diseases

Mitochondrial diseases are a group of clinically and genetically heterogeneous disorders driven by oxidative phosphorylation dysfunction of the mitochondrial respiratory chain which due to pathogenic mutations of mitochondrial DNA (mtDNA) or nuclear DNA (nDNA). Recent progress in molecular genetics and biochemical methodologies has provided a better understanding of the etiology and pathogenesis of mitochondrial diseases, and this has expanded the clinical spectrum of this conditions. But the treatment of mitochondrial diseases is largely symptomatic and thus does not significantly change the course of the disease. Few clinical trials have led to the design of drugs aiming at enhancing mitochondrial function or reversing the consequences of mitochondrial dysfunction which are now used in the clinical treatment of mitochondrial diseases. Several other drugs are currently being evaluated for clinical management of patients with mitochondrial diseases. In this review, the current status of treatments for mitochondrial diseases is described systematically, and newer potential treatment strategies for mitochondrial diseases are also discussed.

HIF hydroxylase inhibitors decrease cellular oxygen consumption depending on their selectivity

Pharmacologic HIF hydroxylase inhibitors (HIs) are effective for the treatment of anemia in chronic kidney disease patients and may also be beneficial for the treatment of diseases such as chronic inflammation and ischemia-reperfusion injury. The selectivities of many HIs for HIF hydroxylases and possible off-target effects in cellulo are unclear, delaying the translation from preclinical studies to clinical trials. We developed a novel assay that discriminates between the inhibition of HIF-α prolyl-4-hydroxylase domain (PHD) enzymes and HIF-α asparagine hydroxylase factor inhibiting HIF (FIH). We characterized 15 clinical and preclinical HIs, categorizing them into pan-HIF-α hydroxylase (broad spectrum), PHD-selective, and FIH-selective inhibitors, and investigated their effects on HIF-dependent transcriptional regulation, erythropoietin production, and cellular energy metabolism. While energy homeostasis was generally maintained following HI treatment, the pan-HIs led to a stronger increase in pericellular pO₂ than the PHD/FIH-selective HIs. Combined knockdown of FIH and PHD-selective inhibition did not further increase pericellular pO₂ . Hence, the additional increase in pericellular pO₂ by pan- over PHD-selective HIs likely reflects HIF hydroxylase independent off-target effects. Overall, these analyses demonstrate that HIs can lead to oxygen redistribution within the cellular microenvironment, which should be considered as a possible contributor to HI effects in the treatment of hypoxia-associated diseases.

Mitochondrially-targeted treatment strategies

Disruption of mitochondrial function is a common feature of inherited mitochondrial diseases (mitochondriopathies) and many other infectious and non-infectious diseases including viral, bacterial and protozoan infections, inflammatory and chronic pain, neurodegeneration, diabetes, obesity and cardiovascular diseases. Mitochondria therefore become an attractive target for developing new therapies. In this review we describe critical mechanisms involved in the maintenance of mitochondrial functionality and discuss strategies used to identify and validate mitochondrial targets in different diseases. We also highlight the most recent preclinical and clinical findings using molecules targeting mitochondrial bioenergetics, morphology, number, content and detoxification systems in common pathologies.

Hypoxia induces a time- and tissue-specific response that elicits intertissue circadian clock misalignment

The occurrence and sequelae of disorders that lead to hypoxic spells such as asthma, chronic obstructive pulmonary disease, and obstructive sleep apnea (OSA) exhibit daily variance. This prompted us to examine the interaction between the hypoxic response and the circadian clock in vivo. We found that the global transcriptional response to acute hypoxia is tissue-specific and time-of-day-dependent. In particular, clock components differentially responded at the transcriptional and posttranscriptional level, and these responses depended on an intact circadian clock. Importantly, exposure to hypoxia phase-shifted clocks in a tissue-dependent manner led to intertissue circadian clock misalignment. This differential response relied on the intrinsic properties of each tissue and could be recapitulated ex vivo. Notably, circadian misalignment was also elicited by intermittent hypoxia, a widely used model for OSA. Given that phase coherence between circadian clocks is considered favorable, we propose that hypoxia leads to circadian misalignment, contributing to the pathophysiology of OSA and potentially other diseases that involve hypoxia.

Do Two Mitochondrial Wrongs Help Make Cells Right?

Using an unbiased genetic screen, To et al. map genes that enhance or suppress growth defects in response to different mitochondrial inhibitors to model mitochondrial disease. The findings have novel implications for the interconnectivity of bioenergetic pathways, and suggest a provocative strategy to treat primary mitochondrial disorders.

Choroidal thickness and the retinal ganglion cell complex in chronic Leber's hereditary optic neuropathy: a prospective study using swept-source optical coherence tomography

Background/Objectives

Choroidal thinning has been suggested in Leber’s hereditary optic neuropathy (LHON). No study has been conducted of the choroid in relation to the retinal ganglion cell-inner plexiform layer (RGC-IPL). We sought to measure choroidal thickness in chronic LHON and to correlate thickness changes with the RGC-IPL.

Subjects/Methods

Chronic LHON, 11778 mitochondrial DNA (mtDNA) mutation, patients (26 eyes; mean age: 35.1 ± 16.1 years) were prospectively recruited at Doheny Eye Center, University of California Los Angeles from March 2016 to July 2017. Age-matched healthy controls (27 eyes; mean age: 32.4 ± 11.1 years) were enroled for comparison. Swept-source optical coherence tomography (SS-OCT) imaging was performed in chronic LHON patients and compared with age-matched healthy controls.

Results

The macular choroid was significantly thinner in chronic LHON (250.5 ± 62.2 μm) compared with controls (313.9 ± 60.2 μm; p < 0.0001). The peripapillary choroid was also significantly thinner in chronic LHON (135.7 ± 51.4 μm) compared with controls (183.0 ± 61.8 μm, p < 0.001). Choroidal thickness strongly correlated with retinal nerve fibre layer (RNFL) thickness in both the macular (R² = 0.72; 95% CI, 0.57–0.84) and peripapillary regions (R² = 0.53; 95% CI, 0.31–0.70). Choroidal thickness was also significantly correlated with macular RGC-IPL thickness (R² = 0.51; 95% CI, 0.26–0.73).

Conclusions

Choroidal thinning in chronic LHON correlated strongly with both RNFL and RGC-IPL thicknesses. These findings may suggest a pathophysiological mechanism involving vascular pathology of the choroid in relation to the retinal ganglion cell complex in LHON.

Cerebral oxygenation during locomotion is modulated by respiration

In the brain, increased neural activity is correlated with increases of cerebral blood flow and tissue oxygenation. However, how cerebral oxygen dynamics are controlled in the behaving animal remains unclear. We investigated to what extent cerebral oxygenation varies during locomotion. We measured oxygen levels in the cortex of awake, head-fixed mice during locomotion using polarography, spectroscopy, and two-photon phosphorescence lifetime measurements of oxygen sensors. We find that locomotion significantly and globally increases cerebral oxygenation, specifically in areas involved in locomotion, as well as in the frontal cortex and the olfactory bulb. The oxygenation increase persists when neural activity and functional hyperemia are blocked, occurred both in the tissue and in arteries feeding the brain, and is tightly correlated with respiration rate and the phase of respiration cycle. Thus, breathing rate is a key modulator of cerebral oxygenation and should be monitored during hemodynamic imaging, such as in BOLD fMRI.

Advances in the treatment of mitochondrial epilepsies

Epilepsy is frequently a severe and sinister symptom in primary mitochondrial diseases, a group of more than 350 different genetic disorders characterized by mitochondrial dysfunction and extreme clinical and biochemical heterogeneity. Mitochondrial epilepsy is notoriously difficult to manage, principally because the vast majority of primary mitochondrial diseases currently lack effective therapies. Treating the underlying mitochondrial disorder is likely to be a more effective strategy than using traditional antiepileptic drugs. This review, initially presented at the 7th London-Innsbruck Colloquium on Status Epilepticus and Acute Seizures at the Francis Crick Institute in London, summarizes the currently available and emerging therapies for mitochondrial epilepsy. Potentially treatable mitochondrial diseases include disorders of coenzyme Q₁₀ biosynthesis and a group of mitochondrial respiratory chain complex I subunit and assembly factor defects that respond to riboflavin (vitamin B2). Approaches that have been adopted in actively recruiting clinical trials include redox modulation, harnessing mitochondrial biogenesis, using rapamycin to target mitophagy, nucleoside supplementation, and gene and cell therapies. Most of the clinical trials are at an early stage (Phase 1 or 2) and none of the currently active trials is specifically targeting mitochondrial epilepsy. This article is part of the Special Issue "Proceedings of the 7th London-Innsbruck Colloquium on Status Epilepticus and Acute Seizures".

Acute Methylmercury Exposure and the Hypoxia-Inducible Factor-1α Signaling Pathway under Normoxic Conditions in the Rat Brain and Astrocytes in Vitro

BACKGROUND

As a ubiquitous environmental pollutant, methylmercury (MeHg) induces toxic effects in the nervous system, one of its main targets. However, the exact mechanisms of its neurotoxicity have not been fully elucidated. Hypoxia-inducible factor- 1 α (HIF- 1 α ), a transcription factor, plays a crucial role in adaptive and cytoprotective responses in cells and is involved in cell survival, proliferation, apoptosis, inflammation, angiogenesis, glucose metabolism, erythropoiesis, and other physiological activities.

OBJECTIVES

The aim of this study was to explore the role of HIF- 1 α in response to acute MeHg exposure in rat brain and primary cultured astrocytes to improve understanding of the mechanisms of MeHg-induced neurotoxicity and the development of effective neuroprotective strategies.

METHODS

Primary rat astrocytes were treated with MeHg (0 - 10 μ M ) for 0.5 h . Cell proliferation and cytotoxicity were assessed with a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl diphenyltetrazolium bromide (MTT) assay and a lactate dehydrogenase (LDH) release assay, respectively. Reactive oxygen species (ROS) levels were analyzed to assess the level of oxidative stress using 2',7'-dichlorofluorescin diacetate (DCFH-DA) fluorescence. HIF- 1 α , and its downstream proteins, glucose transporter 1 (GLUT-1), erythropoietin (EPO), and vascular endothelial growth factor A (VEGF-A) were analyzed by means of Western blotting. Real-time PCR was used to detect the expression of HIF- 1 α mRNA. Pretreatment with protein synthesis inhibitor (CHX), proteasome inhibitor (MG132), or proline hydroxylase inhibitor (DHB) were applied to explore the possible mechanisms of HIF- 1 α inhibition by MeHg. To investigate the role of HIF- 1 α in MeHg-induced neurotoxicity, cobalt chloride (CoC l 2 ), 2-methoxyestradiol (2-MeOE2), small interfering RNA (siRNA) transfection and adenovirus overexpression were used. Pretreatment with N-acetyl-L-cysteine (NAC) and vitamin E (Trolox) were used to investigate the putative role of oxidative stress in MeHg-induced alterations in HIF- 1 α levels. The expression of HIF- 1 α and related downstream proteins was detected in adult rat brain exposed to MeHg (0 - 10 mg / kg ) for 0.5 h in vivo.

RESULTS

MeHg caused lower cell proliferation and higher cytotoxicity in primary rat astrocytes in a time- and concentration-dependent manner. In comparison with the control cells, exposure to 10 μ M MeHg for 0.5 h significantly inhibited the expression of astrocytic HIF- 1 α , and the downstream genes GLUT-1, EPO, and VEGF-A (p < 0.05 ), in the absence of a significant decrease in HIF- 1 α mRNA levels. When protein synthesis was inhibited by CHX, MeHg promoted the degradation rate of HIF- 1 α . MG132 and DHB significantly blocked the MeHg-induced decrease in HIF- 1 α expression (p < 0.05 ). Overexpression of HIF- 1 α significantly attenuated the decline in MeHg-induced cell proliferation, whereas the inhibition of HIF- 1 α significantly increased the decline in cell proliferation (p < 0.05 ). NAC and Trolox, two established antioxidants, reversed the MeHg-induced decline in HIF- 1 α protein levels and the decrease in cell proliferation (p < 0.05 ). MeHg suppressed the expression of HIF- 1 α and related downstream target proteins in adult rat brain.

DISCUSSION

MeHg induced a significant reduction in HIF- 1 α protein by activating proline hydroxylase (PHD) and the ubiquitin proteasome system (UPS) in primary rat astrocytes. Additionally, ROS scavenging by antioxidants played a neuroprotective role via increasing HIF- 1 α expression in response to MeHg toxicity. Moreover, we established that up-regulation of HIF- 1 α might serve to mitigate the acute toxicity of MeHg in astrocytes, affording a novel therapeutic target for future exploration. https://doi.org/10.1289/EHP5139.

A conditional mouse model of complex II deficiency manifesting as Leigh-like syndrome

Leigh syndrome embodies degenerative disorders with a collection of symptoms secondary to inborn errors of metabolism. Combinations of hypomorphic and loss-of-function alleles in many genes have been shown to result in Leigh syndrome. Interestingly, deficiency for the tricarboxylic acid cycle enzyme succinate dehydrogenase (SDH) can lead to Leigh-like syndrome in some circumstances and to cancer (paraganglioma, renal cell carcinoma, gastrointestinal stromal tumor) in others. In our experiments originally intended to create an inducible whole-body SDH-loss mouse model of tumorigenesis, we generated a condition reminiscent of Leigh-like syndrome that is lethal to mice within 4 wk. Remarkably, as has been shown for other mitochondrial diseases, chronic hypoxia offers substantial protection to mice from this condition after systemic SDH loss, allowing survival in the context of profoundly impaired oxidative metabolism.-Al Khazal, F., Holte, M. N., Bolon, B., White, T. A., LeBrasseur, N., Maher, L. J. III. A conditional mouse model of complex II deficiency manifesting as Leigh-like syndrome.

Evidence for the Capability of Roxadustat (FG-4592), an Oral HIF Prolyl-Hydroxylase Inhibitor, to Perturb Membrane Ionic Currents: An Unidentified yet Important Action

Roxadustat (FG-4592), an analog of 2-oxoglutarate, is an orally-administered, heterocyclic small molecule known to be an inhibitor of hypoxia inducible factor (HIF) prolyl hydroxylase. However, none of the studies have thus far thoroughly investigated its possible perturbations on membrane ion currents in endocrine or heart cells. In our studies, the whole-cell current recordings of the patch-clamp technique showed that the presence of roxadustat effectively and differentially suppressed the peak and late components of IK(DR) amplitude in response to membrane depolarization in pituitary tumor (GH3) cells with an IC50 value of 5.71 and 1.32 μM, respectively. The current inactivation of IK(DR) elicited by 10-sec membrane depolarization became raised in the presence of roxadustatt. When cells were exposed to either CoCl2 or deferoxamine (DFO), the IK(DR) elicited by membrane depolarization was not modified; however, nonactin, a K+-selective ionophore, in continued presence of roxadustat, attenuated roxadustat-mediated inhibition of the amplitude. The steady-state inactivation of IK(DR) could be constructed in the presence of roxadustat. Recovery of IK(DR) block by roxadustat (3 and 10 μM) could be fitted by a single exponential with 382 and 523 msec, respectively. The roxadustat addition slightly suppressed erg-mediated K+ or hyperpolarization-activated cation currents. This drug also decreased the peak amplitude of voltage-gated Na+ current with a slowing in inactivation rate of the current. Likewise, in H9c2 heart-derived cells, the addition of roxadustat suppressed IK(DR) amplitude in combination with the shortening in inactivation time course of the current. In high glucose-treated H9c2 cells, roxadustat-mediated inhibition of IK(DR) remained unchanged. Collectively, despite its suppression of HIF prolyl hydroxylase, inhibitory actions of roxadustat on different types of ionic currents possibly in a non-genomic fashion might provide another yet unidentified mechanism through which cellular functions are seriously perturbed, if similar findings occur in vivo.

Mitocellular communication: Shaping health and disease

Throughout the animal kingdom, mitochondria are the only organelles that retain their own genome and the transcription and translation machineries that are all essential for energy harvesting. Mitochondria have developed a complex communication network, allowing them to stay in tune with cellular needs and nuclear transcriptional programs and to alleviate mitochondrial dysfunction. Here, we review recent findings on the wide array of mechanisms that contribute to these mitocellular communication networks, spanning from well-studied messenger molecules to mitonuclear genetic interactions. Based on these observations and developments, we advocate a broad and inclusive view on mitocellular interactions, which can have profound impacts on physiological, pathological, and evolutionary processes.

A Compendium of Genetic Modifiers of Mitochondrial Dysfunction Reveals Intra-organelle Buffering

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

Cellular Stress-Modulating Drugs Can Potentially Be Identified by in Silico Screening with Connectivity Map (CMap)

Accompanied by increased life span, aging-associated diseases, such as metabolic diseases and cancers, have become serious health threats. Recent studies have documented that aging-associated diseases are caused by prolonged cellular stresses such as endoplasmic reticulum (ER) stress, mitochondrial stress, and oxidative stress. Thus, ameliorating cellular stresses could be an effective approach to treat aging-associated diseases and, more importantly, to prevent such diseases from happening. However, cellular stresses and their molecular responses within the cell are typically mediated by a variety of factors encompassing different signaling pathways. Therefore, a target-based drug discovery method currently being used widely (reverse pharmacology) may not be adequate to uncover novel drugs targeting cellular stresses and related diseases. The connectivity map (CMap) is an online pharmacogenomic database cataloging gene expression data from cultured cells treated individually with various chemicals, including a variety of phytochemicals. Moreover, by querying through CMap, researchers may screen registered chemicals in silico and obtain the likelihood of drugs showing a similar gene expression profile with desired and chemopreventive conditions. Thus, CMap is an effective genome-based tool to discover novel chemopreventive drugs.

Analysis of functional variants in mitochondrial DNA of Finnish athletes

Background

We have previously reported on paucity of mitochondrial DNA (mtDNA) haplogroups J and K among Finnish endurance athletes. Here we aimed to further explore differences in mtDNA variants between elite endurance and sprint athletes. For this purpose, we determined the rate of functional variants and the mutational load in mtDNA of Finnish athletes (n = 141) and controls (n = 77) and determined the sequence variation in haplogroups.

Results

The distribution of rare and common functional variants differed between endurance athletes, sprint athletes and the controls (p = 0.04) so that rare variants occurred at a higher frequency among endurance athletes. Furthermore, the ratio between rare and common functional variants in haplogroups J and K was 0.42 of that in the remaining haplogroups (p = 0.0005). The subjects with haplogroup J and K also showed a higher mean level of nonsynonymous mutational load attributed to common variants than subjects with the other haplogroups. Interestingly, two of the rare variants detected in the sprint athletes were the disease-causing mutations m.3243A > G in MT-TL1 and m.1555A > G in MT-RNR1.

Conclusions

We propose that endurance athletes harbor an excess of rare mtDNA variants that may be beneficial for oxidative phosphorylation, while sprint athletes may tolerate deleterious mtDNA variants that have detrimental effect on oxidative phosphorylation system. Some of the nonsynonymous mutations defining haplogroup J and K may produce an uncoupling effect on oxidative phosphorylation thus favoring sprint rather than endurance performance.

Fulminant Necrotizing Enterocolitis and Multiple Organ Dysfunction in a Toddler with Mitochondrial DNA Depletion Syndrome-13

Necrotizing enterocolitis (NEC) is exceptional after the neonatal period. A toddler with encephalopathy, mitochondrial myopathy, and hypertrophic cardiomyopathy developed fatal NEC and multiple organ dysfunction within 48 hours of the introduction of enteral feeding. She was subsequently found to have pathogenic mutations in FBXL4 , a cause of mitochondrial DNA depletion syndrome-13. Intestinal dysmotility in the context of deficient mitochondrial respiration may have contributed to the development of NEC. Current paradigms call for early introduction of enteral nutrition to reinstate energy homeostasis. Enteral feeding should be administered with caution during metabolic crises of patients with mitochondrial DNA depletion syndromes.

Breathe: Your Mitochondria Will Do the Rest… If They Are Healthy!

Dysfunctions of the mitochondrial electron transport chain cause severe, currently untreatable, diseases in humans. A new study by Jain et al. (2019) reports increased oxygen levels in the brain of complex-I-deficient mice. Reducing the O2 levels by hypoxia, carbon monoxide, or anemia, improved the clinical phenotype and prolonged the lifespan of the mouse model.

Leigh Syndrome Mouse Model Can Be Rescued by Interventions that Normalize Brain Hyperoxia, but Not HIF Activation

Leigh syndrome is a devastating mitochondrial disease for which there are no proven therapies. We previously showed that breathing chronic, continuous hypoxia can prevent and even reverse neurological disease in the Ndufs4 knockout (KO) mouse model of complex I (CI) deficiency and Leigh syndrome. Here, we show that genetic activation of the hypoxia-inducible factor transcriptional program via any of four different strategies is insufficient to rescue disease. Rather, we observe an age-dependent decline in whole-body oxygen consumption. These mice exhibit brain tissue hyperoxia, which is normalized by hypoxic breathing. Alternative experimental strategies to reduce oxygen delivery, including breathing carbon monoxide (600 ppm in air) or severe anemia, can reverse neurological disease. Therefore, unused oxygen is the most likely culprit in the pathology of this disease. While pharmacologic activation of the hypoxia response is unlikely to alleviate disease in vivo, interventions that safely normalize brain tissue hyperoxia may hold therapeutic potential.

Revealing the transient conformations of a single flavin adenine dinucleotide using an aerolysin nanopore

Flavin adenine dinucleotide (FAD) as a cofactor is involved in numerous important metabolic pathways where the biological function is intrinsically related to its transient conformations. The confined space of enzymes requires FAD set in its specific intermediate conformation. However, conventional methods only detect stable conformations of FAD molecules, while transient intermediates are hidden in ensemble measurements. There still exists a challenge to uncover the transient conformation of each FAD molecule, which hinders the understanding of the structure-activity relationship of the FAD mechanism. Here, we employ the electrochemically confined space of an aerolysin nanopore to directly characterize a series of transient conformations of every individual FAD. Based on distinguishable current blockages, the "stack", "open", and four quasi-stacked FADs are clearly determined in solution, which is further confirmed by temperature-dependent experiments and mutant aerolysin assay. Combined with molecular dynamics simulations, we achieved a direct correlation between the residual current ratio (I/I ₀) and FAD backbone angle. These results would facilitate further understanding of the structure-activity relationship in the flavoprotein.

Advances Towards Therapeutic Approaches for mtDNA Disease

Mitochondria maintain and express their own genome, referred to as mtDNA, which is required for proper mitochondrial function. While mutations in mtDNA can cause a heterogeneous array of disease phenotypes, there is currently no cure for this collection of diseases. Here, we will cover characteristics of the mitochondrial genome important for understanding the pathology associated with mtDNA mutations, and review recent approaches that are being developed to treat and prevent mtDNA disease. First, we will discuss mitochondrial replacement therapy (MRT), where mitochondria from a healthy donor replace maternal mitochondria harbouring mutant mtDNA. In addition to ethical concerns surrounding this procedure, MRT is only applicable in cases where the mother is known or suspected to carry mtDNA mutations. Thus, there remains a need for other strategies to treat patients with mtDNA disease. To this end, we will also discuss several alternative means to reduce the amount of mutant mtDNA present in cells. Such methods, referred to as heteroplasmy shifting, have proven successful in animal models. In particular, we will focus on the approach of targeting engineered endonucleases to specifically cleave mutant mtDNA. Together, these approaches offer hope to prevent the transmission of mtDNA disease and potentially reduce the impact of mtDNA mutations.

Extracellular Mitochondria for Therapy and Diagnosis in Acute Central Nervous System Injury

Objective

Acute central nervous system (CNS) injury after stroke and trauma remains a clinical challenge with limited diagnostic and therapeutic approaches. In this article, we review studies suggesting that after CNS injury, mitochondria can be released into extracellular space as a "help-me" signal to augment recovery. Results are taken from experimental studies in cell and animal models and an initial proof-of-concept analysis in humans suggesting the functional relevance of extracellular mitochondria after acute CNS injury.

Observations

After acute CNS injury, (1) mitochondria may be released into extracellular space, (2) mitochondria may be transferred between cells, and (3) levels of extracellular mitochondria may serve as potential biomarkers for recovery.

Conclusions and Relevance

Further translational and clinical studies are warranted to assess the overall hypothesis of using extracellular mitochondria as a therapy and biomarker in the CNS after stroke and trauma.

Identification and Application of Gene Expression Signatures Associated with Lifespan Extension

Several pharmacological, dietary, and genetic interventions that increase mammalian lifespan are known, but general principles of lifespan extension remain unclear. Here, we performed RNA sequencing (RNA-seq) analyses of mice subjected to 8 longevity interventions. We discovered a feminizing effect associated with growth hormone regulation and diminution of sex-related differences. Expanding this analysis to 17 interventions with public data, we observed that many interventions induced similar gene expression changes. We identified hepatic gene signatures associated with lifespan extension across interventions, including upregulation of oxidative phosphorylation and drug metabolism, and showed that perturbed pathways may be shared across tissues. We further applied the discovered longevity signatures to identify new lifespan-extending candidates, such as chronic hypoxia, KU-0063794, and ascorbyl-palmitate. Finally, we developed GENtervention, an app that visualizes associations between gene expression changes and longevity. Overall, this study describes general and specific transcriptomic programs of lifespan extension in mice and provides tools to discover new interventions.

Defined neuronal populations drive fatal phenotype in a mouse model of Leigh syndrome

Mitochondrial deficits in energy production cause untreatable and fatal pathologies known as mitochondrial disease (MD). Central nervous system affectation is critical in Leigh Syndrome (LS), a common MD presentation, leading to motor and respiratory deficits, seizures and premature death. However, only specific neuronal populations are affected. Furthermore, their molecular identity and their contribution to the disease remains unknown. Here, using a mouse model of LS lacking the mitochondrial complex I subunit Ndufs4, we dissect the critical role of genetically-defined neuronal populations in LS progression. Ndufs4 inactivation in Vglut2-expressing glutamatergic neurons leads to decreased neuronal firing, brainstem inflammation, motor and respiratory deficits, and early death. In contrast, Ndufs4 deletion in GABAergic neurons causes basal ganglia inflammation without motor or respiratory involvement, but accompanied by hypothermia and severe epileptic seizures preceding death. These results provide novel insight in the cell type-specific contribution to the pathology, dissecting the underlying cellular mechanisms of MD.

Mitochondrial disorders and drugs: what every physician should know

Mitochondrial disorders are a group of metabolic conditions caused by impairment of the oxidative phosphorylation system. There is currently no clear evidence supporting any pharmacological interventions for most mitochondrial disorders, except for coenzyme Q10 deficiencies, Leber hereditary optic neuropathy, and mitochondrial neurogastrointestinal encephalomyopathy. Furthermore, some drugs may potentially have detrimental effects on mitochondrial dysfunction. Drugs known to be toxic for mitochondrial functions should be avoided whenever possible. Mitochondrial patients needing one of these treatments should be carefully monitored, clinically and by laboratory exams, including creatine kinase and lactate. In the era of molecular and ‘personalized’ medicine, many different physicians (not only neurologists) should be aware of the basic principles of mitochondrial medicine and its therapeutic implications. Multicenter collaboration is essential for the advancement of therapy for mitochondrial disorders. Whenever possible, randomized clinical trials are necessary to establish efficacy and safety of drugs. In this review we discuss in an accessible way the therapeutic approaches and perspectives in mitochondrial disorders. We will also provide an overview of the drugs that should be used with caution in these patients.

Development of CRISPR-Cas systems for genome editing and beyond

The development of clustered regularly interspaced short-palindromic repeat (CRISPR)-Cas systems for genome editing has transformed the way life science research is conducted and holds enormous potential for the treatment of disease as well as for many aspects of biotechnology. Here, I provide a personal perspective on the development of CRISPR-Cas9 for genome editing within the broader context of the field and discuss our work to discover novel Cas effectors and develop them into additional molecular tools. The initial demonstration of Cas9-mediated genome editing launched the development of many other technologies, enabled new lines of biological inquiry, and motivated a deeper examination of natural CRISPR-Cas systems, including the discovery of new types of CRISPR-Cas systems. These new discoveries in turn spurred further technological developments. I review these exciting discoveries and technologies as well as provide an overview of the broad array of applications of these technologies in basic research and in the improvement of human health. It is clear that we are only just beginning to unravel the potential within microbial diversity, and it is quite likely that we will continue to discover other exciting phenomena, some of which it may be possible to repurpose as molecular technologies. The transformation of mysterious natural phenomena to powerful tools, however, takes a collective effort to discover, characterize, and engineer them, and it has been a privilege to join the numerous researchers who have contributed to this transformation of CRISPR-Cas systems.

Turtles maintain mitochondrial integrity but reduce mitochondrial respiratory capacity in the heart after cold acclimation and anoxia

Mitochondria are important to cellular homeostasis, but can become a dangerous liability when cells recover from hypoxia. Anoxia-tolerant freshwater turtles show reduced mitochondrial respiratory capacity and production of reactive oxygen species (ROS) after prolonged anoxia, but the mechanisms are unclear. Here, we investigated whether this mitochondrial suppression originates from downregulation of mitochondrial content or intrinsic activity by comparing heart mitochondria from (1) warm (25°C) normoxic, (2) cold-acclimated (4°C) normoxic and (3) cold-acclimated anoxic turtles. Transmission electron microscopy of heart ventricle revealed that these treatments did not affect mitochondrial volume density and morphology. Furthermore, neither enzyme activity, protein content nor supercomplex distribution of electron transport chain (ETC) enzymes changed significantly. Instead, our data imply that turtles inhibit mitochondrial respiration rate and ROS production by a cumulative effect of slight inhibition of ETC complexes. Together, these results show that maintaining mitochondrial integrity while inhibiting overall enzyme activities are important aspects of anoxia tolerance.

Hypoxia Rescues Frataxin Loss by Restoring Iron Sulfur Cluster Biogenesis

Friedreich's ataxia (FRDA) is a devastating, multisystemic disorder caused by recessive mutations in the mitochondrial protein frataxin (FXN). FXN participates in the biosynthesis of Fe-S clusters and is considered to be essential for viability. Here we report that when grown in 1% ambient O2, FXN null yeast, human cells, and nematodes are fully viable. In human cells, hypoxia restores steady-state levels of Fe-S clusters and normalizes ATF4, NRF2, and IRP2 signaling events associated with FRDA. Cellular studies and in vitro reconstitution indicate that hypoxia acts through HIF-independent mechanisms that increase bioavailable iron as well as directly activate Fe-S synthesis. In a mouse model of FRDA, breathing 11% O2 attenuates the progression of ataxia, whereas breathing 55% O2 hastens it. Our work identifies oxygen as a key environmental variable in the pathogenesis associated with FXN depletion, with important mechanistic and therapeutic implications.

There Is Something Fishy About Liver Cancer: Zebrafish Models of Hepatocellular Carcinoma

The incidence of hepatocellular carcinoma (HCC) and the mortality resulting from HCC are both increasing. Most patients with HCC are diagnosed at advanced stages when curative treatments are impossible. Current drug therapy extends mean overall survival by only a short period of time. Genetic mutations associated with HCC vary widely. Therefore, transgenic and mutant animal models are needed to investigate the molecular effects of specific mutations, classify them as drivers or passengers, and develop targeted treatments. Cirrhosis, however, is the premalignant state common to 90% of HCC patients. Currently, no specific therapies are available to halt or reverse the progression of cirrhosis to HCC. Understanding the genetic drivers of HCC as well as the biochemical, mechanical, hormonal, and metabolic changes associated with cirrhosis could lead to novel treatments and cancer prevention strategies. Although additional therapies recently received Food and Drug Administration approval, significant clinical breakthroughs have not emerged since the introduction of the multikinase inhibitor sorafenib, necessitating alternate research strategies. Zebrafish (Danio rerio) are effective for disease modeling because of their high degree of gene and organ architecture conservation with human beings, ease of transgenesis and mutagenesis, high fecundity, and low housing cost. Here, we review zebrafish models of HCC and identify areas on which to focus future research efforts to maximize the advantages of the zebrafish model system.

mTORC1 is required for expression of LRPPRC and cytochrome-c oxidase but not HIF-1α in Leigh syndrome French Canadian type patient fibroblasts

Leigh syndrome French Canadian type (LSFC) is a mitochondrial disease caused by mutations in the leucine-rich pentatricopeptide repeat-containing (LRPPRC) gene leading to a reduction of cytochrome-c oxidase (COX) expression reaching 50% in skin fibroblasts. We have shown that under basal conditions, LSFC and control cells display similar ATP levels. We hypothesized that this occurs through upregulation of mechanistic target of rapamycin (mTOR)-mediated metabolic reprogramming. Our results showed that compared with controls, LSFC cells exhibited an upregulation of the mTOR complex 1 (mTORC1)/p70 ribosomal S6 kinase pathway and higher levels of hypoxia-inducible factor 1α (HIF-1α) and its downstream target pyruvate dehydrogenase kinase 1 (PDHK1), a regulator of mitochondrial pyruvate dehydrogenase 1 (PDH1). Consistent with these signaling alterations, LSFC cells displayed a 40-61% increase in [U-¹³C₆]glucose contribution to pyruvate, lactate, and alanine formation, as well as higher levels of the phosphorylated and inactive form of PDH1-α. Interestingly, inhibition of mTOR with rapamycin did not alter HIF-1α or PDHK1 protein levels in LSFC fibroblasts. However, this treatment increased PDH1-α phosphorylation in control and LSFC cells and reduced ATP levels in control cells. Rapamycin also decreased LRPPRC expression by 41 and 11% in LSFC and control cells, respectively, and selectively reduced COX subunit IV expression in LSFC fibroblasts. Taken together, our data demonstrate the importance of mTORC1, independent of the HIF-1α/PDHK1 axis, in maintaining LRPPRC and COX expression in LSFC cells.

SQSTM1/p62-Directed Metabolic Reprogramming Is Essential for Normal Neurodifferentiation

Neurodegenerative disorders are an increasingly common and irreversible burden on society, often affecting the aging population, but their etiology and disease mechanisms are poorly understood. Studying monogenic neurodegenerative diseases with known genetic cause provides an opportunity to understand cellular mechanisms also affected in more complex disorders. We recently reported that loss-of-function mutations in the autophagy adaptor protein SQSTM1/p62 lead to a slowly progressive neurodegenerative disease presenting in childhood. To further elucidate the neuronal involvement, we studied the cellular consequences of loss of p62 in a neuroepithelial stem cell (NESC) model and differentiated neurons derived from reprogrammed p62 patient cells or by CRISPR/Cas9-directed gene editing in NESCs. Transcriptomic and proteomic analyses suggest that p62 is essential for neuronal differentiation by controlling the metabolic shift from aerobic glycolysis to oxidative phosphorylation required for neuronal maturation. This shift is blocked by the failure to sufficiently downregulate lactate dehydrogenase expression due to the loss of p62, possibly through impaired Hif-1α downregulation and increased sensitivity to oxidative stress. The findings imply an important role for p62 in neuronal energy metabolism and particularly in the regulation of the shift between glycolysis and oxidative phosphorylation required for normal neurodifferentiation.

Polyunsaturated Fatty Acid Desaturation Is a Mechanism for Glycolytic NAD+ Recycling

The reactions catalyzed by the delta-5 and delta-6 desaturases (D5D/D6D), key enzymes responsible for highly unsaturated fatty acid (HUFA) synthesis, regenerate NAD⁺ from NADH. Here, we show that D5D/D6D provide a mechanism for glycolytic NAD⁺ recycling that permits ongoing glycolysis and cell viability when the cytosolic NAD⁺/NADH ratio is reduced, analogous to lactate fermentation. Although lesser in magnitude than lactate production, this desaturase-mediated NAD⁺ recycling is acutely adaptive when aerobic respiration is impaired in vivo. Notably, inhibition of either HUFA synthesis or lactate fermentation increases the other, underscoring their interdependence. Consistent with this, a type 2 diabetes risk haplotype in SLC16A11 that reduces pyruvate transport (thus limiting lactate production) increases D5D/D6D activity in vitro and in humans, demonstrating a chronic effect of desaturase-mediated NAD⁺ recycling. These findings highlight key biologic roles for D5D/D6D activity independent of their HUFA end products and expand the current paradigm of glycolytic NAD⁺ regeneration.

Genome-Wide Interrogation of Human Cancers Identifies EGLN1 Dependency in Clear Cell Ovarian Cancers

We hypothesized that candidate dependencies for which there are small molecules that are either approved or in advanced development for a nononcology indication may represent potential therapeutic targets. To test this hypothesis, we performed genome-scale loss-of-function screens in hundreds of cancer cell lines. We found that knockout of EGLN1, which encodes prolyl hydroxylase domain-containing protein 2 (PHD2), reduced the proliferation of a subset of clear cell ovarian cancer cell lines in vitro. EGLN1-dependent cells exhibited sensitivity to the pan-EGLN inhibitor FG-4592. The response to FG-4592 was reversed by deletion of HIF1A, demonstrating that EGLN1 dependency was related to negative regulation of HIF1A. We also found that ovarian clear cell tumors susceptible to both genetic and pharmacologic inhibition of EGLN1 required intact HIF1A. Collectively, these observations identify EGLN1 as a cancer target with therapeutic potential. SIGNIFICANCE: These findings reveal a differential dependency of clear cell ovarian cancers on EGLN1, thus identifying EGLN1 as a potential therapeutic target in clear cell ovarian cancer patients.

HgS Inhibits Oxidative Stress Caused by Hypoxia through Regulation of 5-HT Metabolism Pathway

This study aims to reveal the potential relationship between 5-HT and oxidative stress in the organism. Our in vitro experiments in RIN-14B cells showed that anoxia leads the cells to the state of oxidative stress. Administration of exogenous 5-HT exacerbated this effect, whereas the inhibition of Tph1, LP533401 alleviated the oxidative stress. Several research articles reported that Cinnabar (consists of more than 96% mercury sulfide, HgS), which is widely used in both Chinese and Indian traditional medicine prescriptions, has been involved in the regulation of 5-HT. The present research revealed that HgS relieved the level of oxidative stress of RIN-14B cells. This pharmacological activity was also observed in the prescription drug Zuotai, in which HgS accounts for 54.5%, and these effects were found to be similar to LP533401, an experimental drug to treat pulmonary hypertension. Further, our in vivo experiments revealed that the administration of cinnabar or prescription drug Zuotai in zebrafish reduced the reactive oxygen species (ROS) induced by hypoxia and cured behavioral abnormalities. Taken together, in organisms with hypoxia induced oxidative stress 5-HT levels were found to be abnormally elevated, indicating that 5-HT could regulate oxidative stress, and the decrease in the 5-HT levels, behavioral abnormalities after treatment with cinnabar and Zuotai, we may conclude that the therapeutic and pharmacologic effect of cinnabar and Zuotai may be based on the regulation of 5-HT metabolism and relief of oxidative stress. Even though they aren't toxic at the present dosage in both cell lines and zebrafish, their dose dependent toxicities are yet to be evaluated.

Targeting NAD+ Metabolism as Interventions for Mitochondrial Disease

Leigh syndrome is a mitochondrial disease characterized by neurological disorders, metabolic abnormality and premature death. There is no cure for Leigh syndrome; therefore, new therapeutic targets are urgently needed. In Ndufs4-KO mice, a mouse model of Leigh syndrome, we found that Complex I deficiency led to declines in NAD+ levels and NAD+ redox imbalance. We tested the hypothesis that elevation of NAD+ levels would benefit Ndufs4-KO mice. Administration of NAD+ precursor, nicotinamide mononucleotide (NMN) extended lifespan of Ndufs4-KO mice and attenuated lactic acidosis. NMN increased lifespan by normalizing NAD+ redox imbalance and lowering HIF1a accumulation in Ndufs4-KO skeletal muscle without affecting the brain. NMN up-regulated alpha-ketoglutarate (KG) levels in Ndufs4-KO muscle, a metabolite essential for HIF1a degradation. To test whether supplementation of KG can treat Ndufs4-KO mice, a cell-permeable KG, dimethyl ketoglutarate (DMKG) was administered. DMKG extended lifespan of Ndufs4-KO mice and delayed onset of neurological phenotype. This study identified therapeutic mechanisms that can be targeted pharmacologically to treat Leigh syndrome.

O2 affects mitochondrial functionality ex vivo

Mitochondria have originated in eukaryotic cells by endosymbiosis of a specialized prokaryote approximately 2 billion years ago. They are essential for normal cell function by providing energy through their role in oxidizing carbon substrates. Glutathione (GSH) is a major thiol-disulfide redox buffer of the cell including the mitochondrial matrix and intermembrane space. We have generated cardiomyocyte-specific Grx1-roGFP2 GSH redox potential (E_GSH) biosensor mice in the past, in which the sensor is targeted to the mitochondrial matrix. Using this mouse model a distinct E_GSH of the mitochondrial matrix (−278.9 ± 0.4 mV) in isolated cardiomyocytes is observed. When analyzing the E_GSH in isolated mitochondria from the transgenic hearts, however, the E_GSH in the mitochondrial matrix is significantly oxidized (−247.7 ± 8.7 mV). This is prevented by adding N-Ethylmaleimide during the mitochondria isolation procedure, which precludes disulfide bond formation. A similar reducing effect is observed by isolating mitochondria in hypoxic (0.1–3% O₂) conditions that mimics mitochondrial pO₂ levels in cellulo. The reduced E_GSH is accompanied by lower ROS production, reduced complex III activity but increased ATP levels produced at baseline and after stimulation with succinate/ADP. Altogether, we demonstrate that oxygenation is an essential factor that needs to be considered when analyzing mitochondrial function ex vivo.

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We identified that mitochondria isolated in room air at 20.9% O₂ exhibit a strong oxidation of the E_GSH in the matrix.

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Isolation of mitochondria in hypoxic conditions mimicking their in cellulo conditions prevents oxidation of the E_GSH.

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Normoxic and hypoxic isolated mitochondria differ in ROS production, complex III activity and ATP levels.

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Oxygenation needs to be considered when analyzing mitochondrial function ex vivo.

Multi-omics identify xanthine as a pro-survival metabolite for nematodes with mitochondrial dysfunction

Aberrant mitochondrial function contributes to the pathogenesis of various metabolic and chronic disorders. Inhibition of insulin/IGF‐1 signaling (IIS) represents a promising avenue for the treatment of mitochondrial diseases, although many of the molecular mechanisms underlying this beneficial effect remain elusive. Using an unbiased multi‐omics approach, we report here that IIS inhibition reduces protein synthesis and favors catabolism in mitochondrial deficient Caenorhabditis elegans. We unveil that the lifespan extension does not occur through the restoration of mitochondrial respiration, but as a consequence of an ATP‐saving metabolic rewiring that is associated with an evolutionarily conserved phosphoproteome landscape. Furthermore, we identify xanthine accumulation as a prominent downstream metabolic output of IIS inhibition. We provide evidence that supplementation of FDA‐approved xanthine derivatives is sufficient to promote fitness and survival of nematodes carrying mitochondrial lesions. Together, our data describe previously unknown molecular components of a metabolic network that can extend the lifespan of short‐lived mitochondrial mutant animals.

Dissecting metabolism using zebrafish models of disease

Zebrafish (Danio rerio) are becoming an increasingly powerful model organism to study the role of metabolism in disease. Since its inception, the zebrafish model has relied on unique attributes such as the transparency of embryos, high fecundity and conservation with higher vertebrates, to perform phenotype-driven chemical and genetic screens. In this review, we describe how zebrafish have been used to reveal novel mechanisms by which metabolism regulates embryonic development, obesity, fatty liver disease and cancer. In addition, we will highlight how new approaches in advanced microscopy, transcriptomics and metabolomics using zebrafish as a model system have yielded fundamental insights into the mechanistic underpinnings of disease.