Hypoxia as a therapy for mitochondrial disease

Blindness following hydrogen peroxide ingestion and recovery with hyperbaric oxygen therapy

Hydrogen peroxide (HP) poisoning is rare but potentially life-threatening. It can cause tissue damage through oxygen emboli and reactive oxygen species (ROS). This is the first reported case of blindness caused by cerebral infarctions involving the visual pathway due to oxygen emboli from HP ingestion. A monocular patient presented with profound vision loss and no apparent pharyngeal mucosal injury following ingestion of commercial-grade (35 %) HP. CT imaging revealed gastric wall edema and gas in the portal venous system, suggesting gas emboli. Post-treatment MRI of the brain and orbits with and without contrast confirmed multifocal embolic infarcts along the visual pathway, and transcranial doppler studies identified moderate right-to-left shunting to explain the paradoxical emboli. The patient received hyperbaric oxygen therapy, resulting in a rapid improvement in visual acuity from hand motion to 20/20 and near-total resolution of visual field loss. Remarkably, this recovery occurred despite treatment initiation more than 24 h after symptom onset. This case emphasizes the importance of timely recognition and management of HP poisoning. In the authors' minds it also raised questions about the routine use of 100 % oxygen in hyperbaric therapy due to potential additional oxidative stress. It is the authors' opinion that further research should be done to validate treatment protocols and further interrogate possible risks associated with reactive oxygen species and oxygen toxicity.

Hypoxia in multiple sclerosis

Low oxygen availability (hypoxia) is a prominent but poorly understood feature in multiple sclerosis (MS). Whether hypoxia causes or drives MS pathology and symptoms or whether it is a consequence of other pathological events, such as inflammation and vascular dysfunction, is unknown. Here, we summarize the available literature on the interplay between hypoxia and both pathological and symptomatic features of MS. Severe environmental hypoxia (i.e., altitude) may trigger or facilitate MS-related events, possibly by exacerbating tissue hypoxia in the central nervous system. Accordingly, increasing oxygen supply can mitigate pathological and clinical parameters in MS models. In contrast, stimulating the endogenous hypoxia response and adaptation systems by controlled exposure to hypoxia (hypoxia conditioning) renders the central nervous system more resistant to hypoxic insults, thereby attenuating pathology and symptomatology in MS models. Overlapping mechanisms likely play a role in the benefits conferred by physical activity in MS. We provide an integrative model to explain the paradoxically beneficial outcomes of both increased and decreased ambient oxygen conditions. In conclusion, controlled exposure to hypoxia, perhaps in combination with exercise, is a promising, possibly disease-course modifying therapeutic approach for MS. However, many open questions remain.

Immunoproteasome-specific subunit alterations as a potential therapeutic target for mitochondriopathies

Mitochondria are double-membrane organelles crucial for eukaryotic cells due to their role in ATP production by oxidative phosphorylation (OXPHOS). Most of the ∼1500 proteins of the mitochondrial proteome are encoded in the nuclear genome, synthesized in the cytosol, and actively transported into mitochondria. The proteasome, a major cellular proteolytic machinery, plays an important role in the quality control of their transport by degradation of inefficiently imported mitochondrial proteins in the cytosol. Proteasome inhibition by bortezomib was described as a strategy to alleviate deficiencies stemming from an inefficient import of proteins into the mitochondria. Notably, an impairment of the respiratory complexes was shown to induce a rearrangement of the proteasome composition to incorporate some of the immunoproteasome catalytic subunits, such as PSMB9. In this study, we demonstrated that targeting immunoproteasome inhibited degradation, and thus restored the abundance of inefficiently imported respiratory complex IV proteins in the patient derived fibroblasts. Furthermore, we demonstrated that the immunoproteasome-specific inhibitors displayed a decreased toxicity compared to bortezomib. Our results indicate that immunoproteasome subunits present a novel molecular target for future therapies of mitochondriopathies.

In vitro senescence and senolytic functional assays

A detailed understanding of aging biology and the development of anti-aging therapeutic strategies remain imperative yet inherently challenging due to the protracted nature of aging. Cellular senescence arises naturally through replicative exhaustion and is accelerated by clinical treatments or environmental stressors. The accumulation of senescent cells-defined by a loss of mitogenic potential, resistance to apoptosis, and acquisition of a pro-inflammatory secretory phenotype-has been implicated as a key driver of chronic disease, tissue degeneration, and organismal aging. Recent studies have highlighted the therapeutic promise of senolytic drugs, which selectively eliminate senescent cells. Compelling results from preclinical animal studies and ongoing clinical trials underscore this potential. However, the clinical translation of senolytics requires further pharmacological validation to refine selectivity, minimize toxicity, and determine optimal dosing. Equally important is the evaluation of senolytics' potential to restore tissue structure and function by reducing the senescent cell burden. In vitro tissue culture models offer a powerful platform to advance these efforts. This review summarizes the current landscape of in vitro systems used for inducing cellular senescence-referred to as "senescence assays"-and for screening senolytic drugs-referred to as "senolytic assays". We conclude by discussing key challenges to improving mechanistic insight, predictive accuracy, and clinical relevance in senolytic drug development, as well as emerging applications of senolytic therapies.

Flores S, Esquivel E, Ding Y, Peitzsch M, Robles-Guirado JÁ, Regojo Zapata RM, Pozo-Kreilinger JJ, Iglesias C, Dwight T, Muir CA, Oleaga A, Garrido-Lestache Rodríguez-Monte ME, Del Cerro MJ, Martínez-Bendayán I, Álvarez-González E, Cubiella T, Lourenço DM, A. Pereira MA, Burnichon N, Buffet A, Broberg C, Dickson PV, Fraga MF, Llorente Pendás JL, Rueda Soriano J, Buendía Fuentes F, Toledo SP, Clifton-Bligh R, Dienstmann R, Villanueva J, Capdevila J, Gimenez-Roqueplo AP, Favier J, Nuciforo P, Young WF, Bechmann N, Opotowsky AR, Vaidya A, Bancos I, Weghorn D, Robledo M, Casteràs A, Dos-Subirà L, Adameyko I, Chiara MD, Dahia PL, Toledo RA. Convergent Genetic Adaptation in Human Tumors Developed Under Systemic Hypoxia and in Populations Living at High Altitudes

SIGNIFICANCE

This study reveals a broad convergence in genetic adaptation to hypoxia between natural populations and tumors, suggesting that insights from natural populations could enhance our understanding of cancer biology and identify novel therapeutic targets. See related commentary by Lee, p. 875.

The therapeutic potential of a polyunsaturated fatty acid-enriched high-fat diet in Leigh syndrome: Insights from a preclinical model

INTRODUCTION

Leigh syndrome is often caused by Ndufs4 mutations. The Ndufs4 knockout (KO) mouse model recapitulates key disease features, including systemic inflammation, neurodegeneration, and motor deficits. While dietary interventions such as the ketogenic diet show promise in mitigating mitochondrial dysfunction, conflicting results highlight uncertainties regarding its efficacy. Here, we evaluate the therapeutic potential of a polyunsaturated fatty acid (PUFA)-enriched high-fat diet (HFD) in Ndufs4 KO mice.

METHODS

Dietary intervention began at postnatal day 23, with mice receiving either a normal diet (ND) or a HFD enriched with PUFAs. Phenotypic evaluation, including locomotor function, clasping behaviour, and survival, continued until natural death. In a second group of animals, biochemical analyses were conducted after three weeks on the diets, using Western blot to evaluate neurometabolic and inflammatory regulators, flow cytometry to quantify serum inflammation markers, and metabolic profiling to identify alterations in neurometabolism and the neurolipidome.

RESULTS

The HFD significantly extended lifespan and improved clasping behaviour in Ndufs4 KO mice but had no effect on locomotor activity or grip strength decline. While whole-brain mTOR (p70S6K1, 4E-BP1) and SIRT1 (PGC1-α, TNF-α) signalling pathways remained unaffected, the diet significantly reduced serum pro-inflammatory markers TNF and IL-6. Furthermore, the PUFA-enriched HFD partially restored disruptions in TCA cycle, ketone body, branched-chain amino acid, and lipid metabolism, indicating potential metabolic reprogramming.

CONCLUSION

Dietary interventions, such as a PUFA-enriched HFD, may alleviate systemic inflammation, partially correct metabolic imbalances, and mitigate specific disease phenotypes in Leigh syndrome, warranting further investigation into the underlying mechanisms and broader therapeutic applications.

FG-4592 combined with PRP significantly accelerates the healing of refractory diabetic wounds by upregulating HIF-1α

Chronic refractory wounds are a common, costly and recurrent complication of diabetes. Platelet-rich plasma (PRP), a new therapy for chronic wounds, is limited by a long treatment period and unstable effects. FG-4592(Roxadustat) is a new prolyl-4-hydroxylation domain(PHD) inhibitor, which can stabilize hypoxia-inducible factor-1α(HIF-1α) effectively. It is a promising drug for wound repair and needs to be demonstrated via various appropriate application scenarios. This study investigated the effects of combining FG-4592 and PRP to promote diabetic wound healing. Diabetic rats were randomly assigned to five groups: nondiabetic control, diabetic untreated, diabetic + PRP, diabetic + FG-4592, and diabetic + PRP + FG-4592. Diabetes was induced with streptozotocin (STZ). A full-thickness skin defect was created, and FG-4592 (peritoneal injection) and PRP (periwound injection) were administered alone or together. Wound healing was assessed by histological analysis (Hematoxylin-Eosin (HE) and Masson staining) and protein expression of HIF-1α, VEGF(vascular endothelial growth factor), α-SMA(α-smooth muscle actin), CoL1α1(collagen type 1 alpha 1), and SDF-1(Stromal Cell-derived Factor 1) via Western blotting and qRT-PCR(Quantitative real time polymerase chain reaction). Immunohistochemistry(IHC) and immunofluorescence(IF) were also used to evaluate CD34 (Cluster of Differentiation 34), CD31(Cluster of Differentiation 31), VEGF(vascular endothelial growth factor), SDF-1(Stromal Cell-derived Factor 1), PCNA(Proliferating Cell Nuclear Antigen), and Integrin-β1 expression. The untreated diabetic group exhibited impaired wound healing, histological damage, and reduced expression of key proteins compared to the nondiabetic control group. Both PRP and FG-4592 alone improved wound healing, reduced damage, and upregulated protein expression. However, the combination of FG-4592 and PRP showed the most significant improvement. This study suggests that FG-4592 combined with PRP accelerates diabetic wound healing by enhancing endothelial progenitor cell recruitment, neovascularization, and cell proliferation and migration via upregulation of HIF-1α and its target genes. This combination therapy may provide a novel approach for treating chronic diabetic wounds.

Manipulation of Oxygen Tension in Damaged Regions via Hypoxia-Induced IPN Hydrogel Microspheres for Intervertebral Disc Regeneration

Disruption of low oxygen tension homeostasis during intervertebral disc degeneration inhibits endogenous stem cell viability and function, posing a challenge for endogenous regeneration. Here, to achieve sustained hypoxia manipulation, constructed hypoxia-inducible interpenetrating polymer network (IPN) hydrogel microspheres (HIMS) are constructed by microfluidics to integrate the hypoxic system with a stabilizing network. The IPN is synthesized through a two-step polymerization process, consisting of rapid photo-crosslinked gelatin methacrylate anhydride (GM) polymer I and slow enzyme-crosslinked vanillin-grafted gelatin (GV) polymer II. The enzymatic reaction between GV and laccase is able to create a hypoxic microenvironment to modulate oxygen tension in situ within the injured region. HIMS can reduce microenvironmental oxygen tension by 1/3 and maintain a hypoxic microenvironment for up to 5 days, thereby activating the PI3K/AKT/HIF-1α signaling pathway in endogenous stem cells to promote differentiation into nucleus pulposus-like cells. Additionally, NSC-Exos are loaded onto HIMS to trigger endogenous progenitor/stem cell recruitment and migration. Both in vitro and in vivo assays demonstrate that NSC-Exos@HIMS facilitates stem cell recruitment, targets differentiation, and stimulates extracellular matrix synthesis. Overall, the microspheres established herein provide a novel strategy for manipulating oxygen tension and enhancing endogenous tissue regeneration in injured regions during intervertebral disc degeneration.

Mapping the therapeutic landscape of CRISPR-Cas9 for combating age-related diseases

CRISPR-Cas9 (clustered regularly interspaced short palindromic repeats-associated protein 9) has emerged as a transformative genome-editing tool with significant therapeutic potential for age-related diseases, including Alzheimer's disease, Parkinson's disease, cardiovascular disorders, and osteoporosis. This study presents a bibliometric analysis of CRISPR-Cas9 research in age-related diseases, identifying key contributors, major research hotspots, and critical technological advancements. While promising applications have been demonstrated in gene repair, functional regulation, and molecular interventions, significant barriers persist, including off-target effects, low delivery efficiency, and limited editing in non-dividing cells. Ethical concerns over germline editing and gaps in long-term safety data further complicate clinical translation. Future directions emphasize the development of high-precision Cas9 variants, homology-directed repair-independent tools, and efficient delivery systems, alongside the establishment of international regulatory frameworks and multicenter clinical trials. These efforts are essential to fully realize the potential of CRISPR-Cas9 in addressing the global health challenges of aging.

Small-molecule hypoxia therapy in mitochondrial disease

In this issue of Cell, Blume et al. provide compelling rationale for pursuing pharmacologic optimization of a small-molecule "HypoxyStat," which left-shifts the oxyhemoglobin dissociation curve in red blood cells in an attempt to induce an effective and sustained reduction of chronic tissue hyperoxia in primary mitochondrial disease (PMD) and was well-tolerated and effective for both pre-symptomatic and advanced disease treatment to extend survival and improve neurologic outcomes in a mouse model of Leigh syndrome spectrum.

HypoxyStat, a small-molecule form of hypoxia therapy that increases oxygen-hemoglobin affinity

We have previously demonstrated that chronic inhaled hypoxia is remarkably therapeutic in the premier animal model of mitochondrial Leigh syndrome, the Ndufs4 knockout (KO) mouse. Subsequent work has extended this finding to additional mitochondrial diseases and more common conditions. However, challenges inherent to gas-based therapies have hindered the rapid translation of our findings to the clinic. Here, we tested a small molecule (hereafter termed HypoxyStat) that increases the binding affinity of hemoglobin for oxygen, thereby decreasing oxygen offloading to tissues. Daily oral dosing of HypoxyStat caused systemic hypoxia in mice breathing normoxic (21% O2) air. When administered prior to disease onset, this treatment dramatically extended the lifespan of Ndufs4 KO mice and rescued additional aspects of disease, including behavior, body weight, neuropathology, and body temperature. HypoxyStat was also able to reverse disease at a very late stage, thereby serving as a clinically tractable form of hypoxia therapy.

Leigh Syndrome: A Comprehensive Review of the Disease and Present and Future Treatments

Leigh syndrome (LS) is a severe neurodegenerative condition with an early onset, typically during early childhood or infancy. The disorder exhibits substantial clinical and genetic diversity. From a clinical standpoint, Leigh syndrome showcases a broad range of irregularities, ranging from severe neurological issues to minimal or no discernible abnormalities. The central nervous system is most affected, resulting in psychomotor retardation, seizures, nystagmus, ophthalmoparesis, optic atrophy, ataxia, dystonia, or respiratory failure. Some patients also experience involvement of the peripheral nervous system, such as polyneuropathy or myopathy, as well as non-neurological anomalies, such as diabetes, short stature, hypertrichosis, cardiomyopathy, anemia, renal failure, vomiting, or diarrhea (Leigh-like syndrome). Mutations associated with Leigh syndrome impact genes in both the mitochondrial and nuclear genomes. Presently, LS remains without a cure and shows limited response to various treatments, although certain case reports suggest potential improvement with supplements. Ongoing preclinical studies are actively exploring new treatment approaches. This review comprehensively outlines the genetic underpinnings of LS, its current treatment methods, and preclinical investigations, with a particular focus on treatment.

The Chemical Deformation of a Thermally Cured Polyimide Film Surface into Neutral 1,2,4,5-Benzentetracarbonyliron and 4,4'-Oxydianiline to Remarkably Enhance the Chemical-Mechanical Planarization Polishing Rate

The rapid advancement of 3D packaging technology has emerged as a key solution to overcome the scaling-down limitation of advanced memory and logic devices. Redistribution layer (RDL) fabrication, a critical process in 3D packaging, requires the use of polyimide (PI) films with thicknesses in the micrometer range. However, these polyimide films present surface topography variations in the range of hundreds of nanometers, necessitating chemical-mechanical planarization (CMP) to achieve nanometer-level surface flatness. Polyimide films, composed of copolymers of pyromellitimide and diphenyl ether, possess strong covalent bonds such as C-C, C-O, C=O, and C-N, leading to inherently low polishing rates during CMP. To address this challenge, the introduction of Fe(NO3)3 into CMP slurries has been proposed as a polishing rate accelerator. During CMP, this Fe(NO3)3 deformed the surface of a polyimide film into strongly positively charged 1,2,4,5-benzenetetracarbonyliron and weakly negatively charged 4,4'-oxydianiline (ODA). The chemically dominant polishing rate enhanced with the concentration of the Fe(NO3)3 due to accelerated surface interactions. However, higher Fe(NO3)3 concentrations reduce the attractive electrostatic force between the positively charged wet ceria abrasives and the negatively charged deformed surface of the polyimide film, thereby decreasing the mechanically dominant polishing rate. A comprehensive investigation of the chemical and mechanical polishing rate dynamics revealed that the optimal Fe(NO3)3 concentration to achieve the maximum polyimide film removal rate was 0.05 wt%.

Ndufs4 inactivation in glutamatergic neurons reveals swallow-breathing discoordination in a mouse model of Leigh syndrome

Swallowing, both nutritive and non-nutritive, is highly dysfunctional in children with Leigh Syndrome (LS) and contributes to the need for both gastrostomy and tracheostomy tube placement. Without these interventions aspiration of food, liquid, and mucus occur resulting in repeated bouts of respiratory infection. No study has investigated whether mouse models of LS, a neurometabolic disorder, exhibit dysfunctions in neuromuscular activity of swallow and breathing integration. We used a genetic mouse model of LS in which the NDUFS4 gene is knocked out (KO) specifically in Vglut2 or Gad2 neurons. We found increased variability of the swallow motor pattern, disruption in breathing regeneration post swallow, and water-induced apneas only in Vglut2 KO mice. These physiological changes likely contribute to weight loss and premature death seen in this mouse model. Following chronic hypoxia (CH) exposure, there was no difference in swallow motor pattern, breathing regeneration, weight, and life expectancy in the Vglut2-Ndufs4-KO CH mice compared to control CH, indicating a phenotypic rescue or prevention. These findings show that like patients with LS, Ndufs4 mouse models of LS exhibit swallow impairments as well as swallow-breathing discoordination alongside the other phenotypic traits described in previous studies. Understanding this aspect of LS will open roads for the development of future more efficacious therapeutic intervention for this illness.

Two tales of therapeutic innovations for Leigh syndrome spectrum

Leigh syndrome spectrum is the most common form of childhood-onset mitochondrial encephalopathy and is characterized by progressive neurodegeneration. Treatment options for this condition remain limited to date. Nonetheless, two lines of research endeavor in the past decade have shown encouraging results worthy of further investigations. First, therapeutic hypoxia appears to improve neurological outcomes, which is somewhat counterintuitive but supported by preclinical evidence. Furthermore, nicotinic acid or nicotinamide riboside could be an adjunctive therapy that enhances the neuroprotective effect of hypoxia. Second, preclinical studies and preliminary clinical experience suggest that sildenafil is potentially disease-modifying for Leigh syndrome. Sildenafil has already been used to treat pulmonary hypertension, and its repurposing for Leigh syndrome has been endorsed by European Medicines Agency. This perspective aims to raise awareness about these progresses, as well as to call for more clinical studies to ensure safe and effective implementation of these treatment approaches in clinical practice.

The Role of Hypoxia in Longevity

Aging is marked by a progressive decrease in physiological function and reserve capacity, which results in increased susceptibility to diseases. Understanding the mechanisms of driving aging is crucial for extending health span and promoting human longevity. Hypoxia, marked by reduced oxygen availability, has emerged as a promising area of study within aging research. This review explores recent findings on the potential of oxygen restriction to promote healthy aging and extend lifespan. While the role of hypoxia-inducible factor 1 (HIF-1) in cellular responses to hypoxia is well-established, its impact on lifespan remains complex and context-dependent. Investigations in invertebrate models suggest a role for HIF-1 in longevity, while evidence in mammalian models is limited. Hypoxia extends the lifespan independent of dietary restriction (DR), a known intervention underlying longevity. However, both hypoxia and DR converge on common downstream effectors, such as forkhead box O (FOXO) and flavin-containing monooxygenase (FMOs) to modulate the lifespan. Further work is required to elucidate the molecular mechanisms underlying hypoxia-induced longevity and optimize clinical applications. Understanding the crosstalk between HIF-1 and other longevity-associated pathways is crucial for developing interventions to enhance lifespan and healthspan. Future studies may uncover novel therapeutic strategies to promote healthy aging and longevity in human populations.

Evaluating the efficacy of vatiquinone in preclinical models of Leigh syndrome and GPX4 deficiency

BACKGROUND

Genetic mitochondrial diseases are a major challenge in modern medicine. These impact ~ 1:4,000 individuals and there are currently no effective therapies. Leigh syndrome is the most common pediatric presentation of mitochondrial disease. In humans, patients are often treated with antioxidants, vitamins, and strategies targeting energetics. The vitamin-E related compound vatiquinone (EPI-743, α-tocotrienol quinone) has been the subject of at least 19 clinical trials in the US since 2012, but the effects of vatiquinone on an animal model of mitochondrial disease have not yet been reported. Here, assessed the impact of vatiquinone in cellular assays and animal models of mitochondrial disease.

METHODS

The efficacy of vatiquinone in vitro was assessed using human fibroblasts and HEK293 cells treated with the ferroptosis inducers RSL3 and BSO + Fe(III)Citrate, the mitochondrial oxidative stress inducer paraquat, and the electron transport chain complex I inhibitor rotenone. The therapeutic potential of vatiquinone in vivo was assessed using the tamoxifen-induced mouse model for GPX4 deficiency and the Ndufs4 knockout mouse model of Leigh syndrome.

RESULTS

Vatiquinone robustly prevented death in cultured cells induced by RSL3 or BSO/iron, but had no effect on paraquat induced cell death. Vatiquinone had no impact on disease onset, progression, or survival in either the tamoxifen-inducible GPX4 deficient model or the Ndufs4(-/-) mouse model, though the drug may have reduced seizure risk.

CONCLUSIONS

Vatiquinone prevents ferroptosis, but fails to attenuate cell death induced by paraquat or rotenone and provided no significant benefit to survival in two mouse models of disease. Vatiquinone may prevent seizures in the Ndufs4(-/-) model. Our findings are consistent with recent press statements regarding clinical trial results and have implications for drug trial design and reporting in patients with rare diseases.

Roxadustat improves diabetic myocardial injury by upregulating HIF-1α/UCP2 against oxidative stress

BACKGROUND

Diabetes mellitus (DM), characterized by hyperglycemia, is intricately linked with cardiovascular complications. Hyperglycemia induces oxidative stress, compromising mitochondria energy metabolism disturbances, leading to cardiomyocyte hypoxia and dysregulation of hypoxia-inducible factor-1α (HIF-1α), thereby exacerbating diabetic myocardial injury. Roxadustat (FG-4592), as an inhibitor of HIF-PHD, reduces HIF-1α degradation and regulates the transcription and function of downstream target genes. This study explores the protective effect of FG-4592 on the diabetic myocardium and further investigates the specific mechanisms responsible for this action.

METHODS

We established diabetic myocardial injury mice and high glucose-induced rat cardiomyocyte models, administered FG-4592 pretreatment to clarify the protective effects and related mechanisms of FG-4592 on diabetic myocardial injury by detecting changes in oxidative stress, mitochondrial function, and related pathways.

RESULTS

FG-4592 demonstrated cardioprotective effects in diabetic mice by regulating mitochondrial structure and function, as well as maintaining oxidative stress balance in the myocardium. It stabilized HIF-1α, activated UCP2, and enhanced the PI3K/AKT/Nrf2 pathway, reducing mitochondrial superoxide production, improving mitochondrial respiratory potential, and modulating oxidative stress markers in high glucose-induced cardiomyocytes.

CONCLUSIONS

FG-4592 exerts protective effects against diabetic myocardial injury by reducing oxidative stress. The mechanism is linked with the upregulation of HIF-1α and UCP2, which subsequently activate the PI3K/AKT/Nrf2 signaling pathway.

The interplay of NAD and hypoxic stress and its relevance for ageing

Nicotinamide adenine dinucleotide (NAD) is an essential regulator of cellular metabolism and redox processes. NAD levels and the dynamics of NAD metabolism change with increasing age but can be modulated via the diet or medication. Because NAD metabolism is complex and its regulation still insufficiently understood, achieving specific outcomes without perturbing delicate balances through targeted pharmacological interventions remains challenging. NAD metabolism is also highly sensitive to environmental conditions and can be influenced behaviorally, e.g., by exercise. Changes in oxygen availability directly and indirectly affect NAD levels and may result from exposure to ambient hypoxia, increased oxygen demand during exercise, ageing or disease. Cellular responses to hypoxic stress involve rapid alterations in NAD metabolism and depend on many factors, including age, glucose status, the dose of the hypoxic stress and occurrence of reoxygenation phases, and exhibit complex time-courses. Here we summarize the known determinants of NAD-regulation by hypoxia and evaluate the role of NAD in hypoxic stress. We define the specific NAD responses to hypoxia and identify a great potential of the modulation of NAD metabolism regarding hypoxic injuries. In conclusion, NAD metabolism and cellular hypoxia responses are strongly intertwined and together mediate protective processes against hypoxic insults. Their interactions likely contribute to age-related changes and vulnerabilities. Targeting NAD homeostasis presents a promising avenue to prevent/treat hypoxic insults and - conversely - controlled hypoxia is a potential tool to regulate NAD homeostasis.

Essential role of sulfide oxidation in brain health and neurological disorders

Hydrogen sulfide (H2S) is an environmental hazard well known for its neurotoxicity. In mammalian cells, H2S is predominantly generated by transsulfuration pathway enzymes. In addition, H2S produced by gut microbiome significantly contributes to the total sulfide burden in the body. Although low levels of H2S is believed to exert various physiological functions such as neurotransmission and vasomotor control, elevated levels of H2S inhibit the activity of cytochrome c oxidase (i.e., mitochondrial complex IV), thereby impairing oxidative phosphorylation. To protect the electron transport chain from respiratory poisoning by H2S, the compound is actively oxidized to form persulfides and polysulfides by a mitochondrial resident sulfide oxidation pathway. The reaction, catalyzed by sulfide:quinone oxidoreductase (SQOR), is the initial and critical step in sulfide oxidation. The persulfide species are subsequently oxidized to sulfite, thiosulfate, and sulfate by persulfide dioxygenase (ETHE1 or SDO), thiosulfate sulfurtransferase (TST), and sulfite oxidase (SUOX). While SQOR is abundantly expressed in the colon, liver, lung, and skeletal muscle, its expression is notably low in the brains of most mammals. Consequently, the brain's limited capacity to oxidize H2S renders it particularly sensitive to the deleterious effects of H2S accumulation. Impaired sulfide oxidation can lead to fatal encephalopathy, and the overproduction of H2S has been implicated in the developmental delays observed in Down syndrome. Our recent findings indicate that the brain's limited capacity to oxidize sulfide exacerbates its sensitivity to oxygen deprivation. The beneficial effects of sulfide oxidation are likely to be mediated not only by the detoxification of H2S but also by the formation of persulfide, which exerts cytoprotective effects through multiple mechanisms. Therefore, pharmacological agents designed to scavenge H2S and/or enhance persulfide levels may offer therapeutic potential against neurological disorders characterized by impaired or insufficient sulfide oxidation or excessive H2S production.

Hypoxia as a medicine

Oxygen is essential for human life, yet a growing body of preclinical research is demonstrating that chronic continuous hypoxia can be beneficial in models of mitochondrial disease, autoimmunity, ischemia, and aging. This research is revealing exciting new and unexpected facets of oxygen biology, but translating these findings to patients poses major challenges, because hypoxia can be dangerous. Overcoming these barriers will require integrating insights from basic science, high-altitude physiology, clinical medicine, and sports technology. Here, we explore the foundations of this nascent field and outline a path to determine how chronic continuous hypoxia can be safely, effectively, and practically delivered to patients.

Mitochondrial diseases: from molecular mechanisms to therapeutic advances

Mitochondria are essential for cellular function and viability, serving as central hubs of metabolism and signaling. They possess various metabolic and quality control mechanisms crucial for maintaining normal cellular activities. Mitochondrial genetic disorders can arise from a wide range of mutations in either mitochondrial or nuclear DNA, which encode mitochondrial proteins or other contents. These genetic defects can lead to a breakdown of mitochondrial function and metabolism, such as the collapse of oxidative phosphorylation, one of the mitochondria's most critical functions. Mitochondrial diseases, a common group of genetic disorders, are characterized by significant phenotypic and genetic heterogeneity. Clinical symptoms can manifest in various systems and organs throughout the body, with differing degrees and forms of severity. The complexity of the relationship between mitochondria and mitochondrial diseases results in an inadequate understanding of the genotype-phenotype correlation of these diseases, historically making diagnosis and treatment challenging and often leading to unsatisfactory clinical outcomes. However, recent advancements in research and technology have significantly improved our understanding and management of these conditions. Clinical translations of mitochondria-related therapies are actively progressing. This review focuses on the physiological mechanisms of mitochondria, the pathogenesis of mitochondrial diseases, and potential diagnostic and therapeutic applications. Additionally, this review discusses future perspectives on mitochondrial genetic diseases.

Mitochondrial disease and epilepsy in children

Mitochondria is the cell's powerhouse. Mitochondrial disease refers to a group of clinically heterogeneous disorders caused by dysfunction in the mitochondrial respiratory chain, often due to mutations in mitochondrial DNA (mtDNA) or nuclear DNA (nDNA) that encodes mitochondrial proteins. This dysfunction can lead to a variety of clinical phenotypes, particularly affecting organs with high energy demands, such as the brain and muscles. Epilepsy is a prevalent neurological disorder in children and is also a frequent manifestation of mitochondrial disease. The exact mechanisms underlying epilepsy in mitochondrial disease remain unclear and are thought to involve multiple contributing factors. This review explores common mitochondrial diseases associated with epilepsy, focusing on their prevalence, seizure types, EEG features, therapeutic strategies, and outcomes. It also summarizes the relationship between the molecular genetics of mitochondrial respiratory chain components and the development of epilepsy.

E4F1 coordinates pyruvate metabolism and the activity of the elongator complex to ensure translation fidelity during brain development

Pyruvate metabolism defects lead to severe neuropathies such as the Leigh syndrome (LS) but the molecular mechanisms underlying neuronal cell death remain poorly understood. Here, we unravel a connection between pyruvate metabolism and the regulation of the epitranscriptome that plays an essential role during brain development. Using genetically engineered mouse model and primary neuronal cells, we identify the transcription factor E4F1 as a key coordinator of AcetylCoenzyme A (AcCoA) production by the pyruvate dehydrogenase complex (PDC) and its utilization as an essential co-factor by the Elongator complex to acetylate tRNAs at the wobble position uridine 34 (U34). E4F1-mediated direct transcriptional regulation of Dlat and Elp3, two genes encoding key subunits of the PDC and of the Elongator complex, respectively, ensures proper translation fidelity and cell survival in the central nervous system (CNS) during mouse embryonic development. Furthermore, analysis of PDH-deficient cells highlight a crosstalk linking the PDC to ELP3 expression that is perturbed in LS patients.

Links between mutations in functionally separate arms of mitochondrial complex I and responses to volatile anesthetics

BACKGROUND

Individuals with mitochondrial defects, especially those in Complex I of the electron transport chain, exhibit behavioral hypersensitivity and toxicity to volatile anesthetics. In Drosophila melanogaster, mutation of ND23 (NDUFS8 in mammals), which encodes a subunit of the matrix arm of Complex I, sensitizes flies to toxicity from isoflurane but not an equipotent dose of sevoflurane. Also, in ND23 flies, both anesthetics activate expression of stress response genes, but to different extents. Here, we investigated the generality of these findings by examining flies mutant for ND2 (ND2 in mammals), which encodes a subunit of the membrane arm of Complex I.

METHODS

The serial anesthesia array was used to expose ND2del1 and ND2360114 flies to precise doses of isoflurane, sevoflurane, and oxygen. Behavioral sensitivity was assessed by a climbing assay and toxicity by percent mortality within 24 h of exposure. Changes in expression were determined by qRT-PCR of RNA isolated from heads at 0.5 h after anesthetic exposure.

RESULTS

Unlike ND2360114, ND2del1 did not affect behavioral sensitivity to isoflurane or sevoflurane. Furthermore, sevoflurane in hyperoxia as well as anoxia caused mortality of ND2del1 but not ND2360114 flies. Finally, the mutations had different effects on induction of stress response gene expression by the anesthetics.

CONCLUSION

Mutations in different arms of Complex I resulted in different behavioral sensitivities and toxicities to isoflurane and sevoflurane, indicating that (i) the anesthetics have mechanisms of action that involve arms of Complex I to different extents and (ii) the lack of behavioral hypersensitivity does not preclude susceptibility to anesthetic toxicity.

Feasibility of Delivering 5-Day Normobaric Hypoxia Breathing in a Hospital Setting

BACKGROUND

Beneficial effects of breathing at [Formula: see text] < 0.21 on disease outcomes have been reported in previous preclinical and clinical studies. However, the safety and intra-hospital feasibility of breathing hypoxic gas for 5 d have not been established. In this study, we examined the physiologic effects of breathing a gas mixture with [Formula: see text] as low as 0.11 in 5 healthy volunteers.

METHODS

All 5 subjects completed the study, spending 5 consecutive days in a hypoxic tent, where the ambient oxygen level was lowered in a stepwise manner over 5 d, from [Formula: see text] of 0.16 on the first day to [Formula: see text] of 0.11 on the fifth day of the study. All the subjects returned to an environment at room air on the sixth day. The subjects' [Formula: see text], heart rate, and breathing frequency were continuously recorded, along with daily blood sampling, neurologic evaluations, transthoracic echocardiography, and mental status assessments.

RESULTS

Breathing hypoxia concentration dependently caused profound physiologic changes, including decreased [Formula: see text] and increased heart rate. At [Formula: see text] of 0.14, the mean [Formula: see text] was 92%; at [Formula: see text] of 0.13, the mean [Formula: see text] was 93%; at [Formula: see text] of 0.12, the mean [Formula: see text] was 88%; at [Formula: see text] of 0.11, the mean [Formula: see text] was 85%; and, finally, at an [Formula: see text] of 0.21, the mean [Formula: see text] was 98%. These changes were accompanied by increased erythropoietin levels and reticulocyte counts in blood. All 5 subjects concluded the study with no adverse events. No subjects exhibited signs of mental status changes or pulmonary hypertension.

CONCLUSIONS

Results of the current physiologic study suggests that, within a hospital setting, delivering [Formula: see text] as low as 0.11 is feasible and safe in healthy subjects, and provides the foundation for future studies in which therapeutic effects of hypoxia breathing are tested.

Hypoxia-mediated rescue of retinal ganglion cells deficient in mitochondrial complex I is independent of the hypoxia-inducible factor pathway

Continuous exposure to environmental hypoxia (11% O2) has been shown to markedly slow the progressive degeneration of retinal ganglion cells (RGCs) in a mouse model of mitochondrial optic neuropathy with RGC-specific deletion of the key mitochondrial complex I accessory subunit ndufs4. As a first step toward identifying the therapeutic mechanism of hypoxia in this model, we conducted a series of experiments to investigate the role of the hypoxia-inducible factor (HIF) regulatory pathway in RGC neuroprotection. Vglut2-Cre; ndufs4loxP/loxP mice were crossed with strains bearing floxed alleles of the negative HIF regulatory vhl or of the two major HIF α-subunit isoforms, Hif1α and Hif2α. Deletion of vhl within ndufs4-deficient RGCs failed to prevent RGC degeneration under normoxia, indicating that HIF activation is not sufficient to achieve RGC rescue. Furthermore, the rescue of ndufs4-deficient RGCs by hypoxia remained robust despite genetic inactivation of Hif1α and Hif2α. Our findings demonstrate that the HIF pathway is entirely dispensable to the rescue of RGCs by hypoxia. Future efforts to uncover key HIF-independent molecular pathways induced by hypoxia in this mouse model may be of therapeutic relevance to mitochondrial optic neuropathies such as Leber hereditary optic neuropathy.

A mechanistic analysis of metformin's biphasic effects on lifespan and healthspan in C. elegans: Elixir in youth, poison in elder

Aging, a complex biological process influenced by genetic, environmental, and pharmacological factors, presents a significant challenge in understanding its underlying mechanisms. In this study, we explored the divergent impacts of metformin treatment on the lifespan and healthspan of young and old C. elegans, demonstrating a intriguing "elixir in youth, poison in elder" phenomenon. By scrutinizing the gene expression changes in response to metformin in young (day 1 of adulthood) and old (days 8) groups, we identified nhr-57 and C46G7.1 as potential modulators of age-specific responses. Notably, nhr-57 and C46G7.1 exhibit contrasting regulation patterns, being up-regulated in young worms but down-regulated in old counterparts following metformin treatment. Functional studies employing knockdown approaches targeting nhr-57, a gene under the control of hif-1 with a documented protective function against pore-forming toxins in C. elegans, and C46G7.1, unveiled their critical roles in modulating lifespan and healthspan, as well as in mediating the biphasic effects of metformin. Furthermore, deletion of hif-1 retarded the influence of metformin, implicating the involvement of hif-1/nhr-57 in age-specific drug responses. These findings underscored the necessity of deciphering the mechanisms governing age-related susceptibility to pharmacological agents to tailor interventions for promoting successful aging.

Ndufs4 inactivation in glutamatergic neurons reveals swallow-breathing discoordination in a mouse model of Leigh Syndrome

Swallowing, both nutritive and non-nutritive, is highly dysfunctional in children with Leigh Syndrome (LS) and contributes to the need for both gastrostomy and tracheostomy tube placement. Without these interventions aspiration of food, liquid, and mucus occur resulting in repeated bouts of respiratory infection. No study has investigated whether mouse models of LS, a neurometabolic disorder, exhibit dysfunctions in neuromuscular activity of swallow and breathing integration. We used a genetic mouse model of LS in which the NDUFS4 gene is knocked out (KO) specifically in Vglut2 or Gad2 neurons. We found increased variability of the swallow motor pattern, disruption in breathing regeneration post swallow, and water-induced apneas only in Vglut2 KO mice. These physiological changes likely contribute to weight loss and premature death seen in this mouse model. Following chronic hypoxia (CH) exposure, swallow motor pattern, breathing regeneration, weight, and life expectancy were not changed in the Vglut2-Ndufs4-KO CH mice compared to control, indicating a rescue of phenotypes. These findings show that like patients with LS, Ndufs4 mouse models of LS exhibit swallow impairments as well as swallow-breathing dyscoordination alongside the other phenotypic traits described in previous studies. Understanding this aspect of LS will open roads for the development of future more efficacious therapeutic intervention for this illness.

Cannabidiol ameliorates mitochondrial disease via PPARγ activation in preclinical models

Mutations in mitochondrial energy-producing genes lead to a heterogeneous group of untreatable disorders known as primary mitochondrial diseases (MD). Leigh syndrome (LS) is the most common pediatric MD and is characterized by progressive neuromuscular affectation and premature death. Here, we show that daily cannabidiol (CBD) administration significantly extends lifespan and ameliorates pathology in two LS mouse models, and improves cellular function in fibroblasts from LS patients. CBD delays motor decline and neurodegenerative signs, improves social deficits and breathing abnormalities, decreases thermally induced seizures, and improves neuropathology in affected brain regions. Mechanistically, we identify peroxisome proliferator-activated receptor gamma (PPARγ) as a key nuclear receptor mediating CBD's beneficial effects, while also providing proof of dysregulated PPARγ expression and activity as a common feature in both mouse neurons and fibroblasts from LS patients. Taken together, our results provide the first evidence for CBD as a potential treatment for LS.

FDX2, an iron-sulfur cluster assembly factor, is essential to prevent cellular senescence, apoptosis or ferroptosis of ovarian cancer cells

Recent studies reveal that biosynthesis of iron-sulfur clusters (Fe-Ss) is essential for cell proliferation, including that of cancer cells. Nonetheless, it remains unclear how Fe-S biosynthesis functions in cell proliferation/survival. Here, we report that proper Fe-S biosynthesis is essential to prevent cellular senescence, apoptosis, or ferroptosis, depending on cell context. To assess these outcomes in cancer, we developed an ovarian cancer line with conditional KO of FDX2, a component of the core Fe-S assembly complex. FDX2 loss induced global downregulation of Fe-S-containing proteins and Fe2+ overload, resulting in DNA damage and p53 pathway activation, and driving the senescence program. p53 deficiency augmented DNA damage responses upon FDX2 loss, resulting in apoptosis rather than senescence. FDX2 loss also sensitized cells to ferroptosis, as evidenced by compromised redox homeostasis of membrane phospholipids. Our results suggest that p53 status and phospholipid homeostatic activity are critical determinants of diverse biological outcomes of Fe-S deficiency in cancer cells.

Magnesium Ion: A New Switch in Tumor Treatment

The magnesium ion is an essential cation in the human body and participates in numerous physiological activities. A deficiency in magnesium ions is closely associated with tumor development, and supplementation with magnesium ions has been shown to partially inhibit tumor growth. However, the specific mechanisms by which magnesium ions suppress tumor proliferation remain unclear. Currently, studies have revealed that mitochondria may serve as a crucial intermediate link in the regulation of tumors by magnesium ions. Mitochondria might intervene in the proliferation and invasion of tumor cells by modulating energy metabolism and oxidative stress levels. Regrettably, there has been no comprehensive review of the role of magnesium in cancer therapy to date. Therefore, this article provides a comprehensive scrutiny of the relationship between magnesium ions and tumors, aiming to offer insights for clinical tumor treatment strategies involving magnesium ion intervention.

The Multifaceted Role of Alpha-Lipoic Acid in Cancer Prevention, Occurrence, and Treatment

Alpha-lipoic acid (ALA) is a naturally occurring compound synthesized by mitochondria and widely distributed in both animal and plant tissues. It primarily influences cellular metabolism and oxidative stress networks through its antioxidant properties and is an important drug for treating metabolic diseases associated with oxidative damage. Nevertheless, research indicates that the mechanism by which ALA affects cancer cells is distinct from that observed in normal cells, exhibiting pro-oxidative properties. Therefore, this review aims to describe the main chemical and biological functions of ALA in the cancer environment, including its mechanisms and effects in tumor prevention and anticancer activity, as well as its role as an adjunctive drug in cancer therapy. We specifically focus on the interactions between ALA and various carcinogenic and anti-carcinogenic pathways and discuss ALA's pro-oxidative capabilities in the unique redox environment of cancer cells. Additionally, we elaborate on ALA's roles in nanomedicine, hypoxia-inducible factors, and cancer stem cell research, proposing hypotheses and potential explanations for currently unresolved issues.

Randomized controlled trial of intermittent hypoxia in Parkinson's disease: study rationale and protocol

BACKGROUND

Parkinson's disease (PD) is a neurodegenerative disease for which no disease-modifying therapies exist. Preclinical and clinical evidence suggest that repeated exposure to intermittent hypoxia might have short- and long-term benefits in PD. In a previous exploratory phase I trial, we demonstrated that in-clinic intermittent hypoxia exposure is safe and feasible with short-term symptomatic effects on PD symptoms. The current study aims to explore the safety, tolerability, feasibility, and net symptomatic effects of a four-week intermittent hypoxia protocol, administered at home, in individuals with PD.

METHODS/DESIGN

This is a two-armed double-blinded randomized controlled trial involving 40 individuals with mild to moderate PD. Participants will receive 45 min of normobaric intermittent hypoxia (fraction of inspired oxygen 0.16 for 5 min interspersed with 5 min normoxia), 3 times a week for 4 weeks. Co-primary endpoints include nature and total number of adverse events, and a feasibility-tolerability questionnaire. Secondary endpoints include Movement Disorders Society-Unified Parkinson's Disease Rating Scale (MDS-UPDRS) part II and III scores, gait tests and biomarkers indicative of hypoxic dose and neuroprotective pathway induction.

DISCUSSION

This trial builds on the previous phase I trial and aims to investigate the safety, tolerability, feasibility, and net symptomatic effects of intermittent hypoxia in individuals with PD. Additionally, the study aims to explore induction of relevant neuroprotective pathways as measured in plasma. The results of this trial could provide further insight into the potential of hypoxia-based therapy as a novel treatment approach for PD.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT05948761 (registered June 20th, 2023).

Exclusion of sulfide:quinone oxidoreductase from mitochondria causes Leigh-like disease in mice by impairing sulfide metabolism

Leigh syndrome is the most common inherited mitochondrial disease in children and is often fatal within the first few years of life. In 2020, mutations in the gene encoding sulfide:quinone oxidoreductase (SQOR), a mitochondrial protein, were identified as a cause of Leigh syndrome. Here, we report that mice with a mutation in the gene encoding SQOR (SqorΔN/ΔN mice), which prevented SQOR from entering mitochondria, had clinical and pathological manifestations of Leigh syndrome. SqorΔN/ΔN mice had increased blood lactate levels that were associated with markedly decreased complex IV activity and increased hydrogen sulfide (H2S) levels. Because H2S is produced by both gut microbiota and host tissue, we tested whether metronidazole (a broad-spectrum antibiotic) or a sulfur-restricted diet rescues SqorΔN/ΔN mice from developing Leigh syndrome. Daily treatment with metronidazole alleviated increased H2S levels, normalized complex IV activity and blood lactate levels, and prolonged the survival of SqorΔN/ΔN mice. Similarly, a sulfur-restricted diet normalized blood lactate levels and inhibited the development of Leigh syndrome. Taken together, these observations suggest that mitochondrial SQOR is essential to prevent systemic accumulation of H2S. Metronidazole administration and a sulfur-restricted diet may be therapeutic approaches to treatment of patients with Leigh syndrome caused by mutations in SQOR.

Sphingosine d18:1 promotes nonalcoholic steatohepatitis by inhibiting macrophage HIF-2α

Non-alcoholic steatohepatitis (NASH) is a severe type of the non-alcoholic fatty liver disease (NAFLD). NASH is a growing global health concern due to its increasing morbidity, lack of well-defined biomarkers and lack of clinically effective treatments. Using metabolomic analysis, the most significantly changed active lipid sphingosine d18:1 [So(d18:1)] is selected from NASH patients. So(d18:1) inhibits macrophage HIF-2α as a direct inhibitor and promotes the inflammatory factors secretion. Male macrophage-specific HIF-2α knockout and overexpression mice verified the protective effect of HIF-2α on NASH progression. Importantly, the HIF-2α stabilizer FG-4592 alleviates liver inflammation and fibrosis in NASH, which indicated that macrophage HIF-2α is a potential drug target for NASH treatment. Overall, this study confirms that So(d18:1) promotes NASH and clarifies that So(d18:1) inhibits the transcriptional activity of HIF-2α in liver macrophages by suppressing the interaction of HIF-2α with ARNT, suggesting that macrophage HIF-2α may be a potential target for the treatment of NASH.

Evaluating the efficacy of vatiquinone in preclinical models of mitochondrial disease

Background

Genetic mitochondrial diseases are a major challenge in modern medicine, impacting around 1:4,000 individuals. Leigh syndrome is the most common pediatric presentation of mitochondrial disease. There are currently no effective clinical treatments for mitochondrial disease. In humans, patients are often treated with antioxidants, vitamins, and strategies targeting energetics. The vitamin-E related compound vatiquinone (EPI-743, α-tocotrienol quinone) has been the subject of at least 19 clinical trials in the US since 2012, but the effects of vatiquinone on an animal model of mitochondrial disease have not yet been reported. Here, assessed the impact of vatiquinone on disease progression and in two animal models of mitochondrial disease.

Methods

The efficacy of vatiquinone in vitro was assessed using human fibroblasts treated with the general mitochondrial oxidative stress inducer paraquat, the GPX4 inhibitor RSL3, or the glutathione synthase inhibitor BSO in combination with excess iron. The therapeutic potential of vatiquinone in vivo was assessed using tamoxifen-induced mouse model for GPX4 deficiency and the Ndufs4 knockout mouse model of Leigh syndrome. In both models, animals were treated daily with vatiquinone or vehicle and relevant disease endpoints were assessed.

Results

Vatiquinone robustly prevented death in cultured cells induced by RSL3 or BSO/iron, but had no effect on paraquat induced cell death. Vatiquinone had no impact on disease onset, progression, or survival in either the tamoxifen-inducible GPX4 deficient model or the Ndufs4(-/-) mouse model, though the drug may have reduced seizure risk.

Conclusions

Vatiquinone provided no benefit to survival in two mouse models of disease, but may prevent seizures in the Ndufs4(-/-) model. Our findings are consistent with recent press statements regarding clinical trial results and have implications for drug trial design and reporting in patients with rare diseases.

CRISPR technologies for genome, epigenome and transcriptome editing

Our ability to edit genomes lags behind our capacity to sequence them, but the growing understanding of CRISPR biology and its application to genome, epigenome and transcriptome engineering is narrowing this gap. In this Review, we discuss recent developments of various CRISPR-based systems that can transiently or permanently modify the genome and the transcriptome. The discovery of further CRISPR enzymes and systems through functional metagenomics has meaningfully broadened the applicability of CRISPR-based editing. Engineered Cas variants offer diverse capabilities such as base editing, prime editing, gene insertion and gene regulation, thereby providing a panoply of tools for the scientific community. We highlight the strengths and weaknesses of current CRISPR tools, considering their efficiency, precision, specificity, reliance on cellular DNA repair mechanisms and their applications in both fundamental biology and therapeutics. Finally, we discuss ongoing clinical trials that illustrate the potential impact of CRISPR systems on human health.

Mitochondria at the crossroads of health and disease

Mitochondria reside at the crossroads of catabolic and anabolic metabolism-the essence of life. How their structure and function are dynamically tuned in response to tissue-specific needs for energy, growth repair, and renewal is being increasingly understood. Mitochondria respond to intrinsic and extrinsic stresses and can alter cell and organismal function by inducing metabolic signaling within cells and to distal cells and tissues. Here, we review how the centrality of mitochondrial functions manifests in health and a broad spectrum of diseases and aging.

Illuminating mitochondrial translation through mouse models

Mitochondria are hubs of metabolic activity with a major role in ATP conversion by oxidative phosphorylation (OXPHOS). The mammalian mitochondrial genome encodes 11 mRNAs encoding 13 OXPHOS proteins along with 2 rRNAs and 22 tRNAs, that facilitate their translation on mitoribosomes. Maintaining the internal production of core OXPHOS subunits requires modulation of the mitochondrial capacity to match the cellular requirements and correct insertion of particularly hydrophobic proteins into the inner mitochondrial membrane. The mitochondrial translation system is essential for energy production and defects result in severe, phenotypically diverse diseases, including mitochondrial diseases that typically affect postmitotic tissues with high metabolic demands. Understanding the complex mechanisms that underlie the pathologies of diseases involving impaired mitochondrial translation is key to tailoring specific treatments and effectively targeting the affected organs. Disease mutations have provided a fundamental, yet limited, understanding of mitochondrial protein synthesis, since effective modification of the mitochondrial genome has proven challenging. However, advances in next generation sequencing, cryoelectron microscopy, and multi-omic technologies have revealed unexpected and unusual features of the mitochondrial protein synthesis machinery in the last decade. Genome editing tools have generated unique models that have accelerated our mechanistic understanding of mitochondrial translation and its physiological importance. Here we review the most recent mouse models of disease pathogenesis caused by defects in mitochondrial protein synthesis and discuss their value for preclinical research and therapeutic development.

Impact of dietary ketosis on volatile anesthesia toxicity in a model of Leigh syndrome

BACKGROUND

Genetic mitochondrial diseases impact over 1 in 4000 individuals, most often presenting in infancy or early childhood. Seizures are major clinical sequelae in some mitochondrial diseases including Leigh syndrome, the most common pediatric presentation of mitochondrial disease. Dietary ketosis has been used to manage seizures in mitochondrial disease patients. Mitochondrial disease patients often require surgical interventions, leading to anesthetic exposures. Anesthetics have been shown to be toxic in the setting of mitochondrial disease, but the impact of a ketogenic diet on anesthetic toxicities in this setting has not been studied.

AIMS

Our aim in this study was to determine whether dietary ketosis impacts volatile anesthetic toxicities in the setting of genetic mitochondrial disease.

METHODS

The impact of dietary ketosis on toxicities of volatile anesthetic exposure in mitochondrial disease was studied by exposing young Ndufs4(-/-) mice fed ketogenic or control diet to isoflurane anesthesia. Blood metabolites were measured before and at the end of exposures, and survival and weight were monitored.

RESULTS

Compared to a regular diet, the ketogenic diet exacerbated hyperlactatemia resulting from isoflurane exposure (control vs. ketogenic diet in anesthesia mean difference 1.96 mM, Tukey's multiple comparison adjusted p = .0271) and was associated with a significant increase in mortality during and immediately after exposures (27% vs. 87.5% mortality in the control and ketogenic diet groups, respectively, during the exposure period, Fisher's exact test p = .0121). Our data indicate that dietary ketosis and volatile anesthesia interact negatively in the setting of mitochondrial disease.

CONCLUSIONS

Our findings suggest that extra caution should be taken in the anesthetic management of mitochondrial disease patients in dietary ketosis.

Oxygen enhances antiviral innate immunity through maintenance of EGLN1-catalyzed proline hydroxylation of IRF3

Oxygen is essential for aerobic organisms, but little is known about its role in antiviral immunity. Here, we report that during responses to viral infection, hypoxic conditions repress antiviral-responsive genes independently of HIF signaling. EGLN1 is identified as a key mediator of the oxygen enhancement of antiviral innate immune responses. Under sufficient oxygen conditions, EGLN1 retains its prolyl hydroxylase activity to catalyze the hydroxylation of IRF3 at proline 10. This modification enhances IRF3 phosphorylation, dimerization and nuclear translocation, leading to subsequent IRF3 activation. Furthermore, mice and zebrafish with Egln1 deletion, treatment with the EGLN inhibitor FG4592, or mice carrying an Irf3 P10A mutation are more susceptible to viral infections. These findings not only reveal a direct link between oxygen and antiviral responses, but also provide insight into the mechanisms by which oxygen regulates innate immunity.

Mitochondrial dysfunction induced by HIF-1α under hypoxia contributes to the development of gastric mucosal lesions

INTRODUCTION

Hypoxia is an important characteristic of gastric mucosal diseases, and hypoxia-inducible factor-1α (HIF-1α) contributes to microenvironment disturbance and metabolic spectrum abnormalities. However, the underlying mechanism of HIF-1α and its association with mitochondrial dysfunction in gastric mucosal lesions under hypoxia have not been fully clarified.

OBJECTIVES

To evaluate the effects of hypoxia-induced HIF-1α on the development of gastric mucosal lesions.

METHODS

Portal hypertensive gastropathy (PHG) and gastric cancer (GC) were selected as representative diseases of benign and malignant gastric lesions, respectively. Gastric tissues from patients diagnosed with the above diseases were collected. Portal hypertension (PHT)-induced mouse models in METTL3 mutant or NLRP3-deficient littermates were established, and nude mouse gastric graft tumour models with relevant inhibitors were generated. The mechanisms underlying hypoxic condition, mitochondrial dysfunction and metabolic alterations in gastric mucosal lesions were further analysed.

RESULTS

HIF-1α, which can mediate mitochondrial dysfunction via upregulation of METTL3/IGF2BP3-dependent dynamin-related protein 1 (Drp1) N6-methyladenosine modification to increase mitochondrial reactive oxygen species (mtROS) production, was elevated under hypoxic conditions in human and mouse portal hypertensive gastric mucosa and GC tissues. While blocking HIF-1α with PX-478, inhibiting Drp1-dependent mitochondrial fission via mitochondrial division inhibitor 1 (Mdivi-1) treatment or METTL3 mutation alleviated this process. Furthermore, HIF-1α influenced energy metabolism by enhancing glycolysis via lactate dehydrogenase A. In addition, HIF-1α-induced Drp1-dependent mitochondrial fission also enhanced glycolysis. Drp1-dependent mitochondrial fission and enhanced glycolysis were associated with alterations in antioxidant enzyme activity and dysfunction of the mitochondrial electron transport chain, resulting in massive mtROS production, which was needed for activation of NLRP3 inflammasome to aggravate the development of the PHG and GC.

CONCLUSIONS

Under hypoxic conditions, HIF-1α enhances mitochondrial dysfunction via Drp1-dependent mitochondrial fission and influences the metabolic profile by altering glycolysis to increase mtROS production, which can trigger NLRP3 inflammasome activation and mucosal microenvironment alterations to contribute to the development of benign and malignant gastric mucosal lesions.

The Hypoxia Response Pathway: A Potential Intervention Target in Parkinson's Disease?

Parkinson's disease (PD) is a progressive neurodegenerative disorder for which only symptomatic treatments are available. Both preclinical and clinical studies suggest that moderate hypoxia induces evolutionarily conserved adaptive mechanisms that enhance neuronal viability and survival. Therefore, targeting the hypoxia response pathway might provide neuroprotection by ameliorating the deleterious effects of mitochondrial dysfunction and oxidative stress, which underlie neurodegeneration in PD. Here, we review experimental studies regarding the link between PD pathophysiology and neurophysiological adaptations to hypoxia. We highlight the mechanistic differences between the rescuing effects of chronic hypoxia in neurodegeneration and short-term moderate hypoxia to improve neuronal resilience, termed "hypoxic conditioning". Moreover, we interpret these preclinical observations regarding the pharmacological targeting of the hypoxia response pathway. Finally, we discuss controversies with respect to the differential effects of hypoxia response pathway activation across the PD spectrum, as well as intervention dosing in hypoxic conditioning and potential harmful effects of such interventions. We recommend that initial clinical studies in PD should focus on the safety, physiological responses, and mechanisms of hypoxic conditioning, as well as on repurposing of existing pharmacological compounds. © 2023 International Parkinson and Movement Disorder Society.

Hypoxia and intra-complex genetic suppressors rescue complex I mutants by a shared mechanism

The electron transport chain (ETC) of mitochondria, bacteria, and archaea couples electron flow to proton pumping and is adapted to diverse oxygen environments. Remarkably, in mice, neurological disease due to ETC complex I dysfunction is rescued by hypoxia through unknown mechanisms. Here, we show that hypoxia rescue and hyperoxia sensitivity of complex I deficiency are evolutionarily conserved to C. elegans and are specific to mutants that compromise the electron-conducting matrix arm. We show that hypoxia rescue does not involve the hypoxia-inducible factor pathway or attenuation of reactive oxygen species. To discover the mechanism, we use C. elegans genetic screens to identify suppressor mutations in the complex I accessory subunit NDUFA6/nuo-3 that phenocopy hypoxia rescue. We show that NDUFA6/nuo-3(G60D) or hypoxia directly restores complex I forward activity, with downstream rescue of ETC flux and, in some cases, complex I levels. Additional screens identify residues within the ubiquinone binding pocket as being required for the rescue by NDUFA6/nuo-3(G60D) or hypoxia. This reveals oxygen-sensitive coupling between an accessory subunit and the quinone binding pocket of complex I that can restore forward activity in the same manner as hypoxia.

Free-moving-state microscopic imaging of cerebral oxygenation and hemodynamics with a photoacoustic fiberscope

We report the development of a head-mounted photoacoustic fiberscope for cerebral imaging in a freely behaving mouse. The 4.5-gram imaging probe has a 9-µm lateral resolution and 0.2-Hz frame rate over a 1.2-mm wide area. The probe can continuously monitor cerebral oxygenation and hemodynamic responses at single-vessel resolution, showing significantly different cerebrovascular responses to external stimuli under anesthesia and in the freely moving state. For example, when subjected to high-concentration CO2 respiration, enhanced oxygenation to compensate for hypercapnia can be visualized due to cerebral regulation in the freely moving state. Comparative studies exhibit significantly weakened compensation capabilities in obese rodents. This new imaging modality can be used for investigating both normal and pathological cerebrovascular functions and shows great promise for studying cerebral activity, disorders and their treatments.

Structural insights into respiratory complex I deficiency and assembly from the mitochondrial disease-related ndufs4-/- mouse

Respiratory complex I (NADH:ubiquinone oxidoreductase) is essential for cellular energy production and NAD+ homeostasis. Complex I mutations cause neuromuscular, mitochondrial diseases, such as Leigh Syndrome, but their molecular-level consequences remain poorly understood. Here, we use a popular complex I-linked mitochondrial disease model, the ndufs4-/- mouse, to define the structural, biochemical, and functional consequences of the absence of subunit NDUFS4. Cryo-EM analyses of the complex I from ndufs4-/- mouse hearts revealed a loose association of the NADH-dehydrogenase module, and discrete classes containing either assembly factor NDUFAF2 or subunit NDUFS6. Subunit NDUFA12, which replaces its paralogue NDUFAF2 in mature complex I, is absent from all classes, compounding the deletion of NDUFS4 and preventing maturation of an NDUFS4-free enzyme. We propose that NDUFAF2 recruits the NADH-dehydrogenase module during assembly of the complex. Taken together, the findings provide new molecular-level understanding of the ndufs4-/- mouse model and complex I-linked mitochondrial disease.

Unveiling the hypoxia-induced mitophagy process through two-channel real-time imaging of NTR and viscosity under the same excitation

Mitophagy is an essential physiological process that eliminates damaged mitochondria via lysosomes. It is reported that hypoxia, inflammatory stimuli or other stress conditions could lead to mitochondrial damage and mitochondrial dysfunction, which induces the process of mitophagy. Herein, we report a novel fluorescent probe PC-NTR for imaging hypoxia-induced mitophagy by monitoring the change of nitroreductase and viscosity simultaneously. To our delight, PC-NTR could respond simultaneously to nitroreductase and viscosity at different fluorescence channels with no mutual interference under the same excitation wavelength. The fluorescence emission around 535 nm was enhanced dramatically after addition of nitroreductase while the fluorescence emission around 635 nm heightened as the viscosity increased. The probe would be able to selectively targeting of mitochondria in cells because of the positively charged pyridine salt structure of PC-NTR. The probe was successfully applied to assess the different levels of hypoxia and real-time imaging of mitochondrial autophagy in live cells. More importantly, using dual channel imaging, PC-NTR could be used to distinguish cancer cells from normal cells and was successfully applied to imaging experiments in HeLa-derived tumor-bearing nude mice. Therefore, PC-NTR would be an important molecular tool for hypoxia imaging and detecting solid tumors in vivo.