Mitochondrial generation of superoxide and hydrogen peroxide as the source of mitochondrial redox signaling

Ferroptosis: iron release mechanisms in the bioenergetic process

Ferroptosis, an iron-dependent form of cell death, has been the focus of extensive research over the past decade, leading to the elucidation of key molecules and mechanisms involved in this process. While several studies have highlighted iron sources for the Fenton reaction, the predominant mechanism for iron release in ferroptosis has been identified as ferritinophagy, which occurs in response to iron starvation. However, much of the existing literature has concentrated on lipid peroxidation rather than on the mechanisms of iron release. This review proposes three distinct mechanisms of iron mobilization: ferritinophagy, reductive pathways with selective gating of ferritin pores, and quinone-mediated iron mobilization. Notably, the latter two mechanisms operate independently of iron starvation and rely primarily on reductants such as NADH and O2•-. The inhibition of the respiratory chain, particularly under the activation of α-ketoglutarate dehydrogenase, leads to the accumulation of these reductants, which in turn promotes iron release from ferritin and indirectly inhibits AMP-activated protein kinase through excessive iron levels. In this work, we delineate the intricate relationship between iron mobilization and bioenergetic processes under conditions of oxidative stress. Furthermore, this review aims to enhance the understanding of the connections between ferroptosis and these mechanisms.

Mitochondrial Dysfunction in Diabetes: Shedding Light on a Widespread Oversight

Diabetes mellitus represents a complicated metabolic condition marked by ongoing hyperglycemia arising from impaired insulin secretion, inadequate insulin action, or a combination of both. Mitochondrial dysfunction has emerged as a significant contributor to the aetiology of diabetes, affecting various metabolic processes critical for glucose homeostasis. This review aims to elucidate the complex link between mitochondrial dysfunction and diabetes, covering the spectrum of diabetes types, the role of mitochondria in insulin resistance, highlighting pathophysiological mechanisms, mitochondrial DNA damage, and altered mitochondrial biogenesis and dynamics. Additionally, it discusses the clinical implications and complications of mitochondrial dysfunction in diabetes and its complications, diagnostic approaches for assessing mitochondrial function in diabetics, therapeutic strategies, future directions, and research opportunities.

Mitochondrial potassium channels: New properties and functions

Mitochondria are recently implicated in phenomena such as cytoprotection, cellular senescence, tumor metabolism, and inflammation. The basis of these processes relies on biochemical functions of mitochondria such as the synthesis of reactive oxygen species or biophysical properties such as the integrity of the inner mitochondrial membrane. The transport of potassium cations plays an important role in all these events. The K+ influx is mediated by potassium channels present in the inner mitochondrial membrane. In this article, we present an overview of our new findings on the properties of mitochondrial large-conductance calcium-activated and mitochondrial ATP-regulated potassium channels. This concerns the role of mitochondrial potassium channels in cellular senescence, and interactions with other mitochondrial proteins or small molecules such as quercetin, hemin, and hydrogen sulfide. We also discuss the prospects of research on potassium channels present in mitochondria.

The mitochondrial DNAJC co-chaperone TCAIM reduces α-ketoglutarate dehydrogenase protein levels to regulate metabolism

Mitochondrial heat shock proteins and co-chaperones play crucial roles in maintaining proteostasis by regulating unfolded proteins, usually without specific target preferences. In this study, we identify a DNAJC-type co-chaperone: T cell activation inhibitor, mitochondria (TCAIM), and demonstrate its specific binding to α-ketoglutarate dehydrogenase (OGDH), a key rate-limiting enzyme in mitochondrial metabolism. This interaction suppresses OGDH function and subsequently reduces carbohydrate catabolism in both cultured cells and murine models. Using cryoelectron microscopy (cryo-EM), we resolve the human OGDH-TCAIM complex and reveal that TCAIM binds to OGDH without altering its apo structure. Most importantly, we discover that TCAIM facilitates the reduction of functional OGDH through its interaction, which depends on HSPA9 and LONP1. Our findings unveil a role of the mitochondrial proteostasis system in regulating a critical metabolic enzyme and introduce a previously unrecognized post-translational regulatory mechanism.

Insights into the Sources, Structure, and Action Mechanisms of Quinones on Diabetes: A Review

Quinones, one of the oldest organic compounds, are of increasing interest due to their abundant presence in a wide range of natural sources and their remarkable biological activity. These compounds occur naturally in green leafy vegetables, fruits, herbs, animal and marine sources, and fermented products, and have demonstrated promising potential for use in health interventions, particularly in the prevention and management of type 2 diabetes (T2DM). This review aims to investigate the potential of quinones as a health intervention for T2DM from the multidimensional perspective of their sources, types, structure-activity relationship, glucose-lowering mechanism, toxicity reduction, and bioavailability enhancement. Emerging research highlights the hypoglycemic activities of quinones, mainly driven by their redox properties, which lead to covalent binding, and their structural substituent specificity, which leads to their non-covalent binding to biocomplexes. Quinones can improve insulin resistance and regulate glucose homeostasis by modulating mitochondrial function, inflammation, lipid profile, gastrointestinal absorption, and by acting as insulin mimetics. Meanwhile, increasing attention is being given to research focused on mitigating the toxicity of quinones during administration and enhancing their bioavailability. This review offers a critical foundation for the development of quinone-based health therapies and functional foods aimed at diabetes management.

Mitochondrial ROS modulate presynaptic plasticity in the drosophila neuromuscular junction

The elevated emission of reactive oxygen species (ROS) from presynaptic mitochondria is well-documented in several inflammatory and neurodegenerative diseases. However, the potential role of mitochondrial ROS in presynaptic function and plasticity remains largely understudied beyond the context of disease. Here, we investigated this potential ROS role in presynaptic function and short-term plasticity by combining optogenetics, whole cell electrophysiological recordings, and live confocal imaging using a well-established protocol for induction and measurement of synaptic potentiation in Drosophila melanogaster neuromuscular junctions (NMJ). Optogenetic induction of ROS emission from presynaptic motorneuron mitochondria expressing mitokiller red (mK) resulted in synaptic potentiation, evidenced by an increase in the frequency of spontaneous mini excitatory junction potentials. Notably, this effect was not observed in flies co-expressing catalase, a cytosolic hydrogen peroxide (H2O2) scavenging enzyme. Moreover, the increase in electrical activity did not coincide with synaptic structural changes. The absence of Wnt1/Wg release from synaptic boutons suggested involvement of alternative or non-canonical signaling pathway(s). However, in existing boutons we observed an increase in the active zone (AZ) marker Brp/Erc1, which serves as docking site for the neurotransmitter vesicle release pool. We propose the involvement of putative redox switches in AZ components as the molecular target of mitochondrial H2O2. These findings establish a novel framework for understanding the signaling role of mROS in presynaptic structural and functional plasticity, providing insights into redox-based mechanisms of neuronal communication.

The mitochondrial membrane potential and the sources of reactive oxygen species in the hemocytes of the ark clam Anadara kagoshimensis under hypoosmotic stress

To compensate for changes in cell volume caused by changes in salt concentration, mollusks use regulatory mechanisms such as the regulation of volume decrease (RVD). This may increase the rate of aerobic metabolism and lead to an increase in reactive oxygen species (ROS). This study examined the production of ROS in the mitochondria of Anadara kagoshiensis hemocytes, the effect of mitochondrial inhibitors on osmotic stability in hemocytes, and the dynamics of changes in ROS levels and mitochondrial membrane potential when RVD is activated under hypo-osmotic conditions. Hemocytes maintained at a control osmolarity of 460 mOsm l-1 showed significant decreases in ROS production following incubation with complex III inhibitors (S3QEL). Hypoosmotic shock stimulated RVD in all experimental groups. The cell volume increased by about 70 % immediately after osmolarity was reduced, and then decreased by about 40 % over the next 30 min. A reduction in osmolarity from about 460 to 200 mOsm l-1 significantly decreased ROS and mitochondrial potentials in A. kashimensis hemocyctes. Inhibitors of mitochondrial complexes did not affect changes in ROS or mitochondria potentials in A kashimiensis hemocytes under hypoosmotic conditions or in hemocyte volume regulation mechanisms.

Mitochondria-targeted antioxidant MitoQ improves the quality of low temperature-preserved yak semen via alleviating oxidative stress

Low-temperature preservation of yak semen during transportation and conservation is crucial to accelerate yak breeding. The effects of low-temperature cooling on yak semen quality, however, are poorly understood. This study aimed to determine the dose-dependent effect of mitochondria-targeted antioxidant "MitoQ" on the motility, oxidative status, and mitochondrial function of yak semen during low-temperature preservation. Semen samples were collected from six adult healthy Maiwa yaks and preserved at 4 ℃ in semen extender containing 0, 50, 100, 200, and 400 nM MitoQ, respectively. Firstly, the motility, membrane integrity, acrosome integrity, and abnormity index of yak spermatozoa were evaluated to determine the optimal MitoQ concentration. Next, the effect of MitoQ at the optimal concentration on spermatozoa antioxidant capacity, including reactive oxygen species (ROS) and malondialdehyde (MDA) contents, total antioxidant capacity (T-AOC), and superoxide dismutase content (SOD) levels, as well as mitochondrial membrane potential were analyzed. Up to 96 h of low-temperature storage, 200 nM MitoQ showed the most optimal effect on motility, membrane integrity, and acrosome integrity (P < 0.05) but not on sperm morphology (P > 0.05). Also, 200 nM MitoQ markedly reduced yak spermatozoa ROS and MDA contents for up to 48 h of low-temperature storage (P < 0.05). Finally, 200 nM MitoQ significantly improved T-AOC, SOD, and mitochondrial membrane potential for up to 24, 48, and 72 h of low-temperature storage, respectively (P < 0.05). In summary, semen extender supplementation with 200 nM MitoQ is beneficial for low-temperature yak semen preservation via improving the oxidative status.

A comprehensive review of peroxiredoxin 4, a redox protein evolved in oxidative protein folding coupled with hydrogen peroxide detoxification

Peroxiredoxin (PRDX) primarily employs electrons from thioredoxin in order to reduce peroxides. PRDX4 mainly resides either in the endoplasmic reticulum (ER) lumen or in extracellular spaces. Due to the usage of alternative promoters, a first exon is transcribed from different regions of the Prdx4 gene, which results in two types of mRNAs. The first type is designated as Prdx4. It is translated with a cleavable, hydrophobic signal sequence and is expressed in most cells throughout the body. The second type is designated as Prdx4t. The peroxidase activity of PRDX4 is involved in both the reduction of hydrogen peroxides and in the oxidative folding of nascent proteins in the ER. Prdx4 appears to have evolved from an ancestral gene in Eutherians simultaneously with the evolution of sperm protamine to cysteine-rich peptides, and, therefore, the testis-specific PRDX4t is likely involved in spermatogenesis through the oxidative folding of protamine. The dysfunction of PRDX4 leads to oxidative damage and ER stress, and is related to various diseases including diabetes and cancer. In this review article we refer to the results of biological and medical research in order to unveil the functional consequences of this unique member of the PRDX family.

Exploring the Molecular Interplay Between Oxygen Transport, Cellular Oxygen Sensing, and Mitochondrial Respiration

Significance: The mitochondria play a key role in maintaining oxygen homeostasis under normal oxygen tension (normoxia) and during oxygen deprivation (hypoxia). This is a critical balancing act between the oxygen content of the blood, the tissue oxygen sensing mechanisms, and the mitochondria, which ultimately consume most oxygen for energy production. Recent Advances: We describe the well-defined role of the mitochondria in oxygen metabolism with a special focus on the impact on blood physiology and pathophysiology. Critical Issues: Fundamental questions remain regarding the impact of mitochondrial responses to changes in overall blood oxygen content under normoxic and hypoxic states and in the case of impaired oxygen sensing in various cardiovascular and pulmonary complications including blood disorders involving hemolysis and hemoglobin toxicity, ischemia reperfusion, and even in COVID-19 disease. Future Directions: Understanding the nature of the crosstalk among normal homeostatic pathways, oxygen carrying by hemoglobin, utilization of oxygen by the mitochondrial respiratory chain machinery, and oxygen sensing by hypoxia-inducible factor proteins, may provide a target for future therapeutic interventions. Antioxid. Redox Signal. 00, 000-000.

Physiological Fatty Acid-Stimulated Insulin Secretion and Redox Signaling Versus Lipotoxicity

Significance: Type 2 diabetes as a world-wide epidemic is characterized by the insulin resistance concomitant to a gradual impairment of β-cell mass and function (prominently declining insulin secretion) with dysregulated fatty acids (FAs) and lipids, all involved in multiple pathological development. Recent Advances: Recently, redox signaling was recognized to be essential for insulin secretion stimulated with glucose (GSIS), branched-chain keto-acids, and FAs. FA-stimulated insulin secretion (FASIS) is a normal physiological event upon postprandial incoming chylomicrons. This contrasts with the frequent lipotoxicity observed in rodents. Critical Issues: Overfeeding causes FASIS to overlap with GSIS providing repeating hyperinsulinemia, initiates prediabetic states by lipotoxic effects and low-grade inflammation. In contrast the protective effects of lipid droplets in human β-cells counteract excessive lipids. Insulin by FASIS allows FATP1 recruitment into adipocyte plasma membranes when postprandial chylomicrons come late at already low glycemia. Future Directions: Impaired states of pancreatic β-cells and peripheral organs at prediabetes and type 2 diabetes should be revealed, including the inter-organ crosstalk by extracellular vesicles. Details of FA/lipid molecular physiology are yet to be uncovered, such as complex phenomena of FA uptake into cells, postabsorptive inactivity of G-protein-coupled receptor 40, carnitine carrier substrate specificity, the role of carnitine-O-acetyltransferase in β-cells, and lipid droplet interactions with mitochondria. Antioxid. Redox Signal. 00, 000-000.

Bioluminescent Probes for the Detection of Superoxide and Nitric Oxide

The regulation of reactive oxygen species (ROS) such as superoxide (SO) and nitric oxide (NO) is crucial in biology, influencing metabolism and signaling pathways. Imbalances in these species lead to oxidative stress and various diseases. Traditional methods for measuring SO and NO face challenges in terms of sensitivity and specificity, particularly in complex biological matrices. This report introduces bioluminescent probes that leverage the intrinsic sensitivity of bioluminescence for direct and selective detection of SO and NO. These probes release analogs of d-luciferin upon reaction with their target ROS. Following addition of luciferase, luminescence is generated proportional to the amount of accumulated luciferin, allowing for quantitation of SO or NO. Both probes exhibit high specificity, confirmed through cell-free assays and cell-based studies in macrophages, demonstrating their utility in measuring cellular SO and NO production. These assays offer a robust, high-throughput platform for studying ROS, providing direct insights into oxidative stress-related mechanisms.

A review of the pathogenesis of mitochondria in breast cancer and progress of targeting mitochondria for breast cancer treatment

With breast cancer being the most common tumor among women in the world today, it is also the leading cause of cancer-related deaths. Standard treatments include chemotherapy, surgery, endocrine therapy, and targeted therapy. However, the heterogeneity, drug resistance, and poor prognosis of breast cancer highlight an urgent need for further exploration of its underlying mechanisms. Mitochondria, highly dynamic intracellular organelles, play a pivotal role in maintaining cellular energy metabolism. Altered mitochondrial function plays a critical role in various diseases, and recent studies have elucidated its pathophysiological mechanisms in breast carcinogenesis. This review explores the role of mitochondrial dysfunction in breast cancer pathogenesis and assesses potential mitochondria-targeted therapies.

Cardiolipin deficiency disrupts CoQ-complex III interface in steatohepatitis

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a progressive disorder marked by lipid accumulation, leading to steatohepatitis (MASH). A key feature of the transition to MASH involves oxidative stress resulting from defects in mitochondrial oxidative phosphorylation (OXPHOS). Here, we show that pathological alterations in the lipid composition of the inner mitochondrial membrane (IMM) directly instigate electron transfer inefficiency to promote oxidative stress. Specifically, mitochondrial cardiolipin (CL) was downregulated with MASLD/MASH in mice and in humans. Hepatocyte-specific CL synthase knockout (CLS-LKO) led to spontaneous and robust MASH with extensive steatotic and fibrotic phenotype. Loss of CL paradoxically increased mitochondrial respiratory capacity but also reduced the formation of I+III2+IV1 respiratory supercomplex and interfered with the ability of coenzyme Q (CoQ) to transfer electrons to complex III. In turn, the bottleneck at complex III promoted electron leak primarily at site IIIQ0 as well as other upstream sites in the electron transport chain. Thus, reduction in mitochondrial CL promotes oxidative stress and contributes to pathogenesis of MASH.

Mutations of the Electron Transport Chain Affect Lifespan and ROS Levels in C. elegans

Mutations in highly conserved genes encoding components of the electron transport chain (ETC) provide valuable insights into the mechanisms of oxidative stress and mitochondrial ROS (mtROS) in a wide range of diseases, including cancer, neurodegenerative disorders, and aging. This review explores the structure and function of the ETC in the context of its role in mtROS generation and regulation, emphasizing its dual roles in cellular damage and signaling. Using Caenorhabditis elegans as a model organism, we discuss how ETC mutations manifest as developmental abnormalities, lifespan alterations, and changes in mtROS levels. We highlight the utility of redox sensors in C. elegans for in vivo studies of reactive oxygen species, offering both quantitative and qualitative insights. Finally, we examine the potential of C. elegans as a platform for testing ETC-targeting drug candidates, including OXPHOS inhibitors, which represent promising avenues in cancer therapeutics. This review underscores the translational relevance of ETC research in C. elegans, bridging fundamental biology and therapeutic innovation.

Taurine prevents mitochondrial dysfunction and protects mitochondria from reactive oxygen species and deuterium toxicity

Taurine, although not a coding amino acid, is the most common free amino acid in the body. Taurine has multiple and complex functions in protecting mitochondria against oxidative-nitrosative stress. In this comprehensive review paper, we introduce a novel potential role for taurine in protecting from deuterium (heavy hydrogen) toxicity. This can be of crucial impact to either normal or cancer cells that have highly different mitochondrial redox status. Deuterium is an isotope of hydrogen with a neutron as well as a proton, making it about twice as heavy as hydrogen. We first explain the important role that the gut microbiome and the gut sulfomucin barrier play in deuterium management. We describe the synergistic effects of taurine in the gut to protect against the deleterious accumulation of deuterium in the mitochondria, which disrupts ATP synthesis by ATPase pumps. Moreover, taurine's derivatives, N-chlorotaurine (NCT) and N-bromotaurine (NBrT), produced through spontaneous reaction of taurine with hypochlorite and hypobromite, have fascinating regulatory roles to protect from oxidative stress and beyond. We describe how taurine could potentially alleviate deuterium stress, primarily through metabolic collaboration among various gut microflora to produce deuterium depleted nutrients and deuterium depleted water, and in this way protect against leaky gut barrier, inflammatory bowel disease, and colon cancer.

ANAC044 orchestrates mitochondrial stress signaling to trigger iron-induced stem cell death in root meristems

While iron (Fe) is essential for life and plays important roles for almost all growth related processes, it can trigger cell death in both animals and plants. However, the underlying mechanisms for Fe-induced cell death in plants remain largely unknown. S-nitrosoglutathione reductase (GSNOR) has previously been reported to regulate nitric oxide homeostasis to prevent Fe-induced cell death within root meristems. Here, we found that in the absence of GSNOR, exposure to high Fe treatment results in DNA damage-dependent cell death specifically in vascular stem cells in root meristems within 48 h. Through a series of time-course transcriptomic analyses, we unveil that in the absence of GSNOR, mitochondrial dysfunction emerges as the most prominent response to high Fe treatment. Consistently, the application of mitochondrial respiratory inhibitors leads to stem cell death in root meristems, and pharmacological blockage of the voltage-dependent anion channel that is responsible for the release of mitochondrial-derived molecules into the cytosol or genetic changes that abolish the ANAC017- and ANAC013-mediated mitochondrial retrograde signaling effectively eliminate Fe-induced stem cell death in gsnor root meristems. We further identify the nuclear transcription factor ANAC044 as a mediator of this mitochondrial retrograde signaling. Disruption of ANAC044 completely abolishes the GSNOR-dependent, Fe-induced stem cell death in root meristems, while ectopic expression of ANAC044 causes severe root stem cell death. Collectively, our findings reveal a mechanism responsible for initiating Fe-induced stem cell death in the root meristem, which is the ANAC044-mediated GSNOR-regulated mitochondrial stress signaling pathway.

Abnormalities in mitochondrial energy metabolism induced by cryopreservation negatively affect goat sperm motility

The motility of sperm decreases following cryopreservation, which is closely associated with mitochondrial function. However, the alterations in mitochondrial metabolism after sperm freezing in goats remain unclear. This experiment aimed to investigate the impact of ultra-low temperature freezing on goat sperm's mitochondrial energy metabolism and its potential correlation with sperm motility. The results revealed that goat sperm exhibited mitochondrial vacuolization, reduced matrix density, and significantly decreased levels of high-membrane potential mitochondria and adenosine triphosphate content, accompanied by a substantial increase in reactive oxygen species levels, ultimately leading to a significant decline in sperm viability. Further investigations unveiled that energy-related differential metabolites (capric acid, creatine, and D-glucosamine-6-phosphate) and differential metabolites with antioxidant effects (saikosaponin A, probucol, and cholesterol sulfate) were significantly downregulated. In addition, the activity of key rate-limiting enzymes involved in very long-chain fatty acid biosynthesis and β-oxidation-specifically acetyl-CoA carboxylase, fatty acid synthase, and carnitine palmitoyltransferase I related to capric acid metabolism-was considerably reduced. Furthermore, supplementation of differential metabolite capric acid (500 μM) significantly enhanced the motility of frozen-thawed goat sperm. These findings indicated that the mitochondrial ultrastructure of goat sperm is damaged and energy metabolism becomes abnormal after cryopreservation, potentially affecting sperm viability. The addition of different metabolites such as capric acid to the freezing extender can alleviate the decrease in sperm motility induced by cryopreservation.

Misprogramming of glucose metabolism impairs recovery of hippocampal slices from neuronal GLT-1 knockout mice and contributes to excitotoxic injury through mitochondrial superoxide production

We have previously reported a failure of recovery of synaptic function in the CA1 region of acute hippocampal slices from mice with a conditional neuronal knockout (KO) of GLT-1 (EAAT2, Slc1A2) driven by synapsin-Cre (synGLT-1 KO). The failure of recovery of synaptic function is due to excitotoxic injury. We hypothesized that changes in mitochondrial metabolism contribute to the heightened vulnerability to excitotoxicity in the synGLT-1 KO mice. We found impaired flux of carbon from 13C-glucose into the tricarboxylic acid cycle in synGLT-1 KO cortical and hippocampal slices compared with wild-type (WT) slices. In addition, we found downregulation of the neuronal glucose transporter GLUT3 in both genotypes. Flux of carbon from [1,2-13C]acetate, thought to be astrocyte-specific, was increased in the synGLT-KO hippocampal slices but not cortical slices. Glycogen stores, predominantly localized to astrocytes, are rapidly depleted in slices after cutting, and are replenished during ex vivo incubation. In the synGLT-1 KO, replenishment of glycogen stores during ex vivo incubation was compromised. These results suggest both neuronal and astrocytic metabolic perturbations in the synGLT-1 KO slices. Supplementing incubation medium during recovery with 20 mM D-glucose normalized glycogen replenishment but had no effect on recovery of synaptic function. In contrast, 20 mM non-metabolizable L-glucose substantially improved recovery of synaptic function, suggesting that D-glucose metabolism contributes to the excitotoxic injury in the synGLT-1 KO slices. L-lactate substitution for D-glucose did not promote recovery of synaptic function, implicating mitochondrial metabolism. Consistent with this hypothesis, phosphorylation of pyruvate dehydrogenase, which decreases enzyme activity, was increased in WT slices during the recovery period, but not in synGLT-1 KO slices. Since metabolism of glucose by the mitochondrial electron transport chain is associated with superoxide production, we tested the effect of drugs that scavenge and prevent superoxide production. The superoxide dismutase/catalase mimic EUK-134 conferred complete protection and full recovery of synaptic function. A site-specific inhibitor of complex III superoxide production, S3QEL-2, was also protective, but inhibitors of NADPH oxidase were not. In summary, we find that the failure of recovery of synaptic function in hippocampal slices from the synGLT-1 KO mouse, previously shown to be due to excitotoxic injury, is caused by production of superoxide by mitochondrial metabolism.

Mitochondrial mechanisms in Treg cell regulation: Implications for immunotherapy and disease treatment

Regulatory T cells (Tregs) play a critical role in maintaining immune homeostasis and preventing autoimmune diseases. Recent advances in immunometabolism have revealed the pivotal role of mitochondrial dynamics and metabolism in shaping Treg functionality. Tregs depend on oxidative phosphorylation (OXPHOS) and fatty acid oxidation (FAO) to support their suppressive functions and long-term survival. Mitochondrial processes such as fusion and fission significantly influence Treg activity, with mitochondrial fusion enhancing bioenergetic efficiency and reducing reactive oxygen species (ROS) production, thereby promoting Treg stability. In contrast, excessive mitochondrial fission disrupts ATP synthesis and elevates ROS levels, impairing Treg suppressive capacity. Furthermore, mitochondrial ROS act as critical signaling molecules in Treg regulation, where controlled levels stabilize FoxP3 expression, but excessive ROS leads to mitochondrial dysfunction and immune dysregulation. Mitophagy, as part of mitochondrial quality control, also plays an essential role in preserving Treg function. Understanding the intricate interplay between mitochondrial dynamics and Treg metabolism provides valuable insights for developing novel therapeutic strategies to treat autoimmune disorders and enhance immunotherapy in cancer.

Inducible and reversible SOD2 knockdown in mouse skeletal muscle drives impaired pyruvate oxidation and reduced metabolic flexibility

INTRODUCTION

Skeletal muscle mitochondrial dysfunction is a key characteristic of aging muscle and contributes to age related diseases such as sarcopenia, frailty, and type 2 diabetes. Mitochondrial oxidative stress has been implicated as a driving factor in these age-related diseases, however whether it is a cause, or a consequence of mitochondrial dysfunction remains to be determined. The development of flexible genetic models is an important tool to test the mechanistic role of mitochondrial oxidative stress on skeletal muscle metabolic dysfunction. We characterize a new model of inducible and reversible mitochondrial redox stress using a tetracycline controlled skeletal muscle specific short hairpin RNA targeted to superoxide dismutase 2 (iSOD2).

METHODS

iSOD2 KD and control (CON) animals were administered doxycycline for 3- or 12- weeks and followed for up to 24 weeks and mitochondrial respiration and muscle contraction were measured to define the time course of SOD2 KD and muscle functional changes and recovery.

RESULTS

Maximum knockdown of SOD2 protein occurred by 6 weeks and recovered by 24 weeks after DOX treatment. Mitochondrial aconitase activity and maximum mitochondrial respiration declined in KD muscle by 12 weeks and recovered by 24 weeks. There were no significant differences in antioxidant or mitochondrial biogenesis genes between groups. Twelve-week KD showed a small, but significant decrease in muscle fatigue resistance. The primary phenotype was reduced metabolic flexibility characterized by impaired pyruvate driven respiration when other substrates are present. The pyruvate dehydrogenase kinase inhibitor dichloroacetate partially restored pyruvate driven respiration, while the thiol reductant DTT did not.

CONCLUSION

We use a model of inducible and reversible skeletal muscle SOD2 knockdown to demonstrate that elevated matrix superoxide reversibly impairs mitochondrial substrate flexibility characterized by impaired pyruvate oxidation. Despite the bioenergetic effect, the limited change in gene expression suggests that the elevated redox stress in this model is confined to the mitochondrial matrix.

The Redox Process in Red Blood Cells: Balancing Oxidants and Antioxidants

Red blood cells (RBCs) are a vital component of the body's oxygen supply system. In addition to being pro-oxidants, they are also essential components of the body's antioxidant defense mechanism. RBCs are susceptible to both endogenous and exogenous sources of oxidants. Oxyhemoglobin autoxidation is the primary source of endogenous RBC oxidant production, which produces superoxide radicals and hydrogen peroxide. Potent exogenous oxidants from other blood cells and the surrounding endothelium can also enter RBCs. Both enzymatic (like glutathione peroxidase) and non-enzymatic (like glutathione) mechanisms can neutralize oxidants. These systems are generally referred to as oxidant scavengers or antioxidants, and they work to neutralize these harmful molecules (i.e., oxidants). While their antioxidative capabilities are essential to their physiological functions and delivering oxygen to tissues, their pro-oxidant behavior plays a part in several human pathologies. The redox-related changes in RBCs can have an impact on their function and fate. The balance between pro-oxidants and antioxidants determines the oxidative status of cells, which affects signal transduction, differentiation, and proliferation. When pro-oxidant activity exceeds antioxidative capacity, oxidative stress occurs, leading to cytotoxicity. This type of stress has been linked to various pathologies, including hemolytic anemia. This review compiles the most recent literature investigating the connections between RBC redox biochemistry, antioxidants, and diverse disorders.

Pancreatic β cell interleukin-22 receptor subunit alpha 1 deficiency impairs β cell function in type 2 diabetes via cytochrome b5 reductase 3

Impaired β cell function is a hallmark of type 2 diabetes (T2D), but the underlying cellular signaling machineries that regulate β cell function remain unknown. Here, we identify that the interleukin-22 receptor subunit alpha 1 (IL-22RA1), known as a co-receptor for IL-22, is downregulated in human and mouse T2D β cells. Mice with β cell Il22ra1 knockout (Il22ra1βKO) exhibit defective insulin secretion and impaired glucose tolerance after being fed a high-fat diet (HFD) or an HFD/low dose of streptozotocin (STZ). Mechanistically, β cell IL-22RA1 deficiency inhibits cytochrome b5 reductase 3 (CYB5R3) expression via the IL-22RA1/signal transducer and activator of the transcription 3 (STAT3)/c-Jun axis, thereby impairing mitochondrial function and reducing β cell identity. Overexpression of CYB5R3 reinstates mitochondrial function, β cell identity, and insulin secretion in Il22ra1βKO mice. Moreover, the pharmacological activation of CYB5R3 with tetrahydroindenoindole restores insulin secretion in Il22ra1βKO mice, IL-22RA1-knockdown human islets, and Min6 cells. In conclusion, these findings suggest an important role of IL-22RA1 in preserving β cell function in T2D, which offers a potential therapeutic target for treating diabetes.

Evolution of Theories on Doxorubicin-Induced Late Cardiotoxicity-Role of Topoisomerase

Doxorubicin (DOX) has been widely used as a cytotoxic chemotherapeutic. However, DOX has a number of side effects, such as myelotoxicity or gonadotoxicity, the most dangerous of which is cardiotoxicity. Cardiotoxicity can manifest as cardiac arrhythmias, myocarditis, and pericarditis; life-threatening late cardiotoxicity can result in heart failure months or years after the completion of chemotherapy. The development of late cardiomyopathy is not yet fully understood. The most important question is how DOX reprograms the cardiomyocyte, after which DOX is excreted from the body, initially without symptoms. However, clinically overt cardiomyopathy develops over the following months and years. Since the 1980s, DOX-induced disorders in cardiomyocytes have been thought to be related to oxidative stress and dependent on the Fe/reactive oxygen species (ROS) mechanism. That line of evidence was supported by dexrazoxane (DEX) protection, the only Food and Drug Administration (FDA)-approved drug for preventing DOX-induced cardiomyopathy, which complexes iron. Thus, the hypothesis related to Fe/ROS provides a plausible explanation for the induction of the development of late cardiomyopathy via DOX. However, in subsequent studies, DEX was used to identify another important mechanism in DOX-induced cardiomyopathy that is related to topoisomerase 2β (Top2β). Does the Top2β hypothesis explain the mechanisms of the development of DOX-dependent late heart failure? Several of these mechanisms have been identified to date, proving the involvement of Top2β in the regulation of the redox balance, including oxidative stress. Thus, the development of late cardiomyopathy can be explained based on mechanisms related to Top2β. In this review, we highlight free radical theory, iron imbalance, calcium overload, and finally, a theory based on Top2β.

The Roles of Oxidative Stress and Red Blood Cells in the Pathology of the Varicose Vein

This review discusses sources of reactive oxygen species, enzymatic antioxidant systems, and low molecular weight antioxidants. We present the pathology of varicose veins (VVs), including factors such as hypoxia, inflammation, dysfunctional endothelial cells, risk factors in varicose veins, the role of RBCs in venous thrombus formation, the influence of reactive oxygen species (ROS) and RBCs on VV pathology, and the role of hemoglobin in the damage of particles and macromolecules in VVs. This review discusses the production of ROS, enzymatic and nonenzymatic antioxidants, the pathogenesis of varicose veins as a pathology based on hypoxia, inflammation, and oxidative stress, as well as the participation of red blood cells in the pathology of varicose veins.

Chaperones vs. oxidative stress in the pathobiology of ischemic stroke

As many proteins prioritize functionality over constancy of structure, a proteome is the shortest stave in the Liebig's barrel of cell sustainability. In this regard, both prokaryotes and eukaryotes possess abundant machinery supporting the quality of the proteome in healthy and stressful conditions. This machinery, namely chaperones, assists in folding, refolding, and the utilization of client proteins. The functions of chaperones are especially important for brain cells, which are highly sophisticated in terms of structural and functional organization. Molecular chaperones are known to exert beneficial effects in many brain diseases including one of the most threatening and widespread brain pathologies, ischemic stroke. However, whether and how they exert the antioxidant defense in stroke remains unclear. Herein, we discuss the chaperones shown to fight oxidative stress and the mechanisms of their antioxidant action. In ischemic stroke, during intense production of free radicals, molecular chaperones preserve the proteome by interacting with oxidized proteins, regulating imbalanced mitochondrial function, and directly fighting oxidative stress. For instance, cells recruit Hsp60 and Hsp70 to provide proper folding of newly synthesized proteins-these factors are required for early ischemic response and to refold damaged polypeptides. Additionally, Hsp70 upregulates some dedicated antioxidant pathways such as FOXO3 signaling. Small HSPs decrease oxidative stress via attenuation of mitochondrial function through their involvement in the regulation of Nrf- (Hsp22), Akt and Hippo (Hsp27) signaling pathways as well as mitophagy (Hsp27, Hsp22). A similar function has also been proposed for the Sigma-1 receptor, contributing to the regulation of mitochondrial function. Some chaperones can prevent excessive formation of reactive oxygen species whereas Hsp90 is suggested to be responsible for pro-oxidant effects in ischemic stroke. Finally, heat-resistant obscure proteins (Hero) are able to shield client proteins, thus preventing their possible over oxidation.

Role of Fatty Acids β-Oxidation in the Metabolic Interactions Between Organs

In recent decades, several discoveries have been made that force us to reconsider old ideas about mitochondria and energy metabolism in the light of these discoveries. In this review, we discuss metabolic interaction between various organs, the metabolic significance of the primary substrates and their metabolic pathways, namely aerobic glycolysis, lactate shuttling, and fatty acids β-oxidation. We rely on the new ideas about the supramolecular structure of the mitochondrial respiratory chain (respirasome), the necessity of supporting substrates for fatty acids β-oxidation, and the reverse electron transfer via succinate dehydrogenase during β-oxidation. We conclude that ATP production during fatty acid β-oxidation has its upper limits and thus cannot support high energy demands alone. Meanwhile, β-oxidation creates conditions that significantly accelerate the cycle: glucose-aerobic glycolysis-lactate-gluconeogenesis-glucose. Therefore, glycolytic ATP production becomes an important energy source in high energy demand. In addition, lactate serves as a mitochondrial substrate after converting to pyruvate + H+ by the mitochondrial lactate dehydrogenase. All coupled metabolic pathways are irreversible, and the enzymes are organized into multienzyme structures.

Small-Molecule Probe for Imaging Oxidative Stress-Induced Carbonylation in Live Cells

Protein carbonylation has been known as the major form of irreversible protein modifications and is also widely used as an indicator of oxidative stress in the biological environment. In the presence of oxidative stress, biological systems tend to produce large amounts of carbonyl moieties; these carbonyl groups do not have particular UV-Vis and fluorescence spectroscopic characteristics that we can differentiate, observe, and detect. Thus, their detection and quantification can only be performed using specific chemical probes. Commercially available fluorescent probes to detect specific carbonylation in biological systems have been used, but their chemical portfolio is still very limited. This protocol outlines the methods and procedures employed to synthesize a probe, (E,Z)-2-(2-(2-hydroxybenzylidene)hydrazonyl)-5-nitrophenol (2Hzin5NP), and assess its impact on carbonylation in human cells. The synthesis involves several steps, including the preparation of its hydrazone compounds mimicking cell carbonyls, 2-Hydrazinyl 5-nitrophenol, (E,Z)-2-(2-ethylidenehydrazonyl)-5-nitrophenol, and the final product (E,Z)-2-(2-(2-hydroxybenzylidene)hydrazonyl)-5-nitrophenol. The evaluation of fluorescence quantum yield and subsequent cell culture experiments are detailed for the investigation of 2Hzin5NP effects on cell proliferation and carbonylation. Key features • This protocol builds upon probe development using click chemistry method by Dilek et al. [1], and its biolabeling application in renal cancer cell lines. • The non-fluorescent probe has a fast reaction with carbonyl moieties at neutral pH to form a stable fluorescent product leading to a spectroscopic alteration. • Microscopic and fluorometric analyses can distinguish the exogenous and endogenous ROS-induced carbonylation profile in human dermal fibroblasts along with renal cell carcinoma. • Carbonylation level that differs in response to exogenous and endogenous stress in healthy and cancer cells can be detected by the newly synthesized fluorescent probe.

Abnormal Expression of COX5B Gene and Disorder of Mitochondrial Function in Cryptorchid Rats

Cryptorchidism is one of the most common congenital malformations in the paediatric genitourinary tract. Data analysis of cryptorchidism-related datasets in the GEO database and gene sequencing results from our institution, along with bioinformatic analysis of the merged mitochondrial gene datasets, revealed that COX5B is differentially expressed in the testes of children with cryptorchidism. Its encoded protein has attracted our attention as a key component of the mitochondrial respiratory chain complex IV. This study aims to explore the COX5B gene expression changes and related mitochondrial issues in cryptorchid rats. For this purpose, we established a cryptorchid rat model by surgery and used molecular biology and biochemistry techniques to detect and analyse the expression level of the COX5B gene and mitochondrial function indexes. The results indicated a significant decrease in COX5B gene expression in the affected testis of cryptorchid rats. The knockdown of COX5B expression in TM3 cells could be observed as the aggravation of cellular senescence, which led to the reduction of proliferation, as well as accompanied by the obvious disorders of mitochondrial function, including the increase of ROS and the decrease of ATP, in which MMP was significantly reduced. This suggests that the COX5B gene may play an important role in cryptorchid testis-induced reproductive system damage and may be a new target for small molecule-targeted therapy.

Hypoxia decreases mitochondrial ROS production in cells

We re-examined the reported increase in mitochondrial ROS production during acute hypoxia in cells. Using the Amplex Ultrared/horseradish peroxidase assay we found a decrease, not increase, in hydrogen peroxide release from HEK293 cells under acute hypoxia, at times ranging from 1 min to 3 h. The rates of superoxide/hydrogen peroxide production from each of the three major sites (site IQ in complex I and site IIIQo in complex III in mitochondria, and NADH oxidases (NOX) in the cytosol) were decreased to the same extent by acute hypoxia, with no change in the cells' ability to degrade added hydrogen peroxide. A similar decrease in ROS production under acute hypoxia was found using the diacetyldichlorofluorescein assay. Using a HIF1α reporter cell line we confirmed earlier observations that suppression of superoxide production by site IIIQo decreases HIF1α expression, and found similar effects of suppressing site IQ or NOX. We conclude that increased mitochondrial ROS do not drive the response of HIF1α to acute hypoxia, but suggest that cytosolic H2O2 derived from site IQ, site IIIQo and NOX in cells is necessary to permit HIF1α stabilization by other signals.

Apelin/APJ signaling in IGF-1-induced acute mitochondrial and antioxidant effects in spontaneously hypertensive rat myocardium

IGF-1 and apelin are released in response to exercise training with beneficial effects. Previously we demonstrated that a swimming routine is effective to convert pathological into physiological cardiac hypertrophy, and that IGF-1 improves contractility and the redox state, in spontaneously hypertensive rats (SHR). Now, we hypothesize that the apelinergic pathway is involved in the cardioprotective effects of IGF-1 in the SHR. We assessed the redox state and mitochondrial effects of IGF-1 or apelin in the presence/absence of AG1024 or ML221 [pharmacological antagonists of IGF1 (IGF1R) and apelin (APJ) receptors, respectively] in SHR isolated cardiomyocytes or perfused hearts. Acute IGF-1 (10 nmol/L) significantly: -reduced H2O2 production (IGF-1:62 ± 6; control:100 ± 8.1, %), -increased the activity of superoxide dismutase (IGF-1:193 ± 17, control: 100 ± 13,%), -prevented H2O2-induced ΔΨm loss (TMREF10min/F0 min: IGF-1:0.93 ± 0.017, control: 0.72 ± 0.029), -reduced mitochondrial permeability transition pore (mPTP) opening estimated by the calcium retention capacity (nmol/mg protein, IGF-1:251 ± 34, control:112 ± 5), and -increased P-AMPK (IGF-1:129 ± 0.9, control: 100 ± 2%) and P-AKT (IGF-1:143 ± 17 control:100 ± 6, %). These effects were suppressed not only by the antagonism of IGF1R but also of APJ. Moreover, IGF-1 significantly increased APJ (IGF-1:198 ± 29 control:100 ± 15,%) and apelin mRNAs (IGF-1:251 ± 48, control:100 ± 6,%). On the other hand, an equipotent dose of exogenous apelin (50 nmol/L) emulated IGF-1 effects being cancelled by the antagonism of APJ however not by AG1024. IGF-1/IGF1R stimulates the apelinergic pathway, improving the redox balance and mitochondria status in the pathologically hypertrophied myocardium of the SHR.

Mitochondrial bioenergetics of breast cancer

Breast cancer cells exhibit metabolic heterogeneity based on tumour aggressiveness. Glycolysis and mitochondrial respiration are two major metabolic pathways for ATP production. The oxygen flux, oxygen tension, proton leakage, protonmotive force, inner mitochondrial membrane potential, ECAR and electrochemical proton gradient maintain metabolic homeostasis, ATP production, ROS generation, heat dissipation, and carbon flow and are referred to as "sub-domains" of mitochondrial bioenergetics. Tumour aggressiveness is influenced by these mechanisms, especially when breast cancer cells undergo metastasis. These physiological parameters for healthy mitochondria are as crucial as energy demands for tumour growth and metastasis. The instant energy demands are already elucidated under Warburg effects, while these parameters may have dual functionality to maintain cellular bioenergetics and cellular health. The tumour cell might maintain these mitochondrial parameters for mitochondrial health or avoid apoptosis, while energy production could be a second priority. This review focuses explicitly on the crosstalk between metabolic domains and the utilisation of these parameters by breast cancer cells for their progression. Some major interventions are discussed based on mitochondrial bioenergetics that need further investigation. This review highlights the pathophysiological significance of mitochondrial bioenergetics and the regulation of its sub-domains by breast tumour cells for uncontrolled proliferation.

A mitochondrial redox switch licenses the onset of morphogenesis in animals

Embryos undergo pre-gastrulation cleavage cycles to generate a critical cell mass before transitioning to morphogenesis. The molecular underpinnings of this transition have traditionally centered on zygotic chromatin remodeling and genome activation1,2, as their repression can prevent downstream processes of differentiation and organogenesis. Despite precedents that oxygen depletion can similarly suspend development in early embryos3-6, hinting at a pivotal role for oxygen metabolism in this transition, whether there is a bona fide chemical switch that licenses the onset of morphogenesis remains unknown. Here we discover that a mitochondrial oxidant acts as a metabolic switch to license the onset of animal morphogenesis. Concomitant with the instatement of mitochondrial membrane potential, we found a burst-like accumulation of mitochondrial superoxide (O2 -) during fly blastoderm formation. In vivo chemistry experiments revealed that an electron leak from site IIIQo at ETC Complex III is responsible for O2 - production. Importantly, depleting mitochondrial O2 - fully mimics anoxic conditions and, like anoxia, induces suspended animation prior to morphogenesis, but not after. Specifically, H2O2, and not ONOO-, NO, or HO•, can single-handedly account for this mtROS-based response. We demonstrate that depleting mitochondrial O2 - similarly prevents the onset of morphogenetic events in vertebrate embryos and ichthyosporea, close relatives of animals. We postulate that such redox-based metabolic licensing of morphogenesis is an ancient trait of holozoans that couples the availability of oxygen to development, conserved from early-diverging animal relatives to vertebrates.

Signaling Pathways Concerning Mitochondrial Dysfunction: Implications in Neurodegeneration and Possible Molecular Targets

Mitochondrion is an important organelle present in our cells responsible for meeting energy requirements. All higher organisms rely on efficient mitochondrial bioenergetic machinery to sustain life. No other respiratory process can produce as much power as generated by mitochondria in the form of ATPs. This review is written in order to get an insight into the magnificent working of mitochondrion and its implications in cellular homeostasis, bioenergetics, redox, calcium signaling, and cell death. However, if this machinery gets faulty, it may lead to several disease states. Mitochondrial dysfunctioning is of growing concern today as it is seen in the pathogenesis of several diseases which includes neurodegenerative disorders, cardiovascular disorders, diabetes mellitus, skeletal muscle defects, liver diseases, and so on. To cover all these aspects is beyond the scope of this article; hence, our study is restricted to neurodegenerative disorders only. Moreover, faulty functioning of this organelle can be one of the causes of early ageing in individuals. This review emphasizes mutations in the mitochondrial DNA, defects in oxidative phosphorylation, generation of ROS, and apoptosis. Researchers have looked into new approaches that might be able to control mitochondrial failure and show a lot of promise as treatments.

The Generation of ROS by Exposure to Trihalomethanes Promotes the IκBα/NF-κB/p65 Complex Dissociation in Human Lung Fibroblast

Background: Disinfection by-products used to obtain drinking water, including halomethanes (HMs) such as CH2Cl2, CHCl3, and BrCHCl2, induce cytotoxicity and hyperproliferation in human lung fibroblasts (MRC-5). Enzymes such as superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) modulate these damages through their biotransformation processes, potentially generating toxic metabolites. However, the role of the oxidative stress response in cellular hyperproliferation, modulated by nuclear factor-kappa B (NF-κB), remains unclear. Methods: In this study, MRC-5 cells were treated with these compounds to evaluate reactive oxygen species (ROS) production, lipid peroxidation, phospho-NF-κB/p65 (Ser536) levels, and the activities of SOD, CAT, and GPx. Additionally, the interactions between HMs and ROS with the IκBα/NF-κB/p65 complex were analyzed using molecular docking. Results: Correlation analysis among biomarkers revealed positive relationships between pro-oxidant damage and antioxidant responses, particularly in cells treated with CH2Cl2 and BrCHCl2. Conversely, negative relationships were observed between ROS levels and NF-κB/p65 levels in cells treated with CH2Cl2 and CHCl3. The estimated relative free energy of binding using thermodynamic integration with the p65 subunit of NF-κB was -3.3 kcal/mol for BrCHCl2, -3.5 kcal/mol for both CHCl3 and O2•, and -3.6 kcal/mol for H2O2. Conclusions: Chloride and bromide atoms were found in close contact with IPT domain residues, particularly in the RHD region involved in DNA binding. Ser281 is located within this domain, facilitating the phosphorylation of this protein. Similarly, both ROS interacted with the IPT domain in the RHD region, with H2O2 forming a side-chain oxygen interaction with Leu280 adjacent to the phosphorylation site of p65. However, the negative correlation between ROS and phospho-NF-κB/p65 suggests that steric hindrance by ROS on the C-terminal domain of NF-κB/p65 may play a role in the antioxidant response.

Role of melatonin in mitigation of insulin resistance and ensuing diabetic cardiomyopathy

Addressing insulin resistance or hyperinsulinemia might offer a viable treatment approach to stop the onset of diabetic cardiomyopathy, as these conditions independently predispose to the development of the disease, which is initially characterized by diastolic abnormalities. The development of diabetic cardiomyopathy appears to be driven mainly by insulin resistance or impaired insulin signalling and/or hyperinsulinemia. Oxidative stress, hypertrophy, fibrosis, cardiac diastolic dysfunction, and, ultimately, systolic heart failure are the outcomes of these pathophysiological alterations. Melatonin is a ubiquitous indoleamine, a widely distributed compound secreted mainly by the pineal gland, and serves a variety of purposes in almost every living creature. Melatonin is found to play a leading role by improving myocardial cell metabolism, decreasing vascular endothelial cell death, reversing micro-circulation disorders, reducing myocardial fibrosis, decreasing oxidative and endoplasmic reticulum stress, regulating cell autophagy and apoptosis, and enhancing mitochondrial function. This review highlights a relationship between insulin resistance and associated cardiomyopathy. It explores the potential therapeutic strategies offered by the neurohormone melatonin, an important antioxidant that plays a leading role in maintaining glucose homeostasis by influencing the glucose transporters independently and through its receptors. The vast distribution of melatonin receptors in the body, including beta cells of pancreatic islets, asserts the role of this indole molecule in maintaining glucose homeostasis. Melatonin controls the production of GLUT4 and/or the phosphorylation process of the receptor for insulin and its intracellular substrates, activating the insulin-signalling pathway through its G-protein-coupled membrane receptors.

The Effect of Reactive Oxygen Species on Respiratory Complex I Activity in Liposomes

Respiratory complex I (R-CI) is an essential enzyme in the mitochondrial electron transport chain but also a major source of reactive oxygen species (ROS), which are implicated in neurodegenerative diseases and ageing. While the mechanism of ROS production by R-CI is well-established, the feedback of ROS on R-CI activity is poorly understood. Here, we perform EPR spectroscopy on R-CI incorporated in artificial membrane vesicles to reveal that ROS (particularly hydroxyl radicals) reduce R-CI activity by making the membrane more polar and by increasing its hydrogen bonding capability. Moreover, the mechanism that we have uncovered reveals that the feedback of ROS on R-CI activity via the membrane is transient and not permanent; lipid peroxidation is negligible for the levels of ROS generated under these conditions. Our successful use of modular proteoliposome systems in conjunction with EPR spectroscopy and other biophysical techniques is a powerful approach for investigating ROS effects on other membrane proteins.

Vitrification of Mammalian Oocytes: Recent Studies on Mitochondrial Dysfunction

Vitrification of reproductive cells is definitely essential and integral in animal breeding, as well as in assisted reproduction. However, issues accompanied with this technology such as decreased oocyte competency and relatively low embryo survival rates appear to be a tough conundrum that has long perplexed us. As significant organelles in cell metabolism, mitochondria play pivotal roles in numerous pathways. Nonetheless, extensive evidence has demonstrated that vitrification can seriously impair mitochondrial function in mammalian oocytes. Thus, in this article, we summarize the current progress in oocyte vitrification and particularly outline the common mitochondrial abnormalities alongside subsequent injury cascades seen in mammalian oocytes following vitrification. Based on existing literature, we tentatively come up with the potential mechanisms related to mitochondrial dysfunction and generalize efficacious ways which have been recommended to restore mitochondrial function.

Understanding coenzyme Q

Coenzyme Q (CoQ), also known as ubiquinone, comprises a benzoquinone head group and a long isoprenoid side chain. It is thus extremely hydrophobic and resides in membranes. It is best known for its complex function as an electron transporter in the mitochondrial electron transport chain (ETC) but is also required for several other crucial cellular processes. In fact, CoQ appears to be central to the entire redox balance of the cell. Remarkably, its structure and therefore its properties have not changed from bacteria to vertebrates. In metazoans, it is synthesized in all cells and is found in most, and maybe all, biological membranes. CoQ is also known as a nutritional supplement, mostly because of its involvement with antioxidant defenses. However, whether there is any health benefit from oral consumption of CoQ is not well established. Here we review the function of CoQ as a redox-active molecule in the ETC and other enzymatic systems, its role as a prooxidant in reactive oxygen species generation, and its separate involvement in antioxidant mechanisms. We also review CoQ biosynthesis, which is particularly complex because of its extreme hydrophobicity, as well as the biological consequences of primary and secondary CoQ deficiency, including in human patients. Primary CoQ deficiency is a rare inborn condition due to mutation in CoQ biosynthetic genes. Secondary CoQ deficiency is much more common, as it accompanies a variety of pathological conditions, including mitochondrial disorders as well as aging. In this context, we discuss the importance, but also the great difficulty, of alleviating CoQ deficiency by CoQ supplementation.

Maintaining mitochondrial DNA copy number mitigates ROS-induced oocyte decline and female reproductive aging

Oocytes play a crucial role in transmitting maternal mitochondrial DNA (mtDNA), essential for the continuation of species. However, the effects of mitochondrial reactive oxygen species (ROS) on mammalian oocyte maturation and mtDNA maintenance remain unclear. We investigated this by conditionally knocking out the Sod2 gene in primordial follicles, elevating mitochondrial matrix ROS levels from early oocyte stages. Our data indicates that reproductive aging in Sod2 conditional knockout females begins at 6 months, with oxidative stress impairing oocyte quality, particularly affecting OXPHOS complex II and mtDNA-encoded mRNA levels. Despite unchanged mtDNA mutation load, mtDNA copy numbers exhibited significant variations. Strikingly, reducing mtDNA copy numbers by reducing mtSSB protein, crucial for mtDNA replication, accelerated reproductive aging onset to three months, underscoring the critical role of mtDNA copy number maintenance under oxidative stress conditions. This research provides new insights into the relationship among mitochondrial ROS, mtDNA, and reproductive aging, offering potential strategies for delaying aging-related fertility decline.

Oxidative stress in alcoholic liver disease, focusing on proteins, nucleic acids, and lipids: A review

Oxidative stress is one of the important factors in the development of alcoholic liver disease. The production of reactive oxygen species and other free radicals is an important feature of alcohol metabolism in the liver and an important substance in liver injury. When large amounts of ROS are produced, the homeostasis of the liver REDOX system will be disrupted and liver injury will be caused. Oxidative stress can damage proteins, nucleic acids and lipids, liver dysfunction. In addition, damaging factors produced by oxidative damage to liver tissue can induce the occurrence of inflammation, thereby aggravating the development of ALD. This article reviews the oxidative damage of alcohol on liver proteins, nucleic acids, and lipids, and provides new insights and summaries of the oxidative stress process. We also discussed the relationship between oxidative stress and inflammation in alcoholic liver disease from different perspectives. Finally, the research status of antioxidant therapy in alcoholic liver disease was summarized, hoping to provide better help for learning and developing the understanding of alcoholic liver disease.

Effect of CFTR Modulators on Oxidative Stress and Autophagy in Non-CFTR-Expressing Cells

The triple combination therapy for cystic fibrosis (CF), including elexacaftor, tezacaftor and ivacaftor (ETI or Trikafta), has been shown to improve lung function and reduce pulmonary exacerbations, thereby enhancing the quality of life for most CF patients. Recent findings suggest that both the individual components and ETI may have potential off-target effects, highlighting the need to understand how these modulators impact cellular physiology, particularly in cells that do not express CF transmembrane conductance regulator (CFTR). We used HEK293 cells, as a cell model not expressing the CFTR protein, to evaluate the effect of ETI and each of its components on autophagic machinery and on the Rab5/7 components of the Rab pathway. We firstly demonstrate that the single modulators Teza and Iva, and the combinations ET and ETI, increased ROS production in the absence of their target while decreasing it in cells expressing the CFTR ∆F508del. This increase in cellular stress was followed by an increase in the total level of polyubiquitinated proteins as well as the p62 level and LC3II/LC3I ratio. Furthermore, we found that ETI had the opposite effect on Rabs by increasing Rab5 levels while decreasing Rab7. Interestingly, these changes were abolished by the expression of mutated CFTR. Overall, our data suggest that in the absence of their target, both the individual modulators and ETI increased ROS production and halted both autophagic flux and plasma membrane protein recycling.

Inducible and reversible SOD2 knockdown in mouse skeletal muscle drives impaired pyruvate oxidation and reduced metabolic flexibility

Introduction

Skeletal muscle mitochondrial dysfunction is a key characteristic of aging muscle and contributes to age related diseases such as sarcopenia, frailty, and type 2 diabetes. Mitochondrial oxidative distress has been implicated as a driving factor in these age-related diseases, however whether it is a cause, or a consequence of mitochondrial dysfunction remains to be determined. The development of more flexible genetic models is an important tool to test the mechanistic role of mitochondrial oxidative stress on skeletal muscle metabolic dysfunction. We characterize a new model of inducible and reversible mitochondrial redox stress using a tetracycline controlled skeletal muscle specific short hairpin RNA targeted to superoxide dismutase 2 (iSOD2).

Methods

iSOD2 KD and control (CON) animals were administered doxycycline for 3- or 12- weeks and followed for up to 24 weeks and mitochondrial respiration and muscle contraction were measured to define the time course of SOD2 KD and muscle functional changes and recovery.

Results

Maximum knockdown of SOD2 protein occurred by 6 weeks and recovered by 24 weeks after DOX treatment. Mitochondrial aconitase activity and maximum mitochondrial respiration declined in KD muscle by 12 weeks and recovered by 24 weeks. There were minimal changes in gene expression between KD and CON muscle. Twelve-week KD showed a small, but significant decrease in muscle fatigue resistance. The primary phenotype was reduced metabolic flexibility characterized by impaired pyruvate driven respiration when other substrates are present. The pyruvate dehydrogenase kinase inhibitor dichloroacetate partially restored pyruvate driven respiration, while the thiol reductant DTT did not.

Conclusion

We use a model of inducible and reversible skeletal muscle SOD2 knockdown to demonstrate that elevated matrix superoxide reversibly impairs mitochondrial substrate flexibility characterized by impaired pyruvate oxidation. Despite the bioenergetic effect, the limited change in gene expression suggests that the elevated redox stress in this model is confined to the mitochondrial matrix.

Ergothioneine and mitochondria: An important protective mechanism?

Mitochondrial dysfunction is implicated in a wide range of human disorders including many neurodegenerative and cardiovascular diseases, metabolic diseases, cancers, and respiratory disorders. Studies have suggested the potential of l-ergothioneine (ET), a unique dietary thione, to prevent mitochondrial damage and improve disease outcome. Despite this, no studies have definitively demonstrated uptake of ET into mitochondria. Moreover, the expression of the known ET transporter, OCTN1, on the mitochondria remains controversial. In this study, we utilise mass spectrometry to demonstrate direct ET uptake in isolated mitochondria as well as its presence in mitochondria isolated from ET-treated cells and animals. Mitochondria isolated from OCTN1 knockout mice tissues, have impaired but still detectable ET uptake, raising the possibility of alternative transporter(s) which may facilitate ET uptake into the mitochondria. Our data confirm that ET can enter mitochondria, providing a basis for further work on ET in the prevention of mitochondrial dysfunction in human disease.

Mitochondrial membrane lipids in the regulation of bioenergetic flux

Oxidative phosphorylation (OXPHOS) occurs through and across the inner mitochondrial membrane (IMM). Mitochondrial membranes contain a distinct lipid composition, aided by lipid biosynthetic machinery localized in the IMM and class-specific lipid transporters that limit lipid traffic in and out of mitochondria. This unique lipid composition appears to be essential for functions of mitochondria, particularly OXPHOS, by its effects on direct lipid-to-protein interactions, membrane properties, and cristae ultrastructure. This review highlights the biological significance of mitochondrial lipids, with a particular spotlight on the role of lipids in mitochondrial bioenergetics. We describe pathways for the biosynthesis of mitochondrial lipids and provide evidence for their roles in physiology, their implications in human disease, and the mechanisms by which they regulate mitochondrial bioenergetics.

Mitochondrial DNA transcription and mitochondrial genome-encoded long noncoding RNA in diabetic retinopathy

In diabetic retinopathy, mitochondrial DNA (mtDNA) is damaged and mtDNA-encoded genes and long noncoding RNA cytochrome B (LncCytB) are downregulated. LncRNAs lack an open reading frame, but they can regulate gene expression by associating with DNA/RNA/protein. Double stranded mtDNA has promoters on both heavy (HSP) and light (LSP) strands with binding sites for mitochondrial transcription factor A (TFAM) between them. The aim was to investigate the role of LncCytB in mtDNA transcription in diabetic retinopathy. Using human retinal endothelial cells incubated in high glucose, the effect of regulation of LncCytB on TFAM binding at mtDNA promoters was investigated by Chromatin immunoprecipitation, and binding of LncCytB at TFAM by RNA immunoprecipitation and RNA fluorescence in situ hybridization. High glucose decreased TFAM binding at both HSP and LSP, and binding of LncCytB at TFAM. While LncCytB overexpression ameliorated decrease in TFAM binding and transcription of genes encoded by both H- and L- strands, LncCytB-siRNA further downregulated them. Maintenance of mitochondrial homeostasis by overexpressing mitochondrial superoxide dismutase or Sirtuin-1 protected diabetes-induced decrease in TFAM binding at mtDNA and LncCytB binding at TFAM, and mtDNA transcription. Similar results were obtained from mouse retinal microvessels from streptozotocin-induced diabetic mice. Thus, LncCytB facilitates recruitment of TFAM at HSP and LSP, and its downregulation in diabetes compromises the binding, resulting in the downregulation of polypeptides encoded by mtDNA. Regulation of LncCytB, in addition to protecting mitochondrial genomic stability, should also help in maintaining the transcription of mtDNA encoded genes and electron transport chain integrity in diabetic retinopathy.

Mitochondria to plasma membrane redox signaling is essential for fatty acid β-oxidation-driven insulin secretion

We asked whether acute redox signaling from mitochondria exists concomitantly to fatty acid- (FA-) stimulated insulin secretion (FASIS) at low glucose by pancreatic β-cells. We show that FA β-oxidation produces superoxide/H2O2, providing: i) mitochondria-to-plasma-membrane redox signaling, closing KATP-channels synergically with elevated ATP (substituting NADPH-oxidase-4-mediated H2O2-signaling upon glucose-stimulated insulin secretion); ii) activation of redox-sensitive phospholipase iPLA2γ/PNPLA8, cleaving mitochondrial FAs, enabling metabotropic GPR40 receptors to amplify insulin secretion (IS). At fasting glucose, palmitic acid stimulated IS in wt mice; palmitic, stearic, lauric, oleic, linoleic, and hexanoic acids also in perifused pancreatic islets (PIs), with suppressed 1st phases in iPLA2γ/PNPLA8-knockout mice/PIs. Extracellular/cytosolic H2O2-monitoring indicated knockout-independent redox signals, blocked by mitochondrial antioxidant SkQ1, etomoxir, CPT1 silencing, and catalase overexpression, all inhibiting FASIS, keeping ATP-sensitive K+-channels open, and diminishing cytosolic [Ca2+]-oscillations. FASIS in mice was a postprandially delayed physiological event. Redox signals of FA β-oxidation are thus documented, reaching the plasma membrane, essentially co-stimulating IS.

Mitochondrial Physiology of Cellular Redox Regulations

Mitochondria (mt) represent the vital hub of the molecular physiology of the cell, being decision-makers in cell life/death and information signaling, including major redox regulations and redox signaling. Now we review recent advances in understanding mitochondrial redox homeostasis, including superoxide sources and H2O2 consumers, i.e., antioxidant mechanisms, as well as exemplar situations of physiological redox signaling, including the intramitochondrial one and mt-to-cytosol redox signals, which may be classified as acute and long-term signals. This review exemplifies the acute redox signals in hypoxic cell adaptation and upon insulin secretion in pancreatic beta-cells. We also show how metabolic changes under these circumstances are linked to mitochondrial cristae narrowing at higher intensity of ATP synthesis. Also, we will discuss major redox buffers, namely the peroxiredoxin system, which may also promote redox signaling. We will point out that pathological thresholds exist, specific for each cell type, above which the superoxide sources exceed regular antioxidant capacity and the concomitant harmful processes of oxidative stress subsequently initiate etiology of numerous diseases. The redox signaling may be impaired when sunk in such excessive pro-oxidative state.

Mitochondrial complex III-derived ROS amplify immunometabolic changes in astrocytes and promote dementia pathology

Neurodegenerative disorders alter mitochondrial functions, including the production of reactive oxygen species (ROS). Mitochondrial complex III (CIII) generates ROS implicated in redox signaling, but its triggers, targets, and disease relevance are not clear. Using site-selective suppressors and genetic manipulations together with mitochondrial ROS imaging and multiomic profiling, we found that CIII is the dominant source of ROS production in astrocytes exposed to neuropathology-related stimuli. Astrocytic CIII-ROS production was dependent on nuclear factor-κB (NF-κB) and the mitochondrial sodium-calcium exchanger (NCLX) and caused oxidation of select cysteines within immune and metabolism-associated proteins linked to neurological disease. CIII-ROS amplified metabolomic and pathology-associated transcriptional changes in astrocytes, with STAT3 activity as a major mediator, and facilitated neuronal toxicity in a non-cell-autonomous manner. As proof-of-concept, suppression of CIII-ROS in mice decreased dementia-linked tauopathy and neuroimmune cascades and extended lifespan. Our findings establish CIII-ROS as an important immunometabolic signal transducer and tractable therapeutic target in neurodegenerative disease.