Na+ controls hypoxic signalling by the mitochondrial respiratory chain

Spreading depolarizations exhaust neuronal ATP in a model of cerebral ischemia

Spreading depolarizations (SDs) have been identified in various brain pathologies. SDs increase the cerebral energy demand and, concomitantly, oxygen consumption, which indicates enhanced synthesis of adenosine triphosphate (ATP) by oxidative phosphorylation. Therefore, SDs are considered particularly detrimental during reduced supply of oxygen and glucose. However, measurements of intracellular neuronal ATP ([ATP]i), ultimately reporting the balance of ATP synthesis and consumption during SDs, have not yet been conducted. Here, we investigated neuronal ATP homeostasis during SDs using two-photon imaging in acute brain slices from adult mice expressing the ATP sensor ATeam1.03YEMK in neurons. SDs were induced by application of potassium chloride or by oxygen and glucose deprivation (OGD) and detected by recording the local field potential, extracellular potassium, as well as the intrinsic optical signal. We found that, in the presence of oxygen and glucose, SDs were accompanied by a substantial but transient drop in neuronal ATP sensor signals, corresponding to a drop in ATP. OGD, which prior to SDs was accompanied by only a slight reduction in ATP signals, led to a large, terminal drop in ATP signals during SDs. Subsequently, we investigated whether neurons could still regenerate ATP if oxygen and glucose were promptly resupplied following SD detection, and show that ATP depletion was essentially reversible in most cells. Our findings indicate that SDs are accompanied by a substantial increase in ATP consumption beyond production. This, under conditions that mimic reduced blood supply, leads to a breakdown of [ATP]i. Therefore, our findings support therapeutic strategies targeting SDs after cerebral ischemia.

Crosstalk between calcium and reactive oxygen species signaling in cancer revisited

The homeostasis of cellular reactive oxygen species (ROS) and calcium (Ca2+) are intricately linked. ROS signaling and Ca2+ signaling are reciprocally regulated within cellular microdomains and are crucial for transcription, metabolism and cell function. Tumor cells often highjack ROS and Ca2+ signaling mechanisms to ensure optimal cell survival and tumor progression. Expression and regulation of Ca2+ channels and transporters at the plasma membrane, endoplasmic reticulum, mitochondria and other endomembranes are often altered in tumor cells, and this includes their regulation by ROS and reactive nitrogen species (RNS). Likewise, alterations in cellular Ca2+ levels influence the generation and scavenging of oxidants and thus can alter the redox homeostasis of the cell. This interplay can be either beneficial or detrimental to the cell depending on the localization, duration and levels of ROS and Ca2+ signals. At one end of the spectrum, Ca2+ and ROS/RNS can function as signaling modules while at the other end, lethal surges in these species are associated with cell death. Here, we highlight the interplay between Ca2+ and ROS in cancer progression, emphasize the impact of redox regulation on Ca2+ transport mechanisms, and describe how Ca2+ signaling pathways, in turn, can regulate the cellular redox environment.

Modes of Mitochondrial Reactive Oxygen Species Production in Inflammation

Background: Inflammation is one of the most important pathways in innate immunity and its relationship with redox biology is becoming increasingly clear in the last decades. However, the specific redox modes and pathways by which inflammation is produced are not yet well defined. Significance: In this review, we provide a general explanation of the reactive oxygen species (ROS) production and quenching modes occurring in mammalian mitochondria, as well as a summary of the most recent advances in mitochondrial redox biology and bioenergetics regarding sodium (Na+) homeostasis. In addition, we provide a collection of examples in which several inflammatory pathways have been associated with specific modes of either mitochondrial ROS production or quenching. Innovation: The role of Na+ in mitochondrial biology is being developed. Since its discovery as a second messenger, the research of its role in the immune system has emerged. Now, the role of Na+ in mitochondrial bioenergetics has recently been identified, which owns unprecedented applications. The potential implication of Na+ in inflammatory mechanisms grows as its role does not only cover ROS production and respiration but also the control through the management of mitochondrial membrane potential. Future directions: Na+ is becoming relevant for mitochondrial biology. Thus, processes regarding mitochondrial bioenergetics, redox state, or metabolism may probably need to include the study of Na+ in their road map. Some of these pathways are involved in inflammation and more are possibly to come. This review is expected to serve as a bridge between both fields. Antioxid. Redox Signal. 00, 000-000.

Targeting lipid metabolic reprogramming to alleviate diabetic kidney disease: molecular insights and therapeutic strategies

Diabetic kidney disease (DKD) is one of the major complications of diabetes, and its pathological progression is closely associated with lipid metabolic reprogramming. Under diabetic conditions, renal cells undergo significant lipid metabolic abnormalities, including increased lipid uptake, impaired fatty acid oxidation, disrupted cholesterol efflux, and enhanced lipid catabolism, as adaptive responses to metabolic stress. These changes result in the accumulation of lipids such as free fatty acids, diacylglycerol, and ceramides, leading to lipotoxicity that triggers inflammation and fibrosis. Hypoxia in the DKD microenvironment suppresses fatty acid oxidation and promotes lipid synthesis through the HIF-1α pathway, while chronic inflammation exacerbates lipid metabolic disturbances via inflammatory cytokines, inflammasomes, and macrophage polarization. Targeting lipid metabolism represents a promising therapeutic strategy for alleviating DKD; however, further clinical translational studies are warranted to validate the efficacy and safety of these approaches.

Metabolic Homeostasis of Immune Cells Modulates Cardiovascular Diseases

Recent investigations into the mechanisms underlying inflammation have highlighted the pivotal role of immune cells in regulating cardiac pathophysiology. Notably, these immune cells modulate cardiac processes through alternations in intracellular metabolism, including glycolysis and oxidative phosphorylation, whereas the extracellular metabolic environment is changed during cardiovascular disease, influencing function of immune cells. This dynamic interaction between immune cells and their metabolic environment has given rise to the novel concept of "immune metabolism". Consequently, both the extracellular and intracellular metabolic environment modulate the equilibrium between anti- and pro-inflammatory responses. This regulatory mechanism subsequently influences the processes of myocardial ischemia, cardiac fibrosis, and cardiac remodeling, ultimately leading to a series of cardiovascular events. This review examines how local microenvironmental and systemic environmental changes induce metabolic reprogramming in immune cells and explores the subsequent effects of aberrant activation or polarization of immune cells in the progression of cardiovascular disease. Finally, we discuss potential therapeutic strategies targeting metabolism to counteract abnormal immune activation.

Reversible redox 19F magnetic resonance imaging nanoprobes for monitoring the redox state in vivo

Redox processes are indispensable for physiology, and dysregulated redox balance is critical in various metabolic diseases. The development of imaging diagnosis tools for real-time monitoring of the redox state in vivo is of great importance yet highly challenging. Here, we designed trifluoromethyl (-CF3) grafted selenide polymer nanoprobes for reversible redox sensing in vivo. Based on the reversible shift of the 19F-nuclear magnetic resonance (NMR) peak between oxidation and reduction states of the nanoprobes exposed to different redox species, the 19F-magnetic resonance imaging (MRI) signal ratio of S Ox/(S Ox + S Red) was successfully applied to monitor the redox state in a tumor. These nanoprobes demonstrated good biocompatibility and great potential for exploring physiological and pathological redox processes in deep tissues. We envision that this work will enable the rational design of 19F-MRI nanoprobes with excellent redox response for the real-time monitoring of the redox state at the lesion location.

Rejuvenation of Bone Marrow Mesenchymal Stem Cells: Mechanisms and Their Application in Senile Osteoporosis Treatment

Bone marrow mesenchymal stromal cells (BM-MSCs) are multipotent cells present in bone marrow; they play a crucial role in the process of bone formation. Cellular senescence is defined as a stable state of cell cycle arrest that impairs the functioning of cells. Research has shown that aging triggers a state of senescence in BM-MSCs, leading to a reduced capacity for osteogenic differentiation and the accumulation of senescent cells, which can accelerate the onset of various diseases. Therefore, it is essential to explore mechanisms and strategies for the rejuvenation of senescent BM-MSCs. Senile osteoporosis (SOP) is a metabolic bone disease characterized by reduced bone formation. The senescence of BM-MSCs is considered one of the most important factors in the occurrence and development of SOP. Therefore, the rejuvenation of BM-MSCs for the treatment of SOP represents a promising strategy. This work provides a summary of the functional alterations observed in senescent BM-MSCs and a systematic review of the mechanisms that facilitate the rejuvenation of senescent BM-MSCs. Additionally, we analyze the progress in and the limitations associated with the application of rejuvenated senescent BM-MSCs to treat SOP, with the aim of providing new insights for the prevention and treatment of SOP.

Research progress of hypoxia-inducible factor-1α and zinc in the mechanism of diabetic kidney disease

Diabetic kidney disease is one of the common complications in diabetic patients and has gradually become an important pathogenic factor in chronic kidney disease. Therefore, studying the mechanisms of its occurrence and development is of great significance for the prevention and treatment of diabetic kidney disease. Some researchers have pointed out that there is a phenomenon of hypoxia in diabetic kidney tissue and believe that hypoxia-inducible factor-1α is closely related to the occurrence and progression of diabetic kidney disease. Additionally, the homeostasis of zinc plays a key role in the body's adaptation to hypoxic environments. However, the specific relationship among these three factors remains unclear. This article provides a detailed review of the multiple roles of hypoxia-inducible factor-1α in the pathogenesis of diabetic kidney disease, including: regulating angiogenesis, increasing the expression of erythropoietin, modulating oxidative stress through the PI3K/AKT and HIF-1α/HO-1 pathways, promoting inflammatory cell infiltration and the release of inflammatory factors to induce inflammatory responses, facilitating epithelial-mesenchymal transition, pathological angiogenesis, and promoting the release of fibrotic factors, ultimately leading to renal fibrosis. Furthermore, HIF-1α also participates in the occurrence and development of diabetic kidney disease through mechanisms such as regulating apoptosis, inducing mitochondrial autophagy, and vascular calcification. At the same time, this article clarifies the regulatory role of the trace element zinc on hypoxia-inducible factor-1α in diabetic kidney disease. This article provides references and insights for further research on the pathogenesis and progression of diabetic kidney disease.

Similarities in the Electrographic Patterns of Delayed Cerebral Infarction and Brain Death After Aneurysmal and Traumatic Subarachnoid Hemorrhage

While subarachnoid hemorrhage is the second most common hemorrhagic stroke in epidemiologic studies, the recent DISCHARGE-1 trial has shown that in reality, three-quarters of focal brain damage after subarachnoid hemorrhage is ischemic. Two-fifths of these ischemic infarctions occur early and three-fifths are delayed. The vast majority are cortical infarcts whose pathomorphology corresponds to anemic infarcts. Therefore, we propose in this review that subarachnoid hemorrhage as an ischemic-hemorrhagic stroke is rather a third, separate entity in addition to purely ischemic or hemorrhagic strokes. Cumulative focal brain damage, determined by neuroimaging after the first 2 weeks, is the strongest known predictor of patient outcome half a year after the initial hemorrhage. Because of the unique ability to implant neuromonitoring probes at the brain surface before stroke onset and to perform longitudinal MRI scans before and after stroke, delayed cerebral ischemia is currently the stroke variant in humans whose pathophysiological details are by far the best characterized. Optoelectrodes located directly over newly developing delayed infarcts have shown that, as mechanistic correlates of infarct development, spreading depolarizations trigger (1) spreading ischemia, (2) severe hypoxia, (3) persistent activity depression, and (4) transition from clustered spreading depolarizations to a negative ultraslow potential. Furthermore, traumatic brain injury and subarachnoid hemorrhage are the second and third most common etiologies of brain death during continued systemic circulation. Here, we use examples to illustrate that although the pathophysiological cascades associated with brain death are global, they closely resemble the local cascades associated with the development of delayed cerebral infarcts.

Liposomes-enabled cancer chemoimmunotherapy

Chemoimmunotherapy is an emerging paradigm in the clinic for treating several malignant diseases, such as non-small cell lung cancer, breast cancer, and large B-cell lymphoma. However, the efficacy of this strategy is still restricted by serious adverse events and a high therapeutic termination rate, presumably due to the lack of tumor-targeted distribution of both chemotherapeutic and immunotherapeutic agents. Targeted drug delivery has the potential to address this issue. Among the most promising nanocarriers in clinical translation, liposomes have drawn great attention in cancer chemoimmunotherapy in recent years. Liposomes-enabled cancer chemoimmunotherapy has made significant progress in clinics, with impressive therapeutic outcomes. This review summarizes the latest preclinical and clinical progress in liposome-enabled cancer chemoimmunotherapy and discusses the challenges and future directions of this field.

Acute CCl4-induced intoxication reduces complex I, but not complex II-based mitochondrial bioenergetics - protective role of succinate

The main therapeutic strategy for the treatment of patients with toxic liver failure is the elimination of the toxic agent in combination with the targeted mitigation of pathological processes that have been initiated due to the toxicant. In the current research we evaluated the strategy of metabolic supplementation to improve mitochondrial bioenergetics during acute liver intoxication. In our study, we have shown that acute CCl4-induced intoxication negatively affects Complex I (in the presence of glutamate-malate as energy substrates) based respiration, generation of mitochondrial membrane potential (ΔΨm), mitochondrial NAD(P)H pool and NADH redox index, mitochondrial calcium retention capacity (CRC) and structure and functions of the liver. Boosting of mitochondrial bioenergetics through the complex II, using succinate as metabolic substrate in vitro, significantly improved mitochondrial respiration and generation of ΔΨm, but not mitochondrial CRC. Co-application of rotenone along with succinate, to prevent possible reverse electron flow, didn't show significant differences compared to the effects of succinate alone. Treatment of animals with acute liver failure, using a metabolic supplement containing succinate, inosine, methionine and nicotinamide improved Complex I based respiration, generation of ΔΨm, mitochondrial NAD(P)H pool and NADH redox index, mitochondrial CRC and slightly decreased the level of oxidative stress. These changes resulted in averting destructive and dystrophic changes in the structure of rat liver tissue caused by CCl4 intoxication, concomitantly enhancing hepatic functionality. Thus, we propose that metabolic supplementation targeting complex II could serve as a potential adjunctive therapy in the management of acute liver intoxication.

Interactions between ferroptosis and tumour development mechanisms: Implications for gynaecological cancer therapy (Review)

Ferroptosis is a form of programmed cell death that is distinct from apoptosis. The mechanism involves redox‑active metallic iron and is characterized by an abnormal increase in iron‑dependent lipid reactive oxygen species, which results in high levels of membrane lipid peroxides. The relationship between ferroptosis and gynaecological tumours is complex. Ferroptosis can regulate tumour proliferation, metastasis and chemotherapy resistance, and targeting ferroptosis is a promising antitumour approach. Ferroptosis interacts with mechanisms related to tumorigenesis and development, such as macrophage polarization, the neutrophil trap network, mitochondrial autophagy and cuproptosis. The present review examines recent information on the interaction between the molecular mechanism of ferroptosis and other tumour‑related mechanisms, as well as the involvement of ferroptosis in gynaecological tumours, to identify implications for gynaecological cancer therapy.

Pharmacological Targeting of the NMDAR/TRPM4 Death Signaling Complex with a TwinF Interface Inhibitor Prevents Excitotoxicity-Associated Dendritic Blebbing and Organelle Damage

Focal swellings of dendrites ("dendritic blebbing") together with structural damage of mitochondria and the endoplasmic reticulum (ER) are morphological hallmarks of glutamate neurotoxicity, also known as excitotoxicity. These pathological alterations are generally thought to be caused by the so-called "overactivation" of N-methyl-D-aspartate receptors (NMDARs). Here, we demonstrate that the activation of extrasynaptic NMDARs, specifically when forming a protein-protein complex with TRPM4, drives these pathological traits. In contrast, strong activation of synaptic NMDARs fails to induce cell damage despite evoking plateau-type calcium signals that are comparable to those generated by activation of the NMDAR/TRPM4 complex, indicating that high intracellular calcium levels per se are not toxic to neurons. Using confocal laser scanning microscopy and transmission electron microscopy, we show that disrupting the NMDAR/TRPM4 complex using the recently discovered small-molecule TwinF interface inhibitor FP802 inhibits the NMDA-induced neurotoxicity-associated dendritic blebbing and structural damage to mitochondria and the ER. It also prevents, at least in part, the disruption of ER-mitochondria contact sites. These findings establish the NMDAR/TRPM4 complex as the trigger for the structural damage of dendrites and intracellular organelles associated with excitotoxicity. They also suggest that activation of the NMDAR/TRPM4 complex, in addition to inducing high-amplitude, plateau-type calcium signals, generates a second signal required for glutamate neurotoxicity ("two-hit hypothesis"). As structural damage to organelles, particularly mitochondria, is a common feature of many human neurodegenerative diseases, including Alzheimer's disease and amyotrophic lateral sclerosis (ALS), TwinF interface inhibitors have the potential to provide neuroprotection across a broad spectrum of these diseases.

Calcium signaling hypothesis: A non-negligible pathogenesis in Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD) presents a significant challenge to global healthcare systems, with an exacerbation by an aging population. Although the plethora of hypotheses are proposed to elucidate the underlying mechanisms of AD, from amyloid-beta (Aβ) accumulation and Tau protein aggregation to neuroinflammation, a comprehensive understanding of its pathogenesis remains elusive. Recent research has highlighted the critical role of calcium (Ca2+) signaling pathway in the progression of AD, indicating a complex interplay between Ca2+ dysregulation and various pathological processes.

AIM OF REVIEW

This review aims to consolidate the current understanding of the role of Ca2+ signaling dysregulation in AD, thus emphasizing its central role amidst various pathological hypotheses. We aim to evaluate the potential of the Ca2+ signaling hypothesis to unify existing theories of AD pathogenesis and explore its implications for developing innovative therapeutic strategies through targeting Ca2+ dysregulation.

KEY SCIENTIFIC CONCEPTS OF REVIEW

The review focuses on three principal concepts. First, the indispensable role of Ca2+ homeostasis in neuronal function and its disruption in AD. Second, the interaction between Ca2+ signaling dysfunction and established AD hypotheses posited that Ca2+ dysregulation is a unifying pathway. Third, the dual role of Ca2+ in neurodegeneration and neuroprotection, highlighting the nuanced effects of Ca2+ levels on AD pathology.

How does mitochondrial Ca2+ change during ischemia and reperfusion? Implications for activation of the permeability transition pore

Cardiac ischemia followed by reperfusion results in cardiac cell death, which has been attributed to an increase of mitochondrial Ca2+ concentration, resulting in activation of the mitochondrial permeability transition pore (PTP). Evaluating this hypothesis requires understanding of the mechanisms responsible for control of mitochondrial Ca2+ in physiological conditions and how they are altered during both ischemia and reperfusion. Ca2+ influx is thought to occur through the mitochondrial Ca2+ uniporter (MCU). However, with deletion of the MCU, an increase in mitochondrial Ca2+ still occurs, suggesting an alternative Ca2+ influx mechanism during ischemia. There is less certainty about the mechanisms responsible for Ca2+ efflux, with contributions from both Ca2+/H+ exchange and a Na+-dependent Ca2+ efflux pathway. The molecular details of both mechanisms are not fully resolved. We discuss this and the contributions of both pathways to the accumulation of mitochondrial Ca2+ during ischemia and reperfusion. We further discuss the role of mitochondrial Ca2+ in activation of the PTP.

From oxidative stress to metabolic dysfunction: The role of TRPM2

Metabolic syndromes including atherosclerosis, diabetes, obesity, and hypertension are increasingly prevalent worldwide. The disorders are the primary attributes of oxidative stress and inflammation. The transient receptor potential M2 (TRPM2) channel is a pivotal mediator linking oxidative stress to metabolic dysfunction. TRPM2, a non-selective cation channel activated by reactive oxygen species (ROS) and adenosine diphosphate ribose (ADPR), regulates calcium influx, inflammation, and cell death across various tissues. This review explores the structural and activation mechanisms of TRPM2, emphasizing its significance in metabolic diseases. Elevated levels of TRPM2 play a vital role in the disease progression by influencing physiological and cellular processes such as endothelial dysfunction, immune cell activation, and mitochondrial impairment. In conditions such as atherosclerosis, ischemic stroke, diabetes, obesity, and hypertension; TRPM2 exacerbates oxidative damage, amplifies inflammatory responses, and disrupts metabolic homeostasis. Recent research highlights the potential of TRPM2 as a therapeutic target, developing specified inhibitors. This review underscores the multifaceted role of TRPM2 in metabolic disorders and its promise as a target for therapeutic interventions.

Electrochemical sensing of transient ascorbate fluctuation under hypoxic stress in live rat brain

Hypoxia, a common cause of programmed cell death or apoptosis, represents a neuropathological process. Although certain response proteins to hypoxic stress and their effects on cell status and fate have been identified, the real-time quantification of smaller neurochemicals to understand pathogenic mechanism in live rat brain during such stress remains unexplored. In this study, by employing a cutting-edge electrochemical tool developed with carbon nanotube-sheathed carbon fiber microelectrode that offers remarkable selectivity and temporal/spatial resolution for monitoring ascorbate, we observed a substantial efflux of ascorbate in response to hypoxic stress in live rat brain. Furthermore, using a small molecule compound as channel inhibitor to investigate the behavior of ascorbate efflux, we found that this efflux is closely correlated with N-methyl-D-aspartic acid receptor-induced neuronal excitability. Notably, antagonistic actions on volume-sensitive anion channel can suppress ascorbate efflux evoked by hypoxic stress, further revealing that ascorbate fluctuation is volume-sensitive anion channel-dependent. This research not only facilitates a greater understanding of the neurochemical mechanism in hypoxia but also uncovers a potential biomarker for future closed-loop therapies.

Oxygen control in cell culture - Your cells may not be experiencing what you think!

Oxygen (O2)-controlled cell culture has been pivotal in studying mammalian mechanisms of O2 sensing, regulation, and utilization. We posit, however, that O2-controlled cell culture is paradoxically not controlling O2. There is overwhelming evidence that the pericellular O2 is lower than the surrounding gas phase due to cellular O2 consumption. Standard hypoxic cell culture is at high risk of inducing pericellular anoxia. We discuss the implications of poor O2 control for cellular O2 regulation mechanisms, bioenergetics, and redox signaling. We also highlight the evidence of frequent under-oxygenation in standard (i.e., normoxic) cell culture. This issue has been largely overlooked because strategies to control pericellular O2 have been lacking. Here, we propose a framework to control pericellular O2 based on our recent investigation into the nature of the gas/pericellular O2 gradient. Implementing this framework into standard practice will unlock quantitative O2 control in vitro, improving our ability to understand the role of O2 in biology.

SGLT2 inhibitors for alleviating heart failure through non-hypoglycemic mechanisms

Sodium-glucose cotransporter-2 (SGLT2) inhibitors afford significant cardiovascular benefits to patients with diabetes mellitus and heart failure. Three large randomized clinical trials (EMPAREG-Outcomes, DECLARE-TIMI58, and DAPA-HF) have shown that SGLT2 inhibitors prevent cardiovascular events and reduce the risk of death and hospital admission resulting from heart failure. Patients without type 2 diabetes mellitus (T2DM) also experience a similar degree of cardiovascular benefit as those with T2DM do. SGLT2 inhibitors could improve cardiac function through potential non-hypoglycemic mechanisms, including the reduction of the circulatory volume load, regulation of energy metabolism, maintenance of ion homeostasis, alleviation of inflammation and oxidative stress, and direct inhibition of cardiac SGLT1 receptors and antimyocardial fibrosis. This article reviews the mechanism through which SGLT2 inhibitors prevent/alleviate heart failure through non-hypoglycemic pathways, to support their use for the treatment of heart failure in non-T2DM patients.

Inhibiting Mitochondrial Damage for Efficient Treatment of Cerebral Ischemia-Reperfusion Injury Through Sequential Targeting Nanomedicine of Neuronal Mitochondria in Affected Brain Tissue

Oxidative stress, predominantly from neuronal mitochondrial damage and the resultant cytokine storm, is central to cerebral ischemia-reperfusion injury (CIRI). However, delivering drugs to neuronal mitochondria remains challenging due to the blood-brain barrier (BBB), which impedes drug entry into affected brain tissues. This study introduces an innovative tannic acid (TA) and melanin-modified heteropolyacid nanomedicine (MHT), which highly specifically eliminates the neuronal mitochondrial reactive oxygen radicals burst to efficiently reduce neuronal mitochondrial damage through a strategically designed sequential targeting strategy from affected brain tissue to neuronal mitochondria. TA endows MHT with sequential targeting ability by binding to matrix proteins exposed to the damaged BBB and mitochondrial outer membrane proteins of neurons, while melanin significantly enhances the antioxidant capacity of MHT. Consequently, MHT effectively inhibits neuronal apoptosis by protecting mitochondria and reversing the inflammatory immune environment through the deactivation of the cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway. MHT demonstrated a strong therapeutic effect on CIRI, with an ultralow dose (2 mg kg-1) proving effective in reversing the condition. This work not only introduces a new avenue to significantly reduce CIRI through sequential targeting therapy but also offers a new paradigm for treating other ischemia-reperfusion injury diseases.

TET3 regulates terminal cell differentiation at the metabolic level

TET-family members play a critical role in cell fate commitment. Indeed, TET3 is essential to postnatal development due to yet unknown reasons. To define TET3 function in cell differentiation, we have profiled the intestinal epithelium at single-cell level from wild-type and Tet3 knockout mice. We have found that Tet3 is mostly expressed in differentiated enterocytes. In the absence of TET3, enterocytes exhibit an aberrant differentiation trajectory and do not acquire a physiological cell identity due to an impairment in oxidative phosphorylation, specifically due to an ATP synthase assembly deficiency. Moreover, spatial metabolomics analysis has revealed that Tet3 knockout enterocytes exhibit an unphysiological metabolic profile when compared with their wild-type counterparts. In contrast, no metabolic differences have been observed between both genotypes in the stem cell compartment where Tet3 is mainly not expressed. Collectively, our findings suggest a mechanism by which TET3 regulates mitochondrial function and, thus, terminal cell differentiation at the metabolic level.

A transmitochondrial sodium gradient controls membrane potential in mammalian mitochondria

Eukaryotic cell function and survival rely on the use of a mitochondrial H+ electrochemical gradient (Δp), which is composed of an inner mitochondrial membrane (IMM) potential (ΔΨmt) and a pH gradient (ΔpH). So far, ΔΨmt has been assumed to be composed exclusively of H+. Here, using a rainbow of mitochondrial and nuclear genetic models, we have discovered that a Na+ gradient equates with the H+ gradient and controls half of ΔΨmt in coupled-respiring mammalian mitochondria. This parallelism is controlled by the activity of the long-sought Na+-specific Na+/H+ exchanger (mNHE), which we have identified as the P-module of complex I (CI). Deregulation of this mNHE function, without affecting the canonical enzymatic activity or the assembly of CI, occurs in Leber's hereditary optic neuropathy (LHON), which has profound consequences in ΔΨmt and mitochondrial Ca2+ homeostasis and explains the previously unknown molecular pathogenesis of this neurodegenerative disease.

The mitochondrial Na+/Ca2+ exchanger NCLX is implied in the activation of hypoxia-inducible factors

Eukaryotic cells and organisms depend on oxygen for basic living functions, and they display a panoply of adaptations to situations in which oxygen availability is diminished (hypoxia). A number of these responses in animals are mediated by changes in gene expression programs directed by hypoxia-inducible factors (HIFs), whose main mechanism of stabilization and functional activation in response to decreased cytosolic oxygen concentration was elucidated two decades ago. Human acute responses to hypoxia have been known for decades, although their precise molecular mechanism for oxygen sensing is not fully understood. It is already known that a redox component, linked with reactive oxygen species (ROS) production of mitochondrial origin, is implied in these responses. We have recently described a mechanism by which the mitochondrial sodium/calcium exchanger, NCLX, participates in mitochondrial electron transport chain regulation and ROS production in response to acute hypoxia. Here we show that NCLX is also implied in the response to hypoxia mediated by the HIFs. By using a NCLX inhibitor and interference RNA we show that NCLX activity is necessary for HIF-α subunits stabilization in hypoxia and for HIF-1-dependent transcriptional activity. We also show that hypoxic mitochondrial ROS production is not required for HIF-1α stabilization under all circumstances, suggesting that the basal cytosolic redox state or other mechanism(s) could be operating in the NCLX-mediated response to hypoxia that operates through HIF-α stabilization. This finding provides a link between acute and medium-term responses to hypoxia, reinforcing a central role of mitochondrial cell signalling in the response to hypoxia.

Sodium chloride in the tumor microenvironment enhances T cell metabolic fitness and cytotoxicity

The efficacy of antitumor immunity is associated with the metabolic state of cytotoxic T cells, which is sensitive to the tumor microenvironment. Whether ionic signals affect adaptive antitumor immune responses is unclear. In the present study, we show that there is an enrichment of sodium in solid tumors from patients with breast cancer. Sodium chloride (NaCl) enhances the activation state and effector functions of human CD8+ T cells, which is associated with enhanced metabolic fitness. These NaCl-induced effects translate into increased tumor cell killing in vitro and in vivo. Mechanistically, NaCl-induced changes in CD8+ T cells are linked to sodium-induced upregulation of Na+/K+-ATPase activity, followed by membrane hyperpolarization, which magnifies the electromotive force for T cell receptor (TCR)-induced calcium influx and downstream TCR signaling. We therefore propose that NaCl is a positive regulator of acute antitumor immunity that might be modulated for ex vivo conditioning of therapeutic T cells, such as CAR T cells.

The Influence of Oxidative Stress Markers in Patients with Ischemic Stroke

Stroke is the second leading cause of death worldwide, and its incidence is rising rapidly. Acute ischemic stroke is a subtype of stroke that accounts for the majority of stroke cases and has a high mortality rate. An effective treatment for stroke is to minimize damage to the brain's neural tissue by restoring blood flow to decreased perfusion areas of the brain. Many reports have concluded that both oxidative stress and excitotoxicity are the main pathological processes associated with ischemic stroke. Current measures to protect the brain against serious damage caused by stroke are insufficient. For this reason, it is important to investigate oxidative and antioxidant strategies to reduce oxidative damage. This review focuses on studies assessing the concentration of oxidative stress biomarkers and the level of antioxidants (enzymatic and non-enzymatic) and their impact on the clinical prognosis of patients after stroke. Mechanisms related to the production of ROS/RNS and the role of oxidative stress in the pathogenesis of ischemic stroke are presented, as well as new therapeutic strategies aimed at reducing the effects of ischemia and reperfusion.

Mitochondrial Calcium Regulation of Cardiac Metabolism in Health and Disease

Oxidative phosphorylation is regulated by mitochondrial calcium (Ca2+) in health and disease. In physiological states, Ca2+ enters via the mitochondrial Ca2+ uniporter and rapidly enhances NADH and ATP production. However, maintaining Ca2+ homeostasis is critical: insufficient Ca2+ impairs stress adaptation, and Ca2+ overload can trigger cell death. In this review, we delve into recent insights further defining the relationship between mitochondrial Ca2+ dynamics and oxidative phosphorylation. Our focus is on how such regulation affects cardiac function in health and disease, including heart failure, ischemia-reperfusion, arrhythmias, catecholaminergic polymorphic ventricular tachycardia, mitochondrial cardiomyopathies, Barth syndrome, and Friedreich's ataxia. Several themes emerge from recent data. First, mitochondrial Ca2+ regulation is critical for fuel substrate selection, metabolite import, and matching of ATP supply to demand. Second, mitochondrial Ca2+ regulates both the production and response to reactive oxygen species (ROS), and the balance between its pro- and antioxidant effects is key to how it contributes to physiological and pathological states. Third, Ca2+ exerts localized effects on the electron transport chain (ETC), not through traditional allosteric mechanisms but rather indirectly. These effects hinge on specific transporters, such as the uniporter or the Na+/Ca2+ exchanger, and may not be noticeable acutely, contributing differently to phenotypes depending on whether Ca2+ transporters are acutely or chronically modified. Perturbations in these novel relationships during disease states may either serve as compensatory mechanisms or exacerbate impairments in oxidative phosphorylation. Consequently, targeting mitochondrial Ca2+ holds promise as a therapeutic strategy for a variety of cardiac diseases characterized by contractile failure or arrhythmias.

Mitochondrial calcium uniporter complex: Unveiling the interplay between its regulators and calcium homeostasis

The mitochondrial calcium uniporter complex (MCUc), serving as the specific channel for calcium influx into the mitochondrial matrix, is integral to calcium homeostasis and cellular integrity. Given its importance, ongoing research spans various disease models to understand the properties of the MCUc in pathophysiological contexts, but reported a different conclusion. Therefore, this review delves into the profound connection between MCUc-mediated calcium transients and cellular signaling pathways, mitochondrial dynamics, metabolism, and cell death. Additionally, we shed light on the recent advancements concerning the structural intricacies and auxiliary components of the MCUc in both resting and activated states. Furthermore, emphasis is placed on novel extrinsic and intrinsic regulators of the MCUc and their therapeutic implications across a spectrum of diseases. Meanwhile, we employed molecular docking simulations and identified candidate traditional Chinese medicine components with potential binding sites to the MCUc, potentially offering insights for further research on MCUc modulation.

Revisiting reactive oxygen species production in hypoxia

Cellular responses to hypoxia are crucial in various physiological and pathophysiological contexts and have thus been extensively studied. This has led to a comprehensive understanding of the transcriptional response to hypoxia, which is regulated by hypoxia-inducible factors (HIFs). However, the detailed molecular mechanisms of HIF regulation in hypoxia remain incompletely understood. In particular, there is controversy surrounding the production of mitochondrial reactive oxygen species (ROS) in hypoxia and how this affects the stabilization and activity of HIFs. This review examines this controversy and attempts to shed light on its origin. We discuss the role of physioxia versus normoxia as baseline conditions that can affect the subsequent cellular response to hypoxia and highlight the paucity of data on pericellular oxygen levels in most experiments, leading to variable levels of hypoxia that might progress to anoxia over time. We analyze the different outcomes reported in isolated mitochondria, versus intact cells or whole organisms, and evaluate the reliability of various ROS-detecting tools. Finally, we examine the cell-type and context specificity of oxygen's various effects. We conclude that while recent evidence suggests that the effect of hypoxia on ROS production is highly dependent on the cell type and the duration of exposure, efforts should be made to conduct experiments under carefully controlled, physiological microenvironmental conditions in order to rule out potential artifacts and improve reproducibility in research.

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 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.

Hif1α-dependent mitochondrial acute O2 sensing and signaling to myocyte Ca2+ channels mediate arterial hypoxic vasodilation

Vasodilation in response to low oxygen (O2) tension (hypoxic vasodilation) is an essential homeostatic response of systemic arteries that facilitates O2 supply to tissues according to demand. However, how blood vessels react to O2 deficiency is not well understood. A common belief is that arterial myocytes are O2-sensitive. Supporting this concept, it has been shown that the activity of myocyte L-type Ca2+channels, the main ion channels responsible for vascular contractility, is reversibly inhibited by hypoxia, although the underlying molecular mechanisms have remained elusive. Here, we show that genetic or pharmacological disruption of mitochondrial electron transport selectively abolishes O2 modulation of Ca2+ channels and hypoxic vasodilation. Mitochondria function as O2 sensors and effectors that signal myocyte Ca2+ channels due to constitutive Hif1α-mediated expression of specific electron transport subunit isoforms. These findings reveal the acute O2-sensing mechanisms of vascular cells and may guide new developments in vascular pharmacology.

The Emerging Role of the Mitochondrial Respiratory Chain in Skeletal Aging

Maintenance of mitochondrial homeostasis is crucial for ensuring healthy mitochondria and normal cellular function. This process is primarily responsible for regulating processes that include mitochondrial OXPHOS, which generates ATP, as well as mitochondrial oxidative stress, apoptosis, calcium homeostasis, and mitophagy. Bone mesenchymal stem cells express factors that aid in bone formation and vascular growth. Positive regulation of hematopoietic stem cells in the bone marrow affects the differentiation of osteoclasts. Furthermore, the metabolic regulation of cells that play fundamental roles in various regions of the bone, as well as interactions within the bone microenvironment, actively participates in regulating bone integrity and aging. The maintenance of cellular homeostasis is dependent on the regulation of intracellular organelles, thus understanding the impact of mitochondrial functional changes on overall bone metabolism is crucially important. Recent studies have revealed that mitochondrial homeostasis can lead to morphological and functional abnormalities in senescent cells, particularly in the context of bone diseases. Mitochondrial dysfunction in skeletal diseases results in abnormal metabolism of bone-associated cells and a secondary dysregulated microenvironment within bone tissue. This imbalance in the oxidative system and immune disruption in the bone microenvironment ultimately leads to bone dysplasia. In this review, we examine the latest developments in mitochondrial respiratory chain regulation and its impacts on maintenance of bone health. Specifically, we explored whether enhancing mitochondrial function can reduce the occurrence of bone cell deterioration and improve bone metabolism. These findings offer prospects for developing bone remodeling biology strategies to treat age-related degenerative diseases.

Cox7a1 controls skeletal muscle physiology and heart regeneration through complex IV dimerization

The oxidative phosphorylation (OXPHOS) system is intricately organized, with respiratory complexes forming super-assembled quaternary structures whose assembly mechanisms and physiological roles remain under investigation. Cox7a2l, also known as Scaf1, facilitates complex III and complex IV (CIII-CIV) super-assembly, enhancing energetic efficiency in various species. We examined the role of Cox7a1, another Cox7a family member, in supercomplex assembly and muscle physiology. Zebrafish lacking Cox7a1 exhibited reduced CIV2 formation, metabolic alterations, and non-pathological muscle performance decline. Additionally, cox7a1-/- hearts displayed a pro-regenerative metabolic profile, impacting cardiac regenerative response. The distinct phenotypic effects of cox7a1-/- and cox7a2l-/- underscore the diverse metabolic and physiological consequences of impaired supercomplex formation, emphasizing the significance of Cox7a1 in muscle maturation within the OXPHOS system.

Mitochondrial mechanisms in the pathogenesis of chronic inflammatory musculoskeletal disorders

Chronic inflammatory musculoskeletal disorders characterized by prolonged muscle inflammation, resulting in enduring pain and diminished functionality, pose significant challenges for the patients. Emerging scientific evidence points to mitochondrial malfunction as a pivotal factor contributing to these ailments. Mitochondria play a critical role in powering skeletal muscle activity, but in the context of persistent inflammation, disruptions in their quantity, configuration, and performance have been well-documented. Various disturbances, encompassing alterations in mitochondrial dynamics (such as fission and fusion), calcium regulation, oxidative stress, biogenesis, and the process of mitophagy, are believed to play a central role in the progression of these disorders. Additionally, unfolded protein responses and the accumulation of fatty acids within muscle cells may adversely affect the internal milieu, impairing the equilibrium of mitochondrial functioning. The structural discrepancies between different mitochondrial subsets namely, intramyofibrillar and subsarcolemmal mitochondria likely impact their metabolic capabilities and susceptibility to inflammatory influences. The release of signals from damaged mitochondria is known to incite inflammatory responses. Intriguingly, migrasomes and extracellular vesicles serve as vehicles for intercellular transfer of mitochondria, aiding in the removal of impaired mitochondria and regulation of inflammation. Viral infections have been implicated in inducing stress on mitochondria. Prolonged dysfunction of these vital organelles sustains oxidative harm, metabolic irregularities, and heightened cytokine release, impeding the body's ability to repair tissues. This review provides a comprehensive analysis of advancements in understanding changes in the intracellular environment, mitochondrial architecture and distribution, biogenesis, dynamics, autophagy, oxidative stress, cytokines associated with mitochondria, vesicular structures, and associated membranes in the context of chronic inflammatory musculoskeletal disorders. Strategies targeting key elements regulating mitochondrial quality exhibit promise in the restoration of mitochondrial function, alleviation of inflammation, and enhancement of overall outcomes.

Redox regulation of UPR signalling and mitochondrial ER contact sites

Mitochondria and the endoplasmic reticulum (ER) have a synergistic relationship and are key regulatory hubs in maintaining cell homeostasis. Communication between these organelles is mediated by mitochondria ER contact sites (MERCS), allowing the exchange of material and information, modulating calcium homeostasis, redox signalling, lipid transfer and the regulation of mitochondrial dynamics. MERCS are dynamic structures that allow cells to respond to changes in the intracellular environment under normal homeostatic conditions, while their assembly/disassembly are affected by pathophysiological conditions such as ageing and disease. Disruption of protein folding in the ER lumen can activate the Unfolded Protein Response (UPR), promoting the remodelling of ER membranes and MERCS formation. The UPR stress receptor kinases PERK and IRE1, are located at or close to MERCS. UPR signalling can be adaptive or maladaptive, depending on whether the disruption in protein folding or ER stress is transient or sustained. Adaptive UPR signalling via MERCS can increase mitochondrial calcium import, metabolism and dynamics, while maladaptive UPR signalling can result in excessive calcium import and activation of apoptotic pathways. Targeting UPR signalling and the assembly of MERCS is an attractive therapeutic approach for a range of age-related conditions such as neurodegeneration and sarcopenia. This review highlights the emerging evidence related to the role of redox mediated UPR activation in orchestrating inter-organelle communication between the ER and mitochondria, and ultimately the determination of cell function and fate.

Replenishment of mitochondrial Na+ and H+ by ionophores potentiates cutaneous wound healing in diabetes

Diabetic foot ulcer (DFU) is a highly morbid complication in patients with diabetes mellitus, necessitating the development of innovative pharmaceuticals to address unmet medical needs. Sodium ion (Na+) is a well-established mediator for membrane potential and osmotic equilibrium. Recently, Na+ transporters have been identified as a functional regulator of regeneration. However, the role of Na+ in the intricate healing process of mammalian wounds remains elusive. Here, we found that the skin wounds in hyponatremic mice display a hard-to-heal phenotype. Na+ ionophores that were employed to increase intracellular Na+ content could facilitate keratinocyte proliferation and migration, and promote angiogenesis, exhibiting diverse biological activities. Among of them, monensin A emerges as a promising agent for accelerating the healing dynamics of skin wounds in diabetes. Mechanistically, the elevated mitochondrial Na+ decelerates inner mitochondrial membrane fluidity, instigating the production of reactive oxygen species (ROS), which is identified as a critical effector on the monensin A-induced improvement of wound healing. Concurrently, Na+ ionophores replenish H+ to the mitochondrial matrix, causing an enhancement of mitochondrial energy metabolism to support productive wound healing programs. Our study unfolds a new role of Na+, which is a pivotal determinant in wound healing. Furthermore, it directs a roadmap for developing Na+ ionophores as innovative pharmaceuticals for treating chronic dermal wounds in diabetic patients.

Monitoring mitochondrial calcium in cardiomyocytes during coverslip hypoxia using a fluorescent lifetime indicator

An increase in mitochondrial calcium via the mitochondrial calcium uniporter (MCU) has been implicated in initiating cell death in the heart during ischemia-reperfusion (I/R) injury. Measurement of calcium during I/R has been challenging due to the pH sensitivity of indicators coupled with the fall in pH during I/R. The development of a pH-insensitive indicator, mitochondrial localized Turquoise Calcium fluorescence Lifetime Sensor (mito-TqFLITS), allows for quantifying mitochondrial calcium during I/R via fluorescent lifetime imaging. Mitochondrial calcium was monitored using mito-TqFLITS, in neonatal mouse ventricular myocytes (NMVM) isolated from germline MCU-KO mice and MCUfl/fl treated with CRE-recombinase to acutely knockout MCU. To simulate ischemia, a coverslip was placed on a monolayer of NMVMs to prevent access to oxygen and nutrients. Reperfusion was induced by removing the coverslip. Mitochondrial calcium increases threefold during coverslip hypoxia in MCU-WT. There is a significant increase in mitochondrial calcium during coverslip hypoxia in germline MCU-KO, but it is significantly lower than in MCU-WT. We also found that compared to WT, acute MCU-KO resulted in no difference in mitochondrial calcium during coverslip hypoxia and reoxygenation. To determine the role of mitochondrial calcium uptake via MCU in initiating cell death, we used propidium iodide to measure cell death. We found a significant increase in cell death in both the germline MCU-KO and acute MCU-KO, but this was similar to their respective WTs. These data demonstrate the utility of mito-TqFLITS to monitor mitochondrial calcium during simulated I/R and further show that germline loss of MCU attenuates the rise in mitochondrial calcium during ischemia but does not reduce cell death.

Functional hypoxia reduces mitochondrial calcium uptake

Mitochondrial respiration extends beyond ATP generation, with the organelle participating in many cellular and physiological processes. Parallel changes in components of the mitochondrial electron transfer system with respiration render it an appropriate hub for coordinating cellular adaption to changes in oxygen levels. How changes in respiration under functional hypoxia (i.e., when intracellular O2 levels limit mitochondrial respiration) are relayed by the electron transfer system to impact mitochondrial adaption and remodeling after hypoxic exposure remains poorly defined. This is largely due to challenges integrating findings under controlled and defined O2 levels in studies connecting functions of isolated mitochondria to humans during physical exercise. Here we present experiments under conditions of hypoxia in isolated mitochondria, myotubes and exercising humans. Performing steady-state respirometry with isolated mitochondria we found that oxygen limitation of respiration reduced electron flow and oxidative phosphorylation, lowered the mitochondrial membrane potential difference, and decreased mitochondrial calcium influx. Similarly, in myotubes under functional hypoxia mitochondrial calcium uptake decreased in response to sarcoplasmic reticulum calcium release for contraction. In both myotubes and human skeletal muscle this blunted mitochondrial adaptive responses and remodeling upon contractions. Our results suggest that by regulating calcium uptake the mitochondrial electron transfer system is a hub for coordinating cellular adaption under functional hypoxia.

The involvement of ROS-regulated programmed cell death in hepatocellular carcinoma

Reactive oxidative species (ROS) is a crucial factor in the regulation of cellular biological activity and function, and aberrant levels of ROS can contribute to the development of a variety of diseases, particularly cancer. Numerous discoveries have affirmed that this process is strongly associated with "programmed cell death (PCD)," which refers to the suicide protection mechanism initiated by cells in response to external stimuli, such as apoptosis, autophagy, ferroptosis, etc. Research has demonstrated that ROS-induced PCD is crucial for the development of hepatocellular carcinoma (HCC). These activities serve a dual function in both facilitating and inhibiting cancer, suggesting the existence of a delicate balance within healthy cells that can be disrupted by the abnormal generation of reactive oxygen species (ROS), thereby influencing the eventual advancement or regression of a tumor. In this review, we summarize how ROS regulates PCD to influence the tumorigenesis and progression of HCC. Studying how ROS-induced PCD affects the progression of HCC at a molecular level can help develop better prevention and treatment methods and facilitate the design of more effective preventative and therapeutic strategies.

Crosstalk between hypoxia-induced pyroptosis and immune escape in cancer: From mechanisms to therapy

Pyroptosis can be triggered through both canonical and non-canonical inflammasome pathways, involving the cleavage of gasdermin (GSDM) protein family members, like GSDMD and GSDME. The impact of pyroptosis on tumors is nuanced, because its role in regulating cancer progression and anti-tumor immunity may vary depending on the tumor type, stage, location, and immune status. However, pyroptosis cannot be simply categorized as promoting or inhibiting tumors based solely on whether it is acute or chronic in nature. The interplay between pyroptosis and cancer is intricate, with some evidence suggesting that chronic pyroptosis may facilitate tumor growth, while the acute induction of pyroptosis could stimulate anti-cancer immune responses. Tumor hypoxia activates hypoxia inducible factor (HIF) signaling to modulate pyroptosis and immune checkpoint expression. Targeting this hypoxia-pyroptosis-immune escape axis could be a promising therapeutic strategy. This review highlights the complex crosstalk between hypoxia, pyroptosis, and immune evasion in the TME.

Reactive oxygen species generation by reverse electron transfer at mitochondrial complex I under simulated early reperfusion conditions

Ischemic tissues accumulate succinate, which is rapidly oxidized upon reperfusion, driving a burst of mitochondrial reactive oxygen species (ROS) generation that triggers cell death. In isolated mitochondria with succinate as the sole metabolic substrate under non-phosphorylating conditions, 90 % of ROS generation is from reverse electron transfer (RET) at the Q site of respiratory complex I (Cx-I). Together, these observations suggest Cx-I RET is the source of pathologic ROS in reperfusion injury. However, numerous factors present in early reperfusion may impact Cx-I RET, including: (i) High [NADH]; (ii) High [lactate]; (iii) Mildly acidic pH; (iv) Defined ATP/ADP ratios; (v) Presence of the nucleosides adenosine and inosine; and (vi) Defined free [Ca2+]. Herein, experiments with mouse cardiac mitochondria revealed that under simulated early reperfusion conditions including these factors, total mitochondrial ROS generation was only 56 ± 17 % of that seen with succinate alone (mean ± 95 % confidence intervals). Of this ROS, only 52 ± 20 % was assignable to Cx-I RET. A further 14 ± 7 % could be assigned to complex III, with the remainder (34 ± 11 %) likely originating from other ROS sources upstream of the Cx-I Q site. Together, these data suggest the relative contribution of Cx-I RET ROS to reperfusion injury may be overestimated, and other ROS sources may contribute a significant fraction of ROS in early reperfusion.

Are reactive oxygen species always bad? Lessons from hypoxic ectotherms

Oxygen (O2) is required for aerobic energy metabolism but can produce reactive oxygen species (ROS), which are a wide variety of oxidant molecules with a range of biological functions from causing cell damage (oxidative distress) to cell signalling (oxidative eustress). The balance between the rate and amount of ROS generated and the capacity for scavenging systems to remove them is affected by several biological and environmental factors, including oxygen availability. Ectotherms, and in particular hypoxia-tolerant ectotherms, are hypothesized to avoid oxidative damage caused by hypoxia, although it is unclear whether this translates to an increase in ecological fitness. In this Review, we highlight the differences between oxidative distress and eustress, the current mechanistic understanding of the two and how they may affect ectothermic physiology. We discuss the evidence of occurrence of oxidative damage with hypoxia in ectotherms, and that ectotherms may avoid oxidative damage through (1) high levels of antioxidant and scavenging systems and/or (2) low(ering) levels of ROS generation. We argue that the disagreements in the literature as to how hypoxia affects antioxidant enzyme activity and the variable metabolism of ectotherms makes the latter strategy more amenable to ectotherm physiology. Finally, we argue that observed changes in ROS production and oxidative status with hypoxia may be a signalling mechanism and an adaptive strategy for ectotherms encountering hypoxia.

Mechanical Stress Induces Sodium Entry and Osmoprotective Responses in Murine Synovial Fibroblasts

Osteoarthritis (OA) is a multifactorial disease depending on molecular, genetic, and environmental factors like mechanical strain. Next to the cartilage and the subchondral bone, OA also affects the synovium, which is critically involved in the maintenance of joint homeostasis. As there is a correlation between the extracellular sodium content in the knee joint and OA, this study investigates the impact of sodium on OA-associated processes like inflammation and bone remodeling without and with mechanical loading in synovial fibroblasts. For that purpose, murine synovial fibroblasts from the knee joint were exposed to three different extracellular sodium chloride concentrations (-20 mM, ±0 mM and +50 mM NaCl) in the absence or presence of compressive or intermittent tensile strain. In addition to the intracellular Na+ content and gene expression of the osmoprotective transcription factor nuclear factor of activated T cells 5 (Nfat5), the gene and protein expression of inflammatory mediators (interleukin-6 (IL6), prostaglandin endoperoxide synthase-2 (Ptgs2)/prostaglandin E2 (PGE2)), and factors involved in bone metabolism (receptor activator of NF-κB ligand (RANKL), osteoprotegerin (OPG)) were analyzed by qPCR and ELISA. Mechanical strain already increased intracellular Na+ and Nfat5 gene expression at standard salt conditions to levels obtained by exposure to increased extracellular Na+ content. Both high salt and compressive strain resulted in elevated IL6 and PGE2 release. Intermittent tensile strain did not increase Il6 mRNA expression or IL6 protein secretion but triggered Ptgs2 expression and PGE2 production. Increased extracellular Na+ levels and compressive strain increased RANKL expression. In contrast, intermittent tension suppressed RANKL expression without this response being subject to modification by extracellular sodium availability. OPG expression was only induced by compressive strain. Changes in extracellular Na+ levels modified the inflammatory response and altered the expression of mediators involved in bone metabolism in cells exposed to mechanical strain. These findings indicate that Na+ balance and Nfat5 are important players in synovial fibroblast responses to mechanical stress. The integration of Na+ and Na+-dependent signaling will help to improve the understanding of the pathogenesis of osteoarthritis and could lead to the establishment of new therapeutic targets.

Sodium as an Important Regulator of Immunometabolism

Salt sensitivity concerns blood pressure alterations after a change in salt intake (sodium chloride). The heart is a pump, and vessels are tubes; sodium can affect both. A high salt intake increases cardiac output, promotes vascular dysfunction and capillary rarefaction, and chronically leads to increased systemic vascular resistance. More recent findings suggest that sodium also acts as an important second messenger regulating energy metabolism and cellular functions. Besides endothelial cells and fibroblasts, sodium also affects innate and adaptive immunometabolism, immune cell function, and influences certain microbes and microbiota-derived metabolites. We propose the idea that the definition of salt sensitivity should be expanded beyond high blood pressure to cellular and molecular salt sensitivity.

Current advances in modulating tumor hypoxia for enhanced therapeutic efficacy

Hypoxia is a common feature of most solid tumors, which promotes the proliferation, invasion, metastasis, and therapeutic resistance of tumors. Researchers have been developing advanced strategies and nanoplatforms to modulate tumor hypoxia to enhance therapeutic effects. A timely review of this rapidly developing research topic is therefore highly desirable. For this purpose, this review first introduces the impact of hypoxia on tumor development and therapeutic resistance in detail. Current developments in the construction of various nanoplatforms to enhance tumor treatment in response to hypoxia are also systematically summarized, including hypoxia-overcoming, hypoxia-exploiting, and hypoxia-disregarding strategies. We provide a detailed discussion of the rationale and research progress of these strategies. Through a review of current trends, it is hoped that this comprehensive overview can provide new prospects for clinical application in tumor treatment. STATEMENT OF SIGNIFICANCE: As a common feature of most solid tumors, hypoxia significantly promotes tumor progression. Advanced nanoplatforms have been developed to modulate tumor hypoxia to enhanced therapeutic effects. In this review, we first introduce the impact of hypoxia on tumor progression. Current developments in the construction of various nanoplatforms to enhance tumor treatment in response to hypoxia are systematically summarized, including hypoxia-overcoming, hypoxia-exploiting, and hypoxia-disregarding strategies. We discuss the rationale and research progress of the above strategies in detail, and finally introduce future challenges for treatment of hypoxic tumors. By reviewing the current trends, this comprehensive overview can provide new prospects for clinical translatable tumor therapy.

Research progress on the physiological response and molecular mechanism of cold response in plants

Low temperature is a critical environmental stress factor that restricts crop growth and geographical distribution, significantly impacting crop quality and yield. When plants are exposed to low temperatures, a series of changes occur in their external morphology and internal physiological and biochemical metabolism. This article comprehensively reviews the alterations and regulatory mechanisms of physiological and biochemical indices, such as membrane system stability, redox system, fatty acid content, photosynthesis, and osmoregulatory substances, in response to low-temperature stress in plants. Furthermore, we summarize recent research on signal transduction and regulatory pathways, phytohormones, epigenetic modifications, and other molecular mechanisms mediating the response to low temperatures in higher plants. In addition, we outline cultivation practices to improve plant cold resistance and highlight the cold-related genes used in molecular breeding. Last, we discuss future research directions, potential application prospects of plant cold resistance breeding, and recent significant breakthroughs in the research and application of cold resistance mechanisms.

Progress in understanding of relationship between inflammation and tumors

Over the past decade, there has been clear evidence that inflammation plays a key role in tumorigenesis. Tumor extrinsic inflammation is caused by many factors, including bacterial and viral infections, autoimmune diseases, obesity, smoking, excessive alcohol consumption, etc., all of which can increase cancer risk and stimulate malignant progression. Conversely, inflammation inherent in cancer or caused by cancer can be triggered by cancer-initiating mutations and can promote malignant progression through recruitment and activation of inflammatory cells. Both exogenous and endogenous inflammation can lead to immunosuppression, thus providing a preferred opportunity for tumor development. Studies have confirmed that chronic inflammation is involved in various steps of tumorigenesis, including cell transformation, promotion, survival, prolifer-ation, invasion, angiogenesis, and metastasis. Recent research has shed new light on the molecular and cellular circuits between inflammation and cancer. Two pathways have been preliminarily identified: Intrinsic and extrinsic. In the intrinsic pathway, genetic events leading to tumors initiate the expression of inflammatory related programs and guide the construction of the inflammatory microenvironment. In the extrinsic pathway, inflammatory conditions promote the development of cancer. This article reviews the recent progress in the understanding of the relationship between inflammation and tumors.

Prospects of Intravenous Coenzyme Q10 Administration in Emergency Ischemic Conditions

Coenzyme CoQ10 (CoQ10) is an endogenous lipid-soluble antioxidant that effectively protects lipids, proteins, and DNA from oxidation due to its ability to undergo redox transitions between oxidized and reduced forms. Various oxidative stress-associated infectious and somatic diseases have been observed to disrupt the balance of CoQ10 concentration in tissues. As a high molecular weight polar lipophilic compound, CoQ10 exhibits very limited oral bioavailability, which restrains its therapeutic potential. Nevertheless, numerous studies have confirmed the clinical efficacy of CoQ10 therapy through oral administration of high doses over extended time periods. Experimental studies have demonstrated that in emergency situations, intravenous administration of both oxidized and reduced-form CoQ10 leads to a rapid increase in its concentration in organ tissues, offering protection for organ tissues in ischemic conditions. This suggests that the cardio- and neuroprotective efficacy of intravenously administered CoQ10 forms could present new opportunities in treating acute ischemic conditions. Based on these findings, the review provides reasoning supporting further research and implementation of CoQ10 dosage forms for intravenous administration in emergency situations into clinical practice.

mROS‑calcium feedback loop promotes lethal ventricular arrhythmias and sudden cardiac death in early myocardial ischemia

Lethal ventricular arrhythmia‑sudden cardiac death (LVA‑SCD) occurs frequently during the early stage of myocardial ischemia (MI). However, the mechanism underlying higher LVA‑SCD incidence is still poorly understood. The present study aimed to explore the role of mitochondrial reactive oxygen species (mROS) and Ca2+ crosstalk in promoting LVA‑SCD in early MI. RyR2 S2814A mice and their wild‑type littermates were used. MitoTEMPO was applied to scavenge mitochondrial ROS (mROS). Mice were subjected to severe MI and the occurrence of LVA‑SCD was evaluated. Levels of mitochondrial ROS and calcium (mitoCa2+), cytosolic ROS (cytoROS), and calcium (cytoCa2+), RyR2 Ser‑2814 phosphorylation, CaMKII Met‑282 oxidation, mitochondrial membrane potential (MMP), and glutathione/oxidized glutathione (GSH/GSSG) ratio in the myocardia were detected. Dynamic changes in mROS after hypoxia were investigated using H9c2 cells. Moreover, the myocardial phosphoproteome was analyzed to explore the related mechanisms facilitating mROS‑Ca2+ crosstalk and LVA‑SCD. There was a high incidence (~33.9%) of LVA‑SCD in early MI. Mice who underwent SCD displayed notably elevated levels of myocardial ROS and mROS, and the latter was validated in H9c2 cells. These mice also demonstrated overloads of cytoplasmic and mitochondrial Ca2+, decreased MMP and reduced GSH/GSSG ratio, upregulated RyR2‑S2814 phosphorylation and CaMKII‑M282 oxidation and transient hyperphosphorylation of mitochondrial proteomes in the myocardium. mROS‑specific scavenging by a mitochondria‑targeted antioxidant agent (MitoTEMPO) corrected these SCD‑induced alterations. S2814A mice with a genetically inactivated CaMKII phosphorylation site in RyR2 exhibited decreased overloads in cytoplasmic and mitochondrial Ca2+ and demonstrated similar effects as MitoTEMPO to correct SCD‑induced changes and prevent SCD post‑MI. The data confirmed crosstalk between mROS and Ca2+ in promoting LVA‑SCD. Therefore, we provided evidence that there is a higher incidence of LVA‑SCD in early MI, which may be attributed to a positive feedback loop between mROS and Ca2+ imbalance.