Review: Using isolated mitochondria to investigate mitochondrial hydrogen peroxide metabolism

From workout to molecular switches: How does skeletal muscle produce, sense, and transduce subcellular redox signals?

Skeletal muscle is crucial for maintaining human health and overall quality of life. Acute exercise introduces a multifaceted intracellular stress, with numerous post-translational modifications believed to underpin the health benefits of sustained exercise training. Reactive oxygen species (ROS) are posited to serve as second messengers, triggering cytoprotective adaptations such as the upregulation of enzymatic scavenger systems. However, a significant knowledge gap exists between the generation of oxidants in muscle and the exact mechanisms driving muscle adaptations. This review delves into the current research on subcellular redox biochemistry and its role in the physiological adaptations to exercise. We propose that the subcellular regulation of specific redox modifications is key to ensuring specificity in the intracellular response.

Mitochondria as intracellular signalling organelles. An update

Traditionally, mitochondria are known as "the powerhouse of the cell," responsible for energy (ATP) generation (by the electron transport chain, oxidative phosphorylation, the tricarboxylic acid cycle, and fatty acid ß-oxidation), and for the regulation of several metabolic processes, including redox homeostasis, calcium signalling, and cellular apoptosis. The extensive studies conducted in the last decades portray mitochondria as multifaceted signalling organelles that ultimately command cells' survival or death. Based on current knowledge, we'll outline the mitochondrial signalling to other intracellular compartments in homeostasis and pathology-related mitochondrial stress conditions here. The following topics are discussed: (i) oxidative stress and mtROS signalling in mitohormesis, (ii) mitochondrial Ca²⁺ signalling; (iii) the anterograde (nucleus-to-mitochondria) and retrograde (mitochondria-to-nucleus) signal transduction, (iv) the mtDNA role in immunity and inflammation, (v) the induction of mitophagy- and apoptosis - signalling cascades, (vi) the mitochondrial dysfunctions (mitochondriopathies) in cardiovascular, neurodegenerative, and malignant diseases. The novel insights into molecular mechanisms of mitochondria-mediated signalling can explain mitochondria adaptation to metabolic and environmental stresses to achieve cell survival.

Rates of warming impact oxidative stress in zebrafish (Danio rerio)

Potentially negative effects of thermal variation on physiological functions may be modulated by compensatory responses, but their efficacy depends on the timescale of phenotypic adjustment relative to the rate of temperature change. Increasing temperatures in particular can affect mitochondrial bioenergetics and rates of reactive oxygen species (ROS) production. Our aim was to test whether different rates of temperature increase impact mitochondrial bioenergetics and modulate oxidative stress. We exposed zebrafish (Danio rerio) to warming from 20 to 28°C over 3, 6, 24, or 48 h, and compared these to a control group that was kept at constant 20°C. Fish exposed to the fastest (3 h) and slowest (48 h) rates of warming had significantly higher rates of H2O2 production relative to the control treatment, and the proportion of O2 converted to H2O2 (H2O2/O2 ratio) was significantly greater in these groups. However, ROS production was not paralleled by differences in mitochondrial substrate oxidation rates, leak respiration rates, or coupling (respiratory control ratios). Increased rates of ROS production did not lead to damage of proteins or membranes, which may be explained by a moderate increase in catalase activity at the fastest, but not the slowest rate of warming. The increase in ROS production at the slowest rate of heating indicates that even seemingly benign environments may be stressful. Understanding how animals respond to different rates of temperature change is important, because the rate determines the time period for phenotypic adjustments and it also alters the environmental thermal signal that triggers compensatory pathways.

Is Ferroptosis a Key Component of the Process Leading to Multiorgan Damage in COVID-19?

Even though COVID-19 is mostly well-known for affecting respiratory pathology, it can also result in several extrapulmonary manifestations, leading to multiorgan damage. A recent reported case of SARS-CoV-2 myocarditis with cardiogenic shock showed a signature of myocardial and kidney ferroptosis, a novel, iron-dependent programmed cell death. The term ferroptosis was coined in the last decade to describe the form of cell death induced by the small molecule erastin. As a specific inducer of ferroptosis, erastin inhibits cystine-glutamate antiporter system Xc-, blocking transportation into the cytoplasm of cystine, a precursor of glutathione (GSH) in exchange with glutamate and the consequent malfunction of GPX4. Ferroptosis is also promoted by intracellular iron overload and by the iron-dependent accumulation of polyunsaturated fatty acids (PUFA)-derived lipid peroxides. Since depletion of GSH, inactivation of GPX4, altered iron metabolism, and upregulation of PUFA peroxidation by reactive oxygen species are peculiar signs of COVID-19, there is the possibility that SARS-CoV-2 may trigger ferroptosis in the cells of multiple organs, thus contributing to multiorgan damage. Here, we review the molecular mechanisms of ferroptosis and its possible relationship with SARS-CoV-2 infection and multiorgan damage. Finally, we analyze the potential interventions that may combat ferroptosis and, therefore, reduce multiorgan damage.