How does density of the inner mitochondrial membrane influence mitochondrial performance?

Photothermal imaging of cellular responses to glucose deprivation

In solid tumours, cancer cells modify their metabolic processes to endure environments with nutrient and oxygen scarcity due to inadequate blood flow. A thorough understanding of this adaptive mechanism, which requires reliable microscopic techniques, is crucial for developing effective cancer treatments. In the present study, we used multi-wavelength photothermal (PT) microscopy to visualise the cellular response to glucose deprivation in living cells derived from cervical cancer. We found increased mitochondrial PT signal intensity under glucose deprivation conditions, which is indicative of a correlation between mitochondrial crista density and PT signal intensity. Furthermore, PT microscopy revealed that the activity of the autophagy-lysosome system can be evaluated by detecting substances accumulated in lysosomes. Using this method, we confirmed that ferritin and denatured proteins from the endoplasmic reticulum were present within the lysosomes. The detectability of these substances using PT microscopy at visible wavelengths indicated the presence of iron ions. This method does not require labeling of molecules and provides reliable information and detailed insights into the cellular responses associated with the adaptation of cancer cell metabolism to nutrient stress conditions.

Product of Traditional Chinese Medicine Longgui Yangxinwan Protects the Human Body from Altitude Sickness Damage by Reducing Oxidative Stress and Preventing Mitochondrial Dysfunction

Yu Liu, Zhengyang Zhang, Yongting Luo, Peng An, Jingyi Qi, Xu Zhang, Shuaishuai Zhou, Yongzhi Li, Chong Xu, Junjie Luo, and Jiaping Wang. Product of traditional Chinese medicine longgui yangxinwan protects the human body from altitude sickness damage by reducing oxidative stress and preventing mitochondrial dysfunction. High Alt Med Biol. 26:20-29, 2025. Background: Plateau reaction, caused by high-altitude exposure, results in symptoms like headaches, dyspnea, palpitations, fatigue, shortness of breath, and insomnia due to reduced oxygen levels. Mitochondria are crucial for high-altitude acclimatization as they regulate oxygen metabolism and cellular energy, reducing oxidative stress and maintaining bodily functions. Methods: The study participants were randomly divided into placebo group, Rhodiola group and longgui yangxinwan (Original name: taikong yangxinwan) group, with 20 people in each group. Three groups of subjects were sampled at three time points (PI: pre-intervention; P-D1: high-altitude day 1; P-D7: high-altitude day 7), and blood pressure, blood oxygen, heart rate, hemoglobin, and red blood cell count were measured. The ATP content, mitochondrial DNA copy number, expression of mitochondria-related genes, reactive oxygen species (ROS), glutathione peroxidase (GSH-PX) and malondialdehyde (MDA) levels, and mitochondrial morphology were measured in blood at each time point. Results: Our study results demonstrate that longgui yangxinwan keeps the selected human physiological indicators stable and prevents mitochondrial dysfunction in the high altitude. Mechanically, longgui yangxinwan decreases the level of ROS in human serum, whereas increases the activity of the antioxidant enzyme GSH-PX. At high-altitude day 1 (P-D1) and high-altitude day 7 (P-D7), ROS in the placebo group were 1.5 and 2.2-fold higher than those of the longgui yangxinwan group, respectively. In addition, longgui yangxinwan enhances ATP production capacity, restores the levels of mitochondrial respiratory chain complexes, and effectively maintains mitochondrial morphology and integrity. At P-D1 and P-D7, the ATP levels in the longgui yangxinwan group were 19-fold and 26-fold higher than those in the placebo group, respectively. Conclusions: Our study highlights longgui yangxinwan as a potential drug for protecting humans from high-altitude damage by reducing oxidative stress and preventing mitochondrial dysfunction.

How the Topology of the Mitochondrial Inner Membrane Modulates ATP Production

Cells in heart muscle need to generate ATP at or near peak capacity to meet their energy demands. Over 90% of this ATP comes from mitochondria, strategically located near myofibrils and densely packed with cristae to concentrate ATP generation per unit volume. However, a consequence of dense inner membrane (IM) packing is that restricted metabolite diffusion inside mitochondria may limit ATP production. Under physiological conditions, the flux of ATP synthase is set by ADP levels in the matrix, which in turn depends on diffusion-dependent concentration of ADP inside cristae. Computer simulations show how ADP diffusion and consequently rates of ATP synthesis are modulated by IM topology, in particular (i) number, size, and positioning of crista junctions that connect cristae to the IM boundary region, and (ii) branching of cristae. Predictions are compared with the actual IM topology of a cardiomyocyte mitochondrion in which cristae vary systematically in length and morphology. The analysis indicates that this IM topology decreases but does not eliminate the "diffusion penalty" on ATP output. It is proposed that IM topology normally attenuates mitochondrial ATP output under conditions of low workload and can be regulated by the cell to better match ATP supply to demand.

Mechanisms that Alter Capacity for Adenosine Triphosphate Production and Oxidative Phosphorylation: Insights from Avian Migration

Avian migration is among the most energetically demanding feats observed in animals. Studies evaluating the physiological underpinnings of migration have repeatedly shown that migratory birds display numerous adaptations that ultimately supply the flight muscle mitochondria with abundant fuel and oxygen during long-distance flights. To make use of this high input, the organs and mitochondria of migrants are predicted to display several traits that maximize their capacity to produce adenosine triphosphate (ATP). This review aims to introduce readers to several mechanisms by which organs and mitochondria can alter their capacity for oxidative phosphorylation and ATP production. The role of organ size, mitochondrial volume, substrate, and oxygen delivery to the electron transport system are discussed. A central theme of this review is the role of changes in electron chain complex activity, mitochondrial morphology and dynamics, and supercomplexes in allowing avian migrants and other taxa to alter the performance of the electron transport system with predictable shifts in demand. It is my hope that this review will serve as a springboard for future studies exploring the mechanisms that alter bioenergetic capacity across animal species.

Ferroptosis in Cardiovascular Diseases and Ferroptosis-Related Intervention Approaches

OBJECTIVE

Cardiovascular diseases (CVDs) are major public health problems that threaten the lives and health of individuals. The article has reviewed recent progresses about ferroptosis and ferroptosis-related intervention approaches for the treatment of CVDs and provided more references and strategies for targeting ferroptosis to prevent and treat CVDs.

METHODS

A comprehensive review was conducted using the literature researches.

RESULTS AND DISCUSSION

Many ferroptosis-targeted compounds and ferroptosis-related genes may be prospective targets for treating CVDs and our review provides a solid foundation for further studies about the detailed pathological mechanisms of CVDs.

CONCLUSION

There are challenges and limitations about the translation of ferroptosis-targeted potential therapies from experimental research to clinical practice. It warrants further exploration to pursure safer and more effective ferroptosis-targeted thereapeutic approaches for CVDs.

Mitochondria and MICOS - function and modeling

An extensive review is presented on mitochondrial structure and function, mitochondrial proteins, the outer and inner membranes, cristae, the role of F1FO-ATP synthase, the mitochondrial contact site and cristae organizing system (MICOS), the sorting and assembly machinery morphology and function, and phospholipids, in particular cardiolipin. Aspects of mitochondrial regulation under physiological and pathological conditions are outlined, in particular the role of dysregulated MICOS protein subunit Mic60 in Parkinson's disease, the relations between mitochondrial quality control and proteins, and mitochondria as signaling organelles. A mathematical modeling approach of cristae and MICOS using mechanical beam theory is introduced and outlined. The proposed modeling is based on the premise that an optimization framework can be used for a better understanding of critical mitochondrial function and also to better map certain experiments and clinical interventions.

Heterogeneous distribution of mitochondria and succinate dehydrogenase activity in human airway smooth muscle cells

Succinate dehydrogenase (SDH) is a key mitochondrial enzyme involved in the tricarboxylic acid cycle, where it facilitates the oxidation of succinate to fumarate, and is coupled to the reduction of ubiquinone in the electron transport chain as Complex II. Previously, we developed a confocal-based quantitative histochemical technique to determine the maximum velocity of the SDH reaction (SDHmax) in single cells and observed that SDHmax corresponds with mitochondrial volume density. In addition, mitochondrial volume and motility varied within different compartments of human airway smooth muscle (hASM) cells. Therefore, we hypothesize that the SDH activity varies relative to the intracellular mitochondrial volume within hASM cells. Using 3D confocal imaging of labeled mitochondria and a concentric shell method for analysis, we quantified mitochondrial volume density, mitochondrial complexity index, and SDHmax relative to the distance from the nuclear membrane. The mitochondria within individual hASM cells were more filamentous in the immediate perinuclear region and were more fragmented in the distal parts of the cell. Within each shell, SDHmax also corresponded to mitochondrial volume density, where both peaked in the perinuclear region and decreased in more distal parts of the cell. Additionally, when normalized to mitochondrial volume, SDHmax was lower in the perinuclear region when compared to the distal parts of the cell. In summary, our results demonstrate that SDHmax measures differences in SDH activity within different cellular compartments. Importantly, our data indicate that mitochondria within individual cells are morphologically heterogeneous, and their distribution varies substantially within different cellular compartments, with distinct functional properties.

Alcohol Triggers the Accumulation of Oxidatively Damaged Proteins in Neuronal Cells and Tissues

Alcohol is toxic to neurons and can trigger alcohol-related brain damage, neuronal loss, and cognitive decline. Neuronal cells may be vulnerable to alcohol toxicity and damage from oxidative stress after differentiation. To consider this further, the toxicity of alcohol to undifferentiated SH-SY5Y cells was compared with that of cells that had been acutely differentiated. Cells were exposed to alcohol over a concentration range of 0-200 mM for up to 24 h and alcohol effects on cell viability were evaluated via MTT and LDH assays. Effects on mitochondrial morphology were examined via transmission electron microscopy, and mitochondrial functionality was examined using measurements of ATP and the production of reactive oxygen species (ROS). Alcohol reduced cell viability and depleted ATP levels in a concentration- and exposure duration-dependent manner, with undifferentiated cells more vulnerable to toxicity. Alcohol exposure resulted in neurite retraction, altered mitochondrial morphology, and increased the levels of ROS in proportion to alcohol concentration; these peaked after 3 and 6 h exposures and were significantly higher in differentiated cells. Protein carbonyl content (PCC) lagged behind ROS production and peaked after 12 and 24 h, increasing in proportion to alcohol concentration, with higher levels in differentiated cells. Carbonylated proteins were characterised by their denatured molecular weights and overlapped with those from adult post-mortem brain tissue, with levels of PCC higher in alcoholic subjects than matched controls. Hence, alcohol can potentially trigger cell and tissue damage from oxidative stress and the accumulation of oxidatively damaged proteins.

Cardiac lipidomic profiles in mice undergo changes from fetus to adult

AIMS

Lipids are essential cellular components with many important biological functions. Disturbed lipid biosynthesis and metabolism has been shown to cause cardiac developmental abnormality and cardiovascular diseases. In this study, we aimed to investigate the composition and the molecular profiles of lipids in mammalian hearts between embryonic and adult stages and uncover the underlying links between lipid and cardiac development and maturation.

MATERIALS AND METHODS

We collected mouse hearts at the embryonic day 11.5 (E11.5), E15.5, and the age of 2 months, 4 months and 10 months, and performed lipidomic analysis to determine the changes of the composition, molecular species, and relative abundance of cardiac lipids between embryonic and adult stages. Additionally, we also performed the electronic microscopy and RNA sequencing in both embryonic and adult mouse hearts.

KEY FINDINGS

The relative abundances of certain phospholipids and sphingolipids including cardiolipin, phosphatidylglycerol, phosphatidylethanolamine, and ceramide, are different between embryonic and adult hearts. Such lipidomic changes are accompanied with increased densities of mitochondrial membranes and elevated expression of genes related to mitochondrial formation in adult mouse hearts. We also analyzed individual molecular species of phospholipids and sphingolipids, and revealed that the composition and distribution of lipid molecular species in hearts also change with development.

SIGNIFICANCE

Our study provides not only a lipidomic view of mammalian hearts when developing from the embryonic to the adult stage, but also a potential pool of lipid indicators for cardiac cell development and maturation.

Skeletal muscle mitochondria demonstrate similar respiration per cristae surface area independent of training status and sex in healthy humans

The impact of training status and sex on intrinsic skeletal muscle mitochondrial respiratory capacity remains unclear. We examined this by analysing human skeletal muscle mitochondrial respiration relative to mitochondrial volume and cristae density across training statuses and sexes. Mitochondrial cristae density was estimated in skeletal muscle biopsies originating from previous independent studies. Participants included females (n = 12) and males (n = 41) across training statuses ranging from untrained (UT, n = 8), recreationally active (RA, n = 9), active-to-elite runners (RUN, n = 27) and cross-country skiers (XC, n = 9). The XC and RUN groups demonstrated higher mitochondrial volume density than the RA and UT groups while all active groups (RA, RUN and XC) displayed higher mass-specific capacity of oxidative phosphorylation (OXPHOS) and mitochondrial cristae density than UT. Differences in OXPHOS diminished between active groups and UT when normalising to mitochondrial volume density and were lost when normalising to muscle cristae surface area density. Moreover, active females (n = 6-9) and males (n = 15-18) did not differ in mitochondrial volume and cristae density, OXPHOS, or when normalising OXPHOS to mitochondrial volume density and muscle cristae surface area density. These findings demonstrate: (1) differences in OXPHOS between active and untrained individuals may be explained by both higher mitochondrial volume and cristae density in active individuals, with no difference in intrinsic mitochondrial respiratory capacity (OXPHOS per muscle cristae surface area density); and (2) no sex differences in mitochondrial volume and cristae density or mass-specific and normalised OXPHOS. This highlights the importance of normalising OXPHOS to muscle cristae surface area density when studying skeletal muscle mitochondrial biology. KEY POINTS: Oxidative phosphorylation is the mitochondrial process by which ATP is produced, governed by the electrochemical gradient across the inner mitochondrial membrane with infoldings named cristae. In human skeletal muscle, the mass-specific capacity of oxidative phosphorylation (OXPHOS) can change independently of shifts in mitochondrial volume density, which may be attributed to variations in cristae density. We demonstrate that differences in skeletal muscle OXPHOS between healthy females and males, ranging from untrained to elite endurance athletes, are matched by differences in cristae density. This suggests that higher OXPHOS in skeletal muscles of active individuals is attributable to an increase in the density of cristae. These findings broaden our understanding of the variability in human skeletal muscle OXPHOS and highlight the significance of cristae, specific to mitochondrial respiration.

Structural Analysis of Mitochondria in Cardiomyocytes: Insights into Bioenergetics and Membrane Remodeling

Mitochondria in mammalian cardiomyocytes display considerable structural heterogeneity, the significance of which is not currently understood. We use electron microscopic tomography to analyze a dataset of 68 mitochondrial subvolumes to look for correlations among mitochondrial size and shape, crista morphology and membrane density, and organelle location within rat cardiac myocytes. A tomographic analysis guided the definition of four classes of crista morphology: lamellar, tubular, mixed and transitional, the last associated with remodeling between lamellar and tubular cristae. Correlations include an apparent bias for mitochondria with lamellar cristae to be located in the regions between myofibrils and a two-fold larger crista membrane density in mitochondria with lamellar cristae relative to mitochondria with tubular cristae. The examination of individual cristae inside mitochondria reveals local variations in crista topology, such as extent of branching, alignment of fenestrations and progressive changes in membrane morphology and packing density. The findings suggest both a rationale for the interfibrillar location of lamellar mitochondria and a pathway for crista remodeling from lamellar to tubular morphology.

Using Live Cell STED Imaging to Visualize Mitochondrial Inner Membrane Ultrastructure in Neuronal Cell Models

Mitochondria play many essential roles in the cell, including energy production, regulation of Ca2+ homeostasis, lipid biosynthesis, and production of reactive oxygen species (ROS). These mitochondria-mediated processes take on specialized roles in neurons, coordinating aerobic metabolism to meet the high energy demands of these cells, modulating Ca2+ signaling, providing lipids for axon growth and regeneration, and tuning ROS production for neuronal development and function. Mitochondrial dysfunction is therefore a central driver in neurodegenerative diseases. Mitochondrial structure and function are inextricably linked. The morphologically complex inner membrane with structural infolds called cristae harbors many molecular systems that perform the signature processes of the mitochondrion. The architectural features of the inner membrane are ultrastructural and therefore, too small to be visualized by traditional diffraction-limited resolved microscopy. Thus, most insights on mitochondrial ultrastructure have come from electron microscopy on fixed samples. However, emerging technologies in super-resolution fluorescence microscopy now provide resolution down to tens of nanometers, allowing visualization of ultrastructural features in live cells. Super-resolution imaging therefore offers an unprecedented ability to directly image fine details of mitochondrial structure, nanoscale protein distributions, and cristae dynamics, providing fundamental new insights that link mitochondria to human health and disease. This protocol presents the use of stimulated emission depletion (STED) super-resolution microscopy to visualize the mitochondrial ultrastructure of live human neuroblastoma cells and primary rat neurons. This procedure is organized into five sections: (1) growth and differentiation of the SH-SY5Y cell line, (2) isolation, plating, and growth of primary rat hippocampal neurons, (3) procedures for staining cells for live STED imaging, (4) procedures for live cell STED experiments using a STED microscope for reference, and (5) guidance for segmentation and image processing using examples to measure and quantify morphological features of the inner membrane.

Exploration of Optimal pH in Hypothermic Machine Perfusion for Rat Liver Grafts Retrieved after Circulatory Death

Ex vivo hypothermic machine perfusion (HMP) is a strategy for controlling ischemia-reperfusion injury in donation after circulatory death (DCD) liver transplantation. The pH of blood increases with a decrease in temperature and water dissociation, leading to a decrease in [H⁺]. This study aimed to verify the optimal pH of HMP for DCD livers. Rat livers were retrieved 30 min post-cardiac arrest and subjected to 3-h cold storage (CS) in UW solution (CS group) or HMP with UW-gluconate solution (machine perfusion [MP] group) of pH 7.4 (original), 7.6, 7.8, and 8.0 (MP-pH 7.6, 7.8, 8.0 groups, respectively) at 7-10 °C. The livers were subjected to normothermic perfusion to simulate reperfusion after HMP. All HMP groups showed greater graft protection compared to the CS group due to the lower levels of liver enzymes in the former. The MP-pH 7.8 group showed significant protection, evidenced by bile production, diminished tissue injury, and reduced flavin mononucleotide leakage, and further analysis by scanning electron microscopy revealed a well-preserved structure of the mitochondrial cristae. Therefore, the optimum pH of 7.8 enhanced the protective effect of HMP by preserving the structure and function of the mitochondria, leading to reduced reperfusion injury in the DCD liver.