Mitochondrial Morphology and Mitophagy in Heart Diseases: Qualitative and Quantitative Analyses Using Transmission Electron Microscopy

Gastrodin exerts perioperative myocardial protection by improving mitophagy through the PINK1/Parkin pathway to reduce myocardial ischemia-reperfusion injury

BACKGROUND

Although blood flow is restored after treatment of myocardial infarction (MI), myocardial ischemia and reperfusion (I/R) can cause cardiac injury, which is a leading cause of heart failure. Gastrodin (GAS) exerts protective effects against brain, heart, and kidney I/R. However, its pharmacological mechanism in myocardial I/R injury (MIRI) remains unclear.

PURPOSE

GAS regulates autophagy in various diseases, such as acute hepatitis, vascular dementia, and stroke. We hypothesized that GAS could repair mitochondrial damage and regulate autophagy to protect against MIRI.

STUDY DESIGN

Male C57BL/6 mice and H9C2 cells were subjected to I/R and hypoxia-reoxygenation (H/R) injury after GAS administration, respectively, to assess the impact of GAS on cardiomyocyte phenotypes, heart, and mitochondrial structure and function. The effect of GAS on cardiac function and mitochondrial structure in patients undergoing cardiac surgery has been observed in clinical practice.

METHODS

The effects of GAS on cardiac structure and function, mitochondrial structure, and expression of related molecules in an animal model of MIRI were evaluated using immunohistochemical staining, enzyme-linked immunosorbent assay (ELISA), transmission electron microscopy, western blotting, and gene sequencing. Its effects on the morphological, molecular, and functional phenotypes of cardiomyocytes undergoing H/R were observed using immunohistochemical staining, real-time quantitative PCR, and western blotting.

RESULTS

GAS significantly reduces myocardial infarct size and improves cardiac function in MIRI mice in animal models and increases cardiomyocyte viability and reduces cardiomyocyte damage in cellular models. In clinical practice, myocardial injury was alleviated with better cardiac function in patients undergoing cardiac surgery after the application of GAS; improvements in mitochondria and autophagy activation were also observed. GAS primarily exerts cardioprotective effects through activation of the PINK1/Parkin pathway, which promotes mitochondrial autophagy to clear damaged mitochondria.

CONCLUSION

GAS can promote mitophagy and preserve mitochondria through PINK1/Parkin, thus indicating its tremendous potential as an effective perioperative myocardial protective agent.

MICOS Complex Loss Governs Age-Associated Murine Mitochondrial Architecture and Metabolism in the Liver, While Sam50 Dictates Diet Changes

The liver, the largest internal organ and a metabolic hub, undergoes significant declines due to aging, affecting mitochondrial function and increasing the risk of systemic liver diseases. How the mitochondrial three-dimensional (3D) structure changes in the liver across aging, and the biological mechanisms regulating such changes confers remain unclear. In this study, we employed Serial Block Face-Scanning Electron Microscopy (SBF-SEM) to achieve high-resolution 3D reconstructions of murine liver mitochondria to observe diverse phenotypes and structural alterations that occur with age, marked by a reduction in size and complexity. We also show concomitant metabolomic and lipidomic changes in aged samples. Aged human samples reflected altered disease risk. To find potential regulators of this change, we examined the Mitochondrial Contact Site and Cristae Organizing System (MICOS) complex, which plays a crucial role in maintaining mitochondrial architecture. We observe that the MICOS complex is lost during aging, but not Sam50. Sam50 is a component of the sorting and assembly machinery (SAM) complex that acts in tandem with the MICOS complex to modulate cristae morphology. In murine models subjected to a high-fat diet, there is a marked depletion of the mitochondrial protein SAM50. This reduction in Sam50 expression may heighten the susceptibility to liver disease, as our human biobank studies corroborate that Sam50 plays a genetically regulated role in the predisposition to multiple liver diseases. We further show that changes in mitochondrial calcium dysregulation and oxidative stress accompany the disruption of the MICOS complex. Together, we establish that a decrease in mitochondrial complexity and dysregulated metabolism occur with murine liver aging. While these changes are partially be regulated by age-related loss of the MICOS complex, the confluence of a murine high-fat diet can also cause loss of Sam50, which contributes to liver diseases. In summary, our study reveals potential regulators that affect age-related changes in mitochondrial structure and metabolism, which can be targeted in future therapeutic techniques.

Ultrastructural cardiac pathology: the wide (yet so very small) world of cardiac electron microscopy

Electron microscopy (EM) was a popular diagnostic tool in the 1970s and early 80s. With the adoption of newer, less expensive techniques, such as immunohistochemistry, the role of EM in diagnostic surgical pathology has dwindled substantially. Nowadays, even in academic centers, EM interpretation is relegated to renal pathologists and the handful of (aging) pathologists with experience using the technique. As such, EM interpretation is truly arcane-understood by few and mysterious to many. Nevertheless, there remain situations in which EM is the best or only ancillary test to ascertain a specific diagnosis. Thus, there remains a critical need for the younger generation of surgical pathologists to learn EM interpretation. Recognizing this need, cardiac EM was made the theme of the Cardiovascular Evening Specialty Conference at the 2023 United States and Canadian Academy of Pathology (USCAP) annual meeting in New Orleans, Louisiana. Each of the speakers contributed their part to this article, the purpose of which is to review EM as it pertains to myocardial tissue and provide illustrative examples of the spectrum of ultrastructural cardiac pathology seen in storage/metabolic diseases, cardiomyopathies, infiltrative disorders, and cardiotoxicities.

Exploiting sweet relief for preeclampsia by targeting autophagy-lysosomal machinery and proteinopathy

The etiology of preeclampsia (PE), a severe complication of pregnancy with several clinical manifestations and a high incidence of maternal and fetal morbidity and mortality, remains unclear. This issue is a major hurdle for effective treatment strategies. We recently demonstrated that PE exhibits an Alzheimer-like etiology of impaired autophagy and proteinopathy in the placenta. Targeting of these pathological pathways may be a novel therapeutic strategy for PE. Stimulation of autophagy with the natural disaccharide trehalose and its lacto analog lactotrehalose in hypoxia-exposed primary human trophoblasts restored autophagy, inhibited the accumulation of toxic protein aggregates, and restored the ultrastructural features of autophagosomes and autolysosomes. Importantly, trehalose and lactotrehalose inhibited the onset of PE-like features in a humanized mouse model by normalizing autophagy and inhibiting protein aggregation in the placenta. These disaccharides restored the autophagy-lysosomal biogenesis machinery by increasing nuclear translocation of the master transcriptional regulator TFEB. RNA-seq analysis of the placentas of mice with PE indicated the normalization of the PE-associated transcriptome profile in response to trehalose and lactotrehalose. In summary, our results provide a novel molecular rationale for impaired autophagy and proteinopathy in patients with PE and identify treatment with trehalose and its lacto analog as promising therapeutic options for this severe pregnancy complication.

Transcriptome, histological, and physiological responses of Amur sleeper (Perccottus glenii) during cold stress, freezing, and recovery

Freeze tolerance is a survival strategy employed by some ectotherms living in extremely cold environments. Some fish in extremely cold areas can recover from their frozen state, but they also have to endure cold stress. Amur sleeper (Perccottus glenii) can recover from a completely frozen state. To explore the response of freeze-resistant fish to low temperatures, we analyzed histological alterations, and antioxidant and carbohydrate-lipid metabolizing enzymes of P. glenii under low temperatures. So far, sensory genes regulating P. glenii during cold stress, freezing, and recovery have not been identified. Ultrastructure results indicated that glycogen content and mitochondrial ridge decreased during cold stress and freezing, whereas the number of endoplasmic reticulum increased during recovery. Plasma glucose and glycerol levels of the three treatment groups significantly increased. Lactate dehydrogenase and pyruvate kinase levels significantly increased during cold stress and freezing, and hexokinase levels significantly increased during cold stress. In total, 30,560 unigenes were found (average length 1724 bp, N50 2843 bp). In addition, 7370 differentially expressed genes (DEGs; including 2938 upregulated genes and 4432 downregulated genes) were identified. KEGG analysis revealed that the DEGs were enriched in carbohydrate and lipid metabolism, lipid synthesis, immune system, and anti-apoptosis. Genes involved in glycolysis and phospholipid metabolism were significantly upregulated during cold stress; genes related to circadian rhythm, oxidative phosphorylation, and lipid synthesis were significantly upregulated during freezing; and genes involved in the immune system and anti-apoptosis were significantly upregulated during recovery. Our results attempt to offer new insights into the physiological mechanisms of complex adaptation in P. glenii and provide useful information for future studies on the mechanism underlying freezing/recovery in animals.

The interplay between sex, time of day, fasting status, and their impact on cardiac mitochondrial structure, function, and dynamics

Mitochondria morphology and function, and their quality control by mitophagy, are essential for heart function. We investigated whether these are influenced by time of the day (TOD), sex, and fed or fasting status, using transmission electron microscopy (EM), mitochondrial electron transport chain (ETC) activity, and mito-QC reporter mice. We observed peak mitochondrial number at ZT8 in the fed state, which was dependent on the intrinsic cardiac circadian clock, as hearts from cardiomyocyte-specific BMAL1 knockout (CBK) mice exhibit different TOD responses. In contrast to mitochondrial number, mitochondrial ETC activities do not fluctuate across TOD, but decrease immediately and significantly in response to fasting. Concurrent with the loss of ETC activities, ETC proteins were decreased with fasting, simultaneous with significant increases of mitophagy, mitochondrial antioxidant protein SOD2, and the fission protein DRP1. Fasting-induced mitophagy was lost in CBK mice, indicating a direct role of BMAL1 in regulating mitophagy. This is the first of its kind report to demonstrate the interactions between sex, fasting, and TOD on cardiac mitochondrial structure, function and mitophagy. These studies provide a foundation for future investigations of mitochondrial functional perturbation in aging and heart diseases.

RNA binding protein IGF2BP2 expression is induced by stress in the heart and mediates dilated cardiomyopathy

The IGF2BP family of RNA binding proteins consists of three paralogs that regulate intracellular RNA localization, RNA stability, and translational control. Although IGF2BP1 and 3 are oncofetal proteins, IGF2BP2 expression is maintained in many tissues, including the heart, into adulthood. IGF2BP2 is upregulated in cardiomyocytes during cardiac stress and remodeling and returns to normal levels in recovering hearts. We wondered whether IGF2BP2 might play an adaptive role during cardiac stress and recovery. Enhanced expression of an IGF2BP2 transgene in a conditional, inducible mouse line leads to dilated cardiomyopathy (DCM) and death within 3-4 weeks in newborn or adult hearts. Downregulation of the transgene after 2 weeks, however, rescues these mice, with complete recovery by 12 weeks. Hearts overexpressing IGF2BP2 downregulate sarcomeric and mitochondrial proteins and have fragmented mitochondria and elongated, thinner sarcomeres. IGF2BP2 is also upregulated in DCM or myocardial infarction patients. These results suggest that IGF2BP2 may be an attractive target for therapeutic intervention in cardiomyopathies.

Propionic acid induces alterations in mitochondrial morphology and dynamics in SH-SY5Y cells

Propionic acid (PPA) is used to study the role of mitochondrial dysfunction in neurodevelopmental conditions like autism spectrum disorders. PPA is known to disrupt mitochondrial biogenesis, metabolism, and turnover. However, the effect of PPA on mitochondrial dynamics, fission, and fusion remains challenging to study due to the complex temporal nature of these mechanisms. Here, we use complementary quantitative visualization techniques to examine how PPA influences mitochondrial ultrastructure, morphology, and dynamics in neuronal-like SH-SY5Y cells. PPA (5 mM) induced a significant decrease in mitochondrial area (p < 0.01), Feret's diameter and perimeter (p < 0.05), and in area2 (p < 0.01). Mitochondrial event localiser analysis demonstrated a significant increase in fission and fusion events (p < 0.05) that preserved mitochondrial network integrity under stress. Moreover, mRNA expression of cMYC (p < 0.0001), NRF1 (p < 0.01), TFAM (p < 0.05), STOML2 (p < 0.0001), and OPA1 (p < 0.01) was significantly decreased. This illustrates a remodeling of mitochondrial morphology, biogenesis, and dynamics to preserve function under stress. Our data provide new insights into the influence of PPA on mitochondrial dynamics and highlight the utility of visualization techniques to study the complex regulatory mechanisms involved in the mitochondrial stress response.

Ustiloxin A inhibits proliferation of renal tubular epithelial cells in vitro and induces renal injury in mice by disrupting structure and respiratory function of mitochondria

Recently, we found that Ustiloxin A (UA, a mycotoxin) was widely detected in paddy environment and rice samples from several countries, and was also detected in human urine samples from China. However, the current knowledge about the health risks of UA are limited. In this research, the cytotoxicity of UA in mice renal tubular epithelial cells (mRTECs) was evaluated, and the results indicated that UA arrested cell cycle in G2/M phase via altering cellular morphology and microtubule, and inhibited the proliferation and division of mRTECs. Furthermore, UA could inhibit mitochondrial respiration via binding to the CoQ-binding site in dihydro-orotate dehydrogenase (DHODH) protein, and resulted in mitochondrial damage. These adverse effects of UA on mitochondria might be responsible for the cytotoxicity observed in vitro. In vivo, UA at concentrations that were comparable to the realistic concentrations of human exposure induced renal insufficiency in mice, and this might be associated with the renal mitochondrial damage in mice. However, exposure to UA at those realistic concentrations did not promote the progression from renal insufficiency to renal fibrosis and chronic kidney disease was not observed in mice.

Mitochondrial Dynamics during Development

Mitochondria are dynamic membrane-bound organelles in eukaryotic cells. These are important for the generation of chemical energy needed to power various cellular functions and also support metabolic, energetic, and epigenetic regulation in various cells. These organelles are also important for communication with the nucleus and other cellular structures, to maintain developmental sequences and somatic homeostasis, and for cellular adaptation to stress. Increasing information shows mitochondrial defects as an important cause of inherited disorders in different organ systems. In this article, we provide an extensive review of ontogeny, ultrastructural morphology, biogenesis, functional dynamics, important clinical manifestations of mitochondrial dysfunction, and possibilities for clinical intervention. We present information from our own clinical and laboratory research in conjunction with information collected from an extensive search in the databases PubMed, EMBASE, and Scopus.

Structural Analysis of Mitochondrial Dynamics-From Cardiomyocytes to Osteoblasts: A Critical Review

Mitochondria play a crucial role in cell physiology and pathophysiology. In this context, mitochondrial dynamics and, subsequently, mitochondrial ultrastructure have increasingly become hot topics in modern research, with a focus on mitochondrial fission and fusion. Thus, the dynamics of mitochondria in several diseases have been intensively investigated, especially with a view to developing new promising treatment options. However, the majority of recent studies are performed in highly energy-dependent tissues, such as cardiac, hepatic, and neuronal tissues. In contrast, publications on mitochondrial dynamics from the orthopedic or trauma fields are quite rare, even if there are common cellular mechanisms in cardiovascular and bone tissue, especially regarding bone infection. The present report summarizes the spectrum of mitochondrial alterations in the cardiovascular system and compares it to the state of knowledge in the musculoskeletal system. The present paper summarizes recent knowledge regarding mitochondrial dynamics and gives a short, but not exhaustive, overview of its regulation via fission and fusion. Furthermore, the article highlights hypoxia and its accompanying increased mitochondrial fission as a possible link between cardiac ischemia and inflammatory diseases of the bone, such as osteomyelitis. This opens new innovative perspectives not only for the understanding of cellular pathomechanisms in osteomyelitis but also for potential new treatment options.

Electron microscopy of cardiac 3D nanodynamics: form, function, future

The 3D nanostructure of the heart, its dynamic deformation during cycles of contraction and relaxation, and the effects of this deformation on cell function remain largely uncharted territory. Over the past decade, the first inroads have been made towards 3D reconstruction of heart cells, with a native resolution of around 1 nm³, and of individual molecules relevant to heart function at a near-atomic scale. These advances have provided access to a new generation of data and have driven the development of increasingly smart, artificial intelligence-based, deep-learning image-analysis algorithms. By high-pressure freezing of cardiomyocytes with millisecond accuracy after initiation of an action potential, pseudodynamic snapshots of contraction-induced deformation of intracellular organelles can now be captured. In combination with functional studies, such as fluorescence imaging, exciting insights into cardiac autoregulatory processes at nano-to-micro scales are starting to emerge. In this Review, we discuss the progress in this fascinating new field to highlight the fundamental scientific insight that has emerged, based on technological breakthroughs in biological sample preparation, 3D imaging and data analysis; to illustrate the potential clinical relevance of understanding 3D cardiac nanodynamics; and to predict further progress that we can reasonably expect to see over the next 10 years.

Migraine-Associated Mutation in the Na,K-ATPase Leads to Disturbances in Cardiac Metabolism and Reduced Cardiac Function

Background

Mutations in ATP1A2 gene encoding the Na,K‐ATPase α₂ isoform are associated with familial hemiplegic migraine type 2. Migraine with aura is a known risk factor for heart disease. The Na,K‐ATPase is important for cardiac function, but its role for heart disease remains unknown. We hypothesized that ATP1A2 is a susceptibility gene for heart disease and aimed to assess the underlying disease mechanism.

Methods and Results

Mice heterozygous for the familial hemiplegic migraine type 2–associated G301R mutation in the Atp1a2 gene (α₂^+/G301R mice) and matching wild‐type controls were compared. Reduced expression of the Na,K‐ATPase α₂ isoform and increased expression of the α₁ isoform were observed in hearts from α₂^+/G301R mice (Western blot). Left ventricular dilation and reduced ejection fraction were shown in hearts from 8‐month‐old α₂^+/G301R mice (cardiac magnetic resonance imaging), and this was associated with reduced nocturnal blood pressure (radiotelemetry). Cardiac function and blood pressure of 3‐month‐old α₂^+/G301R mice were similar to wild‐type mice. Amplified Na,K‐ATPase–dependent Src kinase/Ras/Erk1/2 (p44/42 mitogen‐activated protein kinase) signaling was observed in hearts from 8‐month‐old α₂^+/G301R mice, and this was associated with mitochondrial uncoupling (respirometry), increased oxidative stress (malondialdehyde measurements), and a heart failure–associated metabolic shift (hyperpolarized magnetic resonance). Mitochondrial membrane potential (5,5´,6,6´‐tetrachloro‐1,1´,3,3´‐tetraethylbenzimidazolocarbocyanine iodide dye assay) and mitochondrial ultrastructure (transmission electron microscopy) were similar between the groups. Proteomics of heart tissue further suggested amplified Src/Ras/Erk1/2 signaling and increased oxidative stress and provided the molecular basis for systolic dysfunction in 8‐month‐old α₂^+/G301R mice.

Conclusions

Our findings suggest that ATP1A2 mutation leads to disturbed cardiac metabolism and reduced cardiac function mediated via Na,K‐ATPase–dependent reactive oxygen species signaling through the Src/Ras/Erk1/2 pathway.