The Combination of Paraformaldehyde and Glutaraldehyde Is a Potential Fixative for Mitochondria

AutoMitoNetwork: Software for analyzing mitochondrial networks in autofluorescence images to enable label-free cell classification

High-resolution mitochondria imaging in combination with image analysis tools have significantly advanced our understanding of cellular function in health and disease. However, most image analysis tools for mitochondrial studies have been designed to work with fluorescently labeled images only. Additionally, efforts to integrate features describing mitochondrial networks with machine learning techniques for the differentiation of cell types have been limited. Herein, we present AutoMitoNetwork software for image-based assessment of mitochondrial networks in label-free autofluorescence images using a range of interpretable morphological, intensity, and textural features. To demonstrate its utility, we characterized unstained mitochondrial networks in healthy retinal cells and in retinal cells exposed to two types of treatments: rotenone, which directly inhibited mitochondrial respiration and ATP production, and iodoacetic acid, which had a milder impact on mitochondrial networks via the inhibition of anaerobic glycolysis. For both cases, our multi-dimensional feature analysis combined with a support vector machine classifier distinguished between healthy cells and those treated with rotenone or iodoacetic acid. Subtle changes in morphological features were measured including increased fragmentation in the treated retinal cells, pointing to an association with metabolic mechanisms. AutoMitoNetwork opens new options for image-based machine learning in label-free imaging, diagnostics, and mitochondrial disease drug development.

Evaluating Bacterial Spore Preparation Methods for Scanning Electron Microscopy

Scanning electron microscopy (SEM) can reveal the ultrastructure of bacterial spores, including morphology, surface features, texture, spore damage, germination, and appendages. Understanding these features can provide a basis for adherence, how physical and environmental stressors affect spore viability, integrity, and functionality, as well as the distribution and function of surface appendages. However, the spore sample preparation method can significantly impact the SEM images' appearance, resolution, and overall quality. In this study, we compare different spore preparation methods to identify optimal approaches for preparation time, spore appearance and resolved features, including the exosporium and spore pili, for SEM imaging. We use Bacillus paranthracis as model species and evaluate the efficacy of preparation protocols using different fixation and drying methods, as well as imaging under room- and cryogenic temperatures. We compare and assess method complexity to the visibility of the spore exosporium and spore appendages across different methods. Additionally, we use Haralick texture features to quantify the differences in spore surface appearance and determine the most suitable method for preserving spore structures and surface features during SEM evaluation. The findings from this study will help establish protocols for preparing bacterial spores for SEM and facilitating accurate and reliable analysis of spores' characteristics.

Approaching Maximum Resolution in Structured Illumination Microscopy via Accurate Noise Modeling

Biological images captured by microscopes are characterized by heterogeneous signal-to-noise ratios (SNRs) due to spatially varying photon emission across the field of view convoluted with camera noise. State-of-the-art unsupervised structured illumination microscopy (SIM) reconstruction algorithms, commonly implemented in the Fourier domain, do not accurately model this noise and suffer from high-frequency artifacts, user-dependent choices of smoothness constraints making assumptions on biological features, and unphysical negative values in the recovered fluorescence intensity map. On the other hand, supervised methods rely on large datasets for training, and often require retraining for new sample structures. Consequently, achieving high contrast near the maximum theoretical resolution in an unsupervised, physically principled, manner remains an open problem. Here, we propose Bayesian-SIM (B-SIM), an unsupervised Bayesian framework to quantitatively reconstruct SIM data, rectifying these shortcomings by accurately incorporating known noise sources in the spatial domain. To accelerate the reconstruction process, we use the finite extent of the point-spread-function to devise a parallelized Monte Carlo strategy involving chunking and restitching of the inferred fluorescence intensity. We benchmark our framework on both simulated and experimental images, and demonstrate improved contrast permitting feature recovery at up to 25% shorter length scales over state-of-the-art methods at both high- and low-SNR. B-SIM enables unsupervised, quantitative, physically accurate reconstruction without the need for labeled training data, democratizing high-quality SIM reconstruction and expands the capabilities of live-cell SIM to lower SNR, potentially revealing biological features in previously inaccessible regimes.

High-Resolution Microscopic Characterization of Tunneling Nanotubes in Living U87 MG and LN229 Glioblastoma Cells

Tunneling nanotubes (TNTs) are fine, nanometer-sized membrane connections between distant cells that provide an efficient communication tool for cellular organization. TNTs are thought to play a critical role in cellular behavior, particularly in cancer cells. The treatment of aggressive cancers such as glioblastoma remains challenging due to their high potential for developing therapy resistance, high infiltration rates, uncontrolled cell growth, and other aggressive features. A better understanding of the cellular organization via cellular communication through TNTs could help to find new therapeutic approaches. In this study, we investigate the properties of TNTs in two glioblastoma cell lines, U87 MG and LN229, including measurements of their diameter by high-resolution live-cell stimulated emission depletion (STED) microscopy and an analysis of their length, morphology, lifetime, and formation by live-cell confocal microscopy. In addition, we discuss how these fine compounds can ideally be studied microscopically. In particular, we show which membrane-labeling method is suitable for studying TNTs in glioblastoma cells and demonstrate that live-cell studies should be preferred to explore the role of TNTs in cellular behavior. Our observations on TNT formation in glioblastoma cells suggest that TNTs could be involved in cell migration and serve as guidance.

Visualizing Lipophagy as a New Mechanism of the Synthesis of Sex Steroids in Human Ovary and Testis Using Immunofluorescence Staining Method

Immunofluorescence, a transformative tool in cellular biology, is employed to dissect the intricate mechanisms of cholesterol trafficking in human reproductive tissues. Autophagy, a key player in cellular homeostasis, particularly lipophagy, emerges as a free cholesterol source for steroidogenesis. In this chapter, we describe a comprehensive immunofluorescence staining protocol, with details provided for the precise visualization of subcellular dynamics of mitochondria, lysosomes, and lipid droplets in ex vivo testicular tissue and primary luteal granulosa cell culture models, pivotal components in sex steroid biosynthesis. Here, we detail the culture, treatment, and immunofluorescence protocols, providing a comprehensive guide for researchers. The provided immunofluorescence toolkit serves as a valuable resource for researchers, paving way for advancements in human reproductive health to investigate the intricate interplay between autophagy, lipophagy, and cholesterol trafficking.

The development and application of a novel reagent for fixing red blood cells with glutaraldehyde and paraformaldehyde

OBJECTIVE

The currently employed red blood cell reagents have a short shelf life. Some hospitals with a small number of specimens will be unable to utilize them within the validity period, resulting in a substantial increase in the purchase price. Therefore, the method of developing long-term red blood cell reagents is a problem worthy of further study.

METHODS

In this experiment, the type and concentration of the red blood cell reagent treatment solution were evaluated based on the red blood cell antigen concentration 24 h after treatment. In addition, the qualified glutaraldehyde/paraformaldehyde reagent was stored for six months, and five red blood cell indices were measured every month. At the same time, the detection indices of treated red blood cell reagents and untreated red blood cell reagents were compared.

RESULTS

It was discovered that treated red blood cells containing 0.005% GA and 0.05% PFA were more suitable for the preservation of red blood cells than other treated concentrations, and the preservation time could reach six months. The test tube method (n = 24) and microcolumn gel card (n = 35) were used to determine the accuracy of the treated blood cells containing 0.005% glutaraldehyde +0.05% paraformaldehyde, with an accuracy of 100%.

CONCLUSION

This experiment resulted in the development of a novel reagent for treating red blood cells with glutaraldehyde/paraformaldehyde fixed solution that can effectively prolong its storage time by two to three times that of red blood cell reagents currently on the market.

Sea buckthorn, its bioactive constituents, and mechanism of action: potential application in female reproduction

Sea buckthorn (Hippophae rhamnoides L.) is a flowering shrub, and its berries have been utilized for decades as a raw ingredient in cuisines and herbal remedies. This evidence-based study focuses on its key bioactive constituents, and mechanism of protective effects with a focus on female reproductive processes. Parts of the plant contain phenols, carotenoids (lycopene, carotene, lutein, and zeaxanthin), flavonoids (isorhamnetin, quercetin, glycosides, and kaempferol), tocopherols, sterols, polyunsaturated fatty acids, minerals, vitamins, omega 3, 6, 9 and rare omega 7 fatty acids etc. Key polyphenolic flavonoids such as isorhamnetin and quercetin are believed to be mainly responsible behind its health benefits (against cardiovascular diseases, metabolic syndrome, obesity etc.) through properties including anti-cancer, antioxidant, and anti-inflammatory activities. These sea buckthorn constituents appear to mediate healthy ovarian cell proliferation, death, and hormone release, as well as decrease ovarian cancer possibly through apoptosis, and hormonal (estrogen) release. Thus, sea buckthorn and its bioactive ingredients may have potential in the management of gynecological problems such as uterine inflammation, endometriosis, and easing symptoms of vulvovaginal atrophy in postmenopausal women (by targeting inflammatory cytokines and vascular endothelial growth factor - VEGF). Apigenin, myricetin, and luteolin have also been recommended as prospective ovarian cancer preventative and adjuvant therapy options as they can inhibit ovarian cancerogenesis by triggering apoptosis and halting the cell cycle in ovarian tumors. Furthermore, its oil (containing carotenoid, sterol, and hypericin) has been speculated as an alternative to estrogen replacement therapy for postmenopausal women particularly to improve vaginal epithelial integrity. However, it is uncertain whether steroid hormone receptors, reactive oxygen species (ROS), and inflammatory regulators are actually behind sea buckhorn's actions. Sea buckthorn, and its compounds' health promoting potential warrants further validation not just in vitro and in animal research, but also in clinical trials to identify and/or standardize optimal methods of delivery of biologically active molecules.

Ultraviolet Radiation-Induced Mitochondrial Disturbances Are Attenuated by Metabolites of Melatonin in Human Epidermal Keratinocytes

Melatonin (N-acetyl-5-methoxytryptamine) is recognized as an effective antioxidant produced by the pineal gland, brain and peripheral organs, which also has anti-inflammatory, immunomodulatory, and anti-tumour capacities. Melatonin has been reported as a substance that counteracts ultraviolet radiation B (UVB)-induced intracellular disturbances. Nevertheless, the mechanistic actions of related molecules including its kynurenic derivatives (N1-acetyl-N2-formyl-5-methoxykynurenine (AFMK)), its indolic derivatives (6-hydroxymelatonin (6(OH)MEL) and 5-methoxytryptamine (5-MT)) and its precursor N-acetylserotonin (NAS) are only poorly understood. Herein, we treated human epidermal keratinocytes with UVB and assessed the protective effect of the studied substances in terms of the maintenance of mitochondrial function or their radical scavenging capacity. Our results show that UVB caused the significant elevation of catalase (CAT) and superoxide dismutase (Mn-SOD), the dissipation of mitochondrial transmembrane potential (mtΔΨ), a reduction in ATP synthesis, and the enhanced release of cytochrome c into cytosol, leading subsequently to UVB-mediated activation of the caspases and apoptosis (appearance of sub-G1 population). Our findings, combined with data reported so far, indicate the counteracting and beneficial actions of melatonin and its molecular derivatives against these deleterious changes within mitochondria. Therefore, they define a path to the development of novel strategies delaying mitochondrial aging and promoting the well-being of human skin.

Surface-enhanced Raman scattering (SERS) by gold nanoparticle characterizes dermal thickening by collagen in bleomycin-treated skin ex vivo

PURPOSE

Current skin imaging modalities, including optical, electron, and confocal microscopy, mostly require tissue fixations that could damage proteins and biological molecules. Live tissue or cell imaging such as ultrasonography and optical coherent microscope may not adequately measure the dynamic spectroscopical changes. Raman spectroscopy has been adopted for skin imaging in vivo, mostly for skin cancer imaging. However, whether the epidermal and dermal thickening in skin could be measured and distinguished by conventional Ramen spectroscopy or the surface-enhanced Raman scattering (SERS), a rapid and label-free method for noninvasive measurement remains unknown.

METHODS

Human skin sections from patients of atopic dermatitis and keloid, which represent epidermal and dermal thickening, respectively, were measured by conventional Ramen spectroscopy. In mice, skin sections from imiquimod (IMQ)- and bleomycin (BLE)-treated mice, which reflect the epidermal and dermal thickening, respectively, were measured by SERS, that incorporates gold nanoparticles to generate surface plasma and enhance Raman signals.

RESULTS

Conventional Ramen spectroscopy failed to consistently show the Raman shift in human samples among the different groups. SERS successfully revealed a prominent peak around 1300 cm-1 in the IMQ-treated skin; and two significant peaks around 1100 and 1300 cm-1 in BLE-treated group. Further quantitative analysis showed 1100 cm-1 peak was significantly accentuated in the BLE-treated skin than that in control skin. SERS identified in vitro a similar 1100 cm-1 peak in solutions of collagen, the major dermal biological molecules.

CONCLUSION

SERS distinguishes the epidermal or dermal thickening in mouse skin with rapid and label-free measures. A prominent 1100 cm-1 SERS peak in the BLE-treated skin may result from collagen. SERS might help precision diagnosis in the future.

MORN4 protects cardiomyocytes against ischemic injury via MFN2-mediated mitochondrial dynamics and mitophagy

The imbalance of mitochondrial fission and fusion dynamics causes ischemic cardiomyocyte apoptosis and heart injury by affecting mitophagy. Regulation of mitochondrial dynamics is an important therapeutic strategy for ischemic heart diseases. Considering the important roles of MORN motifs in heart diseases and chloroplast fission, we aimed to investigate the possible role of MORN repeat-containing protein 4 (MORN4) in the progression of myocardial infarction (MI), ischemic cardiomyocyte apoptosis, mitochondrial dynamics, and mitophagy. We found that in the MI mouse, MORN4 knockdown remarkably accelerated cardiac injury and fibrosis with deteriorating cardiac dysfunction. Sphingosylphosphorylcholine (SPC) alleviated ischemic cardiomyocyte apoptosis and heart injury through increased level of MORN4, indicating a vital function of MORN4 in heart with SPC used to clarify the molecular mechanisms underlying the functions of MORN4. Mechanistically, we found that MORN4 directly binds to MFN2 and promotes the phosphorylation of MFN2 S442 through Rho-associated protein kinase 2 (ROCK2), which mediates beneficial mitophagy induced by mitochondrial dynamics, while SPC promoted the binding of MORN4 and MFN2 and the process. Taken together, our data reveal a new perspective role of MORN4 in ischemic heart injury, and report that SPC could regulate myocardial mitochondrial homeostasis by activating the MORN4-MFN2 axis during the ischemic situation, this finding provides novel targets for improving myocardial ischemia tolerance and rescue of acute myocardial infarction.

Neuronal mitochondrial morphology is significantly affected by both fixative and oxygen level during perfusion

Neurons in the brain have a uniquely polarized structure consisting of multiple dendrites and a single axon generated from a cell body. Interestingly, intracellular mitochondria also show strikingly polarized morphologies along the dendrites and axons: in cortical pyramidal neurons (PNs), dendritic mitochondria have a long and tubular shape, while axonal mitochondria are small and circular. Mitochondria play important roles in each compartment of the neuron by generating adenosine triphosphate (ATP) and buffering calcium, thereby affecting synaptic transmission and neuronal development. In addition, mitochondrial shape, and thereby function, is dynamically altered by environmental stressors such as oxidative stress or in various neurodegenerative diseases including Alzheimer's disease and Parkinson's disease. Although the importance of altered mitochondrial shape has been claimed by multiple studies, methods for studying this stress-sensitive organelle have not been standardized. Here we address pertinent steps that influence mitochondrial morphology during experimental processes. We demonstrate that fixative solutions containing only paraformaldehyde (PFA), or that introduce hypoxic conditions during the procedure, induce dramatic fragmentation of mitochondria both in vitro and in vivo. This disruption was not observed following the use of glutaraldehyde (GA) addition or oxygen supplementation, respectively. Finally, using pre-formed fibril α-synuclein treated neurons, we show fixative choice can alter experimental outcomes. Specifically, α-synuclein-induced mitochondrial remodeling could not be observed with PFA only fixation as fixation itself caused mitochondrial fragmentation. Our study provides optimized methods for examining mitochondrial morphology in neurons and demonstrates that fixation conditions are critical when investigating the underlying cellular mechanisms involving mitochondria in physiological and neurodegenerative disease models.

LSSmScarlet2 and LSSmScarlet3, Chemically Stable Genetically Encoded Red Fluorescent Proteins with a Large Stokes’ Shift

Red fluorescent proteins with a large Stokes’ shift (LSSRFPs) are genetically encoded and efficiently excited by 488 nm light, allowing simultaneous dual-color one- and two-photon fluorescence imaging and fluorescence correlation spectroscopy in combination with green fluorescent proteins FPs. Recently, based on the conventional bright mScarlet RFP, we developed the LSSRFP LSSmScarlet. LSSmScarlet is characterized by two pKa values at pH values of 1.9 and 5.8. In this study, we developed improved versions of LSSmScarlet, named LSSmScarlet2 and LSSmScarlet3, which are characterized by a Stokes’ shift of 128 nm and extreme pH stability with a single pKa value of 2.2. LSSmScarlet2 and LSSmScarlet3 had 1.8-fold faster and 3-fold slower maturation than LSSmScarlet, respectively. In addition, both LSSRFPs were 1.5- to 1.6-fold more photostable and more chemically resistant to denaturation by guanidinium chloride and guanidinium thiocyanate. We also compared the susceptibility of the LSSmScarlet2, LSSmScarlet3, and other LSSRFPs to the reagents used for whole-mount imaging, expansion microscopy, and immunostaining techniques. Due to higher pH stability and faster maturation, the LSSmScarlet3-LAMP3 fusion was 2.2-fold brighter than LSSmScarlet-LAMP3 in lysosomes of mammalian cells. The LSSmScarlet3-hLAMP2A fusion was similar in brightness to LSSmScarlet-hLAMP2A in lysosomes. We successfully applied the monomeric LSSmScarlet2 and LSSmScarlet3 proteins for confocal imaging of structural proteins in live mammalian cells. We also solved the X-ray structure of the LSSmScarlet2 protein at a resolution of 1.41 Å. Site-directed mutagenesis of the LSSmScarlet2 protein demonstrated the key role of the T74 residue in improving the pH and chemical stability of the LSSmScarlet2 protein.

Sphingosylphosphorylcholine ameliorates doxorubicin-induced cardiotoxicity in zebrafish and H9c2 cells by reducing excessive mitophagy and mitochondrial dysfunction

Doxorubicin (DOX, C₂₇H₂₉NO₁₁), is an anthracycline tumor chemotherapy drug, which has significant side effects on many organs including the heart. In recent years, mitochondrial dysfunction caused by DOX was identified as an important reason for cardiotoxic injury. Sphingosylphosphorylcholine (SPC) is essential for mitochondrial homeostasis in our previous report, however, its role in DOX-caused cardiomyopathy has remained elusive. Herein, DOX treated zebrafish embryos (90 μM) and adult fish (2.5 μM/g) were used to simulate DOX-induced cardiotoxic damage. Histopathological and ultrastructural observations showed that SPC (2.5 μM) significantly ameliorated DOX-induced pericardial edema, myocardial vacuolization and apoptosis. Furthermore, SPC (2.5 μM) can significantly inhibit DOX-induced apoptosis and promote cell proliferation in DOX treated H9c2 cells (1 μM), which is dependent on the restoration of mitochondrial homeostasis, including restored mitochondrial membrane potential, mitochondrial superoxide and ATP levels. We finally confirmed that SPC restored mitochondrial homeostasis through ameliorating DOX-induced excessive mitophagy. Mechanistically, SPC reduced calmodulin (CaM) levels and thus inhibiting Parkin activation and Parkin-dependent mitophagy. These results suggest that reducing the cardiotoxicity of chemotherapeutic drugs by targeting SPC may be a new solution to rescue chemotherapy injury.

Glutamate Receptors Mediate Changes to Dendritic Mitochondria in Neurons Grown on Stiff Substrates

The stiffness of brain tissue changes during development and disease. These changes can affect neuronal morphology, specifically dendritic arborization. We previously reported that N-methyl-D-aspartate (NMDA) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors regulate dendrite number and branching in a manner that is dependent on substrate stiffness. Since mitochondria affect the shape of dendrites, in this study, we determined whether the stiffness of substrates on which rat hippocampal neurons are grown affects mitochondrial characteristics and if glutamate receptors mediate the effects of substrate stiffness. Dendritic mitochondria are small, short, simple, and scarce in neurons cultured on substrates of 0.5 kPa stiffness. In contrast, dendritic mitochondria are large, long, complex, and low in number in neurons grown on substrates of 4 kPa stiffness. Dendritic mitochondria of neurons cultured on glass are high in number and small with complex shapes. Treatment of neurons grown on the stiffer gels or glass with the NMDA and AMPA receptor antagonists, 2-amino-5-phosphonopentanoic acid and 6-cyano-7-nitroquinoxaline-2,3-dione, respectively, results in mitochondrial characteristics of neurons grown on the softer substrate. These results suggest that glutamate receptors play important roles in regulating both mitochondrial morphology and dendritic arborization in response to substrate stiffness.

High-quality, large-scale, semi-thin, & ultra-thin sections of the optic nerve in large animals: An optimized procedure

Large animal model of optic nerve (ON) injury is an essential tool for translational medicine. Perfusion fixation with paraformaldehyde is mainly used for preparing the semi-thin (1-2 μm thick) and ultra-thin (<0.5 μm thick) sections of the ON tissues. However, this conventional fixation technique in large animals needs a large volume of fixatives, which increases the risk of toxic exposure and is environmentally unfriendly. Additionally, fixed residual ON cannot be used for other tests that require fresh tissue samples. Although conventional immersion fixation is feasible for preparing a semi-thin section of the ON in small animals (0.2-0.6 mm in diameter), it faces technical challenges when fixing the ON of large animals (3 mm in diameters), as increased diameter limits the permeability of the fixatives into deeper tissue. Therefore, we optimized the immersion-fixation method to obtain high-quality, large-scale, semi-thin, and ultra-thin sections for the ON of goat and rhesus macaques. Using this optimized technique, the ON microstructure was well preserved throughout the entire area of 1.5*1.5 square millimeters, allowing confident quantification of axon density/diameter on semi-thin section and identification of specific organelles and glial cells on ultra-thin sections. Furthermore, the optimized technique is a quick, simple, and environmentally friendly fixation method. Notably, the ON regions of large animals with or without an intact neurovascular system can be prepared for light and electron microscopy. In contrast, the residual unfixed ON from the same animal can be further utilized for experiments such as tissue culture and biomolecular tests.