Quantitative analysis of interactive behavior of mitochondria and lysosomes using structured illumination microscopy

Mitochondrial Structure, Dynamics, and Physiology: Light Microscopy to Disentangle the Network

Mitochondria serve as energetic and signaling hubs of the cell: This function results from the complex interplay between their structure, function, dynamics, interactions, and molecular organization. The ability to observe and quantify these properties often represents the puzzle piece critical for deciphering the mechanisms behind mitochondrial function and dysfunction. Fluorescence microscopy addresses this critical need and has become increasingly powerful with the advent of superresolution methods and context-sensitive fluorescent probes. In this review, we delve into advanced light microscopy methods and analyses for studying mitochondrial ultrastructure, dynamics, and physiology, and highlight notable discoveries they enabled.

Enhanced optical imaging and fluorescent labeling for visualizing drug molecules within living organisms

The visualization of drugs in living systems has become key techniques in modern therapeutics. Recent advancements in optical imaging technologies and molecular design strategies have revolutionized drug visualization. At the subcellular level, super-resolution microscopy has allowed exploration of the molecular landscape within individual cells and the cellular response to drugs. Moving beyond subcellular imaging, researchers have integrated multiple modes, like optical near-infrared II imaging, to study the complex spatiotemporal interactions between drugs and their surroundings. By combining these visualization approaches, researchers gain supplementary information on physiological parameters, metabolic activity, and tissue composition, leading to a comprehensive understanding of drug behavior. This review focuses on cutting-edge technologies in drug visualization, particularly fluorescence imaging, and the main types of fluorescent molecules used. Additionally, we discuss current challenges and prospects in targeted drug research, emphasizing the importance of multidisciplinary cooperation in advancing drug visualization. With the integration of advanced imaging technology and molecular design, drug visualization has the potential to redefine our understanding of pharmacology, enabling the analysis of drug micro-dynamics in subcellular environments from new perspectives and deepening pharmacological research to the levels of the cell and organelles.

Lysosome passivation triggered by silver nanoparticles enhances subcellular-targeted drug therapy

Frequently, subcellular-targeted drugs tend to accumulate in lysosomes after cellular absorption, a process termed the lysosomal trap. This accumulation often interferes with the drug's ability to bind to its target, resulting in decreased efficiency. Existing methods for addressing lysosome-induced drug resistance mainly involve improving the structures of small molecules or enveloping drugs in nanomaterials. Nonetheless, these approaches can lead to changes in the drug structure or potentially trigger unexpected reactions within organisms. To address these issues, we introduced a strategy that involves inactivating the lysosome with the use of Ag nanoparticles (Cy3.5@Ag NPs). In this method, the Cy3.5@Ag NPs gradually accumulate inside lysosomes, leading to permeation of the lysosomal membrane and subsequent lysosomal inactivation. In addition, Cy3.5@Ag NPs also significantly affected the motility of lysosomes and induced the occurrence of lysosome passivation. Importantly, coincubating Cy3.5@Ag NPs with various subcellular-targeted drugs was found to significantly increase the efficiency of these treatments. Our strategy illustrates the potential of using lysosomal inactivation to enhance drug efficacy, providing a promising therapeutic strategy for cancer.

Super-resolution imaging for in situ monitoring sub-cellular micro-dynamics of small molecule drug

Small molecule drugs play a pivotal role in the arsenal of anticancer pharmacological agents. Nonetheless, their small size poses a challenge when directly visualizing their localization, distribution, mechanism of action (MOA), and target engagement at the subcellular level in real time. We propose a strategy for developing triple-functioning drug beacons that seamlessly integrate therapeutically relevant bioactivity, precise subcellular localization, and direct visualization capabilities within a single molecular entity. As a proof of concept, we have meticulously designed and constructed a boronic acid fluorescence drug beacon using coumarin-hemicyanine (CHB). Our CHB design includes three pivotal features: a boronic acid moiety that binds both adenosine triphosphate (ATP) and adenosine diphosphate (ADP), thus depleting their levels and disrupting the energy supply within mitochondria; a positively charged component that targets the drug beacon to mitochondria; and a sizeable conjugated luminophore that emits fluorescence, facilitating the application of structured illumination microscopy (SIM). Our study indicates the exceptional responsiveness of our proof-of-concept drug beacon to ADP and ATP, its efficacy in inhibiting tumor growth, and its ability to facilitate the tracking of ADP and ATP distribution around the mitochondrial cristae. Furthermore, our investigation reveals that the micro-dynamics of CHB induce mitochondrial dysfunction by causing damage to the mitochondrial cristae and mitochondrial DNA. Altogether, our findings highlight the potential of SIM in conjunction with visual drug design as a potent tool for monitoring the in situ MOA of small molecule anticancer compounds. This approach represents a crucial advancement in addressing a current challenge within the field of small molecule drug discovery and validation.

AZI2 mediates TBK1 activation at unresolved selective autophagy cargo receptor complexes with implications for CD8 T-cell infiltration in breast cancer

Most breast cancers do not respond to immune checkpoint inhibitors and there is an urgent need to identify novel sensitization strategies. Herein, we uncovered that activation of the TBK-IFN pathway that is mediated by the TBK1 adapter protein AZI2 is a potent strategy for this purpose. Our initial observations showed that RB1CC1 depletion leads to accumulation of AZI2, in puncta along with selective macroautophagy/autophagy cargo receptors, which are both required for TBK1 activation. Specifically, disrupting the selective autophagy function of RB1CC1 was sufficient to sustain AZI2 puncta accumulation and TBK1 activation. AZI2 then mediates downstream activation of DDX3X, increasing its interaction with IRF3 for transcription of pro-inflammatory chemokines. Consequently, we performed a screen to identify inhibitors that can induce the AZI2-TBK1 pathway, and this revealed Lys05 as a pharmacological agent that induced pro-inflammatory chemokine expression and CD8+ T cell infiltration into tumors. Overall, we have identified a distinct AZI2-TBK1-IFN signaling pathway that is responsive to selective autophagy blockade and can be activated to make breast cancers more immunogenic.Abbreviations: AZI2/NAP1: 5-azacytidine induced 2; CALCOCO2: calcium binding and coiled-coil domain 2; DDX3X: DEAD-box helicase 3 X-linked; FCCP: carbonyl cyanide p-triflouromethoxyphenylhydrazone; a protonophore that depolarizes the mitochondrial inner membrane; ICI: immune checkpoint inhibitor; IFN: interferon; NBR1: NBR1 autophagy cargo receptor; OPTN: optineurin; RB1CC1/FIP200: RB1 inducible coiled-coil 1; SQSTM1/p62: sequestosome 1; TAX1BP1: Tax1 binding protein 1; TBK1: TANK binding kinase 1.

Long-Chain Fluorescent Probe for Straightforward and Nondestructive Staining Mitochondria in Fixed Cells and Tissues

Normally, small-molecule fluorescent probes dependent on the mitochondrial membrane potential (MMP) are invalid for fixed cells and tissues, which limits their clinical applications when the fixation of pathological specimens is imperative. Given that mitochondrial morphology is closely associated with disease, we developed a long-chain mitochondrial probe for fixed cells and tissues, DMPQ-12, by installing a C12-alkyl chain into the quinoline moiety. In fixed cells stained with DMPQ-12, filament mitochondria and folded cristae were observed with confocal and structural illumination microscopy, respectively. In titration test with three major phospholipids, DMPQ-12 exhibited a stronger binding force to mitochondria-exclusive cardiolipin, revealing its targeting mechanism. Moreover, mitochondrial morphological changes in the three lesion models were clearly visualized in fixed cells. Finally, by DMPQ-12, three kinds of mitochondria with different morphologies were observed in situ in fixed muscle tissues. This work breaks the conventional concept that organic fluorescent probes only stain mitochondria with normal membrane potentials and opens new avenues for comprehensive mitochondrial investigations in research and clinical settings.

Mitochondrial nucleoid condensates drive peripheral fission through high membrane curvature

Mitochondria are dynamic organelles that undergo fusion and fission events, in which the mitochondrial membrane and DNA (mtDNA) play critical roles. The spatiotemporal organization of mtDNA reflects and impacts mitochondrial dynamics. Herein, to study the detailed dynamics of mitochondrial membrane and mtDNA, we rationally develop a dual-color fluorescent probe, mtGLP, that could be used for simultaneously monitoring mitochondrial membrane and mtDNA dynamics via separate color outputs. By combining mtGLP with structured illumination microscopy to monitor mitochondrial dynamics, we discover the formation of nucleoid condensates in damaged mitochondria. We further reveal that nucleoid condensates promoted the peripheral fission of damaged mitochondria via asymmetric segregation. Through simulations, we find that the peripheral fission events occurred when the nucleoid condensates interacted with the highly curved membrane regions at the two ends of the mitochondria. Overall, we show that mitochondrial nucleoid condensates utilize peripheral fission to maintain mitochondrial homeostasis.

Probing the dynamic crosstalk of lysosomes and mitochondria with structured illumination microscopy

Structured illumination microscopy (SIM) is a super-resolution technology for imaging living cells and has been used for studying the dynamics of lysosomes and mitochondria. Recently, new probes and analyzing methods have been developed for SIM imaging, enabling the quantitative analysis of these subcellular structures and their interactions. This review provides an overview of the working principle and advances of SIM, as well as the organelle-targeting principles and types of fluorescence probes, including small molecules, metal complexes, nanoparticles, and fluorescent proteins. Additionally, quantitative methods based on organelle morphology and distribution are outlined. Finally, the review provides an outlook on the current challenges and future directions for improving the combination of SIM imaging and image analysis to further advance the study of organelles. We hope that this review will be useful for researchers working in the field of organelle research and help to facilitate the development of SIM imaging and analysis techniques.

Revealing Mitochondrion-Lysosome Dynamic Interactions and pH Variations in Live Cells with a pH-Sensitive Fluorescent Probe

Mitochondrion-lysosome interactions have garnered significant attention in recent research. Numerous studies have shown that mitochondrion-lysosome interactions, including mitochondrion-lysosome contact (MLC) and mitophagy, are involved in various biological processes and pathological conditions. Single fluorescent probes are termed a pivotal chemical tool in unraveling the intricate spatiotemporal interorganelle interplay in live cells. However, current chemical tools are insufficient to deeply understand mitochondrion-lysosome dynamic interactions and related diseases, Moreover, the rational design of mitochondrion-lysosome dual-targeting fluorescent probes is intractable. Herein, we designed and synthesized a pH-sensitive fluorescent probe called INSA, which could simultaneously light up mitochondria (red emission) and lysosomes (green emission) for their internal pH differences. Employing INSA, we successfully recorded long-term dynamic interactions between lysosomes and mitochondria. More importantly, the increasing mitochondrion-lysosome interactions in ferroptotic cells were also revealed by INSA. Further, we observed pH variations in mitochondria and lysosomes during ferroptosis for the first time. In brief, this work not only introduced a pH-sensitive fluorescent probe INSA for the disclosure of the mitochondrion-lysosome dynamic interplays but also pioneered the visualization of the organellar pH alternation in a specific disease model.

Mind the gap: Methods to study membrane contact sites

Organelles are dynamic entities whose functions are essential for the optimum functioning of cells. It is now known that the juxtaposition of organellar membranes is essential for the exchange of metabolites and their communication. These functional apposition sites are termed membrane contact sites. Dynamic membrane contact sites between various sub-cellular structures such as mitochondria, endoplasmic reticulum, peroxisomes, Golgi apparatus, lysosomes, lipid droplets, plasma membrane, endosomes, etc. have been reported in various model systems. The burgeoning area of research on membrane contact sites has witnessed several manuscripts in recent years that identified the contact sites and components involved. Several methods have been developed to identify, measure and analyze the membrane contact sites. In this manuscript, we aim to discuss important methods developed to date that are used to study membrane contact sites.

ULK1 forms distinct oligomeric states and nanoscopic structures during autophagy initiation

Autophagy induction involves extensive molecular and membrane reorganization. Despite substantial progress, the mechanism underlying autophagy initiation remains poorly understood. Here, we used quantitative photoactivated localization microscopy with single-molecule sensitivity to analyze the nanoscopic distribution of endogenous ULK1, the kinase that triggers autophagy. Under amino acid starvation, ULK1 formed large clusters containing up to 161 molecules at the endoplasmic reticulum. Cross-correlation analysis revealed that ULK1 clusters engaging in autophagosome formation require 30 or more molecules. The ULK1 structures with more than the threshold number contained varying levels of Atg13, Atg14, Atg16, LC3B, GEC1, and WIPI2. We found that ULK1 activity is dispensable for the initial clustering of ULK1, but necessary for the subsequent expansion of the clusters, which involves interaction with Atg14, Atg16, and LC3B and relies on Vps34 activity. This quantitative analysis at the single-molecule level has provided unprecedented insights into the behavior of ULK1 during autophagy initiation.

Application of super-resolution microscopy in mitochondria-dynamic diseases

Limited by spatial and temporal resolution, traditional optical microscopy cannot image the delicate ultra-structure organelles and sub-organelles. The emergence of super-resolution microscopy makes it possible. In this review, we focus on mitochondria. We summarize the process of mitochondrial dynamics, the primary proteins that regulate mitochondrial morphology, the diseases related to mitochondrial dynamics. The purpose is to apply super-resolution microscopy developed during recent years to the mitochondrial research. By providing the right research tools, we will help to promote the application of this technique to the in-depth elucidation of the pathogenesis of diseases related to mitochondrial dynamics, assistdiagnosis and develop the therapeutic treatment.

Subcellular visualization: Organelle-specific targeted drug delivery and discovery

Organelles perform critical biological functions due to their distinct molecular composition and internal environment. Disorders in organelles or their interacting networks have been linked to the incidence of numerous diseases, and the research of pharmacological actions at the organelle level has sparked pharmacists' interest. Currently, cell imaging has evolved into a critical tool for drug delivery, drug discovery, and pharmacological research. The introduction of advanced imaging techniques in recent years has provided researchers with richer biological information for viewing and studying the ultrastructure of organelles, protein interactions, and gene transcription activities, leading to the design and delivery of precision-targeted drugs. Therefore, this reviews the research on organelles-targeted drugs based upon imaging technologies and development of fluorescent molecules for medicinal purposes. We also give a thorough analysis of a number of subcellular-level elements of drug development, including subcellular research instruments and methods, organelle biological event investigation, subcellular target and drug identification, and design of subcellular delivery systems. This review will make it possible to promote drug research from the individual/cellular level to the subcellular level, as well as give a new focus based on newly found organelle activities.

Constant Conversion Rate of Endolysosomes Revealed by a pH-Sensitive Fluorescent Probe

Endolysosome dynamics plays an important role in autophagosome biogenesis. Hence, imaging the subcellular dynamics of endolysosomes using high-resolution fluorescent imaging techniques would deepen our understanding of autophagy and benefit the development of pharmaceuticals against endosome-related diseases. Taking advantage of the intramolecular charge-transfer mechanism, herein we report a cationic quinolinium-based fluorescent probe (PyQPMe) that exhibits excellent pH-sensitive fluorescence in endolysosomes at different stages of interest. A systematic photophysical and computational study on PyQPMe was carried out to rationalize its highly pH-dependent absorption and emission spectra. The large Stokes shift and strong fluorescence intensity of PyQPMe can effectively reduce the background noise caused by excitation light and microenvironments and provide a high signal-to-noise ratio for high-resolution imaging of endolysosomes. By applying PyQPMe as a small molecular probe in live cells, we were able to reveal a constant conversion rate from early endosomes to late endosomes/lysosomes during autophagy at the submicron level.

2D MoS2 and BN Nanosheets Damage Mitochondria through Membrane Penetration

With the progression of nanotechnology, a growing number of nanomaterials have been created and incorporated into organisms and ecosystems, which raises significant concern about potential hazards of these materials on human health, wildlife, and the environment. Two-dimensional (2D) nanomaterials are one type of nanomaterials with thicknesses ranging from that of a single atom or of several atoms and have been proposed for a variety of biomedical applications such as drug delivery and gene therapy, but the toxicity thereof on subcellular organelles remains to be studied. In this work, we studied the impact of two typical 2D nanomaterials, MoS₂ and BN nanosheets, on mitochondria, which are a type of membranous subcellular organelle that provides energy to cells. While 2D nanomaterials at a low dose exhibited a negligible cell mortality rate, significant mitochondrial fragmentation and partially reduced mitochondrial functions occurred; cells initiate mitophagy in response to mitochondrial damages, which cleans damaged mitochondria to avoid damage accumulation. Moreover, the molecular dynamics simulation results revealed that both MoS₂ and BN nanosheets can spontaneously penetrate the mitochondrial lipid membrane through the hydrophobic interaction. The membrane penetration induced heterogeneous lipid packing resulting in damages. Our results demonstrate that even at a low dose 2D nanomaterials can physically damage mitochondria by penetrating the membrane, which draws attention to carefully evaluating the cytotoxicity of 2D nanomaterials for the potential biomedical application.

The power of super-resolution microscopy in modern biomedical science

Super-resolution microscopy (SRM) technology that breaks the diffraction limit has revolutionized the field of cell biology since its appearance, which enables researchers to visualize cellular structures with nanometric resolution, multiple colors and single-molecule sensitivity. With the flourishing development of hardware and the availability of novel fluorescent probes, the impact of SRM has already gone beyond cell biology and extended to nanomedicine, material science and nanotechnology, and remarkably boosted important breakthroughs in these fields. In this review, we will mainly highlight the power of SRM in modern biomedical science, discussing how these SRM techniques revolutionize the way we understand cell structures, biomaterials assembly and how assembled biomaterials interact with cellular organelles, and finally their promotion to the clinical pre-diagnosis. Moreover, we also provide an outlook on the current technical challenges and future improvement direction of SRM. We hope this review can provide useful information, inspire new ideas and propel the development both from the perspective of SRM techniques and from the perspective of SRM's applications.

Super-resolution fluorescence microscopic imaging in pathogenesis and drug treatment of neurological disease

Since super-resolution fluorescence microscopic technology breaks the diffraction limit that has existed for a long time in optical imaging, it can observe the process of synapses formed between nerve cells and the protein aggregation related to neurological disease. Thus, super-resolution fluorescence microscopic imaging has significantly impacted several industries, including drug development and pathogenesis research, and it is anticipated that it will significantly alter the future of life science research. Here, we focus on several typical super-resolution fluorescence microscopic technologies, introducing their benefits and drawbacks, as well as applications in several common neurological diseases, in the hope that their services will be expanded and improved in the pathogenesis and drug treatment of neurological diseases.

Construction of a TICT-AIE-Integrated Unimolecular Platform for Imaging Lipid Droplet-Mitochondrion Interactions in Live Cells and In Vivo

Inter-organelle interactions play a vital role in diverse biological processes. Thus, chemical tools are highly desirable for understanding the spatiotemporal dynamic interplay among organelles in live cells and in vivo. However, designing such tools is still a great challenge due to the lack of universal design strategies. To break this bottleneck, herein, a novel unimolecular platform integrating the twisted intramolecular charge transfer (TICT) and aggregation-induced emission (AIE) dual mechanisms was proposed. As a proof of concept, two organelles, lipid droplets (LDs) and mitochondria, were selected as models. Also, the first TICT-AIE integration molecule, BETA-1, was designed for simultaneous and dual-color imaging of LDs and mitochondria. BETA-1 can simultaneously target LDs and mitochondria due to its lipophilicity and cationic structure and emit cyan fluorescence in LDs and red fluorescence in mitochondria. Using BETA-1, for the first time, we obtained long-term tracking of dynamic LD-mitochondrion interactions and identified several impressive types of dynamic interactions between these two organelles. More importantly, the increase in LD-mitochondrion interactions during ferroptosis was revealed with BETA-1, suggesting that intervening in the LD-mitochondrion interactions may modulate this cell death. BETA-1 was also successfully applied for in vivo imaging of LD-mitochondrion interactions in C. elegans. This study not only provides an effective tool for uncovering LD-mitochondrion interactions and deciphering related biological processes but also sheds light on the design of new probes with an integrated TICT-AIE mechanism for imaging of inter-organelle interactions.

Surpassing the resolution limitation of structured illumination microscopy by an untrained neural network

Structured illumination microscopy (SIM), as a flexible tool, has been widely applied to observing subcellular dynamics in live cells. It is noted, however, that SIM still encounters a problem with theoretical resolution limitation being only twice over wide-field microscopy, where imaging of finer biological structures and dynamics are significantly constrained. To surpass the resolution limitation of SIM, we developed an image postprocessing method to further improve the lateral resolution of SIM by an untrained neural network, i.e., deep resolution-enhanced SIM (DRE-SIM). DRE-SIM can further extend the spatial frequency components of SIM by employing the implicit priors based on the neural network without training datasets. The further super-resolution capability of DRE-SIM is verified by theoretical simulations as well as experimental measurements. Our experimental results show that DRE-SIM can achieve the resolution enhancement by a factor of about 1.4 compared with conventional SIM. Given the advantages of improving the lateral resolution while keeping the imaging speed, DRE-SIM will have a wide range of applications in biomedical imaging, especially when high-speed imaging mechanisms are integrated into the conventional SIM system.

Upconversion fluorescence-based PDT nanocomposites with self-oxygenation for malignant tumor therapy

Upconversion fluorescence-based-PDT nanocomposites with self-oxygenation have excellent anti-tumor properties, including deep penetration of the excitation light source and the ability to remodel the anoxic microenvironment, and has feasibility in clinical application.

Exosome derived from stem cell: A promising therapeutics for wound healing

A wound occurs when the epidermis and dermis of the skin are damaged internally and externally. The traditional wound healing method is unsatisfactory, which will prolong the treatment time and increase the treatment cost, which brings economic and psychological burdens to patients. Therefore, there is an urgent need for a new method to accelerate wound healing. As a cell-free therapy, exosome derived from stem cell (EdSC) offers new possibilities for wound healing. EdSC is the smallest extracellular vesicle secreted by stem cells with diameters of 30-150 nm and a lipid bilayer structure. Previous studies have found that EdSC can participate in and promote almost all stages of wound healing, including regulating inflammatory cells; improving activation of fibroblasts, keratinocytes, and endothelial cells; and adjusting the ratio of collagen Ⅰ and Ⅲ. We reviewed the relevant knowledge of wounds; summarized the biogenesis, isolation, and identification of exosomes; and clarified the pharmacological role of exosomes in promoting wound healing. This review provides knowledge support for the pharmacological study of exosomes.

Light-activated mitochondrial fission through optogenetic control of mitochondria-lysosome contacts

Mitochondria are highly dynamic organelles whose fragmentation by fission is critical to their functional integrity and cellular homeostasis. Here, we develop a method via optogenetic control of mitochondria–lysosome contacts (MLCs) to induce mitochondrial fission with spatiotemporal accuracy. MLCs can be achieved by blue-light-induced association of mitochondria and lysosomes through various photoactivatable dimerizers. Real-time optogenetic induction of mitochondrial fission is tracked in living cells to measure the fission rate. The optogenetic method partially restores the mitochondrial functions of SLC25A46^−/− cells, which display defects in mitochondrial fission and hyperfused mitochondria. The optogenetic MLCs system thus provides a platform for studying mitochondrial fission and treating mitochondrial diseases.

Existing methods can lack spatiotemporal accuracy to manipulate dynamic mitochondrial behaviour in live cells. Here the authors report an optogenetic method to control mitochondria-lysosome contacts and induce mitochondrial fission; they use photoactivatable dimerizers including CRY2/CIB and SspB/iLID.

Optical Visualization of Red-GQDs’ Organelles Distribution and Localization in Living Cells

Recently, there has been a rapidly expanding interest in a new nanomaterial, graphene quantum dots (GQDs), owing to its profound potential in various advanced applications. At present, the study of GQDs mainly focuses on the new synthesis methods and surface modification. However, revealing the intracellular distribution of GQDs is currently not available, limiting in-depth understanding of its biological regulatory mechanism. To fill up this gap, the visualization study of red fluorescent graphene quantum dots (Red-GQDs) is helpful to clarify their subcellular distribution and metabolism in living cells system. Here, in this study, two-photon laser confocal microscopy was used to deeply analyze the uptake and subcellular distribution of Red-GQDs by HeLa cells at different concentrations and times through visual observation and discussed the effect of Red-GQDs on the metabolic of HeLa cells. The results indicated that Red-GQDs could be well-absorbed by HeLa cells and further revealed the differential distribution of Red-GQDs in different organelles (lysosomes and mitochondria) in a time-dependent manner. In addition, we confirmed that Red-GQDs significantly affect cell biological functions. Low concentrations of Red-GQDs are related to the autophagy pathway of cells, and high concentrations of Red-GQDs can induce ferroptosis in cells and promote the secretion of cellular exosomes. In the present study, the distribution and metabolic pathways of Red-GQDs in the subcellular structure of cells were characterized in detail through visual analysis, which can bring positive reference for the application of Red-GQDs in the future.

A Dual-Labeling Probe for Super-Resolution Imaging to Detect Mitochondrial Reactive Sulfur Species in Live Cells

Background: Mitochondria are the main sites of reactive sulfur species (RSS) production in living cells. RSS in mitochondria play an important role in physiological and pathological processes of life. In this study, a dual-labeling probe that could simultaneously label the mitochondrial membrane and matrix was designed to quantitatively detect RSS of mitochondria in living cells using nano-level super-resolution imaging.

Methods: A fluorescent probe CPE was designed and synthesized. The cytotoxicity of CPE was determined and co-localization of CPE with a commercial mitochondrial probe was analyzed in HeLa cells. Then, the uptake patterns of CPE in HeLa cells at different temperatures and endocytosis levels were investigated. The staining characteristics of CPE under different conditions were imaged and quantitated under structured illumination microscopy.

Results: A fluorescence probe CPE reacting to RSS was developed, which could simultaneously label the mitochondrial membrane with green fluorescence and the mitochondrial matrix with red fluorescence. CPE was able to demonstrate the mitochondrial morphology and detect the changes of RSS in mitochondria. With the increase of mitochondrial RSS concentration, the light of the red matrix will be quenched.

Conclusion: CPE provides a strategy for the design of probes and an attractive tool for accurate examination to changes of mitochondrial morphology and RSS in mitochondria in living cells at the nanoscale.

Organelle Interaction and Drug Discovery: Towards Correlative Nanoscopy and Molecular Dynamics Simulation

The inter-organelle interactions, including the cytomembrane, endoplasmic reticulum, mitochondrion, lysosome, dictyosome, and nucleus, play the important roles in maintaining the normal function and homeostasis of cells. Organelle dysfunction can lead to a range of diseases (e.g., Alzheimer's disease (AD), Parkinson's disease (PD), and cancer), and provide a new perspective for drug discovery. With the development of imaging techniques and functional fluorescent probes, a variety of algorithms and strategies have been developed for the ever-improving estimation of subcellular structures, organelle interaction, and organelle-related drug discovery with accounting for the dynamic structures of organelles, such as the nanoscopy technology and molecular dynamics (MD) simulations. Accordingly, this work summarizes a series of state-of-the-art examples of the recent progress in this rapidly changing field and uncovering the drug screening based on the structures and interactions of organelles. Finally, we propose the future outlook for exciting applications of organelle-related drug discovery, with the cooperation of nanoscopy and MD simulations.

Super-resolution analyzing spatial organization of lysosomes with an organic fluorescent probe

Lysosomes are multifunctional organelles involved in macromolecule degradation, nutrient sensing and autophagy. Live imaging has revealed lysosome subpopulations with dynamics and characteristic cellular localization. An as-yet unanswered question is whether lysosomes are spatially organized to coordinate and integrate their functions. Combined with super-resolution microscopy, we designed a small organic fluorescent probe, TPAE, that targeted lysosomes with a large Stokes shift. When we analyzed the spatial organization of lysosomes against mitochondria in different cell lines with this probe, we discovered different distance distribution patterns between lysosomes and mitochondria during increased autophagy flux. By using SLC25A46 mutation fibroblasts derived from patients containing highly fused mitochondria with low oxidative phosphorylation, we concluded that unhealthy mitochondria redistributed the subcellular localization of lysosomes, which implies a strong connection between mitochondria and lysosomes.

Restoration of Sarco/Endoplasmic Reticulum Ca2+-ATPase Activity Functions as a Pivotal Therapeutic Target of Anti-Glutamate-Induced Excitotoxicity to Attenuate Endoplasmic Reticulum Ca2+ Depletion

Glutamate-induced excitotoxicity is a pathological basis of many acute/chronic neurodegenerative diseases. Sarco/endoplasmic reticulum Ca2+-ATPase (SERCA2b) is a membrane-embedded P-type ATPase pump that manages the translocation of calcium ions (Ca2+) from cytosol into the lumen of the endoplasmic reticulum (ER) calcium stores. It participates in a wide range of biological functions in the central nervous system (CNS). However, the role of SERCA2b in glutamate-induced excitotoxicity and its mechanism must be elucidated. Herein, we demonstrate that SERCA2b mutants exacerbate the excitotoxicity of hypo-glutamate stimulation on HT22 cells. In this study, SERCA2b mutants accelerated Ca2+ depletion through loss-of-function (reduced pumping capacity) or gain-of-function (acquired leakage), resulting in ER stress. In addition, the occurrence of ER Ca2+ depletion increased mitochondria-associated membrane formation, which led to mitochondrial Ca2+ overload and dysfunction. Moreover, the enhancement of SERCA2b pumping capacity or inhibition of Ca2+ leakage attenuated Ca2+ depletion and impeded excitotoxicity in response to hypo-glutamate stimulation. In conclusion, SERCA2b mutants exacerbate ER Ca2+-depletion-mediated excitotoxicity in glutamate-sensitive HT22 cells. The mechanism of disruption is mainly related to the heterogeneity of SERCA2b mutation sites. Stabilization of SRECA2b function is a critical therapeutic approach against glutamate-induced excitotoxicity. These data will expand understanding of organelle regulatory networks and facilitate the discovery and creation of drugs against excitatory/inhibitory imbalance in the CNS.

Lysosome-Targeted Biosensor for the Super-Resolution Imaging of Lysosome-Mitochondrion Interaction

Background: The interaction between lysosomes and mitochondria includes not only mitophagy but also mitochondrion–lysosome contact (MLC) that enables the two organelles to exchange materials and information. In our study, we synthesised a biosensor with fluorescence characteristics that can image lysosomes for structured illumination microscopy and, in turn, examined morphological changes in mitochondria and the phenomenon of MLC under pathological conditions.

Methods: After designing and synthesising the biosensor, dubbed CNN, we performed an assay with a Cell Counting Kit-8 to detect CNN’s toxicity in relation to H9C2 cardiomyocytes. We next analysed the co-localisation of CNN and the commercial lysosomal probe LTG in cells, qualitatively analysed the imaging characteristics of CNN in different cells (i.e. H9C2, HeLa and HepG2 cells) via structured illumination microscopy and observed how CNN entered cells at different temperatures and levels of endocytosis. Last, we treated the H9C2 cells with mannitol or glucose to observe the morphological changes of mitochondria and their positions relative to lysosomes.

Results: After we endocytosed CNN, a lysosome-targeted biosensor with a wide, stable pH response range, into cells in an energy-dependent manner. SIM also revealed that conditions in high glucose induced stress in lysosomes and changed the morphology of mitochondria from elongated strips to round spheres.

Conclusion: CNN is a new tool for tracking lysosomes in living cells, both physiologically and pathologically, and showcases new options for the design of similar biosensors.

Selective delivery of curcumin to breast cancer cells by self-targeting apoferritin nanocages with pH-responsive and low toxicity

Breast cancer is prevalent and diverse with significantly high incidence and mortality rates. Curcumin (Cur), a polyphenol component of turmeric, has been widely recognized as having strong anti-breast cancer activity. However, its anti-cancer efficiency is largely impaired by some of its concomitant negative properties, including its poor solubility, low cellular uptake, and severe reported side effects. Hence, the necessity arises to develop a novel low-toxic and high-efficiency targeting drug delivery system (DDS). In this study, we developed a pH-sensitive tumor self-targeting DDS (Cur@HFn) based on self-assembled HFn loaded with Cur, in which Cur was encapsulated into HFn cavity by using a disassembly/reassembly strategy, and the Cur@HFn was characterized by ultraviolet–visible (UV–vis), dynamic light scattering (DLS), and transmission electron microscope (TEM). A variety of breast cancer cell models were built to evaluate cytotoxicity, apoptosis, targeting properties, and uptake mechanism of the Cur@HFn. The pharmacodynamics was also evaluated in tumor (4T1) bearing mice after intravenous injection. In vitro release experiments showed that Cur@HFn is pH sensitive and shows sustained drug release under slightly acidic conditions. Compared with Cur, Cur@HFn has stronger cytotoxicity, cellular uptake, and targeting performance. Our study supported that Cur@HFn has a higher in vivo therapeutic effect and lower systemic toxicity. The safety evaluation results indicated that Cur@HFn has no hematotoxicity, hepatotoxicity, and nephrotoxicity. The findings of the present study showed that the Cur@HFn has been successfully prepared and has potential application value in the treatment of breast cancer.

De Novo Design of A Membrane-Anchored Probe for Multidimensional Quantification of Endocytic Dynamics

As a process of cellular uptake, endocytosis, with gradient acidity in different endocytic vesicles, is vital for the homeostasis of intracellular nutrients and other functions. To study the dynamics of endocytic pathway, a membrane-anchored pH probe, ECGreen, is synthesized to visualize endocytic vesicles under structured illumination microscopy (SIM), a super-resolution technology. Being sensitive to acidity with increasing fluorescence at low pH, ECGreen can differentiate early and late endosomes as well as endolysosomes. Meanwhile, membrane anchoring not only improves the durability of ECGreen, but also provides an excellent anti-photobleaching property for long-time imaging with SIM. Moreover, by taking these advantages of ECGreen, a multidimensional analysis model containing spatial, temporal, and pH information is successfully developed for elucidating the dynamics of endocytic vesicles and their interactions with mitochondria during autophagy, and reveals a fast conversion of endosomes near the plasma membrane.

Label-free study on the effect of a bioactive constituent on glioma cells in vitro using terahertz ATR spectroscopy

In this work, we report that the effect of bioactive constituent on living glioma cells can be evaluated using terahertz time-domain attenuated total reflection (THz TD-ATR) spectroscopy in a label-free, non-invasive, and fast manner. The measured THz absorption coefficient of human glioma cells (U87) in cell culture media increases with ginsenoside Rg3 (G-Rg3) concentration in the range from 0 to 50 µM, which can be interpreted as that G-Rg3 deteriorated the cellular state. This is supported either by the cell growth inhibition rate measured using a conventional cell viability test kit or by the cellular morphological changes observed with fluorescence microscopy. These results verify the effectiveness of using the THz TD-ATR spectroscopy to detect the action of G-Rg3 on glioma cells in vitro. The demonstrated technique thus opens a new route to assessing the efficacy of bioactive constituents on cells or helping screen cell-targeted drugs.

Polyadenylated Telomeric Noncoding RNA Functions as a Pivotal Therapeutic Target of Anti-Ageing to Stabilize Telomere Length of Chromosomes Via Collaborating With Zscan4c

Telomeres are closely associated with the development of cell aging. Shortening or erosion of telomeres will cause cell mortality, suggesting that the maintenance of telomere integrity facilitates cell anti-senescence. However, the mechanism of how to keep the telomere length remains fragmentary. Here, we found that polyadenylated telomeric noncoding RNA (TERRA) can promote the self-renewal when overexpressed in mouse embryonic stem cells (mESCs), implying that TERRA with polyadenylation is critical for mESC maintenance. Further studies revealed that TERRA with a polyadenylated tail plays an important role in the sustenance of telomere length. High-throughput sequencing and quantitative real-time PCR show that zinc finger and SCAN domain containing 4C (Zscan4c) may be a potential target of TERRA. Zscan4c is negatively regulated by TERRA and collaborates with TERRA to stabilize the telomere length of chromosomes in mESCs. Our study not only identifies TERRA as a potential novel factor of telomere length regulation and uncovers the new molecular mechanism of cell anti-aging, but also indicates that Zscan4c could be a key therapeutic target candidate for therapy in dysfunctional chromosome diseases. These data will expand our understanding of the cell fate regulatory network and will be beneficial to drug discovery and theragnostics for antiaging and anticancer therapy in the future.

Efficient Synthesis of 2,3'-Spirobi (Indolin)-2'-Ones and Preliminary Evaluation of Their Damage to Mitochondria in HeLa Cells

A novel formal (4 + 1) annulation between N-(o-chloromethyl)aryl amides and 3-chlorooxindoles through in situ generated aza-ortho-QMs with 3-chlorooxindoles is reported for the synthesis of a series of 2,3'-spirobi (indolin)-2'-ones in high yields. Under structured illumination microscopy, compound 3a is found to change the mitochondrial morphology and induce mitophagy pathway, which might then trigger mitophagy in cancer cells.

Opioids Regulate the Immune System: Focusing on Macrophages and Their Organelles

Opioids are the most widely used analgesics and therefore have often been the focus of pharmacological research. Macrophages are the most plastic cells in the hematopoietic system. They show great functional diversity in various organism tissues and are an important consideration for the study of phagocytosis, cellular immunity, and molecular immunology. The expression of opioid receptors in macrophages indicates that opioid drugs act on macrophages and regulate their functions. This article reviewed the collection of research on effects of opioids on macrophage function. Studies show that opioids, both endogenous and exogenous, can affect the function of macrophages, effecting their proliferation, chemotaxis, transport, phagocytosis, expression of cytokines and chemokine receptors, synthesis and secretion of cytokines, polarization, and apoptosis. Many of these effects are closely associated with mitochondrial function and functions of other organelles in macrophages. Therefore, in depth research into effects of opioids on macrophage organelles may lead to some interesting new discoveries. In view of the important role of macrophages in HIV infection and tumor progression, this review also discusses effects of opioids on macrophages in these two pathological conditions.

Real-Time and High-Fidelity Tracking of Lysosomal Dynamics with a Dicyanoisophorone-Based Fluorescent Probe

The development of high-performance probes that can visualize and track the dynamic changes of lysosomes is very important for the in-depth study of lysosomes. Herein, we report that a dicyanoisophorone-based probe (named DCIP) can be used for high-fidelity imaging of lysosomes and lysosomal dynamics. DCIP can be easily prepared and shows strong far-red to near-infrared emissions centered at 653 nm in water with a huge Stokes shift (224 nm), high quantum yield (Φ = 0.15), high pKa value (∼8.79), and good biocompatibility. DCIP also shows good cell permeability and can label lysosomes rapidly with bright fluorescence without a time-consuming washing process before imaging. DCIP also possesses good photostability and negligible background, making it effective for long-term and high spatiotemporal resolution (0.44 s of exposure) imaging of lysosomes. Moreover, DCIP achieved high-fidelity tracking of lysosomal dynamics at an extremely low concentration (1 nM). Finally, we also demonstrated that DCIP could real-time track the interactions of lysosomes with other organelles (damaged mitochondria as a model) and image the drug-escape processes from lysosomes. All of the results show that DCIP holds broad prospects in lysosome-related research.

Physics-based machine learning for subcellular segmentation in living cells

Segmenting subcellular structures in living cells from fluorescence microscope images is a ground truth (GT)-deficient problem. The microscopes’ three-dimensional blurring function, finite optical resolution due to light diffraction, finite pixel resolution and the complex morphological manifestations of the structures all contribute to GT-hardness. Unsupervised segmentation approaches are quite inaccurate. Therefore, manual segmentation relying on heuristics and experience remains the preferred approach. However, this process is tedious, given the countless structures present inside a single cell, and generating analytics across a large population of cells or performing advanced artificial intelligence tasks such as tracking are greatly limited. Here we bring modelling and deep learning to a nexus for solving this GT-hard problem, improving both the accuracy and speed of subcellular segmentation. We introduce a simulation-supervision approach empowered by physics-based GT, which presents two advantages. First, the physics-based GT resolves the GT-hardness. Second, computational modelling of all the relevant physical aspects assists the deep learning models in learning to compensate, to a great extent, for the limitations of physics and the instrument. We show extensive results on the segmentation of small vesicles and mitochondria in diverse and independent living- and fixed-cell datasets. We demonstrate the adaptability of the approach across diverse microscopes through transfer learning, and illustrate biologically relevant applications of automated analytics and motion analysis.

Prefused lysosomes cluster on autophagosomes regulated by VAMP8

Lysosome–autophagosome fusion is critical to autophagosome maturation. Although several proteins that regulate this fusion process have been identified, the prefusion architecture and its regulation remain unclear. Herein, we show that upon stimulation, multiple lysosomes form clusters around individual autophagosomes, setting the stage for membrane fusion. The soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) protein on lysosomes—vesicle-associated membrane protein 8 (VAMP8)—plays an important role in forming this prefusion state of lysosomal clusters. To study the potential role of phosphorylation on spontaneous fusion, we investigated the effect of phosphorylation of C-terminal residues of VAMP8. Using a phosphorylation mimic, we observed a decrease of fusion in an ensemble lipid mixing assay and an increase of unfused lysosomes associated with autophagosomes. These results suggest that phosphorylation not only reduces spontaneous fusion for minimizing autophagic flux under normal conditions, but also preassembles multiple lysosomes to increase the fusion probability for resuming autophagy upon stimulation. VAMP8 phosphorylation may thus play an important role in chemotherapy drug resistance by influencing autophagosome maturation.

Revealing Sulfur Dioxide Regulation to Nucleophagy in Embryo Development by an Adaptive Coloration Probe

Understanding signaling molecules in regulating organelles dynamics and programmed cell death is critical for embryo development but is also challenging because current imaging probes are incapable of simultaneously imaging the signaling molecules and the intracellular organelles they interact with. Here, we report a chemically and environmentally dual-responsive imaging probe that can react with gasotransmitters and label cell nuclei in distinctive fluorescent colors, similar to the adaptive coloration of chameleons. Using this intracellular chameleon-like probe in three-dimensional (3D) super-resolution dynamic imaging of live cells, we discovered SO₂ as a critical upstream signaling molecule that activates nucleophagy in programmed cell death. An elevated level of SO₂ prompts kiss fusion between the lysosomal and nuclear membranes and nucleus shrinkage and rupture. Significantly, we revealed that the gasotransmitter SO₂ is majorly generated in the yolk, induces autophagy there at the initial stage of embryo development, and is highly related to the development of the auditory nervous system.

New insights regarding SNARE proteins in autophagosome-lysosome fusion

Macroautophagy/autophagy refers to the engulfment of cellular contents selected for lysosomal degradation. The final step in autophagy is the fusion of autophagosome with the lysosome, which is mediated by SNARE proteins. Of the SNAREs, autophagosome-localized Q-SNAREs, such as STX17 and SNAP29, and lysosome-localized R-SNAREs, such as VAMP8 or VAMP7, have been reported to be involved. Recent studies also reveal participation of the R-SNARE, YKT6, in autophagosome-lysosome fusion. These SNAREs, with the help of other regulatory factors, act coordinately to spatiotemporally control the fusion process. Besides regulating autophagosome-lysosome fusion, some SNAREs, such as STX17, also function in other autophagic processes, including autophagosome formation and mitophagy. A better understanding of the functions of SNAREs will shed light on the molecular mechanisms of autophagosome-lysosome fusion as well as on the mechanisms by which autophagy is globally regulated.Abbreviations: ATG: autophagy related; DNM1L: dynamin 1 like; ER: endoplasmic reticulum; GABARAP: GABA type A receptor-associated protein; GABARAPL1: GABA type A receptor associated protein like 1; IRGM: immunity related GTPase M; LAMP2: lysosomal associated membrane protein 2; MAP1LC3B/LC3: microtubule associated protein 1 light chain 3 beta; MTOR: mechanistic target of rapamycin kinase; PIK3R4: phosphoinositide-3-kinase regulatory subunit 4; PLEKHM1: pleckstrin homology and RUN domain containing M1; PRKN: PRKN RBR E3 ubiquitin protein ligase; RAB2A: RAB2A, member RAS oncogene family; RAB33B: RAB33B, member RAS oncogene family; RAB7A: RAB7A, member RAS oncogene family; RB1CC1: RB1 inducible coiled-coil 1; RTN3: reticulon 3; RUBCNL: rubicon like autophagy enhancer; SNARE: soluble N-ethylmaleimide-sensitive factor attachment protein receptor; SNAP29: synaptosomal associated protein 29; STX17: syntaxin 17; ULK1: unc-51 like autophagy activating kinase 1; VAMP7: vesicle associated membrane protein 7; VAMP8: vesicle associated membrane protein 8; YKT6: YKT6 v-SNARE homolog.

A Continuous Add-On Probe Reveals the Nonlinear Enlargement of Mitochondria in Light-Activated Oncosis

Oncosis, depending on DNA damage and mitochondrial swelling, is an important approach for treating cancer and other diseases. However, little is known about the behavior of mitochondria during oncosis, due to the lack of probes for in situ visual illumination of the mitochondrial membrane and mtDNA. Herein, a mitochondrial lipid and mtDNA dual-labeled probe, MitoMN, and a continuous add-on assay, are designed to image the dynamic process of mitochondria in conditions that are unobservable with current mitochondrial probes. Meanwhile, the MitoMN can induce oncosis in a light-activated manner, which results in the enlargement of mitochondria and the death of cancer cells. Using structured illumination microscopy (SIM), MitoMN-stained mitochondria with a dual-color response reveals, for the first time, how swelled mitochondria interacts and fuses with each other for a nonlinear enlargement to accelerate oncosis into an irreversible stage. With this sign of irreversible oncosis revealed by MitoMN, oncosis can be segregated into three stages, including before oncosis, initial oncosis, and accelerated oncosis.

Advances in the study of organelle interactions and their role in neurodegenerative diseases enabled by super-resolution microscopy

From the first illustrations of neuronal morphology by Ramón y Cajal to the recent three-dimensional reconstruction of synaptic connections, the development of modern neuroscience has greatly benefited from breakthroughs in imaging technology. This also applies specifically to the study of neurodegenerative diseases. Much of the research into these diseases relies on the direct visualisation of intracellular structures and their dynamics in degenerating neural cells, which cannot be fully resolved by diffraction-limited microscopes. Progress in the field has therefore been closely linked to the development of super-resolution imaging methods. Their application has greatly advanced our understanding of disease mechanisms, ranging from the structural progression of protein aggregates to defects in organelle morphology. Recent super-resolution studies have specifically implicated the disruption of inter-organelle interactions in multiple neurodegenerative diseases. In this article, we describe some of the key super-resolution techniques that have contributed to this field. We then discuss work to visualise changes in the structure and dynamics of organelles and associated dysfunctions. Finally, we consider what future developments in imaging technology may further our knowledge of these processes.

A mitochondria-targeted fluorescent probe for monitoring endogenous cysteine in living cells and zebrafish

At the organelle level, pathogenesis due to abnormal concentrations of cysteine (Cys) is of great significance for the early diagnosis and treatment of related diseases. Generally speaking, organelle localization requires the participation of specific target groups, which increases the difficulty of synthesis. Herein, through simple synthesis, a novel biflavone derivative (BFD) that exhibits excited-state intramolecular proton transfer (ESIPT) was obtained and successfully located in mitochondria without target groups. The probe BFD can distinguish Cys from Hcy and GSH with a rapid response (< 5 s) and showed visual detection for Cys with a large Stokes shift (about 260 nm). Because of its nanomorphology in solution and surface functional groups, the probe BFD can enter the cell smoothly and achieve mitochondrial localization. Owing to its excellent optical performance, the probe BFD was successfully applied to the imaging of endogenous Cys in HeLa cells and zebrafish.

Long-term live-cell lipid droplet-targeted biosensor development for nanoscopic tracking of lipid droplet-mitochondria contact sites

Background: Lipid droplets (LDs) establish a considerable number of contact sites with mitochondria to enable energy transfer and communication. In this study, we developed a fluorescent biosensor to image LD-mitochondria interactions at the nanoscale and further explored the function of LD-mediated matrix transmission in processes involving multi-organelle interactions. Methods: A fluorescent probe called C-Py (C21H19N3O2, 7-(diethylamino) coumarin-3-vinyl-4-pyridine acetonitrile) was designed and synthesized. Colocalization of C-Py and the commercial LD stain Nile Red was analyzed in HeLa cells. The fluorescence stability and signal to background ratio of C-Py under structured illumination microscopy (SIM) were compared to those of the commercial probe BODIPY493/503. The cytotoxicity of C-Py was assessed using CCK-8 assays. The uptake pattern of C-Py in HeLa cells was then observed under various temperatures, metabolic levels, and endocytosis levels. Contact sites between LDs and various organelles, such as mitochondria, nuclei, and cell membrane, were imaged and quantitated using SIM. Physical changes to the contact sites between LDs and mitochondria were monitored after lipopolysaccharide induction. Results: A LD-targeted fluorescent biosensor, C-Py, with good specificity, low background signal, excellent photostability, low cytotoxicity, and high cellular permeability was developed for tracking LD contact sites with multiple organelles using SIM. Using C-Py, the subcellular distribution and dynamic processes of LDs in living cells were observed under SIM. The formation of contact sites between LDs and multiple organelles was visualized at a resolution below ~200 nm. The number of LD-mitochondria contact sites formed was decreased by lipopolysaccharide treatment inducing an inflammatory environment. Conclusions: C-Py provides strategies for the design of ultra-highly selective biosensors and a new tool for investigating the role and regulation of LDs in living cells at the nanoscale.

Nanoscopic quantification of sub-mitochondrial morphology, mitophagy and mitochondrial dynamics in living cells derived from patients with mitochondrial diseases

SLC25A46 mutations have been found to lead to mitochondrial hyper-fusion and reduced mitochondrial respiratory function, which results in optic atrophy, cerebellar atrophy, and other clinical symptoms of mitochondrial disease. However, it is generally believed that mitochondrial fusion is attributable to increased mitochondrial oxidative phosphorylation (OXPHOS), which is inconsistent with the decreased OXPHOS of highly-fused mitochondria observed in previous studies. In this paper, we have used the live-cell nanoscope to observe and quantify the structure of mitochondrial cristae, and the behavior of mitochondria and lysosomes in patient-derived SLC25A46 mutant fibroblasts. The results show that the cristae have been markedly damaged in the mutant fibroblasts, but there is no corresponding increase in mitophagy. This study suggests that severely damaged mitochondrial cristae might be the predominant cause of reduced OXPHOS in SLC25A46 mutant fibroblasts. This study demonstrates the utility of nanoscope-based imaging for realizing the sub-mitochondrial morphology, mitophagy and mitochondrial dynamics in living cells, which may be particularly valuable for the quick evaluation of pathogenesis of mitochondrial morphological abnormalities.

Autophagy mediated lipid catabolism facilitates glioma progression to overcome bioenergetic crisis

BACKGROUND

Activation of mTORC1 plays a significant role in cancer development and progression. However, the metabolic mechanisms to sustain mTORC1 activation of cancer cells within stressed environments are still under-appreciated. We recently revealed high autophagy activity in tumour cells with mTORC1 hyper-activation. Nevertheless, the functions and mechanisms of autophagy in regulating mTORC1 in glioma are not studied.

METHODS

Using glioma patient database and human glioma cells, we assessed the mechanisms and function of selective autophagy to sustain mTORC1 hyper-activation in glioma.

RESULTS

We revealed a strong association of altered mRNA levels in mTORC1 upstream and downstream genes with prognosis of glioma patients. Our results indicated that autophagy-mediated lipid catabolism was essential to sustain mTORC1 activity in glioma cells under energy stresses. We found that autophagy inhibitors or fatty acid oxidation (FAO) inhibitors in combination with 2-Deoxy-D-glucose (2DG) decreased energy production and survival of glioma cells in vitro. Consistently, inhibition of autophagy or FAO inhibitors with 2DG effectively suppressed the progression of xenografted glioma with hyper-activated mTORC1.

CONCLUSIONS

This study established an autophagy/lipid degradation/FAO/ATP generation pathway, which might be used in brain cancer cells under energy stresses to maintain high mTORC1 signalling for tumour progression.

Live cell mitochondrial 3-dimensional dynamic ultrastructures under oxidative phosphorylation revealed by a Pyridine-BODIPY probe

Recent advancements in super-resolution nanoscopy allowed the study of mitochondrial biology at nanoscale and boosted the understanding its correlated cellular processes those were previously poorly understood. Nevertheless, studying mitochondrial ultrastructure remains a challenge due to the lack of probes that could target specific mitochondrial substances (e.g. cristae or mtDNA) and survive under harsh super-resolution optical conditions. Herein, in this work, we have rationally constructed a pyridine-BODIPY (Py-BODIPY) derivative that could target mitochondrial membrane in living cells without interfering its physiological microenvironments. Furthermore, we found Py-BODIPY is a membrane potential independent probe, hence it is not limit to live-cell staining but also showed a strong internalization into pre-fixed and stimulus disrupted sample. Importantly, its cristae specificity and superb photostability allow the observation of mitochondrial dynamic nano-structures with an unprecedented resolution, allow demonstrating how mitochondrial 3D ultrastructure evolved under oxidative phosphorylation condition.

Highly Photostable Fluorescent Tracker with pH-Insensitivity for Long-Term Imaging of Lysosomal Dynamics in Live Cells

Visualizing and tracking lysosomal dynamic changes is crucially important in the fields of physiology and pathology. Most currently used pH-dependent small-molecule lysotrackers and sensors usually fail to visualize and track the changes due to (1) their leakage from lysosomes when the lysosomal pH increases and (2) their low photostability. Therefore, it is of significant interest to develop lysosomal probes for visualizing and tracking lysosomal dynamics independent of pH fluctuations and with high photostability. Herein, we found that the popular dicyanomethylene-4H-pyran (DCM) derivative DCM-NH₂ can selectively target and label lysosomes with bright red fluorescence regardless of pH changes. The fluorescence enhancement in lysosomes has probably resulted from their microenvironment of polarity and viscosity. Compared with the commonly used commercial lysosomal molecular probes (LysoTracker Deep Red (LTDR) and LysoTracker Red DND-99), DCM-NH₂ was demonstrated to exhibit a much stronger tolerance in lysosomes against various treatments and microenvironmental changes, and lysosomal membrane permeability could not cause DCM-NH₂ to lose imaging of their targets as well. Moreover, DCM-NH₂ exhibited a superior anti-photobleaching ability and low (photo-) cytotoxicity, which, along with pH-insensitivity, ensured its capability of long-term visualizing and tracking lysosomal dynamics. Lysosomal dynamic events such as the kiss-and-run process, fusion-fission, and mitophagy were successfully recorded with DCM-NH₂. Our study thus confirms that DCM-NH₂ is highly competitive for lysosomal imaging by overcoming the limitations of the commercial LysoTrackers and highlights the unexplored application of DCM-NH₂ in bioimaging.

An assembly-regulated SNAP-tag fluorogenic probe for long-term super-resolution imaging of mitochondrial dynamics

Super-resolution fluorescence microscopy has emerged as a powerful tool for studying mitochondrial dynamics in living cells. However, the lack of photostable and chemstable probe makes long-term super-resolution imaging of mitochondria still a challenging work. Herein, we reported a 4-azetidinyl-naphthliamide derived SNAP-tag probe AN-BG exhibiting excellent fluorogenicity and photostability for long-term super-resolution imaging of mitochondrial dynamics. The azetidinyl group and naphthalimide fluorophore are in a flat conformation which can effectively suppress twisted intramolecular charge transfer and then effectively improve the brightness and photostability. This planarized molecular structure is conducive to the formation of fluorescence-quenched J-aggregates, and the protein labeling process will depolymerize the probes and restore fluorescence. Fluorescent labeling mitochondrial inner membrane proteins via SNAP tags overcomes the shortcomings that variations in mitochondrial inner membrane potential will release probes attached to mitochondria by electrostatic interactions. Therefore, AN-BG realized the stable labeling of mitochondria and the long-term imaging of mitochondrial dynamics under super-resolution microscopy.

Correlation between the synthesis of pullulan and melanin in Aureobasidium pullulans

The content of pullulan and melanin in 500 mutants of Aureobasidum pullulans obtained by ultraviolet mutagenesis were examined and statistically analyzed, and a strong positive correlation was found between them. The result was further confirmed by culturing wild type strain As3.3984 in different media. Then we constructed melanin-deletion mutant As-Δalb1 and pullulan-deletion mutant As-Δpul. As-Δalb1 was a melanin-free strain with the yield of pullulan decreased by 41.01%. The supplementation of melanin in the culture of As-Δalb1 increased the production of pullulan. As-Δpul synthesized neither pullulan nor melanin and recovered melanin synthesis by adding pullulan to the medium. The results suggested that high concentration- of pullulan induced morphological transformation and synthesis of melanin, and melanin promoted the synthesis of pullulan. The pullulan biosynthetic genes, upt, pgm, ugp, and pul, were down-regulated, while the negative regulatory gene of pullulan synthesis, creA, was up-regulated by melanin deficiency.