Quantitative analysis of autophagic flux by confocal pH-imaging of autophagic intermediates

Simultaneous Live Mapping of pH and Hydrogen Peroxide Fluctuations in Autophagic Vesicles

Hydrogen peroxide (H2O2) plays a critical role in the regulation and progress of autophagy, an essential recycling process that influences cellular homeostasis and stress response. Autophagy is characterized by the formation of intracellular vesicles analogous to recycle "bags" called autophagosomes, which fuse with lysosomes to form autolysosomes, eventually ending up as lysosomes. We have developed two novel autophagic vesicle-targeted peptide-based sensors, ROSA for H2O2 and pHA for pH, to simultaneously track H2O2 and pH dynamics within autophagic vesicles as autophagy advances. Since pH values progressively decrease within autophagic vesicles with the progress of autophagy, we utilized information on vesicular pH to identify stages of autophagic vesicles in live cells. Fluorescence intensities of the H2O2 sensor, ROSA, within autophagic compartments at different autophagic stages, which were identified by simultaneous pH mapping, revealed that H2O2 levels vary significantly within autophagic vesicles as autophagy progresses, with maximum H2O2 levels in the autolysosomal stage. This study provides the first detailed observation of H2O2 fluctuations within autophagic vesicles throughout the entire process of autophagy in living mammalian cells, offering insights into the oxidative changes associated with this vital cellular process.

G-quadruplex in mitochondria as a possible biomarker for mitophagy detection

Mitochondrial autophagy (mitophagy) is a key physiological process that maintains the homeostasis of mitochondrial quality and quantity. Monitoring mitophagy is of great significance for detecting cellular abnormalities and developing therapeutic drugs. However, there are still very few biomarkers specifically developed for monitoring mitophagy. Here, we propose for the first time that mitochondrial G-quadruplex may serve as a biomarker for mitophagy detection, and develope a fluorescent light-up probe AMTC to monitor mitophagy in live cells. During mitophagy, AMTC fluorescence is significantly enhanced, but once mitophagy is inhibited, its fluorescence immediately decreases. The fluorescence behavior of AMTC implicates an increase in the formation of mitochondrial G-quadruplex during mitophagy. This inference has also been supported by the other two G-quadruplex probes. Taken together, this work provides a new possible biomarker and detection tool for the study of mitophagy.

The Role and Mechanism of Metformin in Inflammatory Diseases

Metformin is a classical drug used to treat type 2 diabetes. With the development of research on metformin, it has been found that metformin also has several advantages aside from its hypoglycemic effect, such as anti-inflammatory, anti-aging, anti-cancer, improving intestinal flora, and other effects. The prevention of inflammation is critical because chronic inflammation is associated with numerous diseases of considerable public health. Therefore, there has been growing interest in the role of metformin in treating various inflammatory conditions. However, the precise anti-inflammatory mechanisms of metformin were inconsistent in the reported studies. Thus, this review aims to summarize various currently known possible mechanisms of metformin involved in inflammatory diseases and provide references for the clinical application of metformin.

TFEB SUMOylation in macrophages accelerates atherosclerosis by promoting the formation of foam cells through inhibiting lysosomal activity

Atherosclerosis (AS) is a serious cardiovascular disease. One of its hallmarks is hyperlipidemia. Inhibiting the formation of macrophage foam cells is critical for alleviating AS. Transcription factor EB (TFEB) can limit the formation of macrophage foam cells by upregulating lysosomal activity. We examined whether TFEB SUMOylation is involved in this progress during AS. In this study, we investigated the role of TFEB SUMOylation in macrophages in AS using TFEB SUMOylation deficiency Ldlr-/- (TFEB-KR: Ldlr-/-) transgenic mice and TFEB-KR bone marrow-derived macrophages. We observed that TFEB-KR: Ldlr-/- atherosclerotic mice had thinner plaques and macrophages with higher lysosomal activity when compared to WT: Ldlr-/- mice. TFEB SUMOylation in macrophages decreased after oxidized low-density lipoprotein (OxLDL) treatment in vitro. Compared with wild type macrophages, TFEB-KR macrophages exhibited less lipid deposition after OxLDL treatment. Our study demonstrated that in AS, deSUMOylation of TFEB could inhibit the formation of macrophage foam cells through enhancing lysosomal biogenesis and autophagy, further reducing the accumulation of lipids in macrophages, and ultimately alleviating the development of AS. Thus, TFEB SUMOylation can be a switch to modulate macrophage foam cells formation and used as a potential target for AS therapy.

Mitophagy in Astrocytes Is Required for the Health of Optic Nerve

Mitochondrial dysfunction in astrocytes has been implicated in the development of various neurological disorders. Mitophagy, mitochondrial autophagy, is required for proper mitochondrial function by preventing the accumulation of damaged mitochondria. The importance of mitophagy, specifically in the astrocytes of the optic nerve (ON), has been little studied. We introduce an animal model in which two separate mutations act synergistically to produce severe ON degeneration. The first mutation is in Cryba1, which encodes βA3/A1-crystallin, a lens protein also expressed in astrocytes, where it regulates lysosomal pH. The second mutation is in Bckdk, which encodes branched-chain ketoacid dehydrogenase kinase, which is ubiquitously expressed in the mitochondrial matrix and involved in the catabolism of the branched-chain amino acids. BCKDK is essential for mitochondrial function and the amelioration of oxidative stress. Neither of the mutations in isolation has a significant effect on the ON, but animals homozygous for both mutations (DM) exhibit very serious ON degeneration. ON astrocytes from these double-mutant (DM) animals have lysosomal defects, including impaired mitophagy, and dysfunctional mitochondria. Urolithin A can rescue the mitophagy impairment in DM astrocytes and reduce ON degeneration. These data demonstrate that efficient mitophagy in astrocytes is required for ON health and functional integrity.

Near infrared in and out: Deep imaging for scrap leather induced autophagy in vivo by an ultrasensitive two-photon polarity probe

As one of the important means for eukaryotic cells to maintain homeostasis, autophagy allows for transporting deformed biomacromolecules and damaged organelles to lysosome for digestion and degradation. The process of autophagy entails the merging of autophagosomes and lysosomes, culminating in the breakdown of biomacromolecules. This, in turn, leads to a change in lysosomal polarity. Therefore, fully understanding the changes of lysosomal polarity during autophagy is of significance to the study of membrane fluidity and enzymatic reaction. However, the shorter emission wavelength has greatly damaged the imaging depth, thus seriously limiting its biological application. Therefore, in this work, a near infrared in and out lysosome-targeted polarity-sensitive probe NCIC-Pola was developed. The fluorescence intensity of NCIC-Pola showed an approximate 1160-fold increase when the polarity decreased under two-photon excitation (TPE). In addition, the excellent fluorescence emission wavelength (692 nm) enabled the deep imaging analysis of scrap leather induced autophagy in vivo.

Autophagy and podocytopathy

Autophagy is a complex process of lysosomal-dependent degradation of unwanted cellular material. In response to endogenous or exogenous stimuli, autophagy is induced and regulated by two kinases: the AMP activated kinase and the mammalian target of rapamycin (mTOR). Cells activated by Unc-51-like kinase 1 form a double membrane complex that sequesters the cargo (phagophore) and elongates producing spherical vesicles (autophagosomes). These reach and fuse with lysosomes, which degrade the cargo (autolysosomes). The resulting macromolecules are released back and recycled in the cytosol for reuse. In the podocyte, autophagy is a homeostatic mechanism that contributes to the formation and preservation of the morphological and functional integrity of actin cytoskeleton. Podocytes, fenestrated endothelial cells and glomerular basement membrane compose the glomerular filtration barrier. Podocyte damage may cause dysfunction of the glomerular barrier, proteinuria and glomerulosclerosis in different glomerular diseases and particularly in so-called podocytopathies, namely minimal change disease and focal segmental glomerulosclerosis. Several drugs and molecules may activate autophagic function in murine models. Among them, aldosterone inhibitors, mineralocorticoid inhibitors and vitamin D3 were proven to protect podocyte from injury and reduce proteinuria in clinical studies. However, no clinical trial with autophagy regulators in podocytopathies has been conducted. Caution is needed with other autophagy activators, such as mTOR inhibitors and metformin, because of potential adverse events.

Intermittent inhibition of FYVE finger-containing phosphoinositide kinase induces melanosome degradation in B16F10 melanoma cells

BACKGROUND

Melanosomes are lysosome-related organelles that contain melanogenic factors and synthesize melanin as they mature. FYVE finger-containing phosphoinositide kinase (PIKfyve) regulates late endosome and lysosome morphology, vesicle trafficking, and autophagy. In melanocytes, PIKfyve inhibition has been reported to induce hypopigmentation due to impairments in the metabolism of early-stage melanosomes.

METHODS AND RESULTS

Here, we report a new type of melanosome metabolism: post-PIKfyve inhibition, which was found during the characterization of the endosome/lysosome fluoroprobe GIF-2250. In B16F10 mouse melanoma cells, GIF-2250 highlighted vesicles positive for lysosomal-associated membrane protein 1 (lysosome marker) and other endosome/lysosome markers (CD63 and Rab7/9). When cells were continuously treated with PIKfyve inhibitors, intracellular vacuoles formed, while GIF-2250 fluorescence signals diminished and were diffusely distributed in the vacuoles. After removal of the PIKfyve inhibitors, the GIF-2250 signal intensity was restored, and some GIF-2250-positive vesicles wrapped the melanosomes, which spun at high speed. In addition, intermittent PIKfyve inhibition caused melanin diffusion in the vacuoles and possible leakage into the cytoplasmic compartments, and melanosome degradation was detected by a transmission electron microscope. Melanosome degradation was accompanied by decreased levels of melanin synthesis enzymes and increased levels of the autophagosome maker LC3BII, which is also associated with early melanosomes. However, the protein levels of p62, which is degraded during autophagy, were increased, suggesting an impairment in autophagy flux during intermittent PIKfyve inhibition. Moreover, the autophagy inhibitor 3-methyladenine does not affect these protein levels, suggesting that the melanosome degradation by the intermittent inhibition of PIKfyve is not mediated by canonical autophagy.

CONCLUSIONS

In conclusion, disturbance of PIKfyve activity induces melanosome degradation in a canonical autophagy-independent manner.

CDK5RAP3, a key defender of udder, modulates NLRP3 inflammasome activation by regulating autophagolysosome degradation in S. agalactiae-infected mastitis

Streptococcus agalactiae, as one of the main pathogens of clinical and subclinical mastitis, affects animal welfare and leads to huge economic losses to farms due to the sharp decline in milk yield. However, both the real pathogenic mechanisms of S. agalactiae-induced mastitis and the regulator which controls the inflammation and autophagy are largely unknown. Served as a substrate of ubiquitin-like proteins of E3 ligase, CDK5RAP3 is widely involved in the regulation of multiple signaling pathways. Our findings revealed that CDK5RAP3 was significantly down-regulated in mastitis infected by S. agalactiae. Surprisingly, inflammasome activation was triggered by CDK5RAP3 knockdown: up-regulated NLRP3, IL1β and IL6, and cleaved caspase1 promoting by NF-κB, thereby resulting in pyroptosis. Additionally, the accumulation of autophagy markers (LC3B and p62) after CDK5RAP3 knockdown suggested that the autophagolysosome degradation pathway was inhibited, thereby activating the NF-κB pathway and NLRP3 inflammasome. Hence, our findings suggest that downregulation or ablation of CDK5RAP3 inhibits autophagolysosome degradation, causes inflammation by activating the NF-κB /NLRP3 inflammasome, and triggers cell death. In conclusion, CDK5RAP3 holds the key to understanding the interaction between autophagy and immune responses, its anti-inflammatory role in this study will throw new light on the clinical drug discovery to cure S. agalactiae mastitis.

Cascade Delivery to Golgi Apparatus and On-Site Formation of Subcellular Drug Reservoir for Cancer Metastasis Suppression

As the foremost cause of cancer-related death, metastasis consists of three steps: invasion, circulation, and colonization. Only targeting one single phase of the metastasis cascade may be insufficient since there are many alternative routes for tumor cells to disseminate. Here, to target the whole cascade of metastasis, hybrid erythrocyte and tumor cell membrane-coated nanoparticle (Hyb-NP) is designed with dual functions of increasing circulation time and recognizing primary, circulating, and colonized tumors. After loading with monensin, a recently reported metastasis inhibitor, the delivery system profoundly reduces spontaneous metastasis in an orthotopic breast cancer model. Underlying mechanism studies reveal that Hyb-NP can deliver monensin to its action site in the Golgi apparatus, and in return, monensin can block the exocytosis of Hyb-NP from the Golgi apparatus, forming a reservoir-like subcellular structure. Notably, the Golgi apparatus reservoir displays three vital functions for suppressing metastasis initialization, including enhanced subcellular drug retention, metastasis-related cytokine release inhibition, and directional migration inhibition. Collectively, based on metastasis cascade targeting at the tissue level, further formation of the Golgi apparatus drug reservoir at the subcellular level provides a potential therapeutic strategy for cancer metastasis suppression.

Evaluation of Everolimus Activity against Mycobacterium tuberculosis Using In Vitro Models of Infection

Even though Everolimus has been investigated in a phase II randomized trial as a host-directed therapy (HDT) to treat tuberculosis (TB), an oncological patient treated with Everolimus for a neuroendocrine pancreatic neoplasia developed active TB twice and a non-tuberculous mycobacterial (NTM) infection in a year and a half time span. To investigate this interesting case, we isolated and genotypically characterized the Mycobacterium tuberculosis (Mtb) clinical strain from the patient and tested the effect of Everolimus on its viability in an axenic culture and in a peripheral blood mononuclear cell (PBMCs) infection model. To exclude strain-specific resistance, we tested the activity of Everolimus against Mtb strains of ancient and modern lineages. Furthermore, we investigated the Everolimus effect on ROS production and autophagy modulation during Mtb infection. Everolimus did not have a direct effect on mycobacteria viability and a negligible effect during Mtb infection in host cells, although it stimulated autophagy and ROS production. Despite being a biologically plausible HDT against TB, Everolimus does not exert a direct or indirect activity on Mtb. This case underlines the need for a careful approach to drug repurposing and implementation and the importance of pre-clinical experimental studies.

The Detection and Imaging of pH Values in Living Cells with Hemicyanine Based Colorimetric Mitochondria-Targeted Fluorescent Probe

pH plays a crucial role in cells, especially mitochondria, an important organelle. Developing probes with well-performance for pH detection is still in great demand. Therefore, we first synthesized an indole-based probe (MC-ID-OL) to detect mitochondrial pH changes. The emission wavelength of MC-ID-OL is 649 nm, which does not reach the near-infrared region (650-900 nm). To further enlarge the emission wavelength, probe MC-BI-OL was developed by replacing indolenine with benzoindole. As expected, the emission wavelength changed from 649 to 656 nm. MC-BI-OL probes could also detect pH changes and mitochondria's highly reversible proportional fluorescence localization. In addition, the fluorescence imaging of the MC-BI-OL in HeLa cells demonstrated that this probe could sense changes in the pH of mitochondria in cells.

A noncanonical endocytic pathway is involved in the internalization of 3 μm polystyrene beads into HeLa cells

Extracellular fine particles of various sizes and origins can be taken up by cells, affecting their function. Understanding the cellular uptake processes is crucial for understanding the cellular effects of these particles and the development of means to control their internalization. Although macropinocytosis is a possible pathway for the cellular uptake of particles larger than 0.2 μm, its contribution to cellular uptake in non-phagocytic cells is controversial. Using 3 μm polystyrene beads as a model particle, we aimed to assess the detailed modes of their cellular uptake by non-phagocytic HeLa cells. Cellular uptake was assessed using confocal, scanning electron, and scanning ion conductance microscopy analyses, together with inhibitor studies. Our results revealed that 3 μm beads were taken up by HeLa cells by an actin-, cholesterol-, and membrane protrusions-dependent noncanonical endocytic pathway, different from the canonical macropinocytic and phagocytic pathways. Our work provides a framework for studying the cellular uptake of extracellular fine particles.

Isoginkgetin Synergizes with Doxorubicin for Robust Co-delivery to Induce Autophagic Cell Death in Hepatocellular Carcinoma

Doxorubicin (DOX) widely used in hepatocellular carcinoma (HCC) can induce serious side effects and drug resistance. Herein, we aimed to seek a strategy to improve the efficacy and reduce the side effects of DOX in HCC based on an autophagy inducer drug called isoginkgetin (ISO). The design of multifunctional nanocarriers based on hyaluronic acid-conjugated and manganese-doped mesoporous silica nanoparticles (HM) for the co-delivery of antitumor drugs against HCC provided an effective and promising antitumor strategy. Our results showed that HM@ISO@DOX could efficiently inhibit HCC cell proliferation through activating autophagy through AMPKa-ULK1 pathway. Moreover, intravenous injection of HM@ISO@DOX significantly suppressed HCC tumor progression in nude mouse HCC model. Collectively, our findings revealed an anti-HCC mechanism of HM@ISO@DOX through autophagy and provide an effective therapeutic strategy for HCC. STATEMENT OF SIGNIFICANCE: In our study, we constructed a co-delivery system by loading ISO and DOX in the mesoporous channels of manganese-doped mesoporous silica nanoparticles, which could be further conjugated with hyaluronic acid to obtain HM@ISO@DOX. The nanocarriers had been demonstrated to be biodegradable under the acidic and reducing tumor microenvironment, as well as to possess the tumor targeting capability via the conjugated hyaluronic acid. In addition, HM@ISO@DOX enhanced the therapeutic efficacy against human HCC tumor through the combinatorial therapies of chemotherapeutics, Mn²⁺-mediated chemodynamic therapeutics and autophagic cell death, which might be achieved through AMPK-ULK1 signaling. This work revealed that such a nanomedicine exhibited superior tumor accumulation and antitumor efficiency against HCC with extremely low systemic toxicity in an autophagy-boosted manner.

Recent advances in small-molecule fluorescent probes for studying ferroptosis

Ferroptosis is an iron-dependent, non-apoptotic form of programmed cell death driven by excessive lipid peroxidation (LPO). Mounting evidence suggests that the unique modality of cell death is involved in the development and progression of several diseases including cancer, cardiovascular diseases (CVDs), neurodegenerative disorders, etc. However, the pathogenesis and signalling pathways of ferroptosis are not fully understood, possibly due to the lack of robust tools for the highly selective and sensitive imaging of ferroptosis analytes in complex living systems. Up to now, various small-molecule fluorescent probes have been applied as promising chemosensors for studying ferroptosis through tracking the biomolecules or microenvironment-related parameters in vitro and in vivo. In this review, we comprehensively reviewed the recent development of small-molecule fluorescent probes for studying ferroptosis, with a focus on the analytes, design strategies and bioimaging applications. We also provided new insights to overcome the major challenges in this emerging field.

Autophagy protects against high uric acid-induced hepatic insulin resistance

Uric acid (UA), the end-product of purine metabolism, is closely related to hepatic insulin resistance (IR). Autophagy is a conserved intracellular degradation process maintaining cellular homeostasis. Autophagy plays a protective role in obesity-related hepatic IR, but whether it occurs in high uric acid (HUA)-induced hepatic IR is unclear. In this study, spontaneously elevated UA level induced hepatic IR and facilitated hepatic autophagy degradation in uricase knockout (Uox^-/-) mice. In vitro, HepG2 cells stimulated with HUA medium showed decreased glucose uptake and inhibition of insulin signaling pathways, concomitant with activation of autophagy, as manifested by increased conversion of LC3B-I to -II. Rapamycin, the autophagy activator, alleviated but the autophagy inhibitor trimethyl adenine (3-MA) aggravated HUA-induced IR in HepG2 cells. Similarly, rapamycin ameliorated and 3-MA worsened HUA-induced blood glucose level and hepatic IR in Uox^-/- mice. Mechanistically, HUA enhanced AMPKα phosphorylation (p-AMPKα) and inhibited mammalian target of rapamycin phosphorylation (p-mTOR) in HepG2 cells. The levels of p-AMPKα and LC3B-II/I were downregulated in HepG2 cells transfected with small interfering RNA (siRNA) against AMPKα, which suggests that the AMPKα-mTOR pathway was involved in HUA-induced autophagy. Antioxidant N-acetyl-L-cysteine reversed elevated reactive oxygen species levels induced by HUA in HepG2 cells, and AMPKα level was also inhibited, which suggests that AMPKα activation may be derived from reactive oxygen species. Collectively, these findings demonstrate that HUA increased hepatic autophagy, and autophagy activation plays a protective role in hepatic IR, which may suggest a potential therapeutic target for hepatic IR derived from HUA.

Mogrol suppresses lung cancer cell growth by activating AMPK-dependent autophagic death and inducing p53-dependent cell cycle arrest and apoptosis

Lung carcinoma is the leading cause of cancer-related death worldwide. Chemotherapy remains the cornerstone of lung cancer treatment. Unfortunately, most types of cancer will develop resistance to chemotherapies over the time. One of the efforts to prevent the chemotherapy resistance is to find alternative chemotherapy drugs. Mogrol has been found to have antitumor activity. However, little is known about the pharmacological mechanisms underlying the suppression of mogrol on lung cancers. In this study, we observed that mogrol exposure significantly reduced the tumor volume and weight in tumor-bearing nude mice without obvious effect on body weight and cardiac function. Mogrol also significantly inhibited the proliferation and migration of lung cancer cells, including non-small-cell lung carcinoma cells, A549, H1299, H1975 and SK-MES-1 cells, with no obvious effect on control human bronchial epithelial cells (HBE). Further studies revealed that mogrol stirred excessive autophagy and autophagic flux, and finally, autophagic cell death, in lung cancer cells, which could be attenuated by autophagy inhibitors, 3-MA and chloroquine. Furthermore, mogrol significantly activated AMPK to induce autophagy and autophagic cell death, which could be abrogated by Compound C, an AMPK inhibitor. In addition, mogrol induced a significant increase in p53 activity in lung cancer cells, accompanied with cell cycle arrest and apoptosis, which could be weakened by p53 silence. Our results indicated that mogrol effectively suppressed lung cancer cells in vivo and in vitro by inducing the excessive autophagy and autophagic cell death via activating AMPK signaling pathway, as well as cell cycle arrest and apoptosis via activating p53 pathway.

Interleukin-10 regulates starvation-induced autophagy through the STAT3-mTOR-p70s6k axis in hepatic stellate cells

The degree of activation of hepatic stellate cells (HSCs) is closely related to the level of autophagy in HSCs. We previously showed that interleukin-10 (IL-10) strongly inhibits HSC activation in rat fibrotic liver. However, little is known about the effect of IL-10 on HSC autophagy. For investigation of the effect of IL-10 on starvation-induced autophagy in immortal rat hepatic stellate cells (HSC-T6) and the molecular mechanism, HSC-T6 cells were incubated with serum-free DMEM for different periods and treated with IL-10 at different concentrations. Transmission electron microscopy (TEM), analysis of autophagic flux and Western blotting (WB) assays were used to observe changes in autophagosome morphology and number and autophagy-related protein expression in HSC-T6 cells and to evaluate the regulatory effect of IL-10 on starvation-induced autophagy. Cryptotanshinone (CPT) and rapamycin (Rapa) were used to block activation of the signal transducer and activator of transcription 3 (STAT3) and mTOR signaling pathways, respectively. STAT3-mTOR-p70s6k signaling pathway proteins were analyzed by WB to assess the signaling pathway by which IL-10 regulates autophagy. WB showed an increased LC3II/I ratio, increased Beclin1 expression, and decreased p62 expression in HSC-T6 cells starved for 3 h (p < 0.05). IL-10 inhibited the increases in the LC3II/I ratio and Beclin1 expression and upregulated p62 expression (p < 0.05), and the optimal IL-10 concentration was 20 ng/mL. TEM and double-labeled immunofluorescence analysis showed that IL-10 inhibited autophagosome formation and autophagic flux, as indicated by the decreased numbers of double-membrane autophagosomes and yellow autophagic puncta. Further examination of signaling pathway molecules showed that phosphorylation of the mTOR, STAT3, and p70s6k proteins was significantly decreased during starvation-induced autophagy, but IL-10 could increase mTOR, STAT3, and p70s6k protein phosphorylation (p < 0.05). Blocking either the mTOR or STAT3 pathway reversed the inhibitory effect of IL-10 on starvation-induced autophagy in HSC-T6 cells (p < 0.05). IL-10 suppresses starvation-induced autophagosome formation through activation of the STAT3-mTOR-p70s6k axis in HSC-T6 cells.

Polycation-Mediated Transfection: Mechanisms of Internalization and Intracellular Trafficking

Polyplex-mediated gene transfection is now in its' fourth decade of serious research, but the promise of polyplex-mediated gene therapy has yet to fully materialize. Only approximately one in a million applied plasmids actually expresses. A large part of this is due to an incomplete understanding of the mechanism of polyplex transfection. There is an assumption that internalization must follow a canonical mechanism of receptor mediated endocytosis. Herein, we present arguments that untargeted (and most targeted) polyplexes do not utilize these routes. By incorporating knowledge of syndecan-polyplex interactions, we can show that syndecans are the "target" for polyplexes. Further, it is known that free polycations (which disrupt cell-membranes by acid-catalyzed hydrolysis of phospholipid esters) are necessary for (untargeted) endocytosis. This can be incorporated into the model to produce a novel mechanism of endocytosis, which fits the observed phenomenology. After membrane translocation, polyplex containing vesicles reach the endosome after diffusing through the actin mesh below the cell membrane. From there, they are acidified and trafficked toward the lysosome. Some polyplexes are capable of escaping the endosome and unpacking, while others are not. Herein, it is argued that for some polycations, as acidification proceeds the polyplexes excluding free polycations, which disrupt the endosomal membrane by acid-catalyzed hydrolysis, allowing the polyplex to escape. The polyplex's internal charge ratio is now insufficient for stability and it releases plasmids which diffuse to the nucleus. A small proportion of these plasmids diffuse through the nuclear pore complex (NPC), with aggregation being the major cause of loss. Those plasmids that have diffused through the NPC will also aggregate, and this appears to be the reason such a small proportion of nuclear plasmids express mRNA. Thus, the structural features which promote unpacking in the endosome and allow for endosomal escape can be determined, and better polycations can be designed.

Lysine-selective molecular tweezers are cell penetrant and concentrate in lysosomes

Lysine-selective molecular tweezers are promising drug candidates against proteinopathies, viral infection, and bacterial biofilm. Despite demonstration of their efficacy in multiple cellular and animal models, important questions regarding their mechanism of action, including cell penetrance and intracellular distribution, have not been answered to date. The main impediment to answering these questions has been the low intrinsic fluorescence of the main compound tested to date, called CLR01. Here, we address these questions using new fluorescently labeled molecular tweezers derivatives. We show that these compounds are internalized in neurons and astrocytes, at least partially through dynamin-dependent endocytosis. In addition, we demonstrate that the molecular tweezers concentrate rapidly in acidic compartments, primarily lysosomes. Accumulation of molecular tweezers in lysosomes may occur both through the endosomal-lysosomal pathway and via the autophagy-lysosome pathway. Moreover, by visualizing colocalization of molecular tweezers, lysosomes, and tau aggregates we show that lysosomes likely are the main site for the intracellular anti-amyloid activity of molecular tweezers. These findings have important implications for the mechanism of action of molecular tweezers in vivo, explaining how administration of low doses of the compounds achieves high effective concentrations where they are needed, and supporting the development of these compounds as drugs for currently cureless proteinopathies.

Apolipoproteins L1-6 share key cation channel-regulating residues but have different membrane insertion and ion conductance properties

The human apolipoprotein L gene family encodes the apolipoprotein L1-6 (APOL1-6) proteins, which are effectors of the innate immune response to viruses, bacteria and protozoan parasites. Due to a high degree of similarity between APOL proteins, it is often assumed that they have similar functions to APOL1, which forms cation channels in planar lipid bilayers and membranes resulting in cytolytic activity. However, the channel properties of the remaining APOL proteins have not been reported. Here, we used transient overexpression and a planar lipid bilayer system to study the function of APOL proteins. By measuring lactate dehydrogenase release, we found that APOL1, APOL3, and APOL6 were cytolytic, whereas APOL2, APOL4, and APOL5 were not. Cells expressing APOL1 or APOL3, but not APOL6, developed a distinctive swollen morphology. In planar lipid bilayers, recombinant APOL1 and APOL2 required an acidic environment for the insertion of each protein into the membrane bilayer to form an ion conductance channel. In contrast, recombinant APOL3, APOL4, and APOL5 readily inserted into bilayers to form ion conductance at neutral pH, but required a positive voltage on the side of insertion. Despite these differences in membrane insertion properties, the ion conductances formed by APOL1-4 were similarly pH-dependent and cation-selective, consistent with conservation of the pore-lining region in each protein. Thus, despite structural conservation, the APOL proteins are functionally different. We propose that these proteins interact with different membranes and under different voltage and pH conditions within a cell to effect innate immunity to different microbial pathogens.

Spatio-Temporal Autophagy Tracking with a Cell-Permeable, Water-Soluble, Peptide-Based, Autophagic Vesicle-Targeted Sensor

Autophagy is an essential cellular degradation process. Impaired autophagy has been linked to multiple disorders, including cancer and neurodegeneration. Tracking the autophagic flux in living cells will provide mechanistic insights into autophagy and will allow rapid screening of autophagy modulators as potential therapeutics. Imaging autophagy to track the autophagic flux demands a cell-permeable probe that can specifically target autophagic vesicles and report on the extent of autophagy. Existing fluorescent protein-based probes for imaging autophagy target autophagic vesicles but are cell-impermeable and degrade with the progress of autophagy resulting in ambiguous information on the later stages of autophagy. Although small-molecule-based autophagy probes can be cell-permeable, they are mostly water-insoluble and often target lysosomes instead of autophagic vesicles leading to incomplete evidence of the early stages of the process. Hence, there is a major gap in the ability to link the imaging data obtained by applying fluorescent sensors to the real extent of autophagy in living cells. To address these challenges, we have combined the desirable features of targetability and cell permeability to develop a novel water-soluble, cell-permeable, visible-light excitable, peptide-based, fluorescent sensor, HCFP, for imaging autophagy and tracking the autophagic flux. The probe readily enters living cells within 30 min of incubation, distinctly targets autophagic vesicles, and spatio-temporally tracks the entire autophagy pathway in living cells via a ratiometric pH-sensitive detection scheme. The salient features of the probe combining targetability with cell permeability should provide an edge in high-throughput screening of autophagy modulators by tracking autophagy live.

Maturing Autophagosomes are Transported Towards the Cell Periphery

Autophagosome maturation comprises fusion with lysosomes and acidification. It is a critical step in the degradation of cytosolic protein aggregates that characterize many neurodegenerative diseases. In order to better understand this process, we studied intracellular trafficking of autophagosomes and aggregates of α-synuclein, which characterize Parkinson's disease and other synucleinopathies. The autophagosomal marker LC3 and the aggregation prone A53T mutant of α-synuclein were tagged by fluorescent proteins and expressed in HEK293T cells and primary astrocytes. The subcellular distribution and movement of these vesicle populations were analyzed by (time-lapse) microscopy. Fusion with lysosomes was assayed using the lysosomal marker LAMP1; vesicles with neutral and acidic luminal pH were discriminated using the RFP-GFP "tandem-fluorescence" tag. With respect to vesicle pH, we observed that neutral autophagosomes, marked by LC3 or synuclein, were located more frequently in the cell center, and acidic autophagosomes were observed more frequently in the cell periphery. Acidic autophagosomes were transported towards the cell periphery more often, indicating that acidification occurs in the cell center before transport to the periphery. With respect to autolysosomal fusion, we found that lysosomes preferentially moved towards the cell center, whereas autolysosomes moved towards the cell periphery, suggesting a cycle where lysosomes are generated in the periphery and fuse to autophagosomes in the cell center. Unexpectedly, many acidic autophagosomes were negative for LAMP1, indicating that acidification does not require fusion to lysosomes. Moreover, we found both neutral and acidic vesicles positive for LAMP1, consistent with delayed acidification of the autolysosome lumen. Individual steps of aggregate clearance thus occur in dedicated cellular regions. During aggregate clearance, autophagosomes and autolysosomes form in the center and are transported towards the periphery during maturation. In this process, luminal pH could regulate the direction of vesicle transport. (1) Transport and location of autophagosomes depend on luminal pH: Acidic autophagosomes are preferentially transported to the cell periphery, causing more acidic autophagosomes in the cell periphery and more neutral autophagosomes at the microtubule organizing center (MTOC). (2) Autolysosomes are transported to the cell periphery and lysosomes to the MTOC, suggesting spatial segregation of lysosome reformation and autolysosome fusion. (3) Synuclein aggregates are preferentially located at the MTOC and synuclein-containing vesicles in the cell periphery, consistent with transport of aggregates to the MTOC for autophagy.

Fluorescent Protein-Based Autophagy Biosensors

Autophagy is an essential cellular process of self-degradation for dysfunctional or unnecessary cytosolic constituents and organelles. Dysregulation of autophagy is thus involved in various diseases such as neurodegenerative diseases. To investigate the complex process of autophagy, various biochemical, chemical assays, and imaging methods have been developed. Here we introduce various methods to study autophagy, in particular focusing on the review of designs, principles, and limitations of the fluorescent protein (FP)-based autophagy biosensors. Different physicochemical properties of FPs, such as pH-sensitivity, stability, brightness, spectral profile, and fluorescence resonance energy transfer (FRET), are considered to design autophagy biosensors. These FP-based biosensors allow for sensitive detection and real-time monitoring of autophagy progression in live cells with high spatiotemporal resolution. We also discuss future directions utilizing an optobiochemical strategy to investigate the in-depth mechanisms of autophagy. These cutting-edge technologies will further help us to develop the treatment strategies of autophagy-related diseases.

Late-stage functionalisation of alkyne-modified phospha-xanthene dyes: lysosomal imaging using an off-on-off type of pH probe

Near-infrared (NIR) fluorescent molecules are of great importance for the visualisation of biological processes. Among the most promising dye scaffolds for this purpose are P[double bond, length as m-dash]O-substituted phospha-xanthene (POX) dyes, which show NIR emission with high photostability. Their practical utility for in vitro and in vivo imaging has recently been demonstrated. Although classical modification methods have been used to produce POX-based fluorescent probes, it is still a challenge to introduce additional functional groups to control the localisation of the probe in cells. Herein, we report on the development of POXs that bear a 4-ethynylphenyl group on the phosphorus atom. These dyes can subsequently be functionalised with azide-tagged biomolecules via a late-stage Cu-catalysed azide/alkyne cycloaddition (CuAAC) reaction, thus achieving target-selective labelling. To demonstrate the practical utility of the functionalised POXs, we designed a sophisticated NIR probe that exhibits a bell-shaped off-on-off pH-response and is able to assess the degree of endosomal maturation.

A hybrid aggregate FRET probe from the mixed assembly of cyanine dyes for highly specific monitoring of mitochondria autophagy

Mitochondria autophagy, also known as mitophagy, is a process in which mitochondria are wrapped by autophagosomes and fused with lysosomes for degradation. This process is essential for mitochondrial quality control. Here, we developed a hybrid aggregate FRET probe through mixed assembly of two cyanine dyes FMOTY and AMTC. In live cells, FMOTY and AMTC exist independently in lysosomes and mitochondria and will not produce interfering FRET background signals. The FRET signal is only generated when mitochondria is transported to lysosomes during mitophagy. This allows the hybridized aggregate to be used as a highly specific probe for monitoring mitophagy.

Lansoprazole Alone or in Combination With Gefitinib Shows Antitumor Activity Against Non-small Cell Lung Cancer A549 Cells in vitro and in vivo

Lansoprazole (Lpz) is an FDA-approved proton pump inhibitor (PPI) drug for the therapy of acid-related diseases. Aiming to explore the new application of old drugs, we recently investigated the antitumor effect of Lpz. We demonstrated that the PPI Lpz played a tumor suppressive role in non-small cell lung cancer (NSCLC) A549 cells. Mechanistically, Lpz induced apoptosis and G0/G1 cell cycle arrest by inhibiting the activation of signal transducer and activator of transcription (Stat) 3 and the phosphoinositide 3-kinase (PI3K)/Akt and Raf/ERK pathways. In addition, Lpz inhibited autophagy by blocking the fusion of autophagosomes with lysosomes. Furthermore, Lpz in combination with gefitinib (Gef) showed a synergistic antitumor effect on A549 cells, with enhanced G0/G1 cell cycle arrest and apoptosis. The combination inhibited Stat3 phosphorylation, PI3K/Akt and Raf/ERK signaling, affecting cell cycle-related proteins such as p-Rb, cyclin D1 and p27, as well as apoptotic proteins such as Bax, Bcl-2, caspase-3, and poly (ADP-ribose) polymerase (PARP). In vivo, coadministration with Lpz and Gef significantly attenuated the growth of A549 nude mouse xenograft models. These findings suggest that Lpz might be applied in combination with Gef for NSCLC therapy, but further evidence is required.

Chloroquine-Induced Accumulation of Autophagosomes and Lipids in the Endothelium

Chloroquine (CQ) is an antimalarial drug known to inhibit autophagy flux by impairing autophagosome–lysosome fusion. We hypothesized that autophagy flux altered by CQ has a considerable influence on the lipid composition of endothelial cells. Thus, we investigated endothelial responses induced by CQ on human microvascular endothelial cells (HMEC-1). HMEC-1 cells after CQ exposure were measured using a combined methodology based on label-free Raman and fluorescence imaging. Raman spectroscopy was applied to characterize subtle chemical changes in lipid contents and their distribution in the cells, while the fluorescence staining (LipidTox, LysoTracker and LC3) was used as a reference method. The results showed that CQ was not toxic to endothelial cells and did not result in the endothelial inflammation at concentrations of 1–30 µM. Notwithstanding, it yielded an increased intensity of LipidTox, LysoTracker, and LC3 staining, suggesting changes in the content of neutral lipids, lysosomotropism, and autophagy inhibition, respectively. The CQ-induced endothelial response was associated with lipid accumulation and was characterized by Raman spectroscopy. CQ-induced autophagosome accumulation in the endothelium is featured by a pronounced alteration in the lipid profile, but not in the endothelial inflammation. Raman-based assessment of CQ-induced biochemical changes offers a better understanding of the autophagy mechanism in the endothelial cells.

Genetically Encoded Biosensors Based on Fluorescent Proteins

Genetically encoded biosensors based on fluorescent proteins (FPs) allow for the real-time monitoring of molecular dynamics in space and time, which are crucial for the proper functioning and regulation of complex cellular processes. Depending on the types of molecular events to be monitored, different sensing strategies need to be applied for the best design of FP-based biosensors. Here, we review genetically encoded biosensors based on FPs with various sensing strategies, for example, translocation, fluorescence resonance energy transfer (FRET), reconstitution of split FP, pH sensitivity, maturation speed, and so on. We introduce general principles of each sensing strategy and discuss critical factors to be considered if available, then provide representative examples of these FP-based biosensors. These will help in designing the best sensing strategy for the successful development of new genetically encoded biosensors based on FPs.

A ratiometric fluorescent probe for monitoring pH fluctuations during autophagy in living cells

We present a ratiometric fluorescent probe for monitoring pH featuring superb photostability and chemostability.

Visualization of Autophagy Progression by a Red-Green-Blue Autophagy Sensor

Autophagy is a major degradation process of cytosolic components and misfolded proteins that is crucial for cellular homeostasis and for the pathogenesis of diverse diseases. Autophagy is initiated by the formation of phagophores, which mature to autophagosomes. The autophagosomes then fuse to lysosomes to form autolysosomes. Different stages of autophagy can be deregulated to cause autophagy-related diseases, and thus, an accurate detection of each stage of autophagy progression is critical for efficient therapeutic strategies for these diseases. To identify the different stages of autophagy progression, here, we developed a new autophagy flux sensor, named red-green-blue-LC3 (RGB-LC3). RGB-LC3 is composed of LC3 and red-green-blue (RGB) fluorescent proteins, which were carefully chosen by considering their separate spectral profiles, stability, brightness, and most importantly different pH sensitivities. Utilizing this RGB-LC3 and the predicted pH, we could clearly identify phagophores, autophagosomes, fusion stage, early autolysosomes, and mature autolysosomes in live cells. Furthermore, the RGB-LC3 sensor was successfully applied to distinguish different effects of Aβ monomers and oligomers on autophagy flux. Therefore, we developed a new autophagy flux sensor, RGB-LC3, which may be a valuable tool to further investigate the molecular mechanisms of autophagy and to develop efficient therapeutic strategies for autophagy-related diseases.

Cryo-EM structures and functional characterization of homo- and heteropolymers of human ferritin variants

The role of abnormal brain iron metabolism in neurodegenerative diseases is still insufficiently understood. Here, we investigate the molecular basis of the neurodegenerative disease hereditary ferritinopathy (HF), in which dysregulation of brain iron homeostasis is the primary cause of neurodegeneration. We mutagenized ferritin’s three-fold pores (3FPs), i.e. the main entry route for iron, to investigate ferritin’s iron management when iron must traverse the protein shell through the disrupted four-fold pores (4FPs) generated by mutations in the ferritin light chain (FtL) gene in HF. We assessed the structure and properties of ferritins using cryo-electron microscopy and a range of functional analyses in vitro. Loss of 3FP function did not alter ferritin structure but led to a decrease in protein solubility and iron storage. Abnormal 4FPs acted as alternate routes for iron entry and exit in the absence of functional 3FPs, further reducing ferritin iron-storage capacity. Importantly, even a small number of MtFtL subunits significantly compromises ferritin solubility and function, providing a rationale for the presence of ferritin aggregates in cell types expressing different levels of FtLs in patients with HF. These findings led us to discuss whether modifying pores could be used as a pharmacological target in HF.

Quantitative Imaging of Biochemistry in Situ and at the Nanoscale

Biochemical reactions in eukaryotic cells occur in subcellular, membrane-bound compartments called organelles. Each kind of organelle is characterized by a unique lumenal chemical composition whose stringent regulation is vital to proper organelle function. Disruption of the lumenal ionic content of organelles is inextricably linked to disease. Despite their vital roles in cellular homeostasis, there are large gaps in our knowledge of organellar chemical composition largely from a lack of suitable probes. In this Outlook, we describe how, using organelle-targeted ratiometric probes, one can quantitatively image the lumenal chemical composition and biochemical activity inside organelles. We discuss how excellent fluorescent detection chemistries applied largely to the cytosol may be expanded to study organelles by chemical imaging at subcellular resolution in live cells. DNA-based reporters are a new and versatile platform to enable such approaches because the resultant probes have precise ratiometry and accurate subcellular targeting and are able to map multiple chemicals simultaneously. Quantitatively mapping lumenal ions and biochemical activity can drive the discovery of new biology and biomedical applications.

The fluorescence toolbox for visualizing autophagy

Autophagy is an adaptive catabolic process functioning to promote cell survival in the event of inappropriate living conditions such as nutrient shortage and to cope with diverse cytotoxic insults. It is regarded as one of the key survival mechanisms of living organisms. Cells undergo autophagy to accomplish the lysosomal digestion of intracellular materials including damaged proteins, organelles, and foreign bodies, in a bulk, non-selective or a cargo-specific manner. Studies in the past decades have shed light on the association of autophagy pathways with various diseases and also highlighted the therapeutic value of autophagy modulation. Hence, it is crucial to develop effective approaches for monitoring intracellular autophagy dynamics, as a comprehensive account of methodology establishment is far from complete. In this review, we aim to provide an overview of the major current fluorescence-based techniques utilized for visualizing, sensing or measuring autophagic activities in cells or tissues, which are categorized firstly by targets detected and further by the types of fluorescence tools. We will mainly focus on the working mechanisms of these techniques, put emphasis on the insight into their roles in biomedical science and provide perspectives on the challenges and future opportunities in this field.

Oblongifolin C reverses GEM resistance via suppressing autophagy flux in bladder cancer cells

A number of previous studies have demonstrated that inhibiting autophagy can increase the cellular cytotoxicity of chemotherapeutic agents in urothelial cancer cells. However, the mechanistic roles of autophagy in gemcitabine (GEM) resistant bladder cancer cells have not been thoroughly investigated. In the present study, immunohistochemistry staining of autophagy marker LC3 was performed in bladder cancer and healthy control tissues and demonstrated an essential role of autophagy in cancer development. A GEM-resistant cell line was established to assess the effects of autophagy on the acquisition of GEM resistance. Western blotting of autophagy markers in GEM-resistant bladder cancer cells suggested that GEM resistance was caused, at least partially, by GEM-induced autophagy. GEM resistance was demonstrated to be reversed by the inhibition of autophagy by 3-methyladenine. In addition, oblongifolin C (OC), a novel autophagic flux inhibitor purified from traditional Chinese medicine, was found to enhance the efficiency of GEM in GEM-resistant bladder cancer cells by inhibiting autophagic flux. In conclusion, data from the present study suggest that autophagy serves an important role in bladder cancer development and GEM resistance. OC treatment has the ability to reverse GEM-resistance in bladder cancer cells by suppressing autophagic flux, thereby providing a potential adjunctive therapeutic option for bladder cancer GEM treatment.

In Vitro Assays: Friends or Foes of Cell-Penetrating Peptides

The cell membrane is a complex and highly regulated system that is composed of lipid bilayer and proteins. One of the main functions of the cell membrane is the regulation of cell entry. Cell-penetrating peptides (CPPs) are defined as peptides that can cross the plasma membrane and deliver their cargo inside the cell. The uptake of a peptide is determined by its sequence and biophysicochemical properties. At the same time, the uptake mechanism and efficiency are shown to be dependent on local peptide concentration, cell membrane lipid composition, characteristics of the cargo, and experimental methodology, suggesting that a highly efficient CPP in one system might not be as productive in another. To better understand the dependence of CPPs on the experimental system, we present a review of the in vitro assays that have been employed in the literature to evaluate CPPs and CPP-cargos. Our comprehensive review suggests that utilization of orthogonal assays will be more effective for deciphering the true ability of CPPs to translocate through the membrane and enter the cell cytoplasm.

Assessing Autophagy in Archived Tissue or How to Capture Autophagic Flux from a Tissue Snapshot

Autophagy is a highly conserved degradation mechanism that is essential for maintaining cellular homeostasis. In human disease, autophagy pathways are frequently deregulated and there is immense interest in targeting autophagy for therapeutic approaches. Accordingly, there is a need to determine autophagic activity in human tissues, an endeavor that is hampered by the fact that autophagy is characterized by the flux of substrates whereas histology informs only about amounts and localization of substrates and regulators at a single timepoint. Despite this challenging task, considerable progress in establishing markers of autophagy has been made in recent years. The importance of establishing clear-cut autophagy markers that can be used for tissue analysis cannot be underestimated. In this review, we attempt to summarize known techniques to quantify autophagy in human tissue and their drawbacks. Furthermore, we provide some recommendations that should be taken into consideration to improve the reliability and the interpretation of autophagy biomarkers in human tissue samples.

Polarity-Sensitive Polymer Carbon Dots Prepared at Room-Temperature for Monitoring the Cell Polarity Dynamics during Autophagy

Taking the advantages of excellent optical properties, biocompatibility, and photostability of carbon dots, herein, we developed polarity-sensitive polymer carbon dots (PCDs) for visualizing of cellular polarity to real-time monitoring autophagy changes without perturbing the cellular status. The PCDs can be prepared by simply mixing dopamine (DA), H₂O₂, and o-phenylenediamine (o-PDA) in a common beaker without the need for any special equipment or external energy supply, and the preparation could be completed within 3 min at room temperature. Interestingly, the polarity-sensitive PCDs could emit various types of fluorescence and are insensitive to the excitation light when dispersed in different water/dioxane systems with different polarities. Based on the polarity-sensitive emission of the PCDs, the change of polarity during autophagy has been successfully monitored in living cells. Moreover, the change of polarity detected by PCDs is autophagy-specific (does not occur during apoptosis), occurs under different autophagy-inducing situations (starvation, rapamycin, and trehalose), and requires a normal autophagic flux, showing that PCDs rapidly prepared by polymerization cross-linking at room temperature can be functionally applied in the case of autophagy-related physiological or pathological processes.

Inhibition of Transglutaminase 2 as a Potential Host-Directed Therapy Against Mycobacterium tuberculosis

Host-directed therapies (HDTs) are emerging as a potential valid support in the treatment of drug-resistant tuberculosis (TB). Following our recent report indicating that genetic and pharmacological inhibition of transglutaminase 2 (TG2) restricts Mycobacterium tuberculosis (Mtb) replication in macrophages, we aimed to investigate the potentials of the TG2 inhibitors cystamine and cysteamine as HDTs against TB. We showed that both cysteamine and cystamine restricted Mtb replication in infected macrophages when provided at equimolar concentrations and did not exert any antibacterial activity when administered directly on Mtb cultures. Interestingly, infection of differentiated THP-1 mRFP-GFP-LC3B cells followed by the determination of the autophagic intermediates pH distribution (AIPD) showed that cystamine inhibited the autophagic flux while restricting Mtb replication. Moreover, both cystamine and cysteamine had a similar antimicrobial activity in primary macrophages infected with a panel of Mtb clinical strains belonging to different phylogeographic lineages. Evaluation of cysteamine and cystamine activity in the human ex vivo model of granuloma-like structures (GLS) further confirmed the ability of these drugs to restrict Mtb replication and to reduce the size of GLS. The antimicrobial activity of the TG2 inhibitors synergized with a second-line anti-TB drug as amikacin in human monocyte-derived macrophages and in the GLS model. Overall, the results of this study support the potential usefulness of the TG2-inhibitors cysteamine and cystamine as HDTs against TB.

Altered in vitro muscle differentiation in X-linked myopathy with excessive autophagy

X-linked myopathy with excessive autophagy (XMEA) is a genetic disease associated with weakness of the proximal muscles. It is caused by mutations in the VMA21 gene, coding for a chaperone that functions in the vacuolar ATPase (v-ATPase) assembly. Mutations associated with lower content of assembled v-ATPases lead to an increase in lysosomal pH, culminating in partial blockage of macroautophagy, with accumulation of vacuoles of undigested content. Here, we studied a 5-year-old boy affected by XMEA, caused by a small indel in the VMA21 gene. Detection of sarcoplasmic Lc3 (also known as MAP1LC3B)-positive vacuoles in his muscle biopsy confirmed an autophagy defect. To understand how autophagy is regulated in XMEA myogenesis, we used patient-derived muscle cells to evaluate autophagy during in vitro muscle differentiation. An increase in lysosomal pH was observed in the patient's cells, compatible with predicted functional defect of his mutation. Additionally, there was an increase in autophagic flux in XMEA myotubes. Interestingly, we observed that differentiation of XMEA myoblasts was altered, with increased myotube formation observed through a higher fusion index, which was not dependent on lysosomal acidification. Moreover, no variation in the expression of myogenic factors nor the presence of regenerating fibers in the patient's muscle were observed. Myoblast fusion is a tightly regulated process; therefore, the uncontrolled fusion of XMEA myoblasts might generate cells that are not as functional as normal muscle cells. Our data provide new evidence on the reason for predominant muscle involvement in the context of the XMEA phenotype.

This article has an associated First Person interview with the first author of the paper.

Summary: Here, we show that in X-linked myopathy with excessive autophagy there is increased fusion of myoblasts, which is not caused by the primary lysosomal acidification defect.

Nerve growth factor activates autophagy in Schwann cells to enhance myelin debris clearance and to expedite nerve regeneration

Rationale: Autophagy in Schwann cells (SCs) is crucial for myelin debris degradation and clearance following peripheral nerve injury (PNI). Nerve growth factor (NGF) plays an important role in reconstructing peripheral nerve fibers and promoting axonal regeneration. However, it remains unclear if NGF effect in enhancing nerve regeneration is mediated through autophagic clearance of myelin debris in SCs.

Methods: In vivo, free NGF solution plus with/without pharmacological inhibitors were administered to a rat sciatic nerve crush injury model. In vitro, the primary Schwann cells (SCs) and its cell line were cultured in normal medium containing NGF, their capable of swallowing or clearing degenerated myelin was evaluated through supplement of homogenized myelin fractions.

Results: Administration of exogenous NGF could activate autophagy in dedifferentiated SCs, accelerate myelin debris clearance and phagocytosis, as well as promote axon and myelin regeneration at early stage of PNI. These NGF effects were effectively blocked by autophagy inhibitors. In addition, inhibition of the p75 kD neurotrophin receptor (p75^NTR) signal or inactivation of the AMP-activated protein kinase (AMPK) also inhibited the NGF effect as well.

Conclusions: NGF effect on promoting early nerve regeneration is closely associated with its accelerating autophagic clearance of myelin debris in SCs, which probably regulated by the p75^NTR/AMPK/mTOR axis. Our studies thus provide strong support that NGF may serve as a powerful pharmacological therapy for peripheral nerve injuries.

Age-associated changes in human CD4+ T cells point to mitochondrial dysfunction consequent to impaired autophagy

To gain understanding on the mechanisms that drive immunosenescence in humans, we examined CD4+ T cells obtained from younger (20-39 years-old) and older (70+ years-old) healthy participants of the Baltimore Longitudinal Study on Aging (BLSA). We found that mitochondrial proteins involved in the electron transport chain were overrepresented in cells from older participants, with prevalent dysregulation of oxidative phosphorylation and energy metabolism molecular pathways. Surprisingly, gene transcripts coding for mitochondrial proteins pertaining to oxidative phosphorylation and electron transport chain pathways were underrepresented in older individuals. Paralleling the observed decrease in gene expression, mitochondrial respiration was impaired in CD4+ T cells from older subjects. Though mitochondrial number in both naïve and memory cells visualized with electron microcopy was similar in older versus younger participants, there were a significantly higher number of autophagosomes, many of them containing undegraded mitochondria, in older individuals. The presence of mitochondria inside the accumulated autophagic compartments in CD4+ T cells from older individuals was confirmed by immunofluorescence. These findings suggest that older age is associated with persistence of dysfunctional mitochondria in CD4+ T lymphocytes caused by defective mitochondrial turnover by autophagy, which may trigger chronic inflammation and contribute to the impairment of immune defense in older persons.

Red blood cells membrane micropolarity as a novel diagnostic indicator of type 1 and type 2 diabetes

Classification of the category of diabetes is extremely important for clinicians to diagnose and select the correct treatment plan. Glycosylation, oxidation and other post-translational modifications of membrane and transmembrane proteins, as well as impairment in cholesterol homeostasis, can alter lipid density, packing, and interactions of Red blood cells (RBC) plasma membranes in type 1 and type 2 diabetes, thus varying their membrane micropolarity. This can be estimated, at a submicrometric scale, by determining the membrane relative permittivity, which is the factor by which the electric field between the charges is decreased relative to vacuum. Here, we employed a membrane micropolarity sensitive probe to monitor variations in red blood cells of healthy subjects (n=16) and patients affected by type 1 (T1DM, n=10) and type 2 diabetes mellitus (T2DM, n=24) to provide a cost-effective and supplementary indicator for diabetes classification. We find a less polar membrane microenvironment in T2DM patients, and a more polar membrane microenvironment in T1DM patients compared to control healthy patients. The differences in micropolarity are statistically significant among the three groups (p<0.01). The role of serum cholesterol pool in determining these differences was investigated, and other factors potentially altering the response of the probe were considered in view of developing a clinical assay based on RBC membrane micropolarity. These preliminary data pave the way for the development of an innovative assay which could become a tool for diagnosis and progression monitoring of type 1 and type 2 diabetes.

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Dynamic flux of cholesterol is differentially altered in T1DM and T2DM.

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Red blood cell senses the dynamic flux of lipids by changing its micropolarity.

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Laurdan can measure micropolarity in red blood cells membranes.

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Differences in micropolarity between the three groups are statistically significant.

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Red blood cell Micropolarity is an innovative assay for diabetes classification.

Loss of Cubilin, the intrinsic factor-vitamin B12 receptor, impairs visceral endoderm endocytosis and endodermal patterning in the mouse

The visceral endoderm is a polarized epithelial monolayer necessary for early embryonic development in rodents. A key feature of this epithelium is an active endocytosis and degradation of maternal nutrients, in addition to being the source of various signaling molecules or inhibitors required for the differentiation and patterning of adjacent embryonic tissues. Endocytosis across the visceral endoderm epithelium involves specific cell surface receptors and an extensive sub-membrane vesicular system with numerous apical vacuoles/lysosomes. We previously reported that Cubilin, the endocytic receptor for intrinsic factor-vitamin B12, albumin and apolipoproteinA-I/HDL allows maternal nutrient uptake by the visceral endoderm. In the present study, we show that the germline ablation of Cubilin impairs endodermal and mesodermal patterning, and results in developmental arrest at gastrulation. Notably, visceral endoderm dispersal is impeded in Cubilin null embryos. We further confirm the essential role of Cubilin in nutrient internalization by the early visceral endoderm and highlight its involvement in the formation of apical vacuoles. Our results reveal essential roles for Cubilin in early embryonic development, and suggest that in addition to its nutritive function, Cubilin sustains signaling pathways involved in embryonic differentiation and patterning.

Transgenic expression of a ratiometric autophagy probe specifically in neurons enables the interrogation of brain autophagy in vivo

Autophagy-lysosome pathway (ALP) disruption is considered pathogenic in multiple neurodegenerative diseases; however, current methods are inadequate to investigate macroautophagy/autophagy flux in brain in vivo and its therapeutic modulation. Here, we describe a novel autophagy reporter mouse (TRGL6) stably expressing a dual-fluorescence-tagged LC3 (tfLC3, mRFP-eGFP-LC3) by transgenesis selectively in neurons. The tfLC3 probe distributes widely in the central nervous system, including spinal cord. Expression levels were similar to endogenous LC3 and induced no detectable ALP changes. This ratiometric reporter registers differential pH-dependent changes in color as autophagosomes form, fuse with lysosomes, acidify, and degrade substrates within autolysosomes. We confirmed predicted changes in neuronal autophagy flux following specific experimental ALP perturbations. Furthermore, using a third fluorescence label in TRGL6 brains to identify lysosomes by immunocytochemistry, we validated a novel procedure to detect defective autolysosomal acidification in vivo. Thus, TRGL6 mice represent a unique tool to investigate in vivo ALP dynamics in specific neuron populations in relation to neurological diseases, aging, and disease modifying agents. Abbreviations: ACTB: actin, beta; AD: Alzheimer disease; AL: autolysosomes; ALP: autophagy-lysosome pathway; AP: autophagosome; APP: amyloid beta (Abeta) precursor protein; ATG5: autophagy related 5; ATG7: autophagy related 7; AV: autophagic vacuoles; CNS: central nervous system; CTSD: cathepsin D; CQ: chloroquine; DMEM: Dulbecco's modified Eagle's medium; GFP: green fluorescent protein; GABARAP: gamma-aminobutyric acid receptor associated protein; GABARAPL2/GATE16: gamma-aminobutyric acid (GABA) receptor-associated protein-like 2; ICC: immunocytochemistry; ICV: intra-cerebroventricular; LAMP2: lysosomal-associated membrane protein 2; Leup: leupeptin; LY: lysosomes; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; MTOR: mechanistic target of rapamycin kinase; RBFOX3/NeuN: RNA binding protein, fox-1 homolog (C. elegans) 3; RFP: red fluorescent protein; RPS6KB1: ribosomal protein S6 kinase, polypeptide 1; SDS-PAGE: sodium dodecyl sulfate-polyacrylamide gel electrophoresis; SQSTM1: sequestosome 1; tfLC3: mRFP-eGFP-LC3; TRGL6: Thy1 mRFP eGFP LC3-line 6; PCR: polymerase chain reaction; PD: Parkinson disease.

Real-time visualization of autophagy by monitoring the fluctuation of lysosomal pH with a ratiometric two-photon fluorescent probe

A benzimidazole-decorated two-photon fluorescent probe (Lyso-MPCB) based on the p-methoxyphenylacetylene-substituted carbazole was developed for detecting lysosomal pH with a double-channel signal, which can be used to visualize autophagy by real-time imaging the fluctuation of the pH in the lysosomes.

Fluorescence detection of intracellular pH changes in the mitochondria-associated process of mitophagy using a hemicyanine-based fluorescent probe

Intracellular pH behaves as a vital parameter in the physiological and pathological processes. Novel small molecule probes for precise and dynamic monitoring of pH fluctuations in cellular physiological processes are still highly required. Herein, we present a hemicyanine-based probe (HcPH) detection of the pH changes during the intracellular process of mitochondria-associated autophagy. HcP-H exhibits highly reversible and ratiometric fluorescence detection of pH variation due to the deprotonation/protonation process, showing orange fluorescence (λ_em = 557 nm) in basic media (pH 8.0) and green fluorescence (λ_em = 530 nm) in acidic media (pH 6.2), respectively. Organelle localization experiment in HeLa cells demonstrates that this probe could selectively accumulate in mitochondria, showing almost overlap with that of Mito-Tracker Green FM. More importantly, Fluorescence imaging of HcP-H in HeLa cells subjected to the nutrient deprivation has demonstrated that this probe could monitor the intracellular pH changes in the mitochondria-associated process of mitophagy. It is clearly confirmed that HcP-H would serve as a promising fluorescent probe for tracing mitophagy in living cells.

Genetically encoded fluorescent indicators for live cell pH imaging

BACKGROUND

Intracellular pH underlies most cellular processes. There is emerging evidence of a pH-signaling role in plant cells and microorganisms. Dysregulation of pH is associated with human diseases, such as cancer and Alzheimer's disease.

SCOPE OF REVIEW

In this review, we attempt to provide a summary of the progress that has been made in the field during the past two decades. First, we present an overview of the current state of the design and applications of fluorescent protein (FP)-based pH indicators. Then, we turn our attention to the development and applications of hybrid pH sensors that combine the capabilities of non-GFP fluorophores with the advantages of genetically encoded tags. Finally, we discuss recent advances in multicolor pH imaging and the applications of genetically encoded pH sensors in multiparameter imaging.

MAJOR CONCLUSIONS

Genetically encoded pH sensors have proven to be indispensable noninvasive tools for selective targeting to different cellular locations. Although a variety of genetically encoded pH sensors have been designed and applied at the single cell level, there is still much room for improvements and future developments of novel powerful tools for pH imaging. Among the most pressing challenges in this area is the design of brighter redshifted sensors for tissue research and whole animal experiments.

GENERAL SIGNIFICANCE

The design of precise pH measuring instruments is one of the important goals in cell biochemistry and may give rise to the development of new powerful diagnostic tools for various diseases.