Lysosomes and autophagy in cell death control

The Effect of Cellular Coenzyme Q10 Deficiency on Lysosomal Acidification

Coenzyme Q₁₀ (CoQ₁₀) deficiency currently represents the only treatable mitochondrial disorder, however, little is known about how it may affect other organelles. The lysosome has been found to have a large concentration of CoQ₁₀ localised at its membrane; additionally, it has been suggested that it plays a role in the normal acidification of the lysosomal lumen. As a result, in this study we assessed the effect of CoQ₁₀ deficiency on lysosomal acidification. In order to investigate this, a neuronal cell model of CoQ₁₀ deficiency was established via the treatment of SH-SY5Y cells with para-aminobenzoic acid (PABA). This method works through the competitive inhibition of the CoQ₁₀ biosynthetic pathway enzyme, CoQ₂. A single 1 mM (5 days) treatment with PABA resulted in a decrease of up to 58% in cellular CoQ₁₀ (p < 0.05). It was found that this resulted in a significant decrease in fluorescence of both the LysoSensor (23%) and LysoTracker (35%) probes used to measure lysosomal pH (p < 0.05). It was found that subsequent treatment with CoQ₁₀ (5 µM, 3 days) was able to restore cellular CoQ₁₀ concentration (p < 0.005), which was associated with an increase in fluorescence from both probes to around 90% of controls (p < 0.05), suggesting a restoration of lysosomal pH. This study provides insights into the association between lysosomal pH and cellular CoQ₁₀ status and the possibility that a deficit in the status of this isoprenoid may result in an impairment of lysosomal acidification.

YBX1 mediates autophagy by targeting p110β and decreasing the sensitivity to cisplatin in NSCLC

Y-box binding protein 1 (YBX1) is involved in the development of multiple types of tumors. However, the relationship between YBX1 and autophagy in non-small cell lung cancer (NSCLC) remains unclear. In this study, we analyzed the expression and clinical significance of YBX1 and markers of autophagy (LC3I/II) in NSCLC and examined their roles in regulating sensitivity to cisplatin in NSCLC. The retrospective analysis of patients with NSCLC indicated that YBX1 was positively correlated with autophagy. Increased levels of YBX1 or autophagy also observed in NSCLC cells compared with those in 16HBE cells. Compared to the controls, the knockdown of YBX1 expression suppressed autophagy, increased drug sensitivity and promoted apoptosis in response to cisplatin in NSCLC cells by targeting the p110β promoter and inhibiting p110β/Vps34/beclin1 signaling pathways. We also demonstrated in an in vivo study that the overexpressed YBX1 effectively increased NSCLC growth and progression and decreased the sensitivity to cisplatin by inducing autophagy in a xenograft tumor model, and these effects were concomitant with the increasing of p110β and beclin1 expression. Collectively, these results show that YBX1 plays an essential role in autophagy in NSCLC.

Triarylpyridine Compounds and Chloroquine Act in Concert to Trigger Lysosomal Membrane Permeabilization and Cell Death in Cancer Cells

Lysosomes play a key role in regulating cell death in response to cancer therapies, yet little is known on the possible role of lysosomes in the therapeutic efficacy of G-quadruplex DNA ligands (G4L) in cancer cells. Here, we investigate the relationship between the modulation of lysosomal membrane damage and the degree to which cancer cells respond to the cytotoxic effects of G-quadruplex ligands belonging to the triarylpyridine family. Our results reveal that the lead compound of this family, 20A promotes the enlargement of the lysosome compartment as well as the induction of lysosome-relevant mRNAs. Interestingly, the combination of 20A and chloroquine (an inhibitor of lysosomal functions) led to a significant induction of lysosomal membrane permeabilization coupled to massive cell death. Similar effects were observed when chloroquine was added to three new triarylpyridine derivatives. Our findings thus uncover the lysosomal effects of triarylpyridines compounds and delineate a rationale for combining these compounds with chloroquine to increase their anticancer effects.

PPARδ is a regulator of autophagy by its phosphorylation

In response to nutrient deficiency, autophagy degrades cytoplasmic materials and organelles in lysosomes, which is nutrient recycling, whereas activation of EGFR mediates autophagy suppression in response to growth factors. It is unclear whether PPARδ could be the regulator of autophagy in response to active EGFR. Here we found that EGFR induced PPARδ phosphorylation at tyrosine-108 leading to increased binding of LC3 to PPARδ by its LIR (LC3 interacting region) motif, consequently, inhibited autophagic flux. Conversely, EGFR inhibitor treatment reversed this event. Furthermore, EGFR-mediated PPARδ phosphorylation at tyrosine-108 led to autophagy inhibition and tumor growth. These findings suggest that PPARδ serves as a regulator of autophagy by its phosphorylation.

Manipulation of autophagy by (+) RNA viruses

Autophagy is an evolutionarily conserved process central to host metabolism. Among its major functions are conservation of energy during starvation, recycling organelles, and turnover of long-lived proteins. Besides, autophagy plays a critical role in removing intracellular pathogens and very likely represents a primordial intrinsic cellular defence mechanism. More recent findings indicate that it has not only retained its ability to degrade intracellular pathogens, but also functions to augment and fine tune antiviral immune responses. Interestingly, viruses have also co-evolved strategies to manipulate this pathway and use it to their advantage. Particularly intriguing is infection-dependent activation of autophagy with positive stranded (+)RNA virus infections, which benefit from the pathway without succumbing to lysosomal degradation. In this review we summarise recent data on viral manipulation of autophagy, with a particular emphasis on +RNA viruses and highlight key unanswered questions in the field that we believe merit further attention.

Mitochondria-targeted drug delivery in cancers

Mitochondria are considered one of the most important subcellular organelles for targeting and delivering drugs because mitochondria are the main location for various cellular functions and energy (i.e., ATP) production, and mitochondrial dysfunctions and malfunctions cause diverse diseases such as neurodegenerative disorders, cardiovascular disorders, metabolic disorders, and cancers. In particular, unique mitochondrial characteristics (e.g., negatively polarized membrane potential, alkaline pH, high reactive oxygen species level, high glutathione level, high temperature, and paradoxical mitochondrial dynamics) in pathological cancers have been used as targets, signals, triggers, or driving forces for specific sensing/diagnosing/imaging of characteristic changes in mitochondria, targeted drug delivery on mitochondria, targeted drug delivery/accumulation into mitochondria, or stimuli-triggered drug release in mitochondria. In this review, we describe the distinctive structures, functions, and physiological properties of cancer mitochondria and discuss recent technologies of mitochondria-specific "key characteristic" sensing systems, mitochondria-targeted "drug delivery" systems, and mitochondrial stimuli-specific "drug release" systems as well as their strengths and weaknesses.

Overexpression of microRNA-145 inhibits tumorigenesis through autophagy in chemotherapy and radiation resistant neuroblastoma cells

MicroRNA-145 (miR-145) plays a suppressive role in the process of tumorigenesis and an important role in induction of autophagy. However, the exact role of miR-145 in therapeutically resistant neuroblastoma cells remain elusive. Herein, we sought to evaluate the effects of miR-145 overexpression in chemo‑ and radiation-resistant neuroblastoma cells. We hypothesized that miR-145 affects the aggressiveness of resistant cells by enhancing autophagy. We established Cisplatin-resistant (CDDP-R), Vincristine-resistant (Vin-R), and radiation-resistant (Rad-R) neuroblastoma cells and found that miR-145 expression was significantly decreased in the resistant cells compared to the parental cells. Exogenously expression of miR-145 inhibited oncogenic properties such as proliferation, clonogenicity, anchorage-independent growth, cell migration, and tubule formation in the resistant cells. In addition, we also found that an autophagy protein marker, LC3, was only minimally expressed in the resistant cells. In particular, when miR-145 was overexpressed in the resistant cells, LC3 I and II were expressed and an increased punctate fluorescence of LC3 protein was found indicating the induction of autophagy. Taken together, our data suggests that miR-145 inhibits tumorigenesis and aggressiveness via modulation of autophagy in neuroblastoma.

The Current Understanding of Autophagy in Nanomaterial Toxicity and Its Implementation in Safety Assessment-Related Alternative Testing Strategies

Nanotechnology has rapidly promoted the development of a new generation of industrial and commercial products; however, it has also raised some concerns about human health and safety. To evaluate the toxicity of the great diversity of nanomaterials (NMs) in the traditional manner, a tremendous number of safety assessments and a very large number of animals would be required. For this reason, it is necessary to consider the use of alternative testing strategies or methods that reduce, refine, or replace (3Rs) the use of animals for assessing the toxicity of NMs. Autophagy is considered an early indicator of NM interactions with cells and has been recently recognized as an important form of cell death in nanoparticle-induced toxicity. Impairment of autophagy is related to the accelerated pathogenesis of diseases. By using mechanism-based high-throughput screening in vitro, we can predict the NMs that may lead to the generation of disease outcomes in vivo. Thus, a tiered testing strategy is suggested that includes a set of standardized assays in relevant human cell lines followed by critical validation studies carried out in animals or whole organism models such as C. elegans (Caenorhabditis elegans), zebrafish (Danio rerio), and Drosophila (Drosophila melanogaster)for improved screening of NM safety. A thorough understanding of the mechanisms by which NMs perturb biological systems, including autophagy induction, is critical for a more comprehensive elucidation of nanotoxicity. A more profound understanding of toxicity mechanisms will also facilitate the development of prevention and intervention policies against adverse outcomes induced by NMs. The development of a tiered testing strategy for NM hazard assessment not only promotes a more widespread adoption of non-rodent or 3R principles but also makes nanotoxicology testing more ethical, relevant, and cost- and time-efficient.

Mitophagy in Cardiovascular Diseases

Cardiovascular diseases are one of the leading causes of death. Increasing evidence has shown that pharmacological or genetic targeting of mitochondria can ameliorate each stage of these pathologies, which are strongly associated with mitochondrial dysfunction. Removal of inefficient and dysfunctional mitochondria through the process of mitophagy has been reported to be essential for meeting the energetic requirements and maintaining the biochemical homeostasis of cells. This process is useful for counteracting the negative phenotypic changes that occur during cardiovascular diseases, and understanding the molecular players involved might be crucial for the development of potential therapies. Here, we summarize the current knowledge on mitophagy (and autophagy) mechanisms in the context of heart disease with an important focus on atherosclerosis, ischemic heart disease, cardiomyopathies, heart failure, hypertension, arrhythmia, congenital heart disease and peripheral vascular disease. We aim to provide a complete background on the mechanisms of action of this mitochondrial quality control process in cardiology and in cardiac surgery by also reviewing studies on the use of known compounds able to modulate mitophagy for cardioprotective purposes.

The interrupted effect of autophagic flux and lysosomal function induced by graphene oxide in p62-dependent apoptosis of F98 cells

BACKGROUND

Graphene oxide (GO) nanoparticles (NPs) have been widely applied in various fields, especially in biomedical applications. Extensive studies have suggested that GO can pass through the blood-brain barrier (BBB) and induce abnormal autophagy and cytotoxicity in the central nervous system (CNS). However, the effect and specific mechanism of GO on astrocytes, the most abundant cells in the brain still has not been extensively investigated.

RESULTS

In this study, we systematically explored the toxicity and mechanism of GO exposure in the rat astroglioma-derived F98 cell line using molecular biological techniques (immunofluorescence staining, flow cytometry and Western blot) at the subcellular level and the signaling pathway level. Cells exposed to GO exhibited decreased cell viability and increased lactate dehydrogenase (LDH) release in a concentration- and time-dependent manner. GO-induced autophagy was evidenced by transmission electron microscopy (TEM) and immunofluorescence staining. Western blots showed that LC3II/I and p62 were upregulated and PI3K/Akt/mTOR was downregulated. Detection of lysosomal acidity and cathepsin B activity assay indicated the impairment of lysosomal function. Annexin V-FITC-PI detection showed the occurrence of apoptosis after GO exposure. The decrease in mitochondrial membrane potential (MMP) with an accompanying upregulation of cleaved caspase-3 and Bax/Bcl-2 further suggested that endogenous signaling pathways were involved in GO-induced apoptosis.

CONCLUSION

The exposure of F98 cells to GO can elicit concentration- and time-dependent toxicological effects. Additionally, increased autophagic response can be triggered after GO treatment and that the blocking of autophagy flux plays a vital role in GO cytotoxicity, which was determined to be related to dysfunction of lysosomal degradation. Importantly, the abnormal accumulation of autophagic substrate p62 protein can induce capase-3-mediated apoptosis. Inhibition of abnormal accumulation of autophagic cargo could alleviate the occurrence of GO-induced apoptosis in F98 cells.

A novel mitochondria-targeting method using special staining for the detection of apoptotic hepatocytes

Early detection of apoptotic cells on histological slides is of major importance for both diagnostic and research areas. In the current study, the aim was to propose a convenient method to stain the mitochondria and establish whether hepatocytes undergoing apoptosis can be identified in tissue sections using the proposed method. Liver tissue from five adult chinchillas was fixed with 10% neutral buffered formalin for Goldner's trichrome (GT) and Groat's iron hematoxylin and eosin (HE) stains and with Kolster's fixative for the Heidenhain's iron hematoxylin procedure. The HE and GT-stained sections showed the morphological features consistent with apoptosis i.e., homogenous intensely acidophilic cytoplasm, cell shrinkage with an irregular outline, nuclear shrinkage with cloudy karyoplasm, and karyopyknosis in the late stage. Sections stained with Heidenhain's iron hematoxylin method was used to pinpoint mitochondria and revealed cells which were undergoing the first stages of the apoptosis process i.e., disappearance of mitochondria from the cell, chromatin condensation and margination, paracentral localization of nucleoli, and vacuolated nuclei. In more advanced stages of apoptosis, cells presented significant nuclear and cytoplasmic changes. It was concluded that this is the first report targeting the mitochondria, by performing inexpensive histological staining techniques, in order to assess dead cells in situ.

Endosome/lysosome-detained supramolecular nanogels as an efflux retarder and autophagy inhibitor for repeated photodynamic therapy of multidrug-resistant cancer

The presence of drug efflux pumps and endo/lysosomal entrapment phenomena in multidrug-resistant cancer cells leads to insufficient and off-target accumulation of anticancer drugs in the cells, which severely reduces the drugs' therapeutic efficacies. Here, we prepare a novel type of photosensitizer (PS)-loaded supramolecular nanogel, which can utilize the endo/lysosomal entrapment for enhanced photodynamic therapy (PDT) of multidrug-resistant cancer. The PS-loaded nanogels can elude the drug efflux pumps, and be markedly internalized by drug-resistant cancer cells through the endocytic pathway. With their pH-sensitive properties, the internalized nanogels can aggregate in the acidic endosomes/lysosomes, thus retarding their exocytosis from the cells. Moreover, the lysosomes of the nanogel-treated cells are severely damaged after irradiation, which inhibits the protective autophagy and improves the photodynamic therapeutic performance of the nanogels. Besides, the in vivo experiments show that the nanogels significantly prolong the tumor retention of the PSs, thus enabling multiple PDT treatments after a single drug injection.

The epigenetic regulators and metabolic changes in ferroptosis-associated cancer progression

Ferroptosis, a novel form of regulated cell death, is different from other types of cell death in morphology, genetics and biochemistry. Increasing evidence indicates that ferroptosis has significant implications on cell death linked to cardiomyopathy, tumorigenesis, and cerebral hemorrhage to name a few. Here we summarize current literature on ferroptosis, including organelle dysfunction, signaling transduction pathways, metabolic reprogramming and epigenetic regulators in cancer progression. With regard to organelles, mitochondria-induced cysteine starvation, endoplasmic reticulum-related oxidative stress, lysosome dysfunction and golgi stress-related lipid peroxidation all contribute to induction of ferroptosis. Understanding the underlying mechanism in ferroptosis could provide insight into the treatment of various intractable diseases including cancers.

TmAtg6 Plays an Important Role in Anti-Microbial Defense Against Listeria monocytogenes in the Mealworm, Tenebrio molitor

Autophagy-related gene-6 (Beclin-1 in mammals) plays a pivotal role in autophagy and is involved in autophagosome formation and autolysosome maturation. In this study, we identified and characterized the autophagy-related gene-6 from Tenebrio molitor (TmAtg6) and analyzed its functional role in the survival of the insect against infection. The expression of TmAtg6 was studied using qRT-PCR for the assessment of the transcript levels at various developmental stages in the different tissues. The results showed that TmAtg6 was highly expressed at the 6-day-old pupal stage. Tissue-specific expression studies revealed that TmAtg6 was highly expressed in the hemocytes of late larvae. The induction patterns of TmAtg6 in different tissues of T. molitor larvae were analyzed by injecting Escherichia coli, Staphylococcus aureus, Listeria monocytogenes, or Candida albicans. The intracellular Gram-positive bacteria, L. monocytogenes, solely induced the expression of TmAtg6 in hemocytes at 9 h-post-injection, whilst in the fat body and gut, bimodal expression times were observed. RNAi-mediated knockdown of the TmAtg6 transcripts, followed by a challenge with microbes, showed a significant reduction in larval survival rate against L. monocytogenes. Taken together, our results suggest that TmAtg6 plays an essential role in anti-microbial defense against intracellular bacteria.

Role of endolysosomes and inter-organellar signaling in brain disease

Endosomes and lysosomes (endolysosomes) are membrane bounded organelles that play a key role in cell survival and cell death. These acidic intracellular organelles are the principal sites for intracellular hydrolytic activity required for the maintenance of cellular homeostasis. Endolysosomes are involved in the degradation of plasma membrane components, extracellular macromolecules as well as intracellular macromolecules and cellular fragments. Understanding the physiological significance and pathological relevance of endolysosomes is now complicated by relatively recent findings of physical and functional interactions between endolysosomes with other intracellular organelles including endoplasmic reticulum, mitochondria, plasma membranes, and peroxisomes. Indeed, evidence clearly indicates that endolysosome dysfunction and inter-organellar signaling occurs in different neurodegenerative diseases including Alzheimer's disease (AD), HIV-1 associated neurocognitive disease (HAND), Parkinson's disease (PD) as well as various forms of brain cancer such as glioblastoma multiforme (GBM). These findings open new areas of cell biology research focusing on understanding the physiological actions and pathophysiological consequences of inter-organellar communication. Here, we will review findings of others and us that endolysosome de-acidification and dysfunction coupled with impaired inter-organellar signaling is involved in the pathogenesis of AD, HAND, PD, and GBM. A more comprehensive appreciation of cell biology and inter-organellar signaling could lead to the development of new drugs to prevent or cure these diseases.

Near-Infrared Fluorescent pH Responsive Probe for Targeted Photodynamic Cancer Therapy

We developed a pH dependent amino heptamethine cyanine based theranostic probe (I2-IR783-Mpip) that can be activated by near infrared light. I2-IR783-Mpip, in acidic condition, exhibited an intense, broad NIR absorption band (820-950 nm) with high singlet oxygen generation upon exposure to NIR light (~850 nm). Theoretical calculations showed that the protonation of the probe in an acidic environment decreased the molecular orbital energy gaps and increased the intramolecular charge transfer efficiency. I2-IR783-Mpip exhibited good photodynamic efficiency towards liver hepatocellular carcinoma cells under physiological and slightly acidic conditions while normal human embryonic kidney cells remained alive under the same conditions. Detection of intracellular reactive oxygen species (ROS) in cells treated with I2-IR783-Mpip after NIR light exposure confirmed PDT efficiency of the probe in acidic environment. Moreover, I2-IR783-Mpip also demonstrated efficient phototoxicity under deep-seated tumour cell system. We believed this is the first PDT agent that possesses intrinsic tumour binding and selectively eradicate tumour in acidic environment under 850 nm NIR lamp.

Spatially and temporally defined lysosomal leakage facilitates mitotic chromosome segregation

Lysosomes are membrane-surrounded cytoplasmic organelles filled with a powerful cocktail of hydrolases. Besides degrading cellular constituents inside the lysosomal lumen, lysosomal hydrolases promote tissue remodeling when delivered to the extracellular space and cell death when released to the cytosol. Here, we show that spatially and temporally controlled lysosomal leakage contributes to the accurate chromosome segregation in normal mammalian cell division. One or more chromatin-proximal lysosomes leak in the majority of prometaphases, after which active cathepsin B (CTSB) localizes to the metaphase chromatin and cleaves a small subset of histone H3. Stabilization of lysosomal membranes or inhibition of CTSB activity during mitotic entry results in a significant increase in telomere-related chromosome segregation defects, whereas cells and tissues lacking CTSB and cells expressing CTSB-resistant histone H3 accumulate micronuclei and other nuclear defects. These data suggest that lysosomal leakage and chromatin-associated CTSB contribute to proper chromosome segregation and maintenance of genomic integrity.

Lysosomes are intracellular organelles containing degradative enzymes, and leakage of lysosomal contents into the cell is thought to trigger cell death. Here, the authors report that leaky lysosomes may facilitate chromosome separation during cell division.

A novel BODIPY-based photosensitizer with pH-active singlet oxygen generation for photodynamic therapy in lysosomes

A novel photosensitizer BDPI-lyso has been developed for photodynamic therapy (PDT). The photosensitizer BDPI-lyso showed a high singlet oxygen quantum yield (ΦΔ = 0.95) and low fluorescence quantum yield (ΦF = 0.05) in EtOH. Different singlet oxygen quantum yields were found in acidic solution (pH = 5, ΦΔ = 0.51) and in neutral solution (pH = 7, ΦΔ = 0.38). DFT and TD-DFT calculations of BDPI-lyso and its protonated product BDPI-lysoH+ indicated that the S1/T3 transition was responsible for the intersystem crossing (ISC) enhancement which would promote the production of singlet oxygen. The negligible dark cytotoxicity toward the hepatoma cell line Bel-7402 was confirmed by MTT assay, AO/EB dual staining, and cell images. Upon exposure to a low dose of light illumination, the disruption of the cell plasma membrane and the calculated half-maximal inhibitory concentration (IC50) of 0.4 μM showed a high phototoxicity of the photosensitizer BDPI-lyso. The light-induced intracellular ROS generation was verified as the PDT mechanism of BDPI-lyso. Colocalization experiments of LysoTracker Green and BDPI-lyso in the dark indicated the good lysosome-targeting ability of BDPI-lyso. The images of cells costained with LysoTracker Green and BDPI-lyso, and the appearance of intracellular and extracellular blebs with green fluorescence after light illumination revealed the light-induced dysfunction of lysosomes and cell apoptosis.

An effective FRET-based two-photon ratiometric fluorescent probe with double well-resolved emission bands for lysosomal pH changes in living cells and zebrafish

In cells, lysosome is an acidic organelle (approximately pH 4.5-5.5), whose pH changes plays a key role in mediating various biological processes. To address this issue, a lot of fluorescent probes have been developed and prepared for tracking lysosomal pH changes. However, few of these probes can realize the imaging of lysosomal pH changes in biosystems. Herein, a new two-photon (TP) ratiometric fluorescent probe (NpRhLys-pH) by adopting the fluorescence resonance energy transfer (FRET) strategy has been developed for imaging of lysosomal pH changes in living cells and zebrafish. In this probe NpRhLys-pH, constructed by conjugating a TP fluorophore (D-Π-A-structured naphthalimide derivative) with a rhodamine B fluorophore via a non-conjugated flexible linker, the morpholine moiety serves as a targeting unit for anchoring lysosomes, and the xanthane derivative shows a pH-modulated open/close form of the spirocycle. Such a scaffold affords the NpRhLys-pH is a reliable and specific probe for anchoring lysosomes in living cells and zebrafish with dual-channel emission peaks separated by 85 nm, and responds to lysosomal pH rapidly and reversibly with high selectivity and sensitivity, demonstrating it can be used as a powerful tool for the biological research of the relationship between physiology and pathology and lysosomal pH changes in biological systems.

A near infrared fluorescent probe based on ICT for monitoring mitophagy in living cells

Mitophagy, the process in which cells degrade dysfunctional organelles and recycle their nutrient substances by lysosomes, plays a vital role in cell metabolism and physiology.

A red-emission fluorescent probe for visual monitoring of lysosomal pH changes during mitophagy and cell apoptosis

We report a red-emission pH fluorescent probe (MSO) for visual monitoring of lysosomal pH changes during mitophagy and cell apoptosis in living cells.

A lysosome-targeting viscosity-sensitive fluorescent probe based on a novel functionalised near-infrared xanthene-indolium dye and its application in living cells

The viscosity of lysosomes plays a significant role in modulating biological processes and reflects the status and function of this kind of organelle, e.g., locations, morphologies, and components.

Imaging stressed organellesviasugar-conjugated color-switchable pH sensors

Sugar-conjugated pH sensors discriminate stressed lysosomes in different cell starvation conditionsviared-to-green fluorescence switch.

Targeting Cancer Lysosomes with Good Old Cationic Amphiphilic Drugs

Being originally discovered as cellular recycling bins, lysosomes are today recognized as versatile signaling organelles that control a wide range of cellular functions that are essential not only for the well-being of normal cells but also for malignant transformation and cancer progression. In addition to their core functions in waste disposal and recycling of macromolecules and energy, lysosomes serve as an indispensable support system for malignant phenotype by promoting cell growth, cytoprotective autophagy, drug resistance, pH homeostasis, invasion, metastasis, and genomic integrity. On the other hand, malignant transformation reduces the stability of lysosomal membranes rendering cancer cells sensitive to lysosome-dependent cell death. Notably, many clinically approved cationic amphiphilic drugs widely used for the treatment of other diseases accumulate in lysosomes, interfere with their cancer-promoting and cancer-supporting functions and destabilize their membranes thereby opening intriguing possibilities for cancer therapy. Here, we review the emerging evidence that supports the supplementation of current cancer therapies with lysosome-targeting cationic amphiphilic drugs.

Tizoxanide induces autophagy by inhibiting PI3K/Akt/mTOR pathway in RAW264.7 macrophage cells

As the main metabolite of nitazoxanide, tizoxanide (TIZ) has a broad-spectrum anti-infective effect against parasites, bacteria, and virus. In this study, we investigated the effects of TIZ on autophagy by regulating the PI3K/Akt/mTOR signaling pathway. RAW264.7 macrophage cells were treated with various TIZ concentrations. Cell viability assay, transmission electron microscope, and immunofluorescence staining were used to detect the biological function of the macrophage cells, and the expression levels of the autophagy pathway-related proteins were measured by Western blot. Results revealed that TIZ promoted the conversion of LC3-I to LC3-II, the formation of autophagy vacuoles, and the degradation of SQSTM1/p62 in a concentration- and time-dependent manner in RAW264.7 cells. Treatment with TIZ increased the Beclin-1 expression level and inhibited PI3K, Akt, mTOR, and ULK1 activation. These effects were enhanced by pretreatment with rapamycin but attenuated by pretreatment with LY294002. In addition, the conversion of LC3-I to LC3-II was observed in Vero, 293T, and HepG2 cells treated with TIZ. These data suggested that TIZ may induce autophagy by inhibiting the Akt/mTOR/ULK1 signaling pathway in macrophages and other cells.

Molecular Self-Assembly of Bioorthogonal Aptamer-Prodrug Conjugate Micelles for Hydrogen Peroxide and pH-Independent Cancer Chemodynamic Therapy

Chemodynamic therapy (CDT) has demonstrated new possibilities for selective and logical cancer intervention by specific manipulation of dysregulated tumorous free radical homeostasis. Current CDT methods largely rely on conversion of endogenous hydrogen peroxide (H₂O₂) into highly toxic hydroxyl radicals via classical Fenton or Haber-Weiss chemistry. However, their anticancer efficacies are greatly limited by the requirement of strong acidity for efficient chemical reactions, insufficient tumorous H₂O₂, and upregulated antioxidant defense to counteract free radical-caused oxidative damage. Here, we present a new concept whereby bioorthogonal chemistry and prodrug are combined to create a new type of aptamer drug conjugate (ApDC): aptamer-prodrug conjugate (ApPdC) micelle for improved and cancer-targeted CDT. The hydrophobic prodrug bases can not only promote self-assembly of aptamers but also act as free radical generators via bioorthogonal chemistry. In depth mechanistic studies reveal that, unlike traditional CDT systems, ApPdC micelles enable in situ activation and self-cycling generation of toxic C-centered free radicals in cancer cells through cascading bioorthogonal reactions, with no dependence on either H₂O₂ or pH, yet concurrently with diminished cancerous antioxidation by GSH depletion for a synergistic CDT effect. We expect this work to provide new insights into the design of targeted cancer therapies and studies of free radical-related molecular mechanisms.

Synthesis of highly selective lysosomal markers by coupling 2-(2'-hydroxyphenyl)benzothiazole (HBT) with benzothiazolium cyanine (Cy): the impact of substituents on selectivity and optical properties

HBT-Cy 1 has been previously reported as a highly selective fluorescent probe for lysosome visualization in live cells. To further investigate the role of the structural components of HBT-Cy in lysosome selectivity, cyanine based fluorescent probe series (2-5) have been synthesized in good yields by connecting benzothiazolium cyanine (Cy) with 2-hydroxyphenylbenzothiazole (HBT) via a meta phenylene ring. Probes 2-5 exhibited exceptional photophysical properties including bright red-emission (λ_em≈ 630-650 nm), a large Stokes shift (Δλ > 130 nm) and high fluorescence quantum yields (φ_fl≈ 0.1-0.5). Probes 2, 3, and 5 exhibited exceptional selectivity towards cellular lysosomes in NHLF and MO3.13 cells. Our further study revealed that the phenyl benzothiazolium cyanine component (6) was the lysosome directing group in the HBT-Cy probe structure. The attachment of the hydroxyphenyl benzothiazole (HBT) component to the HBT-Cy probe structure has significantly improved its photophysical properties. Lysosome probes 2, 3 and 5 exhibited excellent biocompatibility, quick staining, bright red fluorescence, and wash-free application for live cell imaging. These probes further exhibited excellent characteristics for bioimaging experiments including a non-alkalinizing nature, high biocompatibility, high photostability and long-term imaging ability (>4 hours).

Lysosomal size matters

Lysosomes are key cellular catabolic centers that also perform fundamental metabolic, signaling and quality control functions. Lysosomes are not static and they respond dynamically to intra‐ and extracellular stimuli triggering changes in organelle numbers, size and position. Such physical changes have a strong impact on lysosomal activity ultimately influencing cellular homeostasis. In this review, we summarize the current knowledge on lysosomal size regulation, on its physiological role(s) and association to several disease conditions.

Lysosomes as a therapeutic target

Lysosomes are membrane-bound organelles with roles in processes involved in degrading and recycling cellular waste, cellular signalling and energy metabolism. Defects in genes encoding lysosomal proteins cause lysosomal storage disorders, in which enzyme replacement therapy has proved successful. Growing evidence also implicates roles for lysosomal dysfunction in more common diseases including inflammatory and autoimmune disorders, neurodegenerative diseases, cancer and metabolic disorders. With a focus on lysosomal dysfunction in autoimmune disorders and neurodegenerative diseases - including lupus, rheumatoid arthritis, multiple sclerosis, Alzheimer disease and Parkinson disease - this Review critically analyses progress and opportunities for therapeutically targeting lysosomal proteins and processes, particularly with small molecules and peptide drugs.

An efficient TP-FRET-based lysosome-targetable fluorescent probe for imaging peroxynitrite with two well-resolved emission channels in living cells, tissues and zebrafish

Peroxynitrite (ONOO^-), an important role of reactive oxygen species (ROS) in vivo, and studies showed abnormal of ROS can induce lysosomal membrane permeabilization (LMP) and lead to the death of cells. Thus, it is of great significance for designing an effective method for investigating relationship between physiology and pathology between ONOO^- and lysosome. Herein, for the first time, we adopted a Förster resonance energy transfer (FRET) strategy to construct a lysosome-targetable small molecular ratiometric two-photon (TP) fluorescent probe (NpRh-ONOO) for detecting ONOO^- in living cells, tissues and zebrafish. Specifically, a TP fluorophore and a rhodamine B fluorophore are directly connected by a flexible piperidine linker to form the TP-FRET-scaffold, a hydrazide as ONOO^- reactive set, and a dimethylamino as lysosome targeting-group, which shows a target-modulated ratiometric TP fluorescence response, two well-resolved emission peaks separated by 73 nm, rapid response (<10 s), high selectivity and sensitivity with the detection limit is as low as 3.3 nM for ONOO^-. These prominent features of probe were then applied for ratiometric bioimaging both exogenous and endogenous peroxynitrite in living cells, tissues and zebrafish, demonstrating it can be used as a powerful tool for biological research of lysosomal peroxynitrite in biological systems.

Punicalagin Prevents Inflammation in LPS-Induced RAW264.7 Macrophages by Inhibiting FoxO3a/Autophagy Signaling Pathway

Punicalagin, a hydrolysable tannin of pomegranate juice, exhibits multiple biological effects, including inhibiting production of pro-inflammatory cytokines in macrophages. Autophagy, an intracellular self-digestion process, has been recently shown to regulate inflammatory responses. In this study, we investigated the anti-inflammatory potential of punicalagin in lipopolysaccharide (LPS) induced RAW264.7 macrophages and uncovered the underlying mechanisms. Punicalagin significantly attenuated, in a concentration-dependent manner, LPS-induced release of NO and decreased pro-inflammatory cytokines TNF-α and IL-6 release at the highest concentration. We found that punicalagin inhibited NF-κB and MAPK activation in LPS-induced RAW264.7 macrophages. Western blot analysis revealed that punicalagin pre-treatment enhanced LC3II, p62 expression, and decreased Beclin1 expression in LPS-induced macrophages. MDC assays were used to determine the autophagic process and the results worked in concert with Western blot analysis. In addition, our observations indicated that LPS-induced releases of NO, TNF-α, and IL-6 were attenuated by treatment with autophagy inhibitor chloroquine, suggesting that autophagy inhibition participated in anti-inflammatory effect. We also found that punicalagin downregulated FoxO3a expression, resulting in autophagy inhibition. Overall these results suggested that punicalagin played an important role in the attenuation of LPS-induced inflammatory responses in RAW264.7 macrophages and that the mechanisms involved downregulation of the FoxO3a/autophagy signaling pathway.

Interleukin-6: Its role and mechanisms in rescuing depression-like behaviors in rat models of depression

Neuronal injury within specific brain regions is considered a critical risk factor in the pathophysiology of depression. However, the underlying mechanisms of this process, and thus the potential for development of novel therapeutic strategies in the treatment of depression, remain largely unknown. Here, we report that Il-6 protects against neuronal anomalies related with depression, in part, by suppressing oxidative stress and consequent autophagic and apoptotic hyperactivity. Specifically, we show that IL-6 is downregulated within the CA1 hippocampus in two animal models of depression and upregulated by antidepressants. Increasing levels of IL-6 in the CA1 region result in pleiotropic protective actions including reductions in oxidative stress and modulation of autophagy, anti-immuno-inflammatory activation and anti-apoptotic effects in CA1 neurons, all of which are associated with the rescue of depression-like behaviors. In contrast, IL-6 downregulation exacerbates neuronal anomalies within the CA1 region and facilitates the genesis of depression phenotypes in rats. Interestingly, in addition to attenuating oxidative damage, the antioxidant, N-acetylcysteine (NAC), is also associated with significantly decreased neuronal deficits and the display of depressive behaviors in rats. These results suggest that IL-6 may exert neuroprotection within CA1 neurons via pleiotropic mechanisms and may serve as a potential therapeutic target for the treatment of depression.

Mitochondrion-Specific Blinking Fluorescent Bioprobe for Nanoscopic Monitoring of Mitophagy

Dynamic changes of mitochondrial morphology play an important role in cellular metabolism. Real-time monitoring mitochondrial ultrastructural dynamics at nanometer-scale resolution is crucially desired for further understanding of the mitochondria-based cellular function. In this work, we introduce a fluorescent carbon dot, which can selectively target mitochondria in live cells (named as MitoCD). MitoCD can effectively accumulate in mitochondria regardless of the decrease or vanishing of mitochondrial membrane potential (MMP), enabling the exploration of MMP-independent mitochondrial process. Moreover, the MitoCD is a thiol-based reaction-free probe that target mitochondria without consuming the thiol groups from mitochondrial proteins. Additionally, the MitoCD possesses good photophysical properties under physiological conditions, such as burst-like blinking, high photon counts, and low "on"/"off" ratio, which are specifically suitable for localization-based nanoscopic imaging. According to the optical microscopic imaging results, dynamical fission and fusion processes from mitochondria have been observed in live cells. During mitophagy, it is found that reticular formation of the mitochondria gradually collapsed, and then a portion of mitochondria split and vanished. Owing to the attractive biological and special photophysical properties, this probe displays promising application in a variety of super-resolution based biological studies and will provide deep insight in mitochondrial metabolism.

Targeting Autophagy for Cancer Treatment and Tumor Chemosensitization

Autophagy is a tightly regulated catabolic process that facilitates nutrient recycling from damaged organelles and other cellular components through lysosomal degradation. Deregulation of this process has been associated with the development of several pathophysiological processes, such as cancer and neurodegenerative diseases. In cancer, autophagy has opposing roles, being either cytoprotective or cytotoxic. Thus, deciphering the role of autophagy in each tumor context is crucial. Moreover, autophagy has been shown to contribute to chemoresistance in some patients. In this regard, autophagy modulation has recently emerged as a promising therapeutic strategy for the treatment and chemosensitization of tumors, and has already demonstrated positive clinical results in patients. In this review, the dual role of autophagy during carcinogenesis is discussed and current therapeutic strategies aimed at targeting autophagy for the treatment of cancer, both under preclinical and clinical development, are presented. The use of autophagy modulators in combination therapies, in order to overcome drug resistance during cancer treatment, is also discussed as well as the potential challenges and limitations for the use of these novel therapeutic strategies in the clinic.

Efficacy of radiation exposure in laryngeal squamous cell carcinoma is mediated by the LAMP3/LAMC2/tenascin-C pathway

The present study explored the role of LAMP3 and related molecular mechanisms in the efficacy of radiation exposure in laryngeal squamous cell carcinoma (LSCC). A lentivirus vector containing the LAMP3 gene was transfected into HEp-2 cells to construct siRNA-LAMP3 and complementation (siLAMP3+LAMP3) groups. Treatment with 4 Gy or 8 Gy radiation was administered to evaluate the role of LAMP3 in radiation therapy. Apoptosis was detected by Annexin V/propidium iodide double staining. Cell migration and invasion were measured in vitro using Transwell and Matrigel assays. Downstream genes regulated by LAMP3 were analyzed using RNA sequencing. Furthermore, a patient-derived xenograft (PDX) model of LSCC was established to verify the efficacy of radiation exposure and the associated signaling pathways downstream of LAMP3. The efficacy of radiation showed that cell proliferation was significantly inhibited by siRNA-LAMP3 knockdown. Increased apoptosis was also observed. Notably, the inhibitory effect was attenuated and apoptosis rates were decreased after LAMP3 complementation. In vitro cellular assays showed that migration and invasion were significantly suppressed by siRNA-LAMP3 knockdown and increased after LAMP3 complementation. Analysis of the efficacy of radiation exposure in the PDX model showed that LAMP3-specific knockdown inhibited tumor growth and that tumor growth was further reduced by the combined radiotherapy treatment. According to transcriptome analysis, the extracellular matrix-receptor interaction pathway is regulated by LAMP3, and further analysis revealed significant differences in key-associated molecules, including laminin subunit gamma-2 (LAMC2) and tenascin-C (TNC). Validation of the in vivo PDX model using qPCR and Western blot analyses supported the abovementioned results. The present findings suggest that reduced LAMP3 expression enhances the efficacy of radiation exposure in LSCC by regulating the LAMP3/LAMC2/TNC signaling pathway.

Phosphofructokinases Axis Controls Glucose-Dependent mTORC1 Activation Driven by E2F1

Cancer cells rely on mTORC1 activity to coordinate mitogenic signaling with nutrients availability for growth. Based on the metabolic function of E2F1, we hypothesize that glucose catabolism driven by E2F1 could participate on mTORC1 activation. Here, we demonstrate that glucose potentiates E2F1-induced mTORC1 activation by promoting mTORC1 translocation to lysosomes, a process that occurs independently of AMPK activation. We showed that E2F1 regulates glucose metabolism by increasing aerobic glycolysis and identified the PFKFB3 regulatory enzyme as an E2F1-regulated gene important for mTORC1 activation. Furthermore, PFKFB3 and PFK1 were found associated to lysosomes and we demonstrated that modulation of PFKFB3 activity, either by substrate accessibility or expression, regulates the translocation of mTORC1 to lysosomes by direct interaction with Rag B and subsequent mTORC1 activity. Our results support a model whereby a glycolytic metabolon containing phosphofructokinases transiently interacts with the lysosome acting as a sensor platform for glucose catabolism toward mTORC1 activity.

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Glucose potentiates E2F1-induced mTORC1 by promoting its translocation to lysosomes

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PFKFB3 activity is involved in the regulation of mTORC1 by glucose

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The glycolytic enzymes PFKFB3 and PFK1 were found associated to lysosomal surface

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PFKFB3 and PFK1 activities regulate mTORC1 lysosomal translocation

Charge Regulation of Self-Assembled Tubules by Protonation for Efficiently Selective and Controlled Drug Delivery

Despite the success for targeted delivery in the body, the efficient release without side effects caused by residual drug remains a challenge. For reducing residual drug, the pH-responsive carriers were prepared by self-assembly from aromatic macrocycles, which were non-toxic and biocompatible. The inner surroundings of aromatic macrocycles could be protonated positively by acid inducing the separation of neighboring macrocycles. Thus, Dox-loaded carriers successfully inhibited the proliferation of carcinoma cells (HepG2 and 4T1) rather than normal cells (HL7702). The effects were further proved in vivo without systemic cytotoxicity. Notably, the responsive environment for drug release depended on the concentration of carriers. Particularly, drug release was promoted by carrier separation. Carrier 2 exhibited preferable anticancer efficacy than carrier 1 due to the efficient release of Dox by full separation of the carrier. Collectively, we have developed a novel strategy serving as a selective and controlled drug release platform for cancer therapeutics.

GD2 ganglioside-binding antibody 14G2a and specific aurora A kinase inhibitor MK-5108 induce autophagy in IMR-32 neuroblastoma cells

The process of autophagy and its role in survival of human neuroblastoma cell cultures was studied upon addition of an anti-GD2 ganglioside (GD2) 14G2a mouse monoclonal antibody (14G2a mAb) and an aurora A kinase specific inhibitor, MK-5108. It was recently shown that combination of these agents significantly potentiates cytotoxicity against IMR-32 and CHP-134 neuroblastoma cells in vitro, as compared to the inhibitor used alone. In this study we gained mechanistic insights on autophagy in the observed cytotoxic effects exerted by both agents using cytotoxicity assays, RT-qPCR, immunoblotting, and autophagy detection methods. Enhancement of the autophagy process in the 14G2a mAb- and MK-5108-treated IMR-32 cells was documented by assessing autophagic flux. Application of a lysosomotropic agent-chloroquine (CQ) affected the 14G2a mAb- and MK-5108-stimulated autophagic flux. It is our conclusion that the 14G2a mAb (40 μg/ml) and MK-5108 inhibitor (0.1 μM) induce autophagy in IMR-32 cells. Moreover, the combinatorial treatment of IMR-32 cells with the 14G2a mAb and CQ significantly potentiates cytotoxic effect, as compared to CQ used alone. Most importantly, we showed that interfering with autophagy at its early and late step augments the 14G2a mAb-induced apoptosis, therefore we can conclude that inhibition of autophagy is the primary mechanism of the CQ-mediated sensitization to the 14G2a mAb-induced apoptosis. Although, there was no virtual stimulation of autophagy in the 14G2a mAb-treated CHP-134 neuroblastoma cells, we were able to show that PHLDA1 protein positively regulates autophagy and this process exists in a mutually exclusive manner with apoptosis in PHLDA1-silenced CHP-134 cells.

Size-Dependent Interaction of Amyloid β Oligomers with Brain Total Lipid Extract Bilayer-Fibrillation Versus Membrane Destruction

Amyloid β, Aβ(1-42), is a component of senile plaques present in the brain of Alzheimer's disease patients and one of the main suspects responsible for pathological consequences of the disease. Herein, we directly visualize the Aβ activity toward a brain-like model membrane and demonstrate that this activity strongly depends on the Aβ oligomer size. PeakForce quantitative nanomechanical mapping mode of atomic force microscopy imaging revealed that the interaction of large-size (LS) Aβ oligomers, corresponding to high-molecular-weight Aβ oligomers, with the brain total lipid extract (BTLE) membrane resulted in accelerated Aβ fibrillogenesis on the membrane surface. Importantly, the fibrillogenesis did not affect integrity of the membrane. In contrast, small-size (SS) Aβ oligomers, corresponding to low-molecular-weight Aβ oligomers, created pores and then disintegrated the BTLE membrane. Both forms of the Aβ oligomers changed nanomechanical properties of the membrane by decreasing its Young's modulus by ∼45%. Our results demonstrated that both forms of Aβ oligomers induce the neurotoxic effect on the brain cells but their action toward the membrane differs significantly.

Ginsenoside Compound K Induces Ros-Mediated Apoptosis and Autophagic Inhibition in Human Neuroblastoma Cells In Vitro and In Vivo

Autophagy can result in cellular adaptation, as well as cell survival or cell death. Modulation of autophagy is increasingly regarded as a promising cancer therapeutic approach. Ginsenoside compound K (CK), an active metabolite of ginsenosides isolated from Panax ginseng C.A. Meyer, has been identified to inhibit growth of cancer cell lines. However, the molecular mechanisms of CK effects on autophagy and neuroblastoma cell death have not yet been investigated. In the present study, CK inhibited neuroblastoma cell proliferation in vitro and in vivo. Treatment by CK also induced the accumulation of sub-G1 population, and caspase-dependent apoptosis in neuroblastoma cells. In addition, CK promotes autophagosome accumulation by inducing early-stage autophagy but inhibits autophagic flux by blocking of autophagosome and lysosome fusion, the step of late-stage autophagy. This effect of CK appears to be mediated through the induction of intracellular reactive oxygen species (ROS) and mitochondria membrane potential loss. Moreover, chloroquine, an autophagy flux inhibitor, further promoted CK-induced apoptosis, mitochondrial ROS induction, and mitochondria damage. Interestingly, those promoted phenomena were rescued by co-treatment with a ROS scavenging agent and an autophagy inducer. Taken together, our findings suggest that ginsenoside CK induced ROS-mediated apoptosis and autophagic flux inhibition, and the combination of CK with chloroquine, a pharmacological inhibitor of autophagy, may be a novel therapeutic potential for the treatment of neuroblastoma.

Correlation of Autophagosome Formation with Degradation and Endocytosis Arabidopsis Regulator of G-Protein Signaling (RGS1) through ATG8a

Damaged or unwanted cellular proteins are degraded by either autophagy or the ubiquitin/proteasome pathway. In Arabidopsis thaliana, sensing of D-glucose is achieved by the heterotrimeric G protein complex and regulator of G-protein signaling 1 (AtRGS1). Here, we showed that starvation increases proteasome-independent AtRGS1 degradation, and it is correlated with increased autophagic flux. RGS1 promoted the production of autophagosomes and autophagic flux; RGS1-yellow fluorescent protein (YFP) was surrounded by vacuolar dye FM4-64 (red fluorescence). RGS1 and autophagosomes co-localized in the root cells of Arabidopsis and BY-2 cells. We demonstrated that the autophagosome marker ATG8a interacts with AtRGS1 and its shorter form with truncation of the seven transmembrane and RGS1 domains in planta. Altogether, our data indicated the correlation of autophagosome formation with degradation and endocytosis of AtRGS1 through ATG8a.