Fluorescence lifetime characterization of novel low-pH probes

Ultraphotostable Phosphorescent Nanosensors for Sensing the Lysosomal pH at the Single-Cell Level over Long Durations

Ultraphotostable phosphorescent nanosensors have been designed for continuously sensing the lysosome pH over a long duration. The nanosensors exhibited excellent photostability, high accuracy, and capability to measure pH values during cell proliferation for up to 7 days. By arranging a metal-ligand complex of long phosphorescence lifetime and pH indicator in silica nanoparticles, we discover efficient Förster resonance energy transfer, which converts the pH-responsive UV-vis absorption signal of the pH indicator into a phosphorescent signal. Both the phosphorescent intensity and lifetime change at different pH values, and intracellular pH values can be accurately measured by our custom-built rapid phosphorescent lifetime imaging microscopy. The excellent photostability, high accuracy, and good biocompatibility prove that these nanosensors are a useful tool for tracing the fluctuation of pH values during endocytosis. The methodology can be easily adapted to design new nanosensors with different pKa or for different kinds of intracellular ions, as there are hundreds of pH and ion indicators readily available.

Automatic segmentation of lysosomes and analysis of intracellular pH with Radachlorin photosensitizer and FLIM

We report application of the fluorescence lifetime imaging microscopy (FLIM) for analysis of distributions of intracellular acidity using a chlorin-e6 based photosensitizer Radachlorin. An almost two-fold increase of the photosensitizer fluorescence lifetime in alkaline microenvironments as compared to acidic ones allowed for clear distinguishing between acidic and alkaline intracellular structures. Clusterization of a phasor plot calculated from fits of the FLIM raw data by two Gaussian distributions provided accurate automatic segmentation of lysosomes featuring acidic contents. The approach was validated in colocalization experiments with LysoTracker fluorescence in living cells of four established lines. The dependence of photosensitizer fluorescence lifetime on microenvironment acidity allowed for estimation of pH inside the cells, except for the nuclei, where photosensitizer does not penetrate. The developed method is promising for combined application of the photosensitizer for both photodynamic treatment and diagnostics.

Exploring lysosomal biology: current approaches and methods

Lysosomes are the degradation centers and signaling hubs in the cell. Lysosomes undergo adaptation to maintain cell homeostasis in response to a wide variety of cues. Dysfunction of lysosomes leads to aging and severe diseases including lysosomal storage diseases (LSDs), neurodegenerative disorders, and cancer. To understand the complexity of lysosome biology, many research approaches and tools have been developed to investigate lysosomal functions and regulatory mechanisms in diverse experimental systems. This review summarizes the current approaches and tools adopted for studying lysosomes, and aims to provide a methodological overview of lysosomal research and related fields.

Intracellularly delivered human lactoferrin functions as an activator of Na+/H+ exchanger 7

Here, we report that human lactoferrin (hLF), known for its anticancer properties, induced intracellular activation of the Na+/H+ exchanger (NHE) 7 in human lung cancer PC-9 cells. Compared to non-fused hLF, the fusion of human serum albumin (HSA) with hLF (hLF-HSA) facilitated its internalization into PC-9 cells in a caveolae-mediated manner, thereby exhibiting enhanced anti-proliferative effects. Although hLF alone did not exhibit any discernible effects, hLF-HSA resulted in organelle alkalization as detected using an acidotropic pH indicator. hLF-HSA-induced elevation of organelle pH and inhibition of cancer growth were abolished by NHE7 siRNA. hLF-HSA upregulated NHE7. Thus, upon cellular uptake, hLF-HSA triggers proton leakage through the upregulation of NHE7. This process led to organelle alkalization, probably in the trans-Golgi network (TGN) as suggested by the localization of NHE7 in PC-9 cells, thereby suppressing lung cancer cell growth. Forcing the cellular uptake of hLF alone using a caveolae-mediated endocytosis activator led to an increase in organelle pH. Furthermore, cell entry of hLF also activated proton-loading NHE7, leading to organelle acidification in the pancreatic cancer cell line MIA PaCa-2. Therefore, the intracellularly delivered hLF functions as an activator of NHE7.

Organelle proteomic profiling reveals lysosomal heterogeneity in association with longevity

Lysosomes are active sites to integrate cellular metabolism and signal transduction. A collection of proteins associated with the lysosome mediate these metabolic and signaling functions. Both lysosomal metabolism and lysosomal signaling have been linked to longevity regulation; however, how lysosomes adjust their protein composition to accommodate this regulation remains unclear. Using deep proteomic profiling, we systemically profiled lysosome-associated proteins linked with four different longevity mechanisms. We discovered the lysosomal recruitment of AMP-activated protein kinase and nucleoporin proteins and their requirements for longevity in response to increased lysosomal lipolysis. Through comparative proteomic analyses of lysosomes from different tissues and labeled with different markers, we further elucidated lysosomal heterogeneity across tissues as well as the increased enrichment of the Ragulator complex on Cystinosin-positive lysosomes. Together, this work uncovers lysosomal proteome heterogeneity across multiple scales and provides resources for understanding the contribution of lysosomal protein dynamics to signal transduction, organelle crosstalk, and organism longevity.

Understanding How Cationic Polymers' Properties Inform Toxic or Immunogenic Responses via Parametric Analysis

Cationic polymers are widely used materials in diverse biotechnologies. Subtle variations in these polymers' properties can change them from exceptional delivery agents to toxic inflammatory hazards. Conventional screening strategies optimize for function in a specific application rather than observing how underlying polymer-cell interactions emerge from polymers' properties. An alternative approach is to map basic underlying responses, such as immunogenicity or toxicity, as a function of basic physicochemical parameters to inform the design of materials for a breadth of applications. To demonstrate the potential of this approach, we synthesized 107 polymers varied in charge, hydrophobicity, and molecular weight. We then screened this library for cytotoxic behavior and immunogenic responses to map how these physicochemical properties inform polymer-cell interactions. We identify three compositional regions of interest and use confocal microscopy to uncover the mechanisms behind the observed responses. Finally, immunogenic activity is confirmed in vivo. Highly cationic polymers disrupted the cellular plasma membrane to induce a toxic phenotype, while high molecular weight, hydrophobic polymers were uptaken by active transport to induce NLRP3 inflammasome activation, an immunogenic phenotype. Tertiary amine- and triethylene glycol-containing polymers did not invoke immunogenic or toxic responses. The framework described herein allows for the systematic characterization of new cationic materials with different physicochemical properties for applications ranging from drug and gene delivery to antimicrobial coatings and tissue scaffolds.

Carbon Dots Embedded Hybrid Microgel with Phenylboronic Acid as Monomer for Fluorescent Glucose Sensing and Glucose-Triggered Insulin Release at Physiological pH

A multifunctional and biocompatible hybrid microgel (poly(VPBA-AAm)-CD) using N, S-doped carbon dots (CDs) and ethylene glycol dimethacrylate (EGDMA) as cross-linking agents, and 4-vinylbenzene boronic acid (VPBA) and acrylamide (AAm) as monomers, was designed in this work. This microgel can be easily prepared by a simple one-pot radical dispersion polymerization of the reactants using a rationally designed hydrogen-bonded complex method. The hybrid microgels were spherical particles with a smooth surface and an average particle size of 234 ± 8 nm. The poly(VPBA-AAm)-CD microgel displayed the glucose-responsive swelling within a clinically concerned range at a physiological pH and could realize the controllable release of insulin. In addition, the release rate of insulin in the hybrid microgel (poly(VPBA-AAm)-CD) could be triggered by glucose concentrations in the solution, and the increasing glucose concentrations can accelerate the insulin release. Further in vitro cytotoxicity studies showed that the microgel had good biocompatibility and no obvious toxicity to the cells. These indicate that the prepared microgel (poly(VPBA-AAm)-CD) may supply a new pattern for the self-regulating therapy of insulin deficiency in diabetes.

A lysosomal regulatory circuit essential for the development and function of microglia

As the primary phagocytic cells of the central nervous system, microglia exquisitely regulate their lysosomal activity to facilitate brain development and homeostasis. However, mechanisms that coordinate lysosomal activity with microglia development, chemotaxis, and function remain unclear. Here, we show that embryonic macrophages require the lysosomal guanosine triphosphatase (GTPase) RagA and the GTPase-activating protein Folliculin to colonize the brain in zebrafish. We demonstrate that embryonic macrophages in rraga mutants show increased expression of lysosomal genes but display significant down-regulation of immune- and chemotaxis-related genes. Furthermore, we find that RagA and Folliculin repress the key lysosomal transcription factor Tfeb and its homologs Tfe3a and Tfe3b in the macrophage lineage. Using RNA sequencing, we establish that Tfeb and Tfe3 are required for activation of lysosomal target genes under conditions of stress but not for basal expression of lysosomal pathways. Collectively, our data define a lysosomal regulatory circuit essential for macrophage development and function in vivo.

Loss of KEAP1 Causes an Accumulation of Nondegradative Organelles

KEAP1 is a cytoplasmic protein that functions as an adaptor for the Cullin-3-based ubiquitin E3 ligase system, which regulates the degradation of many proteins, including NFE2L2/NRF2 and p62/SQSTM1. Loss of KEAP1 leads to an accumulation of protein ubiquitin aggregates and defective autophagy. To better understand the role of KEAP1 in the degradation machinery, we investigated whether Keap1 deficiency affects the endosome-lysosomal pathway. We used KEAP1-deficient mouse embryonic fibroblasts (MEFs) and combined Western blot analysis and fluorescence microscopy with fluorometric and pulse chase assays to analyze the levels of lysosomal-endosomal proteins, lysosomal function, and autophagy activity. We found that the loss of keap1 downregulated the protein levels and activity of the cathepsin D enzyme. Moreover, KEAP1 deficiency caused lysosomal alterations accompanied by an accumulation of autophagosomes. Our study demonstrates that KEAP1 deficiency increases nondegradative lysosomes and identifies a new role for KEAP1 in lysosomal function that may have therapeutic implications.

Ppt1-deficiency dysregulates lysosomal Ca++ homeostasis contributing to pathogenesis in a mouse model of CLN1 disease

Inactivating mutations in the PPT1 gene encoding palmitoyl-protein thioesterase-1 (PPT1) underlie the CLN1 disease, a devastating neurodegenerative lysosomal storage disorder. The mechanism of pathogenesis underlying CLN1 disease has remained elusive. PPT1 is a lysosomal enzyme, which catalyzes the removal of palmitate from S-palmitoylated proteins (constituents of ceroid lipofuscin) facilitating their degradation and clearance by lysosomal hydrolases. Thus, it has been proposed that Ppt1-deficiency leads to lysosomal accumulation of ceroid lipofuscin leading to CLN1 disease. While S-palmitoylation is catalyzed by palmitoyl acyltransferases (called ZDHHCs), palmitoyl-protein thioesterases (PPTs) depalmitoylate these proteins. We sought to determine the mechanism by which Ppt1-deficiency may impair lysosomal degradative function leading to infantile neuronal ceroid lipofuscinosis pathogenesis. Here, we report that in Ppt1^-/- mice, which mimic CLN1 disease, low level of inositol 3-phosphate receptor-1 (IP3R1) that mediates Ca⁺⁺ transport from the endoplasmic reticulum to the lysosome dysregulated lysosomal Ca⁺⁺ homeostasis. Intriguingly, the transcription factor nuclear factor of activated T-cells, cytoplasmic 4 (NFATC4), which regulates IP3R1-expression, required S-palmitoylation for trafficking from the cytoplasm to the nucleus. We identified two palmitoyl acyltransferases, ZDHHC4 and ZDHHC8, which catalyzed S-palmitoylation of NFATC4. Notably, in Ppt1^-/- mice, reduced ZDHHC4 and ZDHHC8 levels markedly lowered S-palmitoylated NFATC4 (active) in the nucleus, which inhibited IP3R1-expression, thereby dysregulating lysosomal Ca⁺⁺ homeostasis. Consequently, Ca⁺⁺ -dependent lysosomal enzyme activities were markedly suppressed. Impaired lysosomal degradative function impaired autophagy, which caused lysosomal storage of undigested cargo. Importantly, IP3R1-overexpression in Ppt1^-/- mouse fibroblasts ameliorated this defect. Our results reveal a previously unrecognized role of Ppt1 in regulating lysosomal Ca⁺⁺ homeostasis and suggest that this defect contributes to pathogenesis of CLN1 disease.

Targeting chalcone binding sites in living Leishmania using a reversible fluorogenic benzochalcone probe

Chalcones (1,3-diphenyl-2-propen-1-ones) either natural or synthetic have a plethora of biological properties including antileishmanial activities, but their development as drugs is hampered by their largely unknown mechanisms of action. We demonstrate herein that our previously described benzochalcone fluorogenic probe (HAB) could be imaged by fluorescence microscopy in live Leishmania amazonensis promastigotes where it targeted the parasite acidocalcisomes, lysosomes and the mitochondrion. As in the live zebrafish model, HAB formed yellow-emitting fluorescent complexes when associated with biological targets in Leishmania. Further, we used HAB as a reversible probe to study the binding of a portfolio of diverse chalcones and analogues in live promastigotes, using a combination of competitive flow cytometry analysis and cell microscopy. This pharmacological evaluation suggested that the binding of HAB in promastigotes was representative of chalcone pharmacology in Leishmania, with certain exogenous chalcones exhibiting competitive inhibition (ca. 20-30%) towards HAB whereas non-chalconic inhibitors showed weak capacity (ca. 3-5%) to block the probe intracellular binding. However, this methodology was restricted by the strong toxicity of several competing chalcones at high concentration, in conjunction with the limited sensitivity of the HAB fluorophore. This advocates for further optimization of this undirect target detection strategy using pharmacophore-derived reversible fluorescent probes.

Intracellular pH Control by Membrane Transport in Mammalian Cells. Insights Into the Selective Advantages of Functional Redundancy

Intracellular pH is a vital parameter that is maintained close to neutrality in all mammalian cells and tissues and acidic in most intracellular compartments. After presenting the main techniques used for intracellular an vesicular pH measurements we will briefly recall the main molecular mechanisms that affect and regulate intracellular pH. Following this we will discuss the large functional redundancy found in the transporters of H⁺ or acid-base equivalents. For this purpose, we will use mathematical modeling to simulate cellular response to persistent and/or transient acidification, in the presence of different transporters, single or in combination. We will also test the presence or absence of intracellular buffering. This latter section will highlight how modeling can yield fundamental insight into deep biological questions such as the utility of functional redundancy in natural selection.

Methods Used to Investigate the Plasmodium falciparum Digestive Vacuole

Plasmodium falciparum malaria remains a global health problem as parasites continue to develop resistance to all antimalarials in use. Infection causes clinical symptoms during the intra-erythrocytic stage of the lifecycle where the parasite infects and replicates within red blood cells (RBC). During this stage, P. falciparum digests the main constituent of the RBC, hemoglobin, in a specialized acidic compartment termed the digestive vacuole (DV), a process essential for survival. Many therapeutics in use target one or multiple aspects of the DV, with chloroquine and its derivatives, as well as artemisinin, having mechanisms of action within this organelle. In order to better understand how current therapeutics and those under development target DV processes, techniques used to investigate the DV are paramount. This review outlines the involvement of the DV in therapeutics currently in use and focuses on the range of techniques that are currently utilized to study this organelle including microscopy, biochemical analysis, genetic approaches and metabolomic studies. Importantly, continued development and application of these techniques will aid in our understanding of the DV and in the development of new therapeutics or therapeutic partners for the future.

Electrocatalytic Reaction Driven Flow: Role of pH in Flow Reversal

Immobilized bimetallic structures generate fluid flow during electrocatalytic reactions with hydrogen peroxide, which is typically driven from the anodic metal to the cathodic metal similar to an electroosmotic flow. However, under low reactive regimes, the generated flow becomes fully reversed, which cannot be explained by the classical electroosmotic theory. This work aims at unraveling the origin and dynamics of this flow hysteresis through a combined experimental and numerical approach. The key electrocatalytic parameters that contribute to flow reversal are analyzed experimentally and numerically under low reactive regimes induced by bulk pH variations. The proton gradient that initiates chemomechanical actuation is probed with the use of fluorescence lifetime imaging. The fluid flow dynamics under reactive regimes are visualized by the use of particle tracking. Our numerical simulations elucidate the role of pH variations and additional ionic species (counterions) toward flow reversal. The combination of these techniques highlights the interplay between electrocatalytic and electrokinetic phenomena on the occurrence of flow reversal.

A zinc transporter, transmembrane protein 163, is critical for the biogenesis of platelet dense granules

Lysosome-related organelles (LROs) are a category of secretory organelles enriched with ions such as calcium, which are maintained by ion transporters or channels. Homeostasis of these ions is important for LRO biogenesis and secretion. Hermansky-Pudlak syndrome (HPS) is a recessive disorder with defects in multiple LROs, typically platelet dense granules (DGs) and melanosomes. However, the underlying mechanism of DG deficiency is largely unknown. Using quantitative proteomics, we identified a previously unreported platelet zinc transporter, transmembrane protein 163 (TMEM163), which was significantly reduced in BLOC-1 (Dtnbp1sdy and Pldnpa)-, BLOC-2 (Hps6ru)-, or AP-3 (Ap3b1pe)-deficient mice and HPS patients (HPS2, HPS3, HPS5, HPS6, or HPS9). We observed similar platelet DG defects and higher intracellular zinc accumulation in platelets of mice deficient in either TMEM163 or dysbindin (a BLOC-1 subunit). In addition, we discovered that BLOC-1 was required for the trafficking of TMEM163 to perinuclear DG and late endosome marker-positive compartments (likely DG precursors) in MEG-01 cells. Our results suggest that TMEM163 is critical for DG biogenesis and that BLOC-1 is required for the trafficking of TMEM163 to putative DG precursors. These new findings suggest that loss of TMEM163 function results in disruption of intracellular zinc homeostasis and provide insights into the pathogenesis of HPS or platelet storage pool deficiency.

Different Sensitivity of Macrophages to Phospholipidosis Induction by Amphiphilic Cationic Drugs

Phospholipidosis (PLD), the intracellular accumulation of phospholipids, is an adaptive response to toxic stimuli and serves as an important parameter in the biological assessment of compounds. Cationic amphiphilic drugs are the main inducers of PLD and may impair the function of alveolar macrophages. In vivo and in vitro models are used for PLD screening but the choice of the cellular model may be important because PLD develops in a cell- and species-specific manner. In this study, a panel of different staining (LysoSensor, Acridine Orange, Nile Red, HCS LipidTOX, LysoID) was evaluated in murine (DMBM-2, J774, RAW264.7) and human (THP-1, monocyte-derived macrophages from peripheral blood) cells to identify the most sensitive and easy to analyze staining method and to detect species-specific differences in the reaction pattern. Amiodarone and chloroquine served as inducers of PLD. High content screening was used to compare number, area, and intensity of the staining. Due to the fast staining protocol and the sensitivity of the detection, LysoID proved to be the most suitable dye of the testing. The lower induction of PLD by chloroquine reported in vivo was also seen in this study. THP-1 macrophages, followed by DMBM-2 cells, produced the most similar reaction pattern to human monocyte-derived macrophages.

α-Synuclein Overexpression Induces Lysosomal Dysfunction and Autophagy Impairment in Human Neuroblastoma SH-SY5Y

Although the etiology of Parkinson's disease (PD) is multifactorial, it has been linked to abnormal accumulation of α-synuclein (α-syn) in dopaminergic neurons, which could lead to dysfunctions on intracellular organelles, with potential neurodegeneration. Patients with familial early-onset PD frequently present mutation in the α-syn gene (SNCA), which encodes mutant α-syn forms, such as A30P and A53T, which potentially regulate Ca2+ unbalance. Here we investigated the effects of overexpression of wild-type α-syn (WT) and the mutant forms A30P and A53T, on modulation of lysosomal Ca2+ stores and further autophagy activation. We found that in α-syn-overexpressing cells, there was a decrease in Ca2+ released from endoplasmic reticulum (ER) which is related to the increase in lysosomal Ca2+ release, coupled to lysosomal pH alkalization. Interestingly, α-syn-overexpressing cells showed lower LAMP1 levels, and a disruption of lysosomal morphology and distribution, affecting autophagy. Interestingly, all these effects were more evident with A53T mutant isoform when compared to A30P and WT α-syn types, indicating that the pathogenic phenotype for PD is potentially related to impairment of α-syn degradation. Taken together, these events directly impact PD-related dysfunctions, being considered possible molecular targets for neuroprotection.

Responsive Metal Complex Probes for Time-Gated Luminescence Biosensing and Imaging

The development of reliable bioanalytical probes for selective and sensitive detection of particular analytes in biological systems is essential for better understanding the roles of the analytes in their native contexts. In the last two decades, luminescent metal complexes have greatly contributed to the development of such probes for biosensing and imaging due to their unique spectral and temporal properties, controllable cell membrane permeability, and cytotoxicity. Conjugating an analyte-activatable moiety to the metal complex luminophores allows the production of responsive metal complex probes for this analyte detection. Owing to their long-lifetime emissions, the responsive metal complex probes are accessible to the technique of time-gated luminescence (TGL) detection and imaging. With a delay time after pulsed excitation, the TGL technique allows for collection of only long-lived luminescence from responsive metal complex probes, while filtering out short-lived background autofluorescence, providing a background-free approach for the detection and imaging of the analyte at subcellular and/or molecular levels. Responsive metal complex probes, therefore, have emerged as complementary sensing and imaging tools of organic dye-based fluorescent probes for the in situ detection of analytes in complicated biological environments.In this Account, we describe the advances in the development of metal complex probes and their applications for TGL bioassays with particular focus on our efforts made in this field. We first introduce the photophysical/-chemical properties of luminescent metal complexes, including lanthanide (europium and terbium) and transition metal (ruthenium and iridium) complexes. The luminescence lifetimes (τ) of lanthanide and transition metal complexes are at micro/millisecond (μs/ms) and hundreds/thousands nanosecond (ns) levels, respectively. The emission lifetimes are significantly longer than the autofluorescence lifetime (τ < 10 ns) of biological samples. Such long-lived luminescence of these metal complexes enables our research on demonstrating responsive probes for background-free TGL detection of some reactive biomolecules, such as reactive oxygen/nitrogen species (ROS/RNS) and biothiols.We conclude this Account by outlining the future directions to further develop new generation responsive TGL probes for promoting their practical applications. The responsive TGL probes are expected to be translated for biomedical and/or (pre)clinical investigations of biomolecules in situ. Reversibility, lower toxicity, ability of excitation at longer wavelength, and potential to be translated are key criteria for the development of next-generation probes. We also anticipate that further development of responsive TGL probes will contribute to the bioassay in more challenging biological systems, such as plants that have significant higher background autofluorescence than animals.

Assays for Intracellular Cyclic Adenosine Monophosphate (cAMP) and Lysosomal Acidification

Cyclic adenosine monophosphate (3',5'-cAMP) is a multifunctional second messenger which controls extremely diverse and physiologically important biochemical pathways. Among its myriad roles, 3',5'-cAMP functions as an intracellular regulator of lysosomal pH, which is essential for the activity of acidic lysosomal enzymes. Defects in lysosomal acidification are attributed to many diseases like macular degeneration, Parkinson's, Alzheimer's, and cystic fibrosis. Strategic re-acidification of defective lysosomes by pharmacological increase of intracellular cAMP offers exciting therapeutic potential in these diseases. Modular assays for accurate assessment of intracellular cAMP and lysosomal pH are a critical component of this research. We describe label-free targeted metabolomics for quantitating intracellular cAMP and integrated assays for measuring lysosomal pH. These hybrid assays offer fast, unbiased information on intracellular cAMP concentrations and lysosomal pH that can be applied to many cell types and putative drug screening strategies.

A strain of the toxic dinoflagellate Karlodinium veneficum isolated from the East China Sea is an omnivorous phagotroph

Karlodinium veneficum is a cosmopolitan, toxic, and harmful algal bloom-forming dinoflagellate, of which the mixotrophy has been suggested to be a key factor in the formation and maintaining of HABs and thus deserves more intensive explorations. Here, we report an investigation on the phagotrophy of K. veneficum using a clonal culture isolated from the coastal water of East China Sea. We found K. veneficum is an omnivorous phagotroph feeding on both live and dead bodies/cells of a fish (Oryzias melastigma), brine shrimp (Artemia salina), rotifer (Brachionus plicatilis), co-cultivated microalgae Akashiwo sanguinea, Margalefidinium polykrikoides, Alexandrium leei, Rhodomonas salina, Isochrysis galbana, and its own species. Karlodinium veneficum extracted the cell contents of all species provided through either a peduncle (i.e. myzocytosis) or by engulfing the whole cell of small preys (i.e. phagotrophy sensu stricto). Karlodinium veneficum preferred to ingest non-motile or newly dead preys, no matter whether they were fish, zooplankton, or phytoplankton. Importantly, K. veneficum exhibited micropredation on animals with sizes much larger than itself (fish, rotifer, and brine shrimp), especially when they were injured or newly dead. The LysoSensor- and LysoTracker-stained lysosomes or/and phagolysosomes of K. veneficum increased when preys were added. Cannibalism in K. veneficum, i.e. a cell feeds on other unhealthy or dead cells of the same species, was observed as the first time in the study, which can help the growth and elongated maintaining of the population under nutrient deficiency (i.e. the culture maintained viable in culture plates without nutrient supplement up to a year). The growth rate of K. veneficum exhibited significant positive correlation with ingestion rate, which differed among prey species, and the highest growth rate was observed when feeding on R. salina. The ingest ability of K. veneficum was triggered by nutrient deficiency. In conclusion, the omnivorous mixotrophy is proposed to be a key autecological mechanism for K. veneficum to widen its ecological niche and succeed in forming a cosmopolitan distribution and frequent blooms.

Gold nanoclusters elicit homeostatic perturbations in glioblastoma cells and adaptive changes of lysosomes

Unique physicochemical features place gold nanoclusters at the forefront of nanotechnology for biological and biomedical applications. To date, information on the interactions of gold nanoclusters with biological macromolecules is limited and restricts their use in living cells. Methods: Our multidisciplinary study begins to fill the current knowledge gap by focusing on lysosomes and associated biological pathways in U251N human glioblastoma cells. We concentrated on lysosomes, because they are the intracellular destination for many nanoparticles, regulate cellular homeostasis and control cell survival. Results: Quantitative data presented here show that gold nanoclusters (with 15 and 25 gold atoms), surface-modified with glutathione or PEG, did not diminish cell viability at concentrations ≤1 µM. However, even at sublethal concentrations, gold nanoclusters modulated the abundance, positioning, pH and enzymatic activities of lysosomes. Gold nanoclusters also affected other aspects of cellular homeostasis. Specifically, they stimulated the transient nuclear accumulation of TFEB and Nrf2, transcription factors that promote lysosome biogenesis and stress responses. Moreover, gold nanoclusters also altered the formation of protein aggregates in the cytoplasm. The cellular responses elicited by gold nanoclusters were largely reversible within a 24-hour period. Conclusions: Taken together, this study explores the subcellular and molecular effects induced by gold nanoclusters and shows their effectiveness to regulate lysosome biology. Our results indicate that gold nanoclusters cause homeostatic perturbations without marked cell loss. Notably, cells adapt to the challenge inflicted by gold nanoclusters. These new insights provide a framework for the further development of gold nanocluster-based applications in biological sciences.

Carbonic anhydrase integrated into a multimarker approach for the detection of the stress status induced by pollution exposure in Mytilus galloprovincialis: A field case study

The work was addressed to study the sensitivity of the enzyme carbonic anhydrase (CA) to chemical pollution in the hepatopancreas of the bioindicator organism Mytilus galloprovincialis in the context of a multimarker approach in view of ecotoxicological biomonitoring and assessment application. The study was carried out by means of a transplanting experiment in the field, using caged organisms from an initial population exposed in the field in two areas of interest: Augusta-Melilli-Priolo, an heavy polluted industrial site (eastern Sicily, Italy), and Brucoli (eastern Sicily, Italy) an area not affected by any contamination and selected as a reference site. Mussels in Augusta presented a significant increase in the digestive gland CA activity and gene expression compared to the animals caged in the control site of Brucoli. The CA response in animals from the polluted site was paralleled by proliferation/increase in the size of lysosomes, as assessed by Lysosensor green charged cells, induction of metallothionein, up-regulation of hif-α (hypoxia-inducible factor), metabolic changes associated with protein metabolism, and changes in the condition factor. Biological responses data were integrated with information about sediment chemical analysis and metal residue concentration in animal soft tissues. In conclusion, obtained results highlighted the induction of CAs in the hepatopancreas of Mytilus galloprovincialis following to pollution exposure, and demonstrated its suitability to be integrated into a multimarker approach for the detection and characterization of the stress status induced by pollution exposure in this bioindicator organism.

SNX11 Identified as an Essential Host Factor for SFTS Virus Infection by CRISPR Knockout Screening

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a highly pathogenic tick-borne bunyavirus that causes lethal infectious disease and severe fever with thrombocytopenia syndrome (SFTS) in humans. The molecular mechanisms and host cellular factors required for SFTSV infection remain uncharacterized. Using a genome-wide CRISPR-based screening strategy, we identified a host cellular protein, sorting nexin 11 (SNX11) which is involved in the intracellular endosomal trafficking pathway, as an essential cell factor for SFTSV infection. An SNX11-KO HeLa cell line was established, and SFTSV replication was significantly reduced. The glycoproteins of SFTSV were detected and remained in later endosomal compartments but were not detectable in the endoplasmic reticulum (ER) or Golgi apparatus. pH values in the endosomal compartments of the SNX11-KO cells increased compared with the pH of normal HeLa cells, and lysosomal-associated membrane protein 1 (LAMP1) expression was significantly elevated in the SNX11-KO cells. Overall, these results indicated that penetration of SFTSV from the endolysosomes into the cytoplasm of host cells was blocked in the cells lacking SNX11. Our study for the first time provides insight into the important role of the SNX11 as an essential host factor in the intracellular trafficking and penetrating process of SFTSV infection via potential regulation of viral protein sorting, membrane fusion, and other endocytic machinery.

Fluorescence lifetime-based pH sensing by platinum nanoclusters

In this work, we report for the first time the application of ultrasmall Pt nanoclusters (Pt NCs) as a fluorescence-lifetime-based pH sensor. The fluorescence properties of our prepared Pt NCs show strong pH dependence, due to the change of the surface states of Pt NCs under alkaline/acidic conditions. Interestingly, both the fluorescence intensity and the fluorescence lifetime of Pt NCs exhibit a good linear relationship in the physiologically relevant pH range of 6.02-7.54. Our Pt NC-based pH sensor possesses many important features as an attractive sensor, including high anti-jamming capability, excellent stability and good reversibility. Moreover, the use of fluorescence lifetime as the optical readout signal rather than the intensity makes the present pH sensor more reliable in practical applications because the fluorescence lifetime is invariant to the probe concentration or changes in excitation conditions. Application of the Pt NC-based system for pH detection in real water samples and simulated intracellular environment samples has also been successfully demonstrated.

Phagocytosis of antibody-opsonized tumor cells leads to the formation of a discrete vacuolar compartment in macrophages

Despite the rapidly expanding use of antibody‐based therapeutics to treat cancer, knowledge of the cellular processes following phagocytosis of antibody‐opsonized tumor cells is limited. Here we report the formation of a phagosome‐associated vacuole that is observed in macrophages as these degradative compartments mature following phagocytosis of HER2‐positive cancer cells in the presence of the HER2‐specific antibody, trastuzumab. We demonstrate that this vacuole is a distinct organelle that is closely apposed to the phagosome. Furthermore, the size of the phagosome‐associated vacuole is increased by inhibition of the mTOR pathway. Collectively, the identification of this vacuolar compartment has implications for understanding the subcellular trafficking processes leading to the destruction of phagocytosed, antibody‐opsonized cancer cells by macrophages.

Fluorescent Probes Based on π-Conjugation Modulation between Hemicyanine and Coumarin Moieties for Ratiometric Detection of pH Changes in Live Cells with Visible and Near-infrared Channels

We report two ratiometric fluorescent probes based on π-conjugation modulation between coumarin and hemicyanine moieties for sensitive ratiometric detection of pH alterations in live cells by monitoring visible and near-infrared fluorescence changes. In a π-conjugation modulation strategy, a coumarin dye was conjugated to a near-infrared hemicyanine dye via a vinyl connection while lysosome-targeting morpholine ligand and o-phenylenediamine residue were introduced to the hemicyanine dye to form closed spirolactam ring structures in probes A and B, respectively. The probes show only visible fluorescence of the coumarin moiety under physiological and basic conditions because the hemicyanine moieties retain their closed spirolactam ring structures. However, decrease of pH to acidic condition causes spirolactam ring opening, and significantly enhances π-conjugation within the probes, thus generating new near-infrared fluorescence peaks of the hemicyanine at 755 nm and 740 nm for probes A and B, respectively. Moreover, the probes display ratiometric fluorescence response to pH with decreases of the coumarin fluorescence and increases of the hemicyanine fluorescence when pH changes from 7.4 to 2.5. The probes are fully capable of imaging pH changes in live cells with good ratiometric responses in visible and near-infrared channels, and effectively avoid fluorescence blind spots under neutral and basic pH conditions - an issue that typical intensity-based pH fluorescent probes run into. The probe design platform reported herein can be easily applied to prepare a variety of ratiometric fluorescent probes for detection of biological thiols, metal ions, reactive oxygen and nitrogen species by introducing appropriate functional groups to hemicyanine moiety.

Fluorescent Probes for Sensitive and Selective Detection of pH Changes in Live Cells in Visible and Near-infrared Channels

We report five fluorescent probes based on coumarin-hybridized fluorescent dyes with spirolactam ring structures (A-E) to detect pH changes in live cell by monitoring visible and near-infrared fluorescence changes. Under physiological or basic conditions, the fluorescent probes A, B, C, D and E preserve their spirolactam ring-closed forms and only display fluorescent peaks in the visible region corresponding to coumarin moieties at 497, 483, 498, 497 and 482 nm, respectively. However, at acidic pH, the rings of the spirolactam forms of the fluorescent probes A, B, C, D and E open up, generating new near-infrared fluorescence peaks at 711, 696, 707, 715, and 697 nm, respectively, through significantly extended π-conjugation to coumarin moieties of the fluorophores. The fluorescent probes B and E can be applied to visualize pH changes by monitoring visible as well as near-infrared fluorescence changes. This helps avoid fluorescence imaging blind spots at neutral or basic pH, which typical pH fluorescent probes encounter. The probes exhibit high sensitivity to pH changes, excellent photostability, low auto-fluorescence background and good cell membrane permeability.

Luminescent Probes for Sensitive Detection of pH Changes in Live Cells through Two Near-Infrared Luminescence Channels

Two water-soluble near-infrared luminescent probes, which possess both conventional intense Stokes fluorescence and unique single-photon frequency upconversion luminescence (FUCL), were developed for sensitive and selective detection of pH changes in live cells. The water solubility and biocompatibility of these probes were achieved by introducing mannose residues through 2,2'-(ethylenedioxy)diethylamine tethered spacers to a near-infrared conventional fluorescence (CF) and FUCL organic fluorophore. At a pH higher than 7.4, the probes have ring-closed spirocyclic lactam structures, thus are colorless and nonfluorescent. Nevertheless, they sensitively respond to acidic pH values, with a drastic structural change to ring-opened spirocyclic lactam forms, which cause significant absorbance increases at 714 nm. Correspondingly, their near-infrared CF and FUCL intensities at 740 nm are also significantly enhanced when excited by 690 and 808 nm, respectively. The probes hold a variety of advantages such as high sensitivity, excellent reversibility and selectivity to pH over metal ions, low cellular autofluorescence background interference, good cell membrane permeability and photostability, as well as low cytotoxicity. Our results have successfully proven that these probes can visualize intracellular lysosomal pH changes in live cells by monitoring both near-infrared CF and FUCL changes.

A novel FbFP-based biosensor toolbox for sensitive in vivo determination of intracellular pH

The intracellular pH is an important modulator of various bio(techno)logical processes such as enzymatic conversion of metabolites or transport across the cell membrane. Changes of intracellular pH due to altered proton distribution can thus cause dysfunction of cellular processes. Consequently, accurate monitoring of intracellular pH allows elucidating the pH-dependency of (patho)physiological and biotechnological processes. In this context, genetically encoded biosensors represent a powerful tool to determine intracellular pH values non-invasively and with high spatiotemporal resolution. We have constructed a toolbox of novel genetically encoded FRET-based pH biosensors (named Fluorescence Biosensors for pH or FluBpH) that utilizes the FMN-binding fluorescent protein EcFbFP as donor domain. In contrast to many fluorescent proteins of the GFP family, EcFbFP exhibits a remarkable tolerance towards acidic pH (pK_a∼3.2). To cover the broad range of physiologically relevant pH values, three EYFP variants exhibiting pK_a values of 5.7, 6.1 and 7.5 were used as pH-sensing FRET acceptor domains. The resulting biosensors FluBpH 5.7, FluBpH 6.1 and FluBpH 7.5 were calibrated in vitro and in vivo to accurately evaluate their pH indicator properties. To demonstrate the in vivo applicability of FluBpH, changes of intracellular pH were ratiometrically measured in E. coli cells during acid stress.

Cationic liposomes promote antigen cross-presentation in dendritic cells by alkalizing the lysosomal pH and limiting the degradation of antigens

Cationic liposomes (CLs) have been widely examined as vaccine delivery nanoparticles since they can form complexes with biomacromolecules, promote delivery of antigens and adjuvant molecules to antigen-presenting cells (APCs), and mediate cellular uptake of vaccine components. CLs are also known to trigger antigen cross-presentation - the process by which APCs internalize extracellular protein antigens, degrade them into minimal CD8⁺ T-cell epitopes, and present them in the context of major histocompatibility complex-I (MHC-I). However, the precise mechanisms behind CL-mediated induction of cross-presentation and cross-priming of CD8⁺ T-cells remain to be elucidated. In this study, we have developed two distinct CL systems and examined their impact on the lysosomal pH in dendritic cells (DCs), antigen degradation, and presentation of peptide:MHC-I complexes to antigen-specific CD8⁺ T-cells. To achieve this, we have used 3β-[N-(N',N'-dimethylaminoethane)-carbamoyl] cholesterol (DC-Chol) and 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) as the prototypical components of CLs with tertiary amine groups and compared the effect of CLs and anionic liposomes on lysosomal pH, antigen degradation, and cross-presentation by DCs. Our results showed that CLs, but not anionic liposomes, elevated the lysosomal pH in DCs and reduced antigen degradation, thereby promoting cross-presentation and cross-priming of CD8⁺ T-cell responses. These studies shed new light on CL-mediated cross-presentation and suggest that intracellular fate of vaccine components and subsequent immunological responses can be controlled by rational design of nanomaterials.

Lowering Endogenous Cathepsin D Abundance Results in Reactive Oxygen Species Accumulation and Cell Senescence

Cathepsin D is reportedly to be closely associated with tumor development, migration, and invasion, but its pathological mechanism is not fully elucidated. We aimed to evaluate phenotypic changes and molecular events in response to cathepsin D knockdown. Lowering endogenous cathepsin D abundance (CR) induced senescence in HeLa cells, leading to reduced rate of cell proliferation and impaired tumorigenesis in a mouse model. Quantitative proteomics revealed that compared with control cells (EV), the abundances of several typical lysosomal proteases were decreased in the lysosomal fraction in CR cells. We further showed that cathepsin D knockdown caused increased permeability of lysosomal membrane and reactive oxygen species accumulation in CR cells, and the scavenging of reactive oxygen species by antioxidant was able to rescue cell senescence. Despite the increased reactive oxygen species, the proteomic data suggested a global reduction of redox-related proteins in CR cells. Subsequent analysis indicated that the transcriptional activity of nuclear factor erythroid-related factor 2 (Nrf2), which regulates the expression of groups of antioxidant enzymes, was down-regulated by cathepsin D knockdown. Importantly, Nrf2 overexpression significantly reduced cell senescence. Although transient oxidative stress promoted the accumulation of Nrf2 in the nucleus, we showed that the Nrf2 protein exited nucleus if oxidative stress persisted. In addition, when cathepsin D was transiently knocked down, the cathepsin-related events followed a sequential order, including lysosomal leakage during the early stage, followed by oxidative stress augmentation, and ultimately Nrf2 down-regulation and senescence. Our results suggest the roles of cathepsin D in cancer cells in maintaining lysosomal integrity, redox balance, and Nrf2 activity, thus promoting tumorigenesis. The MS Data are available via ProteomeXchange with identifier PXD002844.

Determination of cell uptake pathways for tumor inhibitor lysyl oxidase propeptide

The lysyl oxidase propeptide (LOX-PP) is derived from pro-lysyl oxidase (Pro-LOX) by extracellular biosynthetic proteolysis. LOX-PP inhibits breast and prostate cancer xenograft tumor growth and has tumor suppressor activity. Although, several intracellular targets and molecular mechanisms of action of LOX-PP have been identified, LOX-PP uptake pathways have not been reported. Here we demonstrate that the major uptake pathway for recombinant LOX-PP (rLOX-PP) is PI3K-dependent macropinocytosis in PWR-1E, PC3, SCC9, MDA-MB-231 cell lines. A secondary pathway appears to be dynamin- and caveola dependent. The ionic properties of highly basic rLOX-PP provide buffering capacity at both high and low pHs. We suggest that the buffering capacity of rLOX-PP, which serves to limit endosomal acidification, sustains PI3K-dependent macropinocytosis in endosomes which in turn is likely to facilitate LOX-PP endosomal escape into the cytoplasm and its observed interactions with cytoplasmic targets and nuclear uptake.

Near-infrared fluorescent probes based on piperazine-functionalized BODIPY dyes for sensitive detection of lysosomal pH

Three acidotropic, near-infrared fluorescent probes based on piperazine-modified BODIPY dyes (A, B and C) have been developed for the sensitive and selective detection of lysosomal pH in living cells. Probes A and B display low solubilities in aqueous solutions, whereas probe C is highly water-soluble. The fluorescent responsive mechanism of these probes to lysosomal pH is based on intramolecular charge transfer (ICT) and potential photo-induced electron transfer from piperazine moieties at 3,5-positions to BODIPY cores in the near-infrared region. The sensitivity and selectivity of the probes to pH over metal ions have been investigated by spectroscopic analysis in aqueous solutions. The probes have low auto-fluorescence at physiological pH conditions, whereas their fluorescence intensities significantly increase when pH is shifted to an acidic condition. Furthermore, these three probes were successfully applied to the in vitro lysosome imaging inside normal endothelial and breast cancer cells.

Ultrasonically triggered drug delivery: breaking the barrier

The adverse side-effects of chemotherapy can be minimized by delivering the therapeutics in time and space to only the desired target site. Ultrasound offers one fairly non-invasive method of accomplishing such precise delivery because its energy can disrupt nanosized containers that are designed to sequester the drug until the ultrasonic event. Such containers include micelles, liposomes and solid nanoparticles. Conventional micelles and liposomes are less acoustically sensitive to ultrasound because the strongest forces associated with ultrasound are generated by gas-liquid interfaces, which both of these conventional constructs lack. Acoustically activated carriers often incorporate a gas phase, either actively as preformed bubbles, or passively such as taking advantage of dissolved gasses that form bubbles upon insonation. Newer concepts include using liquids that form gas when insonated. This review focuses on the ultrasonically activated delivery of therapeutics from micelles, liposomes and solid particles. In vitro and in vivo results are summarized and discussed. Novel structural concepts from micelles and liposomes are presented. Mechanisms of ultrasonically activated release are discussed. The future of ultrasound in drug delivery is envisioned.

Enhancing photoinduced electron transfer efficiency of fluorescent pH-probes with halogenated phenols

Photoinduced electron transfer (PET), which causes pH-dependent quenching of fluorescent dyes, is more effectively introduced by phenolic groups than by amino groups which have been much more commonly used so far. That is demonstrated by fluorescence measurements involving several classes of fluorophores. Electrochemical measurements show that PET in several amino-modified dyes is thermodynamically favorable, even though it was not experimentally found, underlining the importance of kinetic aspects to the process. Consequently, the attachment of phenolic groups allows for fast and simple preparation of a wide selection of fluorescent pH-probes with tailor-made spectral properties, sensitive ranges, and individual advantages, so that a large number of applications can be realized. Fluorophores carrying phenolic groups may also be used for sensing analytes other than pH or molecular switching and signaling.

HPS6 interacts with dynactin p150Glued to mediate retrograde trafficking and maturation of lysosomes

Hermansky-Pudlak syndrome 6 protein (HPS6) has originally been identified as a subunit of the BLOC-2 protein complex that is involved in the biogenesis of lysosome-related organelles. Here, we demonstrate that HPS6 directly interacts with the dynactin p150(Glued) subunit of the dynein-dynactin motor complex and acts as cargo adaptor for the retrograde motor to mediate the transport of lysosomes from the cell periphery to the perinuclear region. Small interfering RNA (siRNA)-mediated knockdown of HPS6 in HeLa cells not only partially blocks centripetal movement of lysosomes but also causes delay in lysosome-mediated protein degradation. Moreover, lysosomal acidification and degradative capacity, as well as fusion between late endosomes and/or multivesicular bodies and lysosomes are also impaired when HPS6 is depleted, suggesting that perinuclear positioning mediated by the dynein-dynactin motor complex is required for lysosome maturation and activity. Our results have uncovered a so-far-unknown specific role for HPS6 in the spatial distribution of the lysosomal compartment.

How chemistry supports cell biology: the chemical toolbox at your service

Chemical biology is a young and rapidly developing scientific field. In this field, chemistry is inspired by biology to create various tools to monitor and modulate biochemical and cell biological processes. Chemical contributions such as small-molecule inhibitors and activity-based probes (ABPs) can provide new and unique insights into previously unexplored cellular processes. This review provides an overview of recent breakthroughs in chemical biology that are likely to have a significant impact on cell biology. We also discuss the application of several chemical tools in cell biology research.

Aberrant autolysosomal regulation is linked to the induction of embryonic senescence: differential roles of Beclin 1 and p53 in vertebrate Spns1 deficiency

Spinster (Spin) in Drosophila or Spinster homolog 1 (Spns1) in vertebrates is a putative lysosomal H⁺-carbohydrate transporter, which functions at a late stage of autophagy. The Spin/Spns1 defect induces aberrant autolysosome formation that leads to embryonic senescence and accelerated aging symptoms, but little is known about the mechanisms leading to the pathogenesis in vivo. Beclin 1 and p53 are two pivotal tumor suppressors that are critically involved in the autophagic process and its regulation. Using zebrafish as a genetic model, we show that Beclin 1 suppression ameliorates Spns1 loss-mediated senescence as well as autophagic impairment, whereas unexpectedly p53 deficit exacerbates both of these characteristics. We demonstrate that ‘basal p53’ activity plays a certain protective role(s) against the Spns1 defect-induced senescence via suppressing autophagy, lysosomal biogenesis, and subsequent autolysosomal formation and maturation, and that p53 loss can counteract the effect of Beclin 1 suppression to rescue the Spns1 defect. By contrast, in response to DNA damage, ‘activated p53’ showed an apparent enhancement of the Spns1-deficient phenotype, by inducing both autophagy and apoptosis. Moreover, we found that a chemical and genetic blockage of lysosomal acidification and biogenesis mediated by the vacuolar-type H⁺-ATPase, as well as of subsequent autophagosome-lysosome fusion, prevents the appearance of the hallmarks caused by the Spns1 deficiency, irrespective of the basal p53 state. Thus, these results provide evidence that Spns1 operates during autophagy and senescence differentially with Beclin 1 and p53.

Spinster homolog 1 (Spns1) in vertebrates, as well as Spinster (Spin) in Drosophila, is a hypothetical lysosomal H⁺-carbohydrate transporter, which functions at a late stage of autophagy. The Spin/Spns1 defect induces aberrant autolysosome formation that leads to embryonic senescence and accelerated aging symptoms, while the molecular mechanisms of the pathogenesis are unknown in vivo. Using zebrafish, we show that Beclin 1 suppression ameliorates Spns1 loss-mediated senescence as well as autolysosomal impairment, whereas p53 deficit unexpectedly exacerbates these characteristics. We demonstrate that basal p53 activity has a certain protective role(s) against the Spns1 defect via suppressing autophagosome-lysosome fusion, while p53 activated by ultraviolet radiation amplifies the Spns1 deficit. In addition, we found that excessive lysosomal biogenesis and prolonged suboptimal acidification, modulated by v-ATPase, could be the primary reason for the appearance on the hallmarks of Spns1 deficiency. Our findings thus suggest that Spns1 is critically involved in lysosomal acidification and trafficking during autophagy, and differentially acts in a pathway with Beclin 1 and p53 in the regulation of senescence.

Lansoprazole induces apoptosis of breast cancer cells through inhibition of intracellular proton extrusion

The increased glycolysis and proton secretion in tumors is proposed to contribute to the proliferation and invasion of cancer cells during the process of tumorigenesis and metastasis. Here, treatment of human breast cancer cells with proton pump inhibitor (PPI) lansoprazole (LPZ) induces cell apoptosis in a dose-dependent manner. In the implantation of the MDA-MB-231 xenografts in nude mice, administration of LPZ significantly inhibits tumorigenesis and induces large-scale apopotosis of tumor cells. LPZ markedly inhibits intracellular proton extrusion, induces an increase in intracellular ATP level, lysosomal alkalinization and accumulation of reactive oxygen species (ROS) in breast cancer cells. The ROS scavenger N-acetyl-l-cysteine (NAC) and diphenyleneiodonium (DPI), a specific pharmacological inhibitor of NADPH oxidases (NOX), significantly abolish LPZ-induced ROS accumulation in breast cancer cells. Our results suggested that LPZ may be used as a new therapeutic drug for breast tumor.

pH-activatable near-infrared fluorescent probes for detection of lysosomal pH inside living cells

Four near-infrared fluorescent probes have been synthesized, characterized, and evaluated for detection of lysosomal pH inside living cells.

Synthesis of nitric oxide probes with fluorescence lifetime sensitivity

We present the rationale, synthesis and evaluation of the first activatable fluorescent probe that utilizes fluorescence lifetime change for detection of nitric oxide. The new probe DAP-LT1 features a near-infrared polymethine skeleton with a diaminobenzene functionality incorporated into the meso-position. The probe is partially quenched, and upon reaction with nitric oxide shows an increase in the fluorescence lifetime from 1.08 ns to 1.24 ns.

Glucosylceramide modulates endolysosomal pH in Gaucher disease

GlcCer accumulation causes Gaucher disease where GlcCer breakdown is inhibited due to a hereditary deficiency in glucocerebrosidase. Glycolipids are endocytosed and targeted to the Golgi apparatus in normal cells but in Gaucher disease they are mistargeted to lysosomes. To better understand the role of GlcCer in endocytic sorting RAW macrophages were treated with Conduritol B-epoxide to inhibit GlcCer breakdown. Lipid analysis found increases in GlcCer led to accumulation of both triacylglycerol and cholesterol consistent with increased lysosomal pH. Ratio imaging of macrophages using both acridine orange and lysosensor yellow/blue to measure endolysosomal pH revealed increases in Conduritol B-epoxide treated RAW macrophages and Gaucher patient lymphoblasts. Increased endolysosomal pH was restricted to Gaucher lymphoblasts as no significant increases in pH were seen in Fabry, Krabbe, Tay-Sachs and GM1-gangliosidosis lymphoblasts. Substrate reduction therapy utilises inhibitors of GlcCer synthase to reduce storage in Gaucher disease. The addition of inhibitors of GlcCer synthesis to RAW macrophages also led to increases in cholesterol and triacylglycerol and an endolysosomal pH increase of up to 1 pH unit. GlcCer modulation appears specific since glucosylsphingosine but not galactosylsphingosine reversed the effects of GlcCer depletion. Although no acute effects on glycolipid trafficking were observed using bafilomycin A the results are consistent with a multistep model whereby increases in pH lead to altered trafficking via cholesterol accumulation. GlcCer modulates endolysosomal pH in lymphocytes suggesting an important role in normal lysosomes which may be disrupted in Gaucher disease.