Regulation of intracellular pH mediates Bax activation in HeLa cells treated with staurosporine or tumor necrosis factor-alpha

Monitoring the Intracellular pH and Metabolic State of Cancer Cells in Response to Chemotherapy Using a Combination of Phosphorescence Lifetime Imaging Microscopy and Fluorescence Lifetime Imaging Microscopy

The extracellular matrix (ECM), in which collagen is the most abundant protein, impacts many aspects of tumor physiology, including cellular metabolism and intracellular pH (pHi), as well as the efficacy of chemotherapy. Meanwhile, the role of collagen in differential cell responses to treatment within heterogeneous tumor environments remains poorly investigated. In the present study, we simultaneously monitored the changes in pHi and metabolism in living colorectal cancer cells in vitro upon treatment with a chemotherapeutic combination, FOLFOX (5-fluorouracil, oxaliplatin and leucovorin). The pHi was followed using the new pH-sensitive probe BC-Ga-Ir, working in the mode of phosphorescence lifetime imaging (PLIM), and metabolism was assessed from the autofluorescence of the metabolic cofactor NAD(P)H using fluorescence lifetime imaging (FLIM) with a two-photon laser scanning microscope. To model the ECM, 3D collagen-based hydrogels were used, and comparisons with conventional monolayer cells were made. It was found that FOLFOX treatment caused an early temporal intracellular acidification (reduction in pHi), followed by a shift to more alkaline values, and changed cellular metabolism to a more oxidative state. The presence of unstructured collagen markedly reduced the cytotoxic effects of FOLFOX, and delayed and diminished the pHi and metabolic responses. These results support the observation that collagen is a factor in the heterogeneous response of cancer cells to chemotherapy and a powerful regulator of their metabolic behavior.

Kinetic study of NADPH activation using ubiquinone-rhodol fluorescent probe and an IrIII-complex promoter at the cell interior

Nicotine adenine dinucleotide derivatives NADH and NADPH are intimately involved in energy and electron transport within cells. The fluorescent ubiquinone-rhodol (Q-Rh) probe is used for NADPH activation monitoring. Q-Rh reacts with NADPH yielding its quenched hydroquinone-rhodol (H2Q-Rh) form with concurrent NADPH activation (i.e. NADP+ formation). NADPH activation can be enhanced by the addition of an IrIII-complex (i.e. [(η5-C5Me5)Ir(phen)(H2O)]2+) as a promoter. The rate of the Q-Rh fluorescence quenching process is proportional to the NADPH activation rate, which can be used to monitor NADPH. Experiments were performed in phosphate-buffered saline (PBS) solution and on HeLa cell cultures to analyze the kinetics of Q-Rh reduction and the influence of the IrIII-complex promoter on the activation of NADPH (in PBS) and of other intracellular reducing agents (in HeLa cells). There is a substantial increase in Q-Rh reduction rate inside HeLa cells especially after the addition of IrIII-complex promoter. This increase is partly due to a leakage process (caused by IrIII-complex-induced downstream processes which result in cell membrane disintegration) but also involves the nonspecific activation of other intracellular reducing agents, including NADH, FADH2, FMNH2 or GSH. In the presence only of Q-Rh, the activation rate of intracellular reducing agents is 2 to 8 times faster in HeLa cells than in PBS solution. When both Q-Rh and IrIII-complex are present, the rate of the IrIII-complex catalyzed reduction reaction is 7 to 23 times more rapid in HeLa cells. Concentration- and time-dependent fluorescence attenuation of Q-Rh with third-order reaction kinetics (reasonably approximated as pseudo-first-order in Q-Rh) has been observed and modelled. This reaction and its kinetics present an example of "bioparallel chemistry", where the activation of a molecule can trigger a unique chemical process. This approach stands in contrast to the conventional concept of "bioorthogonal chemistry", which refers to chemical reactions that occur without disrupting native biological processes.

Recent Advances in Excimer-Based Fluorescence Probes for Biological Applications

The fluorescent probe is a powerful tool for biological sensing and optical imaging, which can directly display analytes at the molecular level. It provides not only direct visualization of biological structures and processes, but also the capability of drug delivery systems regarding the target therapy. Conventional fluorescent probes are mainly based on monomer emission which has two distinguishing shortcomings in practice: small Stokes shifts and short lifetimes. Compared with monomer-based emission, excimer-based fluorescent probes have large Stokes shifts and long lifetimes which benefit biological applications. Recent progress in excimer-based fluorescent sensors (organic small molecules only) for biological applications are highlighted in this review, including materials and mechanisms as well as their representative applications. The progress suggests that excimer-based fluorescent probes have advantages and potential for bioanalytical applications.

A water-dependent reversible photoacidity strategy for cancer treatment

In the reported mechanisms of reversible photoacidity, protons were dissociated from compounds which contained hydroxyl, indazole or formed hydroxyl via intramolecular hydrogen abstraction under irradiation. Herein, a water-dependent reversible photoacidity (W-RPA) mechanism mediated by a thiadiazoloquinoxaline compound (TQs-Th-PEG5) has been found, in which the proton is not dissociated from TQs-Th-PEG5 itself but from a water locked by TQs-Th-PEG5 under the irradiation of a 660 nm laser. After turning off the laser, the produced acid will disappear quickly. This process is repeatable with no consumption of TQs-Th-PEG5. More importantly, water is indispensable. Furthermore, it is confirmed that there is no other element involved in the process except TQs-Th-PEG5, light and water. Excitingly, W-RPA therapy mediated by TQs-Th-PEG5 nanoparticle exhibits remarkable antitumor effect both in vitro and in vivo, especially in hypoxic tumors with diameter larger than 10 mm owing to its oxygen-independent feature. This study not only discovers a W-RPA mechanism but also provides a novel phototherapy strategy for cancer treatment.

Phototriggered Apoptotic Cell Death (PTA) Using the Light-Driven Outward Proton Pump Rhodopsin Archaerhodopsin-3

Apoptosis is a type of programmed cell death that commonly occurs in multicellular organisms including humans and that is essential to eliminate unnecessary cells to keep organisms healthy. Indeed, inappropriate apoptosis leads to various diseases such as cancer and autoimmune disease. Here, we developed an optical method to regulate apoptotic cell death by controlling the intracellular pH with outward or inward proton pump rhodopsins, Archaerhodopsin-3 (AR3) or Rubricoccus marinas xenorhodopsin (RmXeR), respectively. The alkalization-induced shrinking of human HeLa cells cultured at pH 9.0 was significantly accelerated or decelerated by light-activated AR3 or RmXeR, respectively, implying the contribution of intracellular alkalization to the cell death. The light-activated AR3 induced cell shrinking at a physiologically neutral pH 7.4 and biochemical analysis revealed that the intracellular alkalization caused by AR3 triggered the mitochondrial apoptotic signaling pathway, which resulted in cell death accompanied by morphological changes. Phototriggered apoptosis (PTA) was also observed for other human cell lines, SH-SY5Y and A549 cells, implying its general applicability. We then used the PTA method with the nematode Caenorhabditis elegans as a model for living animals. Irradiation of transgenic worms expressing AR3 in chemosensing amphid sensory neurons significantly decreased their chemotaxis responses, which suggests that AR3 induced the cell death of amphid sensory neurons and the depression of chemotaxis responses. Thus, the PTA method has a high applicability both in vivo and in vitro, which suggests its potential as an optogenetic tool to selectively eliminate target cells with a high spatiotemporal resolution.

A ratiometric pH probe for acidification tracking in dysfunctional mitochondria and tumour tissue in vivo

With an ideal pKa (7.4) for mitochondrial pH monitoring, CouDa could immobilize in mitochondria independent of MMP. Acidification tracking was realized in dysfunctional mitochondria and tumour tissue.

Unsymmetrical pentamethine cyanines for visualizing physiological acidities from the whole-animal to the cellular scale with pH-responsive deep-red fluorescence

Unsymmetrical pentamethine cyanine fluorophores were developed and used to visualize physiological acidities from the whole-animal to the cellular scale with pH-responsive deep-red fluorescence.

AND-Logic Based Fluorescent Probe for Selective Detection of Lysosomal Bisulfite in Living Cells

Sulfur dioxide (SO₂) plays significant roles in regulating cell apotosis and inflammation. However, there are complex interactions between small biomolecules in cells, and the identification of these coexisting biomarkers remains a challenge. Herein, we report an AND logic gate based fluorescent probe (NY-Lyso), operating by responding to pH differences between organelles in cell and selectively reacting with bisulfite (HSO₃^-). This approach allows the fluorescence of the probe to remain silent under neutral or alkaline conditions, notably, is activated by costimulation of lower pH and bisulfite. Furthermore, it was confirmed to be biocompatible and could be employed to monitor HSO₃^- in lysosomes of living cells. The proposed method demonstrated more practical and outstanding capabilities in targeted and real-time monitoring, providing an effective optical tool for biomarker sensing.

Cellular stress is a prerequisite for glucose-induced mitochondrial matrix alkalinization in pancreatic β-cells

Changes in mitochondrial and cytosolic pH alter the chemical gradient across the inner mitochondrial membrane. The proton chemical gradient contributes to mitochondrial ATP synthesis as well as the uptake and release of metabolites and ions from the organelle. Here mitochondrial pH and ΔpH were studied for the first time in human pancreatic β-cells. Adenoviruses were used for rat insulin promoter dependent expression of the pH sensor SypHer targeted to either the mitochondrial matrix or the cytosol. The matrix pH in resting human β-cells is low (pH = 7.50 ± SD 0.17) compared to published values in other cell types. Consequently, the ΔpH of β-cells mitochondria is small. Glucose stimulation consistently resulted in acidification of the matrix pH in INS-1E insulinoma cells and β-cells in intact human islets or islet monolayer cultures. We registered acidification with similar kinetics but of slightly smaller amplitude in the cytosol of β-cells, thus glucose stimulation further reduced the ΔpH. Infection of human islets with high levels of adenoviruses caused the mitochondrial pH to increase. The apoptosis inducer and broad-spectrum kinase inhibitor staurosporine had similar effects on pH homeostasis. Although staurosporine alone does not affect the mitochondrial pH, glucose slightly increases the matrix pH of staurosporine treated cells. These two cellular stressors alter the normal mitochondrial pH response to glucose in pancreatic β-cells.

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

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

A Zero Cross-Talk Ratiometric Two-Photon Probe for Imaging of Acid pH in Living Cells and Tissues and Early Detection of Tumor in Mouse Model

Acid-base disorders disrupt proper cellular functions, which are associated with diverse diseases. Development of highly sensitive pH probes being capable of detecting and monitoring the minor changes of pH environment in living systems is of considerable interest to diagnose disease as well as investigate biochemical processes in vivo. We report herein two novel high-resolution ratiometric two-photon (TP) fluorescent probes, namely, PSIOH and PSIBOH derived from carbazole-oxazolidine π-conjugated system for effective sensing and monitoring acid pH in a biological system. Remarkably, PSIOH exhibited the largest emission shift of ∼169 nm from 435 to 604 nm upon pH changing from basic to acidic with an ideal p K_a value of 6.6 within a linear pH variation range of 6.2-7.0, which is highly desirable for high-resolution tracking and imaging the minor fluctuation of pH in live cells and tissues. PSIOH also exhibits high pH sensitivity, excellent photostability, and reversibility as well as low cytotoxicity. More importantly, this probe was successfully applied to (i) sense and visualize the pH alteration in HeLa cells caused by various types of exogenous stimulation and (ii) detect and differentiate cancer and tumors in liver tissues and a mouse model, realizing its practical in vitro and in vivo applications.

Identification of Chlamydia pneumoniae candidate genes that interact with human apoptotic factor caspase-9

Chlamydia pneumoniae is an obligate intracellular pathogen responsible for respiratory diseases, including pneumonia and bronchitis, and is highly involved in chronic diseases, including atherosclerosis, asthma, and Alzheimer's disease. We previously showed that the host apoptotic factor caspase-9 played a crucial role for chlamydial multiplication and host apoptosis inhibition by chlamydial infection. To identify chlamydial genes interacting with human caspase-9, yeast two-hybrid screening was performed and 5 chlamydial genes, including Cpj0838 and pmpG were isolated from the C. pneumoniae genomic library. Pull-down experiments showed that caspase-9 physically bound to the Cpj0838 product and chlamydial cells, which contain PmpG proteins. This study could provide a clue to understanding host-Chlamydia interactions, especially the apoptosis repression by Chlamydia infection.

Extracellular Acidic pH Activates the Sterol Regulatory Element-Binding Protein 2 to Promote Tumor Progression

Conditions of the tumor microenvironment, such as hypoxia and nutrient starvation, play critical roles in cancer progression. However, the role of acidic extracellular pH in cancer progression is not studied as extensively as that of hypoxia. Here, we show that extracellular acidic pH (pH 6.8) triggered activation of sterol regulatory element-binding protein 2 (SREBP2) by stimulating nuclear translocation and promoter binding to its targets, along with intracellular acidification. Interestingly, inhibition of SREBP2, but not SREBP1, suppressed the upregulation of low pH-induced cholesterol biosynthesis-related genes. Moreover, acyl-CoA synthetase short-chain family member 2 (ACSS2), a direct SREBP2 target, provided a growth advantage to cancer cells under acidic pH. Furthermore, acidic pH-responsive SREBP2 target genes were associated with reduced overall survival of cancer patients. Thus, our findings show that SREBP2 is a key transcriptional regulator of metabolic genes and progression of cancer cells, partly in response to extracellular acidification.

Dual-Responsive Molecular Probe for Tumor Targeted Imaging and Photodynamic Therapy

The precision oncology significantly relies on the development of multifunctional agents to integrate tumor targeting, imaging and therapeutics. In this study, a first small-molecule theranostic probe, RhoSSCy is constructed by conjugating 5'-carboxyrhodamines (Rho) and heptamethine cyanine IR765 (Cy) using a reducible disulfide linker and pH tunable amino-group to realize thiols/pH dual sensing. In vitro experiments verify that RhoSSCy is highly sensitive for quantitative analysis and imaging intracellular pH gradient and biothiols. Furthermore, RhoSSCy shows superb tumor targeted dual-modal imaging via near-infrared fluorescence (NIRF) and photoacoustic (PA). Importantly, RhoSSCy also induces strongly reactive oxygen species for tumor photodynamic therapy (PDT) with robust antitumor activity both in vitro and in vivo. Such versatile small-molecule theranostic probe may be promising for tumor targeted imaging and precision therapy.

Focal photodynamic intracellular acidification as a cancer therapeutic

Cancer cells utilize an array of proton transporters to regulate intra- and extracellular pH to thrive in hypoxic conditions, and to increase tumor growth and metastasis. Efforts to target many of the transporters involved in cancer cell pH regulation have yielded promising results, however, many productive attempts to disrupt pH regulation appear to be non-specific to cancer cells, and more effective in some cancer cells than others. Following a review of the status of photodynamic cancer therapy, a novel light-activated process is presented which creates very focal, rapid, and significant decreases in only intracellular pH (pHi), leading to cell death. The light-activation of the H⁺ carrier, nitrobenzaldehyde, has been effective at initiating pH-induced apoptosis in non-cancerous and numerous cancerous cell lines in vitro, to include breast, prostate, and pancreatic cancers. Also, this intracellular acidification technique caused significant reductions in tumor growth rate and enhanced survival in mice bearing triple negative breast cancer tumors. The efficacy of an NBA-upconverting nanoparticle to kill breast cancer cells in vitro is described, as well as a discussion of the potential intracellular mechanisms underlying the pH-induced apoptosis.

JNK3 phosphorylates Bax protein and induces ability to form pore on bilayer lipid membrane

Bax is a pro-apoptotic cytosolic protein. In this work native (unphosphorylated) and JNK3 phosphorylated Bax proteins are studied on artificial bilayer membranes for pore formation. Phosphorylated Bax formed pore on the bilayer lipid membrane whereas native one does not. In cells undergoing apoptosis the pore formed by the phosphorylated Bax could be important in cytochrome c release from the mitochondrial intermembrane space to the cytosol. The low conductance (1.5 nS) of the open state of the phosphorylated Bax pore corresponds to pore diameter of 0.9 nm which is small to release cytochrome c (∼3.4 nm). We hypothesized that JNK3 phosphorylated Bax protein can form bigger pores after forming complexes with other mitochondrial proteins like VDAC, t-Bid etc. to release cytochrome c.

Relationship between intracellular pH, metabolic co-factors and caspase-3 activation in cancer cells during apoptosis

A complex cascade of molecular events occurs in apoptotic cells but cell-to-cell variability significantly complicates determination of the order and interconnections between different processes. For better understanding of the mechanisms of programmed cell death, dynamic simultaneous registration of several parameters is required. In this paper we used multiparameter fluorescence microscopy to analyze energy metabolism, intracellular pH and caspase-3 activation in living cancer cells in vitro during staurosporine-induced apoptosis. We performed metabolic imaging of two co-factors, NAD(P)H and FAD, and used the genetically encoded pH-indicator SypHer1 and the FRET-based sensor for caspase-3 activity, mKate2-DEVD-iRFP, to visualize these parameters by confocal fluorescence microscopy and two-photon fluorescence lifetime imaging microscopy. The correlation between energy metabolism, intracellular pH and caspase-3 activation and their dynamic changes were studied in CT26 cancer cells during apoptosis. Induction of apoptosis was accompanied by a switch to oxidative phosphorylation, cytosol acidification and caspase-3 activation. We showed that alterations in cytosolic pH and the activation of oxidative phosphorylation are relatively early events associated with the induction of apoptosis.

A fluorescent pH probe for acidic organelles in living cells

The molecular design of pH sensor ADA is based on combining photoinduced electron transfer (PET) and intramolecular charge transfer (ICT). The fluorescent emission response against a pH value is suitable for probing acidic organelles in living cells.

The inhibition of voltage-gated H+ channel (HVCN1) induces acidification of leukemic Jurkat T cells promoting cell death by apoptosis

Cellular energetic deregulation is widely known to produce an overproduction of acidic species in cancer cells. This acid overload must be counterbalanced with a high rate of H⁺ extrusion to maintain cell viability. In this sense, many H⁺ transporters have been reported to be crucial for cell survival and proposed as antineoplastic target. By the way, voltage-gated proton channels (Hv1) mediate highly selective H⁺ outward currents, capable to compensate acid burden in brief periods of time. This structure is canonically described acting as NADPH oxidase counterbalance in reactive oxygen species production. In this work, we show, for the first time in a oncohematologic cell line, that inhibition of Hv1 channels by Zn²⁺ and the more selective blocker 2-(6-chloro-1H-benzimidazol-2-yl)guanidine (ClGBI) progressively decreases intracellular pH in resting conditions. This acidification is evident minutes after blockade and progresses under prolonged exposure (2, 17, and 48 h), and we firstly demonstrate that this is followed by cell death through apoptosis (annexin V binding). Altogether, these results contribute strong evidence that this channel might be a new therapeutic target in cancer.

Design principles of spectroscopic probes for biological applications

Spectroscopic (chromogenic, fluorescent, or chemiluminescent) probes have been widely used in many fields due to their high sensitivity and unrivaled spatiotemporal resolution. This area is an old one but always full of activity, because the rapid development of science and technology requires not only new probes for specific purposes (e.g., subcellular imaging) but also the update of current probes with more satisfactory properties. Based on our experiences and including existing knowledge, in this mini-review we briefly discuss the design strategies, response modes, and bioapplications of small molecular spectroscopic probes, in particular their advantages and disadvantages as well as possible research trends, which may be helpful to those who are interested in this continually growing research area.

In vivo observation of the pH alternation in mitochondria for various external stimuli

The pH of mitochondria (pHm) has a close relationship with many biological processes. Here we developed a new indicator Mito-pH-1 for the ratiometric fluorescence detection of the mitochondria pH value, which has excellent tolerance to environmental change. And Mito-pH-1 has been used for the first time to monitor the change of pHm under temperature and H2O2 stimuli in living cells.

Functionalized Carbon Quantum Dots with Dopamine for Tyrosinase Activity Monitoring and Inhibitor Screening: In Vitro and Intracellular Investigation

Sensitive assay of tyrosinase (TYR) activity is in urgent demand for both fundamental research and practical application, but the exploration of functional materials with good biocompatibility for its activity evaluation at the intracellular level is still challenging until now. In this work, we develop a convenient and real-time assay with high sensitivity for TYR activity/level monitoring and its inhibitor screening based on biocompatible dopamine functionalized carbon quantum dots (Dopa-CQDs). Dopamine with redox property was functionalized on the surface of carbon quantum dots to construct a Dopa-CQDs conjugate with strong bluish green fluorescence. When the dopamine moiety in Dopa-CQDs conjugate was oxidized to a dopaquinone derivative under specific catalysis of TYR, an intraparticle photoinduced electron transfer (PET) process between CQDs and dopaquinone moiety took place, and then the fluorescence of the conjugate could be quenched simultaneously. Quantitative evaluation of TYR activity was established in terms of the relationship between fluorescence quenching efficiency and TYR activity. The assay covered a broad linear range of up to 800 U/L with a low detection limit of 7.0 U/L. Arbutin, a typical inhibitor of TYR, was chosen as an example to assess its function of inhibitor screening, and positive results were observed that fluorescence quenching extent of the probe was reduced in the presence of arbutin. It is also demonstrated that Dopa-CQD conjugate possesses excellent biocompatibility, and can sensitively monitor intracellular tyrosinase level in melanoma cells and intracellular pH changes in living cells, which provides great potential in application of TYR/pH-associated disease monitoring and medical diagnostics.

Nanoprobing the acidification process during intracellular uptake and trafficking

Many nanoparticular drug delivery approaches rely on a detailed knowledge of the acidification process during intracellular trafficking of endocytosed nanoparticles (NPs). Therefore we produced a nanoparticular pH sensor composed of the fluorescent pH-sensitive dual wavelength dye carboxy seminaphthorhodafluor-1 (carboxy SNARF-1) coupled to the surface of amino-functionalized polystyrene NPs (SNARF-1-NP). By applying a calibration fit function to confocal laser scanning microscopy (CLSM) images, local pH values were determined. The acidification and ripening process of endo/lysosomal compartments containing nanoparticles was followed over time and was found to progress up to 6h to reach an equilibrium pH distribution (maximum pH5.2 [±0.2]). The SNARF-1-NP localization in endo/lysosomal compartments was confirmed by transmission electron microscopy (TEM) and quantitative co-localization analysis with fluorescent endolysosomal marker Rab-proteins by confocal laser scanning microscopy (CLSM). The herein described nanoparticular pH-sensor is a versatile tool to monitor dynamic pH processes inside the endolysosomal compartments.

FROM THE CLINICAL EDITOR

In this interesting article, the authors elegantly designed a nanoparticular pH sensor with fluorescence probe with the capability to measure intracellular and intravesicular pH changes. The application of this method would enable the further understanding of nanoparticle uptake and intracellular physiology.

A smart "sense-act-treat" system: combining a ratiometric pH sensor with a near infrared therapeutic gold nanocage

Herein, we design a "sense-act-treat" system via the combination of a ratiometric pH sensor with a therapeutic gold nanocage. Our design could "sense" the tumor through two-state switching of fluorescence and further provide chemotherapy and hyperthermia for "treating" the tumor, showing the potential for future biomedical applications.

Polypeptide micelles with dual pH activatable dyes for sensing cells and cancer imaging

pH is an important control parameter for maintenance of cell viability and tissue functions. pH monitoring provides valuable information on cell metabolic processes and the living environment. In this study, we prepared dual pH-sensitive, fluorescent dye-loaded polypeptide nanoparticles (DPNs) for ratiometric sensing of pH changes in living cells. DPNs contain two types of dyes: N-(rhodamine B) lactam cystamine (RBLC), an acid activatable fluorescent dye with increased fluorescence in an acidic environment, and fluorescein isothiocyanate (FITC), a base activatable fluorescent dye with enhanced fluorescence in an alkaline environment. Hence, DPNs exhibited a dual response signal with strong red fluorescence and weak green fluorescence under acidic conditions; in contrast, they showed strong green fluorescence and almost no red fluorescence under alkaline and neutral conditions. The favorable inverse pH responses of the two fluorescent dyes resulted in ratiometric pH determination for DPNs with an optimized pH-sensitive range of pH 4.5-7.5. Quantitative analysis of the intracellular pH of intact MCF-7 cells has been successfully demonstrated with our nanosensor. Moreover, single acid activatable fluorescent dye doped polypeptide nanoparticles that only contained RBLC can distinguish tumor tissue from normal tissue by monitoring the acidic extracellular environment.

SIRT3 protects from hypoxia and staurosporine-mediated cell death by maintaining mitochondrial membrane potential and intracellular pH

Mitochondrial sirtuin 3 (SIRT3) mediates cellular resistance toward various forms of stress. Here, we show that in mammalian cells subjected to hypoxia and staurosporine treatment SIRT3 prevents loss of mitochondrial membrane potential (ΔΨ(mt)), intracellular acidification and reactive oxygen species accumulation. Our results indicate that: (i) SIRT3 inhibits mitochondrial permeability transition and loss of membrane potential by preventing HKII binding to the mitochondria, (ii) SIRT3 increases catalytic activity of the mitochondrial carbonic anhydrase VB, thereby preventing intracellular acidification, Bax activation and apoptotic cell death. In conclusion we propose that, in mammalian cells, SIRT3 has a central role in connecting changes in ΔΨ(mt), intracellular pH and mitochondrial-regulated apoptotic pathways.

Intracellular pH sensing using autofluorescence lifetime microscopy

Fluorescence lifetime images of reduced nicotinamide adenine dinucleotide (NADH) that is a key cofactor in cellular metabolism were obtained in a cell at various values of intracellular pH. The average fluorescence lifetime of NADH is found to become shorter monotonically with increasing pH, indicating that pH in a single cell can be determined by fluorescence lifetime imaging of NADH without adding exogenous fluorescent probes. The magnitude of the pH-induced lifetime change is higher in cells than that in buffer solution. The fluorescence lifetime of NADH is not uniform inside a cell; the fluorescence lifetime of nuclear NADH is shorter than that of mitochondrial NADH at each pH, and the magnitude of the pH-induced change is larger in nuclei than in other areas. The local electric field effect on the fluorescence lifetime is discussed since this effect may be one of the strong possibilities for the nonuniformity of the autofluorescence lifetime of NADH in cells.

Bax and calpain mediate excitotoxic oligodendrocyte death induced by activation of both AMPA and kainate receptors

Sustained activation of AMPA and kainate receptors in rat oligodendrocytes induces cytosolic calcium overload, mitochondrial depolarization, and an increase of reactive oxygen species, resulting in cell death. Here, we provide evidence that Bax, a proapoptotic member of the Bcl-2 protein family, is involved in excitotoxic apoptotic death of oligodendrocytes and that calpain mediates Bax activation. Cultured Bax(-/-) oligodendrocytes, obtained from the optic nerve of Bax knock-out mice, were resistant to AMPA and kainate receptor-mediated insults. In turn, both mitochondrial calcium uptake and mitochondrial alterations after excitotoxic insults were diminished in Bax-null oligodendrocytes. Moreover, pretreatment with furosemide, a blocker of Bax translocation to mitochondria, significantly protected rat and mouse oligodendrocytes from AMPA- and kainate-induced damage; in contrast, bongkrekic acid, a blocker of the mitochondrial permeability transition pore, had no effect. Finally, we analyzed the participation of calpain, which cleaves Bax and is activated by AMPA and kainate, in oligodendrocyte death. Pretreatment with 3-(4-iodophenyl)-2-mercapto-(Z)-2-propenoic acid (PD150606), a broad cell-permeable calpain inhibitor, and two additional calpain inhibitors diminished Bax activation, inhibited its translocation to mitochondria, and attenuated all apoptotic events resulting from excitotoxic insults to rat oligodendrocytes. Together, these results indicate that Bax and calpain are essential intermediaries of the mitochondria-dependent death pathway, triggered by AMPA and kainate receptor activation in oligodendrocytes.

Lysosomal positioning coordinates cellular nutrient responses

Mammalian target of rapamycin (mTOR) signalling and macroautophagy (henceforth autophagy) regulate numerous pathological and physiological processes including cellular responses to altered nutrient levels. However, the mechanisms regulating mTOR and autophagy remain incompletely understood. Lysosomes are dynamic intracellular organelles 1, 2 intimately involved both in the activation of mTOR complex 1 (mTORC1) signalling and in degrading autophagic substrates 3-8. Here we report that lysosomal positioning coordinates anabolic and catabolic responses to changes in nutrient availability by orchestrating early plasma membrane signalling events, mTORC1 signalling and autophagy. Activation of mTORC1 by nutrients correlates with its presence on peripheral lysosomes that are physically close to the upstream signalling modules, while starvation causes perinuclear clustering of lysosomes, driven by changes in intracellular pH (pH_i). Lysosomal positioning regulates mTORC1 signalling, which, in turn, influences autophagosome formation. Lysosome positioning also influences autophagosome-lysosome fusion rates, and thus controls autophagic flux by acting both at the initiation and termination stages of the process. Our findings provide a fundamental physiological role for the dynamic state of lysosomal positioning in cells as a coordinator of mTORC1 signalling with autophagic flux.

Non-canonical β-catenin degradation mediates reactive oxygen species-induced epidermal cell death

β-catenin is constantly degraded through the ubiquitin-proteasomal pathway. We here report that a different type of β-catenin degradation is causally involved in epidermal cell death. We observed that reactive oxygen species (ROS) caused β-catenin degradation in the epidermal cells through a caspase-dependent mechanism, which results in disruption of cell adhesion. Disruption of cell adhesion increased ROS and activated caspases. Upregulation of the intact β-catenin blocked ROS accumulation and caspase activation. These results indicate that a feed-forward loop consisting of ROS, caspases activation and β-catenin degradation induces epidermal cell death.

Rottlerin Inhibits Lonicera japonica-Induced Photokilling in Human Lung Cancer Cells through Cytoskeleton-Related Signaling Cascade

This study demonstrated that many apoptotic signaling pathways, such as Rho family, PKC family, MAP kinase family, and mitochondria-mediated apoptotic pathway, were triggered by Lonicera japonica extracts and irradiation in CH27 cells. Rottlerin, a PKCδ -selective inhibitor, reversed the photoactivated Lonicera japonica extract-induced decrease in PKCδ protein expression and change in cell morphology in this study. In addition, rottlerin inhibited the photoactivated Lonicera japonica-induced decrease in protein expression of Ras, ERK, p38, PKCα, and PKCε, which are the kinases of prosurvival signaling pathway. We also demonstrated that pretreatment with rottlerin prevented actin microfilaments and microtubules from damage during the photoactivated Lonicera japonica-induced CH27 cell death. Furthermore, the promotion of the cytoskeleton-related signaling cascade following rottlerin by upregulation of cytoskeleton-related mediators (p38, HSP27, FAK, paxillin, and tubulin) and molecules of downstream of F-actin (mitochondria-mediated apoptosis pathway) reduces CH27 cell death, indicating that cytoskeleton is the potential target in the photoactivated Lonicera japonicaextract-induced photokilling of CH27 cells.

MicroRNA-125b expands hematopoietic stem cells and enriches for the lymphoid-balanced and lymphoid-biased subsets

MicroRNAs profoundly impact hematopoietic cells by regulating progenitor cell-fate decisions, as well as mature immune effector function. However to date, microRNAs that regulate hematopoietic stem cell (HSC) function have been less well characterized. Here we show that microRNA-125b (miR-125b) is highly expressed in HSCs and its expression decreases in committed progenitors. Overexpression of miR-125b in mouse HSC enhances their function, demonstrated through serial transplantation of highly purified HSC, and enriches for the previously described Slamf1(lo)CD34(-) lymphoid-balanced and the Slamf1(neg)CD34(-) lymphoid-biased cell subsets within the multipotent HSC (CD34-KLS) fraction. Mature peripheral blood cells derived from the miR-125b-overexpressing HSC are skewed toward the lymphoid lineage. Consistent with this observation, miR-125b overexpression significantly increases the number of early B-progenitor cells within the spleen and induces the expansion and enrichment of the lymphoid-balanced and lymphoid-biased HSC subset via an antiapoptotic mechanism, reducing the mRNA expression levels of two proapoptotic targets, Bmf and KLF13. The antiapoptotic effect of miR-125b is more pronounced in the lymphoid-biased HSC subset because of their intrinsic higher baseline levels of apoptosis. These effects of miR-125b are associated with the development of lymphoproliferative disease, marked by expansion of CD8(+) T lymphocytes. Taken together, these data reveal that miR-125b regulates HSC survival and can promote lymphoid-fate decisions at the level of the HSC by preferentially expanding lymphoid-balanced and lymphoid-biased HSC.

Oestrogen modulates human macrophage apoptosis via differential signalling through oestrogen receptor-alpha and beta

Human macrophages express oestrogen receptors and are therefore competent to respond to the hormone present in their microenvironment, which is implicated in sexual dimorphism observed in several immune and autoimmune phenomena. An earlier study from this laboratory demonstrated 17beta-oestradiol (E2) induced apoptosis in macrophages derived from human peripheral blood monocytes and THP-1 acute monocytic leukaemia cell line when Bcl-2 was down-regulated; however, the involvement of E2 receptor subtypes in the modulation of death pathways in these cells remain unknown. Using macrophages derived from THP-1 human acute monocytic leukaemia cells as a model, we demonstrate that plasma membrane associated oestrogen receptor (ER) -alpha participate in E2 induced Bcl-2 increase, through activation of the mitogen activated protein kinase (MAPK) pathway whereas cytosolic ER-beta transmits signals for the pro-apoptotic event of Bax translocation. The mechanistic basis of Bax translocation comprised of ER-beta mediated increase in intracellular pH, facilitated by activation of the Na(+)-H(+) exchanger. Intracellular alkalinization accompanied by concomitant Bcl-2 increase and Bax migration does not cause cellular apoptosis; however, siRNA mediated down-regulation of ER-alpha during E2 exposure leads to inhibition of Bcl-2 increase and consequently apoptosis due to the unopposed action of mitochondrial Bax. In summary, this study underscores the importance of integrative signalling modality from multiple oestrogen receptor pools in modulating oestrogen effects on human monocyte-derived macrophage apoptotic signalling pathway, which opens new vistas to explore the use of selective oestrogen receptor modulators in apoptosis-based therapies.

LPLI inhibits apoptosis upstream of Bax translocation via a GSK-3beta-inactivation mechanism

Low-power laser irradiation (LPLI), a non-damage physical therapy, which has been used clinically for decades of years, is shown to promote cell proliferation and prevent apoptosis. However, the underlying mechanisms that LPLI prevents cell apoptosis remain undefined. In this study, based on real-time single-cell analysis, we demonstrated for the first time that LPLI inhibits staurosporine (STS)-induced cell apoptosis by inactivating the GSK-3beta/Bax pathway. LPLI could inhibit the activation of GSK-3beta, Bax, and caspase-3 induced by STS. In the searching for the mechanism, we found that, LPLI can activate Akt, which was consistence with our former research, even in the presence of STS. In this anti-apoptotic process, the interaction between Akt and GSK-3beta increased gradually, indicating Akt interacts with and inactivates GSK-3beta directly. Conversely, LPLI decreased the interaction between GSK-3beta and Bax, with the suppression of Bax translocation to mitochondria, suggesting LPLI inhibits Bax translocation through inactivating GSK-3beta. These results were further confirmed by the experiments of co-immunoprecipitation. Wortmannin, an inhibitor of phosphatidylinositol 3'-OH kinase (PI3K), potently suppressed the activation of Akt and subsequent anti-apoptotic processes induced by LPLI. Taken together, we conclude that LPLI protects against STS-induced apoptosis upstream of Bax translocation via the PI3K/Akt/GSK-3beta pathway. These findings raise the possibility of LPLI as a promising therapy for neuron-degeneration disease induced by GSK-3beta.

Activated macrophages utilize glycolytic ATP to maintain mitochondrial membrane potential and prevent apoptotic cell death

We have previously analysed the bioenergetic consequences of activating J774.A1 macrophages (MΦ) with interferon-γ (IFN-γ) and lipopolysaccharide (LPS) and found that there is a nitric oxide (NO)-dependent mitochondrial impairment and stabilization of hypoxia-inducible factor (HIF)-1α, which synergize to activate glycolysis and generate large quantities of ATP. We now show, using tetramethylrhodamine methyl ester (TMRM) fluorescence and time-lapse confocal microscopy, that these cells maintain a high mitochondrial membrane potential (ΔΨ(m)) despite the complete inhibition of respiration. The maintenance of high ΔΨ(m) is due to the use of a significant proportion of glycolytically generated ATP as a defence mechanism against cell death. This is achieved by the reverse functioning of F(o)F(1)-ATP synthase and adenine nucleotide translocase (ANT). Treatment of activated MΦ with inhibitors of either of these enzymes, but not with inhibitors of the respiratory chain complexes I to IV, led to a collapse in ΔΨ(m) and to an immediate increase in intracellular [ATP], due to the prevention of ATP hydrolysis by the F(o)F(1)-ATP synthase. This collapse in ΔΨ(m) was followed by translocation of Bax from cytosol to the mitochondria, release of cytochrome c into the cytosol, activation of caspases 3 and 9 and subsequent apoptotic cell death. Our results indicate that during inflammatory activation 'glycolytically competent cells' such as MΦ use significant amounts of the glycolytically generated ATP to maintain ΔΨ(m) and thereby prevent apoptosis.