Novel fluo-4 analogs for fluorescent calcium measurements

Synthetic Heparan Sulfate Hydrogels Regulate Neurotrophic Factor Signaling and Neuronal Network Activity

Three-dimensional (3D) synthetic heparan sulfate (HS) constructs possess promising attributes for neural tissue engineering applications. However, their sulfation-dependent ability to facilitate molecular recognition and cell signaling has not yet been investigated. We hypothesized that fully sulfated synthetic HS constructs (bearing compound 1) that are functionalized with neural adhesion peptides will enhance fibroblast growth factor-2 (FGF2) binding and complexation with FGF receptor-1 (FGFR1) to promote the proliferation and neuronal differentiation of human neural stem cells (hNSCs) when compared to constructs with unsulfated controls (bearing compound 2). We tested this hypothesis in vitro using 2D and 3D substrates consisting of different combinations of HS tetrasaccharides (compounds 3 and 4) and an engineered integrin-binding chimeric peptide (CP), which were assembled using strain-promoted alkyne-azide cycloaddition (SPAAC) chemistry. Results indicated that the adhesion of hNSCs increased significantly when cultured on 2D glass substrates functionalized with chimeric peptide. hNSCs encapsulated in 1-CP hydrogels and cultured in media containing the mitogen FGF2 exhibited significantly higher neuronal differentiation when compared to hNSCs in 2-CP hydrogels. These observations were corroborated by Western blot analysis, which indicated the enhanced binding and retention of both FGF2 and FGFR1 by 1 as well as downstream phosphorylation of extracellular signal-regulated kinases (ERK1/2) and enhanced proliferation of hNSCs. Lastly, calcium activity imaging revealed that both 1 and 2 hydrogels supported the neuronal growth and activity of pre-differentiated human prefrontal cortex neurons. Collectively, these results demonstrate that synthetic HS hydrogels can be tailored to regulate growth factor signaling and neuronal fate and activity.

Cellular Stress Pathways Are Linked to Acetamiprid-Induced Apoptosis in SH-SY5Y Neural Cells

Simple Summary

Neonicotinoids constitute more than one-quarter of the insecticides on the market. Acetamiprid, a widely used neonicotinoid, has been found to be linked with neurological symptoms and there is an urge to understand its molecular mechanisms. It decreased cellular viability in millimole concentrations after 24 h in SH-SY5Y neural cells. Additionally, it increased reactive oxygen species, intracellular calcium and endoplasmic reticulum stress. Since overwhelmed cellular stress can destroy cellular structures and cause cell death, we also evaluated cellular death mechanisms. Acetamiprid induced apoptosis rather than necrosis indicating that cells undergo suicide initiated by self-generated death signals. Even though acetamiprid is considered to be a safe option in the struggle against harmful agricultural insects, these results suggest that the widespread use should be taken under strict control in order not to cause damage to the mammals.

Abstract

Acetamiprid (ACE), a commonly used neonicotinoid insecticide, is correlated with neurological symptoms, immunotoxicity and hepatotoxicity. Cellular stress and damage could play an important role in ACE-induced neurotoxicity; however, its mechanism has not been fully understood. We evaluated the effects of ACE on oxidative stress, endoplasmic reticulum (ER) stress, cellular death, mRNA expression levels of related genes and protein expressions of related molecular mechanisms in SH-SY5Y human neuroblastoma cells. The half maximal inhibition of enzyme activity (IC₅₀) value of ACE was determined as 4.26 mM after 24 h of treatment by MTT assay. We revealed an increase in reactive oxygen species (ROS) production and calcium release. Significant increases were measured in inositol-requiring enzyme 1-alpha (IRE1-α) and binding immunoglobulin protein 90 (GRP90) levels as well as mRNA expression levels of caspase 3, 4 and 9 genes indicating enhanced ER stress. Apoptosis and ER stress-related genes were significantly upregulated at ≥2 mM. Indeed, ACE caused apoptosis and necroptosis while necrosis was not observed. There was a significant increase in the protein level of mitogen-activated protein kinase-8 (MAPK8) at 4 mM of ACE while no change was seen for nuclear factor kappa-B (NF-κB) and tumor necrosis factor-alpha (TNF-α). In conclusion, increased cellular stress markers could be proposed as an underlying mechanism of ACE-induced cell death in neural cells.

Intracellular Calcium Determines the Adipogenic Differentiation Potential of Human Umbilical Cord Blood-Derived Mesenchymal Stem Cells via the Wnt5a/β-Catenin Signaling Pathway

Mesenchymal stem cells- (MSCs-) based therapies show different degrees of efficacies for the treatment of various diseases, including lipogenesis. We evaluated the adipogenic differentiation ability of human umbilical cord blood-derived MSCs (hUCB-MSCs) from different donors and examined the contribution of the intracellular calcium (Ca²⁺) level to this diversity. hUCB-MSCs treated with Ca²⁺ or the Ca²⁺ chelator BAPTA-AM increased and decreased adipogenic differentiation, respectively. Canonical Wnt5a/β-catenin expression decreased during adipogenic differentiation of hUCB-MSCs. Treatment with Wnt5a blocked the adipogenic differentiation of hUCB-MSCs and activated the Wnt pathway, with a decrease in the adipogenesis markers PPARγ and leptin, and reduced lipid vacuole-associated Oil red O activity. In contrast, inhibition of the Wnt pathway with dickkopf-1 and β-catenin small interfering RNA transfection promoted the adipogenic potential of hUCB-MSCs. Interestingly, the Ca²⁺-based system exhibited a synergic effect on adipogenic potential through the Wnt5a/β-catenin pathway. Our data suggest that the variable adipogenic differentiation potential of hUCB-MSCs from different lots is due to variation in the intracellular Ca²⁺ level, which can be used as a marker to predict hUCB-MSCs selection for lipogenesis therapy. Overall, these results demonstrate that exogenous calcium treatment enhanced the adipogenic differentiation of hUCB-MSCs via negatively regulating the Wnt5a/β-catenin signaling pathway.

A High-Throughput Automated Microfluidic Platform for Calcium Imaging of Taste Sensing

The human enteroendocrine L cell line NCI-H716, expressing taste receptors and taste signaling elements, constitutes a unique model for the studies of cellular responses to glucose, appetite regulation, gastrointestinal motility, and insulin secretion. Targeting these gut taste receptors may provide novel treatments for diabetes and obesity. However, NCI-H716 cells are cultured in suspension and tend to form multicellular aggregates, preventing high-throughput calcium imaging due to interferences caused by laborious immobilization and stimulus delivery procedures. Here, we have developed an automated microfluidic platform that is capable of trapping more than 500 single cells into microwells with a loading efficiency of 77% within two minutes, delivering multiple chemical stimuli and performing calcium imaging with enhanced spatial and temporal resolutions when compared to bath perfusion systems. Results revealed the presence of heterogeneity in cellular responses to the type, concentration, and order of applied sweet and bitter stimuli. Sucralose and denatonium benzoate elicited robust increases in the intracellular Ca(2+) concentration. However, glucose evoked a rapid elevation of intracellular Ca(2+) followed by reduced responses to subsequent glucose stimulation. Using Gymnema sylvestre as a blocking agent for the sweet taste receptor confirmed that different taste receptors were utilized for sweet and bitter tastes. This automated microfluidic platform is cost-effective, easy to fabricate and operate, and may be generally applicable for high-throughput and high-content single-cell analysis and drug screening.

Direct action of capsaicin in brown adipogenesis and activation of brown adipocytes

The ingestion of capsaicin, the principle pungent component of red and chili peppers, induces thermogenesis, in part, through the activation of brown adipocytes expressing genes related to mitochondrial biogenesis and uncoupling such as peroxisome proliferator-activated receptor (Ppar) γ coactivator-1α (Pgc-1α) and uncoupling protein 1 (Ucp1). Capsaicin has been suggested to induce the activation of brown adipocytes, which is mediated by the stimulation of sympathetic nerves. However, capsaicin may directly affect the differentiation of brown preadipocytes, brown adipocyte function, or both, through its significant absorption. We herein demonstrated that Trpv1, a capsaicin receptor, is expressed in brown adipose tissue, and that its expression level is increased during the differentiation of HB2 brown preadipocytes. Furthermore, capsaicin induced calcium influx in brown preadipocytes. A treatment with capsaicin in the early stage of brown adipogenesis did not affect lipid accumulation or the expression levels of Fabp4 (a gene expressed in mature adipocytes), Pparγ2 (a master regulator of adipogenesis) or brown adipocyte-selective genes. In contrast, a treatment with capsaicin in the late stage of brown adipogenesis slightly increased the expression levels of Fabp4, Pparγ2 and Pgc-1α. Although capsaicin did not affect the basal expression level of Ucp1, Ucp1 induction by forskolin was partially inhibited by capsaicin, irrespective of the dose of capsaicin. The results of the present study suggest the direct effects of capsaicin on brown adipocytes or in the late stage of brown adipogenesis.

Protein ligand-tethered synthetic calcium indicator for localization control and spatiotemporal calcium imaging in plant cells

In plant biology, calcium ions are involved in a variety of intriguing biological phenomena as a secondary messenger. However, most conventional calcium indicators are not applicable for plant cells because of the difficulty with their localization control in plant cells. We here introduce a method to monitor spatiotemporal Ca(2+) dynamics in living plant cells based on linking the synthetic calcium indicator Calcium Green-1 to a natural product-based protein ligand. In a proof-of-concept study using cultured BY-2 cells overexpressing the target protein for the ligand, the ligand-tethered probe accumulated in the cytosol and nucleus, and enabled real-time monitoring of the cytosolic and nucleus Ca(2+) dynamics under the physiological condition. The present strategy using ligand-tethered fluorescent sensors may be successfully applied to reveal the spatiotemporal dynamics of calcium ions in living plant cells.

Development of Functional Fluorescent Molecular Probes for the Detection of Biological Substances

This review is confined to sensors that use fluorescence to transmit biochemical information. Fluorescence is, by far, the most frequently exploited phenomenon for chemical sensors and biosensors. Parameters that define the application of such sensors include intensity, decay time, anisotropy, quenching efficiency, and luminescence energy transfer. To achieve selective (bio)molecular recognition based on these fluorescence phenomena, various fluorescent elements such as small organic molecules, enzymes, antibodies, and oligonucleotides have been designed and synthesized over the past decades. This review describes the immense variety of fluorescent probes that have been designed for the recognitions of ions, small and large molecules, and their biological applications in terms of intracellular fluorescent imaging techniques.

New red-fluorescent calcium indicators for optogenetics, photoactivation and multi-color imaging

Most chemical and, with only a few exceptions, all genetically encoded fluorimetric calcium (Ca(2+)) indicators (GECIs) emit green fluorescence. Many of these probes are compatible with red-emitting cell- or organelle markers. But the bulk of available fluorescent-protein constructs and transgenic animals incorporate green or yellow fluorescent protein (GFP and YFP respectively). This is, in part, not only heritage from the tendency to aggregate of early-generation red-emitting FPs, and due to their complicated photochemistry, but also resulting from the compatibility of green-fluorescent probes with standard instrumentation readily available in most laboratories and core imaging facilities. Photochemical constraints like limited water solubility and low quantum yield have contributed to the relative paucity of red-emitting Ca(2+) probes compared to their green counterparts, too. The increasing use of GFP and GFP-based functional reporters, together with recent developments in optogenetics, photostimulation and super-resolution microscopies, has intensified the quest for red-emitting Ca(2+) probes. In response to this demand more red-emitting chemical and FP-based Ca(2+)-sensitive indicators have been developed since 2009 than in the thirty years before. In this topical review, we survey the physicochemical properties of these red-emitting Ca(2+) probes and discuss their utility for biological Ca(2+) imaging. Using the spectral separability index Xijk (Oheim M., 2010. Methods in Molecular Biology 591: 3-16) we evaluate their performance for multi-color excitation/emission experiments, involving the identification of morphological landmarks with GFP/YFP and detecting Ca(2+)-dependent fluorescence in the red spectral band. We also establish a catalog of criteria for evaluating Ca(2+) indicators that ideally should be made available for each probe. This article is part of a Special Issue entitled: Calcium signaling in health and disease. Guest Editors: Geert Bultynck, Jacques Haiech, Claus W. Heizmann, Joachim Krebs, and Marc Moreau.

Synthesis and properties of Asante Calcium Red--a novel family of long excitation wavelength calcium indicators

Although many synthetic calcium indicators are available, a search for compounds with improved characteristics continues. Here, we describe the synthesis and properties of Asante Calcium Red-1 (ACR-1) and its low affinity derivative (ACR-1-LA) created by linking BAPTA to seminaphthofluorescein. The indicators combine a visible light (450-540 nm) excitation with deep-red fluorescence (640 nm). Upon Ca2+ binding, the indicators raise their fluorescence with longer excitation wavelengths producing higher responses. Although the changes occur without any spectral shifts, it is possible to ratio Ca(2+)-dependent (640 nm) and quasi-independent (530 nm) emission when using visible (< 490 nm) or multiphoton (∼780 nm) excitation. Therefore, both probes can be used as single wavelength or, less dynamic, ratiometric indicators. Long indicator emission might allow easy [Ca2+]i measurement in GFP expressing cells. The indicators bind Ca2+ with either high (Kd = 0.49 ± 0.07 μM; ACR-1) or low affinity (Kd = 6.65 ± 0.13 μM; ACR-1-LA). Chelating Zn2+ (Kd = 0.38 ± 0.02 nM) or Mg2+ (Kd∼5mM) slightly raises and binding Co2+ quenches dye fluorescence. New indicators are somewhat pH-sensitive (pKa = 6.31 ± 0.07), but fairly resistant to bleaching. The probes are rather dim, which combined with low AM ester loading efficiency, might complicate in situ imaging. Despite potential drawbacks, ACR-1 and ACR-1-LA are promising new calcium indicators.

Cytosolic [Ca2+] regulation of InsP3-evoked puffs

InsP3-mediated puffs are fundamental building blocks of cellular Ca2+ signalling, and arise through the concerted opening of clustered InsP3Rs (InsP3 receptors) co-ordinated via Ca2+-induced Ca2+ release. Although the Ca2+ dependency of InsP3Rs has been extensively studied at the single channel level, little is known as to how changes in basal cytosolic [Ca2+] would alter the dynamics of InsP3-evoked Ca2+ signals in intact cells. To explore this question, we expressed Ca2+-permeable channels (nicotinic acetylcholine receptors) in the plasma membrane of voltage-clamped Xenopus oocytes to regulate cytosolic [Ca2+] by changing the electrochemical gradient for extracellular Ca2+ entry, and imaged Ca2+ liberation evoked by photolysis of caged InsP3. Elevation of basal cytosolic [Ca2+] strongly increased the amplitude and shortened the latency of global Ca2+ waves. In oocytes loaded with EGTA to localize Ca2+ signals, the number of sites at which puffs were observed and the frequency and latency of puffs were strongly dependent on cytosolic [Ca2+], whereas puff amplitudes were only weakly affected. The results of the present study indicate that basal cytosolic [Ca2+] strongly affects the triggering of puffs, but has less of an effect on puffs once they have been initiated.

Mitochondrial complex I inhibitors, acetogenins, induce HepG2 cell death through the induction of the complete apoptotic mitochondrial pathway

The development of new anti-neoplastic drugs is a key issue for cancer chemotherapy due to the reality that, most likely, certain cancer cells are resistant to current chemotherapy. The past two decades have witnessed tremendous advances in our understanding of the pathogenesis of cancer. These advances have allowed identification new targets as oncogenes, tumor supressor genes and the possible implication of the mitochondria (Fulda et al. Nat Rev Drug Discov 9:447-464, 2010). Annonaceous Acetogenins (ACGs) have been described as the most potent inhibitors of the respiratory chain because of their interaction with mitochondrial Complex I (Degli Esposti and Ghelli Biochim Biophys Acta 1187:116-120, 1994; Zafra-Polo et al. Phytochemistry 42:253-271, 1996; Miyoshi et al. Biochim Biophys Acta 1365:443-452, 1998; Tormo et al. Arch Biochem Biophys 369:119-126, 1999; Motoyama et al. Bioorg Med Chem Lett 12:2089-2092, 2002). To explore a possible application of natural products from Annonaceous plants to cancer treatment, we have selected four bis-tetrahydrofuranic ACGs, three from Annona cherimolia (cherimolin-1, motrilin and laherradurin) and one from Rollinia mucosa (rollinianstatin-1) in order to fully describe their mechanisms responsible within the cell (Fig. 1). In this study, using a hepato-carcinoma cell line (HepG2) as a model, we showed that the bis-THF ACGs caused cell death through the induction of the apoptotic mitochondrial pathway. Their potency and behavior were compared with the classical mitochondrial respiratory chain Complex I inhibitor rotenone in every apoptotic pathway step.

Calcium rubies: a family of red-emitting functionalizable indicators suitable for two-photon Ca2+ imaging

We designed Calcium Rubies, a family of functionalizable BAPTA-based red-fluorescent calcium (Ca(2+)) indicators as new tools for biological Ca(2+) imaging. The specificity of this Ca(2+)-indicator family is its side arm, attached on the ethylene glycol bridge that allows coupling the indicator to various groups while leaving open the possibility of aromatic substitutions on the BAPTA core for tuning the Ca(2+)-binding affinity. Using this possibility we now synthesize and characterize three different CaRubies with affinities between 3 and 22 μM. Their long excitation and emission wavelengths (peaks at 586/604 nm) allow their use in otherwise challenging multicolor experiments, e.g., when combining Ca(2+) uncaging or optogenetic stimulation with Ca(2+) imaging in cells expressing fluorescent proteins. We illustrate this capacity by the detection of Ca(2+) transients evoked by blue light in cultured astrocytes expressing CatCh, a light-sensitive Ca(2+)-translocating channelrhodopsin linked to yellow fluorescent protein. Using time-correlated single-photon counting, we measured fluorescence lifetimes for all CaRubies and demonstrate a 10-fold increase in the average lifetime upon Ca(2+) chelation. Since only the fluorescence quantum yield but not the absorbance of the CaRubies is Ca(2+)-dependent, calibrated two-photon fluorescence excitation measurements of absolute Ca(2+) concentrations are feasible.

Presynaptic imaging of projection fibers by in vivo injection of dextran-conjugated calcium indicators

Dextran-conjugated calcium indicators are stably retained within neurons. As a result, they are well suited to measuring presynaptic calcium at physiological temperatures. In addition, dextran indicators can be used to label neurons and their presynaptic boutons in vivo. This has allowed measurements of calcium in the presynaptic boutons of projection fibers that cannot be stably loaded with other types of indicators. This protocol describes a technique for in vivo loading of the climbing fiber projection to the cerebellum with dextran-conjugated indicators for subsequent presynaptic calcium imaging in brain slices. This technique is applicable to studies of projection fibers in many species from which brain slices can be prepared. The dextran indicator is injected into the inferior olive using a stereotaxic device. After a period of 1-3 d, cerebellar slices are prepared and presynaptic calcium transients are measured at physiological temperature in labeled climbing fibers. The protocol also discusses important considerations for using dextran-conjugated indicators to measure presynaptic calcium.

Cell morphology and intracellular ionic homeostasis explored with a multimodal approach combining epifluorescence and digital holographic microscopy

The authors have developed a live-cell multimodality microscope combining epifluorescence with digital holographic microscopy; it has been implemented with a decoupling procedure allowing to separately measure from the quantitative phase important cell parameters including absolute volume, shape and integral intracellular refractive index. In combination with the numerous different specific fluorescent cellular probes, this multimodality microscopy can address important issues in cell biology. This is demonstrated by the study of intracellular calcium homeostasis associated with the change in cell volume, which play a critical role in the excitotoxicity-induced neuronal death.

Synthesis and Characterization of a New Red-Emitting Ca2+ Indicator, Calcium Ruby

Calcium Ruby m-Cl (X = H, Y = Cl) is a visible-light excited red-emitting calcium concentration ([Ca2+]) indicator dye (579/598 nm peak excitation/emission) with a side arm for conjugation via EDC or click chemistry. Its large molar extinction and high quantum yield rank it among the brightest long-wavelength Ca2+ indicators. Calcium Ruby is a promising alternative to existing dyes for imaging [Ca2+] in multicolor fluorescence applications or in the presence of yellow-green cellular autofluorescence.

Fluorescent metal ion indicators based on benzoannelated crown systems: a green fluorescent indicator for intracellular sodium ions

The synthesis and metal binding properties of cation-sensitive fluorescent indicators intended for biological applications are described. The increase of the crown ether ring size enhances the affinity for larger cations, but weakens the fluorescent response and selectivity. A compound having a 15-crown-5 chelator directly attached to a 2,7-difluoroxanthenone fluorophore loads into live cells and responds to sodium ion concentration changes with large fluorescence increases in the visible wavelength range.

Synthesis of stilbene carboxylic acids as scaffolds for calcium sensors

This communication describes the synthesis and characterization of calcium binding stilbene carboxylic acids.