Atomic force microscopy to study direct neurite-mast cell (RBL) communication in vitro

The Morphology and Ultrastructure of Dermal Telocytes Characterized by TEM and AFM

This investigation delves into the structural foundation of human dermal telocytes (TCs) with the aim of elucidating their role in signal transmission. Dermal TCs were isolated from human foreskins via enzymatic digestion and flow cytometric sorting, and identified by immunohistochemical staining with an antibody against CD34. The ultrastructure of TCs was examined using transmission electron microscopy (TEM). The proliferation rates of sorted TCs and CD34-negative fibroblasts were compared using the MTS assay (Cell Proliferation Assay). Images of viable cultured TCs were analyzed using atomic force microscopy (AFM) under normal atmospheric pressure and temperature. Results demonstrated that dermal TCs were positive for CD34 and vimentin, predominantly distributed in the reticular dermis and subcutaneous tissue, forming interwoven networks. Each TC had a small body with a high nuclear-plasma ratio and two or three extremely long and thin telopodes (TPs), exhibiting a typical 'moniliform' appearance. Compared with CD34-negative fibroblasts, dermal TCs exhibited significantly lower proliferation rates. Cultured TCs displayed typical moniliform projections (namely, TPs) in the AFM images. The distal ends of TPs were enlarged, shaped like a broom, and extended multiple pseudopods to contact other cell bodies. Slender filamentary pseudopodia and thick, short cone-like structures were observed on the surfaces of the dilated segments and terminals of TPs. These structures are assumed to be evidence of the secretion and release of endosomes, such as exosomes, and the communication between cells. TCs form interstitial networks in the reticular dermis and subcutaneous tissue, providing a structural basis for contacts between cells and the secretion of signal-carrying substances, involving intercellular connections and communication.

Quercetin inhibits Mrgprx2-induced pseudo-allergic reaction via PLCγ-IP3R related Ca2+ fluctuations

An allergic reaction is a potentially fatal hypersensitivity response caused by mast cell activation, particularly histamine and lipid mediators. Histamine release caused by reaction to drugs is considered a pseudo-allergic reaction. Quercetin is known for its anti-allergic immune effect. However, at present, its anti-pseudo-allergic effect and its mechanism are less investigated. Therefore, the purpose of this study was to evaluate the anti-pseudo-allergic effect of Quercetin in vivo and to explore the mechanism in vitro. The anti-pseudo-allergic activity of Quercetin was evaluated in vivo using a mouse model, while Quercetin mechanism of action was examined in vitro using HEK293 cells expressing Mrgprx2, a mast cell specific receptor, and LAD2 mast cell line. Our in vivo results showed that Quercetin could attenuate Evans blue leakage in the paws and hind paw thickness in C57BL/6 mice in a dose-dependent manner, and could significantly inhibit serum histamine and chemokines release. In addition, it suppressed calcium mobilization and attenuated the release of histamine and MCP-1 in peritoneal mast cells in a dose-dependent manner. Furthermore, it inhibited the vasodilation due to histamine, the release of eosinophils, and the percentage of degranulated mast cells, indicating that Quercetin antagonized mast cell mediators in vivo, histamine-induced vasodilation and eosinophil release. In vitro results showed that Quercetin reduced pseudo-allergic induced calcium influx, suppressed degranulation and chemokines release in a similar way as dexamethasone (100 μM) (mast cell stabilizer) in LAD2 mast cell line. In addition, Quercetin inhibited Mrgprx2-induced both calcium influx and pseudo-allergic reaction in HEK293 cells expressing Mrgprx2. C48/80, a histamine promoter, and Substance P (a neuropeptide) EC₅₀ was higher when combined with Quercetin compared to the EC₅₀ of these compounds alone, suggesting that Quercetin could inhibit Mrgprx2-induced pseudo-allergic reaction. Furthermore, Quercetin decreased PLCγ-IP3R signaling pathway activation induced by C48/80 in LAD2 mast cell line. In Mrgprx2 knockdown LAD2 cells, the effect of Quercetin (200 μM) reduced C48/80 induced calcium flux and the release of β‑hexosaminidase, histamine, MCP-1 and IL-8 compared with non-atopic control (NC) transfected LAD2 human mast cells, suggesting that Quercetin anti-pseudo-allergic effect was related to Mrgprx2. The docking results showed that Quercetin had a good binding affinity with Mrgprx2 similar to the one of Substance P and C48/80. Therefore, Quercetin inhibited Mrgprx2-induced pseudo-allergic reaction via PLCγ-IP3R associated Ca²⁺ fluctuations. Our results validated Quercetin as an effective small molecule inhibiting Mrgprx2-induced pseudo-allergic reaction via PLCγ-IP3R associated Ca²⁺ fluctuations, thus highlighting a potential candidate to suppress Mrgprx2 induced pseudo-allergic related diseases.

Atomic force microscopy study of ionomycin-induced degranulation in RBL-2H3 cells

Mast cell degranulation is the typical anaphylaxis process of mast cells associated with the release of cytokines, eicosanoids and their secretory granules, which play very important roles in the allergic inflammatory response of the human body upon anaphylactogen stimulation. The calcium ionophore ionomycin is widely used as a degranulation induction agent for mast cell degranulation studies. In the present work, ionomycin-induced degranulation of RBL-2H3 basophilic leukemia cell line cells was investigated in vitro by high resolution atomic force microscopy (AFM). Ionomycin, which could increase the intracellular free Ca²⁺ level and β-Hexosaminidase release, was found to induce the formation of a kind of peculiar vesicles in the cytoplasm area of RBL-2H3 cells. Those vesicles induced by ionomycin would desintegrate to release a larger amount of granules surrounding RBL-2H3 cells by the controlling of F-actin. These results provide the precise morphological information of ionomycin-induced mast cell degranulation at nanoscale, which could benefit our understanding of ionomycin-induced mast cell anaphylaxis model and also validate the applicability of AFM for the detection of allergic inflammatory response in mast cells. SCANNING 38:525-534, 2016. © 2016 Wiley Periodicals, Inc.

Analysis of neuroimmune interactions by an in vitro coculture approach

Nerve fibers innervate every organ of the body and are involved in monitoring changes of the external and internal environment. Innervation directly controls a variety of physiological responses in an adaptive manner. Today, many lines of research indicate that also the immunological response is influenced by the nervous system and that nerve and immune cells directly interact through intercellular signal transduction by cytokines, neurotransmitters, and neuropeptides. For instance, mast cells are often found in close proximity of nerve fibers containing substance P and calcitonin gene-related peptide, two widely studied sensory neuropeptides, in a variety of tissues. To investigate the molecular mechanism of the direct functional interplay between nerve and immune cells, we have studied their communication using an in vitro coculture system and confocal microscopy. Here, we introduce methods for the in vitro coculture of nerve and immune cells and the imaging analysis of cellular activation, and discuss soluble mediators and adhesion molecules involved in the neuroimmune interaction. Improvement of our understanding of neuropeptide functions on these issues would lead to new therapeutic modalities for diseases based on neuroimmune interaction such as neurogenic inflammation, intestinal bowel diseases, asthma, and autoimmune disorders.

Effects of endogenous substance P expression on degranulation in RBL-2H3 cells

OBJECTIVE AND DESIGN

To determine whether RBL-2H3 cells have endogenous substance P (SP) expression under immunoglobulin E (IgE)-activated and inactivated conditions, and to ascertain the function of endogenous SP in the antigen-induced degranulation of RBL-2H3 cells.

MATERIALS AND METHODS

SP mRNA and protein expression in both inactivated and 2,4-dinitrophenol (DNP)-specific IgE-activated RBL-2H3 cells were assessed by real-time PCR and immunofluorescence, respectively. Following activation with DNP-specific IgE, the degranulation of RBL-2H3 cells in response to DNP-bovine serum albumin (BSA), with and without endogenous SP expression, was assessed by monitoring the release of the granular enzyme β-hexosaminidase.

RESULTS

Endogenous SP mRNA and peptide expression increased in activated RBL-2H3 cells, compared with inactivated RBL-2H3 cells. The small hairpin RNA (shRNA)-mediated knockdown of endogenous SP reduced the degranulation ability of RBL-2H3 cells.

CONCLUSIONS

Activated RBL-2H3 cells express endogenous SP which plays a role in antigen-induced degranulation.

Comparative atomic force and scanning electron microscopy: an investigation of structural differentiation of hepatic stellate cells

The molecular mechanism leading to the transdifferentiation of hepatic stellate cells (HSC) into myofibroblast-like cells following liver injury is not well understood. The state of cultured rat HSCs was determined using primarily fluorescence microscopy (UV), immunofluorescence (IF) (Glial fibrillary acidic protein (GFAP), Desmin, alpha-smooth muscle actin (alpha-SMA), F-actin) and immunocytochemistry (ICC) (GFAP, Desmin, alpha-SMA, Fibulin-2). Additionally, tapping-mode atomic force microscopy (TM-AFM) and field-emission scanning electron microscopy (FE-SEM) with low-resistivity indium-tin-oxide (ITO) thin-film were performed to observe the micro-morphological character of cells during HSC differentiation. Quiescent HSCs changed to the activated state were identified via UV, IF, and ICC observations. Normal rat HSCs (NHSCs) and thioacetamide-induced rat HSCs (THSCs) were demonstrated to be UV(-), GFAP(+), Desmin(+), alpha-SMA(+) and Fibulin-2(-). After F-actin staining, lamellipodia and filopodia were found in both NHSCs and THSCs, but membrane ruffles were only seen in THSCs. The micro-structures of lamellipodia and filopodia in both NHSCs and THSCs were confirmed using FE-SEM and TM-AFM with ITO; in contrast, the micro-projection was not found. Moreover, "aerial root" structures were observed for the first time in the filopodia of THSCs using TM-AFM. These results reveal that HSC transdifferentiation to a myofibroblastic-like cell (activated HSC) from thioacetamide-induced rat HSC induces extensive changes in the cytoskeleton.

High-resolution three-dimensional imaging of the rich membrane structures of bone marrow-derived mast cells

Atomic force microscopy (AFM) enables high-resolution three-dimensional (3D) imaging of cultured bone marrow-derived mast cells. Cells were immobilized by a quick centrifugation and fixation to preserve their transient cellular morphologies followed by AFM characterization in buffer. This "fix-and-look" approach preserves the structural integrity of individual cells. Well-known membrane morphologies, such as ridges and microvilli, are visualized, consistent with prior electron microscopy observations. Additional information including the 3D measurements of these characteristic features are attained from AFM topographs. Filopodia and lamellopodia, associated with cell spreading, were captured and visualized in three dimensions. New morphologies are also revealed, such as high-density ridges and micro-craters. This investigation demonstrates that the "fix-and-look" approach followed by AFM imaging provides an effective means to characterize the membrane structure of hydrated cells with high resolution. The quantitative imaging and measurements pave the way for systematic correlation of membrane structural features with the biological status of individual cells.

ATP plays a role in neurite stimulation with activated mast cells

Previously, we showed that nerve-mast cell cross-talk can occur bidirectionally and that substance P is a mediator to activate mast cells. Here, we have studied the mediators to activate nerves cocultured with mast cells. Addition of antigen to the cocultures of superior cervical ganglia (SCG) and rat basophilic leukemia cells (RBLs) elicited Ca(2+) response in RBLs and after a lag period induced Ca(2+) signal in SCG neurites. Pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (purinergic receptor antagonist) or apyrase (ATP-hydrolyzing enzyme) reduced the Ca(2+) signals in neurites, indicating that ATP released from activated mast cells was one of important mediators to activate nerves.

A new image correction method for live cell atomic force microscopy

During live cell imaging via atomic force microscopy (AFM), the interactions between the AFM probe and the membrane yield distorted cell images. In this work, an image correction method was developed based on the force-distance curve and the modified Hertzian model. The normal loading and lateral forces exerted on the cell membrane by the AFM tip were both accounted for during the scanning. Two assumptions were made in modelling based on the experimental measurements: (1) the lateral force on the endothelial cells was linear to the height; (2) the cell membrane Young's modulus could be derived from the displacement measurement of a normal force curve. Results have shown that the model could be used to recover up to 30% of the actual cell height depending on the loading force. The accuracy of the model was also investigated with respect to the loading force and mechanical property of the cell membrane.

[Functional fluctuation]

The discovery of the double-helical structure of DNA, the elucidation of the genetic code, and the determination of the three-dimensional structure of several proteins are some of the outstanding achievements of biochemistry and life sciences in the latter half of the last century. Proteins play key roles in almost all the biological processes and the biological function of a protein depends on its conformation which is defined as the three-dimensional arrangement of the atoms of a molecule. The three-dimensional structure, however, is not rigid but fluctuated. Structural fluctuation plays an important role in bio-macromolecules. How about "functional fluctuation" in biological systems? The present review proposes that functional fluctuation is also very important for understanding the mechanism of supramolecules, biological processes in living cells, and the interaction between biological systems. This new theme is pretty well supported by our recent experiments for neuro-immune crosstalk, gene transfection with cationic liposomes, and cell signaling in embryonic stem cells.

[Confocal laser scanning microscopy to study molecular mechanism of mast cell activation]

In the immune system, mast cells are a key cell type in the pathogenesis of immunoglobulin E (IgE)-dependent hypersensitivity reactions. Engagement of the high-affinity IgE receptors by multivalent antigens initiates the downstream activation of signal-transducing enzymes and evokes degranulation and cytokine production via an increase in the intracellular Ca2+ concentration. In addition, mast cells also play a prominent role in non-IgE-mediated hypersensitivity reactions. Mast cells are closely apposed to nerves in vivo and are likely to be regulated functionally by nerves. However, the molecular mechanisms for mast cell activation in an IgE-dependent and -independent manner have not been fully clarified. Confocal laser scanning microscopy has played an essential role in cell biology by allowing visualization of specific intracellular signaling molecules with high spatiotemporal resolution in living cells. We have studied intracellular movements of Ca2+ using a specific fluorescent probe and several types of signaling molecules using derivatives of green fluorescent protein in a living single mast cell using a microscopic strategy. We here describe our imaging analysis of the calcium signals to the nucleus, the movement of secretory granules in the degranulation process, and the nucleocytoplasmic shuttling of mitogen-activated protein kinase in mast cells. Further, we demonstrate that direct communication between mast cells and nerves occurs. These findings provide useful information from a new perspective to understand the molecular mechanisms of allergic reaction and inflammation.

Live Cell Imaging to Study Signaling Molecules in Allergic Reactions

Mast cells are widely distributed throughout the body, predominantly near blood vessels and nerves, and express effector functions in allergic reactions, inflammatory diseases, and host defense. The activation of mast cells results in secretion of the preformed chemical mediators in their granules by a regulated process of exocytosis and leads to synthesis and secretion of lipid mediators and cytokines. Their soluble factors contribute to allergic inflammation. Mast cells are associated with hypersensitivity reactions, not only in the classical immunoglobulin E (IgE)-dependent mechanism but also in an IgE-independent manner. In particular, investigations of potential anatomical and functional interactions between mast cells and the nervous system have recently attracted great interest. To understand these molecular mechanisms in mast cell activation, the ability to visualize, track, and quantify molecules and events in living mast cells is an essential and powerful tool. Recent dramatic advances in imaging technology and labeling techniques have enabled us to carry out these tasks with high spatiotemporal resolution using confocal laser scanning microscopes, green fluorescent protein and its derivatives, and image analysis systems. Here we review our investigations of the dynamic processes of intracellular signaling molecules, cellular structure, and interactions with neurons in mast cells to provide basic and valuable information for allergy and clinical immunology using these new imaging methods.

Lack of neurokinin-1 receptor expression affects tissue mast cell numbers but not their spatial relationship with nerves

A spatial association between mast cells and nerves has been described in both the gastrointestinal and genitourinary tracts. However, the factors that influence the anatomic relationship between mast cells and nerves have not been completely defined. It has been suggested that the high-affinity receptor for substance P [neurokinin-1 (NK1)] might modulate this interaction. We therefore assessed mast cell-nerve relationships in tissues isolated from wild-type and NK1 receptor knockout (NK1-/-) mice. We now report that, in the complete absence of NK1 receptor expression, there is a significant increase in the number of mast cells without a change in the anatomic relationship between mast cell and nerves in stomach and bladder tissues at the light microscopic level. We next determined whether transplanted mast cells would maintain their spatial distribution, number, and contact with nerve elements. For this purpose, mast cell-deficient Kit(W)/Kit(W-v) mice were reconstituted with wild-type or NK1-/- bone marrow. No differences in mast cell-nerve contact were observed. These results suggest that NK1 receptor expression is important in the regulation of the number of mast cells but is not important in the interaction between mast cells and nerves. Furthermore, the interaction between mast cells and nerves is not mediated through NK1 receptor expression on the mast cell. Further studies are needed to determine the molecular pathway involved in mast cell migration and interaction with nerve elements, but the model of reconstitution of Kit(W)/Kit(W-v) mice with mast cells derived from different genetically engineered mice is a useful approach to further explore these mechanisms.

The relations between neurite development and the subcellular structures of hippocampal neuron somata

The relations between neurite development and the subcellular structures of the hippocampal neuron somata have been studied with atomic force microscopy (AFM). The conformation of the neuron was achieved by the synapse-like structures found by AFM scanning along a neurite of the cell. Hippocampal neuron somata were divided into two or three subcellular parts by one or two horizontal grooves. The upper parts increased while the middle and the lower parts decreased with the number and the length of the neurites and the formation of the neurosynapse-like structures. When neurites sufficiently developed, the middle parts were lost and the lower parts became very small. Mitosis inhibitors could prevent the formation of such subcellular structures of hippocampal neuron somata, which was accompanied by the loss of ability to form synapse-like structures. These results suggest that the upper parts are responsible for neuritogenesis while the middle and the lower parts only have indirect effect on it.

An overview of the biophysical applications of atomic force microscopy

The potentialities of the atomic force microscopy (AFM) make it a tool of undeniable value for the study of biologically relevant samples. AFM is progressively becoming a usual benchtop technique. In average, more than one paper is published every day on AFM biological applications. This figure overcomes materials science applications, showing that 17 years after its invention, AFM has completely crossed the limits of its traditional areas of application. Its potential to image the structure of biomolecules or bio-surfaces with molecular or even sub-molecular resolution, study samples under physiological conditions (which allows to follow in situ the real time dynamics of some biological events), measure local chemical, physical and mechanical properties of a sample and manipulate single molecules should be emphasized.

N-Cadherin Plays a Role in the Synapse-Like Structures between Mast Cells and Neurites

Communication between nerves and mast cells is a prototypic demonstration of neuro-immune interaction. Numerous studies have shown that the stimulation of nerves (or addition of neurotransmitters) can evoke activation of mast cells, and that mast cell-derived mediators can influence neuronal activity. However, the molecules involved in the membrane-membrane contacts between nerves and mast cells are still unknown. Here, we used an in vitro co-culture approach comprising interaction between immune (bone marrow-derived mast cell, BMMC) and nerve cells (superior cervical ganglia, SCG). The experiments showed clearly that the nerve-mast cell communication was supported by synapse-like structure and that N-cadherin, not E-cadherin, played an essential role in the synapse-like structure. In addition, we found that the synapse-like structure was assisted by clustering of beta-catenin to N-cadherin.

Calcium signals in rat basophilic leukemia (RBL-2H3) cells primed with the neuropeptide substance P

Communication between nerves and mast cells is a prototypic demonstration of neuroimmune interaction. We have recently shown that direct nerve-mast cell cross-talk can occur in the absence of an intermediary transducing cell and that the neuropeptide substance P is an important mediator of this communication. Here we study the calcium signals in rat basophilic leukemia cells (RBL-2H3; mucosal-type mast cells) primed with substance P. RBL cells responded only slightly to stimulation with compound 48/80, however they responded to the stimulation when the cells had been primed with substance P (0.5 microM) for one week. The present results provide a foundation to study the neuroimmune cross-talk in a co-culture system.

Bi-directional relationship of in vitro mast cell-nerve communication observed by confocal laser scanning microscopy

Communication between nerves and mast cells is a prototypic demonstration of neuro-immune interaction. Recently, we used an in vitro co-culture approach comprising cultured murine superior cervical ganglia (SCG) and rat basophilic leukemia (RBL) cells to study this interaction. Previously, we concentrated mainly on the activation signal from neurites to mast cells (RBL). However, it is proposed that mast cell-nerve communication is not a one-sided relationship but a bi-directional one. In the present work, we studied the communication from mast cells to neurites. We observed that binding of anti-IgE receptor antibodies to mast cells increases calcium ion concentration [Ca2+]i in SCG neurites. This indicates that mast cell-nerve communication is bi-directional. Confocal fluorescence microscopic images indicated that [Ca2+]i in neurites increased after an increase of [Ca2+]i in mast cells. The lag-time of neurite activation was several times longer than that of mast cell activation. The correlation coefficient between the lag-times for mast cell and nerve activation was calculated to be 0.81. In addition, the fluorescence images showed that calcium signals in SCG neurites were able to extend to a long distance (100-200 microm) from the site where mast cells (RBL) attached to neurites.