Cationic liposomes suppress intracellular calcium ion concentration increase via inhibition of PI3 kinase pathway in mast cells

Quercetin and Kaempferol inhibit HMC-1 activation via SOCE/NFATc2 signaling and suppress hippocampal mast cell activation in lipopolysaccharide-induced depressive mice

OBJECTIVE AND DESIGN

Mast cells (MCs), as the fastest immune responders, play a critical role in the progression of neuroinflammation-related diseases, especially in depression. Quercetin (Que) and kaempferol (Kae), as two major diet-derived flavonoids, inhibit MC activation and exhibit significant antidepressant effect due to their anti-inflammatory capacity. The study aimed to explore the mechanisms of inhibitory effect of Que and Kae on MC activation, and whether Que and Kae suppress hippocampal mast cell activation in LPS-induced depressive mice.

SUBJECTS AND TREATMENT

In vitro assays, human mast cells (HMC-1) were pretreated with Que or Kae for 1 h, then stimulated by phorbol 12-myristate 13-acetate (PMA) and 2,5-di-t-butyl-1,4-benzohydroquinone (tBHQ) for 3 h or 12 h. In vivo assays, Que or Kae was administered by oral gavage once daily for 14 days and then lipopolysaccharide (LPS) intraperitoneally injection to induce depressive behaviors.

METHODS

The secretion and expression of TNF-α were determined by ELISA and Western blotting. The nuclear factor of activated T cells (NFAT) transcriptional activity was measured in HMC-1 stably expressing NFAT luciferase reporter gene. Nuclear translocation of NFATc2 was detected by nuclear protein extraction and also was fluorescently detected in HMC-1 stably expressing eGFP-NFATc2. We used Ca2+ imaging to evaluate changes of store-operated calcium entry (SOCE) in HMC-1 stably expressing fluorescent Ca2+ indicator jGCamP7s. Molecular docking was used to assess interaction between the Que or Kae and calcium release-activated calcium modulator (ORAI). The  hippocampal mast cell accumulation and activation  were detected by toluidine blue staining and immunohistochemistry with β-tryptase.

RESULTS

In vitro assays of HMC-1 activated by PtBHQ (PMA and tBHQ), Que and Kae significantly decreased expression and secretion of TNF-α. Moreover, NFAT transcriptional activity and nuclear translocation of NFATc2 were remarkably inhibited by Que and Kae. In addition, the Ca2+ influx mediated by SOCE was suppressed by Que, Kae and the YM58483 (ORAI inhibitor), respectively. Importantly, the combination of YM58483 with Que or Kae had no additive effect on the inhibition of SOCE. The molecular docking also showed that Que and Kae both exhibit high binding affinities with ORAI at the same binding site as YM58483. In vivo assays, Que and Kae significantly reversed LPS-induced depression-like behaviors in mice, and inhibited hippocampal mast cell activation  in LPS-induced depressive mice.

CONCLUSIONS

Our results indicated that suppression of SOCE/NFATc2 pathway-mediated by ORAI channels may be the mechanism of inhibitory effect of Que and Kae on MC activation, and also suggested Que and Kae may exert the antidepressant effect through suppressing hippocampal mast cell activation.

Methiothepin downregulates SNAP-23 and inhibits degranulation of rat basophilic leukemia cells and mouse bone marrow-derived mast cells

In the present study, we found that methiothepin (a nonselective 5-hydroxytryptamine [5-HT] receptor antagonist) inhibited antigen-induced degranulation in rat basophilic leukemia cells and mouse bone marrow-derived mast cells. Although antigen stimulation induces release of histamine and serotonin (5-HT) by exocytosis and mast cells express several types of 5-HT receptor, the detailed role of these receptors remains unclear. Here, pretreatment of cells with methiothepin attenuated increased intracellular Ca2+ concentration, phosphorylated critical upstream signaling components (Src family tyrosine kinases, Syk, and PLCγ1), and suppressed TNF-α secretion via inhibition of Akt (a Ser/Thr kinase activated by PI3K)and ERK phosphorylation. Furthermore, it inhibited PMA/ionomycin-induced degranulation; this finding suggested that methiothepin affected downstream signaling. IκB kinase β phosphorylates synaptosomal associated protein 23, which regulates the fusion events of the secretory granule/plasma membrane after mast cell activation, resulting in degranulation. We showed that methiothepin blocked PMA/ionomycin-induced phosphorylation of synaptosomal associated protein 23 by inhibiting its interaction with IκB kinase β. Together with the results of selective 5-HT antagonists, it is suggested that methiothepin inhibits mast cell degranulation by downregulating upstream signaling pathways and exocytotic fusion machinery through mainly 5-HT1A receptor. Our findings provide that 5-HT antagonists may be used to relieve allergic reactions.

Fabrication and Characterization of Calcium-Phosphate Lipid System for Potential Dental Application

Lipid has been widely studied as a vehicle and loading vector, but there have been no reports of any such related application in the dental field. The purpose of this research was to fabricate and characterize a nano-size calcium-phosphate lipid (CL) system as a potential vehicle in dental regeneration study, wherein the biocompatibility with dental pulp stem cells (DPSCs) was evaluated. The effect of CL on DPSCs proliferation was analyzed by a CCK-8 assay, and the anti-inflammatory effect was investigated by quantitative polymerase chain reaction (qPCR). Moreover, the effect of CL on odontogenic differentiation of inflamed DPSCs (iDPSCs) was studied by Alizarin red staining, tissue-non-specific alkaline phosphatase (TNAP) staining, qPCR, and western blot analyses. The results of this study showed that CL did not affect the proliferation of DPSCs, it down-regulated the inflammatory-associated markers (IL-1β, IL-6, TNF-α, COX-2) of DPSCs treated with Escherichia coli lipopolysaccharide (LPS), and enhanced the in-vitro odontogenic differentiation potential of iDPSCs. This novel biomaterial has a broad application prospect for its bioactivity and flexible physical property, and thus represents a promising pulpal regeneration material.

Store-Operated Calcium Entry via STIM1 Contributes to MRGPRX2 Induced Mast Cell Functions

Mast cells are inflammatory immune cells that play an essential role in mediating allergic reactions in humans. It is well-known that mast cell activation is critically regulated by intracellular calcium ion (Ca²⁺) concentrations. MAS-related G-protein coupled receptor-X2 (MRGPRX2) is a G-protein coupled receptor (GPCR) expressed on mast cells that is activated by various ligands, including several FDA approved drugs; consequently, this receptor has been implicated in causing pseudo-allergic reactions in humans. MRGPRX2 activation leads to an increase in intracellular Ca²⁺ levels; however, the Ca²⁺ mobilizing mechanisms utilized by this receptor are largely unknown. Previous reports showed that store-operated Ca²⁺ entry (SOCE) via the calcium sensor, stromal interaction molecule 1 (STIM1), regulates mast cell response induced by the high-affinity IgE receptor (FcεRI). In this study, using complementary pharmacologic and genetic ablation approaches we demonstrate that SOCE through STIM1 promotes MRGPRX2-induced human mast cell response in vitro. Importantly, SOCE also critically modulates MrgprB2 (mouse ortholog of human MRGPRX2) dependent inflammation in in vivo mouse models of pseudo-allergy. Collectively, our data suggests that MRGPRX2/MrgprB2 activation of mast cells is dependent on SOCE via STIM1, and further characterization of the MRGPRX2-SOCE-STIM1 pathway will lead to the identification of novel targets for the treatment of pseudo-allergic reactions in humans.

Involvement of intracellular caveolin-1 distribution in the suppression of antigen-induced mast cell activation by cationic liposomes

Cationic liposomes are commonly used as vectors to effectively introduce foreign genes into target cells. In another function, we recently showed that cationic liposomes bound to the mast cell surface suppress the degranulation induced by the cross-linking of high-affinity immunoglobulin E receptor in a time- and dose-dependent manner. This suppression is mediated by the impairment of the sustained level of intracellular Ca²⁺ concentration ([Ca²⁺ ]_i ) via the inhibition of store-operated Ca²⁺ entry. Further, we revealed that the mechanism underlying an impaired [Ca²⁺ ]_i increase is the inhibition of the activation of the phosphatidylinositol 3-kinase (PI3K)-Akt pathway. Yet, how cationic liposomes inhibit the PI3K-Akt pathway is still unclear. Here, we focused on caveolin-1, a major component of caveolae, which is reported to be involved in the activation of the PI3K-Akt pathway in various cell lines. In this study, we showed that caveolin-1 translocated from the cytoplasm to the plasma membrane after the activation of mast cells and colocalized with the p85 subunit of PI3K, which seemed to be essential for PI3K activity. Meanwhile, cationic liposomes suppressed the translocation of caveolin-1 to the plasma membrane and the colocalization of caveolin-1 with PI3K p85 also at the plasma membrane. This finding provides new information for the development of therapies using cationic liposomes against allergies.

Inhibition of degranulation in mast cells attached to a hydrogel through defective microtubule tracts

Mast cells (MCs) are important effectors of the immediate allergic response. MCs are distributed throughout various tissues and organs, and adhere to extracellular matrix (ECM) with broad stiffness in the body. Here we compared cellular responses following antigen stimulation in MCs on glass-base dishes with and without a hydrogel. We found that an antigen-induced increase in intracellular Ca²⁺ concentration was suppressed slightly in cells on hydrogel-coated dishes compared with those on non-coated dishes, whereas their subsequent degranulation was largely inhibited in cells adherent to the hydrogel. Focusing on focal adhesions (FAs), vinculin was distributed in a dot-like manner at the bottom of resting cells on non-coated dishes but not on hydrogel-coated dishes. According to antigen stimulation, phosphorylation of focal adhesion kinase and additive vinculin accumulation to FAs were promoted in cells on non-coated dishes, but were diminished on hydrogel-coated dishes. Moreover, microtubule reorganization and acetylation (which have important roles in MC degranulation) were also suppressed in activated MCs adherent to the hydrogel. These findings suggest that adhesion to a hydrogel led to failure of composition of functional FAs and microtubule tracts, which resulted in suppression of MC degranulation following antigen stimulation.

Calcium release-activated calcium modulator 1 as a therapeutic target in allergic skin diseases

Allergic skin disease is the most common skin condition, and considerably affects patients' life quality because of its recurrence and pruritus. Numbers of studies point out that immune cells, including mast cells and T cells, play pathogenic roles in allergic skin diseases, and share similarities in the activation and secretion of cytokines. Calcium Release-Activated Calcium Modulator 1(CRACM1/ORAI1) is a subtype of Ca²⁺ membrane channel, causing Ca²⁺ influx into the cells. As a second messenger, Ca²⁺ is an essential element that regulates immune responses, especially in the development and function of T and B cells. Thus, ORAI1 is considered to participate in allergic diseases. However, the specific mechanism of ORAI1 in skin disorders is still unclear. In order to investigate the roles of ORAI1 in allergic skin disorders, we reviewed the related articles and concluded that ORAI1 could be a potential therapeutic target for allergic skin diseases.

Video-Rate Bioluminescence Imaging of Degranulation of Mast Cells Attached to the Extracellular Matrix

Degranulation refers to the secretion of inflammatory mediators, such as histamine, serotonin, and proteases, that are stored within the granules of mast cells and that trigger allergic reactions. The amount of these released mediators has been measured biochemically using cell mass. To investigate degranulation in living single cells, fluorescence microscopy has traditionally been used to observe the disappearance of granules and the appearance of these discharged granules within the plasma membrane by membrane fusion and the movement of granules inside the cells. Here, we developed a method of video-rate bioluminescence imaging to directly detect degranulation from a single mast cell by measuring luminescence activity derived from the enzymatic reaction between Gaussia luciferase (GLase) and its substrate coelenterazine. The neuropeptide Y (NPY), which was reported to colocalize with serotonin in the secretory granules, fused to GLase (NPY-GLase) was efficiently expressed in rat basophilic leukemia (RBL-2H3) cells, a mast-cell line, using a preferred human codon-optimized gene. Bioluminescence imaging analysis of RBL-2H3 cells expressing NPY-GLase and adhered on a glass-bottomed dish showed that the luminescence signals from the resting cells were negligible, while the luminescence signals of the secreted NPY-GLase were repeatedly detected after the addition of an antigen. In addition, this imaging method was applicable for observing degranulation in RBL-2H3 cells that adhered to the extracellular matrix (ECM). These results indicated that video-rate bioluminescence imaging using GLase will be a useful tool for detecting degranulation in single mast cells adhered to a variety of ECM proteins.

Overcoming Multidrug Resistance by Codelivery of MDR1-Targeting siRNA and Doxorubicin Using EphA10-Mediated pH-Sensitive Lipoplexes: In Vitro and In Vivo Evaluation

The therapeutic efficacy of chemotherapy is dramatically hindered by multidrug resistance (MDR), which is induced by the overexpression of P-glycoprotein (P-gp). The codelivery of an antitumor drug and siRNA is an effective strategy recently applied in overcoming P-gp-related MDR. In this study, a multifunctional drug delivery system with both pH-sensitive feature and active targetability was designed, in which MDR1-siRNA and DOX were successfully loaded. The resulting carrier EphA10 antibody-conjugated pH-sensitive doxorubicin (DOX), MDR1-siRNA coloading lipoplexes (shortened as DOX + siRNA/ePL) with high serum stability had favorable physicochemical properties. DOX + siRNA/ePL exhibited an incremental cellular uptake, enhanced P-gp downregulation efficacy, as well as a better cell cytotoxicity in human breast cancer cell line/adriamycin drug-resistant (MCF-7/ADR) cells. The results of the intracellular colocalization study indicated that DOX + siRNA/ePL possessed the ability for pH-responsive rapid endosomal escape in a time-dependent characteristic. Meanwhile, the in vivo antitumor activities suggested that DOX + siRNA/ePL could prolong the circulation time as well as specifically accumulate in the tumor cells via receptor-mediated endocytosis after intravenous administration into the blood system. The histological study further demonstrated that DOX + siRNA/ePL could inhibit the proliferation, induce apoptosis effect, and downregulate the P-gp expression in vivo. Altogether, DOX + siRNA/ePL was expected to be a suitable codelivery system for overcoming the MDR effect.