Interferon-gamma inhibits endocytosis of soluble animated beta-1,3-D-glucan and neutral red in mouse peritoneal macrophages

A β-1,3/1,6-glucan from Durvillaea Antarctica inhibits tumor progression in vivo as an immune stimulator

β-glucans trigger the proinflammatory responses of innate immune cells to enhance the host defense. A variety of β-glucans were identified as strong immune stimulator and exerted antitumor activities. Our previous work indicates that a β-1,3/1,6-glucan (BG136) derived from marina alga Durvillaea antarctica promotes the proinflammatory responses in macrophage cell line RAW264.7. In the present study, we further explored its antitumor effects in vivo as an immune stimulator. The data shows that BG136 alone decreases the tumor burdens in DLD1 xenograft and AOM-DSS induced tumor models. BG136 also augments the antitumor effects of PD-1 antibody in B16 syngeneic tumor model. BG136 increases macrophage phagocytosis, enhances cytokine/chemokine secretion and modulates the systemic and intratumoral immune cell composition. Collectively, these data suggest that BG136 might act as an immune stimulator to exert antitumor effects in vivo.

TIMAP repression by TGFβ and HDAC3-associated Smad signaling regulates macrophage M2 phenotypic phagocytosis

TIMAP (TGFβ-inhibited membrane-associated protein) is an endothelium-enriched TGFβ downstream protein and structurally belongs to the targeting subunit of myosin phosphatase; however, the mechanism of TGFβ repressing TIMAP and its functional relevance to TGFβ bioactivity remain largely unknown. Here, we report that TIMAP is reduced in TGFβ-elevated mouse fibrotic kidney and highly expressed in macrophages. TGFβ repression of TIMAP is associated with HDAC3 upregulation and its recruitment by Smad2/3 at the Smad binding element on TIMAP promoter, whereas specific HDAC3 inhibition reversed the TIMAP repression, suggesting that TGFβ transcriptionally downregulates TIMAP through HDAC3-associated Smad signaling. Further investigation showed that TIMAP over-expression interrupted TGFβ-associated Smad signaling and TIMAP repression by TGFβ correlated with TGFβ-induced macrophage M2 polarization markers, migration, and phagocytosis-the processes promoted by phosphorylation of the putative TIMAP substrate myosin light chain (MLC). Consistently, TIMAP dephosphorylated MLC in macrophages and TGFβ induced macrophage migration and phagocytosis in TIMAP- and MLC phosphorylation-dependent manners, suggesting that TIMAP dephosphorylation of MLC constitutes an essential regulatory loop mitigating TGFβ-associated macrophage M2 phenotypic activities. Given that hyperactive TGFβ often causes excessive macrophage phagocytic activities potentially leading to various chronic disorders, the strategies targeting HDAC3/TIMAP axis might improve TGFβ-associated pathological processes.

KEY MESSAGE

TIMAP is enriched in the endothelium and highly expressed in macrophages. TIMAP is suppressed by TGFβ via HDAC3-associated Smad signaling. TIMAP inhibits TGFβ signaling and TGFβ-associated macrophage M2 polarization. TIMAP dephosphorylation of MLC counteracts TGFβ-induced macrophage phagocytosis.

Functional characterization of mannose receptor expressed by immunocompetent mouse microglia

The mannose receptor is a pattern-recognition receptor involved in innate and adaptive immunity. The receptor is mainly expressed by macrophages and, within the brain, by astrocytes and microglia. This study reports for the first time the effects of two classical proinflammatory (interferon-gamma, IFNgamma) and anti-inflammatory (interleukin-4, IL-4) cytokines on the levels of expression and activity of the mannose receptor expressed by mouse microglia, the brain resident macrophages. As observed for macrophages, IFNgamma treatment led to a decrease and IL-4 to an increase of mannose receptor expression. Consequently, the rates of pinocytosis were strongly upregulated by IL-4 and inhibited by IFNgamma. This latter, however, resumed with time and reached again the constitutive rate of pinocytosis. This recovery resulted from an increased pinocytic activity of the few mannose receptor molecules still expressed by IFNgamma-treated microglia. This may suggest a brain-specific regulation of the effects of IFNgamma since such a phenomenon has not been observed in macrophages. Together, these observations demonstrate that cytokine-stimulated immunocompetent microglia express a functional mannose receptor.

Effect of fumonisin B1 on structure and function of macrophage plasma membrane

Fumonisin B1 (FB1), a mycotoxin produced by Fusarium moniliforme and related fungi, is nephrotoxic, neurotoxic, hepatotoxic, carcinogenic and immunosuppressive in animals and man. In this study we evaluate the modifications of fluidity, endocytosis and peroxidative damage of plasma membrane induced by FB1 in macrophage cell line J774A.1. In these immune cells FB1 (1-10 microM) enhances membrane fluidity and increases, time-dependently, the horseradish peroxidase (HRP) endocytosis. This effect is concentration-dependent, significant at 10 microM, and reverted by IFN-gamma (100 U/ml). Moreover, FB1 (1-10 microM) induces a membrane peroxidative damage as evident by the increase of malondialdehyde (MDA) production. All these mycotoxin effects provide additional insight into potential mechanism by which FB1, in macrophages, might enhance membrane damage and oxidative stress contributing to the pathogenesis of mycotoxin induced diseases.

Primary culture of rat taste bud cells that retain molecular markers for taste buds and permit functional expression of foreign genes

Taste buds are constituted of several kinds of cells which have distinct characteristics and play different roles. In this study, we have established an in vitro culture system by optimizing the method for isolating the cells and by selecting culture media and reagents effective for cell viability and adhesion. As a result, the taste bud cells were adhesive and viable for over 3 days when cultured onto Matrigel-coated dishes in medium based on keratinocyte growth medium. The cells retained molecular markers for both the cytoskeleton and intracellular signaling such as cytokeratin 8 and phospholipase Cbeta2. In addition, three intracellular signaling molecules, gustducin, phospholipase Cbeta2, and inositol 1,4,5-trisphosphate receptor type 3, are expressed in the same correlation as those in vivo, although the ratio of signaling molecule-positive cells vs. total cells was somewhat lower in the culture than in vivo. Next, we tried several methods to introduce foreign genes into the cells, and obtained a greater than 90% efficiency of introduction using an adenovirus vector. Finally, we show that an exogenously expressed myc-tagged alpha1A-adrenoceptor sorts into the plasma membrane, and transduces a ligand-dependent signal resulting in intracellular [Ca(2+)] increase in about half of the infected cells. These results suggest that taste bud cells after 3 days of culture retain characteristic molecular markers, and may prove useful for describing the molecular and physiological features of taste bud cells, and that these cells can be further manipulated by adenovirus-mediated gene introduction.

Phagocytic clearance of apoptotic neurons by Microglia/Brain macrophages in vitro: involvement of lectin-, integrin-, and phosphatidylserine-mediated recognition

Microglia, the tissue macrophages of the brain, play a crucial role in recognition and phagocytic removal of apoptotic neurons. The microglial receptors for recognition of apoptotic neurons are not yet characterized. Here we established a co-culture model of primary microglia and cerebellar granule neurons to examine the receptor systems involved in recognition/uptake of apoptotic neurons. Treatment with 100 microM S-nitrosocysteine induced apoptosis of cerebellar neurons as indicated by nuclear condensation and phosphatidylserine exposure to the exoplasmic leaflet of the plasma membrane. Microglial cells were added to neurons 2 h after apoptosis induction and co-cultured for 6 h in the presence of ligands that inhibit recognition by binding to respective receptors. Binding/phagocytosis was determined after combined 4', 6-diamidino-2-phenylindole/propidium iodide (for apoptotic/necrotic neurons) and lectin staining (for microglia). Uptake of apoptotic neurons was reduced by N-acetylglucosamine or galactose, suggesting that recognition involves asialoglycoprotein-like lectins. Furthermore, the inhibition of microglial binding/uptake of apoptotic neurons by RGDS peptide suggests a role of microglial vitronectin receptor. As microglia selectively bind lipid vesicles enriched in phosphatidylserine and O-phospho-L-serine interfered with the uptake of apoptotic neurons, an involvement of phosphatidylserine receptor is rather likely. Apoptotic neurons do not release soluble signals that serve to attract or activate microglia. Collectively, these results suggest that apoptotic neurons generate a complex surface signal recognized by different receptor systems on microglia.

Neutral red assay modification to prevent cytotoxicity and improve reproducibility using E-63 rat skeletal muscle cells

Cellular uptake of neutral red dye (NR) is currently used as an indirect measure of viable cells in cultures. We used E-63 rat skeletal muscle cells to identify causes of NR assay variability and to develop modifications that substantially reduce it. Three methods of NR preparation and/or addition to cells were used. When NR medium was prepared, incubated overnight, and filtered to remove precipitates, the amount of dye precipitated varied greatly. Coefficients of variation (CVs) in NR uptake were greater than 25% between assays. Higher NR concentrations, longer incubation times, increased pH, and decreased temperature promoted NR precipitation in media. NR media prepared and filtered just prior to use or direct addition of prefiltered NR stock solution to cell cultures resulted in much smaller CVs between assays. NR was cytotoxic to E-63 rat muscle and primary quail myoblasts in a time- and concentration-dependent manner. NR exposure to E-63 cells for greater than 1.25 and 2 hr at 157 or 127 microg/ml, respectively, was associated with swelling and rupture of lysosomes. By contrast, there was no evidence of cytotoxicity when E-63 cells were exposed to NR for 1 hr at either 127 or 157 microg/ml. Primary quail myoblasts developed lysosomal swelling and ruptured more rapidly than E-63 cells when exposed to NR at either 127 or 157 microg/ml. For confluent 10-day cultures of E-63 cells exposed to NR at 127 microg/ml for 1 hr, the CVs within assay and between assays were 3.3-3.9% and 5.1%, respectively. For similarly exposed, actively replicating 3-day cultures of E-63 cells, the CVs within and between assays were 6.2-9.6% and 2.4%, respectively. NR uptake by the E-63 cells was linear with respect to viable cell number.