Switch activation of PI-PLC downstream signals in activated macrophages with wortmannin

Different expression and subcellular localization of Phosphoinositide-specific Phospholipase C enzymes in differently polarized macrophages

Macrophages' phenotypic and functional diversity depends on differentiating programs related to local environmental factors. Recent interest was deserved to the signal transduction pathways acting in macrophage polarization, including the phosphoinositide (PI) system and related phospholipase C (PLC) family of enzymes. The expression panel of PLCs and the subcellular localization differs in quiescent cells compared to the pathological counterpart. We analyzed the expression of PLC enzymes in unpolarized (M0), as well as in M1 and M2 macrophages to list the expressed isoforms and their subcellular localization. Furthermore, we investigated whether inflammatory stimulation modified the basal panel of PLCs' expression and subcellular localization. All PLC enzymes were detected within both M1 and M2 cells, but not in M0 cells. M0, as well as M1 and M2 cells own a specific panel of expression, different for both genes' mRNA expression and intracellular localization of PLC enzymes. The panel of PLC genes' expression and PLC proteins' presence slightly changes after inflammatory stimulation. PLC enzymes might play a complex role in macrophages during inflammation and probably also during polarization.

Antiproliferative Activity of Hinokitiol, a Tropolone Derivative, Is Mediated via the Inductions of p-JNK and p-PLCγ1 Signaling in PDGF-BB-Stimulated Vascular Smooth Muscle Cells

Abnormal proliferation of vascular smooth muscle cells (VSMCs) is important in the pathogenesis of vascular disorders such as atherosclerosis and restenosis. Hinokitiol, a tropolone derivative found in Chamacyparis taiwanensis, has been found to exhibit anticancer activity in a variety of cancers through inhibition of cell proliferation. In the present study, the possible anti-proliferative effect of hinokitiol was investigated on VSMCs. Our results showed that hinokitiol significantly attenuated the PDGF-BB-stimulated proliferation of VSMCs without cytotoxicity. Hinokitiol suppressed the expression of proliferating cell nuclear antigen (PCNA), a maker for cell cycle arrest, and caused G0/G1 phase arrest in cell cycle progression. To investigate the mechanism underlying the anti-proliferative effect of hinokitiol, we examined the effects of hinokitiol on phosphorylations of Akt, ERK1/2, p38 and JNK1/2. Phospholipase C (PLC)-γ1 phosphorylation, its phosphorylated substrates and p27^kip1 expression was also analyzed. Pre-treatment of VSMCs with hinikitiol was found to significantly inhibit the PDGF-BB-induced phosphorylations of JNK1/2 and PLC-γ1, however no effects on Akt, ERK1/2, and p38. The up-regulation of p27^kip1 was also observed in hinokitiol-treated VSMCs. Taken together, our results suggest that hinokitiol inhibits PDGF-BB-induced proliferation of VSMCs by inducing cell cycle arrest, suppressing JNK1/2 phosphorylation and PLC-γ1, and stimulating p27^kip1 expression. These findings suggest that hinokitiol may be beneficial for the treatment of vascular-related disorders and diseases.

A Taiwanese Propolis Derivative Induces Apoptosis through Inducing Endoplasmic Reticular Stress and Activating Transcription Factor-3 in Human Hepatoma Cells

Activating transcription factor-(ATF-) 3, a stress-inducible transcription factor, is rapidly upregulated under various stress conditions and plays an important role in inducing cancer cell apoptosis. NBM-TP-007-GS-002 (GS-002) is a Taiwanese propolin G (PPG) derivative. In this study, we examined the antitumor effects of GS-002 in human hepatoma Hep3B and HepG2 cells in vitro. First, we found that GS-002 significantly inhibited cell proliferation and induced cell apoptosis in dose-dependent manners. Several main apoptotic indicators were found in GS-002-treated cells, such as the cleaved forms of caspase-3, caspase-9, and poly(ADP-ribose) polymerase (PARP). GS-002 also induced endoplasmic reticular (ER) stress as evidenced by increases in ER stress-responsive proteins including glucose-regulated protein 78 (GRP78), growth arrest- and DNA damage-inducible gene 153 (GADD153), phosphorylated eukaryotic initiation factor 2α (eIF2α), phosphorylated protein endoplasmic-reticular-resident kinase (PERK), and ATF-3. The induction of ATF-3 expression was mediated by mitogen-activated protein kinase (MAPK) signaling pathways in GS-002-treated cells. Furthermore, we found that GS-002 induced more cell apoptosis in ATF-3-overexpressing cells. These results suggest that the induction of apoptosis by the propolis derivative, GS-002, is partially mediated through ER stress and ATF-3-dependent pathways, and GS-002 has the potential for development as an antitumor drug.

Role of sphingomyelin synthase in controlling the antimicrobial activity of neutrophils against Cryptococcus neoformans

The key host cellular pathway(s) necessary to control the infection caused by inhalation of the environmental fungal pathogen Cryptococcus neoformans are still largely unknown. Here we have identified that the sphingolipid pathway in neutrophils is required for them to exert their killing activity on the fungus. In particular, using both pharmacological and genetic approaches, we show that inhibition of sphingomyelin synthase (SMS) activity profoundly impairs the killing ability of neutrophils by preventing the extracellular release of an antifungal factor(s). We next found that inhibition of protein kinase D (PKD), which controls vesicular sorting and secretion and is regulated by diacylglycerol (DAG) produced by SMS, totally blocks the extracellular killing activity of neutrophils against C. neoformans. The expression of SMS genes, SMS activity and the levels of the lipids regulated by SMS (namely sphingomyelin (SM) and DAG) are up-regulated during neutrophil differentiation. Finally, tissue imaging of lungs infected with C. neoformans using matrix-assisted laser desorption-ionization mass spectrometry (MALDI-MS), revealed that specific SM species are associated with neutrophil infiltration at the site of the infection. This study establishes a key role for SMS in the regulation of the killing activity of neutrophils against C. neoformans through a DAG-PKD dependent mechanism, and provides, for the first time, new insights into the protective role of host sphingolipids against a fungal infection.

Carbon monoxide induces cyclooxygenase-2 expression through MAPKs and PKG in phagocytes

Many biological functions of heme oxygenase (HO) have been attributed to its enzymatic byproduct carbon monoxide (CO). CO has been demonstrated to play an important role in down-regulation of pro-inflammatory cytokines, but few studies have investigated the effects of CO on the cyclooxygenase-2 (COX-2) expression in macrophage. Here, we assessed the induction of COX-2 by CO in macrophage with or without lipopolysaccharide (LPS) stimulation. Tricarbonyldichloro ruthenium (II) dimmer (CORM-2) is a well known CO-releasing molecule, and exhibits anti-inflammatory activity in several cell types. In this study, both CORM-2 and CO gas were used to investigate the induction of COX-2 and the underlying molecular mechanisms in macrophage. Western blot and RT-PCR analysis demonstrated that CORM-2 and CO gas (500 ppm) significantly inhibited the protein and mRNA expression of iNOS in LPS-activated macrophages. In contrast, CORM-2 and CO gas up-regulated COX-2 expression and prostaglandin E₂ (PGE₂) production in the macrophage with or without LPS. CORM-2 time-dependently induced the phosphorylation of Akt and MAPKs, and the induction of COX-2 could be blocked by Akt, PKG, and MAPKs inhibitors. Indomethacin was used to decrease CORM-2-induced PGE₂ production by inhibiting COX-2 enzyme activity. Indomethacin was unable to reverse the decrease of iNOS, but it could restore the IL-1β expression and decrease the IL-10 expression in CORM-2-treated cells. The results suggest that CO induced COX-2 expression and PGE₂ production through activating the Akt, PKG, and MAPK pathways, and CO-induced PGE₂ may modulate inflammation during macrophage activation by suppressing IL-1β expression and inducing IL-10 production.

Suppression of PLCbeta2 by endotoxin plays a role in the adenosine A(2A) receptor-mediated switch of macrophages from an inflammatory to an angiogenic phenotype

Toll-like receptor (TLR) 2, 4, 7, and 9 agonists, together with adenosine A(2A) receptor (A(2A)R) agonists, switch macrophages from an inflammatory (M1) to an angiogenic (M2-like) phenotype. This switch involves induction of A(2A)Rs by TLR agonists, down-regulation of tumor necrosis factor alpha (TNFalpha) and interleukin-12, and up-regulation of vascular endothelial growth factor (VEGF) and interleukin-10 expression. We show here that the TLR4 agonist lipopolysaccharide (LPS) induces rapid and specific post-transcriptional down-regulation of phospholipase C(PLC)beta1 and beta2 expression in macrophages by de-stabilizing their mRNAs. The PLCbeta inhibitor U73122 down-regulates TNFalpha expression by macrophages, and in the presence of A(2A)R agonists, up-regulates VEGF, mimicking the synergistic action of LPS with A(2A)R agonists. Selective down-regulation of PLCbeta2, but not PLCbeta1, using small-interfering RNA resulted in increased VEGF expression in response to A(2A)R agonists, but did not suppress TNFalpha expression. Macrophages from PLCbeta2(-/-) mice also expressed increased VEGF in response to A(2A)R agonists. LPS-mediated suppression of PLCbeta1 and beta2 is MyD88-dependent. In a model of endotoxic shock, LPS (35 microg/mouse, i.p.) suppressed PLCbeta1 and beta2 expression in spleen, liver, and lung of wild-type but not MyD88(-/-) mice. These studies indicate that LPS suppresses PLCbeta1 and beta2 expression in macrophages in vitro and in several tissues in vivo. These results suggest that suppression of PLCbeta2 plays an important role in switching M1 macrophages into an M2-like state.

Osthole, a potential antidiabetic agent, alleviates hyperglycemia in db/db mice

Osthole is an agent isolated from Cnidium monnieri (L.) Cusson and Angelica pubescens and has been used to treat several diseases, including metabolic syndromes. To investigate the hypoglycemic effects of osthole in diabetic db/db mice and the underlying mechanisms of these effects by in vitro assay, diabetic db/db mice and cell experiments were utilized to understand its possible effects. Osthole significantly activated both PPARalpha and PPARgamma in a dose-dependent manner based on the results of the transition transfection assay. The activation of PPARalpha and PPARgamma by osthole also resulted in an increase in the expression of PPAR target genes such as PPAR itself, adipose fatty acid-binding protein 2, acyl-CoA synthetases, and carnitine palmitoyltransferase-1A. In vitro results suggested that osthole might be a dual PPARalpha/gamma activator, but its chemical structure differed from that of the thiazolidinedione class of antidiabetic drugs. In addition, osthole markedly activated the AMP-activated protein kinase and its downstream acetyl CoA carboxylase molecules by increasing their phosphorylation levels. Finally, obese diabetic db/db mice were treated with osthole by different administered routes, and osthole was found to markedly reduce blood glucose level. Interestingly, osthole did not reduce the blood insulin or lipid levels, two phenomena that did occur in animals treated with insulin sensitizers like PPAR agonists. These results suggest that osthole can alleviate hyperglycemia and could be potentially developed into a novel drug for treatment of diabetes mellitus.