Ginsenoside Re mitigates memory impairments in aged GPx-1 KO mice by inhibiting the interplay between PAFR, NFκB, and microgliosis in the hippocampus

Ginsenoside Re (GRe) upregulates anti-aging klotho by mainly upregulating glutathione peroxidase-1 (GPx-1). However, the anti-aging mechanism of GPx-1 remains elusive. Here we investigated whether the GRe-mediated upregulation of GPx-1 modulates oxidative and proinflammatory insults. GPx-1 gene depletion altered redox homeostasis and platelet-activating factor receptor (PAFR) and nuclear factor kappa B (NFκB) expression, whereas the genetic overexpression of GPx-1 or GRe mitigated this phenomenon in aged mice. Importantly, the NFκB inhibitor pyrrolidine dithiocarbamate (PDTC) did not affect PAFR expression, while PAFR inhibition (i.e., PAFR knockout or ginkgolide B) significantly attenuated NFκB nuclear translocation, suggesting that PAFR could be an upstream molecule for NFκB activation. Iba-1-labeled microgliosis was more underlined in aged GPx-1 KO than in aged WT mice. Triple-labeling immunocytochemistry showed that PAFR and NFκB immunoreactivities were co-localized in Iba-1-positive populations in aged mice, indicating that microglia released these proteins. GRe inhibited triple-labeled immunoreactivity. The microglial inhibitor minocycline attenuated aging-related reduction in phospho-ERK. The effect of minocycline was comparable with that of GRe. GRe, ginkgolide B, PDTC, or minocycline also attenuated aging-evoked memory impairments. Therefore, GRe ameliorated aging-associated memory impairments in the absence of GPx-1 by inactivating oxidative insult, PAFR, NFkB, and microgliosis.

PAF Receptor Inhibition Attenuates Neuronal Pyroptosis in Cerebral Ischemia/Reperfusion Injury

Ischemic stroke is an inflammation-related disease, during which process activation of NLRP3 inflammasome and subsequent pyroptosis play crucial roles. Platelet-activating factor (PAF) is a potent phospholipid regulator of inflammation which exerts its effect via binding specific PAF receptor (PAFR). However, whether PAFR contributes to pyroptosis during ischemia/reperfusion (I/R) injury remains to be elucidated. To explore the underlying effect of PAFR on ischemic stroke from the perspective of pyroptosis, mice were subjected to middle cerebral artery occlusion/reperfusion (MCAO/R) injury and primary cultures of mice cerebral cortical neurons were exposed to oxygen-glucose deprivation/reoxygenation (OGD/R) injury to mimic I/R in vivo and in vitro, after which indexes associated with pyroptosis were analyzed. Intriguingly, our results indicated that inhibition of PAFR with its inhibitor XQ-1H or PAFR siRNA exerted a neuroprotective effect against I/R injury both in vivo and in vitro. Furthermore, inflammasome activation and pyroptosis after ischemic challenge were attenuated by XQ-1H or PAFR siRNA. Besides, the protection of XQ-1H was abolished by PAF stimulaiton to some extent. Moreover, XQ-1H or PAFR siRNA alleviated the neuronal pyroptosis induced by LPS and nigericin (an NLRP3 activator) in cortical neurons. Taken together, this study firstly demonstrates that PAFR is involved in neuronal pyroptosis after I/R injury, and XQ-1H, a specific PAFR inhibitor, has a promising prospect in attenuating I/R injury from the perspective of anti-pyroptosis.

Bovine respiratory coronavirus enhances bacterial adherence by upregulating expression of cellular receptors on bovine respiratory epithelial cells

Bovine coronavirus (BCoV) is one of the agents causing bovine respiratory disease complex (BRDC), with single infection tending to be mild to moderate; the probability of developing pneumonia in BRDC may be affected by viral and bacterial combinations. Previously, we reported that bovine respiratory syncytial virus (BRSV) infection enhances adherence of Pasteurella multocida (PM) to cells derived from the bovine lower respiratory tract but that BRSV infection in cells derived from the upper respiratory tract reduces PM adherence. In this study, we sought to clarify whether the modulation of bacterial adherence to cells derived from the bovine upper and lower respiratory tract is shared by other BRDC-related viruses by infecting bovine epithelial cells from the trachea, bronchus and lung with BCoV and/or PM. The results showed that cells derived from both the upper and lower respiratory tract were susceptible to BCoV infection. Furthermore, all cells infected with BCoV exhibited increased PM adherence via upregulation of two major bacterial adhesion molecules, intercellular adhesion molecule-1 (ICAM-1) and platelet-activating factor receptor (PAF-R), suggesting that compared with BRSV infection, BCoV infection differentially modulates bacterial adherence. In summary, we identified distinct interaction between bovine respiratory viruses and bacterial infections.

Platelet-Activating Factor Deteriorates Lysophosphatidylcholine-Induced Demyelination Via Its Receptor-Dependent and -Independent Effects

Accumulating evidence suggests that platelet-activating factor (PAF) increases the inflammatory response in demyelinating diseases such as multiple sclerosis. However, PAF receptor (PAFR) antagonists do not show therapeutic efficacy for MS, and its underlying mechanisms remain poorly understood. In the present study, we investigated the effects of PAF on an ex vivo demyelination cerebellar model following lysophosphatidylcholine (LPC, 0.5 mg/mL) application using wild-type and PAFR conventional knockout (PAFR-KO) mice. Demyelination was induced in cerebellar slices that were cultured with LPC for 18 h. Exogenous PAF (1 μM) acting on cerebellar slices alone did not cause demyelination but increased the severity of LPC-induced demyelination in both wild-type and PAFR-KO mice. LPC inhibited the expression of PAF-AH, MBP, TNF-α, and TGF-β1 but facilitated the expression of IL-1β and IL-6 in wild-type preparations. Of note, exogenous PAF stimulated microglial activation in both wild-type and PAFR-KO mice. The subsequent inflammatory cytokines TNFα, IL-1β, and IL-6 as well as the anti-inflammatory cytokine TGF-β1 demonstrated a diverse transcriptional profile with or without LPC treatment. PAF promoted TNF-α expression and suppressed TGF-β1 expression indiscriminately in wild-type and knockout slices; however, transcription of IL-1β and IL-6 was not significantly affected in both slices. The syntheses of IL-1β and IL-6 were significantly increased in LPC-induced demyelination preparations without PAF but showed a redundancy in PAF-treated wild-type and knockout slices. These data suggest that PAF can play a detrimental role in LPC-induced demyelination probably due to a redundant response of PAFR-dependent and PAFR-independent effects on inflammatory cytokines.

Particulate matter exposure promotes Pseudomonas aeruginosa invasion into airway epithelia by upregulating PAFR via the ROS-mediated PI3K pathway

Over exposure to particulate matter (PM) could irritate respiratory tract infection; while, Pseudomonas aeruginosa (P. aeruginosa) is one of the main common pathogens. Our study aims are to define whether PM exposure enhances the invasion of P. aeruginosa into the airway epithelia and to characterize the underlying mechanisms. Human bronchial epithelial cells (BEAS-2B) or BEAS-2B transfected by PAFR siRNA were challenged with PM and pretreated with N-acetylcysteine (NAC), LY294002 (PI3K inhibitor), BAY 11-7082 (NF-κB inhibitor), or CV-3988 (PAFR antagonist). P. aeruginosa invasion was evaluated using colony-forming units assay and confocal microscopy. Real-time RT-PCR, immunofluorescence, flow cytometry and western blotting were used to detect the genes or proteins expression. PM exposure promoted P. aeruginosa invasion into BEAS-2B cells through ROS-mediated PI3K pathway which enhanced the expression of PAFR, which could be alleviated by treatment with NAC, LY294002, and BAY 11-7082. Furthermore, NAC and PAFR siRNA attenuated PM-stimulated activation of PI3K pathway. Treatment with PAFR antagonist and siRNA also alleviated PM exposure-induced P. aeruginosa invasion into BEAS-2B cells. Our results demonstrated that PM exposure increased the PAFR expression and activated the PI3K pathway in a ROS-dependent manner. Upregulated PAFR and activated PI3K pathway formed a positive regulatory loop and promoted the invasion of P. aeruginosa into airway epithelia. These mechanisms may provide a novel approach against P.aeruginosa invasion.

Blockade of platelet-activating factor receptor attenuates abnormal behaviors induced by phencyclidine in mice through down-regulation of NF-κB

Accumulating evidence suggests that neuroinflammation is one of the important etiologic factors of abusive and neuropsychiatric disorders. Platelet-activating factor (PAF) is potent proinflammatory lipid mediat1or and plays a pivotal role in neuroinflammatory disorders through the specific PAF receptor (PAF-R). Phencyclidine (PCP) induces a psychotomimetic state that closely resembles schizophrenia. Here, we investigated the role of PAF-R in the abnormal behaviors induced by PCP in mice. Repeated treatment with PCP resulted in a significant increase in PAF-R gene expression in the prefrontal cortex (PFC) and in the hippocampus. This increase was more pronounced in the PFC than hippocampus. Treatment with PCP resulted in a significant increase in nuclear translocation of the nuclear factor kappa beta (NF-κB) p65 and DNA binding activity, indicating that the proinflammatory molecule NF-κB was increased through up-regulation of PAF-R. Consistently, NF-κB activation was significantly protected by the PAF-R antagonist, ginkgolide B (Gink B), in PAF-R knockout mice and by the NF-κB inhibitor, pyrrolidine dithiocarbamate (PDTC). In addition, PCP-induced abnormal behaviors (i.e., reduced sociability, depression, cognitive impairment, and behavioral sensitization) were significantly attenuated by Gink B, in PAF-R knockout mice, and by PDTC. Importantly, PDTC did not significantly alter the attenuations observed in Gink B-treated mice or PAF-R knockout mice, indicating that NF-κB is a critical target for neuropsychotoxic modulation of PAF-R. Therefore, the results suggest that PAF-R mediates PCP-induced neuropsychotoxicity via a NF-κB-dependent mechanism, and that up-regulation of PAF-R may be associated with schizophrenia-like behavior in animal models.

Does upregulated host cell receptor expression provide a link between bacterial adhesion and chronic respiratory disease?

Expression of the platelet-activating factor receptor is upregulated in the respiratory epithelium of smokers and chronic obstructive pulmonary disease patients. We have recently determined that increased expression of PAFr correlates with higher levels of adhesion to human bronchial epithelial cells by non-typable Haemophilus influenzae and Streptococcus pneumoniae which are major bacterial pathogens in acute exacerbations of COPD. In addition, we found that a PAFr antagonist decreased the adhesion of both respiratory bacterial pathogens to non-cigarette exposure control levels. This highlights the possibility that epithelial receptors, that are upregulated in response to cigarette smoke, could be targeted to specifically block chronic bacterial infections of the lower respiratory tract. In this commentary, we explore the question of whether adhesion to a temporally-upregulated host receptor is a common event in chronic bacterial disease, and as such, could represent a putative therapeutic target for blocking infection by respiratory and other pathogens.

Influence of platelet-activating factor receptor (PAFR) on Brucella abortus infection: implications for manipulating the phagocytic strategy of B. abortus

BACKGROUND

Brucella abortus is an intracellular pathogen which can infect and persist in host cells through multiple interactions. Above all, its interaction to host cell receptor is important to understand the pathogenic mechanisms of B. abortus. Accordingly, we demonstrated that platelet-activating factor receptor (PAFR) affects host cell response against B. abortus infection.

RESULTS

First of all, B. abortus infection to macrophage induces secretion of platelet-activating factor (PAF), which is a PAFR agonist. The stimulation of PAFR by PAF remarkably increases B. abortus uptake into macrophages. It induces Janus kinase 2 (JAK2) and p38α phosphorylation, indicating that PAFR-mediated activation of JAK2 signaling leads to enhanced uptake of B. abortus. Moreover, the dynamics of F-actin polymerization revealed that PAFR-mediated B. abortus uptake is related with the reorganization of F-actin and JAK2. Upon B. abortus phagocytosis, reduced PAFR in the membrane and subsequently increased levels of PAFR colocalization with endosomes were observed which indicate that B. abortus uptake into macrophages allowed PAFR trafficking to endosomes.

CONCLUSIONS

This study demonstrated that PAFR has a compelling involvement in B. abortus uptake as a promoter of phagocytosis, which is associated with JAK2 activation. Thus, our findings establish a novel insight into a receptor-related phagocytic mechanism of B. abortus.

Bronchial platelet-activating factor receptor in chronic obstructive pulmonary disease

BACKGROUND

Bacteria expressing phosphorylcholine (ChoP) co-opt host-expressed platelet-activating factor receptor (PAFR) to adhere to lower airway cells. Cigarette smoke and rhinovirus (RV) infection upregulate PAFR-dependent bacterial adhesion to airway cells in vitro, and in healthy adults smoking increases the proportion of PAFR positive bronchial epithelial cells. To date the effect of chronic obstructive pulmonary disease (COPD) on smoke-induced PAFR is unknown. We therefore sought to test the hypothesis that bronchial PAFR mRNA expression is increased in smokers with chronic obstructive pulmonary disease (COPD), and further increases after RV infection.

METHODS

Endobronchial biopsies were obtained by fibreoptic bronchoscopy from healthy non-smokers, smokers without airway obstruction, and smokers with COPD, before and after infection with rhinovirus (RV) serotype 16. Endobronchial PAFR mRNA expression was assessed by quantitative PCR and expressed as a ratio of glyceraldehyde-3-phosphate dehydrogenase. The distribution of PAFR was assessed by immunohistochemistry.

RESULTS

Baseline PAFR mRNA expression was increased (p < 0.05) in smokers (n = 16), and smokers with COPD (n = 14) compared with non-smokers (n = 18). In RV16 infected subjects there was no increase in PAFR mRNA expression in either non-smokers (n = 9), smokers (n = 8), or smokers with COPD (n = 7). PAFR immunoreactivity in all 3 groups was predominately restricted to the bronchial epithelium and submucosal glands.

CONCLUSIONS

Endobronchial PAFR mRNA is increased in both smokers without airway obstruction and smokers with COPD. We found preliminary evidence that RV16 infection does not increase PAFR mRNA expression in either smokers or smokers with COPD.

Roles of BN52021 in platelet-activating factor pathway in inflammatory MS1 cells

AIM: To determine the effects of BN52021 on platelet-activating factor receptor (PAFR) signaling molecules under lipopolysaccharide (LPS)-induced inflammatory conditions in MS1 cells.

METHODS: MS1 cells (a mouse pancreatic islet endothelial cell line) were grown in Dulbecco’s modified Eagle’s medium supplemented with 10% fetal bovine serum, 2 mmol/L glutamine and 100 μg/mL penicillin/streptomycin in 5% CO₂ at 37 °C. After growth to confluency in media, the cells were processed for subsequent studies. The MS1 cells received 0, 0.1, 1 and 10 μg/mL LPS in this experiment. The viability/proliferation of the cells induced by LPS was observed using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide colorimetric assay. Apoptosis and necrosis of the cells under the inflammatory condition described previously were observed using Hoechst 33342-propidium iodide staining. Adenylate cyclase (AC), phospholipase A₂ (PLA₂), phospholipase Cβ (PLCβ), protein tyrosine kinase (PTK), G protein-coupled receptor kinases (GRK) and p38-mitogen-activated protein kinase (p38 MAPK) mRNA in the PAFR signaling pathway were measured by real-time polymerase chain reaction. The protein expression level of phosphorylated AC (p-AC), phosphorylated PLA₂ (p-PLA₂), phosphorylated PTK (p-PTK), phosphorylated p38 MAPK (p-p38 MAPK), PLCβ and GRK was measured using Western blotting analysis.

RESULTS: The activity of MS1 cells incubated with different concentrations of LPS for 6 h decreased significantly in the 1 μg/mL LPS group (0.49 ± 0.10 vs 0.67 ± 0.13, P < 0.05) and 10 μg/mL LPS group (0.44 ± 0.10 vs 0.67 ± 0.13, P < 0.001), but not in 0.1 μg/mL group. When the incubation time was extended to 12 h (0.33 ± 0.05, 0.32 ± 0.03 and 0.25 ± 0.03 vs 0.69 ± 0.01) and 24 h (0.31 ± 0.01, 0.29 ± 0.03 and 0.25 ± 0.01 vs 0.63 ± 0.01), MS1 cell activity decreased in all LPS concentration groups compared with the blank control (P < 0.001). BN52021 significantly improved the cell activity when its concentration reached 50 μmol/L compared with the group that received LPS treatment alone, which was consistent with the results obtained from fluorescence staining. The mRNAs levels of AC (4.02 ± 0.14 vs 1.00 ± 0.13), GRK (2.63 ± 0.03 vs 1.00 ± 0.12), p38 MAPK (3.87 ± 0.07 vs 1.00 ± 0.17), PLA₂ (3.31 ± 0.12 vs 1.00 ± 0.12), PLCβ (2.09 ± 0.08 vs 1.00 ± 0.06) and PTK (1.85 ± 0.07 vs 1.00 ± 0.11) were up-regulated after LPS stimulation as compared with the blank control (P < 0.05). The up-regulated mRNAs including AC (2.35 ± 0.13 vs 3.87 ± 0.08), GRK (1.17 ± 0.14 vs 2.65 ± 0.12), p38 MAPK (1.48 ± 0.18 vs 4.30 ± 0.07), PLCβ (1.69 ± 0.10 vs 2.41 ± 0.13) and PLA₂ (1.87 ± 0.11 vs 2.96 ± 0.08) were significantly suppressed by BN52021 except for that of PTK. The level of p-AC (1.11 ± 0.12 vs 0.65 ± 0.08), GRK (0.83 ± 0.07 vs 0.50 ± 0.03), PLCβ (0.83 ± 0.16 vs 0.50 ± 0.10) and p-p38 MAPK (0.74 ± 0.10 vs 0.38 ± 0.05) was up-regulated after LPS stimulation as compared with the blank control (P < 0.05). The up-regulated proteins, including p-AC (0.65 ± 0.15 vs 1.06 ± 0.14), GRK (0.47 ± 0.10 vs 0.80 ± 0.06), PLCβ (0.47 ± 0.04 vs 0.80 ± 0.19) and p-p38 MAPK (0.30 ± 0.10 vs 0.97 ± 0.05), was significantly suppressed by BN52021, but p-PLA₂ and p-PTK protein level were not suppressed.

CONCLUSION: BN52021 could effectively inhibit LPS-induced inflammation by down-regulating the mRNA and protein levels of AC, GRK, p38 MAPK, PLA₂ and PLCβ in the PAFR signaling pathway.