Determination of specific receptor sites for platelet activating factor in bovine neutrophils

Piscirickettsia salmonis-Triggered Extracellular Traps Formation as an Innate Immune Response of Atlantic Salmon-Derived Polymorphonuclear Neutrophils

Simple Summary

Within innate immunity, polymorphonuclear neutrophils (PMN) are the most abundant leukocyte population. Alongside PMN, monocytes, eosinophils, and basophils are also known to exist. All of them can release extracellular traps (ETs), a complex web-like structure composed of chromatin decorated with nuclear histones, granular enzymes, peptides, and proteins, to firmly entrap invasive pathogens, thereby slowing dissemination and helping to develop proper immune responses against bacteria, fungi, viruses, and parasites. Here, we showed for the first time that Atlantic salmon-derived PMN released ETs-like structures in vitro, in response to highly pathogenic facultative intracellular rickettsial bacteria Piscirickettsia salmonis. The release of ET-like structures from PMN could be a new alternative to improve farmed salmon’s defense against pathogens.

Abstract

Extracellular traps (ETs) are webs of DNA, citrullinated histones, anti-microbial peptides, and proteins that were not previously reported in Atlantic salmon (Salmo salar). ETs are mainly released from polymorphonuclear neutrophils (PMN) and are considered a novel PMN-derived effector mechanism against different invasive pathogens. Here, we showed that Atlantic salmon-derived PMN released ETs-like structures in vitro in response to highly pathogenic facultative intracellular rickettsial bacteria Piscirickettsia salmonis. PMN were isolated from pre-smolt Atlantic salmon and stimulated in vitro with oleic acid and P. salmonis. Extracellular DNA was measured using the PicoGreen™ dye, while immunofluorescence image analysis was used to confirm the classical components of salmonid-extruded ETs. Future studies are required to better understand the role of Atlantic salmon-derived ETs orchestrating innate/adaptive immunity and the knowledge on regulation pathways involved in this cell death process. Thus, comprehension of salmonid-derived ETs against P. salmonis might represent novel alternative strategies to improve host innate defense mechanisms of farmed salmon against closely related rickettsial bacteria, as a complement to disease prevention and control strategies.

Mitochondria-derived ATP participates in the formation of neutrophil extracellular traps induced by platelet-activating factor through purinergic signaling in cows

Neutrophil extracellular trap (NET) formation eliminates/prevents the spread of infectious agents. Platelet activating factor (PAF) is involved in infectious diseases of cattle because it recruits and activates neutrophils. However, its ability to induce NET release and the role of metabolism in this process is not known. We investigated if inhibition of glycolysis, mitochondrial-derived adenosine triphosphate (ATP) synthesis and purinergic signaling though P2X₁ purinoceptors interfered with NET formation induced by PAF. We inhibited bovine neutrophils with 2-deoxy-d-glucose, rotenone, carbonyl cyanide 3-chlorophenylhydrazone (CCCP) and NF449 to evaluate PAF-mediated NET extrusion. PAF induced mitochondrial hyperpolarization and triggered extracellular ATP release via pannexin-1. Inhibition of mitochondrial metabolism prevented extracellular ATP release. Inhibition of glycolysis, complex-I activity and oxidative phosphorylation prevented NET formation induced by PAF. Inhibition of P2X₁ purinergic receptors inhibited mitochondrial hyperpolarization and NET formation. We concluded that PAF-induced NET release is dependent upon glycolysis, mitochondrial ATP synthesis and purinergic signaling.

Glycolysis and mitochondrial function regulate the radical oxygen species production induced by platelet-activating factor in bovine polymorphonuclear leukocytes

Dairy cows undergo metabolic disturbances in the peripartum period, during which infectious inflammatory diseases and detrimental polymorphonuclear leukocytes (PMN) functions, such as radical oxygen species (ROS) production, are observed. Platelet-activating factor (PAF) is a key pro-inflammatory mediator that increases PMN ROS production. To date, the role of glycolysis and mitochondria in PAF-induced ROS production in bovine PMN has not been known. The aim of this study was to assess whether inhibition of glycolysis and disruption of mitochondrial function alter the oxidative response induced by PAF. We isolated PMN from non-pregnant Holstein Friesian heifers and pre-incubated them with 2-deoxy-d-glucose (2-DG; 2 mM, 30 min), carbonyl cyanide 3-chlorophenylhydrazone (CCCP; 5 μM, 5 min), oligomycin (10 μM, 30 min) or rotenone (10 μM, 30 min). Respiratory burst was measured by luminol-chemiluminescence assay, while mitochondrial ROS (_mtROS) were evaluated by MitoSOX probe and flow cytometry. Also, we detected the presence of mitochondria by MitoTracker Deep Red FM probe and changes in mitochondrial membrane potential (Δψ_m) were assessed by JC-1 probe and flow cytometry. We observed that all inhibitors separately were able to reduce PAF-induced ROS production. Presence of mitochondria was detected and PAF increased the Δψ_m, while CCCP reduced it. 2-DG and rotenone reduced the _mtROS production induced by PAF. CCCP did not alter the _mtROS and oligomycin administered independently increased _mtROS production. We concluded that PAF-induced ROS production is glycolysis- and mitochondria-dependent. Bovine PMN have a functional mitochondrion and PAF induced _mtROS via glycolysis and mitochondrial complex-I activity. Our results highlight an important modulation of cellular metabolism in the oxidative response induced by proinflammatory agents, which could contribute to PMN disfunction during peripartum in cattle.

Deoxyschizandrin suppresses dss-induced ulcerative colitis in mice

BACKGROUND/AIMS

Deoxyschizandrin as one of the most important component of Schisandra chinensis (Turcz.) Baill plays an immunomodulatory role in a variety of diseases, yet its role in ulcerative colitis remains to be elucidated. We aimed to investigate the role of deoxyschizandrin in DSS-induced ulcerative colitis in mice.

PATIENTS AND METHODS

In the present study, an inflammation model of cells was constructed to confirm the anti-inflammatory effect of deoxyschizandrin. Then a mouse model with Dextran sulfate sodium sulfate (DSS)-induced ulcerative colitis was constructed, and the effects of deoxyschizandrin on mouse colon inflammation, apoptosis, and CD4 T lymphocyte infiltration in ulcerative colitis were examined.

RESULT

Deoxyschizandrin could improve the symptoms of ulcerative colitis, determined by hematoxylin-eosin (HE) staining and histopathological scores. Moreover, deoxyschizandrin reduced the levels of inflammatory cytokines, suppressed CD4 T cell infiltration, and effectively inhibited apoptosis in the colon of DSS-induced ulcerative colitis mice.

CONCLUSION

In summary, deoxyschizandrin can effectively rescue the symptoms of DSS-induced ulcerative colitis in mice by inhibiting inflammation. T cell infiltration and apoptosis in the colon, suggesting that deoxyschizandrin could be a potential drug in treating ulcerative colitis.

Butyric acid stimulates bovine neutrophil functions and potentiates the effect of platelet activating factor

Increased short-chain fatty acid (SCFA) production is associated with subacute ruminal acidosis (SARA) and activation of inflammatory processes. In humans and rodents, SCFAs modulate inflammatory responses in the gut via free fatty acid receptor 2 (FFA2). In bovines, butyric acid is one of the most potent FFA2 agonists. Its expression in bovine neutrophils has recently been demonstrated, suggesting a role in innate immune response in cattle. This study aimed to evaluate if butyric acid modulates oxidative and non-oxidative functions or if it can potentiate other inflammatory mediators in bovine neutrophils. Our results showed that butyric acid can activate bovine neutrophils, inducing calcium (Ca(2+)) influx and mitogen-activated protein kinase (MAPK) phosphorylation, two second messengers involved in FFA2 activation. Ca(2+) influx induced by butyric acid was dependent on the extracellular and intracellular Ca(2+) source and phospholipase C (PLC) activation. Butyric acid alone had no significant effect on reactive oxygen species (ROS) production and chemotaxis; however, a priming effect on platelet-activating factor (PAF), a potent inflammatory mediator, was observed. Butyric acid increased CD63 expression and induced the release of neutrophil granule markers matrix metalloproteinase-9 (MMP-9) and lactoferrin. Finally, we observed that butyric acid induced neutrophil extracellular trap (NET) formation without affecting cellular viability. These findings suggest that butyric acid, a component of the ruminal fermentative process, can modulate the innate immune response of ruminants.

Muramyl dipeptide synergizes with Staphylococcus aureus lipoteichoic acid to recruit neutrophils in the mammary gland and to stimulate mammary epithelial cells

Staphylococcus aureus, a major pathogen for the mammary gland of dairy ruminants, elicits the recruitment of neutrophils into milk during mastitis, but the mechanisms are incompletely understood. We investigated the response of the bovine mammary gland to muramyl dipeptide (MDP), an elementary constituent of the bacterial peptidoglycan, alone or in combination with lipoteichoic acid (LTA), another staphylococcal microbial-associated molecular pattern (MAMP). MDP induced a prompt and marked influx of neutrophils in milk, and its combination with LTA elicited a more intense and prolonged influx than the responses to either stimulus alone. The concentrations of several chemoattractants for neutrophils (CXCL1, CXCL2, CXCL3, CXCL8, and C5a) increased in milk after challenge, and the highest increases followed challenge with the combination of MDP and LTA. MDP and LTA were also synergistic in inducing in vitro chemokine production by bovine mammary epithelial cells (bMEpC). Nucleotide-binding oligomerization domain 2 (NOD2), a major sensor of MDP, was expressed (mRNA) in bovine mammary tissue and by bMEpC in culture. The production of interleukin-8 (IL-8) following the stimulation of bMEpC by LTA and MDP was dependent on the activation of NF-κB. LTA-induced IL-8 production did not depend on platelet-activating factor receptor (PAFR), as the PAFR antagonist WEB2086 was without effect. In contrast, bMEpC and mammary tissue are known to express Toll-like receptor 2 (TLR2) and to respond to TLR2 agonists. Although the levels of expression of the inflammatory cytokines tumor necrosis factor alpha (TNF-α) and IL-1β were increased by LTA and MDP at the mRNA level, no protein could be detected in the bMEpC culture supernatant. The level of induction of IL-6 was low at both the mRNA and protein levels. These results indicate that MDP and LTA exert synergistic effects to induce neutrophilic inflammation in the mammary gland. These results also show that bMEpC could contribute to the inflammatory response by recognizing LTA and MDP and secreting chemokines but not proinflammatory cytokines. Overall, this study indicates that the TLR2 and NOD2 pathways could cooperate to trigger an innate immune response to S. aureus mastitis.

Store-operated calcium entry mediates intracellular alkalinization, ERK1/2, and Akt/PKB phosphorylation in bovine neutrophils

Neutrophil's responses to G protein-coupled chemoattractants are highly dependent on store-operated calcium (Ca(2+)) entry (SOCE). Platelet-activating factor (PAF), a primary chemoattractant, simultaneously increases cytosolic-free Ca(2+), intracellular pH (pH(i)), ERK1/2, and Akt/protein kinase B (PKB) phosphorylation. In this study, we looked at the efficacy of several putative SOCE inhibitors and whether SOCE mediates intracellular alkalinization, ERK1/2, and Akt/PKB phosphorylation in bovine neutrophils. We demonstrated that the absence of external Ca(2+) and the presence of EGTA reduced the intracellular alkalinization and ERK1/2 phosphorylation induced by PAF, apparently via SOCE influx inhibition. Next, we tested the efficacy of several putative SOCE inhibitors such as 2-aminoethoxydiphenyl borate (2-APB), capsaicin, flufenamic acid, 1-{beta-[3-(4-methoxy-phenyl)propoxy]-4-methoxyphenethyl}-1H-imidazole hydrochloride (SK&F 96365), and N-(4-[3,5-bis(trifluoromethyl)-1H-pyrazol-1-yl]phenyl)-4-methyl-1,2,3-thiadiazole-5-carboxamide (BTP2) on Ca(2+) entry induced by PAF or thapsigargin. 2-APB was the most potent SOCE inhibitor, followed by capsaicin and flufenamic acid. Conversely, SK&F 96365 reduced an intracellular calcium ([Ca(2+)](i)) peak but SOCE partially. BTP2 did not show an inhibitory effect on [Ca(2+)](i) following PAF stimuli. 2-APB strongly reduced the pH(i) recovery, whereas the effect of flufenamic acid and SK&F 96365 was partial. Capsaicin and BTP2 did not affect the pH(i) changes induced by PAF. Finally, we observed that 2-APB reduced the ERK1/2 and Akt phosphorylation completely, whereas the inhibition with flufenamic acid was partial. The results suggest that 2-APB is the most potent SOCE inhibitor and support a key role of SOCE in pH alkalinization and PI-3K-ERK1/2 pathway control. Finally, 2-APB could be an important tool to characterize Ca(2+) signaling in neutrophils.

Significance of platelet activating factor receptor expression in pancreatic tissues of rats with severe acute pancreatitis and effects of BN52021

AIM: To investigate the dynamic changes and signi-ficance of platelet activating factor receptor (PAF-R) mRNA and protein in pancreatic tissues of rats with severe acute pancreatitis (SAP) and effects of BN52021 (Ginkgolide B).

METHODS: Wistar male rats were randomly assigned to the negative control group (NC group), SAP model group (SAP group), and BN52051-remedy group (BN group), and each of the groups was divided into 6 subgroups at different time points after operation (1 h, 2 h, 3 h, 6 h, 12 h, and 24 h) (n = 10 in each). PT-PCR and Western blot methods were used to detect PAF-RmRNA and protein expression in pancreatic tissues of rats respectively. Pathological examination of pancreatic tissues was performed and the serum amylase change was detected.

RESULTS: Serum amylase and pathological results showed the that SAP model was successfully prepared, BN52021 was able to decrease serum amylase, and the pathological ratings in BN group at 3 h, 6 h, and 12 h significantly decreased compared with those in the SAP group (8.85 ± 0.39 vs 5.95 ± 0.19, 9.15 ± 0.55 vs 5.55 ± 0.36, 10.10 ± 0.65 vs 6.72 ± 0.30, P < 0.05). The result of PAF-mRNA showed dynamic changes in SAP and BN groups, which increased gradually in early stage, reached a peak at 3 h (0.71 ± 0.14 vs 0.54 ± 0.14, 0.69 ± 0.13 vs 0.59 ± 0.04, P < 0.05), and decreased gradually later. There were significant differences at each time point except 1 h and 2 h, when compared with those in the NC group (0.71 ± 0.14 or 0.69 ± 0.13 vs 0.47 ± 0.10, 0.38 ± 0.08 or 0.59 ± 0.04 vs 0.47 ± 0.09, 0.25 ± 0.07 or 0.29 ± 0.05 vs 0.46 ± 0.10, 0.20 ± 0.06 or 0.20 ± 0.04 vs 0.43 ± 0.09, P < 0.05), whereas there was no significant difference between BN and SAP groups at each time point. The result of PAF-R protein showed that the change of PAF-R protein in the SAP group and the BN group was consistent with that of PAF-R mRNA. There were significant differences at each time point except 1 h, when compared with those in the NC group (0.90 ± 0.02 or 0.80 ± 0.05 vs 0.48 ± 0.02, 1.69 ± 0.06 or 1.58 ± 0.02 vs 0.48 ± 0.03, 1.12 ± 0.10 or 0.98 ± 0.03 vs 0.49 ± 0.09, 1.04 ± 0.14 or 0.87 ± 0.02 vs 0.52 ± 0.08, 0.97 ± 0.16 or 0.90 ± 0.05 vs 0.49 ± 0.10, P < 0.05), whereas there was no significant difference between the BN group and the SAP group.

CONCLUSION: PAF-R plays an important role in occurrence and development of SAP. BN52021 exerts biological effects through competitively inhibiting the binding of increased both PAF and PAF-R expression rather than through decreasing PAF-R expression in pancreatic tissues.

Propionate induces pH(i) changes through calcium flux, ERK1/2, p38, and PKC in bovine neutrophils

Propionate is a short-chain fatty acid produced under normal physiological conditions in the rumen of cattle. It is also involved in the inflammatory process and neutrophil function via calcium release, reactive oxygen species and intracellular pH (pH(i)) changes. This study examined the effect of propionate on the pH(i) of bovine neutrophils; specifically if pH(i) changes are controlled by calcium flux, and the mitogen-activated protein kinase (MAPK) pathway. Propionate caused rapid intracellular acidification and sustained alkalinization in bovine neutrophils loaded with 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein acetoxymethyl ester (BCECF-AM), a fluorescent indicator of pH(i). The acidification phase seems to be controlled by intracellular calcium release and p38 MAPK pathway. The pH recovery phenomenon was mediated by an amiloride-sensitive Na+/H+ exchanger and H+ channel, and was inhibited by UO126 (an ERK1/2 MAPK phosphorylation inhibitor), Gö6850 (a PKC inhibitor) and calcium chelating. Ionomycin, a calcium ionophore, induced intracellular acidification and sustained alkalinization. The intracellular acidification was strongly inhibited by BAPTA-AM (an intracellular calcium chelator) and SB203580 (a p38 MAPK inhibitor). In addition, the intracellular alkalinization was reduced by EGTA (a calcium chelator), UO126, LY294002 (a PI3K inhibitor) and Gö6850. Propionate did not increase superoxide production, however it reduced the superoxide production induced by platelet-activating factor (PAF), and increased the release of superoxide induced by ionomycin. Our results suggest that propionate-induced intracellular acidification is mediated by intracellular calcium release and p38 MAPK activation, and that pH recovery is controlled via ERK1/2 MAPK, PKC and calcium entry in bovine neutrophils.

Andrographolide interferes with binding of nuclear factor-kappaB to DNA in HL-60-derived neutrophilic cells

1. Andrographolide, the major active component from Andrographis paniculata, has shown to possess anti-inflammatory activity. Andrographolide inhibits the expression of several proinflammatory proteins that exhibit a nuclear factor kappa B (NF-kappaB) binding site in their gene. 2. In the present study, we analyzed the effect of andrographolide on the activation of NF-kappaB induced by platelet-activating factor (PAF) and N-formyl-methionyl-leucyl-phenylalanine (fMLP) in HL-60 cells differentiated to neutrophils. 3. PAF (100 nM) and fMLP (100 nM) induced activation of NF-kappaB as determined by degradation of inhibitory factor B alpha (IkappaB alpha) using Western blotting in cytosolic extracts and by binding to DNA using electrophoretic mobility shift assay (EMSA) in nuclear extracts. 4. Andrographolide (5 and 50 microM) inhibited the NF-kappaB-luciferase activity induced by PAF. However, andrographolide did not reduce phosphorylation of p38 MAPK or ERK1/2 and did not change IkappaB alpha degradation induced by PAF and fMLP. 5. Andrographolide reduced the DNA binding of NF-kappaB in whole cells and in nuclear extracts induced by PAF and fMLP. 6. Andrographolide reduced cyclooxygenase-2 (COX-2) expression induced by PAF and fMLP in HL-60/neutrophils. 7. It is concluded that andrographolide exerts its anti-inflammatory effects by inhibiting NF-kappaB binding to DNA, and thus reducing the expression of proinflammatory proteins, such as COX-2.

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