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PAF is involved in the Mycoplasma arthritidis superantigen-triggering pathway for iNOS and COX-2 expression in murine
Marina Tiemi Shio1, Fátima Ribeiro-Dias, Jorge Timenetsky
1Department of Immunology, Institute of Biomedical Sciences, University of São Paulo, Brazil.
Abstract:
We investigated the capacity of Mycoplasma arthritidis mitogen (MAM) to induce (a) expression of the inducible enzymes cyclo-oxygenase (COX-2) and nitric oxide synthase (iNOS), (b) production of prostaglandin E2 (PGE2) and nitric oxide (NO), and (c) involvement of platelet-activating factor (PAF) in the MAM-induced activation pathway. Resident peritoneal cells from C3H/HePas mice were incubated with MAM in the presence or absence of a PAF-antagonist (WEB2170) or COX-2 inhibitors (nimesulide or NS398). Enzyme expression was evaluated by immunoblotting, PGE2 by EIA, and NO by Griess reaction. Following MAM-stimulation of peritoneal cells, expression of COX-2 was detected at 3 h (peak levels at 12 h) and of iNOS at 6 h (peak levels at 20 h). PGE2 increased till 20 h, decreasing thereafter, whereas NO increased with time. WEB2170 (5 x 10(-5) M) treatment caused 44% inhibition of NO output and reduced iNOS expression (48% at the peak of expression). Concomitant treatment with WEB2170 and nimesulide (10(-5) M) reversed these inhibitory effects. WEB2170 reduced COX-2 expression (43% at the peak of expression) and prevented the decline in PGE2 levels after 20 h. These results suggest the involvement of PAF in the signaling pathway triggered by MAM that leads to expression of iNOS and COX-2, and show that PAF regulates the production of NO, possibly by controlling levels of PGE2.
Insights
Mycoplasma arthritidis mitogen (MAM) activates inflammatory pathways involving platelet-activating factor (PAF), cyclo-oxygenase-2 (COX-2), and inducible nitric oxide synthase (iNOS). PAF signaling influences nitric oxide (NO) and prostaglandin E2 (PGE2) production.
Area of Science:
- Immunology
- Molecular Biology
- Pharmacology
Background:
- Mycoplasma arthritidis mitogen (MAM) is a potent activator of immune cells.
- Inflammatory mediators like prostaglandin E2 (PGE2) and nitric oxide (NO) play crucial roles in immune responses.
- Platelet-activating factor (PAF) is implicated in various inflammatory processes.
Purpose of the Study:
- To investigate the capacity of MAM to induce cyclo-oxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) expression.
- To determine the production of PGE2 and NO following MAM stimulation.
- To elucidate the involvement of PAF in the MAM-induced inflammatory pathway.
Main Methods:
- Resident peritoneal cells from C3H/HePas mice were stimulated with MAM.
- Inhibition studies were conducted using a PAF antagonist (WEB2170) and COX-2 inhibitors (nimesulide, NS398).
- Enzyme expression (COX-2, iNOS) was assessed by immunoblotting; PGE2 and NO production were quantified by EIA and Griess reaction, respectively.
Main Results:
- MAM induced COX-2 and iNOS expression, along with increased PGE2 and NO production.
- PAF antagonism (WEB2170) significantly inhibited NO output and iNOS expression, and reduced COX-2 expression.
- Combined PAF antagonism and COX-2 inhibition reversed the inhibitory effects on NO and iNOS, suggesting interplay between pathways.
Conclusions:
- PAF is involved in the signaling pathway triggered by MAM, leading to iNOS and COX-2 expression.
- PAF regulates NO production, potentially by influencing PGE2 levels.
- These findings highlight the complex inflammatory cascade initiated by MAM and the role of PAF in modulating immune mediator production.
