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Peroxisome proliferator-activated receptor-gamma agonists modulate macrophage activation by gram-negative and
Kelly Guyton1, Basilia Zingarelli, Sarah Ashton
1Department of Microbiology, Medical University of South Carolina, 167 Ashley Avenue, Charleston, SC 29425, USA.
Abstract:
Bacterial products, such as lipopolysaccharide (LPS) or heat-killed Escherichia coli (EC), and heat-killed Staphylococcus aureus (SA) are potent activators of macrophages (MØ). When stimulated by these bacterial components, MØ produce inflammatory mediators, such as nitric oxide (NO) and thromboxane (Tx) B(2). Bacterial mediator production is preceded by the activation of various signal transduction pathways. Agonists that activate the peroxisome proliferator-activated receptor-gamma (PPARgamma) have been shown to block MØ mediator production by LPS and other stimuli. However, very little is known about the effects of PPARgamma agonists on SA- or EC-induced MØ activation. Therefore, we investigated whether the PPARgamma agonists 15-deoxy-Delta12,14 prostaglandin J(2) (15-PGJ(2)) and troglitazone block LPS-, EC-, or SA-induced mediator production. Rat peritoneal MØ were stimulated with LPS, EC, or SA (10 microg/mL) with or without increasing concentrations (0.1 to 10 microM) of each PPARgamma agonist and NO and TxB(2) production were measured. 15-PGJ(2) decreased LPS-, EC-, and SA-induced NO and TxB(2) production. However, troglitazone only inhibited the production of TxB(2) by each stimuli. In parallel studies, the effects of PPARgamma agonists on signaling pathways were evaluated. Rat peritoneal MØ were pretreated for 1 h with 15-PGJ(2) or troglitazone (1 or 10 microM) and then stimulated for 40 min with LPS, EC, or SA (10 microg/mL). Western blot analysis demonstrated that 15-PGJ(2) significantly inhibited LPS-, EC-, and SA-induced ERK (1/2) activation and blocked IkappaBalpha degradation. Troglitazone had no significant effect on either signaling protein. The data demonstrate that although both 15-PGJ(2) and troglitazone are considered PPARgamma agonists, they differentially affect mediator production and cell signaling events. PPARgamma-independent effects of 15-PGJ(2) may contribute to its more potent anti-inflammatory effects compared with troglitazone.
Insights
The PPARgamma agonist 15-PGJ(2) effectively reduced inflammatory mediator production and blocked key signaling pathways in macrophages. Troglitazone, another PPARgamma agonist, showed limited effects, suggesting 15-PGJ(2) has potent anti-inflammatory properties.
Area of Science:
- Immunology
- Pharmacology
- Cell Biology
Background:
- Bacterial products like LPS, E. coli (EC), and S. aureus (SA) activate macrophages (MØ), leading to inflammatory mediator production (NO, TxB2).
- Peroxisome proliferator-activated receptor-gamma (PPARgamma) agonists can inhibit MØ mediator production, but their effects on EC- and SA-induced activation are less understood.
- Investigating differential effects of PPARgamma agonists is crucial for understanding anti-inflammatory mechanisms.
Purpose of the Study:
- To determine if PPARgamma agonists 15-deoxy-Delta12,14 prostaglandin J(2) (15-PGJ(2)) and troglitazone inhibit mediator production induced by LPS, EC, or SA.
- To evaluate the impact of these agonists on macrophage signaling pathways, specifically ERK (1/2) activation and IkappaBalpha degradation.
- To compare the anti-inflammatory efficacy of 15-PGJ(2) and troglitazone in macrophage activation models.
Main Methods:
- Rat peritoneal macrophages were stimulated with LPS, EC, or SA in the presence of varying concentrations of 15-PGJ(2) or troglitazone.
- Nitric oxide (NO) and thromboxane B(2) (TxB(2)) production were measured as indicators of mediator release.
- Western blot analysis was used to assess the effects of the agonists on ERK (1/2) activation and IkappaBalpha degradation following stimulation.
Main Results:
- 15-PGJ(2) significantly inhibited LPS-, EC-, and SA-induced production of both NO and TxB(2).
- Troglitazone only inhibited TxB(2) production, with no significant effect on NO production.
- 15-PGJ(2) blocked LPS-, EC-, and SA-induced ERK (1/2) activation and IkappaBalpha degradation, while troglitazone had no significant effect on these pathways.
Conclusions:
- 15-PGJ(2) exhibits potent anti-inflammatory effects by inhibiting mediator production and key signaling pathways (ERK, IkappaBalpha) in macrophages activated by bacterial products.
- Troglitazone demonstrates a more limited anti-inflammatory capacity, primarily affecting TxB(2) production and not significantly impacting the evaluated signaling pathways.
- The differential effects suggest that 15-PGJ(2) may exert anti-inflammatory actions through mechanisms independent of PPARgamma activation, contributing to its greater potency compared to troglitazone.