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Published on: January 30, 2014
Microglia and Astrocyte Activation by Toll-Like Receptor Ligands: Modulation by PPAR-gamma Agonists
Catherine Gurley1, Jessica Nichols, Shuliang Liu
1Department of Neurobiology and Developmental Sciences, College of Medicine, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA.
Abstract:
Microglia and astrocytes express numerous members of the Toll-like receptor (TLR) family that are pivotal for recognizing conserved microbial motifs expressed by a wide array of pathogens. Despite the critical role for TLRs in pathogen recognition, when dysregulated these pathways can also exacerbate CNS tissue destruction. Therefore, a critical balance must be achieved to elicit sufficient immunity to combat CNS infectious insults and downregulate these responses to avoid pathological tissue damage. We performed a comprehensive survey on the efficacy of various PPAR-gamma agonists to modulate proinflammatory mediator release from primary microglia and astrocytes in response to numerous TLR ligands relevant to CNS infectious diseases. The results demonstrated differential abilities of select PPAR-gamma agonists to modulate glial activation. For example, 15d-PGJ(2) and pioglitazone were both effective at reducing IL-12 p40 release by TLR ligand-activated glia, whereas CXCL2 expression was either augmented or inhibited by 15d-PGJ(2), effects that were dependent on the TLR ligand examined. Pioglitazone and troglitazone demonstrated opposing actions on microglial CCL2 production that were TLR ligand-dependent. Collectively, this information may be exploited to modulate the host immune response during CNS infections to maximize host immunity while minimizing inappropriate bystander tissue damage that is often characteristic of such diseases.
Insights
PPAR-gamma agonists differentially modulate glial activation in response to Toll-like receptor (TLR) ligands. This offers a strategy to balance immune response and minimize tissue damage in CNS infections.
Area of Science:
- Neuroimmunology
- Pharmacology
- Infectious Diseases
Background:
- Microglia and astrocytes express Toll-like receptors (TLRs) crucial for pathogen recognition in the central nervous system (CNS).
- Dysregulated TLR signaling can lead to CNS tissue damage, necessitating a balance between immunity and inflammation control.
Purpose of the Study:
- To investigate the efficacy of various PPAR-gamma agonists in modulating pro-inflammatory mediator release from glial cells (microglia and astrocytes).
- To assess the impact of these agonists on glial activation in response to TLR ligands relevant to CNS infections.
Main Methods:
- Primary microglia and astrocytes were treated with various PPAR-gamma agonists.
- Cells were stimulated with different Toll-like receptor (TLR) ligands associated with CNS infections.
- The release of pro-inflammatory mediators (e.g., IL-12 p40, CXCL2, CCL2) was measured.
Main Results:
- Select PPAR-gamma agonists demonstrated differential effects on glial activation.
- 15d-PGJ(2) and pioglitazone reduced IL-12 p40 release, but 15d-PGJ(2) had variable effects on CXCL2.
- Pioglitazone and troglitazone showed opposing effects on microglial CCL2 production, dependent on the TLR ligand.
Conclusions:
- PPAR-gamma agonists can differentially modulate glial inflammatory responses to TLR ligands.
- These findings suggest a potential therapeutic strategy to fine-tune the host immune response in CNS infections.
- Targeting PPAR-gamma may help maximize host immunity while minimizing pathological bystander tissue damage.
