Inhibitory kappaBalpha control of nuclear factor-kappaB is dysregulated in endotoxin tolerant macrophages

Area of Science:

• Immunology
• Molecular Biology
• Cellular Signaling

Background:

• Nuclear factor-kappaB (NF-kappaB) is crucial for endotoxin-induced tumor necrosis factor (TNF) and interleukin (IL)-1 gene transcription.
• NF-kappaB nuclear translocation is regulated by the cytoplasmic inhibitor IkappaBalpha.
• Low-dose lipopolysaccharide (LPS) pretreatment can modulate subsequent LPS-activated signaling pathways, leading to tolerance.

Purpose of the Study:

• To investigate the impact of LPS pretreatment on IkappaBalpha and NF-kappaB levels and activity in murine macrophages (Mphi).
• To determine how LPS tolerance affects NF-kappaB translocation and subsequent cytokine gene transcription.

Main Methods:

• Murine macrophages were pretreated with LPS and then activated with varying LPS concentrations.
• Cytoplasmic IkappaBalpha levels were assessed using Western immunoblotting.
• NF-kappaB translocation and DNA binding activity were analyzed via gel-shift assays.
• TNF gene transcription was quantified using reverse transcription-polymerase chain reaction (RT-PCR).

Main Results:

• In non-tolerant macrophages, IkappaBalpha decreased as NF-kappaB translocated to the nucleus.
• Tolerant macrophages exhibited increased cytoplasmic IkappaBalpha levels and altered NF-kappaB translocation patterns.
• LPS pretreatment did not alter LPS-induced cytokine gene transcription, despite changes in NF-kappaB signaling.
• Endotoxin-tolerant macrophages showed increased cytoplasmic levels of the NF-kappaB p65 subunit.

Conclusions:

• LPS tolerance in macrophages is associated with increased cytoplasmic IkappaBalpha and p65 subunit levels.
• The regulation of NF-kappaB translocation by IkappaBalpha appears to be dysregulated in endotoxin-tolerant macrophages.
• Despite altered NF-kappaB dynamics, cytokine gene transcription remains responsive to LPS activation in tolerant cells.