Inflammatory intracellular pathways activated by electronegative LDL in monocytes

Area of Science:

• Immunology
• Molecular Biology
• Cardiovascular Research

Background:

• Electronegative LDL (LDL(-)) is an LDL subfraction known to trigger cytokine release from monocytes.
• This release is mediated by toll-like receptor 4 (TLR4) activation.
• The specific intracellular signaling pathways downstream of TLR4 activation by LDL(-) remain largely uncharacterized.

Purpose of the Study:

• To elucidate the intracellular molecular pathways activated by LDL(-) following TLR4 engagement in monocytes.
• To identify the key signaling molecules and transcription factors involved in LDL(-)-induced cytokine production.

Main Methods:

• Utilized a multikinase ELISA array to assess kinase activation in monocyte protein extracts.
• Employed specific cell-based assays to confirm kinase activity and pathway dependency.
• Investigated the role of p38 MAPK, PI3K/Akt, NF-kB, AP-1, and CREB in LDL(-)-stimulated monocytes.
• Assessed the impact of pathway inhibitors on cytokine release.

Main Results:

• LDL(-) significantly increased p38 MAPK phosphorylation compared to native LDL, dependent on TLR4 and the PI3K/Akt pathway.
• p38 MAPK activation was crucial for the release of cytokines, including MCP1, IL6, and IL10.
• LDL(-) also activated cAMP response-element binding (CREB) in a p38 MAPK-dependent manner.
• NF-kB and AP-1 activation by LDL(-) were also dependent on p38 MAPK.
• Inhibitors of NF-kB, AP-1, and CREB significantly reduced LDL(-)-induced cytokine release.

Conclusions:

• LDL(-) induces p38 MAPK phosphorylation via TLR4 and PI3K/Akt signaling in monocytes.
• p38 MAPK activation is a key mediator of NF-kB, AP-1, and CREB activation.
• These activated pathways culminate in the release of pro-inflammatory cytokines from monocytes.