Persistent protease-activated receptor 4 signaling mediates thrombin-induced microglial activation

Area of Science:

• Neuroscience
• Immunology
• Pharmacology

Background:

• Thrombin, a coagulation protease, is known to induce brain microglial cell proliferation and activation.
• Protease-activated receptor 1 (PAR1) mediates microglial proliferation but not inflammatory mediator induction by thrombin.

Purpose of the Study:

• To investigate the role of thrombin receptors in mediating inflammatory responses in brain microglia.
• To identify the specific thrombin receptor responsible for inducing inflammatory mediators.

Main Methods:

• Utilized PAR4 agonist peptide (PAR4AP) and PAR1 agonist peptide (TRAP) on cultured murine microglial cells and in vivo rat cortex.
• Employed antisense oligonucleotides to down-regulate PAR4 expression.
• Performed mechanistic studies involving intracellular calcium ([Ca2+]i) increase, p44/42 MAPK phosphorylation, and NF-kappaB activation.

Main Results:

• PAR4AP, but not TRAP, induced tumor necrosis factor-alpha (TNF-alpha) production in microglia in vitro and in vivo.
• Down-regulation of PAR4 significantly reduced PAR4AP-induced TNF-alpha production.
• PAR4 activation led to prolonged [Ca2+]i increase, p44/42 MAPK, and NF-kappaB activation, unlike PAR1 signaling.

Conclusions:

• Protease-activated receptor 4 (PAR4) mediates thrombin-induced inflammatory mediator production in brain microglia.
• PAR4, rather than PAR1, is the key therapeutic target for mitigating neuroinflammation in conditions such as neurotrauma and neurodegeneration.