Protease-Activated Receptor 4 Induces Bladder Pain through High Mobility Group Box-1

Area of Science:

• Urology
• Pain research
• Molecular biology

Background:

• Interstitial Cystitis/Painful Bladder Syndrome (IC/PBS) is characterized by significant bladder pain.
• Protease activated receptor 4 (PAR4) activation in the urothelium leads to pain via macrophage migration inhibitory factor (MIF) release.
• High Mobility Group Box-1 (HMGB1) is implicated in mediating bladder pain in experimental cystitis models.

Purpose of the Study:

• To investigate if PAR4-induced bladder hypersensitivity is dependent on downstream HMGB1.
• To determine if PAR4 stimulation affects urothelial HMGB1 release.
• To assess if blocking MIF inhibits urothelial HMGB1 release and if blocking HMGB1 prevents PAR4-induced bladder hypersensitivity.

Main Methods:

• HMGB1 release was measured in human urothelial cultures (UROtsa) stimulated with PAR4-activating peptide (PAR4-AP).
• Mice were pretreated with HMGB1 inhibitor (glycyrrhizin) or MIF blocker (ISO-1) before intravesical PAR4-AP administration.
• HMGB1 levels in intravesical fluid and urothelium, and abdominal hypersensitivity were assessed.

Main Results:

• PAR4-AP triggered HMGB1 release from both human (in vitro) and mouse (in vivo) urothelial cells.
• Intravesical PAR4 activation induced abdominal hypersensitivity in mice, which was abolished by HMGB1 inhibition.
• MIF inhibition effectively prevented PAR4-mediated HMGB1 release from mouse urothelium.

Conclusions:

• Urothelial HMGB1 release is a downstream consequence of PAR4 activation.
• MIF plays a role in mediating PAR4-induced HMGB1 release.
• Urothelial MIF and HMGB1 represent promising novel therapeutic targets for managing bladder pain.