Related Experiment Video
Updated: Jun 25, 2026
Assessment of Knee Hyperalgesia in Mice using Pressure Application Measurement
Published on: June 13, 2025
Triggering of proteinase-activated receptor 4 leads to joint pain and inflammation in mice
Jason J McDougall1, Chunfen Zhang, Laurie Cellars
1University of Calgary, Calgary, Alberta, Canada. mcdougaj@ucalgary.ca
Objective:
To investigate the role of proteinase-activated receptor 4 (PAR-4) in mediating joint inflammation and pain in mice.
Methods:
Knee joint blood flow, edema, and pain sensitivity (as induced by thermal and mechanical stimuli) were assessed in C57BL/6 mice following intraarticular injection of either the selective PAR-4 agonist AYPGKF-NH(2) or the inactive control peptide YAPGKF-NH(2). The mechanism of action of AYPGKF-NH(2) was examined by pretreatment of each mouse with either the PAR-4 antagonist pepducin P4pal-10 or the bradykinin antagonist HOE 140. Finally, the role of PAR-4 in mediating joint inflammation was tested by pretreating mice with acutely inflamed knees with pepducin P4pal-10.
Results:
PAR-4 activation caused a long-lasting increase in joint blood flow and edema formation, which was not seen following injection of the control peptide. The PAR-4-activating peptide was also found to be pronociceptive in the joint, where it enhanced sensitivity to a noxious thermal stimulus and caused mechanical allodynia and hyperalgesia. The proinflammatory and pronociceptive effects of AYPGKF-NH(2) could be inhibited by pepducin P4pal-10 and HOE 140. Finally, pepducin P4pal-10 ameliorated the clinical and physiologic signs of acute joint inflammation.
Conclusion:
This study demonstrates that local activation of PAR-4 leads to proinflammatory changes in the knee joint that are dependent on the kallikrein-kinin system. We also show for the first time that PARs are involved in the modulation of joint pain, with PAR-4 being pronociceptive in this tissue. Thus, blockade of articular PAR-4 may be a useful means of controlling joint inflammation and pain.
Insights
Proteinase-activated receptor 4 (PAR-4) activation increases joint inflammation and pain in mice. Blocking PAR-4 may offer a new strategy for treating joint inflammation and pain.
Area of Science:
- Biomedical research
- Inflammation and pain pathways
- G protein-coupled receptors
Background:
- Proteinase-activated receptors (PARs) are implicated in inflammatory conditions.
- PAR-4's specific role in joint inflammation and pain requires further elucidation.
Purpose of the Study:
- To investigate the role of PAR-4 in mediating knee joint inflammation and pain in a mouse model.
- To explore the potential of PAR-4 antagonism as a therapeutic strategy.
Main Methods:
- Intraarticular injection of a PAR-4 agonist (AYPGKF-NH2) or control peptide in C57BL/6 mice.
- Assessment of joint blood flow, edema, and pain sensitivity to thermal and mechanical stimuli.
- Inhibition studies using PAR-4 antagonist (pepducin P4pal-10) and bradykinin antagonist (HOE 140).
Main Results:
- PAR-4 activation significantly increased joint blood flow and edema.
- PAR-4 activation induced pronociceptive effects, enhancing sensitivity to noxious stimuli and causing allodynia/hyperalgesia.
- Inhibition of PAR-4 and bradykinin pathways attenuated the pro-inflammatory and pain effects; PAR-4 blockade reduced acute joint inflammation.
Conclusions:
- Local PAR-4 activation drives joint inflammation and pain, dependent on the kallikrein-kinin system.
- PAR-4 plays a significant role in modulating joint pain, acting as a pronociceptive mediator.
- Targeting articular PAR-4 presents a potential therapeutic avenue for managing joint inflammation and pain.
