Cathepsin S causes inflammatory pain via biased agonism of PAR2 and TRPV4 [Neurobiology]

August 12th, 2014 by Zhao, P., Lieu, T., Barlow, N., Metcalf, M., Veldhuis, N., Jensen, D., Kocan, M., Sostegni, S., Haerteis, S., Baraznenok, V., Henderson, I., Lindstrom, E., Guerrero–Alba, R., Valdez–Morales, E., Liedtke, W., McIntyre, P., Vanner, S. J., K

Serine proteases such as trypsin and mast cell tryptase cleave protease-activated receptor-2 (PAR2) at R36/S37 and reveal a tethered ligand that excites nociceptors, causing neurogenic inflammation and pain. Whether proteases that cleave PAR2 at distinct sites induce inflammation and pain by a biased signaling mechanism is unknown. We observed that cathepsin S (Cat-S) cleaved PAR2 at E56/T57. In cell lines and nociceptive neurons, Cat-S and a decapeptide mimicking the Cat-S-revealed tethered ligand stimulated PAR2 coupling to Gs and formation of cAMP. Unlike trypsin, Cat-S did not mobilize intracellular Ca2+, activate ERK1/2, recruit β-arrestins, or induce PAR2 endocytosis. Cat-S caused PAR2-dependent activation of transient receptor potential vanilloid 4 (TRPV4) in Xenopus oocytes, HEK cells and neurons, and stimulated neuronal hyperexcitability by adenylyl cyclase and protein kinase A-dependent mechanisms. Cat-S caused inflammation and hyperalgesia in mice that was attenuated by PAR2 or TRPV4 deletion and adenylyl cyclase inhibition. Cat-S and PAR2 antagonists suppressed formalin-induced inflammation and pain. Our results reveal a novel mechanism of Cat-S-activation of PAR2, and expand the role of PAR2 as a mediator of protease-driven inflammatory pain.