Cathepsin S Is Activated During Colitis and Causes Visceral Hyperalgesia by a PAR2-Dependent Mechanism in Mice

Abstract

Background & Aims Although proteases control inflammation and pain, the identity, cellular origin, mechanism of action, and causative role of proteases that are activated during disease are not defined. We investigated the activation and function of cysteine cathepsins (Cat) in colitis. Methods Since protease activity, rather than expression, is regulated, we treated mice with fluorescent activity-based probes that covalently modify activated cathepsins. Activated proteases were localized by tomographic imaging of intact mice and confocal imaging of tissues, and were identified by electrophoresis and immunoprecipitation. We examined the effects of activated cathepsins on excitability of colonic nociceptors and on colonic pain, and determined their role in colonic inflammatory pain by gene deletion. Results Tomography and magnetic resonance imaging localized activated cathepsins to the inflamed colon of piroxicam-treated il10−/− mice. Confocal imaging detected activated cathepsins in colonic macrophages and spinal neurons and microglial cells of mice with colitis. Gel electrophoresis and immunoprecipitation identified activated Cat-B, Cat-L and Cat-S in colon and spinal cord, and Cat-S was preferentially secreted into the colonic lumen. Intraluminal Cat-S amplified visceromotor responses to colorectal distension and induced hyperexcitability of colonic nociceptors, which required expression of protease-activated receptor-2. Cat-S deletion attenuated colonic inflammatory pain induced with trinitrobenzene sulfonic acid. Conclusions Activity-based probes enable non-invasive detection, cellular localization and proteomic identification of proteases activated during colitis and are potential diagnostic tools for detection of predictive disease biomarkers. Macrophage cathepsins are activated during colitis, and Cat-S activates nociceptors to induce visceral pain via protease-activated receptor-2. Cat-S mediates colitis pain and is a potential therapeutic target.

Cathepsin S Causes Inflammatory Pain via Biased Agonism of PAR2 and TRPV4

“…Cat-S induced inflammation and pain could also be caused by sensitization and activation of other TRP channels, since PAR 2 can sensitize TRPV1 and TRPA1 and induce neurogenic inflammation and pain (27,31). The finding that Cat-S causes PAR 2 -dependent inflammation and pain is consistent with our previous report that Cat-S causes visceral pain, which required expression of PAR 2 (5). Inhibition of adenylyl cyclase strongly inhibited Cat-S-evoked mechanical hyperalgesia, which implicates PAR 2 biased signaling.…”

“…We have previously show that Cat-S causes hyperexcitability of nociceptive neurons in wild-type but not par 2 Ϫ/Ϫ mice, but by unknown signaling pathways (5). In the present study we found that Cat-S also reduced the rheobase and increased action potential discharge, confirming hyperexcitability.…”

“…Whether Cat-S can activate PAR 2 on the central projections of primary sensory neurons within the dorsal horn to cause pain remains to be investigated. Cat-S is also activated in inflammatory diseases including rheumatoid arthritis (4) and colitis (5). Given the established contributions of PAR 2 and TRPV4 to arthritis (63) and colitis (30,64,65), antagonists of Cat-S, PAR 2 , and TRPV4 may be valuable treatments for these and other inflammatory diseases.…”

Selective Cathepsin S Inhibition with MIV-247 Attenuates Mechanical Allodynia and Enhances the Antiallodynic Effects of Gabapentin and Pregabalin in a Mouse Model of Neuropathic Pain

“…However, it is possible that the inhibition of cathepsin S in the periphery may also contribute and increase the effects of pregabalin and gabapentin. Recently, cathepsin S has been shown to activate PAR2 receptors (Reddy et al, 2010;Elmariah et al, 2014;Zhao et al, 2014), and cathepsin S-induced colonic hyperalgesia in the periphery was suggested to be mediated via PAR2 receptors (Cattaruzza et al, 2011). Less is known about PAR2 receptors in the spinal cord, but specific PAR2 receptor agonists cause mechanical and spinal hyperalgesia when administered intrathecally (Alier et al, 2008), possibly via the inhibition of inhibitory GABAergic neurotransmission (Huang et al, 2011).…”

Protease-Activated Receptors as Therapeutic Targets in Visceral Pain

“…This increase in activity was coupled with a decrease of mucosal expression of elafin (endogenous elastase inhibitor) in patients with IBD [49]. In mouse colitis, macrophage cathepsins are activated during colitis, and Cat-S activates nociceptors to induce visceral pain via PAR 2 [50]. These different studies demonstrated an increase in proteolytic activity in IBD patients or in mice under experimentally-induced colitis.…”