Biology subjects

Lomax, A. E.

Publications and source records attributed to Lomax, A. E..

3 recordsLinked to original sources

bioRxiv2026

ENDOSOMAL SIGNALING OF PROTEASE-ACTIVATED RECEPTOR-2 AMPLIFIES HISTAMINE-INDUCED PAIN OF IRRITABLE BOWEL SYNDROME

BackgroundProteases and histamine, co-secreted by mast cells and bacteria, sensitize colonic nociceptors and contribute to irritable bowel syndrome (IBS) pain. ObjectiveTo determine whether irreversible proteolytic cleavage of protease-activated receptor-2 (PAR2) and its continued activity in endosomes amplify and sustain otherwise transient pronociceptive actions of histamine receptors (HRs) to cause recurrent pain, the defining symptom of IBS. DesignWe investigated the coexpression of PAR2 and H1R in nociceptors using RNAscope in situ hybridization and assessed the consequences of coactivation using electrophysiological assays of nociceptor sensitization and biophysical measurements of receptor and effector activity. ResultsPAR2 and H1R were coexpressed by human and mouse dorsal root ganglion nociceptors. Intracolonic infusion of fecal supernatants from IBS patients enhanced mechanosensitivity of colonic nociceptors in mice. Antagonists of PAR2 or H1-4R abolished this response. Combined administration of subthreshold concentrations of trypsin and histamine replicated the effects of fecal supernatant and caused hyperexcitability of isolated nociceptors. Pre-activation of PAR2 sensitized histamine-induced hyperexcitability. Endocytosis inhibitors prevented this hypersensitivity, consistent with sustained endosomal signaling of PAR2 and persistent nociceptor hyperexcitability. Trypsin amplified histamine-induced activation of H1R and {beta}-arrestin2 and Gq effectors at the plasmalemma and in endosomes. Conversely, histamine did not sensitize trypsin-induced hyperexcitability of neurons, in line with the inability of histamine to induce sustained nociceptor hypersensitivity. ConclusionsBy amplifying and maintaining the otherwise transient actions of H1R and possibly other pain receptors, persistent PAR2 endosomal signaling makes a dominant contribution to IBS-related colonic pain. Summary boxO_ST_ABSWhat is already known on this topicC_ST_ABSProteases and histamine are increased in IBS patients and cause visceral pain. What this study addsProlonged intracellular PAR2 signaling sensitizes and maintains H1R activity to amplify and maintain pain. How this might affect research, practice or policyAlthough neuroactive factors can act synergistically to amplify and maintain IBS pain, antagonists of dominant receptors (e.g., PAR2) can provide effective treatment.

neuroscience↗

bioRxiv2025

Probing the activity of cysteine cathepsins in inflammatory bowel diseases

Cathepsin S is a cysteine protease that has been implicated in inflammatory bowel diseases (IBD) for its ability to promote visceral pain. Given its pro-inflammatory roles, we hypothesized that cathepsin S would drive other symptoms associated with IBD. Using activity-based probes, we investigated cysteine cathepsin activation in human and murine colitis. We observed a significant increase in fecal cathepsin S in patients with ulcerative colitis compared to healthy controls, while cathepsin S in mucosal biopsies was unchanged. Mice with experimental colitis exhibited a modest increase in mucosal activity of both cathepsin S and X compared to naive mice. Luminal secretion of cathepsin S was dramatically increased upon colitis induction, although differences between mouse colonies were observed. To investigate the contribution of cathepsin S and cathepsin X to colitis, we induced colitis in cathepsin-deficient mice. Cathepsin X-deficient mice exhibited no clear differences in disease indicators compared to wild-type mice. While cathepsin S-deficient mice exhibited less rectal bleeding, less splenomegaly and marginally improved histological scores, weight loss, diarrhea, colon shortening, and myeloperoxidase activity were not significantly different from wild-type mice. To determine whether pharmacologic inhibition of cathepsin S activity would ameliorate symptoms of colitis, a reversible inhibitor LY3000328 was administered to mice at the initiation of colitis. LY3000328 provoked a clear upregulation of cathepsin S and L activity in the mucosa, most likely through a compensatory mechanism. This increase in protease activity was associated with exacerbated histological scores and splenomegaly. Collectively, these results suggest that cathepsin S, but not cathepsin X, may contribute to some of the symptoms of experimental colitis. While cathepsin S has potential to be a therapeutic target in colitis, improved strategies to sustain its inhibition are required in future.

pathology↗

bioRxiv2025

Identification of a secreted protease from Bacteroides fragilis that induces intestinal pain and inflammation by cleavage of PAR2

Protease-activated receptor 2 (PAR2) is a central regulator of intestinal barrier function, inflammation and pain. Upregulated intestinal proteolysis and PAR2-signaling are implicated in inflammatory bowel diseases (IBDs) and irritable bowel syndrome (IBS). To identify potential bacterial regulators of PAR2 activity, we developed a functional assay for PAR2 processing and used it to screen conditioned media from a library of diverse gut commensal microbes. We found that multiple bacteria secrete proteases that cleave host PAR2. Using chemoproteomic profiling with a covalent irreversible inhibitor, we identified a previously uncharacterized Bacteroides fragilis serine protease Bfp1, and showed that it cleaves and activates PAR2 in multicellular and murine models. PAR2 cleavage by Bfp1 disrupts the intestinal barrier, sensitizes nociceptors, and triggers colonic inflammation and abdominal pain. Collectively, our findings uncover Bfp1-mediated PAR2-processing as a new axis of host-commensal-interaction in the gut that has the potential to be targeted for therapeutic intervention in IBD or IBS.

microbiology↗