Proteases are key mediators of pain and altered enteric neuronal signalling, although the types and sources of these important intestinal mediators are unknown.
Dr Claire Rolland-Fourcade and colleagues hypothesized that intestinal epithelium is a major source of trypsin-like activity in patients with IBS, and this activity signals to primary afferent and enteric nerves and induces visceral hypersensitivity.
Trypsin-like activity was determined in tissues from patients with IBS and in supernatants of Caco-2 cells stimulated or not.
These supernatants were also applied to cultures of primary afferents. mRNA isoforms of trypsin were detected by reverse transcription-PCR, and trypsin-3 protein expression was studied by western blot analysis and immunohistochemistry.
Electrophysiological recordings and Ca2+ imaging in response to trypsin-3 were performed in mouse primary afferent and in human submucosal neurons, respectively.
|Increased trypsin-like activity was associated with the epithelium|
Visceromotor response to colorectal distension was recorded in mice administered intracolonically with trypsin-3.
The research team showed that stimulated intestinal epithelial cells released trypsin-like activity specifically from the basolateral side.
The team observed that this activity was able to activate sensory neurons.
In colons of patients with IBS, increased trypsin-like activity was associated with the epithelium.
The researchers identified that trypsin-3 was the only form of trypsin upregulated in stimulated intestinal epithelial cells and in tissues from patients with IBS.
Trypsin-3 was able to signal to human submucosal enteric neurons and mouse sensory neurons, and to induce visceral hypersensitivity in vivo, all by a protease-activated receptor-2-dependent mechanism.
Dr Rolland-Fourcade's team concludes, "In IBS, the intestinal epithelium produces and releases the active protease trypsin-3, which is able to signal to enteric neurons and to induce visceral hypersensitivity."