Downregulation of iNOS, IL-1β, and P2X7 Expression in Mast Cells via Activation of PAR4 Contributes to the Inhibition of Visceral Hyperalgesia in Rats

Abstract

Protease-activated receptor 4 (PAR4) is implicated in the inhibition of visceral hyperalgesia. In the present study, the effects of PAR4 activation on visceral hypersensitivity and expression of inflammatory mediators, including interleukin-1β (IL-1β), P2RX7 purinergic receptor (P2X7), inducible nitric oxide synthase (iNOS), and tryptase, in mast cells (MCs) were investigated via in vivo and in vitro studies. The numbers of tryptase-positive MCs with extensive PAR4, P2X7, and iNOS expression were increased in the colons of visceral hyperalgesia rats compared with controls. Intracolonic administration of PAR4-activating peptide (PAR4-AP) significantly attenuated the visceral hypersensitivity to colorectal distention and reduced the iNOS, IL-1β, P2X7, and tryptase protein and mRNA levels in the colonic mucosa. Treatment of rat bone marrow MCs (BMMCs) with PAR4-AP also reduced the iNOS, IL-1β, P2X7, and tryptase protein and mRNA levels. ERK1/2 and p38 activators (t-butylhydroquinone, tBHQ, and U-46619) reversed the suppressive effect of PAR4 activation on IL-1β and iNOS expression, whereas ERK1/2 and p38 inhibitors (PD98059 and SB203580) reversed the suppressive effect of PAR4 activation on P2X7 and tryptase expression. Our results indicate that the downregulation of inflammatory mediators, including iNOS, IL-1β, P2X7, and tryptase, in MCs that are mediated by PAR4 activation could inhibit visceral hyperalgesia via the mitogen-activated protein kinase (MAPK) signal pathway.

Proteinase Activated Receptor 4 in the Jejunum of Healthy Horses and of Horses With Epiploic Hernia

“…The mast cells, in the peripheral tissues, modulate the nociceptive pathways, especially those of inflammatory origin. In fact, by means of mediators and cytokines release (tryptase and interleukin 1β) they activate other immune cells (neutrophils, macrophages and T cells) and amplify the inflammatory response (3,31,32). The mast cells in the intestinal tract seem to be particularly involved in the regulation of visceral hypersensitivity through PAR 4 (3,33,34).…”

“…In fact, by means of mediators and cytokines release (tryptase and interleukin 1β) they activate other immune cells (neutrophils, macrophages and T cells) and amplify the inflammatory response (3,31,32). The mast cells in the intestinal tract seem to be particularly involved in the regulation of visceral hypersensitivity through PAR 4 (3,33,34). In fact, in-vitro or in-vivo activation of PAR 4 on mast cells resulted in a suppression of mRNA and protein levels of tryptase and 13 types of proinflammatory cytokines (3,35).…”

“…The mast cells in the intestinal tract seem to be particularly involved in the regulation of visceral hypersensitivity through PAR 4 (3,33,34). In fact, in-vitro or in-vivo activation of PAR 4 on mast cells resulted in a suppression of mRNA and protein levels of tryptase and 13 types of proinflammatory cytokines (3,35). On the contrary the role of the PAR 4 in lymphocytes is still to be clarified, however it does not seem to be involved in the modulation of nociception.…”

“…Based on these results, several authors are further investigating the involvement of PAR 4 in visceral nociception and pain (3,(20)(21)(22). Augé and colleagues found that in mice, the intracolonic administration of a synthetic PAR 4 activating peptide decreased the nociceptive response induced by visceral stimulation and inhibited the colonic hypersensitivity induced by the previous activation of the PAR 2 (22).…”

P2X receptors mediated abnormal interaction between satellite glial cells and neurons in visceral pathological changes

“…Protease‐activated receptor 4 (PAR4) is involved in the inhibition of visceral hyperalgesia. The downregulation of the P2X7 receptor in PAR4‐activated mast cells inhibits visceral hyperalgesia via the MAPK signaling pathway (Hao et al, ). Chronic pancreatitis increased the co‐expression levels of spinal P2X7 receptor and OX‐42 (a microglia marker).…”