Study On The Role And Molecular Mechanism Of PAR-2 In Prurits

Pruritus can be defined as an unpleasant cutaneous sensation associated with the immediate desire to scratch. Pruritus is the most common symptom of various skin diseases, but its specific neurophysiological mechanisms are not fully understood. Chronic or intense scratching leads to the development of skin lesions and the release of inflammatory mediators that potentially induce or aggravate pruritus resulting in reinforcement of scratching. This itch-scratch cycle is frequently resistant to topical and systemic therapy. Histamine is thought to be one of the main mediators for the transmission of itch sensation. However, there are little available information on the role of histamine in scratching behaviour of atopic dermatitis (AD) therefore suggests that histamine is not the main pruritogen of the disease.Protease-activated receptor-2 (PAR2) belongs to a recently described G protein-coupled receptor subfamily that is activated by serine proteinases. Protease-activated receptor-2 has been suggested to mediate widespread inflammation in various tissues including the skin. Recently, protease-activated receptor-2 has been shown to play a key role in the pathophysiology of itch. Expression of tryptase and PAR2 was markedly enhanced on primary afferent nerve fibers of lesional skin in patients with AD, and intracutaneous injection of specific PAR2 agonists provoked sustained and prolonged itch in such patients. These findings suggest that tryptase is an endogenous itch mediator. However, the precise mechanism of PAR2-mediated itch during inflammatory processes remains largely unknown. It is interesting to investigate the relative roles of PAR2 in cutaneous pruritus. In this study, a murine model of passive cutaneous anaphylaxis (PCA) and atopic-like dermatitis were established and the precise mechanism of PAR2-mediated itch has been explored. PAR2 may be an important regulator of skin mast cell function during cutaneous inflammation and hypersensitivity. In the present study, we investigated the role of PAR2 in allergic pruritus by a murine model of PCA. We found that an intravenous injection of dinitrophenyl-ovalbumin solution significantly increased the number of scratches compared with the passive cutaneous anaphylaxis (-) group. Cetirizine and ketanserin significantly inhibited the passive cutaneous anaphylaxis-induced scratching behavior in a dose-dependent manner. In addition, combine cetirizine with ketanserin exhibited significant inhibitory effects for the number of passive cutaneous anaphylaxis-induced scratching behavior. Leupeptin and PAR2-neutralizing antibody significantly inhibited passive cutaneous anaphylaxis-induced scratching behavior in a dose-dependent manner. Nonspecific IgG caused no effect on the scratching behavior. Topical application of tacrolimus significantly inhibited the passive cutaneous anaphylaxis-induced scratching behavior in a dose-dependent manner. Combine cetirizine with tacrolimus exhibited significant inhibitory effects for the number of passive cutaneous anaphylaxis-induced scratching behavior. An intradermal injection of tryptase significantly increased the number of scratches compared with the phosphate-buffered saline group. Tacrolimus significantly reduced the number of scratches induced by tryptase. These results suggest that PAR2 may be involved in passive cutaneous anaphylaxis-induced scratching behavior and tacrolimus produce an anti-allergic pruritus effect in mice.Partâ…¡Study on the regulation mechanism of proteinase-activated receptor-2 in itchingProtease-activated receptor-2 (PAR2) has been shown to play a key role in the pathophysiology of itch. In the present study, we investigated the effects of several agents on the scratching behavior induced by PAR2-activating peptide (SLIGRL-NH2) to study the precise mechanism of PAR2-mediated itch. We found that intradermal injection of SLIGRL-NH2 significantly increased the number of scratches compared to that in the saline group, and cetirizine had little effect on SLIGRL-NH2-induced scratching behavior. Zileuton exhibited a significant inhibitory effect on SLIGRL-NH2-induced scratching behavior, whereas indomethacin was without effect. Topical application of tacrolimus inhibited SLIGRL-NH2-induced scratching behavior in a dose-dependent manner. There was no significant difference in scratching behavior between the LRGILS-NH2 and saline groups. Cutaneous levels of LTB4 and PGE2 were significantly increased after intradermal injection of SLIGRL-NH2. Pretreatment with zileuton or tacrolimus significantly reduced the skin level of LTB4, whereas cetirizine and indomethacin were without effect. Pretreatment with indomethacin or tacrolimus significantly reduced the skin level of PGE2, whereas cetirizine and zileuton were without effect. The cutaneous levels of LTB4 and PGE2 in LRGILS-NH2-treated mice showed no significant difference compared to those in the control group. Results of ELISA demonstrated that the addition of SLIGRL-NH2 enhanced LTB4 release from primary cultures of mouse keratinocytes in a concentration-dependent manner. The SLIGRL-NH2-induced secretion of LTB4 was inhibited by pretreatment of keratinocytes with zileuton or tacrolimus, whereas cetirizine and indomethacin were without effect. The SLIGRL-NH2 peptide also induced increases in PGE2 secretion. The SLIGRL-NH2-induced secretion of PGE2 was inhibited by pretreatment of keratinocytes with indomethacin or tacrolimus, whereas cetirizine and zileuton were without effect. The LRGILS-NH2 peptide had little effect on LTB4 and PGE2 release from keratinocytes. These results indicate that SLIGRL-NH2 stimulates LTB4 and PGE2 release from mouse keratinocytes and that enhancement of LTB4 secretion contributes to SLIGRL-NH2-induced scratching behavior in ICR mice.Partâ…¢Study on the molecular mechanism of proteinase-activated receptor-2 in chronic itchingAtopic dermatitis (AD) is a chronically relapsing inflammatory skin disease associated with high levels of serum immunoglobulin E (lgE). The molecular basis of chronic pruritus in AD remains largely unexplained. Wang et al described a murine model of AD elicited by repeated epicutaneous sensitization (EC) with ovalbumin (OVA). This model displays many of the features of human AD. In the present study, we examined the PAR2 expression use this model to assess the role of PAR2 in the pathophysiology of chronic pruritus. We found that there were thickening and inflammation in the dermis and epidermis at the site of repeated EC with OVA, but not with saline. In the healthy skin, PAR2-like immunoreactivity was present throughout the epidermis. In the lesional skin, epidermal hyperplasia was marked and PAR2-like immunoreactivity was present throughout the expanded epidermis. After repeated EC with OVA, PAR2 mRNA and protein expression significantly increased over baseline respectively. In contrast, there was no increase in PAR2 gene and protein expression in saline sensitized skin. In addition, the total levels of IgE and trytase of the ovalbumin group were significantly increased compared with the saline group. EC with OVA significantly increased the number of scratches compared with the saline group. Cetirizine in doses of 10 mg/kg significantly inhibited the OVA-induced scratching behavior. Leupeptin inhibited the OVA-induced scratching behavior in a dose-dependent manner. PAR2-neutralizing antibody also exhibited significant inhibitory effects for the number of OVA-induced scratching behavior. Topical application of tacrolimus at concentrations of 1.0% and 3.0% significantly inhibited the OVA-induced scratching behavior. These results suggest that PAR2 may be involved in OVA-induced scratching behavior and tacrolimus produce an anti-chronic pruritus effect in a murine model of atopic-like dermatitis.