Mechanisms Underlying the Scratching Behavior Induced by the Activation of Proteinase-Activated Receptor-4 in Mice

Abstract

A role for proteinase-activated receptor-4 (PAR-4) was recently suggested in itch sensation. Here, we investigated the mechanisms underlying the pruriceptive actions of the selective PAR-4 agonist AYPGKF-NH2 (AYP) in mice. Dorsal intradermal (i.d.) administration of AYP elicited intense scratching behavior in mice, which was prevented by the selective PAR-4 antagonist (pepducin P4pal-10). PAR-4 was found to be coexpressed in 32% of tryptase-positive skin mast cells, and AYP caused a 2-fold increase in mast cell degranulation. However, neither the treatment with cromolyn nor the deficiency of mast cells (WBB6F1-Kit(W/Wv) mice) was able to affect AYP-induced itch. PAR-4 was also found on gastrin-releasing peptide (GRP)-positive neurons (pruriceptive fibers), and AYP-induced itch was reduced by the selective GRP receptor antagonist RC-3095. In addition, AYP evoked calcium influx in ∼1.5% of cultured DRG neurons also sensitive to TRPV1 (capsaicin) and/or TRPA1 (AITC) agonists. Importantly, AYP-induced itch was reduced by treatment with either the selective TRPV1 (SB366791), TRPA1 (HC-030031), or NK1 (FK888) receptor antagonists. However, genetic loss of TRPV1, but not of TRPA1, diminished AYP-induced calcium influx in DRG neurons and the scratching behavior in mice. These findings provide evidence that PAR-4 activation by AYP causes pruriceptive itch in mice via a TRPV1/TRPA1-dependent mechanism.

Mast cell‐neural interactions contribute to pain and itch

“…Possibly the itch in this model was evoked directly through PAR‐4 on gastrin‐releasing peptide‐positive pruriceptive fibers. Also, the itch behavior was diminished by TRPV1 knockout or antagonism, but unexpectedly, it was diminished only by TRPA1 antagonism and not by TRPA1 knockout …”

“…Also, the itch behavior was diminished by TRPV1 knockout or antagonism, but unexpectedly, it was diminished only by TRPA1 antagonism and not by TRPA1 knockout. 227 The cutaneous nerve fibers and their interactions with mast cells may be influenced by therapeutic molecules resulting in decreased itch and inflammation. A promising example from this is the NC/Nga mouse model of AD, where the spontaneously developed dorsal skin lesions were treated with intracutaneous injections of semaphorin-3A twice a day for 5 days and then were biopsied on day 11.…”

TRPV1 and TRPA1 in cutaneous neurogenic and chronic inflammation: pro-inflammatory response induced by their activation and their sensitization

“…On the other hand, the involvement of PAR-4 activation in TRPV1 sensitization has been poorly studied. One study demonstrated that PAR-4 activation potentiated TRPV1 activation via a PKC-dependent pathway (Vellani et al, 2010 ; Patricio et al, 2015 ).…”

“…Moreover, neuropeptides and mast cell-released mediators can act on other neighboring target cells, including keratinocytes, dendritic cells, neutrophils and fibroblasts, leading to the disruption of skin homeostasis, with abnormal skin growth, differentiation, and/or immunomodulation (Shim et al, 2007 ; Trevisani et al, 2007 ; Wilson et al, 2013b ; Patricio et al, 2015 ).…”

Protease‐activated receptor 4: from structure to function and back again

“…PAR4 expression is up‐regulated in DRG neurons during nociceptor activation and neurogenic pain (Dattilio et al , ; Chen et al , ) and in sensory neurons of the colon (Auge et al , ), suggesting a potential role for PAR4 in nociception associated with inflammatory pathologies of the viscera, such as inflammatory bowel disease. In addition, PAR4 may be important in transmitting the signals for neurogenic itch (Tsujii et al , ; Papoiu et al , ; Patricio et al , ). PAR4 activation is thought to attenuate nociception via sensory neurons by inhibiting nociceptive signals (Asfaha et al , ).…”