Role Of ASIC3 Activation On Itch Evoked By Bradykinin B1 Agonist In Inflamed Skin

Pruritus or itching is a remarkably common symptom of dermatologic and systemic diseases and seriously impacts a patient's quality of life.Acute itching is usually caused by specific itch substances,while chronic itch is a troublesome clinical problem result from severe systemic disease.And anti-histamine therapy is the most commonly used treatment in clinic.However,anti-histamine sometimes is useless for serious chronic itch.The biomechanism is not clear,this much is certain:there is no singular cause of itch.Rather,itch is caused by a complex interface between pruritogenic molecules,skin,keratinocytes,cutaneous nerve fibers,and the peripheral and central nervous systems.Alloknesis is elicited in complete Freund'S adjuvant(CFA)inflamed skin and the bradykinin receptors involved in it.While bradykinin is currently known as the strongest pain-causing substances are also important inflammatory factors.Bradykinin and its metabolite des-Arg9-bradykinin/des-ArglO-bradykinin mediate their effects through cell membrane attached receptors called bradykinin receptors thatbelong to the G protein-coupled family of receptors.Bradykinin receptor is not express or rare express under normal physiological conditions,and rapidly expressed when face in the inducible factors like bacterial lipopolysaccharide(LPS),inflammation and trauma.Intradermal injection of B1R receptor agonists induce scratching behavior in CFA-inflamed mice,but the downstream mechanism remains unknown.Studies have reported that the expression of acid-sensing ion channels(ASICs)in the dorsal root ganglion(DRG)is increased in the inflammatory state,and the ASIC3 gene knockout or the use of specific blockers Can significantly weaken the scratching behavior.Therefore,Peripheral injection of CFA result in chronic inflammation model,in which further research needs to be made to investigate whether B1R agonist induce abnormal itch response is relate to the upregulation of ASIC3 in DRG neurons.MESTHOLDSThe dorsal hair of the mice was removed and then intradermal injection of CFA(50ul).96 hours after CFA administration,each animal was handled for 30 min for acclimation in an individual plastic chamber.Then ASIC3 blocker(APETx2)were i.p injection with an insulin-syringe coupled to a 30-Gauge needle anesthesia by sevoflurane.Hind limb scratching behavior towards the injection area was then observed for a period of 30 min for each mouse.And the related DRG neurons were picked out from the inflamed mice(normal saline as control).Furthermore,the expression of ASIC3 in DRG was detected with western blot.Then,To further explore whether ASIC3 participates in the itching is selective,the itching induced by DCP,chloroquine,endothelin-1 and 48/80 compound also tested with APETx2.RESULTS1.Blocking ASIC3 signaling decreases BIR agonist-evoked scratching behavior in inflamed skin significantlyScratching response were decrease obviously(Fig 1-1,*P<0.05)by APETx2 were administered intraperitoneally 30 min prior to intradermal B1R agonist injection in the nape of neck in CFA-inflamed skin,suggest that the ASIC3 signaling pathway is involved in transmission of itch sensations in response to B1R agonist treatment in inflamed skin.2.Blocking ASIC3 signaling only decrease some of the pruritogens induced itch.Intraperitoneal injection APETx2 significantly decreases CQ evoked scratching behavior(Fig2-2,*P<0.05),while inefficient for ET-1 and 48/80compound(Fig2-2,*P>0.05).3.Blocking ASIC3 signaling decreases DCP-induced spontaneous scratching behavior significantly.The number of spontaneous scratches in 30min were significantly suppressed by intraperitoneally 30 min prior to observation(Fig 2-1,*P<0.05).4.Inflammation increased the expression of ASIC3 in DRG.Western blot shows that the expression of asic3 increased in CFA-inflamed mice(Fig1-2).ConclusionsInflammation increased the expression of ASIC3 in DRG.And ASIC3 involved in the B1R activator induced scratching,furthermore,the involvement is selective.