Spinal Cord NLRP1 Inflammasome Contributes To Dry Skin Induced Chronic Itch In Mice

Dry skin itch is one of the most common skin diseases and elderly people are believed to be particularly prone to it.The inflammasome has been suggested to play an important role in chronic inflammatory disorders including inflammatory skin diseases such as psoriasis.However,little is known about the role of NLRP1 inflammasome in dry skin-induced chronic itch.Objective To investigate the effect of NLRP1 inflammasome on chronic itch in mice treated with acetone-ether-water(AEW)and the role of NLRP1 inflammasome in the age and sex differences of chronic itch.Methods Dry skin-induced chronic itch model was established by acetone-ether-water(AEW)treatment.Spontaneous scratching behavior was recorded by video monitoring.The expression of nucleotide oligomerization domain(NOD)-like receptor protein 1(NLRP1)inflammasome complexes and the level of inflammatory cytokines were determined by western blot,quantitative real-time PCR,and enzyme-linked immunosorbent assay(ELISA)kits.Nlrp1 a knockdown was performed by an adeno-associated virus(AAV)vector containing Nlrp1a-sh RNA-e GFP infusion.H.E.staining was used to evaluate skin lesion.Results:1.The mice developed marked scratching behavior on the sixth day after AEW treatment, suggesting chronic itch model was established successfully.Compared with control group,the protein expression and the m RNA levels of NLRP1,ASC and caspase-1 are significantly increased in AEW-treated group,indicating that spinal cord NLRP1 inflammasome is activated in mice with chronic itch induced by AEW.2.Compared with control group,AEW treatment significantly increased the expression of IL-1?,IL-18,IL-6 and TNF-? in spinal cord and the levels of these cytokines,indicating that NLRP1 inflammasome-mediated inflammatory signal may be involved in chronic itch induced by AEW.3.4 weeks after AAV-Nlrp1a-sh RNA infusion,it showed clear silencing efficacy.Compared with AEW group,control-sh RNA did not influence AEW-induced scratching behavior.However,Nlrp1a-sh RNA significantly attenuated the number of spontaneous scratches induced by AEW.Also,AEW treatment led to a substantial increase in the thickness of nucleated epidermal layers and Nlrp1a-sh RNA significantly inhibited this effect.Furthermore,Nlrp1a-sh RNA blocked AEW-induced increases in spinal cord ASC,caspase-1,IL-1? and IL-18 expression.All these results indicate that Nlrp1 knockdown prevents the assembly of NLRP1 inflammasome and reduced the release of IL-1? and IL-18 which contribute to AEW-induced chronic itch.4.Compared with the control group,AEW treatment and Control-sh RNA group increased significantly the expression of;compared with the AEW treatment and Control-sh RNA group,TRPV1 protein expression in the Nlrp1a-sh RNA group was significantly reduced.In addition,compared with the control group,the number of spontaneous scratches and the levels of inflammatory factors IL-1?,IL-18,IL-6 and TNF-? in the AEW treatment group were significantly increased,while TRPV1 inhibitor CPZ inhibited these effects.These results suggested that TRPV1 is involved in NLRP1 infalmmasome mediated chronic itch in mice5.Compared with control group,all young mice and elderly mice showed remarkable scratching behavior on the sixth day after AEW treatment.Moreover,elderly mice exerted more significant scratching behavior than young mice.Also,the increases of NLRP1,ASC and caspase-1 proteins expression and m RNA levels in elderly mice were more significant than those in young mice.Additionally,AEW treatment increased the content of IL-1?,IL-18,IL-6 and TNF-?,which was more significant in elderly mice than in young mice.These data suggest that NLRP1 Inflammasome-mediated inflammatory response is involved in enhanced chronic itch in aged mice.6.Compared with control group,all the male and female mice showed remarkable scratching behavior on day 6 after AEW treatment and higher itch intensity was observed in female mice than in male mice.Also,the increases of NLRP1,ASC and caspase-1 proteins expression and m RNA levels in female mice were more significant than those in male mice.Additionally,AEW treatment increased the content of L-1?,IL-18,IL-6 and TNF-?,which was more significant in female mice than in male mice.All these data suggest that NLRP1 inflammasome-mediated inflammatory signal is involved in chronic itch with gender differences.Conclusion The present study demonstrated that NLRP1 inflammasome-mediated inflammatory signal contributes to dry skin-induced chronic itch by TRPV1 channel and plays an important role in itch transduction,and it also connects age and gender to chronic itch.Therefore,inhibition of NLRP1 inflammasome may offer a new therapy for dry skin itch.However,further efforts will be made to clarify the precise mechanism how NLRP1 inflammasome affect the signaling transduction of itch in future research.