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Advances in dermatology and venereology Acta Dermato-Venereologica
Atopic Dermatitis Linked Cytokine Interleukin-31 Induced Itch Mediated via a Neuropeptide Natriuretic Polypeptide B
Saumitra PITAKE # , Patrick C . RALPH # , Jennifer DEBRECHT and Santosh K . MISHRA * Department of Molecular Biomedical Sciences , NC State Veterinary Medicine , 1060 William Moore Drive , Office 242 , Raleigh , NC 27607 , USA . * E-mail : skmishra @ ncsu . edu . # These authors contributed equally . Accepted May 22 , 2018 ; Epub ahead of print May 24 , 2018
Atopic dermatitis ( AD ) is one of the most common itchinducing allergic skin diseases in humans and animals ( 1 , 2 ). Interleukin ( IL ) -31 , a cytokine involved in immune response in inflammatory diseases such as AD , has been demonstrated to cause itch by acting on receptors in a subset of transient receptor potential vanilloid ( TRPV1 ) neurons ( 3 – 5 ). We recently identified a small subset of neurons that function as the primary detectors of chemical pruritic stimuli . We showed that the neuropeptide natriuretic polypeptide b ( NPPB ) is required for the transmission of itch signals and marks the full complement of itch responsive neurons at the periphery ( 6 ). However , it remains unknown how itch signals in AD are transmitted by the primary afferents of the sensory neurons in the dorsal root ganglia ( DRG ) to the spinal cord . This study is aimed to determine if NPPB is involved as a neuropeptide in IL-31-mediated itch in AD via natriuretic polypeptide receptor A ( NPRA ) in the spinal cord .
METHODS ( see Appendix S1 1 )
RESULTS
Cytokine IL-31 transmits its signals through a receptor complex made of IL31R and oncostatin M receptor ( OSMR ). We used double ISH to show that the IL31R is co-expressed with NPPB expressing sensory neurons in the DRG . Our data demonstrated that IL31R is selectively expressed in all NPPB-positive somatosensory neurons ( Fig . 1A ). We further showed that IL31R is exclusively expressed in all OSMR neurons in the DRG ( Fig . 1B ). We showed the co-expression of NPPB with IL31R in almost 98 % of the neurons : 198 / 204 IL31R / OSMR-neurons .
1 https :// www . medicaljournals . se / acta / content / abstract / 10.2340 / 00015555-2977
To assess whether the IL-31-induced pruritogenic response is mediated via NPPB , we compared age-matched wild-type littermates and NPPB knockout ( KO ) mice . We injected IL-31 subcutaneously in both genotypes and measured scratching bouts . We observed a significant reduction in scratching response from NPPB KO mice ( Fig . 1C ). To further demonstrate the IL-31-mediated itch response by NPRA receptors expressed in the spinal cord , we used conjugated NPPB-saporin toxin to eliminate neurons expressing NPRA receptors in the spinal cord ( 6 ). We consistently found a drastic reduction in scratching response from the NPPB-saporin treated mice as compared to the control . To rule out immunogenic involvement of IL-31 in itch production , we administered IL-31 to NOD control mice and the mice lacking functional B and T- cells ( NOD / SCID ). We found no significant difference between NOD control ( black bar ) and NOD / SCID immune-deficient mice ( white bar ; Fig . 1D ) suggesting IL-31-mediated itch is an immuneindependent mechanism .
Contributions of TRPV1- or TRPA1-expressing DRG neurons in itch are important ( 8 ). Recently , individual TRPV1- or TRPA1- KO mice confirmed an important role of TRP-channels in IL31- induced itch ( 5 ); however , single KO have any compensatory effect on itch behavior was unclear . We sought out whether knocking out both TRPV1 and TRPA1-expression might show potential compensatory effect of TRP-channels on itch behavior . To determine the role of TRPV1 / TRPA1 ion channels , we generated double KO mice . We first performed IL-31 induced calcium response on wild-type DRG sensory neurons ( Fig . 2A ). Quantification of the number of cells responding to IL-31 ( 0.3 μM ) revealed a reduction ( approximately 50 %) in calcium response in double KO mice ( Fig . 2B ). Interestingly , our scratching behavior data demonstrated a significant decrease in IL-31 ( 0.3 nmol ) induced itch response ( 80 %) in TRPV1 / TRPA1 double KO mice ( Fig . 2C ) compared to wild type mice . Next , we determined whether NPPB release is induced by cytokine IL-31 and if the release is mediated through TRPV1 / TRPA1-ion channels . To explore this possibility , we cultured mouse DRGs from double KO and control mice and incubated neurons with IL-31 ( 0.3 μM ) over 8 h to measure NPPB release . Indeed , our data showed a reduction ( approximately 20 %) in NPPB release in double KO mice as compared to control mice . These results demonstrate that both TRPV1 and TRPA1 channels are associated with NPPB-release in DRG sensory neurons .
Fig . 1 . ( A ) Double in situ hybridization ( ISH ) reveals that the neuropeptide natriuretic polypeptide b ( NPPB ) ( green ) co-expresses interleukin ( IL ) -31- receptor ( red ). ( B ) Double ISH of IL-31Ra co-expresses oncostatin M receptor ( OSMR ). ( C ) Itch responses to subcutaneously injected IL-31 ( 1.5 nmol ) were significantly attenuated in NPPB knockout mice and mice treated with NPPB-saporin . ( D ) No differences in itch responses were observed in mice lacking B- and T-cell receptors ( NOD / SCID ) compare to control mice ( NOD ). Itch behaviors were observed in mice within 30 min of administering IL-31 . Each column represents the mean ± SEM , n ≥ 6 mice for each group , ** p < 0.01 .
This is an open access article under the CC BY-NC license . www . medicaljournals . se / acta Journal Compilation © 2018 Acta Dermato-Venereologica . doi : 10.2340 / 00015555-2977 Acta Derm Venereol 2018 ; 98 : 795 – 796