Inhibitor of Apoptosis Proteins (IAPs) Limit RIPK1-Mediated Skin Inflammation

Inhibitor of apoptosis proteins (IAPs) are critical regulators of cell death and survival pathways. Mice lacking cIAP1 and either cIAP2 or XIAP die in utero, and myeloid lineage-specific deletion of all IAPs causes sterile inflammation, but their role in the skin is unknown. We generated epidermal-specific IAPedeficient mice and found that combined genetic deletion of cIAP1 (epidermal knockout [EKO]) in keratinocytes and ubiquitous cIAP2 deletion (cIap1(EKO/EKO).cIap2(-/-)) caused profound skin inflammation and keratinocyte death, lethal by postpartum day 10. To investigate their role in skin homeostasis, we injected an IAP antagonist compound subcutaneously into wild-type and knockout mice. This induced a toxic epidermal necrolysis-like local inflammation, which mirrored the phenotype seen in cIap1(EKO/EKO).cIap2(-/-) mice. Loss of one Ripk1 allele limited lesion formation and significantly extended the lifespan of cIap1(EKO/EKO).cIap2(-/-) mice. cIAP activities are important for recruitment of LUBAC to signaling complexes, and loss of LUBAC component SHARPIN, induces dermatitis in mice. Consistent with this relationship between cIAPs and LUBAC, Ripk1 heterozygosity also protected against development of dermatitis in Sharpin-deficient mice. This work therefore refines our molecular understanding of inflammatory signaling in the skin and defines potential targets for treating skin inflammation.