Background: A delicate balance between cell death and keratinocyte proliferation is crucial for normal skin development. Previous studies have reported that cellular FLICE (FADD-like ICE)-inhibitory protein plays a crucial role in prevention of keratinocytes from TNF-α-dependent apoptosis and blocking of dermatitis. However, a role for cellular FLICE-inhibitory protein in TNF-α-independent cell death remains unclear.
Objective: We investigated contribution of TNF-α-dependent and TNF-α-independent signals to the development of dermatitis in epidermis-specific Cflar-deficient (CflarE-KO) mice.
Methods: We examined the histology and expression of epidermal differentiation markers and inflammatory cytokines in the skin of CflarE-KO;Tnfrsf1a+/- and CflarE-KO;Tnfrsf1a-/- mice. Mice were treated with neutralizing antibodies against Fas ligand and TNF-related apoptosis-inducing ligand to block TNF-α-independent cell death of CflarE-KO;Tnfrsf1a-/- mice.
Results: CflarE-KO;Tnfrsf1a-/- mice were born but experienced severe dermatitis and succumbed soon after birth. CflarE-KO;Tnfrsf1a+/- mice exhibited embryonic lethality caused by massive keratinocyte apoptosis. Although keratinocytes from CflarE-KO;Tnfrsf1a-/- mice still died of apoptosis, neutralizing antibodies against Fas ligand and TNF-related apoptosis-inducing ligand substantially prolonged survival of CflarE-KO;Tnfrsf1a-/- mice. Expression of inflammatory cytokines, such as Il6 and Il17a was increased; conversely, expression of epidermal differentiation markers was severely downregulated in the skin of CflarE-KO;Tnfrsf1a-/- mice. Treatment of primary keratinocytes with IL-6 and, to a lesser extent, IL-17A suppressed expression of epidermal differentiation markers.
Conclusion: TNF receptor superfamily 1 (TNFR1)-dependent or TNFR1-independent apoptosis of keratinocytes promotes inflammatory cytokine production, which subsequently blocks epidermal differentiation. Thus blockade of both TNFR1-dependent and TNFR1-independent cell death might be an alternative strategy to treat skin diseases when treatment with anti-TNF-α antibody alone is not sufficient.
Keywords: Cellular FLICE-inhibitory protein; TNF-α; apoptosis; epidermal differentiation.
Copyright © 2018 American Academy of Allergy, Asthma & Immunology. Published by Elsevier Inc. All rights reserved.