The interaction between RIPK1 and FADD controls perinatal lethality and inflammation

Area of Science:

• Cellular Biology
• Developmental Biology
• Immunology

Background:

• Apoptosis and necroptosis are critical cell death pathways influencing embryogenesis.
• Receptor-associated protein kinase-1 (RIPK1) plays a central role in regulating both apoptosis and necroptosis through its interactions with FADD, caspase-8, and cFLIP_L.

Purpose of the Study:

• To investigate the role of the RIPK1-FADD interaction in embryonic development.
• To elucidate the mechanisms underlying embryonic lethality in RIPK1 mutants.
• To determine the involvement of necroptosis and Z-DNA binding protein-1 (ZBP1) pathways in RIPK1-mediated embryonic lethality.

Main Methods:

• Generation and analysis of Ripk1-mutant mice (Ripk1^R588E [RE] and Ripk1^{R588E K45A} [REKA]).
• Genetic ablation of key cell death pathway components, including Ripk3, MLKL, caspase-8, and Zbp1.
• Phenotypic analysis of mutant animals to assess survival, embryonic lethality, and post-natal inflammation.

Main Results:

• Ripk1^RE and Ripk1^REKA mutations disrupt the RIPK1-FADD interaction, leading to embryonic lethality.
• Ablation of Ripk3 rescues embryonic lethality in both Ripk1^RE and Ripk1^REKA mutants.
• While MLKL ablation prevents embryonic lethality in Ripk1^RE mice, Ripk1^REKA mice require combined ablation of MLKL and caspase-8 for survival to adulthood.
• Zbp1 ablation largely prevents embryonic lethality in both Ripk1^RE and Ripk1^REKA embryos, indicating ZBP1-mediated lethality.
• Ripk1^RE mice lacking MLKL survive embryogenesis but succumb to post-natal inflammation.

Conclusions:

• The RIPK1-FADD interaction is essential for preventing ZBP1-induced, RIPK3-caspase-8-mediated embryonic lethality.
• The kinase activity of RIPK1 modulates the contribution of ZBP1 to embryonic lethality.
• Disruption of the RIPK1-FADD interaction leads to complex cell death phenotypes dependent on the specific genetic background.