RIPK1 deficiency prevents thymic NK1.1 expression and subsequent iNKT cell development

Area of Science:

• Immunology
• Cell Biology
• Molecular Biology

Background:

• Receptor Interacting Protein Kinase 1 (RIPK1) and caspase-8 (Casp8) are key regulators of apoptosis and T cell development.
• Mutations in RIPK1 are linked to human autoinflammatory diseases, including Cleavage Resistant RIPK1 Induced Autoinflammatory (CRIA) and Inflammatory Bowel Disease.
• RIPK1 also plays a cell-death-independent role in T cell differentiation and homeostasis.

Purpose of the Study:

• To investigate the in vivo function of RIPK1 in T cell development and homeostasis, particularly in the context of RIPK3 and Caspase-8 deficiency.
• To elucidate the role of RIPK1 in iNKT cell development, NK1.1 expression, and cytokine effector responses.
• To determine whether RIPK1's kinase or scaffolding function is critical for iNKT cell regulation.

Main Methods:

• Utilized Ripk3 and Casp8 deficient mice to enable survival of Ripk1 deficient mice to adulthood for in vivo studies.
• Conducted in vivo and in vitro stimulation assays to assess iNKT cell development, NK1.1 expression, and cytokine production.
• Compared iNKT cell phenotypes in wild-type, DKO (Casp8-, Ripk3- deficient), and TKO (Ripk1-, Casp8-, Ripk3- deficient) mice, as well as mice expressing kinase-dead RIPK1 (RIPK1kd).

Main Results:

• RIPK1 is essential for NK1.1 expression on thymic iNKT cells, a critical step for their development and transition from stage 2 to stage 3.
• Both RIPK1 and Casp8 mediate iNKT cell cytokine effector responses.
• Expanded and hyperactivated iNKT follicular helper (iNKTFH) cells were observed in DKO and TKO mice, indicating a role for RIPK1 and Casp8 in regulating iNKTFH cell homeostasis.
• Kinase-dead RIPK1 (RIPK1kd) did not show developmental or functional iNKT cell aberrations, highlighting the importance of RIPK1's scaffolding function.

Conclusions:

• RIPK1 uniquely regulates thymic iNKT cell development, likely through its scaffolding function in response to T cell receptor engagement.
• RIPK1 and Casp8 jointly regulate iNKT cell effector functions.
• Targeting RIPK1 with small molecule inhibitors may offer a therapeutic strategy for autoinflammatory conditions by modulating iNKT cell development and function.