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Published on: August 7, 2018
A unique death pathway keeps RIPK1 D325A mutant mice in check at embryonic day 10.5
Yingying Zhang1, Kai Huang1, Yuxia Zhang1
1State Key Laboratory of Cellular Stress Biology, Innovation Center for Cell Biology, School of Life Sciences, Xiamen University, Xiamen, Fujian, China.
Abstract:
Tumor necrosis factor receptor-1 (TNFR1) signaling, apart from its pleiotropic functions in inflammation, plays a role in embryogenesis as deficiency of varieties of its downstream molecules leads to embryonic lethality in mice. Caspase-8 noncleavable receptor interacting serine/threonine kinase 1 (RIPK1) mutations occur naturally in humans, and the corresponding D325A mutation in murine RIPK1 leads to death at early midgestation. It is known that both the demise of Ripk1D325A/D325A embryos and the death of Casp8-/- mice are initiated by TNFR1, but they are mediated by apoptosis and necroptosis, respectively. Here, we show that the defects in Ripk1D325A/D325A embryos occur at embryonic day 10.5 (E10.5), earlier than that caused by Casp8 knockout. By analyzing a series of genetically mutated mice, we elucidated a mechanism that leads to the lethality of Ripk1D325A/D325A embryos and compared it with that underlies Casp8 deletion-mediated lethality. We revealed that the apoptosis in Ripk1D325A/D325A embryos requires a scaffold function of RIPK3 and enzymatically active caspase-8. Unexpectedly, caspase-1 and caspase-11 are downstream of activated caspase-8, and concurrent depletion of Casp1 and Casp11 postpones the E10.5 lethality to embryonic day 13.5 (E13.5). Moreover, caspase-3 is an executioner of apoptosis at E10.5 in Ripk1D325A/D325A mice as its deletion extends life of Ripk1D325A/D325A mice to embryonic day 11.5 (E11.5). Hence, an unexpected death pathway of TNFR1 controls RIPK1 D325A mutation-induced lethality at E10.5.
Insights
Tumor necrosis factor receptor-1 (TNFR1) signaling triggers embryonic lethality in mice with RIPK1 D325A mutations via apoptosis. This pathway involves caspase-8, RIPK3, and caspase-3, revealing a novel TNFR1-mediated death mechanism.
Area of Science:
- Developmental biology
- Cellular signaling
- Immunology
Background:
- Tumor necrosis factor receptor-1 (TNFR1) signaling is crucial for inflammation and embryogenesis.
- Mutations in receptor interacting serine/threonine kinase 1 (RIPK1), such as D325A, are found in humans and cause embryonic lethality in mice.
- TNFR1 initiates both apoptosis in Ripk1D325A/D325A embryos and necroptosis in Casp8-/- mice.
Purpose of the Study:
- To elucidate the mechanism of embryonic lethality in Ripk1D325A/D325A embryos.
- To compare this lethality pathway with that of Casp8 deletion-mediated lethality.
- To identify the specific caspases and scaffold proteins involved in TNFR1-induced apoptosis during embryogenesis.
Main Methods:
- Analysis of genetically mutated mice, including Ripk1D325A/D325A, Casp8-/-, Ripk3, Casp1/11 double knockouts, and Caspase-3 deficient mice.
- Investigating embryonic development at specific time points (E10.5, E11.5, E13.5).
- Elucidating molecular pathways involving TNFR1, RIPK1, RIPK3, Caspase-8, Caspase-1, Caspase-11, and Caspase-3.
Main Results:
- Defects in Ripk1D325A/D325A embryos occur at E10.5, preceding Casp8 knockout lethality.
- Apoptosis in Ripk1D325A/D325A embryos requires RIPK3 scaffolding and active Caspase-8.
- Concurrent depletion of Caspase-1 and Caspase-11 delayed lethality to E13.5, while Caspase-3 deletion extended survival to E11.5.
Conclusions:
- A novel TNFR1-mediated apoptosis pathway drives RIPK1 D325A mutation-induced embryonic lethality at E10.5.
- Caspase-8, RIPK3, Caspase-1, Caspase-11, and Caspase-3 are key downstream effectors in this pathway.
- This study reveals an unexpected death pathway initiated by TNFR1 in response to specific RIPK1 mutations.
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