NINJ1 mediates plasma membrane rupture during lytic cell death

Area of Science:

• Cell Biology
• Immunology
• Genetics

Background:

• Plasma membrane rupture (PMR) is the terminal event in lytic cell death, releasing damage-associated molecular patterns (DAMPs) that drive inflammation.
• The molecular mechanisms governing PMR have remained largely unknown.
• NINJ1 protein, a cell-surface protein with two transmembrane regions, was previously identified but its function in cell death was unclear.

Purpose of the Study:

• To elucidate the underlying mechanism of plasma membrane rupture (PMR) during lytic cell death.
• To identify key molecular players involved in the process of PMR.
• To investigate the role of the NINJ1 protein in PMR and its contribution to host defense.

Main Methods:

• Forward-genetic screen in randomly mutagenized mice to identify genes regulating PMR.
• Analysis of Ninj1 knockout (Ninj1-/-) macrophages and mice.
• Assessment of PMR by measuring the release of intracellular proteins like HMGB1 and LDH.
• Microscopy to observe cell morphology during cell death.
• Infection studies using Citrobacter rodentium to evaluate host defense in Ninj1-/- mice.

Main Results:

• NINJ1 protein was identified as an essential mediator of PMR.
• Ninj1-/- macrophages displayed impaired PMR across various cell death pathways (pyroptosis, necrosis, apoptosis).
• Ninj1-/- macrophages exhibited defective cell disintegration with persistent ballooned morphology.
• Ninj1-/- mice showed increased susceptibility to Citrobacter rodentium infection, indicating a role for PMR in anti-bacterial defense.
• NINJ1 functions through oligomerization of its extracellular domain to induce PMR.

Conclusions:

• NINJ1 is a critical and evolutionarily conserved mediator of plasma membrane rupture (PMR).
• The discovery of NINJ1's role challenges the long-standing view of PMR as a passive cellular event.
• NINJ1-mediated PMR plays a significant role in anti-bacterial host defense.