Internalized Components of Membrane Attack Complexes Disrupt Proteostasis and Acquire Alarmin-Like Properties

Area of Science:

• Immunology
• Cell Biology
• Molecular Biology

Background:

• Membrane attack complexes (MAC) are known for causing cell death.
• The pro-inflammatory roles of MACs, particularly C9, beyond cytolysis are less understood.

Purpose of the Study:

• To investigate the non-cytolytic functions of C9.
• To elucidate the mechanisms by which C9 contributes to inflammation.

Main Methods:

• Detection of intracellular C9 aggregates in patient tissues.
• Identification of binding partners and pathways involved in C9 internalization and aggrephagy (NUMBL, Rab35, ZFYVE21, RNF34, LC3B).
• In vivo studies using mouse models to assess the role of ZFYVE21-RNF34 axis in C9 aggrephagy and inflammation.

Main Results:

• Intracellular C9 aggregates are found in inflamed human tissues, associated with endothelial cell (EC) activation, not cell death.
• NUMBL mediates C9 internalization into the endolysosomal pathway.
• C9 aggregates undergo aggrephagy, activating NF-κB via the ZFYVE21-RNF34-LC3B pathway.
• ZFYVE21-RNF34 signaling is essential for C9 aggrephagy and NF-κB-dependent EC activation in vivo.
• Conditional ZFYVE21 loss in ECs reduces C9 aggrephagy, systemic inflammation, and tissue injury.

Conclusions:

• The C9 component of MACs can form intracellular aggregates with alarmin-like properties.
• C9 aggrephagy is a novel pathway contributing to NF-κB activation and endothelial cell inflammation.
• Targeting C9 aggrephagy may offer therapeutic strategies for inflammatory diseases.