Role of membrane complement regulators in neuromyelitis optica

Area of Science:

• Neuroimmunology
• Complement Biology
• Cellular Immunology

Background:

• Neuromyelitis optica spectrum disorder (NMOSD) involves aquaporin-4 (AQP4)-IgG targeting the central nervous system (CNS) via complement activation.
• The mechanism protecting peripheral AQP4-expressing organs from similar damage remains unclear.

Purpose of the Study:

• To investigate whether peripheral AQP4-expressing cells are protected from complement-mediated damage by expressing complement regulatory proteins.
• To elucidate the differential expression of complement regulators in CNS versus peripheral tissues.

Main Methods:

• Immunohistochemical analysis of human tissues (brain, kidney, stomach, skeletal muscle) for AQP4, CD46, CD55, and CD59.
• In vitro studies using cultured human astrocytes, alone and co-cultured with endothelial cells, to assess vulnerability to AQP4-IgG and complement-mediated lysis.

Main Results:

• Central nervous system (CNS) astrocytes express AQP4 but lack complement regulators (CD46, CD55, CD59), unlike peripheral organs where AQP4 is co-expressed with these regulators.
• Astrocytes co-cultured with endothelial cells showed reduced CD59 expression and increased vulnerability to AQP4-IgG and complement-mediated damage compared to astrocytes cultured alone.
• Neuromyelitis optica lesions did not show increased expression of complement regulators.

Conclusions:

• Complement regulatory proteins on peripheral cells shield them from AQP4-IgG and complement-mediated injury.
• The absence of these regulators on CNS astrocytes makes the brain susceptible to damage in NMOSD.
• These findings provide a mechanistic explanation for the CNS-specific pathology observed in NMOSD.