Complement C5 Contributes to Brain Injury After Subarachnoid Hemorrhage

Area of Science:

• Neuroscience
• Immunology
• Genetics

Background:

• Complement activation is linked to poor outcomes in aneurysmal subarachnoid hemorrhage (SAH).
• Understanding the role of complement in SAH-induced brain injury is crucial for developing effective treatments.

Purpose of the Study:

• To investigate the role of complement activation in brain injury following aneurysmal SAH.
• To evaluate complement component 5 (C5) as a potential therapeutic target for SAH.

Main Methods:

• Analysis of complement expression in human brain tissue and plasma from SAH patients.
• Genetic analysis of C3 and C5 gene variants and their association with SAH outcome.
• Time-course measurements of C5a levels in patient cerebrospinal fluid (CSF) and plasma.
• Evaluation of C5a receptor knockout and C5-specific antibody treatment in a mouse model of SAH, assessing microglia activation and cell death.

Main Results:

• Increased presence of complement components C1q and C3/C3b/iC3B in SAH patient brain tissue.
• A C5 single nucleotide polymorphism (SNP) correlated with elevated C5a plasma levels and poorer SAH outcomes.
• C5a levels were significantly elevated in CSF and plasma post-SAH.
• C5-deficient mice and C5-specific antibody treatment reduced microglia activation and cell death by approximately 40% in a mouse SAH model.

Conclusions:

• C5 plays a significant role in mediating brain injury after experimental SAH.
• C5-specific antibodies represent a promising therapeutic strategy for reducing brain injury and improving prognosis in aneurysmal SAH patients.