Expression of complement C4 and C9 genes by human astrocytes

Area of Science:

• Neuroscience
• Immunology
• Cell Biology

Background:

• Complement activation is implicated in Alzheimer's disease (AD) pathogenesis.
• Central nervous system (CNS) resident cells, including astrocytes, can synthesize complement proteins.
• Complement C4 and C9 are crucial proteins in the complement pathway.

Purpose of the Study:

• To investigate the expression and regulation of complement C4 and C9 by primary human astrocytes.
• To determine if astrocytes are a source of complement C4 and C9 in the human CNS.

Main Methods:

• Reverse transcription-polymerase chain reaction (RT-PCR) to detect mRNA.
• Enzyme-linked immunosorbent assay (ELISA) for protein quantification.
• Immunocytochemistry and immunoblot techniques for protein localization and detection.
• Treatment of astrocytes with interferon-gamma and interleukin-1beta (IL-1beta) to study regulation.

Main Results:

• Primary human astrocytes constitutively express complement C4 mRNA and protein.
• Interferon-gamma increased C4 expression, while IL-1beta inhibited it.
• C4 immunoreactivity was localized to glial fibrillary acidic protein (GFAP)-positive astrocytes.
• Stimulated astrocytes expressed complement C9 mRNA, but C9 protein was not detected in supernatants.

Conclusions:

• Astrocytes are a significant source of complement C4 in the human CNS.
• Astrocyte complement C4 expression is differentially regulated by cytokines.
• While astrocytes express C9 mRNA, C9 protein secretion requires further investigation.