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Structural and functional evidence for microglial expression of C1qR(P), the C1q receptor that enhances phagocytosis
S D Webster1, M Park, M I Fonseca
1Department of Molecular Biology and Biochemistry, University of California, Irvine 92697, USA. swebster@uci.edu
Abstract:
Microglial activation has been associated with several degenerative diseases of the central nervous system (CNS). One consequence of activation is the induction of a more efficient phagocytic response, and it is therefore important to determine what factors regulate microglial phagocytosis and whether this capacity influences the progression of neurodegenerative changes. Previous studies have demonstrated that complement component C1q enhances Fc receptor- and CR1-mediated phagocytosis in cells of the myeloid lineage via a cell surface receptor, C1qRp. Because C1q has been found in the area of lesions in several degenerative CNS diseases, the current investigations were carried out to characterize the effects of C1q on microglial phagocytosis. Neonatal rat microglia were shown to express C1qRp, as assessed by flow cytometry and immunocytochemistry. Interaction of these cells with substrate-bound C1q was shown to enhance both FcR-and CR1-mediated phagocytosis two- to fourfold. In addition, introduction of an antibody raised against the carboxy-terminal, cytoplasmic domain of C1qRp into microglia by electroporation markedly diminished the ability of C1q to enhance uptake of IgG-coated targets, whereas nonspecific IgG had no such effect. These results suggest that C1q in areas of active degeneration may promote the phagocytic capacity of microglia via interaction with microglial C1qRp.
Insights
Complement component C1q enhances microglial phagocytosis via C1qRp, a receptor found on microglia. This interaction may promote microglial phagocytic capacity in degenerative central nervous system diseases.
Area of Science:
- Neuroscience
- Immunology
- Cell Biology
Background:
- Microglial activation is linked to central nervous system (CNS) degenerative diseases.
- Microglial phagocytosis is crucial for CNS health and disease progression.
- Complement component C1q (C1q) is present in CNS lesions and may regulate microglial function.
Purpose of the Study:
- To investigate the effects of C1q on microglial phagocytosis.
- To determine if C1q influences microglial phagocytic capacity in neurodegenerative conditions.
- To elucidate the role of C1q receptor (C1qRp) in C1q-mediated microglial phagocytosis.
Main Methods:
- Assessed C1qRp expression in neonatal rat microglia using flow cytometry and immunocytochemistry.
- Studied the interaction of microglia with substrate-bound C1q.
- Quantified phagocytosis of IgG-coated targets.
- Utilized electroporation to introduce an antibody against C1qRp into microglia.
Main Results:
- Neonatal rat microglia express C1qRp.
- C1q significantly enhanced Fc receptor (FcR)- and complement receptor 1 (CR1)-mediated phagocytosis (two- to fourfold).
- Antibody-mediated inhibition of C1qRp function diminished C1q's enhancement of IgG-coated target uptake.
Conclusions:
- Microglial C1qRp mediates the C1q-induced enhancement of phagocytosis.
- C1q may promote microglial phagocytic capacity in degenerative CNS diseases through C1qRp.
- This interaction highlights a potential mechanism regulating microglial clearance in neurodegeneration.