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C1q binding to human vascular smooth muscle cells mediates immune complex deposition and superoxide generation
M Shingu1, K Yoshioka, M Nobunaga
1Department of Internal Medicine, Kyushu University, Beppu, Japan.
Insights
Complement C1q binds to vascular smooth muscle cells, mediating immune complex binding and superoxide generation. This explains how immune complexes deposit in blood vessels, potentially causing tissue damage.
Area of Science:
- Immunology
- Vascular Biology
- Cell Biology
Background:
- Vascular smooth muscle cells (VSMCs) play a role in vascular health and disease.
- The complement system, particularly C1q, is involved in immune responses and tissue homeostasis.
- Mechanisms of immune complex deposition in the vascular wall are not fully understood.
Purpose of the Study:
- To investigate the interaction of C1q with VSMCs.
- To determine if C1q binding influences immune complex adherence to VSMCs.
- To explore the effect of C1q on VSMC-mediated oxidative stress.
Main Methods:
- Cultured human umbilical cord vein VSMCs were used.
- C1q binding assays were performed at different temperatures (4°C and 37°C).
- Aggregated IgG binding and superoxide generation were measured in the presence and absence of C1q.
Main Results:
- C1q bound to the VSMC membrane at 4°C and was internalized at 37°C.
- Pre-incubation with C1q enhanced aggregated IgG binding to VSMCs.
- C1q enhanced superoxide generation in suspended VSMCs but not in monolayer cultures.
- Fibronectin and laminin were not detected on the VSMC membrane.
Conclusions:
- C1q binds to a specific receptor on VSMCs, facilitating immune complex binding.
- C1q-mediated superoxide generation by VSMCs contributes to oxidative stress.
- These findings elucidate a mechanism for immune complex-induced vascular wall damage via VSMC activation.
Abstract:
Evidence was obtained for the binding of C1q to the membrane of cultured vascular smooth muscle cells derived from human umbilical cord veins. C1q was fixed to the cell membrane at 4 degrees C, whereas it was ingested into the cytoplasm, as a cytoplasmic inclusion, when tested at 37 degrees C. The addition of C1q in advance inhibited the subsequent binding of C1q. Neither fibronectin nor laminin was detected on the cell membrane. Aggregated IgG bound to vascular smooth muscle cells in the case of preincubation with C1q at 4 degrees C, whereas aggregated IgG did not bind to the cells in the absence of C1q. The addition of C1q molecules to the cells in suspension enhanced superoxide generation by vascular smooth muscle cells. There was no effect of C1q on superoxide generation by the cells in monolayer. These results suggest that C1q binds on the membrane of vascular smooth muscle cells via its specific receptor that mediates immune complex binding to the cells and superoxide generation. These properties elucidate the mechanisms by which circulating immune complexes deposit in the vascular wall, and subsequent degradation of tissue components surrounding vascular smooth muscle cells occurs through oxidative burst of the cells.