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C5b-8 and C5b-9 modulate the collagen release of human glomerular epithelial cells
I Torbohm1, M Schönermark, A M Wingen
1Institut für Immunologie, Universität Heidelberg, Federal Republic of Germany.
Insights
The late complement component C5b-9 significantly boosts collagen synthesis in human kidney cells. This finding suggests a role for C5b-9 in the development of chronic nephritis and kidney scarring.
Area of Science:
- Nephrology
- Immunology
- Cell Biology
Background:
- Late complement components, specifically C5b-9, are known to induce cellular responses beyond lysis, including the release of inflammatory mediators.
- C5b-9 has been implicated in the pathogenesis of sclerosis in animal models of glomerulonephritis.
- The precise mechanisms by which complement components contribute to kidney disease progression require further elucidation.
Purpose of the Study:
- To investigate the effect of the terminal complement complex C5b-9 on collagen synthesis in human glomerular epithelial cells (GEC).
- To determine if C5b-9 assembly on the cell membrane is necessary for its effect on collagen production.
Main Methods:
- Primary human GEC were cultured and incubated with 14C-proline to label newly synthesized proteins.
- Collagen synthesis was quantified by measuring radioactivity in collagenase-digestible material.
- Collagen types were analyzed using SDS-PAGE, and the role of specific complement components (C7, C8, C9) was assessed.
Main Results:
- Human GEC spontaneously produce collagen type IV.
- Sublytic doses of purified C5b-9 significantly increased collagen synthesis by GEC within 12-24 hours.
- C5b-8 stimulated collagen synthesis similarly to C5b-9, but C5b-7 and C5b-8 complexes without C9 did not, indicating C9's crucial role.
- Fluid-phase C5b-9 complexes were ineffective, highlighting the requirement for membrane assembly.
Conclusions:
- The terminal complement complex C5b-9 stimulates collagen synthesis in human glomerular epithelial cells.
- Membrane-bound C5b-9, requiring C9 for activity, enhances collagen production.
- These findings support the hypothesis that C5b-9 contributes to the development of chronic nephritis and glomerulosclerosis by promoting collagen deposition.
Abstract:
Aside from their lytic function the late complement components C5b-9 stimulate release of prostanoids, interleukin 1 and oxygen radicals from a number of cells. Since C5b-9 has also been connected to the development of sclerosis in animal models of glomerulonephritis, we addressed the question whether C5b-9 would affect the collagen synthesis. We used human glomerular epithelial cells (GEC) obtained as primary outgrowth cultures. The cells were cultivated in the presence of 14C-proline. Collagen synthesis was quantitated by counting the radioactivity associated with collagenase digestible material. Furthermore, collagen was analyzed by SDS-PAGE. GEC in culture produce spontaneously some collagen type IV. Addition of sublytic doses of highly purified C5b-9 increased the collagen synthesis considerably within 12 to 24 hours. In the absence of C9, C5b-8 stimulated collagen synthesis to a similar extent, whereas in the absence of C7 or C8, the collagen synthesis was not enhanced. Furthermore, fluid-phase-formed C5b-9 complexes did not stimulate the collagen synthesis, indicating that assembly of the complex on the target membrane was required. Since C5b-9 deposits are found in sclerotic areas, our data support the hypothesis that C5b-9, by stimulating collagen synthesis as well as release, might contribute to the development of chronic nephritis.