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Murine glomerular mesangial cell uptake of apoptotic cells is inefficient and involves serum-mediated but
J Cortes-Hernandez1, L Fossati-Jimack, A Carugati
1Rheumatology Section and Histopathology Department, Division of Medicine, Faculty of Medicine, Imperial College, Hammersmith Campus, London, UK.
Abstract:
An increased number of apoptotic bodies have been detected in glomeruli of non-nephritic kidneys of C1q-deficient mice. In these mice an in vivo impaired uptake of apoptotic cells by peritoneal macrophages was also demonstrated. Here we investigated whether C1q plays a role in the in vitro clearance of apoptotic cells by glomerular mesangial cells. Phagocytosis was assessed using a novel flow cytometric assay that was validated by immunofluorescence studies. The uptake of apoptotic cells by mesangial cells, measured as percentage of mesangial cells ingesting apoptotic cells, was approximately 25%, 10% and 10% for a T cell lymphoma line (RMA), thymocytes and neutrophils, respectively. The uptake reached a plateau phase after 3 h, was specific for apoptotic cells and was mediated by serum but not by complement components C1q or C3. The phagocytosis of apoptotic cells was significantly inhibited by Arg-Gly-Asp-Ser (RGDS), a peptide capable of blocking the interaction of thrombospondin with CD36 or the vitronectin receptor. Pretreatment of the mesangial cells with dexamethasone (200 nm) but not with LPS increased the uptake markedly. These findings indicate that murine mesangial cells are capable of taking up syngeneic apoptotic cells, although much less efficiently than professional phagocytic cells. They also show that serum proteins other than complement components mediate the removal of apoptotic cells by murine mesangial cells in vitro.
Insights
Complement component C1q deficiency impairs apoptotic cell clearance in mouse kidneys. Glomerular mesangial cells clear apoptotic cells in vitro, but this process is mediated by serum proteins, not C1q or C3.
Area of Science:
- Immunology
- Cell Biology
- Renal Physiology
Background:
- C1q-deficient mice exhibit increased glomerular apoptotic bodies and impaired in vivo macrophage uptake of apoptotic cells.
- The role of C1q in the clearance of apoptotic cells by glomerular mesangial cells in vitro remains unclear.
Purpose of the Study:
- To investigate the role of C1q in the in vitro clearance of apoptotic cells by murine glomerular mesangial cells.
- To characterize the mechanisms involved in apoptotic cell uptake by mesangial cells.
Main Methods:
- A novel flow cytometric assay was developed and validated by immunofluorescence to assess phagocytosis.
- Mesangial cells were incubated with apoptotic T cell lymphoma, thymocytes, and neutrophils.
- Inhibition studies were performed using Arg-Gly-Asp-Ser (RGDS) peptide and pretreatment with dexamethasone or LPS.
Main Results:
- Murine mesangial cells demonstrated uptake of apoptotic cells, with higher efficiency for lymphoma cells compared to thymocytes and neutrophils.
- Apoptotic cell uptake reached a plateau after 3 hours and was specific for apoptotic cells.
- Uptake was mediated by serum factors but not by complement components C1q or C3; RGDS peptide significantly inhibited phagocytosis.
- Dexamethasone pretreatment markedly increased mesangial cell uptake of apoptotic cells.
Conclusions:
- Murine mesangial cells possess the capacity for in vitro clearance of syngeneic apoptotic cells, albeit less efficiently than professional phagocytes.
- Serum proteins, distinct from C1q and C3, are crucial mediators of this clearance process.
- These findings highlight a novel role for mesangial cells in apoptotic cell removal within the glomerulus, independent of C1q and C3.