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Cellular receptors for matrix proteins in normal human kidney and human mesangial cells
F G Cosio1, D D Sedmak, N S Nahman
1Department of Internal Medicine and Pathology, Ohio State University, Columbus.
Abstract:
In the present study we evaluated the distribution of cell adhesion molecules, referred as very late antigens (VLA), in the normal human kidney and in mesangial cells in culture (MC). In addition, we assessed the functional properties of VLA proteins on MC. Normal human kidney and MC were stained by immunoperoxidase with mouse monoclonal antibodies to VLA proteins. We demonstrated that VLA-3, a protein that binds FN, laminin and collagen, is the predominant VLA protein in the human glomerulus and on MC. VLA-3 is located in the mesangium and on the glomerular visceral epithelial cell and endothelial cell surfaces in contact with the glomerular basement membrane. VLA-1 was demonstrated in the glomerular mesangium and VLA-5, an FN specific receptor, was present in the mesangium on glomerular endothelial cells and on MC. VLA-2 and VLA-4 were not present in the normal glomerulus nor on MC. In functional studies we evaluated the binding of MC to FN coated surfaces and the binding and phagocytosis of FN coated fluorescent beads by MC. We showed that MC bind to FN coated surfaces and that the binding is inhibited by anti-FN antibodies, EDTA and peptides containing the amino acid sequence Arg-Gly-Asp (RGD). In addition, anti-VLA-5 but not anti-VLA-3 antibodies inhibited significantly the binding of MC to FN, MC demonstrated binding and phagocytosis of FN coated beads and, purified FN inhibited both phenomena. By affinity chromatography and immunoprecipitation we demonstrated that MC FN binding proteins and MC VLA proteins are composed of two distinct protein chains that have Mr characteristics similar to those of normal human fibroblasts VLA proteins. In conclusion, the glomerular distribution of VLA-3 suggests that this protein is primarily involved on the adhesion of glomerular cells to basement membranes and matrix. MC FN receptors (VLA-5) mediate the binding of MC to FN and could mediate the phagocytosis of FN coated antigen or immune complexes by mesangial cells.
Insights
Very late antigens (VLA) distribution was studied in human kidneys and mesangial cells. VLA-3 is predominant in glomeruli, while VLA-5 mediates mesangial cell binding to fibronectin.
Area of Science:
- Nephrology
- Cell Biology
- Immunology
Background:
- Cell adhesion molecules, specifically very late antigens (VLA), play crucial roles in cellular interactions within tissues.
- Understanding VLA distribution and function in the kidney is essential for comprehending glomerular and mesangial cell behavior.
Purpose of the Study:
- To investigate the distribution of VLA proteins in normal human kidney glomeruli and cultured mesangial cells (MC).
- To assess the functional significance of VLA proteins, particularly their role in MC adhesion to fibronectin (FN).
Main Methods:
- Immunoperoxidase staining of normal human kidney and MC using monoclonal antibodies against VLA proteins.
- Functional assays evaluating MC binding to FN-coated surfaces and phagocytosis of FN-coated beads.
- Affinity chromatography and immunoprecipitation to characterize MC FN-binding proteins and VLA proteins.
Main Results:
- VLA-3 was identified as the predominant VLA protein in the human glomerulus and on MC, localizing to the mesangium and glomerular cell surfaces.
- VLA-5, an FN-specific receptor, was found on MC and glomerular endothelial cells.
- MC binding to FN was mediated by VLA-5 and inhibited by anti-VLA-5 antibodies, anti-FN antibodies, and RGD peptides.
- MC demonstrated binding and phagocytosis of FN-coated beads, inhibited by purified FN.
Conclusions:
- The distribution of VLA-3 suggests its primary role in glomerular cell adhesion to basement membranes and extracellular matrix.
- VLA-5 functions as a key receptor mediating MC adhesion to fibronectin and potentially phagocytosis of FN-associated complexes.