Temporal expression of VLA-2 and modulation of its ligand specificity by rat glomerular epithelial cells in vitro

The interaction of glomerular epithelial cells (GEC) with their underlying basement membrane is of critical importance in maintaining normal glomerular function. Little is known regarding their expression and use of extracellular matrix adhesion receptors in normal conditions and during pathogenic states.

To examine the use of such receptors, we have produced monoclonal antibodies that inhibit the function of the rat alpha 2 beta 1 integrin receptor (VLA-2) and the common beta 1 subunit. The monoclonal antibodies have been used to examine the expression and functional use of these receptors by rat glomerular cells cultured in vitro.

Rat glomerular visceral epithelial cells are unusual in that, unlike many of the epithelium seen in vivo, these cells do not express VLA-2, an integrin receptor with affinity for laminin and collagen. Our results demonstrate that differentiated GEC, newly isolated from glomeruli, do not use VLA-2 for attachment to collagen and laminin-coated surfaces. However, after 3 days of in vitro growth, approximately 50% of these cells express this receptor and, upon their first in vitro passage, selectively utilize VLA-2 for attachment to collagen but not to laminin-coated surfaces. After long-term maintenance in culture, all GEC express VLA-2, and utilize this receptor for binding to collagen and in their interaction with laminin. In contrast, VLA-2 plays only a partial role in the adherence of mesangial cells to collagen and is not involved in their attachment to laminin-coated surfaces.

These results show that, as GEC become adapted to in vitro growth, they begin to synthesize and use the VLA-2 integrin receptor suggesting a simultaneous downregulation or inactivation of other beta 1 type integrin receptors. This ability to modulate their receptor repertoire may allow GEC to respond to pathologic conditions in vivo.