In the development of the kidney and in its recovery from injury, a key step in morphogenesis is polarization of the tubule epithelial cells. Polarization of kidney epithelial cells depends on interactions between cells and the extracellular matrix, and on cell-cell contacts. Although the molecules responsible for transducing these adhesive events into morphogenetic signals are unknown, prime candidates are the integrins, a superfamily of cell adhesion molecules. Integrins are known to be receptors for a variety of extracellular matrix proteins and to associate with the actin cytoskeleton. More recently it has been recognized that they are also involved in cell-cell interactions. Other information suggests that integrins may influence cell differentiation and proliferation, possibly through generation of second messengers. Recent evidence suggests that integrins are characteristically expressed in distinct nephron segments and may play a key role during development in the polarization of the condensed mesenchyme. Integrins may also be significant factors in the pathophysiology of acute renal failure. In this project the involvement of integrins in epithelial polarization will be investigated using complementary in vitro and in vivo approaches. The functions of integrins expressed by MDCK cells will be investigated with cell adhesion assays and immunocytochemical and biochemical techniques using subunit-specific monoclonaI and polyclonaI antibodies and cDNA probes (Specific Aim 1A). Integrin expression, distribution, activation, and targeting will be examined during the polarization process and in cells cultured on different substrata and under conditions which perturb cell-cell contacts (Specific Aim lB). The effects of disrupting integrin function on the polarity of MDCK cells will be investigated with antibodies that interfere with integrin ligand binding and by expression of integrin cDNAs and antisense constructs in MDCK cells. (Specific Aim lC). Integrin function during differentiation of the kidney will be studied in mouse embryos, whole organ cultures, and transfer cultures of kidney primordia using blocking antibodies and antisense constructs (Specific Aim 2A). Alterations in integrin expression during regeneration in vivo will be examined in mouse kidneys made ischemic by clamping of the renal artery (Specific Aim 2B). In the long-term, the results of these experiments will provide important information on the molecular interactions responsible for induction of kidney polarization by cell adhesion. These studies will also aid our understanding of how the kidney epithelium develops and recovers from injury.
