Expression of beta 1 integrins in glomerular tissue of Streptozotocin-induced diabetic rats

Based upon the importance of integrins as receptors for extracellular matri x components as well as transducers of extracellular signals, and since maj or alterations take place in the renal extracellular matrix during diabetes , it is important to study the role played by integrins in the development of the diabetic glomerulosclerosis. Expression of the beta(1) subunit by re nal glomerular cells was evaluated by biochemical and morphological means i n short- and long-term diabetic rats. Western blots of isolated rat renal g lomeruli demonstrated that the expression of beta(1) increases along with a ge as well as with the hyperglycaemic state. These changes were significant as early as 6 weeks of hyperglycaemia. This was further demonstrated by im munocytochemistry, which revealed the presence of the pi subunit at the lev el of the plasma membranes of endothelial, epithelial, and mesangial cells. Quantitation of the immunolabelings confirmed the increased expression of beta(1), under diabetic conditions. Further to this, expression of the foca l adhesion kinase (FAK) was evaluated by immunoblotting showing little incr ease in diabetic conditions. On the other hand, testing the tyrosine phosph orylation of FAK, revealed significant increases in diabetes. To recover th e fraction of FAK associated with the pi subunit, immunoprecipitation of is olated glomeruli homogenates was carried out with the anti-beta(1) antibody . This demonstrated that the amounts of FAK co-precipitated with pi, as wel l as its tyrosine-phosphorylation, are in fact reduced in diabetic conditio ns. Since the changes reported were observed at time points prior to any mo rphological alteration of the renal extracellular matrix, it appears that m odifications in integrins and in their intracellular relays constitute earl y events that precede the onset of the diabetic nephropathy and must then b e associated with the hyperglycaemic condition.