Immunogold studies of monomeric elements from the globular domain (NC1) of type IV collagen in renal basement membranes during experimental diabetes in the rat

The protein A-gold immunocytochemical technique was applied to reveal the monomeric elements M1, M2* and M3 from the non-collagenous globular domain (NC1) of type IV collagen over various renal basement membranes from control and long-term streptozotocin-induced diabetic rats. This study includes the basement membranes of the proximal tubule, the Bowman's capsule and the glomerulus as well as the extracellular matrix of the mesangium. The labellings obtained were confined to basement membrane material. The quantitative analysis demonstrated changes in labelling intensities and distribution between tissues from normal and diabetic animals. Increased labelling intensities were observed for M1 and M2* monomers in all the basement membranes studied except for the mesangial matrix which remained unchanged. In addition, the labelling for M1 monomers, present on the endothelial side of the glomerular basement membrane of control animals, was found to be distributed throughout the entire thickness of the basement membrane of diabetic animals. In contrast, neither the intensity of the labelling, nor the distribution of M3 monomers were altered in diabetic animals. Since M1 monomers are markers of the α1(IV) and α2(IV) chains of type IV collagen while M2* and M3 mark α3(IV) and α4(IV) chains respectively, the present results demonstrate changes in the nature of the collagenous elements of basement membranes during diabetes. Furthermore, the results indicate that the α3(IV) and the α4(IV) chains are not necessarily present in the same molecule. The modifications of the collagenous elements of the basement membranes during diabetes must alter the structural characteristics of these matrices which in turn might influence their functional properties.