Phenotypic Expression of Collagen Types in Mesangial Matrix of Diabetic and Nondiabetic Rats

This study was performed to evaluate the composition of the extracellular matrix of the mesangium in both diabetic and nondiabetic rats. Four groups of rats (n = 10 each) were studied. Nondiabetic rats were injected with saline (group 1) or insulin (3.5 U NPH daily) (group 2). Streptozocin-induced diabetic rats were similarly injected with saline (group 3) or insulin (group 4). Six weeks after initiation of study, glomerular diameter (µm) was increased in groups 2 (147 ± 21), 3 (144 ± 22), and 4 (150 ± 7) compared with group 1 (104 ± 12) (P < .01). Glomerular hypertrophy was associated with an increase in the relative amount of mesangial matrix as determined by staining for fibronectin. By immunofluorescence microscopy (0–4+ scale), type I collagen antigen was not detected in the mesangium of any of the experimental groups. Staining for type V collagen and thrombospondin was similar between the experimental groups. Type III collagen antigen was not detected in the mesangium of control (group 1) or insulin-deficient diabetic rats (group 3); however, it was detected (2–3+) in the mesangium of both insulin-treated diabetic and nondiabetic rats (Mann-Whitney, P < .01). Comparable intensity of staining (1+) for type IV collagen antigen was detected in the mesangium of animals from groups 1, 2, and 4; however, the staining intensity was markedly increased (3+) in insulindeficient diabetic rats (group 3; Mann-Whitney, P < .01). These studies demonstrate that glomerular hypertrophy and an increase in mesangial matrix occur in both hyperglycemic and insulin-treated rats; however, the mesangial matrix composition varies with the metabolic environment. Hyperglycemia is associated with a significant increase in the content of type IV collagen, and insulin treatment is associated with a switch in the matrix composition with the new expression of type III collagen. The significance of these findings in the evolution of diabetic glomerulosclerosis is discussed.