Hyperglycemia, although necessary, alone is insufficient for the development of progressive diabetic nephropathy. Two factors implicated in its pathogenesis are mesangial cell activation and/or proliferation and monocyte/macrophage influx. We have shown that prolonged hyperglycemia in the Goto-Kakizaki (GK) rat is associated with renal structural changes similar to those in patients with diabetes before the onset of progressive nephropathy. The aim of the current study is to examine the role of mesangial cell injury and macrophage influx on renal structure and function. After induction of nephritis in either hyperglycemic GK rats or normoglycemic Wistar rats by the administration of Ox-7 antibody, the degree of mesangiolysis and subsequent mesangial proliferation was no different between GK and Wistar rats. Similarly, macrophage influx and mesangial cell activation (assessed by alpha-smooth actin expression) was no different between the two groups. Wistar rats developed marked albuminuria; conversely, no significant proteinuria or albuminuria was seen in GK rats. Analysis of glomerular proteoglycans (PGs) showed an increase in (35)S incorporation into heparan sulfate PGs of GK compared with Wistar rats, with no alteration in glycosaminoglycan chain size or charge density. These changes were kidney specific and not seen in spleen, lung, or heart tissue. Western blot analysis showed increased agrin core protein expression in whole-kidney homogenates of untreated GK rats. Induction of Thy1.1 nephritis was associated with reduced expression of agrin in both GK and Wistar rats. However, agrin expression was greater in GK rats at all times. In summary, acute mesangial cell injury associated with a macrophage influx did not initiate progressive diabetic nephropathy in GK rats. Despite a similar magnitude of glomerular/mesangial injury, GK rats, in contrast to normoglycemic Wistar rats, did not develop proteinuria after the administration of anti-Thy1 antibody. We postulate that altered expression of agrin in this model accounts for the lack of proteinuria and thus may protect against progressive nephropathy.
Copyright 2002 by the National Kidney Foundation, Inc.