Early mechanisms of renal injury in hypercholesterolemic or hypertriglyceridemic rats.

Abstract

Hyperlipidemia in conjunction with uninephrectomy leads to renal injury in rats. It is unknown whether this is due to mesangial cell or podocyte injury and whether the injuries induced by hypercholesterolemia and hypertriglyceridemia share a similar pathogenesis. Therefore, renal effects of hypercholesterolemia were studied in male rats with dietary hypercholesterolemia compared with rats on a regular diet. Renal effects of hypertriglyceridemia were studied in female Nagase analbuminemic rats (NAR). Hypertriglyceridemia was reduced in NAR by ovariectomy. Both models were studied after uninephrectomy or sham operation. Dietary hypercholesterolemia had little effect on plasma triglycerides, whereas ovariectomy in the NAR had no effect on plasma cholesterol. However, an increase in intermediate density lipoprotein cholesterol was common to both models. Dietary hypercholesterolemia and uninephrectomy separately induced a similar increase in proteinuria after 13 wk, which was additive when these interventions were combined. At this stage, only a minimal increase was present in glomerular alpha-smooth muscle actin staining, a marker of mesangial cell activation, or in mesangial matrix expansion. Moreover, platelet-derived growth factor-B chain, a marker of mesangial cell proliferation, was not increased. However, podocyte injury was prominent as evidenced by podocytic de novo expression of desmin and ultrastructural changes. Glomerular macrophage counts were increased by hypercholesterolemia but not by uninephrectomy, and were not related to the level of proteinuria. Hypertriglyceridemia and uninephrectomy in female NAR induced an increase in proteinuria after 24 wk, which was also associated with an increase in podocyte desmin expression without any mesangial activation and proliferation or matrix accumulation. Hypertriglyceridemia, proteinuria, and the increase in desmin staining were largely prevented by ovariectomy. Interstitial myofibroblast activation and tubulointerstitial injury accompanied proteinuria in both models. These findings indicate that both hypercholesterolemia and hypertriglyceridemia aggravate renal injury primarily via podocyte rather than via mesangial cell damage. Such podocyte injury is accompanied by tubulointerstitial cell activation and injury.