Disparate Effects of Diabetes and Hyperlipidemia on Experimental Kidney Disease

Abstract

It is well established that diabetes is the major cause of chronic kidney disease worldwide. Both hyperglycemia, and more recently, advanced glycation endproducts, have been shown to play critical roles in the development of kidney disease. Moreover, the renin-angiotensin system along with growth factors and cytokines have also been shown to contribute to the onset and progression of diabetic kidney disease; however, the role of lipids in this context is poorly characterized. The current study aimed to compare the effect of 20 weeks of streptozotocin-induced diabetes or western diet feeding on kidney disease in two different mouse strains, C57BL/6 mice and hyperlipidemic apolipoprotein (apo) E knockout (KO) mice. Mice were fed a chow diet (control), a western diet (21% fat, 0.15% cholesterol) or were induced with streptozotocin-diabetes (55 mg/kg/day for 5 days) then fed a chow diet and followed for 20 weeks. The induction of diabetes was associated with a 3-fold elevation in glycated hemoglobin and an increase in kidney to body weight ratio regardless of strain (p < 0.0001). ApoE deficiency significantly increased plasma cholesterol and triglyceride levels and feeding of a western diet exacerbated these effects. Despite this, urinary albumin excretion (UAE) was elevated in diabetic mice to a similar extent in both strains (p < 0.0001) but no effect was seen with a western diet in either strain. Diabetes was also associated with extracellular matrix accumulation in both strains, and western diet feeding to a lesser extent in apoE KO mice. Consistent with this, an increase in renal mRNA expression of the fibrotic marker, fibronectin, was observed in diabetic C57BL/6 mice (p < 0.0001). In summary, these studies demonstrate disparate effects of diabetes and hyperlipidemia on kidney injury, with features of the diabetic milieu other than lipids suggested to play a more prominent role in driving renal pathology.

Keywords: albuminuria; cholesterol; diabetes; lipids; renal disease.

FIGURE 1

Diabetes is associated with increased kidney/body weight ratio and systolic blood pressure. (A) Body weight; (B) Kidney weight; (C) Kidney/body weight ratio; (D) Systolic blood pressure; (A–C), n = 11–24/group; (D), n = 8–22/group. Data represented as mean + SEM. *p < 0.05, ***p < 0.001, ****p < 0.0001 vs. C57BL/6 control; ^∧p < 0.05, ^∧∧∧∧p < 0.0001 vs. apoE KO control; ^†††p < 0.001, ^††††p < 0.0001 vs. C57BL/6 diabetic;^%p < 0.05, ^%%%p < 0.001, ^%%%%p < 0.0001 vs. apoE diabetic.

FIGURE 2

Apolipoprotein E deletion exacerbates the effect of diabetes or feeding of a western diet on plasma lipid levels. (A) Glycated hemoglobin; (B) Plasma total cholesterol levels; (C) Plasma triglyceride levels; (A) n = 12–23/group; (B,C) n = 4–8/group. Data represented as mean + SEM. ****p < 0.0001 vs. C57BL/6 control; ^∧p < 0.05, ^∧∧∧p < 0.001, ^∧∧∧∧p < 0.0001 vs. apoE KO control; ^††††p < 0.0001 vs. C57BL/6 diabetic; ^%%p < 0.01,^%%%%p < 0.0001 vs. apoE diabetic.

FIGURE 3

Apolipoprotein E deletion has no effect on the diabetes-associated increase in urinary albumin excretion. (A) Urinary albumin excretion rate (UAE); Correlation of UAE with (B) Glycated hemoglobin; (C) Kidney weight to body weight ratio; (D) Systolic blood pressure; (E) Plasma cholesterol and (F) Plasma triglycerides; (G) Plasma cystatin C levels; (A) n = 7–21/group. (B) n = 80; (C) n = 78; (D) n = 62; (E,F) n = 34; (G) n = 5–9/group. (A) Data represented as geometric mean + geometric standard deviation; (B–F) linear regression with each dot representing an individual mouse. (G) Data represented as mean + SEM. ****p < 0.0001 vs. C57BL/6 control; ^∧∧∧∧p < 0.0001 vs. apoE KO control; ^††p < 0.01; ^††††p < 0.0001 vs. C57BL/6 diabetic; ^%%%%p < 0.0001 vs. apoE diabetic mice.

FIGURE 4

Extracellular matrix accumulation was increased with diabetes and to a lesser extent with feeding of a western diet. (A) Representative images of PAS staining; (B) Quantitation of mesangial expansion; n = 9–12/group. Data expressed as mean + SEM. *p < 0.05 vs. C57BL/6 control; ^∧p < 0.05, ^∧∧∧p < 0.001 vs. apoE KO control; Bar represents 20 μM.