Mouse Models of Diabetes, Obesity and Related Kidney Disease

Abstract

Multiple rodent models have been used to study diabetic kidney disease (DKD). The purpose of the present study was to compare models of diabetes and obesity-induced metabolic syndrome and determine differences in renal outcomes. C57BL/6 male mice were fed either normal chow or high fat diet (HFD). At postnatal week 8, chow-fed mice were randomly assigned to low-dose streptozotocin (STZ, 55 mg/kg/day, five consecutive days) or vehicle control, whereas HFD-fed mice were given either one high-dose of STZ (100 mg/kg) or vehicle control. Intraperitoneal glucose tolerance tests were performed at Week 14, 20 and 30. Urinary albumin to creatinine ratio (ACR) and serum creatinine were measured, and renal structure was assessed using Periodic Acid Schiff (PAS) staining at Week 32. Results showed that chow-fed mice exposed to five doses of STZ resembled type 1 diabetes mellitus with a lean phenotype, hyperglycaemia, microalbuminuria and increased serum creatinine levels. Their kidneys demonstrated moderate tubular injury with evidence of tubular dilatation and glycogenated nuclear inclusion bodies. HFD-fed mice resembled metabolic syndrome as they were obese with dyslipidaemia, insulin resistance, and significantly impaired glucose tolerance. One dose STZ, in addition to HFD, did not worsen metabolic features (including fasting glucose, non esterified fatty acid, and triglyceride levels). There were significant increases in urinary ACR and serum creatinine levels, and renal structural changes were predominantly related to interstitial vacuolation and tubular dilatation in HFD-fed mice.

Fig 1. Schematic representation of the animal model utilised in this study.

Chow represents control group fed normal chow diet; Chow_lowSTZ depicts the group exposed to normal chow diet and low-dose streptozotocin (STZ) for five consecutive days; HFD depicts the group fed HFD; HFD_hiSTZ depicts the group fed HFD in conjunction with high-dose STZ (one dose only).

Fig 2. Intraperitoneal glucose tolerance tests performed at postnatal Week 14, 20 and 30 in C57Bl/6J mice.

Blood glucose levels were measured at 0,15,30,60 and 90 minutes as seen in A-C. Symbols depicted in A-C: Ctrl, designated with a circle; HFD, designated with a square; HFD-hiSTZ, designated with an inverted triangle. Area under the curve was calculated using the trapezoid rule and is shown in D-F. Results are expressed as mean ± SEM, n = 7–14. *P< 0.05, **P<0.01, ***P<0.001, ****P < 0.0001 compared to control, # compared to HFD. Control: Chow; High fat diet: HFD; and HFD and one high-dose STZ: HFD_hiSTZ.

Fig 3. Renal functional changes demonstrated at postnatal Week 31 and 32.

(A) Urinary albumin to creatinine ratio (ACR) collected at Week 31 from metabolic cage, (B) Serum creatinine at Week 32. Results are expressed as mean ± SEM, n = 9 for ACR, n = 6–9 for 24 h albumin. *P< 0.05, **P<0.01 compared to Ctrl; # P < 0.05 compared to Chow_lowSTZ. Control: Chow; Chow diet and five low-dose STZ: Chow_lowSTZ; High fat diet: HFD; and HFD and one high-dose STZ: HFD_hiSTZ.

Fig 4. Periodic acid Schiff (PAS) staining at Week 32.

(A) Representative images at high magnification of glomerular changes, (B) Representative images at high magnification of tubular damage, (C) Tubular interstitial fibrosis score, and (D) Glomerulosclerosis score. Results are expressed as mean ± SEM, n = 6. *P< 0.05, **P<0.01 compared to Chow_lowSTZ. Control: Chow; Chow diet and five low-dose STZ: Chow_lowSTZ; High fat diet: HFD; and HFD and one high-dose STZ: HFD_hiSTZ.

Fig 5. Periodic acid Schiff (PAS) staining was used to demonstrate tubular injury at Week 32.

Tubular injury was scored according to: (A) Tubular dilation, (B) Tubular vacuolation, (C) Glycogenated nuclei, and (D) Tubular casts. (E) Representative image of nuclear inclusion bodies (due to glycogenation) with PAS, (F) Representative image of the absence of glycogenated nuclei with PAS and diastase (an enzyme used to degrades glycogen). Results are expressed as mean ± SEM, n = 6. *P< 0.05, **P<0.01 compared to Chow_lowSTZ. Control: Chow; Chow diet and five low-dose STZ: Chow_lowSTZ; High fat diet: HFD; and HFD and one high-dose STZ: HFD_hiSTZ.