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The Spontaneously Diabetic Torii (SDT) fatty rat is a relevant type 2 diabetic model to evaluate drugs targeting diabetic nephropathy. To further optimize the model for drug efficacy studies, we here tested the effects of unilateral nephrectomy and salt supplemented diet on kidney function and histology. Using quantitative image analysis, we also assessed podocyte foot process morphology and kidney fibrosis.
Sham operation or unilateral nephrectomy (Unx) were performed on male, 6-week-old, SDT fatty rats. After surgery recovery, Sham and Unx SDT fatty rats were maintained on a 0.3% salt diet for 10 weeks. A group of Sprague Dawley (SD) rats was included as a negative control. Glomerular Filtration Rate (GFR) and urine parameters were m easured at baseline, 5 weeks, and 10 weeks. Kidneys were collected at 10 weeks for histology and quantitative image analysis, including the Podocyte Exact Morphology Measurement Procedure (PEMP) and quantitative digital pathology of kidney fibrosis (FibroNest platform).
Compared to SD rats, sham SDT fatty rats on 0.3% salt diet were strongly hyperglycemic (~630mg/dL versus ~100mg/dL in fed state) and showed significantly higher proteinuria, urine albumin/creatinine ratio (ACR), KIM-1 and cystatin-C levels. SDT fatty rats had greater GFR at baseline (80% higher, p<0.05), but this hyperfiltration was not observed at 5 and 10 weeks. Compared to SD rats, SDT fatty rats also had significantly greater kidney weight, inflammation (ED1 immunostaining), glomerulosclerosis (PAS staining) and fibrosis (Sirius Red and collagen III immunostaining). Compared to SD rats, filtration slit density and filtration slit length (as measured by PEMP) were both significantly reduced, indicating podocytes effacement. FibroNest image analysis also demonstrated a significant increase in phenotypic fibrosis composite scores (Ph-FCS) in SDT fatty rats.
Compared to sham, Unx SDT fatty rats were slightly less hyperglycemic but showed a substantial GFR decline from baseline to 10 weeks, while urine ACR, KIM-1 and cystatin-C levels were further increased. Kidney lesions were significantly greater with higher glomerulosclerosis, inflammation, and fibrosis scores. As well, podocytes effacement and Ph-FCS were significantly aggravated in Unx SDT fatty rats.
Our data demonstrate that Unx and 0.3% salt diet in SDT fatty rats severely impairs kidney function and aggravates kidney lesions, including podocyte effacement and renal fibrosis within 10 weeks. This type 2 diabetic rat model should be useful to evaluate drugs targeting diabetic kidney disease.