Glomerular Collagen Deposition and Lipocalin-2 Expression Are Early Signs of Renal Injury in Prediabetic Obese Rats

Rats fed a high-fat diet with a single streptozotocin (STZ) injection developed obesity, prediabetes, cardiac hypertrophy and diastolic dysfunction. Here we aimed to explore the renal consequences of prediabetes in the same groups of rats. Male Long-Evans rats were fed normal chow (CON; n = 9) or high-fat diet containing 40% lard and were administered STZ at 20 mg/kg (i.p.) at week four (prediabetic rats, PRED, n = 9). At week 21 cardiac functions were examined (Koncsos et al., 2016) and blood and urine samples were taken. Kidney samples were collected for histology, immunohistochemistry and for analysis of gene expression. High-fat diet and streptozotocin increased body weight gain and visceral adiposity, and plasma leptin, elevated fasting blood glucose levels, impaired glucose and insulin tolerance, despite hyperleptinemia, plasma C-reactive protein concentration decreased in PRED rats. Immunohistochemistry revealed elevated collagen IV protein expression in the glomeruli, and Lcn2 mRNA expression increased, while Il-1β mRNA expression decreased in both the renal cortex and medulla in PRED vs. CON rats. Kidney histology, urinary protein excretion, plasma creatinine, glomerular Feret diameter, desmin protein expression and cortical and medullary mRNA expression of TGF-β1, Nrf2, PPARγ were similar in CON and PRED rats. Reduced AMPKα phosphorylation of the autophagy regulator Akt was the first sign of liver damage, while serum lipid and liver enzyme levels were similar. In conclusion, glomerular collagen deposition and increased lipocalin-2 expression were the early signs of kidney injury, while most biomarkers of inflammation, oxidative stress and fibrosis were negative in the kidneys of obese, prediabetic rats with mild heart and liver injury.