Early Hyperglycemic Renal Injury in a Novel One-Kidney Rat Model

Diabetes remains one of the main culprits of end‐stage kidney disease in the US. Investigation into the role of nephron number in chronic kidney disease (CKD) alone or with hypertension has revealed a strong inverse relationship (i.e., lower nephron number ‐‐> increased susceptibility to hypertension and CKD); however, not much is known about the connection between nephron number and diabetic kidney disease. To address this gap in knowledge we utilize the HSRA rat, a novel inbred genetic model of nephron deficiency and chronic kidney disease. HSRA rats exhibit failure of one kidney to develop (HSRA‐S, ~20,400 nephrons) in 50–75% of offspring, while remaining offspring are born with two kidneys (HSRA‐C, ~50,000 nephrons). HSRA‐S rats can be directly compared to nephrectomized HSRA‐C rats (HSRA‐UNX, ~25,100 nephrons), which provides insight into the impact of nephron number differences across the three groups. HSRA‐S rats develop significant renal injury with age when compared with HSRA‐C and HSRA‐UNX; the difference in injury is significantly exacerbated in the presence of DOCA+salt hypertension. The current study sought to address the hypothesis that nephron deficiency in the HSRA rat is a risk factor for renal injury, secondary to hyperglycemia (similar to what is seen with hypertension). Streptozotocin (STZ) was used to induce a diabetic phenotype in HSRA‐S, HSRA‐C, and HSRA‐UNX at nine weeks of age, and animals were followed for 15 weeks. All animals exposed to STZ developed robust hyperglycemia (random glucose averages: 415mg/dL – 456 mg/dL), but in contrast to the response to hypertension, neither HSRA‐S nor HSRA‐UNX developed overt proteinuria, nor were there significant differences between groups at the conclusion of the experiment. There was however, a significant increase in kidney weight to body weight ratio in STZ/hyperglycemic groups versus controls (e.g., kidney weight to body weight ratio [mg/g] 4.8 ± 0.3089 for HSRA‐S vs 7.8 ± 1.204 for HSRA‐S+STZ, p=0.02). STZ/hyperglycemic groups also exhibited significant decreases in creatinine clearance (e.g., creatinine clearance [μL/min/g] 719.0 ± 44.81 for HSRA‐S vs. 455.2 ± 72.91 for HSRA‐S+STZ, p=0.009). Targeted RNA sequencing was performed on isolated glomeruli using a custom panel of 42 genes involved in maintenance of glomerular function. In support of the physiological data stated above, few genes were observed to be dysregulated; however, Nphs1 and Nphs2 genes (associated with the protein nephrin) were increased in two‐kidney rats (HSRA‐C and HSRA‐C+ STZ) versus either one kidney group, regardless of glycemic status. In total, the data indicates that hyperglycemia does not have a significant impact on the onset and progression of injury in young HSRA‐S animals. We are currently investigating a mixed model of hypertension + hyperglycemia in the HSRA, which represents a large cohort of patients that are susceptible to CKD. Animals will be provided a low dose of DOCA+salt (35 mg) to induce moderate hypertension at ten weeks of age, along with 45mg/kg of STZ to induce hyperglycemia. In summary, establishing a role of nephron deficiency as a risk factor for hyperglycemia‐associated CKD will contribute to the growing knowledge of the relationship between nephron number and disease.