Oxidative Response and Kidney Function in Mice with Sickle Cell Disease

Background: In patients with sickle cell disease (SCD) evidence of structural and functional changes in the kidneys can be detected as early as in infancy and evolve as patients age. Abnormal elevation of the glomerular filtration rate (GFR), a reflection of the kidney's ability to filter waste products from the blood is an early sign of kidney dysfunction and a predictor of disease evolution to chronic kidney disease (CKD) and end stage renal disease (ESRD). Glomerular hyperfiltration results from an abnormal blood flow elevation in the renal cortex due to patient's anemia and vaso-occlusive events in the vasa recta. However, the renal molecular response leading to glomerular hyperfiltration and subsequent decline of kidney function are not clearly understood. Hemolysis causing toxic iron and heme deposition leads to oxidative stress and inflammation. Previous studies showed a protective role of the antioxidant and heme degrading enzyme heme oxygenase-1 (HMOX1) in SCD nephropathy, and genetic polymorphisms were shown to influence GFR. However, HMOX1 antioxidant response during GFR evolution in SCD is unknown. In this study, we evaluated the evolution of kidney function reflected by the GFR at different stages of SCD nephropathy in the Townes mouse model of SCD and determined the concurrent renal antioxidant state by measuring the Hmox1 expression.

Methods: We measured GFR in male and female SCD mice at 6-, 12-, and 28-week of age by injecting 75 mg/kg of FITC-sinistrin via the tail vein and measured its clearance for 90 minutes using a transdermal monitor (Medibeacon). We measured renal expression of the Hmox1 at these disease stages by quantifying mRNA expression by quantitative reverse transcription polymerase chain reaction (RT-qPCR). Gene expression was normalized to housekeeping gene Gapdh. Data are expressed using the 2^-DDCt method and a 6-week-old female AA mice as reference sample.

Results: Consistent with previous studies, SCD males but not SCD females experienced glomerular hyperfiltration (p=0.0017), which peaked at 12-weeks-old. GFR then declined toward hypofiltration at 28 weeks of age in male SCD mice, reflecting a transition of the disease to CKD (p=0.0154). Renal Hmox1 expression significantly increases in both male and female SCD mice compared to non-SCD. In female mice, Hmox1 expression shows a peak of expression at 12-week-old (p<0.0001), with a subsequent decrease in 28-week-old mice. This rise of Hmox1 does not occur in SCD male.

Conclusions: We confirmed that SCD mice recapitulate the different stages of SCD nephropathy associated with GFR and indicate that protective mechanisms delay or prevent glomerular hyperfiltration in female. Interestingly, Hmox1 expression in female mice followed the same dynamic profile as GFR in male mice who lack this increase in Hmox1 expression, suggesting that HMOX1 antioxidant response may mediate sex-dimorphic kidney disease caused by early glomerular hyperfiltration. These initial data warrant further investigation of the protective role of HMOX1 antioxidant response against glomerular hyperfiltration and subsequent decline of kidney function.

No relevant conflicts of interest to declare.