Elevated Renal Oxidative Stress and Na+ Transporters are Associated with Hypertension in Postpartum Preeclamptic Rats

Approximately 5-10% of US pregnancies result in preeclampsia (PE). PE is characterized by new onset hypertension (HTN) during pregnancy and is usually accompanied by end-organ damage, especially in the kidneys. Postpartum (PP) women and dams that had PE have an increased risk of developing HTN and chronic kidney disease (CKD) later in life. However, mechanisms linking PE to the long-term development of HTN and CKD are unknown. One aspect that may contribute to renal injury in PP PE women and dams is oxidative stress. Elevated concentrations of oxidative stress have been shown to augment the abundance and activity of renal transporters to increase sodium (Na+) reabsorption and blood volume. These alterations in renal transporters can consequently facilitate HTN. We hypothesize that at 6 weeks PP (~3 human years), PE dams will display oxidative stress, renal Na+ transporter abundance, and elevated blood pressure (BP).

Pregnant Sprague Dawley rats were assigned to two groups: normal (CON) and PE dams. On gestational day 14, the reduced uterine perfusion pressure surgery was performed to generate a model of PE. Dams gave birth naturally and weaned for 3 weeks. After 6 weeks PP, BP was measured via carotid catheterization, and kidneys were removed and sectioned. Western blots were used to quantify renal Na+ transporters: Na+ K+ 2Cl-transporter (NKCC2) in the kidney medulla (KM) and epithelial Na+ channel (ENaC) in both the kidney cortex (KC) and KM. Oxidative stress was evaluated by heat shock protein 1 (HSP-1), copper zinc superoxide dismutase (CuZnSOD), and manganese superoxide dismutase (MnSOD) via Western blots. Hydrogen peroxide (H2O2) and antioxidant capacity concentrations were assessed via colorimetric assays. PP PE dams had increased BP (126.3±6.18vs105.7±3.74 mmHg, p<0.05) at 6 weeks after birth. KC HSP- 1, H2O2, MnSOD, and antioxidant capacity were unchanged between groups. However, KC CuZnSOD protein abundance was decreased in PP PE dams (69.51±11.64vs100±5.73 IU/Protein/Control%, p<0.05). In the KM, HSP-1 abundance (113.7±3.3vs100±5.07 IU/Protein/Control%, p=0.06) and H2O2 concentrations (1.97±0.11vs1.31± 0.38 nM H2O2/mg Protein, p=0.08) were elevated in PP PE dams. MnSOD, CuZnSOD, and antioxidant capacity were unchanged between groups in the KM. No changes occurred in KC and KM ENaC protein abundance. However, NKCC2 protein abundance was elevated by ~50% in PP PE dams (151.71±22.17vs100±5.59 IU/Protein/Control%, p=0.06).

In summary, BP, oxidative stress, and NKCC2 were elevated in PP PE dams at 6 weeks. The presence of oxidative stress in the KM may lead to increased NKCC2 abundance. However, more studies are warranted to make this conclusion. NKCC2 elevation may result in increased Na+ and water reabsorption, leading to an increase in BP. Future studies will assess renal oxidative stress regulation of Na+ transporters in PP PE dams and determine the timeline PP in which changes in oxidative stress, Na+ transporters, and BP occur. This study is clinically relevant, because it indicates oxidative stress and NKCC2 in the KM, separately or together, may have a formative role in the pathogenesis of HTN and CKD in PP PE women later in life.