Alterations of Placental Sodium in Preeclampsia: Trophoblast Responses

BACKGROUND: Evidence suggests that increasing salt intake in pregnancy lowers blood pressure, protecting against preeclampsia. We hypothesized that sodium (Na⁺) evokes beneficial placental signals that are disrupted in preeclampsia. METHODS: Blood and urine were collected from nonpregnant women of reproductive age (n=26) and pregnant women with (n=50) and without (n=55) preeclampsia, along with placental biopsies. Human trophoblast cell lines and primary human trophoblasts were cultured with varying Na⁺ concentrations. RESULTS: Women with preeclampsia had reduced placental and urinary Na⁺ concentrations, yet increased urinary angiotensinogen and reduced active renin, aldosterone concentrations, and osmotic response signal TonEBP (tonicity-responsive enhancer binding protein) expression. In trophoblast cell cultures, TonEBP was consistently increased upon augmented Na⁺ exposure. Mechanistically, inhibiting Na⁺/K⁺-ATPase or adding mannitol evoked the TonEBP response, whereas inhibition of cytoskeletal signaling abolished it. CONCLUSIONS: Enhanced Na⁺ availability induced osmotic gradient-dependent cytoskeletal signals in trophoblasts, resulting in proangiogenic responses. As placental salt availability is compromised in preeclampsia, adverse systemic responses are thus conceivable.