Impaired renal reserve contributes to preeclampsia via the kynurenine and soluble fms–like tyrosine kinase 1 pathway

To understand how kidney donation leads to an increased risk of preeclampsia, we studied pregnant outbred mice with prior uninephrectomy and compared them with sham-operated littermates carrying both kidneys. During pregnancy, uninephrectomized (UNx) mice failed to achieve a physiological increase in the glomerular filtration rate and during late gestation developed hypertension, albuminuria, glomerular endothelial damage, and excess placental production of soluble fms–like tyrosine kinase 1 (sFLT1), an antiangiogenic protein implicated in the pathogenesis of preeclampsia. Maternal hypertension in UNx mice was associated with low plasma volumes, an increased rate of fetal resorption, impaired spiral artery remodeling, and placental ischemia. To evaluate potential mechanisms, we studied plasma metabolite changes using mass spectrometry and noted that l-kynurenine, a metabolite of l-tryptophan, was upregulated approximately 3-fold during pregnancy when compared with prepregnant concentrations in the same animals, consistent with prior reports suggesting a protective role for l-kynurenine in placental health. However, UNx mice failed to show upregulation of l-kynurenine during pregnancy; furthermore, when UNx mice were fed l-kynurenine in drinking water throughout pregnancy, their preeclampsia-like state was rescued, including a reversal of placental ischemia and normalization of sFLT1 levels. In aggregate, we provide a mechanistic basis for how impaired renal reserve and the resulting failure to upregulate l-kynurenine during pregnancy can lead to impaired placentation, placental hypoperfusion, an antiangiogenic state, and subsequent preeclampsia.