Complement Activation in Maternal and Placental Pathology of Preeclampsia

Preeclampsia is a multifactorial, pregnancy-related disorder characterized by new-onset hypertension and proteinuria, with distinct early- and late-onset forms. Although complement dysregulation has been implicated in the pathogenesis of preeclampsia, its causal role remains unclear. In mice, Crry (complement receptor 1-related protein Y) functions as a critical complement regulator at the fetal-maternal interface. Because complete Crry deficiency is embryonically lethal, direct in vivo investigation of complement activation in pregnancy has been challenging.

We generated a placenta-specific, doxycycline-inducible short hairpin RNA mouse model in which Crry expression can be downregulated in a dose-dependent manner. This system employs Cyp19-driven Cre recombinase and a tetracycline-inducible gene expression system regulatory cassette, enabling precise temporal and spatial control of Crry suppression and restricting complement activation specifically to the placenta.

We found that early gestation placental complement activation impairs maternal cardiac and hepatic adaptation, reduces placental efficiency, and causes fetal growth restriction-features consistent with early-onset preeclampsia. Delayed complement activation produces a phenotype resembling late-onset preeclampsia, characterized by maternal hypertension without placental pathology. In the early-onset-like phenotype, fetal growth restriction is accompanied by placental glycogen storage deficiency and impaired endocrine function. Maternal glucose metabolism remains intact; however, compensatory changes in lipid metabolism occur, although these adaptations are insufficient to prevent fetal growth restriction.

This model demonstrates that the timing of placental complement activation determines whether pregnancy develops early- or late-onset-like features. These findings provide mechanistic insight into how complement dysregulation contributes to the spectrum of preeclampsia pathology and establish a powerful experimental platform for studying disease mechanisms and evaluating therapeutic strategies.