Ho et al. (2017) demonstrated that knocking out APLNR in pregnant mice resulted in PE-like symptoms due to defective placental angiogenesis, and this was accompanied by poor placental angiogenesis, elevated apoptosis, and decreased proliferation. Results from analysis of developmental model organisms have suggested that the Apelin/APJ pathway plays an important role in embryo angiogenesis (Kidoya et al., 2008). For example, dysregulated APLNR was associated with growth and migration, as well as cell cycle progression, in ovarian clear cell carcinoma (OCCC) cell lines (Xu and Shen, 2018). Here, APLN is linked to ovarian clear cell cancer.