The placenta is susceptible to diverse insults during human pregnancy. The expression of the protein N-myc down-regulated gene 1 (NDRG1) is regulated during cell proliferation, differentiation, and in response to stress. Nevertheless, the function of this protein in humans remains unknown. We tested the hypothesis that NDRG1 is up-regulated in hypoxic primary human trophoblasts and that NDRG1 modulates trophoblast response to hypoxia. We initially demonstrated that the expression of NDRG1 is enhanced in primary human trophoblasts exposed to hypoxia. Importantly, we found a similar increase in NDRG1 expression in placental samples derived from either singleton gestations complicated by intrauterine growth restriction or from dizygotic twin gestation where one twin exhibited growth restriction. Having established efficient lentivirus-mediated transfection of primary human trophoblasts, we overexpressed NDRG1 in trophoblasts, which resulted in enhanced trophoblast differentiation. In contrast, lentivirus-driven short interfering RNA-mediated silencing of NDRG1 diminished trophoblast viability and differentiation. Consistent with these results, NDRG1 reduced the expression level of p53 in trophoblasts cultured in standard or hypoxic conditions. Furthermore, NDRG1 expression was regulated by the activity of SIRT1 (Sir2-like protein 1), which promotes cell survival. Together, our data indicate that NDRG1 interacts with SIRT1/p53 signaling to attenuate hypoxic injury in human trophoblasts.The trophoblasts at the surface of human placental villi play a pivotal role in gas exchange, nutrition, waste removal, endocrine function, and immunological support for the developing fetus. Trophoblast invasion and early placental development occur in an environment of relative hypoxia (1, 2). Under these conditions hypoxia promotes invasion and angiogenesis (3) and is associated with up-regulation of vascular endothelial growth factor expression and down-regulation of placenta growth factor (4, 5). Trophoblast hypoxia later in pregnancy commonly stems from placental hypoperfusion, vasoconstriction, maternal systemic disease, high altitude, or smoking and may result in hypoxic injury to the placenta and consequently intrauterine growth restriction (IUGR) 2 with its consequences (6).Using high density oligonucleotide microarrays we have previously examined differences in gene expression between placental tissues from pregnancies complicated by IUGR versus matched normal placental tissues as well as from trophoblasts cultured under hypoxic or standard culture conditions (7,8). Combining these paradigms, we characterized a set of hypoxic trophoblast signature transcripts (8). Among these transcripts we consistently identified up-regulation of NDRG1 (N-myc down-regulated gene 1) transcript in hypoxic trophoblasts compared with cells cultured in standard conditions (8).3 NDRG1 (also called RTP, Drg1, Cap 43, rit42, TDD5, Ndr1, and PROXY-1) is a 394-amino acid protein expressed in both the cytoplasm and nucleus (9 -16) and implicated in c...