Vitamin C regulation of human placental trophoblast stem cell function

Poor placental development during the first-trimester of pregnancy can result in fetal growth restriction (FGR), a condition in which a fetus is unable to achieve its genetically determined size. The placenta's functional capacity depends on the coordination between the placental cells called trophoblast stem cells (TSCs) self-renewing (i.e., increasing in number) and differentiating (i.e., transforming) into specialised cell-types. This process is regulated by coordinated changes in sets of genes. Activating these genes require access to DNA regions that is achieved by 'epigenetic' modifications to the DNA. One form of epigenetic regulation (referred to as DNA methylation) is the addition of methyl groups that commonly results in switching off gene expression. The inverse of this is DNA demethylation which removes methyl groups leading to gene activation. Compared to all other tissues, the placenta exhibits low levels of DNA methylation, particularly in early pregnancy as it is believed to be critical for trophoblast development. However, little is known about how DNA demethylation (i.e. methl-group removal) is regulated in the human placenta during this critical stage of pregnancy.

Nutrition plays a vital role during early placental development as both animal and human studies show that diets low in micronutrients such as Vitamin C (VitC) during periconceptional periods (i.e., before conception to early pregnancy) result in decreased placental and fetal growth. This proposal seeks to understand the role of VitC in regulating trophoblast stemness (i.e., the ability of TSCs to self-renew and differentiate). Our preliminary data shows that VitC promotes DNA demethylation and trophoblast stemness at concentrations 100-fold lower than those required to reduce reactive oxygen species (harmful by-products of metabolism). Moreover, VitC exhibits a J-shaped relationship on trophoblast growth with inhibitory effects observed at very low or high levels. Lastly, both low levels of VitC in maternal blood and reduced levels of the placental vitamin C transporter mRNA were associated with FGR.

Our central hypothesis is that physiological VitC concentrations (i.e., concentrations obtained from healthy diets) promote trophoblast self-renewal by DNA demethylation of stemness genes. We will first determine the mechanism by which VitC regulates stemness in human TSCs and establish the optimal dose. We will then determine the effects of the optimal VitC dose on DNA (de)methylation and activation of genes regulating TSC growth. Lastly, we will use existing maternal blood and placental samples from a prospective pregnancy cohort to evaluate if low maternal and placental VitC levels are associated with reduced placental DNA demethylation and increased risk of placenta-related pregnancy complications.

While the objectives of this study are to understand how VitC regulates trophoblast stemness, the study's findings may also have profound public health implications. For example, they may lead to optimal dosing strategies for VitC supplementation during the periconceptional period to reduce the risk of placenta-related complications. They may also explain why previous clinical trials of supplementation with high (supraphysiological) doses of VitC during mid-pregnancy in women at risk of pregnancy disorders have failed to prevent adverse events.