The placenta is an essential organ in mammals that connects the maternal body and the fetus, and it exerts crucial functions such as transporting nutrients, secreting hormones, and mediating defense and immunity. In the modern swine industry, there is an increasing focus on the number of weaned piglets per sow per year. The development of the placenta and the integrity of its function are prerequisites for ensuring the normal growth and development of the fetus.

During pregnancy in pigs, there are two critical periods of high spontaneous embryo/fetal loss, which severely impairs reproductive efficiency: the first peak occurs during the implantation period (days 12–30 of pregnancy), when embryos elongate and attach to the uterus, and approximately 20%–45% of embryos are lost at this stage [1]; the second peak occurs during the mid-pregnancy period (days 50–70 of pregnancy) [2], approximately 10%–15% of fetuses trigger spatial competition at attachment sites due to their rapid growth, resulting in developmental arrest of adjacent littermate fetuses [3,4].

Notably, during the implantation period, the placenta undergoes extensive cell proliferation and migration, which are associated with substantial energy demands. The high rate of embryonic loss during this period (up to 20%–45%) suggests that limited ATP availability may be an important contributing factor to embryonic loss [5]. In addition to ATP, glucose, amino acids, and lipids also play essential roles in the growth and development of the placenta: the trophectoderm can utilize glucose in the uterine cavity through glycolysis to produce energy molecules [6]; fatty acids are crucial for placental vascularization [7], which in turn affects placental function; supplementation of arginine in the diet can improve pregnancy outcomes by promoting placental growth [8], all of which highlight the core role of energy metabolism in placental development.

The results of relevant studies demonstrate that in fetal pig models of intrauterine growth restriction (IUGR), placental tissue exhibits significant downregulation of proteins related to energy metabolism and nutrient transport [9], suggesting that placental metabolic dysfunction may lead to insufficient energy supply and impaired substance exchange. As a critical organ, aberrant activity of core metabolic pathways in placental tissues or metabolic dysfunction in specific cell subtypes may lead to abnormal placental development and impaired placental function during pregnancy, thereby increasing the risk of embryonic loss. However, currently, there remains a lack of analysis at the single-cell resolution level regarding the metabolic profiles of the porcine placenta during the implantation period, as well as the functional differentiation of more refined cell subsets in energy metabolism and other key pathways.

Single cell RNA sequencing (scRNA-seq) is a high-throughput sequencing technology that operates at the single-cell level. It enables accurate identification of the heterogeneity among different cell subtypes and investigates the activity of major metabolic pathways at the genetic level. In this study, by integrating scRNA-seq datasets from early pregnant pig placentas (P16, P20, P24, and P28), we investigated the importance of trophoblast cell metabolism during placental development, characterized the metabolic features of trophoblast cells in early pregnancy, and identified potential signaling patterns among different trophoblast subclusters as well as between trophoblast cells and endothelial cells. Our findings are expected to provide new insights into the development of trophoblast cells and the complex crosstalk between trophoblast cells and endothelial cells (ECs).