Prematurity/preterm birth is the leading cause of perinatal morbidity and mortality both in the U.S. and in California. These babies are at increased risk for long-term disabilities, including cerebral palsy, gastrointestinal problems, and vision and hearing loss. Many premature babies also suffer from low birth weight, which not only increases complications in the perinatal period, but also leads to increased cardiovascular disease and diabetes in adulthood. The majority of these perinatal complications result from abnormal development and function of the placenta, a transient organ that forms the interface between mother and baby. Trophoblasts are the primary cells which carry out major placental functions such as establishing blood supply from the mother to the fetus. In this application, we proposed the placenta as a novel target for stem cell therapy and sought to generate human trophoblast stem (TS) cells, which give rise to all subtypes of trophoblasts in the placenta.
During the past year, we have made significant progress in characterization of p63, a protein we had previously identified as a potential marker of proliferative trophoblast. We now know that this protein: 1) is upregulated in low oxygen, conditions that promote trophoblast proliferation; and 2) it regulates the trophoblast cell cycle at a specific point. When we forcibly increase its production in trophoblast, p63 keeps the cells from differentiating into hCG-secreting syncytiotrophoblast; however, by itself, it is unable to keep human trophoblast cells proliferative in culture. In addition, we now have evidence that p63 plays a major role in differentiation of human embryonic stem cells (hESC) towards the trophoblast lineage. We are now testing culture conditions under which p63-expressing hESC-derived trophoblast can be maintained, and not progress to terminally differentiated trophoblast.
In order to discover additional markers for trophoblast proliferation and regeneration, we have collected samples from placentas of various gestational ages and subjected these to gene expression analysis. It is known that trophoblast in early placenta (especially in first trimester) are more proliferative than those later in pregnancy (i.e. third trimester). By looking at total gene expression in placentas across gestation, we have now identified several other markers like p63, which have a high potential to play a role in trophoblast “stemness.” Over the next year, we will be evaluating the localization of these gene products in the placenta and evaluating their function in trophoblast differentiation.