UCSF DIABETES, ENDOCRINOLOGY & METABOLISM TRAINING PROGRAM FACULTY RESEARCH SUMMARIES

Endocrinology of Placenta Formation and Pregnancy

We are studying the mechanisms by which human trophoblast cells invade the uterus during normal pregnancy. Human fetal development depends on the embryo's ability to rapidly gain access to the maternal circulation. The cytotrophoblasts that form the fetal portion of the human placenta have solved this problem by transiently exhibiting certain invasive, tumor-like properties.

We have been particularly interested in the role of proteinases and adhesion molecules in mediating cytotrophoblast invasion. In these studies, we have used two approaches. One approach is immunolocalization of relevant molecules in biopsy specimens of the maternal-fetal interface. Here, polarized chorionic villus cytotrophoblasts form multilayered columns of nonpolarized cells that leave the fetal compartment and invade the uterus. The other approach is an in vitro model we developed that supports cytotrophoblast differentiation along the invasive pathway. We have used this model to test the function of molecules we suspect play a role in invasion.

Immunolocalization studies show that in normal pregnancy, cytotrophoblast invasion, both in vivo and in vitro, is accompanied by a dramatic switch cellular expression of matrix-degrading metalloproteinases and adhesion molecules. Function-perturbation experiments suggest that cytotrophoblasts carefully regulate their invasive potential by simultaneously expressing a number of molecules that either promote or inhibit invasion. Most recently, we found that cytotrophoblasts that replace the endothelial lining of uterine blood vessels also have the amazing ability to mimic the adhesion phenotype of vascular cells. This phenomenon is likely to be a critical component of normal placentation. What controls this highly unusual differentiation process? Since cytotrophoblasts target large-bore arterioles for invasion, we reasoned that oxygen tension could play a role. Recently, we showed that oxygen controls whether cells proliferate or exit the cell cycle and differentiate.

We are also investigating why cytotrophoblast invasion is abnormally shallow in preeclampsia, a serious complication of pregnancy characterized by high blood pressure, proteinuria, and intrauterine growth retardation. We hypothesized that this syndrome could be associated with a defect in cytotrophoblast differentiation along the invasive pathway. We have now shown that this is the case. In preeclampsia, the cells start to differentiate, but do not complete the process. This has two important consequences. First, cytotrophoblasts fail to express antigens that are critical for invasion. This observation helps explain why shallow placentation is consistently observed in this syndrome. Second, they fail to mimic a vascular adhesion phenotype. We are very interested in how this failure could be related to the maternal vascular disease.

Additionally, we are intrigued by the immune paradox of pregnancy-the only normal situation in which the host tolerates genetically foreign cells. The methods we developed to study trophoblast invasion have allowed us to ask basic questions about cytotrophoblast expression of molecules that could allow the fetus to avoid rejection. We discovered that invasive cells express a very unusual major histocompatibility antigen, HLA-G, that could play an important role in governing the maternal immune response. Recently we also showed that cytotrophoblasts produce large amounts of IL-10, an immunoinhibitory cytokine, as well as chemokines, which regulate maternal immune cell trafficking.

In parallel, our lab has begun studying the earliest stages of human development using human embryonic stem cells as a model system. Our work to date has focused on deriving additional lines using feeders formed from human placental cells. Additionally, we recently made the surprising discovery that the cells are polarized. Currently, we are investigating how this highly specialized phenomenon is related to pluripotency.

Selected References

Weier, J.F., Weier, H.-U.G., Jung, C.K., Gormley, M.G., Zhou, Y., Chu, L.W., Genbacev, O., Wright, A.A., Fisher, S.J. Human cytotrophoblasts acquire aneuploidies as they differentiate to an invasive phenotype. Dev. Biol. 279: 420-432, 2005.

Hardt, M., Thomas, L.R., Dixon, S.E., Newport, G., Agabian, N., Prakobphol, A., Hall, S.C., Witkowska, H.E., and Fisher, S.J. Toward defining the human parotid gland salivary proteome and peptidome: identification and characterization using 2D SDS-PAGE, ultrafiltration, HPLC and mass spectrometry. Biochemistry 44: 2885-2899, 2005.

Genbacev, O., Krtolica, A., Zdravkovic, T., Brunette, E., Powell, S., Nath, A., Caceres, E., McMaster, M., McDonagh, S., Li, Y., Mandalam. R., Lebkowski, J., and Fisher, S.J. Serum-free derivation of human embryonic stem cell lines on human placental fibroblast feeders. Fertil. Steril. 83: 1517-1529, 2005.

Maltepe, E., Krampitz, G.W., Okazaki, K.M., Red-Horse, K., Mak, W.S., Simon, M.C., and Fisher, S.J. Hypoxia-inducible factor-dependent histone deacetylase activity determines stem cell fate in the placenta. Development. 2005 Aug; 132(15):3393-403

back to faculty list