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Date of Award
Daniel A. Rappolee
In general, stress is defined as a noxious factor in a broad spectrum (chemical, biological or physical). Stress response of human body can be divided into three levels----integrate, organ/tissue or cellular response. Trophoblast tem cell (TSC) is one of the earliest differentiated stem cell within blastocyst, which is the stage of preimplantation embryo developed from fertilized egg. Different from another pluripotent embryonic stem cell, which is derived from inner cell mass in blastocyst and develop into fetus, multipotent TSC will specifically differentiate into all kinds of cell subtypes consisting of placenta by which nutrient and oxygen from mom as well as metabolites from fetus can be exchanged.
In our previous studies based upon preimplantation embryo and TSC, four parameters for defining stress are identified: 1) decreased cell accumulation; 2) increased apoptosis; 3) decreased mutipotent markers and increased cell lineage markers; 4) increased activity of stress enzyme SAPK/JNK. By these parameters applying on different oxygen cultured TSC, we identified that 2% oxygen is the optimal oxygen environment for TSC mutipotency maintenance and proliferation. Additionally, TSC cultured in ambient environment in the presence of FGF4 (Fibroblast Growth Factor 4) are actually under a stressful status caused by contradictory signals introduced by FGF4 and 20% oxygen.
Next, we interrogate TSC differentiation at different oxygen levels. Our data show that only TSC differentiated under 20% oxygen can complete the terminal differentiation while differentiation under low oxygen exhibits reduced terminal differentiation by real-time PCR. Even though 0.5%-0% O2 allowed TSC terminal differentiation to some extent, the magnitude of induction of five terminal differentiation markers is significantly reduced comparing with 20% O2, especially those makers for secondary giant cell and syncytiotrophoblast. Mitochondrial charge is at low levels in TSC maintained by FGF4 at all oxygen levels. Upon FGF4 removal, mitochondrial charge undergoes rapid induction at 20% and 2% O2, but remains low level at 0.5% O2. Using SAPK inhibitors, we found that lineage markers for syncytiotrophoblast (GCM1) and for spongiotrophoblast (Tpbpa) were suppressed by SAPK at all oxygen levels, while lineage marker for primary giant cell (Hand-1) was promoted by SAPK. Taken together, our data suggest that 0.5%-0% O2 impaired terminal differentiation of TSC by suppressing mitochondrial activities and ATP production. SAPK play an important role in trophoblast lineage decision-making.
Zhou, Sichang, "Cell lineage choice during differentiation of trophoblast stem cells (tsc) is dependent on oxygen levels, and mediated by stress enzyme pathways and mitochondrial function" (2011). Wayne State University Dissertations. Paper 363.