Focal adhesion kinase is a key mediator of human trophoblast development

Trophoblast differentiation during the first trimester of pregnancy involve s cell proliferation and invasion and extracellular matrix (ECM) remodeling . Reports have indicated that, in a variety of cell types, processes such a s proliferation, invasion, and ECM remodeling require the turnover of focal adhesions mediated by a cytoplasmic tyrosine kinase named focal adhesion k inase (FAKE. Therefore, in the present study we examined the expression and spatial localization of FAK during early human placental development. Immu nocytochemical and immunoblot analysis showed that FAK and a focal adhesion -associated protein named paxillin were highly expressed between the 5th an d 8th weeks of gestation, specifically in villous cytotrophoblast and extra villous trophoblast (EVT) cells. Activated FAK, phosphorylated on Tyr-397, colocalized with alpha5 integrin and matrix metalloproteinase-2 (MMP2) expr ession in EVT cells within a previously characterized Intermediate, invasiv e-restrained region. FAK and paxillin expression dramatically decreased aft er 10 to 12 weeks of gestation coincident with increasing pO(2) levels. Exp osure of human villous explants of 5 to 8 weeks to a 3% O-2 environment res ulted in increased trophoblast outgrowth, cell proliferation, and detection of a5 integrin and MMP2, as well as increased activation of FAK in EVT cel ls compared with explants grown in a 20% O-2 environment. To determine whet her FAK was a key requisite for trophoblast differentiation, villous explan ts of 5 weeks gestation were grown in Matrigel in a 3% O-2 environment and incubated with 20-mer antisense FAK oligonucleotides. A dramatic reduction of trophoblast outgrowth was observed in antisense-treated explants compare d with missense and control cultures, and, in addition, cell proliferation and MMP2 activity in anti sense-treated explants were dramatically reduced. These data suggest that FAK is a key kinase Involved in early trophoblast cell differentiation and plays a role in regulating cell proliferation and motility during early placental development.