PPARgamma regulates trophoblast proliferation and promotes labyrinthine trilineage differentiation.

BACKGROUND: Abnormal trophoblast differentiation and function is the basis of many placenta-based pregnancy disorders, including pre-eclampsia and fetal growth restriction. PPARgamma, a ligand-activated nuclear receptor, plays essential roles in placental development; null murine embryos die at midgestation due to abnormalities in all placental layers, in particular, small labyrinth and expanded giant cell layer. Previous studies have focused mostly on the role of PPARgamma in trophoblast invasion. Based on the previously reported role of PPARgamma in preadipocyte differentiation, we hypothesized that PPARgamma also plays a pivotal role in trophoblast differentiation. To test this hypothesis, we report derivation of wild-type and PPARgamma-null trophoblast stem (TS) cells. METHODOLOGY/PRINCIPAL FINDINGS: PPARgamma-null TS cells showed defects in both proliferation and differentiation, specifically into labyrinthine trophoblast. Detailed marker analysis and functional studies revealed reduced differentiation of all three labyrinthine lineages, and enhanced giant cell differentiation, particularly the invasive subtypes. In addition, rosiglitazone, a specific PPARgamma agonist, reduced giant cell differentiation, while inducing Gcm1, a key regulator in labyrinth. Finally, reintroducing PPARgamma into null TS cells, using an adenovirus, normalized invasion and partially reversed defective labyrinthine differentiation, as assessed both by morphology and marker analysis. CONCLUSIONS/SIGNIFICANCE: In addition to regulating trophoblast invasion, PPARgamma plays a predominant role in differentiation of labyrinthine trophoblast lineages, which, along with fetal endothelium, form the vascular exchange interface with maternal blood. Elucidating cellular and molecular mechanisms mediating PPARgamma action will help determine if modulating PPARgamma activity, for which clinical pharmacologic agonists already exist, might modify the course of pregnancy disorders associated with placental dysfunction.

The roadblock light chain binds a novel region of the cytoplasmic Dynein intermediate chain.

Cytoplasmic dynein is the major minus-end directed microtubule-based motor in eukaryotic cells. It is composed of a number of different subunits including three light chain families: Tctex1, LC8, and roadblock. The incorporation of the roadblock light chains into the cytoplasmic dynein complex had not been determined. There are two roadblock genes in mammals, ROBL-1 and ROBL-2. We find that both members of the roadblock family bind directly to all of the intermediate chain isoforms of mammalian cytoplasmic dynein. This was determined with three complementary approaches. A yeast two-hybrid assay demonstrated that both roadblock light chains interact with intermediate chain isoforms from the IC74-1 and IC74-2 genes in vivo. This was confirmed in vitro with both a solid phase blot overlay assay and a solution-binding assay. The roadblock-binding domain on the intermediate chain was mapped to an approximately 72 residue region. The binding domain is downstream of each of the two alternative splice sites in the intermediate chains. This location is consistent with the finding that both roadblock-1 and roadblock-2 show no binding specificity for a single IC74-1 or IC74-2 intermediate chain isoform. In addition, this roadblock-binding domain is significantly downstream from both the Tctex1- and LC8-binding sites, supporting the hypothesis that multiple light chain family members can bind to the same intermediate chain.