Formation of Syncytial Knots is Increased by Hyperoxia, Hypoxia and Reactive Oxygen Species

(A) The number of syncytial knots are increased in IUGR and pre-eclampsia compared to normal term pregnancy (*p<0.05, **p<0.01). (B) The number of syncytial knots is increased in villous explants cultured in hyperoxic and hypoxic conditions compared to fresh tissue and that cultured in normoxic conditions (**p<0.01, ***p<0.001). (C) The number of syncytial knots is increased following exposure to hydrogen peroxide (*p<0.05, ***p<0.001). (D) Micrograph of terminal villi from normal term placenta showing a single syncytial knot marked by open arrow. (E) Micrograph of terminal villi from pre-eclamptic pregnancy showing increased numbers of syncytial knots (open arrows) and areas of syncytiotrophoblast with few nuclei (shown within ellipse). (F) Micrograph of terminal villi exposed to hydrogen peroxide for 6h showing increased numbers of syncytial knots (open arrows) and areas of syncytiotrophoblast depleted of nuclei (shown within ellipse).

Electron micrographs. (A) Syncytial knot (SKT) in normal term placenta showing nuclei at different stages of degeneration. There is a healthy cytotrophoblast (CT) underlying the SKT. (B) Syncytial knot in placental explant exposed to ROS showing a homogenous appearance of nuclei at similar stages of degeneration. Nuclear pore (NP) complexes can be seen where euchromatin is in contact with the nuclear envelope. NP complexes are absent in nuclei with dense peripheral heterochromatin (marked with open arrows). (C) Syncytial knot in pre-eclampsia. The nuclei show signs of advanced degeneration. (D) Syncytial knot in explant exposed to hypoxia demonstrating condensation of the nuclear membrane (NM) and gap between the nuclear membrane and heterochromatin. (E) Nuclei within a syncytial knot of a post-mature placenta, showing a heterochromatin (HC):euchromatin (EC) ratio. An annulate lamella (AL) is seen in association with a degenerating nucleus. (F) High magnification of syncytial knot in placental explant exposed to hyperoxia showing a longitudinal structure (LS) lying between two degenerating nuclei. All bars: 5μm.

Micrographs of terminal villi showing localisation of (A) Bcl-2, (B) Mdm-2, (C) XIAP, and (D) Survivin. All are present in the syncytiotrophoblast cytoplasm surrounding syncytial knots (SKT). (E) Negative control incubated with non-immune mouse IgG. (F) Negative control with 10% normal goat serum. All micrographs: original magnification ×1000. Scale bar: 10μm.