Overexpression of Copper Zinc Superoxide Dismutase Impairs Human Trophoblast Cell Fusion and Differentiation

Abstract

The syncytiotrophoblast is the major component of the human placenta, involved in feto-maternal exchanges and secretion of pregnancy-specific hormones. Multinucleated syncytiotrophoblast arises from fusion of mononuclear cytotrophoblast cells. In trisomy 21-affected placentas, we recently have shown that there is a defect in syncytiotrophoblast formation and a decrease in the production of pregnancy-specific hormones. Due to the role of oxygen free radicals in trophoblast cell differentiation, we investigated the role of the key antioxidant enzyme, copper/zinc superoxide dismutase, encoded by chromosome 21 in in vitro trophoblast differentiation. We first observed that overexpression of superoxide dismutase in normal cytotrophoblasts impaired syncytiotrophoblast formation. This was associated with a significant decrease in mRNA transcript levels and secretion of hCG and other hormonal markers of syncytiotrophoblast. We confirmed abnormal cell fusion by overexpression of green fluorescence protein-tagged superoxide dismutase in cytotrophoblasts. In addition, a significant decrease in syncytin transcript levels was observed in superoxide dismutase-transfected cells. We then examined superoxide dismutase expression and activity in isolated trophoblast cells from trisomy 21-affected placentas. Superoxide dismutase mRNA expression (P < 0.05), protein levels (P < 0.01), and activity (P < 0.05) were significantly higher in trophoblast cells isolated from trisomy 21-affected placentas than in those from normal placentas. These results suggest that superoxide dismutase overexpression may directly impair trophoblast cell differentiation and fusion, and superoxide dismutase overexpression in Down's syndrome may be responsible at least in part for the failure of syncytiotrophoblast formation observed in trisomy 21-affected placentas.

Hyperglycosylated human chorionic gonadotropin and the source of pregnancy failures

“…Abnormalities in chromosome 21 would seem to be an unlikely cause of our findings. Multiple studies have indicated that genetic abnormalities are a major cause of early pregnancy loss and spontaneous abortion (1)(2)(3)(33)(34)(35). Our data indicate that proportion of hCG-H is the cause, but we cannot totally exclude the possibility these findings could result from genetic abnormalities other than trisomy 21 that may limit hCG-H synthesis and alter cytotrophoblast cell metabolism.…”

“…The possibility that hCG-H imbalance is an effect of genetic abnormalities modulating differentiation of the cytotrophoblast cells must be considered. We examined Down syndrome, or chromosome 21-related abnormalities, as the most common genetic abnormality and as the only disorder equated with hCG-H (33)(34)(35)(36). This genetic abnormality limits the differentiation of cytotrophoblasts to syncytiotrophoblasts, leading to a build up of cytotrophoblast cells (33)(34)(35)(36).…”

“…Seven failures yielded hCG-H proportions very similar to those of the term pregnancies. We inferred that in these seven cases the failure was due to other reasons than hCG-H and implantation, including genetic abnormalities (33)(34)(35), maternal-fetal immune factors (3,4), or factors beyond implantation such as maternal phospholipid antibody syndrome or other known causes of recurrent failure of otherwise normal pregnancies (1,2).…”

Oxidative stress in the placenta

“…Exposure to 9% O 2 impairs cell fusion and differentiation since desmoplakin and E-cadherin persist and a 70% decrease of hCG secretion was observed, suggesting cytotrophoblast aggregation without fusion (Alsat et al 1996). Impaired fusion and differentiation were also observed following overexpression of Cu/ZnSOD, a gene product of chromosome 21, in cytotrophoblasts (Frendo et al 2001). Interestingly, higher levels of Cu/ZnSOD mRNA, protein, as well as enzymatic activity were observed in trisomy 21-affected placentas, where there is a defect in syncytiotrophoblast formation and a decrease in the production of pregnancy-specific hormones.…”

Les raisons de l'élévation de l'hCG dans le sérum de mères porteuses d'un fœtus trisomique

“…La concentration en ARN a été déterminée à 260 nm et leur intégrité a été vérifiée par électrophorèse sur gel d'agarose 1 %. Les niveaux de transcription de la β hCG ont été mesurés dans des homogénats placentaires totaux comme pré-cédemment décrit [15]. Le niveau des transcrits de la sialyltransférase-1 et de la fucosyl-tranférase-1 a été mesuré à partir des cellules en culture.…”