Expression of Mammalian Target of Rapamycin and Downstream Targets in Normal and Gestational Diabetic Human Term Placenta

Mammalian target of rapamycin (mTOR) signaling serves as a central regulator of cell growth, proliferation, and survival by interacting with various proteins. To date, few studies implicated mTOR in placenta. Human placenta in gestational diabetes mellitus (GDM) shows several alterations including villous immaturity, impaired placental function, and overgrowth. Hence, we aimed to investigate the expression of mTOR, phospho-mTOR (p-mTOR), and the 2 phosphorylated downstream targets of mTOR, ribosomal protein S6 kinase 1 (p-p70S6K), and eukaryotic initiation factor 4E-binding protein 1 (p-4EBP1) in normal term and gestational diabetic human placentas. Immunohistochemistry and Western blot were performed with antibodies against mTOR, p-mTOR, p-p70S6K, and p-4EBP1 (Thr37/46) in normal and diabetic placentas (n = 6 each) and quantified by ImageJ. All mTOR pathway components that we studied were immunolocalized in both normal and diabetic placenta groups. Syncytiotrophoblast and the vascular wall in villi displayed cytoplasmic mTOR and p-mTOR (S2448) immunoreactivities in all placenta samples. However, increased expression of p70S6K in syncytiotrophoblast and p-4EBP1 (Thr37/46) in villous stromal cells was observed in gestational diabetic placentas. Western blot analysis also confirmed the statistically significant increase in p-p70S6K (T389) expression in diabetic placentas. The altered expression of downstream components of mTOR signaling in gestational diabetic placentas suggests an involvement of mTOR activity in the placental pathology of GDM. However, whether increased nutrient transport via this pathway will stimulate fetal and placental overgrowth is still unknown. Although this is a descriptive study, further studies with a functional analysis to highlight the molecular mechanisms underlying this placental pathology are proposed.