Critical Role of TRPC1-Mediated Ca2+ Entry in Decidualization of Human Endometrial Stromal Cells

Decidualization is an ovarian steroid-induced remodeling/differentiation process of uterus essential for embryo implantation and placentation. Here, we investigated the possible involvement of enhanced Ca2+ dynamics in the decidualization process in human endometrial stromal cells (hESC) in its connection with a recently emerging nonvoltage-gated Ca2+ entry channel superfamily, the transient receptor potential (TRP) protein. Combined application of 17β-estradiol (E2) (10 nm) and progesterone (P4) (1 μm) for 7–14 d resulted in morphological changes of hESC characteristic of decidualization (i.e. cell size increase), whereas sole application of E2 exerted little effects. A 7- to 14-d E2/P4 treatment greatly increased the expression level of decidualization markers IGF binding protein-1 (IGFBP-1) and prolactin and also up-regulated the expression of TRPC1, a canonical TRP subfamily member that has been implicated in store-operated Ca2+ influx (SOC) in other cell types. In parallel with this up-regulation, SOC activity in hESC, the nuclear translocation of phosphorylated cAMP responsive element binding protein (p-CREB) and the expression of Forkhead box protein 01 were enhanced significantly. Small interfering RNA knockdown of TRPC1 counteracted the E2/P4-induced up-regulation of IGFBP-1 and prolactin and enhancement of SOC activity together with the inhibition of hESC size increase, p-CREB nuclear translocation, and FOXO1 up-regulation. Coadministration of SOC inhibitors SK&F96365 or Gd3+ with E2/P4 also suppressed the up-regulation of IGFBP-1 and hESC size increase. Similar inhibitory effects were observed with extracellularly applied TRPC1 extracellular loop 3-directed antibody, which is known to bind a near-pore domain of TRPC1 channel and block its Ca2+ transporting activity. These results strongly suggest that up-regulation of TRPC1 protein and consequent enhancement of SOC-mediated Ca2+ influx may serve as a crucial step for the decidualization process of hESC probably via p-CREB-dependent transcriptional activity associated with FOXO1 activation.