Parathyroid hormone-like hormone (PTHLH) is abundantly expressed by human endometrial stromal cells during decidualization. However, the role for PTHLH in the decidualization process is unknown.

To examine the effects of PTHLH on the induction and maintenance of decidualization of human uterine fibroblast (HUF) cells in vitro.

HUF cells were treated with a PTHLH siRNA or a PTHLH receptor antagonist (bPTH_7-34) before or after decidualization with medroxyprogesterone acetate (MPA), estradiol (E₂), and prostaglandin E₂ (PGE₂). Decidualization was monitored by immunocytochemistry and the induction of decidualization-specific marker genes, including IGFBP-1, prolactin, lefty, and transcription factor FOXO1.

HUF cells decidualized after pretreatment with a PTHLH siRNA showed greater morphologic changes of decidualization, greater IGFBP-1 protein, and two- to threefold more IGFBP-1, prolactin, lefty, and FOXO1 mRNAs than cells pretreated with a nonsilencing RNA. The PTHLH siRNA pretreated cells also had 31% less DNA fragmentation (TUNEL assay) and 30–35% less caspase 3 levels during decidualization than cells pretreated treated with nonsilencing RNA. Treatment of HUF cells with PTHLH siRNA or bPTH_7-34 at 9 d after the induction of decidualization also resulted in 2.1- to 3.2-fold greater IGFBP-1, prolactin, lefty, and FOXO1 mRNA levels than that noted in control cells treated with nonsilencing RNA.

These finding strongly suggest that PTHLH represses the induction of human decidualization, stimulates stromal cell apoptosis, and limits the extent of uterine stromal cell differentiation. Because PTHLH and its receptor are expressed by HUF cells and placental cells, the inhibitory effect of PTHLH on decidualization appears to be due, at least in part, to an autocrine/paracrine mechanism.