Expression and function of the luteinizing hormone choriogonadotropin receptor in human endometrial stromal cells.

The human luteinising hormone choriogonadotropin receptor (LHCGR) is a G-protein coupled receptor activated by both human chorionic gonadotropin (hCG) and luteinizing hormone (LH), two structurally related gonadotropins with essential roles in ovulation and maintenance of the corpus luteum. LHCGR expression predominates in ovarian tissues where it elicits functional responses through cyclic adenosine mononucleotide (cAMP), Ca2+ and extracellular signal-regulated kinase (ERK) signalling. LHCGR expression has also been localized to the human endometrium, with purported roles in decidualization and implantation. However, these observations are contentious. In this investigation, transcripts encoding LHCGR were undetectable in bulk RNA sequencing datasets from whole cycling endometrial tissue and cultured human endometrial stromal cells (EnSC). However, analysis of single-cell RNA sequencing data revealed cell-to-cell transcriptional heterogeneity, and we identified a small subpopulation of stromal cells with detectable LHCGR transcripts. In HEK-293 cells expressing recombinant LHCGR, both hCG and LH elicited robust cAMP, Ca2+ and ERK signals that were absent in wild-type HEK-293 cells. However, none of these responses were recapitulated in primary EnSC cultures. In addition, proliferation, viability and decidual transformation of EnSC were refractory to both hCG and LH, irrespective of treatment to induce differentiation. Although we challenge the assertion that LHCGR is expressed at a functionally active level in the human endometrium, the discovery of a discrete subpopulation of EnSC that express LHCGR transcripts may plausibly account for the conflicting evidence in the literature.

Bradykinin-activated contractile signalling pathways in human myometrial cells are differentially regulated by arrestin proteins.

Bradykinin is associated with infections and inflammation, which given the strong correlation between uterine infection and preterm labour may imply that it could play a role in this process. Therefore, we investigated bradykinin signalling, and the roles that arrestin proteins play in their regulation in human myometrial cells. Bradykinin induced rapid, transient intracellular Ca(2+) increases that were inhibited following B2 receptor (B2R) antagonism. Arrestin2 or arrestin3 depletion enhanced and prolonged bradykinin-stimulated Ca(2+) responses, and attenuated B2R desensitisation. Knockdown of either arrestin enhanced B2R-stimulated ERK1/2 signals. Moreover, depletion of either arrestin elevated peak-phase p38-MAPK signalling, yet only arrestin3 depletion prolonged B2R-induced p38-MAPK signals. Arrestin2-knockdown augmented bradykinin-induced cell movement. Bradykinin stimulates pro-contractile signalling mechanisms in human myometrial cells and arrestin proteins play key roles in their regulation. Our data suggest bradykinin not only acts as an utertonin, but may also have the potential to enhance the contractile environment of the uterus.