Background
Uncovering the processes that drive labour onset is essential to reduce the adverse consequences of dysfunctional labour. Myometrial cAMP signalling is upregulated during pregnancy promoting uterine quiescence. Changes in its components and effectors have been identified at the onset of term labour. Preterm labour (PTL) treatments targeting this pathway have limited effectiveness and serious maternal effects. In this study, real-time FRET imaging was used to investigate compartmentalised cAMP signals at distinct cellular sites.
Methods
Myometrial biopsies were obtained from women at term or in distinct causes of PTL. Tissues were processed for mRNA and protein extraction or cell isolation. Primary myometrial cells (HPMCs) and an hTERT-HM cell line expressed either a cytosolic (EPAC-SH187) or plasmalemma (AKAP79-CUTie) genetically encoded FRET sensor. The florescence emission changes were monitored following isoproterenol and PGE2 treatment to determine intracellular cAMP concentrations.
Results
Differences in cAMP signalling components were detected in PTL compared to term with variations in effector predominance and an associated increase in OTR expression in twin-PTL. Stimulus-specific subcellular compartmentalisation of cAMP was identified in both cell types with differential regulation by phosphodiesterases (PDEs). Significant disparities were detected in the amplitude, kinetics, and regulation of cAMP signals between the two cell types. For the HPMCs, a prolonged time in culture was associated with a reduction in PDE activity and altered cell phenotype.
Conclusion
The cAMP signalling system is influential in the final pathway of labour, primarily regulating OTR expression. This study established the technique of FRET imaging in human myometrial cells, determining the cell model of choice and culture conditions to explore localised cAMP signalling. The findings provide new insights into the spatial and temporal dynamics of cAMP in the human myometrium and pave the way for unravelling the details of how this fundamental pathway operates and its role in pregnancy and labour.