Progesterone Via its Type-A Receptor Promotes Myometrial Gap Junction Coupling

Area of Science:

• Reproductive biology
• Cellular signaling
• Molecular endocrinology

Background:

• Effective labor contractions depend on myometrial cell synchronization via gap junctions (GJs).
• Progesterone (P4) traditionally inhibits connexin-43 (Cx43), the primary GJ component, and GJ formation in the myometrium.
• This study challenges the classical view by investigating P4's differential effects on Cx43 localization.

Purpose of the Study:

• To investigate the role of progesterone receptor isoforms (PRA and PRB) in regulating Cx43 trafficking and GJ formation.
• To elucidate the signaling pathways involved in P4-mediated Cx43 regulation.
• To re-evaluate the role of P4 in myometrial cell synchronization for labor.

Main Methods:

• Immunofluorescence microscopy to assess Cx43 intracellular localization in PRA and PRB expressing myocytes.
• Western blotting to detect Cx43 isoforms and assess protein expression.
• Pharmacological inhibition of mTOR signaling pathway.

Main Results:

• P4 stimulation leads to differential Cx43 localization: GJ formation in PRA-expressing cells but inhibited trafficking in PRB-expressing cells.
• P4, via PRA/B, regulates Cx43 translation, generating a Cx43-20K isoform that promotes full-length Cx43 transport to the plasma membrane.
• P4-mediated Cx43 trafficking and GJ formation occur via a non-genomic pathway involving mTOR signaling; mTOR inhibition rescues the trafficking defect in PRB cells.

Conclusions:

• Progesterone receptor A (PRA) acts as a master regulator of Cx43 expression and GJ formation.
• PRA facilitates Cx43 trafficking and GJ assembly, essential for myocyte connectivity and synchronization during labor.
• Non-genomic P4 signaling through mTOR pathway modulates Cx43 trafficking, impacting myometrial function.