Postpartum acute myometritis suppresses expression of contraction-associated proteins in the gravid uterus.

Uterine atony is a major contributor to postpartum hemorrhage. We previously proposed the novel histological concept of postpartum acute myometritis (PAM) to elucidate the pathophysiology of uterine atony. This concept involves the infiltration of macrophages and neutrophils, as well as mast cell and complement activation in the myometrium. However, the pathological mechanism underlying uterine atony in the context of PAM remains unclear. Herein, we focused on uterine contraction-associated proteins (CAPs) including connexin 43 (Cx43), oxytocin receptors (OXR), prostaglandin receptors EP1, EP3, FP, and protease-activated receptor (PAR)-1. This follow-up study aimed to compare CAP expression between PAM and control groups. We selected 38 PAM subjects from the cases enrolled in our amniotic fluid embolism registry between 2011 and 2018. Control tissues from 10 parturients were collected during cesarean section. We stained the myometrial tissues with the following CAP markers, inflammatory cell markers, and other markers: Cx43, OXR, EP1, EP3, FP, PAR-1, C5a receptor, tryptase, neutrophil elastase, CD68, β-actin, and Na ⁺ /K ⁺ -ATPase. The immunostaining-positive areas of Cx43, OXR, EP1, EP3, and FP standardized by β-actin in the PAM tissue were significantly smaller than in the control group, whereas those of PAR-1 and Na ⁺ /K ⁺ -ATPase increased significantly in the PAM group. The Cx43- and OXR-positive areas correlated negatively with the immunostaining-positive cell numbers of CD68 and tryptase with halo, respectively. PAM may impair individual and synchronized myocyte contraction, leading to uterine atony refractory to uterotonics. Further cell-based studies are needed to elucidate the molecular mechanism by which inflammatory cells suppress CAP expression.
Competing Interests: Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Tomoaki Oda, Naoaki Tamura, Naomi Furuta-Isomura, Naohiro Kanayama, and Hiroaki Itoh report financial support was provided by Japan Society for the Promotion of Science. Hiroaki Itoh reports financial support was provided by Japan Agency for Medical Research and Development. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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