Context: The initiation of term and preterm labor is associated with an up-regulated inflammatory response in myometrium; however, the underlying signaling pathways remain incompletely defined.
Objective: To define the regulatory mechanisms that mediate the increased myometrial inflammatory response leading to labor, we investigated the roles of microRNAs (miRNA/miR).
Design and setting: Human myometrial tissues, isolated smooth muscle cells, and animal models were used to study miR-181a regulation of uterine inflammatory pathways and contractility.
Patients: Myometrial tissues from 15 term pregnant women undergoing elective cesarean section (not in labor) and 10 term pregnant women undergoing emergency cesarean section (in labor) were used.
Results: Expression of the highly conserved microRNA, miR-181a, was significantly decreased in mouse and human myometrium during late gestation. By contrast, the putative miR-181a targets, TNF-α, and estrogen receptor (ER)-α, and the validated target, c-Fos, key factors in the inflammatory response leading to parturition, were coordinately up-regulated. In studies using human myometrial cells, overexpression of miR-181a mimics repressed basal as well as IL-1β-induced TNF-α, C-C motif chemokine ligand 2 and 8 expression, whereas the expression of the antiinflammatory cytokine, IL-10, was increased. Overexpression of miR-181a dramatically inhibited both spontaneous and IL-1β-induced contraction of human myometrial cells. Notably, miR-181a directly targeted ERα and decreased its expression, whereas estradiol-17β reciprocally inhibited expression of mature miR-181a in myometrial cells.
Conclusions: Thus, increased estradiol-17β/ERα signaling in myometrium near term inhibits miR-181a, resulting in a further increase in ERα and proinflammatory signaling. This escalating feedback loop provides novel targets and therapeutic strategies for the prevention of preterm labor and its consequences.