Anoctamin Channels in Human Myometrium: A Novel Target for Tocolysis

Background: Spontaneous preterm labor leading to preterm birth is a significant obstetric problem leading to neonatal morbidity and mortality. Current tocolytics are not completely effective and novel targets may afford a therapeutic benefit. Objective: To determine whether the anoctamin (ANO) family, including the calcium-activated chloride channel ANOI, is present in pregnant human uterine smooth muscle (USM) and whether pharmacological and genetic modulation of ANOI modulates USM contraction. Methods: Reverse transcription-polymerase chain reaction (RT-PCR), quantitative RT-PCR, and immuno-histochemical staining were done to determine which members of the ANO family are expressed in human USM. Uterine smooth muscle strips were studied in an organ bath to determine whether ANO I antagonists inhibit oxytocin-induced USM contractions. Anoctamin I small interfering RNA (siRNA) knockdown was performed to determine its effect on filamentous-/globular (F/G)-actin ratio, a measurement of actin polymerization’s role in promoting smooth muscle contraction. Results: Messenger RNA (mRNA) encoding all members of the ANO family (except AN07) are expressed in pregnant USM tissue. Anoctamin I mRNA expression was decreased 15.2-fold in pregnant USM compared to nonpregnant. Anoctamin I protein is expressed in pregnant human USM tissue. Functional organ bath studies with pregnant human USM tissue demonstrated that the ANOI antagonist benzbromarone attenuates the force and frequency of oxytocin-induced contractions. In human USM cells, siRNA knockdown of ANOI decreases F-/G-actin ratios. Conclusion: Multiple members of the ANO family, including the calcium-activated chloride channel ANO I, are expressed in human USM. Antagonism of ANO I by pharmacological inhibition and genetic knockdown leads to an attenuation of contraction in pregnant human USM. Anoctamin I is a potentially novel target for tocolysis.