$STUDY\; QUESTION$: Does endothelin-1 (ET-1) regulate matrix metalloproteinase (MMP) 14 and 15 production and invasion of human first trimester trophoblasts?

$SUMMARY\; ANSWER$: ET-1 in pathophysiological concentrations down-regulates MMP14 and MMP15 expression via endothelin receptor (ETR) type B and decreases trophoblast migration and invasion.

$WHAT\; IS\; KNOWN\; ALREADY$: MMP14 and MMP15 are involved in trophoblast invasion. Impairment of invasion has been linked to pregnancy complications such as pre-eclampsia (PE). ET-1 is up-regulated in PE.

$STUDY\; DESIGN,\; SIZE,\; DURATION$: $In\; vitro$ study using primary human trophoblasts from 50 first trimester placentas (gestational week 7-12).

$PARTICIPANTS/MATERIALS,\; SETTING,\; METHODS$: Trophoblasts were cultured in the absence or presence of 10-100 nM ET-1. MMP14 and MMP15 mRNA and protein were quantified by RT-qPCR and Western blotting, respectively. Selective antagonists for ETRA (BQ-123) or ETRB (BQ-788) were used to identify ETR subtypes involved. Functional ET-1 effects were tested in first trimester chorionic villous explants and transwell invasion assays. The roles of tumor necrosis factor (TNF)-α (25 ng/ml) and oxygen (1%) in ET-1 regulation of MMP14 and 15 expression were assessed by Western blotting.

$MAIN\; RESULTS\; AND\; THE\; ROLE\; OF\; CHANCE$: ET-1 down-regulated MMP14 and MMP15 mRNA (-21% and -26%, respectively, $P$ < 0.05) and protein levels (-18% and -22%, respectively, $P$ < 0.05). This effect was mediated via ETRB. ET-1 decreased trophoblast outgrowth in placental explants (-24%, $P$ < 0.05) and trophoblast invasion (-26%, $P$ ≤ 0.01). TNF-α enhanced ET-1 mediated MMP15 down-regulation (by 10%, $P$ < 0.05), whereas hypoxia abolished the effect of ET-1 on both MMPs.

$LARGE\; SCALE\; DATA$: N/A.

$LIMITATIONS,\; REASONS\; FOR\; CAUTION$: Only primary trophoblasts were used in this study. Since trophoblast yield from first trimester placental material is limited, further aspects of MMP14 and 15 regulation could not be characterized. Other anti-invasive factors may be altered by ET-1 in trophoblasts and, thus, contribute to the reduced invasion, but have not been investigated. Oxygen levels similar to those found in the decidua (5-8% O2) were not analyzed in this study.

$WIDER\; IMPLICATIONS\; OF\; THE\; FINDINGS$: ET-1 modifies placental function already during the first trimester of pregnancy, the time-window when the placental changes implicated in PE occur. Thus, our results improve the understanding of the placental mechanisms underlying trophoblast invasion and PE.