Evaluation of changes of apelin and apelin receptor (APJ) expression in cervix-uterus and placental axis in an LPS-induced labor model

Although preterm birth is among the preventable causes of maternal and infant death, its mechanism has not yet been clarified. When evaluated in terms of the results, the psycho-social burden of mother-infant losses and the costs of rehabilitation, care, and treatment for postpartum sequelae are high. When evaluated in terms of its causes, infection/inflammation has an important place. Therefore, it is essential to understand the role of pro-and anti-inflammatory proteins in the process. In our study, apelin and apelin receptor (APJ) expression in the cervix-uterus and placental axis were evaluated at tissue and protein levels in pregnant and non-pregnant control, sham, PBS, and LPS groups in the infection model in which LPS induction was performed by midline laparotomy, in CD-1 mice. The evaluation of this axis regarding apelin and apelin receptor in the preterm birth model is new in the literature. Apelin is expressed more intensely in uterine epithelial cells than in the cervix. In the placenta, expression is more intense in the junctional zone compared to other zones. Apelin protein levels decrease significantly in the cervix and placenta whereas it increases in the uterus. While no change was observed in the expres- sion of the apelin receptor at the tissue and protein level in the cervix and uterus, it increased in both aspects in the placenta in the invasive procedure groups. We propose that the decrease in apelin protein due to LPS in the preterm delivery model may be related to the effort to compensate for the balance deteriorated in the pro-inflammatory direction with post-transitional modification at the tissue level. The tendency of apelin to increase with pregnancy has led to the conclusion that it is necessary for a healthy pregnancy. Although the apelin receptor does not change with inflammation, it is necessary to investigate the mechanisms associated with its stress and trauma-induced increase, since it increases in the invasive procedure group.