Reproductive Phenotype of Adrenomedullin2 (ADM2) knockout mice

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Abstract Adrenomedullin2 (ADM2) is a novel hypotensive peptide that promotes trophoblast invasion. Lower ADM2 levels are associated with pregnancy complications such as spontaneous abortion, fetal growth restriction (FGR) and preeclampsia (PE).Pilot data shows that ablation of ADM2 gene causes PE-like manifestations such as elevated blood pressure (BP) and increased serum levels of soluble fms-like tyrosine kinase-1 (sFLT- 1), along with early parturition and increased pup mortality in pregnant ADM2 knockout (ADM-/-) mice. This data strongly supports our published studies showing: 1) Higher placental and serum levels of ADM2 during the invasive phase of placental development in human pregnancy, 2) ADM2 mediated increases in the invasive capacity of 1st trimester extravillous trophoblast cells (EVCTs) in human pregnancy, 3) decreased serum and placental ADM2 levels in PE and decreased ADM2 in amniotic fluid of pregnant women in 2nd trimester who develop PE. Further, while impaired nitric oxide (NO) production and elevated synthesis and secretion of placental sFLT-1 is reported to cause endothelial dysfunction in PE, blocking ADM2 in rat pregnancy decrease placental NO/ matrix metallo-proteinase (MMP) system accompanied with FGR and impaired placental vasculature. In addition, knockdown of ADM2 in trophoblast cells decreases the expression of MMP2, MMP-9 and eNOS mRNA. Therefore, based on above mentioned reports and pilot data, our central hypothesis is that “Global ablation of ADM2 results in pregnancy complications mimicking preeclampsia in human and that, it functions through NO/MMP system “. This hypothesis will be tested using three specific aims. Specific Aim-1: Assess the effect of ADM2 ablation on feto-placental growth, circulatory levels of nitric oxide, 17β-estradiol, progesterone and blood pressure regulation during pregnancy; and identify if NO supplementation can rescue early parturition and increased pup mortality, in ADM2-/- animals, Specific Aim-2: Determine if ablation of ADM2 in mice advances uterine contractility and potentiates uterine contractile responses to stimuli such as oxytocin and prostaglandin-F2α, through increase in their receptor expression and, Specific Aim-3: Identify 1) downstream signaling mechanism involved in the invasive function of ADM2 in EVCTs and, 2) assess if ADM2 supplementation can increase the invasive capacity of EVCTs from PE, which are reported to exhibit less invasive phenotype compared to those from normal pregnancy. Since the majority of studies in humans are limited by their inherent correlative nature, our proposed approach will allow us to characterize the endogenous functions of ADM2 in pregnancy in a series of mechanistic experiments and its potential role in the pathophysiology of PE. These studies could potentially fill the gaps in the knowledge of mediators of placental functions that may hold great potential for the design and implementation of an effective prevention/treatment for pathological pregnancies in women at high risk.