adrenomedullin and Fetal-Death

Adrenomedullin (AM) is a multifunctional peptide vasodilator that is essential for life. To date, numerous in vitro studies have suggested that AM can mediate its biological effects through at least three different receptors. To determine the in vivo importance of the most likely candidate receptor, calcitonin receptor-like receptor, a gene-targeted knockout model of the gene was generated. Mice heterozygous for the targeted Calcrl allele appear normal, survive to adulthood, and reproduce. However, heterozygote matings fail to produce viable Calcrl-/- pups, demonstrating that Calcrl is essential for survival. Timed matings confirmed that Calcrl-/- embryos die between embryonic day 13.5 (E13.5) and E14.5 of gestation. The Calcrl-/- embryos exhibit extreme hydrops fetalis and cardiovascular defects, including thin vascular smooth muscle walls and small, disorganized hearts remarkably similar to the previously characterized AM-/- phenotype. In vivo assays of cellular proliferation and apoptosis in the hearts and vasculature of Calcrl-/- and AM-/- embryos support the concept that AM signaling is a crucial mediator of cardiovascular development. The Calcrl gene targeted mice provide the first in vivo genetic evidence that CLR functions as an AM receptor during embryonic development.

Topics: Adrenomedullin; Animals; Apoptosis; Cardiovascular Abnormalities; Cell Proliferation; Embryo Loss; Fetal Death; Gestational Age; Hydrops Fetalis; Mice; Mice, Knockout; Muscle, Smooth, Vascular; Myocardium; Myocytes, Cardiac; Peptides; Receptors, Calcitonin; Recombination, Genetic

Adrenomedullin (AM) is a multifunctional peptide vasodilator that is essential for life. Plasma AM expression dramatically increases during pregnancy, and alterations in its levels are associated with complications of pregnancy including fetal growth restriction (FGR) and preeclampsia. Using AM+/- female mice with genetically reduced AM expression, we demonstrate that fetal growth and placental development are seriously compromised by this modest decrease in expression. AM+/- female mice had reduced fertility characterized by FGR. The incidence of FGR was also influenced by the genotype of the embryo, since AM-/- embryos were more often affected than either AM+/- or AM+/+ embryos. We demonstrate that fetal trophoblast cells and the maternal uterine wall have coordinated and localized increases in AM gene expression at the time of implantation. Placentas from growth-restricted embryos showed defects in trophoblast cell invasion, similar to defects that underlie human preeclampsia and placenta accreta. Our data provide a genetic in vivo model to implicate both maternal and, to a lesser extent, embryonic levels of AM in the processes of implantation, placentation, and subsequent fetal growth. This study provides the first genetic evidence to our knowledge to suggest that a modest reduction in human AM expression during pregnancy may have an unfavorable impact on reproduction.

Topics: Adrenomedullin; Animals; Decidua; Embryo Implantation; Embryo Loss; Embryonic Development; Female; Fertility; Fetal Death; Fetal Development; Fetal Growth Retardation; Gene Expression; Genotype; Heterozygote; Litter Size; Mice; Mice, Knockout; Placenta; Placentation; Pregnancy; Sex Factors; Trophoblasts; Uterus

Adrenomedullin, a recently identified potent vasodilator, is expressed widely and has been suggested to have functions ranging from reproduction to blood pressure regulation. To elucidate these functions and define more precisely sites of Adm expression, we replaced the coding region of the Adm gene in mice with a sequence encoding enhanced green fluorescent protein while leaving the Adm promoter intact. We find that Adm(-/-) embryos die at midgestation with extreme hydrops fetalis and cardiovascular abnormalities, including overdeveloped ventricular trabeculae and underdeveloped arterial walls. These data suggest that genetically determined absence of Adm may be one cause of nonimmune hydrops fetalis in humans.

Topics: Abnormalities, Multiple; Adrenomedullin; Animals; Aorta; Carotid Arteries; Chimera; DNA, Complementary; Female; Fetal Death; Fetal Heart; Gene Expression Regulation, Developmental; Gene Targeting; Genes, Reporter; Genotype; Gestational Age; Green Fluorescent Proteins; Heart Ventricles; Hydrops Fetalis; Luminescent Proteins; Male; Mice; Mice, Knockout; Peptides; Recombinant Fusion Proteins; Reverse Transcriptase Polymerase Chain Reaction