Lessons from the adrenomedullin knockout mouse

Adrenomedullin is expressed during rodent dental tissue development and promotes cell growth and mineralization

BACKGROUND INFORMATION

ADM (adrenomedullin) has pleiotropic effects, including regulation of inflammation, infection, angiogenesis, mineralized-tissue formation and development. Recently, we demonstrated up-regulation of the ADM transcript in diseased pulpal tissue while the protein is sequestered within the dentine extracellular matrix during dentinogenesis. The present study aimed to characterize ADM localization during rodent dental tissue development and determine its potential effects on dental cells. Finally, we sought to profile ADM transcript levels in adult organs and tissues to compare its expression in teeth relative to other tissues.

RESULTS

Immunohistochemical analysis of developmental rat oral tissues indicated that, at E16 (embryonic day 16), ADM was present in dental epithelium and, by E18, ADM localized to the dental papilla and inner and outer dental epithelia. By E20, ADM was detected in secretory odontoblasts and ameloblasts and exhibited a similar expression profile to that of the key dentinogenesis signalling molecule, TGF-beta1 (transforming growth factor-beta1). Cell growth analysis in the dental MDPC-23, OD-21 and control 3T3 cell lines exposed to ADM (range 10(-15)-10(-7) M) together with EDTA-extracted DMPs (dentine matrix proteins) (range 0.00001-1000 mg/ml) containing comparable concentrations of ADM demonstrated that ADM stimulated a biphasic response in dental cell growth, comparable with that of DMPs, with peak stimulation observed at approximately 10(-11) M. For mineralization analysis, cell lines were exposed to combinations of 50 microg/ml ascorbic acid, 10 mM beta-G (beta-glycerophosphate), 10(-8) M DEX (dexamethasone) and ADM (range 10(-15)-10(-7) M). The results demonstrated that ADM could substitute for DEX to stimulate mineralization. Postnatally, multiple tissue expression profiling indicated abundant ADM levels in tongue and pulpal tissues.

CONCLUSIONS

During oral and dental tissue development ADM initially localizes to epithelial tissue, whereas during later stages it is present in mineralized secreting cells, including odontoblasts. ADM may regulate proliferation and mineralization processes during development, whereas, in adulthood, it may be important for maintaining dental tissue homoeostasis.

Increased adrenomedullin protein content and mRNA expression in human fetal membranes but not placental tissue in pre-eclampsia

The relationship between Pre-eclampsia (PE) and placental production of Adrenomedullin (AdM) is not completely understood. This study measured placental and fetal membrane AdM protein concentrations by specific radioimmunoassay and mRNA expression by Northern blot analysis in samples obtained at either term or preterm gestation from women either in labour or not in labour. Samples were obtained from women with normotensive and pre-eclamptic pregnancies. There were significant increases in immunoreactive AdM protein concentration (pg/mg DNA) in choriodecidua and amnion of women with PE compared to normal pregnancy for the preterm not-in-labour group (choriodecidua: control 124 +/- 16, n = 10, PE 361 +/- 35, n = 10; amnion: control 94 +/- 12, n = 10, PE 153 +/- 19, n = 10) and for the term not-in-labour (choriodecidua: control 128 +/- 17, n = 14, PE 459 +/- 51, n = 8; amnion: control 112 +/- 15, n = 14, PE 253 +/- 57, n = 8) and in-labour (choriodecidua: control 531 +/- 74, n = 14, PE 881 +/- 188, n = 8; amnion: control 545 +/- 84, n = 14, PE 1008 +/- 230, n = 8) groups. AdM mRNA relative abundance was greater in preterm, not-in-labour choriodecidual samples in PE, but not in amnion. In addition, this study observed labour-associated increases in choriodecidual and amniotic irAdM in term pre-eclamptic and control patients. However, there were no significant changes in AdM protein or mRNA expressions between any of the groups for placental tissue. These results suggest that fetal membranes, but not placental, production of AdM is increased at the post-translational level during PE in preterm and term tissues and at the pre-translational level during PE in preterm tissues. Fetal membranes, AdM may play an important role in the regulation of feto-placental hemodynamics and fetal physiology during pre-eclampsia.

New pharmacological strategies in chronic heart failure

Diuretics, ACE inhibitors and betablockers form the cornerstone of pharmacological treatment of chronic heart failure (CHF), while angiotensin receptor blockers are gaining ground. However, despite optimal treatment CHF remains a syndrome with poor prognosis. For this reason, a large number of new agents have been developed as add-on treatment over the last few years. Vasopeptidase inhibitors, moxonidine, endothelin antagonists, vasopressin antagonists, and selective aldosterone antagonists, are some of the new agents that were designed to interfere with different neurohormonal pathways. Immunomodulating agents, growth hormone, caspase inhibitors, adrenomedullin, and erythropoietin have different modes of action, which in general are less understood. Although most of the agents exhibited efficacy in preclinical trials, the clinical results have not always been similarly positive. The results of trials involving vasopeptidase inhibitors, endothelin antagonists, immunomodulating agents, and growth hormone have been disappointing. Other compounds like caspase inhibitors, adrenomedullin, and vasopressin antagonists are still at the early stages of development. Currently, the two most promising agents seem to be erythropoietin and the selective aldosterone receptor blocker eplerenone. In the present article an overview of new pharmacological developments for CHF is given, and the clinical value of these developments is discussed.

Haplotype-Based Case-Control Study Revealing an Association between the Adrenomedullin Gene and Proteinuria in Subjects with Essential Hypertension

Adrenomedullin (AM) has various physiological actions on the cardiovascular system, including vasodilatation, diuresis, natriuresis, inhibition of aldosterone secretion, and increases of the cardiac output, all of which cause hypotension. Since AM plays a role in the pathophysiology of vascular diseases, genes controlling AM might be involved in the development and etiology of essential hypertension (EH). However, there have been few studies examining the relationship between the AM gene and hypertension. The aims of this study were to genotype some of the genetic markers for the human AM gene in Japanese subjects, and via a haplotype-based case-control study, assess the association between and the AM gene and EH or its risk factors, such as hyperlipidemia, renal damage, and proteinuria. We genotyped 205 EH patients and 210 age-matched normotensive (NT) individuals for two single nucleotide polymorphisms of rs4399321, rs7944706 and a microsatellite polymorphism located approximately 5,400 base pairs downstream of the 3' end of the human AM gene. The overall distribution in each variant and haplotype did not significantly differ between the two groups. However, after dividing the groups into those subjects with and without proteinuria, the haplotype analysis revealed a positive association. In conclusion, a possible mutation linked to the haplotype may indicate a genetic predisposition for proteinuria in EH.

Adrenomedullin in vascular diseases

A novel vasodilator, adrenomedullin (AM), which acts as an autocrine/paracrine factor in cardiovascular system, has antiproliferative and antimigrative effects. AM gene transfer prevents the development of cuff-induced vascular injury. Moreover, AM knockout mice exhibited an increase in angiotensin (Ang) II/salt loading-induced coronary arterial lesion, hypoxia-induced pulmonary vascular damage, and cuff-induced vascular injury associated with enhancement in reactive oxygen species (ROS) generation. In addition, AM expression was stimulated by ROS, and AM directly inhibits oxidative stress so that AM might be a negative feedback substance against ROS-induced organ damages. In addition, AM increases nitric oxide and ameliorates insulin resistance, leading to oxidative stress. Consequently, endogenous AM might compensatively inhibit the development of vascular diseases at least partly through an antioxidative effect.