Adrenomedullin stimulates the growth of cultured normal human osteoblasts as an autocrine/paracine regulator

Calcitonin and Bone Physiology: In Vitro, In Vivo, and Clinical Investigations

Calcitonin was discovered as a peptide hormone that was known to reduce the calcium levels in the systemic circulation. This hypocalcemic effect is produced due to multiple reasons such as inhibition of bone resorption or suppression of calcium release from the bone. Thus, calcitonin was said as a primary regulator of the bone resorption process. This is the reason why calcitonin has been used widely in clinics for the treatment of bone disorders such as osteoporosis, hypercalcemia, and Paget's disease. However, presently calcitonin usage is declined due to the development of efficacious formulations of new drugs. Calcitonin gene-related peptides and several other peptides such as intermedin, amylin, and adrenomedullin (ADM) are categorized in calcitonin family. These peptides are known for the structural similarity with calcitonin. Aside from having a similar structure, these peptides have few overlapping biological activities and signal transduction action through related receptors. However, several other activities are also present that are peptide specific. In vitro and in vivo studies documented the posttreatment effects of calcitonin peptides, i.e., positive effect on bone osteoblasts and their formation and negative effect on osteoclasts and their resorption. The recent research studies carried out on genetically modified mice showed the inhibition of osteoclast activity by amylin, while astonishingly calcitonin plays its role by suppressing osteoblast and bone turnover. This article describes the review of the bone, the activity of the calcitonin family of peptides, and the link between them.

The Activity of Peptides of the Calcitonin Family in Bone

Calcitonin was discovered over 50 yr ago as a new hormone that rapidly lowers circulating calcium levels. This effect is caused by the inhibition of calcium efflux from bone, as calcitonin is a potent inhibitor of bone resorption. Calcitonin has been in clinical use for conditions of accelerated bone turnover, including Paget's disease and osteoporosis; although in recent years, with the development of drugs that are more potent inhibitors of bone resorption, its use has declined. A number of peptides that are structurally similar to calcitonin form the calcitonin family, which currently includes calcitonin gene-related peptides (αCGRP and βCGRP), amylin, adrenomedullin, and intermedin. Apart from being structurally similar, the peptides signal through related receptors and have some overlapping biological activities, although other activities are peptide specific. In bone, in vitro studies and administration of the peptides to animals generally found inhibitory effects on osteoclasts and bone resorption and positive effects on osteoblasts and bone formation. Surprisingly, studies in genetically modified mice have demonstrated that the physiological role of calcitonin appears to be the inhibition of osteoblast activity and bone turnover, whereas amylin inhibits osteoclast activity. The review article focuses on the activities of peptides of the calcitonin family in bone and the challenges in understanding the relationship between the pharmacological effects and the physiological roles of these peptides.

Adrenomedullin facilitates calcium channel currents in osteoblasts

Osteoblasts play a major role in bone formation. Osteoblasts employ intracellular Ca(2+) as a second messenger to modulate hormonal responses and a cofactor for bone mineralization. Adrenomedullin (ADM) promotes osteoblast growth and proliferation, inducing an increase in bone mass. Voltage-dependent Ca(2+) channels (VDCCs) mediate the influx of Ca(2+) in response to membrane depolarization. Voltage-dependent Ca(2+) channels serve as crucial mediators of many Ca(2+)-dependent functions, including growth of bone and regulation of proliferation. The purpose of this study was to investigate the effects of ADM on VDCC currents in osteoblasts using a patch-clamp recording method. To our knowledge, the data presented here demonstrate for the first time that ADM facilitates VDCCs in osteoblasts.

Poly(lactic-co-glycolic) acid/nanohydroxyapatite scaffold containing chitosan microspheres with adrenomedullin delivery for modulation activity of osteoblasts and vascular endothelial cells

Adrenomedullin (ADM) is a bioactive regulatory peptide that affects migration and proliferation of diverse cell types, including endothelial cells, smooth muscle cells, and osteoblast-like cells. This study investigated the effects of sustained release of ADM on the modulation activity of osteoblasts and vascular endothelial cells in vitro. Chitosan microspheres (CMs) were developed for ADM delivery. Poly(lactic-co-glycolic) acid and nano-hydroxyapatite were used to prepare scaffolds containing microspheres with ADM. The CMs showed rough surface morphology and high porosity, and they were well-distributed. The scaffolds exhibited relatively uniform pore sizes with interconnected pores. The addition of CMs improved the mechanical properties of the scaffolds without affecting their high porosity. In vitro degradation tests indicated that the addition of CMs increased the water absorption of the scaffolds and inhibited pH decline of phosphate-buffered saline medium. The expression levels of osteogenic-related and angiogenic-related genes were determined in MG63 cells and in human umbilical vein endothelial cells cultured on the scaffolds, respectively. The expression levels of osteogenic-related and angiogenic-related proteins were also detected by western blot analysis. Their expression levels in cells were improved on the ADM delivery scaffolds at a certain time point. The in vitro evaluation suggests that the microsphere-scaffold system is suitable as a model for bone tissue engineering.

Signal transduction pathways mediating the effect of adrenomedullin on osteoblast survival

Adrenomedullin (ADM) plays an important role in the regulation of osteoblastic cells through both a proliferative and an anti-apoptotic effects. The present study investigated mechanisms involved in the effect of ADM on survival. We report that ADM can act in osteoblasts both through a non-transcriptional action, by phosphorylation of different kinases and components, and through a transcriptional effect by activation of CREB. So, we observed by Western blot analysis, modifications in the downstream targets of ERK, the pro-apoptotic protein Bad, which is inactivated by increase in Ser155 phosphorylation, and the transcription factor CREB, which is activated by phosphorylation at Ser133. CREB activation was confirmed by a CRE-dependent gene transcription assay and an immunocytochemical study. This increase in CREB phosphorylation could lead to its enhanced transcriptional activity, as indicated by the induced expression of the proliferation marker, PCNA. Moreover, ADM could also activate the tyrosine kinase Src and the PI3-Kinase, both of which are implicated in survival. The use of specific pharmacological inhibitors allowed to establish that ADM could activate a signaling cascade involving Src, MEK, ERK, p90RSK, and that the effect of ADM, in particular on the CREB protein, greatly depends on the regulatory control of interfering signaling pathways. Moreover, as Wnt signaling plays an important role in the control of osteoblast apoptosis, we explored a major component of this pathway, protein GSK3β. ADM-induced inactivation of GSK3β by phosphorylation at Ser9, highly suggests that ADM could also exert its survival effect in osteoblast via components of the Wnt pathway.

Plasma adrenomedullin and proadrenomedullin N-terminal 20 peptide in patients diagnosed as having early rheumatoid arthritis

The aim of this study was to investigate plasma adrenomedullin (AM) and proadrenomedullin N-terminal 20 peptide (PAMP) level in patients diagnosed with early rheumatoid arthritis (RA). Furthermore, several inflammatory cytokines were measured in those patients to clarify the roles of AM and PAMP. Forty patients diagnosed with early RA (women 46 +/- 8.5 years old) and 10 healthy controls (women 57 +/- 5 years old) were studied. Plasma levels of AM, PAMP, matrix metalloprotease 3 (MMP-3), interleukin 6 (IL-6), tumor necrosis factor alpha (TNF-alpha), and C-reactive protein (CRP) were measured using an immunoradiometric assay and enzyme-linked immunosorbent asay (ELISA) methods. The plasma levels of AM (17.5 +/- 8.4 fmol/ml) and PAMP (2.01 +/- 0.57 fmol/ml) in patients exceeded those in healthy controls (AM 8.6 +/- 1.7, PAMP 1.17 +/- 0.34 fmol/ml). Moreover, plasma AM and PAMP levels demonstrated a significantly positive correlation with plasma MMP-3 and IL-6 levels. Nevertheless, CRP and TNF-alpha levels in these patients showed no significant correlation with plasma AM and PAMP levels. These data support the possible role for AM and PAMP in the pathophysiology of early RA.

Gastrointestinal peptides and bone health

PURPOSE OF REVIEW

To outline recent developments in research surrounding gastrointestinal peptides and their role in skeletal regulation.

RECENT FINDINGS

Bone remodeling is influenced by many regulatory systems, which interact to ensure that the complex demands upon mineralized tissue are met without undue compromise. These include local actions such as mechanical factors, but are dominated by systemic endocrine factors. Although the involvement of hypothalamo-pituitary actions on bone homeostasis is well defined, growing evidence suggests that peripheral tissues and the circulating factors they produce represent an important regulatory axis in bone. Given the critical role of diet in mineral homeostasis, the gastrointestinal tract is a rich source of circulating factors capable of regulating bone homeostasis. After a review of manuscripts on known mechanisms and effects of gastrointestinal peptide on bone, these were summarized.

SUMMARY

Although clearly an exciting and emergent field of research, more studies are required to define the specific actions of gastrointestinal regulator in bone, in particular, the relative contribution of systemic and local effects, to aid interpretation of their potential impact on human health and disease. Nonetheless, this exciting research will further our understanding on bone physiology and provide novel approaches to therapy in a wide range of skeletal conditions.

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.

Adrenomedullin is anti-apoptotic in osteoblasts through CGRP1 receptors and MEK-ERK pathway

Adrenomedullin (ADM) has been shown to mediate multifunctional responses in cell culture and animal system such as regulation of growth and apoptosis. ADM stimulates the proliferation of osteoblasts in vitro and promotes bone growth in vivo. The ability of ADM to influence osteoblastic cell number through inhibition of apoptosis has not yet been studied. To address this question we have investigated its effect on the apoptosis of serum-deprived osteoblastic cells using mouse MC3T3-E1 cells which express both ADM and ADM receptors. Treatment with ADM significantly blunted apoptosis, evaluated by caspase-3 activity, DNA fragmentation quantification and annexin V-FITC labeling. This effect was abolished by the subtype-1 CGRP receptor antagonist, CGRP(8-37). Both ADM and its specific receptor antagonist, the (22-52) ADM fragment exhibited a similar anti-apoptotic effect. Thus, our data suggest that ADM exerts anti-apoptotic effects through CGRP1 receptors. This was substantiated by a similar protective effect of CGRP on MC3T3-E1 cells apoptosis. Accordingly, neutralization of endogenous ADM by a specific antibody enhanced apoptosis. Finally, the selective inhibitor of MAPK kinase (MEK), PD98059, abolished the apoptosis protective effect of ADM and prevented ADM activation of ERK1/2. These data show that ADM acts as a survival factor in osteoblastic cells via a CGRP1 receptor-MEK-ERK pathway, which provides further understanding on the physiological function of ADM in osteoblasts.

Expression of type 2 iodothyronine deiodinase in human osteoblast is stimulated by thyrotropin

Thyroid hormones play important roles in bone growth, development, and turnover. To exert its biological activity, T(4) needs to be converted to T(3) by iodothyronine deiodinase. In human thyroid gland as well as rat brown adipose tissue, type 2 iodothyronine deiodinase (D2) expression is regulated by a TSH receptor-cAMP-mediated mechanism. TSH receptor knockout mice demonstrated the direct effects of TSH on bone via TSH receptors found on osteoblast and osteoclast precursors. In the present study we investigated the possible expression and function of iodothyronine deiodinase and TSH receptors in human osteoblast-like osteosarcoma (SaOS-2) cells and normal human osteoblast (NHOst) cells. Iodothyronine deiodinase activity was detected in SaOS-2 cells and NHOst cells, and all of the characteristics of deiodinating activity were compatible with those of D2. Northern analysis demonstrated D2 mRNA expression in SaOS-2 cells and NHOst cells. D2 mRNA levels as well as D2 activities were rapidly increased by dibutyryl cAMP or forskolin in SaOS-2 cells and NHOst cells. TSH receptor mRNA was demonstrated in SaOS-2 cells and NHOst cells, and D2 mRNA and D2 activity were stimulated by TSH in both cells. In addition, all T(3) receptor isoforms were detected by RT-PCR in SaOS-2 cells and NHOst cells. The present results indicate the expression of functional TSH receptors and D2 in human osteoblasts and suggest previously unrecognized roles of TSH receptors and local T(3) production by D2 in the pathophysiology of human osteoblasts.

Effects of peptides, with emphasis on feeding, pain, and behavior A 5-year (1999-2003) review of publications in Peptides

Novel effects of naturally occurring peptides are continuing to be discovered, and their mechanisms of actions as well as interactions with other substances, organs, and systems have been elucidated. Synthetic analogs may have actions similar or antagonistic to the endogenous peptides, and both the native peptides and analogs have potential as drugs or drug targets. The journal Peptides publishes many leading articles on the structure-activity relationship of peptides as well as outstanding reviews on some families of peptides. Complementary to the reviews, here we extract information from the original papers published during the past five years in Peptides (1999-2003) to summarize the effects of different classes of peptides, their modulation by other chemicals and various pathophysiological states, and the mechanisms by which the effects are exerted. Special attention is given to peptides related to feeding, pain, and other behaviors. By presenting in condensed form the effects of peptides which are essential for systems biology, we hope that this summary of existing knowledge will encourage additional novel research to be presented in Peptides.

RAMPs and CRLR expressions in osteoblastic cells after dexamethasone treatment

Adrenomedullin (ADM) is a potent stimulator of osteoblastic activity and promotes bone growth in vivo. ADM receptors are formed by heterodimerization of the CRLR and a RAMP2 or RAMP3 molecule. Since glucocorticoid responsive elements were recently identified in the human CRLR promoter and that glucocorticoids exert a major action in bones, we investigated the acute effect of dexamethasone (Dex) treatment on ADM receptor components in osteoblastic cell types: the MC3T3-E1 cells and calvaria-derived osteoblastic cells. Changes in expression of CRLR and RAMPs molecules were evaluated at mRNA levels using RT-PCR and at protein levels by Western blot analysis. We found that Dex increased expression of RAMP1 and RAMP2 mRNA in a time-dependent but dose-independent manner, while RAMP3 was unchanged. In contrast, Dex decreased the CRLR mRNA expression and these changes were reflected at protein levels. We suggest that Dex, in osteoblastic cells, altered ADM receptor by inhibition of CRLR expression and consequently could impair the ADM anabolic effect on bone. Our findings could explain in part, the detrimental side effects observed at bone level during glucocorticoid therapy.