Expression of the adrenomedullin gene in adipose tissue

Higher serum adrenomedullin concentration is associated with an increased risk of gestational diabetes mellitus: A nested case-control study in Wuhan, China

Adrenomedullin (ADM) is thought to play a significant role in regulating insulin secretion and glucose metabolism. However, studies on the relationship between ADM and gestational diabetes mellitus (GDM) are limited. We hypothesized that a higher serum ADM concentration would be associated with an increased risk of GDM. Therefore, a nested case-control study of 65 GDM cases and 130 prepregnancy body mass index, age, parity, and gestational age of blood collection-matched controls was conducted to prospectively evaluate the association between circulating ADM concentrations in early pregnancy and the risk of GDM in pregnant women based on the Tongji Birth Cohort. Serum ADM concentrations in the GDM group were higher than those in the control group (2125.04 ± 644.97 vs 1880.76 ± 581.13 pg/mL) (P = .008). Serum ADM concentration was positively associated with the risk of developing GDM (P_trend < .05). The adjusted odds ratio (OR) comparing the highest tertile of ADM with the lowest was 2.74 (95% CI, 1.17-6.43). The risk of GDM increased by 49% (OR, 1.49; 95% CI, 1.05-2.12) for each SD increment of serum ADM. Moreover, serum ADM concentration was positively correlated with circulating total cholesterol (r = 0.204), triglycerides (r = 0.197), and systolic blood pressure (r = 0.173), but negatively correlated with circulating high-density lipoprotein cholesterol concentration (r = -0.176). Pregnant women with higher serum ADM concentrations have a markedly increased risk of developing GDM. Further studies are warranted to explore the possible thresholds of ADM that increase the risk of GDM and to confirm and elucidate the underlying mechanisms.

Associations of the vasoactive peptides CT-proET-1 and MR-proADM with incident type 2 diabetes: results from the BiomarCaRE Consortium

BACKGROUND

Endothelin-1 (ET-1) and adrenomedullin (ADM) are commonly known as vasoactive peptides that regulate vascular homeostasis. Less recognised is the fact that both peptides could affect glucose metabolism. Here, we investigated whether ET-1 and ADM, measured as C-terminal-proET-1 (CT-proET-1) and mid-regional-proADM (MR-proADM), respectively, were associated with incident type 2 diabetes.

METHODS

Based on the population-based Biomarkers for Cardiovascular Risk Assessment in Europe (BiomarCaRE) Consortium data, we performed a prospective cohort study to examine associations of CT-proET-1 and MR-proADM with incident type 2 diabetes in 12,006 participants. During a median follow-up time of 13.8 years, 862 participants developed type 2 diabetes. The associations were examined in Cox proportional hazard models. Additionally, we performed two-sample Mendelian randomisation analyses using published data.

RESULTS

CT-proET-1 and MR-proADM were positively associated with incident type 2 diabetes. The multivariable hazard ratios (HRs) [95% confidence intervals (CI)] were 1.10 [1.03; 1.18], P = 0.008 per 1-SD increase of CT-proET-1 and 1.11 [1.02; 1.21], P = 0.016 per 1-SD increase of log MR-proADM, respectively. We observed a stronger association of MR-proADM with incident type 2 diabetes in obese than in non-obese individuals (P-interaction with BMI < 0.001). The HRs [95%CIs] were 1.19 [1.05; 1.34], P = 0.005 and 1.02 [0.90; 1.15], P = 0.741 in obese and non-obese individuals, respectively. Our Mendelian randomisation analyses yielded a significant association of CT-proET-1, but not of MR-proADM with type 2 diabetes risk.

CONCLUSIONS

Higher concentrations of CT-proET-1 and MR-proADM are associated with incident type 2 diabetes, but our Mendelian randomisation analysis suggests a probable causal link for CT-proET-1 only. The association of MR-proADM seems to be modified by body composition.

Endoglin and Activin Receptor-like Kinase 1 (Alk1) Modify Adrenomedullin Expression in an Organ-Specific Manner in Mice

Simple Summary

Hereditary hemorrhagic telangiectasia (HHT) is called a rare disease because it affects relatively few people. It is characterized by malformations in some blood vessels and usually results in profuse nose bleedings. In a recent article, we found that these patients have higher levels of adrenomedullin (AM), a molecule with cardiovascular activities, than healthy people. Thus we wanted to know whether the mutations that cause the HHT disease are directly responsible for these higher levels of AM. To investigate this issue, we used mutant mice, which express lower levels of the genes involved in the disease (called Eng and Acvrl1), and measured how much AM was found in different tissues. Although we expected a higher amount of AM in all organs, that was not the case. Some organs showed no variation, some had lower levels of AM than normal mice (fat, skin, and adrenals), and others had a higher expression (cerebellum and colon). Interestingly, our results suggest that these genes and the related molecule BMP-9 may have novel functions, which have not been yet investigated, which may shed more light on the physiopathology of HHT.

Abstract

Hereditary hemorrhagic telangiectasia (HHT) is a rare disease characterized by vascular malformations and profuse bleeding. The disease is caused by mutations in the components of the BMP-9 receptor: endoglin (ENG) and activin receptor-like kinase 1 (ACVRL1) genes. Recently, we reported that HHT patients expressed higher serum levels of adrenomedullin (AM) than healthy volunteers; thus, we studied the expression of AM (by enzyme immunoassay, qRT-PCR, immunohistochemistry, and Western blotting) in mice deficient in either one of the receptor components to investigate whether these defects may be the cause of that elevated AM in patients. We found that AM expression is not affected by these mutations in a consistent pattern. On the contrary, in some organs (blood, lungs, stomach, pancreas, heart, kidneys, ovaries, brain cortex, hippocampus, foot skin, and microvessels), there were no significant changes, whereas in others we found either a reduced expression (fat, skin, and adrenals) or an enhanced production of AM (cerebellum and colon). These results contradict our initial hypothesis that the increased AM expression found in HHT patients may be due directly to the mutations, but open intriguing questions about the potential phenotypic manifestations of Eng and Acvrl1 mutants that have not yet been studied and that may offer, in the future, a new focus for research on HHT.

Plasma adrenomedullin level and year-by-year variability of body mass index in the general population

Plasma levels of the hypotensive peptides of adrenomedullin and atrial and B-type natriuretic peptides (AM, ANP, BNP) are possible biomarkers for cardiovascular diseases. Increased variability of body mass index (BMI) over a certain period of time has been reported to be associated with cardiovascular morbidity or mortality. The aim of this study is to examine clinical significance of those hypotensive peptides as biomarkers by analyzing the relationship between plasma levels of the peptides and year-by-year variability of BMI in the general population without overt cardiovascular diseases. The subjects were 427 local residents (141 males and 286 females) attending their annual health check-up, who had been examined at least 5 times over the preceding period of 10 years. They were divided into two groups of low or high variability by the median of coefficient of variation (CV) of BMI values for each gender. Plasma AM levels of those with high year-by-year variability of BMI were significantly increased, as compared to the group with low variability, in both genders; meanwhile, such a difference was not noted in plasma levels of the natriuretic peptides. No significant differences were found in the basal parameters, which could affect plasma AM level, such as age, BMI, blood pressure or serum creatinine, between two groups. In conclusion, increase in plasma AM was associated with high year-by-year variability of BMI in the general population without overt heart disease. This relationship between the two suggests that increased plasma AM level is a cardiovascular risk marker.

Brief high fat high sugar diet results in altered energy and fat metabolism during pregnancy in mice

During pregnancy several maternal adaptations occur in order to support the growing fetus which are further exacerbated by gestational diabetes mellitus (GDM). Previously we developed a mouse model of GDM, however we did not evaluate alterations to energy and fat metabolism. We have also shown that alterations in lipid metabolism are mediated by adrenomedullin (ADM) in normal and GDM pregnancies. Our objectives were: (1) evaluate energy and fat homeostasis in our GDM mouse model and (2) determine if ADM may play a role in these changes. Female mice were placed on either control (P-CD) or high fat, high sucrose diet (P-HFHS) 1 week prior to and throughout pregnancy. Mice were placed into comprehensive lab animal monitoring system (CLAMS) chambers throughout pregnancy. Visceral adipose tissue (VAT) was collected at d17.5 of pregnancy for analysis. Energy Expenditure was significantly increased (p < 0.05) in P-HFHS dams compared to all other groups. VAT ex-vivo lipolysis was increased (p < 0.05) in P-HFHS compared to P-CD dams. VAT gene expression of ADM receptors Crlr, Ramp2, and Ramp3 was increased (p < 0.05) in P-HFHS dams. ADM dose dependently increased ex vivo lipolysis. This data further validates our animal model of GDM and is usefulness in investigating the pathophysiology of GDM.

Midregional Proadrenomedullin Can Reflect the Accumulation of Visceral Adipose Tissue-A Key to Explaining the Obesity Paradox

Background: The aim of this study was to investigate whether plasma midregional proadrenomedullin (MR-proADM) reflected body composition, such as body mass index (BMI), visceral adipose tissue (VAT), subcutaneous adipose tissue (SAT), VAT/SAT ratio, body fat mass (BFM), and skeletal muscle mass (SMM). Methods: A total of 2244 individuals (727 men and 1517 women) were included in the study. Multiple regression analysis was performed to assess the combined influence of variables: age, daily alcohol consumption, Brinkman index, sleeping time, metabolic equivalents, anamnesis for hypertension, dyslipidemia, diabetes, and body composition of MR-proADM, by using a stepwise forward selection method. Results: MR-proADM was significantly related to all anthropometric indices (BMI, VAT, SAT, VAT/SAT ratio, BFM, and SMM) in men and women. On the basis of a stepwise forward selection method, VAT (men: beta = 0.184, p < 0.001, women: beta = 0.203, p < 0.001) and BFM (beta = 0.181, p < 0.001) in women, were found to be significantly associated with MR-proADM. Conclusion: This study suggests that plasma MR-proADM concentration is a more reliable indicator of VAT for fat distribution, and thus, MR-proADM may help better understand the obesity paradox. Changes in circulating levels of MR-proADM could possibly reflect changes in body composition, endocrine, and metabolic milieu.

Dietary intake of bioactive ingredients impacts liver and adipose tissue transcriptomes in a porcine model of prepubertal early obesity

Global prevalence of obesity has increased to epidemic proportions over the past 40 years, with childhood obesity reaching alarming rates. In this study, we determined changes in liver and adipose tissue transcriptomes of a porcine model for prepubertal early obesity induced by a high-calorie diet and supplemented with bioactive ingredients. A total of 43 nine-weeks-old animals distributed in four pens were fed with four different dietary treatments for 10 weeks: a conventional diet; a western-type diet; and a western-type diet with Bifidobacterium breve and rice hydrolysate, either adding or not omega-3 fatty acids. Animals fed a western-type diet increased body weight and total fat content and exhibited elevated serum concentrations of cholesterol, whereas animals supplemented with bioactive ingredients showed lower body weight gain and tended to accumulate less fat. An RNA-seq experiment was performed with a total of 20 animals (five per group). Differential expression analyses revealed an increase in lipogenesis, cholesterogenesis and inflammatory processes in animals on the western-type diet while the supplementation with bioactive ingredients induced fatty acid oxidation and cholesterol catabolism, and decreased adipogenesis and inflammation. These results reveal molecular mechanisms underlying the beneficial effects of bioactive ingredient supplementation in an obese pig model.

Adrenomedullin has a role in angiogenic effects of resveratrol in adipose tissues of obese female rats

Obesity is a complex, chronic disease that arises according to the interaction between genetic and environmental factors. The expansion and growth of white adipose tissue (WAT) could be related to angiogenesis. Resveratrol and adrenomedullin (AdM) were used for the inhibition of angiogenesis in metabolically passive WAT for inhibiting the expansion of this tissue, and the activation of angiogenesis in metabolically active brown adipose tissue (BAT) for increasing daily energy consumption as a way of reducing obesity. Rats were divided into eight groups. Four obese groups were fed with a high-fat diet containing 60% fat as energy for three months. After obtaining obesity, 2.5 nmol/kg AdM and 10 mg/kg resveratrol were treated to experiment groups intraperitoneally (i.p.) every other day for four weeks. AdM and vascular endothelial growth factor A (VEGF-A) mRNA levels were detected with semi-quantitative PCR; protein levels were detected with Western Blotting. AdM and resveratrol are multifactorial molecules, thus, this study has revealed a few novel evidence. The results were distinct in the group and treatment levels. The results showed that resveratrol has a role in angiogenesis in obesity and contributed to AdM production. It is observed that AdM has regulated its expression and increased the effect of resveratrol in WAT. AdM and VEGF-A gene expressions could not be detected in BAT; however, it is suggested that resveratrol may have a pro-angiogenic effect in BAT of obese rats according to the protein levels. AdM also has regulated VEGF-A level according to the metabolic situation of the organism.

Impact of adrenomedullin blockage on lipid metabolism in female mice exposed to high-fat diet

PURPOSE

Adrenomedullin (ADM) levels are elevated in gestational and type 2 diabetic patients. ADM also stimulates lipolysis in vitro. Disturbed lipid metabolism has been implicated in the pathogenesis of diabetes. Here, we explore whether blockade of ADM is beneficial for metabolic homeostasis in a diabetic mouse model.

METHODS

C57BL/6J female mice were placed on either a control or a high fat high sucrose (HFHS) diet for 8 weeks. At week 4, osmotic mini-pumps were implanted for constant infusion of either saline or ADM antagonist, ADM_22-52. Glucose tolerance tests were performed prior to infusion and 4 weeks after infusion began. Animals were then sacrificed and visceral adipose tissue collected for further analysis.

RESULTS

Mice fed HFHS displayed glucose intolerance, increased mRNA expressions in VAT for Adm and its receptor components, Crlr. HFHS fed mice also had increased basal and isoprenaline-induced glycerol release by VAT explants. ADM_22-52 did not significantly affect glucose intolerance. ADM_22-52 did suppress basal and isoprenaline-induced glycerol release by VAT explants. This alteration was associated with enhanced mRNA expression of insulin signaling factors Insr and Glut4, and adipogenic factor Pck1.

CONCLUSIONS

HFHS diet induces glucose intolerance and enhances ADM and its receptor expressions in VAT in female mice. ADM_22-52 treatment did not affect glucose intolerance in HFHS mice, but reduced both basal and isoprenaline-induced lipolysis, which is associated with enhanced expression of genes involved in adipogenesis. These results warrant further research on the effects of ADM blockade in improving lipid homeostasis in diabetic patients.

Adrenomedullin as a Protein with Multifunctional Behavior and Effects in Various Organs and Tissues

In literature, it has been reported that adrenomedullin, which is generally thought to have vasodilator, natriuretic and diuretic effects, is synthesized in almost all body, especially CNS, vascular muscles and endothelium, heart, liver, lung, kidney, gastric mocosa, intestinal endothelium and various blood cells. It has been found that the possible effects of adrenomedullin can be demonstrated directly or indirectly by means of active mediators, neuropeptides, enzymes and hormones. It is also suggested that it regulates the endocrine system by affecting the hypothalamic-pituitary axis. It increases in heart failure, acute coronary syndromes, hypertensive conditions, cerebrovascular accessory, chronic renal failure and periodontitis and decreases in peptic ulcer and intestinal diseases. However, it is still not clear whether increase/decrease in adrenomedullin level is a cause of a disease or is a result of damage due to an illness. This peptide, which could be thought to multifunctional, should be considered as a molecule with genetic coding that may have different effects on different tissues and conditions. For all these reasons, we aimed to review the multifonctional behavior of adrenomedullin in the light of the current literature to pioneer new hypotheses and discuss possible mechanisms.

RAMP3 deficiency enhances postmenopausal obesity and metabolic disorders

There is a marked increase in the incidence of visceral adiposity and insulin resistance among women following menopause. Adrenomedullin (AM) is an endogenous peptide first identified as a vasodilator, but now known to exert a variety of physiological effects. RAMP3 is a receptor activity-modifying protein that binds to the AM receptor (calcitonin receptor-like receptor). As expression of both AM and RAMP3 is reportedly activated by estrogen, we hypothesized that RAMP3 is crucially involved in the pathophysiology of postmenopausal obesity. To test this idea, we compared the effects of ovariectomy (OVX) and a high-fat diet for 10 weeks (a model of postmenopausal obesity) between RAMP3 knockout (RAMP3-/-) and wild-type mice. RAMP3-/- OVX mice exhibited greater obesity and adipose tissue weight gain as compared to wild-type OVX mice. RAMP3-/- OVX mice also exhibited higher serum insulin levels. In periuterine WAT from RAMP3-/- OVX mice, expression of lipolysis-related factors was lower and expression of inflammation-related factors was higher than in wild-type OVX mice. Hepatic steatosis was also exacerbated in RAMP3-/- OVX. Notably, expression of the membrane-type estrogen receptor GPR30 was downregulated in periuterine WAT from RAMP3-/- OVX mice. These findings raise the possibility that a GPR30-RAMP3 interaction is involved in the pathophysiology of postmenopausal obesity and suggest RAMP3 plays a key role in the regulation of energy metabolism and exerts a hepatoprotective effect in this model of postmenopausal obesity. RAMP3 may thus be a useful therapeutic target for treatment of postmenopausal obesity and metabolic disorders.

Gender-related alterations in plasma adrenomedullin level and its correlation with body weight gain

Plasma levels of adrenomedullin (AM), a bioactive peptide produced in adipose tissue, have been shown to be higher in obese patients than in non-obese patients, but little is known about gender differences in plasma AM levels. The aims of this study were to clarify gender-related alterations in plasma AM levels and to examine the body weight (BW) gain-plasma AM relationship in the general population. We measured plasma AM levels of 346 local residents (62.0±8.9 years, mean±s.d.) in the Kiyotake area, Japan, who underwent a regular health check-up, by a specific fluorescence immunoassay. Plasma AM levels in the female residents were lower than that in the males, and multiple regression analysis revealed a possible gender difference in plasma AM. The AM levels were significantly correlated with BMI or waist circumference in women, but such a relationship was not seen in men. When the subjects were divided into two groups by results of a questionnaire about BW gain of 10 kg or more since the age of 20 years, the plasma AM level of women with BW gain ≧10 kg was significantly higher than that in those without BW gain, although no difference was noted between the men with and without BW gain. In conclusion, possible gender differences were noted in the plasma AM levels and in the BW gain-plasma AM relationship in the general population. The plasma AM levels in the female residents without BW gain seem partly attributable to the lower AM of women.

Plasma adrenomedullin level is related to a single nucleotide polymorphism in the adrenomedullin gene

OBJECTIVE

Adrenomedullin (ADM) plays an important role in inflammation and is a marker of future cardiovascular events. We studied common single nucleotide polymorphisms (SNPs) in the gene encoding ADM and their relationship with the plasma levels of ADM and other inflammatory markers.

DESIGN AND METHODS

Plasma ADM, interleukin 6 (IL6), fibrinogen, and C-reactive protein (CRP) were measured in 476 subjects from the population-based Hong Kong Cardiovascular Risk Factor Prevalence Study-2. Four tag SNPs in ADM were genotyped.

RESULTS

Plasma ADM level increased with decreasing plasma IL6 level (β=-0.116, P=0.014). Plasma ADM level was not related to plasma levels of CRP and fibrinogen, and other clinical characteristics, except age (P=0.049). The four SNPs, rs3814700, rs11042725, rs34354539, and rs4910118, had minor allele frequencies of 31.1, 28.7, 33.8, and 23.4% respectively. Carriers of the minor allele of rs4910118 had a mean plasma ADM level that was 10.5% (95% confidential interval: 2.5-17.8%) lower than the non-carriers (β=-0.115, P=0.011). Haplotype analysis revealed a similar significant association with plasma ADM (P=0.040). In multivariate analysis, the presence of the minor allele of rs4910118, but not plasma IL6, was independently associated with plasma ADM (P=0.010).

CONCLUSION

Plasma ADM correlates with plasma IL6 level, consistent with its role in inflammation. It is related to an SNP common in Chinese, independent of other covariates. ADM genotype should be included in future studies of cardiovascular risk prediction.

Adrenomedullin protects against fructose-induced insulin resistance and myocardial hypertrophy in rats

Adrenomedullin (ADM) has been recognized as a multipotent multifunctional peptide. To explore the pathophysiological roles of ADM in insulin resistance (IR), we studied the changes in ADM mRNA level in the myocardium and vessels and the effect of ADM supplementation on rats with IR induced by fructose feeding. Rats were fed 4% fructose in drinking water for 8 weeks, and ADM was administered subcutaneously in pure water through an Alzet Mini-osmotic Pump at 300 ng/kg/h for the last 4 weeks. Compared with controls, rats with IR showed increased levels of fasting blood sugar and serum insulin, by 95% and 67%, respectively (all P<0.01), and glycogen synthesis and glucose transport activity of the soleus decreased by 54% and 55% (all P<0.01). mRNA level and content of brain natriuretic peptide (BNP) in myocardial were all increased significantly. Fructose-fed rats showed increased immunoreactive-ADM content in plasma by 110% and in myocardia by 55% and increased mRNA level in myocardia and vessels (all P<0.01). ADM administration ameliorated the induced IR and myocardial hypertrophy. The glycogen synthesis and glucose transport activity of the soleus muscle increased by 41% (P<0.01) and 32% (P<0.05). ADM therapy attenuated myocardial and soleus lipid peroxidation injury and enhanced the antioxidant ability. Our results showed upregulation of endogenous ADM during fructose-induced IR and the protective effect of ADM on fructose-induced IR and concomitant cardiovascular hypertrophy probably by its antioxidant effect, which suggests that ADM could be an endogenous protective factor in IR.

A genetic variant in the gene encoding adrenomedullin predicts the development of dysglycemia over 6.4 years in Chinese

BACKGROUND

Adrenomedullin, a vasodilatory peptide, facilitates the differentiation of pre-adipocytes, and affects lipolysis and glucose uptake. We investigated the association of common single nucleotide polymorphisms (SNPs) in the gene encoding adrenomedullin (ADM) with dysglycemia in the Hong Kong Chinese population.

METHODS

Four SNPs were genotyped in 1391 subjects without dysglycemia at baseline from the Hong Kong Cardiovascular Risk Factor Prevalence Study-2, which had a median follow-up time of 6.4 years. Dysglycemia included impaired fasting glucose, impaired glucose tolerance, and diabetes according to the WHO 1998 criteria. At follow-up, 382 subjects had developed dysglycemia.

RESULTS

In stepwise logistic regression, the SNP rs11042725 was a significant independent predictor of the development of dysglycemia (OR=1.31, P=0.012), together with baseline age (P<0.001), plasma triglycerides (P<0.001), body mass index (P=0.004), 2-h glucose after oral glucose tolerance test (P<0.001), homeostasis model assessment of insulin resistance index (P=0.045), and follow-up duration (P=0.009). The association was more significant in women (P=0.002) and in subjects without regular exercise (P=0.001).

CONCLUSIONS

Our study suggests a potential role of genetic variants in the ADM gene in the development of dysglycemia in our local Chinese population.

A Western-like fat diet is sufficient to induce a gradual enhancement in fat mass over generations

The prevalence of obesity has steadily increased over the last few decades. During this time, populations of industrialized countries have been exposed to diets rich in fat with a high content of linoleic acid and a low content of alpha-linolenic acid compared with recommended intake. To assess the contribution of dietary fatty acids, male and female mice fed a high-fat diet (35% energy as fat, linoleic acid:alpha-linolenic acid ratio of 28) were mated randomly and maintained after breeding on the same diet for successive generations. Offspring showed, over four generations, a gradual enhancement in fat mass due to combined hyperplasia and hypertrophy with no change in food intake. Transgenerational alterations in adipokine levels were accompanied by hyperinsulinemia. Gene expression analyses of the stromal vascular fraction of adipose tissue, over generations, revealed discrete and steady changes in certain important players, such as CSF3 and Nocturnin. Thus, under conditions of genome stability and with no change in the regimen over four generations, we show that a Western-like fat diet induces a gradual fat mass enhancement, in accordance with the increasing prevalence of obesity observed in humans.

Increased plasma levels of the mature and intermediate forms of adrenomedullin in obesity

Adrenomedullin (AM) is a cardiovascular protective peptide produced in various organs and tissues including adipose tissue. In the present study, we measured the plasma AM levels of subjects with or without obesity by two assay methods to separately evaluate the biologically active AM-NH(2) and the intermediate form of AM-glycine (AM-Gly). We measured the total AM and AM-NH(2) levels of plasma in 52 obese and 172 non-obese residents of a Japanese community, who received regular health check-ups and had no overt cardiovascular disease. AM-Gly values were obtained by subtracting AM-NH(2) levels from those of total AM. Both the AM-NH(2) and AM-Gly levels of the subjects with obesity were higher than those without obesity, and significant relationships were noted between body mass index (BMI) and the plasma levels of the two molecular forms of AM in a simple regression analysis. Moreover, the significant factors identified by multivariate analyses were BMI and serum triglyceride for AM-NH(2) and diastolic blood pressure, insulin, high-density lipoprotein-cholesterol, and plasma renin activity for AM-Gly. These results suggest active roles for the two molecular forms of AM in metabolic disorders associated with obesity in subjects without overt cardiovascular disease.

The Krüppel-like factor KLF15 inhibits transcription of the adrenomedullin gene in adipocytes

KLF15 (Krüppel-like factor 15) plays a key role in adipocyte differentiation and glucose transport in adipocytes through activation of its target genes. We have now identified six target genes regulated directly by KLF15 in 3T3-L1 mouse adipocytes with the use of a combination of microarray-based chromatin immunoprecipitation and gene expression analyses. We confirmed the direct regulation by KLF15 of one of these genes, that for adrenomedullin, with the use of a luciferase reporter assay in 3T3-L1 preadipocytes and adipocytes. Such analysis revealed that the most proximal CACCC element in the promoter of the human adrenomedullin gene (located in the region spanning nucleotides -70 and -29) is required for trans-inhibition by KLF15. Furthermore, chromatin immunoprecipitation showed that KLF15 binds to this region of the human adrenomedullin gene promoter in cultured human adipocytes. These results thus implicate KLF15 in the regulation of adrenomedullin expression in adipose tissue.

Role of adrenomedullin system in lipid metabolism and its signaling mechanism in cultured adipocytes

We investigated the levels of adrenomedullin (AM) system during the process of preadipocyte differentiation and its role in lipid metabolism and cellular signaling mechanism in differentiated adipocytes. We cultured rat preadipocytes and measured the following during the process of differentiation: two molecular forms of AM in the culture medium using a specific immunoradiometric assay and gene expression of AM and its receptor component using RT-PCR analysis. In differentiated adipocytes, we measured the effects of AM on the intracellular cAMP level, lipolysis, glucose incorporation, and the protein levels. Two molecular forms of AM were secreted into the medium, and the AM-mature/AM-total ratio was increased after 6 days of differentiation. Cultured rat preadipocytes highly expressed the genes of AM and its receptor components at day 1, and they increased at day 10. Administration of AM to preadipocytes increased the number of Oil Red O-positive adipocytes and spectrophotometric absorbance of Oil Red O. AM dose dependently increased cAMP level and lipolysis, and its effect was blocked by CGRP(8-37). Isoproterenol increased lipolysis, and AM had additive effects on isoproterenol-induced lipolysis. KT5720 and U0126 significantly inhibited the AM-induced lipolysis, whereas KT5720, but not U0126, significantly inhibited the isoproterenol-induced lipolysis. AM increased glucose incorporation and its effect was blocked by wortmannin. Western blot analysis revealed that AM increased phospho PKA, ERK, and Akt. These results indicate that AM and its receptor component are highly expressed in cultured adipocytes and may play a role in lipid metabolism via a different signaling pathway.

Expression of adrenomedullin in human epicardial adipose tissue: role of coronary status

Epicardial white adipose tissue (eWAT) is in close contact with coronary vessels and therefore could alter coronary homeostasis. Adrenomedullin (AM) is a potent vasodilatator and antioxidative peptide which has been shown to play a cytoprotective role in experimental models of acute myocardial infarction. We studied, using immunohistochemistry and qRT-PCR, the expression of AM and its receptors calcitonin receptor-like receptor (CRLR), and receptor activity-modifying protein (RAMP)2 and -3 in paired biopsies of subcutaneous WAT (sWAT) and eWAT obtained from patients with coronary artery disease (CAD) or without CAD (NCAD). In eWAT obtained from NCAD or CAD patients, immunoreactivity for AM, CRLR, and RAMP2 and -3 was detected in blood vessel walls and isolated stromal cells close to adipocytes. Some of the AM positive stromal cells colocalized CD68 immunoreactivity. eWAT from CAD patients showed increased AM immunoreactivity and AM gene expression. CRLR mRNA levels were comparable in sWAT of both groups and decreased by 40-50% in eWAT, irrespectively of the coronary status. RAMP2 mRNA concentrations did not change while RAMP3 mRNA levels increased in sWAT from CAD patients. There was a positive linear relationship between eWAT 11beta-hydroxysteroid dehydrogenase type 1 mRNA (11beta-HSD-1, the enzyme that converts inactive to active glucocorticoids) and AM mRNA. In conclusion, we demonstrate that AM and its receptors are expressed in eWAT. Our data suggest that eWAT AM, which could originate from macrophages, is related to 11beta-HSD-1 expression. AM synthesis, which is increased in eWAT during chronic CAD in humans, can play a cardioprotective role.

Adrenomedullin is a novel adipokine: adrenomedullin in adipocytes and adipose tissues

Adrenomedullin (AM) is a multifunctional regulatory peptide that is produced and secreted by various types of cells. The production and the secretion of AM have been demonstrated in cultured adipocytes and adipose tissues. Inflammatory cytokines such as tumor necrosis factor-alpha (TNF-alpha) and lipopolysaccharide are strong stimulators for AM expression in adipocytes. Furthermore, AM expression in the adipose tissue is increased in obesity, and plasma concentrations of AM are increased in obese subjects. One possible (patho)physiological role of AM secreted by adipose tissue may be actions against complications of the metabolic syndrome characterized by obesity, type 2 diabetic mellitus and hypertension, via its antioxidant and potent vasodilator effects. These findings indicate that AM is a new member of the adipokine family.

Adrenomedullin and its receptor components in adipose tissues: Differences between white and brown fats and the effects of adrenergic stimulation

Male Sprague-Dawley rats were subcutaneously injected with 2.5mg/kg phenylephrine or 2.5mg/kg isoproterenol or both (2.5mg/kg for each drug) for 4 days, twice a day. Samples of scapular brown adipose tissue (BAT) and epididymal white adipose tissue (WAT) were collected for the measurement of adrenomedullin (AM) levels and the gene expression of preproAM, calcitonin receptor like receptor (CRLR) and its activity modifying proteins (RAMPs) by radioimmunoassay and RT-PCR. These values were compared with those in the rats that received 0.9% saline. The gene expression of AM and AM receptor components in BAT are much less than that in epididymal WAT. In BAT there were an increase in AM peptide level after a combined treatment of alpha(1) and beta adrenoceptor agonists and increases in preproAM mRNA levels for rats treated with alpha(1) and beta receptor agonists alone or in combination. Both CRLR and RAMP2 mRNA levels of alphabeta group were increased significantly. In WAT, AM peptide level, RAMP1 and RAMP2 mRNA expression levels were augmented in the alpha group while CRLR mRNA level was enhanced in the beta group. The levels of AM, its receptor and RAMPs are much less in BAT than in WAT but adrenergic stimulation has a greater effect on the AM and its receptor components in BAT than those in WAT. AM stimulates lipolysis and increases the level of uncoupling protein-1 (UCP-1) in BAT. It may therefore enhance thermogenesis by increasing the availability of free fatty acids substrate as well as the UCP-1 level on the mitochondrial membrane.

Adrenomedullin inhibits adipogenesis under transcriptional control of insulin

We generated preadipocyte cell lines impaired in adrenomedullin production through integration of an adrenomedullin small interfering RNA expression vector. The reduction of adrenomedullin synthesis strongly accelerated adipose differentiation. These results were bolstered when overexpression of active adrenomedullin peptide led to delayed differentiation. Therefore, we propose that adrenomedullin is an antiadipogenic factor. Moreover, we checked whether insulin, a proadipogenic factor, regulates expression of adrenomedullin. We observed that insulin had an inhibitory effect on adrenomedullin expression in isolated human adipocyte cells. This response was dose dependent and was reversed by resistin, a new anti-insulin agent. We quantified circulating adrenomedullin in healthy obese patients and observed a threefold increase of adrenomedullin compared with lean patients. Furthermore, adrenomedullin plasma levels are negatively correlated to plasma insulin levels in these obese patients. The insulin inhibitory response was also observed in vivo in Sprague-Dawley rats but not in the insulin-resistant Zucker rat, suggesting that adrenomedullin expression is upregulated in insulin-resistant adipose cells. Using adrenomedullin promoter-luciferase reporter gene constructs, we have shown that the adrenomedullin response to insulin is mediated by insulin-responsive elements. These findings provide new insight into fat mass development and the relationship between obesity and elevated circulating adrenomedullin levels in diabetic patients.

Type 2 diabetes and cardiovascular disease: getting to the fat of the matterThis paper is one of a selection of papers published in this Special Issue, entitled Young Investigators' Forum

The increasing national prevalence of obesity is a major public health concern and a substantial burden on the health care resources of Canada. In addition to the direct health impact of obesity, this condition is a well-established risk factor for the development of various prevalent comorbidities including type 2 diabetes, hypertension, and cardiovascular disease. Historically, adipose tissue has been regarded primarily as an organ for energy storage. However, the discovery of leptin in the mid 1990’s revolutionized our understanding of this tissue and has focused attention on the endocrine function of adipose tissue as a source of secreted bioactive peptides. These compounds, collectively termed adipokines, regulate a number of biological functions including appetite and energy balance, insulin sensitivity, lipid metabolism, blood pressure, and inflammation. The physiological importance of adipokines has led to the hypothesis that changes in the synthesis and secretion of these compounds in the obese are a causative factor contributing to the development of obesity and obesity-related diseases in these individuals. Following from this it has been proposed that pharmacologic manipulation of adipokine levels may provide novel effective therapeutic strategies to treat and prevent obesity, type 2 diabetes, and cardiovascular disease.

Adrenomedullin in adipocyte differentiation of human mesenchymal stem cells

Expression of adrenomedullin (AM), a potent vasodilator peptide, was studied during adipocyte differentiation of human mesenchymal stem cells (hMSCs). Immunoreactive AM levels in the medium were increased at day 4 and 8 of the adipocyte differentiation. Northern blot analysis showed increased expression of AM mRNA in hMSCs-derived adipocytes at day 4, 8, 12, and 18. Transient transfection assay showed that the promoter activity was higher in hMSCs-derived adipocytes than in hMSCs, when cells were transfected with plasmids containing a cis-acting region (-70/-29) of the human AM gene. Electrophoretic mobility shift assay showed that specific bands bound to the region (-70/-29) in hMSCs-derived adipocytes but not in hMSCs, and were abolished by the stimulatory protein 1 (Sp1) antibody. The present study has shown that AM expression is up-regulated during adipocyte differentiation of hMSCs probably via the interaction between Sp1 or Sp1-related factor(s) and the AM promoter region (-70/-29).

Plasma adrenomedullin level and development of hypertension

The hypotensive peptide adrenomedullin (AM) is assumed to act as a factor inhibitory on elevation of blood pressure and on progression of the hypertensive organ damage, and plasma AM levels are elevated in patients with hypertension. The aim of the present study is to explore whether or not a rise in plasma AM levels precedes the development of hypertension. Normotensive local residents without apparent cardiovascular or renal disease (n = 177) were divided into low and high AM groups based on the median concentration of AM in plasma (11.9 fmol/ml), and followed up for 3 years for development of hypertension. The incidence of hypertension was higher in the residents with high AM than low AM levels (27.8 vs 11.5%, P < 0.01), whereas a similar analysis of plasma levels of atrial or brain natriuretic peptides revealed no such difference. The plasma AM level was found to be a significant parameter for the development of hypertension in a univariate analysis (P < 0.01), but not in a multivariate analysis. Meanwhile, the plasma AM level was significantly (P < 0.01) correlated with age and body mass index (BMI), two variables independently significant for the development of hypertension. The present findings suggest that an elevation of the plasma AM level associated with aging and increased BMI precedes the development of hypertension in the normotensive subjects.