alpha2-Adrenoreceptors restrain sympathetic nervous outflows and inhibit release of noradrenaline from sympathetic nerves. In-frame deletion of the alpha2C-adrenoreceptor subtype (alpha2CDel322-325) increases the risk of congestive heart failure. Increased delivery of catecholamines to cardiovascular receptors might explain this increased risk.
Twenty-nine healthy African-Americans genotyped for alpha2-adrenoreceptor subtype polymorphisms underwent 3H-noradrenaline and 3H-adrenaline intravenous infusion and arterial blood sampling for measurements of rates of entry of endogenous noradrenaline and adrenaline into arterial plasma (total body spillovers) by the tracer dilution technique. Eleven subjects were homozygotes for the alpha2CDel322-325 polymorphism, nine heterozygotes, and nine non-carriers. Subjects were studied during supine rest and during and after i.v. infusion of the alpha2-adrenoreceptor antagonist, yohimbine.
At rest, homozygotes for the alpha2CDel322-325 polymorphism had higher total body noradrenaline spillover than did heterozygotes (t=2.90, df=18, P=0.023) or non-carriers (t=3.22, df=18, P=0.010). Adrenaline spillover was higher in homozygotes than non-carriers (t=2.61, df=18, P=0.045). Administration of yohimbine produced larger, more sustained increments in noradrenaline spillover, heart rate, and anxiety in homozygotes than in the other groups.
In healthy people, alpha2CDel322-325 polymorphism is associated with increased sympathetic nervous and adrenomedullary hormonal activities, both during supine rest and during pharmacologically evoked catecholamine release. Polymorphisms of the alpha2C-adrenoreceptor may help explain individual differences in predisposition to a variety of disorders of catecholaminergic function, such as cardiovascular disorders, depression or anxiety disorders.
"The lack of clear genetic linkages may be due to the finding that both variant forms of α2 ARs exist as multiple haplotypes, and expression of specific haplotypes may be more important determinants of cardiovascular disease risk (Small et al. 2004; Small et al. 2006). Despite the lack of a clear linkage to cardiovascular disease, it has been demonstrated that human α2C Δ322- 325 AR homozygotic volunteers have the pathophysiological trait of increased sympathoneural drive (Neumeister et al. 2005). Subsequent pharmacological analysis of α2C Δ322-325 ARs using intact HEK293 cells suggested no loss-of-function phenotype, suggesting that if this variant form did have a linkage to pathophysiological conditions (such as increased sympathoneural drive), other cellular mechanisms of receptor dysfunction must play a role. "
[Show abstract][Hide abstract] ABSTRACT: Various naturally occurring polymorphic forms of human G protein-coupled receptors (GPCRs) have been identified and linked to diverse pathological diseases, including receptors for vasopressin type 2 (nephrogenic diabetes insipidus) and gonadotropin releasing hormone (hypogonadotropic hypogonadism). In most cases, polymorphic amino acid mutations disrupt protein folding, altering receptor function as well as plasma membrane expression. Other pathological GPCR variants have been found that do not alter receptor function, but instead affect only plasma membrane trafficking (e.g., delta opiate and histamine type 1 receptors). Thus, altered membrane trafficking with retained receptor function may be another mechanism causing polymorphic GPCR dysfunction. Two common human α2A and α2C adrenergic receptor (AR) variants have been identified (α2A N251K and α2C Δ322-325 ARs), but pharmacological analysis of ligand binding and second messenger signaling has not consistently demonstrated altered receptor function. However, possible alterations in plasma membrane trafficking have not been investigated. We utilized a systematic approach previously developed for the study of GPCR trafficking motifs and accessory proteins to assess whether these α2 AR variants affected intracellular trafficking or plasma membrane expression. By combining immunofluorescent microscopy, glycosidic processing analysis, and quantitative fluorescent-activated cell sorting (FACS), we demonstrate that neither variant receptor had altered intracellular localization, glycosylation, nor plasma membrane expression compared to wild-type α2 ARs. Therefore, pathopharmacological properties of α2A N251K and α2C Δ322-325 ARs do not appear to be due to altered receptor pharmacology or plasma membrane trafficking, but may involve interactions with other intracellular signaling cascades or proteins.
Archiv für Experimentelle Pathologie und Pharmakologie 03/2014; 387(6). DOI:10.1007/s00210-014-0972-6 · 2.47 Impact Factor
"In addition, the human α2CAR Del322–325 genetic variant that displays impaired signaling and sympatho-inhibitory function is associated with increased risk of HF in homozygous African-American carriers, especially when co-carried with the hyperfunctional cardiac β1AR Arg389 genetic variant, with the most probable mechanism being attenuated auto-inhibitory feedback of, and thus enhanced NE release from, the cardiac sympathetic nerves.43 In fact, even in healthy humans, the α2CAR Del322–325 variant is associated with increased sympathetic nervous and adrenomedullary hormonal activities, during both supine rest and pharmacologically evoked catecholamine release.44 Thus, presynaptic inhibitory α2-adrenergic autoreceptors crucially regulate SNS cardiac nerve activity and NE release into the heart, and any dysfunction of these receptors, either due to genetic polymorphisms or enhanced desensitization/downregulation (see GRK targets for HF therapy), translate into increased morbidity and mortality in chronic HF (Figure 1). "
[Show abstract][Hide abstract] ABSTRACT: Although there have been significant advances in the therapy of heart failure in recent decades, such as the introduction of β-blockers and antagonists of the renin-angiotensin-aldosterone system, this devastating disease still carries tremendous morbidity and mortality in the western world. G protein-coupled receptors, such as β-adrenergic and angiotensin II receptors, located in the membranes of all three major cardiac cell types, ie, myocytes, fibroblasts, and endothelial cells, play crucial roles in regulation of cardiac function in health and disease. Their importance is reflected by the fact that, collectively, they represent the direct targets of over one-third of the currently approved cardiovascular drugs used in clinical practice. Over the past few decades, advances in elucidation of the signaling pathways they elicit, specifically in the heart, have led to identification of an increasing number of new molecular targets for heart failure therapy. Here, we review these possible targets for heart failure therapy that have emerged from studies of cardiac G protein-coupled receptor signaling in health and disease, with a particular focus on the main cardiac G protein-coupled receptor types, ie, the β-adrenergic and the angiotensin II type 1 receptors. We also highlight key issues that need to be addressed to improve the chances of success of novel therapies directed against these targets.
Drug Design, Development and Therapy 10/2013; 7:1209-1222. DOI:10.2147/DDDT.S35905 · 3.03 Impact Factor
"However, the contribution of genetic factors to the ethnic differences in health is often very small and the results are often difficult to replicate (Cooper and Zhu 2001, Cruickshank et al. 2001, Cooper 2003, Li et al. 2006). For example, sequence variations in the human a 2 adrenergic receptor genes (ADRA2A and ADRA2C) were implicated as a cause of hypertension in African-American subjects (Lockette et al. 1995, Neumeister et al. 2005). From a stratified random population sample of 1767 subjects, however, Li et al. (2006) found no association of either variant with hypertension in African-Americans. "
[Show abstract][Hide abstract] ABSTRACT: Chronic diseases such as cardiovascular diseases (CVD) are major health problems in most ethnic minority and migrant populations living in high income countries. By the same token, CVD is a looming threat that is creating a double burden in most of the countries where these populations originate from. The causes of the rising burden are unclear, but they are likely to be multifaceted. Traditionally, ethnicity and health research have mostly concentrated on comparing the health of ethnic minority groups with the majority populations of the countries in which they live. This is an important area of research which illuminates ethnic inequalities in health. However, a few studies on international comparisons show that a lot can be learned from comparing similar ethnic groups living in different industrialised countries. Equally, comparing ethnic minority and migrant populations to similar populations in their countries of origin will generate new knowledge about factors that predispose them to poor health outcomes. Thus, to make progress in the field of ethnicity and health research, we need a new conceptual framework that simultaneously studies migrant/ethnic groups in the country of settlement, in similar countries of settlement, and in the countries of ancestral origin. Such studies need to go beyond the commonest design of cross-sectional studies to include more cohort studies, interventions and linkage studies. This article discusses (1) the burden of CVD in ethnic minority and migrant populations; (2) approaches to understanding predisposing factors; and (3) application of the results to give insight into the potential threats that their countries of origin are likely to face.
Ethnicity and Health 12/2012; 17(6):579-596. DOI:10.1080/13557858.2012.730607 · 1.67 Impact Factor
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