An asn to lys polymorphism in the third intracellular loop of the human alpha 2A-adrenergic receptor imparts enhanced agonist-promoted Gi coupling

Propranolol blocks osteosarcoma cell cycle progression, inhibits angiogenesis and slows xenograft growth in combination with cisplatin-based chemotherapy

Osteosarcoma is still associated with limited response to standard-of-care therapy and alarmingly elevated mortality rates, especially in low- and middle-income countries. Despite multiple efforts to repurpose β-blocker propranolol in oncology, its potential application in osteosarcoma management remains largely unexplored. Considering the unsatisfied clinical needs of this aggressive disease, we evaluated the antitumoral activity of propranolol using different in vitro and in vivo osteosarcoma preclinical models, alone or in addition to chemotherapy. Propranolol significantly impaired cellular growth in β2-adrenergic receptor-expressing MG-63 and U-2OS cells, and was capable of blocking growth-stimulating effects triggered by catecholamines. siRNA-mediated ADRB2 knockdown in MG-63 cells was associated with decreased cell survival and a significant attenuation of PPN anti-osteosarcoma activity. Direct cytostatic effects of propranolol were independent of apoptosis induction and were associated with reduced mitosis, G0/G1 cell cycle arrest and a significant down-regulation of cell cycle regulator Cyclin D1. Moreover, colony formation, 3D spheroid growth, cell chemotaxis and capillary-like tube formation were drastically impaired after propranolol treatment. Interestingly, anti-migratory activity of β-blocker was associated with altered actin cytoskeleton dynamics. In vivo, propranolol treatment (10 mg/kg/day i.p.) reduced the early angiogenic response triggered by MG-63 cells in nude mice. Synergistic effects were observed in vitro after combining propranolol with chemotherapeutic agent cisplatin. Sustained administration of propranolol (10 mg/kg/day i.p., five days a week), alone and especially in addition to low-dose metronomic cisplatin (2 mg/kg/day i.p., three times a week), markedly reduced xenograft progression. After histological analysis, propranolol and cisplatin combination resulted in low tumor mitotic index and increased tumor necrosis. β-blockade using propranolol seems to be an achievable and cost-effective therapeutic approach to modulate osteosarcoma aggressiveness. Further translational studies of propranolol repurposing in osteosarcoma are warranted.

Antidepressant Drugs Effects on Blood Pressure

Individuals suffering from depressive disorders display a greater incidence of hypertension compared with the general population, despite reports of the association between depression and hypotension. This phenomenon may depend, at least in part, on the use of antidepressant drugs, which may influence blood pressure through different effects on adrenergic and serotoninergic pathways, as well as on histaminergic, dopaminergic, and cholinergic systems. This review summarizes extant literature on the effect of antidepressant drugs on blood pressure. Selective serotonin reuptake inhibitors are characterized by limited effects on autonomic system activity and a lower impact on blood pressure. Thus, they represent the safest class—particularly among elderly and cardiovascular patients. Serotonin–norepinephrine reuptake inhibitors, particularly venlafaxine, carry a greater risk of hypertension, possibly related to greater effects on the sympathetic nervous system. The norepinephrine reuptake inhibitor reboxetine is considered a safe option because of its neutral effects on blood pressure in long-term studies, even if both hypotensive and hypertensive effects are reported. The dopamine–norepinephrine reuptake inhibitor bupropion can lead to blood pressure increases, usually at high doses, but may also cause orthostatic hypotension, especially in patients with cardiovascular diseases. The norepinephrine–serotonin modulators, mirtazapine and mianserin, have minimal effects on blood pressure but may rarely lead to orthostatic hypotension and falls. These adverse effects are also observed with the serotonin-reuptake modulators, nefazodone and trazodone, but seldomly with vortioxetine and vilazodone. Agomelatine, the only melatonergic antidepressant drug, may also have limited effects on blood pressure. Tricyclic antidepressants have been associated with increases in blood pressure, as well as orthostatic hypotension, particularly imipramine. Oral monoamine–oxidase inhibitors, less frequently skin patch formulations, have been associated with orthostatic hypotension or, conversely, with hypertensive crisis due to ingestion of tyramine-containing food (i.e., cheese reaction). Lastly, a hypertensive crisis may complicate antidepressant treatment as a part of the serotonin syndrome, also including neuromuscular, cognitive, and autonomic dysfunctions. Clinicians treating depressive patients should carefully consider their blood pressure status and cardiovascular comorbidities because of the effects of antidepressant drugs on blood pressure profiles and potential interactions with antihypertensive treatments.

GPCRs: The most promiscuous druggable receptor of the mankind

All physiological events in living organisms originated as specific chemical/biochemical signals on the cell surface and transmitted into the cytoplasm. This signal is translated within milliseconds-hours to a specific and unique order required to maintain optimum performance and homeostasis of living organisms. Examples of daily biological functions include neuronal communication and neurotransmission in the process of learning and memory, secretion (hormones, sweat, and saliva), muscle contraction, cellular growth, differentiation and migration during wound healing, and immunity to fight infections. Among the different transducers for such life-dependent signals is the large family of G protein-coupled receptors (GPCRs). GPCRs constitute roughly 800 genes, corresponding to 2% of the human genome. While GPCRs control a plethora of pathophysiological disorders, only approximately one-third of GPCR families have been deorphanized and characterized. Recent drug data show that around 40% of the recommended drugs available in the market target mainly GPCRs. In this review, we presented how such system signals, either through G protein or via other players, independent of G protein, function within the biological system. We also discussed drugs in the market or clinical trials targeting mainly GPCRs in various diseases, including cancer.

Sarcolemmal α2-adrenoceptors in feedback control of myocardial response to sympathetic challenge

α2-adrenoceptor (α2-AR) isoforms, abundant in sympathetic synapses and noradrenergic neurons of the central nervous system, are integral in the presynaptic feed-back loop mechanism that moderates norepinephrine surges. We recently identified that postsynaptic α2-ARs, found in the myocellular sarcolemma, also contribute to a muscle-delimited feedback control capable of attenuating mobilization of intracellular Ca²⁺ and myocardial contractility. This previously unrecognized α2-AR-dependent rheostat is able to counteract competing adrenergic receptor actions in cardiac muscle. Specifically, in ventricular myocytes, nitric oxide (NO) and cGMP are the intracellular messengers of α2-AR signal transduction pathways that gauge the kinase-phosphatase balance and manage cellular Ca²⁺ handling preventing catecholamine-induced Ca²⁺ overload. Moreover, α2-AR signaling counterbalances phospholipase C - PKC-dependent mechanisms underscoring a broader cardioprotective potential under sympathoadrenergic and angiotensinergic challenge. Recruitment of such tissue-specific features of α2-AR under sustained sympathoadrenergic drive may, in principle, be harnessed to mitigate or prevent cardiac malfunction. However, cardiovascular disease may compromise peripheral α2-AR signaling limiting pharmacological targeting of these receptors. Prospective cardiac-specific gene or cell-based therapeutic approaches aimed at repairing or improving stress-protective α2-AR signaling may offer an alternative towards enhanced preservation of cardiac muscle structure and function.

Individual variations in platelet reactivity towards ADP, epinephrine, collagen and nitric oxide, and the association to arterial function in young, healthy adults

INTRODUCTION

Platelet aggregation and secretion can be induced by a large number of endogenous activators, such as collagen, adenosine diphosphate (ADP) and epinephrine. Conversely, the blood vessel endothelium constitutively release platelet inhibitors including nitric oxide (NO) and prostacyclin. NO and prostacyclin are also well-known vasodilators and contribute to alterations in local blood flow and systemic blood pressure.

MATERIALS AND METHODS

In this study we investigated individual variations in platelet reactivity and arterial functions including blood pressure and flow-mediated vasodilation (FMD) in 43 young, healthy individuals participating in the Lifestyle, Biomarkers and Atherosclerosis (LBA) study. Platelet aggregation and dense granule secretion were measured simultaneously by light transmission and luminescence. FMD was measured with ultrasound.

RESULTS

The platelet function assay showed inter-individual differences in platelet reactivity. Specifically, a sub-group of individuals had platelets with an increased response to low concentrations of ADP and epinephrine, but not collagen. When the NO-donor S-nitroso-N-acetyl-DL-penicillamine (SNAP) was combined with high doses of these platelet activators, the results indicated for sub-groups of NO-sensitive and NO-insensitive platelets. The individuals with NO-sensitive platelets in response to SNAP in combination with collagen had a higher capacity of FMD of the arteria brachialis.

CONCLUSIONS

Platelet reactivity towards ADP, epinephrine and NO differs between young, healthy individuals. Some individuals have a more effective response towards NO, both in the aspect of platelet inhibition ex vivo, as well as vasodilation in vivo.

Molecular Mechanisms of Prothrombotic Risk Due to Genetic Variations in Platelet Genes: Enhanced Outside-In Signaling Through the Pro33 Variant of Integrin β3

In recent years inherited variations in platelet proteins have emerged as potential risk factors that could predispose individuals to arterial thrombosis. Although many studies have examined the association of platelet gene polymorphisms with particular disease states, the underlying mechanisms by which most of these polymorphisms contribute to the pathophysiology of thrombosis have remained largely unexplored. This review will focus on the cellular and molecular features by which these genetic changes affect platelet physiology. Although many genes have been investigated in this regard, only the genes encoding integrins β3 and α2, and the platelet Fc receptor, FcγRIIA, have been studied in any depth. In some cases (such as integrin α2), evidence supports a quantitative trait locus. For other genes, nonsynonymous nucleotide substitutions lead to structural and functional consequences. A large portion of this review will focus on the widely studied Leu33Pro (PIA) polymorphism of integrin β3, and will consider the potential mechanisms by which the Pro33 polymorphism could induce a prothrombotic risk. A detailed understanding of how polymorphisms modulate platelet physiology will be important for understanding individual differences in response to antiplatelet therapy.

Roles of catecholamine related polymorphisms in hypertension

The objective of this review is to summarize current data obtained so far in catecholamine-essential hypertension (EH) relationships on a genetic basis. As the major elements driving the sympathetic system’s actions, catecholamines modulate a variety of physiological processes and mutations related to the system. This could generate serious disorders, such as severe mental illnesses, stress-induced disorders, or impaired control of blood pressure or motor pathways. EH is idiopathic, and the genetic basis of its causes and substantial interindividual discrepancies in response to different types of treatments are the focus of interest. Susceptibility to disease or efficacy of treatments are thought to reflect genomic variabilities among individuals. Therefore, outlining the available knowledge in functional genetic polymorphisms linked to EH will make the picture clearer and will help to establish future prospects in the field.

Common α2A and α2C adrenergic receptor polymorphisms do not affect plasma membrane trafficking

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.

Pharmacogenetics of the G protein-coupled receptors

Pharmacogenetics investigates the influence of genetic variants on physiological phenotypes related to drug response and disease, while pharmacogenomics takes a genome-wide approach to advancing this knowledge. Both play an important role in identifying responders and nonresponders to medication, avoiding adverse drug reactions, and optimizing drug dose for the individual. G protein-coupled receptors (GPCRs) are the primary target of therapeutic drugs and have been the focus of these studies. With the advance of genomic technologies, there has been a substantial increase in the inventory of naturally occurring rare and common GPCR variants. These variants include single-nucleotide polymorphisms and insertion or deletions that have potential to alter GPCR expression of function. In vivo and in vitro studies have determined functional roles for many GPCR variants, but genetic association studies that define the physiological impact of the majority of these common variants are still limited. Despite the breadth of pharmacogenetic data available, GPCR variants have not been included in drug labeling and are only occasionally considered in optimizing clinical use of GPCR-targeted agents. In this chapter, pharmacogenetic and genomic studies on GPCR variants are reviewed with respect to a subset of GPCR systems, including the adrenergic, calcium sensing, cysteinyl leukotriene, cannabinoid CB1 and CB2 receptors, and the de-orphanized receptors such as GPR55. The nature of the disruption to receptor function is discussed with respect to regulation of gene expression, expression on the cell surface (affected by receptor trafficking, dimerization, desensitization/downregulation), or perturbation of receptor function (altered ligand binding, G protein coupling, constitutive activity). The large body of experimental data generated on structure and function relationships and receptor-ligand interactions are being harnessed for the in silico functional prediction of naturally occurring GPCR variants. We provide information on online resources dedicated to GPCRs and present applications of publically available computational tools for pharmacogenetic studies of GPCRs. As the breadth of GPCR pharmacogenomic data becomes clearer, the opportunity for routine assessment of GPCR variants to predict disease risk, drug response, and potential adverse drug effects will become possible.

α2 adrenergic receptor dysregulation in depressive disorders: implications for the neurobiology of depression and antidepressant therapy

Dysfunction in noradrenergic neurotransmission has long been theorized to occur in depressive disorders. The α2 adrenergic receptor (AR) family, as a group of key players in regulating the noradrenergic system, has been investigated for involvement in the neurobiology of depression and mechanisms of antidepressant therapies. However, a clear picture of the α2ARs in depressive disorders has not been established due to the existence of apparently conflicting findings in the literature. In this article, we report that a careful accounting of methodological differences within the literature can resolve the present lack of consensus on involvement of α2ARs in depression. In particular, the pharmacological properties of the radioligand (e.g. agonist versus antagonist) utilized for determining receptor density are crucial in determining study outcome. Upregulation of α2AR density detected by radiolabeled agonists but not by antagonists in patients with depressive disorders suggests a selective increase in the density of high-affinity conformational state α2ARs, which is indicative of enhanced G protein coupling to the receptor. Importantly, this high-affinity state α2AR upregulation can be normalized with antidepressant treatments. Thus, depressive disorders appear to be associated with increased α2AR sensitivity and responsiveness, which may represent a physiological basis for the putative noradrenergic dysfunction in depressive disorders. In addition, we review changes in some key α2AR accessory proteins in depressive disorders and discuss their potential contribution to α2AR dysfunction.

Genetic variation, β-blockers, and perioperative myocardial infarction

Perioperative myocardial infarction is a common and potentially fatal complication after noncardiac surgery, particular among patients with cardiovascular risk factors. β-blockers have been considered a mainstay in prevention and treatment of perioperative myocardial infarction, yet recent evidence suggests that β-blockers may have an unfavorable risk profile in this setting, and the use has become controversial. What seems conspicuously absent from the current discussion is the appreciation of how much interindividual genetic variation influences the clinical response to β-blocker therapy. Genetic variation in the adrenergic signaling pathway is common, and has a major impact on adrenergic receptor function and β-blocker efficacy in other cardiovascular diseases, such as heart failure and hypertension. Genetic variation in the cytochrome P450 2D6, or CYP2D6, enzyme, which is responsible for the metabolism of most β-blockers, is also important and can lead to poor metabolizing of β-blockers (potential toxicity) or their ultra-rapid degradation (decreased efficacy). Here, we review the molecular, cellular, and physiologic consequences of polymorphisms in the adrenergic signaling pathway and CYP2D6 gene, and show that these are likely relevant factors influencing efficacy, safety, and toxicity of β-blocker therapy in prevention and treatment of perioperative myocardial infarction.

Genetic variations in the α(2A)-adrenoreceptor are associated with blood pressure response to the agonist dexmedetomidine

BACKGROUND

α(2A)-Adrenoceptors (α(2A)-ARs) have important roles in sympathetic cardiovascular regulation. Variants of ADRA2A affect gene transcription and expression and are associated with insulin release and risk for type 2 diabetes. We examined whether ADRA2A variants are also associated with cardiovascular responses to the selective α(2)-AR-agonist dexmedetomidine.

METHODS AND RESULTS

Seventy-three healthy subjects participated in a placebo-controlled, single-blind study. After 3 infusions of placebo, subjects received 3 incremental infusions of dexmedetomidine (cumulative dose, 0.4 μg/kg). Primary outcomes were changes in systolic blood pressure (SBP) and plasma norepinephrine concentrations, measured as difference of the area-under-the-curve during placebo and dexmedetomidine infusions (ΔAUC). We used multiple linear regression analysis to examine the associations between 9 ADRA2A tagging variants and 5 inferred haplotypes and ΔAUC after adjustment for covariates. Homozygous carriers of rs553668 and the corresponding haplotype 4, previously associated with increased α(2A)-AR expression, had a 2.2-fold greater decrease in AUC(SBP) after dexmedetomidine (adjusted P=0.006); similarly, the maximum decrease in SBP was 24.7±8.1 mm Hg compared with 13.6±5.9 mm Hg in carriers of the wild-type allele (P=0.007). Carriers of haplotype 3, previously associated with reduced α(2A)-AR expression, had a 44% smaller decrease in AUC(SBP) (P=0.013). Haplotype information significantly improved the model predicting the decrease in SBP (P<0.001). There were similar but nonsignificant trends for diastolic blood pressure and heart rate. Genotypes were not significantly associated with norepinephrine responses.

CONCLUSIONS

Common ADRA2A variants are associated with the hypotensive response to dexmedetomidine. Effects of specific variants/haplotypes in vivo are compatible with their known effects on gene expression in vitro.

Resting sympathetic nerve activity is related to age, sex and arterial pressure but not to α2-adrenergic receptor subtype

OBJECTIVE

Sympathetic nerve hyperactivity has been associated with hypertension and heart failure and their cardiovascular complications. The α2-adrenergic receptors have been proposed to play a prominent role in the control of sympathetic neural output, and their malfunction to constitute a potential central mechanism for sympathetic hyperactivity of essential hypertension. Reports on the relationship between variant alleles of α2-adrenergic receptor subtypes and sympathetic drive or its effects, however, have not been consistent. Therefore, this study was planned to test the hypothesis that variant alleles of subtypes of α2-adrenergic receptors are associated with raised muscle sympathetic nerve activity (MSNA) in man.

METHODS

One hundred and seventy-two individuals, with a wide range of arterial pressure, were prospectively examined. Resting MSNA was quantified from multiunit bursts and from single units, and α2-adrenergic receptor subtypes were genotyped from DNA extracted from leucocytes and quantified by spectrophotometry.

RESULTS

No significant relationships between variant alleles of any of the α2A, α2B or α2C subtypes and raised muscle sympathetic activity were found. In contrast, MSNA showed a marked significant curvilinear relationship with age and systolic pressure; sex had a small but statistically significant effect. The α2-adrenergic receptor variants had a similar frequency when hypertensive and normotensive individuals were compared.

CONCLUSION

Variant alleles of three α2-adrenergic receptor subtypes were not related to resting muscle sympathetic nerve hyperactivity, indicating that their functional differences shown in vitro are not reflected in sympathetic activity in man. Age had a marked effect likely influencing arterial pressure through sympathetic activity.

RAAS and adrenergic genes in heart failure: Function, predisposition and survival implications

It is well appreciated that several neurohormones and signaling cascades are activated that promote long-term deterioration of cardiac function and structure. Activation of the renin-angiotensin-aldosterone system (RAAS) and the adrenergic system is closely related to heart failure. Common gene variants that encode neurohormonal, adrenergic and intracellular proteins have been demonstrated to modulate the course and consequences of heart failure. However, the literature is replete with conflicting results and it remains uncertain as to whether particular gene variants predispose heart failure. Therefore, the main purpose of this review was to discuss the effects of single nucleotide polymorphisms (SNPs) that are located in genes encoding elements of the RAAS and the adrenergic system on the predisposition to and survival from heart failure. Most studies indicate that common SNPs encoding elements of the RAAS and the adrenergic system do not predispose individuals to heart failure. Conversely, it has been demonstrated that ARB1 Arg389Gly, GRK5 Gln41Leu, ACE I/D, CYP11B2 C-344T and AGTR1 A+1166C modulate pharmacological responses and have a considerable impact on cardiac-related survival. It should not be expected, however, that a single polymorphism determines survival, given that multiple gene products and environmental factors contribute to the pathogenesis of heart failure. Therefore, future studies should consider the interaction effects of multiple genes in populations that are as homogeneous as possible with respect to environmental characteristics.

Sympathetic alpha(2)-adrenoceptors prevent cardiac hypertrophy and fibrosis in mice at baseline but not after chronic pressure overload

AIMS

alpha(2)-Adrenoceptors modulate cardiovascular function by vasoconstriction or dilatation, by central inhibition of sympathetic activity, or by feedback inhibition of norepinephrine release from sympathetic neurons. Despite detailed knowledge about subtype-specific functions of alpha(2)-receptors, the relative contributions of sympathetic vs. non-sympathetic receptors involved in these cardiovascular effects have not been identified. The aim of this study was to define the physiological and pharmacological role of alpha(2A)-adrenoceptors in adrenergic vs. non-adrenergic cells at baseline and during sympathetic stress.

METHODS AND RESULTS

Transgenic mice expressing alpha(2A)-adrenoceptors under control of the dopamine beta-hydroxylase (Dbh) promoter were generated and crossed with mice carrying a constitutive deletion in the alpha(2A)- and alpha(2C)-adrenoceptor genes. alpha(2AC)-deficient mice showed increased norepinephrine plasma levels, cardiac hypertrophy, and fibrosis at baseline. Expression of the Dbh-alpha(2A) transgene in sympathetic neurons prevented these effects. In contrast, Dbh-alpha(2A) receptors mediated only a minor part of the bradycardic and hypotensive effects of the alpha(2)-agonist medetomidine. After chronic pressure overload as induced by transverse aortic constriction in mice, the Dbh-alpha(2A) transgene did not reduce norepinephrine spillover, cardiac dysfunction, hypertrophy, or fibrosis. In isolated wild-type atria, alpha(2)-agonist-induced inhibition of [3H]norepinephrine release was significantly desensitized after pressure overload. In primary sympathetic neurons from Dbh-alpha(2A) transgenic mice, norepinephrine and medetomidine induced endocytosis of alpha(2A)-adrenoceptors into neurite processes.

CONCLUSION

alpha(2A)-Adrenoceptors expressed in adrenergic cells are essential feedback inhibitors of sympathetic norepinephrine release to prevent cardiac hypertrophy and fibrosis at baseline. However, these receptors are desensitized by chronic pressure overload which in turn may contribute to the pathogenesis of this condition.

Genetic influences on cardiovascular stress reactivity

Individual differences in the cardiovascular response to stress play a central role in the reactivity hypothesis linking frequent exposure to psychosocial stress to adverse outcomes in cardiovascular health. To assess the importance of genetic factors, a meta-analysis was performed on all published twin studies that assessed heart rate (HR) or blood pressure (BP) reactivity to the cold pressor test or various mental stress tasks. For reactivity to mental stress, the pooled heritability estimate ranged from 0.26 to 0.43. Reactivity to the cold pressor test yielded heritability estimates from 0.21 to 0.55. An ensuing review of genetic association studies revealed a number of genes, mostly within the sympathoadrenal pathway, that may account for part of the heritability of cardiovascular stress reactivity. Future progress in gene finding, that should include measures of sympathetic and vagal stress reactivity, may help uncover the molecular pathways from genetic variation to stress reactivity.

Association analysis between the C-1291G polymorphism in the promoter region of the adrenergic alpha2A receptor gene and polydipsia in schizophrenia

Several lines of studies have shown the existence of an important inhibitory mechanism for the control of water intake involving adrenergic alpha2A receptors (ADRA2A). A human study using patients with schizophrenia demonstrated an exacerbation of polydipsia by the administration of clonidine, an ADRA2A-agonist, and a relief of polydipsia by mianserin, an ADRA2A-antagonist, suggesting the involvement of the central adrenergic system in the drinking behavior of patients with schizophrenia. Based on these findings we examined a possible association between the C-1291G polymorphism in the promoter region of the ADRA2A gene and polydipsia in schizophrenia using a Japanese case-control sample. Our sample includes 348 patients with schizophrenia (DSM-IV) (84 with polydipsia and 264 without polydipsia). No significant association between the ADRA2A C-1291G polymorphism and polydipsia was found. Our result suggests that the ADRA2A C-1291G polymorphism may not confer susceptibility to polydipsia in schizophrenia in our sample. Further studies with larger samples are warranted.

Identification of single nucleotide polymorphisms of the human metabotropic glutamate receptor 1 gene and pharmacological characterization of a P993S variant

mGluR1 receptors are believed to play major roles in the pathophysiology of diseases such as anxiety and chronic pain and are being actively investigated as targets for drug development. Sequence polymorphisms can potentially influence the efficacy of drugs in patient populations and are therefore an important consideration in the drug development process. To identify DNA sequence variants of the mGluR1 receptor, comparative DNA sequencing was performed on DNA samples (n=186) from apparently healthy subjects representing two ethnic groups. In total, eight non-synonymous single nucleotide polymorphisms (SNPs) were identified and one SNP (c2977>T) was found to be particularly common, this SNP results in a proline to serine substitution at residue 993 (P993S). The WT (P993) and S993 variants were expressed in an inducible system which allowed us to titrate gene expression to equivalent levels and were pharmacologically characterized. We determined the potency and affinity of standard antagonist compounds as well as the potency and efficacy of the endogenous ligand glutamate and other agonist compounds at both receptor variants. Agonist evoked increases in intracellular Ca(2+) were measured by fluorometric imaging plate reader (FLIPR). The potency of mGluR1 antagonists was evaluated by their ability to inhibit quisqualate induced increases in intracellular Ca(2+), while their affinities were determined by radio-ligand binding studies. This study demonstrates that the Pro993Ser amino acid exchange is highly frequent in the human mGluR1 gene. This polymorphism however, does not appear to affect the potency of agonist compounds or the potencies or affinities of small molecule antagonist compounds.

Association of alpha2A-adrenergic receptor gene polymorphism with susceptibility to suicide in Japanese females

OBJECTIVES

It has been suggested that noradrenergic system abnormalities are involved in suicide. Postmortem brain studies have shown that molecular and functional alterations in alpha2A-adrenergic receptor-induced signal transduction are associated with suicide and depression. Recently, a single nucleotide polymorphism (SNP) within a coding region of the alpha2A-adrenergic receptor gene (ADRA2A), which results in an Asn-to-Lys change at amino acid 251 (N251K), has been implicated in susceptibility to suicide in Caucasians. The aim of our study is to determine whether genetic variants of the ADRA2A gene are also associated with suicide in a Japanese population.

METHODS

Three SNPs, C-1291G, N251K and rs3750625C/A, and one insertion/deletion polymorphism in the ADRA2A gene were genotyped in 184 completed suicides and 221 control subjects with the polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP) method.

RESULTS

Neither variation of the N251K SNP nor the insertion/deletion polymorphism was found in our Japanese samples. The C-1291G SNP in the promoter region was found to be significantly associated with suicide in females (P=0.043 and 0.013 for genotypic and allelic comparisons, respectively). One of the common haplotypes, CC of C-1291G and rs3750625C/A, was also associated with suicide in females (P=0.015). These associations were also significant in the female violent suicide victims (P=0.009 and 0.009 for allelic and CC haplotypic comparisons, respectively). Although the significance was nominal, it was maintained even after correction for multiple comparisons. By contrast, neither of these two SNPs showed any association with violent and/or non-violent suicide in males.

CONCLUSION

Our results raise the possibility that promoter genetic variation in the ADRA2A gene is associated with either suicide or violent suicide in females.

G protein-coupled receptor pharmacogenetics

Common G protein-coupled receptor (GPCR) gene variants that encode receptor proteins with a distinct sequence may alter drug efficacy without always resulting in a disease phenotype. GPCR genetic loci harbor numerous variants, such as DNA insertions or deletions and single-nucleotide polymorphisms that alter GPCR expression and function, thereby contributing to interindividual differences in disease susceptibility/progression and drug responses. In this chapter, these pharmacogenetic phenomena are reviewed with respect to a limited sampling of GPCR systems, including the beta(2)-adrenergic receptors, the cysteinyl leukotriene receptors, and the calcium-sensing receptor. In each example, the nature of the disruption to receptor function that results from each variant is discussed with respect to the regulation of gene expression, expression on cell surface (affected by receptor trafficking, dimerization, desensitization/downregulation), or perturbation of receptor function (by altering ligand binding, G protein coupling, and receptor constitutive activity). Despite the breadth of pharmacogenetic knowledge available, assessment for genetic variants is only occasionally applied to drug development projects involving pharmacogenomics or to optimizing the clinical use of GPCR drugs. The continued effort by the basic science of pharmacogenetics may draw the attention of drug discovery projects and clinicians alike to the utility of personalized pharmacogenomics as a means to optimize novel GPCR drug targets.

Alpha-adrenoceptor gene variants and autonomic nervous system function in a young healthy Japanese population

alpha(1A)-adrenergic receptor (alpha(1A)-AR) regulates the cardiac and peripheral vascular system through sympathetic activation, and alpha(2A)-AR and alpha(2C)-AR subtypes are essential for presynaptic feedback regulation of catecholamine release from the central and peripheral sympathetic nerve. Genetic variations in each human alpha-AR subtype gene have been identified and have been implicated in hypertension and cardiovascular disease. It is not yet clear whether these genetic variations actually have an effect on sympatho-vagal modulation. The aim of the present study was to evaluate the relation between the five representative genetic polymorphisms of alpha-AR subtypes (Arg347Cys of alpha(1A)-AR; C-1291G, Asn251Lys, and DraI RFLP of alpha(2A)-AR; and Del322-325 of alpha(2C)-AR) and autonomic nervous system (ANS) function in young and healthy Japanese males. One hundred forty-nine subjects were genotyped for each alpha-AR polymorphism, and underwent evaluation of ANS function by power spectral analysis of heart rate variability (HRV) during supine rest and in a standing position. In a supine position, the alpha(1A)-AR 347Cys allele was significantly associated with lower HRV sympathetic index (normalized low frequency power [LF(%)] and LF:HF ratio) and higher HRV parasympathetic index [HF(%)]. Meanwhile, subjects with the alpha(2C)-AR Del322-325 allele had markedly higher LF(%) and LF:HF ratio and lower HF(%) than noncarriers. Thus, the alpha(1A)-AR and alpha(2C)-AR genetic variations influence sympatho-vagal balance even in young and healthy normotensive states, which could be postulated to constitute an intermediate phenotype for future pathological episodes of various ANS dysfunction-related diseases.

Airway smooth muscle prostaglandin-EP1 receptors directly modulate beta2-adrenergic receptors within a unique heterodimeric complex

Multiple and paradoxical effects of airway smooth muscle (ASM) 7-transmembrane-spanning receptors activated during asthma, or by treatment with bronchodilators such as beta(2)-adrenergic receptor (beta(2)AR) agonists, indicate extensive receptor crosstalk. We examined the signaling of the prostanoid-EP(1) receptor, since its endogenous agonist prostaglandin E(2) is abundant in the airway, but its functional implications are poorly defined. Activation of EP(1) failed to elicit ASM contraction in mouse trachea via this G(alphaq)-coupled receptor. However, EP(1) activation markedly reduced the bronchodilatory function of beta(2)AR agonist, but not forskolin, indicating an early pathway interaction. Activation of EP(1) reduced beta(2)AR-stimulated cAMP in ASM but did not promote or augment beta(2)AR phosphorylation or alter beta(2)AR trafficking. Bioluminescence resonant energy transfer showed EP(1) and beta(2)AR formed heterodimers, which were further modified by EP(1) agonist. In cell membrane [(35)S]GTPgammaS binding studies, the presence of the EP(1) component of the dimer uncoupled beta(2)AR from G(alphas), an effect accentuated by EP(1) agonist activation. Thus alone, EP(1) does not appear to have a significant direct effect on airway tone but acts as a modulator of the beta(2)AR, altering G(alphas) coupling via steric interactions imposed by the EP(1):beta(2)AR heterodimeric signaling complex and ultimately affecting beta(2)AR-mediated bronchial relaxation. This mechanism may contribute to beta-agonist resistance found in asthma.

Complex haplotypes derived from noncoding polymorphisms of the intronless alpha2A-adrenergic gene diversify receptor expression

Alpha(2A)-adrenergic receptors (alpha(2A)AR) regulate multiple central nervous system, cardiovascular, and metabolic processes including neurotransmitter release, platelet aggregation, blood pressure, insulin secretion, and lipolysis. Complex diseases associated with alpha(2A)AR dysfunction display familial clustering, phenotypic heterogeneity, and interindividual variability in response to therapy targeted to alpha(2A)ARs, suggesting common, functional polymorphisms. In a multiethnic discovery cohort we identified 16 single-nucleotide polymorphisms (SNPs) in the alpha(2A)AR gene organized into 17 haplotypes of two major phylogenetic clades. In contrast to other adrenergic genes, variability of the alpha(2A)AR was primarily due to SNPs in the promoter, 5' UTR and 3' UTR, as opposed to the coding block. Marked ethnic variability in the frequency of SNPs and haplotypes was observed: one haplotype represented 70% of Caucasians, whereas Africans and Asians had a wide distribution of less common haplotypes, with the highest haplotype frequencies being 16% and 35%, respectively. Despite the compact nature of this intronless gene, local linkage disequilibrium between a number of SNPs was low and ethnic-dependent. Whole-gene transfections into BE(2)-C human neuronal cells using vectors containing the entire approximately 5.3-kb gene without exogenous promoters were used to ascertain the effects of haplotypes on alpha(2A)AR expression. Substantial differences (P < 0.001) in transcript and cell-surface protein expression, by as much as approximately 5-fold, was observed between haplotypes, including those with common frequencies. Thus, signaling by this virtually ubiquitous receptor is under major genetic influence, which may be the basis for highly divergent phenotypes in complex diseases such as systemic and pulmonary hypertension, heart failure, diabetes, and obesity.

The N251K functional polymorphism in the alpha(2A)-adrenoceptor gene is not associated with depression: a study in suicide completers

RATIONALE

alpha(2A)-Adrenoceptor up-regulation and supersensitivity have been described in the postmortem brains of depressed suicide victims and in the platelets of depressed subjects. The C to G transversion at nucleotide 753 (Asn to Lys change at amino acid 251 or N251K) is a low-frequency polymorphism of the alpha(2A)-adrenoceptor gene that results in a gain-of-function phenotype. A previous study has suggested an association between completed suicide and this polymorphism.

OBJECTIVES

The single functional polymorphism N251K was tested in a large sample (n=214) of completed suicides, controlling for the antemortem psychiatric diagnosis, and matched controls (n=176).

METHODS

Postmortem brain DNA was extracted and the alpha(2A)-adrenoceptor gene fragment was amplified by polymerase chain reaction, followed by a StyI restriction endonuclease digestion. Amplified products were sequenced to confirm the presence of the alpha(2A)-adrenoceptor gene fragment where the polymorphism is located.

RESULTS

The N251K polymorphism was absent in both suicide victim and control groups. No association between the polymorphism and suicide or depression was established.

CONCLUSIONS

The N251K polymorphism does not represent a genetic factor to explain the alpha(2A)-adrenoceptor hyperactivity in the brains of depressed suicide victims. Association between suicide and this polymorphism was not replicated.

The G protein-coupled receptors: pharmacogenetics and disease

Genetic variation in G-protein coupled receptors (GPCRs) is associated with a wide spectrum of disease phenotypes and predispositions that are of special significance because they are the targets of therapeutic agents. Each variant provides an opportunity to understand receptor function that complements a plethora of available in vitro data elucidating the pharmacology of the GPCRs. For example, discrete portions of the proximal tail of the dopamine D1 receptor have been discovered, in vitro, that may be involved in desensitization, recycling and trafficking. Similar in vitro strategies have been used to elucidate naturally occurring GPCR mutations. Inactive, over-active or constitutively active receptors have been identified by changes in ligand binding, G-protein coupling, receptor desensitization and receptor recycling. Selected examples reviewed include those disorders resulting from mutations in rhodopsin, thyrotropin, luteinizing hormone, vasopressin and angiotensin receptors. By comparison, the recurrent pharmacogenetic variants are more likely to result in an altered predisposition to complex disease in the population. These common variants may affect receptor sequence without intrinsic phenotype change or spontaneous induction of disease and yet result in significant alteration in drug efficacy. These pharmacogenetic phenomena will be reviewed with respect to a limited sampling of GPCR systems including the orexin/hypocretin system, the beta2 adrenergic receptors, the cysteinyl leukotriene receptors and the calcium-sensing receptor. These developments will be discussed with respect to strategies for drug discovery that take into account the potential for the development of drugs targeted at mutated and wild-type proteins.

Genetic variation in G-protein-coupled receptors – consequences for G-protein-coupled receptors as drug targets

G-protein-coupled receptors (GPCRs), including 'orphan' GPCRs whose natural ligands are unknown, comprise the largest membrane receptor superfamily and are the most commonly used therapeutic targets. GPCR genetic loci harbour numerous variants, such as DNA insertions or deletions and single nucleotide polymorphisms that alter GPCR expression and function, thereby contributing to inter-individual differences in disease susceptibility/progression and drug responses. In this article, the authors review examples of GPCR genetic variants that influence transcription, translation, receptor folding and expression on cell surface (by affecting receptor trafficking, dimerisation, desensitisation/downregulation), or perturb receptor function (by altering ligand binding, G-protein coupling and receptor constitutive activity). In spite of such effects, assessment for genetic variants is not currently applied to the drug development and approval process or in the clinical use of GPCR drugs. Further insights will, the authors believe, alter drug discovery/development, therapeutics and likely provide new GPCR drug targets.

Functional adrenergic receptor polymorphisms and idiopathic orthostatic intolerance

OBJECTIVES

Idiopathic orthostatic intolerance (IOI) is a common disorder that is characterized by chronic orthostatic symptoms and substantial increases in heart rate and plasma norepinephrine concentrations that are disproportionately high while standing. Several features of the syndrome, including the tachycardia, tremulousness, and exaggerated norepinephrine have been considered potentially due to hypoactive or hyperactive states of adrenergic receptors of the sympathetic nervous system. The aim of this study was therefore to ascertain whether genotypes at eight polymorphic loci within five relevant adrenergic receptor genes (alpha2A, alpha2B, alpha2C, beta1 and beta2) influence the risk for IOI.

METHODS

We studied 80 young men in military service (20 patients with IOI and 60 age-matched controls). All participants underwent a tilt table test including monitoring of blood pressure, heart rate and plasma catecholamines, in the supine position and during 30 min of standing. Genotyping at the eight loci (alpha2ALys251, alpha2BDel301-303, alpha2CDel322-325, beta1Gly49, beta1Arg389, beta2Arg16, beta2Glu27, beta2Ile164) was performed in all participants. Chi-square tests of independence were used to test for associations between IOI and genotype. In addition, an association of the polymorphisms with haemodynamic variables (heart rate, supine and upright blood pressure) was ascertained using one-way variance analysis.

RESULTS

For the beta1Gly49 polymorphism we found a decrease in the risk of IOI among persons who were homozygous (odds ratio, 0.88; 95% confidence interval, 0.81-0.97). In addition, we found an association between beta1Gly49 and decreased heart rate in the upright position, regardless of IOI diagnosis. There were no associations with the other studied polymorphisms and IOI.

CONCLUSIONS

Our current results suggest that the beta1Gly49 polymorphism is protective for IOI. This is likely one of several common genetic loci that may represent modifiers of IOI phenotypes.

Pharmacogenomics of adrenoceptors

Adrenoceptors (ARs) consist of nine subtypes (alpha(1A)-, alpha(1B)-, alpha(1D)-, beta(1)-, beta(2)-, beta(3)-, alpha(2A)-, alpha(2B)- and alpha(2C)-AR), which are involved in a wide spectrum of physiological functions and are the site of action for a considerable percentage of currently prescribed therapeutics. With the exception of alpha(1D), all AR subtypes are polymorphic with genetic variations in the coding and non-coding regions. This review discusses the biochemical consequences of these genetic variations and their impact in receptor function, disease pathophysiology, and drug response. Pharmacogenomic principles that have been discovered are also discussed.

Haplotype-based analysis of alpha 2A, 2B, and 2C adrenergic receptor genes captures information on common functional loci at each gene

The alpha 2-adrenergic receptors (alpha2-AR) mediate physiological effects of epinephrine and norepinephrine. Three genes encode alpha2-AR subtypes carrying common functional polymorphisms (ADRA2A Asn251Lys, ADRA2B Ins/Del301-303 and ADRA2C Ins/Del322-325). We genotyped these functional markers plus a panel of single nucleotide polymorphisms evenly spaced over the gene regions to identify gene haplotype block structure. A total of 24 markers were genotyped in 96 Caucasians and 96 African Americans. ADRA2A and ADRA2B each had a single haplotype block at least 11 and 16 kb in size, respectively, in both populations. ADRA2C had one haplotype block of 10 kb in Caucasians only. For the three genes, haplotype diversity and the number of common haplotypes were highest in African Americans, but a similar number of markers (3-6) per block was sufficient to capture maximum diversity in either population. For each of the three genes, the haplotype was capable of capturing the information content of the known functional locus even when that locus was not genotyped. The alpha2-AR haplotype maps and marker panels are useful tools for genetic linkage studies to detect effects of known and unknown alpha2-AR functional loci.

Clinical and pharmacological significance of α2-adrenoceptor polymorphisms in cardiovascular diseases

The alpha2-adrenoceptors (alpha2-ARs) are receptors for endogenous catecholamines (norepinephrine and epinephrine) that mediate a number of physiological and pharmacological responses such as hypotension and sedation. Three distinct subtypes, denoted alpha2A-, alpha2B- and alpha2C-AR, have been characterized and cloned. Employment of mutation screening in the study of human populations from various ethnic backgrounds has shown that alpha2-AR genes are polymorphic. The functional and biochemical consequences of these polymorphisms have been analyzed by expressing the wild-type receptors and their respective genetic variants in heterologous systems such as CHO and COS-7 cells. Changes include alteration in G-protein coupling and in agonist-promoted receptor phosphorylation and desensitization. Case-control and population-based studies have shown clinical association with cardiovascular risk. Further investigation of the genetic variants in specialized cells and transgenic animals will provide the molecular basis of cardiovascular disease and may reveal alpha2-AR variants as potential targets for selective pharmacological interventions.

Polymorphisms of adrenergic receptors: variations on a theme

Recent studies have revealed that most of the adrenergic receptor genes are polymorphic, leading to changes in the amino sequence of the encoded receptor. The variations occur in multiple functional regions of the receptors, and appear as haplotypes with other coding and noncoding polymorphisms in their genes. The consequences of such genetic variability have been explored in recombinant cell-based systems and in human studies. Adrenergic receptor polymorphisms have been shown to alter receptor binding, G-protein coupling, regulation, and expression compared with their allelic counterparts. Here, the genetic and molecular characterization of these polymorphisms is reviewed, as well as their potential impact on pharmacogenetics, disease risk, and disease modification.

Cloning, characterisation and identification of several polymorphisms in the promoter region of the human alpha2B-adrenergic receptor gene

Screening of a foetal brain genomic DNA library allowed to isolate a 10-kb fragment of the gene encoding the human alpha2B-adrenergic receptor, that contained 5.5 kb of the 5'-flanking region, the open reading frame and 2.9 kb of the 3'-flanking region. The 1-kb fragment upstream from the start codon was rich in GC, lacked consensus TATA or CAAT box, but contained several Sp1-binding sites. Other potential cis-regulatory elements found in the 5'-flanking region included AP2, USF, Stat-6, NFkappaB and Olf-1. A single canonical polyadenylation signal (AATAAA) was found at position +3252/+3257 and the polyadenylation site was 3274 nucleotides downstream from ATG. Transfection experiments with chimeric luciferase constructs containing various truncated fragments of the 5'-region showed that the fragment -3160/+3 exhibited promoter activity in all tested cell lines and permitted the definition of a minimal 200-bp promoter (-603/-411) containing three putative Sp1-binding sites and two initiator elements. Transcriptional activity of this region was inhibited by the addition of mithramycin, a specific inhibitor of Sp1 binding to GC-rich sequences. The search for sequence variants within a fragment covering 1.7 kb of 5'-flanking region and the coding region allowed us to identify five novel single nucleotide polymorphisms. Interestingly, the G/C substitution at position -98 relative to the start codon was common and in complete linkage with a previously identified insertion/deletion polymorphism in the coding region which was showed to affect alpha2B-adrenergic receptor function. Based on transfection data and computer-assisted sequence analysis, the -98 G/C single nucleotide polymorphism was located within a portion of the 5'-UTR (-127/+3) affecting luciferase activity and it created additional putative binding site for Sp1. However, G/C substitution had no significant incidence on promoter activity in BHK-21 or HeLa cells.

Autonomic Nervous System Pharmacogenomics: A Progress Report

Pharmacogenetics, the inherited basis for interindividual differences in drug response, has rapidly expanded with the advent of new molecular tools and the sequencing of the human genome, yielding pharmacogenomics. We review here recent ideas and findings regarding pharmacogenomics of components of the autonomic nervous system, in particular, neuronal nicotinic acetylcholine receptors, postsynaptic receptors with which the parasympathetic and sympathetic neurotransmitters, acetylcholine (ACh) and norepinephrine, respectively, interact. The receptor subtypes that mediate these responses, M(1-3) muscarinic cholinergic receptors (mAChRs), and alpha(1A,B,D)-, alpha(2A,B,C)-, and beta(1,2,3)-adrenergic receptors (AR), show highly variable expression of genetic variants; variants of mAChRs and alpha(1)-ARs are relatively rare, whereas alpha(2)-AR and beta-AR subtype variants are quite common. The largest amount of data is available regarding variants of the latter ARs and represents efforts to associate certain receptor genotypes, most commonly, single nucleotide polymorphisms, with particular phenotypes (e.g., cardiovascular and metabolic responses). In vitro and in vivo studies have yielded inconsistent results; definitive conclusions are limited. We identify several conceptual and methodological problems with available data: sample size, ethnicity, tissue differences, coding versus noncoding variants, limited studies of haplotypes, and interaction among variants. Thus, although progress has been made in identifying genetic variation that influences drug response fo autonomic nervous system components, we are still at the early stages of defining the most critical genetic determinants and their role in human physiology and pharmacology.

Alpha 2A adrenergic receptor gene and suicide

Suicide is a complex trait resulting from the interaction of several predisposing factors, among which genes seem to play an important role. Alterations in the noradrenergic system have been observed in postmortem brain studies of suicide victims when compared to controls. The purpose of this study was to test the hypothesis that genetic variants of the alpha(2A) adrenergic receptor gene are implicated in suicide and/or have a modulatory effect on personality traits that are believed to mediate suicidal behavior. We studied a sample of suicides (N=110) and control subjects (N=130) for genetic variation at four loci, including three in the promoter region (g-1800t, c-1291 g and the g-261a) of the alpha(2A) adrenergic receptor gene, and a potentially functional locus, N251K, which leads to an amino acid change (asparagine to lysine). No significant differences were observed at the promoter loci in terms of allelic or genotypic distribution between suicides and controls. However, analysis of the functional polymorphism N251K revealed that the 251 K allele was only present among suicides, though only three suicide cases had this allele, two of which were homozygous. These results are preliminary. If confirmed, they suggest that variation at the alpha(2A) adrenergic receptor gene may play a role in a small proportion of suicide cases.

Pharmacology and physiology of human adrenergic receptor polymorphisms

Adrenergic receptors are expressed on virtually every cell type in the body and are the receptors for epinephrine and norepinephrine within the sympathetic nervous system. They serve critical roles in maintaining homeostasis in normal physiologic settings as well as pathologic states. These receptors are also targets for therapeutically administered agonists and antagonists. Recent studies have shown that at least seven adrenergic receptor subtypes display variation in amino acid sequence in the human population due to common genetic polymorphisms. Variations in potential regulatory domains in noncoding sequence are also present. Here, we review the consequences of these polymorphisms in terms of signaling, human physiology and disease, and response to therapy.

Feedback inhibition of catecholamine release by two different alpha2-adrenoceptor subtypes prevents progression of heart failure

BACKGROUND

Elevated plasma norepinephrine levels are associated with increased mortality in patients and in animal models with chronic heart failure. To test which alpha2-adrenoceptor subtypes operate as presynaptic inhibitory receptors to control norepinephrine release in heart failure, we investigated the response of gene-targeted mice lacking alpha2-adrenoceptor subtypes (alpha2-KO) to chronic left ventricular pressure overload. In addition, we determined the functional consequences of genetic variants of alpha2-adrenoceptors in human patients with chronic heart failure.

METHODS AND RESULTS

Cardiac pressure overload was induced by transverse aortic constriction. Three months after aortic banding, survival was dramatically reduced in alpha2A-KO (52%) and alpha2C-KO (47%) mice compared with wild-type and alpha2B-deficient (86%) animals. Excess mortality in alpha2A- and alpha2C-KO strains was attributable to heart failure with enhanced left ventricular hypertrophy and fibrosis and elevated circulating catecholamines. The clinical importance of this finding is emphasized by the fact that heart failure patients with a dysfunctional variant of the alpha2C-adrenoceptor had a worse clinical status and decreased cardiac function as determined by invasive catheterization and by echocardiography.

CONCLUSIONS

Our results indicate an essential function of alpha2A- and alpha2C-adrenoceptors in the prevention of heart failure progression in mice and human patients. Identification of heart failure patients with genetic alpha2-adrenoceptor variants as well as new alpha2-receptor subtype-selective drugs may represent novel therapeutic strategies in chronic heart failure and other diseases with enhanced sympathetic activation.

Gbetagamma affinity for bovine rhodopsin is determined by the carboxyl-terminal sequences of the gamma subunit

Two native betagamma dimers, beta(1)gamma(1) and beta(1)gamma(2), display very different affinities for receptors. Since these gamma subunits differ in both primary structure and isoprenoid modification, we examined the relative contributions of each to Gbetagamma interaction with receptors. We constructed baculoviruses encoding gamma(1) and gamma(2) subunits with altered CAAX (where A is an aliphatic amino acid) motifs to direct alternate or no prenylation of the gamma chains and a set of gamma(1) and gamma(2) chimeras with the gamma(2) CAAX motif at the carboxyl terminus. All the gamma constructs coexpressed with beta(1) in Sf9 cells yielded beta(1)gamma dimers, which were purified to near homogeneity, and their affinities for receptors and Galpha were quantitatively determined. Whereas alteration of the isoprenoid of gamma(1) from farnesyl to geranylgeranyl and of gamma(2) from geranylgeranyl to farnesyl had no impact on the affinities of beta(1)gamma dimers for Galpha(t), the non-prenylated beta(1)gamma(2) dimer had significantly diminished affinity. Altered prenylation resulted in a <2-fold decrease in affinity of the beta(1)gamma(2) dimer for rhodopsin and a <3-fold change for the beta(1)gamma(1) dimer. In each case with identical isoprenylation, the beta(1)gamma(2) dimer displayed significantly greater affinity for rhodopsin compared with the beta(1)gamma(1) dimer. Furthermore, dimers containing chimeric Ggamma chains with identical geranylgeranyl modification displayed rhodopsin affinities largely determined by the carboxyl-terminal one-third of the protein. These results indicate that isoprenoid modification of the Ggamma subunit is essential for binding to both Galpha and receptors. The isoprenoid type influences the binding affinity for receptors, but not for Galpha. Finally, the primary structure of the Ggamma subunit provides a major contribution to receptor binding of Gbetagamma, with the carboxyl-terminal sequence conferring receptor selectivity.

Single nucleotide polymorphism of human platelet-activating factor receptor impairs G-protein activation

Various proinflammatory and vasoactive actions of platelet-activating factor (PAF) are mediated through a specific G-protein-coupled PAF receptor (PAFR). We identified a novel DNA variant in the human PAFR gene, which substitutes an aspartic acid for an alanine residue at position 224 (A224D) in the putative third cytoplasmic loop. This mutation was observed in a Japanese population at an allele frequency of 7.8%. To delineate the functional consequences of this structural alteration, Chinese hamster ovary cells were stably transfected with constructs encoding either wild-type or A224D mutated PAFR. No significant difference was observed in the expression level of the receptor or the affinity to PAF or to an antagonist, WEB2086, between the cells transfected with wild-type and mutant PAFR. Chinese hamster ovary cells expressing A224D mutant PAFR displayed partial but significant reduction of PAF-induced intracellular signals such as calcium mobilization, inositol phosphate production, inhibition of adenylyl cyclase, and chemotaxis. These findings suggest that this variant receptor produced by a naturally occurring mutation exhibits impaired coupling to G-proteins and may be a basis for interindividual variation in PAF-related physiological responses, disease predisposition or phenotypes, and drug responsiveness.

Platelets in nonresponders to epinephrine stimulation showed reduced response to ADP

It has been reported that platelets from some healthy donors did not respond to epinephrine (Epi). To identify the cause for the lack of response, we examined the alpha(2) adrenoceptor in the platelets and their signal transduction pathways. No differences in the genomic (-2076 to 1526 bp) and coding region of alpha(2A) adrenoceptor complementary DNA (cDNA) were found between the responders (R) and nonresponders (NR). No expression of alpha(2B) or alpha(2C) adrenoceptor was detected in platelets. When UK14,304 was used to induce platelet aggregation, similar effect to Epi was observed between R and NR, and any involvement of the alpha(1) and beta adrenoceptor was ruled out. Radioligand binding assay showed similar number of alpha(2) binding sites between the two groups (139+/-25/platelet vs. 145+/-37/platelets). However, platelets from NR showed a weaker response to adenosine diphosphate (ADP, 52.3+/-17.8% vs. 80.5+/-8.7% from R, P<.01). In the presence of P2Y(1) antagonist adenosine 3',5'-diphosphosulfate (A3P5PS), ADP failed to induce platelet aggregation in NR (7.8+/-4.7% vs. 64.7+/-11.2% in R, P<.01). Addition of SQ22,536 to inhibit adenylyl cyclase did not convert NR to R. These observations demonstrate that there is an impaired platelet responsiveness to ADP as well as to Epi in NR, due to a difference in downstream of the signal transduction pathway but independent of adenylyl cyclase inhibition.

Identification and functional characterization of alpha(2)-adrenoceptor polymorphisms

For each alpha(2)-adrenoceptor subtype (alpha(2A), alpha(2B) and alpha(2C)), sequence variations within the coding region of each gene have been identified in humans. These result in substitutions or deletions of amino acids in the third intracellular loops of each receptor. This article summarizes the genetics and molecular biology of alpha(2)-adrenoceptor polymorphisms, including the consequences of each polymorphism on receptor signaling, as determined in transfected cells. These effects include alterations in G-protein coupling, desensitization and G-protein receptor kinase-mediated phosphorylation. Studies so far provide the mechanistic basis for future studies to investigate genetic risk factors and pharmacogenetics in pathophysiological conditions linked to alpha(2)-adrenoceptor function.

Genetic variations in human G protein-coupled receptors: implications for drug therapy

Numerous genes encode G protein-coupled receptors (GPCRs)-a main molecular target for drug therapy. Estimates indicate that the human genome contains approximately 600 GPCR genes. This article addresses therapeutic implications of sequence variations in GPCR genes. A number of inactivating and activating receptor mutations have been shown to cause a variety of (mostly rare) genetic disorders. However, pharmacogenetic and pharmacogenomic studies on GPCRs are scarce, and therapeutic relevance of variant receptor alleles often remains unclear. Confounding factors in assessing the therapeutic relevance of variant GPCR alleles include 1) interaction of a single drug with multiple closely related receptors, 2) poorly defined binding pockets that can accommodate drug ligands in different orientations or at alternative receptor domains, 3) possibility of multiple receptor conformations with distinct functions, and 4) multiple signaling pathways engaged by a single receptor. For example, antischizophrenic drugs bind to numerous receptors, several of which might be relevant to therapeutic outcome. Without knowing accurately what role a given receptor subtype plays in clinical outcome and how a sequence variation affects drug-induced signal transduction, we cannot predict the therapeutic relevance of a receptor variant. Genome-wide association studies with single nucleotide polymorphisms could identify critical target receptors for disease susceptibility and drug efficacy or toxicity.

A Glu-496 to Ala polymorphism leads to loss of function of the human P2X7 receptor

The P2X(7) receptor is a ligand-gated cation-selective channel that mediates ATP-induced apoptosis of cells of the immune system. We and others have shown that P2X(7) is nonfunctional both in lymphocytes and monocytes from some subjects. To study a possible genetic basis we sequenced DNA coding for the carboxyl-terminal tail of P2X(7). In 9 of 45 normal subjects a heterozygous nucleotide substitution (1513A-->C) was found, whereas 1 subject carried the homozygous substitution that codes for glutamic acid to alanine at amino acid position 496. Surface expression of P2X(7) on lymphocytes was not affected by this E496A polymorphism, demonstrated both by confocal microscopy and immunofluorescent staining. Monocytes and lymphocytes from the E496A homozygote subject expressed nonfunctional receptor, whereas heterozygotes showed P2X(7) function that was half that of germline P2X(7). Results of transfection experiments showed that the mutant P2X(7) receptor was nonfunctional when expressed at low receptor density but regained function at a high receptor density. This density dependence of mutant P2X(7) function was also seen on differentiation of fresh monocytes to macrophages with interferon-gamma, which up-regulated mutant P2X(7) and partially restored its function. P2X(7)-mediated apoptosis of lymphocytes was impaired in homozygous mutant P2X(7) compared with germline (8.6 versus 35.2%). The data suggest that the glutamic acid at position 496 is required for optimal assembly of the P2X(7) receptor.

Genetic polymorphisms of adrenergic receptors

Recent advances in molecular biology have enhanced the understanding of adrenergic receptors. They have allowed the characterization of the several subtypes of adrenergic receptors expressed and have expanded the research about the potential physiologic functions they mediate. Furthermore, variant forms, or polymorphims, of the genes that code for these receptors are being identified. These genetic variants may or may not result in functional differences in the receptors they encode. There is obvious interest in determining the physiologic and clinical relevance of these polymorphisms. The purpose of this review is to describe these polymorphisms and the often contradictory literature pertaining to their clinical significance. Progress in this area is being made at a rapid pace. As the allele-disease relations become less equivocal, it might be possible to predict individual differences in susceptibility to a disease, disease prognosis, and response to treatment.