Alpha 1-adrenoceptors: subtypes, signaling, and roles in health and disease

α-1 Adrenergic receptor antagonist doxazosin reverses hepatic stellate cells activation via induction of senescence

BACKGROUND

Activated hepatic stellate cells (aHSCs) are the main effector cells during liver fibrogenesis. α-1 adrenergic antagonist doxazosin (DX) was shown to be anti-fibrotic in an in vivo model of liver fibrosis (LF), but the mechanism remains to be elucidated. Recent studies suggest that reversion of LF can be achieved by inducing cellular senescence characterized by irreversible cell-cycle arrest and acquisition of the senescence-associated secretory phenotype (SASP).

AIM

To elucidate the mechanism of the anti-fibrotic effect of DX and determine whether it induces senescence.

METHODS

Primary culture-activated rat HSCs were used. mRNA and protein expression were measured by qPCR and Western blot, respectively. Cell proliferation was assessed by BrdU incorporation and xCelligence analysis. TGF-β was used for maximal HSC activation. Norepinephrine (NE), PMA and m-3M3FBS were used to activate alpha-1 adrenergic signaling.

RESULTS

Expression of Col1α1 was significantly decreased by DX (10 µmol/L) at mRNA (-30 %) and protein level (-50 %) in TGF-β treated aHSCs. DX significantly reduced aHSCs proliferation and increased expression of senescence and SASP markers. PMA and m-3M3FBS reversed the effect of DX on senescence markers.

CONCLUSION

Doxazosin reverses the fibrogenic phenotype of aHSCs and induces the senescence phenotype.

Updates in the function and regulation of α1 -adrenoceptors

α₁ -Adrenoceptors are seven transmembrane domain GPCRs involved in numerous physiological functions controlled by the endogenous catecholamines, noradrenaline and adrenaline, and targeted by drugs useful in therapeutics. Three separate genes, whose products are named α_1A -, α_1B -, and α_1D - adrenoceptors, encode these receptors. Although the existence of multiple α₁ -adrenoceptors has been acknowledged for almost 25 years, the specific functions regulated by each subtype are still largely unknown. Despite the limited comprehension, the identification of a single class of subtype-selective ligands for the α_1A - adrenoceptors, the so-called α-blockers for prostate dysfunction, has led to major improvement in therapeutics, demonstrating the need for continued efforts in the field. This review article surveys the tissue distribution of the three α₁ -adrenoceptor subtypes in the cardiovascular system, genitourinary system, and CNS, highlighting the functions already identified as mediated by the predominant activation of specific subtypes. In addition, this review covers the recent advances in the understanding of the molecular mechanisms involved in the regulation of each of the α₁ -adrenoceptor subtypes by phosphorylation and interaction with proteins involved in their desensitization and internalization. LINKED ARTICLES: This article is part of a themed section on Adrenoceptors-New Roles for Old Players. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.14/issuetoc.

Novel Structural Approaches to Study GPCR Regulation

BACKGROUND

Upon natural agonist or pharmacological stimulation, G protein-coupled receptors (GPCRs) are subjected to posttranslational modifications, such as phosphorylation and ubiquitination. These posttranslational modifications allow protein-protein interactions that turn off and/or switch receptor signaling as well as trigger receptor internalization, recycling or degradation, among other responses. Characterization of these processes is essential to unravel the function and regulation of GPCR.

METHODS

In silico analysis and methods such as mass spectrometry have emerged as novel powerful tools. Both approaches have allowed proteomic studies to detect not only GPCR posttranslational modifications and receptor association with other signaling macromolecules but also to assess receptor conformational dynamics after ligand (agonist/antagonist) association.

RESULTS

this review aims to provide insights into some of these methodologies and to highlight how their use is enhancing our comprehension of GPCR function. We present an overview using data from different laboratories (including our own), particularly focusing on free fatty acid receptor 4 (FFA4) (previously known as GPR120) and α1A- and α1D-adrenergic receptors. From our perspective, these studies contribute to the understanding of GPCR regulation and will help to design better therapeutic agents.

LPA receptor activity is basal specific and coincident with early pregnancy and involution during mammary gland postnatal development

During pregnancy, luminal and basal epithelial cells of the adult mammary gland proliferate and differentiate resulting in remodeling of the adult gland. While pathways that control this process have been characterized in the gland as a whole, the contribution of specific cell subtypes, in particular the basal compartment, remains largely unknown. Basal cells provide structural and contractile support, however they also orchestrate the communication between the stroma and the luminal compartment at all developmental stages. Using RNA-seq, we show that basal cells are extraordinarily transcriptionally dynamic throughout pregnancy when compared to luminal cells. We identified gene expression changes that define specific basal functions acquired during development that led to the identification of novel markers. Enrichment analysis of gene sets from 24 mouse models for breast cancer pinpoint to a potential new function for insulin-like growth factor 1 (Igf1r) in the basal epithelium during lactogenesis. We establish that β-catenin signaling is activated in basal cells during early pregnancy, and demonstrate that this activity is mediated by lysophosphatidic acid receptor 3 (Lpar3). These findings identify novel pathways active during functional maturation of the adult mammary gland.

Carboxyl terminus-truncated α1D-adrenoceptors inhibit the ERK pathway

Human α1D-adrenoceptors are G protein-coupled receptors that mediate adrenaline/noradrenaline actions. There is a growing interest in identifying regulatory domains in these receptors and determining how they function. In this work, we show that the absence of the human α1D-adrenoceptor carboxyl tail results in altered ERK (extracellular signal-regulated kinase) and p38 phosphorylation states. Amino terminus-truncated and both amino and carboxyl termini-truncated α1D-adrenoceptors were transfected into Rat-1, HEK293, and B103 cells, and changes in the phosphorylation state of extracellular signal-regulated kinase was assessed using biochemical and biophysical approaches. The phosphorylation state of other protein kinases (p38, MEK1, and Raf-1) was also studied. Noradrenaline-induced ERK phosphorylation in Rat-1 fibroblasts expressing amino termini-truncated α1D-adrenoceptors. However, in cells expressing receptors with both amino and carboxyl termini truncations, noradrenaline-induced activation was abrogated. Interestingly, ERK phosphorylation that normally occurs through activation of endogenous G protein-coupled receptors, EGF receptors, and protein kinase C, was also decreased, suggesting that downstream steps in the mitogen-activated protein kinase pathway were affected. A similar effect was observed in B103 cells but not in HEK 293 cells. Phosphorylation of Raf-1 and MEK1 was also diminished in Rat-1 fibroblasts expressing amino- and carboxyl-truncated α1D-adrenoceptors. Our data indicate that expression of carboxyl terminus-truncated α1D-adrenoceptors alters ERK and p38 phosphorylation state.

Kallikrein-related peptidase 8 is expressed in myocardium and induces cardiac hypertrophy

The tissue kallikrein-related peptidase family (KLK) is a group of trypsin- and chymotrypsin-like serine proteases that share a similar homology to parent tissue kallikrein (KLK1). KLK1 is identified in heart and has anti-hypertrophic effects. However, whether other KLK family members play a role in regulating cardiac function remains unknown. In the present study, we demonstrated for the first time that KLK8 was expressed in myocardium. KLK8 expression was upregulated in left ventricle of cardiac hypertrophy models. Both intra-cardiac adenovirus-mediated and transgenic-mediated KLK8 overexpression led to cardiac hypertrophy in vivo. In primary neonatal rat cardiomyocytes, KLK8 knockdown inhibited phenylephrine (PE)-induced cardiomyocyte hypertrophy, whereas KLK8 overexpression promoted cardiomyocyte hypertrophy via a serine protease activity-dependent but kinin receptor-independent pathway. KLK8 overexpression increased epidermal growth factor (EGF) production, which was blocked by the inhibitors of serine protease. EGF receptor (EGFR) antagonist and EGFR knockdown reversed the hypertrophy induced by KLK8 overexpression. KLK8-induced cardiomyocyte hypertrophy was also significantly decreased by blocking the protease-activated receptor 1 (PAR1) or PAR2 pathway. Our data suggest that KLK8 may promote cardiomyocyte hypertrophy through EGF signaling- and PARs-dependent but a kinin receptor-independent pathway. It is implied that different KLK family members can subtly regulate cardiac function and remodeling.

Animal models of post-traumatic stress disorder and recent neurobiological insights

Post-traumatic stress disorder (PTSD) is a complex psychiatric disorder characterized by the intrusive re-experiencing of past trauma, avoidant behavior, enhanced fear, and hyperarousal following a traumatic event in vulnerable populations. Preclinical animal models do not replicate the human condition in its entirety, but seek to mimic symptoms or endophenotypes associated with PTSD. Although many models of traumatic stress exist, few adequately capture the complex nature of the disorder and the observed individual variability in susceptibility of humans to PTSD. In addition, various types of stressors may produce different molecular neuroadaptations that likely contribute to the various behavioral disruptions produced by each model, although certain consistent neurobiological themes related to PTSD have emerged. For example, animal models report traumatic stress-induced and trauma reminder-induced alterations in neuronal activity in the amygdala and prefrontal cortex, in agreement with the human PTSD literature. Models have also provided a conceptual framework for the often-observed combination of PTSD and comorbid conditions such as alcohol use disorder. Future studies will continue to refine preclinical PTSD models in hope of capitalizing on their potential to deliver new and more efficacious treatments for PTSD and associated psychiatric disorders.

α1B-adrenergic receptors differentially associate with Rab proteins during homologous and heterologous desensitization

Internalization of G protein-coupled receptors can be triggered by agonists or by other stimuli. The process begins within seconds of cell activation and contributes to receptor desensitization. The Rab GTPase family controls endocytosis, vesicular trafficking, and endosomal fusion. Among their remarkable properties is the differential distribution of its members on the surface of various organelles. In the endocytic pathway, Rab 5 controls traffic from the plasma membrane to early endosomes, whereas Rab 4 and Rab 11 regulate rapid and slow recycling from early endosomes to the plasma membrane, respectively. Moreover, Rab 7 and Rab 9 regulate the traffic from late endosomes to lysosomes and recycling to the trans-Golgi. We explore the possibility that α_1B-adrenergic receptor internalization induced by agonists (homologous) and by unrelated stimuli (heterologous) could involve different Rab proteins. This possibility was explored by Fluorescence Resonance Energy Transfer (FRET) using cells coexpressing α_1B-adrenergic receptors tagged with the red fluorescent protein, DsRed, and different Rab proteins tagged with the green fluorescent protein. It was observed that when α_1B-adrenergic receptors were stimulated with noradrenaline, the receptors interacted with proteins present in early endosomes, such as the early endosomes antigen 1, Rab 5, Rab 4, and Rab 11 but not with late endosome markers, such as Rab 9 and Rab 7. In contrast, sphingosine 1-phosphate stimulation induced rapid and transient α_1B-adrenergic receptor interaction of relatively small magnitude with Rab 5 and a more pronounced and sustained one with Rab 9; interaction was also observed with Rab 7. Moreover, the GTPase activity of the Rab proteins appears to be required because no FRET was observed when dominant-negative Rab mutants were employed. These data indicate that α_1B-adrenergic receptors are directed to different endocytic vesicles depending on the desensitization type (homologous vs. heterologous).

Regulation of Calcium-Independent Phospholipase A2 Expression by Adrenoceptors and Sterol Regulatory Element Binding Protein-Potential Crosstalk Between Sterol and Glycerophospholipid Mediators

Calcium-independent phospholipase A2 (iPLA2) is an 85-kDa enzyme that releases docosahexaenoic acid (DHA) from glycerophospholipids. DHA can be metabolized to resolvins and neuroprotectins that have anti-inflammatory properties and effects on neural plasticity. Recent studies show an important role of prefrontal cortical iPLA2 in hippocampo-prefrontal cortical LTP and antidepressant-like effect of the norepinephrine reuptake inhibitor (NRI) antidepressant, maprotiline. In this study, we elucidated the cellular mechanisms through which stimulation of adrenergic receptors could lead to increased iPLA2 expression. Treatment of SH-SY5Y neuroblastoma cells with maprotiline, another tricyclic antidepressant with noradrenaline reuptake inhibiting properties, nortriptyline, and the adrenergic receptor agonist, phenylephrine, resulted in increased iPLA2β mRNA expression. This increase was blocked by inhibitors to alpha-1 adrenergic receptor, mitogen-activated protein (MAP) kinase or extracellular signal-regulated kinase (ERK) 1/2, and sterol regulatory element-binding protein (SREBP). Maprotiline and phenylephrine induced binding of SREBP-2 to sterol regulatory element (SRE) region on the iPLA2 promoter, as determined by electrophoretic mobility shift assay (EMSA). Together, results indicate that stimulation of adrenoreceptors causes increased iPLA2 expression via MAP kinase/ERK 1/2 and SREBP, and suggest a possible mechanism for effect of CNS noradrenaline on neural plasticity and crosstalk between sterol and glycerophospholipid mediators, that may play a role in physiological or pathophysiological processes in the brain and other organs.

Altered expression profile of renal α(1D)-adrenergic receptor in diabetes and its modulation by PPAR agonists

Alpha(1D)-adrenergic receptor (α(1D)-AR) plays important roles in regulating physiological and pathological responses mediated by catecholamines, particularly in the cardiovascular and urinary systems. The present study was designed to investigate the expression profile of α(1D)-AR in the diabetic kidneys and its modulation by activation of peroxisome proliferator-activated receptors (PPARs). 12-week-old Zucker lean (ZL) and Zucker diabetic fatty (ZD) rats were treated with fenofibrate or rosiglitazone for 8-10 weeks. Gene microarray, real-time PCR, and confocal immunofluorescence microscopy were performed to assess mRNA and protein expression of α(1D)-AR in rat kidney tissue. Using microarray, we found that α(1D)-AR gene was dramatically upregulated in 22-week-old ZD rats compared to ZL controls. Quantitative PCR analysis verified a 16-fold increase in α(1D)-AR mRNA in renal cortex from ZD animals compared to normal controls. Chronic treatment with fenofibrate or rosiglitazone reduced renal cortical α(1D)-AR gene. Immunofluorescence staining confirmed that α(1D)-AR protein was induced in the glomeruli and tubules of diabetic rats. Moreover, dual immunostaining for α(1D)-AR and kidney injury molecule-1 indicated that α(1D)-AR was expressed in dedifferentiated proximal tubules of diabetic Zucker rats. Taken together, our results show that α(1D)-AR expression is upregulated in the diabetic kidneys. PPAR activation suppressed renal expression of α(1D)-AR in diabetic nephropathy.

Pharmacological characterization of N1-(2-methoxyphenyl)-N4-hexylpiperazine as a multi-target antagonist of α1A/α1D-adrenoceptors and 5-HT1A receptors that blocks prostate contraction and cell growth

Benign prostatic hyperplasia (BPH) is a progressive disease related to the imbalance of cell growth and apoptosis, and it plays a key role in the development of lower urinary tract symptoms (LUTS). The main pharmacological treatment is based on α1A-adrenoceptor blockers, but in several cases monotherapy has failed. Recent studies of prostate pathophysiology have noted the role of α1D-adrenoceptors and 5-HT1A receptors in prostate cell proliferation in addition to the usual role of α1A-adrenoceptors in prostate contraction. N-phenylpiperazine is a scaffold structure that may confer drug affinity for these three receptors. Therefore, the present work aimed to investigate the pharmacological characteristics of N1-(2-methoxyphenyl)-N4-hexylpiperazine (LDT66). Using isometric contraction assays with rat prostate and aorta, LDT66 reduced phenylephrine-induced contractions and showed K B values of 3.4 and 2.2 nM for α1A- and α1D-adrenoceptors, respectively. According to the functional binding assays data, LDT66 showed a high affinity (nanomolar range) for the 5-HT1A receptors, behaving as an antagonist. LDT66 also showed a low affinity (micromolar range) for receptors unrelated to BPH such as α1B-adrenoceptors, α2A-adrenoceptors, muscarinic and 5-HT2A receptors, which is a desirable profile in order to prevent putative side effects. Accordingly, LDT66 (100 μg/kg) showed a marginal hypotensive effect. Using the DU-145 prostate cells, control experiments characterized the α1D-adrenoceptor- and 5-HT1A receptor-mediated cell growth by phenylephrine and 5-HT, respectively. LDT66 (50 nM) prevented both effects similarly. In conclusion, LDT66 is a high-affinity multi-target antagonist of relevant receptors for BPH, and it may be a new starting point for multi-target drug development to treat BPH and LUTS.

α1D-Adrenoceptors are responsible for the high sensitivity and the slow time-course of noradrenaline-mediated contraction in conductance arteries

The objective of this study was to determine whether the different time-course characteristics of α₁-adrenoceptor-mediated contraction in arteries can be related to the subtypes involved. Contractile responses to noradrenaline (NA) were compared with inositol phosphate accumulation and extracellular signal-regulated kinase (ERK)1/2 phosphorylation after α₁-agonist stimuli in the same vessels in the presence or absence of α₁-antagonists in rat or in α₁-subtype knockout (KO) mice. Aorta, where α_1D-AR is the main functional subtype, had higher sensitivity to NA (in respect of inositol phosphate [IP], pERK1/2, and contractile response) than tail artery, where the α_1A-adrenoceptor subtype is predominant. Furthermore, the contraction in aorta exhibited a slower decay after agonist removal and this was consistent in all strains harboring α_1D-adrenoceptors (from rat, α_1B-KO, and wild-type [WT] mice) but was not observed in the absence of the α_1D-adrenoceptor signal (α_1D-adrenoceptor blocked rat aorta or aorta from α_1D-KO). IP formation paralleled α₁-adrenoceptor-mediated contraction (agonist present or postagonist) in aorta and tail artery. High sensitivity to agonist and persistence of response after agonist removal is a property of α_1D-adrenoceptors. Therefore, the preponderance of this subtype in noninnervated conductance arteries such as aorta allows responsiveness to circulating catecholamines and prevents abrupt changes in vessel caliber when the stimulus fluctuates. Conversely, in innervated distributing arteries, high local concentrations of NA are required to activate α_1A-adrenoceptors for a response that is rapid but short lived allowing fine adjustment of the contractile tone by perivascular sympathetic nerves.

Initial orthostatic hypotension and cerebral blood flow regulation: effect of α1-adrenoreceptor activity

We examined the hypothesis that α1-adrenergic blockade would lead to an inability to correct initial orthostatic hypotension (IOH) and cerebral hypoperfusion, leading to symptoms of presyncope. Twelve normotensive humans (aged 25 ± 1 yr; means ± SE) attempted to complete a 3-min upright stand, 90 min after the administration of either α1-blockade (prazosin, 1 mg/20 kg body wt) or placebo. Continuous beat-to-beat measurements of middle cerebral artery velocity (MCAv; Doppler), blood pressure (finometer), heart rate, and end-tidal Pco2were obtained. Compared with placebo, the α1-blockade reduced resting mean arterial blood pressure (MAP) (−15%; P < 0.01); MCAv remained unaltered ( P ≥ 0.28). Upon standing, although the absolute level of MAP was lower following α1-blockade (39 ± 10 mmHg vs. 51 ± 14 mmHg), the relative difference in IOH was negligible in both trials (mean difference in MAP: 2 ± 2 mmHg; P = 0.50). Compared with the placebo trial, the declines in MCAv and PetCO2during IOH were greater in the α1-blockade trial by 12 ± 4 cm/s and 4.4 ± 1.3 mmHg, respectively ( P ≤ 0.01). Standing tolerance was markedly reduced in the α1-blockade trial (75 ± 17 s vs. 180 ± 0 s; P < 0.001). In summary, while IOH was little affected by α1-blockade, the associated decline in MCAv was greater in the blockade condition. Unlike in the placebo trial, the extent of IOH and cerebral hypoperfusion failed to recover toward baseline in the α1-blockade trial leading to presyncope. Although the development of IOH is not influenced by the α1-adrenergic receptor pathway, this pathway is critical in the recovery from IOH to prevent cerebral hypoperfusion and ultimately syncope.

Sphingosine 1-phosphate-mediated α1B-adrenoceptor desensitization and phosphorylation. Direct and paracrine/autocrine actions

Sphingosine-1-phosphate-induced α1B-adrenergic receptor desensitization and phosphorylation were studied in rat-1 fibroblasts stably expressing enhanced green fluorescent protein-tagged adrenoceptors. Sphingosine-1-phosphate induced adrenoceptor desensitization and phosphorylation through a signaling cascade that involved phosphoinositide 3-kinase and protein kinase C activities. The autocrine/paracrine role of sphingosine-1-phosphate was also studied. It was observed that activation of receptor tyrosine kinases, such as insulin growth factor-1 (IGF-I) and epidermal growth factor (EGF) receptors increased sphingosine kinase activity. Such activation and consequent production of sphingosine-1-phosphate appear to be functionally relevant in IGF-I- and EGF-induced α1B-adrenoceptor phosphorylation and desensitization as evidenced by the following facts: a) expression of a catalytically inactive (dominant-negative) mutant of sphingosine kinase 1 or b) S1P1 receptor knockdown markedly reduced this growth factor action. This action of sphingosine-1-phosphate involves EGF receptor transactivation. In addition, taking advantage of the presence of the eGFP tag in the receptor construction, we showed that S1P was capable of inducing α1B-adrenergic receptor internalization and that its autocrine/paracrine generation was relevant for internalization induced by IGF-I. Four distinct hormone receptors and two autocrine/paracrine mediators participate in IGF-I receptor-α1B-adrenergic receptor crosstalk.

Roles of the α1A-adrenergic receptor carboxyl tail in protein kinase C-induced phosphorylation and desensitization

Noradrenaline- and tetradecanoyl phorbol acetate (TPA)-induced phosphorylation and functional desensitization of the following receptors were studied: (1) wild-type bovine α(1A)- and hamster α(1B)-adrenergic receptors (ARs), (2) chimeric ARs in which the carboxyl terminus tails were exchanged (α(1AB)- and α(1BA)-ARs), and (3) carboxyl terminus-truncated α(1A)-ARs fussed to enhanced green fluorescent protein. Noradrenaline and TPA pronouncedly increased α(1B)-AR phosphorylation while TPA markedly desensitized these receptors. In contrast, TPA-induced desensitization and TPA- and noradrenaline-induced phosphorylation of α(1A)-ARs were clearly of lesser magnitude. Chimeric ARs with exchanged carboxyl terminus tails showed that the extent of phosphorylation reflected the carboxyl domain rather than the receptor core. Surprisingly, there was no correlation between phosphorylation and functional desensitization, i.e., activation of protein kinase C clearly desensitized both chimeric receptors to a similar extent. Interestingly, TPA and noradrenaline increased carboxyl terminus-truncated α(1A)-AR phosphorylation and TPA also induced receptor desensitization. We were unable to detect carboxyl terminus-truncated α(1A)-AR internalization after 5-min stimulations with noradrenaline or TPA. Our results suggest the following: (a) the α(1A)-AR carboxyl terminus tail was not essential for signaling or desensitization; (b) carboxyl terminus tail exchange "transplanted" the phosphorylation pattern of the receptors, but the functional consequences of such a transplant were very limited; (c) α(1A)-AR desensitization was not associated to receptor internalization.

Extraendothelial and constitutive COX-2 expression is involved in the contractile effect of angiotensin II in the rat aorta

1 The role of the extraendothelial and constitutive isoforms of cyclo-oxygenase-2 (COX-2) in the contractile effect of angiotensin II (Ang II) was investigated using thoracic and abdominal aortic rings without endothelium from young Wistar rats. 2 Ang II elicited similar contractions in both aortic segments, and the effect was inhibited by pretreatment with NS398 (a selective COX-2 inhibitor) but not SC-560 [selective cyclo-oxygenase-1 (COX-1) inhibitor]. 3 COX-2 mRNA was expressed under basal conditions in both aortic segments. Additionally, Ang II increased COX-2 mRNA expression in the abdominal but not the thoracic segment, while cycloheximide (a protein synthesis inhibitor) did not affect the contractile response to Ang II in either of the two segments; this suggests that the effect is not associated with de novo COX-2 synthesis. 4 In conclusion, the basal amount of COX-2 found in aortic smooth muscle cells is sufficient to explain the production of the prostanoids related to the contractile effect of Ang II. The production of these prostanoids, which are derived from constitutive COX-2, occurs independently of the endothelium vascular system.

Molecular distinction between physiological and pathological cardiac hypertrophy: experimental findings and therapeutic strategies

Cardiac hypertrophy can be defined as an increase in heart mass. Pathological cardiac hypertrophy (heart growth that occurs in settings of disease, e.g. hypertension) is a key risk factor for heart failure. Pathological hypertrophy is associated with increased interstitial fibrosis, cell death and cardiac dysfunction. In contrast, physiological cardiac hypertrophy (heart growth that occurs in response to chronic exercise training, i.e. the 'athlete's heart') is reversible and is characterized by normal cardiac morphology (i.e. no fibrosis or apoptosis) and normal or enhanced cardiac function. Given that there are clear functional, structural, metabolic and molecular differences between pathological and physiological hypertrophy, a key question in cardiovascular medicine is whether mechanisms responsible for enhancing function of the athlete's heart can be exploited to benefit patients with pathological hypertrophy and heart failure. This review summarizes key experimental findings that have contributed to our understanding of pathological and physiological heart growth. In particular, we focus on signaling pathways that play a causal role in the development of pathological and physiological hypertrophy. We discuss molecular mechanisms associated with features of cardiac hypertrophy, including protein synthesis, sarcomeric organization, fibrosis, cell death and energy metabolism and provide a summary of profiling studies that have examined genes, microRNAs and proteins that are differentially expressed in models of pathological and physiological hypertrophy. How gender and sex hormones affect cardiac hypertrophy is also discussed. Finally, we explore how knowledge of molecular mechanisms underlying pathological and physiological hypertrophy may influence therapeutic strategies for the treatment of cardiovascular disease and heart failure.

Signaling properties of human alpha(1D)-adrenoceptors lacking the carboxyl terminus: intrinsic activity, agonist-mediated activation, and desensitization

alpha(1)-Adrenoceptors are differentially regulated by protein kinase C-mediated phosphorylation. The most sensitive member of this family is the alpha(1D)-subtype, which is also characterized by a constitutive activity and a reduced expression at the plasma membrane controlled by the amino terminus. Information on the structural domains that determine the function and regulation of this receptor subtype is scarce. Therefore, the function and phosphorylation of amino terminus-truncated (Delta1-79, (DeltaN)) alpha(1D)-adrenoceptors were studied and compared with those of alpha(1D)-adrenoceptors truncated both at the amino and carboxyl termini (Delta1-79 and Delta441-572, (DeltaN-DeltaC)). These receptors were stably expressed in rat-1 fibroblast, at relatively high density ( approximately 2 pmol/mg of membrane protein), and showed intrinsic activity that was markedly increased by noradrenaline. Interestingly, activation of protein kinase C markedly attenuated (desensitized) the function of both DeltaN and DeltaN-DeltaC alpha(1D)-adrenoceptors. These receptors were photolabeled and immunoprecitated with an antibody directed against an influenza hemagglutinin epitope inserted at the amino termini. Metabolic labeling with radioactive phosphate and receptor immunoprecipitation studies indicated that these receptors are phosphoproteins whose phosphorylation state is increased by noradrenaline and by activation of protein kinase C. Our data indicate that carboxyl terminus-truncated alpha(1D)-adrenoceptors are fully functional and subjected to regulation by phosphorylation. The roles of the carboxyl termini differ among alpha(1)-adrenoceptor subtypes.

Receptor tyrosine kinases regulate alpha1D-adrenoceptor signaling properties: phosphorylation and desensitization

Human alpha(1D)-adrenoceptors (truncated at the amino terminus (Delta1-79) to increase their membrane expression) were stably expressed in Rat-1 fibroblasts (1-1.5 pmol/mg protein). The receptors were functional as evidenced by a robust increase in intracellular calcium in response to noradrenaline. Using this cell line, the possibility that activation of receptor tyrosine kinases could modulate this adrenoceptor subtype was studied. It was observed that cell preincubation with insulin, IGF-I, EGF or PDGF markedly reduced the intracellular calcium increase observed in response to noradrenaline. Inhibitors of PI3K and PKC essentially blocked insulin-, IGF-I- and EGF-induced desensitizations. Interestingly, PDGF-induced alpha(1D)-adrenergic desensitization was only partially ameliorated by PI3K inhibitors and was not affected by those of PKC. Insulin, IGF-I, EGF and PDGF induced concentration-dependent increases in the phosphorylation state of alpha(1D)-adrenoceptors; phosphorylation took place on serine residues. Inhibitors of PI3K and PKC markedly reduced the effects of insulin, IGF-I and EGF on this parameter. These inhibitors only marginally reduced PDGF-induced alpha(1D)-adrenoceptors phosphorylation. The ability of IGF-I to induce alpha(1D)-adrenergic desensitization and phosphorylation was confirmed in cells expressing non-truncated rat alpha(1D)-adrenoceptors. Our data indicate that the function and phosphorylation state of alpha(1D)-adrenoceptors is modulated by activation of receptor tyrosine kinases. Insulin, IGF-I and EGF actions take place through the action of PI3K and PKC; additional pathway(s) seem to participate in PDGF-induced alpha(1D)-adrenoceptor desensitization and phosphorylation.

Norepinephrine reversibly regulates the proliferation and phenotypic transformation of vascular smooth muscle cells

OBJECTIVE

To investigate the effect of norepinephrine (NE) on the proliferation and phenotypic transformation of vascular smooth muscle cells (VSMCs) and the mechanisms underlying this effect.

METHODS

VSMCs were isolated from the rat abdominal aorta. VSMCs cultured in both serum-containing or in a serum-free medium were treated with NE, oxidized low-density lipoprotein (ox-LDL), alpha-adrenergic receptor agonist (alpha1-R(-)), beta1-adrenergic receptor antagonist (beta1-R(-)) and various combinations of these factors. VSMC proliferation was determined by bromodeoxyuridine (BrdU) assays. The mRNA expression level of HRG-1 and SM22 alpha were determined by reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

The expressions of HRG-1 and SM22 alpha mRNA in NE- or OX-LDL-treated VSMCs was down-regulated, and the proliferation of BrdU-labeled cells increased; the expression of the above mentioned genes in the VSMCs treated with a combination of NE, alpha1-R, and beta1-R was significantly up-regulated. However, NE was observed to up-regulate the expression of HRG-1 and SM22 alpha mRNA in serum-starved VSMCs.

CONCLUSION

NE could reversibly regulate the proliferation and phenotypic transformation of VSMCs. This regulation might be mediated via its receptors.

The alpha1D-adrenergic receptor is expressed intracellularly and coupled to increases in intracellular calcium and reactive oxygen species in human aortic smooth muscle cells

BACKGROUND

The cellular localization of the alpha1D-adrenergic receptor (alpha1D-AR) is controversial. Studies in heterologous cell systems have shown that this receptor is expressed in intracellular compartments. Other studies show that dimerization with other ARs promotes the cell surface expression of the alpha1D-AR. To assess the cellular localization in vascular smooth muscle cells, we developed an adenoviral vector for the efficient expression of a GFP labeled alpha1D-AR. We also measured cellular localization with immunocytochemistry. Intracellular calcium levels, measurement of reactive oxygen species and contraction of the rat aorta were used as measures of functional activity.

RESULTS

The adenovirally expressed alpha1D-AR was expressed in intracellular compartments in human aortic smooth muscle cells. The intracellular localization of the alpha1D-AR was also demonstrated with immunocytochemistry using an alpha1D-AR specific antibody. RT-PCR analysis detected mRNA transcripts corresponding to the alpha1A-alpha1B- and alpha1D-ARs in these aortic smooth muscle cells. Therefore, the presence of the other alpha1-ARs, and the potential for dimerization with these receptors, does not alter the intracellular expression of the alpha1D-AR. Despite the predominant intracellular localization in vascular smooth muscle cells, the alpha1D-AR remained signaling competent and mediated the phenylephrine-induced increases in intracellular calcium. The alpha1D-AR also was coupled to the generation of reactive oxygen species in smooth muscle cells. There is evidence from heterologous systems that the alpha1D-AR heterodimerizes with the beta2-AR and that desensitization of the beta2-AR results in alpha1D-AR desensitization. In the rat aorta, desensitization of the beta2-AR had no effect on contractile responses mediated by the alpha1D-AR.

CONCLUSION

Our results suggest that the dimerization of the alpha1D-AR with other ARs does not alter the cellular expression or functional response characteristics of the alpha1D-AR.

Evidence of alpha1-adrenoceptor functional changes in omental arteries of patients with end-stage renal disease

1 Alpha1-Adrenoceptor (alpha1-AR) subtypes were characterized in isolated omental arteries obtained after abdominal surgery in patients with end-stage renal disease (ESRD) or with Diabetes Mellitus type 2 plus ESRD (ESRD-DM). 2 Omental arteries from patients with ESRD and ESRD-DM elicited a significant increase in sensitivity to phenylephrine with a pD(2) (-log EC50) of 6.7 and 6.6, respectively, vs. the control (5.8, P < 0.001). 3 Stimulation with phenylephrine was conducted in the presence or absence of selective alpha1-AR competitive antagonists: 5-methylurapidil (alpha1A-), AH11110A (1-[biphenyl-2-yloxy]-4-imino-4-piperidin-1-yl-butan-2-ol; alpha1B-) and BMY7378 (8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro [4.5] decane-7,9-dione; alpha(1D)-). The relative abundance of mRNA for all three alpha(1)-ARs was determined. 4 The maximal contractile responses to phenylephrine were: E(max) 1.59 +/- 0.17, 1.48 +/- 0.08 and 1.55 +/- 0.14 g for the ESRD, ESRD-DM and control groups, respectively. 5 Functionally, there was an increment in the affinity for the alpha(1A)-AR antagonist (pA2: control 7.45, ESRD 8.36, ESRD-DM 8.0; P < 0.01), and a reduction in the alpha1B-AR antagonist affinity (8.3 for controls, 7.6 for ESRD and 7.3 for ESRD-DM; P < 0.01) associated with renal disease. The affinities for the alpha1D-AR antagonist were similar among the studied groups (8.5 for the controls, 8.7 for the ESRD and 8.1 for the ESRD-DM groups). 6 Renal disease increased mRNA expression of alpha(1B)-ARs and reduced both alpha1A- and alpha(1D)-ARs subtypes in ESRD and ESRD-DM patients. 7 The results suggest that human omental arteries exposed to chronic uraemia show vascular hypersensitivity to phenylephrine, because of functional alpha1-AR changes.

Roles of c-Src in alpha1B-adrenoceptor phosphorylation and desensitization

1 The role of the protein tyrosine kinase, c-Src, on the function and phosphorylation of alpha1B-adrenoceptors (alpha1B-AR) and their association with G-protein-coupled receptor kinase (GRK) isozymes was studied. 2 Inhibitors of this kinase (PP2 and Src Inhibitor II) decreased ( approximately 50-75%) noradrenaline- (NA) and phorbol myristate acetate-mediated receptor phosphorylation. Expression of a dominant-negative mutant of c-Src similarly reduced receptor phosphorylation induced by the natural agonists, active phorbol esters and endothelin-1 (ET-1). 3 c-Src, GRK2, GRK3 and GRK5 coimmunoprecipitate with alpha1B-ARs in the basal state. In cells treated with NA or phorbol myristate acetate the amount of coimmunoprecipitated GRK2 and GRK3 increased ( approximately 2- to 3-fold), while treatment with ET-1 only augmented the amount of coimmunoprecipitated GRK2 ( approximately 2-fold). The Src inhibitor, PP2, markedly attenuated all these increases. 4 Cell pretreatment with PP2 amplified the increase in intracellular-free calcium observed with NA, in the basal state and after the stimulation (desensitization) induced by ET-1. 5 The data suggest a role of c-Src in alpha1B-AR desensitization/phosphorylation and in the interaction of these ARs with GRKs.

Immunohistochemical localization of adrenergic receptors in the rat organ of corti and spiral ganglion

Alpha(1)-, beta(1)-, and beta(2)-adrenergic receptors (ARs), which mediate responses to adrenergic input, have been immunohistochemically identified within the organ of Corti and spiral ganglion with polyclonal antibodies of established specificity. Alpha(1)-AR was immunolocalized to sites overlapping supranuclear regions of inner hair cells as well as to nerve fibers approaching the base of inner hair cells, most evident in the basal cochlear turn. A similar preponderance across cochlear turns for alpha(1)-AR in afferent cell bodies in the spiral ganglion pointed to type I afferent dendrites as a possible neural source of alpha(1)-AR beneath the inner hair cell. Foci of immunoreactivity for alpha(1)-AR, putatively neural, were found overlapping supranuclear and basal sites of outer hair cells for all turns. Beta(1)- and beta(2)-ARs were immunolocalized to sites overlapping apical and basal poles of the inner and outer hair cells, putatively neural in part, with immunoreactive nerve fibers observed passing through the habenula perforata. Beta(1)- and beta(2)-ARs were also detected in the cell bodies of Deiters' and Hensen's cells. Within the spiral ganglion, beta(1)- and beta(2)-ARs were immunolocalized to afferent cell bodies, with highest expression in the basal cochlear turn, constituting one possible neural source of receptors within the organ of Corti, specifically on type I afferent dendrites. Beta(1)- and beta(2)-ARs in Hensen's and Deiters' cells would couple to Galphas, known to be present specifically in the supporting cells. Overall, adrenergic modulation of neural/supporting cell function within the organ of Corti represents a newly considered mechanism for modifying afferent signaling.

Effect of exercise with and without a thermal clamp on the plasma heat shock protein 72 response

The contribution of heat and exercise related stress to the release of heat shock protein 72 (HSP72) is currently unknown. The purpose of the present study was to determine the combined and independent effects of heat and exercise on the extracellular (e)HSP72 response. Eleven moderately trained male volunteers [means ± SD: age 21 ± 4 yr; body mass 75.7 ± 7.7 kg; maximal oxygen uptake (V̇o2 max) 57.8 ± 3.3 ml·kg−1·min−1] completed four 2-h, heat-manipulated, water-immersion trials. Trials were exercise-induced heat (EIH; rectal temperature change +2.2°C), clamped exercise (CEx; 0°C), passive heating (PHT; +2.3°C), and control (Con; 0°C). Exercise trials (EIH and CEx) comprised deep-water running at 58.5 ± 2.4 and 59.1 ± 1.7% v̇o2max. eHSP72 and catecholamine concentrations were determined by ELISA and HPLC, respectively, pre- and postimmersion. All trials induced an eHSP72 response ( P < 0.05) with postimmersion values significantly greater on EIH compared with other trials (6.0 ± 3.4; CEx 3.8 ± 2.6; PHT 2.7 ± 2.1; Con 2.2 ± 1.9 ng/ml). Exercising with a thermal clamp blunted the eHSP72 response, but postimmersion values were also greater than Con. PHT induced a large catecholamine response, but postimmersion eHSP72 values did not reach significance vs. Con. Given that exercising with a thermal clamp evoked a significant increase in plasma eHSP72 concentration, exercise-related stressors other than heat appeared influential in stimulating HSP72 release. Moreover, the catecholamine data from PHT suggest neither epinephrine nor norepinephrine was solely responsible for eHSP72 release.

Trophic effects induced by α1D-adrenoceptors on endothelial cells are potentiated by hypoxia

Catecholamines have been shown to be involved in vascular remodeling through the stimulation of α1-adrenoceptors (α1-ARs). Recently, it has been demonstrated that catecholamines can stimulate angiogenesis in pathological conditions, even if the mechanisms and the AR subtypes involved still remain unclear. We investigated the influence of hypoxia (3% O2) on the ability of picomolar concentrations of phenylephrine (PHE), which are unable to induce any vascular contraction, to induce a trophic effect in human endothelial cells through stimulation of the α1D-subtype ARs. PHE, at picomolar concentrations, significantly promoted pseudocapillary formation from fragments of human mature vessels in vitro. Exposure to hypoxia significantly potentiated this effect, which was inhibited by the selective α1D-AR antagonist BMY-7378 and by the nitric oxide synthase inhibitor l-NAME, suggesting that α1D-ARs were involved in this effect through activation of the nitric oxide pathway. Proliferation and migration of HUVEC were also affected by picomolar PHE concentrations. Again, these effects were significantly potentiated in cells exposed to hypoxia and were inhibited by BMY-7378 and by NG-nitro-l-arginine methyl ester. Conversely, the α1A-AR-selective antagonist ( S)-(+)-niguldipine hydrochloride and the α1B-AR antagonist chloroethylclonidine dihydrochloride did not modify endothelial cell migration and proliferation in response to PHE. These results demonstrate that the stimulation of α1D-ARs, triggered by picomolar PHE concentrations devoid of any contractile vascular effects, induces a proangiogenic phenotype in human endothelial cells that is enhanced in a hypoxic environment. The role of α1D-ARs may become more prominent in the adaptive responses to hypoxic vasculature injury.

Episodic stimulation of alpha1-adrenoreceptors induces protein kinase C-dependent persistent changes in motoneuronal excitability

In vitro long-term facilitation (ivLTF) is a novel form of activity-independent postsynaptic enhancement of AMPA receptor function in hypoglossal (XII) motoneurons that can be induced by intermittent activation of 5-HT2 receptors. In vivo respiratory long-term facilitation (LTF) is characterized by a persistent 5-HT2 receptor-dependent increase in respiratory motor output or ventilation after episodic exposures to hypoxia in adult rats. Here, we demonstrate that ivLTF can also be induced by episodic but not continuous stimulation of alpha1-adrenergic receptors that requires protein kinase C (PKC), but not PKA (protein kinase A), activation. Additionally, we show that in vivo respiratory LTF is also alpha1-adrenergic receptor dependent. We suggest that, in vivo, concurrent episodic activation of 5-HT2 and alpha1-adrenergic receptors is necessary to produce long-lasting changes in the excitability of respiratory motoneurons, possibly involving PKC activation via the G alpha(q)-PLC (phospholipase C) signaling pathway common to both receptor subtypes. Such plasticity of XII motor output may increase upper airway muscle (innervated by XII nerve) tone and improve the likelihood that airway patency will be maintained. Elucidating the mechanism underlying LTF can be of clinical importance to the patients suffering from sleep-disordered breathing.

Internalization and distribution of three alpha1-adrenoceptor subtypes in HEK293A cells before and after agonist stimulation

AIM

To examine the subcellular distribution of the 3 alpha1-adrenoceptor (alpha1-AR) subtypes and their internalization and trafficking upon agonist stimulation in human embryonic kidney 293A cells.

METHODS

Confocal real-time imaging, enzyme linked immunosorbent assay (ELISA) and whole cell [3H]-prazosin binding assay were applied to detect the distribution and localization of the 3 alpha1-AR subtypes.

RESULTS

alpha1A-AR was found both on the cell surface and in the cytoplasm; alpha1BAR, however, was predominantly detected on the cell surface, while alpha1D-AR was detected mainly in the intracellular compartments. After stimulation with phenylephrine, localization changes were detected by confocal microscopy for alpha1A- and alpha1B-AR,but the localization of alpha1D-AR were unaffected. Phenylephrine stimulation promoted a more rapid internalization of alpha1B-AR than alpha1A-AR. alpha1D-AR internalization was detected only by ELISA. Whole cell [3H]-prazosin binding assay showed that alpha1A-AR functional receptors were detected both on the cell surface and in the cytoplasm; alpha1B-AR, however, were detected predominantly on the cell surface, while alpha1D-AR were detected mainly in intracellular compartments. Phenylephrine stimulation promoted internalization of alpha1A- and alpha1B-AR.

CONCLUSION

Phenylephrine stimulation induced changes in the localization of the 3 alpha1-AR.

Insulin-like growth factor-I induces alpha(1B)-adrenergic receptor phosphorylation through G beta gamma and epidermal growth factor receptor transactivation

IGF-I induces alpha(1B)-adrenoceptor (alpha(1B)-AR) phosphorylation. The effect of IGF-I was rapid and transient, reaching near-maximal values at 10 min and decreasing after 30 min; it was observed at low IGF-I concentrations (EC(50) approximately 10 ng/ml) and was associated to receptor desensitization as evidenced by a decreased alpha(1B)-adrenergic effect on intracellular calcium and production of inositol phosphates. The effect of IGF-I was markedly decreased in cells treated with pertussis toxin suggesting involvement of pertussis toxin-sensitive G proteins. Transfection of the carboxyl terminus of the beta-adrenergic receptor kinase or the Deltap85 mutant of phosphoinositide 3-kinase (PI3K) markedly decreased the alpha(1B)-AR phosphorylation induced by IGF-I without decreasing the receptor phosphorylation induced by noradrenaline. Inhibitors of PI3K and protein kinase C blocked IGF-I-induced alpha(1B)-AR phosphorylation. In addition, it was observed that AG1478, an inhibitor of the epidermal growth factor (EGF) receptor kinase, and BB-94, a metalloproteinase inhibitor, also diminished IGF-I-induced adrenoceptor phosphorylation. The data clearly show that IGF-I triggers a complex signaling pathway, which leads to the phosphorylation and desensitization of a serpentine G protein-coupled receptor, suggesting the following hypothetical model: 1) stimulation of IGF-I receptors activate pertussis toxin-sensitive G proteins; 2) the growth factor action activates metalloproteinases, which catalyze heparin binding-EGF shedding, and transactivation of EGF receptors, and 3) dissociated Gbetagamma subunits and phosphotyrosine residues seem to trigger PI3K activity, which leads to activation of protein kinase C, resulting in alpha(1B)-AR phosphorylation and desensitization.

Effect of caffeine supplementation on the extracellular heat shock protein 72 response to exercise

The stimulus for the release of 72-kDa heat shock protein (HSP72) during exercise in humans is currently unclear. Recent evidence in an animal model is suggestive of an involvement of catecholamines. The present study, therefore, investigated the effect of caffeine supplementation, a known stimulator of sympathetic activity, on the extracellular (e)HSP72 response to prolonged exercise. Ten healthy male endurance-trained cyclists were recruited (age: 21 +/- 1 yr, maximum O(2) uptake 61.1 +/- 1.7 ml x kg(-1) x min(-1), mean +/- SE). Each subject was randomly assigned to ingest either 6 mg/kg body mass of caffeine (Caff) or placebo (Pla) 60 min before one of two 90-min bouts of cycling at 74 +/- 1% maximum O(2) uptake. Trials were performed at least 7 days apart in a counterbalanced design. Venous blood samples were collected by venepuncture at pretreatment, preexercise, postexercise, and 1 h postexercise. Serum caffeine and plasma catecholamines were determined using a spectrophotometric assay and high-performance liquid chromatography, respectively. Plasma HSP72 and cortisol were determined by ELISA. Serum caffeine concentrations were significantly increased throughout Caff, while no increases were detected in Pla. Caffeine supplementation and exercise was associated with a greater eHSP72 response than exercise alone (postexercise Caff 8.6 +/- 1.3 ng/ml; Pla 5.9 +/- 0.9 ng/ml). This greater eHSP72 response was associated with a greater epinephrine response to exercise in Caff. There was a significant increase in norepinephrine and cortisol, with no intertrial differences. The present data suggest that, in humans, catecholamines may be an important mediator of the exercise-induced increase in eHSP72 concentration.

Role of epidermal growth factor receptor transactivation in alpha1B-adrenoceptor phosphorylation

Phosphorylation of G protein-coupled receptors is one of the earliest events that regulate their function. Current evidence indicates that homologous desensitization of these receptors mainly involves G protein-coupled receptor kinases whereas in heterologous desensitization second messenger-activated kinases play key roles. Recent data show that transactivation of EGF (epidermal growth factor) receptors may also play a role in receptor phosphorylation. The role of this process was studied for the alpha1B-adrenoceptor phosphorylation induced by agents acting through different processes using inhibitors to block the EGF receptor transactivation process at different levels. Experiments were performed using transfected rat-1 fibroblasts that express alpha1B-adrenoceptors in a stably fashion. A metalloproteinase inhibitor, an anti-heparin-binding-EGF-selective antibody, and a selective EGF-receptor kinase inhibitor blocked the alpha1B-adrenoceptor phosphorylation induced by noradrenaline or endothelin-1. Our results indicate that shedding of heparin-binding-EGF, transactivation of EGF receptors plays a more general role in alpha1B-adrenoceptor phosphorylation than previously anticipated. It is possible that other receptors/channels could be modulated through a similar pathway.

Estrogens Cross-Talk to α1b-Adrenergic Receptors

beta-Estradiol induced alpha1b-adrenergic receptor desensitization in U373 MG cells stably expressing alpha1b-adrenoceptors, as evidenced by a reduction in the adrenergic-mediated Ca2+ mobilization; desensitization was associated with receptor phosphorylation and internalization. These effects of beta-estradiol were rapid (taking place during 15 min) and were blocked by the estrogen receptor antagonist ICI 182,780 (faslodex). Likewise, inhibitors of phosphoinositide 3-kinase [wortmannin and 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002)] and of protein kinase C [staurosporine, 3-[1-[3-(amidinothio)propyl-1H-indol-3-yl]-3-(1-methyl-1H-indol-3-yl) maleimide (Ro31-8220), and rottlerin] blocked the desensitization and phosphorylation of alpha1b-adrenoceptors induced by estradiol. The formation of a complex was suggested by coimmunoprecipitation assays. The regulatory and catalytic subunits of phosphoinositide 3-kinase (p85 and p110) and protein kinase C delta were associated with alpha1b-adrenoceptors in the absence of stimulus, and such association further increased in a dynamic fashion in response to beta-estradiol. In cells cotransfected with the estrogen receptor alpha and alpha1b-adrenoceptors, beta-estradiol induced phosphorylation, desensitization and internalization of the adrenergic receptors; pretreatment with ICI 182,780 inhibited these effects. Our data support the idea that estrogens modulate alpha1b-adrenergic action through estrogen receptor alpha.

Pharmacological characterization of alpha1-adrenoceptors in equine digital veins

Alpha-adrenoceptors mediate contractile responses in equine digital veins (EDVs) and arteries. Vascular smooth muscle alpha(1)-adrenoceptor subtypes have been implicated in a number of conditions, such as acute equine laminitis, and are therapeutic targets for the treatment of this condition. Digital veins, rather than arteries, were investigated in the present study because they have been specifically implicated in the pathophysiology of acute laminitis. The order of potency of a series of alpha(1)-adrenoceptor-selective agonists and antagonists was determined in isolated rings of EDVs under conditions of isometric tension. A61603 was the most potent agonist, with a higher potency (76-fold greater) than phenylephrine (PHE), suggesting the presence of the alpha(1A)-adrenoceptor subtype. Prazosin (30 nm) caused competitive inhibition of the responses to A61603 and PHE, with pK(b) values of 8.05 +/- 0.28 and 8.20 +/- 0.27, respectively. In addition, the alpha(1A)-adrenoceptor antagonist, WB4101 (10 nm), also caused competitive inhibition of the responses to the two agonists, with pK(b) values of 8.37 +/- 0.16 and 8.54 +/- 0.23, respectively, confirming the presence of the alpha(1A)-adrenoceptor subtype in EDVs. The selective alpha(1D)-adrenoceptor antagonist, BMY7378 (100 nm) did not cause a significant change in the response to the agonists, giving lower pK(b) values (6.97 +/- 0.27 and 6.88 +/- 0.17 vs. A61603 and PHE, respectively). Chloroethylclonidine dihydrochloride (45 microm, 30 min), used to produce selective inactivation of alpha(1B)-adrenoceptors, caused noncompetitive inhibition of the response to PHE, but was without effect on the response to A61603. These findings indicate that EDVs possess at least two different alpha(1)-adrenoceptor populations, which are predominantly of the alpha(1A) and alpha(1B) subtypes. These data may assist in the development of more selective antagonists for therapeutic use in horses.

Captopril therapy decreases both expression and function of alpha1D-adrenoceptors in pre- hypertensive rat aorta

1.-- The effects of captopril on alpha(1)-adrenoceptor mRNA and protein and phenylephrine-induced contraction was assessed in aorta of pre-hypertensive spontaneously hypertensive rats. 2.-- Four-week-old SHR and WKY rats were treated with captopril [an angiotensin-converting enzyme (ACE) inhibitor] 3 mg kg(-1) day(-1) for 1 week. 3.-- pA(2) values for BMY 7378, an alpha(1D)-adrenoceptor antagonist, were 8.63-9.20 among the different groups. Schild slopes were close to unity suggesting that contraction was produced primarily by alpha(1D)-adrenoceptor stimulation and was not changed with therapy. 4.-- Alpha(1D)-adrenoceptor mRNA and protein values were higher in pre-hypertensive SHR than in WKY, whereas alpha(1A)-adrenoceptor mRNA was higher in WKY and alpha(1B)-adrenoceptors were similar in both strains, and protein was not significantly different for alpha(1A)- and alpha(1B)-subtypes. 5.-- Captopril decreased maximal contraction in SHR, without having effect in WKY rats, while alpha(1D)-adrenoceptor mRNA was decreased in both rat strains but alpha(1D)-adrenoceptor protein was significantly decreased only in SHR, and increased alpha(1A)-mRNA in SHR, no effect of captopril treatment was observed on alpha(1B)-adrenoceptor mRNA and protein nor on alpha(1A)-adrenoceptor protein. 6.-- These data suggest that ACE inhibition by captopril influences both expression and function of alpha(1D)-adrenoceptors in aorta of pre-hypertensive rats, probably avoiding alpha(1D)-subtype expression by blockade of angiotensin II synthesis.

Modulation of hypoglossal motoneuron excitability by intracellular signal transduction cascades

Motoneuronal excitability is highly modulated by various inputs; however, comparatively little is known about postsynaptic signal transduction cascades that affect motoneuron excitability. In this review, we discuss the role of intracellular signaling cascades in the modulation of respiratory motoneuronal excitability. In particular, protein kinases and phosphatases dynamically and constitutively modulate respiratory-modulated inputs to XII motoneurons: (i) activation of protein kinase A (PKA) potentiates both excitatory and inhibitory drive currents; (ii) protein kinase G (PKG) depresses excitatory currents, and (iii) inhibition of protein phosphatases potentiates excitatory drive currents. We also describe a novel form of persistent plasticity (in vitro long-term facilitation; ivLTF) of motoneuronal output. ivLTF is induced by episodic activation of 5-HT(2) or alpha(1)-adrenoreceptors and is manifested as an increase in the amplitude of XII nerve output due to an increase in alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)-mediated motoneuronal drive currents. Blockade of Group 1 metabotropic glutamate receptors or protein kinase C (PKC) prevents the induction of ivLTF.

The elusive alpha(1D)-adrenoceptor: molecular and cellular characteristics and integrative roles

alpha(1)-Adrenoceptors seem to play key roles in cardiovascular, genitourinary, and central nervous system functions. This review will be focused on alpha(1D)-adrenoceptors. These receptors have intrinsic activity, and many of the more commonly used antagonists are in reality inverse agonists. alpha(1D)-Adrenoceptors are phosphorylated in the basal state, and the natural agonists, adrenaline and noradrenaline, increase their phosphorylation; similar effects are induced by direct activation of protein kinase C and through activation of nonadrenergic receptors. Interestingly, a large proportion of alpha(1D)-adrenoceptors are located in intracellular vesicles. Such intracellular location can be changed to surface expression through the use of inverse agonists and coexpression of alpha(1B)-adrenoceptors, which seem to act as pharmacological chaperons for proper plasma membrane insertion. The alpha(1D)-adrenoceptor amino terminus seems to contain a signal that keeps the receptor intracellularly, but interaction with other proteins may also contribute. The precise relationship between the intrinsic activity, phosphorylation, and intracellular location is currently unknown. alpha(1D)-Adrenoceptor activation induces contraction in a variety of vessels, and a role in the control of blood pressure has been suggested. Studies using young prehypertensive and adult spontaneously hypertensive rats as well as knockout mice suggest that vascular alpha(1D)-adrenoceptors are involved in the genesis/maintenance of hypertension.

Central noradrenergic mechanisms underlying acute stress responses of the Hypothalamo-pituitary-adrenal axis: adaptations through pregnancy and lactation

Hypothalamo-pituitary-adrenal axis responses to stress are attenuated perinatally, and may contribute towards conservation of energy stores and/or prevention of overexposure to glucocorticoid and its adverse effects in the developing fetus/neonate. Previous work has shown that reduced central drive to the hypothalamo-pituitary-adrenal axis is responsible, since parvocellular paraventricular nucleus neurone responses are reduced. One of the main input pathways to the paraventricular nucleus that is activated by the majority of stressors is the brainstem noradrenergic system. This review outlines key noradrenergic mechanisms that mediate hypothalamo-pituitary-adrenal axis responses to acute stress, and addresses aspects of their adaptation in pregnancy and lactation that can explain the stress hyporesponsiveness at that time. In summary, reduced noradrenaline release and adrenergic receptor expression in the paraventricular nucleus may lead to reduced sensitivity of the hypothalamo-pituitary-adrenal axis to adrenergic antagonists and agonists and its responses to stress. While there are subtle differences in these changes between pregnancy and lactation, it would appear that reduced effectiveness of the noradrenergic input can at least partly account for the reduced hypothalamo-pituitary-adrenal axis responses both pre- and post-natally.

Doxazosin treatment causes differential alterations of alpha 1-adrenoceptor subtypes in the rat kidney, heart and aorta

We have previously demonstrated that long-term administration of doxazosin, an alpha(1)-adrenoceptor (alpha(1)-AR) antagonist, causes an up-regulation in the expression of alpha(1)-AR subtype mRNAs in the rat genitourinary tract and suggested that these changes may affect long-term effectiveness of alpha(1)-AR antagonists when used to treat the lower urinary tract symptoms of benign prostatic hyperplasia. As chronic administration of alpha(1)-AR antagonists may cause similar alterations in other tissues in which alpha(1)-ARs play a physiologic role, we examined the effects of long-term administration of doxazosin on the expression of alpha(1)-AR subtype mRNAs in several rat tissues. Rats were treated with doxazosin (4 mg/kg/day subcutaneously, supplemented with 4 mg/kg/day orally) for 12 weeks. The cDNA was prepared by reverse transcription of RNA extracted from the rat kidney, heart and aorta. alpha(1A), alpha(1B) and alpha(1D)-AR mRNA expression levels were quantified by real-time reverse transcription polymerase chain reaction. The rank order of expression levels of the alpha(1)-AR mRNAs in rat tissues were: alpha(1A)-AR, kidney > heart > aorta; alpha(1B)-AR, heart > kidney > aorta; alpha(1D)-AR, aorta > kidney = heart. Chronic administration of doxazosin caused an up-regulation in the mRNA level of alpha(1A), alpha(1B) and alpha(1D)-ARs in the rat kidney, heart and aorta, respectively. Our data demonstrate that doxazosin treatment causes differential alterations in the expression of alpha(1)-AR subtype mRNAs in different rat tissues. These findings may provide insight into the long-term effects of alpha(1)-AR antagonists in the treatment of diseases involving tissues whose function is regulated by alpha(1)-ARs.

Human alpha1D-adrenoceptor phosphorylation and desensitization

Rat-1 fibroblast were transfected with a plasmid containing the cDNA of the human alpha(1D)-adrenoceptor. A cell line was isolated that stably expressed the receptor as evidenced by BMY 7378-sensitive noradrenaline-induced increases in intracellular calcium concentration. The effect of noradrenaline was blocked by active phorbol esters; such blockade was mediated by protein kinase C (PKC) as evidenced by its inhibition by staurosporine or the downregulation of this protein kinase. Radioligand binding experiments showed expression of receptors with high affinity for [3H]tamsulosin (K(D) 0.30 +/- 0.05 nM) but low density (B(max) 35 +/- 4 fmol/mg protein). The receptors had the expected orders of potency for agonists (adrenaline = noradrenaline > oxymetazoline) and antagonists (BMY 7378 > 5-methyl-urapidil = phentolamine). Photoaffinity labeling identified the receptor as a band of M(r) 70-80kDa, which could be immunoprecipitated with a selective anti-alpha(1D)-adrenoceptor antiserum. In cells metabolically labeled with radioactive phosphate the adrenoceptor was identified as a phosphoprotein whose phosphorylation state was increased by the agonist, noradrenaline, and by phorbol myristate acetate. The data indicate that the human alpha(1D)-adrenoceptor function was regulated through phosphorylation by PKC.

Simvastatin Decreases Nitric Oxide Overproduction and Reverts the Impaired Vascular Responsiveness Induced by Endotoxic Shock in Rats

Lipopolysaccharides (LPS) can be used to induce experimental endotoxic shock, which is characterized by a significant decrease in mean arterial pressure (MAP) and a decreased vasoconstrictor response that have been attributed to excessive nitric oxide production. Inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase), in addition to lowering serum cholesterol levels, exert many pleiotropic effects, including anti-inflammatory action. In the present study, we investigated the effect of simvastatin, an HMG-CoA reductase inhibitor, on the production of nitric oxide and the cardiovascular response to LPS. Male Wistar rats were pretreated with different doses of simvastatin (10, 20, 40, and 80 mg/kg, i.p.) or saline 20 min before i.v. injection of LPS (1.5 mg/kg) or saline (control). MAP was continuously recorded and nitrate plasma concentration was determined during the 6-h experimental session at 1-h intervals. The pressor response to phenylephrine (1 microg/kg) was evaluated before and 6 h after LPS administration. In the LPS-treated group, there was a time-dependent increase in nitrate plasma concentration (P<0.001), and this response was decreased in simvastatin pretreated rats (P<0.001). We also observed that LPS decreased the pressor response to phenylephrine (P<0.001), an effect that was reverted by simvastatin pretreatment (P<0.05). However, simvastatin did not modify the decrease of MAP induced by LPS. We concluded that simvastatin decreases nitrate plasma concentration in response to LPS and recovers vascular responsiveness during an experimental endotoxic shock. These data suggest the potential use of HMG-CoA reductase inhibitors as a coadjuvant in the treatment of septic shock.

Emerging evidence for a central epinephrine-innervated alpha 1-adrenergic system that regulates behavioral activation and is impaired in depression

Currently, most basic and clinical research on depression is focused on either central serotonergic, noradrenergic, or dopaminergic neurotransmission as affected by various etiological and predisposing factors. Recent evidence suggests that there is another system that consists of a subset of brain alpha(1B)-adrenoceptors innervated primarily by brain epinephrine (EPI) that potentially modulates the above three monoamine systems in parallel and plays a critical role in depression. The present review covers the evidence for this system and includes findings that brain alpha(1)-adrenoceptors are instrumental in behavioral activation, are located near the major monoamine cell groups or target areas, receive EPI as their neurotransmitter, are impaired or inhibited in depressed patients or after stress in animal models, and are restored by a number of antidepressants. This "EPI-alpha(1) system" may therefore represent a new target system for this disorder.

Lymphosarcoma-induced alterations in hepatic adrenergic receptors: implications to the hypoglycemia of cancer cachexia

A highly malignant transplantable rat lymphosarcoma was studied to determine the involvement of hepatic adrenergic receptors in the development of the hypoglycemia of cancer cachexia. Following inoculation of Fischer 344 rats with lymphosarcoma cells, rats were examined at 2 and 4 weeks, at the pre-cachexic stage; 6 weeks, at the transitional stage; and 7 weeks, at the cachexic hypoglycemic stage of lymphosarcoma progression. Death occurred by the 8th week. Blood glucose levels in lymphosarcoma-bearing rats relative to control rats were: unaffected at week 2; significantly reduced 8% at weeks 4 and 6; and reduced 24% at week 7. Alpha1 adrenergic receptor binding to plasma membranes isolated from the livers of lymphosarcoma-bearing rats was: 114, 89, 67 and 30% of control at weeks 2, 4, 6, and 7, respectively. Kinetic analysis indicated that the lymphosarcoma-induced decrease at week 7 was due to a decrease in numbers of receptors with no change in affinity: B(max)(control): 1411.1 fmol/mg: Kd(control): 0.44 nm; B(max)(lympho): 345.5 fmol/mg; Kd(lympho): 0.50 nm. Alpha2 adrenergic receptor binding to plasma membranes isolated from the livers of lymphosarcoma-bearing rats was: 130, 137, 243 and 212% of control at weeks 2,4, 6, and 7, respectively. The pattern of changes in hepatic alpha1, alpha2 and beta adrenergic receptors at week 6 was comparable to that of 17 day fetal liver: a decrease in alpha1 and beta and an increase in alpha2. Hepatic adrenergic receptor changes occurred in the absence of liver damage and were not due to contamination of the liver plasma membrane fractions with lymphosarcoma cells. Plasma insulin levels displayed modest (10-15%), but not statistically significant, increases post-inoculation after week 4. Plasma glucagon levels fluctuated post-inoculation until week 7 where they were significantly increased: 202% of control. Plasma T3 and T4 levels displayed an early and steady decline after lymphosarcoma inoculation: T3: unchanged at week 2 and significantly decreased 14, 44 and 50% at weeks 4, 6 and 7, respectively. T4 increased 20% at week 1; decreased 9% at week 4 and significantly decreased thereafter: 55 and 49% at weeks 6 and 7, respectively. We propose that the development of the hypoglycemia of cancer cachexia in this lymphosarcoma model is due primarily to an early and progressive thyroid hormone dependent decrease in the number of hepatic alpha1 adrenergic receptors, compounded by an increase and decrease, respectively, in the hepatic beta and alpha2 adrenergic receptors.

Differential cardiovascular regulatory activities of the alpha 1B- and alpha 1D-adrenoceptor subtypes

The regulation of cardiac and vascular function by the alpha 1B- and alpha 1D-adrenoceptors (ARs) has been assessed in two lines of transgenic mice, one over-expressing a constitutively active alpha 1B-AR mutation (alpha 1B-ARC128F) and the other an alpha 1D-AR knockout line. The advantage of using mice expressing a constitutively active alpha 1B-AR is that the receptor is tonically active, thus avoiding the use of nonselective agonists that can activate all subtypes. In hearts from animals expressing alpha 1B-ARC128F, the activities of the mitogen-activated protein kinases, extracellular signal-regulated kinase, and c-Jun N-terminal kinase were significantly elevated compared with nontransgenic control animals. Mice over-expressing the alpha 1B-ARC128F had echocardiographic evidence of contractile dysfunction and increases in chamber dimensions. In isolated-perfused hearts or left ventricular slices from alpha 1B-ARC128F-expressing animals, the ability of isoproterenol to increase contractile force or increase cAMP levels was significantly decreased. In contrast to the prominent effects on the heart, constitutive activation of the alpha 1B-AR had little effect on the ability of phenylephrine to induce vascular smooth muscle contraction in the isolated aorta. The ability of phenylephrine to stimulate coronary vasoconstriction was diminished in alpha 1D-AR knockout mice. In alpha 1D-AR knockout animals, no negative effects on cardiac contractile function were noted. These results show that the alpha1-ARs regulate distinctly different physiologic processes. The alpha 1B-AR appears to be involved in the regulation of cardiac growth and contractile function, whereas the alpha 1D-AR is coupled to smooth muscle contraction and the regulation of systemic arterial blood pressure.

Essential fatty acids and the brain

OBJECTIVE

To review the role of essential fatty acids in brain membrane function and in the genesis of psychiatric disease.

METHOD

Medline databases were searched for published articles with links among the following key words: essential fatty acids, omega-3 fatty acids, docosahexanoic acid, eicosapentanoic acid, arachidonic acid, neurotransmission, phospholipase A2, depression, schizophrenia, mental performance, attention-deficit hyperactivity disorder, and Alzheimer's disease. Biochemistry textbooks were consulted on the role of fatty acids in membrane function, neurotransmission, and eicosanoid formation. The 3-dimensional structures of fatty acids were obtained from the Web site of the Biochemistry Department, University of Arizona (2001).

RESULTS

The fatty acid composition of neuronal cell membrane phospholipids reflects their intake in the diet. The degree of a fatty acid's desaturation determines its 3-dimensional structure and, thus, membrane fluidity and function. The ratio between omega-3 and omega-6 polyunsaturated fatty acids (PUFAs), in particular, influences various aspects of serotoninergic and catecholaminergic neurotransmission, as shown by studies in animal models. Phospholipase A2 (PLA2) hydrolyzes fatty acids from membrane phospholipids: liberated omega-6 PUFAs are metabolized to prostaglandins with a higher inflammatory potential, compared with those generated from the omega-3 family. Thus the activity of PLA2 coupled with membrane fatty acid composition may play a central role in the development of neuronal dysfunction. Intervention trials in human subjects show that omega-3 fatty acids have possible positive effects in the treatment of various psychiatric disorders, but more data are needed to make conclusive directives in this regard.

CONCLUSION

The ratio of membrane omega-3 to omega-6 PUFAs can be modulated by dietary intake. This ratio influences neurotransmission and prostaglandin formation, processes that are vital in the maintenance of normal brain function.

Comparison of signalling mechanisms involved in rat mesenteric microvessel contraction by noradrenaline and sphingosylphosphorylcholine

1 We have compared the signalling mechanisms involved in the pertussis toxin-sensitive and -insensitive contraction of rat isolated mesenteric microvessels elicited by sphingosylphosphorylcholine (SPC) and noradrenaline (NA), respectively. 2 The phospholipase D inhibitor butan-1-ol (0.3%), the store-operated Ca(2+) channel inhibitor SK>F 96,365 (10 microM), the tyrosine kinase inhibitor genistein (10 microM), and the src inhibitor PP2 (10 microM) as well as the negative controls (0.3% butan-2-ol and 10 microM diadzein and PP3) had only little effect against either agonist. 3 Inhibitors of phosphatidylinositol-3-kinase (wortmannin and LY 294,002, 10 microM each) or of mitogen-activated protein kinase kinase (PD 98,059 and U 126, 10 microM each) did not consistently attenuate NA- and SPC-induced contraction as compared to their vehicles or negative controls (LY 303,511 or U 124). 4 The phospholipase C inhibitor U 73,122 (10 microM) markedly inhibited the SPC- and NA-induced contraction (70% and 88% inhibition of the response to the highest NA and SPC concentration, respectively), whereas its negative control U 73,343 (10 microM) caused only less than 30% inhibition. 5 The rho-kinase inhibitors Y 27,632 (10 microM) and fasudil (30 microM) caused a rightward-shift of the NA concentration-response curve by 0.7-0.8 log units and reduced the response to 10 microM SPC by 88% and 83%, respectively. 6 These data suggest that SPC and NA, while acting on different receptors coupling to different G-protein classes, elicit contraction of rat mesenteric microvessels by similar signalling pathways including phospholipase C and rho-kinase.