Activation of Erk mitogen-activated protein kinase proteins by vascular serotonin receptors

A Review of Serotonin in the Developing Lung and Neonatal Pulmonary Hypertension

Serotonin (5-HT) is a bioamine that has been implicated in the pathogenesis of pulmonary hypertension (PH). The lung serves as an important site of 5-HT synthesis, uptake, and metabolism with signaling primarily regulated by tryptophan hydroxylase (TPH), the 5-HT transporter (SERT), and numerous unique 5-HT receptors. The 5-HT hypothesis of PH was first proposed in the 1960s and, since that time, preclinical and clinical studies have worked to elucidate the role of 5-HT in adult PH. Over the past several decades, accumulating evidence from both clinical and preclinical studies has suggested that the 5-HT signaling pathway may play an important role in neonatal cardiopulmonary transition and the development of PH in newborns. The expression of TPH, SERT, and the 5-HT receptors is developmentally regulated, with alterations resulting in pulmonary vasoconstriction and pulmonary vascular remodeling. However, much remains unknown about the role of 5-HT in the developing and newborn lung. The purpose of this review is to discuss the implications of 5-HT on fetal and neonatal pulmonary circulation and summarize the existing preclinical and clinical literature on 5-HT in neonatal PH.

Quetiapine attenuates the acquisition of morphine-induced conditioned place preference and reduces ERK phosphorylation in the hippocampus and cerebral cortex

Background: Quetiapine is an atypical antipsychotic that antagonizes dopamine and serotonin receptors. It has been suggested that quetiapine can be used to treat substance use disorders, including opioid use disorder. Opioids modulate dopaminergic functions associated with conditioned reinforcement and these effects can be measured via the conditioned place preference (CPP) paradigm. Opioids' unconditioned effects are regulated by several proteins, including extracellular signal-regulated kinase (ERK) and cAMP-responsive element-binding (CREB).Objective: To assess the effect of quetiapine on morphine-induced CPP and motor activity levels, and on the levels of ERK and CREB proteins in the hippocampus and cerebral cortex.Methods: 42 male rats were exposed to a CPP protocol, in which they underwent a conditioning paradigm with saline, quetiapine (40 mg/kg), morphine (10 mg/kg), morphine plus quetiapine (10, 20, or 40 mg/kg), or morphine plus memantine (7.5 mg/kg, a positive control drug) (n = 6 per group). The rats were tested for CPP and exploratory activity. Levels of ERK and CREB proteins in the hippocampus and cerebral cortex were also measured.Results: Quetiapine co-administered with morphine inhibited morphine-induced CPP [F (6, 70) = 11.67, p < .001] and morphine's effects on motor activity (p < .001). Morphine enhanced ERK phosphorylation in the hippocampus (p < .001) and cerebral cortex (p < .001), an effect inhibited by quetiapine.Conclusion: Quetiapine attenuates morphine-induced CPP and locomotion and these effects are associated with a reduction of ERK phosphorylation in the hippocampus and cerebral cortex. These results suggest that quetiapine should be further explored as a potential treatment for opioid use disorder.

International Union of Basic and Clinical Pharmacology. CX. Classification of Receptors for 5-hydroxytryptamine; Pharmacology and Function

5-HT receptors expressed throughout the human body are targets for established therapeutics and various drugs in development. Their diversity of structure and function reflects the important role 5-HT receptors play in physiologic and pathophysiological processes. The present review offers a framework for the official receptor nomenclature and a detailed understanding of each of the 14 5-HT receptor subtypes, their roles in the systems of the body, and, where appropriate, the (potential) utility of therapeutics targeting these receptors. SIGNIFICANCE STATEMENT: This review provides a comprehensive account of the classification and function of 5-hydroxytryptamine receptors, including how they are targeted for therapeutic benefit.

Redundant Gs-coupled serotonin receptors regulate amyloid-β metabolism in vivo

BACKGROUND

The aggregation of amyloid-β (Aβ) into insoluble plaques is a hallmark pathology of Alzheimer's disease (AD). Previous work has shown increasing serotonin levels with selective serotonin re-uptake inhibitor (SSRI) compounds reduces Aβ in the brain interstitial fluid (ISF) in a mouse model of AD and in the cerebrospinal fluid of humans. We investigated which serotonin receptor (5-HTR) subtypes and downstream effectors were responsible for this reduction.

RESULTS

Agonists of 5-HT4R, 5-HT6R, and 5-HT7R significantly reduced ISF Aβ, but agonists of other receptor subtypes did not. Additionally, inhibition of Protein Kinase A (PKA) blocked the effects of citalopram, an SSRI, on ISF Aβ levels. Serotonin signaling does not appear to change gene expression to reduce Aβ levels in acute timeframes, but likely acts within the cytoplasm to increase α-secretase enzymatic activity. Broad pharmacological inhibition of putative α-secretases increased ISF Aβ and blocked the effects of citalopram.

CONCLUSIONS

In total, these studies map the major signaling components linking serotonin receptors to suppression of brain ISF Aβ. These results suggest the reduction in ISF Aβ is mediated by a select group of 5-HTRs and open future avenues for targeted therapy of AD.

Effect of 5-HT7 receptor blockade on liver regeneration after 60-70% partial hepatectomy

Background

Serotonin exhibits a vast repertoire of actions including cell proliferation and differentiation. The effect of serotonin, as an incomplete mitogen, on liver regeneration has recently been unveiled and is mediated through 5-HT₂ receptor. The aim of the present study was to investigate the effect of 5-HT₇ receptor blockade on liver regeneration after partial hepatectomy.

Methods

Male Wistar rats were subjected to 60-70% partial hepatectomy. 5-HT₇ receptor blockade was applied by intraperitoneal administration of SB-269970 hydrochloride two hours prior to and sixteen hours after partial hepatectomy and by intraperitoneal administration of SB-258719 sixteen hours after partial hepatectomy. Animals were sacrificed at different time points until 72 h after partial hepatectomy. Liver regeneration was evaluated by [³H]-thymidine incorporation into hepatic DNA, the mitotic index in hematoxylin-eosin (HE) sections and by immunochemical detection of Ki67 nuclear antigen. Reversion of 5-HT₇ blockade was performed by intraperitoneal administration of AS-19. Serum and liver tissue lipids were also quantified.

Results

Liver regeneration peaked at 24 h ([³H]-thymidine incorporation into hepatic DNA and mitotic index by immunochemical detection of Ki67) and at 32 h (mitotic index in HE sections) in the control group of rats. 5-HT₇ receptor blockade had no effect on liver regeneration when applied 2 h prior to partial hepatectomy. Liver regeneration was greatly attenuated when blockade of 5-HT₇ receptor was applied (by SB-258719 and SB-269970) at 16 h after partial hepatectomy and peaked at 32 h ([³H]-thymidine incorporation into hepatic DNA and mitotic index by immunochemical detection of Ki67) and 40 h (mitotic index in HE sections) after partial hepatectomy. AS-19 administration totally reversed the observed attenuation of liver regeneration.

Conclusions

In conclusion, 5-HT₇ receptor is a novel type of serotonin receptor implicated in hepatocyte proliferation.

Serotonin receptor 6 mediates defective brain development in monoamine oxidase A-deficient mouse embryos

Monoamine oxidases A and B (MAO-A and MAO-B) are enzymes of the outer mitochondrial membrane that metabolize biogenic amines. In the adult central nervous system, MAOs have important functions for neurotransmitter homeostasis. Expression of MAO isoforms has been detected in the developing embryo. However, suppression of MAO-B does not induce developmental alterations. In contrast, targeted inhibition and knockdown of MAO-A expression (E7.5-E10.5) caused structural abnormalities in the brain. Here we explored the molecular mechanisms underlying defective brain development induced by MAO-A knockdown during in vitro embryogenesis. The developmental alterations were paralleled by diminished apoptotic activity in the affected neuronal structures. Moreover, dysfunctional MAO-A expression led to elevated levels of embryonic serotonin (5-hydroxytryptamine (5-HT)), and we found that knockdown of serotonin receptor-6 (5-Htr6) expression or pharmacologic inhibition of 5-Htr6 activity rescued the MAO-A knockdown phenotype and restored apoptotic activity in the developing brain. Our data suggest that excessive 5-Htr6 activation reduces activation of caspase-3 and -9 of the intrinsic apoptotic pathway and enhances expression of antiapoptotic proteins Bcl-2 and Bcl-XL. Moreover, we found that elevated 5-HT levels in MAO-A knockdown embryos coincided with an enhanced activation of extracellular signal-regulated kinase 1/2 (ERK1/2) and a reduction of proliferating cell numbers. In summary, our findings suggest that excessive 5-HT in MAO-A-deficient mouse embryos triggers cellular signaling cascades via 5-Htr6, which suppresses developmental apoptosis in the brain and thus induces developmental retardations.

Molecular interactions of serotonin (5-HT) and endothelin-1 in vascular smooth muscle cells: in vitro and ex vivo analyses

Elevated levels of serotonin (5-HT) and endothelin-1 (ET-1) may be involved in cardiovascular complications of diabetes mellitus. Data suggest supraphysiological concentrations of 5-HT (10(-6) M) potentiate the ability of ET-1 to stimulate DNA synthesis and vascular smooth muscle cell (VSMC) proliferation in vitro via activation of mitogen-activated protein kinase (p42/44 MAPK) and Janus kinase 2 (JAK2) pathways. Additionally, 5-HT enhances agonist-induced contractions via p42/44 MAPK and an unknown tyrosine kinase. However, the exact mechanisms of the 5-HT/ET-1 interactions and whether these effects occur at physiological levels (10(-9) M) are unknown. Therefore, we hypothesized that interactions between 5-HT and ET-1 at physiological concentrations in VSMC enhanced activation of both p42/44 MAPK and JAK2 pathways contributing to vascular growth and contractile responses. With the use of rat VSMC and Western blot analysis, our data suggest no effect of acute (30 min) preincubation with 5-HT (10(-9) M) and/or ET-1 (10(-9) M) on the activation of either pathway in normal or high glucose conditions. To determine if there was altered vascular reactivity in intact vessels we tested the effects of 5-HT and ET-1 interaction using myographs to measure isometric contractions of rat thoracic aortic rings. 5-HT (10(-9) M) and ET-1 (10(-12) M) stimulate enhanced contractile responses to each other that were inhibited by JAK2 and p42/44 MAPK antagonists. Our findings demonstrate that both 5-HT and ET-1 at physiological concentrations could interact with each other and activate p42/44 MAPK and JAK2 signaling pathways to cause an increase in smooth muscle contraction that could lead to altered vascular function.

Serotonin contributes to high pulmonary vascular tone in a sheep model of persistent pulmonary hypertension of the newborn

Although past studies demonstrate that altered serotonin (5-HT) signaling is present in adults with idiopathic pulmonary arterial hypertension, whether serotonin contributes to the pathogenesis of persistent pulmonary hypertension of the newborn (PPHN) is unknown. We hypothesized that 5-HT contributes to increased pulmonary vascular resistance (PVR) in a sheep model of PPHN and that selective 5-HT reuptake inhibitor (SSRI) treatment increases PVR in this model. We studied the hemodynamic effects of 5-HT, ketanserin (5-HT2A receptor antagonist), and sertraline, an SSRI, on pulmonary hemodynamics of the late gestation fetal sheep with PPHN caused by prolonged constriction of the ductus arteriosis. Brief intrapulmonary infusions of 5-HT increased PVR from 1.0 ± 0.07 (baseline) to 1.4 ± 0.22 mmHg/ml per minute of treatment (P < 0.05). Ketanserin decreased PVR from 1.1 ± 0.15 (baseline) to 0.82 ± 0.09 mmHg/ml per minute of treatment (P < 0.05). Sertraline increased PVR from 1.1 ± 0.17 (baseline) to 1.4 ± 0.17 mmHg/ml per minute of treatment (P = 0.01). In addition, we studied 5-HT production and activity in vitro in experimental PPHN. Compared with controls, pulmonary artery endothelial cells from fetal sheep with PPHN exhibited increased expression of tryptophan hydroxylase 1 and 5-HT production by twofold and 56%, respectively. Compared with controls, 5-HT2A R expression was increased in lung homogenates and pulmonary artery smooth muscle cell lysates by 35% and 32%, respectively. We concluded that increased 5-HT contributes to high PVR in experimental PPHN through activation of the 5-HT2A receptor and that SSRI infusion further increases PVR in this model.

The mechanism through which octreotide inhibits hepatic stellate cell activity

Hepatic stellate cells (HSCs) are important in the development of liver fibrosis and in the pathogenesis of portal hypertension. Octreotide, an analogue of somatostatin, has been demonstrated to effectively treat fibrosis and portal hypertension; however, its relative mechanism in HSCs remains unknown. LX‑2, the immortalized HSC line, was used to study the mechanism whereby octreotide functions at different concentrations. Real‑time polymerase chain reaction (PCR) and western blot analysis were used to analyze the expression of fibrosis markers and transcription factors following treatment with octreotide. Soluble secreted endothelin‑1 (ET‑1), collagen I and vascular endothelial growth factor (VEGF) were assessed in the supernatants of cultured cells by enzyme-linked immunosorbent assay (ELISA). In the present study, it was shown that octreotide was able to inhibit the proliferative ability of the LX‑2 cells and decrease the expression of transforming growth factor β (TGF‑β), α‑smooth muscle actin (α‑SMA) and smad‑4a. The transcription factors, including c‑Jun and sp‑1, were downregulated in a dose‑dependent manner following treatment with octreotide. The levels of ET‑1 and collagen I in the supernatant decreased significantly in contrast with the normal levels, whereas the levels of VEGF in the LX‑2 cells and the supernatant increased at a high octreotide concentration (10‑5 nM). Octreotide may exert its effects on ET‑1 or other targeting genes in HSCs through the downregulation of c‑Jun and specificity protein 1 (sp‑1), and the increased levels of VEGF may be the reason for the side effects observed at high concentrations of octreotide.

Serotonin inhibits apoptosis of pulmonary artery smooth muscle cells through 5-HT2A receptors involved in the pulmonary artery remodeling of pulmonary artery hypertension

Decreased pulmonary artery smooth muscle cell (PASMC) apoptosis play a key role in pulmonary artery remodeling during pulmonary artery hypertension (PAH), but the mechanisms involved are unclear. Serotonin (5-HT) inhibits apoptosis in many pathologic processes by activating the 5-HT2A receptor. Therefore, we hypothesized that 5-HT may be the promoter of decreased apoptosis in PAH through the 5-HT2A receptor. We found that inhibition of the 5-HT2A receptor prevented the increase in pulmonary artery pressure and pulmonary artery remodeling in rats stimulated by monocrotaline. This effect was accompanied by increased apoptosis in the pulmonary artery. Cultured PASMCs stimulated with 5-HT showed a decrease in apoptosis with increased phosphorylation of extracellular signal regulated kinase 1/2 (ERK1/2), pyruvate dehydrogenase kinase (PDK), and mitochondrial transmembrane potential. These effects were markedly prevented by a 5-HT2A receptor inhibitor, an ERK1/2 activation inhibitor peptide I, or a PDK inhibitor. In conclusion, 5-HT inhibited PASMC apoptosis by activating the 5-HT2A receptor through the pERK1/2 and PDK pathways.5-HT decreasing apoptosis through 5-HT2A receptor is involved, at least in part, in pulmonary artery remolding.

Distribution of 5-ht(1E) receptors in the mammalian brain and cerebral vasculature: an immunohistochemical and pharmacological study

BACKGROUND AND PURPOSE

The 5-ht(1E) receptor is highly expressed in the human brain and its structure is conserved in humans, suggesting an important physiological role for 5-ht(1E) receptors. However, neither the function nor the distribution of this receptor has been characterized in the mammalian brain.

EXPERIMENTAL APPROACH

Rats and mice lack the 5-ht(1E) receptor gene; thus, we used guinea pig brain tissue and immunofluorescent staining techniques to provide the first specific localization of 5-ht(1E) receptors in the mammalian brain.

KEY RESULTS

High levels of 5-ht(1E) receptors are detected in olfactory bulb glomeruli as well as the molecular layer of the dentate gyrus (DG). In DG membranes, BRL54443, a 5-ht(1E) /5-HT(1F) agonist, selectively stimulated 5-ht(1E) receptors and potently inhibited forskolin-dependent cAMP production (IC₅₀ = 14 nM). The staining pattern of 5-ht(1E) receptors in brain tissue suggests that this receptor is expressed predominantly in neurons rather than in glia. Additionally, 5-ht(1E) receptors were detected in the adventitial layer of cerebral arteries but not in the microvasculature, venous tissue or other brain arteries.

CONCLUSIONS AND IMPLICATIONS

These observations should help to predict clinical effects of 5-ht(1E) -selective drugs. For example, the stimulation of 5-ht(1E) receptors and subsequent inhibition of adenylate cyclase activity in the DG suggests that 5-ht(1E) receptors may mediate regulation of hippocampal activity by 5-HT, making it a possible drug target for the treatment of neuropsychiatric disorders characterized by memory deficits (such as Alzheimer's disease) or as a target for the treatment of temporal lobe epilepsy.

c-Jun NH₂-terminal kinase contributes to dexmedetomidine-induced contraction in isolated rat aortic smooth muscle

PURPOSE

Dexmedetomidine, a full agonist of α2B-adrenoceptors, is used for analgesia and sedation in the intensive care units. Dexmedetomidine produces an initial transient hypertension due to the activation of post-junctional α2B-adrenoceptors on vascular smooth muscle cells (SMCs). The aims of this in vitro study were to identify mitogen-activated protein kinase (MAPK) isoforms that are primarily involved in full, α2B-adrenoceptor agonist, dexmedetomidine-induced contraction of isolated rat aortic SMCs.

MATERIALS AND METHODS

Rat thoracic aortic rings without endothelium were isolated and suspended for isometric tension recording. Cumulative dexmedetomidine (10⁻⁹ to 10⁻⁶ M) dose-response curves were generated in the presence or absence of extracellular signal-regulated kinase (ERK) inhibitor PD 98059, p38 MAPK inhibitor SB 203580, c-Jun NH₂-terminal kinase (JNK) inhibitor SP 600125, L-type calcium channel blocker (verapamil and nifedipine), and α₂-adrenoceptor inhibitor atipamezole. Dexmedetomidine-induced phosphorylation of ERK, JNK, and p38 MAPK in rat aortic SMCs was detected using Western blotting.

RESULTS

SP 600125 (10⁻⁶ to 10⁻⁵ M) attenuated dexmedetomidine-evoked contraction in a concentration- dependent manner, whereas PD 98059 had no effect on dexmedetomidine- induced contraction. SB 203580 (10⁻⁵ M) attenuated dexmedetomidine-induced contraction. Dexmedetomidine-evoked contractions were both abolished by atipamezole and attenuated by verapamil and nifedipine. Dexmedetomidine induced phosphorylation of JNK and p38 MAPK in rat aortic SMCs, but did not induce phosphorylation of ERK.

CONCLUSION

Dexmedetomidine-induced contraction involves a JNK- and p38 MAPK-mediated pathway downstream of α₂-adrenoceptor stimulation in rat aortic SMCs. In addition, dexmedetomidine-induced contractions are primarily dependent on calcium influx via L-type calcium channels.

Serotonin receptors in rat jugular vein: presence and involvement in the contraction

Serotonin (5-hydroxytryptamine; 5-HT) is released during platelet aggregation, a phenomenon commonly observed in blood clot formation and venous diseases. Once released, 5-HT can interact with its receptors in the peripheral vasculature to modify vascular tone. The goal of this study was to perform a detailed pharmacological characterization of the 5-HT receptors involved in the contractile response of the rat jugular vein (RJV) using recently developed drugs with greater selectivity toward 5-HT receptor subtypes. We hypothesized that, as for other blood vessels, the 5-HT(1B/1D) and 5-HT(2B) receptor subtypes mediate contraction in RJV alongside the 5-HT(2A) receptor subtype. Endothelium-intact RJV rings were set up in an isolated organ bath for isometric tension recordings, and contractile concentration-effect curves were obtained for 13 distinct serotonergic receptor agonists. Surprisingly, the 5-HT(1A) and the mixed 5-HT(1A/1B) receptor agonists (+/-)-2-dipropyl-amino-8-hydroxyl-1,2,3,4-tetrahydronapthalene (8-OH-DPAT) and 5-methoxy-3 (1,2,3,6-tetrahydropyridin-4-yl) (1H indole) (RU24969) caused contractions that were antagonized by the 5-HT(1A) receptor antagonist [O-methyl-3H]-N-(2-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl)-N-(2-pyridinyl)cyclohexanecarboxamide (WAY100135). The contractile curve to 5-HT was shifted to the right by WAY100135, 3-[2-[4-(4-fluoro benzoyl)-piperidin-1-yl]ethyl]-1H-quinazoline-2,4-dione (ketanserin; 5-HT(2A/C) receptor antagonist), and 1-(2-chloro-3,4-dimethoxybenzyl)-6-methyl-1,2,3,4-tetrahydro-9H-pyrido[3,4-b]indole hydrochloride (LY266097; 5-HT(2B) receptor antagonist). Ketanserin also caused rightward shifts of the contractile curves to 8-OH-DPAT, RU24969, and the 5-HT(2B) receptor agonist (alpha-methyl-5-(2-thienylmethoxy)-1H-indole-3-ethanamine) (BW723C86). Agonists for 5-HT(1B/1D/1F), 5-HT(3), 5-HT(6), and 5-HT(7) receptors were inactive. In real-time polymerase chain reaction experiments that have never been performed in this tissue previously, we observed mRNA expression for the 5-HT(2A), 5-HT(2B), and 5-HT(7) receptors, whereas no significant mRNA expression was found for 5-HT(1A), 5-HT(1B), and 5-HT(1D) receptors. These results support the 5-HT(2A) receptor as the main subtype targeted by 5-HT to contract the RJV.

Pharmacological properties and discriminative stimulus effects of a novel and selective 5-HT2 receptor agonist AL-38022A [(S)-2-(8,9-dihydro-7H-pyrano[2,3-g]indazol-1-yl)-1-methylethylamine]

AL-38022A is a novel synthetic serotonergic (5-HT) ligand that exhibited high affinity for each of the 5-HT2 receptor subtypes (Ki100-fold less) affinity for other 5-HT receptors. In addition, AL-38022A displayed a very low affinity for a broad array of other receptors, neurotransmitter transport sites, ion channels, and second messenger elements, making it a relatively selective agent. AL-38022A potently stimulated functional responses via native and cloned rat (EC50 range: 1.9-22.5 nM) and human (EC50 range: 0.5-2.2 nM) 5-HT2 receptor subtypes including [Ca2+]i mobilization and tissue contractions with apparently similar potencies and intrinsic activities and was a full agonist at all 5-HT2 receptor subtypes. The CNS activity of AL-38022A was assessed by evaluating its discriminative stimulus effects in both a rat and a monkey drug discrimination paradigm using DOM as the training drug. AL-38022A fully generalized to the DOM stimulus in each of these studies; in monkeys MDL 100907 antagonized both DOM and AL-38022A. The pharmacological profile of AL-38022A suggests that it could be a useful tool in defining 5-HT2 receptor signaling and receptor characterization where 5-HT may function as a neurotransmitter.

c-Src tyrosine kinase, a critical component for 5-HT2A receptor-mediated contraction in rat aorta

Serotonin (5-hydroxytryptamine, 5-HT) receptors (5-HTRs) play critical roles in brain and cardiovascular functions. In the vasculature, 5-HT induces potent vasoconstrictions, which in aorta are mainly mediated by activation of the 5-HT(2A)R subtype. We previously proposed that one signalling mechanism of 5-HT-induced vasoconstriction could be c-Src, a member of the Src tyrosine kinase family. We now provide evidence for a central role of c-Src in 5-HT(2A)R-mediated contraction. Inhibition of Src kinase activity with 10 mum 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP2) prior to contraction resulted in approximately 90-99% inhibition of contractions induced by 5-HT or by alpha-methyl-5-HT (5-HT(2)R agonist). In contrast, PP2 pretreatment only partly inhibited contractions induced by angiotensin II and the thromboxane A(2) mimetic, U46619, and had no significant action on phenylephrine-induced contractions. 5-Hydroxytryptamine increased Src kinase activity and PP2-sensitive tyrosine-phosphorylated proteins. As expected for c-Src identity, PP2 pretreatment inhibited 5-HT-induced contraction with an IC(50) of approximately 1 mum. Ketanserin (10 nm), a 5-HT(2A) antagonist, but not antagonists of 5-HT(2B)R (100 nm SB204741) or 5-HT(2C)R (20 nm RS102221), prevented 5-HT-induced contractions, mimicking PP2 and implicating 5-HT(2A)R as the major receptor subtype coupled to c-Src. In HEK 293T cells, c-Src and 5-HT(2A)R were reciprocally co-immunoprecipitated and co-localized at the cell periphery. Finally, 5-HT-induced Src activity was unaffected by inhibition of Rho kinase, supporting a role of c-Src upstream of Rho kinase. Together, the results highlight c-Src activation as one of the early and pivotal mechanisms in 5-HT(2A)R contractile signalling in aorta.

Schistosoma mansoni infection enhances host portal vein contraction: role of potassium channels and p38 MAP kinase

Murine Schistosoma mansoni infection is related to an increased contraction of portal vein in response to 5-hydroxytryptamine (5-HT). The present study addressed a putative alteration of ion channels and enzymes involved in vascular contraction. In control group, either inhibition of K+ channels sensitive to ATP (K(ATP)) or Ca2+ (BK(Ca)) increased 5-HT-induced contraction, but the same did not occur in infected mice. On the other hand, inhibition of p38 MAP kinase markedly decreased the vascular contraction to 5-HT in the infected mice with minor effects in the control group. Accordingly, we observed a higher density of phospho-p38 MAP kinase, that refers to the fully active state of the enzyme, in portal veins from infected mice as compared to control animals. These results suggest that the reduced function of K(ATP) and BK(Ca) channels along with an increased contribution of p38 MAP kinase contribute to the increased contraction of portal veins to 5-HT observed in murine schistosomiasis.

Vasoactive peptides in cardiovascular (patho)physiology

Numerous vasoactive agents play an important physiological role in regulating vascular tone, reactivity and structure. In pathological conditions, alterations in the regulation of vasoactive peptides result in endothelial dysfunction, vascular remodeling and vascular inflammation, which are important processes underlying vascular damage in cardiovascular disease. Among the many vasoactive agents implicated in vascular (patho)biology, angiotensin II (Ang II), endothelin (ET), serotonin and natriuretic peptides appear to be particularly important because of their many pleiotropic actions and because they have been identified as potential therapeutic targets in cardiovascular disease. Ang II, ET-1, serotonin and natriuretic peptides mediate effects via specific receptors, which belong to the group of G-protein-coupled receptors. ET, serotonin and Ang II are primarily vasoconstrictors with growth-promoting actions, whereas natriuretic peptides, specifically atrial, brain and C-type natriuretic peptides, are vasodilators with natriuretic effects. Inhibition of vasoconstrictor actions with drugs that block peptide receptors, compounds that inhibit enzymes that generate vasoactive peptides or agents that increase levels of natriuretic peptides are potentially valuable therapeutic tools in the management of cardiovascular diseases. This review focuses on ET, natriuretic peptides and serotonin. The properties and distribution of these vasoactive agents and their receptors, mechanisms of action and implications in cardiovascular (patho)physiology will be discussed.

Increased 5-HT contractile response in late pregnant rat myometrium is associated with a higher density of 5-HT2A receptors

The 5-hydroxytryptamine (5-HT) type 2 receptor family is involved in multiple physiological functions in smooth muscle including proliferation, differentiation and contraction. In myometrium, 5-HT2 receptors not only play a role in contraction but also regulate the activity of hypertrophic genes during pregnancy. Here we investigated whether 5-HT2A receptors were up-regulated during gestation and whether changes in expression could be correlated with changes in 5-HT-induced contractions in late pregnant myometrium. 5-HT tension dose-response curves showed that 5-HT-induced myometrial contractility is drastically increased in late pregnancy when compared to non-pregnant conditions. The 5-HT maximum tension (% of 80 mM KCl contracture) increased from 17 +/- 2% in non-pregnant to 54 +/- 7% in late pregnant myometrium. This tension increase took place without significant changes in the 5-HT sensitivity as EC50 values were similar in non-pregnant and late pregnant myometrium (0.11 +/- 0.03 microM and 0.17 +/- 0.02 microM, respectively). The increased 5-HT-induced contraction at the end of pregnancy was associated with up-regulation of 5-HT2A transcript (approximately 5-fold) and protein (approximately 6-fold) levels. These functional and biochemical studies provide evidence that myometrium remodelling during pregnancy is in part associated with up-regulation of 5-HT2A transcript and protein levels resulting in higher 5-HT-induced contractile responses. We conclude that the higher 5-HT-induced contractile response results from a higher density of 5-HT2A receptors having the same properties as in non-pregnant myometrium.

ERK activation contributes to regulation of spontaneous contractile tone via superoxide anion in isolated rat aorta of angiotensin II-induced hypertension

Arteries from hypertensive animals and humans have increased spontaneous tone. Increased superoxide anion (superoxide) contributes to elevated blood pressure (BP) and spontaneous tone in hypertension. The association between the extracellular signaling-regulated kinase 1/2 (ERK1/2)-mitogen-activated protein kinase (MAPK) signaling pathway and generation of superoxide and spontaneous tone in isolated aorta was studied in angiotensin II (ANG II)-infused hypertensive (HT) rats. Systolic BP, phosphorylation of ERK, aortic superoxide formation, and aortic spontaneous tone were compared in sham normotensive and HT rats. Infusion of ANG II (0.5 mg x kg(-1) x day(-1) for 6 days) significantly elevated the systolic BP (P<0.01). The phosphorylation of ERK1/2 vs. total ERK1/2 in thoracic aorta was enhanced, and superoxide was increased in the HT vs. the sham group (P<0.01). Spontaneous tone developed in the HT group, but not in the normotensive group. MAPK/ERK1/2 (MEK1/2)-ERK1/2 signaling pathway inhibitors, PD-98059 (10 micromol/l), and U-0126 (10 micromol/l), significantly reduced the phosphorylation of ERK1/2, superoxide generation (P<0.01), and spontaneous tone (P<0.01) in HT. These findings suggest that ANG II infusion induces the production of superoxide and spontaneous tone and that both are dependent on ERK-MAPK activation. In endothelium-denuded aorta, however, MEK1/2 inhibitors did not inhibit the spontaneous tone, even though they significantly reduced superoxide generation similar to endothelium-intact aorta. These data suggest that inhibition of ERK1/2 signaling pathway, via PD-98059 or U-0126, may regulate spontaneous tone in an endothelium-dependent manner. In conclusion, these findings support the importance of the ERK1/2 signaling pathway in modulating vascular oxidative stress and subsequently mediating spontaneous tone in HT.

The 5-HT2A serotoninergic receptor is expressed in the MCF-7 human breast cancer cell line and reveals a mitogenic effect of serotonin

Serotonin (5-hydroxytryptamine, 5-HT) has been described as a mitogen in a variety of cell types and carcinomas. It exerts its mitogenic effect by interacting with a wide range of 5-HT receptor types. Certain studies suggest that some selective serotonin re-uptake inhibitors promote breast cancer in animals and humans. This study attempts to clarify the role of serotonin in promoting the growth of neoplastic mammary cells. Expression of the 5-HT(2A) serotoninergic receptor subtype in MCF-7 cells was determined by RT-PCR, Western blotting, and immunofluorescence analysis. The mitogenic effect of 5-HT on MCF-7 cells was determined by means of the MTT proliferation assay. We have demonstrated that the 5-HT(2A) receptor subtype is fully expressed in the MCF-7 human breast cancer cell line, in terms of encoding mRNA and receptor protein. Automated sequencing has confirmed that the 5-HT(2A) receptor present in this cell line is identical to the 5-HT(2A) receptor found in human platelets and in human cerebral cortex. Furthermore, this receptor was found by immunofluorescence to be on the plasma membrane. MTT proliferation assays revealed that 5-HT and DOI, a selective 5-HT(2A) receptor subtype agonist, stimulated MCF-7 cell. These results indicate that 5-HT plays a mitogenic role in neoplastic mammary cells. Our data also indicate that 5-HT exerts this positive growth effect on MCF-7 cells through, in part, the 5-HT(2A) receptor subtype, which is fully expressed in this cell line.

Expression of the 5-HT2A Serotoninergic Receptor in Human Placenta and Choriocarcinoma Cells: Mitogenic Implications of Serotonin

Serotonin (5-hydroxytryptamine, 5-HT) has diverse physiological functions and acts as a mitogen in a variety of cell types, including bovine placental cells. It exerts its mitogenic effect by interacting with a wide range of 5-HT receptor types. Previous studies have reported the presence of 5-HT(2) binding sites in human placental trophoblastic cells, but this has never been confirmed at the molecular level. In this study, we demonstrated that the 5-HT(2A) receptor subtype is fully expressed in the human choriocarcinoma cell lines JEG-3 and BeWo as well as in normal human placental tissue. DNA sequencing has confirmed that the 5-HT(2A) receptor present in these cell lines and tissues is identical to the human 5-HT(2A) receptor found in platelets and in the cerebral cortex. This receptor was localized by immunofluorescence on the plasma membrane, in JEG-3 and BeWo cells. Furthermore, MTT proliferation assays revealed a positive effect of 5-HT on the proliferation of JEG-3 and BeWo cells. These results suggest that 5-HT constitutes a potent mitogen for neoplastic placental cells.

5-Hydroxytryptamine-induced proliferation of pulmonary artery smooth muscle cells are extracellular signal-regulated kinase pathway dependent

AIM

To investigate the effect of 5-hydroxytryptamine transporter (5-HTT) inhibitor fluoxetine and antisense oligodeoxynucleotide (ODN) to extracelluar signal-regulated kinases (ERKs) on pulmonary arterial smooth muscle cells (PASMCs) proliferation induced by 5-HT.

METHODS

Liposomal transfection was used to introduce ODNs to ERK1/2 into cultured rat PASMCs and the transfection efficiency was measured by observing the uptake of the fluorecein isothiocynate (FITC)-labeled antisense ODN in PASMCs. The effects of 5-HTT selective inhibitor fluoxetine and ODNs on the proliferation of PASMCs were evaluated by cell number counting and cell cycle analysis, and measured by microculture tetrazolium (MTT) assay and flow cytometry (FCM), respectively.

RESULTS

Liposomes mediated the transfection of ODNs into PASMCs with high efficiency. MTT assay showed fluoxetine (10 micromol/L, 1 micromol/L, and 100 nmol/L) concentration dependently inhibited the proliferation of PASMCs induced by 5-HT (1 micromol/L) in vitro. The proliferation rate of PASMCs by 5-HT was significantly inhibited by pretreatment with ERK1/2 antisense ODN (0.2 micromol/L) from 251%+/-18% to 86%+/-5% (P<0.01). Flow cytometric analysis of cell cycle distribution showed that the increase of 5-HT induced S phase fraction (SPF) and proliferation index (PI) were significantly inhibited by fluoxetine (1 micromol/L) or antisense ODN with SPF from 36%+/-4% to 26%+/-3% and 24%+/-4%, and PI from 34%+/-2% to 29%+/-2% and 24%+/-2%, respectively.

CONCLUSION

5-HTT mediates the mitogenic effect of 5-HT on PASMCs and the proliferation of PASMCs induced by 5-HT is dependent on ERKs signal pathway.

Clozapine and the mitogen-activated protein kinase signal transduction pathway: implications for antipsychotic actions

BACKGROUND

Mitogen-activated protein kinase (MAPK) signaling pathways respond to dopaminergic and serotonergic agents and mediate short- and long-term effects of intracellular signaling in neurons. Here we show that the antipsychotic agent, clozapine, selectively activates the MEK/ERK MAPK pathway, and inhibition of this pathway reverses clozapine's actions in the conditioned avoidance response (CAR) paradigm, a rodent behavioral assay of antipsychotic activity.

METHODS

Phosphorylation patterns of MAPK pathway enzymes were determined by quantitative immunoblot analysis and immunohistochemistry of rat prefrontal cortex. Kinase inhibitors were used to assess the role of MAPK signaling pathways in mediating clozapine-induced suppression of CAR.

RESULTS

Clozapine administration selectively increased phosphorylation of MEK1/2 but had no effect on p38 or JNK phosphorylation. Pretreatment with the 5-HT2A agonist (+/-)-2,5-dimethoxy-4-iodoamphetamine hydrochloride blocked the clozapine-induced increase in MEK1/2 phosphorylation. Immunohistochemistry revealed that clozapine treatment elevated the number of cells in the prefrontal cortex positive for phosphoERK, the downstream substrate of MEK1/2. Prior administration of MEK1/2 inhibitors U0126 or Sl327, or ERK inhibitor 5-iodotubercidin, reversed suppression of CAR induced by clozapine, whereas administration of vehicle, JNK or p38 inhibitors (L-JNK-1 and SB203580, respectively) had no effect. Inhibition of kinases upstream to MEK1/2 (PI-3K, PKC, and CaMKII) by administration of LY294002, bisindolylmaleimide, or KN-62, respectively, also reversed clozapine-induced suppression of CAR.

CONCLUSIONS

These data support the hypothesis that the MEK/ERK signal transduction cascade participates in clozapine's antipsychotic actions.

Activation of the JAK/STAT pathway in vascular smooth muscle by serotonin

Serotonin (5-hydroxytryptamine, 5-HT) is a vasoconstrictor and mitogen whose levels are elevated in diabetes. Previous studies have shown the presence of 5-HT2A, 5-HT2B, and 5-HT1B receptors in vascular smooth muscle cells (VSMCs). There are currently no data regarding 5-HT2B and 5-HT1B receptor activation of the JAK/STAT pathway in VSMCs and resultant potential alterations in 5-HT signaling in diabetes. Therefore, we tested the hypothesis that 5-HT differentially activates the JAK/STAT pathway in VSMCs under conditions of normal (5 mM) and high (25 mM) glucose. Treatment of rat VSMCs with 5-HT (10(-6) M) resulted in time-dependent activation ( approximately 2-fold) of JAK2, JAK1, and STAT1, but not STAT3 (maximal at 5 min, returned to baseline by 30 min). The 5-HT2B receptor agonist BW723C86 and the 5-HT1B receptor agonist CGS12066A (10(-9)-10(-5) M, 5-min stimulation) did not activate the JAK/STAT pathway. Treatment with the 5-HT2A receptor antagonist ketanserin (10 nM) inhibited JAK2 activation by 5-HT. Treatment of streptozotocin-induced diabetic rats with ketanserin (5 mg.kg-1.day-1) reduced activation of JAK2 and STAT1 but not STAT3 in endothelium-denuded thoracic aorta in vivo. 5-HT (10(-6) M) treatment resulted in increased cell proliferation and increased DNA synthesis, which were inhibited by the JAK2 inhibitor AG490. Further studies with apocynin, diphenyleneiodonium chloride, catalase, and virally transfected superoxide dismutase had no effect at either glucose concentration on activation of the JAK/STAT pathway by 5-HT. Therefore, we conclude that 5-HT activates JAK2, JAK1, and STAT1 via the 5-HT2A receptors in a reactive oxygen species-independent manner under both normal and high glucose conditions.

5-Hydroxytryptamine-induced vasodilator responses in the hindquarters of the anaesthetized rat, involve beta2-adrenoceptors

These studies were conducted to examine the role of the vasoactive mediators nitric oxide (NO) and adrenaline (epinephrine) in the serotonin (5-hydroxytryptamine; 5-HT)-induced vasodilator response in the hindquarter vascular bed of anaesthetized rats. Intra-arterial administration of doses of 5-HT in the range 0.12-25 ng kg(-1) produced a dose-independent vasodilator effect in the hindquarters. The selective 5-HT(1D/1B) receptor agonist, L-694,247 at intra-arterial doses of 0.0012-1000 ng kg(-1), as well as adrenaline (at doses of 0.05-50 ng kg(-1) i.a.), mimicked the dose-independent vasodilator effect induced by intra-arterial administration of 5-HT. Intravenous pre-treatment with the selective beta2-receptor antagonist ICI 118,551 (0.5 mg kg(-1)) blocked the vasodilator effect of 5-HT, adrenaline and L-694,247. Additionally, the inhibitor of NO synthase NG-nitro-L-arginine (L-NAME) (at a dose of 10 mg kg(-1) i.v.) blocked the vasodilator action of acetylcholine 300-3000 ng kg(-1)) but did not modify 5-HT-induced vasodilatation. The vasodilator effect produced by intra-arterial administration of 5-HT in the hindquarters was significantly inhibited both 30 min after denervation of the lumbar sympathetic chains and 1 h after bilateral adrenalectomy. Our data suggest that in the in-situ autoperfused hindquarters of the rat 5-HT-induced vasodilatation is mediated by a local 5-HT(1D) or 5-HT(1D/1B) activation, which in turn mediates the adrenal release of adrenaline, which then produces beta2-activation and vasodilatation.

Importance of ERK activation in behavioral and biochemical effects induced by MDMA in mice

Little is known about the cellular effects induced by 3,4-methylenedioxymethamphetamine (MDMA, ecstasy), although changes in gene expression have been observed following treatments with other psychostimulants. Thus, the aim of this study was to investigate in mice, the relationships between the ras-dependent protein kinase ERK and MDMA-induced reinforcement using the conditioned place preference (CPP) and locomotor activity measurements. This was completed using real-time quantitative PCR method by a study of immediate early-genes (IEGs) transcription known to be involved in neuronal plasticity. A significant CPP was observed after repeated MDMA treatment in CD-1 mice at a dose of 9 mg kg-1 i.p. but not at 3 and 6 mg kg-1. This rewarding effect was abolished by the selective inhibitor of ERK activation, SL327 (50 mg kg-1; i.p.). Similar results were obtained on MDMA-induced locomotor activity, clearly suggesting a role of ERK pathway in these behavioral responses. Following acute i.p. injection, MDMA induced a strong c-fos transcription in brain structures, such as caudate putamen, nucleus accumbens and hippocampus, whereas egr-1 and egr-3 transcripts were only increased in the caudate putamen. MDMA-induced IEGs transcription was selectively suppressed by SL327 in the caudate putamen, suggesting a role for other signaling pathways in regulation of IEGs transcription in the other brain structures. In agreement with these results, MDMA-induced c-fos protein expression was blocked by SL327 in the caudate putamen. This study confirms and extends to mice the reported role of ERK pathway in the development of addiction-like properties of MDMA. This could facilitate studies about the molecular mechanism of this process by using mutant mice.

Arterial expression of 5-HT2B and 5-HT1B receptors during development of DOCA-salt hypertension

BACKGROUND

5-hydroxytryptamine (5-HT)2B and 5-HT1B receptors are upregulated in arteries from hypertensive DOCA-salt rats and directly by mineralocorticoids. We hypothesized that increased 5-HT2B and 5-HT1B receptor density and contractile function would precede increased blood pressure in DOCA-high salt rats. We performed DOCA-salt time course (days 1, 3, 5 and 7) studies using treatment groups of: DOCA-high salt, DOCA-low salt, Sham and Sham-high salt rats.

RESULTS

In isolated-tissue baths, DOCA-high salt aorta contracted to the 5-HT2B receptor agonist BW723C86 on day 1; Sham aorta did not contract. The 5-HT1B receptor agonist CP93129 had no effect in arteries from any group. On days 3, 5 and 7 CP93129 and BW723C86 contracted DOCA-high salt and Sham-high salt aorta; Sham and DOCA-low salt aorta did not respond. Western analysis of DOCA-high salt aortic homogenates revealed increased 5-HT2B receptor levels by day 3; 5-HT1B receptor density was unchanged. Aortic homogenates from the other groups showed unchanged 5-HT2B and 5-HT1B receptor levels.

CONCLUSION

These data suggest that functional changes of 5-HT2B but not 5-HT1B receptors may play a role in the development of DOCA-salt hypertension.

Mitogen-induced activation of Na+/H+ exchange in vascular smooth muscle cells involves janus kinase 2 and Ca2+/calmodulin

The sodium/proton exchanger type 1 (NHE-1) plays an important role in the proliferation of vascular smooth muscle cells (VSMC). We have examined the regulation of NHE-1 by two potent mitogens, serotonin (5-HT, 5-hydroxytryptamine) and angiotensin II (Ang II), in cultured VSMC derived from rat aorta. 5-HT and Ang II rapidly activated NHE-1 via their G protein-coupled receptors (5-HT(2A) and AT(1)) as assessed by proton microphysiometry of quiescent cells and by measurements of intracellular pH on a FLIPR (fluorometric imaging plate reader). Activation of NHE-1 was blocked by inhibitors of phospholipase C, CaM, and Jak2 but not by pertussis toxin or inhibitors of protein kinase C. Immunoprecipitation/immunoblot studies showed that 5-HT and Ang II induce phosphorylation of Jak2 and induce the formation of signal transduction complexes that included Jak2, CaM, and NHE-1. The cell-permeable Ca(2+) chelator BAPTA-AM blocked activation of Jak2, complex formation between Jak2 and CaM, and tyrosine phosphorylation of CaM, demonstrating that elevated intracellular Ca(2+) is essential for those events. Thus, mitogen-induced activation of NHE-1 in VSMC is dependent upon elevated intracellular Ca(2+) and is mediated by the Jak2-dependent tyrosine phosphorylation of CaM and subsequent increased binding of CaM to NHE-1, similar to the pathway previously described for the bradykinin B(2) receptor in inner medullary collecting duct cells of the kidney [Mukhin, Y. V., et al. (2001) J. Biol. Chem. 276, 17339-17346]. We propose that this pathway represents a fundamental mechanism for the rapid regulation of NHE-1 by G(q/11) protein-coupled receptors in multiple cell types.

Inability of serotonin to activate the c-Jun N-terminal kinase and p38 kinase pathways in rat aortic vascular smooth muscle cells

BACKGROUND

Serotonin (5-HT, 5-hydroxytryptamine) activates the Extracellular Signal-Regulated Kinase (ERK)/ Mitogen-Activated Protein Kinase (MAPK) pathways, in vascular smooth muscle cells. Parallel MAPK pathways, the c-Jun N-terminal Kinase (JNK) and p38 pathway, are activated by stimulators of the ERK/MAPK pathway. We hypothesized that 5-HT would activate the JNK and p38 pathways in rat vascular smooth muscle cells.

RESULTS

Results were determined using standard Western analysis and phosphospecific JNK and p38 antibodies. No significant activation by 5-HT (10(-9) - 10(-5) M; 30 min) of the JNK or p38 pathways, as measured by protein phosphorylation, was observed in any of these experiments. These experiments were repeated in the presence of the serine/threonine phosphatase inhibitor okadaic acid (1 uM) and the tyrosine phosphatase inhibitor sodium orthovanadate (1 uM) to maximize any observable signal. Even under these optimized conditions, no activation of the JNK or p38 pathways by 5-HT was observed. Time course experiments (5-HT 10(-5) M; 5 min, 15 min, 30 min and 60 min) showed no significant activation of JNK after incubation with 5-HT at any time point. However, we detected strong activation of JNK p54 and p46 (5- and 7 fold increases in bands p54 and p46, respectively over control levels) by anisomycin (500 ng/ml, 30 min). Similarly, a JNK activity assay failed to reveal activation of JNK by 5-HT, in contrast to the strong stimulation by anisomycin.

CONCLUSION

Collectively, these data support the conclusion that 5-HT does not activate the JNK or p38 pathways in rat vascular smooth muscle cells.