SUMMARY1. The function of the serotonin transporter (SERT) is to take up and release serotonin (5-hydroxytyptamine (5-HT)) from cells and this function of SERT in the central nervous system (CNS) is well-documented; SERT is the target of selective serotonin reuptake inhibitors used in the treatment of CNS disorders, such as depression.2. The aim of the present review is to discuss our current knowledge of 5-HT and SERT in the cardiovascular (CV) system, as well as their function in physiological and pathophysiological states.3. The SERT protein has been located in multiple CV tissues, including the heart, blood vessels, brain, platelets, adrenal gland and kidney. Modification of SERT function occurs at both transcriptional and translational levels. The functions of SERT in these tissues is largely unexplored, but includes modulation of cardiac and smooth muscle contractility, platelet aggregation, cellular mitogenesis, modulating neuronal activity and urinary excretion.4. Recent studies have uncovered potential relationships between the expression of SERT gene promoter variants (long (l) or short (s)) with CV diseases. Specifically, the risk of myocardial infarction and pulmonary hypertension is increased with expression of the ll promoter, a variant associated with increased expression and function of SERT. The relationship between promoter variants and other CV diseases has not been investigated.5. Newly available experimental tools, such as pharmacological compounds and genetically altered mice, should prove useful in the investigation of the function of SERT in the CV system. 6. In summary, the function of SERT in the CV system is just beginning to be revealed.

Faithful genome integrity maintenance plays an essential role in cell survival. Here, we identify the RNA demethylase ALKBH5 as a key regulator that protects cells from DNA damage and apoptosis during reactive oxygen species (ROS)-induced stress. We find that ROS significantly induces global mRNA N6-methyladenosine (m6A) levels by modulating ALKBH5 post-translational modifications (PTMs), leading to the rapid and efficient induction of thousands of genes involved in a variety of biological processes including DNA damage repair. Mechanistically, ROS promotes ALKBH5 SUMOylation through activating ERK/JNK signaling, leading to inhibition of ALKBH5 m6A demethylase activity by blocking substrate accessibility. Moreover, ERK/JNK/ALKBH5-PTMs/m6A axis is activated by ROS in hematopoietic stem/progenitor cells (HSPCs) in vivo in mice, suggesting a physiological role of this molecular pathway in the maintenance of genome stability in HSPCs. Together, our study uncovers a molecular mechanism involving ALKBH5 PTMs and increased mRNA m6A levels that protect genomic integrity of cells in response to ROS.

Arterial hyper-responsiveness to 5-hydroxytryptamine (5-HT) is a hallmark of hypertension, and plasma levels of free 5-HT are elevated in hypertension. We hypothesized that chronic administration of 5-HT would cause blood pressure to 1) rise in normotensive rats and 2) rise significantly more in hypertensive rats. The deoxycorticosterone acetate (DOCA)-salt hypertensive and sham normotensive rat were used. Animals were implanted with minipumps that delivered 5-HT (or vehicle) at a rate of 25 g/kg/min for 7 days. Free plasma 5-HT was elevated significantly by this protocol. Within 48 h, mean arterial blood pressure measured telemetrically decreased in sham (106 Ϯ 2 to 83 Ϯ 2 mm Hg) and in DOCA-salt hypertensive (166 Ϯ 9 to 112 Ϯ 3 mm Hg) rats; vehicle did not change blood pressure in either group. Ganglionic blockade (hexamethonium) reduced blood pressure to a greater magnitude in DOCA vehicle-administered rats (peak fall arterial pressure, 91 Ϯ 14 mm Hg) compared with DOCA 5-HT-administered rats (40 Ϯ 6 mm Hg). Maximal acetylcholine-induced (NO-dependent) relaxation in phenylephrine-contracted aortic strips was greater in 5-HTadministered (69.2 Ϯ 9.1% relaxation) versus vehicle-administered (39.7 Ϯ 14.2%) DOCA rats; aortic endothelial cell nitric oxide synthase expression was higher in the 5-HT-versus vehicle-administered DOCA-salt rats. In normotensive and DOCAsalt hypertensive rats, the nitric oxide synthase (NOS) inhibitor N -nitro-L-arginine (0.5 g/l in water) prevented the fall in blood pressure to 5-HT. We conclude that chronic exogenous 5-HT reduces blood pressure in normotensive and hypertensive rats through mechanisms critically dependent on NOS.Serotonin [5-hydroxytryptamine (5-HT)] was discovered and characterized over 60 years ago by the Italian scientist Erspamer (Erspamer and Asero, 1952) and by Irving Page (Rapport et al., 1948; Page and McCubbin, 1953a,b). In the periphery, 5-HT is made primarily in the enterochromaffin cells of the intestine. The circulatory system is exposed to 5-HT through aggregation of platelets (which take up and store a millimolar concentration of 5-HT), release from adrenergic nerves that have taken up 5-HT, and through direct exposure to 5-HT that is free in the blood. In many tissues, 5-HT is taken up and concentrated by the serotonin transporter (SERT) and is rapidly metabolized to an inactive metabolite, 5-hydroxyindole acetic acid (5-HIAA), by intracellular monoamine oxidase.5-HT was originally described as a substance derived from serum (sero) that increased the tone of smooth muscle (tonin). Because of the close association of the platelet with the blood vessel, there has been a long-standing question as to the role of 5-HT in controlling vascular tone and modifying blood pressure under normotensive and hypertensive conditions. Several findings suggest that 5-HT contributes to systemic hypertension. These include the following findings: 1) plasma levels (free) of 5-HT are elevated in experimental and human models of hypertension (Fetkovska et al., 1990;Carr...

Background and purpose: 5-HT is a vasoconstrictor exhibiting enhanced effects in systemic arteries from subjects with cardiovascular disease. The effect of endogenous 5-HT on arteries is controversial, because the concentration of free circulating 5-HT is low and a 5-hydroxytryptaminergic system has not been identified in peripheral arteries. We hypothesized that a local 5-hydroxytryptaminergic system (including 5-HT synthesis, metabolism, uptake and release) with physiological function exists in peripheral arteries. Experimental approach: The presence of key components of a 5-hydroxytryptaminergic system in rat aorta and superior mesenteric artery was examined using western blot analyses, immunohistochemistry and immunocytochemistry. The function of the rate-limiting enzyme in 5-HT biosynthesis, tryptophan hydroxylase (TPH), and 5-HT transporter was tested by measuring enzyme activity and 5-HT uptake, respectively. Isometric contraction of arterial strips was used to demonstrate the function of released endogenous 5-HT in arterial tissues. Key results: mRNA for TPH-1 was present in arteries, with low levels of TPH protein and TPH activity. Expression and function of MAO A (5-HT metabolizing enzyme) was supported by immunohistochemistry, western analyses and the elevation of concentrations of 5-hydroxyindoleacetic acid (5-HT metabolite) after exposure to exogenous 5-HT. The 5-HT transporter was localized to the plasma membrane of freshly isolated aortic smooth muscle cells. Peripheral arteries actively took up 5-HT in a time-dependent and 5-HT transporter-dependent manner. The 5-HT transporter substrate, ( þ )-fenfluramine, released endogenous 5-HT from peripheral arteries, which potentiated noradrenaline-induced arterial contraction. Conclusions and implications:This study revealed the existence of a local 5-hydroxytryptaminergic system in peripheral arteries.

We tested the hypothesis that the 5-HT transporter (5-HTT) is present and functional in peripheral arterial smooth muscle. In aorta and mesenteric resistance arteries, real time RT-PCR and western analyses indicated the presence of 5-HTT mRNA and a 74 kDa 5-HTT protein. Immunohistochemistry localized the transporter to smooth muscle and endothelial cells. 5-HT and the metabolite 5-hydroxyindole acetic acid (5-HIAA) were detected in aorta, carotid, and superior mesenteric arteries using HPLC; the MAOA inhibitor pargyline significantly increased (over 400%) arterial 5-HT concentration. 5-HT was taken up by arteries in a time-dependent manner and uptake was independent of the endothelium, sympathetic nerves, and norepinephrine transporter. 5-HT-induced contraction of normal aorta was potentiated by the 5-HTT inhibitor fluvoxamine. A change in arterial 5-HTT function occurs in deoxycorticosterone (DOCA)-salt hypertension as the potency and threshold of 5-HT in contracting aorta from the DOCA-salt rat was increased by fluoxetine and fluvoxamine (1 micromol/L; DOCA fluvoxamine -log EC50 [mol/L] = 6.85 +/- 0.08, DOCA-control = 6.44 +/- 0.08); expression of transporter was significantly increased in aorta of DOCA salt rats (145% Sham). These studies show for the first time the presence of the 5-HTT in peripheral arterial smooth muscle and raise the question as to the function of the 5-HTT in regulating peripheral effects of 5-HT.

We hypothesized that the 5-hydroxytryptamine (5-HT; serotonin) system is present and functional in veins. In vena cava (VC), the presence of the 5-HT synthesis rate-limiting enzyme tryptophan hydroxylase-1 mRNA and accumulation of the 5-HT synthesis intermediate 5-hydroxytryptophan after incubation with tryptophan supported the ability of veins to synthesize 5-HT. The presence of 5-HT and its metabolite 5-hydroxyindole acetic acid was measured by high-performance liquid chromatography in VC and jugular vein (JV), and it was compared with similarly sized arteries aorta (RA) and carotid (CA), respectively. In rats treated with the monoamine oxidase-A (MAO-A) inhibitor pargyline to prevent 5-HT metabolism, basal 5-HT levels were higher in veins than in arteries. 5-HT uptake was observed after exposure to exogenous 5-HT in all vessels. The presence of MAO-A and the 5-HT transporter (SERT) in VC was observed by immunohistochemistry and Western analysis. However, 5-HT uptake was not inhibited by the SERT inhibitors fluoxetine and/or fluvoxamine in VC and JV, as opposed to the inhibition in RA and CA. Moreover, studies performed in VC from mutant rats lacking SERT showed no differences in 5-HT uptake compared with VC from wild type. These data suggest the SERT is not functional under physiological conditions in veins. The differences in 5-HT handling between veins and arteries may represent alternative avenues for targeting the 5-HT system in the peripheral circulation for controlling vascular tone.5-Hydroxytryptamine (5-HT; serotonin) was first described as a substance that causes contraction of smooth muscle (Rapport et al., 1948;Erspamer and Asero, 1952). The function of 5-HT as a neurotransmitter is well established, as drugs that affect 5-HT concentration [e.g., Prozac (fluoxetine hydrochloride)] are widely used to treat conditions such as depression, anxiety, and obesity. However, its role in the cardiovascular system is far from being elucidated. For the last decade, accumulating evidence supports the involvement of 5-HT in the control of pulmonary circulation under normal and hypertensive conditions. However, a role for 5-HT in systemic vasculature is a matter of debate (for review, see Watts, 2005).In the periphery, platelets represent a large 5-HT storage site, and they may function as a buffer, keeping the free circulating 5-HT in low levels (Nilsson et al., 1985;Vanhoutte, 1991;Brenner et al., 2007). Indeed, platelet 5-HT uptake is decreased with age and in hypertension accompanied by an increase in free 5-HT circulating levels (Amstein et al., 1991;Brenner et al., 2007).5-HT is abundantly synthesized in the enterochromaffin cells of the intestine, representing more than 95% of total body 5-HT. 5-HT is also synthesized in the raphe nuclei of the brain, pineal gland, and in endothelial cells lining the lung. Potential sites of 5-HT synthesis in the systemic vasculature have not yet been identified. 5-HT is synthesized from the essential amino acid tryptophan in a two-step pathway. The hydroxylation o...

The handling of serotonin [5-hydroxytryptamine (5-HT)] depends on the serotonin transporter (SERT). A SERT knockout (KO) rat is a useful model to test the hypothesis that SERT is the primary mechanism for arterial 5-HT uptake and to investigate the impact of SERT removal on blood pressure. Wild-type (WT) and KO rats were used to measure 5-HT content (plasma, raphe, aorta, carotid, and mesenteric artery), aortic isometric contraction, and blood pressure. HPLC supported the lack of circulating 5-HT in plasma (ng/ml plasma, WT, 310 +/- 96; and KO, 1.0 +/- 0.5; P < 0.05). Immunohistochemistry and Western blot analyses validated the presence of the SERT protein in the WT rats and a lesser expression in the KO rat. The aorta isolated from KO rats had a normal contraction to phenylephrine and norepinephrine and a normal relaxation to the endothelium-dependent agonist acetylcholine compared with the aorta from WT. In contrast, the potency of 5-HT was increased in the aorta from KO rats compared with WT rats [-log EC(50) (M); WT, 5.71 +/- 0.08; and KO, 6.7 +/- 0.18] and maximum contraction was reduced [%phenylephrine (10 muM) contraction, WT, 113 +/- 6%; and KO, 52 +/- 12%]. 5-HT uptake was reduced but not abolished in arteries of the KO compared with the WT rats. Diurnal mean arterial blood pressure, heart rate, and locomotor activity level of the KO rats were similar to the WT rats. These data suggest that there are other mechanisms of 5-HT uptake in the arteries of the rat and that although the absence of circulating 5-HT and/or SERT function sensitizes arteries to 5-HT, SERT dysfunction does not impair normal blood pressure.

Drug repurposing has become an alternative therapeutic strategy for cancer treatment given the known pharmacokinetics and toxicity. The inhibitory effects of artesunate have been reported in various cancers. In this work, we investigated the effects of artesunate in nasopharyngeal carcinoma (NPC). We demonstrate that artesunate significantly inhibits proliferation via arresting NPC cells at G2/M phase. It also induces apoptosis through caspase-dependent and mitochondria-independent pathways in multiple NPC cell lines. The combination of artesunate and cisplatin is synergistic in targeting NPC cells in in vitro cellular culture system and in vivo xenograft tumor models. Artesunate inhibits phosphorylation of essential molecules involved in Akt/mTOR pathway in NPC cells, such as Akt, mTOR, and 4EBP1, and its inhibitory effects are partially abolished by overexpression of constitutively active Akt. In addition, artesunate also induces mitochondrial dysfunction and oxidative stress via inhibiting mitochondrial respiration, increasing levels of mitochondrial superoxide and cellular reactive oxygen species (ROS), leading to decreased ATP levels. Two ROS scavengers partially abolish the inhibitory effects of artesunate in NPC cells. These data suggest that both inhibition of Akt/mTOR pathway and induction of ROS are required for the action of artesunate in NPC cells. Our work demonstrates that artesunate is a potential candidate for NPC treatment. Our work also highlights the critical roles of Akt/mTOR pathway and mitochondrial function in NPC cells.