Effect of Tryptophan Hydroxylase 1 Deficiency on the Development of Hypoxia-Induced Pulmonary Hypertension (original) (raw)
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The Journal of pharmacology and experimental therapeutics, 2017
Pulmonary arterial hypertension (PAH) is a progressive disease defined by a chronic elevation in pulmonary arterial pressure with extensive pulmonary vascular remodeling and perivascular inflammation characterized by an accumulation of macrophages, lymphocytes, dendritic cells, and mast cells. Although the exact etiology of the disease is unknown, clinical as well as preclinical data strongly implicate a role for serotonin (5-HT) in the process. Here, we investigated the chronic effects of pharmacological inhibition of tryptophan hydroxylase 1 (TPH1), the rate-limiting enzyme in peripheral 5-HT biosynthesis, in two preclinical models of pulmonary hypertension (PH), the monocrotaline (MCT) rat and the semaxanib (SUGEN, Medinoah, Suzhou, China)-hypoxia rat. In both PH models, ethyl (S)-8-(2-amino-6-((R)-1-(5-chloro-[1,1'-biphenyl]-2-yl)-2,2,2-trifluoroethoxy)pyrimidin-4-yl)-2,8-diazaspiro[4.5]decane-3-carboxylate and ethyl (S)-8-(2-amino-6-((R)-1-(3',4'-dimethyl-3-(3-methy...
Inhibition of gut- and lung-derived serotonin attenuates pulmonary hypertension in mice
AJP: Lung Cellular and Molecular Physiology, 2012
Decreasing the bioavailability of serotonin (5-HT) by inhibiting its biosynthesis may represent a useful adjunctive treatment of pulmonary hypertension (PH). We assessed this hypothesis using LP533401, which inhibits the rate-limiting enzyme tryptophan hydroxylase 1 (Tph1) expressed in the gut and lung, without inhibiting Tph2 expressed in neurons. Mice treated repeatedly with LP533401 (30–250 mg/kg per day) exhibited marked 5-HT content reductions in the gut, lungs, and blood, but not in the brain. After a single LP533401 dose (250 mg/kg), lung and gut 5-HT contents decreased by 50%, whereas blood 5-HT levels remained unchanged, suggesting gut and lung 5-HT synthesis. Treatment with the 5-HT transporter (5-HTT) inhibitor citalopram decreased 5-HT contents in the blood and lungs but not in the gut. In transgenic SM22-5-HTT+ mice, which overexpress 5-HTT in smooth muscle cells and spontaneously develop PH, 250 mg/kg per day LP533401 or 10 mg/kg per day citalopram for 21 days markedly...
The biogenic amine serotonin (5-HT) is a multi-faceted hormone that is synthesized from dietary tryptophan with the rate limiting step being catalyzed by the enzyme tryptophan hydroxylase (TPH). The therapeutic potential of peripheral 5-HT synthesis inhibitors has been demonstrated in a number of clinical and pre-clinical studies in diseases including carcinoid syndrome, lung fibrosis, ulcerative colitis and obesity. Due to the long half-life of 5-HT in blood and lung, changes in steady-state levels are slow to manifest themselves. Here, the administration of stable isotope labeled tryptophan (heavy “h-Trp”) and resultant in vivo conversion to h-5-HT is used to monitor 5-HT synthesis in rats. Dose responses for the blockade of h-5-HT appearance in blood with the TPH inhibitors L-para-chlorophenylalanine (30 and 100mg/kg) and telotristat etiprate (6, 20 and 60mg/kg), demonstrated that the method enables robust quantification of pharmacodynamic effects on a short time-scale, opening the possibility for rapid screening of TPH1 inhibitors in vivo. In the bleomycin-induced lung fibrosis rat model, the mechanism of lung 5-HT increase was investigated using a combination of synthesis and steady state 5-HT measurement. Elevated 5-HT synthesis measured in the injured lungs was an early predictor of disease induced increases in total 5-HT.
Experimental Neurology, 1999
In the present study we have further studied the previous findings that rat hypothalamic dopaminergic neuronal cell groups may express tryptophan hydroxylase (TpH), the serotonin synthesizing enzyme, without a detectable serotonin synthesis. Chemical and mechanical neuronal injuries, namely colchicine treatment and axonal transection, respectively, were performed, and distributions of neurons exhibiting immunoreactivity for TpH and/or tyrosine hydroxylase (TH), the dopamine synthesizing enzyme, were analyzed throughout the hypothalamic periventricular and arcuate nuclei. After colchicine treatment there was a statistically significant 87% (P ؍ 0,01) increase in the number of TpH expressing neurons, while TH expression remained essentially similar. Axonal transection resulted also in a statistically significant 131% (P F 0,01) increase in the number of TpH expressing neurons, while TH expression was not significantly altered. All TpH expression coexisted with TH expression, and the induction of TpH expression by neuronal injuries occurred evenly throughout the rostrocaudal length of the territory studied. A possible serotonin synthesis by TpH was examined by giving drugs that increase brain serotonin synthesis, but no immunohistochemically detectable serotonin synthesis could be found in any of the TpH expressing neurons. Finally the possibility was studied that the relative shortage of the cofactor tetrahydrobiopterin would limit serotonin synthesis. However, an administration of tetrahydrobiopterin did not result in detectable serotonin synthesis in these neurons. Taken together these results suggest that dopaminergic neurons in the hypothalamic periventricular and arcuate nuclei are able to express TpH, this expression is induced after neuronal injury, and this induction occurs similarly throughout the territories studied. TpH expression occurs independently of TH expression, and the newly expressed TpH appears not to synthesize serotonin, regardless of pharmacological pretreatments. Thus, our findings (i) support the idea that neurons may possess inducible expression of nonfunctional transmittersynthesizing enzymes, in this case TpH, and (ii) suggest that expression of an enzyme synthesizing a certain transmitter may not necessarily imply the corresponding transmitter phenotype. 1999 Academic Press
Different properties of the central and peripheral forms of human tryptophan hydroxylase
Journal of Neurochemistry, 2005
Tryptophan hydroxylase (TPH) catalyses the rate-limiting reaction in the biosynthesis of serotonin. In humans, two different TPH genes exist, located on chromosomes 11 and 12, respectively, and encoding two enzymes (TPH1 and TPH2) with an overall sequence identity of 71%. We have expressed both enzymes as various fusion proteins in Escherichia coli and using an in vitro transcription/translation system, and compared their solubility and kinetic properties. TPH2 is more soluble than TPH1, has a higher molecular weight and different kinetic properties, including a lower catalytic efficiency towards phenylalanine than TPH1. Both enzymes are phosphorylated by cAMP-dependent protein kinase A. TPH2 was phosphorylated at Ser19, a phosphorylation site not present in TPH1. The differences between TPH1 and TPH2 have important implications for the regulation of serotonin production in the brain and the periphery and may provide an explanation for some of the diverging results reported for TPH from different sources in the past.
Characterization of wild-type and mutant forms of human tryptophan hydroxylase�2
Journal of Neurochemistry, 2006
Tryptophan hydroxylase (TPH) catalyses the rate-limiting step in the biosynthesis of serotonin. In vertebrates, the homologous genes tph1 and tph2 encode two different enzymes with distinct patterns of expression, enzyme kinetics and regulation. Variants of TPH2 have recently reported to be associated with reduced serotonin production and behavioural alterations in man and mice. We have produced the human forms of these enzymes in Esherichia coli and in human embryonic kidney cell lines (HEK293) and examined the effects of mutations on their heterologous expression levels, solubility, thermal stability, secondary structure, and catalytic properties. Pure human TPH2 P449R (corresponds to mouse P447R) had comparable catalytic activity (V max ) and solubility relative to the wild type, but had decreased thermal stability; whereas human TPH2 R441H had decreased activity, solubility and stability. Thus, we consider the variations in kinetic values between wild-type and TPH2 mutants to be of secondary importance to their effects on protein stability and solubility. These findings provide potential molecular explanations for disorders related to the central serotonergic system, such as depression or suicidal behaviour.
Antihypertensive effects of l-tryptophan are not mediated by brain serotonin
Brain Research, 1984
L-Tryptophan produces a significant antihypertensive effect in spontaneously hypertensive rats while D-tryptophan does not change blood pressure. Both isomers of tryptophan significantly increase brain serotonin to the same extent at a time when the antihypertensire effect of L-tryptophan is maximal. Thus, the antihypertensive effects of L-tryptophan do not appear to be mediated by brain serotonin.
Growth retardation and altered autonomic control in mice lacking brain serotonin
Proceedings of the National Academy of Sciences, 2009
Serotonin synthesis in mammals is initiated by 2 distinct tryptophan hydroxylases (TPH), TPH1 and TPH2. By genetically ablating TPH2, we created mice (Tph2 ؊/؊ ) that lack serotonin in the central nervous system. Surprisingly, these mice can be born and survive until adulthood. However, depletion of serotonin signaling in the brain leads to growth retardation and 50% lethality in the first 4 weeks of postnatal life. Telemetric monitoring revealed more extended daytime sleep, suppressed respiration, altered body temperature control, and decreased blood pressure (BP) and heart rate (HR) during nighttime in Tph2 ؊/؊ mice. Moreover, Tph2 ؊/؊ females, despite being fertile and producing milk, exhibit impaired maternal care leading to poor survival of their pups. These data confirm that the majority of central serotonin is generated by TPH2. TPH2-derived serotonin is involved in the regulation of behavior and autonomic pathways but is not essential for adult life.