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Tyrosine hydroxylase and regulation of dopamine synthesis.

ABSTRACT: Tyrosine hydroxylase is the rate-limiting enzyme of catecholamine biosynthesis; it uses tetrahydrobiopterin and molecular oxygen to convert tyrosine to DOPA. Its amino terminal 150 amino acids comprise a domain whose structure is involved in regulating the enzyme's activity. Modes of regulation include phosphorylation by multiple kinases at four different serine residues, and dephosphorylation by two phosphatases. The enzyme is inhibited in feedback fashion by the catecholamine neurotransmitters. Dopamine binds to TyrH competitively with tetrahydrobiopterin, and interacts with the R domain. TyrH activity is modulated by protein-protein interactions with enzymes in the same pathway or the tetrahydrobiopterin pathway, structural proteins considered to be chaperones that mediate the neuron's oxidative state, and the protein that transfers dopamine into secretory vesicles. TyrH is modified in the presence of NO, resulting in nitration of tyrosine residues and the glutathionylation of cysteine residues.

SUBMITTER: Daubner SC

PROVIDER: S-EPMC3065393 | biostudies-literature | 2011 Apr

REPOSITORIES: biostudies-literature

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Tyrosine hydroxylase and regulation of dopamine synthesis.

Daubner S Colette SC Le Tiffany T Wang Shanzhi S

Archives of biochemistry and biophysics 20101219 1

Tyrosine hydroxylase is the rate-limiting enzyme of catecholamine biosynthesis; it uses tetrahydrobiopterin and molecular oxygen to convert tyrosine to DOPA. Its amino terminal 150 amino acids comprise a domain whose structure is involved in regulating the enzyme's activity. Modes of regulation include phosphorylation by multiple kinases at four different serine residues, and dephosphorylation by two phosphatases. The enzyme is inhibited in feedback fashion by the catecholamine neurotransmitters ...[more]

PMID: 21176768

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Project description:In the sympatho-adrenal system, angiotensin II (Ang II) acts as a key neuromodulatory component. At sympathetic nerve terminals, Ang II influences sympathetic transmission by enhancing norepinephrine (NE) synthesis, facilitating NE release and inhibiting NE uptake. Previously, it was demonstrated that tyrosine hydroxylase (TH) mRNA is trafficked to the distal axons of primary superior cervical ganglia (SCG) neurons, directed by a cis-acting regulatory element (i.e. zipcode) located in the 3'UTR of the transcript. Results of metabolic labeling studies established that the mRNA is locally translated. It was further shown that the axonal trafficking of the mRNA encoding the enzyme plays an important role in mediating dopamine (DA) and NE synthesis and may facilitate the maintenance of axonal catecholamine levels. In the present study, the hypothesis was tested that Ang II induces NE synthesis in rat primary SCG neurons via the modulation of the trafficking of the mRNAs encoding the catecholamine synthesizing enzymes TH and dopamine β-hydroxylase (DBH). Treatment of SCG neurons with the Ang II receptor type 1 (AT1R) agonist, L-162,313, increases the axonal levels of TH and DBH mRNA and protein and results in elevated NE levels. Conversely, treatment of rat SCG neurons with the AT1R antagonist, Eprosartan, abolished the L-162,313-mediated increase in axonal levels of TH and DBH mRNA and protein. In a first attempt to identify the proteins involved in the Ang II-mediated axonal transport of TH mRNA, we used a biotinylated 50-nucleotide TH RNA zipcode as bait in the affinity purification of TH zipcode-associated proteins. Mass spectrometric analysis of the TH zipcode ribonucleoprotein (RNP) complex immune-purified from SCG neurons led to the identification of 163 somal and 127 axonal proteins functionally involved in binding nucleic acids, the translational machinery or acting as subunits of cytoskeletal and motor proteins. Surprisingly, immune-purification of the TH axonal trafficking complex, results in the acquisition of DBH mRNA, suggesting that these mRNAs maybe transported to the axon together, possibly in the same RNP complex. Taken together, our results point to a novel mechanism by which Ang II participates in the regulation of axonal synthesis of NE by modulating the local trafficking and expression of TH and DBH, two key enzymes involved in the catecholamine biosynthetic pathway.

Project description:The mesotelencephalic dopamine system shows substantial genetic variation which fundamentally affects normal and pathological behaviors related to motor function, motivation, and learning. Our earlier radioenzyme assay studies demonstrated significantly higher activity of tyrosine hydroxylase (TH), the first and rate limiting enzyme in the biosynthesis of catecholamine neurotransmitters, in the substantia nigra-ventral tegmental area of BALB/cJ mice in comparison with that of C57BL/6ByJ mice. Here, using quantitative immunoblotting and immunocytochemistry, we tested the hypothesis that mesencephalic TH protein content and number of nigral TH-positive neurons show strain-dependent differences in C57BL/6ByJ and BALB/cJ parallel to those observed in the TH activity studies. Immunoblotting experiments detected significantly higher mesencephalic TH protein content in BALB/cJ in comparison to C57BL/6ByJ (P<0.05). Immunocytochemical studies demonstrated that the number of TH-positive cells in substantia nigra was 31.3% higher in BALB/cJ than that in C57BL/6ByJ (P<0.01), while the average dopamine neuron volume was not significantly different. In a search for candidate genes that modulate TH content and the size of mesencephalic dopamine neuron populations we also studied near-isogenic mouse sublines derived from the C57BL/6ByJ and BALB/cJ progenitor strains. A whole-genome scan with 768 single nucleotide polymorphism markers indicated that two sublines, C4A6/N and C4A6/B, were genetically very similar (98.3%). We found significantly higher mesencephalic TH protein content in C4A6/B in comparison to C4A6/N (P=0.01), and a tendency for higher number of dopamine neurons in the substantia nigra in C4A6/B in comparison to C4A6/N, which, however, did not reach statistical significance. To identify the genetic source of the TH content difference we analyzed the single nucleotide polymorphism (SNP) genotype data of the whole-genome scan, and detected two small differential chromosome segments on chr. 13 and chr. 14. Microarray gene expression studies and bioinformatic analysis of the two differential regions implicated two cis-regulated genes (Spock1 and Cxcl14, chr. 13), and two growth factor genes [bone morphogenetic protein 6 (Bmp6) (chr. 13), and fibroblast growth factor 14 (Fgf14) (chr. 14)]. Taken together, the results suggest that (1) nigral dopamine neuron number and TH protein content may be genetically associated but further studies are needed to establish unequivocally this linkage, and (2) Spock1, Cxcl14, Bmp6, and Fgf14 are novel candidates for modulating the expression and maintenance of TH content in mesencephalic dopamine neurons in vivo.

Project description:INTRODUCTION:Despite the importance of dopamine neurotransmission in schizophrenia, very few studies have addressed anomalies in the mesencephalic dopaminergic neurons of the substantia nigra/ventral tegmental area (SN/VTA). Tyrosine hydroxylase (TH) is the rate-limiting enzyme for the production of dopamine, and a possible contributor to the anomalies in the dopaminergic neurotransmission observed in schizophrenia. OBJECTIVES:In this study, we had three objectives: (1) Compare TH expression (mRNA and protein) in the SN/VTA of schizophrenia and control postmortem samples. (2) Assess the effect of antipsychotic medications on the expression of TH in the SN/VTA. (3) Examine possible regional differences in TH expression anomalies within the SN/VTA. METHODS:To achieve these objectives three independent studies were conducted: (1) A pilot study to compare TH mRNA and TH protein levels in the SN/VTA of postmortem samples from schizophrenia and controls. (2) A chronic treatment study was performed in rodents to assess the effect of antipsychotic medications in TH protein levels in the SN/VTA. (3) A second postmortem study was performed to assess TH and phosphorylated TH protein levels in two types of samples: schizophrenia and control samples containing the entire rostro-caudal extent of the SN/VTA, and schizophrenia and control samples containing only mid-caudal regions of the SN/VTA. RESULTS AND CONCLUSION:Our studies showed impairment in the dopaminergic system in schizophrenia that could be mainly (or exclusively) located in the rostral region of the SN/VTA. Our studies also showed that TH protein levels were significantly abnormal in schizophrenia, while mRNA expression levels were not affected, indicating that TH pathology in this region may occur posttranscriptionally. Lastly, our antipsychotic animal treatment study showed that TH protein levels were not significantly affected by antipsychotic treatment, indicating that these anomalies are an intrinsic pathology rather than a treatment effect.

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Tyrosine hydroxylase and regulation of dopamine synthesis.

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Tyrosine hydroxylase and regulation of dopamine synthesis.

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