Tyrosine hydroxylase

Effects of Methylphenidate on the Dopamine Transporter and Beyond

The dopamine transporter (DAT) is the main target of methylphenidate (MPH), which remains the number one drug prescribed worldwide for the treatment of Attention-Deficit Hyperactivity Disorder (ADHD). In addition, abnormalities of the DAT have been widely associated with ADHD. Based on clinical and preclinical studies, the direction of DAT abnormalities in ADHD are, however, still unclear. Moreover, chronic treatment of MPH has been shown to increase brain DAT expression in both animals and ADHD patients, suggesting that findings of overexpressed levels of DAT in ADHD patients are possibly attributable to the effects of long-term MPH treatment rather than the pathology of the condition itself. In this chapter, we will discuss some of the effects exerted by MPH, which are related to its actions on catecholamine protein targets and brain metabolites, together with genes and proteins mediating neuronal plasticity. For this purpose, we present data from biochemical, proton nuclear magnetic resonance spectroscopy (¹H-NMR) and gene/protein expression studies. Overall, results of the studies discussed in this chapter show that MPH has a complex biological/pharmacological action well beyond the DAT.

Dietary intake of branched-chain amino acids in relation to depression, anxiety and psychological distress

BACKGROUND

There is no previous study that examined the association between branched-chain amino acids (BCAAs) intake and odds of psychological disorders. The aim of this study was to investigate the association between dietary BCAAs and odds of psychological disorders including depression, anxiety, and psychological distress in a large sample of Iranian adults.

METHODS

In this cross-sectional study on 3175 Iranian adults aged 18-55 years, a validated food frequency questionnaire was used to assess dietary intakes. BCAAs intake was computed by summing up the amount of valine, leucine, and isoleucine intake from all food items in the questionnaire. Psychological health was examined through the use of Iranian validated version of the Hospital Anxiety and Depression Scale (HADS). Psychological distress was assessed using General Health Questionnaire (GHQ). For depression and anxiety, scores of 8 or more on either subscale were considered as psychological disorders and scores of 0-7 were defined as "normal". In terms of psychological distress, the score of 4 or more was defined as psychological distress.

RESULTS

Mean age of study participants was 36.2 ± 7.8 years. Overall, 26.4% (n = 837) of study subjects had depression, 11.9% (n = 378) had anxiety and 20.9% (n = 665) were affected by psychological distress. After controlling for potential confounders, participants in the highest tertile of total BCAAs intake had lower odds of depression (OR: 0.76; 95% CI: 0.60-0.96) and anxiety (OR: 0.66; 95% CI: 0.47-0.91) compared with those in the lowest tertile. Participants in the top tertile of valine intake had a lower odds of depression (OR: 0.76; 95% CI: 0.60-0.96) and anxiety (OR: 0.65; 95% CI: 0.47-0.90) compared with those in the bottom tertile. A significant inverse association was also seen between leucine intake and depression (OR: 0.77; 95% CI: 0.61-0.98) and anxiety (OR: 0.66; 95% CI: 0.47-0.91). In addition, a significant inverse association was observed between isoleucine intake and odds of depression (OR: 0.75; 95% CI: 0.59-0.95) and anxiety (OR: 0.62; 95% CI: 0.45-0.86). There was no significant association between isoleucine intake and odds of psychological distress.

CONCLUSION

Evidence indicating an inverse association between dietary intake of BCAAs and odds of depression and anxiety was found. Prospective studies are required to confirm these findings.

Subcellular distribution of human tyrosine hydroxylase isoforms 1 and 4 in SH-SY5Y cells

Tyrosine hydroxylase (TH) is the key enzyme that controls the rate of synthesis of the catecholamines. SH-SY5Y cells with stable transfections of either human tyrosine hydroxylase isoform 1 (hTH1) or human tyrosine hydroxylase isoform 4 (hTH4) were used to determined the subcellular distribution of TH protein and phosphorylated TH, under basal conditions and after muscarine stimulation. Muscarine was previously shown to increase the phosphorylation of only serine 19 and serine 40 in hTH1 cells. Under basal conditions, the hTH1 and hTH4 proteins, their serine 19 phosphorylated forms and hTH1 phosphorylated at serine 40 were all similarly distributed; with ~80% in the cytosolic fraction, ~20% in the membrane fraction, and less than 1%, or not detectable, in the nuclear fraction. However, hTH4 phosphorylated at serine 71 had a significantly different distribution with ~65% cytosolic and ~35% membrane associated. Muscarine stimulation led to hTH1 being redistributed from the cytosol and nuclear fractions to the membrane fraction and hTH4 being redistributed from the cytosol to the nuclear fraction. These muscarine stimulated redistributions were not due to TH phosphorylation at serine 19, serine 40, or serine 71 and were most likely due to TH binding to proteins whose phosphorylation was increased by muscarine. This is the first study to show a difference in subcellular distribution between two human TH isoforms under basal and stimulated conditions.

The expression of tyrosine hydroxylase and DARPP-32 in the house crow (Corvus splendens) brain

Birds of the family Corvidae which includes diverse species such as crows, rooks, ravens, magpies, jays, and jackdaws are known for their amazing abilities at problem-solving. Since the catecholaminergic system, especially the neurotransmitter dopamine, plays a role in cognition, we decided to study the distribution of tyrosine hydroxylase (TH), the rate-limiting enzyme in the synthesis of catecholamines in the brain of house crows (Corvus splendens). We also studied the expression of DARPP-32 (dopamine and cAMP-regulated phosphoprotein), which is expressed in dopaminoceptive neurons. Our results demonstrated that as in other avian species, the expression of both TH and DARPP-32 was highest in the house crow striatum. The caudolateral nidopallium (NCL, the avian analogue of the mammalian prefrontal cortex) could be differentiated from the surrounding pallial regions based on a larger number of TH-positive "baskets" of fibers around neurons in this region and greater intensity of DARPP-32 staining in the neuropil in this region. House crows also possessed distinct nuclei in their brains which corresponded to song control regions in other songbirds. Whereas immunoreactivity for TH was higher in the vocal control region Area X compared to the surrounding MSt (medial striatum) in house crows, staining in RA and HVC was not as prominent. Furthermore, the arcopallial song control regions RA (nucleus robustus arcopallialis) and AId (intermediate arcopallium) were strikingly negative for DARPP-32 staining, in contrast to the surrounding arcopallium. Patterns of immunoreactivity for TH and DARPP-32 in "limbic" areas such as the hippocampus, septum, and extended amygdala have also been described.

Valproic acid attenuates manganese-induced reduction in expression of GLT-1 and GLAST with concomitant changes in murine dopaminergic neurotoxicity

Exposure to elevated levels of manganese (Mn) causes manganism, a neurological disorder with similar characteristics to those of Parkinson's disease (PD). Valproic acid (VPA), an antiepileptic, is known to inhibit histone deacetylases and exert neuroprotective effects in many experimental models of neurological disorders. In the present study, we investigated if VPA attenuated Mn-induced dopaminergic neurotoxicity and the possible mechanisms involved in VPA's neuroprotection, focusing on modulation of astrocytic glutamate transporters (glutamate aspartate transporter, GLAST and glutamate transporter 1, GLT-1) and histone acetylation in H4 astrocyte culture and mouse models. The results showed that VPA increased promoter activity, mRNA/protein levels of GLAST/GLT-1 and glutamate uptake, and reversed Mn-reduced GLAST/GLT-1 in in vitro astrocyte cultures. VPA also attenuated Mn-induced reduction of GLAST and GLT-1 mRNA/protein levels in midbrain and striatal regions of the mouse brain when VPA (200 mg/kg, i.p., daily, 21 d) was administered 30 min prior to Mn exposure (30 mg/kg, intranasal instillation, daily, 21 d). Importantly, VPA attenuated Mn-induced dopaminergic neuronal damage by reversing Mn-induced decrease of tyrosine hydroxylase (TH) mRNA/protein levels in the nigrostriatal regions. VPA also reversed Mn-induced reduction of histone acetylation in astrocytes as well as mouse brain tissue. Taken together, VPA exerts attenuation against Mn-induced decrease of astrocytic glutamate transporters parallel with reversing Mn-induced dopaminergic neurotoxicity and Mn-reduced histone acetylation. Our findings suggest that VPA could serve as a potential neuroprotectant against Mn neurotoxicity as well as other neurodegenerative diseases associated with excitotoxicity and impaired astrocytic glutamate transporters.

Methylphenidate and Guanfacine Ameliorate ADHD-Like Phenotypes in Fez1-Deficient Mice

Attention-deficit/hyperactivity disorder (ADHD) is a neurodevelopmental disorder that, while prevalent, has a stagnant track record for advances in treatment. The limited availability of animal models with appropriate face and predictive validities has hampered progress in developing novel neurobiological hypotheses and testing new therapeutic options for this condition. Here, we report that mice deficient in Fez1, a gene specifically expressed in the nervous system with documented functions in neurodevelopment, show hyperactivity and impulsivity phenotypes, which are ameliorated by administering methylphenidate (MPH) or guanfacine (GFC), two pharmacological agents used for ADHD treatment. Fez1-knockout (KO) mice show reduced expression of tyrosine hydroxylase in the midbrain and the brain stem and have reduced levels of dopamine, norepinephrine, or their metabolites in both the nucleus accumbens and the prefrontal cortex. These neurochemical changes in Fez1-KO mice were normalized by MPH or GFC. We propose that Fez1-KO mice can be used as a model to evaluate the role of altered neurodevelopment in the manifestation of ADHD-like behavioral phenotypes, as well as to investigate the neurobiological mechanisms of existing and new pharmacotherapeutic agents for ADHD.

Achyranthes bidentata polypeptide protects dopaminergic neurons from apoptosis in Parkinson's disease models both in vitro and in vivo

BACKGROUND AND PURPOSE

Parkinson's disease (PD) is a neurodegenerative disorder closely associated with dopaminergic neuron loss. It is well documented that Achyranthes bidentata polypeptides (ABPP) are potent neuroprotective agents in several kinds of neurons. Therefore, we proposed that ABPP might play a beneficial role against PD by protecting dopaminergic neurons from apoptosis.

EXPERIMENTAL APPROACH

SH-SY5Y cells and primary rat dopaminergic neurons were pretreated with ABPP fraction k (ABPPk), a purified fraction of ABPP, and then the cells were exposed to 1-methyl-4-phenylpyridinium iodide (MPP⁺ ) to induce apoptosis. Cell viability, LDH activity, a Tunel assay and protein levels of Bcl-2 and Bax were analysed. In an in vivo PD model induced by MPTP, ABPPk was intranasally delivered to mice. Behavioural tests, immunohistochemistry, immunostaining, Nissl staining, qRT-PCR and Western blot were employed to evaluate the potential effects of ABPPk on PD in mice.

KEY RESULTS

The application of ABPPk markedly enhanced the viability of SH-SY5Y cells and primary dopaminergic neurons treated with neurotoxic agent MPP⁺ . In an in vivo MPTP-induced PD model, ABPPk significantly improved behavioural performances and prevented tyrosine hydroxylase loss in the substantia nigra pars compacta and striatum. Furthermore, we showed that MPTP-induced astrocyte and microglia activation were largely attenuated by ABPPk, leading to low levels of neuroinflammation and a downregulation of the apoptotic signalling pathway.

CONCLUSION AND IMPLICATIONS

Taken together, our data show that ABPPk protects dopaminergic neurons from apoptosis, suggesting that ABPPk might be an effective intervention for treating the neuron loss associated with disorders such as PD.

L-Tyrosine availability affects basal and stimulated catecholamine indices in prefrontal cortex and striatum of the rat

We previously found that L-tyrosine (L-TYR) but not D-TYR administered by reverse dialysis elevated catecholamine synthesis in vivo in medial prefrontal cortex (MPFC) and striatum of the rat (Brodnik et al., 2012). We now report L-TYR effects on extracellular levels of catecholamines and their metabolites. In MPFC, reverse dialysis of L-TYR elevated in vivo levels of dihydroxyphenylacetic acid (DOPAC) (L-TYR 250-1000 μM), homovanillic acid (HVA) (L-TYR 1000 μM) and 3-methoxy-4-hydroxyphenylglycol (MHPG) (L-TYR 500-1000 μM). In striatum L-TYR 250 μM elevated DOPAC. We also examined L-TYR effects on extracellular dopamine (DA) and norepinephrine (NE) levels during two 30 min pulses (P2 and P1) of K+ (37.5 mM) separated by t = 2.0 h. L-TYR significantly elevated the ratio P2/P1 for DA (L-TYR 125 μM) and NE (L-TYR 125-250 μM) in MPFC but lowered P2/P1 for DA (L-TYR 250 μM) in striatum. Finally, we measured DA levels in brain slices using ex-vivo voltammetry. Perfusion with L-TYR (12.5-50 μM) dose-dependently elevated stimulated DA levels in striatum. In all the above studies, D-TYR had no effect. We conclude that acute increases within the physiological range of L-TYR levels can increase catecholamine metabolism and efflux in MPFC and striatum. Chronically, such repeated increases in L-TYR availability could induce adaptive changes in catecholamine transmission while amplifying the metabolic cost of catecholamine synthesis and degradation. This has implications for neuropsychiatric conditions in which neurotoxicity and/or disordered L-TYR transport have been implicated.

The sympathetic nervous system and tendinopathy: a systematic review

BACKGROUND

Tendinopathy is a clinical diagnosis of localised tendon pain often confirmed by imaging findings. The pathophysiological cause of the pain is unknown and the sympathetic nervous system (SNS) may be implicated.

OBJECTIVE

To review what is known regarding the role of the SNS in human tendinopathy.

STUDY SELECTION

Published data describing sympathetic innervation or an index of sympathetic activity in human tendons were eligible for inclusion.

DATA SOURCES

Bibliographical databases (AMED, Biological Abstracts, CINAHL Plus, EMBASE, MEDLINE, Scopus, SPORTDiscus and Web of Science) were searched for relevant articles. Reference lists from included articles were screened for additional articles.

STUDY APPRAISAL

Studies were scored with a quality assessment tool to identify potential sources of bias. Each question had an explicit decision rule to guide assessment.

RESULTS

Nine case-control and four cross-sectional studies examined sympathetic innervation of tendons. There was evidence suggesting a lack of difference in sympathetic innervation of tendon proper between tendinopathy biopsies and healthy controls. In contrast, the paratendinous tissue showed evidence of increased sympathetic innervation in painful tendons. The most notable increase in SNS markers was seen in abnormal tenocytes from painful tendons. Data from two studies were suitable for meta-analysis. These heterogeneous studies revealed no difference in sympathetic innervation between painful and pain-free tendons. No studies recorded SNS activity in vivo.

CONCLUSION

Sympathetic innervation in painful tendons depends on tissue type. Abnormal tenocytes may have increased capacity for self-production of sympathetic neurotransmitters. Future insight may be gained by measuring global in vivo sympathetic drive in tendinopathy.

Transcription factor Nr4a1 couples sympathetic and inflammatory cues in CNS-recruited macrophages to limit neuroinflammation

The molecular mechanisms that link the sympathetic stress response and inflammation remain obscure. Here we found that the transcription factor Nr4a1 regulated the production of norepinephrine (NE) in macrophages and thereby limited experimental autoimmune encephalomyelitis (EAE), a mouse model of multiple sclerosis. Lack of Nr4a1 in myeloid cells led to enhanced NE production, accelerated infiltration of leukocytes into the central nervous system (CNS) and disease exacerbation in vivo. In contrast, myeloid-specific deletion of tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine biosynthesis, protected mice against EAE. Furthermore, we found that Nr4a1 repressed autocrine NE production in macrophages by recruiting the corepressor CoREST to the Th promoter. Our data reveal a new role for macrophages in neuroinflammation and identify Nr4a1 as a key regulator of catecholamine production by macrophages.

Recruitment of dorsal midbrain catecholaminergic pathways in the recovery from nerve injury evoked disabilities

BACKGROUND

The periaqueductal gray region (PAG) is one of several brain areas identified to be vulnerable to structural and functional change following peripheral nerve injury. Sciatic nerve constriction injury (CCI) triggers neuropathic pain and three distinct profiles of changes in complex behaviours, which include altered social and sleep-wake behaviours as well as changes in endocrine function. The PAG encompasses subgroups of the A10 dopaminergic and A6 noradrenergic cell groups; the origins of significant ascending projections to hypothalamic and forebrain regions, which regulate sleep, complex behaviours and endocrine function. We used RT-PCR, western blots and immunohistochemistry for tyrosine hydroxylase to determine whether (1) tyrosine hydroxylase increased in the A10/A6 cells and/or; (2) de novo synthesis of tyrosine hydroxylase, in a 'TH-naïve' population of ventral PAG neurons characterized rats with distinct patterns of behavioural and endocrine change co-morbid with CCI evoked-pain.

RESULTS

Evidence for increased tyrosine hydroxylase transcription and translation in the constitutive A10/A6 cells was found in the midbrain of rats that showed an initial 2-3 day post-CCI, behavioural and endocrine change, which recovered by days 5-6 post-CCI. Furthermore these rats showed significant increases in the density of TH-IR fibres in the vPAG.

CONCLUSIONS

Our data provide evidence for: (1) potential increases in dopamine and noradrenaline synthesis in vPAG cells; and (2) increased catecholaminergic drive on vPAG neurons in rats in which transient changes in social behavior are seen following CCI. The data suggests a role for dopaminergic and noradrenergic outputs, and catecholaminergic inputs of the vPAG in the expression of one of the profiles of behavioural and endocrine change triggered by nerve injury.

Interactions with the bifunctional interface of the transcriptional coactivator DCoH1 are kinetically regulated

Pterin-4a-carbinolamine dehydratase (PCD) is a highly conserved enzyme that evolved a second, unrelated function in mammals, as a transcriptional coactivator. As a coactivator, PCD is known as DCoH or dimerization cofactor of the transcription factor HNF-1. These two activities are associated with a change in oligomeric state: from two dimers interacting as an enzyme in the cytoplasm to a dimer interacting with a dimer of HNF-1 in the nucleus. The same interface of DCoH forms both complexes. To determine how DCoH partitions between its two functions, we studied the folding and stability of the DCoH homotetramer. We show that the DCoH1 homotetramer is kinetically trapped, meaning once it forms it will not dissociate to interact with HNF-1. In contrast, DCoH2, a paralog of DCoH1, unfolds within hours. A simple mutation in the interface of DCoH2 from Ser-51 to Thr, as found in DCoH1, increases the kinetic stability by 9 orders of magnitude, to τ(½) ∼ 2 million years. This suggests that the DCoH1·HNF-1 complex must co-fold to interact. We conclude that simple mutations can dramatically affect the dissociation kinetics of a complex. Residue 51 represents a "kinetic hot spot" instead of a "thermodynamic hot spot." Kinetic regulation allows PCD to adopt two distinct functions. Mutations in DCoH1 associated with diabetes affect both functions of DCoH1, perhaps by disrupting the balance between the two DCoH complexes.

In silico thermodynamics stability change analysis involved in BH4 responsive mutations in phenylalanine hydroxylase: QM/MM and MD simulations analysis

The mammalian tetrahydrobiopterin (BH4)-dependent phenylalanine hydroxylases (PAH), involved in important metabolic pathways of phenylalanine, belong to non-heme iron-containing aromatic acid hydroxylases' enzyme (AAH) family. AAHs utilize BH4 as protein co-factor and thus promote hydroxylation reactions of their substrates. Any alterations in BH4 -mediated AAH's pathway or mutations in these enzymes are responsible for various disorders, and thus highlights the importance of mutational analysis to assess the effect on their biosynthetic pathways. Our present studies are aimed at single-site mutations in PAH that lead to thermodynamic stability change upon folding and further validation of designed non-reduced BH2 designed co-factors. We have presented single-site mutational analysis of PAH where single-site mutations have been identified from known literature. Further, in silico studies with the PAH, in silico mutant PAH, and crystallized known mutant A313T forms, involved QM/MM and Molecular Dynamics (MD) simulations analysis. The modified co-factor A showed high affinity with PAH and all mutant PAH with high G-score of -14.851. The best pose high affinity co-factor A subjected to QM/MM optimization which leads to square-pyramidal coordination of non-heme active site. The structural and energetic information obtained from the production phase of 20 ns MD simulation of co-factor-metalloprotein complex results helped to understand the binding mode and involvement of three molecules throughout the reaction pathways' catalysis of PAH. The free energies of binding (dG) of A were found to be -68.181 kcal/mol and -72.249 for 1DMW and 1TDW for A313T mutant. Binding of Co-factor A do not perturb the coordination environment of iron at the active site which resides in 2-Histdine and 1-Glutamate triad, and may enhance the percentage response towards co-factor-mediated therapy.

Branched-chain amino acids alter neurobehavioral function in rats

Recently, we have described a strong association of branched-chain amino acids (BCAA) and aromatic amino acids (AAA) with obesity and insulin resistance. In the current study, we have investigated the potential impact of BCAA on behavioral functions. We demonstrate that supplementation of either a high-sucrose or a high-fat diet with BCAA induces anxiety-like behavior in rats compared with control groups fed on unsupplemented diets. These behavioral changes are associated with a significant decrease in the concentration of tryptophan (Trp) in brain tissues and a consequent decrease in serotonin but no difference in indices of serotonin synaptic function. The anxiety-like behaviors and decreased levels of Trp in the brain of BCAA-fed rats were reversed by supplementation of Trp in the drinking water but not by administration of fluoxetine, a selective serotonin reuptake inhibitor, suggesting that the behavioral changes are independent of the serotonergic pathway of Trp metabolism. Instead, BCAA supplementation lowers the brain levels of another Trp-derived metabolite, kynurenic acid, and these levels are normalized by Trp supplementation. We conclude that supplementation of high-energy diets with BCAA causes neurobehavioral impairment. Since BCAA are elevated spontaneously in human obesity, our studies suggest a potential mechanism for explaining the strong association of obesity and mood disorders.

The peripheral binding of 14-3-3γ to membranes involves isoform-specific histidine residues

Mammalian 14-3-3 protein scaffolds include seven conserved isoforms that bind numerous phosphorylated protein partners and regulate many cellular processes. Some 14-3-3-isoforms, notably γ, have elevated affinity for membranes, which might contribute to modulate the subcellular localization of the partners and substantiate the importance of investigating molecular mechanisms of membrane interaction. By applying surface plasmon resonance we here show that the binding to phospholipid bilayers is stimulated when 14-3-3γ is complexed with its partner, a peptide corresponding to the Ser19-phosphorylated N-terminal region of tyrosine hydroxylase. Moreover, membrane interaction is dependent on salts of kosmotropic ions, which also stabilize 14-3-3γ. Electrostatic analysis of available crystal structures of γ and of the non-membrane-binding ζ-isoform, complemented with molecular dynamics simulations, indicate that the electrostatic potential distribution of phosphopeptide-bound 14-3-3γ is optimal for interaction with the membrane through amphipathic helices at the N-terminal dimerization region. In addition, His158, and especially His195, both specific to 14-3-3γ and located at the convex lateral side, appeared to be pivotal for the ligand induced membrane interaction, as corroborated by site-directed mutagenesis. The participation of these histidine residues might be associated to their increased protonation upon membrane binding. Overall, these results reveal membrane-targeting motifs and give insights on mechanisms that furnish the 14-3-3γ scaffold with the capacity for tuned shuffling from soluble to membrane-bound states.

A synopsis on the role of tyrosine hydroxylase in Parkinson's disease

Parkinson's disease (PD) is a common chronic progressive neurodegenerative disorder in elderly people. A consistent neurochemical abnormality in PD is degeneration of dopaminergic neurons in substantia nigra pars compacta, leading to a reduction of striatal dopamine (DA) levels. As tyrosine hydroxylase (TH) catalyses the formation of L-dihydroxyphenylalanine (L-DOPA), the rate-limiting step in the biosynthesis of DA, the disease can be considered as a TH-deficiency syndrome of the striatum. Problems related to PD usually build up when vesicular storage of DA is altered by the presence of either α-synuclein protofibrils or oxidative stress. Phosphorylation of three physiologically-regulated specific sites of N-terminal domain of TH is vital in regulating its kinetic and protein interaction. The concept of physiological significance of TH isoforms is another interesting aspect to be explored further for a comprehensive understanding of its role in PD. Thus, a logical and efficient strategy for PD treatment is based on correcting or bypassing the enzyme deficiency by the treatment with L-DOPA, DA agonists, inhibitors of DA metabolism or brain grafts with cells expressing a high level of TH. Neurotrophic factors are also attracting the attention of neuroscientists because they provide the essential neuroprotective and neurorestorative properties to the nigrostriatal DA system. PPAR-γ, a key regulator of immune responses, is likewise a promising target for the treatment of PD, which can be achieved by the use of agonists with the potential to impact the expression of pro- and anti-inflammatory cytokines at the transcriptional level in immune cells via expression of TH. Herein, we review the primary biochemical and pathological features of PD, and describe both classical and developing approaches aimed to ameliorate disease symptoms and its progression.

Peripheral assessment of the genes AQP4, PBP and TH in patients with Parkinson's disease

Parkinson's disease (PD) typically appears in late middle-aged and in elderly persons progressing over a period of several years. The characteristic pathological features of PD patients include defective motor function and cognitive function affecting the quality of life of PD patients. Oxidative stress is considered to a play a central role along with various other factors in the pathogenesis of PD and the incidence and prevalence of the disease is incessantly increasing worldwide. The objective of the current study was to assess mRNA expressional changes of AQP4, TH and PBP in blood samples of control and patients with PD. The study included 30 healthy controls and 90 PD patients subjected to treatment through the entire period of the study. RNA isolation was carried out using blood samples of the subjects recruited in the study and used for RT-PCR analysis of AQP4, TH as well as PBP. The mRNA expressions of AQP4 and TH were found to be reduced whereas that of PBP was found to be elevated when compared with those of healthy control samples. The statistically analysed data were presented which could be helpful for appreciation of PD pathology reflecting in the blood samples of PD population.

Three-way interaction between 14-3-3 proteins, the N-terminal region of tyrosine hydroxylase, and negatively charged membranes

Tyrosine hydroxylase (TH), the rate-limiting enzyme in the synthesis of catecholamines, is activated by phosphorylation-dependent binding to 14-3-3 proteins. The N-terminal domain of TH is also involved in interaction with lipid membranes. We investigated the binding of the N-terminal domain to its different partners, both in the unphosphorylated (TH-(1-43)) and Ser(19)-phosphorylated (THp-(1-43)) states by surface plasmon resonance. THp-(1-43) showed high affinity for 14-3-3 proteins (K(d) approximately 0.5 microM for 14-3-3gamma and -zeta and 7 microM for 14-3-3eta). The domains also bind to negatively charged membranes with intermediate affinity (concentration at half-maximal binding S(0.5) = 25-58 microM (TH-(1-43)) and S(0.5) = 135-475 microM (THp-(1-43)), depending on phospholipid composition) and concomitant formation of helical structure. 14-3-3gamma showed a preferential binding to membranes, compared with 14-3-3zeta, both in chromaffin granules and with liposomes at neutral pH. The affinity of 14-3-3gamma for negatively charged membranes (S(0.5) = 1-9 microM) is much higher than the affinity of TH for the same membranes, compatible with the formation of a ternary complex between Ser(19)-phosphorylated TH, 14-3-3gamma, and membranes. Our results shed light on interaction mechanisms that might be relevant for the modulation of the distribution of TH in the cytoplasm and membrane fractions and regulation of L-DOPA and dopamine synthesis.

Catecholaminergic systems in stress: structural and molecular genetic approaches

Stressful stimuli evoke complex endocrine, autonomic, and behavioral responses that are extremely variable and specific depending on the type and nature of the stressors. We first provide a short overview of physiology, biochemistry, and molecular genetics of sympatho-adrenomedullary, sympatho-neural, and brain catecholaminergic systems. Important processes of catecholamine biosynthesis, storage, release, secretion, uptake, reuptake, degradation, and transporters in acutely or chronically stressed organisms are described. We emphasize the structural variability of catecholamine systems and the molecular genetics of enzymes involved in biosynthesis and degradation of catecholamines and transporters. Characterization of enzyme gene promoters, transcriptional and posttranscriptional mechanisms, transcription factors, gene expression and protein translation, as well as different phases of stress-activated transcription and quantitative determination of mRNA levels in stressed organisms are discussed. Data from catecholamine enzyme gene knockout mice are shown. Interaction of catecholaminergic systems with other neurotransmitter and hormonal systems are discussed. We describe the effects of homotypic and heterotypic stressors, adaptation and maladaptation of the organism, and the specificity of stressors (physical, emotional, metabolic, etc.) on activation of catecholaminergic systems at all levels from plasma catecholamines to gene expression of catecholamine enzymes. We also discuss cross-adaptation and the effect of novel heterotypic stressors on organisms adapted to long-term monotypic stressors. The extra-adrenal nonneuronal adrenergic system is described. Stress-related central neuronal regulatory circuits and central organization of responses to various stressors are presented with selected examples of regulatory molecular mechanisms. Data summarized here indicate that catecholaminergic systems are activated in different ways following exposure to distinct stressful stimuli.

Developmental expression of tryptophan hydroxylase gene in Ciona intestinalis

To describe the serotonergic system in a tunicate larva, we cloned a gene encoding for tryptophan hydroxylase (TPH), the rate-limiting enzyme in serotonin synthesis, in the ascidian Ciona intestinalis and studied its expression pattern during development. Ci-TPH expression was found from tailbud stage in the precursor cells of the visceral ganglion and in the tail. In the larva, TPH-expressing neurons formed two clusters in the anterior central nervous system at the level of the visceral ganglion. Moreover, we found Ci-TPH expression at the level of the muscle cells of the tail and suggested that this localisation might be at the level of neuro-muscular junctions. Moreover, we discussed the involvement of serotonin in the control of larval locomotory activity.

Substrate-induced conformational transition in human phenylalanine hydroxylase as studied by surface plasmon resonance analyses: the effect of terminal deletions, substrate analogues and phosphorylation

The optical biosensor technique, based on the surface plasmon resonance (SPR) phenomenon, was used for real-time measurements of the slow conformational transition (isomerization) which occurs in human phenylalanine hydroxylase (hPAH) on the binding/dissociation of L-phenylalanine (L-Phe). The binding to immobilized tetrameric wt-hPAH resulted in a time-dependent increase in the refractive index (up to approx. 3 min at 25 degrees C) with an end point of approx. 75 RU (resonance units)/(pmol subunit/mm(2)). By contrast, the contribution of binding the substrate (165 Da) to its catalytic core enzyme [DeltaN(1-102)/DeltaC(428-452)-hPAH] was only approx. 2 RU/(pmol subunit/mm(2)). The binding isotherm for tetrameric and dimeric wt-hPAH revealed a [S](0.5)-value of 98+/-7 microM (h =1.0) and 158+/-11 microM, respectively, i.e. for the tetramer it is slightly lower than the value (145+/-5 microM) obtained for the co-operative binding (h =1.6+/-0.4) of L-Phe as measured by the change in intrinsic tryptophan fluorescence. The responses obtained by SPR and intrinsic tryptophan fluorescence are both considered to be related to the slow reversible conformational transition which occurs in the enzyme upon L-Phe binding, i.e. by the transition from a low-activity state ('T-state') to a relaxed high-activity state ('R-state') characteristic of this hysteretic enzyme, however, the two methods reflect different elements of the transition. Studies on the N- and C-terminal truncated forms revealed that the N-terminal regulatory domain (residues 1-117) plus catalytic domain (residues 118-411) were required for the full signal amplitude of the SPR response. Both the on- and off-rates for the conformational transition were biphasic, which is interpreted in terms of a difference in the energy barrier and the rate by which the two domains (catalytic and regulatory) undergo a conformational change. The substrate analogue 3-(2-thienyl)-L-alanine revealed an SPR response comparable with that of L-Phe on binding to wild-type hPAH.

Sodium nitroprusside inhibits the tyrosine hydroxylase activity of the median eminence in the rat

Nitric oxide (NO) has been involved in the modulation of various neuroendocrine responses. This work is a study of dose-response and time-course of the effect of intracerebroventricular (i.c.v.) administration of (NO) generator sodium nitroprusside (SNP), on tyrosine hydroxylase (TH) activity of the median eminence (ME) and serum prolactin levels, performed on conscious male rats. SNP (1, 5 and 10 microg) inhibited the TH activity of the ME, 15 min following injection in a dose-dependent way, although the effect was only significant with the highest dose, and also increased in a dose-dependent manner the serum prolactin levels. Both actions were transient but vanished at different times following injection of 10 microg of SNP. These results suggest that NO, released from SNP, inhibits the tuberoinfundibular dopaminergic neurons of the basal hypothalamus to stimulate prolactin secretion.

Tyrosine hydroxylase and Parkinson's disease

A consistent neurochemical abnormality in Parkinson's disease (PD) is degeneration of dopaminergic neurons in substantia nigra, leading to a reduction of striatal dopamine (DA) levels. As tyrosine hydroxylase (TH) catalyses the formation of L-DOPA, the rate-limiting step in the biosynthesis of DA, the disease can be considered as a TH-deficiency syndrome of the striatum. Similarly, some patients with hereditary L-DOPA-responsive dystonia, a neurological disorder with clinical similarities to PD, have mutations in the TH gene and decreased TH activity and/or stability. Thus, a logical and efficient treatment strategy for PD is based on correcting or bypassing the enzyme deficiency by treatment with L-DOPA, DA agonists, inhibitors of DA metabolism, or brain grafts with cells expressing TH. A direct pathogenetic role of TH has also been suggested, as the enzyme is a source of reactive oxygen species (ROS) in vitro and a target for radical-mediated oxidative injury. Recently, it has been demonstrated that L-DOPA is effectively oxidized by mammalian TH in vitro, possibly contributing to the cytotoxic effects of DOPA. This enzyme may therefore be involved in the pathogenesis of PD at several different levels, in addition to being a promising candidate for developing new treatments of this disease.

Phosphodiesterase type 4 that regulates cAMP level in cortical neurons shows high sensitivity to rolipram

To characterize the role of phosphodiesterase type 4 (a cAMP-specific and rolipram-sensitive phosphodiesterase) among phosphodiesterases in the regulation of the intracellular cAMP level in cortical neurons, we investigated the effects of phosphodiesterase inhibitors on the intracellular cAMP levels in primary cultured rat cortical neurons. Selective inhibitors of phosphodiesterase type 4 and type 2 significantly enhanced beta-adrenoceptor-mediated cAMP increase. Selective inhibitors of phosphodiesterase type 1, type 3 and type 5/6 had no effect on the cAMP level. Rolipram enhanced the beta-adrenoceptor-mediated cAMP increase in cortical neurons, astrocytes and vascular smooth muscle cells at different minimum effective concentrations (10, 100 and 1000 nM, respectively). These findings indicate that phosphodiesterase type 4, showing a high-sensitivity to rolipram, plays a major role in regulating cAMP in the cortical neurons, and that rolipram at low doses enhances the intracellular cAMP increase in the cortical neurons selectively.

Characterization of a novel pterin intermediate formed in the catalytic cycle of tyrosine hydroxylase

A novel pterin intermediate, in addition to the expected 4a-hydroxytetrahydrobiopterin (4a-OH-BH4) and quinonoid dihydrobiopterin, was generated during catalytic turnover of tyrosine hydroxylase (TH) with tetrahydrobiopterin as the cofactor. Based on chromatographic, spectroscopic and stability properties its structure is proposed to be similar to the product formed by the non-enzymic conversion of synthetic 4a-OH-BH4 [Bailey, Rebrin, Boerth and Ayling (1995) J. Am. Chem. Soc. 117, 10203-10211]. This compound was tentatively described as a 4a-adduct of a side-chain hydroxy group, i.e. the O2', 4a-cyclic-tetrahydrobiopterin (4a-Cyc-BH4). The intermediate generated in the TH reaction has a UV spectrum which is similar to that of 4a-OH-BH4, but elutes with a longer retention time (tR = 1.69 min compared with 1.06 min) on reversed-phase chromatography. Its conversion into quinonoid dihydrobiopterin is catalysed by pterin-4a-carbinolamine dehydratase (EC 4.2.1.96), although 4a-OH-BH4 is the preferred substrate for that enzyme. A precursor-product relationship was demonstrated between 4a-OH-BH4 and the putative 4a-Cyc-BH4 intermediate. The apparent stability of this compound is dependent on pH as well as on the nature of the buffer ions. At pH 8.0 a large amount was generated in Hepes and Tris, but little in phosphate buffer. At pH 7.0 in Hepes (standard assay conditions) and Tris buffer the putative 4a-Cyc-BH4, but no 4a-OH-BH4, was observed. None of the intermediates was observed at pH 6.0. The accumulation of these intermediates in the absence of dehydratase has important implications for the assay of TH and phenylalanine hydroxylase activities, and is also compatible with a possible physiological role of the dehydratase in the synthesis of catecholamines in vivo.