Regulation Of Tryptophan Hydroxylase Research Articles

Butyrate regulation of tryptophan hydroxylase 1 and serotonin (5HT) requires transcription factor ZBP-89

Butyrate regulation of tryptophan hydroxylase 1 and serotonin (5HT) requires transcription factor ZBP-89

Blunted epidermal L‐tryptophan metabolism in vitiligo affects immune response and ROS scavenging by Fenton chemistry, part 1: epidermal H2O2/ONOO–‐mediated stress abrogates tryptophan hydroxylase and dopa decarboxylase activities, leading to low serotonin and melatonin levels

Vitiligo is characterized by a progressive loss of inherited skin color. The cause of the disease is still unknown. To date, there is accumulating in vivo and in vitro evidence for massive oxidative stress via hydrogen peroxide (H(2)O(2)) and peroxynitrite (ONOO(-)) in the skin of affected individuals. Autoimmune etiology is the favored theory. Since depletion of the essential amino acid L-tryptophan (Trp) affects immune response mechanisms, we here looked at epidermal Trp metabolism via tryptophan hydroxylase (TPH) with its downstream cascade, including serotonin and melatonin. Our in situ immunofluorescence and Western blot data reveal significantly lower TPH1 expression in patients with vitiligo. Expression is also low in melanocytes and keratinocytes under in vitro conditions. Although in vivo Fourier transform-Raman spectroscopy proves the presence of 5-hydroxytryptophan, epidermal TPH activity is completely absent. Regulation of TPH via microphthalmia-associated transcription factor and L-type calcium channels is severely affected. Moreover, dopa decarboxylase (DDC) expression is significantly lower, in association with decreased serotonin and melatonin levels. Computer simulation supports H(2)O(2)/ONOO(-)-mediated oxidation/nitration of TPH1 and DDC, affecting, in turn, enzyme functionality. Taken together, our data point to depletion of epidermal Trp by Fenton chemistry and exclude melatonin as a relevant contributor to epidermal redox balance and immune response in vitiligo.

Role of serotonin transporter inhibition in the regulation of tryptophan hydroxylase in brainstem raphe nuclei: time course and regional specificity

Drugs that selectively inhibit the serotonin transporter (SERT) are widely prescribed for treatment of depression and a range of anxiety disorders. We studied the time course of changes in tryptophan hydroxylase (TPH) in four raphe nuclei after initiation of two different SERT inhibitors, citalopram and fluoxetine. In the first experiment, groups of Sprague–Dawley rats received daily meals of rice pudding either alone (n=9) or mixed with citalopram 5 mg/kg/day (n=27). Rats were sacrificed after 24 h, 7 days or 28 days of treatment. Sections of dorsal raphe nucleus (DRN), median raphe nucleus (MRN), raphe magnus nucleus (RMN) and caudal linear nucleus (CLN) were processed for TPH immunohistochemistry. Citalopram induced a significant reduction in DRN TPH-positive cell counts at 24 h (41%), 7 days (38%) and 28 days (52%). Similar reductions in TPH-positive cell counts were also observed at each timepoint in the MRN and in the RMN. In the MRN, citalopram resulted in significant reductions at 24 h (26%), 7 days (16%) and 28 days (23%). In the RMN, citalopram induced significant reductions of TPH-positive cell counts at 24 h (45%), 7 days (34%) and 28 days (43%). By contrast, no significant differences between control and treatment groups were observed in the CLN at any of the time points that we studied. To investigate whether these changes would occur with other SERT inhibitors, we conducted a second experiment, this time with a 28-day course of fluoxetine. As was observed with citalopram, fluoxetine induced significant reductions of TPH cell counts in the DRN (39%), MRN (38%) and RMN (41%), with no significant differences in the CLN. These results indicate that SERT inhibition can alter the regulation of TPH, the rate limiting enzyme for serotonin biosynthesis. This persistent and regionally specific downregulation of serotonin biosynthesis may account for some of the clinical withdrawal symptoms associated with drugs that inhibit SERT.

Regulation of Tryptophan Hydroxylase by Cyclic AMP, Calcium, Norepinephrine, and Light in Cultured Chick Pineal Cells

The level of 35S incorporation into tryptophan hydroxylase (TPH) shows a circadian rhythm in cultured chick pineal cells. The TPH oscillation peaks in the early subjective night, persists in constant darkness, and can be phase shifted by light, in parallel to the effect of these treatments on melatonin synthesis. Using quantitative two-dimensional polyacrylamide gel electrophoresis, we have examined the regulation of TPH by agents known to affect melatonin synthesis in the chick pineal. We report here that 35S incorporation into TPH is induced by cyclic AMP and calcium, and partially inhibited by acute exposure to light. Cyclic AMP also causes a proportional increase in the radiolabeling of one of the TPH isoforms and a concomitant decrease in another isoform, possibly reflecting a change in the phosphorylation state of TPH. This effect is reversed by treatments known to reduce intracellular cyclic AMP levels in the chick pineal. Cyclic AMP thus appears to be involved in both translational and posttranslational processes regulating the expression of TPH in chick pineal cells.

Modulation of tryptophan hydroxylase activity by phospholipids: stimulation followed by inactivation.

The activity of tryptophan hydroxylase from the rat brainstem was stimulated rapidly three- to fourfold by the addition of phosphatidylinositol or phosphatidylserine. However, the activity of the enzyme once stimulated was decreased gradually by subsequent incubation with the phospholipid at 37 degrees C, reaching a level below the original activity after 1 h of incubation. The presence of ferrous ion almost perfectly protected the enzyme against this phospholipid inactivation. The activity of the enzyme inactivated by incubation with the phospholipid was not only restored, but also increased further by incubation at 37 degrees C with ferrous ion and dithiothreitol. Gel filtration analysis revealed that the enzyme stimulated by phosphatidylinositol was eluted in a void volume together with the phospholipid vesicles, but the enzyme inactivated by incubation with phosphatidylinositol was eluted at a later region apart from the vesicles. These results, taken together, suggest the possible involvement of cellular membranes in the regulation of tryptophan hydroxylase in the central nervous system.

Non-equilibrium behavior of some brain enzyme and receptor systems.

The previous article in this review dealing with the regulatory properties of brain tyrosine (TOH) and tryptophan hydroxylase (TPOH) systems (1 ) empha­ sized (a) multidimensional ity: almost all the components present under phys ­ iological and assay conditions, ranging from electromagnetic fields through hydrophobic ligands to reducing equivalents, influence in one way or another the rate functions representing catalytic activities; (b) nonlinearity: critical zones of ligand concentration, curvilinear, even intermittent amount-effect functions, and inconsistencies among results depending on small differences in parameter values are consonant with the prominent role of cooperative interac­ tions among the many stated and unstated dimensions (coordinates) regulating catalytic systems; (c) conformational instability: in the protein macromolecular components of TOH and TPOH, conformational instabilities are evidenced by 20 years offailure to purify the enzyme proteins in amounts useful for systemat­ ic extensive kinetic characterization , by their extreme friability under condi­ tions of storage, by their multiplicity of reported molecular weigh ts and kinetic constants, and by their markedly increased ease of denaturation and precipita­ tion after the removal of components from their normal milieu by dialysis and enrichment procedures. That article expressed hope that a multivariate approach to studies of TOH and TPOH regulation could be developed to allow data reduction through pattern analysis in place of one-or two-variable kinetic experiments and quantification by Michaelis or Hill constants (1 ). This review updates the 1978 one with respect to research on the regulatory properties of TOH and TPOH as reported in the literature through early 1983 with the exception of the cyclic nucleotide-prote in phosphorylati on schemata (recently involving calmodulin), the current status of which is reviewed else

Developmental-regulatory aspects of brain tryptophan hydroxylase.

Several articles in this volume deal with the roles of serotonin and other neurohumoral substances in the regulation of neurogenesis. It should be emphasized that the maturation of the serotonergic system itself must also be subjected to regulation by a variety of biochemical events. In our laboratory, we are concerned with the developmental regulation of tryptophan hydroxylase (TPH), the enzyme that catalyzes the initial and probably rate-limiting step in the biosynthesis of serotonin from tryptophan. Two regulatory aspects are described in this article. One involves adrenal glucocorticoids as a regulatory factor for the enzyme during postnatal development of the brain. The other involves the activation of the enzyme by ATP-magnesium and its developmental relevance. Some of the unpublished experiments summarized here were conducted in collaboration with my energetic colleagues, Tom Lysz, Andy Towle, and Ralph F. Alderson. Their contribution to the overall work was no less important than mine.