Kazuhisa Ikemoto

Differential involvement of striosome and matrix dopamine systems in a transgenic model of dopa-responsive dystonia

Dopa-responsive dystonia (DRD) is a hereditary dystonia characterized by a childhood onset of fixed dystonic posture with a dramatic and sustained response to relatively low doses of levodopa. DRD is thought to result from striatal dopamine deficiency due to a reduced synthesis and activity of tyrosine hydroxylase (TH), the synthetic enzyme for dopamine. The mechanisms underlying the genesis of dystonia in DRD present a challenge to models of basal ganglia movement control, given that striatal dopamine deficiency is the hallmark of Parkinsons disease. We report here behavioral and anatomical observations on a transgenic mouse model for DRD in which the gene for 6-pyruvoyl-tetrahydropterin synthase is targeted to render selective dysfunction of TH synthesis in the striatum. Mutant mice exhibited motor deficits phenotypically resembling symptoms of human DRD and manifested a major depletion of TH labeling in the striatum, with a marked posterior-to-anterior gradient resulting in near total loss caudally. Strikingly, within the regions of remaining TH staining in the striatum, there was a greater loss of TH labeling in striosomes than in the surrounding matrix. The predominant loss of TH expression in striosomes occurred during the early postnatal period, when motor symptoms first appeared. We suggest that the differential striosome-matrix pattern of dopamine loss could be a key to identifying the mechanisms underlying the genesis of dystonia in DRD.

Augmentation of Vascular Remodeling by Uncoupled Endothelial Nitric Oxide Synthase in a Mouse Model of Diabetes Mellitus

Objective—Diabetes mellitus is associated with increased oxidative stress, which induces oxidation of tetrahydrobiopterin (BH4) in vessel wall. Without enough BH4, eNOS is uncoupled to L-arginine and produces superoxide rather than NO. We examined the role of uncoupled eNOS in vascular remodeling in diabetes. Methods and Results—Diabetes mellitus was produced by streptozotocin in C57BL/6J mice. Under stable hyperglycemia, the common carotid artery was ligated, and neointimal formation was examined 4 weeks later. In diabetic mice, the neointimal area was dramatically augmented. This augmentation was associated with increased aortic superoxide formation, reduced aortic BH4/dihydrobiopterin (BH2) ratio, and decreased plasma nitrite and nitrate (NOx) levels compared with nondiabetic mice. Chronic BH4 treatment (10 mg/kg/d) reduced the neointimal area in association with suppressed superoxide production and inflammatory changes in vessels. BH4/BH2 ratio in vessel wall was preserved, and plasma NOx levels increased. Furthermore, in the presence of diabetes, overexpression of bovine eNOS resulted in augmentation of neointimal area, accompanied by increased superoxide production in the endothelium. Conclusions—In diabetes, increased oxidative stress by uncoupled NOSs, particularly eNOS, causes augmentation of vascular remodeling. These findings indicate restoration of eNOS coupling has an atheroprotective benefit in diabetes.

Partial biopterin deficiency disturbs postnatal development of the dopaminergic system in the brain.

Postnatal development of dopaminergic system is closely related to the development of psychomotor function. Tyrosine hydroxylase (TH) is the rate-limiting enzyme in the biosynthesis of dopamine and requires tetrahydrobiopterin (BH4) as a cofactor. To clarify the effect of partial BH4 deficiency on postnatal development of the dopaminergic system, we examined two lines of mutant mice lacking a BH4-biosynthesizing enzyme, including sepiapterin reductase knock-out (Spr−/−) mice and genetically rescued 6-pyruvoyltetrahydropterin synthase knock-out (DPS-Pts−/−) mice. We found that biopterin contents in the brains of these knock-out mice were moderately decreased from postnatal day 0 (P0) and remained constant up to P21. In contrast, the effects of BH4 deficiency on dopamine and TH protein levels were more manifested during the postnatal development. Both of dopamine and TH protein levels were greatly increased from P0 to P21 in wild-type mice but not in those mutant mice. Serotonin levels in those mutant mice were also severely suppressed after P7. Moreover, striatal TH immunoreactivity in Spr−/− mice showed a drop in the late developmental stage, when those mice exhibited hind-limb clasping behavior, a type of motor dysfunction. Our results demonstrate a critical role of biopterin in the augmentation of TH protein in the postnatal period. The developmental manifestation of psychomotor symptoms in BH4 deficiency might be attributable at least partially to high dependence of dopaminergic development on BH4 availability.

Genetically rescued tetrahydrobiopterin-depleted mice survive with hyperphenylalaninemia and region-specific monoaminergic abnormalities

One of the possibly mutated genes in DOPA‐responsive dystonia (DRD, Segawas disease) is the gene encoding GTP cyclohydrolase I, which is the rate‐limiting enzyme for tetrahydrobiopterin (BH4) biosynthesis. Based on our findings on 6‐pyruvoyltetrahydropterin synthase (PTS) gene‐disrupted (Pts–/–) mice, we suggested that the amount of tyrosine hydroxylase (TH) protein in dopaminergic nerve terminals is regulated by the intracellular concentration of BH4. In this present work, we rescued Pts–/– mice by transgenic introduction of human PTS cDNA under the control of the dopamine β‐hydroxylase promoter to examine regional differences in the sensitivity of dopaminergic neurons to BH4‐insufficiency. The DPS‐rescued (Pts–/–, DPS) mice showed severe hyperphenylalaninemia. Human PTS was efficiently expressed in noradrenergic regions but only in a small number of dopaminergic neurons. Biopterin and dopamine contents, and TH activity in the striatum were poorly restored compared with those in the midbrain. TH‐immunoreactivity in the lateral region of the striatum was far weaker than that in the medial region or in the nucleus accumbens. We concluded that dopaminergic nerve terminals projecting to the lateral region of the striatum are the most sensitive to BH4‐insufficiency. Biochemical and pathological changes in DPS‐rescued mice were similar to those in human malignant hyperphenylalaninemia and DRD.

(6R)-5,6,7,8-Tetrahydro-L-Monapterin from Escherichia coli, a Novel Natural Unconjugated Tetrahydropterin

Abstract The structure of the major tetrahydropterin in Escherichia coli was determined as (6R)-5,6,7,8-tetrahydroLmonapterin, i. e. (6R)-2-amino-5,6,7,8-tetrahydro 6-[(1S,2S)-1,2,3-trihydroxypropyl]pteridin-4(3H)one. Although the stereochemical structure of the trihydroxypropyl side chain has been determined previously by fluorescence detected circular dichroism analysis on its aromatic derivative, the most important configuration at C(6) has not been clarified. The major difficulties for the determination of the chirality were instability toward air oxidation and very low concentration of the tetrahydropterin derivative. In the present study, the C(6)configuration was determined as R by comparing its stable hexaacetyl derivative with authentic (6R) and (6S)hexaacetyl-5,6,7,8- tetrahydroLmonapterins by high performance liquid chromatography (HPLC) and HPLCmass spectrometry (LCMS). (6R)-5,6,7,8-TetrahydroLmonapterin is a new unconjugated tetrahydropterin from natural sources.

2,4-Diamino-6-hydroxypyrimidine (DAHP) suppresses cytokine-induced VCAM-1 expression on the cell surface of human umbilical vein endothelial cells in a BH4-independent manner

2,4-Diamino-6-hydroxypyrimidine (DAHP) is considered a specific inhibitor of BH(4) biosynthesis and is widely used in order to elucidate the possible biological function of BH(4) in various cells. In the present study, we found that both the synthesis of tetrahydrobiopterin (BH(4)) and expression of vascular cell adhesion molecule 1 (VCAM-1) were increased in human umbilical vein endothelial cells (HUVEC) treated with proinflammatory cytokines. Thus we examined the effects of DAHP to clarify whether BH(4) might be involved in the expression of VCAM-1 in HUVEC. DAHP reduced the levels of both BH(4) and VCAM-1 induced by TNF-alpha and IFN-gamma. However, the dose-response curves of DAHP for the suppression of the VCAM-1 level and that of BH(4) level were markedly different. Supplementation with sepiapterin failed to restore the depressed VCAM-1 level, although it completely restored the BH(4) level. Furthermore, DAHP significantly reduced the VCAM-1 level under the experimental conditions using TNF-alpha alone, which failed to induce BH(4) production. Taken together, these results indicate that DAHP inhibited the expression of VCAM-1 in a BH(4)-independent manner in HUVEC. In the present study, we also found that DAHP significantly suppressed the accumulation of cytokine-induced NF-kappaB (p65) in the nucleus as well as the mRNA levels of VCAM-1 and GTP cyclohydrolase I (GTPCH), the rate-limiting enzyme of BH(4) synthesis. The data obtained in this study suggest that DAHP reduced VCAM-1 and GTPCH protein synthesis at least partially via suppressing the NF-kappaB level in the nucleus of HUVEC.

Stereochemistry of Fully Acetylated Tetrahydropterins and Tetrahydroquinoxalines

Completely acetylated derivatives of naturally occurring tetrahydro-D-monapterin, (6R)-2-acetamido-6-[(1R,2R)-1,2,3-triacetoxypropyl]-5,8-diacetyl-5,6,7,8-tetrahydropteridin-4(3H)-one, show plus and minus CD signs at X 280 and 240 nm, respectively. Similar CD spectra are obtained on (2S)-1,4-diacetyl-1,2,3,4-tetrahydro-2-isopropylquinoxaline and (2S)-1,4-diacetyl-1,2,3,4-tetrahydro-2-isobutylquinoxaline but not on (25)-1,4-diacetyl-1,2,3,4-tetrahydro-2-methylquinoxaline nor on the 2-ethyl derivative. The similarity of their CD spectra is represented the same stereogenic structure based on the boat conformation confirmed by X-Ray crystallographic analyses.

Sepiapterin reductase gene‐disrupted mice suffer from hypertension with fluctuation and bradycardia

(6R)‐l‐erythro‐5,6,7,8‐Tetrahydrobiopterin (BH4) is an essential cofactor for monoamine and nitric oxide (NO) production. Sepiapterin reductase (SPR) catalyzes the final step in BH4 biosynthesis. We analyzed the cardiovascular function of adult Spr gene‐disrupted (Spr−/−) mice for the first time. After weaning, Spr−/− mice suffered from hypertension with fluctuation and bradycardia, while the monoamine contents in these mice were less than 10% of those in the wild‐type mice as a result of BH4 depletion. Heart rate variability analysis indicated the sympathetic dominant state in Spr−/− mice. The endothelium‐dependent vascular relaxation in response to acetylcholine was significantly impaired in Spr−/− mice after sexual maturation (above 4 months old). Protein amounts of α1 adrenergic receptor and eNOS in the aorta were not altered. Spr−/− mice exhibited hypoglycemia and elevation of plasma renin activity. Our results suggest that the hypertension with fluctuation and bradycardia of Spr−/− mice would be caused by an imbalance of sympathetic and parasympathetic input and impaired nitric oxide production in endothelial cells. We suggest an important role of BH4 and SPR in age‐related hypertension and a possible relationship with the cardiovascular instabilities in autonomic diseases, including Parkinsons disease and spinal cord injury.

A Highly Sensitive and Specific FDCD Method for Chirality Analysis of Naturally Occurring Pteridines

Absolute configurations of 6-(1-hydroxyalkyl)pterin derivatives are determined by fluorescence detected circular dichroism (FDCD) spectroscopy. This method is at least 10 times more sensitive than CD analysis and specificeven existence of 10 times excess amounts of chiral sugars or nucleic acids.