Developmental disturbance in model mice with abnormal pterin metabolism

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Tetrahydrobiopterin (BH4) is an essential cofactor for phenylalanine hydroxylase, tyrosine hydroxylase (TH), tryptophan hydroxylase (TPH), and all types of nitric oxide synthase. Previously, we established BH4-defficient mice (Pts^<-/->) by disruption of the gene encoding 6-pyruvoyltetrahydropterin synthase (PTS), which catalyzes the second step of BH4 biosynthesis. For Pts^<-/-> mice died shortly after birth, we rescued those by transgenic introduction of human PTS cDNA under the control of 5.8 kb human dopamine β-hydroxyklase 5' promoter (DPS). We performed biochemical analysis using 2-7 months old male DPS-rescued mice (Pts^<-/->,DPS). PTS activity in the liver of DPS-rescued mice was 2.1 % of that of wild type (Pts^<+/+>) ones. Plasma phenylalanine concentration of DPS-rescued mice was 37 times higher than that of wild type, and reduced to 15% 1 hour after intraperitoneal injection of 20g/kg BH4. It was confirmed that human PTS efficiently expressed in the adrenal medulla and noradrenergic cells including locus ceruleus by immunohistochemistory using anti-human PTS antibody, and also by double-immunofluorescence staining using anti-human PTS antibody with anti-bovine TH antibody. However, human PTS expressed in a part of the dopaminergic cells in the substantia nigra and ventral tegmental area. Content of biopterin and dopamine in the midbrain of DPS-rescued mice were 84% and 52% of those of wild type, respectively. On the other hand, content of biopterin and dopamine in the striatum of DPS-rescued mice were 21% of those of wild type. The nucleus accumbens and medial part of the striatum of DPS-rescued mice were immunoreactive to anti-TH antibody as strongly as those of wild type. On the contrary, lateral region of the striatum of DPS-rescued mice was far weakly stained by anti-TH antibody. Thus we concluded that TH protein in dopaminergic nerve terminals projecting to the lateral region of striatum is the most sensitive to BH4-insyfficiency.