Inactivation of tyrosine hydroxylase by nitration following exposure to peroxynitrite and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)

Abstract

The decrement in dopamine levels exceeds the loss of dopaminergic neurons in Parkinson's disease (PD) patients and experimental models of PD. This discrepancy is poorly understood and may represent an important event in the pathogenesis of PD. Herein, we report that the ratelimiting enzyme in dopamine synthesis, tyrosine hydroxylase (TH), is a selective target for nitration following exposure of PC12 cells to either peroxynitrite or 1-methyl-4-phenylpyridiniun ion (MPP ؉ ). Nitration of TH also occurs in mouse striatum after MPTP administration. Nitration of tyrosine residues in TH results in loss of enzymatic activity. In the mouse striatum, tyrosine nitration-mediated loss in TH activity parallels the decline in dopamine levels whereas the levels of TH protein remain unchanged for the first 6 hr post MPTP injection. Striatal TH was not nitrated in mice overexpressing copper͞zinc superoxide dismutase after MPTP administration, supporting a critical role for superoxide in TH tyrosine nitration. These results indicate that tyrosine nitration-induced TH inactivation and consequently dopamine synthesis failure, represents an early and thus far unidentified biochemical event in MPTP neurotoxic process. The resemblance of the MPTP model with PD suggests that a similar phenomenon may occur in PD, inf luencing the severity of parkisonian symptoms.Parkinson's disease (PD) is a common neurodegenerative disorder characterized by disabling motor abnormalities attributed to a profound deficit in dopamine (1). The decline in dopamine level has been thought to arise solely from the severe loss of dopaminergic neurons in the nigrostriatal pathway. However, the dopamine deficit in the affected regions of the brain significantly exceed the loss of dopaminergic neurons (2, 3), suggesting that dopamine synthesis is impaired before cellular demise. Support for this hypothesis comes from studies of experimental models of PD demonstrating that the reduction in dopamine metabolism-related markers such as tyrosine hydroxylase (TH) and dopamine transporter is far greater than the loss of neuronal cell bodies (4-6). Because the severity of PD symptoms correlates with the magnitude of dopamine deficit, elucidating mechanisms that impair dopamine synthesis and metabolism in neurons that undergo selective degeneration in PD may have important therapeutic implications.There is experimental evidence from studies of humans and animals in support of the hypothesis that oxidative stress contributes to the pathogenesis of PD (7). Studies performed in the MPTP model of PD suggest that peroxynitrite, a reactive species formed by the nearly diffusion-limited reaction of nitric oxide with superoxide, may be a mediator of nigrostriatal damage in PD (8-10). The potential role of peroxynitrite in the pathogenesis of PD is further supported by demonstrating that exposure of the monoamine-producing PC12 cells to peroxynitrite induced a dose-dependent alteration in dopamine synthesis that was not due to cell death or the oxidation of dopamine (11)....

Regulation of nitric oxide production in limb and ventilatory muscles during chronic exercise training

“…This finding supports (yet cannot prove) the notion that muscle protein tyrosine nitration might be dependent on NO production, since both NOS activity and protein expression were elevated in limb muscles. An interesting observation in our study is that the intensity of specific tyrosine-nitrated proteins increased significantly with exercise training, whereas other tyrosine-nitrated proteins were less sensitive to the effect of exercise training, which suggests that the process of protein tyrosine nitration is highly selective to specific proteins (1,2,17,18). However, the influence of tyrosine nitration on protein function remains, in most cases, unclear.…”

Role of copper,zinc-superoxide dismutase in catalyzing nitrotyrosine formation in murine liver

“…Overexpression of SOD1 in mice prevented nitration of tyrosine hydroxylase [54] and APAP toxicity [31]. Those impacts by the elevated SOD1 activity represented pharmacological rather than the actual metabolic roles of SOD1.…”

Biological chemistry of reactive oxygen and nitrogen and radiation-induced signal transduction mechanisms

“…Tyrosine nitration has been shown to inhibit tyrosine hydroxylase activity under conditions of oxidative stress induced with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, a model for Parkinson's disease (Ara et al, 1998). Addition of ONOO À has also been reported to induce tyrosine nitration and activation of P38, JNK and MAPK and block the interaction of the p85 regulatory subunit of phosphatidylinositol 3-kinase with the catalytic subunit (Hellberg et al, 1998;Schieke et al, 1999).…”