Mechanisms of Parkinson Disease and Related Disorders

点击翻译按钮获取中文摘要

By applying a unique and novel neuroimaging-neurochemical approach, we obtained the first evidence for decreased vesicular uptake of neuronal catecholamines in sympathetic neurons in Lewy body diseases (Goldstein et al., J Clin Invest 2011;121:3320-3330). We found that putamen tissue from patients with end-stage PD contains an increased concentration of DOPAL after adjustment for decreased dopaminergic innervation and that ALDH activity measured by the DOPAC:DOPAL ratio is decreased. These findings are consistent with DOPAL buildup and decreased putamen ALDH activity in PD (Goldstein et al., Eur J Neurol 2011;18:703-710). In rat pheochromocytoma PC12 cells, which contain endogenous dopamine and DOPAL, we tested whether vesicular uptake blockade augments endogenous DOPAL production. We also examined whether intracellular DOPAL contributes to apoptosis and, since alpha-synuclein oligomers may be pathogenetic in PD, oligomerizes alpha-synuclein. Catechols were assayed in PC12 cells after reserpine to block vesicular uptake, with or without inhibition of enzymes metabolizing DOPALdaidzein for aldehyde dehydrogenase and AL1576 for aldehyde reductase. Vesicular uptake was quantified by novel HPLC methodology based on 6F-dopamine or LCMS methodology using 13C-dopamine incubation; DOPAL toxicity by apoptosis responses to exogenous dopamine, with or without daidzein+AL1576; and DOPAL-induced synuclein oligomerization by synuclein dimer production during DOPA incubation, with or without inhibition of L-aromatic-amino-acid decarboxylase or monoamine oxidase. Reserpine inhibited vesicular uptake by 95-97% and rapidly increased cell DOPAL content (p=0.0008), and daidzein+AL1576 augmented DOPAL responses to reserpine. Intracellular DOPAL contributed to dopamine-evoked apoptosis and DOPA-evoked synuclein dimerization. The findings fit with the catecholaldehyde hypothesis, according to which decreased vesicular sequestration of cytosolic catecholamines and impaired catecholaldehyde detoxification contribute to the catecholaminergic denervation that characterizes PD (Goldstein et al., J Neurochem (in press)). The catecholaldehyde hypothesis predicts that mice with inherited low ALDH activity should have aging-related nigrostriatal neurogeneration manifesting as Parkinsonism. In a collaborative study with R. Strong (Univ. of Texas, San Antonio) we tested this prediction directly in mice with knockout of ALDH1A1 and ALDH2, the two isoforms known to be expressed in substantia nigra dopamine neurons. Double knockout mice had congenitally increased striatal DOPAL and age-dependent deficits in motor performance, loss of tyrosine hydroxylase-immunoreactive neurons in the substantia nigra, and reduced striatal dopamine (Wey et al., PLoS ONE 2012;7:e31522). The catecholaldehyde hypothesis also predicts that mice with inherited low activity of the type 2 vesicular monoamine transporter (VMAT2-Lo) should have striatal dopamine depletion and aging-related Parkinsonism. In an ongoing collaborative study with G. Miller (Emory) we have confirmed decreased striatal dopamine and cardiac norepinephrine contents for given rates of catecholamine synthesis as indicated by tissue DOPA in VMAT2-Lo mice. These mice are now known to develop both motor and non-motor abnormalities mimicking PD. We are conducting studies involving i.v. injection of 6F-dopamine and HPLC-electrochemical assays or 13C-dopamine and LCMS assays to confirm in vivo that VMAT2-Lo mice have decreased vesicular uptake of intra-neuronal catecholamines. Using these and numerous other data from collaborative studies under the Catecholamine Resource Initiative, we are surveying DOPAL concentrations across brain areas and relationships among DOPAL, dopamine, DOPAC, dihydroxyphenylethanol (DOPET, an alternative deaminated metabolite of dopamine), and DOPA (the precursor of dopamine). Data from mouse models have been used to validate dopamine:DOPA as an index of vesicular uptake for a given amount of dopamine synthesis and DOPAC:DOPAL to indicate ALDH activity. We are applying these indices in post-mortem striatal tissues from PD patients. Preliminarily, mouse and human striatum contain more than 10-fold greater DOPAL levels than found in any other brain region. Across regions and individuals of both species, DOPAL correlates with dopamine, DOPAC, and DOPET but not with DOPA. Importantly, PD patients have been found to have low putamen dopamine:DOPA and low DOPAC:DOPAL, compared to controls. These findings provide novel neurochemical evidence for decreased vesicular uptake of dopamine and decreased ALDH activity in striatum in PD, as predicted by the catecholaldehyde hypothesis. In vitro studies have shown that DOPAL potently oligomerizes alpha-synuclein. We have found that metal ions (especially Cu+2) augment DOPAL-induced oligomerization of alpha-synuclein, suggesting that deleterious interactions of catecholaldehydes, metal ions, and alpha-synuclein might explain relatively selective loss of catecholaminergic neurons in Lewy body diseases. The Braak staging concept of Lewy body disease pathogenesis is based on post-mortem evidence for a spatiotemporal sequence of alpha-synuclein deposition, with autonomic nervous system involvement before synucleinopathy in substantia nigra neurons. A patient with primary chronic autonomic failure underwent biennial brain 18F-DOPA and myocardial 18F-dopamine scanning over four years. Low myocardial radioactivity indicated cardiac noradrenergic denervation that persisted. Striatal 18F-DOPA-derived radioactivity initially was normal, two years later was decreased subtly, and by four years was clearly decreased and accompanied by dementia and Parkinsonism. In this case, neuroimaging evidence of cardiac noradrenergic denervation and subsequent progressive striatal dopaminergic denervation provided in vivo support for Braak staging (Goldstein et al., Clin Auton Res 2012;22:57-61).