Oxidative Modifications and Down-regulation of Ubiquitin Carboxyl-terminal Hydrolase L1 Associated with Idiopathic Parkinson's and Alzheimer's Diseases

Abstract

Alzheimer's disease (AD) and Parkinson's disease (PD) are the two most common neurodegenerative diseases that occur either in relatively rare, familial forms or in common, sporadic forms. The genetic defects underlying several monogenic familial forms of AD and PD have recently been identified, however, the causes of other AD and PD cases, particularly sporadic cases, remain unclear. To gain insights into the pathogenic mechanisms involved in AD and PD, we used a proteomic approach to identify proteins with altered expression levels and/or oxidative modifications in idiopathic AD and PD brains. Here, we report that the protein level of ubiquitin carboxyl-terminal hydrolase L1 (UCH-L1), a neuronal de-ubiquitinating enzyme whose mutation has been linked to an early-onset familial PD, is down-regulated in idiopathic PD as well as AD brains. By using a combination of two-dimensional gel electrophoresis and mass spectrometry, we have identified three human brain UCH-L1 isoforms, a full-length form and two amino-terminally truncated forms. Our proteomic analyses reveal that the full-length UCH-L1 is a major target of oxidative damage in AD and PD brains, which is extensively modified by carbonyl formation, methionine oxidation, and cysteine oxidation. Furthermore, immunohistochemical studies show that prominent UCH-L1 immunostaining is associated with neurofibrillary tangles and that the level of soluble UCH-L1 protein is inversely proportional to the number of tangles in AD brains. Together, these results provide evidence supporting a direct link between oxidative damage to the neuronal ubiquitination/de-ubiquitination machinery and the pathogenesis of sporadic AD and PD.Alzheimer's disease (AD) 1 and Parkinson's disease (PD) are the two most common neurodegenerative disorders in humans, however, the causes of AD and PD, particularly the sporadic cases, remain unclear. A prominent feature of AD and PD as well as other neurodegenerative diseases is the accumulation of insoluble proteinaceous deposits, such as senile plaques and neurofibrillary tangles in AD and Lewy bodies in PD (1). Although these deposits have different protein compositions, they all contain ubiquitin and ubiquitinated proteins (2). Interestingly, mutations in two enzymes of the ubiquitination/de-ubiquitination system, parkin and ubiquitin carboxyl-terminal hydrolase L1 (UCH-L1), have been identified as causative genetic defects for certain familial forms of PD (3). In familial AD patients, an aberrant form of ubiquitin resulting from a ϩ1 frameshift mutation in the ubiquitin-B gene has been detected (4). Moreover, impaired proteasome function has been reported in idiopathic AD and PD brains (2). Collectively, these different lines of evidence support a role for dysfunction of the ubiquitinproteasome pathway in the pathogenesis of AD and PD.Oxidative stress is another important factor that has been implicated in the pathogenesis of a number of age-related neurodegenerative diseases, including AD and PD (5, 6). Both AD and PD have been associated wit...

Altered gene expression in cells from patients with lysosomal storage disorders suggests impairment of the ubiquitin pathway

“…We determined that UCH-L1 protein levels were reduced approximately twofold in the brain extracts of the HEXBÀ/À animals when compared to the wild-type animals. Recent data indicated that in the brains of patients affected with Alzheimer's disease and Parkinson's disease, UCH-L1 undergoes post-translational modifications such as carbonylation, methionine oxidation and cysteine oxidation, 21 which significantly alter its activity. Our experiments also detected the presence of the UCH-L1 isoforms with three oxidized methionine residues, but the ratio between modified and nonmodified protein was similar for HEXB þ / þ and HEXBÀ/ À animals (not shown).…”

S-Nitrosylation and uncompetitive/fast off-rate (UFO) drug therapy in neurodegenerative disorders of protein misfolding

“…However, we and others have shown that S-nitrosylation and further oxidation of parkin, a ubiquitin E3 ligase, or UCH-L1, a deubiquitinating enzyme that recycles ubiquitin, results in dysfunction of these enzymes and thus of the UPS. 17,20,[68][69][70][71] We found that nitrosative stress triggers S-nitrosylation of parkin (forming SNO-parkin) not only in rodent models of PD but also in the brains of human patients with PD and Lewy bodies. SNO-parkin initially stimulates ubiquitin E3 ligase activity, resulting in enhanced ubiquitination, as observed in Lewy bodies, followed by a decrease in enzyme activity, producing a futile cycle of dysfunctional UPS (Figure 2).…”

Nitrosative and oxidative stress links dysfunctional ubiquitination to Parkinson's disease

“…15 Furthermore, Nishikawa et al 17 found that oxidation of UCH-L1 by 4-hydroxynonenal (a putative endogenous mediator of oxidative stress) results in loss of hydrolase activity. In a complementary study, Choi et al 16 identified an oxidized form of UCH-L1 in sporadic PD brains. Decreased UCH-L1 activity could potentially contribute to UPS dysfunction, accumulation of damaged proteins, and formation of aggregates.…”

“…Interestingly, four studies have provided mounting evidence that nitrosative or oxidative stress results in the malfunction of parkin and UCH-L1 via S-nitrosylation or oxidation, and thereby contributes to the pathogenesis of the sporadic form of PD. [14][15][16][17] S-nitrosylation (SNO) is a redox-based modification of specific cysteine thiol groups, whereby nitric oxide (NO) reacts with thiol to form an SNO-protein, and thus regulates protein activity. 18,19 We and others recently reported that the RING-finger E3 ligase, parkin, is S-nitrosylated in the brains of human patients with PD as well as in rodent brains of models of the disease.…”