Early α-synuclein lipoxidation in neocortex in Lewy body diseases
Introduction
Parkinson's disease (PD), characterized by resting tremor, slowness of initial movement, rigidity, and general postural instability, is one of the most prevalent neurodegenerative disorders among the elderly population. The disease is pathologically defined by loss of neurons in the substantia nigra pars compacta, locus ceruleus, other nuclei of the brain stem, basal nucleus of Meynert and amygdala, and by the presence of eosinophilic intraneuronal proteinaceous inclusions called Lewy bodies and aberrant neurites (Forno, 1996, Jellinger and Mizuno, 2003). Parkinson-like pathology restricted to the medulla oblongata and pons, associated or not with mild midbrain involvement in the absence of motor symptoms, is known as (asymptomatic) incidental or pre-clinical PD (iPD) (Forno, 1996, Jellinger and Mizuno, 2003). Dementia with Lewy bodies (DLB) is manifested as progressive cognitive impairment, dementia and parkinsonism, and it is characterized by the additional widespread distribution of LBs and neurites in the cerebral cortex (Ince and McKeith, 2003, Ince et al., 1998). DLB is often accompanied by Alzheimer's disease (AD) and this is considered the common form; DLB with minimal Aβ-amyloid deposits and no tau pathology characterizes the pure form (Kosaka, 1990, Kosaka, 1993). PD and DLB are within the spectrum of Lewy body diseases (LBDs). Staging of brain pathology related to sporadic PD has been proposed (Braak et al., 2003). This instrumental classification is useful as it delineates the topography of lesions in the different stages and correlates and matches with clinical symptoms in the majority of cases. Thus stages 1 and 2 are coincidental with pre-clinical PD, stages 3 and 4 may have PD, and stages 5 and 6 are manifested as PD with cognitive impairment and DLB.
α-Synuclein is the major component of protein aggregates in Lewy bodies and aberrant neurites (Baba et al., 1998, Hashimoto and Masliah, 1999, Iwatsubo, 2003, Spillantini et al., 1998). Mutations in the α-synuclein gene (A53T, A30P, E46K) are associated with familial PD and DLB (Kruger et al., 1998, Polymeropoulos et al., 1997, Zarranz et al., 2004). Triplication or duplication of the α-synuclein locus is a cause of PD (Chartier-Harlin et al., 2004, Ibanez et al., 2004, Nishioka et al., 2006, Singleton et al., 2003). Based on these characteristics, LBDs have been categorized as α-synucleinopathies.
Mutations in the α-synuclein gene, increased levels of α-synuclein, and oxidative stress lead to α-synuclein aggregation in vitro (Hashimoto et al., 1999, Narhi et al., 1999, Paik et al., 2000). Yet oxidative stress is also a main contributory factor in the pathogenesis of PD and related α-synucleinopathies (Jenner, 2003, Markesberry et al., 2001). Studies in the substantia nigra and midbrain have shown decreased levels of reduced glutathione (Perry et al., 1982, Sian et al., 1994), increased Cu/ZN superoxide dismutase I and Mn superoxide dismutase (SOD2) protein and mRNA levels (Ceballos et al., 1990, Marttila et al., 1988, Saggu et al., 1989), and increased protein carbonyls, lipid peroxides (Alam et al., 1997a, Alam et al., 1997b, Floor and Wetzel, 1998), and 4-hydroxy-2-nonenal (Dexter et al., 1986, Yoritaka et al., 1996), as well as changes in polyunsaturated fatty acids sustaining lipid peroxidation (Shelley, 1998), leading to increased generation of malondialdehyde and hydroperoxides (Dexter et al., 1989). Advanced glycation end products (AGE) have also been found in the substantia nigra and locus ceruleus in PD (Jenner, 1998). Finally, oxidative RNA and DNA damage also occurs in the substantia nigra in PD (Alam et al., 1997a, Alam et al., 1997b, Castellani et al., 1996). Oxidative stress has also been observed in other brain regions in LBDs. A generalized increase in protein carbonyls has been found in the telencephalon in PD (Alam et al., 1997a, Alam et al., 1997b). Oxidative DNA damage, as revealed by increased levels of 8-hydroxyguanine, occurs not only in the substantia nigra but also in the basal ganglia and cerebral cortex in PD (Sanchez-Ramos et al., 1994, Zhang et al., 1999). Indices of oxidative stress with altered mitochondrial function have been observed in the cerebral cortex in iPD (Dexter et al., 1994). Moreover, recent studies have shown mass spectrometric and immunochemical evidence of abnormal lipid composition, increased lipoxidative damage by the markers malondialdehyde-lysine (MDA-Lys) and 4-hydroxynonenal-lysine, increased AGE modifications, and increased RAGE cellular expression in the frontal cortex in LBDs including iPD (Dalfo et al., 2005). Preliminary proteomic studies have also revealed β-synuclein and SOD2 as targets of lipoxidative damage in iPD (Dalfo et al., 2005).
In line with our previous studies, the present work is focused on α-synuclein as a possible target of lipoxidative damage in the substantia nigra and frontal cortex in LBDs. Results show not only MDA-Lys-lipoxidation of α-synuclein in the substantia nigra and frontal cortex in all DLB and PD cases examined, but also in the frontal cortex in 3/3 and in the substantia nigra in 2/3 cases with iPD. This work provides for the first time evidence of extended lipoxidative modification of α-synuclein in LBDs.
Section snippets
Tissue samples
Clinically, all cases of PD had suffered from classical PD lasting from 8 to 15 years, and none of them had cognitive impairment. Cases with DLB fulfilled the clinical criteria proposed by the consortium on DLB international workshop (McKeith et al., 2000, McKeith et al., 1996). Brain samples were obtained from the Institute of Neuropathology and University of Barcelona Brain Banks.
The brains of five patients with PD, five DLB, three iPD and seven aged-matched controls were obtained at autopsy,
General comments
Representative images of α-synuclein pathology in the frontal cortex and substantia nigra in the present series are shown in Fig. 1. Lewy bodies and aberrant neurites are absent in control cases and in cases 8 and 10 with iPD. A few α-synuclein-immunoractive neurites and cytoplasmic inclusions in substantia nigra neurons are seen in case 9. Large numbers of Lewy bodies and neurites occur in the substantia nigra in PD, whereas the frontal cortex is devoid of α-synuclein inclusions. Finally, Lewy
Discussion
MDA is one of the most abundant lipoperoxidation products in cells, and it can also be produced endogenously via prostaglandin biosynthesis (Esterbauer et al., 1991). MDA is also reactive with amino acids and proteins under certain physiological conditions (Esterbauer et al., 1991, Uchida, 2000). MDA can form adducts primarily with lysine residues of proteins and also, to some extent, with histidine, tyrosine, arginine and methionine residues (Esterbauer et al., 1991, Uchida, 2000). It has been
Acknowledgements
This work was funded by grants from the Spanish Ministry of Health, Instituto de Salud Carlos III PI05/1570 and PI05/2214, and supported by the European Commission under the Sixth Framework Programme (BrainNet Europe II, LSHM-CT-2004-503039). We thank T. Yohannan for editorial help.
There is no conflict of interest including any financial, personal or other relationships with other people or organizations within the three years of beginning the work.
Brain samples were obtained from the Institute
References (53)
- et al.
Staging of brain pathology related to sporadic Parkinson's disease
Neurobiol. Aging
(2003) - et al.
Glycoxidation and oxidative stress in Parkinson's disease and Diffuse Lewy Body disease
Brain Res.
(1996) - et al.
Superoxide dismutase and Parkinson's disease
Lancet
(1990) - et al.
Lipid peroxidation as a cause of nigral death in Parkinson's disease
Lancet
(1986) - et al.
Chemistry and biochemistry of 4-hydroxynonenal, malonaldehyde and related aldehydes
Free Radic. Biol. Med.
(1991) - et al.
Mutant and wild type human alpha-synucleins assemble into elongated filaments with distinct morphologies in vitro
J. Biol. Chem.
(1999) - et al.
Causal relation between alpha-synuclein gene duplication and familial Parkinson's disease
Lancet
(2004) - et al.
Oxygen toxicity protecting enzymes in Parkinson's disease. Increase of superoxide dismutase-like activity in the substantia nigra and basal nucleus
J. Neurol. Sci.
(1988) - et al.
Both familial Parkinson's disease mutations accelerate α-synuclein aggregation
J. Biol. Chem.
(1999) - et al.
Metal-catalyzed oxidation of α-synuclein in the presence of Copper(II) and hydrogen peroxide
Arch. Biochem. Biophys.
(2000)