Research reportContribution of somal Lewy bodies to neuronal death
Introduction
Parkinson's disease and other Lewy body-associated disorders are characterized neuropathologically by the presence of LBs in the SNpc, as well as in other brainstem, cortical and peripheral nervous system sites [8]. Lewy bodies are eosinophilic inclusion bodies occurring in the cell body, axons and dendrites of neurons, which appear to be composed mainly of neurofilaments that may be inappropriately phosphorylated, proteolytically truncated and ubiquinated (reviewed in 17, 30). Advanced glycation end-products, which are potentiated by oxidative stress, have also been described in LBs [5]. Thus LBs may be correlated with pathological changes in the cell.
Apoptosis is a type of cell death with specific morphological and biochemical distinctions (reviewed in [4]). Morphological changes include nuclear and cytoplasmic condensation, formation of membrane-bound apoptotic bodies variably containing organelles and chromatin in condensed cytoplasm, and subsequent phagocytosis by surrounding cells, including macrophages or microglia. DNA undergoes specific endonucleolytic cleavage during apoptosis 2, 39, leaving free 3′-hydroxyl ends that can be detected using an in situ end-labeling technique (ISEL) 12, 37.
The death of neurons by apoptosis or an apoptotic-like process has been recently described in several neurodegenerative disorders, including Lewy body-associated disorders (Parkinson's disease (PD), concomitant Alzheimer/Parkinson's disease (AD/PD) and diffuse Lewy body disease (DLBD) 1, 34), Alzheimer's disease (AD) 12, 23, 32, amyotrophic lateral sclerosis (ALS) 7, 36, 43and Huntington's chorea 7, 31, although other studies have not seen evidence of apoptosis in AD [26], ALS [26]and PD [7]. Apoptosis in culture and in developmental systems have specific molecular cascades [4]which as yet have not been described in human postmortem tissue; we have therefore described the morphological changes resembling apoptosis as `apoptotic-like changes'.
There is some evidence that neuropathological inclusions may affect the rate of cell death. For example, Alzheimer neurofibrillary tangles, like LBs, are cytoskeletal accumulations which are abnormally phosphorylated and ubiquinated. They are composed of the A68 phosphorylated form of the microtubule-associated protein tau [24]. Neurons with and without neurofibrillary tangles have been shown to undergo apoptosis in AD 12, 23; one study [23]showed tangle-bearing neurons to be three times more likely to undergo apoptotic cell death than neurons without tangles.
It is not known whether LBs have deleterious effects on the cells containing them. As LBs are composed of abnormal neurofilaments, their presence may indicate a general aberration of the cytoskeleton, and could directly contribute to the death of SNpc neurons [17]. Alternatively, LBs may occur as an epiphenomenon of the primary pathology and have little or no effect on neuronal death. We have previously shown that many SNpc neurons die by an apoptotic-like process in patients with Lewy body-associated disorders. In the present study, we address the question of whether the presence of a somal LB correlates with increased apoptotic-like cell death, by examining the occurrence of apoptotic-like changes in SNpc neurons with and without somal LBs.
Section snippets
Human tissue
The McLean Hospital Brain Tissue Resource Center at Harvard Medical School (Boston, MA) provided archival human tissue. Cases of concomitant AD/PD met standard neuropathological criteria for both diseases, and are likely to be classified as the Lewy body variant of Alzheimer's disease by current standards at McLean Hospital (Dr. Jean P. Vonsattel, personal communication, and [34]). DLBD cases did not meet the consensus criteria for AD, but demonstrated extensive cortical LBs and subcortical
Results
In situ end-labeling of AD/PD and DLBD cases demonstrated apoptotic-like changes in LB-containing SNpc neurons (Fig. 1). SNpc neurons and their remnants can be unequivocally identified by the presence of neuromelanin. In contrast to a normal euchromatic nucleus (Fig. 1A), SNpc nuclei undergoing early apoptotic-like changes were ISEL+ and condensed (Fig. 1C–H). We have defined early apoptotic-like changes as those ISEL+ neurons having an intact cell body (Fig. 1C–H). LB-containing neurons can
Discussion
Apoptotic-like changes have recently been described in the SNpc of PD, AD/PD and DLBD cases, using ISEL and ultrastructural analysis 1, 34. The current study employed anti-ubiquitin immunohistochemistry in conjunction with ISEL to show that some of the SNpc neurons undergoing apoptotic-like changes contained somal LBs, while many did not. However, SNpc neurons without somal LBs may contain dendritic or axonal LBs (9, 10, 25, 40, 41, Hill, unpublished observations), which could be harmful or
Acknowledgements
We thank Dr. Theresa Harrison for critical review of the manuscript and Drs. Edward D. Bird, Jean P. Vonsattel and Ms. Lisa A. Kanaley of the Brain Tissue Resource Center of McLean Hospital, Harvard Medical School, for brain tissue, as well as the donors and their families. Supported by National Institutes of Health Grant NS32835 (W.D.H.), Medical College of Georgia Research Institute Grant 2004-66 (W.D.H.), Fraternal Order of Eagles Golden Eagle Fund Grant (W.D.H.), and Public Health Service
References (43)
- et al.
Glycoxidation and oxidative stress in Parkinson disease and diffuse Lewy body disease
Brain Res.
(1996) - et al.
Stability of cell size and nucleolar size in Lewy body containing neurons of substantia nigra in Parkinson's disease
Brain Res.
(1994) - et al.
Decreased tyrosine hydroxylase messenger RNA in the surviving dopaminergic neurons of the substantia nigra in Parkinson's disease: an in situ hybridization study
Neuroscience
(1990) - et al.
Evidence for apoptotic cell death in Alzheimer's disease
Exp. Neurol.
(1995) - et al.
Metal-catalyzed oxidation of bovine neurofilaments in vitro
Free Rad. Biol. Med.
(1995) - et al.
In situ labeling of granule cells for apoptosis-associated DNA fragmentation reveals different mechanisms of cell loss in developing cerebellum
Neuron
(1993) - P. Anglade, S. Vyas, F. Javoy-Agid et al., Apoptosis and autophagy in nigral neurons of patients with Parkinson's...
- et al.
Apoptosis. The role of the endonuclease
Am. J. Pathol.
(1990) - et al.
Altered neurofilament expression does not contribute to Lewy body formation
Am. J. Pathol.
(1996) - et al.
Apoptosis and necrosis: basic types and mechanisms of cell death
Arch. Pathol. Lab. Med.
(1993)