Oxidative Stress and Autophagy in the Regulation of Lysosome-Dependent Neuron Death

Department of Pathology, Neuropathology Division, University of Alabama at Birmingham, Birmingham, Alabama, USA.
Antioxidants & Redox Signaling (Impact Factor: 7.41). 10/2008; 11(3):481-96. DOI: 10.1089/ARS.2008.2263
Source: PubMed


Lysosomes critically regulate the pH-dependent catabolism of extracellular and intracellular macromolecules delivered from the endocytic/heterophagy and autophagy pathways, respectively. The importance of lysosomes to cell survival is underscored not only by their unique ability effectively to degrade metalloproteins and oxidatively damaged macromolecules, but also by the distinct potential for induction of both caspase-dependent and -independent cell death with a compromise in the integrity of lysosome function. Oxidative stress and free radical damage play a principal role in cell death induced by lysosome dysfunction and may be linked to several upstream and downstream stimuli, including alterations in the autophagy degradation pathway, inhibition of lysosome enzyme function, and lysosome membrane damage. Neurons are sensitive to lysosome dysfunction, and the contribution of oxidative stress and free radical damage to lysosome dysfunction may contribute to the etiology of neurodegenerative disease. This review provides a broad overview of lysosome function and explores the contribution of oxidative stress and autophagy to lysosome dysfunction-induced neuron death. Putative signaling pathways that either induce lysosome dysfunction or result from lysosome dysfunction or both, and the role of oxidative stress, free radical damage, and lysosome dysfunction in pediatric lysosomal storage disorders (neuronal ceroid lipofuscinoses or NCL/Batten disease) and in Alzheimer's disease are emphasized.

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    • "Lysosomes were traditionally thought of as just the " garbage disposals " of the cell, but research over the past few years has identified lysosomal involvement in a large number of cell functions , with lysosomal pH a key component to these functions (Settembre et al., 2013). In some cell types, lysosomes act as storage sites for signaling molecules like ATP and cytokines, and can influence lipid oxidation (Dou et al., 2012; Pivtoraiko et al., 2009; Stanley and Lacy, 2010; Zhang et al., 2007). Investigations to determine whether lysosomes serve similar functions in RPE cells are underway. "
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    ABSTRACT: Lysosomes contribute to a multitude of cellular processes, and the pH of the lysosomal lumen plays a central mechanistic role in many of these functions. In addition to controlling the rate of enzymatic degradation for material delivered through autophagic or phagocytotic pathways, lysosomal pH regulates events such as lysosomal fusion with autophagosomes and the release of lysosomal calcium into the cytoplasm. Disruption of either the steady state lysosomal pH or of the regulated manipulations to lysosomal pH may be pathological. For example, chloroquine elevates the lysosomal pH of retinal pigmented epithelial (RPE) cells and triggers a retinopathy characterized by the accumulation of lipofuscin-like material in both humans and animals. Compensatory responses to restore lysosomal pH are observed; new data illustrate that chronic chloroquine treatment increases mRNA expression of the lysosomal/autophagy master transcription factor TcFEB and of the vesicular proton pump vHATPase in the RPE/choroid of mice. An elevated lysosomal pH with upregulation of TcFEB and vHATPase resembles the pathology in fibroblasts of patients with mutant presenilin 1 (PS1), suggesting a common link between age-related macular degeneration (AMD) and Alzheimer's disease. While the absolute rise in pH is often small in these disorders, elevations of only a few tenths of a pH unit can have a major impact on both lysosomal function and the accumulation of waste over decades. Accurate measurement of lysosomal pH can be complex, and imprecise measurements have clouded the field. Protocols to optimize pH measurement from fresh and cultured cells are discussed, and indirect measurements to confirm changes in lysosomal pH and degradative capacity are addressed. The ability of reacidifying treatments to restore degradative function confirms the central role of lysosomal pH in these disorders and identifies potential approaches to treat diseases of lysosomal accumulation like AMD and Alzheimer's disease. In summary, various approaches to determine lysosomal pH in fresh and cultured cells, as well as the potential to restore pH levels to an optimal range, can help identify and repair pathologies associated with lysosomal defects in RPE cells and perhaps also suggest new approaches to treat lysosomal storage diseases throughout the body.
    Full-text · Article · Sep 2014 · Experimental Eye Research
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    • "While our IHC results indicate increased punctate LC3 immunoreactivity (Figure 1), a relative lack of autophagosomes was observed by electron microscopic analysis (Figure 4). A possible explanation for this discrepancy may be the localization of LC3 with ceroid lipofuscin (Figure 4), considered to be an accumulation of autophagic material that is unable to be effectively degraded [37, 39]. However, recent in vitro analyses of α-Gal A deficiency indicated an increase in basal levels of LC3-II, the isoform of LC3 that is associated with double-membraned autophagosomes [23, 40], resulting possibly from aberrant autophagy induction [41]. "
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    ABSTRACT: BACKGROUND: Mutations in the gene for alpha-galactosidase A result in Fabry disease, a rare, X-linked lysosomal storage disorder characterized by a loss of alpha-galactosidase A enzymatic activity. The resultant accumulation of glycosphingolipids throughout the body leads to widespread vasculopathy with particular detriment to the kidneys, heart and nervous system. Disruption in the autophagy-lysosome pathway has been documented previously in Fabry disease but its relative contribution to nervous system pathology in Fabry disease is unknown. Using an experimental mouse model of Fabry disease, alpha-galactosidase A deficiency, we examined brain pathology in 20-24 month old mice with particular emphasis on the autophagy-lysosome pathway.
    Full-text · Article · Feb 2014
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    • "FOXO controls the superoxide dismutase (SOD) and catalase genes [166], so its attenuation during aging causes increased oxidative injuries. This oxidative stress damages the lysosome and may lead to macroautophagy inhibition if the result of sustained oxidative stress is a net compromise in lysosome function [167]. Conceptually translating invertebrate FOXO activity to appropriate human homologous activity should be done with some care. "
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    ABSTRACT: Late-onset Alzheimer's disease (LOAD) is the most common neurodegenerative disorder in older adults, affecting over 50% of those over age 85. Aging is the most important risk factor for the development of LOAD. Aging is associated with the decrease in the ability of cells to cope with cellular stress, especially protein aggregation. Here we describe how the process of aging affects pathways that control the processing and degradation of abnormal proteins including amyloid-β (Aβ). Genetic association studies in LOAD have successfully identified a large number of genetic variants involved in the development of the disease. However, there is a gap in understanding the interconnections between these pathomolecular events that prevent us from discovering therapeutic targets. We propose novel, pertinent links to elucidate how the biology of aging affects the sequence of events in the development of LOAD. Furthermore we analyze and synthesize the molecular-pathologic-clinical correlations of the aging process, involving the HSF1 and FOXO family pathways, Aβ metabolic pathway, and the different clinical stages of LOAD. Our new model postulates that the aging process would precede Aβ accumulation, and attenuation of HSF1 is an "upstream" event in the cascade that results in excess Aβ and synaptic dysfunction, which may lead to cognitive impairment and/or trigger "downstream" neurodegeneration and synaptic loss. Specific host factors, such as the activity of FOXO family pathways, would mediate the response to Aβ toxicity and the pace of progression toward the clinical manifestations of AD.
    Full-text · Article · Dec 2013 · Journal of Alzheimer's disease: JAD
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