The Role of Autophagy in Age-Related Neurodegeneration

Department of Neurology, University of Pennsylvania School of Medicine, Philadelphia, PA, USA.
Neurosignals (Impact Factor: 2). 02/2008; 16(1):75-84. DOI: 10.1159/000109761
Source: PubMed


Most age-related neurodegenerative diseases are characterized by accumulation of aberrant protein aggregates in affected brain regions. In many cases, these proteinaceous deposits are composed of ubiquitin conjugates, suggesting a failure in the clearance of proteins targeted for degradation. The 2 principal routes of intracellular protein catabolism are the ubiquitin proteasome system and the autophagy-lysosome system (autophagy). Both of these degradation pathways have been implicated as playing important roles in the pathogenesis of neurodegenerative disease. Here we describe autophagy and review the evidence suggesting that impairment of autophagy contributes to the initiation or progression of age-related neurodegeneration. We also review recent evidence indicating that autophagy may be exploited to remove toxic protein species, suggesting novel strategies for therapeutic intervention for a class of diseases for which no effective treatments presently exist.

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    • "By contrast, the increased contents of autophagy markers, Atg5 and LC3, are recently evidenced in RPE/choroids in aged mice as well as in drusen in the retina of old eyes of AMD patients (Wang et al., 2009b), implicating the involvement of autophagic dysfunction in the AMD pathogenesis . The function of autophagy machinery in aged cells has been previously proposed to be impaired by an intracellular burden of ROS-damaged macromolecules and organelles (McCray and Taylor, 2008). In the context of MGO-related cytotoxicity in ocular component cells, to date MGO exposure is only known to result in apoptosis of retinal pericytes (Kim et al., 2004) and lens epithelial cells (Kim et al., 2012). "
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    ABSTRACT: Methylglyoxal (MGO), a glycolytic metabolite, induces oxidative injury and apoptotic cell death that play a pathogenetic role in age-related macular degeneration (AMD). This study examined the impact of MGO on cell proliferation and autophagy flux in retinal pigment epithelium (RPE) ARPE-19 cells and elucidated the underlying mechanism. Short-term MGO exposure suppressed cell proliferation without induction of apoptotic cell death, increased production of reactive oxygen species, and potentiated H2O2-exhibited cytotoxicity in ARPE-19 cells. Conversely, pretreatment with N-acetylcysteine, a ROS scavenger, and aminoguanidine, an MGO blocker, prevented MGO-induced growth retardation. MGO significantly enhanced autophagy flux and increased intracellular accumulation of autophagosomes, which was functionally confirmed by addition of autophagy enhancer or inhibitors. Signaling kinetic observation indicated that MGO remarkably triggered phosphorylation of Akt, ERK1/2, p38 MAPK, and JNK1/2. Blockade of kinase activity demonstrated that the hyperphosphorylation of Akt, ERK1/2, JNK, and p38 MAPK were all involved in the MGO-enhanced autophagy and growth-arresting effect in ARPE-19 cells. Moreover, pretreatment with autophagic flux inhibitors including 3-methyladenine, bafilomycin A, and chloroquine effectively ameliorated MGO- but not H2O2-mediated ARPE-19 cytotoxicity. In conclusion, modulation of autophagy flux activity by using autophagic or kinase inhibitors may be an applicable modality to treat AMD. Copyright © 2015. Published by Elsevier Ltd.
    Toxicology in Vitro 05/2015; 29(7). DOI:10.1016/j.tiv.2015.05.014 · 2.90 Impact Factor
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    • "Several neurodegenerative diseases are characterized by the formation of intracellular protein aggregates in affected brain regions, indicating a failure of protein degradation system (McCray and Taylor, 2008). Autophagy is a stress-induced catabolic process responsible for the degradation of long-lived proteins and damaged organelles (Levine and Klionsky, 2004) that was shown to decline with aging (Bergamini, 2006) and to determine cell and individual lifespan (Juhasz et al., 2007). "
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    ABSTRACT: Age-related neurodegenerative diseases have been associated with chronic neuroinflammation and microglia activation. However, cumulative evidence supports that inflammation only occurs at an early stage once microglia change the endogenous characteristics with ageing and switch to irresponsive/senescent and dystrophic phenotypes with disease progression. Thus, it will be important to have the means to assess the role of reactive and aged microglia when studying advanced brain neurodegeneration processes and age-associated related disorders. Yet, most studies are done with microglia from neonates since there are no adequate means to isolate degenerating microglia for experimentation. Indeed, only a few studies report microglia isolation from aged animals, using either short-term cultures or high concentrations of mitogens in the medium, which trigger microglia reactivity. The purpose of this study was to develop an experimental process to naturally age microglia after isolation from neonatal mice and to characterize the cultured cells at 2 days in vitro (DIV), 10 DIV and 16 DIV. We found that 2 DIV (young) microglia had predominant amoeboid morphology and markers of stressed/reactive phenotype. In contrast, 16 DIV (aged) microglia evidenced ramified morphology and increased metalloproteinase (MMP)-2 activation, as well as reduced MMP-9, glutamate release and nuclear factor kappa-B activation, in parallel with decreased expression of Toll-like receptor (TLR)-2 and TLR-4, capacity to migrate and phagocytose. These findings together with the reduced expression of microRNA (miR)-124, and miR-155, decreased autophagy, enhanced senescence associated beta-galactosidase activity and elevated miR-146a expression, are suggestive that 16 DIV cells mainly correspond to irresponsive/senescent microglia. Data indicate that the model represent an opportunity to understand and control microglial aging, as well as to explore strategies to recover microglia surveillance function.
    Frontiers in Cellular Neuroscience 06/2014; 8:152. DOI:10.3389/fncel.2014.00152 · 4.29 Impact Factor
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    • "Autophagy is an evolutionarily conserved pathway that involves the sequestration and delivery of cytoplasmic materials to the lysosomes, where cellular constituents are degraded and recycled12,13,14,15. Autophagy is known to be activated during ischemic insult, but its contribution to neuronal death/survival is still being debated16,17,18. "
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    ABSTRACT: Aim: To investigate whether endoplasmic reticulum (ER) stress participates in the neuroprotective effects of ischemic preconditioning (IPC)-induced neuroprotection and autophagy activation in rat brains. Methods: The right middle cerebral artery in SD rats was occluded for 10 min to induce focal cerebral IPC, and was occluded permanently 24 h later to induce permanent focal ischemia (PFI). ER stress inhibitor salubrinal (SAL) was injected via intracerebral ventricle infusion 10 min before the onset of IPC. Infarct volume and motor behavior deficits were examined after the ischemic insult. The protein levels of LC3, p62, HSP70, glucose-regulated protein 78 (GRP 78), p-eIF2α and caspase-12 in the ipsilateral cortex were analyzed using immunoblotting. LC3 expression pattern in the sections of ipsilateral cortex was observed with immunofluorescence. Results: Pretreatment with SAL (150 pmol) abolished the neuroprotective effects of IPC, as evidenced by the significant increases in mortality, infarct volume and motor deficits after PFI. At the molecular levels, pretreatment with SAL (150 pmol) significantly increased p-eIF2α level, and decreased GRP78 level after PFI, suggesting that SAL effectively inhibited ER stress in the cortex. Furthermore, the pretreatment with SAL blocked the IPC-induced upregulation of LC3-II and downregulation of p62 in the cortex, thus inhibiting the activation of autophagy. Moreover,SAL blocked the upregulation of HSP70, but significantly increased the cleaved caspase-12 level, thus promoting ER stress-dependent apoptotic signaling in the cortex. Conclusion: ER stress-induced autophagy might contribute to the neuroprotective effect of brain ischemic preconditioning.
    Acta Pharmacologica Sinica 04/2013; 34(5). DOI:10.1038/aps.2013.34 · 2.91 Impact Factor
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