Pathogenic Lysosomal Depletion in Parkinson's Disease

Abstract

Mounting evidence suggests a role for autophagy dysregulation in Parkinson's disease (PD). The bulk degradation of cytoplasmic proteins (including ␣-synuclein) and organelles (such as mitochondria) is mediated by macroautophagy, which involves the sequestration of cytosolic components into autophagosomes (AP) and its delivery to lysosomes. Accumulation of AP occurs in postmortem brain samples from PD patients, which has been widely attributed to an induction of autophagy. However, the cause and pathogenic significance of these changes remain unknown. Here we found in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine mouse model of PD that AP accumulation and dopaminergic cell death are preceded by a marked decrease in the amount of lysosomes within dopaminergic neurons. Lysosomal depletion was secondary to the abnormal permeabilization of lysosomal membranes induced by increased mitochondrialderived reactive oxygen species. Lysosomal permeabilization resulted in a defective clearance and subsequent accumulation of undegraded AP and contributed directly to neurodegeneration by the ectopic release of lysosomal proteases into the cytosol. Lysosomal breakdown and AP accumulation also occurred in PD brain samples, where Lewy bodies were strongly immunoreactive for AP markers. Induction of lysosomal biogenesis by genetic or pharmacological activation of lysosomal transcription factor EB restored lysosomal levels, increased AP clearance and attenuated 1-methyl-4-phenylpyridinium-induced cell death. Similarly, the autophagy-enhancer compound rapamycin attenuated PD-related dopaminergic neurodegeneration, both in vitro and in vivo, by restoring lysosomal levels. Our results indicate that AP accumulation in PD results from defective lysosomal-mediated AP clearance secondary to lysosomal depletion. Restoration of lysosomal levels and function may thus represent a novel neuroprotective strategy in PD.

Rotenone Inhibits Autophagic Flux Prior to Inducing Cell Death

“…LAMP-1 is best known for its regulation of lysosomal motility and endosomal-lysosomal fusion with autophagic vacuoles, 29 and has been shown to fluctuate with changes in lysosomal volume and/or number. 9,30 Western blot analysis indicated an increase in LAMP-1 levels following treatment with 10 μM rotenone ( Figure 6A), an effect that was significantly different vs vehicle control at 6 h but not 24 h ( Figure 6B). This increase in LAMP-1-suggests an increase in either the number or size of acidic vesicles that may be a consequence of lysosome dysfunction ( Figure 4) and inhibition of autophagic flux (Figure 2).…”

“…Conversely, LAMP-1 may also increase as a function of de novo lysosome biogenesis, as shown recently under stressful conditions and as a response to alterations in autophagy. 9,30 To address this possibility the effects of rotenone on endogenous levels of the transcription factor EB (TFEB) were assessed by Western blot analysis, as TFEB has been shown previously to regulate transcription of LAMP-1 in addition to other lysosomal targets. 9,30 Levels of TFEB at 6 and 24 h following rotenone treatment were similar in rotenone vs vehicle control cells (Figure 7), suggesting that the increase in LAMP-1 observed following rotenone treatment does not result from lysosome biogenesis, but rather from the inhibition of lysosomal degradation.…”

Autophagy in motor neuron disease: Key pathogenetic mechanisms and therapeutic targets

“…Rapamycin, an mTOR dependent inducer of autophagy, has been shown to up-regulate autophagy, reducing aberrant protein aggregation in ALS (Sarkar et al, 2008;Harrison et al, 2009;Malagelada et al, 2010;Dehay et al, 2010;Caccamo et al, 2011;Hetz et al, 2009). However, rapamycin was demonstrated to worsen motor neuron loss and to reduce the survival of SOD1 G93A mice when administrated in advanced stages of the disease, while at early stages it may exert positive effects .…”

Glucocerebrosidase, a new player changing the old rules in Lewy body diseases

“…Human dopaminergic BE-M17 neuroblastoma cells show a decrease in the number of lysosomes, an increase in cell death, and autophagosome accumulation in a dose-dependent manner when treated with the dopaminergic neurotoxin 1-methyl-4-phenylpyridine (Dehay et al , 2010 ). In addition, 1-methyl-4-phenylpyridinetreated cells show enhanced lysosomal membrane permeability, thereby causing release of soluble lysosomal components such as cathepsin D from lysosomes into the cytosol (Dehay et al , 2010 ).…”

“…In addition, 1-methyl-4-phenylpyridinetreated cells show enhanced lysosomal membrane permeability, thereby causing release of soluble lysosomal components such as cathepsin D from lysosomes into the cytosol (Dehay et al , 2010 ). In the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine mouse model and postmortem SN of patients with PD, neurons exhibit depleted lysosomes and accumulation of autophagosomes (Dehay et al , 2010 ).…”