Evidence from human postmortem material, transgenic mice, and cellular/animal models of PD link alpha-synuclein accumulation to alterations in the autophagy lysosomal pathway. Conversely, ...alpha-synuclein mutations related to PD pathogenesis, as well as post-translational modifications of the wild-type protein, result in the generation of aberrant species that may impair further the function of the autophagy lysosomal pathway, thus generating a vicious cycle leading to neuronal death. Moreover, PD-linked mutations in lysosomal-related genes, such as glucocerebrosidase, have been also shown to contribute to alpha-synuclein accumulation and related toxicity, indicating that lysosomal dysfunction may, in part, account for the neurodegeneration observed in synucleinopathies. In the current review, we summarize findings related to the inter-relationship between alpha-synuclein and lysosomal proteolytic pathways, focusing especially on recent experimental strategies based on the manipulation of the autophagy lysosomal pathway to counteract alpha-synuclein-mediated neurotoxicity in vivo. Pinpointing the factors that regulate alpha-synuclein association to the lysosome may represent potential targets for therapeutic interventions in PD and related synucleinopathies.
A major pathological feature of Parkinson's disease (PD) is the aberrant accumulation of misfolded assemblies of alpha‐synuclein (α‐Syn). Protein clearance appears as a regulator of the ‘α‐Syn ...burden’ underlying PD pathogenesis. The picture emerging is that a combination of pathways with complementary roles, including the Proteasome System and the Autophagy–Lysosome Pathway, contributes to the intracellular degradation of α‐Syn. This study addresses the mechanisms governing the degradation of α‐Syn species seeded by exogenous fibrils in neuronally differentiated SH‐SY5Y neuroblastoma cells with inducible expression of α‐Syn. Using human α‐Syn recombinant fibrils (pre‐formed fibrils, PFFs), seeding and aggregation of endogenous Proteinase K (PK)‐resistant α‐Syn species occurs within a time frame of 6 days, and is still prominent after 12 days of PFF addition. Clearance of α‐Syn assemblies in this inducible model was enhanced after switching off α‐Syn expression with doxycycline. Lysosomal inhibition led to accumulation of SDS‐soluble α‐Syn aggregates 6 days after PFF‐addition or when switching off α‐Syn expression. Additionally, the autophagic enhancer, rapamycin, induced the clearance of α‐Syn aggregates 13 days post‐PFF addition, indicating that autophagy is the major pathway for aggregated α‐Syn clearance. SDS‐soluble phosphorylated α‐Syn at S129 was only apparent at 7 days of incubation with a higher amount of PFFs. Proteasomal inhibition resulted in further accumulation of SDS‐soluble phosphorylated α‐Syn at S129, with limited PK resistance. Our data suggest that in this inducible model autophagy is mainly responsible for the degradation of fibrillar α‐Syn, whereas the proteasome system is responsible, at least in part, for the selective clearance of phosphorylated α‐Syn oligomers.
Different degradation pathways induce the clearance of distinct α‐Syn aggregated species. Upon incubation with recombinant fibrils (PFF), endogenous α‐Syn aggregates are formed and Autophagy serves as the major pathway for clearance. pS129 α‐Syn oligomers are apparent only upon incubation with high‐dose PFFs, and the Proteasome system is implicated in the degradation process. Our findings represent new and important insights into the biology of α‐Syn aggregation and turnover.
How is alpha‐synuclein cleared from the cell? Stefanis, Leonidas; Emmanouilidou, Evangelia; Pantazopoulou, Marina ...
Journal of neurochemistry,
September 2019, Letnik:
150, Številka:
5
Journal Article
Recenzirano
Odprti dostop
The levels and conformers of alpha‐synuclein are critical in the pathogenesis of Parkinson's Disease and related synucleinopathies. Homeostatic mechanisms in protein degradation and secretion have ...been identified as regulators of alpha‐synuclein at different stages of its intracellular trafficking and transcellular propagation. Here we review pathways involved in the removal of various forms of alpha‐synuclein from both the intracellular and extracellular environment. Proteasomes and lysosomes are likely to play complementary roles in the removal of intracellular alpha‐synuclein species, in a manner that depends on alpha‐synuclein post‐translational modifications. Extracellular alpha‐synuclein is cleared by extracellular proteolytic enzymes, or taken up by neighboring cells, especially microglia and astrocytes, and degraded within lysosomes. Exosomes, on the other hand, represent a vehicle for egress of excess burden of the intracellular protein, potentially contributing to the transfer of alpha‐synuclein between cells. Dysfunction in any one of these clearance mechanisms, or a combination thereof, may be involved in the initiation or progression of Parkinson's disease, whereas targeting these pathways may offer an opportunity for therapeutic intervention.
This article is part of the Special Issue “Synuclein”.
The levels and conformers of alpha‐synuclein are critical in the pathogenesis of synucleinopathies including Parkinson's Disease. This review is focused on the pathways involved in the removal of various forms of alpha‐synuclein either intracellularly (mainly by proteasomes and lysosomes) or extracellularly (by proteolytic enzymes). Uptake by neighbouring cells (neurons, microglia and astrocytes) of alpha‐synuclein, whose secretion could be partly mediated by exosomes, contributes to the clearance of the extracellular protein. Dysfunction in any one of these clearance mechanisms, or a combination thereof, could facilitate the initiation or progression of Parkinson's disease, whereas targeting these pathways may offer an opportunity for therapeutic intervention.
This article is part of the Special Issue “Synuclein”.
The mechanisms through which aberrant alpha-synuclein (ASYN) leads to neuronal death in Parkinson's disease (PD) are uncertain. In isolated liver lysosomes, mutant ASYNs impair Chaperone Mediated ...Autophagy (CMA), a targeted lysosomal degradation pathway; however, whether this occurs in a cellular context, and whether it mediates ASYN toxicity, is unknown. We have investigated presently the effects of WT or mutant ASYN on the lysosomal pathways of CMA and macroautophagy in neuronal cells and assessed their impact on ASYN-mediated toxicity.
Novel inducible SH-SY5Y and PC12 cell lines expressing human WT and A53T ASYN, as well as two mutant forms that lack the CMA-targeting motif were generated. Such forms were also expressed in primary cortical neurons, using adenoviral transduction. In each case, effects on long-lived protein degradation, LC3 II levels (as a macroautophagy index), and cell death and survival were assessed. In both PC12 and SH-SY5Y cycling cells, induction of A53T ASYN evoked a significant decrease in lysosomal degradation, largely due to CMA impairment. In neuronally differentiated SH-SH5Y cells, both WT and A53T ASYN induction resulted in gradual toxicity, which was partly dependent on CMA impairment and compensatory macroautophagy induction. In primary neurons both WT and A53T ASYN were toxic, but only in the case of A53T ASYN did CMA dysfunction and compensatory macroautophagy induction occur and participate in death.
Expression of mutant A53T, and, in some cases, WT ASYN in neuronal cells leads to CMA dysfunction, and this in turn leads to compensatory induction of macroautophagy. Inhibition of these lysosomal effects mitigates ASYN toxicity. Therefore, CMA dysfunction mediates aberrant ASYN toxicity, and may be a target for therapeutic intervention in PD and related disorders. Furthermore, macroautophagy induction in the context of ASYN over-expression, in contrast to other settings, appears to be a detrimental response, leading to neuronal death.
α-Synuclein in Parkinson's disease Stefanis, Leonidas
Cold Spring Harbor perspectives in medicine,
02/2012, Letnik:
2, Številka:
2
Journal Article
Recenzirano
Odprti dostop
α-Synuclein is a presynaptic neuronal protein that is linked genetically and neuropathologically to Parkinson's disease (PD). α-Synuclein may contribute to PD pathogenesis in a number of ways, but it ...is generally thought that its aberrant soluble oligomeric conformations, termed protofibrils, are the toxic species that mediate disruption of cellular homeostasis and neuronal death, through effects on various intracellular targets, including synaptic function. Furthermore, secreted α-synuclein may exert deleterious effects on neighboring cells, including seeding of aggregation, thus possibly contributing to disease propagation. Although the extent to which α-synuclein is involved in all cases of PD is not clear, targeting the toxic functions conferred by this protein when it is dysregulated may lead to novel therapeutic strategies not only in PD, but also in other neurodegenerative conditions, termed synucleinopathies.
Chaperone-mediated autophagy (CMA) involves the selective lysosomal degradation of cytosolic proteins such as SNCA (synuclein α), a protein strongly implicated in Parkinson disease (PD) pathogenesis. ...However, the physiological role of CMA and the consequences of CMA failure in the living brain remain elusive. Here we show that CMA inhibition in the adult rat substantia nigra via adeno-associated virus-mediated delivery of short hairpin RNAs targeting the LAMP2A receptor, involved in CMA's rate limiting step, was accompanied by intracellular accumulation of SNCA-positive puncta, which were also positive for UBIQUITIN, and in accumulation of autophagic vacuoles within LAMP2A-deficient nigral neurons. Strikingly, LAMP2A downregulation resulted in progressive loss of nigral dopaminergic neurons, severe reduction in striatal dopamine levels/terminals, increased astro- and microgliosis and relevant motor deficits. Thus, this study highlights for the first time the importance of the CMA pathway in the dopaminergic system and suggests that CMA impairment may underlie PD pathogenesis.
Summary Substantial genetic, neuropathological, and biochemical evidence implicates the presynaptic neuronal protein α-synuclein in Parkinson's disease and related Lewy body disorders. How ...dysregulation of α-synuclein leads to neurodegeneration is, however, unclear. Soluble oligomeric, but not fully fibrillar, α-synuclein is thought to be toxic. The major neuronal target of aberrant α-synuclein might be the synapse. The effects of aberrant α-synuclein might include alteration of calcium homoeostasis or mitochondrial fragmentation and, in turn, mitochondrial dysfunction, which could link α-synuclein dysfunction to recessive and toxin-induced parkinsonism. α-Synuclein also seems to be linked to other genetic forms of Parkinson's disease, such as those linked to mutations in GBA or LRRK2 , possibly through common effects on autophagy and lysosomal function. Finally, α-synuclein is physiologically secreted, and this extracellular form could lead to the spread of pathological accumulations and disease progression. Consequently, factors that regulate the levels, post-translational modifications, specific aberrant cellular effects, or secretion of α-synuclein might be targets for therapy.
The autophagy-lysosomal pathway is a major proteolytic pathway that in mammalian systems mainly comprises of macroautophagy and chaperone-mediated autophagy. The former is relatively non-selective ...and involves bulk degradation of proteins and organelles, whereas the latter is selective for certain cytosolic proteins. These autophagy pathways are important in development, differentiation, cellular remodeling and survival during nutrient starvation. Autophagy is crucial for neuronal homeostasis and acts as a local housekeeping process, since neurons are post-mitotic cells and require effective protein degradation to prevent accumulation of toxic aggregates. A growing body of evidence now suggests that dysfunction of autophagy causes accumulation of abnormal proteins and/or damaged organelles. Such accumulation has been linked to synaptic dysfunction, cellular stress and neuronal death. Abnormal autophagy may be involved in the pathology of both chronic nervous system disorders, such as proteinopathies (Alzheimer's, Parkinson's, Huntington's disease) and acute brain injuries. Although autophagy is generally beneficial, its aberrant activation may also exert a detrimental role in neurological diseases depending on the environment and the insult, leading to autophagic neuronal death. In this review we summarize the current knowledge regarding the role of autophagy-lysosomal pathway in the central nervous system and discuss the implication of autophagy dysregulation in human neurological diseases and animal models.
Background
Driving is a complex task requiring the integrity and the cooperation of cognition, motor, and somatosensory skills, all of which are impacted by neurological diseases.
Objective
...Identification of neurologist’s role when assessing fitness to drive of cognitively impaired individuals.
Methods
We performed a systematic review of the guidelines/recommendations (G/Rs) regarding the evaluation of driving fitness of patients with mild cognitive impairment (MCI) and/or dementia. Emphasis was put on the neurological and neuropsychological aspects of the evaluation.
Results
Eighteen G/Rs were included in the review (9 national guidelines, 5 recommendation papers, 3 consensus statements, and 1 position paper). All G/Rs referred to drivers with dementia and 9/18 referred to drivers with MCI. A common approach among G/Rs is the initial trichotomization of patients in safe to drive, unsafe to drive, and undetermined cases, which are referred to a second-line evaluator. First-line evaluators are general practitioners in 10/18 G/Rs; second-line evaluators are neurologists in 7/18 G/Rs. Specific neuropsychological tests are proposed in 11/18 G/Rs and relative cut-off values in 7/18. The most commonly used tests are the MMSE, TMT, and CDT. A thorough neurological examination is proposed in only 1/18 G/R.
Conclusion
Although extensive multi-disciplinary research has provided useful information for driving behavior of cognitively impaired individuals, we are still far from a widely accepted approach of driving ability evaluation in this increasing population. A comprehensive assessment from a multi-disciplinary team in which the neurologist plays a critical role seems to be required, although this has not yet been implemented in any G/Rs.
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