Rab7 induces clearance of α-synuclein aggregates

FYCO1 mediates clearance of α-synuclein aggregates through a Rab7-dependent mechanism

Parkinson's disease can be caused by mutations in the α-synuclein gene and is characterized by aggregates of α-synuclein protein. We have previously shown that over-expression of the small GTPase Rab7 can induce clearance of α-synuclein aggregates. In this study, we investigate which Rab7 effectors mediate this effect. To model Parkinson's disease, we expressed the pathogenic A53T mutant of α-synuclein in HEK293T cells and Drosophila melanogaster. We tested the Rab7 effectors FYVE and coiled-coil domain-containing protein 1 (FYCO1) and Rab-interacting lysosomal protein (RILP). FYCO1-EGFP-decorated vesicles containing α-synuclein. RILP-EGFP also decorated vesicular structures, but they did not contain α-synuclein. FYCO1 over-expression reduced the number of cells with α-synuclein aggregates, defined as visible particles of EGFP-tagged α-synuclein, whereas RILP did not. FYCO1 but not RILP reduced the amount of α-synuclein protein as assayed by western blot, increased the disappearance of α-synuclein aggregates in time-lapse microscopy and decreased α-synuclein-induced toxicity assayed by the Trypan blue assay. siRNA-mediated knockdown of FYCO1 but not RILP reduced Rab7-induced aggregate clearance. Collectively, these findings indicate that FYCO1 and not RILP mediates Rab7-induced aggregate clearance. The effect of FYCO1 on aggregate clearance was blocked by dominant negative Rab7 indicating that FYCO1 requires active Rab7 to function. Electron microscopic analysis and insertion of lysosomal membranes into the plasma membrane indicate that FYCO1 could lead to secretion of α-synuclein aggregates. Extracellular α-synuclein as assayed by ELISA was, however, not increased with FYCO1. Coexpression of FYCO1 in the fly model decreased α-synuclein aggregates as shown by the filter trap assay and rescued the locomotor deficit resulting from neuronal A53T-α-synuclein expression. This latter finding confirms that a pathway involving Rab7 and FYCO1 stimulates degradation of α-synuclein and could be beneficial in patients with Parkinson's disease. Open Data: Materials are available on https://cos.io/our-services/open-science-badges/ https://osf.io/93n6m/.

Autophagy and lysosomal pathways in nervous system disorders

Autophagy is an evolutionarily conserved pathway for delivering cytoplasmic cargo to lysosomes for degradation. In its classically studied form, autophagy is a stress response induced by starvation to recycle building blocks for essential cellular processes. In addition, autophagy maintains basal cellular homeostasis by degrading endogenous substrates such as cytoplasmic proteins, protein aggregates, damaged organelles, as well as exogenous substrates such as bacteria and viruses. Given their important role in homeostasis, autophagy and lysosomal machinery are genetically linked to multiple human disorders such as chronic inflammatory diseases, cardiomyopathies, cancer, and neurodegenerative diseases. Multiple targets within the autophagy and lysosomal pathways offer therapeutic opportunities to benefit patients with these disorders. Here, I will summarize the mechanisms of autophagy pathways, the evidence supporting a pathogenic role for disturbed autophagy and lysosomal degradation in nervous system disorders, and the therapeutic potential of autophagy modulators in the clinic.

Modeling Parkinson's Disease in Drosophila: What Have We Learned for Dominant Traits?

Parkinson’s disease (PD) is recognized as the second most common neurodegenerative disorder after Alzheimer’s disease. Unfortunately, there is no cure or proven disease modifying therapy for PD. The recent discovery of a number of genes involved in both sporadic and familial forms of PD has enabled disease modeling in easily manipulable model systems. Various model systems have been developed to study the pathobiology of PD and provided tremendous insights into the molecular mechanisms underlying dopaminergic neurodegeneration. Among all the model systems, the power of Drosophila has revealed many genetic factors involved in the various pathways, and provided potential therapeutic targets. This review focuses on Drosophila models of PD, with emphasis on how Drosophila models have provided new insights into the mutations of dominant genes causing PD and what are the convergent mechanisms.

RTP801 is a critical factor in the neurodegeneration process of A53T α-synuclein in a mouse model of Parkinson's disease under chronic restraint stress

BACKGROUND AND PURPOSE

Recently, the incidence of Parkinson's disease has shown a tendency to move to a younger population, linked to the constantly increasing stressors of modern society. However, this relationship remains obscure. Here, we have investigated the contribution of stress and the mechanisms underlying this change.

EXPERIMENTAL APPROACH

Ten-month-old α-synuclein A53T mice, a model of Parkinson's disease (PD), were treated with chronic restraint stress (CRS) to simulate a PD-sensitive person with constant stress stimulation. PD-like behavioural tests and pathological changes were evaluated. Differentiated PC12-A53T cells were treated with corticosterone in vitro. We used Western blot, microRNA expression analysis, immunofluorescence staining, dual luciferase reporter assay and HPLC electrochemical detection to assess cellular and molecular networks after stress treatment. In vivo, stereotaxic injection of shRNA lentivirus was used to confirm our in vitro results.

KEY RESULTS

The protein RTP801 is encoded by DNA-damage-inducible transcript 4, and it was specifically increased in dopaminergic neurons of the substantia nigra after CRS treatment. RTP801 was post-transcriptionally inhibited by the down-regulation of miR-7. Delayed turnover of RTP801, through the inhibition of proteasome degradation also contributed to its high content. Elevated RTP801 blocked autophagy, thus increasing accumulation of oligomeric α-synuclein and aggravating endoplasmic reticulum stress. RTP801 inhibition alleviated the symptoms of neurodegeneration during this process.

CONCLUSIONS AND IMPLICATIONS

RTP801 is a promising target for the treatment of PD, especially for PD-sensitive patients who live under increased social pressure. Down-regulation of RTP801 could inhibit the current tendency to an earlier onset of PD.

Alpha-synuclein, epigenetics, mitochondria, metabolism, calcium traffic, & circadian dysfunction in Parkinson's disease. An integrated strategy for management

The motor deficits which characterise the sporadic form of Parkinson's disease arise from age-related loss of a subset of dopamine neurons in the substantia nigra. Although motor symptoms respond to dopamine replacement therapies, the underlying disease process remains. This review details some features of the progressive molecular pathology and proposes deployment of a combination of nutrients: R-lipoic acid, acetyl-l-carnitine, ubiquinol, melatonin (or receptor agonists) and vitamin D3, with the collective potential to slow progression of these features. The main nutrient targets include impaired mitochondria and the associated oxidative/nitrosative stress, calcium stress and impaired gene transcription induced by pathogenic forms of alpha- synuclein. Benefits may be achieved via nutrient influence on epigenetic signaling pathways governing transcription factors for mitochondrial biogenesis, antioxidant defences and the autophagy-lysosomal pathway, via regulation of the metabolic energy sensor AMP activated protein kinase (AMPK) and the mammalian target of rapamycin mTOR. Nutrients also benefit expression of the transcription factor for neuronal survival (NR4A2), trophic factors GDNF and BDNF, and age-related calcium signals. In addition a number of non-motor related dysfunctions in circadian control, clock genes and associated metabolic, endocrine and sleep-wake activity are briefly addressed, as are late-stage complications in respect of cognitive decline and osteoporosis. Analysis of the network of nutrient effects reveals how beneficial synergies may counter the accumulation and promote clearance of pathogenic alpha-synuclein.

The LRRK2-macroautophagy axis and its relevance to Parkinson's disease

A wide variety of different functions and an impressive array of interactors have been associated with leucine-rich repeat kinase 2 (LRRK2) over the years. Here, I discuss the hypothesis that LRRK2 may be capable of interacting with different proteins at different times and places, therefore, controlling a plethora of diverse functions based on the different complexes formed. Among these, I will then focus on macroautophagy in the general context of the endolysosomal system. First, the relevance of autophagy in Parkinson's disease will be evaluated giving a brief overview of all the relevant Parkinson's disease genes; then, the association of LRRK2 with macroautophagy and the endolysosomal pathway will be analyzed based on the supporting literature.