Update on the association between alpha-synuclein and tau with mitochondrial dysfunction: Implications for Parkinson's disease

Pathogenesis of Neurodegenerative Diseases and the Protective Role of Natural Bioactive Components

Neurodegenerative diseases are a serious problem throughout the world. There are several causes of neurodegenerative diseases; these include genetic predisposition, accumulation of misfolded proteins, oxidative stress, neuroinflammation, and excitotoxicity. Oxidative stress increases the production of reactive oxygen species (ROS) that advance lipid peroxidation, DNA damage, and neuroinflammation. The cellular antioxidant system (superoxide dismutase, catalase, peroxidase, and reduced glutathione) plays a crucial role in scavenging free radicals. An imbalance in the defensive actions of antioxidants and overproduction of ROS intensify neurodegeneration. The formation of misfolded proteins, glutamate toxicity, oxidative stress, and cytokine imbalance promote the pathogenesis of Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis. Antioxidants are now attractive molecules to fight against neurodegeneration. Certain vitamins (A, E, C) and polyphenolic compounds (flavonoids) show excellent antioxidant properties. Diet is the major source of antioxidants. However, diet medicinal herbs are also rich sources of numerous flavonoids. Antioxidants prevent ROS-mediated neuronal degeneration in post-oxidative stress conditions. The present review is focused on the pathogenesis of neurodegenerative diseases and the protective role of antioxidants. KEY TEACHING POINTSThis review shows that multiple factors are directly or indirectly associated with the pathogenesis of neurodegenerative diseases.Failure to cellular antioxidant capacity increases oxidative stress that intensifies neuroinflammation and disease progression.Different vitamins, carotenoids, and flavonoids, having antioxidant capacity, can be considered protective agents.

Mitochondrial Dysfunction as a Signaling Target for Therapeutic Intervention in Major Neurodegenerative Disease

Neurodegenerative diseases (NDD) are incurable and the most prevalent cognitive and motor disorders of elderly. Mitochondria are essential for a wide range of cellular processes playing a pivotal role in a number of cellular functions like metabolism, intracellular signaling, apoptosis, and immunity. A plethora of evidence indicates the central role of mitochondrial functions in pathogenesis of many aging related NDD. Considering how mitochondria function in neurodegenerative diseases, oxidative stress, and mutations in mtDNA both contribute to aging. Many substantial reports suggested the involvement of numerous contributing factors including, mitochondrial dysfunction, oxidative stress, mitophagy, accumulation of somatic mtDNA mutations, compromised mitochondrial dynamics, and transport within axons in neurodegenerative disorders including Alzheimer's disease, Parkinson's disease, Huntington's disease, and Amyotrophic Lateral Sclerosis. Therapies therefore target fundamental mitochondrial processes such as energy metabolism, free-radical generation, mitochondrial biogenesis, mitochondrial redox state, mitochondrial dynamics, mitochondrial protein synthesis, mitochondrial quality control, and metabolism hold great promise to develop pharmacological based therapies in NDD. By emphasizing the most efficient pharmacological strategies to target dysfunction of mitochondria in the treatment of neurodegenerative diseases, this review serves the scientific community engaged in translational medical science by focusing on the establishment of novel, mitochondria-targeted treatment strategies.

Neuroprotective Effects of Tinospora cordifolia via Reducing the Oxidative Stress and Mitochondrial Dysfunction against Rotenone-Induced PD Mice

Oxidative stress and mitochondrial dysfunction are leading mechanisms that play a crucial role in the progression of Parkinson's disease (PD). Tinospora cordifolia shows a wide range of biological activities including immunomodulatory, antimicrobial, antioxidant, and anti-inflammatory properties. This study explored the neuroprotective activities of T. cordifolia ethanolic extract (TCE) against Rotenone (ROT)-intoxicated Parkinsonian mice. Four experimental groups of mice were formed: control, ROT (2 mg/kg body wt, subcutaneously), TCE (200 mg/kg body wt, oral) + ROT, and TCE only. Mice were pretreated with TCE for a week and then simultaneously injected with ROT for 35 days. Following ROT-intoxication, motor activities, antioxidative potential, and mitochondrial dysfunction were analyzed. Decrease in the activity of the mitochondrial electron transport chain (mETC) complex, loss of mitochondrial membrane potential (Ψm), increase in Bax/Bcl-2 (B-cell lymphoma 2) ratio, and caspase-3 expression are observed in the ROT-intoxicated mice group. Our results further showed ROT-induced reactive oxygen species (ROS)-mediated alpha-synuclein (α-syn) accumulation and mitochondrial dysfunction. However, pre- and cotreatment with TCE along with ROT-intoxication significantly reduced α-syn aggregation and improved mitochondrial functioning in cells by altering mitochondrial potential and increasing mETC activity. TCE also decreases the Bax/Bcl-2 ratio and also the expression of caspase-3, thus reducing apoptosis of the cell. Altogether, TCE is effective in protecting neurons from rotenone-induced cytotoxicity in the Parkinsonian mouse model by modulating oxidative stress, ultimately reducing mitochondrial dysfunction and cell death.

Genetic modifiers of synucleinopathies-lessons from experimental models

α-Synuclein is a pleiotropic protein underlying a group of progressive neurodegenerative diseases, including Parkinson's disease and dementia with Lewy bodies. Together, these are known as synucleinopathies. Like all neurological diseases, understanding of disease mechanisms is hampered by the lack of access to biopsy tissues, precluding a real-time view of disease progression in the human body. This has driven researchers to devise various experimental models ranging from yeast to flies to human brain organoids, aiming to recapitulate aspects of synucleinopathies. Studies of these models have uncovered numerous genetic modifiers of α-synuclein, most of which are evolutionarily conserved. This review discusses what we have learned about disease mechanisms from these modifiers, and ways in which the study of modifiers have supported ongoing efforts to engineer disease-modifying interventions for synucleinopathies.

Fibril treatment changes protein interactions of tau and α-synuclein in human neurons

In several neurodegenerative disorders, the neuronal proteins tau and α-synuclein adopt aggregation-prone conformations capable of replicating within and between cells. To better understand how these conformational changes drive neuropathology, we compared the interactomes of tau and α-synuclein in the presence or the absence of recombinant fibril seeds. Human embryonic stem cells with an inducible neurogenin-2 transgene were differentiated into glutamatergic neurons expressing (1) WT 0N4R tau, (2) mutant (P301L) 0N4R tau, (3) WT α-synuclein, or (4) mutant (A53T) α-synuclein, each genetically fused to a promiscuous biotin ligase (BioID2). Neurons expressing unfused BioID2 served as controls. After treatment with fibrils or PBS, interacting proteins were labeled with biotin in situ and quantified using mass spectrometry via tandem mass tag labeling. By comparing interactions in mutant versus WT neurons and in fibril- versus PBS-treated neurons, we observed changes in protein interactions that are likely relevant to disease progression. We identified 45 shared interactors, suggesting that tau and α-synuclein function within some of the same pathways. Potential loci of shared interactions include microtubules, Wnt signaling complexes, and RNA granules. Following fibril treatment, physiological interactions decreased, whereas other interactions, including those between tau and 14-3-3 η, increased. We confirmed that 14-3-3 proteins, which are known to colocalize with protein aggregates during neurodegeneration, can promote or inhibit tau aggregation in vitro depending on the specific combination of 14-3-3 isoform and tau sequence.

Mitochondrial dysfunctions, oxidative stress and neuroinflammation as therapeutic targets for neurodegenerative diseases: An update on current advances and impediments

Neurodegenerative diseases (NDs) such as Alzheimer disease (AD), Parkinson disease (PD), and Huntington disease (HD) represent a major socio-economic challenge in view of their high prevalence yet poor treatment outcomes affecting quality of life. The major challenge in drug development for these NDs is insufficient clarity about the mechanisms involved in pathogenesis and pathophysiology. Mitochondrial dysfunction, oxidative stress and inflammation are common pathways that are linked to neuronal abnormalities and initiation of these diseases. Thus, elucidating the shared initial molecular and cellular mechanisms is crucial for recognizing novel remedial targets, and developing therapeutics to impede or stop disease progression. In this context, use of multifunctional compounds at early stages of disease development unclogs new avenues as it acts on act on multiple targets in comparison to single target concept. In this review, we summarize overview of the major findings and advancements in recent years focusing on shared mechanisms for better understanding might become beneficial in searching more potent pharmacological interventions thereby reducing the onset or severity of various NDs.

Sulforaphane Upregulates Cultured Mouse Astrocytic Aquaporin-4 Expression through p38 MAPK Pathway

Protein misfolding and/or aggregation are common pathological features associated with a number of neurodegenerative diseases, including Alzheimer's disease (AD) and Parkinson disease (PD). Abnormal protein aggregation may be caused by misfolding of the protein and/or dysfunction of the protein clearance system. Recent studies have demonstrated that the specific water channel protein, aquaporin-4 (AQP4), plays a role in the pathogenesis of neurodegenerative diseases involving protein clearance system. In this study, we aimed to investigate the role of sulforaphane (SFN) in the upregulation of AQP4 expression, along with its underlying mechanism using cultured mouse astrocytes as a model system. At low concentrations, SFN was found to increase cell proliferation and result in the activation of astrocytes. However, high SFN concentrations were found to suppress cell proliferation of astrocytes. In addition, our study found that a 1 μM concentration of SFN resulted in the upregulation of AQP4 expression and p38 MAPK phosphorylation in cultured mouse astrocytes. Moreover, we demonstrated that the upregulation of AQP4 expression was significantly attenuated when cells were pretreated with SB203580, a p38 MAPK inhibitor. In conclusion, our findings from this study revealed that SFN exerts hormesis effect on cultured mouse astrocytes and can upregulate astrocytic AQP4 expression by targeting the p38 MAPK pathway.

Exploration of the α-syn/T199678/miR-519-3p/KLF9 pathway in a PD-related α-syn pathology

BACKGROUND

Kruppel-like factor 9 (KLF9) plays a key role as an inducer of cellular oxidative stress in the modulation of cell death and in oxidant-dependent tissue injury. Our previous study indicated that lncRNA-T199678 (T199678) affected the expression of KLF9 in an α-synuclein (α-syn) induced cellular model. However, the roles of interactions among α-syn, T199678, KLF9 and related microRNAs (miRNAs) in the Parkinson's disease (PD)-related α-syn pathology are unclear and were therefore investigated in this study.

METHODS

An α-syn-injected mouse model and an α-syn exposed SY-SH5Y cellular model were used in this study. We confirmed the utility of these established models with morphological and behavioral methods. We checked how expression of T199678 and KLF9 were affected by α-syn and demonstrated their interaction by fluorescence in situ hybridization (FISH) staining and western blots. We analyzed expression in ROS+ cells by immunohistochemistry. Finally, we obtained seven miRNAs through bioinformatic analysis simultaneously affected by T199678 and α-syn and verified these with RT-PCR.

RESULTS

We found that expression of KLF9 was regulated by T199678, whereas expression of T199678 was not affected by KLF9 in the α-syn exposed SY-SH5Y cells. These findings suggest that KLF9 is the downstream gene regulated by T199678, whereas miR-519-3p may play a contributing role. We also confirmed that α-syn injection upregulated the expression of ROS, which could be downregulated by upregulation of T199678, indicating an anti-oxidative role of T199678 in the α-syn-related mechanisms.

CONCLUSIONS

Our results indicate the existence of a potential α-syn/T199678/miR-519-3p /KLF9 pathway in PD-related α-syn pathology. This pathway might explain oxidative stress processes in α-syn-related mechanisms, which requires further verification.

Neuroprotective effect of Ginsenoside Re against neurotoxin‑induced Parkinson's disease models via induction of Nrf2

The aim of the present study was to examine the neuroprotective effects of a panel of active components of ginseng and to explore their molecular mechanisms of action in two rotenone (Rot)-induced models of Parkinson's disease: An in vitro model using the human neuroblastoma cell line SH-SY5Y and an in vivo model using Drosophila. Ginsenoside Re (Re) was identified as the most potent inhibitor of Rot-induced cytotoxicity in SH-SY5Y cells by Cell Counting kit-8 assay and lactate dehydrogenase release assay. Flow cytometry, Hoechst staining, Rhodamine 123 staining, ATP and cytochrome c release revealed that Re rescue of Rot-induced mitochondrial dysfunction and inhibition of the mitochondrial apoptotic pathway. Western blot analysis demonstrated that Re alleviated Rot-induced oxidative stress by activating the nuclear factor erythroid 2-related factor 2 (Nrf2) anti-oxidant pathway, and these effects were abolished by RNA interference-mediated knockdown of Nrf2. Re enhanced phosphorylation of components of the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT) and extracellular regulated protein kinase (ERK) pathways, and pharmacological inhibition of these pathways reduced Re-mediated Nrf2 activation and neuroprotection. In the Drosophila model, Immunofluorescence microscopy, reactive oxygen species (ROS), hydrogen peroxide and knockdown analysis revealed that Re reversed Rot-induced motor deficits and dopaminergic neuron loss while concomitantly alleviating Rot-induced oxidative damage. The findings of the present study suggest that Re protects neurons against Rot-induced mitochondrial dysfunction and oxidative damage, at least in part, by inducing Nrf2/heme oxygenase-1 expression and activation of the dual PI3K/AKT and ERK pathways.

Severe Primary Open-Angle Glaucoma and Agricultural Profession: A Retrospective Cohort Study

While exposure to pesticides is a known risk factor for neurodegenerative brain diseases, little is known about the influence of environment on glaucoma neuropathy. We aimed to determine whether farmers are at higher risk of developing severe primary open-angle glaucoma (POAG). This retrospective cohort study (tertiary referral center, Reims University Hospital, France) included patients diagnosed with POAG in the last two years. Univariate analysis and adjusted multivariate logistic regression were performed to evaluate the association between agricultural profession and all recorded data. Glaucoma severity (primary outcome) and the number of patients who underwent filtering surgery (secondary outcome) were analyzed. In total, 2065 records were screened, and 772 patients were included (66 in the farmer group and 706 in the nonfarmer group). The risk of severe glaucoma was higher in the farmer group (adjusted odds ratio (aOR) 1.87, p = 0.03). More patients underwent filtering surgery in the farmer group in univariate analysis (p = 0.02) but with no statistical significance after adjustment (p = 0.08). These results suggest pesticide exposure may be a factor accelerating the neurodegeneration in POAG, although a direct link between the agricultural profession and the disease requires further extended studies to be demonstrated.

Mitochondria-Microbiota Interaction in Neurodegeneration

Alzheimer’s and Parkinson’s are the two best-known neurodegenerative diseases. Each is associated with the excessive aggregation in the brain and elsewhere of its own characteristic amyloid proteins. Yet the two afflictions have much in common and often the same amyloids play a role in both. These amyloids need not be toxic and can help regulate bile secretion, synaptic plasticity, and immune defense. Moreover, when they do form toxic aggregates, amyloids typically harm not just patients but their pathogens too. A major port of entry for pathogens is the gut. Keeping the gut’s microbe community (microbiota) healthy and under control requires that our cells’ main energy producers (mitochondria) support the gut-blood barrier and immune system. As we age, these mitochondria eventually succumb to the corrosive byproducts they themselves release, our defenses break down, pathogens or their toxins break through, and the side effects of inflammation and amyloid aggregation become problematic. Although it gets most of the attention, local amyloid aggregation in the brain merely points to a bigger problem: the systemic breakdown of the entire human superorganism, exemplified by an interaction turning bad between mitochondria and microbiota.

FRET-based assay for intracellular evaluation of α-synuclein aggregation inhibitors

Aggregation of small neuronal protein α-synuclein (αSyn) in amyloid fibrils is considered to be one of the main causes of Parkinson's disease. Inhibition of this aggregation is a promising approach for disease treatment. Dozens of compounds able to inhibit αSyn fibrillization in solution were developed during the last decade. However, the applicability of most of them in the cellular environment was not established because of the absence of a suitable cell-based assay. In this work, we developed an assay for testing αSyn aggregation inhibitors in cells that is based on fluorescence resonance energy transfer (FRET) between labeled αSyn molecules in fibrils. The assay directly reports the amount of fibrillized αSyn and is more reliable than the assays based on cell viability. Moreover, we showed that cell viability decline does not always correlate with the amount of misfolded αSyn. The developed FRET-based assay does not interfere with the aggregation process and is suitable for high-throughput testing of αSyn aggregation inhibitors. Its application can sort out non-specific inhibitors and thus significantly facilitate the development of drugs for Parkinson`s disease.

Annexin A2 degradation contributes to dopaminergic cell apoptosis via regulating p53 in neurodegenerative conditions

BACKGROUND

P53 overexpression has been shown to involve in mitochondria-mediated dapaminergic neuron cell death in Parkinson's disease. However, the exactly molecular mechanisms responsible for the p53-dependent intrinsic cell death in neurodegenerative conditions remain unclearly. Annexin A2 is a multifunctional protein that negatively regulates p53 expression. The purpose of this study was to explore the mechanism of p53 dependent dopaminergic cell death and implication of Annexin A2 in cellular apoptosis in 1-methyl-4-phenylpyridinium (MPP+)-induced PC12 cells.

METHODS

The cell viability of neural PC12 cells was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltet-razolium bromide assay. Flow cytometry was used to evaluate the apoptosis and mitochondrial transmembrane potential of neural PC12 cells. The expression of p53 and Annexin A2 was analyzed by western blot assay.

RESULTS

The present study showed that the exposure of PC12 cells to neurotoxin MPP+ increased the expression levels of p53 and the discharge of mitochondrial transmembrane potential. Notably, Annexin A2 degradation was also observed in this cellular model of Parkinson's disease, in a time and dose-dependent manner. This expressing change of Annexin A2 was in direct proportion to the loss of cell viability of PC12 cells, and this expression pattern was in inverse proportion to p53 levels in this cellular model of Parkinson's disease.

CONCLUSION

These results indicated that Annexin A2 degradation plays a crucial role the degeneration of dapaminergic cells of Parkinson's disease, and Annexin A2 downregulation-mediated the cell death is closely associated with mitochondrial dysfunction via p53-dependent pathway; thus provide a novel therapeutic target for Parkinson's disease treatment.

Roles for α-Synuclein in Gene Expression

α-Synuclein (α-Syn) is a small cytosolic protein associated with a range of cellular compartments, including synaptic vesicles, the nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, and lysosomes. In addition to its physiological role in regulating presynaptic function, the protein plays a central role in both sporadic and familial Parkinson’s disease (PD) via a gain-of-function mechanism. Because of this, several recent strategies propose to decrease α-Syn levels in PD patients. While these therapies may offer breakthroughs in PD management, the normal functions of α-Syn and potential side effects of its depletion require careful evaluation. Here, we review recent evidence on physiological and pathological roles of α-Syn in regulating activity-dependent signal transduction and gene expression pathways that play fundamental role in synaptic plasticity.

Inhibition of dynamin-related protein 1 ameliorates the mitochondrial ultrastructure via PINK1 and Parkin in the mice model of Parkinson's disease

Parkinson's disease (PD) is the prevalent neurodegenerative disorder characterized by the degeneration of the nigrostriatal neurons. Dynamin-related protein 1 (Drp1) is a key regulator mediating mitochondrial fission and affecting mitophagy in neurons. It has been reported that the inhibition of Drp1 may be beneficial to PD. However, the role of Drp1 and mitophagy in PD remains elusive. Therefore, in this research, we investigated the role of Drp1 and the underlying mechanisms in the mice model of PD. We used the dynasore, a GTPase inhibitor, to inhibit the expression of Drp1. We found that inhibition of Drp1 could ameliorate the motor deficits and the expression of tyrosine hydroxylase in the mice of the PD model. But Drp1 inhibition did not affect mitochondria number and morphological parameters. Moreover, suppression of Drp1 up-regulated the mitochondrial expressions of PINK1 and Parkin while not affected the expressions of NIX and BNIP3. Conclusively, our findings suggest that the inhibition of Drp1 ameliorated the mitochondrial ultrastructure at least via regulating PINK1 and Parkin in the mice of the PD model. This study also implicates that inhibition of Drp1 might impact mitophagy and recover mitochondrial homeostasis in PD.

Mitophagy, a Form of Selective Autophagy, Plays an Essential Role in Mitochondrial Dynamics of Parkinson's Disease

Parkinson's disease (PD) is a severe neurodegenerative disorder caused by the progressive loss of dopaminergic neurons in the substantia nigra and affects millions of people. Currently, mitochondrial dysfunction is considered as a central role in the pathogenesis of both sporadic and familial forms of PD. Mitophagy, a process that selectively targets damaged or redundant mitochondria to the lysosome for elimination via the autophagy devices, is crucial in preserving mitochondrial health. So far, aberrant mitophagy has been observed in the postmortem of PD patients and genetic or toxin-induced models of PD. Except for mitochondrial dysfunction, mitophagy is involved in regulating several other PD-related pathological mechanisms as well, e.g., oxidative stress and calcium imbalance. So far, the mitophagy mechanisms induced by PD-related proteins, PINK1 and Parkin, have been studied widely, and several other PD-associated genes, e.g., DJ-1, LRRK2, and alpha-synuclein, have been discovered to participate in the regulation of mitophagy as well, which further strengthens the link between mitophagy and PD. Thus, in this view, we reviewed mitophagy pathways in belief and discussed the interactions between mitophagy and several PD's pathological mechanisms and how PD-related genes modulate the mitophagy process.

Role of mitophagy in mitochondrial quality control: Mechanisms and potential implications for neurodegenerative diseases

Neurodegenerative diseases (e.g., Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis) commonly characterized by the gradual loss of neurons have a seriously bad impact on motor and cognitive abilities of affected humans and bring great inconvenience to their lives. Mitochondrial dysfunction has been considered the key and common factor for the pathologies of neurodegenerative diseases for that neurons are extremely energy-intensive due to their unique properties in structures and functions. Thus, mitophagy, as a central role of mitochondrial quality control and currently believed to be the most effective pathway to clear dysfunctional or unwanted mitochondria, is rather crucial in the preservation of neuronal health. In addition, mitophagy establishes an intimated link with several other pathways of mitochondrial quality control (e.g., mitochondrial biogenesis and mitochondrial dynamics), and they work together to preserve mitochondrial health. Therefore, in this review, we summarized the recent process on the mechanisms of mitophagy pathways in mammals, it's linking to mitochondrial quality control, its role in several major neurodegenerative diseases, and possible therapeutic interventions focusing on mitophagy pathways. And we expect that it can provide us with more understanding of the mitophagy pathways and more promising approaches for the treatment of neurodegenerative diseases.

(D620N) VPS35 causes the impairment of Wnt/β-catenin signaling cascade and mitochondrial dysfunction in a PARK17 knockin mouse model

Patients with familial type 17 of Parkinson’s disease (PARK17) manifest autosomal dominant pattern and late-onset parkinsonian syndromes. Heterozygous (D620N) mutation of vacuolar protein sorting 35 (VPS35) is genetic cause of PARK17. We prepared heterozygous VPS35^D620N/+ knockin mouse, which is an ideal animal model of (D620N) VPS35-induced autosomal dominant PARK17. Late-onset loss of substantia nigra pars compacta (SNpc) dopaminergic (DAergic) neurons and motor deficits of Parkinson’s disease were found in 16-month-old VPS35^D620N/+ mice. Normal function of VPS35-containing retromer is needed for activity of Wnt/β-catenin cascade, which participates in protection and survival of SNpc DAergic neurons. It was hypothesized that (D620N) VPS35 mutation causes the malfunction of VPS35 and resulting impaired activity of Wnt/β-catenin pathway. Protein levels of Wnt1 and nuclear β-catenin were reduced in SN of 16-month-old VPS35^D620N/+ knockin mice. Downregulated protein expression of survivin, which is a target gene of nuclear β-catenin, and upregulated protein levels of active caspase-8 and active caspase-9 were observed in SN of VPS35^D620N/+ mice at age of 16 months. VPS35 is involved in controlling morphology and function of mitochondria. Impaired function of VPS35 caused by (D620N) mutation could lead to abnormal morphology and malfunction of mitochondria. A significant decrease in mitochondrial size and resulting mitochondrial fragmentation was found in tyrosine hydroxylase-positive and neuromelanin-positive SNpc DAergic neurons of 16-month-old VPS35^D620N/+ mice. Mitochondrial complex I activity or complex IV activity was reduced in SN of 16-month-old VPS35^D620N/+ mice. Increased level of mitochondrial ROS and oxidative stress were found in SN of 16-month-old VPS35^D620N/+ mice. Levels of cytosolic cytochrome c and active caspase-3 were increased in SN of VPS35^D620N/+ mice aged 16 months. Our results suggest that PARK17 mutant (D620N) VPS35 impairs activity of Wnt/β-catenin signaling pathway and causes abnormal morphology and dysfunction of mitochondria, which could lead to neurodegeneration of SNpc DAergic cells.

Tau and Alpha Synuclein Synergistic Effect in Neurodegenerative Diseases: When the Periphery Is the Core

In neuronal cells, tau is a microtubule-associated protein placed in axons and alpha synuclein is enriched at presynaptic terminals. They display a propensity to form pathologic aggregates, which are considered the underlying cause of Alzheimer's and Parkinson's diseases. Their functional impairment induces loss of axonal transport, synaptic and mitochondrial disarray, leading to a "dying back" pattern of degeneration, which starts at the periphery of cells. In addition, pathologic spreading of alpha-synuclein from the peripheral nervous system to the brain through anatomical connectivity has been demonstrated for Parkinson's disease. Thus, examination of the extent and types of tau and alpha-synuclein in peripheral tissues and their relation to brain neurodegenerative diseases is of relevance since it may provide insights into patterns of protein aggregation and neurodegeneration. Moreover, peripheral nervous tissues are easily accessible in-vivo and can play a relevant role in the early diagnosis of these conditions. Up-to-date investigations of tau species in peripheral tissues are scant and have mainly been restricted to rodents, whereas, more evidence is available on alpha synuclein in peripheral tissues. Here we aim to review the literature on the functional role of tau and alpha synuclein in physiological conditions and disease at the axonal level, their distribution in peripheral tissues, and discuss possible commonalities/diversities as well as their interaction in proteinopathies.

Parkin, an E3 Ubiquitin Ligase, Plays an Essential Role in Mitochondrial Quality Control in Parkinson's Disease

Parkinson's disease (PD), as one of the complex neurodegenerative disorders, affects millions of aged people. Although the precise pathogenesis remains mostly unknown, a significant number of studies have demonstrated that mitochondrial dysfunction acts as a major role in the pathogeny of PD. Both nuclear and mitochondrial DNA mutations can damage mitochondrial integrity. Especially, mutations in several genes that PD-linked have a closed association with mitochondrial dysfunction (e.g., Parkin, PINK1, DJ-1, alpha-synuclein, and LRRK2). Parkin, whose mutation causes autosomal-recessive juvenile parkinsonism, plays an essential role in mitochondrial quality control of mitochondrial biogenesis, mitochondrial dynamics, and mitophagy. Therefore, we summarized the advanced studies of Parkin's role in mitochondrial quality control and hoped it could be studied further as a therapeutic target for PD.