6-Hydroxydopamine induces autophagic flux dysfunction by impairing transcription factor EB activation and lysosomal function in dopaminergic neurons and SH-SY5Y cells

Piperine promotes PI3K/AKT/mTOR-mediated gut-brain autophagy to degrade α-Synuclein in Parkinson's disease rats

ETHNOPHARMACOLOGICAL RELEVANCE

Piper longum L., a medicinal and food homologous herb, has a traditional history of use in treating gastrointestinal and neurological disorders. Piperine (PIP) the main alkaloid of P. longum, exists neuroprotective effects on various animal models of Parkinson's disease (PD). Nevertheless, the underlying mechanism, particularly the role of PIP in promoting gut-brain autophagy for α-Synuclein (α-Syn) degradation in PD, remains incompletely understood.

AIM OF THE STUDY

To explore the role of PIP in regulating the gut-brain autophagy signaling pathway to reduce α-Syn levels in both the colon and substantia nigra (SN) of PD model rats.

MATERIALS AND METHODS

Behavioral experiments were conducted to assess the impact of PIP on 6-hydroxydopamine (6-OHDA)-induced PD rats. The intestinal microbiome composition and intestinal metabolites were analyzed by metagenomics and GC-MS/MS. The auto-phagosomes were visualized by transmission electron microscopy. Immunohistochemistry, immunofluorescence, and western blotting were performed to assess the levels of tyrosine hydroxylase (TH), α-Syn, LC3II/LC3I, p62, and the PI3K/AKT/mTOR pathway in both the SN and colon of the rats. The pathway-related inhibitor and agonist were used to verify the autophagy mechanism in the SH-SY5Y cells overexpressing A53T mutant α-Syn (A53T-α-Syn).

RESULTS

PIP improved autonomic movement and gastrointestinal dysfunctions, reduced α-Syn aggregation and attenuated the loss of dopaminergic neurons in 6-OHDA-induced PD rats. After oral administration of PIP, the radio of LC3II/LC3I increased and the expression of p62 was degraded, as well as the phosphorylation levels of PI3K, AKT and mTOR decreased in the SN and colon of rats. The effect of PIP on reducing A53T-α-Syn through the activation of the PI3K/AKT/mTOR-mediated autophagy pathway was further confirmed in A53T-α-Syn transgenic SH-SY5Y cells. This effect could be inhibited by the autophagy inhibitor bafilomycin A1 and the PI3K agonist 740 Y-P.

CONCLUSIONS

Our findings suggested that PIP could protect neurons by activating autophagy to degrade α-Syn in the SN and colon, which were related to the suppression of PIP on the activation of PI3K/AKT/mTOR signaling pathway.

Animal models of Parkinson's disease: bridging the gap between disease hallmarks and research questions

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized by motor and non-motor symptoms. More than 200 years after its first clinical description, PD remains a serious affliction that affects a growing proportion of the population. Prevailing treatments only alleviate symptoms; there is still neither a cure that targets the neurodegenerative processes nor therapies that modify the course of the disease. Over the past decades, several animal models have been developed to study PD. Although no model precisely recapitulates the pathology, they still provide valuable information that contributes to our understanding of the disease and the limitations of our treatment options. This review comprehensively summarizes the different animal models available for Parkinson's research, with a focus on those induced by drugs, neurotoxins, pesticides, genetic alterations, α-synuclein inoculation, and viral vector injections. We highlight their characteristics and ability to reproduce PD-like phenotypes. It is essential to realize that the strengths and weaknesses of each model and the induction technique at our disposal are determined by the research question being asked. Our review, therefore, seeks to better aid researchers by ensuring a concrete discernment of classical and novel animal models in PD research.

Irisin Ameliorates PM2.5-Induced Acute Lung Injury by Regulation of Autophagy Through AMPK/mTOR Pathway

Background

PM2.5 exposure is one of the major inducements of various respiratory diseases and related mortality. Meanwhile, irisin, a metabolism and thermogenesis-related hormone, is found to be protective against acute lung injury induced by LPS, which indicates its therapeutic function in lung injury. However, the function and underlying mechanism of irisin in PM2.5-induced acute lung injury (ALI) are still unclear. This study is aimed to discover the potential mechanisms of irisin in PM2.5-induced acute lung injury.

Methods

Atg5 deficient mice and cells were established to clarify the relationship between irisin and autophagy in PM2.5-induced ALI. We also used Ad-mCherry-GFP-LC3B as a monitor of autophagy flux to claim the effects of irisin on autophagy. Western blotting and qPCR were used to reveal the molecular mechanism.

Results

As a result, PM2.5 exposure induced lung injury whereas mitigated by irisin. Moreover, PM2.5 hampered autophagy flux, characterized by accumulation of p62, and autophagosomes, as well as blocked autolysosomes. Irisin improved the disturbed autophagy flux, which was abrogated by deficiency of Atg5. Additionally, we demonstrated that irisin activated AMPK and inhibited mTOR, which indicated the enhanced autophagy. Moreover, blockage of AMPK by compound C terminated irisin's induction of autophagy in cultured MH-S cells.

Conclusion

Our findings reveal that irisin performs protective effects against PM2.5-induced ALI by activating autophagy through AMPK/mTOR signaling pathway.

Crosstalk of organelles in Parkinson's disease - MiT family transcription factors as central players in signaling pathways connecting mitochondria and lysosomes

Living organisms constantly need to adapt to their surrounding environment and have evolved sophisticated mechanisms to deal with stress. Mitochondria and lysosomes are central organelles in the response to energy and nutrient availability within a cell and act through interconnected mechanisms. However, when such processes become overwhelmed, it can lead to pathologies. Parkinson's disease (PD) is a common neurodegenerative disorder (NDD) characterized by proteinaceous intracellular inclusions and progressive loss of dopaminergic neurons, which causes motor and non-motor symptoms. Genetic and environmental factors may contribute to the disease etiology. Mitochondrial dysfunction has long been recognized as a hallmark of PD pathogenesis, and several aspects of mitochondrial biology are impaired in PD patients and models. In addition, defects of the autophagy-lysosomal pathway have extensively been observed in cell and animal models as well as PD patients' brains, where constitutive autophagy is indispensable for adaptation to stress and energy deficiency. Genetic and molecular studies have shown that the functions of mitochondria and lysosomal compartments are tightly linked and influence each other. Connections between these organelles are constituted among others by mitophagy, organellar dynamics and cellular signaling cascades, such as calcium (Ca²⁺) and mTOR (mammalian target of rapamycin) signaling and the activation of transcription factors. Members of the Microphthalmia-associated transcription factor family (MiT), including MITF, TFE3 and TFEB, play a central role in regulating cellular homeostasis in response to metabolic pressure and are considered master regulators of lysosomal biogenesis. As such, they are part of the interconnection between mitochondria and lysosome functions and therefore represent attractive targets for therapeutic approaches against NDD, including PD. The activation of MiT transcription factors through genetic and pharmacological approaches have shown encouraging results at ameliorating PD-related phenotypes in in vitro and in vivo models. In this review, we summarize the relationship between mitochondrial and autophagy-lysosomal functions in the context of PD etiology and focus on the role of the MiT pathway and its potential as pharmacological target against PD.

Incomplete autophagy: Trouble is a friend

Incomplete autophagy is an impaired self-eating process of intracellular macromolecules and organelles in which accumulated autophagosomes do not fuse with lysosomes for degradation, resulting in the blockage of autophagic flux. In this review, we summarized the literature over the past decade describing incomplete autophagy, and found that different from the double-edged sword effect of general autophagy on promoting cell survival or death, incomplete autophagy plays a crucial role in disrupting cellular homeostasis, and promotes only cell death. What matters is that incomplete autophagy is closely relevant to the pathogenesis and progression of various human diseases, which, meanwhile, intimately linking to the pharmacologic and toxicologic effects of several compounds. Here, we comprehensively reviewed the latest progress of incomplete autophagy on molecular mechanisms and signaling pathways. Moreover, implications of incomplete autophagy for pharmacotherapy are also discussed, which has great relevance for our understanding of the distinctive role of incomplete autophagy in cellular physiology and disease. Consequently, targeting incomplete autophagy may contribute to the development of novel generation therapeutic agents for diverse human diseases.

Deacetylation of ZKSCAN3 by SIRT1 induces autophagy and protects SN4741 cells against MPP+-induced oxidative stress

Mitochondrial dysfunction, oxidative stress and misfolded protein aggregation are related to autophagy-lysosomal dysregulation and contribute to the pathogenesis of Parkinson' s disease (PD). ZKSCAN3, a transcriptional repressor, plays a crucial role in autophagy and lysosomal biogenesis. However, the role and modification of ZKSCAN3 in the defection of ALP, along with the molecular mechanism involved in pathogenesis of PD, still remain unclear. In this study, we demonstrated that cellular reactive oxygen species (ROS) generated by MPP⁺ exposure and the resulting oxidative damage were counteracted by SIRT1-ZKSCAN3 pathway induction. Here we showed that nuclear ZKSCAN3 significantly increased in ventral midbrain of MPTP-treated mice and MPP⁺-treated SN4741 cells. Knockdown of ZKSCAN3 alleviated MPP⁺-induced ALP defect, Tyrosine Hydroxylase (TH) declination and neuronal death. NAC, a ROS scavenger, reduced the nuclear translocation of ZKSCAN3 and sequentially improved ALP function in MPP⁺-treated SN4741 cells. SRT2104, a SIRT1 activator, attenuated impairment of ALP in MPP⁺-treated SN47417 cells through decreasing nuclear accumulation of ZKSCAN3 and protected dopaminergic neurons from MPTP injury. Moreover, SRT2104 relieved impairment in locomotor activities and coordination skills upon treatment of MPTP in C57/BL6J mice through behavior tests including rotarod, pole climbing and grid. Furthermore, ZKSCAN3 was a novel substrate of SIRT1 which was deacetylated at lysine 148 residues by SIRT1. This subsequently facilitated the shuttling of ZKSCAN3 to the cytoplasm. Therefore, our study identifies a novel acetylation-dependent regulatory mechanism of nuclear translocation of ZKSCAN3. It results in autophagy-lysosomal dysfunction and then leads to DA neuronal death in MPTP/MPP⁺ model of PD.

Ghrelin alleviates 6-hydroxydopamine-induced neurotoxicity in SH-SY5Y cells

Ghrelin is a neuropeptide that has various physiological functions and has been demonstrated to be neuroprotective in a number of neurological disease models. However, the underlying mechanisms of ghrelin in Parkinson’s disease remain largely unexplored. The current study aimed to study the effects of ghrelin in a 6-hydroxydopamine (6-OHDA)-induced Parkinson’s disease model and evaluate the potential underlying mechanisms. In the present study, we treated an SH-SY5Y cell model with 6-OHDA, and observed that pretreatment with different concentrations of ghrelin (1, 10, and 100 nM) for 30 minutes relieved the neurotoxic effects of 6-OHDA, as revealed by Cell Counting Kit-8 and Annexin V/propidium iodide (PI) apoptosis assays. Reverse transcription quantitative polymerase chain reaction and western blot assay results demonstrated that 6-OHDA treatment upregulated α-synuclein and lincRNA-p21 and downregulated TG-interacting factor 1 (TGIF1), which was predicted as a potential transcription regulator of the gene encoding α-synuclein (SNCA). Ghrelin pretreatment was able to reverse the trends caused by 6-OHDA. The Annexin V/PI apoptosis assay results revealed that inhibiting either α-synuclein or lincRNA-p21 expression with small interfering RNA (siRNA) relieved 6-OHDA-induced cell apoptosis. Furthermore, inhibiting lincRNA-p21 also partially upregulated TGIF1. By retrieving information from a bioinformatics database and performing both double luciferase and RNA immunoprecipitation assays, we found that lincRNA-p21 and TGIF1 were able to form a double-stranded RNA-binding protein Staufen homolog 1 (STAU1) binding site and further activate the STAU1-mediated mRNA decay pathway. In addition, TGIF1 was able to transcriptionally regulate α-synuclein expression by binding to the promoter of SNCA. The Annexin V/PI apoptosis assay results showed that either knockdown of TGIF1 or overexpression of lincRNA-p21 notably abolished the neuroprotective effects of ghrelin against 6-OHDA-induced neurotoxicity. Collectively, these findings suggest that ghrelin exerts neuroprotective effects against 6-OHDA-induced neurotoxicity via the lincRNA-p21/TGIF1/α-synuclein pathway.

Animal models of Parkinson's disease: a guide to selecting the optimal model for your research

Parkinson's disease (PD) is a complex, multisystem disorder characterised by α-synuclein (SNCA) pathology, degeneration of nigrostriatal dopaminergic neurons, multifactorial pathogenetic mechanisms and expression of a plethora of motor and non-motor symptoms. Animal models of PD have already been instructive in helping us unravel some of these aspects. However, much remains to be discovered, requiring continued interrogation by the research community. In contrast with the situation for many neurological disorders, PD benefits from of a wide range of available animal models (pharmacological, toxin, genetic and α-synuclein) but this makes selection of the optimal one for a given study difficult. This is especially so when a study demands a model that displays a specific combination of features. While many excellent reviews of animal models already exist, this review takes a different approach with the intention of more readily informing this decision-making process. We have considered each feature of PD in turn - aetiology, pathology, pathogenesis, motor dysfunctions and non-motor symptoms (NMS) - highlighting those animal models that replicate each. By compiling easily accessible tables and a summary figure, we aim to provide the reader with a simple, go-to resource for selecting the optimal animal model of PD to suit their research needs.

6-Hydroxydopamine disrupts cellular copper homeostasis in human neuroblastoma SH-SY5Y cells

Copper (Cu) is an essential trace element that plays an important role in maintaining neuronal functions such as the biosynthesis of neurotransmitters. In contrast, exposure to excess Cu results in cell injury. Therefore, intracellular Cu levels are strictly regulated by proteins related to Cu-trafficking, including ATP7A. Parkinson's disease (PD) is a neurodegenerative disorder and is characterized by the loss of dopaminergic neurons in the substantia nigra. Recently, the abnormality of Cu homeostasis was demonstrated to be related to the pathogenesis of PD. However, the association between Cu dyshomeostasis and PD remains unclear. In this study, we examined the effects of 6-hydroxydopamine (6-OHDA), a neurotoxin used for the production of PD model animals, on cellular Cu trafficking in human neuroblastoma SH-SY5Y cells. 6-OHDA reduced the protein levels of the Cu exporter ATP7A and the Cu chaperone Atox1, but not CTR1, a Cu importer; however, it did not affect the expression of ATP7A and Atox1 mRNAs. The decreased levels of ATP7A and Atox1 proteins were restored by the antioxidant N-acetylcysteine and the lysosomal inhibitor bafilomycin A1. This suggests that 6-OHDA-induced oxidative stress facilitates the degradation of these proteins. In addition, the amount of intracellular Cu after exposure to CuCl2 was significantly higher in cells pretreated with 6-OHDA than in untreated cells. Moreover, 6-OHDA reduced the protein levels of the cuproenzyme dopamine β-hydroxylase that converts dopamine to noradrenaline. Thus, this study suggests that 6-OHDA disrupts Cu homeostasis through the dysregulation of cellular Cu trafficking, resulting in the dysfunction of neuronal cells.

Autophagy as a gateway for the effects of methamphetamine: From neurotransmitter release and synaptic plasticity to psychiatric and neurodegenerative disorders

As a major eukaryotic cell clearing machinery, autophagy grants cell proteostasis, which is key for neurotransmitter release, synaptic plasticity, and neuronal survival. In line with this, besides neuropathological events, autophagy dysfunctions are bound to synaptic alterations that occur in mental disorders, and early on, in neurodegenerative diseases. This is also the case of methamphetamine (METH) abuse, which leads to psychiatric disturbances and neurotoxicity. While consistently altering the autophagy machinery, METH produces behavioral and neurotoxic effects through molecular and biochemical events that can be recapitulated by autophagy blockade. These consist of altered physiological dopamine (DA) release, abnormal stimulation of DA and glutamate receptors, as well as oxidative, excitotoxic, and neuroinflammatory events. Recent molecular insights suggest that METH early impairs the autophagy machinery, though its functional significance remains to be investigated. Here we discuss evidence suggesting that alterations of DA transmission and autophagy are intermingled within a chain of events underlying behavioral alterations and neurodegenerative phenomena produced by METH. Understanding how METH alters the autophagy machinery is expected to provide novel insights into the neurobiology of METH addiction sharing some features with psychiatric disorders and parkinsonism.

Natural Phytochemicals as Novel Therapeutic Strategies to Prevent and Treat Parkinson's Disease: Current Knowledge and Future Perspectives

Parkinson's disease (PD) is the second-most common neurodegenerative chronic disease affecting both cognitive performance and motor functions in aged people. Yet despite the prevalence of this disease, the current therapeutic options for the management of PD can only alleviate motor symptoms. Research has explored novel substances for naturally derived antioxidant phytochemicals with potential therapeutic benefits for PD patients through their neuroprotective mechanism, targeting oxidative stress, neuroinflammation, abnormal protein accumulation, mitochondrial dysfunction, endoplasmic reticulum stress, neurotrophic factor deficit, and apoptosis. The aim of the present study is to perform a comprehensive evaluation of naturally derived antioxidant phytochemicals with neuroprotective or therapeutic activities in PD, focusing on their neuropharmacological mechanisms, including modulation of antioxidant and anti-inflammatory activity, growth factor induction, neurotransmitter activity, direct regulation of mitochondrial apoptotic machinery, prevention of protein aggregation via modulation of protein folding, modification of cell signaling pathways, enhanced systemic immunity, autophagy, and proteasome activity. In addition, we provide data showing the relationship between nuclear factor E2-related factor 2 (Nrf2) and PD is supported by studies demonstrating that antiparkinsonian phytochemicals can activate the Nrf2/antioxidant response element (ARE) signaling pathway and Nrf2-dependent protein expression, preventing cellular oxidative damage and PD. Furthermore, we explore several experimental models that evaluated the potential neuroprotective efficacy of antioxidant phytochemical derivatives for their inhibitory effects on oxidative stress and neuroinflammation in the brain. Finally, we highlight recent developments in the nanodelivery of antioxidant phytochemicals and its neuroprotective application against pathological conditions associated with oxidative stress. In conclusion, naturally derived antioxidant phytochemicals can be considered as future pharmaceutical drug candidates to potentially alleviate symptoms or slow the progression of PD. However, further well-designed clinical studies are required to evaluate the protective and therapeutic benefits of phytochemicals as promising drugs in the management of PD.

Acylated Ghrelin is Protective Against 6-OHDA-induced Neurotoxicity by Regulating Autophagic Flux

Parkinson’s disease (PD) is one of the most common neurodegenerative disorders, and our previous study revealed that autophagic flux dysfunction contributes to the neuron death in 6-OHDA-induced PD models. Acylated ghrelin is a neuropeptide that has a variety of actions in the central nervous system. In the current study, we aimed to investigate whether ghrelin is neuroprotective in 6-OHDA-induced rat model and SH-SY5Y cell model and whether it is related to autophagic flux regulation. We observed that ghrelin could effectively reduce apomorphine-induced contralateral rotation in 6-OHDA-induced PD rats, preserve the expression of tyrosine hydroxylase (TH) and increase the cell viability. It could upregulate the expression of autophagy related proteins like Atg7 and LC3-II and downregulate p62, and downregulate apoptosis related proteins like bax and cleaved caspase 3. SH-SY5Y cells transfected with adenovirus Ad-mCherry-GFP-LC3B further revealed that ghrelin could relieve the autophagic flux dysfunction induced by 6-OHDA. Lysotracker staining showed that ghrelin could reverse the decrease in lysosomes induced by 6-OHDA and immunofluorescence staining revealed a reverse of TFEB level in SH-SY5Y cells. Blocking autophagy activation with 3-methyladenine (3-MA) in rats treated with ghrelin and 6-OHDA showed no notable change in apoptosis-related markers, while blocking autophagosome fusion with lysosomes with chloroquine could notably reverse the downregulation of bax/bcl-2 ratio and cleaved caspase three expression by ghrelin. Additionally, knockdown ATG7, the upstream regulator of autophagy, with siRNA could further decrease the number of apoptotic cells in SH-SY5Y cells exposed to 6-OHDA and treated with ghrelin, while knockdown TFEB, a key transcription factor for lysosome biosynthesis and function, with siRNA could completely abolish the anti-apoptosis effect of ghrelin. These data suggest that ghrelin is neuroprotective in 6-OHDA-induced PD models via improving autophagic flux dysfunction and restoration of TFEB level.

Autophagy status as a gateway for stress-induced catecholamine interplay in neurodegeneration

The catecholamine-containing brainstem nuclei locus coeruleus (LC) and ventral tegmental area (VTA) are critically involved in stress responses. Alterations of catecholamine systems during chronic stress may contribute to neurodegeneration, including cognitive decline. Stress-related catecholamine alterations, while contributing to anxiety and depression, might accelerate neuronal degeneration by increasing the formation of toxic dopamine and norepinephrine by-products. These, in turn, may impair proteostasis within a variety of cortical and subcortical areas. In particular, the molecular events governing neurotransmission, neuroplasticity, and proteostasis within LC and VTA affect a variety of brain areas. Therefore, we focus on alterations of autophagy machinery in these nuclei as a relevant trigger in this chain of events. In fact, these catecholamine-containing areas are mostly prone to autophagy-dependent neurodegeneration. Thus, we propose a dynamic hypothesis according to which stress-induced autophagy alterations within the LC-VTA network foster a cascade towards early neurodegeneration within these nuclei.

Exosome Release Is Modulated by the Mitochondrial-Lysosomal Crosstalk in Parkinson's Disease Stress Conditions

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the progressive loss of dopaminergic neurons in the substantia nigra (SN) pars compacta region of the brain. The main pathological hallmark involves cytoplasmic inclusions of α-synuclein and mitochondrial dysfunction, which is observed in other part of the central nervous system other than SN suggesting the spread of pathogenesis to bystander neurons. The inter-neuronal communication through exosomes may play an important role in the spread of the disease; however, the mechanisms are not well elucidated. Mitochondria and its role in inter-organellar crosstalk with multivesicular body (MVB) and lysosome and its role in modulation of exosome release in PD is not well understood. In the current study, we investigated the mitochondria-lysosome crosstalk modulating the exosome release in neuronal and glial cells. We observed that PD stress showed enhanced release of exosomes in dopaminergic neurons and glial cells. The PD stress condition in these cells showed fragmented network and mitochondrial dysfunction which further leads to functional deficit of lysosomes and hence inhibition of autophagy flux. Neuronal and glial cells treated with rapamycin showed enhanced autophagy and inhibited the exosomal release. The results here suggest that maintenance of mitochondrial function is important for the lysosomal function and hence exosomal release which is important for the pathogenesis of PD.

Mitochondrial and Organellar Crosstalk in Parkinson's Disease

Mitochondrial dysfunction is a well-established pathological event in Parkinson's disease (PD). Proteins misfolding and its impaired cellular clearance due to altered autophagy/mitophagy/pexophagy contribute to PD progression. It has been shown that mitochondria have contact sites with endoplasmic reticulum (ER), peroxisomes and lysosomes that are involved in regulating various physiological processes. In pathological conditions, the crosstalk at the contact sites initiates alterations in intracellular vesicular transport, calcium homeostasis and causes activation of proteases, protein misfolding and impairment of autophagy. Apart from the well-reported molecular changes like mitochondrial dysfunction, impaired autophagy/mitophagy and oxidative stress in PD, here we have summarized the recent scientific reports to provide the mechanistic insights on the altered communications between ER, peroxisomes, and lysosomes at mitochondrial contact sites. Furthermore, the manuscript elaborates on the contributions of mitochondrial contact sites and organelles dysfunction to the pathogenesis of PD and suggests potential therapeutic targets.

Autophagy Induction Contributes to the Neuroprotective Impact of Intermittent Fasting on the Acutely Injured Spinal Cord

Spinal cord injury (SCI) is one of the leading causes of neurological disability and death. So far, there is no satisfactory treatment for SCI, because of its complex and ill-defined pathophysiology. Recently, autophagy has been implicated as protective in acute SCI rat models. Here, we investigated the therapeutic value of a dietary intervention, namely, intermittent fasting (IF), on neuronal survival after acute SCI in rats, and its underlying mechanism related to autophagy regulation. We found remarkable improvement in both behavioral performance and neuronal survival at the injured segment of the spinal cord of animals previously subjected to IF. Western blotting revealed a marked decrease in apoptosis-related markers such as cleaved caspase 3 levels and the bax/bcl-2 ratio in the IF group, which suggested an inhibition of the intrinsic apoptosis pathway. In addition, the expression of the autophagy markers LC3-II and beclin 1 was also increased in the IF group compared with ad libitum fed animals. In parallel, IF decreased the levels of the substrate protein of autophagy, p62, indicative of an upregulation of the autophagic processes. Treatment with 3-methyladenine (3-MA), a selective inhibitor of autophagy, reversed the downregulated apoptosis-related markers by IF. Finally, IF could activate the adenosine monophosphate (AMP)-activated protein kinase (AMPK)/mammalian target of rapamycin (mTOR) pathway and enhance lysosome function by upregulating transcription factor (TF)EB expression. Altogether, the present findings suggest that IF exerts a neuroprotective effect after acute SCI via the upregulation of autophagy, and further points to dietary interventions as a promising combinatorial treatment for SCI.

Merging the Multi-Target Effects of Phytochemicals in Neurodegeneration: From Oxidative Stress to Protein Aggregation and Inflammation

Wide experimental evidence has been provided in the last decade concerning the neuroprotective effects of phytochemicals in a variety of neurodegenerative disorders. Generally, the neuroprotective effects of bioactive compounds belonging to different phytochemical classes are attributed to antioxidant, anti-aggregation, and anti-inflammatory activity along with the restoration of mitochondrial homeostasis and targeting alterations of cell-clearing systems. Far from being independent, these multi-target effects represent interconnected events that are commonly implicated in the pathogenesis of most neurodegenerative diseases, independently of etiology, nosography, and the specific misfolded proteins being involved. Nonetheless, the increasing amount of data applying to a variety of neurodegenerative disorders joined with the multiple effects exerted by the wide variety of plant-derived neuroprotective agents may rather confound the reader. The present review is an attempt to provide a general guideline about the most relevant mechanisms through which naturally occurring agents may counteract neurodegeneration. With such an aim, we focus on some popular phytochemical classes and bioactive compounds as representative examples to design a sort of main highway aimed at deciphering the most relevant protective mechanisms which make phytochemicals potentially useful in counteracting neurodegeneration. In this frame, we emphasize the potential role of the cell-clearing machinery as a kernel in the antioxidant, anti-aggregation, anti-inflammatory, and mitochondrial protecting effects of phytochemicals.

Deferred Administration of Afobazole Induces Sigma1R-Dependent Restoration of Striatal Dopamine Content in a Mouse Model of Parkinson's Disease

Previously, we demonstrated that the immediate administration of multitarget anxiolytic afobazole slows down the progression of neuronal damage in a 6-hydroxidodamine (6-OHDA) model of Parkinson's disease due to the activation of chaperone Sigma1R. The aim of the present study is to evaluate the therapeutic potential of deferred afobazole administration in this model. Male ICR mice received a unilateral 6-OHDA lesion of the striatum. Fourteen days after the surgery, mice were treated with afobazole, selective Sigma1R agonist PRE-084, selective Sigma1R antagonist BD-1047, and a combination of BD-1047 with afobazole or PRE-084 for another 14 days. The deferred administration of afobazole restored the intrastriatal dopamine content in the 6-OHDA-lesioned striatum and facilitated motor behavior in rotarod tests. The action of afobazole accorded with the effect of Sigma1R selective agonist PRE-084 and was blocked by Sigma1R selective antagonist BD-1047. The present study illustrates the Sigma1R-dependent effects of afobazole in a 6-OHDA model of Parkinson's disease and reveals the therapeutic potential of Sigma1R agonists in treatment of the condition.

Pharmacological enhancement of TFEB-mediated autophagy alleviated neuronal death in oxidative stress-induced Parkinson's disease models

Autophagy, a conserved cellular degradation and recycling process, can be enhanced by nutrient depletion, oxidative stress or other harmful conditions to maintain cell survival. 6-Hydroxydopamine/ascorbic acid (6-OHDA/AA) is commonly used to induce experimental Parkinson’s disease (PD) lesions by causing oxidative damage to dopaminergic neurons. Activation of autophagy has been observed in the 6-OHDA-induced PD models. However, the mechanism and exact role of autophagy activation in 6-OHDA PD model remain inconclusive. In this study, we report that autophagy was triggered via mucolipin 1/calcium/calcineurin/TFEB (transcription factor EB) pathway upon oxidative stress induced by 6-OHDA/AA. Interestingly, overexpression of TFEB alleviated 6-OHDA/AA toxicity. Moreover, autophagy enhancers, Torin1 (an mTOR-dependent TFEB/autophagy enhancer) and curcumin analog C1 (a TFEB-dependent and mTOR-independent autophagy enhancer), significantly rescued 6-OHDA/AA-induced cell death in SH-SY5Y cells, iPSC-derived DA neurons and mice nigral DA neurons. The behavioral abnormality of 6-OHDA/AA-treated mice can also be rescued by Torin 1 or C1 administration. The protective effects of Torin 1 and C1 can be blocked by autophagy inhibitors like chloroquine (CQ) or by knocking down autophagy-related genes TFEB and ATG5. Taken together, this study supports that TFEB-mediated autophagy is a survival mechanism during oxidative stress and pharmacological enhancement of this process is a neuroprotective strategy against oxidative stress-associated PD lesions.

Iron chelator Deferoxamine protects human neuroblastoma cell line SH-SY5Y from 6-Hydroxydopamine-induced apoptosis and autophagy dysfunction

BACKGROUND

Intracellular iron involves in Fenton's reaction-mediated Hydroxyl radical (OH·) generation by reacting with the neurotoxic agent 6-Hydroxydopamine (6-OHDA) autoxidation derivative Hydrogen Peroxide (H₂O₂). Several studies have been conducted so far on the neuroprotective activities of the iron chelator Deferoxamine (DFO) but little or no clear evidence about the underlying cellular mechanism is available.

METHODS

The present study was conducted on Human neuroblastoma cell line SH-SY5Y in the absence or presence of 6-OHDA or H₂O₂ and / or DFO. Following incubation, cell viability assay, intracellular reactive oxygen species (ROS) determination, flow cytometric quantification of apoptotic cells followed by nuclear staining, intracellular tracking of transfected fusion construct of microtubule-associated protein 1B-light chain with Green fluorescent protein - Red fluorescent protein (LC3B-GFP-RFP reporters) and immunocytochemistry of intracellular Cathepsin protein by confocal microscopy, were conducted. In addition, western blotting was carried out to detect expressions of apoptotic and autophagy related proteins.

RESULTS

This study confirmed the neuroprotective potential of DFO by inhibiting 6-OHDA-mediated cell death and ROS generation. Reduced percentage of apoptotic cells and appearance of altered nuclei architecture followed by a reduced expression of cleaved PARP (Poly-ADP-ribose Polymerase) and cleaved Caspase-3 were observed upon DFO treatment against 6-OHDA, and as well as against H₂O₂ in SH-SY5Y cell lines. Besides, DFO induced the intracellular autophagolysosome formation (red puncta) rather than autophagosome (yellow puncta) only. Thereafter it was observed that DFO restored the expression of intracellular lysosomal protease Cathepsin and reduced the expression of the LC3-II.

CONCLUSION

Taken together, this study clearly demonstrated that the anti-Fenton activity of DFO inhibited apoptosis and caused blockade in ALP or autophagy dysfunction in SH-SY5Y cell lines. These outcomes further suggest that DFO provides neuroprotection by inhibiting apoptosis and inducing the progression of Autophagy- lysosomal pathway (ALP).

Role of c-Abl-GSK3β Signaling in MPP+-Induced Autophagy-Lysosomal Dysfunction

Impairment in autophagy-lysosomal pathway (ALP) results in accumulation of misfolded proteins and dysfunctional organelles, which is the hallmark of neurodegenerative diseases including Parkinson's disease (PD). Recent studies revealed activated nonreceptor tyrosine kinase Abelson (c-Abl) in PD models and brain specimen of PD patients. Inhibition of c-Abl through pharmacological inhibitors has been shown to enhance ALP function and provide neuroprotective effects in cells and animal models of PD. However, the molecular mechanisms of neuroprotective effects underlying c-Abl inhibition remain elusive. In this study, STI-571, a c-Abl inhibitor, rescued the ALP function through facilitating the nuclear translocation of TFEB and protected against MPP+-induced neuronal cell death. Furthermore, siRNA-mediated knock-down or pharmacological inhibition of GSK3β mitigated the MPP+-induced neuronal cell death, which was achieved through promoting TFEB nuclear localization and subsequently reversing the function of ALP. Intriguingly, either DPH, c-Abl activator, or MPP+ led to the activation of GSK3β, which is a negative regulator of TFEB. In addition, c-Abl directly interacted with GSK3β and catalyzed its phosphorylation at tyrosine 216, and their interaction was enhanced under MPP+ treatment. In contrast, STI-571 abrogated phosphorylation of GSK3β-Tyr216 induced by MPP+ in SN4741 cells and in primary midbrain neurons. Taken together, these results demonstrate that GSK3β is a novel c-Abl substrate, and c-Abl-GSk3β pathway mediates MPP+-induced ALP defects and neuronal cell death, which may represent a potential therapeutic target for PD.

Phytochemicals Bridging Autophagy Induction and Alpha-Synuclein Degradation in Parkinsonism

Among nutraceuticals, phytochemical-rich compounds represent a source of naturally-derived bioactive principles, which are extensively studied for potential beneficial effects in a variety of disorders ranging from cardiovascular and metabolic diseases to cancer and neurodegeneration. In the brain, phytochemicals produce a number of biological effects such as modulation of neurotransmitter activity, growth factor induction, antioxidant and anti-inflammatory activity, stem cell modulation/neurogenesis, regulation of mitochondrial homeostasis, and counteracting protein aggregation through modulation of protein-folding chaperones and the cell clearing systems autophagy and proteasome. In particular, the ability of phytochemicals in restoring proteostasis through autophagy induction took center stage in recent research on neurodegenerative disorders such as Parkinson’s disease (PD). Indeed, autophagy dysfunctions and α-syn aggregation represent two interdependent downstream biochemical events, which concur in the parkinsonian brain, and which are targeted by phytochemicals administration. Therefore, in the present review we discuss evidence about the autophagy-based neuroprotective effects of specific phytochemical-rich plants in experimental parkinsonism, with a special focus on their ability to counteract alpha-synuclein aggregation and toxicity. Although further studies are needed to confirm the autophagy-based effects of some phytochemicals in parkinsonism, the evidence discussed here suggests that rescuing autophagy through natural compounds may play a role in preserving dopamine (DA) neuron integrity by counteracting the aggregation, toxicity, and prion-like spreading of α-syn, which remains a hallmark of PD.

Cell Clearing Systems Bridging Neuro-Immunity and Synaptic Plasticity

In recent years, functional interconnections emerged between synaptic transmission, inflammatory/immune mediators, and central nervous system (CNS) (patho)-physiology. Such interconnections rose up to a level that involves synaptic plasticity, both concerning its molecular mechanisms and the clinical outcomes related to its behavioral abnormalities. Within this context, synaptic plasticity, apart from being modulated by classic CNS molecules, is strongly affected by the immune system, and vice versa. This is not surprising, given the common molecular pathways that operate at the cross-road between the CNS and immune system. When searching for a common pathway bridging neuro-immune and synaptic dysregulations, the two major cell-clearing cell clearing systems, namely the ubiquitin proteasome system (UPS) and autophagy, take center stage. In fact, just like is happening for the turnover of key proteins involved in neurotransmitter release, antigen processing within both peripheral and CNS-resident antigen presenting cells is carried out by UPS and autophagy. Recent evidence unravelling the functional cross-talk between the cell-clearing pathways challenged the traditional concept of autophagy and UPS as independent systems. In fact, autophagy and UPS are simultaneously affected in a variety of CNS disorders where synaptic and inflammatory/immune alterations concur. In this review, we discuss the role of autophagy and UPS in bridging synaptic plasticity with neuro-immunity, while posing a special emphasis on their interactions, which may be key to defining the role of immunity in synaptic plasticity in health and disease.

Exosomes derived from mesenchymal stem cells attenuate inflammation and demyelination of the central nervous system in EAE rats by regulating the polarization of microglia

Multiple sclerosis (MS) is a chronic demyelinating disease caused by central nervous system (CNS) inflammation and immune dysfunction, which often leaves patients with severe physical disabilities. Microglia function in the surveillance of the CNS, and an imbalance in the M1/M2 phenotypes of microglia contribute to the progression of MS. Recent studies indicate that exosomes secreted by bone marrow mesenchymal stem cells (BMSCs) play therapeutic roles in many autoimmune diseases and aid in tissue repair. However, it is not clear whether BMSC-derived exosomes can attenuate MS-associated inflammation and immune dysfunction, or how BMSC exosomes protect neurons. The experimental autoimmune encephalomyelitis (EAE) rat model was used to investigate the effect of exosomes on microglia polarization and inflammation in CNS. The results showed that exosome treatment significantly decreased neural behavioral scores, reduced the infiltration of inflammatory cells into the CNS, and decreased demyelination in comparison to untreated EAE rats. In addition, exosome treatment resulted in significant increases in the levels of M2-related cytokines such as interleukin (IL)-10 and transforming growth factor (TGF)-β, whereas M1-related tumor necrosis factor (TNF)-α and IL-12 levels decreased significantly. Moreover, compared with the untreated EAE group, the exosome group displayed significantly increased protein and mRNA expression levels of M2 phenotype markers, whereas M1 marker expression decreased. Our findings were further confirmed in an in vitro HAPI microglia cell line model. In conclusion, these findings indicate that BMSC-derived exosomes can attenuate inflammation and demyelination of the CNS in the EAE rat model by regulating the polarization of microglia. Therefore, the use of BMSC-derived exosomes may be a potential therapeutic approach for the treatment of autoimmune and inflammatory diseases.

Dysregulated autophagy contributes to caspase-dependent neuronal apoptosis

Autophagy is a regulated, intracellular degradation process that delivers unnecessary or dysfunctional cargo to the lysosome. Autophagy has been viewed as an adaptive survival response to various stresses, whereas in other cases, it promotes cell death. Therefore, both deficient and excessive autophagy may lead to cell death. In this study, we specifically attempted to explore whether and how dysregulated autophagy contributes to caspase-dependent neuronal cell death induced by the neurotoxin 6-hydroxydopamine (6-OHDA). Ultrastructural and biochemical analyses indicated that MN9D neuronal cells and primary cultures of cortical neurons challenged with 6-OHDA displayed typical features of autophagy. Cotreatment with chloroquine and monitoring autophagic flux by a tandem mRFP-EGFP-tagged LC3 probe indicated that the autophagic phenomena were primarily caused by dysregulated autophagic flux. Consequently, cotreatment with an antioxidant but not with a pan-caspase inhibitor significantly blocked 6-OHDA-stimulated dysregulated autophagy. These results indicated that 6-OHDA-induced generation of reactive oxygen species (ROS) played a critical role in triggering neuronal death by causing dysregulated autophagy and subsequent caspase-dependent apoptosis. The results of the MTT reduction, caspase-3 activation, and TUNEL assays indicated that pharmacological inhibition of autophagy using 3-methyladenine or deletion of the autophagy-related gene Atg5 significantly inhibited 6-OHDA-induced cell death. Taken together, our results suggest that abnormal induction of autophagic flux promotes apoptotic neuronal cell death, and that the treatments limiting dysregulated autophagy may have a strong neuroprotective potential.